Department of Energy Engineering YEARBOOK16 by Laboratory for Heat and Power

Department of Energy Engineering Laboratory for Heat and Power Laboratory for Hydraulic Turbomachinery Laboratory for Internal Combustion Engines and Electromobility YEARBOOK16

Title of publication Yearbook 2016, Department of Energy Engineering, Faculty of Mechanical Engineering, University of Ljubljana Title page & Design arnoldvuga+ Publisher ©University of Ljubljana, Faculty of Mechanical Engineering, Department of Energy Engineering Aškerčeva cesta 6, SI-1000 Ljubljana, Slovenia ISSN 2463-8994 Editor Prof. Dr. Mihael Sekavčnik Print Camera Edition 150 copies Price free copy Ljubljana, 2016

Preface

Department of Energy Engineering (DEE) is responsible for educational and R&D activities in the field of energy-conversion technologies and the transfer of leadingedge knowledge to a variety of study programs. Over the years the DEE has established strong links with industry in Slovenia and abroad, where it is widely recognized as a partner that provides vital information, fresh ideas, the latest research equipment and an understanding of the business environment to enable knowledge transfer and the development of industry. The extent of DEE’s activities has gradually grown during recent years despite of challenging circumstances in the industry affected by the financial crisis. As the diagram shows DEE succeeded to obtain more financing from research projects as well as from the industry while the budget from the educational activities remains below 25 % of the total budget. As a result of this, we have decided to promote an awareness of the scientific and industrial achievements of the DEE’s most recent successes by launching an active dissemination program. The Yearbook 2016 is part of this program. With it, we intend to highlight the current research projects being performed by senior researchers and PhD students. Each of these projects is briefly described, with the emphasis being on the expected or already-achieved results. The aim of this report is to attract your attention, and we are looking forward to sharing the details of particular projects with you and working with you on new ideas, proposals and projects. The Yearbook 2016 divides the project descriptions into three sections, one for each laboratory: the Laboratory for Heat and Power, the Laboratory of Hydraulic Turbomachinery and the Laboratory for Internal Combustion Engines and Electromobility. Many of the descriptions relate to industrial PhD projects, reflecting the strong industrial connections with the laboratories. In addition, we are committed to taking a pro-active role in new international research programs. 6

Contribution by Laboratories 1500 1400

laboratory for Internal Combustion Engines and Electromobility

1300 1200

budget / 1000 €

1100 1000 900

Laboratory for InHydraulic Turbomachinery

800 700 600 500 400 300

Laboratory for Heat and Power

200 100

2010

2011

2012

2013

2014

2015

100

education

200

budget / 1000 €

300 400 500

research

600 700 800 900 1000 1100

industry

1200 1300 1400 1500

Contribution by source

In year 2015 there were 15 students who graduated either masters study program or previous (equivalently ranking) university diploma program. Their diploma titles and abstracts are also included in the present Yearbook 2016. We hope that browsing through the Yearbook will provide an interesting insight into the activities of the members of DEE and you that might find some possibilities for future cooperation with us. Head of Department of Energy Engineering Prof.Dr. Mihael Sekavčnik

Contents LABORATORY FOR HEAT AND POWER

Prof.Dr. Mihael Sekavčnik

CHP system based on HT PEMFC stack

Andrej Lotrič

Scaling-Up of a Fast Internal Circulating Fluidized Bed Gasifier – An Experimental Approach

Jernej Mele, Ph.D.

Heat treatment furnace modelling with CFD

Boštjan Drobnič

The Mass-Flow Distribution of Pulverized-Coal Using an Array of Intrusive Electrostatic Sensors

Boštjan Jurjevčič

Connecting hydrogen chp energy systems with renewables into different sized grids

Rok Stropnik

The Influence of Operational phase on Environmental Impacts of a Fuel Cell UPS

Mitja Mori

Operation Optimization of Power Plant Ljubljana

Igor Kuštrin

The integration of hydrogen technologies for utilisation of distributed renewable energy sources

Rok Lacko

LABORATORY FOR HYDRAULIC TURBOMACHINERY

Prof.Dr. Branko Širok

Noise Generation in the Air Gap of an Axial Fan

Marko Hočevar

Method for assessment of product quality during paper production process

Tom Bajcar

Close-range air-assisted precision spot-spraying for robotic applications: aerodynamics and spray coverage analysis

Aleš Malneršič

Cavitation damage in water at elevated temperatures

Matevž Dular

High-speed thermal imaging of high-temperature processes

Benjamin Bizjan

Numerical modeling of dust lifting from a complexgeometry industrial stockpile

Lovrenc Novak

Mineral wool primary layer formation in collecting chamber

Marko Peternelj

Influence of cavitation on preparation of aqueous detergent solutions

Tadej Stepišnik Perdih

Experimental study of the thermodynamic effecs in a cavitating flow

Martin Petkovšek

Factors Affecting Volatile Phenol Production During Fermentations with Pure and Mixed Cultures of Dekkerabruxellensis and Saccharomyces cerevisiae

Janez Kosel

LABORATORY FOR INTERNAL COMBUSTION ENGINES AND ELECTROMOBILITY

Assoc.Prof.Dr. Tomaž Katrašnik 88

A computationally efficient hybrid 3D analyticnumerical approach for system level modelling of PEM fuel cells

Gregor Tavčar

Use of equivalent circuit in modeling voltage response to dynamic load current cycle

Igor Mele

Analysis and digital processing of in-cylinder pressure signal for combustion diagnosis of internal combustion engine

Rok Vihar

Challenges and Experiences at Converting HeavyDuty Diesel Engines to Dual-fuel Operation

Samuel Rodman Oprešnik

100

Combustion in microturbines - assessment of methodology and innovative solutions for utilization of alternative fuels

Tine Seljak

104

Advanced combustion concepts with innovative waste derived fuels

Urban Žvar Baškovič

108

PROJECTS

112

Short step into the history

Matija Tuma

130

Exergy and Anergy

Matija Tuma

134

Study programme

138

Graduated students in 2015

140

Prof.Dr. Mihael Sekavčnik, Assoc.Prof.Dr. Andrej Senegačnik

Laboratory for Heat and Power The Laboratory for Heat and Power’s activities cover two large, partially related, fields of study and research, while the latest developments in technology also drive its activities into other multidisciplinary fields. One of the basic research areas is energy-conversion systems, while the other has a closer focus on fuels and combustion. Recently, the research has spread to alternative, environmentally friendly, energy-conversion technologies as well as studies of the environmental impacts of energy engineering.

The primary activity of the Laboratory is education, both undergraduate and postgraduate. The Laboratory boasts modern equipment for its education and research purposes. Various power- and process-engineering-related models enable students to become familiar with many processes, machines and devices. In addition, state-ofthe-art software packages are available to the students for undergraduate studies as well as for postgraduate research. The lectures cover issues concerned with power engineering in utility and industrial power and thermal plants. They include gas and steam turbines, heat generators, fuel and combustion processes, utility and industrial energy systems, planning, operation, maintenance and the reliability of various power and thermal plants, etc. The theoretical lectures are upgraded with experimental work, especially during master’s studies. All the members of the Laboratory for Heat and Power are also involved in research activities. These are normally closely connected with expert activities. Therefore, most of the problems being studied arise from practice. State-ofthe-art measuring equipment as well as professional and custom-developed software enable high-quality theoretical and experiential research activities. The experimental

work takes place in the laboratory as well as in various utility and industrial plants. Both postgraduate and undergraduate students are also encouraged to cooperate in these research activities. Our research results have been published in many important international journals or were presented at conferences and seminars all over the world. Furthermore, many results find their way back to the application where they originated, and in this way lead to performance improvements. While the Laboratory for Heat and Power finds its direct cooperation with industrial partners very valuable, it is its role in larger national and international consortia working on various research projects that provides the opportunity for a further augmentation of our knowledge and experience. FORMER PROFESSORS: Prof.Dr. Zoran Rant, Prof. Leopold Andreé, Prof. Boris Černigoj, Assoc.Prof.Mag. Roman Povše, Prof.Dr. Matija Tuma, Prof.Dr. Dušan Florjančič, Prof.Dr. Janez Oman

CHP system based on HT PEMFC stack ABSTRACT → A concept of a compact system of endothermic methanol steam reformer (MSR) and exothermic PEM fuel cell (PEMFC) stack is proposed. First task was to identify possible configurations and prove the concept of such system with a numerical model. Three systems were modeled based on different PEMFC stacks. Low-temperature (LT) and conventional high-temperature (cHT) PEMFC stack characteristics were based on available data. Since, a novel hightemperature (nHT) PEMFC is under development a system with nHT PEMFC stack was also modeled because its operating temperature will coincide with that of cHT MSR. The systems were modeled in Aspen Plus software, where mass and energy balance equations are used in conjunction with reaction kinetic

modelling. Based on a real geometry, heat transfer between reactors is modeled in Comsol Multyphysics software. The results from both simulations are interdependent and coupled together to obtain the full system design. Also, a new LT catalyst for MSR was recently developed which now allows direct thermal coupling of LT MSR and cHT PEMFC stack. The second task is to use the same numerical approach and obtain geometrical and operational characteristics of such system. Ultimately, the results will be used to construct a prototype that will enable to experimentally validate the characteristics of LT MSR - cHT PEMFC stack system (later also possibility of cHT MSR - nHT PEMFC stack system).

INTRODUCTION Andrej Lotrič Laboratory: Laboratory for Heat and Power E-mail: andrej.lotric@fs.uni-lj.si Room: 306 Phone: +386-1-4771-306 Status: PhD student (started: October 2011, to be completed: September 2016) Research area: Hydrogen technologies, PEM fuel cell, methanol reforming Mentor: dr. Mihael Sekavčnik

One of the major constraints for the PEMFCs is that they use hydrogen as a fuel which has a very low volumetric energy density at conditions of standard ambient temperature and pressure (SATP). Compared to hydrogen at 800 bar, methanol at SATP has more than 2.6 times higher volumetric energy density and is in liquid state which greatly facilitates its handling, storage and transportation. However, to use it in a PEMFC it first needs to be converted into hydrogen. Methanol steam reforming is more attractive than methanol auto-thermal reforming because of its higher attainable hydrogen concentration and smaller amount of carbon monoxide (CO) in the reformate stream. At operating temperatures of LT PEMFCs CO tends to strongly adsorb onto the active sites of platinum (Pt) catalyst. Cleaning processes are needed to reduce the concentration of CO. With Pt-Ru catalyst around 10 ppm of CO can be tolerated in the stream or with air-bleeding technique even up to 50 ppm [1]. The phenomenon of CO adsorption on Pt is far less pronounced at higher temperatures. That is why cHT

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

PEMFC operate reasonably unaffected at temperatures above 160 °C and tolerate up to several percent of CO [2]. Other advantages of cHT over LT PEMFCs are simplified water management (no humidification needed and only water vapor is present) and higher temperature level of produced heat which can be used to preheat incoming gases or vaporize water-methanol mixture. Despite higher tolerance of cHT PEMFC to CO a major drawback is the adsorption of acid anions (H2PO4-) on active sites of Pt catalyst. This slows down the oxygen reduction reaction (ORR) kinetics more than in the case of LT PEMFC, hence, lower power density is achieved. Since H3PO4 is highly soluble in water and can leach out from the membrane, the lower temperature limit of cHT PEMFC is about 130 °C. Conversely, at temperatures higher than 180 °C, the vapor pressure of H3PO4 becomes prohibitively high, which also leads to losses of acid from the fuel cell. The main challenge of every energy system is to recuperate heat available within the system to maximize its efficiency. Since some reactors in combined MSR PEMFC systems are

exothermic (catalytic combustor, PEMFC stack) and others endothermic (vaporizer, MSR) the goal is to direct heat from sources to sinks within the system. The most obvious step that applies such action is direct thermal coupling of the MSR and the HT PEMFC stack which can be done in two ways (see Figure 1). One is to use the conventional catalyst in the MSR which enables to attain practically full conversion of methanol between 250 300 °C. This however depends on geometry, flow characteristics, catalysts loading, and steam-to-carbon ratio (S/C). Typically, conversions above 95% are achieved at 250 °C with S/C ≤ 2:1 while some researches also achieved 100% conversion with S/C ≤ 1.5:1 [3, 4]. Since conventional PEMFCs operate at lower temperature than the MSR there is a need for development of a nHT PEMFC that could operate at temperatures higher than 250 °C and consequently enable direct thermal coupling of the nHT PEMFC stack and the MSR. Some research efforts in this direction have been published with the development of so-called solid acid fuel cell (SAFC) [5, 6]. Also, a completely new nHT PEMFC is under development [7] by our partners from National Institute of Chemistry Slovenia (NICS). The second way is to use cHT PEMFCs and newly developed LT catalyst [8, 9] that will allow the MSR to operate at temperatures below 200 °C and still achieve near to 100% conversions. In a small system fuel processing reactors are necessarily extremely proximate, and yet must be allowed to attain unique temperatures optimal for their operation. Because elements in thermal contact tend to approach the same temperature a selection of suitable materials and a strategy for thermal insulation of the system is a necessity. Also, finding appropriate sealing materials is crucial. Relatively high temperatures and various fluids present in the system may pose certain problems for conventional sealing materials. NUMERICAL MODELING Proof of concept First objective of numerical modeling was to study and show the concept of compact and highly integrated system with cHT MSR (operating between 230 250 °C) and PEMFC stack. In all designed systems the fuel processing reactors have planar configuration and are stacked into a compact form and arranged in a thermal cascade. Three possible system configurations were analyzed: a) MSR combined with LT PEMFC (Nafion® membranes) that operate between 70 90 °C; b) MSR combined with cHT PEMFC (PBI/H3PO4 membranes) that operate between 130 200 °C; c) MSR combined with nHT PEMFC that operate between 190 300 °C. Two different pathways are used to more thoroughly examine the conceived systems. First, applies a zerodimensional model based on mass and energy balances of the systems. This is done by using Aspen Plus® where all the system model units are studied at their operating, isothermal and stationary conditions (example shown in Figure 2) in conjunction with cHT MSR reaction kinetics.

Second, uses COMSOL Multiphysics® to simulate physical models of integrated systems (example shown in Figure 3). Here, heat transfer is also studied at stationary conditions where the volume average temperature of model units closely corresponds to the temperatures used in mass and energy balance calculations. The two pathways are interdependent and coupled together. The calculation process, design and modeling of the systems are explained more in detail in [11] and the results are shown in Table 1. The conclusion of research was that the system with nHT PEMFC stack is the most efficient because it does not need additional methanol to be burned in catalytic combustor to supply heat to the cHT MSR, unlike in the case of other two systems. Modeling the prototypes Basic design of the prototype system has been developed in 3D modelling software Solidworks. The model is used to visualize the prototype system while it also allows determining construction issues and making quick changes or adaptations of the system. Blueprints for manufacturing the individual components of the system are generated from this model. The system is designed in such a way that it will enable to test LT MSR combined with cHT PEMFCstack as well as cHT MSR combined with nHT PEMFCstack.

Figure 1: Fuel processors sorted according to their operating temperature range

Figure 2: Flowchart of the system with LT PEMFC stack used in Aspen Plus modelling

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

Figure 3: Conceptual design of the system with LT PEMFC stack used in COMSOL modelling

Since, the nHT PEMFC is still under development and currently available materials allow the construction of the combined LT MSR and cHT PEMFC stack system this is the focus of future research. The same numerical approach as explained in scientific paper [11] will be used to obtain geometrical and operational characteristics of such system. For the proper application of the developed simulation approach it is first necessary to determine the kinetics of LT MSR. Also, characteristics of the cHT PEMFC stack need to be determined in order to adequately predict the working regime of the stack. Experimental determination of LT MSR reaction kinetics is still under way but the first results have already been obtained. The tests were carried out in a cylindrical packed bed reactor (10 mm x Φ6 mm), where steam-tomethanol ratio (SMR) of a mixture was 1.3 2, liquid flow rates 0.01 0.16 mL/min, and temperature 180 200 °C. The regression analysis was performed in MATLAB® where the kinetic parameters were fitted to the kinetic model and equations obtained from source [10]. The obtained kinetic parameters where then used in a 3D CFD model

of a MSR with geometry corresponding to the prototype reactor. The results showed that the designed reactor is capable of 100% conversion of methanol at 180 °C, SMR = 1.3 and flow rates up to 0.2 mL/min (see Figure 4). With higher flow rates the conversion starts to drop because the space velocity through the reactor is too high. A special device was used to measure the performance of a single cHT PEMFC which was supplied from Danish Power Systems (DaPoSy). The results were used as a benchmark to further predict the behavior of the cHT PEMFC stack coupled to the LT MSR. Based on measurements shown in Figure 5 operating point of a prototype 2-cell system was determined (see Table 2). Mass and heat flows within the system were assessed using the Excel software and the estimation of heat losses was based on previous research [11]. It can be seen from Table 2 that the predicted flow rate of water-methanol mixture is within the capability of MSR to achieve 100% conversion. Also, estimated heat flows consumed within the system (heating of air, heating and vaporization of mixture, MSR heat consumption and heat losses of the system) are equal to the estimated heat flow generated by the cHT PEMFC stack. Although initial estimates for the combined system have been obtained more in-depth analysis of the LT MSR kinetics and characterization of cHT PEMFC stack is in progress. The results of these analyzes will be used to model the real system based on real experimental data.

Figure 4: Predicted methanol conversion from a 3D CFD model of MSR

Table 1: Comparison of the integrated systems

Integrated system

Stack temp.

Gross electricGross efficiency cogeneration efficiency

Methanol consumption

Methanol Excess Heat conversion air ratio losses

LT PEMFC

70 °C

39.2%

50.5%

7.34∙10-5 mol s-1 a 1.64∙10-5 mol s-1 b

99.0%

9.0

16.1 W c 3.6 W d

cHT PEMFC 180 °C

35.9%

79.2%

9.8∙10-5 mol s-1

97.1%

7.4

3.4 W

nHT PEMFC 255 °C

42.2%

81.6%

8.3∙10-5 mol s-1

98.3%

4.7

3.8 W

used in the MSR used in the catalytic combustor c uninsulated part of the system (natural convection) d insulated part of the system a

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

Figure 5: Blue line represents benchmark measurements for a single cHT PEMFC performed at λO2 = 2.5, λH2 = 1.5, T = 160 °C, pO2,H2 = 1 bar. Green line represents corrected values for conditions λair = 2.5, λreformat = 1.5, T = 185 °C, pair,reformate = 1 bar. Table 2: Estimated characteristics for a 2-cell cHT PEMFC stack – LT MSR system Air Vol. Flow (mL/min)

Mixture Vol. Flow (mL/min)

Pstack (W)

Generated Consumed Heat Flow Heat Flow (W) (W)

911.3

0.19

8.8

15.1

15.0

EXPERIMENTAL SETUP Simultaneously, the construction of the prototype system is taking place. The PEMFC stack will be constructed from composite-graphite bipolar plates and custom designed membrane electrode assemblies (MEAs), purchased from DaPoSy. MSR and vaporizer micro-reactors have been manufactured using laser cutting and welding of stainless steel sheets. DC electric heaters were custom designed and ordered from a commercial supplier. Custom made gaskets from Viton® and other materials used in the system (e.g. insulation, electric collectors, connection tubes, etc.) have also been acquired, as well as measuring and regulation equipment for the prototype system. Work in progress is the individual characterization of the cHT PEMFC stack and the LT MSR. After operational characteristic of both reactors are obtained the operational point (or region) of the combined system can be predicted. Also, a complex measuring system is under development which will be connected to the computer via a program application made in LabVIEW software. This application will be responsible for regulation and control of all process variables in the combined system. CONCLUSIONS

Since nHT PEMFC is still under development and a novel LT MSR catalyst is already available the decision has been made to experimentally prove the concept of the thermally coupled system with LT MSR and stack of cHT PEMFCs. The initial result of modelling show that the LT MSR will be able to provide cHT PEMFC stack with sufficient amount of hydrogen while the cHT PEMFC stack will generate enough heat to cover the needs of the whole system. The ultimate goal of modelling is to find the optimum geometry, temperature profile and operation point of the combined system and further to use these results to construct the prototype system and experimentally validate its characteristics. References [1] GORE, GORE® PRIMEA® MEAs, http://www.gore. com/en_xx/products/electronic/fuelcells/series_56_ mea_fuel_cells.html, Accessed on: 28.1.2014 [2] BASF, Celtec® P1100W, http://www.fuel-cell.basf. com/cm/internet/Fuel_Cell/en_GB/, Accessed on: 28.1.2014 [3] C. Pan, R. He, Q. Li, J.O. Jensen, N.J. Bjerrum, H.A. Hjulmand, A.B. Jensen, Journal of Power Sources, 145 (2005), 392-398. [4] J.D. Morse, R.S. Upadhye, R.T. Graff, C. Spadaccini, H.G. Park, E.K. Hart, Journal of Micromechanics and Microengineering, 17 (2007), S237. [5] C.R.I. Chisholm, D.A. Boysen, A.B. Papandrew, S. Zecevic, S. Cha, K.A. Sasaki, Á. Varga, K.P. Giapis, S.M. Haile, Interface, 18 (2009), 53-59. [6] A. Hindhede Jensen, L. Qingfeng, E. Christensen, N.J. Bjerrum, Journal of the Electrochemical Society, 161 (2014), F72. [7] S. Hočevar, A. Kržan, Patent application PCT/ EP2014/070697. [8] K.M.K. Yu, W. Tong, A. West, K. Cheung, S.C.E. Tsang, Y. Guo, T. Li, G. Smith, Nature Communications, 3 (2012). [9] W. Tong, K. Cheung, A. West, K.-M. Yu, S.C.E. Tsang, Physical Chemistry Chemical Physics, 15 (2013), 7240-7248. [10] H. Purnama, T. Ressler, R.E. Jentoft, H. Soerijanto, R. Schlögl, R. Schomäcker, Applied Catalysis A: General, 259 (2004), 83-94. List of publications [11] A. Lotrič, M. Sekavčnik, S. Hočevar, Journal of Power Sources, 270 (2014), 166-182. [12] A. Lotrič, S. Hočevar, Methanol steam reformer - high temperature PEM fuel cell system analysis, Military Green 2012, Brussels, 2012, 115-126

The numerical modelling proved the concept of integrated MSR–PEMFC-stack systems and provided the basis for the design of experimental setup. The results showed it is more reasonable to use HT PEMFC in the integrated system because it has advantages over LT PEMFC (no water management, no reformate clean-up, higher tolerance to CO) and also shows higher system efficiencies.

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

Scaling-Up of a Fast Internal Circulating Fluidized Bed Gasifier – An Experimental Approach ABSTRACT → This short presentation deals with the study of particles dynamics in a cold flow model of FICFB (Fast Internal Circulating Fluidized Bed) biomass gasification process and its scale-up to a hot semi-industrial plant. The process was designed and experimentally tested on a cold-flow model and scaled-

up to 1 MWth semi-industrial process. For a reliable scaling up, similar flow conditions were achieved in both units, by the use of a set of dimensionless numbers.

INTRODUCTION Jernej Mele, Ph.D. Laboratory: Laboratory for Heat and Power E-mail: melejernej@gmail.com Company: Bosio d.o.o., Obrtniška cesta 3, SI-3220 Štore Phone: +386-31-799-674 Status: Former PhD student (Finished post-graduate study: June 2014), Head of research and development in company Bosio d.o.o. Research area: Biomass gasification, pyrolysis, fluidized beds Mentor: Assoc. Prof. Dr. Andrej Senegačnik Co-mentor: Ass. Prof. Dušan Klinar, Ph.D.

While researching the 1 MWth Fast Internal Circulating Fluidized Bed gasification process certain questions concerning particle dynamics in gas flows arose. The gas-solid flow of FICFB is almost impossible to precisely model either analytically or numerically. Building a semi-industrial plant is very expensive and there is no certainty that the semi-industrial apparatus will perform the planned task. Therefore, building a much cheaper, small-scale cold flow model in order to design a large scale system more confidently can be economically justified. The FICFB gasifier being studied and discussed in this article is divided into two major fluidized bed reactors/ zones: a gasification zone and a combustion zone (Fig. 1). The solid fuel is fed into the gasification zone fluidized with superheated water steam (A). The bed material together with some remaining char moves to the combustion zone though the chute (B). In the combustion zone (C), the remaining carbon burns and heats up the bed material. Hot bed material is pneumatically transported through the riser (C) to the cyclone (D) where it is separated and collected in a siphon (E). The siphon fully filled with hot bed material acts as a gas barrier between reactors i.e. syngas and flue gas. Hot bed material supports the endothermic gasification reactions with heat. A dual fluidized bed system allows the treatment of

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

separated gas streams with the same circulating solid and the production of a high-grade syngas that is practically nitrogen free. The most commonly described approach in the literature [1] to achieve hydrodynamic and reactive similarity in two fluidized beds is to use sets of dimensionless numbers which have to be kept constant in both scales. These sets of dimensionless numbers have been modified and extended by several authors in order to provide a more integrated view of the diverse phenomena taking place in fluidized bed reactors. Successful scaling can be evaluated by various validation tools from classical timeseries analysis to novel methods adapted from chaos theory. The key point and novelty of our study is that the scale-up criteria compares the units for different fluidized bed regimes and considers the change in the process parameters. Stable particle circulation can be achieved with different pressure profiles but with a high impact on the thermo-chemical part of the process. EXPERIMENTAL EQUIPMENT The experiments were performed in cold-flow model of 1 MWth semi-industrial gasifier that operates in Celje. To achieve hydrodynamic similarity between the cold-flow model and the semi-industrial process, the full set of Glicksman scaling rules [2] were applied.

Cold-flow model The cold-flow model was designed in order to simulate the hydrodynamic process of FICFB gasification with cold air under arbitrary conditions. It was made from stainless steel and glass, so that the particle behavior could be observed. The dimensions of the cold flow laboratory unit were ~3 times smaller than 1MWth semi industrial plant by applying the scaling criteria of Glicksman (1984) [2]. Accordingly, the cold-flow model was operated with ambient air and lower B Geldart’s particles of quartz sand as the bed material. FICFB semi-industrial plant The semi-industrial plant (Fig. 1) was designed to take into account the heavy thermal and abrasive conditions which occur in it. Gas chambers are made of heat resistant stainless steel and protected by thermo concretes so that the hot gas-solid flow does not trite the steel walls. The main gas inlets are superheated water steam and preheated air; the main outlets are hot flue gas from cyclone and syngas from the reactor. This semi-industrial plant was designed on the basis of a study carried out on a cold-flow model. The scale-up procedure was evaluated by comparing these two systems. MATHEMATICAL MODEL Two physical phenomena or processes are similar if at corresponding moments of time at corresponding points, the values of the variable quantities that characterize the sys-

tem state are proportional to the corresponding quantities of the second system. From similarity theory we know of a few types of similarities like geometrical, kinematical, dynamical, thermal, chemical, economical, etc. Practice shows us that all criteria of similarity cannot be satisfied at the same time. In other words all similarity factors between the laboratory and industrial model cannot be alike. Process designers have to determine which factors should be considered. The inner circulation flows and fluidization should first be treated, followed by the energy and mass balance. Cause if the desired fluidization state is not achieved than the following chemical process will not work as planned. Dynamic similarity Glicksman derived the “full set” of relevant dimensionless scaling laws by non-dimensionalising the equations of motion and conservation of mass of the gas and particle phase:

This set includes the Reynolds number Rep (ratio: inertial vs. viscous forces), the Froude number Frp (ratio: inertial vs. gravitational forces), the ratio between gas ρg and particle ρp density, the particle size distribution (psd), the ratio between particle dp and reactor diameter D, the particle sphericity FS, the superficial gas velocity vg, the dynamic viscosity ηg as well as the geometric similarity in terms of reactor shape, diameter, height, etc. Under Glicksman scaling laws, only hydrodynamic similarity is taken into account, while similitude in terms of kinetics, heat and mass transfer or chemical reactions due to gasification is blatantly neglected [3]. The novelty of our approach was in additional criteria of phase changes during gasification and causes conical reactor geometry. Fluidizing velocities FICFB system is a multiple-fluidized bed system, with a bubbling fluidized bed in the reactor, chute and siphon, and pneumatic transport in the riser. To achieve circulation of the bed material, the correct regimes must be reached at the same time. For small particles and low Reynolds numbers, the viscous energy losses predominate. Running the gasification in the vicinity of minimal fluidization velocity lowers the consumption of gasifying agent in the reactor, as well as lowering the consumption of energy and moisture in raw syngas. For the estimation of minimal fluidization velocity vmf we use Ergun’s equation where εmf is bed voidage at minimum fluidization velocity [3]:

For large particles only the kinetic energy losses need to be considered:

Figure 1: Pressure measuring points in semi-industrial unit

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

Scale-up and designing the model On the basis of the mathematical model, an estimation of flow conditions in the reactor and the combustion zone can be made. Comparison of physical, thermodynamic and transport properties between the laboratory and the semi-industrial unit are presented in Table 1. The operating temperature of the semi-industrial unit is much higher and therefore the influence on transport properties should be considered (Girimonte and Formisani 2009 [4]). In the laboratory unit, gas-solid flows are generated with upward-blowing arbitrary air whereas in the semi-industrial unit the bed material is fluidized with superheated steam and in the riser with hot air. Endothermic chemical reactions of pyrolysis and a water-gas-shift reaction are running in the reactor while exothermic combustion occurs in the combustion zone. Flue gas exits the combustion zone with a temperature Tg,comb ≈ 900°C and syngas exits the reactor with a Tsyn ≈ 780°C. Gases in the semi-industrial unit have lower densities and higher dynamic viscosities than the air in the laboratory unit. The bed material is quartz sand with an average diameter of 400-600 μm. In order to establish similar conditions, we have to use smaller particles in the lab unit – quartz sand with average particle diameter of 100-300 μm. In industrial applications, the flow of fluidizing fluid is typically chosen as a function of the desired fluidization state and/or required mass and energy balances, etc. From a reactor design point of view, it is important to define the reactor dimensions - especially its cross section. At the reactors inlet and outlet operational superficial gas velocity for gasification vlim,g and combustion vlim,t zone must be greater than minimal required for desired fluidization state. So we can define the following:

In this way the diameter becomes function of a superficial gas velocity. With respect to mass and energy balances in conical reactors the following holds:

(8)

(9)

By simplifying equations and introduction of volume flow at inlet ΦV,0 and outlet ΦV,1 a new expression can be obtained: (10)

If the changes of temperature, pressure, and chemical composition of the gas does not impacts the superficial gas velocity on the inlet and outlet vg0≈vg1 the approximation can be made:

(11)

So theoretically, if a gas is incompressible and there is no changes in volume flow ΦV,0 = ΦV,1 , vg,0 = vg,1 the reactor could be cylindrical.

(12)

But even in a cold flow model we must have slight conical areas were a gas velocity and non-mono size distribution of particles are compensated. EXPERIMENTAL WORK

for combustion zone (5)

In the reactor (A) a bubbling fluidized bed was established. The angle of the chute (B) is designed such that there is no solid flow if the particles are not fluidized. All the particles transported to combustion cone (C) are pneumatically lifted to the cyclone (D) and simultaneously heated up. With long dwelling times of particles in the combustion cone, particles collect as much heat as possible. Red-hot particles are separated from the flue gas in cyclone and finally gathered in siphon (E). The auxiliary inlet (I2) acts to fluidize the gathered hot particles and transport them to the reactor. This process is controlled using a statistical method, i.e. the pressure drop across the bed versus superficial gas velocity. Monitoring the pressures and temperatures is important for experimental work. The measuring equipment was an Endress+Hauser PDM75 with a measuring range from 0–1000 Pa ± 1 Pa for gas flow and Siemens Sitrans 250 delta bar with a measuring range from 0–100 mbar ± 0.5 mbar for the fluidized bed pressure drop measurements. In the case of the semi-industrial FICFB gasifier, temperatures were measured using NiCr-Ni thermocouples (type K) with a measuring range of 0–1250 °C ± 9.4 °C. The semi-industrial unit has a solid-flow sensor SWR SolidFlow FSM installed for measuring the mass particle flow. All the gas flows are measured with orifices. The locations of the measuring places are presented in Fig. 1, Fig. 2.

(6)

Gasification and combustion reactions impacts two important parameters. Firstly with change of chemical composition and temperature the gas density ρg and viscosity ηg changes. So the lower limits for superficial gas velocity changes over the zone. Secondly, with expansion of gas volume in non-conical reactors, the superficial gas velocity would rapidly increase along reactor height. The goal is to keep the superficial gas velocity close as possible to a vmf and vt. For efficient heat transfer between gas and solid particles we need long dwelling times of solid particles in the reactor. The suggested construction solution is to increase reactor inner cross section over the height. The mass flow of gas goes perpendicularly through a flat plane area of a reactor and we can presume a basic fluid dynamics equation:

(7)

for gasification zone (4)

In the reactor, gas volume increases due to chemical reactions of gasification, steam reforming and combustion. For example some reactions like water-gas formation (6), increases the volume. From one mole of gas (water steam) we get two moles of gas, CO and H2.

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

Table 1. Technical and process data for the cold-flow model and the semi-industrial reactor

Parameter

Symbol

Cold-flow model

Semi-industrial unit

Reactor diameter at gas entrance

dreak,1 [mm]

100

300

Reactor diameter above the fluidized bed

dreak,2 [μm]

190

500

Conical bed angle

α [°]

Gas distributor type

Sandwiching nets Bubble cap

Bed material

Quartz sand

100–300

400–600

lower B

middle B

Particle size

dp [μm]

Geldard’s classification Particle density

ρp [kg/m ]

2650

Bulk density

ρp,b [kg/m3]

1575

1550

Stationary bed height

L [mm]

130

400

Fluidization medium

Air

Steam*

Syngas**

Temperature

Tg,reak/Tsyn[°C]

550

780

Density

ρg [kg/m3]

1.124

Dynamic viscosity

ηg [Pas]

1.8·10

3.1·10

4.6∙10-5

Volume flow of fluidization medium

ΦV,reak [m3/h]

31.1

517.1

4275

Gas velocity (experimental)

vg0 / vg1 [m/s]

1.11

2.03

6.05

Gas velocity (predicted)

vg0 / vg1 [m/s]

0.397

1.40

1.66

Pressure drop (experimental)

p2,3 [mbar]

13.5

47.8

Pressure drop (predicted)

p2,3 [mbar]

13.9

42.6

0.288 -5

0.192 -5

SCALE-UP SET OF DIMENSIONLESS NUMBERS Particle Reynolds number

Rep

4.96

6.52

2.13

Froude number

Frp

0.161

0.67

0.21

Gas: particle density ratio

ρg / ρp

0.00042

0.00012

0.00007

Diameter: combustion cone height ratio

dreak,1/L dreak,2/L

0.77 1.46

0.75

1.25

Particle: combustion cone diameter ratio

dp/ dreak,1 dp/ dreak,2

0.002 0.001

0.0017

0.0008

Particle sphericity

0.9

Particle size distribution

psd

100–300

400–600

* Gas inlet at the bottom of the reactor ** Gas outlet above the fluidized bed in the reactor

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

Figure 2. Scheme of the FICFB laboratory and semi-industrial unit

CONCLUSIONS Modern gasification systems use fluidized beds. These provide a more homogenous temperature profile in the bed and better heat transfer, as well as allow the possible use of the catalyst as the bed material and allow the use of a gasifying fuel with a wide size distribution of particles. At the outset, we carried out basic engineering procedures for the actual 1 MWth FICFB gasifier. Due to high cost that would be incurred if there were errors in our model, the decision was made to test the process in a low cost small-scale unit. The units were designed according to full set of Glicksman scaling laws. The assumption of particle flow similarity is based on a direct comparison of particle Reynolds numbers, Froude numbers, the ratio between gas ρg and particle ρp density, the particle size distribution (psd), the ratio between particle dp and the reactor diameter D, the particle sphericity FS, superficial gas velocity vg, dynamic viscosity ηg as well as the geometric similarity in terms of reactor shape, diameter, height, etc. Chemical reactions during gasification and combustion cause variations in temperature, density, and dynamic viscosity, all of which affect particle dynamics. It is practically impossible to create similarity by equalizing all the criteria in the scale-up set. Even though, if we would have been able to equalize all the scale-up parameters, it would be still made on assumptions, e.g. the composition of syngas is predicted on the basis of a mathematical model until the chemical composition is known. The aim was to stay within a 50 % deviation of the dimensionless numbers between the units. Some of them differed only by 3 % and some of them were above 100 % (Table 1). The scale-up protocol was confirmed with the successful demonstration of the FICFB semi-industrial unit located in Celje, Slovenia.

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References [1] Rüdisüli, M., Schildhauer, T. J., Biollaz, S. M. A., Van Ommen, J. R. (2012). Scale-up of bubbling fluidized bed reactors – A review. Powder technology, 217, 2012, 21-38. [2] Leon R. Glicksman (1982), Scaling Relationships For Fluidized Beds. Chemical engineering science, 39, 1373-1384. [3] Gupta S. K., Agarwal V. K., Singh S. N., Seshadri V., Mills D., Singh J., Prakash C. (2009). Prediction of minimimum fluidization velocity for fine tailing materials. Powder Technology, 196, 263-271. [4] Girimonte, R., Formisani, B. (2009). Bubbling velocity of fluidized beds operating at high temperature. Powder Technology, 189, 74-81. List of publications [5] Mele J., Golobič I., Senegačnik A., A method to detect and control fully fluidized conical beds with a wide size distribution of particles in the vicinity of the minimum fluidization velocity. Thermal science, ISSN 0354-9836, 2014 [6] Mele J., Oman J., Krope J. Scale-up of a cold flow model of FICFB biomass gasification process to an industrial pilot plant - hydrodynamics of particles. WSEAS transactions on fluid mechanics, Jan. 2010, vol. 5, iss. 1, str. 15-24. [7] Mele J., Senegačnik A. Teorija podobnosti pri načrtovanju uplinjevalnika biomase v lebdečem sloju. V. Voršič, Jože (ur.). Komunalna energetika : oskrba z energijo. Maribor: Fakulteta za elektrotehniko, računalništvo in informatiko, 2013, str. 1-12 [8] Mele J., Senegačnik A. Minimal velocity of full fluidization a new determination method. 21. Mednarodno posvetovanje Komunalna energetika, 15. do 17. maj 2012, Maribor, Slovenija. Voršič, J. (ur.). Proceedings. Maribor: Fakulteta za elektrotehniko, računalništvo in informatiko, 2012, str. 1-9

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

Heat treatment furnace modelling with CFD ABSTRACT → Heat treating is a common term describing various procedures of altering properties of metals and other materials heating and cooling to extreme temperatures in order to improve specific characteristics of the materials. The courses of the procedures are precisely defined in order to achieve the target characteristics of the materials. Appropriate numerical simulations of the process can provide useful guidelines for optimal furnace design and procedure regulation that will result in homogeneous

treatment of large scale products with complex geometry. Fuel combustion as well as radiative, convective and conductive heat transfer has to be taken into consideration simultanously. Basic numerical models need to be enhanced with empirical models so combination of numerical simulations and experiments is essential for the development of good numerical simulations.

INTRODUCTION Boštjan Drobnič Laboratory: Laboratory for Heat and Power E-mail: bostjan.drobnic@fs.uni-lj.si Room: S-I/67 Phone: +386-1-4771-715 Status: researcher Research area: Energy systems, numerical simulations

During the production phase of various materials it is essential to give the material proper characteristics to suit the final product‘s functional requirements. Among other procedures to alter materials‘ properties heat treating is widely used particularly for metals and alloys. Their mechanical properties depend on size, shape and distribution of various microconstituents. These can be changed by a process of heating the material to a specific temperature, holding at this temperature and cooling. During the process the metal remains in solid state, but the internal structures of the material change, [1].

natural gas from multiple burners distributed around the workpiece. Proper regulation and accurate monitoring of the process are essential for achieving requested results, i.e. material properties. In order to optimize design and operation of heat treatment furnaces numerical modelling of temperature conditions within the furnace as well as the workpiece can be employed. Although fluid flow, heat transfer and combustion can be modelled with existing commercial CFD tools several issues need to be addressed to set up an accurate model that can be used with limited computational capacities and in an acceptable time frame. It should be noted that the heat treatment process is time dependent and should be treated as a transient case, thus requiring notably larger number of calculation steps and also longer computational time. NUMERICAL MODELLING

Figure 1: Example of heating and cooling curve for a heat treatment process

Every heat treatment process should follow appropriate heating and cooling curve (Fig. 1). The temperature levels, temperature gradients, intervals of constant temperatures etc. are ensured by appropriate heat input. Large scale heat treatment furnaces are frequently fired with 24

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

Basic numerical modeling consist of building geometrical model of the computational domain, meshing the geometry, defining boundary conditions, choosing appropriate numerical models, running the simulation and post-processing the results. Since there are several models available to model fluid flow (turbulence models), heat transfer (including radiation) and combustion, [2], it is important to choose the models that give the most accurate results

REFERENCE EXPERIMENTAL CASE For the initial comparison of numerical results measured values from a typical operation of the observed heat treatment furnace were used. The furnace has rectangular shape, 8.25 m long, 4.5 m wide and 3.4 m high. It includes two cylindrical work pieces approximately 7.5 m long and 1.2 m in diameter, Fig. 2.

Figure 2: Furnace and work pieces geometry

Heat is supplied through 12 burners, 6 on the lower edge of each side wall. The burners operate sequentially with constant time of operation for each burner, while pause between ignitions are adjusted to the desired heat input, i.e. temperature gradient. During the reference operation of the furnace five temperatures were measured: • three temperatures of the furnace interior at the top of the furnace, • surface temperature of each of the work. Since temperatures of the interior do not differ significantly and surface temperatures of both work pieces are also very similar, only one temperature curve for the furnace and one for the work pieces are shown in Fig. 3.

Figure 3: Temperature curve of actual heat treatment

PRELIMINARY NUMERICAL SIMULATIONS To develop a procedure and numerical model that provides results of suitable accuracy without requiring extreme computational resources and computational time numerical simulations of the reference heat treatment furnace were performed. Since the entire process lasts over 400 hours while the burner operating time is 20 seconds, it was initially decided to model only a short interval in the range of quasi stationary operation at the maximum temperature. The entire simulated interval was 160 s long and was divided into 2 s time steps. Temperature was monitored in five points within computational domain corresponding to the experimental measuring points. Two different operating regimes were compared where burners were switched on for 20 s, while pause between two subsequent burners was 20 s and 30 s for cases A and B, respectively. Burner ignition sequence was identical in both cases with alternating ignitions on both sides of the furnace. Temperature curves for both cases are show in Figs. 4 and 5. Both figures show similar response of the temperatures of the furnace interior to ignition. It can also be noticed that the temperatures of both work pieces is rising with a significantly smaller gradient compared to changes of furnace temperatures.

temperature / °C

for the given conditions within a heat treatment furnace. Numerical results must therefore be validated with experimental results in order to find an appropriate combination of models employed, [3]. Major issue that needs to be resolved when modeling large scale heat treatment furnace are extreme scale ranges for both time and space. Heat treatment processes typically last for several days and gradients of temperature in the work piece are of the order of 1 K per minute. On the other hand, intervals of burner operation are measured in seconds. Appropriate time steps that sufficiently describe the dynamics of the burners should be in the order of 1 second, which would require thousands of time steps to cover the entire process. Similarly the size of the entire computational domain is of the order of several meters. Heat transfer, on the other hand, appears in the boundary layer next to furnace walls and work piece surface. If boundary layer is to be meshed appropriately extreme computational resources and computational time would be required. Both of the abovementioned scale related limitations call for simplification of the numerical model with implementation of suitable empirical models.

Figure 4: Temperature curves from numerical simulation of case A

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

temperature / °C

Figure 5: Temperature curves from numerical simulation of case B

temperature / °C

The response to the ignition of the first burner differs significantly from the later ignitions in both cases. This indicates that a certain number of precalculation steps should be done in order to ‚prepare‘ flow and temperature conditions within the computational domain for the actual simulation. For a comparison Fig. 6 shows measured values of the temperatures shown in Figs. 4 and 5 during an interval of the same length as the simulated interval. Since the sampling was done in 60 second intervals it is obvious that the dynamics of the process cannot be properly presented with this kind of measurements.

Figure 6: Measured temperature curves in time interval comparable to simulations

The simulation time for the presented cases was longer than the actual simulated time by factor of over 300 with available computational resources. Therefore it is necessary to employ certain simplifications to numerical model in order to make numerical simulations feasible. SIMPLIFICATIONS OF NUMERICAL MODEL When making simplifications of a numerical model the desired output of the simulation should be taken into consideration, [4], [5]. Numerical simulations of a heat treatment furnace can be approached to in two ways: 1) Thermal conditions within work piece material are of primary focus, to monitor heat distribution, thermal stresses etc. 2) Temperature conditions within furnace 26

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

are monitored in order to provide optimal conditions for heat treatment with appropriate regulation of heat supply. In case 1 the conditions within furnace is only important through its influence on the heat input in the work piece. Modelling could be simplified by finding the influence of separate burners on heat flux distribution over the surface of the work piece. The acquired heat flux distribution can be used as boundary condition for relatively simple simulations of heat conduction through work piece material disregarding the furnace. Detailed simulation of stationary operation of a single burner is first modelled and heat flux profile of the entire work piece surface is acquired as a result, Fig. 7. The profile is simplified and applied as boundary condition in a simulation of work piece without furnace.

Figure 7: Simplification of numerical model: a) heat flux distribution, b) simplification of data, c) applying boundary conditions

The simulations of heat conduction in solid material do not require high grid density and due to non-moving material several equations can be omitted from numerical model. This results in shorter simulation times enabling transient simulations of longer intervals or entire heat treatment process. Case 2 focuses on heat treatment furnace design and regulation where it is important to provide conditions that will enable optimal heat treatment process. Due to relatively large computational domain grid density should be reduced which requires additional attention to modelling small scale processes such as fluid-solid heat transfer and combustion. Furthermore, timesteps of the transient simulation will have to be longer than burner operation interval therefore the effects of burners will have to be modelled with a separate empirical model. In both cases simplifications as additional models will have to be based and thoroughly validated both with experiments and detailed numerical modelling of particular shorter intervals of heat treatment process.

CONCLUSIONS Heat treatment of metals is an important part of material processing to provide appropriate properties of the material. The experiments in a high temperature environment of a heat treatment furnace are difficult and due to time consuming due to the length of the process. It is expected that numerical simulations could provide deeper insight of the processes during heat treatment. Furthermore it enables optimization of both heat treatment furnaces design and the process itself taking into consideration particular geometry of work pieces and the requested characteristics of the final product. Since detailed numerical simulations of the entire process are extremely time and computational resources consuming, simplifications of numerical model are proposed. The simplifications and additional empirical models must, though, be based on experimental data and results of detailed numerical simulations. While development and validation of simplified models will require considerable initial investment both in time and resources, it is expected that accurate simplified numerical model can provide a useful tool for heat treatment furnace design as well as optimization of the heat treatment process. References [1] Rajan, T. V., Sharma, C. P., Sharma, A.: Heat Treatment: Principles and Techniques, PHI Learning Pvt. Ltd., Jan 1, 2011. [2] ANSYS 16.1 Help: CFX-Solver Modeling Guide [3] Oreskes, N., Shrader-Frechette, K., Belitz, K.: Verification, Validation, and Confirmation of Numerical Models in the Earth Sciences, Science, New Series, Vol. 263, No. 5147 (Feb. 4, 1994), pp. 641-646. [4] Srebric, J., Chen, Q.: Simplified numerical models for complex air supply diffusers, HVAC&R Research, 8(3), pp. 277-294. [5] Sutriso, W., Wahyuni, E.: Simplification of Numerical Model to Analyze the Uniformly Heated one Way Reinforced Concrete Slabs Exposed by Fire, International Journal of Engineering and Innovative Technology (IJEIT), Volume 4, Issue 6, December 2014, pp. 197-201.

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

The Mass-Flow Distribution of Pulverized-Coal Using an Array of Intrusive Electrostatic Sensors ABSTRACT → Fan/impact mills are commonly applied for the grinding and dilute-pneumatic transportation of lignite or brown coals with high moisture contents to the furnaces in large steam boilers. Each of the 2 to 8 mills feeds pulverized coal into two or more burner nozzles. An online detection of the pulverized-coal mass-flow distribution among the burners is vital for the control of the combustion process. Knowing the distribution, actions for the redistribution of the coal, or alternatively, for the adjustment of the combustionair flow according to the actual distribution, can be employed. Determining the characteristics of gas-solid

two-phase flow using an electrostatic principle is a promising online method of measurement because it is robust and inexpensive. Furthermore, due to their better spatial sensitivity, rod sensors are more suitable for large rectangular ducts related to fan/impact mills than ring-, pin- or arc-shaped sensors. Sets of 1D and 2D electrostatic-sensor arrays with a corresponding data-acquisition system were employed to determine the mass-flow distribution in the cross-section of the duct that feeds the pulverized lignite to the four burner nozzles.

INTRODUCTION Boštjan Jurjevčič Laboratory: Laboratory for Heat and Power E-mail: bostjan.jurjevcic@fs.uni-lj.si Room: S-I/67 Phone: +386-1-4771-715 Status: PhD student (started: October 2013, to be completed: November 2016) Research area: Electrostatic measurements in pneumatic transport Mentor: Assoc. Prof. Dr. Andrej Senegačnik

The share of renewables in the world’s energy production is increasing constantly. As a result, more dynamic and flexible power generation in fossil-fuel-fired power plants requires precise coal-combustion control over a wider range. A measuring method based on the electrostatic principle can be exploited for the characterization of the pneumatic transport of pulverized coal from the mills to the burners. Other measuring techniques are available for measurements in pneumatic transport, based on capacitance, thermal, modulation and the attenuation of ultrasonic waves, radiation and optics. They all have their own advantages and disadvantages [1]. Most of them involve complicated and expensive installations and are unsuitable for operations in harsh environments. Besides the inherent low cost and robustness, the lack of the need for an external power source makes electrostatic sensors very attractive for multi-point online measurements. Research in the field of electrostatic measurements used in pneumatic transport began a few decades ago [2]; this has resulted in different shapes of sensors being developed. Electrostatic sensors can be divided into two main categories, i.e., intrusive and non-intrusive. In the past decade, non-intrusive ring-

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

shaped [3], [4], arc-shaped [5] and pin-shaped [6] sensors have received the most attention. A strong argument for the use of non-intrusive electrostatic sensors is that they do not obstruct the flow. However, they do have some disadvantages. The installation and replacement of the circular sensor in a power plant can be difficult and expensive. A part of the duct needs to be replaced, which offsets the cost effectiveness that is generally associated with the electrostatic method. In addition, sensing is most effective in the immediate vicinity of the sensor and there is a lack of information about the flow phenomena that are far from the sensor, i.e., in the center of the duct or pipe [1]. Even more problematic is the use of nonintrusive sensors in rectangular ducts, where the sharp corners additionally affect the spatial sensitivity [7]. An alternative option is the use of rod-shaped, intrusive electrostatic sensors that are much easier and less expensive to install. Only small openings in the duct wall are needed to insert the sensors into the duct. The sensors do present some restrictions to the flow, but the area covered by rod sensors is negligible in comparison with the cross-sectional area of the duct. This shortcoming is outweighed by their good spatial sensitivity [7], [8].

Many studies on electrostatic sensors were made under controlled conditions using laboratory test rigs, but many fewer involved real power-plant systems. Measurements of the velocities of pulverized coal, the mass flow, the mass concentration and the particle distribution at real facilities were mostly carried out in thermal power plants that burn hard coals, where the grinding is carried out in central mills that feed pulverized coal to the burners via pipes with relatively small diameters (< 300 mm). Less research was conducted on lignite-fired boilers with 2 to 8 fan/impact mills, each feeding pulverized coal to several burner nozzles. The cross-sectional area of the duct that is common to all burner nozzles is usually large and often rectangular in shape. In this case it is more convenient to use intrusive, rod-type electrostatic sensors to determine the distribution of the pulverized lignite in the duct. In the past, wire-mesh-type sensors were investigated for the detection of the mean particle size. They have great spatial sensitivity and great potential, particularly in large ducts, but unfortunately they only give integral information over the whole cross-section of the duct [8]. With the aim to obtain local information about the flow characteristics in large ducts, two different concepts of measuring system were tested: a one-dimensional (1D) system using a set of 8 fixed non-segmented rod-type electrostatic sensors, and a two-dimensional (2D) system using a single, segmented electrostatic sensor placed sequentially at positions matching the positions of fixed, non-segmented, rod sensors.

The electrostatic sensor is wired through a measuring resistor to the ground and an electrical current I caused by the released electrical charge emerges. With a suitable measuring system a time series (signal) of fluctuating-voltage drops on the measuring resistor can be acquired. The signals are related to the mass flow and the velocity of the particles, the electrical properties of the particles, the dimensions of the sensors, the chemical composition of the particles, etc.

ELECTROSTATIC MEASUREMENTS An array of intrusive rod sensors with a multichannel dataacquisition system is proposed as a way of obtaining more detailed information about the flow characteristics in large duct of rectangular cross section. A set of electrostatic sensors protruding through the whole duct (Figure 1, right side) enables a 1D measurement in the metering plane that is perpendicular to the flow direction in the duct. To obtain more detailed information about the flow in the duct, the 2D measuring method needs to be employed. A segmented, rod-type, electrostatic sensor (Figure 1, left side) wired to a multichannel data-acquisition system (Figure 2) is proposedÂ [9]. By using several fixed segmented electrostatic sensors or by shifting a single portable segmented sensor to different locations across the metering plane during the stationary operating regime a 2D distribution of the pneumatic transport characteristics can be obtained.

Figure 2: Segmented sensor with a multichannel data acquisition system.

According to a non-dimensional analysis of the PiTheorem [3] the mass flow through the quadrant qm assigned to the sensor can be estimated as : (1) where U is the measured voltage drop over the resistor R and v is velocity. Most of the equations proposed by different authors [3],Â [4] treat the velocity as one of the most influential parameters. For an absolute mass-flow calculation knowing the function gn is required. It can be assumed that for this particular case the mass flow qm is proportional to the ratio W. With the time-averaged value of the measured voltage drop Uu over the resistor Ru for a particular rod sensor and the velocities vu measured at the u-th position, the normalized mass flow wu per quadrant assigned to the u-th position (Figure 1) is expressed as. (2) where N refers to the number of positions u.

Figure 1: Cross section of the duct with four partitions and installation positions for the segmented or nonsegmented sensors. YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

In the large duct using a segmented sensor, the normalized mass flow wu,s per quadrant assigned to the u-th position and the sth segment (Figure 1) is expressed as . (3) where N refers to the number of positions u, and M to the number of the segments s. After a normalized mass flow for each measuring quadrant is calculated, a suitable interpolation method can be used to provide a three-dimensional plot and thus visualize the normalized mass flow per unit of cross-section across the measuring plane. The Kriging method, a weighted moving-averaging method, was used in this case. SYSTEM DESIGN The electrostatic measuring method was tested on a lignite-fired power plant with a power output of 345 MW. Each of the six fan/impact-type mills feeds pulverized coal to the four burner nozzles. The grinding and conveying system is schematically presented in Figure 3. During the measurements were the mill-rotating speed and feederrotating speed set to 486 rpm to 140 rpm respectively.

Figure 3: Thermal power plant’s coal grinding and transport system to the burner.

The duct is physically divided into four partitions, i.e., I–IV, as seen in Figure 1. Each partition leads to one of the four nozzles. The 1D and 2D measuring systems were applied. The 1D measuring system consists of 8 rod sensors mounted at the positions u1,…,u8 (Figure 1). The diameter and length of each rod sensor were 15 mm and 1200 mm respectively. The sensors were manufactured of abrasion-resistant stainless steel. The sensors occupied 4.4 % of the duct’s cross-sectional area. Each sensor was grounded via a measuring resistor. On each resistor (Figure 2) the voltage time series Uu(t) was measured with a 30

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

sample rate of 1000 Hz. The internal impedance of the data-acquisition module was 10 GW, the measuring range was ±10 V, the absolute accuracy was 6230 μV, the random noise was 240 μV, the sensitivity was 96 μV and the ADC conversion was 16 bit. The 2D measurements were carried out with a single electrostatic segmented sensor. The sensor had six, 190-mm-long segments (s1,…,s6) with a diameter of 21 mm (Figure 2). The segments were electrically isolated from each other. Each segment was grounded via a measuring resistor. The segmented electrostatic sensor was placed consecutively into the positions u1,…,u8 (Figure 1) during the stationary (mill’s control system was set to manual operation) operation of the coal feeder and the mill. The voltage time series Uu,s(t) were measured and recorded for all the segments and positions. In total there were 48 measuring points recorded with the same dataacquisition system that was employed for the 1D measurement so as to avoid any systematic errors. For the analysis, all the voltage time series for the 1D and 2D measurements were trimmed to 36,000 readings recorded over an interval of 36 seconds. The carryinggas velocities vu,s were measured with a pitot-like probe at 48 positions that matched the positions of the sensor segments. RESULTS Figure 4 shows the 1D and 2D distributions of the normalized mass flow per unit of the cross-section and the 2D distribution of the velocity. An uneven left-to-right distribution of the normalized mass flow is evident from Figure 4a. The distribution of the normalized mass flow indicates that the mass flow to the burner nozzles receiving the coal from the left-hand side of the duct is considerably larger than to the burner nozzles receiving the coal from the right-hand side of the duct. Furthermore, the normalized mass flow near to the left- and the right-hand walls is larger than in the central area. The normalized mass flow is the largest in partition IV, approximately 30 % above the arithmetic mean for the duct. The smallest normalized mass flow is in partition III, approximately 25 % below the arithmetic mean. The 1D-array of electrostatic sensors is therefore suitable for the online monitoring of the distribution of the coal among the burners. If this information is provided, boiler operators can take appropriate actions for the redistribution of the pulverized coal or, alternatively, for the adjustment of the combustion-air flow according to the actual distribution of the pulverized coal. A 2D array of electrostatic sensors is able to provide even more detailed information about the flow conditions in the duct. Figure 4b shows that the maximum normalized mass flow occurs at the minimum depth, i.e., near the duct wall, with taps for inserting the sensor. The maximum normalized mass flow at this wall is caused by the radial forces acting on the gas-solid flow exiting the classifier (Figure 3). Figure 4c shows the distribution of the velocity across the duct cross-section. An increased normalized mass flow, but not to such a large extent, also occurs near the other walls of the duct. In the central region of the duct the normalized mass flow is

decreased. Typically, the dilute gas-solid flow has the highest particle concentration, exactly at the wall surface. Despite this highest concentration being at the wall surface, the velocity, and consequently the mass flow are reduced by the boundary layer [10]. The highest normalized mass flow is therefore located in the vicinity of the wall, where the particle concentration is still high and the velocity is less reduced by the boundary layer. An extremely uneven mass flow is caused by the centrifugal forces acting on the coal particles and by the complex geometry of the duct sections preceding and following the measuring plane (Fig. 3).

Figure 4: Distributions in the duct (a) 1D normalized mass flow w, (b) 2D normalized mass flow w, (c) 2-D velocity.

CONCLUSIONS Novel systems for the online one- and two-dimensional distribution monitoring of pulverized-coal in large ducts were developed and tested on a real power plant. The most important results of the data analysis are: Intrusive electrostatic rod sensors are suitable for large ducts due to the good spatial sensitivity, especially for ducts of the fan/impact mill’s system in coal-fired power plants. An one-dimensional set of electrostatic rod sensors can provide essential information about the distribution of pulverized coal between the burner nozzles. A combination of electrostatic segmented sensors and velocity measurements can provide information about the two-dimensional distribution of the pulverized coal in the duct and more detailed local information about the gassolid two-phase flow.

Further testing of the methods presented in this paper will be carried out under controlled conditions on a laboratory test rig. References [1] Y. Yan, “Guide to the Flow Measurement of Particulate Solids in Pipelines,” Int. Juornal Storing, Handl. Process. Powder, vol. 13, no. 4, pp. 343–352, 2001. [2] B. A. Batch, J. Dalmon, and E. T. Hignett, “An Electrostatic Probe for Measuring the Particle Flux in TwoPhase Flow,” 1963. [3] J. Zhang, “Air-Solids Flow Measurement Using Electrostatic Techniques,” in Electrostatics, H. Canbolat, Ed. InTech, 2012, pp. 61–80. [4] J. B. Gajewski, “Electrostatic Nonintrusive Method for Measuring the Electric Charge, Mass Flow Rate, and Velocity of Particulates in the Two-Phase Gas–Solid Pipe Flows—Its Only or as Many as 50 Years of Historical Evolution,” IEEE Trans. Ind. Appl., vol. 44, no. 5, pp. 1418–1430, Sep. 2008. [5] X. Qian, Y. Yan, J. Shao, L. Wang, H. Zhou, and C. Wang, “Quantitative characterization of pulverized coal and biomass–coal blends in pneumatic conveying pipelines using electrostatic sensor arrays and data fusion techniques,” Meas. Sci. Technol., vol. 23, no. 8, pp. 1–13, Aug. 2012. [6] M. Fua, A. D. Bin, H. J. Rahmat, D. A. N. Yaw, and W. E. E. Lee, “Electrostatic sensor for real-time mass flow rate measurement of particle conveying in pneumatic pipeline,” J. Teknol., vol. 41, no. D, pp. 91–104, 2007. [7] J. Krabicka and Y. Yan, “Finite-element modeling of electrostatic sensors for the flow measurement of particles in pneumatic pipelines,” IEEE Trans. Instrum. Meas., vol. 58, no. 8, pp. 2730–2736, 2009. [8] J. Q. Zhang and Y. Yan, “On-line continuous measurement of particle size using electrostatic sensors,” in Instrumentation and Measurement Technology Conference, 2003, vol. 135–136, no. May, pp. 164–168. [9] B. Jurjevčič and I. Kuštrin, “SEGMENTNA ELEKTROSTATIČNA SONDA ZA MERJENJE V PNEVMATSKEM TRANSPORTU,” P-201400424, 2014. [10] N. Yutani, T. C. Ho, L. T. Fan, W. P. Walawender, and J. C. Song, “Statistical study of the grid zone behavior in a shallow gas — solid fluidized bed using a minicapacitance probe,” Chem. Eng. Sci., vol. 38, no. 4, pp. 575–582, 1983.

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

Connecting hydrogen chp energy systems with renewables into different sized grids ABSTRACT → Hybrid energy systems with renewable energy sources, coupled with hydrogen energy storage are a potential future alternative for stand-alone electricity and heat supply in the residential sector. While single users of such technology have already been thoroughly analysed, the effects of connecting individual households into a joint (micro-) grid are less known. The objective of this work is, therefore, to analyse how increasing the number of connected (reference) households to an isolated micro-grid affects the optimal design of the stand-alone renewable combined heat and power system with hydrogen

technologies. Eighty actual household’s electricity and heat consumptions have been (numerically) grouped to form different sized energy systems and have been analysed with respect to the optimal energy system design using HOMER energy systems’ analysis tool. The results show that connecting users into larger groups enables a less dynamic operation of hydrogen technologies, which is indicated by larger load factor, smaller fuel cell specific operating capacity and lower specific net present cost for a system with 80 households compared to a single one.

INTRODUCTION Rok Stropnik Laboratory: Laboratory for Heat and Power E-mail: rok.stropnik@fs.uni-lj.si Room: S-I/60 Phone: +386-1-4771-723 Status: PhD student (started: October 2015, to be completed: September 2019) Research area: Hydrogen technologies, CHP, RES Mentor: prof. dr. Mihael Sekavčnik

An energy system based solely on renewables (wind, solar radiation, etc.) is subjected to their random nature, causing short-term and long-term fluctuations in their energy output. Mismatches between production from renewable sources and consumption, which are shown in Fig. 1, can be solved with the use of energy storage during periods of surplus energy production, with a view to subsequent replacement during periods of scarcity of the energy (electricity or heat). Some studies deal with the use of hydrogen as an energy carrier in self-sufficient stand-alone energy systems using renewable energy sources [1-4]. Independent user energy consumption represents the most complex example of the integration of renewable energy sources due to its

inability to import or export surplus energy and due to the nature of unpredictable energy consumption dynamics. Combining and enhancing consumers in the energy network, we can reduce the consumption dynamics, because of the behavioural patterns of energy use, especially their random consumption dynamics in the shorter period of observation (despite the fact that there are certain characteristic patterns of electricity use within an extended period - a day or week). Higher share of renewable energy systems calls for lower energy consumption and more flexibility in balancing energy supply and consumption [5]. Fewer dynamics of consumption usually has a positive effect on the design of the energy system because it lowers the required nominal power, narrower requires operating range of devices and allows smaller gradients of power generating

Figure 1: A mismatch of energy production from renewable energy sources and consumption by households

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

plants. The system cost is minimized while matching the electricity supply with the demand [6]. Positive impacts are expected to be seen in a longer operational life time, reduced maintenance costs and lower investment costs. This paper investigate the benefit from interconnecting more of the same (reference) RES-hydrogen CHP systems to provide less dynamic, less dependent system on the local factors and random nature of RES to achieve better efficiency, longer operational life of components and lower costs of the system. SENSITIVITY ANALYSIS WITH COMPUTATIONAL SIMULATION This study is a continuation of our previous work [7, 8] with the purpose to analyse how increasing the number of connected reference households affects an isolated microgrid and the optimal design of the stand-alone hydrogen system with the renewables for the supply of electricity and heat. The study of the effects of a larger number of stand-alone hydrogen systems at the system design represents a sensitivity analysis of a pre-designed single standalone hydrogen CHP system with renewables. Sensitivity analyses of pre-designed energy system are numerically analysed with numerical simulation software hybrid optimization model for electric renewable (HOMER). We analysed only the design of renewable energy system (the third scenario), in accordance with the methodology, which has been described in detail in our previous work [7]. We also made a computations how increasing number of households [1, 2, 5, 10, 20, 30, 40, 60, 80] effects on operating characteristics of power supply, economic indicators and optimal design of the system. Electricity consumers Based on measurements of power consumption in the same period we have gained real average hourly electricity consumption of actual 86 households in Germany for a period of one year, which was used in the analysis. The average daily electricity consumption of selected households is 14.0 kWh, which is slightly higher than the actual Slovenian average, because of intentional selection of major customers. The measurements were made with a 1-hour period in various places in Germany. The structure of the users, based on the amount of electricity consumed, is presented in Table 1. Table 1: The number of household consumers according to average daily electricity consumption. Electricity consumption

<5 kWh

< 10 kWh

< 15 kWh

< 20 kWh

>= 20 kWh

Number of households

For analysis we used 80 households and normalize the yearly consumption of electricity, which corresponds to the typical daily average of 11 kWh (4015 kWh per year) for each household separately. The energy needs of the 80 households are precisely 80 times more energy than one household.

For that we use the Eq. 1,

Where is the normalized electric power at time interval, is actual power measured at time interval and is the average daily electricity consumption of specific household. Information about consumed electricity for increasing number of households is presented with Eq. 2,

Where denotes average total hourly electricity consumption and denotes average hourly electricity consumption for different number of households n at time interval . Heat consumers To calculate the heat consumption we use average hourly thermal power in district heating system of public company Energetika Ljubljana d.o.o., which already takes into account the loss of heat in distribution. The values of hourly thermal power consumption we normalize such, that the annual consumption is 5500 kWh (660 l of heating oil). The value 5500 kWh represents the sum for heating of 100 m2 household energy class B (30 kWh/m2 yearly) and 2500 kWh for domestic hot water. We assume that the dependence of the thermal power and the temperature of the outside air are equal for all consumers. Eq. 3 shows how we calculate the thermal power for different number of households in this paper.

where is average total hourly heat consumption of nnumber households at time interval and is average total hourly heat consumption of one household at time interval . RESULTS Optimal design For optimal design, based on electrical consumers, of different number of households we made computational analysis focused on fuel cell, electrolyser, inverter and hydrogen storage tank capacity. For sensitivity analysis we use unchanged input parameters for electricity consumption based on Eq. 1 and 2 (Fig. 2). Results show that the normalized net power of electrolyzer, hydrogen storage and production of electricity decreases by increasing of system size. More significantly increases the rated power of the inverter and the fuel cell, namely 82%. Results of computational analysis also show high increasing the load factor of fuel cell and reducing the share of proportional part in electricity production. Absolute electricity production (PV + wind + fuel cell) increase from 34 to 2282 kW Absolute rated power of fuel cell increases from 6 to 82 kW and proportional rated power of fuel cell decreases from 5,7 to 1 kW. Absolute rated power of electrolyser increases from 4 to 250 kW and propor-

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

Figure 2: Annual electricity consumption depending on the number of consumers

tional rated power of electrolyser decreases from 33,7 to 28,5. Absolute capacity of hydrogen storage increases from 54 to 3200 kg and proportional capacity of hydrogen storage decrease from 53,6 to 40 kg . Furthermore computational analysis show increasing number of household consumer’s effect on optimal design of stand-alone renewable energy system by using electricity surplus and unused heat from fuel cell and electrolyser. For our sensitivity analysis of different number of consumers and combined heat and power consumption we use the same scenarios (Reference energy system, Alternative energy system, Renewable energy system) and methodology from our previous work for individual stand-alone renewable CHP system with hydrogen technologies [7]. For every scenario the calculation was made based on Eq. 3, how different number of household consumers affects system characteristics. Average hourly thermal power for 80 household consumers is shown in figure 3. For reference energy system the fuel consumption for proportional part of individual household did not change due to increasing number of households.

For alternative energy system analysis show that the fuel consumption decreases for 13% and renewable energy system doesn’t need any fuel for heating. Other results worth mentioning for renewable energy system are: • rated power of electric heater drops from 8 to 4kW for proportional part of individual household, • share of utilization of surpluses of electricity into heat ranges from 35 for one household to 62% for 80 households, • share of exploited available unused heat from fuel cell increases for 11% for proportional part of individual household, • share of exploited available unused heat from electrolyser increases from 77% for one household to 100% for 80 households. Economic analysis We also made economic analysis for optimal design of energy system depending on different number of household consumers. Economic analysis based on electricity consumption results show that: • initial investment of energy system decreases for 29% for proportional part of individual household, • operating costs decreases from 3500 € per year for an individual household to 1188 € per year for 80 households, • the cost price of electricity decreases from 3,5 to 2,2 €/kWh for proportional part of individual household.

Figure 3: Average hourly heat power of 80 household consumers 34

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

CONCLUSIONS This paper deals with computational analysis how increasing the number of household consumers effects on stand-alone renewable energy system characteristics. Eighty actual households was analysed regarding to an individual household with stand-alone hydrogen energy system based on electricity and heat consumption. Numerically was evaluated a different number of household consumers connected into micro-grid for which we want to achieve to be a self-sufficient for heat and electricity consumption. Data on heat consumption were analysed more simplified, because we believe that, in comparison with power consumption, heat consumption is negligible subjected to random behavioural patterns of people. Results reveal that the dynamics of electricity consumption lowers with increasing the number of household consumers. These changes in the dynamics of electricity consumption affect the optimal design of the energy system with renewables and hydrogen technologies. Grater effect is seen with the fuel cell and inverter where the normalized values drop for 82 % and share of fuel cell nominal power in whole production of electricity drops for 78 %. Results of computational analysis of operating characteristics for optimal system design shows 391 % load factor increase of fuel cell. Further calculations of heat supply for different number of household consumers show that we can achieve self-sufficient energy system for electricity and heat with available waste heat from electrolyser and fuel cell, if we install appropriately-sized heat storage and electric heater. Proportional part of rated power of electric heater drops for 50 % for 80 households compared to an individual household. It turns out that the potential of heat exploitation from electrolyser and fuel cell increases to 100 and 97 % for 80 household consumers of available waste heat. Economic analysis delivers very promising results which are the result of a less dynamic operation and better system characteristics due to connecting different number of stand-alone energy system with renewables coupled with hydrogen technologies. With increasing the number of household consumers the economic indicators show that the initial investment for stand-alone energy system with renewables for 80 households lowers for 29%, maintenance costs drops for 66% and the cost price of electricity drops from 3,5 €/kWh to 2,2 €/kWh compared to an individual household consumer. The analyses confirmed that increasing the size of the considered energy system is technically and economically more favourable.

References [1] B. Shabani, J. Andrews, S.Watkins. Energy and cost analysis of a solar-hydrogen combined heat and power system for a remote power supply using a computersimulation, Sol. Energy 84 (2010), pp. 144-155. [2] S. Zafar, I. Dincer. Energy, exergy and exergoeconomic analysis of a combined renewable energy system for residential applications, Energy Build 71 (2014), pp. 68-79. [3] R. Jallouli, L Krichen. Sizing, Tecno-economic and generation management analysis of a stand-alone photovoltaic power unit including storage devices, Energy 40 (2012), pp. 196-209. [4] A. Chauhan, R.P. Saini. A review on integrated renewable energy system based power generation for stand-alone applications: Configurations, storage, options, sizing methodologies and control, Renew. Sust. Energy Rev, 38 (2014), pp. 99-120. [5] B. Zakeri, S. Syri, S. Rinne. Higher renewable energy integration into the existing energy sistem of Finland – Is there any maximum limit?, in press (2015), pp. 1-16. [6] A. González, J. R. Riba, A. Rious, R. Puig. Optimal sizing of hybrid grid-connected photovoltaic and wind power system, Applied Energy, 154 (2015), pp. 752-762. [7] R. Lacko, B. Drobnič, M. Mori, M. Sekavčnik, M. Vidmar. Stand-alone renewable combined heat and power system with hydrogen technologies for household application. Energy, 77 (2014), pp. 153-163. [8] R. Lacko, B. Drobnič, M. Sekavčnik, M. Mori. Hydrogen energy system with renewables for isolated households: The optimal system design, numerical analysis and experimental evaluation. Energy and Buildings, 80(2014), pp. 106-113.

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

The Influence of Operational phase on Environmental Impacts of a Fuel Cell UPS ABSTRACT → Environmental impacts of a 3 kW UPS system based on PEM fuel cell are evaluated in manufacturing and operating stage. The LCA method was applied; models set up using Gabi 6; and CML 2001 for evaluating environmental impacts. The scope was cradle-to-end of utilization with functional unit 1 kWh of produced electricity. Hydrogen is produced with electrolysis, gas steam reforming and through theoretical EU H2 pipeline. In manufacturing phase main impacts come from fuel cell stack, battery, auxiliary components and cabinet production. In operational phase the lowest environmental impact

comes from operation with hydrogen from electrolysis in Norway and the highest environmental impact when hydrogen is produced with electrolysis in Morocco. Till the end of operation UPS’s GW is 278 g of CO2 eq. per 1 kWh of electricity if operated in Norway, 416 g with hydrogen from EU H2 pipeline, 1,042 g with gas reforming and 4,390 g with electrolysis in Morocco. It is shown that hydrogen production method plays a key role in environmental print of hydrogen based UPS.

METHODS Mitja Mori Laboratory: Laboratory for Heat and Power E-mail: mitja.mori@fs.uni-lj.si Room: S-I/60 Phone: +386-1-4771-715 Status: AsistantProfessor Research area: Hydrogen technologies – Life cycle assessment

For the assessment and comparison of the environmental impacts, the life-cycle assessment method (LCA) was applied, and numerical models were developed using GaBi 6 software. For the life-cycle inventory analysis, quantitative data was collected with on-site measurements, data from manufacturers, GaBi software generic databases and available literature. The CML 2001 method was applied to evaluate the system’s environmental impacts, [1-3]. BOUNDARY CONDITIONS OF THE MODEL Functional unit is defined as 1 kWh of electrical energy produced with UPS. The study is focused on one UPS system on the basis of PEM fuel cell with rated output of 3 kW. Reference flow is 30,000 kWh of produced electrical energy during the system’s life cycle. Type of the study is cradle to end-of-utilization phase. The study is physically limited to UPS system, while hydrogen production facility was not included in LCA numerical model. Geographically system is assumed to be installed in northern Africa (Marrakesh, Morocco) or northern Europe (Oslo, Norway). Transport via railway, cargo ship and

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

truck is included in the numerical models. Operation phase is considered for 10,000 h in approximately 10 years’ time. In the model maintenance of the system is excluded since it has to operate without maintenance for 10,000 h. The basic scenario was hydrogen production with electrolysis on-site. Since the production facility was not in the scope of the study, the main contributor to environmental impact is electrical energy mix in the country. In the case of Morocco, the energy mix consist of electricity produced: 43% from coal, 24% from oil, 23% natural gas, 7% hydro and 2% of wind power. In contrary on Norway 95 % of energy mix consist of energy from hydro power. Since statistical data from 2008 shows that hydrogen production worldwide was 49% from natural gas, 29% from liquid hydrocarbons, 18% from coal and just 4 % with electrolysis, additional processes are included in the study for comparison: steam reforming from natural gas and EU pipeline that represent future possible hydrogen pipeline manufactured with steam cracking as a by-product in oil-refinery, [6].

Figure 1: left: fuel cell and developed balance of plant components; right: FluMaBack UPS system.

Figure 2: The numerical LCA model of 3 kW UPS system with boundaries.

INVENTORY ANALYSIS

RESULTS AND DISCUSSION

All virgin material mass flows in BoP components manufacturing process are included in the study as well as emissions during the phases of materials extraction, manufacturing, transport and operation. Data consist of primary data gathered on the basis of manufacturers’ masses of materials as inputs in manufacturing process. Secondary data are used in all cases where primary data are not available. In this case reference studies, generic databases and literature are used, [6].

Manufacturing phase Concerning manufacturing phase (Table 1) fuel cell stack, batteries and auxiliary components (due to electronic components) have the biggest environmental impact. In global warming (GW) criteria battery represents 23 % of overall GW, steel cabinet 21.4 % and FC stack 35.9 %. In acidification (A) criteria FC stack is by far the most influential and represents 43 % of all acidification

Table 1: Contribution of components impacts in manufacturing’s phase total impact. AD

POC

air blower

18.1 %

4.4 %

24.4 %

3.5 %

17.0 %

0.1 %

4.4 %

H2 blower

2.8 %

1.1 %

3.8 %

1.2 %

4.5 %

0.0 %

1.1 %

battery

23.7 %

23.3 %

5.7 %

23.0 %

2.5 %

0.0 %

21.1 %

humidifier

0.0 %

0.2 %

0.1 %

0.4 %

0.0 %

0.3 %

external climate

0.1 %

2.8 %

0.7 %

4.4 %

6.6 %

0.0 %

3.8 %

19.5 %

43.0 %

10.7 %

35.9 %

20.8 %

99.5 %

31.4 %

0.0 %

14.0 %

4.3 %

21.4 %

3.1 %

0.0 %

26.1 %

35.8 %

11.3 %

50.3 %

10.2 %

45.1 %

0.3 %

11.7 %

0.177 kg SO2 eq.

12.2 kg SO2 eq.

3.40 kg PO4 eq.

2157 kg CO2 eq.

1766 kg DCB eq.

0.0046 kg R11 eq.

0.89g kg Eth. eq.

fuel cell stack cabinet auxiliary components Total – abs. value

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

Figure 3: Acidification in operating phase in kg SO2 eq

in manufacturing phase. Furthermore the FC stack has 99.5Â % of all environmental impact in ozone depletion (OD), 20.8 % in human toxicity (HT) and 31.4 % in photochemical ozone creation (POC). Auxiliary components contribute the highest impact in abiotic eutrophication (E) with 50.3 %, human toxicity (HT) with 45.1 % and abiotic depletion (AD) with 35.8 % of overall impacts in manufacturing phase. In Transport has on other hand almost negligible effect in all impact criteria. Hydrogen production Concerning just operation for 10.000 hours at 3 kW operational phase is by far the most influential just in the case of Morocco (Table 2) what brings down the significance of primary energy source use for hydrogen production. If hydrogen is produced via electrolysis that uses electricity as the only energy source, the energy mix in the country of operation has the biggest influence on environmental impacts. The acidification (A) diagram in figure 3 partly generalize all environmental indicators. The best

choice for hydrogen production is electrolysis in Norway in which case in 95 % hydro energy is used in electricity production. This is also the reason that abiotic depletion (AD) has in this case the highest value. Steam reforming of natural gas is the most frequently used hydrogen production in the world and is the best production method directly from fossil fuels regarding environmental impact criteria, [8]. The impacts of hydrogen produced by reforming are in general 2 to 3 times higher than in the case of electrolysis in Norway, except for ozone depletion that has the lowest value in the case of hydrogen from natural gas. EU pipeline hydrogen represents the future idea of hydrogen pipeline in the Europe that is mainly produced with steam cracking as a by-product in the process. Environmental impacts show up to 5 times more environmental impact than in cases with electrolysis in countries with RES hydro energy mix. In addition the hydrogen from steam reforming and cracking needs additional cleaning that is linked with more energy consumption and additional environmental impacts.

Figure 4: ACO2 equivalent comparison of the different types of power generation technologies, per 1 kWh produced electricity. 38

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

In Figure 4 CO2 emissions in the case of several technologies for electricity generation are presented. Majority of technologies are not UPS system’s applications, but diesel, Wiltec ICE and FC natural gas reforming are or could be used in the case of UPS systems. Compared to 3 kW UPS system on the basis of Wiltec gasoline engine that generates almost 1200 gCO2/kWh, [4], FluMaBack 3 kW UPS system is environmentally sounder in the case of Norway electrolysis, EU pipe line and even in the case of hydrogen production with natural gas steam reforming. CONCLUSIONS A hydrogen technology based UPS system’s environmental impacts were analyzed with LCA method in its manufacturing and operational phase. Hydrogen for operational phase was produced with three different technologies: electrolysis, EU steam reforming, EU pipe line – steam cracking. In the case of electrolysis for two geographical locations Norway and Morocco. Study shows that the main environmental impacts come from operational phase and that hydrogen production method is the key for making HT-UPS system environmentally acceptable. Results show: Operational phase has the major environmental impact and in the case of electrolysis in Morocco that represents more than 90 % of all environmental load. In manufacturing phase the biggest share of environmental impacts comes from manufacturing of battery and fuel cell stack. The production of hydrogen with electrolysis in Norway has the lowest environmental impact of all four methods due to favorable energy mix that includes 95 % of hydro power. Energy and mass balances were introduced for all phases for production of 30,000 kWh electricity with HT-UPS. It was found out that in the case of electrolysis 139,125 kWh is needed for hydrogen production with electrolysis that represents 94 % of all required energy input in manufacturing and operational phase. Regarding the intensive R & D efforts in hydrogen technologies production and operation energy efficiencies are expected to improve in the future. That will lower environmental impacts of HT-UPS systems, but as presented in the study the major contributor will be hydrogen production method. Therefore, awareness is needed in the case of hydrogen technologies implementation in existing power production systems, so it could play a key role in lowering of overall environmental impacts in the future.

References [1] ISO 14040, ISO 14044 – Environmental management – Life cycle assessment – Principle and framework & Requirements and guidelines, 2006 [2] Intergovernmental Panel on Climate Change, C/O World Meteorological Organization, Genève, Swiss [3] Handbook on impact categories “CML 2001”, Institute of Environmental Sciences, Leiden University, Nederland [4] Mori, M.; Jensterle, M.; Mržljak, T.; Drobnič, B. Lifecycle assessment of a hydrogen-based uninterruptible power supply system using renewable energy. The international journal of life cycle assessment, nov. 2014, vol. 19, iss. 11, pp. 1810-1822 [5] Guinée, J.B.; Gorrée, M.; Heijungs, R.; Huppes, G.; Kleijn, R.; Koning, A. de; Oers, L. van; Wegener Sleeswijk, A.; Suh, S.; Udo de Haes, H.A.; Bruijn, H. de; Duin, R. van; Huijbregts, M.A.J.: Handbook on life cycle assessment. Operational guide to the ISO standards. I: LCA in perspective. IIa: Guide. IIb: Operational annex. III: Scientific background. Kluwer Academic Publishers, ISBN 1-4020-0228-9, Dordrecht, 2002, 692 pp. [6] PE International, Gabi Database (April 2013) [7] Masoni, P.; Zamagni, A.; Guidance document for performing LCA on Fuel Cells - FC-Hy Guide, Guidance Document for performing LCAs on Fuel Cells and H2 Technologies, 2011 [8] Rostrup-Nielsen JR, Rostrup-Nielsen T (2002) Largescale hydrogen production. Cattech, 6(4), 150-159

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

Operation Optimization of Power Plant Ljubljana ABSTRACT → Power Plant Ljubljana produces heat and power in co-generation. It consists of three units with maximum heat output of 340 MW and maximum power output of 120 MW. The main fuels are Indonesian brown coal and wood-chips. The method for loadsharing optimization between the three units is presented. Due to ever-changing coal composition and wear of coal mills, the completely automated control over the combustion process is almost impossible. The role of coal-fired boilers’ operators is still very important. To enable and to motivate effective operators’

interventions few important and manually adjustable parameters indicating quality of operation were identified. Target values of the parameters were set according to the analysis of the results of dedicated tests and experience. They can be arbitrarily adjusted to reflect the current condition of boilers. The on-line bigscreen display, located in the control room and showing the deviation from the target heat rate for each boiler, proves to be a strong motivation for operators to take appropriate actions.

INTRODUCTION Igor Kuštrin Laboratory: Laboratory for Heat and Power E-mail: igor.kustrin@fs.uni-lj.si Room: 304 Phone: +386-1-4771-304 Status: Research assistant Research area: Coal-Fired Thermal Power Plants

Power Plant Ljubljana is a combined heat and power plant. According to the criteria, stated in [1] Power Plant Ljubljana demonstrates highefficiency cogeneration. It consists of three units. Units 1 and 2 were put in operation in 1967. Unit 3 operates since 1985. Maximum capacity of boilers 1 and 2 is 180 t/h each and of boiler 3 270 t/h of superheated steam at 95 bar and 530 °C. Maximum total heat output is 340 MW and maximum total power output is 120 MW. All three steam boilers are fired with coal. Besides that, boiler 3 has a grate for wood chips co-firing. Experience shows that the changes in coal composition and wear of main components of the combustion system have significant impact on the combustion process. These changes are difficult to detect and a sophisticated control algorithms need to be employed to compensate for them in an efficient manner. In most cases, it is practically impossible to eliminate the need for human intervention. The operators therefore need a tool to detect the deviations from the optimal operation to be able to minimize them. Besides this, live-steam production needs to be properly distributed among the boilers to minimize the overall power-plant heat rate.

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

This paper shows a practical approach how this was accomplished in Power Plant Ljubljana. OPTIMAL COMBINATION OF BOILERS Which boiler combination is optimal in a certain time period, depends on many factors like, head demand, scheduled and unscheduled maintenance activity, availability and price of main and alternative fuel, price of electricity etc. These factors are beyond the reach of the boiler operators and need to be addressed by the management. Table 1: Yearly scheme of units operation Month

Number of units

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Table 1 shows typical yearly scheme of operation for the three units. The scheme is tuned to synchronize the actual heat demand and the heat production along with maximization of primary energy savings. There are mainly three different periods throughout the year with respect to ambient temperature: cold period (November until March), hot period (May until September) and warm/ cool period (April and October). Table 1 shows that 3 units are in operation during the cold period, 2 units are in operation during warm/cool period and that 1 unit is in operation during the hot period. The operating units are selected according to the factors mentioned in the previous paragraph. MAXIMAL EFFICIENCY OF EACH BOILER The actual boiler efficiencies were measured during the performance tests that are periodically performed in accordance with [2] by the Faculty of Mechanical Engineering of Ljubljana. Due to smaller size and older design, boilers 1 and 2 have lower efficiency than boiler 3 (Figure 1). Thermal efficiency of boiler 3 is reduced during woodchips co-firing due to relatively high moisture content in wood-chips. This is illustrated by the two efficiency curves for boiler 3: the efficiency without woodchips co-firing and the efficiency with maximum woodchips co-firing.

Assuming that soot blowing and other maintenance actions are done according to boiler-operation instructions, the operators have practically no impact on the flue-gas temperature. That is why the flue-gas temperature is not included in this optimization. On the contrary, the operators can have significant impact on the air ratio (i.e. O2 content) and air distribution. In some cases, efficient combustion is possible even with lower air ratio if the air is properly distributed among the available nozzles. Due to progressing wear of mills and different mill combinations, the optimization of air distribution cannot be completely automated. In general, the higher air ratio enables more comfortable but uneconomic operation resulting in a higher stack loss. Besides this, the higher air ratio also promotes the unwanted NOx formation. During the performance tests and according to operational experience the realistic and optimal “O2 content – load” relation was established for each boiler. This relation takes into account the margin that is needed for safe and reliable operation. Using the relations established during the tests, the deviation of the actual O2 content from the target O2 content is recomputed to a deviation of the actual boiler heat rate from the target boiler heat rate. It is important to emphasize that, instead of the absolute heat rate, only the deviation from the target heat rate is computed:

In equations (1) to (3) Ki are the coefficients obtained by fitting the results of the equation to measured values. Using the available controls operators need to keep the O2 deviation as low as possible. Knowing the fact, that the target O2 content incorporates a certain safety and reliability margin, a skillful operator can keep the actual O2 content even lower than the target value if the other criteria for safe and sustainable operation are met.

Figure 1: Measured boiler efficiencies

Using the results of the tests [3], [4], [5] two important relations were derived: • stack losses in relation to O2 content in flue gas • losses due to unburnt gas and unburnt matter in slag and fly ash in relation to CO content in flue gas It needs to be noted that these relations are valid as long as there is no significant change in fuel composition. When the fuel changes, new relations need to be derived. Minimal stack losses To ensure that boilers operate at maximal achievable efficiency, it is essential to keep the stack losses as low as possible. Two parameters determine this loss: flue-gas temperature and O2 content in flue-gas exiting the boiler.

Minimal unburnt gas and unburnt-matter losses A reliable on-line chemical analysis of slag and ash is practically unfeasible. Any time delay required for the chemical analysis is too long for the analysis to be applicable. Instead, CO content in flue gas exiting the boiler is employed for the estimation of boiler losses that are related to the unburnt CO and the unburnt matter in slag and ash. The relations, established during the tests, were approximated using the linear equation:

MAXIMAL EFFICIENCY OF EACH UNIT As soon as a portion of the heat is rejected to the environment, the mean temperature of heat addition becomes important for the thermal efficiency of the steam power cycle. The ratio is employed for the estimation of losses related to the deviation in live-steam temperature from the nominal live-steam temperature. Using the mathematical models that were built on the basis of experimental data, unit heat rate was computed YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

in relation to the temperature of live steam and the ratio. This computation was done for different live steam mass flows. It was determined that live-steam mass flow has no impact on the result. The deviation of live-steam temperature of -35 K from the design live-steam temperature was simulated for various ratios. The deviation of heat rate at 35 K deviation of live-steam temperature is shown on figure 2 and approximated with:

Example:

At 90 kg/s total live-steam mass flow, three different combinations of boilers are can be employed. Let us observe two different load-sharing situations. Large black dot represents optimal load sharing situation and small black dot represent extreme not-optimal load sharing situation for “1+3” boiler combination. The load sharing has significantly lower impact on combined boiler heat rate than the choice of operating boilers. ACHIEVABLE SAVINGS

There is no deviation in heat rate if the live-steam temperature is equal to the design live-steam temperature. A linear interpolation is employed to determine the heat-rate deviation at different live-steam temperature deviations:

The calculation of achievable savings in 2013 and 2015 is done by comparing the actual operation to the optimal operation using the principles presented in the preceding chapters. Figure 4 shows savings achievable by optimal operation compared to actual operation for each hour of the years 2013 and 2015.

Figure 4: Achievable savings

Figure 2: Deviation of heat rate in at -35 K deviation of live steam temperature

OPTIMAL LOAD SHARING The optimal load sharing is relevant when more than one boiler is in operation. Figure 3 shows the combined boiler heat rate achievable at various total live-steam mass flows using different boiler combinations. Bold gray line highlights the minimal achievable combined-boiler heat rate.

Figure 3: Achievable boiler heat rate 42

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

During 2013 the optimization was not operational yet contrary to the year 2015. The parameters of operation were recorded by the plant DCS system. The deviations from the optimal heat rate were computed according to the presented optimization. Knowing that heat and power outputs in 2013 and 2015 were almost equal, the best representation of achievable savings is shown on Figure 4 showing the deviation fuel-energy consumption for each hour of the year. In 2015, when the optimization was already operational, there were almost no more achievable savings i.e. the operation was close to being optimal. On the contrary, in 2013 when the optimization was not yet operational, the achievable savings represented approximately 0.6 % of yearly fuel-energy consumption. This optimization is running in manual mode. It means that fine tuning of combustion parameters and load sharing depends on the plant operators. As mentioned earlier, it is almost impossible to automate all tasks related to combustion fine-tuning due to ever-changing condition of coal mills and coal composition.

CONCLUSIONS This paper shows a practical approach to the optimization of the operation of a coal-fired power plant. It is a low-cost approach giving good results if reliable data are available for derivation of the required algorithms and relations. The on-line big-screen display, located in the control room and showing the deviation from the target heat rate for each boiler and unit, proves to be a strong motivation for operators to take appropriate actions. Due to their involvement, the savings of 0.6 % of yearly coal-energy consumption were accomplished. References [1] Directive 2004/8/EC of the European Parliament and of the Council of 11 February 2004 on the promotion of cogeneration based on a useful heat demand in the internal energy market and amending Directive 92/42/EEC. [2] EN 12952-15:2003, Water-tube boilers and auxiliary installations-Part 15: Acceptance tests. [3] Kuštrin, I., Senegačnik, A., Oman, J.: Net Heat Rate of Unit 3, Power Plant Ljubljana : 21. - 27. June 2001. Ljubljana: Faculty of Mechanical Engineering. [4] Kuštrin, I., Senegačnik, A., Oman, J., Mori, M.: Net Heat Rate of Unit 1, Power Plant Ljubljana: 9. - 11. October 2001. Ljubljana: Faculty of Mechanical Engineering. [5] Kuštrin, I., Oman, J., Mori, M.: Net Heat Rate of Unit 2, Power Plant Ljubljana: (3. - 5. December 2002). Ljubljana: Faculty of Mechanical Engineering. List of publications [6] Kuštrin, I., Bole, I., Senegačnik, A., Practical Approach to Optimization of Operation of Three Units in Power Plant Ljubljana, ECOS, June 19. - 23. 2016, Portorož, Slovenia, submitted for publication,

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

The integration of hydrogen technologies for utilisation of distributed renewable energy sources ABSTRACT → A hybrid energy system, based on renewable energy sources and with hydrogen storage, can become an alternative for stand-alone electricity and heat supply. The objective of my work is a numerical and experimental evaluation of the feasibility of a completely renewable supply of power and heat for

an isolated household, and a comparison to reference and alternative energy supply scenarios, including a sensitivity analysis of the effects of size (number of households included in the energy system) and geographical location on the energy system design.

INTRODUCTION Rok Lacko Laboratory Laboratory for Heat and Power E-mail rok.lacko@inea.si Room S-I/60 Phone +386-41-279-041 Status PhD-finished, January 2015 Research area Hydrogen technologies Mentor prof. dr. Mihael Sekavčnik

Climate change mitigation, natural environment preservation, increasing needs for energy and uncertain costs of fossil fuel supply in the future are the reasons for the increasing interest in local and renewable energy sources (RES), as opposed to fossil energy use. While fully energy self-sufficient dwellings are still rare, solar and wind power units have been widely adopted for private family homes. The introduction of RES into the energy supply, however, raises certain issues in load balancing due to their intermittent and non-storable nature. This especially applies to wind and solar energy, and to a lesser respect to other RES. Furthermore, a single self-sufficient user presents the most challenging case of RES integration, due to its inability to import and export surplus energy. Electricity supply based on renewable energy sources, coupled with hydrogen storage, has already been proposed as a technically viable solution [1]. Several technical and economic analyses of stand-alone RES energy systems with hydrogen storage, focusing on electricity supply only, have already been discussed [2]. Such hybrid energy systems have been experimentally demonstrated [3]. Furthermore, studies on REShydrogen energy systems considering combined heat and power (CHP) have been reporting on energy and exergy analysis [4], system performance assessment methodology [5] and a mathematical model of a wind-

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

hydrogen CHP system with metal hydride storage [6]. RES-hydrogen CHP systems have also been successfully demonstrated [7]. In my research an optimal selfsufficient renewable hydrogen energy system has been numerically determined, based on an actual geographical location (Slovenia’s coastal area), the availability of energy sources, electric load dynamics and components’ technical and economical characteristics [8]. Numerical results were experimentally proven using a demonstration system with hydrogen technologies [9]. The results of both studies have shown that the required relatively large production capacity causes excess electricity generation, which is not used by the household. Although stand-alone REShydrogen energy systems have been proposed and studied, common shortcomings of those analyses include (a) a pre-determined system design, (b) optimization of system’s performance without preliminary optimising its configuration or design, (c) overgeneralised input parameters, such as using typical daily consumption data sets only, (d) short term simulation only (day, week) and finally (e) numerical models and simulation results not being experimentally evaluated and verified. Studies also show that results are highly dependent on numerous local factors, e.g. meteorological conditions; therefore, a site-specific analysis is needed for credible results [5]. Additionally, the influence of energy system size to its optimal design has not been analysed.

In my research I aim to overcome the detected shortcomings by considering the topics of optimal hydrogenRES system design based on relevant, site specific and actual measured input data, hourly system’s dynamics analysis for a period of one year, including experimental evaluation of numerical results. In the analysed energy system hydrogen is produced (and stored in a tank) by an electrolyser, which is powered by the surplus electricity from renewable energy sources, using solar and wind technologies (specifically at summer daytime). When RES are scarce, or demand is high, additional power is needed; therefore, the fuel cell converts the chemical energy of the stored hydrogen gas directly into electricity (usually at night and in winter).

Table 2: Optimal system configuration electrical production and consumption. Production PV array

18025

3609

Fuel cell

2397

24030

100

Total Consumption

kWh/year

AC primary load (household)

4159

Electrolyser

9287

13446

100

Other

Numerical simulation results A feasible system is defined as a hybrid system configuration that is capable of meeting the required load. Under given conditions, one system configuration was found to be feasible. The optimal combination, with the lowest total net present cost (€136,063), is presented in Table 1. The cost of energy for optimal system combination is €2.8/kWh. The combined nominal primary (RES) and secondary (fuel cell) power source capacity is 33 kW, while peak demand is 3.8 kW. The optimal electrolyser and converter size is 4 kW, each, with tank capacity being 30 kg of hydrogen. Figure 1-3 show the principal components’ operating characteristics: electrolyser input power, fuel cell output power and their duration curves and hydrogen storage level, respectively. Hydrogen energy storage shows the ability to store inter-seasonal fluctuations of RES availability. Summers’ higher RES energy density is stored to be used during the colder half of the year (Figure 3). Unlike the fuel cell (Figure 2), the electrolyser (Figure 1) operates during 74% of the operation time at nominal power (Figure 3). In Figure 3, the difference between electrolyser electricity consumption and fuel cell electricity production, which represents the overall efficiency of hydrogen energy storage (averaging 26%) is also shown.

Wind turbines

Total

RESULTS AND DISCUSSION

kWh/year

10122

42.1a

462

11.1b

Unmet electric load

Capacity shortage

Renewable fraction

100

Excess electricity DC/AC conversion loss

a share of total production b share of AC primary load

Figure 1: The result of annual simulation of electrolyser’s input power in steps of one hour.

Table 1: Optimal system configuration, based on lowest net present cost. Component

Size

PV array

17 kW

Wind turbine

12 kW

Electrolyser

4 kW

Fuel cell

4 kW

Power converter

4 kW

Hydrogen tank

30 kg

Table 2: presents an optimal system’s electrical production and consumption values. The PV arrays produce 75%, while the secondary power source (fuel cell) produces 10% of the electricity. The electrolyser’s electricity consumption rate is 69%, while the household consumes 31%. All electric load was met throughout the year, and the excess electricity is 42% of overall production.

Figure 2: The result of a simulation of fuel cell’s output power: full year scale

Experimental results Figure 4 presents the chosen one-week period with both numerical and experimental results of the fuel cell and electrolyser power. Both typically start once per day. The electrolyser operates in periods of excess electricity production during the daylight. In contrast, the fuel cell mostly operates during the night, acting as a substitute for the missing solar irradiation. A comparison of integral YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

parameters, both simulation and experiment, presented in Table 4, shows remarkably good matches of both results, with differences of less than 3%.

household consumes 663 litres of oil annually; at an oil price of 1 €/litre, annual heating costs are €663. ALTERNATIVE ENERGY SYSTEM (FUEL CELL CHP + DUMP LOAD) The alternative scenario aims to offset fossil fuel consumption by using surplus energy to supply the thermal load as much as possible. HOMER enables excess electricity conversion into heat via dump load (1,512 kWh) and fuel cell waste heat use (1,513 kWh in CHP mode). Nevertheless, the renewable energy available for heating is not fully utilised; therefore, some (2,523 kWh or 302 litres of oil equivalent) fossil fuel has to be used. The alternative system utilises 15% of excess electricity and 79% of the fuel cell’s available heat. Even though there is a sufficient amount of excess energy available for heating, not all could be utilised due to the low availability of RES and a mismatch between production and demand. Thermal operation diagrams with different time scopes (day – upper, week – middle, year – lower) are shown on Figure 6. Annual operation (fuel) savings, compared to the reference scenario, account for €361.

Figure 3: Electrolyser and fuel cell duration curves (top) and hourly averaged hydrogen storage content (bottom).

Figure 5: Alternative system thermal operation

Figure 4: Simulation and experimental power distribution of a 1-week period in summer.

Parameter

EL model

EL Index experiment

FC FC Index model experiment

energy

4.20 kWh

4.17 kWh

0.99

0.74 kWh

0.72 kWh

0.97

H2 amount

0.077 kg

0.075 kg

0.97

0.046 kg

0.045 kg

0.98

70.9%

0.98

40.9%

40.6%

0.99

el. 72.2% efficiency

RENEWABLE ENERGY SYSTEM Since the alternative scenario’s amount of unused energy for heating remains sufficient to fully offset remaining fossil fuel consumption (2,523 kWh), a thermal storage was introduced to the renewable scenario. A custom numerical model was set to analyse the thermal storage operation. The results show that a 1,000 kWh storage capacity with an 8 kW electric heater (dump load) enables 100 % renewable heat and electricity supply of a reference household. The annual thermal storage heat content is shown in Figure 7. The fossil fuel consumption is replaced by better utilisation of the excess electricity (39%), of the fuel cell waste heat (87%) and of the electrolyser waste heat (77%). Since renewable scenario requires no fuel, annual operational savings are €663, compared to the reference, and €302 compared to the alternative scenario.

Table 3: Simulation and experiment results comparison.

CHP hydrogen energy system for household application REFERENCE ENERGY SYSTEM In the reference scenario, heat is supplied independently of the renewable system, by burning oil in a boiler. The

LABORATORY FOR HEAT AND POWER YEARBOOK 2016

Figure 6: Storing renewable heat during the year requires a seasonal thermal storage.

Sensitivity analysis ENERGY SYSTEM SIZE The sensitivity of the optimal energy system design to its size (with respect to the number of households included) has been performed by based on the energy consumption patterns of 80 different households. Several different sizes energy systems that consist of 1, 2, 5, 10, 20, 30, 40, 60 and 80 households have been numerically analysed and compared. Results show that the (relative) dynamics of electricity consumption decrease with size (from 1 to 80 consumers interconnected), since • the (proportional) power range of electricity consumption decreases – maximal power decreases from 5.59 to 1.02 kW (- 82%) while simultaneously minimal power increases from 0.00 to 0.20 kW, • the standard deviation of consumption decreases from 0.43 to 0.15 kW (+ 65%), • the load factor increases from 0.12 to 0.45 kW (+ 270%), • the area under the (normalised) load curve increases. The described changes in the dynamics of electricity consumption result in a slight decrease in the normalised production capacity of the entire production, electrolyser capacity and hydrogen tank by 15, 22 and 25%, respectively. More notably, the normalised inverter and fuel cell capacities decrease by 82%. Furthermore, the share of fuel cell capacity within the total production capacity is decreased from 0.17 to 0.04 (- 78%). The reduction of the share of hydrogen technologies within the energy system lowers the economical parameters, such as the initial capital (- 29%), operating costs (- 66%), net present cost (- 38%) and levelised cost of energy (- 38%). The results of simulation of the physical behaviour of the energy system show that the fuel cell’s load factor increases with size by 391 %. The other operating characteristics (i.e. average power, electricity production and consumption, hydrogen production and consumption, operating hours, excess electricity) show less dependence to the size of the system (18 to 27% difference). Additional results show sufficient heat supply with increasing the energy system size, which is utilised from available sources. Proportional heat storage size varies between 1,000 and 1,525 kWh per household, while rated power of the electric heater (dump load) decreases from 8.0 to 3.4 kW (58%). With the increasing number of consumers all available heat from hydrogen technologies (fuel cell and electrolyser) is utilised. In contrast, the utilisation rate of the available excess electricity for heating does not significantly increase and varies between 39 and 67%. Installing the thermal storages dispersedly increases its total heat capacity by 33%. GEOGRAPHICAL LOCATION The optimal system design calculations have been performed for 5 different locations in Slovenia. The required total electrical production capacity varies by less than 12%, while the size of a thermal storage varies by 114%, with its maximum size in Ljubljana. The economically most efficient location to install the energy system is Portorož where NPC is 136,000 EUR. The difference to other locations is less than 32%.

References

[1] Mathiesen BV, Lund H. Fuel-efficiency of hydrogen and heat storage technologies for integration of fluctuating renewable energy sources. 2005 IEEE St. Peterbg. powertech Conf. Proc., St. Peterburg: Faculty of Mechanical Engineering and Naval Architecture; 2005, p. 1–7. [2] Vosen SR, Keller JO. Hybrid energy storage systems for stand-alone electric power systems : optimization of system performance and cost through control strategies. Int J Hydrogen Energy 1999;24:1139–56. [3] Chaparro a. M, Soler J, Escudero MJ, de Ceballos EML, Wittstadt U, Daza L. Data results and operational experience with a solar hydrogen system. J Power Sources 2005;144:165–9. [4] Xie D, Wang Z, Jin L, Zhang Y. Energy and exergy analysis of a fuel cell based micro combined heat and power cogeneration system. Energy Build 2012;50:266–72. [5] Dorer V, Weber R, Weber a. Performance assessment of fuel cell micro-cogeneration systems for residential buildings. Energy Build 2005;37:1132–46. [6] Pedrazzi S, Zini G, Tartarini P. Modelling and simulation of a wind-hydrogen CHP system with metal hydride storage. Renew Energy 2012;46:14–22. [7] Voss K, Goetzberger A, Bopp G, Haeberle A, Heinzel A, Lehmberg H. The self-sufficient solar house in Freiburg results of 3 years of operation. Sol Energy 1996;58:17–23. [8] Lacko R, Drobnič B, Mori M, Sekavčnik M. Planning of a self-sufficient energy system with 100 % renewable energy sources and hydrogen storage. 22nd Int. Expert Meet. Power Eng., Maribor: 2013, p. 1–13. [9] Lacko R, Drobnič B, Leban M. Hydrogen technologies in a self-sufficient energy system with renewables. In: Avsec J, Konovšek D, Špeh N, Štumberger B, Žerdin F, editors. 3rd Int. Conf. Energy Technol. Clim. Chang., Velenje: 2013, p. 1–12.

List of publications

[1] Lacko R, Drobnič B, Mori M, Sekavčnik M, Vidmar M. Stand-alone renewable combined heat and power system with hydrogen technologies for household application. Energy 2014:1–7. [1] Lacko R, Drobnič B, Leban M. Hydrogen technologies in a self-sufficient energy system with renewables. In: Avsec J, Konovšek D, Špeh N, Štumberger B, Žerdin F, editors. 3rd Int. Conf. Energy Technol. Clim. Chang., Velenje: 2013, p. 1–12. [2] Lacko R, Drobnič B, Mori M, Sekavčnik M. Planning of a self-sufficient energy system with 100 % renewable energy sources and hydrogen storage. 22nd Int. Expert Meet. Power Eng., Maribor: 2013, p. 1–13. [3] Lacko R, Drobnič B, Mori M, Sekavčnik M, Vidmar M. Stand-alone renewable CHP system with hydrogen technologies. 6th Int. Conf. Sustain. Energy Environ. Prot., Maribor: 2013, p. 588–93. [4] Lacko R, Drobnič B, Sekavčnik M, Mori M. Hydrogen energy system with renewables for isolated households: The optimal system design, numerical analysis and experimental evaluation. Energy Build 2014;80:106–13. [5] Lacko R, Leban M. Hydrogen technologies in a self-sufficient energy system with renewables. J Energy Technol 2013;6:11–24. [6] Lacko R, Pirc A, Mori M, Drobnič B. Step By Step Numerical Approach to a Self-Sufficient Micro Energy System Design. Int J Eng Res Appl 2014;4:1–10.

YEARBOOK 2016 LABORATORY FOR HEAT AND POWER

Prof.Dr. Branko Širok

Laboratory for Hydraulic Turbomachinery The laboratory is involved in general research in development of water and turbine machinery for various applications. The work is performed under funding of national in international projects and industry funded research. In the following we will present applications, processes and methods involved in laboratory activities.

Applications cover broad field of turbine machinery, where we focus on aerodynamic and hydrodynamic processes; among them are water turbines, large domestic appliances, small domestic appliances, pumps and fans for special purposes or applications, HVAC fans, suction units, aerodynamic tunnels design, collection chambers for mineral wool and glass wool productions, drying chambers, polymerization chambers, cooling applications, noise improvements of turbine machinery, agricultural spraying machinery, gas transmission systems, wastewater treatment systems etc. Among the processes we study cavitation and cavitation erosion, turbulence, image processing, risk prediction etc. Processes are in most cases related to turbine machinery applications. Among others, we pioneer cavitation process for the use in wastewater treatment and water processing applications and for modeling of cavitation erosion in turbine machinery and precision spraying for agricultural applications. Above mentioned applications and processes are addressed in a variety of ways using numeric modeling, experimental modeling, laboratory testing or field testing. In the laboratory dedicated equipment is available. Available are several laboratory measurement stations, high performance computer, modeling software, fast black and white camera, fast thermal camera, various data acquisition systems, sensors, scanners, actuators, analysers etc. Work for industry includes cooperation with small and medium enterprises and large international companies. Among our clients from abroad were Philips, Saint Gobain, Auma, Gamma Meccanica, Uralita, KSB, Electrabel, Knauf Insulation, Bosch Siemens and many other Slovenian companies, Gorenje, Hidria, Skupina Kolektor, Soške Elektrarne, Termoelektrarna Šoštanj, Izoteh, Domel, TIP95, LIMOS, Turboinštitut etc.

We have in the past participated in several international projects, 5th, 6th and 6th EU Framework projects, CORNET, European Space Agency, EUREKA and COST projects and several national projects. We are open for future cooperation and application to EU projects. In the Laboratory for Hydraulic Turbomachinery we try our best to join above mentioned research and development activities with teaching activities. Students are able to work during laboratory exercises with modern measurement equipment. Students are invited to participate in the research and development activities for research projects and industrial projects during diploma and M.Sc. thesis seminary work. Also in the future we will aim to make teaching process more efficient and appealing to students. FORMER PROFESSORS: Prof.Dr. Albert Struna, Prof.Dr. Franc Schweiger, Prof.Dr. Boris Velenšek

Noise Generation in the Air Gap of an Axial Fan ABSTRACT → Kinematics of the air-flow in the gap between the rotor and the stator is aerodynamically born noise which is generally predominant source of the emitted noise by most of the fans and is the most intensive within the human audible spectrum. Two different rotor blade tip shapes A and B forming the air-gap were analysed in details. Their influence on the emitted noise was determined by measurements of the integral aerodynamic characteristic and by the level of the sound pressure level of the fan. It was confirmed that the kinematics of the air-flow within the blade tip gap is significantly different for both observed blade tip designs and plays a crucial role when generation and size of the total emitted noise power is concerned.

Frequency spectra of the measured noise pressure level for both observed blade designs was also essentially different and served to confirm the wellknown fact that intensity of the sound pressure level decrease in the frequency spectrum helps to assess and identify mechanisms of the noise generation and nature of the flow kinematics. A typical measured amplitude decrease of the sound pressure level was observed for both blade tip versions for the frequency range f >1000 Hz: appropriate angle of decrease for the blade tip A is determined by ω-2.8 and for the blade tip B by ω-10/3. Distinctive differences between the two observed frequency spectra were established.

INTRODUCTION Marko Hočevar Laboratory: Laboratory for Water Turbine Machinery E-mail: marko.hocevar@fs.uni-lj.si Room: 314 Phone: +386-1-4771-314 Status: associate professor Research area: turbine machinery

Development of advanced fans is, besides optimum efficiency, use of environment-friendly materials, more and more oriented towards the products with lower noise emission. Total noise emission of a fan is made up of the structure-born and the aerodynamic noise which emits the highest amplitudes within the human audible spectrum. Total aero dynamical noise emitted by a fan is the sum of different noise sources and is the consequence of energy dissipation of the air-flow within its flowing tract. Review of various contributions that significantly relate to the flow kinematics through the air-gap between the rotor blade tip and the fan housing. Production of vortex structures in the flow and their dissipation was described by Kolmogorov [1] in detail. He was founder of the theory of cascade decay or energy decomposition of vortex fluid structures. His findings [1] were confirmed by numerous authors. Noise emission as the consequence of decay of isotropic vortex structures was described and published by Zhou and Rubinstein [2]. They found out that the decrease of the emitted noise pressure level when the frequency is increased follows the law – coefficient of the decrease ω-4/3

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

(in the double-logarithmic scale) [2]. Negative slope of the emitted noise pressure level as the function of the increasing frequency assumes, in the case of enlarged turbulence anisotropy which is the consequence of shear stresses within the fluid layers, the theoretical value ω-10/3 [2]. EXPERIMENT Emitted sound power and appropriate aerodynamic characteristic are the most important integral parameters that determine working capability and quality of an axial fan. Integral measurements of the aerodynamic characteristics of the observed fan were performed according to the standards EN-ISO-5801 [3], whereas measurements of the emitted sound power followed standards EN-ISO-3741 [4] and EN-ISO -13347[5]. Detailed description of measurements of the integral fan characteristic as well as of the performed local measurements of pressure fluctuations, with the aim to explain distinction and to prove the validity of the obtained results, was given in [6]. Technical and geometrical characteristics of the applied axial fan are presented in the Table 1 and are common for all measurements with both different design blade tips A and B.

The shape of the blade tip section (Fig.1, tip form A) follows the shape of the lower part of the blade unchanged. Blade tip design B is characterized by a backswept winglet oriented towards the suction side of the blade (Fig.1, tip form B). Minimum average air-gap width d0 between the blade tip and the fan housing was kept unchanged for both tested blade tip versions. Measurement results of the integral aerodynamic and emitted sound power level measurements for both blade tip designs differ from one another and are the consequence of different local flow kinematics in the air-gap of both observed blade tip designs. Figure 2: Aerodynamic and acoustic characteristics.

Figure 1: Axial fan used for the tests; location of the exchangeable blade tip geometry is marked (left); both design versions of the blade tip A and B (midsection); longitudinal section through both blades with different tip shape (right) Table 1: Fan geometrical characteristics Dshroud

0.635

[m]

Dhub

0.135

[m]

Dblade-tipe

0.6

[m]

d0 air-gap width

0.004

[m]

Z blade number

blade profile

NACA four digits

tip chord length

0.174

Driving electric motor

HEC-R10

rotational speed

650

Detailed analysis of the measured pressure sound level change within the observed frequency range for the operation point OP3, where the emitted sound power assumed its maximum value is presented in Fig. 3 and Fig. 4 and is not A-weighted. Fig. 3 shows the frequency spectra from 11.6 to 5000 Hz of the sound pressure level for both blade tip designs A and B with frequency resolution 1.46 Hz. Frequency spectra of the sound pressure level within the span width 11.7 Hz to 5000 Hz and with the resolution 11.7 Hz for both blade tip designs is presented in Fig. 4. There is a significant difference observed between the sound pressure level amplitudes for the blade tip versions A and B within the frequency range 160 and 5000 Hz, Fig. 3 and 4 (painted area); rotor blade with tip A exerts distinctly higher sound pressure level in comparison with the rotor blade, tip design B.

[m]

[rpm]

RESULTS Results of integral measurements of the aerodynamic characteristic as well as of the total emitted noise power level of the observed fan with two different rotor blade tip designs A and B are presented in Fig. 3 and 4. Operating points for both blade tip designs OP1-A, OP1-B to OP4-A and OP4-B represent working conditions – characteristic changes of the pressure number Y as the function of the flow number f. Influence of the backswept winglet on the blade tip (tip design B) on the selected fan characteristic ψ(φ) can be observed particularly in the zone of low and moderate pressure numbers ψ. Appropriate difference diminishes above the operation point OP2) and assumes the value that is within the range of the measurement uncertainty. Differences of the measured sound power level LWA are, on the other hand, significant for all observed operation points: 4.2 dBA for the operation points OP1-A and OP1-B and 6.3 dBA for the operation points OP2-A and OP2-B. Maximum measured difference of 8.6 dBA corresponds to the operation points OP3-A and OP3-B, whereas this difference diminishes to 3 dBA in the operation points OP4-A and OP4-B respectively.

Figure 3: Frequency spectra of the sound pressure level between 1.46 to 500Hz for the observed fan operating in the working point OP3.

Typical increase of the sound pressure amplitudes within the frequency range between 600 to 1000 Hz generated by the blade tip design A is followed by a gradual decrease at higher frequencies. In the vicinity of 2200 Hz there is a turning point of the sound pressure curve (blade tip A) which then assumes the form of a straight line with the angle of declination α=-10/3 up to the end of the measurement range. No evident increase of the sound pressure level is observed in the case of the blade tip B; after 1200 Hz the small amplitude curve assumes straight line form with the angle of declination α=-4/3. The difference of the sound pressure level for the two observed blade tip forms A and B diminishes for the frequencies above 2000 Hz and finally at 8000 Hz disappears. YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

It is possible to identify and to assess mechanisms of the noise generation as well as properties of the flow kinematics by observing intensity of decrease of the frequency spectrum (angle of declination α) [2]. Straight lines representing interdepended between the intensity of the sound pressure level and the frequency are also recorded in the Fig. 4 representing: 1) decay of the isotropic turbulence according to Zhou – Rubinstein and represented by the angle of declination α=-4/3, and 2) the case of the sound pressure decrease as the consequence of the decay of shear turbulence [2] denoted by the angle of declination α=-10/3.

Figure 4: Frequency spectra of the sound pressure for the operation point OP3.

There is one more typical straight line presented in the Fig. 4 with the angle of declination α=-2.8. This relation was calculated by Rubinstein and Zhou [2] from the measurements of the noise emission performed by Tam and Golebiowski [7] on sub and supersonic outflow through different nozzles where the portion of the shear turbulence was predominant. They found out that compressibility of the medium doesn’t affect too much turbulent generation of the noise with the exception of the near sonic flows. Their findings were also experimentally approved by Papamoschou and Roshko [8] and Bogdanoff [9]. The last mentioned coefficient of the noise pressure decrease determined by Tam at al [10] coincide with the sound pressure spectrum of the here presented axial fan with the blade tip form A for the frequency range above 2200 Hz. The shape of this spectrum is also similar to the theoretically determined straight line law that determines decrease of the sound pressure spectrum for the case of predominant shear turbulence. It can also be concluded from Fig. 4 (blade tip form A) that there is a moderate increase of the sound pressure in the frequency range between 600 and 900 Hz. This tendency can also be compared with the form of the theoretically determined energy spectrum [1]; as the result one can identify production of eddy structures in the frequency range up to 900 Hz followed by inertia and dissipation range of the spectrum. Increase of the sound pressure level in the frequency spectrum can be observed for the blade tip form A up to 1000 Hz and is then followed by a moderate decrease which is almost independent of the frequency. Sound pressure spectrum has a near linear form after passing the turning point at approx. 2000 Hz. There is no evidence of the eddy structure production which is the consequence of the flow kinematics through 52

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

the air-gap at the rotor blade tip for the sound pressure spectrum of the blade tip form B. Difference in the air-flow kinematics for both blade tip designs is schematically presented in Fig. 4. Induced vortex and distinctive unsettled, higher frequency (up to 1000 Hz) and smaller size eddy structures are the consequence of the flow separation from the sharp edged tip of the blade tip form A, Fig. 5 (left). Formation of a basic vortex and its progressive decay into smaller structures that are finally choked on the molecular level is typical for the air-flow through the rounded off terminal of the blade tip form B (Fig. 5, right). It can be concluded from the results in Fig. 3 and 4 that the difference of the emitted sound pressure level between the blade tip designs A and B is the consequence of the significantly different air-flow kinematics over the blade tip.

Figure. 5: Representation of the flow kinematics around the rotor blade tip.

CONCLUSIONS A typical sound pressure level increase up to 900 Hz is observed for the blade tip design A and is (above 2200 Hz) followed by a decrease assuming the form of a straight line with coefficient - angle of degression ω-2.8 up to the end of the measurement range. This value almost coincide with the theoretically determined angle of degression ω-10/3. The obtained relation ω-2.8 indicates presence of shear stresses in the fluid – presence of anisotropic turbulence together with the production of lower size eddy structures. Coefficient of degression that corresponds to the blade tip design B coincides with the coefficient value ω-5/4 which is typical for the emission of the sound pressure where decay of isotropic turbulence is present.

References [1] Kolmogorov, A. N., Dissipation of Energy in the Locally Isotropic Turbulence, Proceedings of the USSR Academy of Sciences, 32, 16–18, 1941 [2] Rubinstein, R., Zhou, Y., Time correlations and the frequency spectrum of sound radiated by turbulent flows, Institute for Computer Applications in Science and Engineering NASA Langley Research Centre, (1997) [3] International organization for standardization ISO 5801: Industrial fans; Performance testing using standardizied airways (2009) [4] International organization for standardization ISO 3741: Acoustics; determination of sound powerlevels of noise sources using sound pressure - precision methods for reverberation rooms (2010) [5] International organization for standardization ISO 13347-1/2: Industrial fans; Determination of fan sound power levels under standardized laboratory conditions - reverberant room method (2004) [6] Milavec, M., Širok, B., Vidal de Ventós, D., Hočevar, M. Influence of the shape of the blade tip on the emitted noise in the air-gap between the rotor and the housing of an axial fan. Forschung im Ingenieurwesen, vol. 78 (3/4), 107-119, 2014. [7] Holeček, N., Širok, B., Hočevar, M., Podgornik, Experimental research of aerodynamic noise induced by condenser of drying machine, International Journal of Acoustics and Vibrations, 10(1), 26-32, 2005. [8] Papamoschou, D., Roshko, A., The compressible turbulent shear layers: An experimental study, Fluid Mechanics, 197, 453-477, 1988. [9] Bogdanof, D.W., Compressible effects in turbulent shear layers, AIAA J., 21, 926-927, 1988. [10] Tam, C.,K.,W., Golebiowski, M., On the two components of turbulent mixing noise from supersonic jets, NASA Langley Research Centre, 1996. List of publications [11] Milavec, M., Širok, B., Vidal de Ventós, D., Hočevar, M. Identification of noise generation and flow kinematics in the air gap for two different blade tip designs of an axial fan. Forschung im Ingenieurwesen, 2015, 1-11.

YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

Method for assessment of product quality during paper production process ABSTRACT â&#x2020;&#x2019; Computer-aided visualization methods can be applied as a valuable tool for monitoring of paper quality during paper production process. The presented visualization method focuses on processing of images of paper mass layer before it enters the drier, as well as of paper after it exits the drier. Fibrous structure of the paper is scanned and monitored in selected observation windows. The size of the observation windows is adapted according to the paper mass velocity through the paper production machine. Image processing is carried out by applying some basic statistic methods in

order to gain quick response of the monitoring system. The presented method is able to detect anomalies in paper through time series of average greyscale level intensities in observation windows. Presented relations enable the assessment of suitability of the raw paper mass to achieve the desired gramature of the end product. Further development of the method shall focus on adjustment of observation windowsâ&#x20AC;&#x2122; size, on optimization of prediction for low gramatures and on determination of tolerance limits for different paper gramatures.

INTRODUCTION Tom Bajcar Laboratory: Laboratory for Hydraulic Turbomachinery E-mail: tom.bajcar@fs.uni-lj.si Room: N-4 Phone: +386-1-4771-422 Status: PhD researcher Research area: Visualization techniques Mentor: -

Paper represents an important product with numerous applications in industry or in everyday life, from packing medium, office material to self-hygiene means. Therefore, the need for paper is not likely to decline. Due to large demands as well as inherent raw material and energy consumption, there is a need for constant optimization of the paper production process. This in turn affects not only the amount of costs and level of product quality, but can also significantly contribute to the reduction of negative ecological consequences of such a production process. There were several methods developed in the last two decades that focus either on monitoring of the whole paper production process in order to check for mechanical damage (i.e. ripping of the paper film [1]), or on monitoring the quality of the paper. A need for monitoring the paper quality spawned some studies and patents in the field of intrusive optical computer-aided methods for monitoring the fibrous structure of the paper during its production process: a neural network method [2], a method of frequency analysis [3], a method of frequency-time analysis [4,5] and a method of multi-variate analysis of paper images [6]. These methods enable the monitoring of several parameters of the paper that

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

influence the paper quality, shape of anomalies and direction of fibres in the paper. The main problem with these methods is in their complex algorithms, which require tedious calculations and aggravate the process of real-time monitoring. Paper production often requires quick responses regarding the seeking for anomalies. Apart from that, there can be parameters or information processed in more complex methods that are less relevant in a certain segment of the production process. The main focus of the presented study is on determination of basic relations that enable the assessment of paper quality. The proposed method is a computer-aided visualization method that can be used for monitoring of key information about the momentarily state of paper during its production process with the main emphasis on robustness of the applied equipment and quick response of the monitoring system. EXPERIMENT Experimental layout The experiment was carried out on a paper production machine [7]. The paper mass was filmed before its entrance into the dryer, while the images of the dried paper were taken at the exit of the dryer. Figure 1 shows

the schematic view of the experimental layout. The paper mass from the reservoir is conducted onto the mesh belt, where it evens out by periodic transversal oscilations of the mesh belt. After that the wet paper mass travels through the dryer of the paper production machine, where it exits as a band of dried paper. Image acquisition was carried out by a digital camera Fastec HiSpec 4 that was controlled by a computer. Acquisition frequency was equal to 300 images per second. Belt-type LED diodes positioned under the mesh belt (in front of the dryer) or under the paper ribbon (behind the exit of the dryer) perpendicularly to the movement of wet paper mass (or dry paper) served for lighting purposes. Emitted light was strong enough to enable the observation and filming of the fibrous structure of the paper mass/ dry paper.

Figure 1: Experimental layout (depicted camera position in front of the dryer).

Three different types of paper mass were used during the experiment. They differed from each other by means of the gramature of the end product (i.e. dry paper). Thus, the selected types of paper mass resulted in three different values of paper gramature: 50 g/m2, 110 g/m2 ali 210 g/m2. There were six sequences of images acquired during the experiment, i.e. two for each chosen gramature of the end product â&#x20AC;&#x201C; one before the dryer (paper mass) and the other after the exit from the dryer (paper). Figures 2 and 3 show typical images of the fibrous structure of the paper mass and end product for two different gramatures. Fibrous structure is depicted on the images as areas of different greyscale intensity, which can stretch through 256 levels â&#x20AC;&#x201C; from black (intensity level 0) to white (intensity level 255). It can be seen from Figs. 2 and 3 that the uniformity (homogeneity) of the fibrous structure (greyscale intensity levels) increases with the value of gramature of the end product. Greyscale intensity levels were analysed inside square observation windows. These were placed on the top, middle and bottom of each image in the sequence (Figure 4) in order to cope with the differences in lighting intensity across the mesh belt or paper ribbon. The size of each window k corresponded to the spatial shift of the wet paper mass (or dry paper) between two successive images. In this way, no information of greyscale intensity inside a particular observation window could be lost or doubled during the movement of the mesh belt or dry paper ribbon. Values of greyscale intensity inside each observation window were further statistically processed.

Figure 2: Fibrous structure of wet paper mass (top) and dry paper (bottom): gramature 50 g/m2.

Figure 3: Fibrous structure of wet paper mass (top) and dry paper (bottom): gramature 210 g/m2.

YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

a particular image with respect to the mean greyscale intensity value of the whole sequence show that the oscillations are more pronounced in the case of lower gramature value. Accordingly, it is expected that the dissipation and standard deviation of the average greyscale intensity value are higher with the lower gramature as well.

Figure 4: Position of observation windows k.

Each observation window k was composed of several pixels, each pixel having its own greyscale intensity. Average greyscale intensity A in a particular observation window on a particular image can be determined with the following expression [8]:

where k denotes a particular observation window, t denotes a successive number of the image within the sequence. E stands for greyscale intensity of a particular pixel inside the window k, while l and m denote coordinates of a particular pixel within the window k. Standard deviation s of greyscale intensity in a particular observation window k through the whole sequence of images was then calculated [9]:

where n refers to a number of images in the sequence, while A(k) denotes an average value of greyscale intensity in the observation window k for the whole sequence of images. RESULTS Figure 5 shows time series of average greyscale intensities in the sequence of images of wet paper mass and dry paper with the gramature value of 110 g/m2. Both time series are similar between wet paper mass and dry paper, albeit the oscillation amplitude of average greyscale intensity is somewhat lower in the case of dry paper. Significant alternations in greyscale intensity usually indicate the presence of unwanted inclusions or anomalies within the paper mass. Difference in time series of greyscale intensities in observation windows between different paper gramature values is evident in Figure 6, where a comparison between paper gramatures of 50 g/m2 and 210 g/m2 at the exit of the dryer is shown. Observations of the amplitude of the average greyscale intensity in the observation window of

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

Figure 5: Comparison of time series of greyscale intensity in the middle observation window (k = 2) for wet paper mass (top) and dry paper (bottom) – gramature 110 g/m2.

Figure 6: Comparison of time series of greyscale intensity in the middle observation window (k = 2) for dry paper with gramature of 50 g/m2(top) and 210 g/m2 (bottom).

Diagram in Figure 7 shows that the value of average standard deviation of greyscale intensity in the observation windows k at the exit of the dryer (i.e. for dry paper) typically lessens with increasing gramature. At gramature values of 110 g/m2 and 210 g/m2 this holds for wet paper mass in front of the dryer as well; in both cases the values of standard deviation beforet the entrance of the dryer are slightly higher than those after the exit of the dryer. Images of dry paper are namely more transparent than those of wet paper mass. Local changes in greyscale intensities are less pronounced due to the dryness of the paper. However, it seems from Figure 7 that the values of average standard deviation of greyscale intensity in the case of gramature value of 50 g/m2 do not follow the above stated rule. Average standard deviation value is in this case higher at the exit of the dryer. The reason for this “anomaly” is very likely in the mesh belt (Figure 1) and its structure. Images of the latter comprise of distinctive lines close to each other and positioned at the angle of 85 degrees to the direction of mesh belt movement. Such a structure partially attenuates the light intensity that penetrates through it and causes the increase in homogeneity of greyscale intensity values on images of otherwise quite thin paper mass (due to low gramature). Therefore, the value of average standard deviation of greyscale intensity on the wet paper mass images lessens below that of the dry paper at the same gramature value.

Figure 7: Average standard deviation of greyscale intensity for a particular sequence of images with respect to paper gramature.

CONCLUSIONS The study presents a method that enables monitoring of paper quality during its production process in a paper machine from wet paper mass to the end product at the exit from the dryer. The quality of paper was assessed through the level of greyscale intensity – transparency of fibrous structure on a selected surface that was determined using images of the paper mass before the entrance of the dryer and after it left the dryer in a form of dry paper. Statistical methods were applied on selected observation windows within the images of both, wet paper mass on the mesh belt and dry paper leaving the dryer. Results demonstrated that the average value of greyscale intensity in selected observation windows and its mean standard deviation in the sequence of images can be used as a measure for paper quality. Time series of average greyscale intensities in selected observation windows can serve for detection of anomalies, their size and location within the wet paper mass or dry paper. Standard deviation of greyscale intensity as a measure of dispersion about the mean value can provide information on the quality of fibrous structure and therefore on the achievability of a desired gramature value of the end product. Experiment showed that higher gramature values implicate lower values of standard deviation of greyscale intensity in selected observation windows in the sequence of images. At identical gramature values, the values of standard deviation of greyscale intensities of dry paper images seem to be lower than those of wet paper mass images. Presented method is robust and uses simple statistical algorithms that enable quick responses. It could therefore be used not only for real-time monitoring of suitability of selected paper mass for production of paper with a desired gramature value, but also for quick detection of potential anomalies in the paper during its production process. Potential future development of the method should comprise additional optimization of the method regarding the expansion of different tested gramature values, optimization of observation window sizes, determination of acceptable values of standard deviation for specific gramature values and elimination of certain deficiencies of the method, which appeared mostly in data processing at very low gramature values.

References [1] Trunkhardt, M., Wiericks, C., 2012. Faster and More Accurate Decision-making Using Integrated Solutions Throughout the Paper Manufacturing Process. O Papel 73, pp. 69-73. [2] Lampinen, J., 1994. Optimization and Simulation of Quality Properties in Paper Machine with Neural Networks. Proc. IEEE World Congres on Computational Inteligence, Orlando, Florida, June 28 – July 2, 1994, pp. 3812-3815. [3] Bernié, J.-P., Murray Douglas, W.J., 2001. Paper quality determination and control using scale of formation data. United States Patent, Patent No. US 6,301,373 B1. [4] Reis, M.S., Bauer, A., 2009. Using Wavelet Texture Analysis in Image-Based Classification and Statistical Process Control of Paper Surface Quality. 10th International Symposium on Process Systems Engineering - PSE2009, Rita Maria de Brito Alves, Claudio Augusto Oller do Nascimento and Evaristo Chalbaud Biscaia Jr. (Editors), pp. 1209-1214. [5] Reis, M.S., Bauer, A., 2009. Wavelet texture analysis of on-line acquired images for paper formation assessment and monitoring. Chemometrics and Intelligent Laboratory Systems 95, pp. 129-137. [6] Facco, P., Masiero, A., Bezz, F., Barol, M., Beghi, A., 2011. Improved multivariate image analysis for product quality monitoring. Chemometrics and Intelligent Laboratory Systems 109, pp. 42-50. [7] Bajcar, T., Šinkovec, A., Malneršič, A., Širok, B., Novak, L., 2015. Metoda za spremljanje kakovosti izdelka v proizvodnji papirja. Ventil 21, pp. 120-124. [8] Širok, B., Blagojević, B., Novak, M., 2002. Influence of blow away velocity field on the primary layer fibre structure in the mineral wool production process. Glass Technology 43, pp. 188-194. [9] Sachs, L., 2003. Angewandte Statistik – Anwendung statistischer Methoden. Springer, Berlin.

YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

Close-range air-assisted precision spot-spraying for robotic applications: aerodynamics and spray coverage analysis ABSTRACT → Computer-aided visualization methods can be applied as a valuable tool for monitoring of paper quality during paper production process. The presented visualization method focuses on processing of images of paper mass layer before it enters the drier, as well as of paper after it exits the drier. Fibrous structure of the paper is scanned and monitored in selected observation windows. The size of the observation windows is adapted according to the paper mass velocity through the paper production machine. Image processing is carried out by applying some basic statistic methods in

order to gain quick response of the monitoring system. The presented method is able to detect anomalies in paper through time series of average greyscale level intensities in observation windows. Presented relations enable the assessment of suitability of the raw paper mass to achieve the desired gramature of the end product. Further development of the method shall focus on adjustment of observation windows’ size, on optimization of prediction for low gramatures and on determination of tolerance limits for different paper gramatures.

INTRODUCTION Aleš Malneršič Laboratory: Laboratory for Water and Turbine Machines E-mail: ales.malnersic@fs.uni-lj.si Room: N4 Phone: +386-1-4771-422 Status: PhD student (started: September 2014, to be completed: November 2017) Research area: System for precision spraying in orchards and vineyards Mentor: Assoc. Prof. Dr. Marko Hočevar, univ. dipl. phys.

Application of agrochemicals is at present the method most used to protect plants from diseases, pests and weeds [1]. To do this, pesticide formulations are diluted in water and distributed over the vegetation in form of sprays. To protect plants from diseases and pests, agrochemicals are sprayed uniformly to ensure coverage of susceptible targets at the appropriate time in the season. Current robotic technologies can be applied to crop protection [2] enabling the possibility of precise and selective targeting of the spray [3]. This represents one of the most promising options for reducing the amount of used pesticide, whilst maintaining crop-protection efficiency. The concept of precise application of pesticides also involves the possibility of real-time adjustments of spraying application to the local needs of the target (plant, or part of the plant) on which the treatment is being applied. Hence, there is a need to develop and introduce techniques and systems for disease detection and pesticide distribution [4] which are able to optimise the spot-application of pesticides according to the specific characteristics of the target, such as disease susceptibility, or the presence of infection symptoms.

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

In the broad field of agricultural robotics, research work is focused on the development and validation of intelligent and selective agricultural robots with crops-care capabilities by integrated use of cutting-edge robotics and further advancing of sensing technologies [5],[6]. Here a new technique of spraying is introduced. For close range precision spraying small patches of disease are required to be treated during their early development. For this a close range precision application a spraying end effector (SEEF) is required. In the following an SEEF design will be presented and measurements of the properties of the airflow around the plant will be investigated. CLOSE-RANGE SPRAYING END EFFECTOR (SEEF) SEEF design The SEEF was designed such that pesticide could be locally applied to the position of the disease and consisted of the following components: an airflow generator (axial fan), an airflow nozzle, a pesticide nozzle, a pesticide pump, electrical connections for power supply and control signals, a pesticide connection and a chassis. A schematic diagram of the SEEF is shown in Fig.1.

Figure 2: Measurement setup for SEEF airflow properties measurements with hot-wire anemometry, left: Rear view, right: Right side view; (1) SEEF, (2) electric motor with rotating airflow screen, (3) electric motor variable drive, (4) personal computer with multifunctional data acquisition board, (5) signal conditioner, (6) constant temperature anemometer and (7) hot wire sensor. Figure 1: Close range spraying end effector. 1. Axial fan, 2. Flow straightener, 3. Airflow diffuser, 4. Pesticide nozzle, 5. Pesticide valve, 6. SEEF case with voltage regulator and pesticide nozzle switch

Airflow structure The airflow at the exit from aerodynamic nozzle of SEEF should contain only small tangential and radial velocity components since both components cause expansion of the airflow with the increasing distance from the SEEF. Unwanted expansion of the airflow prevents spot spraying of diseased plant parts occurring particularly for targets located far away from the SEEF and deep within the canopy. To reduce airflow expansion, the SEEF was equipped with flow straightener and a conical aerodynamic nozzle. Lack of large coherent structures decreases probability of spray depositing on the back of leaves. In general, large coherent structures feature low frequencies, while small coherent structures feature high frequencies. Large coherent structures, with their low frequency can coincide with the natural frequencies of branches and leaves and may produce increased plant movement causing the back of leaves to be exposed to spray. As a possible remedy to the expected limited deposition on the back of leaves, pulsations in the airflow were deliberately introduced via a rotating screen. The rotating screen operated as a device that alternately stopped and allowed the airflow to pass through. Such arrangement was considered able to produce high airflow pulsations without significantly expanding the spray plume. Measurement and analysis methods Three measurement techniques were used to evaluate the operation of the SEEF: (1) aerodynamics measurements using hot-wire anemometry, (2) spray coverage and determination of the number of spray impacts using by water sensitive papers and (3) measurement the motion of plants and leaves using high speed imaging and analysis. They are described more in detail in the following subsections. Pulsations of the airflow were achieved using a rotating circular airflow screen with four unevenly distributed openings. The diameter of each opening was 80 mm and the airflow screen was rotated by an electric motor, driven by a variable frequency drive.

Figure 3: Measurement setup for plant and leaves motion analysis, left: Rear view, right: Right side view; (1) SEEF, (2) electric motor with rotating airflow screen, (3) electric motor variable drive, (4) personal computer, (5) pesticide pump, (6) plant, (7) high speed camera with lens and (8) water sensitive papers.

SEEF aerodynamic measurements During measurements of aerodynamic flow properties SEEF spray nozzle was not operated. The SEEF was located at the same height and axis as hot wire anemometer probe and the probe was mounted with its hot-wire perpendicular to the direction of the main flow. The distance between SEEF nozzle and the hot-wire anemometer probe varied according to different operation points as shown in Table 1, being 0.7 m, 0.5 m and 0.3 m. Mean velocity, root mean square (RMS) velocity and turbulence level were calculated from the measurements according to guidelines in hot-wire anemometers turbulence measurements [7]. The RMS velocity was used as a measure for leaf velocity fluctuations, since the average velocity of leaves is zero, because leaves are attached to the plant. Mean velocity: Velocity root mean square (RMS): Turbulence level:

Spray coverage and number of impacts Within the grapevine (Vitis vinifera L.), two positions on both sides of the leaves were selected for an analysis of spray coverage and deposition as shown in Fig. 4. To analyse spray deposit Water Sensitive Papers of size 75 mm x 26 mm were attached to the plants. The number of spray droplet spots and the percentage of coverage were evaluated for each WSP. For each analysis, WSP were placed at equivalent places and were attached to the selected leaves

YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

on both surfaces at fixed positions. Spot-spraying time was set to 1 s, corresponding to a realistic application time and spraying was carried out using mains water. Measurements were performed indoors in a laboratory. Air temperature during measurements was 22 °C and relative humidity was around 50 %. After each experiment, the plant was allowed to dry completely and the WSPs were carefully detached and stored in sealed labelled plastic bags for subsequent imaging. Colour digital images of WSPs were acquired using a digital scanner at 1200 dpi, resulting in a nominal resolution of 21 µm pixel-1. The obtained RGB images were processed by custom software written in to obtain quantitative descriptors of spray deposit on the target. Plant and leaves motion analysis by image analysis The camera used for image acquisition of plant motion was FASTEC HISPEC 4. The camera operated at a resolution 800×858 pixel at 150 frames s-1 and was positioned above and slightly behind the SEEF. The number of acquired images in each series was 5000. A Nikkor 50 mm f/1.2 lens was used with the camera. A dark background was used for easier separation of the plant from the background. The plant was illuminated from two sides with 4 led lights CREE XM-L T5 in a row placed on each side at distance 0.8 m between them and 0.5 m from the plant. During visualization, leaves were spatially variable illuminated or screened by neighbouring leaves. Custom software program for image analysis was used, which was written in LabVIEW using the Vision Development Module library. Operational set-points for spray coverage and number of impacts measurements Several operating conditions were explored during the experiments for measurements of spray coverage, number of impacts and plant and leaves motion with high speed imaging as shown in Table 1. Spraying and imaging was done simultaneously. Table 1: Selection of operational-set points. Oper- Rep- Disational eti- tance settions [m] point

Air velocity Pulsation Spray at the locafrequency tion of target [Hz] [ms-1]

0.3

6.1

1.2

yes

0.5

7.5

yes

0.7

7.5

RESULTS AND DISCUSSION Results of aerodynamic measurements Figure 4 shows a decrease of axial velocity with increasing distance from the SEEF. Velocity is presented for the two settings of the fan rotational speed, one producing airflow with an average velocity of 10 m s-1 and the other 7.5 m s-1 both measured at a distance of 0.3 m from the SEEF. Measurements of aerodynamic properties of SEEF were performed in the absence of the plant according to experimental setup shown in Fig. 2. Experimental results show that number of discrete peaks in velocity fluctuations decreases with distance of the measurement location from 60

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

SEEF, number of discrete peaks in velocity fluctuations being the highest for operational-set points 1 and the lowest in operational-set point 3.

Figure 4: Relationship between distance from SEEF and airflow axial velocity.

The airflow from the SEEF without the rotating screen contains only limited flow fluctuations. Since the generation of large velocity fluctuations and associated coherent structures occurs at the location of the rotating screen, then with increasing distance from the SEEF the discrete structures decay and a more coherent airflow occurs. At greater distances from SEEF (operational-set point 3), discrete peaks of velocity fluctuations are not discernible. Results of spray coverage and number of impacts measurements Droplet density on front side of the leaves was good. At the operational-set point 1 and repetition 1, spray coverage on right leaf was excessive (94.4 %) and the spray droplets were not distinct. The droplet density selected for this study cover largely the most commonly spraying patterns recommended by Syngenta [8] to provide satisfactory results of crop-protection: 20 to 30 drops cm-2 for insecticide or pre-emergence herbicide applications, 30 to 40 drops cm-2 for contact post-emergence herbicides, and 50 to 70 drops cm-2 for fungicide applications [9]. Droplet density on the back of the leaves was <40 droplets cm-2 except at the operational-set point 1 and repetition 2, where on one leaf the droplet density reached 118 drops cm-2 whilst on the other it was 61 drops cm-2. Average spray droplet volume diameter was 167 µm with standard deviation 40µm. Limited movement of the plant leaves, combined with small turbulent structures in the airflow, essentially prohibited spray being deposited on both sides of leaves. As a result, when spraying by SEEF, only front sides of the leaves were sprayed. Table 2: Integral parameters of spraying. Operational Repeti- set point tion

average leaf velocity [m s-1]

leaf RMS velocity [m s-1]

0.029

0.346

0.0052

0.243

0.0058

0.168

0.0073

0.193

0.0014

0.157

0.028

0.328

turbulence level [%]

spray coverage front side [%]

spray coverage back side [%]

droplet density front side [drops cm-2]

droplet density back side [drops cm-2] left

left

right

left

right

left

right

48.8

94.4

0.2

138

n.a.

31.5

13.9

9.5

2.1

133

177

118

42.8

27.0

0.5

0.7

157

218

50.7

39.6

0.7

0.2

130

190

16.9

53.4

0.3

0.4

190

Results of plant and leaves motion analysis by image analysis Average RMS velocity vectors are overlaid on representing image for each operation point (Fig. 5). Velocity vectors are shown in grey colour. Intensity of the colour represents percent of successfully calculated velocities at certain point. Since the RMS values of velocity fluctuations were always positive and velocity vectors were calculated as a RMS value of individual velocities of the complete sequence the vectors always points down and to the right

Figure 5: Sample Average RMS velocity vectors. The location of water sensitive papers can also be seen.

Leaf RMS velocity of fluctuations corresponded well with airflow turbulence levels for all operational-set points. In the case of operational-set point 2 (turbulence level 52%) leaf RMS velocity was from 0.157 m s-1 to 0.193 m s-1. In the case of operational-set point 1 (turbulence level 66 %) leaf RMS velocity was 0.243 m s-1 and 0.346 m s-1. DISCUSSION Our understanding of precision spraying with the SEEF is the following. The requirement for precision spraying requires a controlled airflow without noteworthy flow fluctuations (in the form of large coherent structures like vortices), otherwise, the airflow fluctuations (high flow turbulence levels) disturb the airflow and prevent precise delivery of the spray. Due to the limited size of the sprayed area the focus is on the movement of single leaves instead of branches. At the location of a targeted leaf, the

airflow from a SEEF acts on the leaf with a constant force which moves the leaf from its equilibrium position to an extreme point, causing bending. This situation changes only slightly when airflow pulsations are introduced. The airflow acts on the leaf with an intermittent force, but the force direction and size remain essentially the same. In a very simplified view, leaf is excited by intermittent force and thus fluctuates from its equilibrium point to both maxima We believe that the very limited spray reaching the back of the leaves with the SEEF is due to the two factors: (1) the absence of large coherent structures within the spraying airflow carrying spray around plant leaves and (2) the small size of the SEEF not providing large coherent flow structures. References [1] Oerke E.C., Dehne H.W., 2004, Safeguarding production-losses in major crops and the role of crop protection, Crop Protection 23(4), 275–285. [2] Mulla D. J., 2013, Twenty five years of remote sensing in precision agriculture: Key advances and remaining knowledge gaps, Biosystems Engineering, Vol. 114, 4, 358–371. [3] Khot L. R., Ehsani R., Albrigo G., Larbi P. A., Landers A., Campoy J., Wellington C., 2012, Air-assisted sprayer adapted for precision horticulture: Spray patterns and deposition assessments in small-sized citrus canopies, Biosystems Engineering, Vol. 113, 1, 76–85. [4] Dekeyser D., Duga A. T., Verboven P., Endalew A. M., Hendrickx N., Nuyttens D., 2013,Assessment of orchard sprayers using laboratory experiments and computational fluid dynamics modelling, Biosystems engineering 114 (2), 157-169. [5] Bontsema, J., Hemming, J., Pekkeriet, E., Saeys, W., Edan, Y., Shapiro, A., Hočevar, M., Hellström, T., Oberti, R., Armada, M., Ulbrich, H., Baur, J., Debilde, B., Best, S., Evain, S., Gauchel, W., Ringdahl, O., 2014, CROPS: high tech agricultural robots. International Conference of Agricultural Engineering, Zurich. [6] Oberti R., Marchi M., Tirelli P., Calcante A., Iriti M., Hočevar M., Baur J., Schütz C., Pfaff J., Ulbrich H., 2014, Selective precision spraying of grapevine’s diseases by crops robot platforms, CROPS: high tech agricultural robots. International Conference of Agricultural Engineering, Zurich. [7] Jørgensen, F.E., 2005, How to measure turbulence with hot-wire anemometers, A practical guide, Dantec Dynamics. [8] Syngenta, 2002, Water-sensitive paper for monitoring spray distributions, Basel: Syngenta Crop Protection AG. [9] Cunha M., Carvalho C., Marcal A.R.S., 2012a, Assessing the ability of image processing software to analyse spray quality on water-sensitive papers used as artificial targets, Biosystems Engineering 111(1), 11–23. List of publications [10] Malneršič A., Dular M., Širok B., Oberti R., Hočevar M., Close-range air-assisted precision spot-spraying for robotic applications: aerodynamics and spray coverage analysis, Biosystems Engineering, 2016.

YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

Cavitation damage in water at elevated temperatures ABSTRACT → In the present study we show experimental campaign where cavitation erosion in water at different temperatures was investigated. In contrary to other studies, where cavitation is generated by ultrasound, we employed hydrodynamic cavitation, which more closely resembles the conditions in applications – it is known that the results obtained by ultrasonic cavitation can be misleading. The tests were performed in a radial flow test-section, which can generate very aggressive type of cavitation. Polished aluminum samples were used to investigate

the damage. Temperatures in the range between 30 and 100°C were investigated. We found out that the temperature of the water significantly influences the cavitation aggressiveness –maximum aggressiveness was found at 60°C. In the last part of the work two theories were developed and tested. Micro-jet approach correctly predicted the trend but the influence of the temperature was marginal. On the other hand, the theory of the spherical bubble collapse with consideration of thermodynamic effects of cavitation produced a very good agreement to the experiments.

INTRODUCTION Matevž Dular Laboratory: Laboratory Hydraulic Turbomachinery E-mail: matevz.dular@fs.uni-lj.si Room: 314 Phone: +386-1-4771-314 Status: Associated Professor Research area: Cavitation

Cavitation is a phenomenon characterized by vapor generation and condensation in high-speed liquid flows. The understanding and the prediction cavitation effects in such cases is crucial in many applications; for example the turbopumps for liquid hydrogen LH2 and oxygen LOX in space launcher engines need to have an inducer rotor installed upstream from the main impellers, in order to achieve high suction performance [1]. The inducer is designed to operate in moderate cavitating conditions, hence a minimum pressure level in the tanks must be ensured, in order to avoid the occurrence of large sheet cavities on the blades, which are often associated with large-scale instabilities. A wide range of studies related to various aspects of the cavitation erosion problem – bubble dynamics, model development, CFD prediction, material testing etc. – have been performed in the past [2]. They all aim at improving the physical understanding of the phenomenon. The effects of medium temperature on the aggressiveness of cavitation erosion were studied as early as 1960‘s ans 70’s. It was concluded that the decrease in the damage observed at higher temperatures can be attributed to either the increase in vapor pressure or the fact that the condensation driven collapse of a bubble at a higher temperature is slower, since more heat needs

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

to be conducted into the surrounding fluid as a result of higher vapor density - when the temperature and pressure of the uncondensed vapor are raised, they arrest the bubble collapse, decrease collapse pressures and consequently damage. More recently the effects of medium and its temperature on acoustic cavitation aggressiveness were studied by Hatori [3]. While they show that both play significant role in the process, few conclusions on the physical background of the measured results are provided. In contrary to other studies, where cavitation is generated by ultrasound, we employed hydrodynamic cavitation, which more closely resembles the conditions in space propulsion applications. Cavitation aggressiveness on aluminum samples in water with different temperatures (from low to significant level of thermodynamic effects) was observed. In the discussion we derive a bubble dynamics model, which explains the dependency between the temperature of the medium (its thermodynamic parameter) and cavitation aggressiveness. The present study is a step towards evaluation of erosion in cryogenic liquids under a scope of the continuous work for the European Space Agency (ESA).

EXPERIMENT Cavitation tests were performed in a small cavitation tunnel. The geometry was adopted from the facility at the LEGI Grenoble. Test-rig The cavitation tunnel (Fig. 1) has a closed circuit which enables to vary the system pressure.

radius of curvature of the feed nozzle exit is 0.75 mm. The gap between the front and back plates is 2 mm wide. As the fluid moves radially outwards between the plates the pressure recuperates rapidly and cavitation zone abruptly closes. The flow exits the section axially through 8 holes in the back plate. The position of the specimen center lies at a radial distance of 22.2 mm from the center of the feed nozzle. Specimens Specimens (Fig. 3) were manufactured out of aluminum. The diameter of the surface which was exposed to cavitation is 30 mm.

Figure 1: Cavitation test-rig.

A 4.5 kW pump (1) enables the variation of the rotation frequency in order to set the flow rate. Downstream of the pump, a partially filled tank (2) is installed for water heating and for damping the periodical flow rate and pressure fluctuations. Cavitation and its effects are observed in a test section (3). The water enters the section axially through the nozzle and exits it by 8 flexible pipes. The tank further downstream (4) is used for cooling of the circulation water - a secondary cooling water loop is installed in it. The valves (5) and (6) enable easy and fast disconnection of the test section from the main loop. The flow rate is measured by an electromagnetic flow meter (7) ABB ProcessMaster 300 (DN 40) with a 2% uncertainty on measurements. Temperature is obtained with a type K thermocouple (8). The reference pressure is measured 35 mm upstream from the test-section by an ABB 266AST pressure transducer (9) – the uncertainty of the measurements is 8 mbar. The pressure in the test rig is adjusted in the partially filled tank (2) connected to a compressor (10) and a vacuum pump (11).

Figure 3: Dimensions of the specimen (in mm) and its picture prior to the exposure to cavitation.

The surface was polished down to 1mm. The surface hardness was measured to be 65HV. Observation of cavitation For the purpose cavitation observation the front plate of the test-section was replaced with a transparent one. The idea of this test was to obtain some general characteristics of cavitation behavior inside the section. High speed camera Fastec Imaging HiSpec4 2G mono was used for image acquisition. Figure 4 shows images of cavitation in the test section recorded at a frame rate of 50000 frames per second (only every 10th image is shown in Fig. 4). Images of cavitation were recorded at a resolution of 176×86 pixels.

Test-section Highly aggressive cavitation conditions are achieved in the so-called radial jet test-section shown schematically in Fig. 2.

Figure 4: A single image (frontal view) and a high speed sequence showing cavitation in the test-section (T=30°C, v=20.5 m/s, p∞=4.305 bar)- The position of the specimen is shown by dashed line

Figure 2: Test section design with indicated flow pattern.

The flow enters the section axially at a high velocity through a nozzle with a diameter of 10 mm. It then forced to turn at an angle of 90°, which makes it cavitate. The

Our results relate well to the observations in the original design from LEGI laboratory [21]. As mentioned, the water begins to cavitate at a 90° bend as it enters the gap between the plates. Cavitation clouds separate from the attached cavity and travel radially outwards to a higher pressure region where they collapse – roughly 20 to 25 mm YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

from the center of the plate. We expect the highest erosion rate in the region of cavitation cloud collapse – near the outer perimeter of cavitation zone. A circle in Fig. 4 shows the position of the specimen. EROSION EVALUATION After the exposure to cavitation the specimen was photographed with a TESA-VISIO 300 GL DCC system. To photograph the entire surface of the specimen about 80 images were taken, each covering the area of 5.5 by 4 mm at a pixel size of approximately 7 mm (Fig. 5).

Figure 5: High resolution image of specimen surface, which has been exposed to cavitation for 120 minutes in water at T=30°C.

Comparing the two individual images the damaged area can clearly be seen. As expected the damage follows a circle with the center in the middle of the test-section – the maximum damage lies at a radius of about 22 mm - the same as the closure region of cavitation. The evaluation followed the pit-counting technique [4]. Pits are recognized as the darker regions in an image, while the brighter area is assumed to be undamaged surface. The pit-count method gives a distribution of the number and the area of the pits and consequently, the distribution of the magnitude of cavitation erosion on the surface. RESULTS The results are presented in diagrams showing the percentage of the damaged surface as a function of radial distance from the center of the section. Figure 8 shows the results of measurements where the specimens were exposed to cavitation for a period of 120 minutes at water temperatures between 30 and 100°C (Fig. 6). One can clearly see that cavitation aggressiveness is strongly dependent on the temperature of the medium. As the temperature was increased from 30°C also the damage extent rose. The maximum is achieved at around 60°C. The cavitation remains aggressive for water of 70°C, then it sharply drops to level below the one at 30°C. The effected region did not change significantly between the tests – most of the damage is concentrated around the cavity closure line at R=22 mm.

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

Figure 6: Damage distributions for tests at temperatures from 30 to 100°C for exposure time of 120 minutes.

DISCUSSION Although the micro-jet theory predicts the maximum to lie at 60°C, what agrees with experiments, the predicted temperature influence on cavitation aggressiveness is insignificant – only about 3%. Such a small variation in the predicted water hammer pressure cannot explain the obvious and dependence of cavitation aggressiveness on the medium temperature. On the basis of these results we can deem the micro-jet approach as questionable or even false in the present case. The second widely accepted mechanism that takes place in creating a pit is the shock wave, which is emitted at a spherical collapse of an even smaller bubble. The pressure field, in terms of the distance from the bubble center and the time pcs(r,t), can be determined by solving the Reyleigh-Plesset equation, which, for the case of fluids with considerable themodynamic effect, needs to be modified. By investigating several boundary conditions we concluded that the choice of the initial bubble size and the ambient pressure evolution do not influence the general (non-dimensional) outcome of the calculation – although the bubble dynamics and shock wave magnitudes change significantly, the predicted dependency of the shock wave magnitude on the temperature does not change. Figure 7 shows the dynamics of cavitation bubble (its radius) in time as a function of the temperature. A bubble with an initial radius of 2 mm was subjected to an oscillatory pressure field with amplitude. A constant pressure amplitude f p∞,max-pv(T)=1.4 bar and frequency of 25 kHz was used (this way constant cavitation conditions (constant cavitation number) in terms of the temperature were assured).

Figure 8: Prediction according to the spherical collapse theory.

The maximal magnitude of the shockwave is predicted at 50°C, which somewhat differs from the maximum of measured erosion (60°C). Also the prediction does not comply well with the experiment at lower temperatures, although the trend is correct. Nevertheless we conclude that the spherical bubble collapse theory with the addition of thermodynamic effects is a valuable tool for the prediction of cavitation aggressiveness in thermosensible fluids.

Figure 7: Predicted bubble radius as a function of time for temperatures between 30 and 100°C.

We can see that the collapse occurs roughly between 17 and 20 ms after the bubble is exposed to the oscillatory pressure field. The bubble reaches the greatest size in the case at 50°C – about 27 mm, compared to, for example, only 12mm for the case of 100°C. It is important to notice that the time taken for the collapse (from the instant when the bubble reaches its maximal size to the time of the first rebound) is almost the same to all temperatures – about 3 ms. Hence, the velocity of the collapse strongly depends on the temperature of the medium. Equation 7 states that the faster the collapse, the greater will the shock wave be. Figure 8 shows the prediction of the shock wave amplitude as a function of temperature together with the measured integral damage (Aint) – we use a non-dimensional scale for the magnitude of the shock wave. A secondary x-axis gives the values of the thermodynamic parameter S. For the sake of comparison we assume that a relationship between the magnitude of the shockwave and damage exists.

References [1] K. Kamijo, H. Yamada, N. Sakazume, S. Warashina, Developmental History of Liquid Oxygen Turbopumps for the LE-7 Engine, Trans. Japan Soc. Aero. Space Sci. 44(145) (2001), 155–163. [2] Advanced Experimental and Numerical Techniques for Cavitation Erosion Prediction. Fluid Mechanics and Its Applications 106. Edts.: Kim, K.H., Chahine, G., Franc, J.P., Karimi, A., Springer 2014. [3] S. Hattori, K. Taruya, K. Kikuta, H. Tomaru, Cavitation erosion of silver plated coatings considering thermodynamic effect, Wear 300(1-2)(2013) 136-142. [4] M. Dular, B. Bachert, B. Stoffel, B. Sirok, Relationship between cavitation structures and cavitation damage. Wear 257 (2004) 1176–1184. List of publications [5] M. Dular, Hydrodynamic cavitation damage in water at elevated temperatures, Wear 346–347 (2015), 78-86.

YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

High-speed thermal imaging of high-temperature processes ABSTRACT → This paper presents the research work regarding non-contact temperature measurement by standard (visible light) digital cameras. The proposed measurement method addresses the problem of high equipment cost and limited spatiotemporal resolution of infrared thermometry, especially in high-speed processes. The method was evaluated in a laboratory environment by blackbody furnace measurements, and then applied to the industrial mineral wool fiberization process. Laboratory evaluation of our method was conducted for temperatures between

800 °C and 1500 °C, where the available temperature measurement range was about 300 K without the need for temperature recalibration. In the case of a stationary black body, the proposed method was able to produce deviations of less than 5 K from the reference (thermocouple-measured) temperature in a measurement range within ±100 K from the calibration temperature. The method was also tested by visualization of rotating melt film in the rock wool production process, yielding temperature fields with a very good spatial and temporal resolution.

INTRODUCTION Benjamin Bizjan Laboratory: Laboratory for Water and Turbine Machines E-mail: benjamin.bizjan@fs.uni-lj.si Room: N/5 Phone: +386-1-4771-423 Status: Researcher with PhD Research area: Mineral wool production, cavitation, flow visualization

In many industrial processes, temperature must be precisely monitored to attain desired chemical or mechanical properties of the products. With that said, the selection of temperature measurement methods is often limited due to aggressive working media or very high temperatures. An example of such a difficult measurement environment is melt fiberization on a mineral (e.g. rock and stone) wool spinning machine where melt viscosity and thus fiber properties are very sensitive to temperature fluctuations [1]. Melt film temperatures typically reach up to 1400 °C while film velocity exceeds 100 m/s, meaning that only non-contact temperature measurement methods, such as the infrared thermal imaging, can be applied. However, the use of infrared cameras is restricted by their insufficient spatiotemporal resolution and high unit cost. In the technological processes such as mineral melt fiberization, a significant amount of visible light is emitted by hot glowing bodies and flows, meaning that the color and intensity of the emitted light can be used to determine temperature. Well known is the approach by color temperature [2] where the temperature is estimated based on the color of the glowing surface. However, this method, performed by a camera or a special color temperature meter, produces readings with a relatively

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

poor accuracy and dynamic response. To measure temperature fields with good spatial and temporal resolution, the light intensity approach can be employed using a standard digital camera [3], assuming the absolute temperature to be proportional to the image luminosity (i.e., gray level). THEORETICAL BACKGROUND CCD and CMOS sensors of visible light cameras are usually sensitive for electromagnetic radiation between 400 nm and 1000 nm in wavelength, meaning that the thermal radiation from objects hotter than about 500°C can be detected. The image gray level 0 (black) ≤ G ≤ 1 (white) rises with the absolute temperature T of the glowing body, and the relationship T(G) was derived by the algorithm presented below. For a known image gray level, image plane illuminance, Ev, can be defined by two different relationships:

In Eq. (1), k is the camera sensor sensitivity with unit lux-1∙s-1, tE is exposure time in seconds, η is the radiating body light efficacy, ξ is a proportionality constant and j = σT4 is the radiant exitance (σ = 5.67∙10-8 Wm-2K-4 denotes the Stefan-Boltzmann constant).

The light efficacy η represents the ratio between luminous flux and total radiation power:

In Eq. (2), Y ∈ [0,1] is the quantum efficiency of the camera defining the relative response of the camera sensor depending on the wavelength of incoming light. The variable Bλ is the spectral radiance as derived by Planck, such that:

In Eq. (3), h = 6.626∙10-34 J∙s is the Planck constant, kB = 1.381∙10-34 J/K is the Boltzmann constant and c is the speed of light in the surrounding medium. The temperature dependence of η can be obtained by computation of Eq. (2) over a desired discrete temperature range. By combining Eqs. (2) and (3), we obtain a temperature relation given by the following implicit equation:

In Eq. (4), a new constant was defined as C = (ξ∙ε)1/4, assuming that ε does not change significantly with time and temperature. Apart from ε, C also depends on the imaging set-up (e.g. exposure time, aperture setting, lens type, distance and angle of the camera sensor to the body surface). C is obtained from Eq. (4) by calibration to an area with a known reference temperature and the corresponding image gray level at that location. The reference temperature is measured by a reference method, most commonly a pyrometer or a thermocouple. Using Eq. (4), glowing body temperature fields are obtained by element-wise transformation of image gray level matrices.

The furnace cavity was visualized by a high-speed camera Fastec Hispec 4 mono 2G at one frame/second and using a 50 mm lens. The sensitivity of the camera CMOS sensor was k = 1.524 lux-1∙s-1, and the following light efficacy (η) values were obtained from Eq. (2): 0.018% at 800°C, 0.39% at 1200°C and 2.0% at 1600°C. The reference blackbody temperature was measured by a calibrated thermocouple with its cold junction immersed in an ice point bath. Temperature readings Tref (t) were synchronized with image acquisition. Two different temperature transitions were recorded (Table 1) between the initial and final temperature (TL and TH, respectively). Temperature calibration was performed at TL and TH, obtaining coefficients CUP at TL and CDN at TH. Table 1: Black body temperature transitions Measur. No.

TL, °C

TH, °C

tE, µs

CUP

CDN

800

1000

.8806

.8334

1300

1500

1.001

.9526

Visualization of mineral melt fiberization In the next step, the proposed temperature measurement method was applied to the industrial rock wool manufactruring process. The experiment was conducted on a four-wheel rock wool spinner (Fig. 2) with the region of interest focused on the first spinner wheel (spun with 6800 rpm) where three distinctive regions were present, marked (A), (B) and (C) in Fig. 2.

Figure 2: Four-wheel industrial spinner for rock wool production.

EXPERIMENTAL SETUP Black body experiments The purpose of this experimental section was to evaluate the accuracy of our temperature measurement method by comparison to the reference method. Experiments were performed with a blackbody furnace in the form of a heatpipe (consider experimental setup in Fig. 1). The method of blackbody temperature calibration of thermal imaging devices was described in detail by Miklavec et al. [4], and by Grgić and Pušnik [5].

In region (A) the melt stream impinges the wheel’s surface, and is drawn into motion whereas in region (B), a thin melt film is formed. On the film surface, initial fiberization occurs by means of liquid ligament formation driven by hydrodynamic instabilities. Region (C) then denotes the area adjacent to the wheel where the partly formed fibers move towards the blow-in flow. The melt film was visualized using the same imaging set-up as in the black body experiments (i.e., Fastec high speed camera with a 50 mm lens). The camera was placed at a distance of 5 m from the first spinner wheel and at an angle of 45° relative to the wheel’s rotational axis. Two different sets of images were recorded (Table 2), the first one containing the melt impingement area where all three distinct fiberization zones were visible, and the second one focused on the rotating melt film (Fig. 2, area B).

Figure 1: Experimental set-up for the black body temperature measurement.

YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

Table 2: Visualization settings for recorded image sets img. set No.

framerate, 1/s

pix. size, mm

tE, µs

8000

0.57

18700

0.38

RESULTS Black body experiments In the first step of data analysis, the mean gray level was calculated for each of the recorded blackbody cavity images to form a scalar time series G(t). Then, using Eq. (4), the black body temperature was calculated for image sets 1 and 2 (Fig. 3 and 4, respectively). Two different schemes were used for temperature calculation. The temperature curve TUP was predicted from the initial reference temperature TL using an upwards calculation scheme (i.e. towards the temperature TH) and the constant CUP (see Table 1). The curve TDN was predicted from the final temperature TH using a downwards calculation scheme (i.e. towards TL) and the constant CDN.

Besides the temperature calculation scheme, the image gray level (G) values also have an effect on the method’s accuracy. Figures 3 and 4 evidently show that for both calculation schemes the calculation error rises rapidly at low gray levels (G < 0.2). Therefore, very dark image areas should be excluded from temperature calculation, but caution should also be taken to avoid image saturation (G = 1). With that said, the available measurement range can be estimated to approximately 300 K, while the most accurate results can be obtained within ±100 K from the calibration temperature. Mineral melt fiberization experiments To assess the performance in an industrial environment, our temperature measurement method was tested on high-speed images of the rock wool fiberization process. In Fig. 5, a temperature field calculated by Eq. (4) is shown for a sample image from the image set No. 1.

Figure 5: Temperature field obtained from a sample image of image set No. 1 (melt film rotates to the right). Figure 3: Comparison of reference and calculated black body temperature for measurement No. 1.

Figure 4: Comparison of reference and calculated black body temperature for measurement No. 2.

Both Fig. 3 and Fig. 4 suggest that the downwards temperature calculation scheme (TDN curve) is significantly more accurate than the upwards calculation scheme (TUP curve). In the former case, the difference between the calculated and reference temperature is very low for calculations less than 100 K from the calibration temperature TH. At TH – T = 100 K, the difference is 1.5 K at 900 °C (measurement No. 1) and 4.1 K at 1400 °C (measurement No. 2). For the upwards calculation scheme, temperature calculation errors are increased to 17 K at 900 °C and 33 K at 1400 °C. 68

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

In the region of the falling melt stream, temperature inhomogeneities are clearly visible. A bright spot in the upper right section of the melt stream was caused by a fragment of unfiberized material hitting the stream and exposing the melt below the surface which was approximately 50 K hotter. On the lower left section of the stream, melt surface temperature is locally reduced by up to 40 K due to impacting fibers which are then reabsorbed in the melt. After impinging on the spinning wheel, the fresh melt flows in an unsteady manner while it is accelerated by the fast-moving wheel surface. Compared to the melt film upstream of the impingement point, its mean temperature is approximately 160 K higher, and its viscosity can be expected to be approximately 4 times lower. Consequently, fiber properties such as thickness and length may vary significantly with the wheel angular position. Spatial resolution achieved in image sequence No. 1 is comparable to the resolution of professional infrared cameras while the available image size is significantly larger (e.g. 1710x1710 pixels for our high speed camera versus 640x480 pixels for a typical FLIR camera). This means that a much larger area can be covered without moving and recalibrating the camera. While the available temperature measurement range is relatively narrow in comparison with infrared cameras, it is certainly sufficient for the application to the rock wool fiberization process as the melt stream and film are fully visible.

In Fig. 6, melt film temperature fields calculated from sample images apart are shown. Due to the non-uniform melt film thickness, its temperature field is inhomogeneous with local temperature fluctuations in excess of 100 K. Although individual fibers cannot be seen, the image resolution, sharpness and frame rate are sufficient to give an insight in the medium-scale thermo- and hydrodynamics of the melt film.

Figure 6: Temperature fields obtained from visualization images taken 107 µs apart (image set No. 2, melt film rotates to the left).

CONCLUSIONS A temperature field measurement method by high-speed camera visualization was proposed and experimentally evaluated. Black body experiments show good agreement between temperatures obtained by our visualization method and those measured by the reference (thermocouple) method in a range between 800 °C and 1500°C. To achieve an optimal measurement accuracy, visualization setup should be adjusted to view the majority of the relevant process phenomena in the gray level range of 0.25 < G < 1 while selecting the calibration point just below the maximum expected temperature. Although the available temperature measurement range of the presented method (up to 300 K) is not as wide as for infrared thermometry, it is sufficient to monitor the complete melt stream and film area on the rock wool spinner wheel. On the other hand, spatial and temporal resolution of our method is significantly better, allowing for accurate temperature field measurement in high-velocity flows with large temperature gradients which is not possible or economically viable by other measurement methods. Consequently, the proposed method can provide valuable information about the underlying process dynamics. In the mineral wool industry, measured temperature fields reflect the thermodynamic and topological melt structure and may be used to form models for real-time process monitoring. The main purpose of such models is to increase the uniformity of fiberization conditions (e.g. melt velocity, viscosity and thickness), resulting in improved end product quality. References [1] ŠIROK, B., BLAGOJEVIĆ, B., BULLEN, P.R. Mineral wool: production and properties. Cambridge: Woodhead Publishing Limited, 2008. [2] MA, Z., ZHANG, Y. High Temperature Measurement Using Very High Shutter Speed to Avoid Image Saturation. Proceedings of the 8th International Symposium on Measurement Techniques for Multiphase Flows, Guangzhou, China, December 13–15 2013, 246-253.

[3] GUO, H., CASTILLO, J.A., SUNDERLAND, P.B. Digital camera measurements of soot temperature and soot volume fraction in axisymmetric flames. Applied Optics, 2013, 52, 8040-8047. [4] MIKLAVEC, A., PUŠNIK, I., BATAGELJ, V., DRNOVŠEK, J. A large aperture blackbody bath for calibration of thermal imagers. Measurement science & technology, 2013, 2, 1-8. [5] GRGIĆ, G., PUŠNIK, I. Analysis of thermal imagers. International journal of thermophysics, 2011, 32, 237-247. [6] List of publications [7] BIZJAN, B., ŠIROK, B., DRNOVŠEK, J., PUŠNIK, I. Temperature measurement of mineral melt by means of a high-speed camera. Applied optics, 2015, 54, 7978-7984. [8] BIZJAN, B., ŠIROK, B.. Sistem in metoda za brezkontaktno merjenje temperature s kamero, delujočo v vidnem delu svetlobnega spektra : SI 24410 A, 31.12.2014. Ljubljana: Urad RS za intelektualno lastnino, 2014. 7 f., 2 f. pril., ilustr. [9] BIZJAN, B., ŠIROK, B. Experimental investigation and modeling of mineral wool melt adhesion on a spinner wheel. Proceedings of the 3. International Conference on Computational Methods for Thermal Problems, Bled, June 2-4, 2014, 321-324. [10] BIZJAN, B., PETERNELJ, M., ŠIROK, B. Experimental investigation of melt fiberization from a perforated rotor spinning machine. Chemical engineering research & design, 2015, 104, 626-637. [11] BIZJAN, B., ŠIROK, B., HOČEVAR, M., ORBANIĆ, A. Ligament-type liquid disintegration by a spinning wheel. Chemical Engineering Science, 2014, 116, 172182. [12] BIZJAN, B., ŠIROK, B., HOČEVAR, M., ORBANIĆ, A. Liquid ligament formation dynamics on a spinning wheel. Chemical Engineering Science, 2014, 119, 187-198. [13] BIZJAN, B., ORBANIĆ, A., ŠIROK, B., KOVAČ, B., BAJCAR, T., KAVKLER, I. A computer-aided visualization method for flow analysis. Flow measurement and instrumentation, 2014, 38, 1-8. [14] BIZJAN, B., ORBANIĆ, A, ŠIROK, B., BAJCAR, T., NOVAK, L., KOVAČ, B. Flow Image Velocimetry Method Based on Advection-Diffusion Equation. Strojniški vestnik, 2014, 60, 483-494. [15] ŠIROK, B., BAJCAR, T., BIZJAN, B., ORBANIĆ, A. Mineral wool melt fiberization on a spinner wheel. Chemical engineering research & design, 2014, 92, 80-90. [16] MENCINGER, J., BIZJAN, B., ŠIROK, B. Numerical simulation of ligament-growth on a spinning wheel. International Journal of Multiphase Flow, 2015, 77, 90-103. [17] KRAŠEVEC, B., ŠIROK, B., HOČEVAR, M., BIZJAN, B. Fibre density distribution in a layer of glass wool. Glass Technology, 2015, 56, 145-152. [18] NOVAK, L., BIZJAN, B., PRAŽNIKAR, J., HORVAT, B., ORBANIĆ, A., ŠIROK, B. Numerical modeling of dust lifting from a complex-geometry industrial stockpile. Strojniški vestnik, 2015, 61, 621-631.

YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

Numerical modeling of dust lifting from a complex-geometry industrial stockpile ABSTRACT â&#x2020;&#x2019; Dust lifting at the coal and iron ore stockpile at the Port of Koper, Slovenia, was investigated by performing CFD simulations. Wind velocity fields above the piles were calculated for the current stockpile layout and for several modified cases with rearranged piles and added porous barriers. Results from numerical modelling were used in the USEPA model to determine dust emission factors.

Comparison of selected cases shows a positive, although limited effect of porous fences and barriers on reduction of local velocities and consequently, dust erosion rate. The angle of incoming wind is a key factor influencing effectiveness of both solid and porous wind barriers. The proposed placement of porous barriers between the piles has shown to be effective in reducing wind exposure and dust emission.

INTRODUCTION Lovrenc Novak Laboratory: Laboratory for Water and Turbine Machines E-mail: lovrenc.novak@fs.uni-lj.si Room: N5 Phone: +386-1-4771-423 Status: Researcher / Assistant Research area: Computational and experimental fluid dynamics

Wind-driven erosion of fine particles from granular materials stored in open stockpiles, also known as dust lifting, is one of the main environmental and safety issues of modern-day seaport operations. Most problematic in this respect are loose dry materials such as coal and iron ore due to the high fugitive emission potential during handling and storage. Large open stockpiles, such as those typically encountered in cargo ports, are especially problematic due to their exposure to wind. The windinduced fugitive dust emissions result in material loss from the stockpile and at the same time increase particulate matter concentrations, with significant health hazards when particles are transported to urban areas. Analysis of wind-induced erosion in ports and other industrial sites must consider interaction of several elements. An aggregate storage yard is composed of many piles in addition to obstacles such as buildings and cranes, which can affect local wind distribution. Dust emissions from stockpiles can be reduced by optimizing pile layout, but options for pile rearrangement are highly limited in port terminals. Since coal is received from different sources and is then delivered to various customers, it cannot be â&#x20AC;&#x153;mixed upâ&#x20AC;? to form a large single pile, therefore it is common that coal is warehoused in a large number of piles. Additionally, rearrangement

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

or resizing of piles is often restricted by crane capabilities and placement of adjacent buildings, meaning that large-scale modifications may not be practical and economically justified. Dust emission reduction is more commonly achieved by other dust control measures such as placement of wind barriers and spraying of coal with water and crust-forming liquids. In this study, we focused on wind protection by solid and porous barriers in the Port of Koper. At one particular terminal, named the European energy terminal (EET), the port handles and stores coal and iron ore. This terminal presents an open storage area of 108,500 m2 and is one of the largest bulk cargo terminals in southern Europe. We have used measured wind speeds and directions to simulate realistic scenarios in the cargo port. The height, size, arrangement and shape of piles were set to represent the most commonly used distribution of coal at the fully occupied port terminal. Moreover, surrounding buildings, solid fence and cranes were also included to achieve a more realistic model. Simulations of air flow in the model were performed by employing CFD simulations. Additionally, simulated data were used to estimate emission rates by using the United States Environmental Protection Agency (EPA) emission formulation.

WIND DATA Statistical analysis of local wind speed recorded data (at 50 m above terrain) for the period between august 2012 and august 2013 at the Port of Koper are shown in Fig. 1. The box plot (Fig. 1d) shows that gusts above 10 m/s are more frequent from east direction. Nevertheless, maximum gust of 29 m/s was recorded from west direction. Further analysis reveals that the highest speeds were observed from 75° and 250° direction. In summary, it is evident that winds from east and occasionally west can reach very high speeds and are capable of causing significant dust emissions from the EET stockpile.

Figure 1: c) Wind rose; d) box plot of measured wind speed for west and east direction.

NUMERICAL SETUP The geometric 3D model of the site was built on the basis of a satellite image (Fig. 2a). It presents an area of 1380 m length in east-west direction and 730 m length in northsouth direction (Fig. 2b). Vertically, the model was limited to the height of 200 m above terrain or sea. Port authorities provided all necessary information about stockpiles, adjacent buildings and cranes. Basic distribution of piles in the model was made on the basis of the satellite picture and information provided by port authorities. The height of all piles was 10 m and base dimension was between 65 meters and 80 meters.

tions, which provide sufficient accuracy for flows around buildings. Ansys Fluent 14.5 software was used for the CFD calculations. A Reynolds averaged Navier-Stokes (RANS) method, which is an industry-standard approach for simulation of atmospheric flows around buildings, was employed. Turbulence was modeled by the k-ε model, which is a proven and robust model, often employed in similar problems. Constants of the model were adjusted to the recommended values for simulation of atmospheric flows. Standard wall functions with Fluent’s default rough wall formulation were employed. Air was used as a working fluid assuming incompressibility (i.e. constant density). Steady state conditions were simulated. Second order discretization schemes were used for all equations. Boundary Conditions The inlet and outlet boundary surfaces were set in pairs depending on the simulated wind direction. Inlets were defined as velocity inlets with velocity (U) and turbulence quantities (k, ε) as functions of the vertical coordinate. Standard logarithmic profiles for atmospheric boundary layers were used. Terrain roughness length of 0.1 m was assumed for the profiles. Outlet boundaries were set as pressure outlets with average relative pressure of 0 Pa. Walls of buildings and other structures, including the fence, were defined as hydraulically smooth walls with zero slip. Walls representing piles and terrain inside the stockpile fence were set as rough walls with equivalent sand grain roughness of 0.045 m. Terrain outside the fence (both land and sea) was treated as rough wall with equivalent sand grain roughness of 1 m, which takes into account the presence of different objects such as cars, trucks, trains, piers, sea waves etc. Wall at the top of the model was set as a wall with zero shear stress. Porous walls were used to represent certain structures, for example cranes located north of the stockpile that were simplified to a cuboid shape. Porous walls were also used to simulate perforated walls and barriers that were included in some of the calculated cases. The porous jump boundary condition type, which can be seen as a model for a thin membrane that has known velocity (pressure-drop) characteristics, was employed for all cases of porous walls. COMPUTED CASES

Figure 2: a) Satellite image of the coal and iron ore stockpile with surroundings; b) top view of the geometrical model

Numerical grid was created in the Ansys ICEM CFD software. The final hybrid grid consisted of 14.5 million hexahedral, tetrahedral and prismatic elements. Near wall grid density was designed for the use of wall func-

Simulations were performed for two prevalent wind directions (75° and 250°) and two wind velocity magnitudes at 50 m height (18 m/s and 22 m/s). Here, only cases at 18 m/s will be presented. According to the logarithmic velocity profile, 18 m/s at the height of 50 m reduces to 14.85 m/s at the height of 10 m. In addition to the simulation of base condition representing currently existing structures and fully occupied storage area, additional cases were computed. All the modifications to the base condition were done with the aim of reducing exposure of piles to high wind velocities. The cases were designated with letters: (A) basic – current condition; (B) existing fence changed into a porous fence; (D) basic condition with piles on the south-west extended closer to the fence; (H) insertion of porous barriers between piles with heights of 11 meters. YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

RESULTS CFD results will be presented in form of figures which show a top view of the different degrees of wind exposure over the piles. The piles were divided into subareas of constant us/ur, where us is wind speed measured 25 cm from the pile surface and ur is wind speed reference measured at the height of 10 m above terrain. Furthermore, the emission factors were calculated according to the EPA method * [1] where threshold velocity for coal u t = 1 m/s was used. The EPA method by itself is only used to quantify sources of particulate emissions and does not model subsequent transport and dispersion of airborne particles. EPA defines emission factors as statistical averages of the rate at which a pollutant is released to the atmosphere as a result of some activity, divided by the level of that activity. Formulae for their calculation are mostly based on regression analysis of relevant measured data. Case A – Current state Fig. 3 presents current state conditions (case A) for both west and east direction. Wind exposure in case of west wind is higher than in case of the equally strong east wind, which indicates that existing wind protection is less effective in case of the west wind. In fact, the solid fence in the western part of the site is placed further away from the piles and at an angle, which provides favorable conditions for air currents to penetrate lower. The west wind also has fewer obstructions on its way over the central east-west oriented road, which is used by the coal stacking and reclaiming machinery. Therefore, higher wind exposure on the piles downwind from the central road can be seen for the case of west wind. Case B – Porous fence Replacement of the solid fence with a porous one was the first simulated measure for wind exposure reduction. Porous barriers allow passing of fluid, but at a reduced velocity. This means that a region of reduced wind speed without any vortices is expected to form and stretch further downstream compared to the solid barrier case. Effectiveness of porous fences for prevention of wind erosion has been studied and demonstrated by several researchers. Fig. 4 shows normalized velocity distributions above piles for both east and west wind with the porous fence. Reduced wind exposure compared to the solid fence (Fig. 3) can be seen on some of the piles, while on the other piles wind exposure seems to be unaffected or even increased. Reasons for limited porous fence effectiveness can be attributed to the large size of the terminal, which stretches in the direction of dominant winds, and to the sharp angle of incoming winds relative to the fence. Nevertheless, the largest wind speed reduction occurs at locations with the largest velocity magnitude while an increase mostly occurs at spots with relatively low wind velocities. Since wind erosion is only problematic at a relatively large wind velocity over piles, there is clearly an advantage of a porous fence (case B) in comparison with a solid fence (case A). This is confirmed by a reduction in total dust emissions (consider further sections and figures for more details).

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

Case D – Distribution of stockpiles Numerous combinations of pile locations and sizes are possible in theory but in practice they are limited by the technical possibilities of the stacking and reclaiming machinery. Furthermore, filling and emptying of the stockpile and the length of individual piles is dictated by technical and logistical requirements. Therefore it is difficult to perform such optimization in reality, even if simulations indicated significant benefits. Case D pile layout was very similar to case A, but with piles on the south-west extended closer to the fence. No significant differences in normalized velocities were computed relative to case A.

Figure 3: Case A for east and west wind; top view of us/ur contours

Figure 4: Case B for east and west wind; top view of us/ur contours

Case H – Transverse porous barriers Effectiveness of both solid and porous fences in reducing wind velocities above the EET stockpile is greatly limited due the shape and orientation of the terminal relative to the incoming wind direction. Major portions of the fence are hit by wind at sharp angles and the resulting area of reduced wind velocity downstream the fence is too short to reach piles further away. Therefore, a different approach

for wind damping was proposed. Porous barriers between the piles that were oriented transverse to the main winds were included into the numerical model. Three porous barriers were placed at the south-western part of the stockpile to test the method mostly for west wind and another barrier was placed on the eastern edge of the south-western row of piles. All the barriers were 11 m high. Effects of the barriers are analyzed in more detail in the following subsection.

pile and partially also for the second pile downwind from the barrier. In case of west wind positive effects of barriers can be seen also on other piles in the wider stockpile area. Reduction in emission rates in case H is observed only for west wind (Fig. 7). The reason is that most barriers in the model were intentionally placed at the south-western part of the stockpile to test their effectiveness mostly for west wind.

Comparison of B-A and H-D cases Effects of modified wind protection measures compared to the basic (current state) conditions are presented in Fig. 6. Case B (porous fence) is compared to case A by calculating absolute difference between the normalized velocities at U=18 m/s. In the same way, case H (four porous barriers) is compared to case D. Calculated differences are presented in form of contour plots.

Figure 7: Total dust emissions under west and east wind for A, B, D and H case

CONCLUSIONS

Figure 6: Top view of difference between us/ur contours for B-A and H-D case (U=18 m/s)

Comparison of case B to case A shows that replacement of the existing solid fence by a porous fence would produce extensive regions of both reduced and increased wind exposure for the both wind directions. Judging from the normalized velocity differences, replacement of solid fence with a porous one seems to yield no overall benefits in wind protection, however, when taking into account emissions (see Fig. 7), benefits become evident. Results shown in Fig. 7 reveal that dust emission rates are lower for case B (porous fence) by 50 % for both east and west wind. When comparing west and east wind emission rates it can be seen that the west wind emission rate is almost 10-times higher than the east wind emission rate (Fig. 7). The reason for much higher west wind emission rate is that fence in the western part of the site is less efficient in wind protection. On the other hand, placement of porous barriers that are oriented transverse to the main wind directions (case H) clearly shows a highly positive effect. In this case, normalized velocities are significantly reduced for the first

Simulations of wind conditions at the coal and iron ore stockpile at the Port of Koper were performed by employing CFD tools to assess the problem of dusting. Wind exposure of piles was analyzed for different wind conditions and by application of various physical measures for reduction of wind velocity. Results of simulations show that the existing solid fence provides a very limited protection from high winds due to the size and stretched shape of the stockpile area and its orientation relative to the main wind directions. Modifications to the fence by replacing it with porous structures were simulated and showed that their efficiency is limited for the same reasons as in the case of solid fence, although the total emission rate could be significantly reduced. An efficient measure for reduction of wind velocity over the piles was found to be placement of porous barriers between the piles, oriented transverse to the main wind directions. However, such barriers on the real stockpile could impose significant limitations for the material stacking and reclaiming machinery. Watering and spraying with crust-forming liquids still remain a necessary step for prevention of wind erosion and fugitive emissions. References [1] EPA (2006). Update of Fugitive Dust Emissions Factors In AP-42 Section 13.2.5 – Wind Erosion. Midwest Research Institute, Kansas City. List of publications [2] Novak L.; Bizjan B.; Pražnikar J.; Horvat B.; Orbanić A.; Širok B. (2015). Numerical Modeling of Dust Lifting from a Complex-Geometry Industrial Stockpile, Strojniški vestnik – Journal of Mechanical Engineering, Vol. 61, No. 11, 621-631.

YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

Mineral wool primary layer formation in collecting chamber ABSTRACT → The process of the mineral wool primary layer formation was investigated experimentally on a model spinning machine with sucrose as a working medium. The fibers were pneumatically transported from the spinner rotor to the accumulation grid with the aid of the blow-away and the suction airflow. The fiber primary layer formed on the accumulation grid was visualized by a camera for several different operating regimes. Acquired images were post-processed to determine the light absorption in the primary layer,

which was then used to calculate the bulk density and the surface density of the layer. Based on the measured process quantities, we were able to form multiple regression models with a relatively good correlation to the experimental data. The models as well as the qualitative image analysis show a significant effect of spinner rotor rotational speed, pneumatic transport velocity and fiber deposit mass on primary layer bulk density and spatial distribution of fibers.

INTRODUCTION Marko Peternelj Laboratory: Laboratory for Water and Turbine Machines E-mail: marko.peternlej@fs.uni-lj.si Company: Izoteh d.o.o., Brnčičeva ulica 15b, 1231 Ljubljana Phone: +386-31-427-783 Status: PhD student Research area: Kinematics of mineral wool fibers in air flow Mentor: Prof. Brane Širok, Ph.D.

Mineral wool is a fibrous material commonly used for thermal and acoustic insulation and can be divided into subtypes such as the stone wool and the glass wool. Mineral wool production process is highly complex, consisting of several different production phases. Sufficient understanding and control of each phase is required in order to optimize the properties (e.g. thermal conductivity, homogeneity and mechanical properties) and production costs of the end products. Production phases which most significantly affect the mineral wool quality are the melt fiberization on the spinning machine, fiber pneumatic transport and primary layer formation in the collecting chamber [1]. Two most commonly used spinner geometries are solid spinning wheels, used mainly for mineral wool production, and hollow perforated rotors, used for glass wool production. The melt fiberization process was a subject of several experimental and numerical studies for both solid wheel spinners and perforated rotors. Fiber formation phase is followed by pneumatic transport of fibers in the blow-away flow to the collecting chamber where a primary layer of mineral wool is formed. A good quality primary layer is defined by a low degree of spatial fluctuations in thickness and density of the fiber deposit, and is very important for achieving optimal insulation and

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

mechanical properties of the end products. Due to the high complexity and multiphase nature of the flow, experimental investigation of the primary layer formation is difficult and mostly limited to the measurement of aerodynamic characteristics and flow visualization. To overcome the complexity of the industrial mineral wool production environment and the limited range in which the operating parameters can be varied, we have developed a model spinning machine similar to the glass wool spinners. The primary layer was analyzed by a visualization method, and its quality was characterized by multiple regression models. THEORETICAL BACKGROUND The primary layer formation process is an important part of the mineral wool production line (see Fig. 1 for an example of a stone wool production line). Mineral melt is prepared in the melting furnace from which it first enters the melt reservoir and is then supplied to the spinning machine in form of a free falling melt stream. In a stone wool production line, the melt typically impinges on a mantle surface of one or more spinning wheels, forming a film, which continuously disintegrates into liquid ligaments. In manufacturing of glass wool, the fiberization process is different as the melt stream flows inside a spinning perforated rotor, forming a film on its

internal mantle surface. Under the action of centrifugal force, melt film is then extruded through the perforations to form ligaments. Nevertheless, the phase following the ligament formation is similar for both spinner designs. Shortly after formation, melt ligaments solidify to fibers and are impregnated by the binder liquid. The fibers then enter the coaxial blow-away airflow (also known as the primary flow) and detach from the spinning machine, forming complex multiphase flow structures. The blowaway flow with fibers enters the collecting chamber while its velocity is reduced from an initial magnitude in excess of 100 m/s to below 10 m/s. Apart from the blow-away flow, the suction flow (also known as the secondary flow) is also present in the collecting chamber to allow the fibers to settle on the accumulation grid and thus form the primary layer.

the X-ray measurement method, the calculations of µ and ρ were performed based on the measured light absorption ratio I/I0 (Fig. 3).

Figure 3: Light absorption over the primary layer

Local primary layer thickness h (Eq. (2)) at position (x,y) can be obtained from the Beer-Lambert absorption law (Eq. (1)).

With a known primary layer mass m (determined by weighing) and total volume of primary layer, the mean bulk density of the layer ρ can now be calculated as . Another characteristic primary layer property is the local area density µ and its normalized standard deviation σµn: Figure 1: stone wool production line between the melting furnace and the primary layer formation zone [1]

The exact mechanism of the primary layer formation, including the fiber pneumatic transport, breakage and settling on the accumulation grid, is still largely unknown due its complexity and difficulty in observation on smaller length scales. While the primary layer quality control on industrial production lines is still mostly manual [1], there have been several attempts to quantitatively characterize the primary layer quality for the purpose of process automation. The most commonly used measurement method is the camera visualization of the mineral wool primary layer. A sample primary layer image is shown in Fig. 2. A good quality primary layer is characterized by a homogeneous structure of the fiber deposit (Fig. 2a) whereas an inhomogeneous structure with large variations in thickness and density indicates a poor quality of the primary layer.

Figure 2: Primary layer on the accumulation grid; a) homogeneous structure; b) inhomogeneous structure [1]

Based on the overview of the available literature, the area density µ and the bulk density ρ were determined to be the most representative primary layer properties in our experiments. To measure µ and ρ, a measurement setup with a visible light camera and lighting source was used so that the fibers were illuminated from behind. Similarly to

Note that listed calculation procedures assume a stationary accumulation grid. In the case of a moving grid, mass and volume would be replaced with their temporal derivatives (i.e. flows). EXPERIMENT Experiments were conducted on a model spinning machine with a hollow perforated rotor and a vertical collecting chamber (Fig. 4a). The spinning machine used was basically a modified version of a cotton candy machine “The Breeze 3030EX”. The rotor (Fig. 4b) had an integrated heater and was supplied with crystalline sucrose prior to each experiment. During the spinner operation, sucrose was melted by the heater at a rate of approximately 0.75 g/s while the rotor rotational speed was regulated by a single-phase variable frequency drive (VFD) in a range between 40 Hz and 50 Hz. Coaxial blow-away airflow was supplied through 45 circular nozzles with 1 mm diameter, evenly distributed around the supply ring. The blow-away flow was regulated by a valve so that the overpressure in the supply ring Δp was between 0 and 50 kPa. The spinning machine was placed inside a vertical collecting chamber with a circular cross section (0.63 m in diameter) and a transparent wall. Secondary (i.e. suction) airflow was generated by a 7-blade axial fan powered by a three-phase VFD. The fan was placed on top of the collecting chamber immediately after the horizontal accumulation grid. VFD power supply frequency was varied between 0 and 40 Hz, which resulted in fan rotational speeds between 0 and 18.4 Hz. YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

Figure 4: Experimental setup; a) spinner operation; b) spinner head (detail); c) primary layer visualization

About 40 seconds after the start of the spinner and air supply operation, fibers started to appear on the spinner rotor and were blown to the collecting chamber. After additional 10-30 seconds, the heater was turned off, and upon the end of fiber formation, rotor and airflows were stopped. Then, the fiber primary layer was photographed, removed from the accumulation grid and weighed, with mass being an additional parameter (range between 7 g and 33 g).

Figure 5: Sample visualization images (OP 3c); a) raw image; b) area density field; c) primary layer side view

In each operating point, primary layer was visualized as follows. After stopping the spinner operation, the suction fan was removed and the primary layer was illuminated from above by diffuse light. A camera (Casio EX-F1) was placed underneath the accumulation grid and an image of the layer was taken (Fig. 5) using manual aperture and shutter time settings (f/7.5 and 0.08 s, respectively). For reference, the background (grid without fibers) was also photographed using the same visualization setup. Images were then processed by the method presented above so that the bulk and area density (Fig. 5b) was calculated. Also, the maximum thickness of the primary layer was manually measured (Fig. 5c) and used in Eq. (1) to obtain the attenuation coefficient α. RESULTS Primary layer mass distribution in Fig. 6 shows a significant effect of all operating parameters varied in the experiments. An increase of the spinner rotational speed (operating points 12 and 4 represent fc = 40 Hz and fc = 50 Hz, respectively) increases the primary layer area due to the larger centrifugal forces which widen the fibrous flow. At the same time, the layer becomes more uniform. 76

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

Figure 6: Fields of primary layer area density for different operating points; given are the OP numbers

An even greater effect on the primary layer structure can be seen with regard to the airflow characteristics. In Fig. 6, the effect of the blow-away pressure (and consequently, flow rate) is seen by comparison of plots for OP 9, 6 and 3b, where Δp was 0 kPa, 20 kPa and 50 kPa, respectively. When the fibers are transported only by the suction flow (OP 9, Δp = 0, Qp = 0), the primary layer is asymmetrically shaped and scattered across the large portion of the accumulation grid. In this operating mode, large chunks of fiber wool were observed on the grid, leading to an unwanted inhomogeneity in the layer structure. As the blow-away pressure was raised towards 50 kPa (OP 4 and 3b), the primary layer shape became more axisymmetric and with fewer visible inhomogneities. However, the layer became pile-shaped with a large thickness in the center, and its mean bulk density slightly increased. Such pile formation is unfavorable as the layer thickness should be as uniform as possible, but could largely be avoided by using a moving mesh. Apart from the primary flow, the secondary (suction) flow also has a large effect on the quality of the primary layer. When the suction flow is not present and pneumatic transport depends entirely on the blow-away flow (OP 19, fs = 18.4 Hz), the fibers may still reach the accumulation grid, but the flow is unstable and the primary layer can form far from the grid center. An increase in the suction flow rate, as clearly shown by data for the operating points 4 and 6 (fs = 7.0 Hz and fs = 11.4 Hz, respectively), causes the primary layer to shrink in area while its bulk density increases. If the suction flow rate is further increased (OP 20, fs = 18.4 Hz), the layer bulk density rapidly increases while the area density distribution becomes practically axisymmetric. This is partly due to the fact that at larger Qs, the pressure drop over the primary layer rises, resulting in a more intense layer compression. Another contributing factor to the large bulk density in OP 20 was a relatively large primary layer mass (m = 33.0 g), which, due to the larger quantity of fibers, reduced the permeability of the accumulation grid and thus further increased the pressure drop over the layer. In OP 3c where the mass of the primary layer is similar (m = 30.0 g), the spatial distribution and maximum of µ is comparable to OP 3c, but the bulk density is about 50% lower, meaning that the layer is much less compact. For comparison, the layer bulk density in operating points 3a, 3b and 3c only varies by 28% despite the mass range of approximately 1:3 (ρ rises monotonously with m, though). This suggests that the bulk density more sensitive to the suction flow rate than the primary layer mass, but both parameters are significant. Due to the specific experimental setup (i.e. stationary accumulation grid), it is important to note that the

primary layer formation is a transient process. The layer mass (or equally, fiber deposition time) is analogous to the combination of the fiberization mass flow and the accumulation grid velocity in a typical mineral wool manufacturing process. Based on the results we suspect a strong correlation between the characteristic properties of the primary layer (ρ and σµn) and the process input parameters (fc, Qp, Qs, m). This hypothesis will be confirmed by the following power law multiple regression models: Figure 8: Correlation between measured and modeled values of σµn (R2 = 0.78)

The exponents a0-a4 and b0-b4 were determined by fitting of the power law models in Eqs. (5) and (6) to data. Operating points with Qp = 0 or Qs = 0 were excluded from the model to avoid singularities. These points were only intended to demonstrate the most extreme operating conditions unsuitable for an industrial manufacturing process. For Eq. (5) we obtain a0 = 112, a1 = -0.141, a2 = 0.225, a3 = 0.389, a4 = 0.498 and a relatively high coefficient of determination (R2 = 0.88). This indicates a good correlation between modeled and input parameters. For Eq. (6), the following values were calculated: b0 = 14.2, b1 = -0.842, b2 = 0.262, b3 = 0.116, b4 = -0.589 and a R2 = 0.78. The R2 value is sufficiently high to conclude that the σµn statistical parameter is representative of the process quality and can be modeled from selected input parameters. Regression models can now be rewritten in a final form:

The goodness of fit of these regression models can also be shown graphically – Figs. 7 and 8. It is evident that most of the measurements are in a good agreement with the model. The model in Eq. (7) indicates that the bulk density of the primary layer increases with the flow rate of the blow-away and suction air as well as with the layer mass. As said, this can be explained by layer compression due to increased pressure drop over the accumulation grid. On the other hand, ρ falls with rotational speed of the spinner rotor as fiber centrifugal forces are increased, scattering fibers to a larger area. Consequently, the layer thickness is reduced, leading to a reduction of the pressure drop across the accumulation grid.

Figure 7: Correlation between measured and modeled values of ρ (R2 = 0.88)

CONCLUSIONS Light absorption method provided a good measure for the layer structure and thickness. The bulk density, which should ideally be as low as possible, was found to depend on the spinner rotational speed, flow rates of the blow-away and suction air as well as the mass of accumulated fibers. The bulk density of the primary layer was shown to increase with its own permeability until a new equilibrium is reached. An important step in optimization of investigated process is to determine an envelope of the operating parameters which yields a good quality primary layer. The spinner rotational speed was shown to control the layer width and height profile while the size and spatial distribution of inhomogeneities is mostly determined by the pressure and flow rate of the blow-away airflow. On the other hand, the primary layer bulk density is most significantly affected by the suction flow rate and layer mass. Further research should include the modeling of an actual mineral wool manufacturing process with a moving accumulating grid where primary layer formation is continuous. New experimental and numerical models will improve the understanding of the fiber transport and primary layer formation process and introduce new possibilities for automatization of the process control. References [1] Širok B., Blagojević B., Bullen P.: Mineral Wool: Production and Properties; Woodhead Publishing Limited, Cambridge, (2008). [2] Bajcar T., Širok B., Bizjan B., Orbanić A.: Mineral wool melt fiberization on a spinner wheel. Chemical Engineering Research and Design, vol. 91, (2013) [3] Dimovski D., Širok B., Blagojević B., Kariž Z. Mineral wool primary layer structure influence on the fibre distribution in the final product. Glass technology, (2004) [4] Bajcar T., Blagojević B., Širok B., Dular M. Influence of flow properties on a structure of a mineral wool primary layer. Experimental thermal and fluid science, (2007) [5] Širok, B., Blagojević, B., Novak, M. (2002). Influence of blow away velocity field on the primary layer fibre structure in the mineral wool production process. Glass Technology, vol. 43, no. 5, p. 188–194 List of publications [1] Bizjan B., Peternelj M., Širok B.: Experimental investigation of melt fiberization from a perforated rotor spinning machine. Chemical engineering research and design, vol. 104, 2015, p. 626–637 YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

Influence of cavitation on preparation of aqueous detergent solutions ABSTRACT → Despite the constant development of household appliances, domestic sector is still second most intensive sector in terms of end energy consumption in European Union, where washing machines are one of the most energy consuming household devices. This article is focusing on preparation of aqueous detergent solution. Washing mixture is crucial for laundry process, yet its preparation is not optimised. The detergent dissolution of commercially available washing machines can

take more than 10 minutes of washing cycle. We have investigated influence of cavitation on detergent dissolution rates. For this purpose special rotary hydrodynamic cavitation generator has been designed. The cavitation generator has been tested on a laboratory model of washing machine and dissolution rates have been experimentally evaluated. Our research indicates that cavitation significantly improves the preparation of aqueous detergent solution for use in commercial washing machines.

INTRODUCTION Tadej Stepišnik Perdih Laboratory: Laboratory for Water and Turbine Machines E-mail: tadej.stepisnik @fs.uni-lj.si Room: N5 Phone: +386-1-4771-423

In recent years, we have witnessed tremendous improvements in the energy efficiency of home appliances [1] [2]. Despite this fact, domestic sector remains second most energy intensive sector in terms of energy end consumption inside EU-28 area (figure 1) [3] and a lot is still to be done if EU is to achieve 20 % energy consumption cut (compared to projected levels) by 2020.

Status: PhD student (started: October 2014, to be completed: March 2017)

Figure 1: Ownership of washing machines in households around the world

Research area: Hydrodynamic cavitation Mentor: prof. dr. Širok Brane, univ. dipl. inž izr. prof. dr. Dular Matevž, univ. dipl. inž Figure 1: End energy consumption inside EU-28 by sectors

This paper is focused on development of commercial washing machines. Together with refrigerators and freezers, washing machines contribute the most to the household energy consumption. Additionally, laundry is one of most outspread house works on the planet (figure 2). Many advances in washing machines are already reported in literature. Measures like high efficiency electromotor, reduction in thermal 78

losses, improved fill control, rinsing and water extraction, detergent composition, recycled or rain water use, etc., all led to higher energy efficiency and lower water consumption [1] [2] [4] [5] [6] [7] [8]. Another new technique drawing great attention of researchers is use of cavitation

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Cavitation is a physical phenomenon characterized by formation, growth and subsequent collapse of micro bubbles in a bulk liquid. Based on generation, we classify cavitation in four types: acoustic, hydrodynamic, optical and particle induced. The collapses of micro-bubbles create millions of local hot spots, releasing extreme amounts of energy [9]. The primary parameter determining the presence and intensity of cavitation is the non-dimensional cavitation number:

Decreasing the cavitation number results in a higher probability of cavitation occurrence or in an increase in the magnitude of already present

cavitation. The violent circumstances at bubble collapses are being widely utilised to clean solid surfaces in different industries and medical and scientific laboratories for over 40 years [10]. Recently, researchers showed that cavitation could also be used to clean textile. With different laboratory cavitation setups, 30 % reduction in energy and 20 % reduction in water consumption have been achieved with comparable or improved cleaning effect than commercial washing machines [11] [12] [13]. It has also been discovered that cavitation cause less mechanical damage to the fabric than conventional horizontal-axis washing machine We have investigated use of cavitation for aqueous detergent solution preparation. Although cavitation is already recognised as an efficient method for dyeing solutions in textile industry [11] [14], this is to our knowledge the first research where cavitation is used to prepare detergent solutions for textile washings. Current washing machines available on the market prepare washing dissolution in the drum. Water from the supply network piping enters the machine and is led through detergent tray, washing the detergent into the drum. There the detergent is mixed with clothes and the dissolution starts due to agitation of the drum. The dissolution process consists of two steps. First, the interaction between the solute and the solvent molecules at the solid–liquid interface. Second, the diffusion of the solute molecules away from the interface to the bulk. The slowest step in this sequential process is the rate-determining step [15]. The preparation of proper aqueous detergent solution lasts for 10 minutes or more. We assume this process would be accelerated if the detergent would be washed into special bath, where it would be exposed to cavitation, before it enters the drum. For this purpose, special rotary hydrodynamic cavitation generator (RHCG) has been designed. The detergent dissolution rates were experimentally evaluated, for both cavitation and non-cavitation flow regime, on a setup simulating an actual washing machine

Figure 1: Rotor (top) and stator (bottom) of RHCG

EXPERIMENTAL SETUP Experimental setup has been designed in a way to simulate an actual washing machine. Our goal has been to determine to what extent hydrodynamic cavitation contributes to the dissolution time. To achieve that, two sets of experiments have been conducted – one with cavitation and one with non-cavitation flow regime. This has been achieved by static pressure modulation inside the cavitation chamber.

ROTARY HYDRODYNAMIC CAVITATION GENERATOR The rotary hydrodynamic cavitation generator is an assembly of rotor and stator discs (figure 2) with special geometry inside a closed chamber. Both rotor’s and stator’s diameter is 50 mm. They have 12 radial indentations, 3 mm deep and 4 mm wide. Unindented area of rotor disc has been machined in a way the surfaces are angled at an 8° angle, giving them sharp edge. Stator surface has not been modified. Distance between rotor and stator was set to 0.95 mm. The assembly is presented in figure 4. The RHCG operation causes periodically repeating pressure drops inside the chamber. These conditions are favourable for cavitation. Due to the rotation of the rotor, also centrifugal force is exerted on the fluid, which maintains the flow through the reactor.

Figure 1: Experimental setup

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Alongside RHCG, the experimental setup consisted of a closed tank, connection pipes and pressure, flow and temperature sensors (figure 3). The generator has been driven with single-phase electromotor, which is already present in most of washing machines.

Figure 1: Physical conditions inside cavitation chamber during experiments

The dissolution rate experiments have been performed in alignment to standard Clothes washing machines for household use – Methods for measuring the performance [16]. The tank has been filled with 2 L of water at 23.5 °C. 11 g of standard IEC-A detergent purchased from WFK Institute, Germany, has been accurately weighed and added to water and left to be treated by generator for specified time. The RHCG rotational speed has been set to 7000 rpm, which established a flow 11,3 L/min. In the cavitation regime, the tank has been open to atmospheric pressure (101 kPa). In an actual washing machine with implemented RHCG, this would regime would correspondent to the washing machine operation. Non-cavitation regime has been achieved by closing the tank air valves and raising the static pressure to 253 kPa. The conditions that get established inside the cavitation chamber, together with calculated cavitation numbers are schematically presented on figure 4 High-speed camera Fastec HiSpec has been used in order to monitor cavitation presence. Sequences of images for cavitation and non-cavitation regime are presented on figure 5. On images rotor is in black colour and cavitation bubbles are visible in white After the specified time, the detergent solution has been poured through textile filter. Undissolved detergent remained on the filter in form of residues. Filter textile was purchased at Gorenjska Predilnica, Slovenia (100 % cotton, Swiss pique knit, yarn count 17 tex, double threaded). Fabric fulfilled the IEC 60456 standard requirements. After experiments, filters were left to dry at ambient for 24h. The filters were weighed prior and after the experiment and the percentage of detergent residues have been recorded.

Figure 1: Monitoring cavitation regime (left) and non-cavitation regime (right) with high-speed camera images

In the standard the dissolution test is performed with magnetic stirrer instead of RHCG. For comparison with standard data and validation of materials used, tests with magnetic stirrer were also performed. Rotational speed of magnetic stirrer was set to 200 rpm. RESULTS 32 experiments were done in order to determine the detergent dissolution rate. The measurements are presented on a graph (figure 6). Trend lines are added for easier interpretation. As expected, the dissolution process is slowest using the magnetic stirrer. After 300 s still more than 35 % of detergent remains undissolved. Much better results are achieved using RHCG. Additionally results clearly show, that cavitation significantly improves the dissolution of the detergent. In the cavitation regime, more than 80 % of the detergent is dissolved in order of few seconds. With the same rotation frequency but without cavitation, 150 seconds of RHCG operation are required to dissolve the same amount of detergent

Figure 1: Measurements of detergent dissolution rate

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

Our work indicates that cavitation has great influence on dissolution process. Considering that dissolution process is a two steps process, we believe cavitation especially improves the first step – that is the interactions between the solute and the solvent molecules at the solid–liquid interface, and that the second step - the diffusion of the solute molecules away from the interface to the bulk – is improved by the RHCG operation itself, due to aggressive mixing inside RHCG chamber even without cavitation References [1] P. Bansal, E. Vineyard in O. Abdelaziz, „Advances in household appliances - A review,“ Applied Thermal Engineering 31, pp. 3748-3760, 2011. [2] A. Milani, C. Camarda in L. Savoldi, „A simplified model for the electrical energy consumption of washing machines,“ Journal of Building Engineering 2, pp. 69-76, 2015. [3] EUROSTAT, „Consumption of energy,“ 5 2015. [Elektronski]. Available: http://ec.europa.eu/eurostat/ statistics-explained/index.php/Consumption_of_energy. [Poskus dostopa 10 11 2015]. [4] Z. Chen, H. Ngo, W. Guo, A. Listowski, O‘Halloran, M. Thompson in M. Muthukarup, „Multi-Criteria analysis towards the new end use of recycled water for household laundry: A case study in Sydney,“ Science of the Total Environment 438, pp. 59-65, 2012. [5] T. Morales-Pinzon, R. Luruena, X. Gabarrell, C. M. Gasol in J. Rieradevall, „Financial and environmental modelling of water hardness - Implications for utilising harvested rainwater in washing machines,“ Science of Total Environment 470-471, pp. 1257-1271, 2014. [6] P. Ivarsson, M. Johansson, N. Hojer, C. KrantzRuckler, F. Winquist in I. Lundstrom, „Supervision of rinses in a washing machine by voltammetric electronic tongue,“ Sensors and Actuators 108, pp. 851-857, 2005.

[7] Y. Yu, J. Zhao in A. E. Bayly, „Development of Surfactants and Builders in Detergent Formulations,“ Chinese Journal of Chemical Engineering 16, pp. 517527, 2008. [8] L. Vojcic, C. Pitzler, G. Korfer, F. Jakob, R. Martinez, K.-H. Maurer in U. Schwaneberg, „Advances in protease engineering for laundry detergents,“ New Biotechnology, 2015. [9] B. Širok, M. Dular in B. Stoffel, Kavitacija, Ljubljana: i2, 2006. [10] T. J. Mason, „Ultrasonic cleaning: An historical perspective,“ Ultrasonics Sonochemistry, 2015. [11] M. Vouters, P. Rumeau, P. Tierce in S. Costes, „Ultrasounds: and industrial solution to optimise costs, environmental requests and quality for textile finihsing,“ Ultrasonics Sonochemistry 11, pp. 33-38, 2004. [12] J. A. Gallego-Juarez, E. Riera, V. Acosta, G. Rodriguez in A. Blanco, „Ultrasonic system for contunuous washing of textiles in liquid layers,“ Ultrasonics Sonochemistry 17, pp. 234-238, 2010. [13] K. Gotoh in K. Harayama, „Appliocation of ultrasound to textiles washing in aqueous solutions,“ Ultrasonics Sonochemistry 20, pp. 747-753, 2013. [14] A. Hasanbeigi in L. Price, „A technical review of emerging technologies for energy and water efficiency and pollution reduction in the textile industry,“ Journal of Cleaner Production 95, pp. 30-44, 2015. [15] J. Wang in D. R. Flanagan, „General solution for diffusion-controlled dissolution of spherical particles. 1. Theory,“ Journal of Pharmaceutical Sciences 88, pp. 731-738, 1999. [16] IEC, IEC 60456: Clothes washing machines for household use – methods for measuring the performance.

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Experimental study of the thermodynamic effecs in a cavitating flow ABSTRACT → When dealing with liquids, which operating temperature gets close to its critical temperature, cavitation cannot be assumed as an isothermal phenomenon. Due to high density vapor, by cavity growth, the thermodynamic effect becomes considerable and must not be neglected. For applications like pumping cryogenics in liquid propulsion space launchers, consideration of the thermodynamic effect is crucial and that is why the understanding of this phenomenon and its direct experimental observation has such a great value. In this study the thermodynamic effects in a cavitating

flow are observed on a simple Venturi profile. A thorough experimental investigation of the temperature field on cavitating flow has been performed in water of 100°C at different operating conditions. Temperature measurements were performed with Infra-Red (IR) high-speed camera, while visualization was made with conventional high-speed camera. Both, average temperature fields and temperature dynamics are presented at different operating conditions and compared with collected data in visual spectrum. In the vicinity of the throat a temperature depression up to 0.5 K was recorded.

INTRODUCTION Martin Petkovšek Laboratory: Laboratory for Water and Turbine Machines E-mail: martin.petkovsek@fs.uni-lj.si Room: N4 Phone: +386-1-4771-453 Status: PhD student (started: September 2011, to be completed: 2016) Research area: Cavitation in thermosensible liquids, wastewater treatment Mentor: izr. prof. dr. Matevž Dular prof. dr. Brane Širok

Cavitation is a physical phenomenon simply described as a growth and collapse of multiple small vapor bubbles within a liquid by approximately constant temperature. While an exact process of cavitation development is still not fully understood and scientifically described, it is assumed that cavitation is mainly a process of vaporization by cavity growth and condensation by cavity collapse, which is a consequence of heat transfer and temperature divergence between the bulk liquid and vapor + gas inside the cavitation bubbles. Dealing with liquids like cold water, the local temperature variations caused by cavitation can be neglected, while this must not be the case in liquids, which operate close to its critical temperature (e.g. cryogenics), where the temperature variations are big enough to affect the cavitation development – these phenomena are described as thermodynamic effects. Experimental studies of these phenomena are rare and most of them only observed the integral consequences (cavitation delayed inception and reduced extent) of the presence of the thermodynamic effects. Hord et al. [1-4] have made an extensive experimental observation on different geometries in liquid cryogens, while observing cavitation inception

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

and extent at different operating conditions. Experimental studies on temperature depression measurements in individual points within cavitating flow were performed by Fruman et al. [5] and Franc et al. [6]. Rimbert et al. [7] presented experimental data of temperature depression in microchannel cavitation with two-color laser in several individual points, while Petkovšek & Dular [8] presented the first 2D temperature field of the cavitating flow on a small Venturi geometry with a non-invasive IR method. Dular & Coutier-Delgosha [9] used IR method to investigate thermodynamic effects on a single cavitation bubble. Due to lack of the temperature experimental data within a cavitating flow, the improvement of the cavitation numerical models, with thermodynamic effects consideration, cannot progress. To fill up the void in cavitation temperature database, the present study is performed. EXPERIMENTAL SET-UP Cavitation tests were performed in a cavitation tunnel at the Laboratory for Water and Turbine machines, University of Ljubljana. The cavitation tunnel (Fig. 1) has a closed circuit which enables to vary the system pressure and the tempera-

ture of the used liquid, water in our case. Circulation of the water is obtained with 4.5 kW pump (1) that enables the variation of the rotation frequency in order to set the flow rate. At the pump delivery, a tank (2) partially filled with the circulation water is used for water heating, 10 kW electric heater is installed, and for damping the periodical flow rate and pressure fluctuations due to the passage of the pump blades. Cavitation and thermodynamic effects are observed in a transparent polycarbonate test section (3). The tank downstream of the test section (4) is used for cooling of the circulation water, cooling water flows inside the tank in a secondary loop, which is connected to cold tap water. The temperature of the water is monitored with a Pt100 sensor (5) installed in the downstream tank and with a thermocouple J type directly installed in the test section. The pressure inside the cavitation tunnel can be varied with a vacuum pump connected to the downstream tank or with a compressor connected to the upstream tank in order to provide a wide range of hydrodynamic conditions. The flow rate is monitored with electromagnetic flowmeter (6).

pointed into the side observation window and second, where cameras were pointed into bottom part of Venturi. In both cases the IR camera was perpendicular to observation surface, while the conventional camera was slightly at an angle to the IR camera.

Figure 3: Cameras position set (left – side view, right – bottom view).

Conventional black and white high-speed camera, HiSpec4 2G mono, was used to perform visualization, to capture cavitating flow in the test section. The camera enables capturing images at 523 fps (frames per second) at 3M pixel resolution. For the present experiments frame rate of 10,000 and 12,000 fps was used to observe cavitating flow from side and bottom view respectively. High-speed IR camera, CMT384SM-Thermosensorik was used for temperature measurements. The IR camera has a cooled mercury cadmium telluride detector type, with maximum resolution of 384×288 pixels and detector pitch of 20 μm. The IR camera has a spectral range between 1.5 and 5 μm and enables to adjust the integration time down to 0.02 ms. RESULTS AND DISCUSSION

Figure 1: Cavitation tunnel

Specially designed test section (Fig. 2), constructed out of transparent polycarbonate and sapphire glass observation windows enables to withstand temperatures up to 120°C. Side window and part of Venturi are manufactured from sapphire glass, which enables visualization with conventional high-speed camera and thermography with IR high-speed camera. Side window allows to observe cavitation conditions from the side view, while part of Venturi constriction (part made out of sapphire) serves as a bottom observation window. The basic geometry was a 10 mm wide Venturi section with a converging angle of 18° and diverging angle of 8°. The throat cross-section dimensions were 8x10 mm2.

Figure 2: Test section

As mentioned, two types of measurements were conducted, where the thermodynamic effects were investigated from both, the side and the bottom view of Venturi profile. In both observation positions, average temperature fields and temperature dynamics were observed at different cavitating conditions. All measurements were performed in tap water at approximately 100°C ± 2°C. For presented results the conventional high-speed camera operated at 10,000 and 12,000 fps, while IR camera operated at 830 and 920 fps for side and bottom view, respectively. Since the water is opaque in IR spectrum, one can only measure temperatures with IR thermography on a boundary layer between the sapphire glass observation window and water flow. Figure 4 presents the average temperature fields (averaged for a period of time of 1 second) for three different cavitation extents, from side (upper images) and bottom (middle images) view. In case (A) cavitation extents over one fourth of the diverging part of Venturi, in case (B) cavitation extents approximately over one half of the diverging part, while in case (C) cavitation extent over the whole diverging part. In order to compare data, temperature evolutions along the drawn lines in temperature fields are shown (bottom images, solid lines – side view, dashed lines – bottom view). The flow is from left to right, where position x=0 mm corresponds to the Venturi throat position.

To observe cavitation phenomena, cameras were set at two different positions. First the cameras (conventional high-speed camera and IR high-speed camera) were YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

Figure 4: Mean temperature fields and average cavitation extents from side and bottom view.

As one can see by all three cases, there is a clear temperature drop behind the Venturi throat, after which temperature slowly rise back to approximately initial (freestream) temperature. When the liquid is forced through the constriction, their velocity accelerates which causes pressure drop within the liquid flow. When the pressure drops below the vapor pressure, cavitation stars to form. The temperature of the liquid flow drops due to cavitation bubbles growth, by which evaporation and gas expansion occurs. Along the divergent part of constriction, the pressure recovers due to velocity drop, which causes cavitation bubbles to collapse, what results in temperature recuperation. Temperature rises due to condensation process and gas compression inside the bubbles. Comparing the selected three cases A, B and C, one can noticed, that the temperature depression depends on cavitation extent. The bigger the extent, the more intense the temperature drop occurs, and also the bigger extent of the cooling area is formed. Operating conditions for side and bottom view were chosen to be approximately the same, which result in very similar temperature evolutions along the constriction (between side and bottom view in each case). Temperature decrease for presented cases is between 0.12 K and 0.27 K, which corresponds with the results from the experiments of the Petkovšek & Dular [8] at the much smaller Venturi test section. One must be aware, that this are averaged temperature depressions and that the local temperature variations can reach up to 0.5 K in our observations. After the temperature decreases the temperature of the fluid flow returns to the initial free stream temperature, where no obvious temperature increase above the free stream temperature is noticed. Observing individual temperature fields on figure 5 gives us more thorough insight into the temperature dynamics, from the side view. Left images present cavitation extent, while right images presents time resolved temperature fields. As one can see in the presented case the cavitation is strongly developed and attached, without any obvious cloud shedding, since the temperature conditions are much more dynamic. The reason for this is the lim-

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

itation of the IR thermography, since the water is opaque in IR spectrum and parts of cavity, which do not touch the boundary layer between the observation window and water flow, cannot be detected by IR camera.

Figure 5: Time resolved temperature fields (side view).

Figure 6 presents time resolved temperature fields from bottom view for a case, where cavitation forms on a very small area in the vicinity of the Venturi throat. This specific case shows that in the area, where cavitation appears, the liquid flow suffers the temperature decrease. Here it is shown, that only in the near cavitation area one gets temperature depression of the flow.

[8] Petkovšek, M. & Dular, M. 2013 IR measurements of the thermodynamic effects in cavitating flow. Int. J. of Heat and Fluid Flow, 44, 756-763. [9] Dular, M. & Coutier-Delgosha, O. 2013 Thermodynamic Effects during the Growth and Collapse of a Single Cavitation Bubble. J. Fluid Mech. 736, 44-66.

Figure 6: Time resolved temperature fields (bottom view).

CONCLUSIONS The study presents a continuation of the previous work, Petkovšek & Dular [8], where the thermodynamic effects were observed in much smaller Venturi geometry. Scientific contribution is not just in scaling up the test section, but also that for the first time the thermodynamic effects were observed from the bottom view of the Venturi geometry. It was shown that the temperature depression, due to cavitation, can be measurable already in water of 100°C, by which conditions, our experiments were performed. With 2D temperature measurements in a cavitating flow, a presence of thermodynamic effect was confirmed. 2D temperature fields were compared with conventional high-speed visualization and can serve as an experimental support for numerical models evaluation and development.

List of publications [10] Petkovšek, M. & Dular, M. 2013 IR measurements of the thermodynamic effects in cavitating flow. Int. J. of Heat and Fluid Flow, 44, 756-763. [11] Dular, M. & Coutier-Delgosha, O. 2013 Thermodynamic Effects during the Growth and Collapse of a Single Cavitation Bubble. J. Fluid Mech. 736, 44-66. [12] Petkovšek, M. & Dular, M. 2015 Experimental study of the thermodynamic effect in a cavitating flow on a simple Venturi geometry. CAV2015 Journal of Physics – Conference series, 656.

ACKNOWLEDGMENTS The study was performed under a grant by the European Space Agency (ESA). References [1] Hord, J., Anderson, L. M., Hall, W. J. 1972 Cavitation in Liquid Cryogens I-Venturi. NASA CR-2054. [2] Hord, J. 1973a Cavitation in Liquid Cryogens IIHydrofoil. NASA CR-2156. [3] Hord, J. 1973b Cavitation in Liquid Cryogens IIIOgives. NASA CR-2242. [4] Hord, J., 1974 Cavitation in liquid cryogens. NASA CR-2448. [5] Fruman, D.H., Reboud, J.L., Stutz, B. 1999 Estimation of thermal effects in cavitation of thermosensible liquids. Heat and Mass Transfer, 42, 3195-3204. [6] Franc, J. P., Boitel, G., Riondet, M., Janson, E., Ramina, P. & Rebattet, C. 2010 Thermodynamic Effect on a Cavitating Inducer-Part II: On-board Measurements of Temperature Depression Within Leading Edge Cavities. ASME J. Fluids Eng., 132(2), 1-9. [7] Rimbert, N., Castanet, G. & Funfschilling, D. 2012 Experimental Study by Two-Colors Laser-Induced_ Fluorescence of the Thermodynamic Effect in MicroChannel Cavitation. Proceedings of the 8th International Symposium on Cavitation, Singapore.

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Factors Affecting Volatile Phenol Production During Fermentations with Pure and Mixed Cultures of Dekkerabruxellensis and Saccharomyces cerevisiae ABSTRACT → We have examined the impact of hidroxycinnamic acids on the production of volatile phenols in fermentations of mixed and pure cultures of yeasts Saccharomyces cerevisiae and Dekkera bruxellensis. Generally, the results showed that in

Janez Kosel Laboratory: Laboratory for Water Turbine Machinery E-mail: janez.kosel@fs.uni-lj.si Room: N-4 Phone: +386-1-4771-422 Status: phd assistant Research area: wine fermentation

mixed culture fermentations less vinylphenols and more ethylphenols were produced in comparison with D. bruxellensis pure culture fermentations. Vinylphenol precursors significantly inhibited the growth of S. cerevisiae and the production of ethylphenols.

INTRODUCTION

EXPERIMENT

Dekkera bruxellensis (anamorph: Brettanomyces bruxellensis) produces phenolic off-flavours that cause undesirable taints described as ‚medicinal‘ and ‚clove-like‘ in white wines (due to vinylphenols) and as ‚leather‘, ‚horse sweat‘ and ‚barnyard‘ in red wines (due to ethylphenols). These faults cause large economic losses and are difficult to avoid, firstly because of the low hygiene level which can be reached in winemaking, and secondly because of the resistance and growth of this yeast in strict environmental conditions (1). Wine fermentation is a complex process involving a microflora of wine microorganisms and their interactions including: antagonism and competition. The few existing studies of D. bruxellensis and S. cerevisiae mixed culture fermentations are limited to just a few experiments (2–4) and a physiological study should be conducted to assess the impact of microbial competition on the consumption of precursors (hydroxycinnamic acids (HCAs) and vinylphenols) and on the production of volatile phenols. In order to study the impact of microbial competition on the metabolism of volatile phenols, we have made a series of fermentations with pure and mixed cultures of wine yeast S. cerevisiae and of three different isolates of D. bruxellensis.

All fermentations were carried out under microaerobic conditions in 250-mL Erlenmeyer flasks filled with 200 mL of synthetic must MS300 and sealed with rubber stoppers with a CO2 outlet. For pure culture fermentations, a single strain of D. bruxellensis or S. cerevisiae was inoculated into MS300 medium (supplemented with eighter 100 mg/L of HCAs or 100 mg/L of vinylphenols) to a final concentration of 106 cells per mL. For mixed culture fermentations, a single strain of D. bruxellensis and a single strain of S. cerevisiae were inoculated together, each having a final concentration of 106 cells per ethylphenols was not complete, reaching 65 % (Figs. 1c and 1d). Furthermore, in the mixed cultures the assimilation of vinylphenols by D. bruxellensis was strongly reduced (Fig. 1e) and consequently ethylphenol production greatly decreased in comparison with D. bruxellensis ZIM 701 pure culture fermentations (Fig. 1d). mL. The fermentation temperature was 22 °C and the inoculated synthetic must was under constant magnetic stirring. For the purpose of measuring volatile phenols the samples were centrifuged at 4000×g for 5 min. Supernatants were filtered through a 0.22-mm pore filter and analyzed by high-performance liquid chromatography apparatus.

LABORATORY FOR HYDRAULIC TURBOMACHINERY YEARBOOK 2016

Figure 1: Volatile phenol production in synthetic must MS300 supplemented with either 100 mg/L of hydroxycinnamic acids (filled symbols) or 100 mg/L of vinylphenols (open symbols): a) and b) S. cerevisiae pure culture fermentations, c) and d) D. bruxellensis ZIM 701 pure culture fermentations, and e) and f) mixed culture fermentations. Production of 4-vinylguaiacol (squares) and 4-vinylphenol triangles) is presented in graphs a), c) and e) and production of 4-ethylguaiacol (circles) and 4-ethylphenol (diamonds) in graphs b), d) and f). Standard deviations of each point are represented by error bars

RESULTS In D. bruxellensis ZIM 701 pure culture fermentations, HCAs were rapidly metabolized to vinylphenols in an intracellular fashion and a complete conversion to ethylphenols was observed. On the other hand, in mixed cultures the conversion was delayed and ethylphenol production was reduced by 30 % (Fig. 1). It therefore seems that for ethylphenol production, the assimilation of HCAs and intracellular decarboxylation to vinylphenols is the preferable metabolic pathway in comparison with the direct assimilation of vinylphenols accumulated by S. cerevisiae. Under these conditions, D. bruxellensis ZIM 701 started to assimilate vinylphenols only after 70 h of fermentation, when vinylphenol concentrations in the medium had already reached or exceeded those measured in S. cerevisiae pure culture fermentations. Since most of ethylphenols were produced during the exponential growth phase of D. bruxellensis (starts from 50 h on), a certain amount of HCAs that was transformed to vinylphenols by S. cerevisiae was unavailable for assimilation by D. bruxellensis. Consequently, the levels of intracellular vinylphenols dropped and the production of ethylphenols stagnated. In pure culture fermentations, D. bruxellensis completely assimilated the externally added vinylphenols from chemically defined medium; however, the conversion to

REFERENCES [1] Suárez, J.A. Suárez-Lepe, A. Morata, F. Calderón, The production of ethylphenols in wine by yeasts of the generanBrettanomyces and Dekkera: A review, Food Chem. 102 (2007) 10–21. [2] L. Dias, S. Pereira-da-Silva, M. Tavares, M. MalfeitoFerreira, V. Loureiro, Factors affecting the production of 4-ethylphenol by the yeast Dekkera bruxellensis in enological conditions, Food Microbiol. 20 (2003) 377–384. [3] S.L. Jensen, N.L. Umiker, N. Arneborg, C.G. Edwards, Identification and characterization of Dekkera bruxellensis, Candida pararugosa, and Pichia guilliermondii isolated from commercial red wines, Food Microbiol. 26 (2009) 915–921. [4] J.S. Sáez, C.A. Lopes, V.C. Kirs, M.P. Sangorrín, Enhanced volatile phenols in wine fermented with Saccharomyces cerevisiae and spoiled with Pichia guilliermondii and Dekkera

CONCLUSIONS In mixed cultures of D. bruxellensis and S. cerevisiae supplemented with HCAs, the accumulation of ethylphenols was lower in comparison with fermentations using pure cultures. This could be partially explained by the lower availability of intracellular vinylphenol precursors. Moreover the substitution of HCAs with vinylphenols strongly reduced yeast growth and the production of ethylphenols.

YEARBOOK 2016 LABORATORY FOR HYDRAULIC TURBOMACHINERY

Assoc.Prof.Dr. Tomaž Katrašnik

Laboratory for Internal Combustion Engines and Electromobility The research and teaching activities of the Laboratory with more than 45 years of experience is focused on internal combustion engines for stationary and mobile applications and on hybrid and fully electric powertrains including fuel cell electric powertrains.

The activities are structured in five areas: • Advanced engine concepts including engine control, • Advanced and alternative fuels and combustion concepts, • Optimization of real world energy consumption and exhaust emissions, • Hybrid and fully electric powertrains including fuel cell electric powertrains, and • Development of mechanistic simulation models in these fields. 88

In the area of Advanced engine concepts including engine control there is a strong focus on Closed Loop Combustion Control and development of demonstrators using real-time hardware. CLCC modules incorporate selfdeveloped prototypes of model based controllers relying on thermodynamics and combustion parameters as well as on virtual emission sensors, with the aim of optimizing Diesel and Otto combustion processes as well as various types of CAI or LTC combustion concepts, e.g. HCCI, PCCI, RCCi...

This area fully interacts with the Development of advanced and alternative fuels and combustion concepts area. In this area we research all commercially available fuels for mobile application including dual-fuel operation and extend this focus on innovative waste or bio derived fuels, where the later ones have a significant potential in stationary application. Knowledge arising from previous areas combined with state-of-the-art equipment and profound expertize in real world testing form a solid basis for research in the area of Optimization of real world energy consumption and exhaust emissions. In this area we perform analyses of exhaust emissions and vehicle dynamics on various vehicle types ranging from ICE powered and hybrid-electric vehicles to heavy duty and off-road vehicles utilizing conventional and advanced/alternative fuels. In the area of Hybrid and fully electric powertrains that includes fuel cell electric powertrains we are engaged in R&D activities on the component level and on the system level since the optimization on the system level is crucial for achieving high energy efficiency and low exhaust emissions. This forms a crucial interaction with the area Development of mechanistic simulation models where we focus on fully coupled multi-domain mechanistically based models,

which feature high level of predictability and high level of accuracy. In this are we have long term cooperation with the market leader on the development of professional modelling tools that are in use by multiple OEMs. In all of the above mentioned areas we have a fully equipped laboratory with state-of-the-art hardware and software facilities. Moreover, in these areas we are also engaged in public funded national and international (EU Framework, COST and FFG-Austria) projects as well as direct industrial projects with domestic and foreign partners, which confirms high research level of the Laboratory. All these engagements form a solid basis for the teaching activities that fully reflect all our research activities. During their studies students work with modern research equipment and their work during seminars and thesis is generally interrelated with research work of the Laboratory establishing a challenging and highly motivated working environment. FORMER PROFESSORS: Prof. Dobromil Uran, Prof.Dr. Radoslav PavletiÄ?, Prof.Dr. Ferdinand Trenc

A computationally efficient hybrid 3D analytic-numerical approach for system level modelling of PEM fuel cells ABSTRACT â&#x2020;&#x2019; System level simulations, which are gaining on importance in the product design process and in the Hardware-in-the-Loop (HiL) applications, require models that feature high level of accuracy, high level of predictability and short computational times. While such system level models of e.g. internal combustion engines are commonplace, system level models of fuel cells are only slowly becoming available. This paper summarises the key features of a hybrid 3D analytic-numerical (HAN) modelling approach and presents an innovative computationally optimized version of the HAN modelling framework denoted HAN-RT (RT standing for Real Time) that complies with the real-time constraints imposed by the HiL systems.

HAN-RT shares with other HAN models the semianalytic nature of species transport modelling and the efficient computational coupling of electrochemical kinetics to this transport, while featuring a specific computationally optimized framework for treating the governing equations. A comparative evaluation shows very good agreement between the HAN-RT results and the CFD results. HAN-RT achieves high fidelity results at very short computational times. Accuracy of the results and computational speed thus confirm that HAN-RT efficiently combines hybrid 3D analytic-numerical mechanistic modelling basis and HiL compliant computational times.

INTRODUCTION Gregor TavÄ?ar Laboratory: Laboratory for Internal Combustion Engines and Electromobility E-mail: gregor.tavcar@fs.uni-lj.si Room: 310 Phone: +386-1-4771-310 Status: PhD assistant Research area: Fuel cell modelling

Modern approaches to developing and optimising dynamic systems (i.e. ICE road vehicles) rely on modelling in virtual environment by means of well-established system level simulations. Not surprisingly, the application of such system level simulations also to the development process of fuel cell dynamic systems is recently quickly gaining on importance. System level simulations aim at modelling the whole system by means of a system super-model comprising interconnected individual models of systemâ&#x20AC;&#x2122;s components (e.g. components of energy storage devices, energy converters and energy consumers). In order to support tasks in early stages of development a system level component model must feature high level of predictability and generality, meaning that it is capable of modelling not only a single specific component but a wider range of components of the same type. These predictability and generality enable, on one hand, virtual development of the whole system already before any physical prototypes of the component or its performance data are available and, on the other hand, gives guide lines

for component development on the basis of the simulated componentsystem interaction. System level models can also enable short computational times. Among others there are two distinct applications of system level models where short computational times are of great importance: 1.) application in early stages of development where the optimisation of a dynamic system inherently requires performing a large number of simulations to cover various operational scenarios. 2.) application as plant models in the validation and calibration stages of development in the office off-line and in the online HiL (hardware-in-the-loop) environments. To support these tasks, system level simulation models have to feature very fast computational times, whereas in HiL environments it is mandatory to strictly fulfil the realtime constraints. It is also very beneficial from the workload point of view and from the plant model consistency point of view when the same model can be used in the early design stages of development and in the validation and calibration stages of development.

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The so called reduced dimensionality models in their broader sense, i.e. any model that does not address all three dimensions equally, are a typically answer to the need for a balance between computational speed and accuracy of results. Common reduced dimensionality models are the 2D models (e.g [1], the 2D model in [2]) and the so called 1D+1D models (e.g. [3]), which are a simplification of the 2D models (models where only the most dominant physical phenomena - e.g. mass transport via bulk gas flow in channel - are addressed in the dimension that runs along direction of gas flow). The 2D modelling approach leads to certain systematic discrepancies that are sometimes compensated by means of correction parameters yielding the pseudo 3D modelling approach (e.g. [4,5] and Sherwood number adjusted 2D model in [2]). An alternative to this pseudo 3D approach is the so called 2D+1D approach (as found in [2]) where the physical phenomena are fully addressed in the plane perpendicular to the gas flow and, analogously to 1D+1D approach, only the dominant physical phenomena are addressed in the direction of the gas flow. The pseudo 3D and 2D+1D models aim to take into account all three dimensions whilst achieving considerably shorter computational times than 3D CFD simulations. However, with the exception of [4], they still cannot achieve computational times comparable to the 1D models due to their inherent numerical nature. Owing to its analytic nature the quasi 3D model found in [4] features computational times comparable to the 1D models. However [4] offers an approximate analytic solution for direct liquid fuel cells that is only valid when constant velocity along channels is assumed. Articles of TavÄ?ar and KatraĹĄnik [6-8] propose aHybrid 3D Analytic Numerical approach to modelling species transport (HAN) in a PEM fuel cell as a way to obtain results with full 3D resolution whilst achieving short computational times. The principles of HAN modelling in [6-8] are presented on a straight channel co-flow and counter-flow fuel cell and its core principle can be summarized as: A hybrid 3D model constructed by taking a 1D numerical model for the gas-flow along the channel with a superimposed 2D analytic solution for the plane perpendicular to the gas-flow. The additional computational load introduced by the calculation of the 2D analytic solution was shown to be of the same order of magnitude as the computational load of the base 1D calculation proving this hybrid 3D approach to be computationally efficient. The HAN modelling approach has been comparatively evaluated against CFD simulation results [6-8] and also against experimental measurements [9]. Although the HAN modelling approach is characterized by a very good ratio between computational times on one side and model resolution and its accuracy on the other, the HAN models presented in [6,8] are not realtime capable, which is the cost of their high spatial resolution. To comply with the realtime constraints imposed by the HiL applications, this paper presents results of a computationally optimized HAN modelling approach denoted HAN-RT (Real-Time), which is based on the optimized modelling framework that efficiently combines sufficient level of model complexity and short computational times. Although HAN-RT gives results on species distribution

with lower resolution compared to the HAN models found in [6-8], it still captures the essential 3D geometrical characteristics of the modelled fuel cell leading to high fidelity of the results relevant for system level simulation (i.e. the net electric current, power, fuel utilisation...) Furthermore the HAN-RT model features interfaces that enable its integration in an arbitrary FC system topology by connecting it to the components for balance of plant including cooling system and other electric components. This allows for modelling a broad range of mobile and stationary applications in virtual representation of real operating conditions making it a system level model that is also suitable for optimization of the entire system including its control. SOME HAN-RT RESULTS

Figure 1: Fuel cell geometry schematic.

The modelled fuel cell is made of a number of equal parallel symmetrical ribs as schematically shown in Figure 1. As the most indicative simulation result is the polarisation curve shown in Figure 2 where close agreement between a high resolution high accuracy CFD and the computationally optimised HAN-RT can be observed.

Figure 1: Comparative plot of the simulated polarisation curve.

However, the average current density that is plotted in polarisation curve is an integral value and does not reveal how well the model predicts the distribution of current density and species concentration within the fuel cell. Thus it is instructive to take a closer look at these distributions and assess the agreement between CFD and HAN-RT under higher scrutiny. The HAN-RT model features only the minimal possible resolution in the direction perpendicular to channel

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gas flow and parallel to the membrane plane distinguishing only average values under (cathode) channel and values under rib. For easier comparison the detailed CFD results are also gathered and averaged to give corresponding “under channel” and “under rib” values and plotted alongside the HAN-RT results in Figure 3. Table 1: Computational times on a desktop computer Model

No. of iterations

CPU time [s]

CFD

5000

2400

HAN (high res.) [8]

0.7

HAN-RT

0.01

The computational times obtained for the CFD and the higher resolution HAN reported in Table 1. correspond to the time required for calculating a converged steady state operational point while the computational time reported for HAN-RT corresponds to the time needed for calculation of a single time-step in a simulation of a transient operation. The 10 ms computational time of HAN-RT makes possible real time applications with refreshing frequencies of almost up to 100Hz. The comparative HAN-RT versus CFD plots have demonstrated HAN’s ability to adequately simulate the spatial distribution of key physical quantities in a fuel cell. The fact that HAN-RT results show a good agreement with the CFD results validates the HAN-RT’s hybrid 2D analytic + 1D numerical approach to modelling the fundamental fuel cell governing mechanism, i.e.: the diffusive and convective transport of species. CONCLUSIONS Overall, HAN-RT proves to be accurate and computationally efficient and as such a very promising fuel cell model for system level simulations. Further challenges in developing HAN-RT are the adequate treatment of liquid water in the GDL-s and channels which has already been addressed by the high resolution versions of HAN [9].

Figure 3: Plots of distribution of values of various variables over cathode catalyst surface and in the cathode channel of the representative unit at 0.656V. The surface under channel and surface under rib are distinguished. The z-axis runs along the channel gas flow direction with the anode inlet and the cathode outlet are at z = -13.5 mm..

LABORATORY FOR INTERNAL COMBUSTION ENGINES AND ELECTROMOBILITY YEARBOOK 2016

References [1] Ee, Sher Lin and Birgersson, Erik. Two-Dimensional Approximate Analytical Solutions for the Direct Liquid Fuel Cell. J. Electrochem. Soc. 10, 2011, Vol. 158, 81224-81234. [2] Kim, Gwang-Soo, et al. Reduced-dimensional models for straight-channel proton exchange membrane fuel cells. J. Power Sources. 10, 2010, Vol. 195, 3240-3249. [3] Esmaili, Q., Ranjbar, A. A. and Abdollahzadeh, M. Numerical Simulation of a Direct Methanol Fuel Cell through a 1D+1D Approach. International J. Green Energy. 2, 2013, Vol. 10, 190-204. [4] Ling, Chun Yu, Ee, Sher Lin and Birgersson, Erik. Three-dimensional approximate analytical solutions for direct liquid fuel cells. Electrochimica Acta. 30, 2013, Vol. 109, 305-315. [5] Chang, Paul, et al. Reduced dimensional computational models of polymer electrolyte membrane fuel cell stacks. J. Computational Physics. 2, 2007, Vol. 223, 797-821. List of publications [6] Tavčar, Gregor and Katrašnik, Tomaž. An Innovative Hybrid 3D Analytic-Numerical Approach for System Level Modelling of PEM Fuel Cells. Energies. 10, 2013, Vol. 6, 5426-5485. [7] Tavčar, Gregor and Katrašnik, Tomaž. A computationally efficient hybrid 3D analytic-numerical approach for modelling species transport in a proton exchange membrane fuel cell. J. Power Sources. 2013, Vol. 236, 321-340. [8] Tavčar, Gregor and Katrašnik, Tomaž. An Innovative Hybrid 3D Analytic-numerical Model for Air Breathing Parallel Channel Counter-flow PEM Fuel Cells. Acta Chim. Slov. 2014, Vol. 61, 308–315. [9] Tavčar, Gregor. Analytic-numerical 3D model for treatment of species transport phenomena in fuel cells. Doctoral Thesis. University of Ljubljana, March 2014..

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Use of equivalent circuit in modeling voltage response to dynamic load current cycle ABSTRACT → Efficient and fast approach with equivalent circuit for modeling battery‘s potential will be presented. Governing equations form system

of ordinary differential equations. Their numerical solution and comparison with experimental data will be analysed on a case with dynamic load current.

INTRODUCTION Igor Mele Laboratory: Laboratory for Internal Combustion Engines and Electromobility E-mail: igor.mele@fs.uni-lj.si Room: 311 Phone: +386-1-4771-311 Status: Researcher Research area: Next-generation lithium-ion batteries Mentor: Tomaž Katrašnik

With emergence of hybrid (PHEV) and fully electric vehicles (FEV), there is an increasing demand for accurate and efficient battery modeling to ensure high performance of the battery pack during operation. Important aspect in battery modeling field is prediction of voltage response to the load current in order to estimate variety of battery parameters, for example heat generation. One of the widely used techniques is to construct an equivalent circuit (EC) model which is usually based upon electrochemical impedance spectroscopy (EIS) measurement of the battery cell. EQUIVALENT CIRCUIT Equivalent circuits comprise with elements known from standard electric circuits, i.e. resistors, capacitors, inductors... With the EC model we try to capture important electrochemical processes within the battery cells.

Figure 1: Equivalent circuit scheme

Figure 1 shows schematic representation of EC used in [1]. Governing equations of the EC can be written in two domains: time and frequency domain. In frequency domain we write where represents frequency dependent complex-valued impedance, represents solution resistance in the 94

electrolyte, and are two RC circuits. Equation (1) is obtained with sum and inverse sum of complex impedances in serial and parallel connections, respectively. Its representation is shown on Figure 2. In order to model battery cell parameters during operation, we need to write governing equations of the EC in time domain. Voltage across capacitors and is time dependent and constant across resistors. We obtain a system of ordinary differential equations (ODE) that can be solved with numerical integration routines [2]:

where and represent potential drop across first and second RC circuit, respectively. Ultimately, we want to calculate potential difference between both battery terminals : where represents cell‘s open circuit voltage and is dependent on the battery‘s SOC, represents load current which is applied to the cell. Additionally, SOC is also time dependent and is evaluated by integrating load current (also known as Coulombcounting approach)

where represents capacity of the battery cell. ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY Electrochemical impedance spectroscopy (EIS) is nowadays used as a standard characterization technique in studying electrochemical behav-

LABORATORY FOR INTERNAL COMBUSTION ENGINES AND ELECTROMOBILITY YEARBOOK 2016

iour of the battery cell [1]. With the EIS, the battery cell is introduced to the range of low frequency alternating currents [3][4] by measuring its voltage response, which is highly non-linear. With known voltage amplitude, current amplitude and phase shift between both, complex impedance can be calculated [3]. It is usually displayed in form of Nyquist plot with the real part of on x-axis and imaginary part of on y-axis. Typical EIS spectrum of Li-ion battery is shown on Figure 2. However, it does not reveal any informations regarding frequency .

EC model additionally requires load current and initial as input values. These parameters were then used in equations (2)-(4) as initial values. Later, some additional fine tuning of the parameters was performed in order to minimize differences to the experimental data.

Figure 4: Deviation of predicted voltage from the experimental values.

Figure 2: Nyquist plot of EC from Figure 1.

Analysis of the spectrum allows us to determine certain kinetic parameters of the battery cell such as charge transfer resistance and diffusion coefficient of Li+ [5]. Typically it is composed of one or two overlapping semicircles. First/ left semicircle corresponds to charge transfer dynamics (high frequency portion of Nyquist plot) in EC and is represented with first pair of RC elements, namely and . Second semicircle corresponds to diffusion phenomena and lies in the low frequency portion. Elements that represent this semicircle are and . Ohmic resistance can be determined from the intersection of curve with real axis [5]. RESULTS Measurements and model are based on the commercial Li-ion cell LGChem. Basic characteristics of the cell are gathered in Table 1 provided by manufacturer. Validation of EC model was performed on a data featuring dynamic driving profile. Both measurement data and EIS fitted parameters (resistors and capacitors) were provided within FP7 project ASTERICS [6]. Table 1: Basic characteristics of LGChem Li-ion cell Application

FEV/PHEV

Nominal capacity

41 Ah

Nominal voltage

3.75 V

Weight

965 g

Energy density

159 Wh/kg

Figure 3 shows good agreement between measured and modeled cell potential. Relative errors on figure 4 confirm capability of the EC model to predict voltage trace for a dynamic load current cycle by most of the erors being well under 1% threshold. CONCLUSIONS Short overview of equivalent circuit technique for modeling battery cells was presented. Although a fairly simple model of EC was implemented, prediction level of battery cell‘s voltage compared to the measurement data is relatively high. Further improvements of the model are related to the temperature dependent parameters and ageing effects. References [1] T. Katrašnik, Y.Olofsson, B. Brunnsteiner. Battery models including ageing effects (physically based, equivalent circuit and empiric) that fits. ASTERICS project deliverable 2015. [2] Numerical Recipes 3rd Edition: The Art of Scientific Computing. Cambridge University Press, New York, NY, USA, 2007. [3] N. Lohmann, P. Wesskamp, P. Haussman, J. Melbert. Electrochemical impedance spectroscopy for lithiumion cells: Test equipment and procedures for aging and fast characterization in time and frequency domain. J. Power Sources 2015; 273: 613-623. [4] A. Seaman, T. Dao, J. McPhee. A survey of mathematics-based equivalent-circuit and electrochemical battery models for hybrid and electric vehicle simulation. J. Power Sources 2014; 256: 410-423. [5] Y. Olofsson. Electrochemical Impedance Spectroscopy in battery testing and modeling. ASTERICS project deliverable 2013. [6] Y. Olofsson, J. Groot, T. Katrašnik, G. Tavčar. Impedance spectroscopy characterisation of automotive NMC/graphite Li-ion cells aged with realistic PHEV load profile. IEEE International Electric Vehicle Conference, Florence, Italy, 2014.

Figure 3: Comparison between measured potential and modeled one from the EC model. YEARBOOK 2016 LABORATORY FOR INTERNAL COMBUSTION ENGINES AND ELECTROMOBILITY

Analysis and digital processing of in-cylinder pressure signal for combustion diagnosis of internal combustion engine ABSTRACT → In the present work measurements of the in-cylinder pressure were performed with two separate pressure transducers placed in the cylinder of a compression ignition internal combustion engine. Comparison was done between high-frequency laboratory and low-frequency large-series commercial pressure transducer. The impact of position and type of the pressure transducer on accuracy of the

results of thermodynamic model with respect to the cylinder pressure oscillations and noise was analyzed. Measured data were analyzed with Direct Fourier Transform (DFT) and Short time Fourier Transform (STFT). The main contribution of the proposed article is in the determination of the most appropriate strategy for processing the signal in order to control the combustion process in a closed loop.

INTRODUCTION Rok Vihar Laboratory: Laboratory for Internal Combustion Engines and Electromobility E-mail: rok.vihar@fs.uni-lj.si Room: 311 Phone: +386-1-4771-311 Status: PhD student (started: December 2012, to be completed: May 2016) Research area: Internal combustion engines Mentor: Assoc. Prof. dr. Tomaž Katrašnik

The tightening of emissions regulations is forcing vehicle manufacturers towards continual reduction of emissions of pollutants. Especially in vehicles equipped with diesel engines, whose popularity is increasing in recent years due to higher effective efficiency, the most problematic pollutants are nitrogen oxides (NOx) and particulate matter (PM). There are two ways of reducing tail pipe emissions: directly inside the cylinder by adoption of the control strategy and indirectly by exhaust after-treatment systems (DOC, DPF, SCR ...). To improve engine performance and reduce costs of the after-treatment systems it is beneficial to apply also direct in-cylinder control strategy thus acting as active prevention of the formation of pollutants. A very promising tool for prediction of the formation of pollutants is in-cylinder pressure sensor in combination with a thermodynamic model operate as a virtual NOx/PM sensor. This can be further used as an input for the models for controlling the combustion process in a closed loop (CLCC). The pressure signal from the engine cylinder is measured locally and therefore in addition to the information of the globally averaged pressure of the combustion chamber also includes pressure oscillations, combustion noise and measurement

uncertainty. This becomes even more evident at large-series low-frequency pressure transducer which will be largely built into the diesel engines in the future. Thermodynamic models need a reliable in-cylinder pressure signal on real-time basis and therefore an efficient methodology for elimination of pressure oscillation, combustion noise and measurement uncertainty reduction is required. In this work the impact of the differences in pressure signal quality to calculated rate of heat release (ROHR) and techniques for the successful removal of unwanted components from the pressure signal will be investigated. RESEARCH PROBLEM Intense heat release in the premixed combustion phase is resulting in the excitation of the pressure fluctuations in the combustion chamber [1]. Therefore pressure measured by the pressure transducer represents only the local pressure at the point of transducer location. In addition to the pressure fluctuations also influence of combustion noise and measurement uncertainty must be considered. For calculation of thermodynamic parameters it is necessary to know the evolution of global-spatially averaged in-cylinder pressure, which can be reproduced only with the successful elimination of the impact of natural

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frequencies in the combustion chamber, combustion noise and measurement uncertainty. In off-line analysis of the combustion process wherein the evolution of the in-cylinder pressure is an input parameter for thermodynamic model and shall be carried out after the measurement, the intake pressure trace is usually determined by averaging of a large number of values of successive measurements. This way, a part of the combustion noise from the signal is effectively eliminated. To remove the contribution of pressure fluctuations and measurement uncertainty, more complex computational algorithms could be used since the optimization of the modelâ&#x20AC;&#x2122;s accuracy is significantly more important than calculation time of the model. In the real-time analysis, where the input variable of the thermodynamic model is a pressure trace from only one analyzed cycle, the signal processing is significantly more difficult, since pressure fluctuations, combustion noise and measurement uncertainty should be eliminated by processing pressure trace from only one engine cycle while taking into account computational constraints. METHODOLOGY Analyses were carried out on a commercial 1.6 L, 4-cylinder, diesel engine (Figure 1) equipped with a turbocharger and intercooler, coupled with an eddy-current dynamometer. The in-cylinder pressure was measured by a variety of piezo pressure sensors in combination with a charge amplifier connected to a 16 bit measuring card with a sampling frequency of 1 MS/s/channel. Matrix of analyzed operating points can be seen in Table 1.

Figure 1. DV6 ATED4 Engine Table 1. Analyzed operational points Operating point

Engine RPM [min-1]

Engine load [Nm]

1 (1200_20)

1200

2 (1200_100)

1200

100

3 (2000_20)

2000

4 (2000_100)

2000

100

5 (2000_160)

2000

160

6 (3000_20)

3000

7 (3000_100)

3000

100

8 (3000_160)

3000

160

Two different types of pressure transducers were used: high-frequency (HF) laboratory and low-frequency (LF) large-series with the analysis carried out for the combination of HF-HF and HF-LF transducer. Pressure traces were

acquired with frequencies between 72 and 140 kHz with HF transducer and at with frequencies between 7.2 and 14 kHz with LF transducer. Measured in-cylinder pressure traces were further processed for the calculation of thermodynamic parameters. Acquired data were used for analysis of pressure oscillations in the combustion chamber, analysis of the combustion noise and measurement uncertainty. The accuracy of the calculated parameters was compared for different methods. In addition to the analytical calculation of natural frequency, also results of spectral analysis of a large number of cycles and Short Term Fourier Transformation (STFT) were analyzed. The combination of the two mentioned methods enable for competent analysis of the combustion process which is characterized by high variation within single cycle and partial variation between multiple cycles. Furthermore an analysis of a large number of cycles allows for identification of whole multiples of the analyzed number of cycles and therefore serves in combination with other methods for determining critical frequencies. Relevance of the certain results was significantly enhanced by the analysis of the two pressure traces, simultaneously acquired form the same cylinder. These data were used as a guide for selecting the most appropriate filter and determination of the filter parameters. CALCULATION OF ROHR ROHR is an essential thermodynamic parameter for combustion analyses that can be calculated from in-cylinder pressure trace (equation 1) and can serve as a basis for determination of other thermodynamic parameters (e.g. Temperature, composition)

In the equation 1 [2] p represents in-cylinder pressure, V is the current volume and is the adiabatic coefficient. ROHR is also the most appropriate parameter for determination of impact of pressure transducer type and location since it is susceptible to all pressure based irregularities listed in the previous section. Comparison of ROHR traces (Figure 2), calculated from the pressure traces that were acquired simultaneously with two HF pressure transducer mounted on different location inside combustion chamber reveal the same frequency of pressure fluctuation while there is a pronounced difference in the amplitude. That can be attributed mainly to different location of the pressure transducers.

Figure 2 Comparison of ROHR from AVL vs. Kistler transducer at 3000 1/min and 160Nm

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In the second analysis Kistler HF pressure transducer was replaced with Beru LF pressure transducer. As can be seen from Figure 3, not only the amplitude of pressure oscillations but also frequency of the signal is different, which is clearly reflected in calculated ROHR. That means despite the impact of different location of pressure transducer, also high impact of combustion noise is expressed on the pressure trace.

Figure 3. Comparison of ROHR from AVL vs. Beru transducer at 3000 1/min and 160Nm

It can be clearly seen that elimination of disturbances from the pressure trace is essential for accuracy of the combustion model, especially when using low-frequency pressure transducer. This kind of disturbances can be effectively eliminated using numerical filters. Therefore in the next chapters methodology for selecting appropriate filter parameters will be presented. DFT ANALYSIS The result of the DFT analysis will be shown in one selected operating point of the engine at 2000 min-1 and 100 Nm. For the analysis 25 sequential in-cylinder pressure cycles were used on which the DFT analysis was carried out (Figure 4). For comparison, additional pressure cycle was used, that was defined as the average of 100 consecutive cycles at the same operational point and is normally used for offline analysis of combustion. The difference in the length of the x axis occurs due to the different lengths of the sample, and does not affect the further analysis. It can be seen that the averaging eliminates the cycles that are not multiplier of the value of the number of analyzed cycles (Figure 4), which can be clearly seen on the graph of 25 consecutive cycles. This means that analysis of a large number of individual sequentially bonded cycles give information on the location and amplitude of disturbance, which is an important consideration in the design of a digital filter.

Figure 4. DFT analysis at 2000 1/min and 100Nm 98

Based on the analysis of the harmonics it is often easier to distinguish between periodic and non-periodic phenomena, which is clearly illustrated in Figure 4. Furthermore, it can be observed on Figure 4 that at higher amplitudes harmonics that are multiples of 25 (number of analyzed cycles) are visible, and represent phenomena related to the piston kinematics and combustion process. This is followed by the pressure oscillations in the cylinder. Disturbances at low amplitudes (between harmonics that are multiples of 25) are primarily attributed to noise caused by thermal effects, sensor resonance and vibrations. In the domain of harmonics the cutoff frequency can be determined with calculation of the difference between the amplitude of the harmonic and the average of harmonics, which determine the relationship between pressure signal and disturbances (signal-to-noise ratio). When this ratio converge towards 0, it can be assumed that the amplitude of the pressure signal is equal to the disturbance, and thus determine the point from which further the signal mostly consist of unwanted components. Figure 5 shows the normalized difference of the amplitude of harmonics as a function of the n-th harmonic frequency. The graph shows the amplitude interval from 0 to 3,5 and the interval of the harmonics interval from 0 to12750-th harmonic. For clear demonstration, harmonics are shown on the upper abscissa and at the bottom the conversion from harmonic into frequency domain is made. From Figure 5 it can be observed that the normalized difference firstly achieves a relatively low value at about 1500 Hz and then the next big growth can be observed between 5400 and 6000 Hz, where it is assumed that in-cylinder pressure oscillations occur. It can be concluded that appropriate area of determining the cutoff frequency should be between 1500 and 5400 Hz.

Figure 5. Harmonics at 2000 1/min and 100Nm

STFT ANALYSIS When analyzing the signal with DFT the information of time is lost, as graphs do not reveal whether the natural frequencies occur continuously or they are present only at certain intervals. One of the solutions is introduction of the sliding window function with a given length of the window which passes through the signal on the time domain and performs time localized Fourier Transform (FT), which is called the Short-time Fourier Transform (STFT). By applying continuous FT on each time interval, the FT of the entire signal is carried out. For each considered segment, signal is assumed to be approximately stationary. STFT divided signal to the time domain in a 2D

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time-frequency domain, which are visible to the variation in frequency within each window. In the analysis Hanning window function has been used, the window width was set to 8096 points, length of the FFT transformation was 2048 points and the overlap between segments was 0.99. The sampling frequency is engine speed dependent on the engine speed and was 120 kHz at 2000 min-1. Figure 6 shows an example of the calculation of STFT in the present operational point. The area of the occurrence of pressure oscillations coincides with the range specified by the DFT, where a slightly greater spreading of the cycles can be observed, so that it is recommended to move the cutting area below 4800 Hz.

Table 2. FIR filter settings for laboratory application

Operational point

Transition band [Hz]

Filter order

1200_20

600 – 3650

1200_100

750 – 5000

2000_20

750 – 4000

2000_100

750 – 4600

2000_160

600 – 5000

3000_20

1500 – 4250

3000_100

1600 – 3750

3000_160

1650 – 4000

Table 3. FIR filter settings for industrial application

Figure 6. DFT analysis at 2000 1/min and 100Nm

DESIGN OF A FIR FILTER It turns out that the most commonly used filter is a FIR filter type whose operation is subject to the selection of an appropriate order and frequencies. There are numerous methods for FIR filter design. The most commonly used method is window function method, equiripple method and frequency sampling method. Window function is a simple and flexible method for calculating coefficients of FIR filter, but does not allow flexibility and control over the parameters of the filter. The main advantage of frequency sampling method is a fast and efficient recursive calculation of the coefficients of FIR filter, but on the other hand is not flexible when setting filter parameters. Engine applications are limited in terms of system memory so control over the filter order is very important. The FIR filter parameters were determined using MATLAB software, where the minimum FIR filter order was calculated using the Parks-McClellan algorithm, on the basis of passband frequency, stopband frequency, passband ripple, stopband ripple and the sampling frequency. Table 2 shows the cut-off frequency and FIR filter order for laboratory application, where there is a sufficient calculation speed and the accuracy of the results is of utmost importance. Since ECU’s have limited computational power the values of FIR filter settings for a commercial application with reduced computational power are shown in Table 3.

Operational point

Transition band [Hz]

Filter order

1200_20

600 – 2800

1200_100

850 – 3300

2000_20

800 – 3500

2000_100

750 – 3200

2000_160

600 – 3000

3000_20

750 – 3000

3000_100

900 – 4500

3000_160

750 – 3500

CONCLUSION Performed analysis of in-cylinder pressure data acquired from two different types of pressure transducers simultaneously located inside the combustion chamber serves as a good basis for further research in combination with computationally efficient 2-zone combustion model and virtual NOx sensor, which were both fully developed in our laboratory. Reliable pressure input and efficient filter technique is a key input parameter for real-time combustion model which can be further expanded for closed loop combustion control. References [1] R. Vihar, T. Seljak, S. Rodman Oprešnik, and T. Katrašnik, “Combustion characteristics of tire pyrolysis oil in turbo charged compression ignition engine,” Fuel, vol. 150, pp. 226–235, 2015. [2] Katrasnik T, Trenc F, Rodman Opresnik S. A New Criterion to Determine the Start of Combustion in Diesel Engines. Journal of Enginering for Gas Turbines and Power 2006; 128, 4: 928-933. [3] Prah I, Katrasnik T. Application of Optimization Techniques to Determine Parameters of the Vibe Combustion Model. Strojniški vestnik - Journal of Mechanical Engineering 2009; 55, 11: 715-726.

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Challenges and Experiences at Converting Heavy-Duty Diesel Engines to Dual-fuel Operation ABSTRACT → High volatility of fuel prices represents one of the major business risks and opportunities for transport companies since the fuel cost is the highest cost in transport. The most common fuel in heavy-duty transport sector is diesel fuel. To lower the fuel cost, conversion of diesel engines to dual-fuel operation is a tempting option. During dual-fuel operation both fuels - diesel and gaseous fuel are used simultaneously. Commonly two types of gaseous fuels are used: Liquid Petroleum Gas (LPG) and Natural Gas (NG). Availability on EU market and ease of handling is LPG advantage, while lower prices per energy unit and higher diesel fuel substitution rate makes NG more appealing. Apart

from the economic effect environmental impact is also important since particle emissions, that are one of the primary concerns of diesel engines, can be lowered to high extent. Additionally the EU transport sector almost 100% dependence on crude oil can be substantially lowered. Paper will address different conversion kits offered on the market. Some crucial experiences gained during multiple conversions of diesel engines to dual-fuel operation will be presented. Challenges and troubleshooting issues will be emphasized and discussed.

INTRODUCTION Samuel Rodman Oprešnik Laboratory: Laboratory for Internal Combustion Engines and Electromobility E-mail: samuel.rodman@fs.uni-lj.si Room: 310 Phone: +386-1-4771-310 Status: PhD assistant Research area: Alternative Fuels and I.C.E. Exhaust emission Measurements

EU strives to diversify the fuel palette used in transport due to several reasons. Dependence of the transport sector on crude oil should be lowered since there are scarce crude oil reserves in the EU countries and has to be approx. 90% imported [1]. There is also an environmental target to decrease CO2 emissions where transport sector is one of the major sources. Directive 2014/94/EU of the European parliament and of the council [2] sets out minimum requirements for the building-up of alternative fuels infrastructure. LPG and NG are by directive definition alternative gaseous fuels. Both fuels have potential for lower carbon footprint due to favorable H/C ratio compared to diesel fuel (Table 1). LPG is used pressurized so that can be transported and handled in

liquid form and consists mainly from propane and butane and is offered in different mixing ratios. Gauge pressure in the LPG container is around 10bar; vapor pressure is dependent upon composition and temperature. It origins from fossil fuels (crude oil and natural gas extraction). NG, that in Slovenia and neighboring countries consists mostly of methane, is offered in two forms: Compressed Natural Gas (CNG) and Liquefied Natural Gas (LNG). Compressed natural gas is kept at approx. 200 bar pressure in gas cylinders mounted on the vehicles. Due to relatively low density it is used as a fuel for personal vehicles or in HD vehicle fleet with lower daily mileage (city transport, garbage collectors,…). Gas cylinder to gaseous fuel weight ratio is high and can be lowered to some extent by using new lightweight composite gas cylinders (Type II to Type V).

Table 1: Diesel fuel, LPG and NG properties

100

H/C ratio

RON

lower heating value

price per energy unit

unit

[/]

[MJ/kg]

[€cent/MJ]

diesel fuel

~ 1.9

15–25

43.0

2.849

LPG

~ 2.61

~ 105

46.1

2.144

~ 120

49.5

1.857

LABORATORY FOR INTERNAL COMBUSTION ENGINES AND ELECTROMOBILITY YEARBOOK 2016

LNG is kept in liquid form in isolated containers at -163°C. Due to higher energy density per unit volume it is more suitable for international long-haul transport. LNG containers are capable to withstand pressure above ambient to keep the boiled-off natural gas in the tank for several days to mitigate the fuel loss. Namely, emitting NG in the ambient air has also big greenhouse effect. Some properties of diesel fuel, LPG and NG are presented in Table 1. Stated prices were collected on 3rd of January, 2016 in Slovenia and are subjected to constant changes. But price relationship has been constant for many years where diesel fuel price is the highest and natural gas price the lowest. There are HD vehicles offered on the market equipped with spark ignition engines that use NG as a fuel. Due to lower effective efficiency of spark ignition engines compared to compression ignition engines CO2 emission of NG fueled HD vehicles is comparable with CO2 emissions of diesel fueled HD vehicles [3]. Moreover the positive economic effect of lower fuel prices per energy unit of NG is mitigated with lower engine efficiency [4]. With dual fuel operation gaseous fuels are converted in the engine to mechanical energy with the efficiency of a compression ignition engine. When using aftermarket conversion kit compressed homogeneous mixture of air and gaseous fuel is ignited with diesel fuel injection. Duel fuel conversion of a HD vehicle powered by compression ignition engine is not cost and time demanding and return on investment (ROI) is reported short – from ½ a year to 1½ year. ROI is shorter with LPG system due to lower cost of fuel tank system, but fuel savings are higher with NG due to lower price per energy unit and higher Research Octane Number (RON) that enables higher diesel fuel substitution rate (Table 1). DUAL FUEL CONVERSION There are several systems offered on the market for a dualfuel conversion. The system is identical for both fuels (LPG and NG) from gas pressure regulator on. Depending on the type of the fuel the fuel tank system with gasifier/pressure regulator is different for LPG; CNG and LNG. Gaseous fuel storage on the vehicle and pressure control devices The fuel tank for LPG on HD vehicles is a vessel with a volume of several hundreds of dm3. Volume is stated in volume units of water capacity. Full vessel contains approx. 80% of liquid LPG, rest is in gaseous state. Optimal size of the vessel has to be carefully determined to provide suitable autonomy in-between refills and not to big mass gain of the HD vehicle when the tank is full. Vessel is equipped with fuel gauge, filling valve, overpressure safety valve and outlet solenoid valve (Figure 1). Liquefied gas is vaporized in a reducer that is a combined vaporizer and pressure regulator. Vaporizer is heated with engine cooling liquid. Since the dual-fuel engines are equipped with turbochargers and gas is usually injected after compressor, the gas pressure at the reducer exit is sum of the pressure after compressor and preset overpressure. Due to this reason reducer has to be connected by a hose

to the inlet manifold to get the manifold pressure information to be able to regulate preset pressure difference.

Figure 1: LPG tank - 250 liters water capacity – mounted on a truck;, A- filling valve, B- overpressure safety valve, C- outlet solenoid valve, D- fuel gauge with electric output

CNG is stored in a gas cylinders on the vehicle at approx. 200bar when full. Energy to volume and mass ratio is not optimal for long-haul operation. There are five types of gas cylinders present on the market. Type I is fully metal cylinder and is the cheapest and the heaviest option. Type II and Type III cylinders have a metal liner and a fiber-reinforced polymer overwrap. Type IV and V are of metal-free construction. They are the most expensive and the lightest, certified use time is twice longer, storage pressure can be higher than above mentioned 200bar (up to 350 bar). Pressure regulators are usually two-stage regulators heated with engine cooling liquid. The same as with LPG reducer a CNG pressure regulator provides constant overpressure over manifold pressure. LNG is usually stored on the vehicle in double wall tanks with a combined vacuum and insulation system. Newer designs omit vacuumed double wall systems and replace it with a low heat-leak insulation (e.g. aerogels). The tank is sealed since methane emission from the tank is not allowed. The heat penetrates the insulation and some of LNG vaporizes. If the engine is running the boiled-off methane is consumed by the engine. The tank is capable to withstand the pressure that builds up in the tank up to five days or more of vehicle non-use that is a rare case with commercial vehicles. Fuel is delivered to the engine through delivery valves, vaporizer, pressure regulator chain with different topologies. Fuel delivery system The fuel system can be identical and independent of the gaseous fuel used from pressure regulator on. Dual-fuel systems are usually developed on the basis of the gasoline engine bi-fuel (gasoline, gaseous fuel) conversion kit. Fuel is filtered after pressure regulator, gaseous fuel temperature and pressure are measured before being delivered to the injection valves. Gaseous fuel can be injected at several places in the intake system. First option is to fumigate the intake air in front of the compressor. Since the pressure at the compressor inlet is approx. the ambient pressure, pressure regula-

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tor should deliver constant absolute pressure at the outlet. Second option is to inject the fuel into the intake air after compressor; before or after intercooler (Figure 2). Pressure regulator delivers the gaseous fuel at the outlet at the constant pressure difference between pressure regulator outlet pressure and pressure after compressor. Injection at earlier stages insures better mixture homogenization but special care should be devoted to mixture handling at the engine stop. Diesel only engine operation just before engine stop is preferred to avoid the possible escape of the mixture to the atmosphere and is common and usually inherent to idling.

communication with vehicle information network offers additional opportunity for fine tuning of GFECU control parameters. The most advanced GFECU’s take control over diesel fuel injector timing. Wires from engine ECU to the diesel injectors are interrupted and connected to GFECU to obtain the diesel fuel injection timing information. Diesel injectors are controlled and energized by GFECU. Some newer systems are equipped also with knock sensor that is attached to the engine block. Since to big diesel fuel substitution rate can lead to engine knock (see Table 1 for fuel specific RON) the sensor supports either GFECU calibration and is inactive during normal operation or detects knocking and lowers gaseous fuel quantity also during normal operation. CONVERSION CHALLENGES AND EXPERIENCES

Figure 2: Fuel delivery system of diesel-LPG dual fuel conversion kit: 1- reducer, 2- gas filter, 3- injection valves, 4- injection into intake manifold, a- intake manifold and gas pressure sensor, breducer temperature sensor, c- gas temperature sensor, d- engine cooling liquid inlet and outlet, e- gas outlet, f- intake manifold pressure to pressure sensor and reducer

Third option is sequential injection to the intake port. Gaseous fuel delivery to the each individual cylinder is more precise. Camshaft position signal has to be delivered to the Gaseous Fuel Electronic Control Unit (GFECU) for precise injection timing. Special care has to be devoted to insure adequate (homogeneous) in-cylinder gas-air mixture. The most advance option is the direct injection of the gaseous fuel to the cylinder after short diesel injection that assures favorable conditions for gaseous fuel combustion. Although this option is the most promising dual-fuel technology for OEM’s there is a low probability that it will be suitable also for aftermarket conversions due to higher complexity, demanding conversion, where engine head has to be modified, and price. Electronic control unit GFECU manages injection of the gaseous fuel into the intake system. GFECU with diverse complexity can be found on the market. Simpler systems, that are also cheaper to produce, control the injection of the fuel before or after compressor. Operation and delivery quantity is determined upon several measured parameters: reducer temperature, gaseous fuel temperature and pressure, intake manifold pressure, exhaust gases temperature, accelerator pedal position, engine speed and pre-calibrated look-up tables. To reduce the injected diesel fuel quantity that is replaced by gaseous fuel, accelerator pedal position signal is emulated - lowered accordingly. More complex GFECU’s offer sequential injection of the gaseous fuel into intake port. Additionally camshaft position sensor signal is required for that purpose. CAN 102

HD vehicles are designed for longer operation than light duty vehicles. For example: long-haul truck is expected to cover over 1 million kilometer without major engine overhaul. Expected range of light duty vehicle is about four times shorter. This has to be taken into account also during the design of dual-fuel conversion kit for HD vehicles. The conversion should effect the truck reliability as low as possible. The gaseous fuel tank(s) equipped with safety valves, electric shut-off valves, fuel gauges, filling valves,… is(are) usually mounted in-between the front and rear wheel (Figure 1) or in the space between the cabin and the trailer. Other components are mounted in the vicinity of the injection valves to make the connections as short as possible to lower the risk of hose or wire damage and to shorten the system response time. Reducers (pressure regulators) needs to be heated with engine cooling liquid. Suitable outlet and inlet should be defined on the engine cooling systems. GFECU is preferably mounted in the cabin where ambient conditions are more favorable. It is important to follow and mimic OEM HD vehicle cabling layout. That enables fast servicing of the vehicle. A big advantage of a dual-fuel engine conversion is that with a simplified systems, where GFECU does not interfere with engine ECU signals, a malfunction of a gaseous fuel system in most cases doesn’t interrupt truck operation. Gaseous fuel system is simply switched off and engine is power only by diesel fuel. More advanced systems that offer higher level of diesel and gaseous fuel injection control are sometimes prone to higher risks of malfunction. Malfunction of the GFECU can in such case jeopardize the truck operation. Direct connection to the vehicle information network (usually CAN protocol) represents another risk for reliable operation. Namely, original network was not designed for connection of GFECU to the network and information about CAN network available from OEM’s is usually limited. Such system can on the other hand offer somewhat higher diesel fuel substitution rate and better engine control. Homologation of the vehicle dual-fuel conversion is not standardized on the EU level and there are big discrep-

LABORATORY FOR INTERNAL COMBUSTION ENGINES AND ELECTROMOBILITY YEARBOOK 2016

ancies in the homologation procedures. In some countries vehicles are submitted to strict EURO exhaust emission type approvals, in some countries all the gaseous fuel system components should prove CE marking and vehicle is still considered and inspected as diesel only fueled vehicle. After dual-fuel conversion kit installation additional care has to be devoted to system servicing and maintenance. Gaseous fuel filters need to be replaced at defined intervals, maintenance of pressure regulators/vaporizers and injection valves is mandatory. Systems detect system malfunction and possible fuel leaks and switch immediately to diesel only operation. Since duel-fuel conversion procedure is relatively simple and not time demanding there is always the possibility to transfer the system from vehicle to vehicle if necessary. This is especially important for CNG and LNG fuel containers that represent the most expensive part of the conversion kits. The environmental impact of the dual-duel conversion should also be considered. Authors [5], [6] report that PM10 mass emission could be substantially lowered by duel-fuel operation. NOx emission are reported to be at the same level whereas CO and THC emission usually increase since there are regions in the cylinder where combustion of lean homogeneous air fuel mixture is not optimal: crevice between the piston and cylinder wall, near cylinder wall regions,.. The use of diesel oxidation catalyst should be considered. If already existing, catalyst capacity should be revised. Special methane catalysts may be necessary for NG dual-fuel operation. CONCLUSIONS Dual-fuel aftermarket conversions could serve as an important incentive on the deployment of natural gas infrastructure, especially LNG. ROI for LNG infrastructure could be relatively long and unstimulating if it would depend only on newly purchased NG vehicles. Aftermarket conversion of diesel fueled HD vehicle to dual-fuel operation could increase the use of gaseous fuels to such extent that would additionally stimulate setting up the infrastructure. It is necessary to harmonize the homologation procedures on the EU level to mitigate the discrepancies existing between the countries. Homologation procedures should motivate also aftermarket conversion and lower administrative and bureaucratic obstacles. The emphasis should be devoted to harmful exhaust emissions and safety issues. Dual-fuel conversions offer possibility to tackle fuel costs and harmful exhaust emission (especially particles) of older diesel fueled HD vehicles that are still numerous in eastern and south-eastern European countries and are expected to be in use still for many years. Reduced fuel costs is the motivation for the owners. Legislators are motivated also by reduced particle and CO2 emissions.

References [1] ERTRAC. Energy Carriers for Powertrains - for a clean and efficient mobility, Version: 1.0, ERTRAC Working Group: Energy and Environment, NGVA Europe, 27.02.2014. [2] Directive 2014/94/EU of the European parliament and of the council of 22 October 2014 on the deployment of alternative fuels infrastructure [3] RODMAN OPREŠNIK, Samuel, SELJAK, Tine, VIHAR, Rok, KATRAŠNIK, Tomaž. Real-world emissions and vehicle parameters of different bus powertrain technologies. V: 6th International Conference on Sustainable Energy and environmental protection, SEEP 2013, 20th - 23rd of August 2013, Maribor [4] GERBEC, Marko, RODMAN OPREŠNIK, Samuel, KONTIĆ, Davor. Cost benefit analysis of three different urban bus drive systems using real driving data. Transportation research. Part D, Transport and environment, vol. 41, pp. 433-444, 2015 [5] LIJIANG, Wei, PENG, Geng. A review on natural gas/ diesel dual fuel combustion, emissions and performance, Review Article, Fuel Processing Technology, Volume 142, pp. 264-278, February 2016 [6] ASHOK, B., DENIS ASHOK, S., RAMESH KUMAR, C.. LPG diesel dual fuel engine – A critical review, Alexandria Engineering Journal, Volume 54, Issue 2, pp. 105-126, June 2015 List of publications [7] GERBEC, Marko, RODMAN OPREŠNIK, Samuel, KONTIĆ, Davor. Cost benefit analysis of three different urban bus drive systems using real driving data. Transportation research. Part D, Transport and environment, vol. 41, pp. 433-444, 2015 [8] VIHAR, Rok, SELJAK, Tine, RODMAN OPREŠNIK, Samuel, KATRAŠNIK, Tomaž. Combustion characteristics of tire pyrolysis oil in turbo charged compression ignition engine, Fuel, vol. 150, pp. 226-235, Jun. 2015, [9] RODMAN OPREŠNIK, Samuel, SELJAK, Tine, BIZJAN, Frančišek, KATRAŠNIK, Tomaž. Exhaust emissions and fuel consumption of a triple-fuel sparkignition engine powered passenger car, Transportation research. Part D, Transport and environment, vol. 17, iss. 3, pp. 221-227, 2012

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Combustion in microturbines assessment of methodology and innovative solutions for utilization of alternative fuels ABSTRACT → The paper presents an insight into interrelation between specific fuel properties and their impact on mixture formation, combustion and emission formation phenomena in a MGT for stationary power generation as well as their impact on material corrosion and deposit formation. The objective of this study is to identify potential issues that can be related to specific fuel properties and to propose counter measures for achieving stable, durable, efficient and low emission operation of the MGT while utilizing advanced/innovative fuels. In addition, cross influences of particular counter measures are also addressed as the MGT system needs to be addressed holistically. Holistic approach is reflected in the scope of the analysis that covers entire fuel and gas path as well as in the applied methods. Analysis of spray velocity field via fast spray imaging revealed promoted mixture

formation process and thus reduced spray penetration lengths by increasing the atomizing air pressure and the fuel temperature, which is of particular importance for the fuels with high viscosity. Cross-relation of these results with exhaust emissions provided boundaries of the multi-objective constraint space in terms of fuel composition, temperature, primary air temperature (PAT) and turbine inlet temperature (TIT) for efficient operation of the MGT with tested fuels. Cross influences as for example positive effect of low pH neutralization, should be balanced with increased NOx emissions imposed by the neutralization, while both need to be balanced with optimum fuel temperature in the case of high viscosity fuels. Considering the deposits, sulphur content and several sulphate as well as oxide deposits are critically influencing hot-corrosion phenomena and abrasion damage of hot components.

INTRODUCTION Tine Seljak Laboratory: Laboratory for internal combustion engines and electromobility E-mail: tine.seljak@fs.uni-lj.si Room: 305 Phone: +386-1-4771-701 Status: PhD student (started: September 2011, to be completed: November 2016) Research area: Alternative fuels Mentor: assoc. prof. Tomaž Katrašnik assoc. prof. Matjaž Kunaver

104

In general, research of alternative/ innovative fuels initially focuses on fuel properties and mixture formation, combustion as well as emission formation phenomena. This 1st level analysis is certainly a prerequisite for utilization of such fuel. However, to ensure also stable and durable operation of the MGT while using alternative/innovative fuels a 2nd level analysis is necessary, that addresses also degradation of materials and degradation of component functionality. In case of diesel-like fuels, a decoupled 1st and 2nd level analysis is often sufficient. This is not necessarily the case for fuels with deviant and thus less favorable properties, where potentially a strong interrelation of the phenomena listed in blocks in Figure 1 might exist. In this case a coupled analysis addressing fuel properties, mixture formation, combustion and emission formation phenomena as well as degradation of materials and degradation of component functionality is necessary. Such holistic ap-

proach ensures that the design space is constrained early in the design or adaptation process, providing a basis for efficient and optimized engine adaptation process and eliminating the need for reverse steps in adaptation procedure. To steer and to support such a decision-making process, the paper presents methodologies and innovative approaches for defining borders of design space and for identifying interrelated phenomena among fuel properties, combustion and emission formation, degradation of materials and degradation of component functionality.

Figure 1: Feasibility analysis of innovative fuels.

LABORATORY FOR INTERNAL COMBUSTION ENGINES AND ELECTROMOBILITY YEARBOOK 2016

MATERIALS Fuels Analysed fuels were selected with the aim to demonstrate the applicability and robustness of methodology and to demonstrate significantly different adaptation requirements of MGT driven by significantly different fuel properties. Waste tire pyrolysis oil (TPO) [1] and liquefied wood [LW] was thus selected as a fuel, which features physical properties that are similar to the ones of the conventional diesel fuel, and liquefied wood (LW) was selected as a fuel, which represents a fuel with significantly deviant physical and chemical properties. Findings from the LW can be, with reasonable caution, transferred also to the biomass pyrolysis oil. Two different formulations were tested; LW1 with pH value 2.5 and LW2 with partially neutralized acid catalyst giving a pH value of 5.5 (as visible from Table 1)

AFter immersion, corrosion rates were caluclated according to Equation 1.

Gaseous combustion products in combustion engines, particularly in those with diffusive combustion process, are accompanied by soot and in case of impurities in the fuel also by ash which might significantly reduce the functionality of hot components. In case of high quality and purified fuels these are mainly consisting of soot, in low quality fuels originating from materials rich in inorganic constituents also notable amount of ash can be present. Combustion deposits were collected on location shown in Figure 2 and analyzed with electron-dispersive x-ray (EDX) spectroscopy.

Table 1: Properties of the tested fuel

TPO

LW 1

LW 2

C [wt.%]

84.53

87.0

47.60

47.52

H [wt.%]

10.66

13.0

7.98

8.00

N [wt.%]

0.725

0.19

0.34

S [wt.%]

0.960 0.001

0.89

O [wt.%]

2.03

43.34

43.26

Density [kg/dm3]

0.923

0.838

1.30

20.2

Water [mg/kg]

118

200

LHV [MJ/kg]

41.0

42.2

Stoichiometric ratio

13.8

14.7

6.8

Viscosity [mm2/s]

3.94 @ 20°C

3.25 @ 40°C

80 @ 100°C

pH value

4-5

5.5

2.5

5.5

Figure 1: Location for collection of deposits.

Combustion and emission formation characteristics are evaluated through emission and thermodynamic readings. The wet emissions were measured with: • non-dispersive infrared method • chemiluminiscence method • flame ionization detector… To remove the ambiguity of results with different equivalence ratios, the emissions were corrected to 15% excess O2 in exhaust gasses. RESULTS, DISCUSSION

Analysis of corrosion, deposits and emissions Immersion tests were performed for both LW formulations at two different temperatures of the fuel, 80°C and 120°C. The first temperature corresponds to the minimum required temperature for obtaining the stable combustion process and the second corresponds to the maximum estimated temperature in the preheating system (heater surface temperature). The shape of the specimens is given in Figure 3. Tested materials included three major austenitic steels, which are most often used in the process equipment. They are listed in Table 2 along with key immersion and specimen conditions.

Material degradation The corrosion rates for LW1 are presented in Figure 2 for LW1 and LW2.

able 2: Tested materials and conditions DIN EN

AISI

Immersion time and temperature

Sample preparation

X2CrNiMo17132

316L

X6CrNiMoTi1712 2

316Ti

X5CrNi1810

304

Sanding P80 -> P220 720 h @ 120°C, 80°C -> P120 (hand finish)

Figure 2: Corrosion rate for LW1 (left) and LW2 (right).

Corrosion rates in case of LW1 and fuel temperature 80°C were low and barely noticeable and are also well below generally acceptable limit for precise equipment (valves, pumps) -120 µm/year. In case if precise

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tolerances would be required, (i.e. high pressure pumps, fuel injectors) lower limits of acceptable corrosion rate might be applicable. In case of elevated temperature (120°C), the corrosion rates are increased significantly (Figure 2 – left). 304 stainless steel thus turns out as unsuitable, whereas 316L and 316Ti are on the borderline of suitability for process equipment in the fuel system. Unlike for the LW1, corrosion rates are unaffected by the temperature increase for the LW2 – pH 5.5. Note that the changes in corrosion rates between materials and temperatures for LW2 (Figure 2- right) are in the range of mass measurement uncertainty. This confirmed the known fact that pH value is one of the main factors responsible for corrosion rate increase. Therefore, measures to elevate the pH value of the fuel by additional after treatment step could expand the list of suitable materials for equipment in fuel conditioning system. Hot path deposits The major constituents of LW1 ash should mainly consist of wood ash - Ca and K, followed by Mg, Mn and P [2]. After performing SEM and EDX analysis, the results in Figure 3 were surprising to a certain extend as large amounts of Fe were detected, hence the red colour of deposits. The colour most likely corresponds to a large amount of Fe2O3 (having a light red colour) and less likely to Fe3O4. To exclude the possibility of significant Fe3O4 content deposits were tested in magnetic field which revealed that deposits do not exhibit ferrimagnetic properties, but are well attracted to magnetic field (a property of Fe2O3). Other possible constituents are also Fe(OH)2 and also FeSO4 or Fe2(SO4)3 due to significant sulphur presence. Since basic constituents of LW1 do not contain notable amounts of Fe, this should be considered as a contaminant, introduced either through impurities in fuel production process or through corrosion products on process equipment used. On Figure 4, deposit morphology is presented, revealing mainly cenospheres.

Figure 3: EDX spectra of deposits

Figure 4: Morphology of deposits and area for acquiring EDX spectrum

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The formation of aforementioned oxides most likely happens in near-flame region, where sufficiently high temperatures (>1000°C) result in melting of inclusions in the fuel. After leaving the primary zone of the combustion chamber the metal oxides quickly solidify and follow the hot gasses flow path, thus taking the shape of cenospheres, which are visible in Figure 16. While oxides have a relatively high melting point it is likely that they hit the hot path surfaces in solid form which can cause significant abrasion problems. Unlike iron oxides, listed iron sulphates have significantly lower melting point (below 800°C) and are at the point of deposit collection and turbine rotor most likely still in the liquid form. The molten ash then usually sticks to the surface of hot components [3] which can cause fouling problems that influence the efficiency and dynamics of the turbine rotor. Additional problem that occurs with sulphates is the occurrence of hot corrosion through sulphidation attack. Emissions LW1 and TPO was characterized against PAT and TIT. For both fuels significant impact of PAT and TIT on CO (Figure 5 - left) and NOx (Figure 5 - right) emissions was revealed. At lower TIT, significantly higher CO emissions are characteristic for LW1 than for other fuels in the entire range of operating parameters, which is in line with physical and chemical properties of the LW1. CO emissions of LW1 are then notably reduced with higher TIT. Similar influence can be observed with high PAT, where CO emissions are notably reduced with increasing PAT. These findings indicate that in the current state of the art MGT systems, where TIT is above 950°C and PAT is also very high due to the use of regenerative Brayton cycle, the CO emissions of LW1 could drop to a manageable level. CO emissions of the TPO and the baseline D2 fuel exhibit very little or no dependence on the TIT and on the PAT, thus even relatively low temperature levels in the combustion chamber (i.e. low PAT and low TIT) lead to an efficient combustion process. At the same time, increasing PAT increases NOx emissions of all analyzed fuels. Simultaneously, it can be seen from the results at high PAT NOx emissions increase with TIT for all analyzed fuels. This indicates that high PAT, combined with high TIT might be beneficial for CO reduction, but could pose a problem when optimizing the NOx emissions. The differences between different fuels in terms of NOx emissions can be mainly attributed to high fuel bound nitrogen content (FBN) in TPO and slightly lower FBN in LW.

Figure 5: CO(left) and NOx(right) emissions at different primary air temperatures

LABORATORY FOR INTERNAL COMBUSTION ENGINES AND ELECTROMOBILITY YEARBOOK 2016

In addition to analyses on the impact of TIT and PAT, it is important to assess also the impact of fuel preheating temperature on the emission trends, which was performed for the LW1 representing fuel with high viscosity that needs to be subjected to fuel preheating. It was shown in that starting at low fuel temperature, CO emissions first decrease from 90°C to 100°C and then again increase towards fuel temperature 110°C as shown in Figure 6 - left, with decreasing trend being more pronounced at low TITs and increasing trend being more pronounced at high TIT. The first trend can be attributed to reduction of viscosity with increasing fuel temperature, while the latter trend is a consequence of coke formation on fuel injection nozzle, suggesting that fuel preheat temperature should be precisely controlled not to exceed 100°C. It was also shown in that fuel temperature does not significantly alter NOx emissions and thus NOx emissions need not to be treated as a design constraint for fuel conditioning system.

Figure 6: CO and NOx emissions at different fuel temperatures (left) and different fuel formulations (right)

In Figure 6 – right it is shown that fuel neutralization insignificantly influences CO emissions, whereas it is also shown that elevation of NOx emissions is directly proportional to the degree of neutralization. The increase in pH value from pH 2,5 to pH 5,5 results in approximately 30% increase in NOx emissions. Neutralization, being a significant measure to reduce corrosiveness of the fuel, increases NOx emissions through the FBN mechanism, however despite this fact it can be seen as an efficient measure as it significantly increases range of potential material for the fuel supply system while only moderately increasing NOx emissions. CONCLUSIONS • Immersion tests and weight-loss analyses revealed that fuel temperature of 80°C allows the use of 304, 316L and 316Ti steels in the fuel system components for relatively wide range of pH values. • The effect of partial neutralization of the fuels translated into increased NOx emissions over entire operating range of the MGT due to higher amount of the FBN in the fuel, while CO and THC emissions were not influenced. • In case of fuels with significant amount of impurities, sulphur, iron, potassium and calcium deposits in form of sulphates and oxides were identified, leading to occurrence of hot-corrosion. • Regarding thermodynamic parameters, the use of high PAT is beneficial to reduce the CO emissions, however this again influences the NOx emissions by elevating them.

• Similar influence is also observable with TIT, but the maximum achievable TIT would most likely be constrained by NOx emissions. • For high viscosity fuels, reduction of CO emissions is also possible through elevation of fuel temperature, although in the case of low pH values this is constrained by corrosion in fuel system, which is offset by neutralization that in turn elevates NOx emission. For a fuel with high viscosity and low pH value, a trade-off between PAT, TIT and pH value of the fuel is necessary to obtain minimum CO and NOx emissions. • Corrosion in the fuel system during optimization of emissions must be necessarily avoided as it can also influence the quantity and composition of deposits on hot components of the MGT. References [1] Martinez J.D., Puy N., Murillo R., Garcia T., Victoria N., Mastral A.M. Waste tyre pyrolysis – A review. Renewable and Sustainable Energy Reviews, Vol. 23, pp 179-213, 2013. [2] Werkelin J., Skrifvars B.J., Hupa M. Ash-forming elements in four Scandinavian [3] wood species. Part 1: Summer harvest. Biomass Bioenerg Vol. 29, pp 451-466, 2005. [4] Sreedharan S.S., Tafti D.K. Composition dependent model for the prediction of syngas ash deposition in turbine gas hotpath. International journal of heat and fluid flow. Vol. 32, pp 201-211, 2011.Phasellus cursus justo non tellus sodales maximus. List of publications [5] Seljak T., Kunaver M., Katrašnik T. Emission evaluation of different types of liquefied wood. Stroj Vestn-J Mech E, Vol. 60, pp 221-231, 2014 [6] Seljak T., Rodman O.S., Katrašnik T. Microturbine combustion and emission characterisation of waste polymer-derived fuels. Energy, Vol. 77, pp 226-234, 2014. [7] Seljak T., Rodman O.S., Kunaver M., Katrašnik T. Wood, liquefied in polyhydroxy alcohols as a fuel for gas turbines. Applied Energ, Vol. 99, pp 40-49, 2012. [8] Seljak T., Rodman O.S., Kunaver M., Katrašnik T. Effect of primary air temperature on emissions of a gas turbine, fired by liquefied spruce wood. Biomass Bioenerg, Vol. 71, pp 394-407, 2014. [9] Seljak T., Širok B., Katrašnik T. Combustion in microturbines: assessment of methodology and innovative solutions for utilization of alternative fuels. 10th Conference on Sustainable Development of Energy, Water and Environment Systems, September 27 - October 2, 2015, Dubrovnik, Croatia [10] Seljak T., Katrašnik T. Designing the microturbine engine for waste-derived fuels. Waste Manage, Vol. 47, pp 299-310, 2016.

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Advanced combustion concepts with innovative waste derived fuels ABSTRACT → Strict European emission standards and rising fuel prices demand engines with cleaner combustion and increased fuel efficiency. Therefore an experimental dual-fuel engine that allows for reactivity controlled compression ignition or homogeneous charge compression ignition is being developed on the basis of the diesel engine from a mid-sized passenger car. To achieve sufficient results, the control of fuel injection has to be capable to adapt the fuel injection

depending on the operating point of the engine. Goal of the research is to modify Diesel engine in order to achieve low emissions and high thermal efficiency of the engine while still enabling as wide operating range as possible in terms of engine load and speed, transient operation and varying ambient conditions while utilizing innovative waste derived fuel that have not yet been used in similar combustion strategies.

INTRODUCTION Urban Žvar Baškovič Laboratory: Laboratory for Internal Combustion Engines E-mail: urban.zvar-baskovic@fs.uni-lj.si Room: 310 Phone: +386-1-4771-310 Status: PhD student (started: December 2013, to be completed: September 2016) Research area: Internal combustion engines Mentor: Assoc. Prof. dr. Tomaž Katrašnik

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Figure 1: Low temperature combustion concepts

Compression ignition engines with heterogeneous charge (Diesel engines) are widespread both in transport as well as in stationary systems for generation of the electricity because of their higher efficiency in comparison to the Spark Ignition (SI) Otto engines. Diesel engines are characterized by high concentrations of particulate matter and nitrogen oxides (NOx) emissions due to the combustion of heterogeneous charge. In order to comply with stricter emission limits, use of complex exhaust aftertreatment systems and/or the introduction of advanced combustion strategies is required. Complex exhaust aftertreatment systems cause an increase in weight, complexity and price of the vehicle. Therefore the advanced combustion concepts which possess the potential for reducing the emissions of pollutants while maintaining or even increasing the indicated engine efficiency are being intensively researched. The development is focused on the Low-Temperature Combustion (LTC) concepts, as the low local tem-

perature prevents local formation of high NOx concentrations, with a high degree of charge homogenization or homogeneous charge, which is crucial for achieving low emissions of particulate matter. LTC concepts with high degree of charge homogenization thus potentially enable achieving low tailpipe-out emissions by using only an oxidizing catalytic converter, which significantly simplifies the exhaust aftertreatment systems. Currently the most widely used strategies for the LTC concepts with a high degree of charge homogenization are Homogenous Charge Compression Ignition (HCCI), Premixed Charge Compression Ignition (PCCI) and Reactivity-Controlled Compression Ignition (RCCI), as presented in Figure 1. In HCCI engines fuel is homogenously mixed with the inlet gas generally consisting of air and high concentration of recirculated exhaust gasses (EGR) and thus combustion process is driven by local chemical kinetics. In HCCI engine there is no explicit control over the start of combustion and therefore several engine operating parameters, among which gas temperature, air/fuel ratio and exhaust gas recirculation (EGR) rate have to be adjusted in order to achieve a desired combustion evolution, where knocking should be avoided on one hand and incomplete combustion or even misfire on the other. Therefore, very complex control is required to run the HCCI engines even in stationary applications, whereas operating over wide range of

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engine speeds and load, fast transient and varying ambient conditions impose sever additional challenges limiting applicability of the HCCI combustion concept. One of the approaches to increase robustness of the combustion process over the HCCI is a premixed charge compression ignition (PCCI). In the PCCI engine the fuel is injected at the beginning of the compression stroke and late injection follows when the piston is approaching the top dead center. With the late injection it is possible to better control the start of combustion, which makes the PCCI engine more applicable to real world vehicle application and easier to control. The third LTC concept is a reactivity controlled compression ignition (RCCI) combustion concept, where multiple (typically two) fuels with different reactivity are employed to obtain better control over the combustion process. Low-reactivity fuel is injected in the cylinder with port injection and high-reactivity one follows with direct injection later in the cycle. In addition to increasing efficiency and lowering emissions of internal combustion engines, the search for alternative sources of energy to power internal combustion engines continues because of reduction of fossil oil reserves. Furthermore, growing problem of disposal of slowly degradable waste, among which car tires represent a big portion, makes waste-to-fuel technologies a logical step towards the alternative fuels. Several conversion processes have been developed to transform solid waste disposals into liquid fuels which have similar physical characteristics to conventional automotive fuels and could be therefore used in the conventional engines with small adaptations of the engine control. Various types of pyrolysis are widely used for producing the fuels. One of the waste derived fuels that can be of interest for the LTC is Tire Pyrolysis Oil (TPO), which features Diesel-like fuel physical properties that allow its direct injection at high pressures without additives. It features lower Cetane number then the Diesel fuel due to a high aromatic content, which is very favorable for combustion concepts with high level of charge homogenization. One potential usage is local TPO production and its direct use in stationary power generation. RESEARCH PROBLEM In the research we will thus focus on fuels with similar physical characteristics as the Diesel fuel and lower reactivity rate, which will be denoted Diesel-like Fuels with Lower Reactivity (DFLR). One of the main representatives of the DFLR that will be examined is certainly the TPO, however the research is open to find potential DFLRs that better fulfill requirement of the PCCI or RCCI with research partners in the fuel production area. Many studies of DFLRs and in particular of the TPO therefore propose blending a DFLR with the Diesel fuel, using Cetane improvers or pre-heating of the air in the intake system, when applying it in the Diesel combustion process. Possible solution for the addressed issue is the use of DFLR in LTC engines in which highly homogenous charge is desired calling for fuel with lower reactivity compared to the Diesel fuels. In the PCCI engine, low reactivity of the fuel reduces risk of the engine knocking, therefore higher compression ratios can be used for the application of DFLR in

the PCCI engine, which results in higher thermal efficiency. Furthermore lower reactivity of the fuel allows the controller to inject higher percentage of the desired fuel towards the beginning of the compression stroke, which results in more homogenous charge, lower local combustion temperatures and lower NOx emissions. It is anticipated that the PCCI combustion concept could be used in combination with DFLRs at low to mid loads, whereas to achieve higher Break Mean Effective Pressures (BMEP) and to avoid low level of charge homogenization, the RCCI combustion concept could be beneficial. In this case the second fuel will feature lower reactivity than the DFLR and will be denoted as Low Reactivity Fuels (LRF). One of the potential candidates due to its low reactivity, wide availability and low price is the natural gas (NG). The aim of this approach is thus to ensure high level of charge homogenization in compression ignition engines to achieve low emissions and high efficiency while still enabling as wide operating range as possible in terms of engine load and speed, transient operation and varying ambient conditions. To investigate PCCI and RCCI combustion concepts it is necessary to extend hardware and software functionalities of the baseline engine. A moderate set of extension thus generally cover fuel injection and EGR systems as well as engine control. Fuel injection system should allow for fast control over injection pressure and timing, while additional port injector needs to be added for the RCCI combustion concept. EGR systems have various topologies among which a combination of cooled and uncooled recirculated gases is the best choice for the use in LTC engines, which are operated without external heaters. Originally, various sensors and actuators that control described sub-systems are controlled by an engine control unit (ECU) with restricted access for the user and therefore, development of an independent controller that allows for fast and independent actuation of all actuators required for the PCCI and RCCI combustion concept is inevitable. A significant challenge from the hardware and software point of view is thus in particular fast and independent actuation, whereas it is certainly necessary to ensure also high level of robustness. Historically, engine experimental studies were carried out by the Âťone factor at a timeÂŤ approach, in which just one factor is being varied while others are held at the constant position. As such an approach is not feasible to explore the vast multidimensional space imposed by the PCCI and RCCI combustion concepts. A design of experiment theory can be used to determine simultaneous factor variations with the aim to efficiently explore the design space. Furthermore, these inputs can be used for optimization of the controlled parameters with the Pareto optimum theory, which delivers input parameters to calibrate the engine controller. One of the most important control parameters for PCCI and RCCI combustion concepts is the in-cylinder pressure, which is commonly measured with the piezo technology that does not yield the absolute in-cylinder pressure. Procedures of referencing an indicated incylinder pressure to the absolute in-cylinder pressure are called pegging. Second issue when calculating representative thermodynamic combustion parameters of

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the engine is the precise knowledge of the piston TDC position, which crucially influences accuracy of the RateOf-Heat-Release (ROHR) and Indicated Mean Effective Pressure (IMEP) evaluation. To efficiently control PCCI and RCCI combustion concepts in real-time, the third focus of the research will be directed into development of the innovative numerical method for simultaneous determination of the pressure offset and the TDC position. METHODOLOGY Within the framework of the doctoral thesis, an experimental engine for analyzing PCCI and RCCI combustion concepts will be designed by converting one of cylinders of a commercial turbocharged Diesel engine to allow for the PCCI and RCCI operation. In the PCCI combustion concept engine will be powered by an innovative DFLR, for which no additives have to be used and no modifications of fuel system have to be made. It is expected that the use of the DFLR will allow for a wide range of operating conditions in the PCCI combustion concept. Transition to the RCCI operation and addition of the LRF is expected to enable operation at higher engine loads because of lower reactivity of the DFLR compared to other commonly used high reactivity fuels. The aim of this approach is to ensure high level of charge homogenization in compression ignition engines to achieve low emissions and high thermal efficiency while still enabling as wide operating range as possible in terms of engine load and speed, transient operation and varying ambient conditions while utilizing innovative waste derived fuels that have not yet been used in similar combustion concepts. It is not feasible to equip high volume series production engines with very accurate sensors for determination of the absolute pressure and the TDC position, which provide essential input parameters for engine control parameters calculation. Even in these cases it is necessary to have some level of redundancy, therefore innovative numerical method for simultaneous determination of absolute pressure and the TDC on the basis of calculated ROHR trace will be developed. Most of the methods for TDC position determination, presented in the overview of the literature are based on the motoring in-cylinder pressure, which cannot be measured during fired operation of the engine and thus those methods cannot determine the TDC position for various operating points of the engine. Although some pressure offset determination methods are based on the in-cylinder pressure of fired engine, TDC position has to be known in order to acquire accurate results. The developed method will be able to determine simultaneously TDC position and pressure offset based on the in-cylinder pressure, indicated under fired conditions of the engine. To acquire accurate results, it will need at most two but preferably only one iteration, which is much less than the combinations of pressure offset and TDC position determination methods, developed in the past. An innovative computationally efficient method that simultaneously determines pressure offset and TDC position of the piston will be based on the ROHR trace, while considering specific deviations of the ROHR traces due to TDC and pressure offset in different phases of the high pressure cycle. ROHR curves for various TDC and pressure offsets are presented in Figure 2. 110

Figure 3: Rate of heat release for various TDC and absolute pressure variations

These characteristic deviations will be mapped over the engine operating region and thus used for simultaneous correction of both parameters. A ROHR trace will be evaluated based on the filtered in-cylinder pressure trace using a first law of thermodynamics and considering heat transfer to the combustion chamber and variable gas properties being a function of air-fuel ratio and temperature. During operation, engine fuel injection, EGR rate and temperature as well as intake and exhaust pressure will be controlled using real-time hardware incorporating the FPGA integrated circuit. Control algorithms will be developed in LabView environment and implemented on the FPGA integrated circuit and on the real-time processor unit. Communication between FPGA circuit and PC is presented in Figure 3.

Figure 2: Communication between PC and FPGA integrated circuit processing units

Regulation of the engine sub-systems will be based on the thermodynamic parameters derived from indicated in-cylinder pressure traces. It is expected that, one thermodynamic calculation of the entire high pressure phase will be performed in less than 2ms for a single cylinder, which opens possibilities to control all cylinders of a multi-cylinder engine simultaneously and to extend the control algorithms. To develop an efficient controller, the design space of the engine will be explored with statistical methods based on the design of experiment theory. Pareto optimality concept will be used to determine optimal values of the controlled parameters. Developed controller will be used on a modified modern four-stroke four-cylinder PSA DV6ATED4 engine

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with a displacement of 1.6 liters, which features common rail fuel injection system, an intercooler and an EGR system, cooled by the engine coolant. One of the cylinders including the entire gas path and fuel supply system will be modified to allow for the PCCI and RCCI operation. To achieve the desired conditions in the intake manifold of this particular cylinder, the EGR system with two separate gas-paths will be installed, among which one of them will be cooled by water from the laboratory water distribution system. A share of cooled recirculated exhaust gasses will be regulated by a flap in the mixing chamber, which will be over the actuator connected to the control system. The overall proportion of recirculated exhaust gasses will be regulated by a valve in the exhaust system of the engine, which will influence exhaust backpressure. Control scheme of engine sub-systems is presented in the Figure 4.

Figure 4: Control of engine sub-systems

The pressure in the cylinder will be indicated with a piezo pressure transducer in combination with a charge amplifier. Fuel system will consist of two parts, where the DFLR will be injected directly in the cylinder and the LRF in the intake port. For direct injection various injector spray angles will be evaluated to best suit the PCCI and RCCI operation. CONCLUSIONS Within the research, Numerical method for determination of the TDC position and pressure offset between the relative and the absolute in-cylinder pressure will be developed and validated on two various size Diesel engines. The method will be based on the thermodynamical calculation of ROHR and will take into account the heat transfer to the combustion chamber walls and laws of conservation of mass and energy. Developed method will be the first one to simultaneously determine the TDC position and the pressure offset in two but preferably only one iteration from under fired conditions indicated in-cylinder pressure, which significantly reduces computational time compared to the present methods. Furthermore, Diesel engine will be modified to achieve low emissions and high thermal efficiency while still enabling as wide operating range as possible in terms

of engine load and speed, transient operation and varying ambient conditions while utilizing innovative waste derived fuel that have not yet been used in similar combustion strategies. PCCI combustion will be established with an innovative Diesel-like Fuel with Lower Reactivity (DFLR), for which no additives have to be used and no modifications of fuel system have to be made. It is expected that the use of the DFLR will allow for a wide range of operating conditions in the PCCI combustion concept at high level of charge homogenization due to its low reactivity. At higher engine loads engine will operate in the RCCI combustion concept with an addition of the fuel with lower reactivity (LRF) than the DFLR. Thereby it is expected to raise the BMEP at which high degree of charge homogenization can be achieved with all associated benefits due to lower reactivity of the DFLR compared to other commonly used high reactivity fuels. References [1] PRAH, Ivo, KATRAŠNIK, Tomaž Application of Optimization Techniques to Determine Parameters of the Vibe Combustion Model, 2009, Journal of Mechanical Engineering 55 11, 715-726 [2] SELJAK, Tine, KUNAVER, Matjaž, KATRAŠNIK, Tomaž. Emission evaluation of different types of liquefied wood. Journal of Mechanical Engineering, ISSN 0039-2480, Apr. 2014, vol. 60, no. 4, str. 221-231, ilustr., doi: 10.5545/sv-jme.2013.1242. [3] RODMAN OPREŠNIK, Samuel, SELJAK, Tine, BIZJAN, Frančišek, KATRAŠNIK, Tomaž. Exhaust emissions and fuel consumption of a triple-fuel spark-ignition engine powered passenger car. Transportation research. Part D, Transport and environment, ISSN 1361-9209. [Print ed.], 2012, vol. 17, iss. 3, str. 221-227. doi: 10.1016/j.trd.2011.08.002. [4] TAVČAR, Gregor, BIZJAN, Frančišek, KATRAŠNIK, Tomaž. Methods for improving transient response of diesel engines – influences of different electrically assisted turbocharging topologies. Proceedings of the Institution of Mechanical Engineers. Part D, Journal of automobile engineering, ISSN 0954-4070, Sep. 2011, vol. 225, iss. 9, str. 1167-1-1167-16. [5] KATRAŠNIK, Tomaž, TRENC, Ferdinand. Innovative approach to air management strategy for turbocharged diesel aircraft engines. Proceedings of the Institution of Mechanical Engineers. Part G, Journal of aerospace engineering, ISSN 0954-4100, 2012, vol. 226, no. 8, str. 966-979, doi: 10.1177/0954410011416750.

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PROJECTS Recently, many important projects have been running at the Department of Energy Engineering, which we are very proud of as they prove our competences on one hand as well as our commitment in being part of the leading edge of the newest technologies worldwide on the other hand. Some of those projects have been selected for brief introduction in the Yearbook 2016.

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Cavitation and Cavitation Erosion in Cryogenic Liquids – Project for the European Space Agency (ESA) Optimal operation of turbopumps is crucial for all liquid fuel rocket engines. To reduce weight, these pumps often operate at critical conditions, where dynamic instability and cavitation are unavoidable. In cryogenic engines, the fuel and oxidizer used are liquid usually hydrogen and liquid oxygen at very low temperatures (about 14 and 90 K, respectively). Usually we treat cavitation as an isothermal phenomenon, but this assumption is not valid for such propellants: flows are characterized by a substantial cooling during the vaporization process due to cavitation. This phenomenon delays the further development of cavitation, so it plays a moderation role in the cavitation increase. The numerical prediction of the thermal effect is therefore a major industrial issue. Similarly a more in-deep understanding of cavitation erosion is extremely important for future reusable components, designed in order to withstand longer lifetimes without suffering potentially dangerous damages. Many studies were already performed to investigate these phenomena, yet, due to the complexity of the measurements, most avoid experiments in cryogenic fluids. Hence no data on thermodynamic effects of cavitation or on the specifics of cavitation erosion in cryogenic fluids exist, what threatens further progression of technology. In the proposed project we intend to perform experiments in cryogenic fluids where cavitation will be initiated acoustically – by ultrasound. We intend to characterize the development, the dynamics and the erosion of cavitation on an ultrasonic horn, which will be operated at elevated pressures in different cryogenic fluids. Although the mechanism for generating fluid cavitation in this method differs from that occurring in flowing systems and hydraulic machines, its nature is believed to be basically similar. Specifically we intend to investigate a state, which appears somehow intermediate between hydrodynamic and acoustic cavitation, namely a large cavity attached to an ultrasonic horn tip and collapsing with its self-generated subharmonic cycle frequency (the so called “acoustic supercavitation”) and which resembles the conditions in the turbopump inducer. Moreover the rapidly changing pressure field in ultrasonic cavitation could mimic the conditions at turbopump fast startup – the experimental data would therefore be valuable for accurate prediction of cavitation during this period of pump operation. Direct users of the results are researchers and industry that are dealing with cavitation erosion and specific topics of cavitating flow. The critical project requirement is that we design and construct a device which will enable the characterization 114

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of cavitation and cavitation erosion in cryogenic liquids. This will enable the study of the physics of cavitation and cavitation erosion in cryogenic liquids and even more importantly the characterization of various engineering materials resistance to the aggressive cavitating flow. Briefly the experimental set-up (Fig. 1) consists of an ultrasonic transducer with different Ti horns, insulated vessel containing cryogenic fluid and a pressure chamber.

Figure 1: Experimental set-up.

This proposed approach utilizes a 20-kHz ultrasonic transducer to which is attached a suitably designed Titanium “horn” or velocity transformer. The vibratory apparatus produces axial oscillations which are generated by a magnetostrictive or piezoelectric transducer, driven by a suitable electronic oscillator and power amplifier. Insulated vessel (vacuum flask) is used to contain the cryogenic liquid and to lengthen its state in the liquid phase. Pressure chamber enables the variation of ambient pressure by which different intensities of cavitation can be achieved. Moreover the evaporation rate of the liquid can be minimised. Excessive vapour pressure is released automatically through safety valves. Several sapphire windows are installed for observation of the flow in the vicinity of the horn. Three main research topics are pursued: I) study of cryogenic cavitation dynamics in rapidly changing pressure field (Fig. 2), II) simulations of cryogenic cavitation dynamics in rapidly changing pressure field, III) study of cavitation erosion in cryogenic fluids.

the liquid, and the collapsing cavities produce the damage to and erosion (material loss) of the specimen.

Figure 2: Acoustic supercavitation in cold water.

We utilize several high speed cameras to observe the cavitation dynamics: Fastec Imaging HiSpec4 2G mono, Motion Blitz EoSens mini 1 and Photron FASTCAM SAZ. LED diodes will be used for illumination and the reduction of exposure times down to 1 μs. A calibrated hydrophone will be used for acoustic pressure acquisition. Both the hydrophone and the highspeed camera will be triggered simultaneously (Fig. 3).

Figure 3: Results of in warm water at 65°C.

Simulations are developed and compared with experiments. Specifically we intend to develop new numerical techniques that enable simulation of a “peculiar” case, which appears somehow intermediate between hydrodynamic and acoustic cavitation, namely a large cavity attached to an ultrasonic horn tip and collapsing with its self-generated subharmonic cycle frequency (“acoustic supercavitation”) and which resembles the condition in the turbopump inducer. Cavitation erosion is a relatively well known phenomenon yet in many cases it still lacks rigid physical explanation. Moreover never before cavitation erosion was studied in cryogenic fluids – a phenomenon, which is always present in turbopump inducers.

Figure 4: Sequence showing a simulation of cavitation on an ultrasonic horn with the new cavitation model for 164 l m horn oscillation amplitude at a frequency of 20 kHz.

The test method covers the production of cavitation damage on the face of a material specimen vibrated at high frequency while immersed in a cryogenic liquid. The vibration induces the formation and collapse of cavities in

Each of the three research topics (i, ii and iii) will deliver specific achievements, which will enable the advancement of the technology. Namely: I) Study of cryogenic cavitation dynamics in rapidly changing pressure field - Determination of the influence of the cryogenic temperature on the topology and the dynamical behaviour of cavitation in a rapidly changing pressure field. - Fine tuning of the theory of the thermal delay of cavitation in liquids near critical point conditions. - Benchmark data for further development of the physics and simulations of cavitation. II) Simulations of cryogenic cavitation dynamics in rapidly changing pressure field - Cavitation model which takes into an account the presence of a rapidly changing pressure field and the ambience of cryogenic liquid. - A tool for accurate prediction of cavitation development at fast pump transients in cryogenic liquids. III) Study of cavitation erosion in cryogenic fluids - The first characterization of different engineering materials resistance to cavitation erosion in cryogenic liquids. - A corrected model of the physics of cavitation erosion which will take into an account the specifics of cavitation in cryogenic liquids. - A facility for evaluation of future materials under extreme cavitation conditions. The proposed project (part i) Study of cryogenic cavitation dynamics in rapidly changing pressure field) is related to the work that will be performed in LML (Laboratoire de Mécanique de Lille, France) for the contractors CNES (Centre National d’Etudes Spatiales, French Space Agency) and SNECMA (Société Nationale d’Etudes et de Construction de Moteurs d’Aviation, Manufacturer of Ariane V engines), where operation of turbopump inducers in liquid nitrogen will be studied. The scheduled start of their activity is mid 2015, hence our experience will be valuable to their work plan. An improved method of numerical prediction of cavitation in cryogenic liquid (part ii) of the project proposal) relates well to the ongoing collaboration with LEGI Grenoble within the ESA funded project “THERMOCAV”. The final application is the development of a numerical tool that will enable to take into account the supplementary hydraulic margins provided by thermal effects, for the development of future turbopump inducers. The final part (iii) Study of cavitation erosion in cryogenic fluids) will contribute significantly to the understanding the specific physics of cavitation erosion in cryogenic liquids. It also relates well (but does not interfere) with the ESA intended ITT. The knowledge and data gained during the proposed project will consequently lead to better design of turbopump inducer and more reliable operation of the rocket engine. Direct users of the results are researchers that are working on developing of new numerical and experimental methods (LML laboratory (Lille), LEGI Grenoble and University of Pisa, Snecma and Alta Space). YEARBOOK 2016 PROJECTS

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Water Flow Resistance of Plankton Net ABSTRACT â&#x2020;&#x2019; Purpose. The paper provides CFD study of open water sampling manta trawl with a fixed geometry of water inlet. The recommended procedures of sampling, including trawling speed as well as monitoring of net clogging, are empirical and have no theoretical background. It can be therefore assumed that a certain inaccuracy of the volume of sampled water is present. Numerical studies focus on the influence of both net clogging and trawling speed on the actual volume of sampled water. Methods. In the first step experimental set-up was designed to obtain the relationship between water speed and pressure drop through plankton net. CFD model of plankton net was also set up and compared with experimental results for clean plankton net. Experimental study was done with 13 different speeds and with 5 different sizes of resistance elements that imitate clogging of the net. In addition the shape of resistance element was changed to find a possible effect on pressure drop. Experimental results yielded netâ&#x20AC;&#x2122;s flow resistance coefficients that were used in a 2D manta trawl numerical model. Results and discussion. The experiments show no significant difference between pressure drops of circular and rectangular resistance elements that

simulate net clogging. Significant influence of the resistance elements on pressure drop was noticed. A 2D manta trawl numerical model was set up based on the real geometry. With reference resistance coefficient obtained with experiment the variation of the net resistance and trawling speed was made in order to study the phenomena. Conclusions. Experimental and numerical models are appropriate for further studies. Higher flow resistance of the net results in more pronounced flow deflection and decreased volume of sampled water. Higher trawling speed forces more water through the trawl and results in slightly increased volume of sampled water. It is evident that clogging of the net has a significant impact on pressure drop through plankton net and consequently on the speed of the water through the net. While clogging of the net could not be numerically simulated experimental results provided useful information on changes of resistance coefficients used in numerical models. It was shown that clogging has a considerable impact on the difference between actually sampled and assumed water volume flow through manta trawl.

INTRODUCTION

speed as well as monitoring of net clogging are empirical and do not have any theoretical background. To analyze flow conditions during the sampling procedure a CFD study of plankton net and manta trawl with a fixed geometry of the water inlet opening was conducted. It was assumed that since an empirical and non-structured approach is used in litter sampling procedure possible mistake in sampled water volume flow is done. The phenomena of the net clogging and the speed of manta trawl were studied.

Marine litter is defined as any persistent, manufactured or processed solid material discarded, disposed of or abandoned in the marine and coastal environment and is thus globally recognized as a persistent and growing problem with environmental, economic, safety, health and cultural implications that expand beyond borders. More specifically, the emerging microplastics pollution (threat to marine environment caused by plastic particles of a diameter smaller than 5 mm) and negative impact of the derelict fishing gear (lost and abandoned fishing nets) to the marine species and habitats have raised the need for a joint action on regional level which goes beyond borders of these particular issues. DeFishGear1 project originated as a response to the need for effective dealing with the issue of marine litter in the Adriatic macro region, towards litter free coasts and sea. One of the actions in the project is to define a joint monitoring and assessment approach to marine litter through a participatory process. The majority of microplastics monitoring studies in marine and riverine environments are conducted using plankton trawls. The most common type used is a manta trawl with a fixed geometry of the water inlet opening. Recommendations for trawling 1 DERELICT FISHING GEAR PROJECT IN THE ADRIATIC SEA: WWW.DEFISHGEAR.NET

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LITTER SAMPLING METHOD Sampling is done with manta trawl with a fixed geometry of the water inlet opening shown in Fig. 1.

Figure 1: Sampling of plastics with manta trawl The body of the manta trawl is made of 300 micrometers size plankton net, the opening at water inlet is 66 cm x 15 cm (Fig. 2).

Figure 4: left: part with plankton net; right: bottom view of inserted net

Experimental matrix was constituted from 13 different velocities with 5 circular and 5 perpendicular resistance elements resulting in 143 different operating points.

Figure 2: Studied manta trawl

Recommended relative speed between trawl and water is 3 knots or 1.5 m/s which was also the reference speed used for numerical simulations. EXPERIMENTAL SET-UP In order to get proper input data, boundary conditions and make a study of certain phenomena, experimental setup (Fig. 3) was build to measure pressure drop through plankton net at different velocities of water. Water velocity was varied from 0 m/s up to 2.2 m/s which is more that 45 % above the recommended speed of 1.5 m/s. Experimental setup consisted of • centrifugal pump, • pipings and valves, • water reservoir, • orifice with pressure tapings for water volume flow measurements • custom made fitting for pressure drop mesurements through plankton net (Fig. 4). In order to simulate clogging of the plankton net, resistance elements were placed on the net that blocked from 10 % up to 50 % of cross sectional area.

Figure 3: Experimental facility

In order to test the influence of litter distribution in plankton net on pressure drop different shapes of resistance elements were used: 5 circular and 5 perpendicular resistance elements (Fig. 5).

Figure 5: Resistance elements

In Fig. 6 pressure drops obtained by different sizes and shapes of resistance elements are presented. It can be seen that the shape of resistance element has negligible effect, so it can be assumed that distribution of plastic inside manta net wouldn’t have a significant effect on overall pressure drop through net. As expected the pressure drop rises with second power of water flow rate. In the case of clean net the maximum pressure drop at 2.08 m/s is 2834 Pa, while with resistance element covering 50 % of the net water velocity of 2 m/s could not be reached. Pressure drop at water velocity of 1.5 m/s (approx. 3 knots) is compared for different resistance elements in Table 1. It can be seen that clogging of the net has a very big impact on the pressure drop through the net and if pressure sensor could be mounted on the manta trawl it would be easy to detect the clogging of the net.

Figure 6: Pressure drops at different velocities, sizes and shapes of resistance elements

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Table 1: Pressure drops for different resistance elements and the growth of pressure drop in comparison to clean net at water speed 1.5 m/s.

element %

Δpmesured, Pa

growth of Δp, %

1625

2500

4000

146

5959

267

5959

267

15375

846

NUMERICAL EXPERIMENT Plankton net The basic numerical model was the model of the real plankton net showed in Fig. 7. This model enabled comparison of numerical with experimental results and to obtain resistance coefficients required for 2D manta numerical model (Fig 9).

Figure 8: Numerical vs. experimental results and clogging effect.

2D Manta model Geometry of numerical model follows the design of an actual experimental trawl tested within the DeFishGear project. Reference flow resistance is obtained with plankton net numerical model and validated with experiment (Fig. 8). Reference trawl speed was set to 1.5 m/s (approx. 3 knots) which is a recommended speed of manta trawl for sampling.

Figure 7: Numerical model (top) and water flow (bottom) through plankton net.

The results showed a good agreement of pressure drop in the case of numerical and experimental results (Fig. 8). 2D numerical manta model was setup with known and experimentally validated resistance coefficients that represent clogging of the manta trawl. where v is trawl speed, Clin and Cquad are constants. Trawl speed (v) is the relative speed of trawl versus water, in practice the trawl moves through stationary water, while for numerical experiments water moves around stationary trawl. In Fig. 8 it can be seen that comparison of experimental and numerical was only possible for clean net. In the next step the experimental results will be the basis for calculation of resistance coefficient of clogged net.

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Figure 9: Numerical model of 2D manta trawl.

Actual geometry is simplified to a two-dimensional model with 76,455 elements (Fig. 9). Inflow boundary condition is velocity of water and outflow boundary condition is static pressure. Mesh was refined at the solid walls and the net to improve accuracy of the calculations. Results obtained with the 2D model cannot be directly applied to actual 3D device, but certain phenomena and interdependences of the observed parameters can be studied.

RESULTS AND DISCUSSION

CONCLUSIONS AND OUTLINE

Based on the 2D model the influence of flow resistance (clogging of the plankton net) and trawl speed on the relative flow rate on are studied. Relative flow rate is the ratio of actual volume flow rate of water at the trawl’s inlet and the product of trawl speed and cross-section area of the trawl’s inlet (theoretical flow rate):

In the study sampling phenomena was studied in terms of numerical modelling. A 2D numerical model of the manta trawl was set up in order to study the influence of trawling speed and clogging of the plankton net on sampled volume of water. The results suggest the following conclusions: • Numerical and experimental results in the case of clean plankton net are in good agreement. • Experiment showed that clogging of plankton net by 50 % cross sectional area results in 8.5 times higher differential pressure at reference water speed of 1.5 m/s. • Higher flow resistance of the net (more particles caught on the net) results in more pronounced flow deflection and notably decreased volume of sampled water. • Higher trawl velocity produces higher pressure difference on the net which forces slightly more water through the trawl and results in slightly increased volume of sampled water. • Experimental and numerical models are appropriate for further studies. Since in most cases true volume of sampled water is calculated on the basis of ship average speed not concerning clogging of the plankton net that has evidently a big effect on real sampled water, it can be assumed that the litter gathered with manta trawl correspond even to smaller water volume flow that calculated with usual approach. In other words water is even more polluted with micro plastic because true volume water flow is in most cases underestimated.

Relative flow resistance is defined as multiplication factor for both linear and quadratic flow resistance coefficients that define flow resistance through the net. The factor i in Eq. (3) is exponentially increasing from 0.4 to 20 with 1 representing the experimentally acquired resistance of a clean net.

Figure 10: Relative flow resistance influence.

References [1] Drobinč, B., Jurjevčič, B., Palatinus, A., Kržan, A., Mori, M.. Water flow modelling through plankton net. V: Seminar on Microplastics Issues, Piran, May 4-6 2015. KRŽAN, Andrej (ur.), HORVAT, Petra (ur.). Micro 2015: book of abstracts. [Ljubljana]: DeFishGear, 2015, str. 44. [2] Drobnič, B., Jurjevčič, B., Palatinus, A., Kržan, A., Mori, M. Water flow modelling through plankton net : presentation at the Mediterranean Conference on Combating Marine Litter in the Adriatic MacroRegion, 12 - 13 May 2014, Athens

Figure 11: Trawl velocity influence.

Fig. 10 shows the influence of relative flow resistance on relative flow rate which simulates the effect of plankton net clogging. The right side of the figure shows pressure distribution and velocity vectors for four calculated points. Higher flow resistance of the net (more particles caught on the net) results in more pronounced flow deflection and notably decreased volume of sampled water. In Fig. 11 the influence of trawl speed on the relative flow rate is presented. Higher trawl speed produces higher pressure difference on the net which results in slightly increased volume of sampled water. YEARBOOK 2016 PROJECTS

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FluMaBack - Improving the operation of Balance of Plant components ABSTRACT → Effectiveness and reliability of power supply are very important in various applications under vast variety of environmental conditions. Fuel cell based power supply systems are an interesting alternative to conventional systems but their reliability, lifetime, efficiency and costs still need improvements to be competitive. EU funded international project

FluMaBack focused on improvement of operating characteristics, lifetime and cost effectiveness of balance of plant (BoP) components in back up fuel cell systems. This improvements further provide stable, reliable and efficient operation of the core components, the fuel cells.

INTRODUCTION The development of sustainable, environmentally friendly sources of energy is a global research priority. However, while a great deal of attention has been focused on developing new core technologies, there is also significant potential to improve existing balance of plant (BoP) components of power supply systems to achieve optimal operation of fuel cell systems. This particular issue was the scope of the FluMaBack project. The general aim of the project is to improve the performance, life time and cost of several BoP components for backup fuel cell systems including air blower, humidifier, heat exchanger and hydrogen recirculation pump (Fig. 1).

FULL PROJECT TITLE Fluid Management component improvement for Back up fuel cell systems (FluMaBack). http://www.flumaback.eu/ PROJECT OBJECTIVES The FluMaBack project aims to improve the performance and life time of balance of plant (BoP) components for back up fuel cell systems while reducing production costs. PROJECT FUNDING Project budget: €4.44 million Project funding: €2.77 million. MAIN GOALS • Improving BoP components performance, in terms of reliability; • Improving the lifetime of BoP components; • Reducing cost in a mass production perspective;

Figure 1:Balance of plant components developed in the FluMaBack project

The project consortium comprised partners from across the EU which had experience with development of BoP components for power supply systems. The available components were either too robust, too expensive or not optimally designed for application in a fuel cell system. The project therefore focused on improvement of existing and development of new BoP components. Finally the BoP components were integrated with an existing fuel cell stack into a backup fuel cell system. The efficiency and lifetime of both BoP components and the entire system were improved and production costs were reduced while required performance criteria were still met.

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• Simplifying the manufacturing/assembly process of the entire fuel cell system

DEVELOPMENT OF BOP COMPONENTS The BoP components can have significant influence on the performance of fuel cells (Fig. 2), potentially improving their efficiency, reliability and durability. In order to achieve that the BoP components must meet specific technical requirements of fuel cells if they are to be operational. Using an existing BoP component in a fuel cell system might enable the system to operate, but will not provide optimal performance regarding efficiency and reliability. Within FluMaBack project development and production of BoP components was focused specifically on 3 kilowatt and 6 kilowatt backup fuel cell systems which results in specific requirements that the BoP components must meet.

throughout the system, was developed as a modified version of an existing blower with characteristics similar to those required by the fuel cell system (Fig. 4).

Figure 2:Fuel cell stack

Fuel cells are very sensitive to impurities in fuel. The polymer exchange membrane fuel cell, which is the heart of the system, requires the hydrogen to be 99.999 % pure. Other properties of hydrogen and air provided for the operation of the fuel cell must also be considered. The air needs to be saturated with moisture since dry air can cause the membrane to dry out. This leads to membrane degradation, which results in reduced power and a shorter lifetime of both the fuel cell and entire system. Both air and hydrogen must be supplied to the fuel cell stack with volume flows within specific boundaries depending on the fuel cell requirements. At the same time the total head of the blower must provide enough pressure to overcome all pressure losses throughout the system. The design of other components must provide as little flow resistance as possible to reduce energy losses in the system and increase its overall efficiency.

Figure 4:Air blower (left) and hydrogen recirculation pump (right)

On the other hand, the hydrogen recirculation pump was developed from scratch, as no suitable version of the pump was available. Furthermore it was decided to employ the centrifugal principle instead of more often used volumetric one. The result is a new product that, although there are still some issues to be resolved, is capable of meeting the requirements of the fuel cell system (Fig. 4). A new product was also developed for humidification of air entering the fuel cell stack as the commercially available solutions did not meet the required criteria; most notably the costs were too high. The newly developed design of the humidifier (Fig. 5) is simple in terms of manufacturing, thus being very competitive considering the costs, while it is still providing required functionality.

Figure 5: Air humidifier with hollow semi-permeable fibres

Figure 3: Numerical simulations of pressure stream lines in air blower (left) and velocity contours in humidifier (right)

The technology is available today to address these issues and ensure that fuel cells can work more efficiently. A sound understanding of the fluid dynamics phenomena in BoP components is essential in these terms therefore detailed numerical analyses of particular components were performed in order to improve the design and identify possible issues within the components (Fig. 3). To improve durability, components are usually more robust and thus more material is needed. If in addition more energy is needed, the component will be more expensive. Most criteria in design process preclude each other, which makes the development of an optimal component as even bigger challenge. In order to achieve optimal performance the research teams had different approaches for component development. Air blower, needed to supply appropriate air flow to the fuel stack while covering numerous pressure drops

The studies of heat management in the fuel cell system resulted in the development of an effective cooling system for the fuel cell stack including an external heat exchanger. Heat recovery within the system that was provided by an internal heat exchanger proved to have little effect on the efficiency of the entire system and was therefore removed from the final design of the system. DELICATE BALANCE A delicate balance needs to be struck between the criteria for BoP component design, and this remains a key priority in development. The performance priorities of the components depends to a degree on the intended application and the likely market; while the project initially focused on emerging markets, later the project focused towards Europe and North Africa. Furthermore, some components are also very useful in other applications. If the automotive industry decides to use fuel cells very intensively, then the results of the FluMaBack project could prove to be very useful in this area as well.

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Figure 6:LCA model from cradle to the end of operation

To find the suitability of particular components and their influence on the overall performance of the fuel cell system the components were thoroughly tested during various operating conditions within an actual system. A few components will be used in both the 3 kilowatt and 6 kilowatt systems, which is very positive from the cost point of view. However, developing BoP components which will fit in both systems is quite a challenge, as the larger system has twice the power and thus requires twice as much air, hydrogen etc. as the smaller system. The project was testing all components to identify such issues and further improve their performance, with the hydrogen blower proving a particular challenge. A special test rig was built for testing the hydrogen blower’s performance and durability. Hydrogen as a working medium always presents particular challenges, because hydrogen is prone to leaking and is not compatible with some common materials used for component body, sealing, lubrication, etc. Durability is a research priority for all of the components being developed within the project. The components should last for 10,000 hours without maintenance. But not just the components – the overall system itself should also last for 10,000 hours without maintenance. Special durability tests were therefore performed not only on the components but also on the entire system to prove that it will be capable of reliable operation during its lifetime which is planned to be around 10 years.

The operational stage of a backup fuel cell system is when the greatest environmental impact occurs, so the hydrogen production technology and performance characteristics of BoP components, and of the overall system, are the most important considerations (Fig. 7).

Figure 7: Contribution of lifetime phases to overall global warming impact

The analysis also showed the influence of particular system components on the overall global warming impact (Fig. 8). The BoP components proved to have little influence, while the fuel cell stack itself produces the biggest environmental impact.

LIFE CYCLE ASSESSMENT Part of the work was also life cycle assessment of the system in the manufacturing and operational phases. It is important to show that hydrogen technologies in backup systems are environmentally sounder and have a lower environmental impact than conventional backup systems. Limiting the environmental impact of production and addressing sustainability issues are key priorities for most companies, a trend that is likely to grow more pronounced in future. A complex model of the entire production and operation phase of a backup fuel cell system was set up (Fig. 6) including materials, energy sources and manufacturing processes for all of the BoP components, transportation and hydrogen production process during system’s operation. 122

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Figure 8: Contribution of system’s components to overall global warming impact

STRUCTURE OF THE PROJECT Work in the FluMaBack project was organized in seven work packages (WP) including partners from four European countries (Fig. 9). The coordinator was Electro power systems from Turin, Italy.

[10] Energia e idrogeno, L’esperienza italiana nel programma europeo Idrogeno e celle a combustibile [Energy and hydrogen, the Italian experience in the European Hydrogen and Fuel Cells], Organizzato da H2IT, Milano, 13. December 2012, Italy

PROJECT PARTNERS • Electro Power Systems: Project Coordinator, Torino, Italy • Tubiflex SPA, Italy • Parco Scientifico e Tecnologico per L’Ambiente - Environment Park Spa, Italy • Institut Jožef Stefan, Slovenia • Fundacion Para el Desarrollo de las Nuevas Tecnologias del Hidrogeno en Aragon, Spain Figure 9: Partners involved in FluMaBack project

Main BoP and system research/development was done in WP 3 and WP 4 while WP 5 was focused on testing of components and the system. In WP 6 RCS (regulation, codes and standards) and market preparation was included as well as the LCA analysis of system manufacturing, operation and end-of-life.

• Nedstack Fuel Cell Technology BV, Netherlands • Onda Spa, Italy • University of Ljubljana, Slovenia • JRC -Joint Research Centre - European Commission, Belgium • Domel d.o.o., Slovenia

References [1] A. Debenjak, P. Boškoski, B. Musizza, J. Petrovčič and Đ. Juričić: Fast measurement of PEM fuel cell impedance based on PRBS perturbation signals and Continuous Wavelet Transform, Journal of Power Sources, 254 (2014) 112 - 118 [2] Sinenergija: Slovenian academia and industry in development of hydrogen technology equipment, 2014 [3] Čemažar, Domen. Design and development of hydrogen recirculation blower for fuel cell application: master thesis. Ljubljana: [D. Čemažar], 2013. XIV f., 90 pg., illustrated. [4] Presentation of Domel’s BoP component (air blower) by The Fuel Cells and Hydrogen Joint Undertaking, Hannover Messe, 7. April – 11. April 2014, Germany [5] Lange Nacht der Forschung, Alpen-Adria, Universität Klagenfurt Lakeside Science & Technology Park, http://www.langenachtderforschung.at/, Poster: Flumaback activities and LCA results, Klagenfurt, 4th of April, Austria [6] European Fuel Cell Technology & Applications Piero Lunghi Conference, Poster, Side Event Dissemination of European Projects, Poster Session | Project Cocktail 12th December, 11.-13. December 2013 [7] Development and economic challenges of hydrogen technologies breakthrough into practice, Chemical Institute, Ljubljana, 15. November 2013 [8] Programme Review Days by FCH JU, 11. November 2013, Brussels [9] FP7 Fuel Cells and Hydrogen Joint Undertaking, MIUR, Piazza Kennedy 20, Roma: Link to web, 21. January 2013 YEARBOOK 2016 PROJECTS

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HYTECHCYCLING - New technologies and strategies for fuel cells and hydrogen technologies in the phase of recycling and dismantling ABSTRACT → Rapid deployment of fuel cells and hydrogen technologies is expected in the near future in order to enable decarbonization of energy and transport sectors in the EU. One of the main ideas behind hydogen technologies is to produce vast amounts of green hydrogen from the expected surplus of renewable energy sources (implemented policies are

INTRODUCTION To follow its low carbon energy supply agenda the EU will need to intensify the deployment of fuel cells and hydrogen (FCH) technologies in energy and transport sectors in the near future. Relying on renewable energy sources (RES) necessitates the use of effective and reliable energy storage technologies. Combining hydrogen technologies with RES will enable energy storage through production of green hydrogen from the expected surplus of RES (implemented EU policies are going towards 65 % of electricity from RES by 2050) to be used in transport for fuel cell powered electric vehicles, utility energy supply (re-electrification, stationary cogeneration fuel cells systems, backup systems and adding hydrogen into existing natural gas grid) and industries (hydrogen generation for chemical industries). However, the expected commercial FCH technologies (mainly PEM and alkaline electrolysers as well as PEM and Solid Oxide fuel cells) are not prepared for full deployment when considering recycling and dismantling stage. Specifically, these devices still comprise significant amounts of harmful, expensive and scarce materials (e.g. PGM in PEM fuel cells), therefore some novel dedicated recycling processes for these FCH technologies could be applied. At this point the involvement of FCH manufacturers is necessary to design new systems with also with consideration of compatibility with new recycling processes, thus allowing full recovery of critical materials (i.e. redesign for material compatibility at recycling and dismantling). Furthermore, there is a lack of end of life (EoL) strategies devoted to reusing and remanufacturing of FCH technologies to save these materials and take advantage of still useable components and subsystems. In this field, it is especially important to involve not only manufacturers but also end users to ensure collaboration and provision of FCH products for reverse logistics processes. HYTECHCYCLING objectives are focusing on tackling the aforementioned challenges and setting the basis 124

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going towards 65 % of electricity from renewable energy sources by 2050) to be used in transport (fuel cell electric vehicles), energy (re-electrification, stationary fuel cells for cogeneration, backup systems or injecting hydrogen into the gas grid) and industries (hydrogen generation for chemical industries).

FULL PROJECT TITLE New technologies and strategies for fuel cells and hydrogen technologies in the phase of recycling and dismantling → HYTECHCYCLING MAIN GOAL HYTECHCYCLING’s main goal is to deliver reference documentation and studies about existing and new recycling and dismantling technologies and strategies applied to fuel cells and hydrogen technologies, paving the way for future demonstration actions and advances in roadmaps and regulations PROJECT FUNDING REQUEST: 497.666,25 €. KEY STEPS • Pre-study and techno-economic, environmental, RCS assessment related to dismantling & recycling of FCH technologies to detect future needs and challenges. • Development of new technologies and strategies applied to FCH technologies in the phase of recycling & dismantling and LCA analysis considering critical, expensive and scarce materials inventory. • Proposal of new business model, implementation roadmap and development of reference recommendations and guidelines to focus the sector and pave the way for future demonstrations and introduction of the concept among FCH stakeholders.

for the FCH community in the field of recycling and dismantling. This paper presents the main goal, which is divided into specific achievements to ensure and guide its implementation.

introduction to all the agents involved in the lifetime of the FCH products. • Develop business model looking for wide implementation of the new technologies. In order to achieve the objectives HYTECHCYCLING will be divided in 7 work packages (WP), Figure 2. Laboratory for Heat and Power (UL FS) as one of 5 partners in the project is leading partner in WP4 where Life Cycle Assessment methodology and tools will be used to evaluate new recycling strategies in terms of environmental impacts.

Figure 1: Circular economy vision of the European Commission

Regarding future trends in EU Laws, the European Commission (EC) aims to create a new economic model related to products life cycle titled “Circular economy” (Figure 1). Formally called “Towards a circular economy: A zero waste programme for Europe” this new vision wants to keep the added value of the products as long as possible, eliminating waste. When a product has reached the end of its life its parts, or the whole system, can be used again and again and hence create further value. MAIN OBJECTIVES AND WORK PLAN The main goal of the new “Circular economy” programme will be, for the FCH technologies, achieved by means of the following objectives: • Identification of critical materials and components in FCH products. • Mapping of existing and novel recycling technologies applicable to the selected FCH materials and components, considering experiences from different member states to select the most suitable approaches. • Analysis of challenges considering the limitations of the current status of recycling and dismantling of FCH products. • Development of new strategies and a roadmap for implementation of recycling & dismantling technologies for critical materials and components included in FCH technologies. • Impact quantification of the introduction of the new strategies and technologies by means of LCA analysis covering a wide spectrum of FCH products and technologies in the field of energy and transport. • Evaluation of requirements for existing FCH actors to implement the new strategies and technologies, re-adaptation of existing recycling centers, demoevents and showcases in a recycling centre. • Collect the new strategies and technologies as guidelines and recommendations for their

Figure 2: Work plan of the project

RECYCLING AND DISMANTLING STRATEGIES FOR FCH PRODUCTS The lack of a specific plan to dismantle and recycle FCH products may lead to a significant environmental impact during the disposal stage of the product. Furthermore it can result in: • damages in human health: radiation, carcinogens, respiratory inorganics, global warming; • damages in ecosystem diversity: carbon footprint, water footprint, ozone depletion, acidification, eutrophication, human – toxicity, summer smog; • resource scarcity: land – use, resource consumption (materials and energy carriers). Recycling is therefore essential to mitigate the aforementioned issues. Dismantling and separation of materials is the first step of the disposal stage. After that, materials can be reused, remanufactured, used for energy recovery, landfilled or recycled. Although, as described below, all the options should be considered, HYTECHCYCLING project is focused mainly on recycling while reuse & remanufacturing are also considered in the reverse logistics strategy. The recovery options follow the logic shown in Figure 3. Reuse and remanufacturing are recycling and disposal strategies expected in the long term, due to the requirement for an effective technology market to be established. Energy recovery is an option with a high environmental impact and low recovery benefits, taking into account the high value of the components and materials mostly used in the FCH products manufacturing. Landfilling is an option restricted by the EC to certain cases in which no other option is feasible, therefore, it is not an option acceptable to the present study. Additionally, it is considered as a non-cost effective option, similarly to the case of energy recovery, thus, YEARBOOK 2016 PROJECTS

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recycling, reuse and remanufacturing are the options to be considered in the HYTECHCYCLING project, and those can pave the way to a business case in the recovery of FCH products at its end of life. A summary of the advantages and disadvantages of the different recovery options are presented in Table 1. Table 1: Advantages () and disadvantages () of the FCH products recovery options Reuse

ReEnergy Landfill- Recymanurecovery ing cling facturing

Energy savings



Raw material savings



Disposal cost





Transportation cost



Environmental protection Human health

 





















Having these options in mind, different recycling strategies have been tested and utilized over the last few decades. These strategies are, mainly: Reverse logistics: Reverse Logistics is the process of planning, implementing, and controlling flows of raw materials, in-process inventory, and finished goods, from a manufacturing, distribution or use point to a point of recovery or point of proper disposal. Reduction or replacement of critical raw materials: The scarcity of critical raw materials, with their economic importance, together with the distribution of them in specific geographical areas (mainly outside of Europe), makes it necessary to explore new possibilities for reduction or replacement of these critical materials. Material compatibility and hardware separation: Materials are incompatible for recycling when they cannot be processed together. For example, steel and copper are incompatible in recycling process. During any product

Figure 3: Recovery options in a product end-of-life

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design, recycling compatibility charts are a useful tool for materials selection. They are typically presented for classes of materials (e.g. plastics, metals, etc.). Unless recycling is to be dominated by reuse or remanufacturing, material compatibility is a key strategy in the recycling of a product. Eco design for recycling: With the current knowledge coming from the first recycling steps in the FCH industry, eco design concepts must be applied to the design of new FCH products in order to simplify the recycling processes in the short term. Recycling technologies Recycling of complex products (FCH technologies) demand different types of recycling technologies. The main technologies that apply to this waste typology are: shredding, sorting and recovery of metals; mechanical methods of recycling plastics and pyrolysis; chemical or feedstock recycling; and recycling of electronic components as printed circuit boards, liquid crystal displays, cooling and freezing appliances and batteries. Obviously these technologies are not the proper option to recycle high added value products such as FCH. The HYTECHCYCLING project will strive to define the best technologies for the recycling of PEMFC, SOFC, and PEM and alkaline electrolysers. Critical raw and rare materials in FCH products The scarcity of critical raw materials makes it necessary to explore new avenues towards reduction or replacing of these materials in Europe, where the presence of these valuable materials is really low. A recent study of the EU has identified 20 critical raw materials that are creating a growing concern within the EU from the point of view of their supply risk and economic importance. European and national regulations Approximately 200 or so environmental laws cover most eventualities nowadays. To manage such environmental policies, the EU has developed a framework which helps to group together different directives, regulations, etc., called Environment Action Programme (EAP). The current 7th EAP will be effective until 2020, guiding EU environment policy: “The Union has set itself the objective of becoming a smart, sustainable and inclusive economy by 2020 with a set of policies and actions aimed at making it a low car-

Figure 4: Approach and methodology to reach impact

bon and resource efficient economy”. To comply with the requirements of the 7th EAP, the HYTECHCYCLING project will have to identify the necessary actions for disposal of the FCH systems, providing useful recommendations to the EU policy makers. LCA for FCH products Valuable information on how to conduct LCA for FCH technologies was provided by the FC–HyGuide, a FCH JU funded project. The HyGuide guidance documents are based on the ILCD Handbook and ISO 14040 and 14044 standards. Four years after the presentation of the HyGuide results, which was in 2011, it is clear that the recycling, recovery and disposal phase of the FCH products is gaining importance due to the current state of technological development. The FCH technologies are in its deployment stage and near the market penetration at large scale in the mid-term. The HYTECHCYCLING project will cope with the issues that will inevitably arise with the widespread presence of the FCH products – recovery, reuse and recycling of the products – in order to cover the overall lifetime of the product. Further guidelines will be provided for LCA methodology of FCH products including the final step in the product life. The first analysis will be developed during the project progress specifically in PEMFC, SOFC, and PEM and alkaline hydrogen production technologies. Business model for FCH actors The business model for recycling FCH technologies starts when they reach their EoL. At this point, the product can be sent by the user to a recycling centre with waste electrical and electronic equipment (WEEE) treatment or to the FCH product manufacturer. Initially, in the short term, as the FCH products are in an early stage of deployment returning of products to the manufacturers will be the preferred option. HYTECHCLING will help the manufacturers to find the proper business model in the recovery of their products in their EoL. As it has been mentioned previously, with the present state of technological development, in an early deployment step, very few efforts and progresses have been made to dismantle and recycle the active parts of fuel cells and electrolysers. In consequence, the use of recycled materials for the manufacturing is not a common practice, and very few recycling centers have started to work or offer services in this field.

IMPACT Figure 4 shows the overall six step approach followed to accomplish HYTECHCYCLING objectives and reach the appropriate impacts. The project will contribute the following impacts, which are consistent with those described in the topic text: • Delivery of a first reference on needs and focus of recycling technologies and strategies for FCH technologies; • Establishment of a detailed timeline for introduction of recycling and dismantling technologies encompassing FCH technologies expected penetration; • Harmonization and standardization of methods and procedures in the phase of recycling and dismantling; • Added value for FCH 2 JU: contributions to MAWP 2014 – 2020; • Involvement and awareness of FCH actors and stakeholders for business model implementation; • Quantification of importance of proper recycling and dismantling and incorporation to LCA approaches; PROJECT PARTNERS • Fundacion Para el Desarrollo de las Nuevas Tecnologias del Hidrogeno en Aragon, Spain • University of Ljubljana, Faculty of Mechanical Engineering, Slovenia • Fundación IMDEA Energía, Spain • Industrias López Soriano S.A., Spain, • Environment Park, Italy Contact Details - Coordinator Parque tecnológico Walqa Ctra. N-330a, Km. 566 22197 Huesca, Spain E: info@hidrogenoaragon.org W: www.hidrogenoaragon.org

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Planica Wind Tunnel ABSTRACT → Planica Nordic Center is a nordic skiing complex with one ski flying hill, seven ski jumping hills and cross-country skiing track in Planica. In year 2015, the new wind tunnel was opened with dual ski jumping and skydiving sections. The purpose of the study was to design dynamic aero system NC-Planica. The inlet conditions of the study were to determine the geometry

of the aerodynamic system, limit power consumption on the fan assembly to 1.8 MW, achieve average speed in a vertical wind tunnel (180 km / h to 265 km / h) and average speed in the horizontal wind tunnel (110 km / h to 150 km / h). Preferred was a homogeneous velocity profile in the vertical and horizontal sections of the system.

INTRODUCTION

of guiding vanes to the existing channels (Figure 2, left). However, very unfavourable flow properties were found, the amount of turbulence and mixing of the air. Based on the CFD results the electric power required exceeded available resources by several MW. In the second part of the study, design included internal flow channels like seen in Figure 2 (middle and right)

Planica Nordic Center (slovene: Nordijski center Planica) is a nordic skiing complex with one ski flying hill, seven ski jumping hills and cross-country skiing track in Planica, Slovenia. This is the only nordic center in the world with record eight hills that are all in one place and the only one of this kind with hills of all sizes at one place: small, medium, normal, large and flying hills. The origins of ski flying started in 1936 in Planica, when 18-year-old Austrian Josef “Sepp” Bradl became the first man in history to land a ski jump of over 100 metres (330 ft). It is a place where the most of the ski jumping world records were set on two different hills, and also the historic first jumps over 100 meters by Sepp Bradl on Bloudkova velikanka and over 200 meters by Toni Nieminen on Letalnica bratov Gorišek.

Figure 2: Several geometries were tested during wind tunnel design

Figure 1: Planica nordic center

In 2015, the Planica Nordic Centre reconstruction was finished. In the current form Planica Nordic Center boast 9 ski-jumping facilities, a cross-country centre, main facility with horizontal and vertical wind tunnel and covered one-kilometre running track that can be used 365 days a year. Within this, our task was to design a dual purpose wind tunnel with vertical and horizontal sections within the limited geometry of the main nordic centre building. This was done using a CFD and 1/36 scale model. CFD MODEL Existing geometry of the main Planica Nordic centre building imposed several serious constraints to the design of the wind tunnel. Initial studies included addition 128

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Figure 3: Results of CFD analysis

In the final geometry version, the results of the calculation of the kinematics of the air flow within the system indicate a significant reduction in the pressure drop and required aerodynamic power versus early geometry versions. Due to a reduced flow resistance of the system, guide vanes, flow laminators and safety nets may be installed to achieve full functionality of the aerodynamic system. The CFD analysis was performed on the high performance computer at the Faculty of Mechanical Engineering.

Results of measurements on physical model agreed very well with CFD analysis. CONSTRUCTION OF THE WIND TUNNEL The wind tunnel features 3,6 m diameter skydiving section and 5x6x3m ski jumping section. The installed power of both fans combined is 1,8 MW

PHYSICAL MODEL To confirm the validity of the CFD calculations due to very high costs of entire project and with it associated risks, the physical 1/36 scale model was built. It is shown in Fig. 4. The model was intended to run with hot water to achieve as good as possible model similarity. However, a 10x reduction of Reynolds number was required to have a manageable power requirements of the propulsion. The propulsion was implemented with two water ship model screws of appropriate size, while a suitable guide vanes were added.

Figure 5: A team of students participated in the design of the wind tunnel, shown after fans installation.

Figure 4: Physical model, left: design, right: detail of the pressure section

Several measurements were performed on the physical model, which included, pressure drop measurement of individual sections, aerodynamic power measurements, five hole probe measurements and visualisation with image sequence acquisition any analysis. Five hole prove and measurements and visualisation were performed in skydiving and ski jumping sections. Several students participated in the design of the physical model (Figure 5). The physical model was built of aluminium and plexiglass and was manufactured at the Faculty of Mechanical Engineering.

Figure 5: Wind tunnel skydiving section

CONCLUSIONS

Figure 4: Physical model of the Planica wind tunnel

The dual design of the Planica Nordic Centre wind tunnel is unique as it includes skydiving and ski flying sections. Within this study, the aerodynamic flow design was performed. The wind tunnel in the proposed form was built and successfully tested. In the future, some minor refinements of the flow properties in the ski jumping sections will be performed.

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Matija Tuma

Short step into the history The Department of Energy Engineering is one of the oldest and biggest departments of the Faculty of Mechanical Engineering of Ljubljana. It has a rich and long lasting tradition. Its existence started in 1946 when “the old building” was built. In 1960 the Department of Power Engines and Thermal Devices was constituted. Later it was renamed to Department of Energy Engineering.

CONSTITUTION OF THE UNIVERSITY OF LJUBLJANA University of Ljubljana was constituted by the law issued on 23 July 1919. The law consisted of only four paragraphs. The last paragraph was saying: “This law becomes official after it is undersigned by the King and becomes mandatory after it is declared”. This is an example how uncomplicated the legislation was in the Kingdom of Serbs, Croats and Slovenes. One of the main initiators for the immediate constitution of the national university was Dr. Mihajlo Rostohar an assistant professor at the University of Prague. Nevertheless, he never was teaching at the University of Ljubljana. Dr. Danilo Marjoram was the first president of the University’s Commission. Dr. Josip Plemelj was the first rector and Dr. Richard Zupančič, who was also the corresponding member of the Academy of Sciences in Toulouse, was the first vice-rector. Both of them were mathematicians. The first dean of the Faculty of Engineering became Dr. Karol Hinterlechner, a geologist and an external member of the Czechoslovak Academy of Sciences in Prague. All of them were known as the top experts even outside the borders of the Austro-Hungarian Monarchy. Perhaps they were ranking even higher in the Europe than today’s university professors. They have returned to their native land, the newly formed Kingdom of Serbs, Croats and Slovenes, and took over the teaching at the local university. Upon the establishment the University has combined five faculties: Faculty of Law, Faculty of Philosophy, Faculty of Engineering, Faculty of Medicine (two years of introductory courses) and the Faculty of Theology (seminary). Within the Faculty of Engineering the courses have been divided into sections: mathematics, science, construction and architecture, mechanical and electrical engineering, 130

mining and metallurgy, social science and legislation and two miscellaneous courses. 31 August 1919 the first 18 teachers were appointed for the five faculties. A specialist in electro-mechanical engineering Dr. Milan Vidmar was one of them. The University courses at the future Faculty of Engineering were held even before the formal establishment of the University of Ljubljana. The courses were launched on 19 May 1919. Till the autumn the students have already graduated the first year of their studies. Consequently the courses for the first two years were held simultaneously in the first official academic year 1919/1920. In the first years of its existence Faculty of Engineering did not have suitable facilities neither for holding the lectures nor for the laboratory exercises. Nevertheless the professors were top experts recognized all over the Europe. In the first academic year 286 students, among them two ladies, were enrolled for the section of mechanical and electrical engineering. Each subsequent year 100 to 180 new students were enrolled. The enrollment in the first year was so high due to simultaneous courses for the first two years. The significant drop in enrollment had happened between 1931 and 1938. The economic crisis was the reason for this. The threatening Second World War had led to an increased enrollment because studying at the University was one of the ways to avoid the recruitment into the army. Although electrical engineering was his main interest, Milan Vidmar was a doctor of classical mechanical engineering. The title of his dissertation was “Die Theorie der Kreiselpumpe”, (“The Theory of Centrifugal Pumps”). He was well aware of the importance of mechanical engineering. According to the curriculum of the Faculty of Engineering, the first and the second semester consisted of theoretical courses: mathematics, mechanics, chem-

istry, descriptive geometry and technical documentation. These courses were mandatory for the students of mechanical and electrical engineering. In the third and fourth semester of the academic year 1919/1920 dr. Milan Vidmar started lecturing on electrical engineering and theory of machining. Simultaneously assistant professor Vladimir Stanek lectured on machine elements. After one year Vladimir Stanek left the University of Ljubljana and accepted a job in Czechoslovakia. He was replaced by a part-time lecturer Josip Boncelj. In 1923 he became an assistant professor and got a regular job at the Faculty. In autumn 1928 he moved to University of Zagreb where he was immediately habilitated to a full professorship and also became the head of the newly established Institute for Construction of Machine Components. Soon after he graduated Josip Boncelj was employed by the company Hardware Factories and Foundries of Ljubljana. Under his leadership it evolved from a craft workshop to a modern industrial system. The company became a source of quality engineers. Some of them later became university teachers: Milan Vidmar, Dobromil Uran, Albert Struna and Bojan Kraut. After the departure of Josip Boncelj part-time lecturers Stane Premelč and Romeo Strojnik (employed by the Faculty in the year 1919/1920) continued to teach at the mechanical engineering section. THE ARRIVAL OF FELIKS LOBE Ten years after being established the University of Ljubljana displayed a great progress but the section for the mechanical engineering was stagnating. As a great educator Milan Vidmar noticed this fact. In the beginning of 1929 he issued a tender for the acquiring of new lecturers. Since there were not many candidates the tender had to be repeated. In the response to Vidmar’s personal invitation Feliks Lobe, who later became the honorary doctor of University of Ljubljana and the member of Slovenian Academy of Sciences and Arts, applied for the lecturer position. At that time he was the head of technical section in the company “First Yugoslav Factory of TrainWagons, Machines and Bridges” in Slavonski Brod. Feliks Lobe was immediately given an associate professorship. His arrival proved to be of the great importance for the strengthening of the mechanical-engineering section at the Faculty of Engineering. But it was too late for establishing the complete mechanical-engineering studies in Ljubljana before the Second World War. The students of mechanical engineering were forced to continue and complete their studies outside Ljubljana, mostly in Prague, Brno or Zagreb. The main reason for slow progress and expansion of mechanical engineering was the lack of known and established experts. Above-the-average mechanical engineer was also not interested in extremely low wages at the University of Ljubljana. For example, Feliks Lobe’s income was less than one third of the income that he had received in Slavonski Brod. The second reason for very low interest in teaching at the University may be too slow a career progression. For example, Josip Boncelj as a high-profile expert started at Faculty of Engineering as part-time lecturer and needed two years to become an assistant profes-

sor. After he switched to the University of Zagreb he was immediately habilitated for the full professorship. Stane Premelč, for example, remained part-time lecturer for 17 years. Then he quit lecturing due to the health condition at the age of 49. He died 22 years later. Milan Vidmar can be considered as an initiator of complete mechanical-engineering studies at the University of Ljubljana. He comprehended the importance of mechanical-engineering studies and supported it all the way. He invested many years of personal effort, will and sometimes cunningness to succeed in the realization of his goals. Zoran Rant is also a very important scientist from the Faculty of Mechanical Engineering who made University of Ljubljana known throughout the world. Immediately after his arrival to the Faculty of Engineering, Feliks Lobe started lecturing on the energy related courses “Thermodynamics” and “Power Engines”. This can be considered as an embryo of today’s Department of Energy Engineering. After the year 1937 he lectured also on the course “Manufacturing Technologies”. His first teaching assistants were Leopold Andrée and Boris Černigoj. After the Second World War they both became lecturers at the Department of Energy Engineering. Feliks Lobe had two primary goals: the complete studies of mechanical engineering in Ljubljana and the construction of much-needed facilities. After many complications, that Feliks Lobe ably solved, the construction of the building named Institute of Mechanical Engineering commenced in the autumn 1938 and was stopped at the end of 1939. The construction of the building was completed only after the war and solemnly opened on 15 March 1946. Nowadays this building is known as “the old building”. In the basement and high ground of this building, in the tract along the Aškerčeva Street, there was the Laboratory for Manufacturing Technology”. In the tract along “Murnikova Street” there was “Caloric Laboratory”. Feliks Lobe’s open mind obviously foresaw a simultaneous development of two mechanical-engineering branches: solidbody mechanics and fluid mechanics or, in other words, manufacturing and energy engineering. The “Caloric Laboratory” was connected to the basement containing heating station with two boilers and coal compartment. “The old building” was heated by means of this heating station. The successor of the “Caloric Laboratory” is today’s Laboratory for Heat and Power”. After the employment of new part-time lecturers everything was ready for the complete studies of mechanical engineering in Ljubljana. Finally, according to the Yugoslav-government decree from 5 April 1941, an independent mechanical engineering section of Faculty of Engineering was constituted. Next day the war between Yugoslavia and Germany burst out and the decree was not actually realized. According to the written documents the courses at mechanical-engineering section were held even during the Second World War until the summer of 1943. In July 1944 the supervision over the University of Ljubljana moved from the chief of Ljubljana regional administration directly to the supreme commissioner of the Jadransko Primorje region located in Trieste. Such an arrangement remained valid till the end of the war. The under and post-graduate exams and promotions continued even during this time.

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THE MECHANICAL-ENGINEERING SECTION AT THE FACULTY OF ENGINEERING After the Second World War the council of the Faculty of Engineering on 23. June 1945 decided to divide the Faculty to seven departments: • • • • • • •

Department of Architecture, Department of Electrical Engineering, Department of Civil and Geodetic Engineering, Department of Chemistry, Department of Mining and Metallurgy, Department of Mechanical Engineering, Department for Supplementary Courses.

The curriculum of mechanical-engineering studies was upgraded and many new lecturers were hired. Feliks Lobe was personally involved in the majority of the selection and appointment process. During the year 1946 the following lecturers were habilitated: assistant professor Leopold Andree, professor Leon Kavčnik (left the Faculty of Engineering after one year), associate professor Franček Kovačec, associate professor Bojan Kraut, professor Zoran Rant, and professor Anton Vakselj. In the year 1948 and 1949 the following lecturers were habilitated: assistant professor Boris Černigoj, associate professor Boleslav Likar, professor Ivo Vuškovič (left the Faculty of Engineering after three years) and professor Dobromil Uran. Nine so called institutes were formed inside the mechanical-engineering section although they cannot be compared to nowadays institutes, chairs or departments. They comprised only specialized mechanical-engineering courses: • Institute for Theory of Machining, head: Zoran Rant, courses: thermodynamics, mechanisms, • Institute for Steam Engines, head Feliks Lobe, courses: technology of metals, manufacturing machines, steam engines, • Institute for Hydraulic Power Engines, head Albert Struna, courses: water turbines and pumps, lubrication and lubricants, internal combustion engines, motor-driven vehicles, • Institute for Aeronautics, head: Anton Kuhelj, courses: aeronautics. Anton Kuhelj was a member of the Department for Supplementary Courses but held lectures at the Department of Mechanical Engineering for about 30 years. • Institute for Measurements in Mechanical Engineering, head: Leopold Andree, courses: steam boilers, technical-measurement techniques, • Institute for Manufacturing Technologies, head: Leon Kavčnik, courses: technology of metals. Leon Kavčnik took over the courses that were previously lectured by a chemist prof.dr. Maks Samec. • Institute for Design of Lokomotives, head: Bojan Kraut, subjects, railroad vehicles, technology of manufacturing, thermodynamics and power engines for electrical engineers, • Institute for Elevators and Transportation Devices, head: Franček Kovačec, subjects: elevators and transportation devices, introduction to mechanical

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engineering • Institute for Machine Elements, head Romeo Strojnik, courses: machine elements, technical documentation. According to the names of the institutes and the lecturers, approximately half of the institutes were energy and the other half technology related. Today’s Department of Energy Engineering is a direct successor of the Institute for Theory of Machining and partly a successor of the Institute for Steam Engines, Institute for Hydraulic Power Engines and Institute for Measurements in Mechanical Engineering. On 31 July 1948 the first two students graduated the complete mechanical-engineering studies in Ljubljana: Jožef Herman and Josip Kuralt. One of the first doctors of mechanical engineering became Zoran Rant in 1950. He was the professor at the University of Ljubljana and later at the Technical University of Braunschweig, Germany. For years 1919 to 1945 it was characteristic that mechanical engineering in Slovenia had a hard time ploughing its independent route, recruiting quality teaching staff and was facing a lack of suitable facilities. We can say that after the end of the Second World War the pioneering period of Slovene university-level mechanical engineering had ended. During this period professors were mainly occupied with teaching and writing of the textbooks, acquiring equipment for the laboratories and with manufacturing or purchasing various teaching tools. Expert work and scientific research was neglected in this period. The leadership of the University was facing many administrative and financial obstacles caused by the government in Belgrade and the Second World War. In the year 1950 University of Ljubljana, first time after thirty years of its existence, faced a major reform: Faculty of Engineering and Faculty of Medicine separated from the University and constituted their own rectorates and administration. Former departments at the Faculty of Engineering were renamed to faculties except for the Department for Supplementary Courses. After a period of four years Faculty of Engineering and Faculty of Medicine returned into the University of Ljubljana. In the year 1952 Faculty of Theology was removed from the list of national institutions. In 1957 Faculty of Engineering was discontinued. During this reorganization the Departments for Mechanical Engineering and Electrical Engineering merged to form the Faculty of Electrical and Mechanical Engineering which lasted for only three years. INDEPENDENT FACULTY OF MECHANICAL ENGINEERING According to the decision of the University Council from 1 October 1960 during summer vacations the Faculty of Electrical and Mechanical Engineering was divided to two independent units: Faculty of Electrical Engineering and Faculty of Mechanical Engineering. The first dean of the independent Faculty of Mechanical Engineering was Zoran Rant. Along with this reorganization three-stage studies were introduced ending with a diploma, a master thesis and a doctorate dissertation. The Faculty of Mechanical

Engineering moved away from a decade-lasting tradition and significantly lengthened the path to the doctorate. This system had lasted for about 40 years. Lately the old traditional two-stage path was reintroduced: ten-semester undergraduate studies ending with a diploma and postgraduate studies ending with a doctorate dissertation. In 1960 when the Department for Mechanical Engineering was upgraded to the Faculty of Mechanical Engineering, it consisted of four units named “deparments” defined as organizational units where teachers along with assistants and other staff carried out pedagogic, scientific and expert work. This definition of the departments is still valid. From the names of these departments three classical mechanical engineering fields can be sensed: Construction and Mechanics, Manufacturing Technologies, Energy and process engineering: • Department of Working Machines and Transportation • Department of Manufacturing Technology • Department of Power Engines and Thermal Devices • Unit for Mathematics and Other Supplementary Courses In the school year 1962/63 the Institute of Mechanical Engineering was constituted in the scope of the Faculty of Mechanical Engineering. It was a financially independent subject employing the staff from the Faculty of Mechanical Engineering. Its first goal was to establish the cooperation with industry and to carry out scientific-research work. In the year 1966/67 studies were divided into two main branches: technology and energy related. The names of the departments remained unchanged. The number of students rapidly increased after the end of the Second World War and current facilities were not adequate any more. In the year 1958 location documentation for “the new building” was issued. The project documentation was finalized in 1962. In the year 1964 the construction of the building commenced but was suspended due to the financial reasons in 1965. The construction continued in 1968 and ended in 1971. The great role in finalizing the construction of “the new building” played Bojan Kraut who later became the honorary doctor of the University of Maribor and professor emeritus. Years from 1945 to 1971 can be considered a period of classical university-level mechanical engineering in Slovenia. The Faculty of Mechanical Energy gained respect in industry which craved for its expert work and support after the Second World War. Almost all new professors originated from the industry and that is one of the reasons why the teaching staff of the Department for Mechanical Engineering and later Faculty of Mechanical Engineering successfully cooperated with many companies offering their expert and scientific knowledge. University teachers were extensively involved in the design, repair and maintenance work on machines and devices. Namely at that time Yugoslavia was politically and economically isolated from the developed western countries. Modern Slovene terminology was evolving and a big role was played by honorary doctor Albert Struna who promoted and initiated the publishing of the Journal of Mechanical Engineering. New expert societies were emerging and first

Mechanical Engineering Handbook Guide was published by Bojan Kraut (“Kraut’s” Mechanical Engineering Handbook Guide). The conditions for scientific-research work were still unfavorable although Zoran Rant should be mentioned due to his pioneering and world-widely recognized research work dealing with the quality of energy. Introduction of terms “Exergy” (1953) and “Anergy” built him an everlasting monument and placed University of Ljubljana among the established universities of the world. MODERN FACULTY OF MECHANICAL ENGINEERING In the year 1971, when the construction of “the new building” was finished and populated, a period of classical university-level mechanical engineering came to its end. Characteristic for the first period (1919-1945) was a lack of facilities and teaching staff which prevented the complete studies of mechanical engineering. The Second World War contributed a lot to this unfavorable situation. During the second period (1945-1971) complete studies of mechanical engineering were realized and gained the reputation in Slovenia. Simultaneously cooperation of Faculty of Mechanical Engineering and industry began. After 1971 a period of modern development of the Faculty of Mechanical Engineering began. New square footage in “the new building” enabled the expansion of scientific-research work. Faculty of Mechanical Engineering opened its door to the world. In the school year 1971/1972 the number of departments increased to six and the next year to seven: • • • • • • •

Department of Energy Engineering Department of Heating and Process Engineering Department of Working Machines Department of Cybernetics Department of Manufacturing Technologies Department of Materials Unit for Supplementary Division

The number of departments remained unchanged for 25 years. Two thirds of the departments were dealing with manufacturing technologies and only one third of them with energy: From the day it was constituted the Department of Energy Engineering contains three laboratories: Laboratory for Heat and Power, Laboratory for Internal Combustion Engines and Laboratory for Hydraulic Machines. Nowadays Faculty of Mechanical Engineering comprises 19 departments.

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Introduction of Prof. Dr. Zoran Rant (1904-1972) Text by Prof.Dr. Matija Tuma

Exergy and Anergy In May 1953, The Society of German Engineers (VDI) and The German Association for refrigeration (DKV) organised a joint consultation on heating and cooling technology in Lindau / Bad Schachen at Lake Constance. After the lectures about the evaluation processes and the definition of efficiency by taking into account the other main sentence of thermodynamics, a discussion on “technical working ability” has developed. Debate was attended by well-known professors Fran Bošnjaković (1902 - 1993), Peter Grassmann (1907 - 1994) and Rudolf Plank (18861973). It was Prof. Plank who has already suggested for several times that a “technical working ability” should find a label that would be typical and internationally understandable. At this occasion, Prof. Zoran Rant stepped in the classroom and wrote the word “Exergy” on the board. By the philological way he explained the prefix “ex” and the root “ergon”. His proposal to introduce a new word exergy instead of technical working ability, was well accepted especially Rudolf Plank warmly welcomed the new word. Photography from this event is still preserved [1]. This is the short description of the event, published at the 90th Anniversary of the birth of Prof. Dr. Zoran Rant, by Prof. Hans Dieter Baehr (1928 - 2014), a well-known university lecturer and a good friend of Zoran Rant. Prof. Rant, the author of the concept “exergy” will be presented in details as follows. Zoran Rant was born on 14 September 1904 in Ljubljana. His father Dr. Alojzij Rant was a lawyer, a very knowledgeable expert who has served in high places in the Austro-Hungarian Empire and later in the Yugoslav Navy. At the end of career, he was financial director of the City of Ljubljana. His mother Tilka, born Verbič, originated from a wealthy family, born in a small town near Ljubljana. They had four children: the firstborn son died at childbirth, Zoran was the second child and later he got a younger brother and a sister. He was attending schools in different places of the Austro-Hungarian Empire, he graduated in 1922 at the Classical Secondary School in Ljubljana and reached diploma in December 1926 at the Technical High School in Vienna. He finished Military service in 1927 as an officer in the Yugoslav Air Navy. In early 1928 he worked for a brief period in the ironworks Ravne and in the same year exceeded to the Soda Factory Lukavac in Bosnia, which was then part of the Belgian Solvay Group. In 1932 he worked in the General Directorate of the Group in Vienna for a short time, in 1939 and 1940 in the General Directorate in Zürich and from 1943 to October 1945 in the Commercial Directorate in Zagreb. Zoran Rant was one of the few Slovenians who provided himself a visible place in the world treasury of technical knowledge with the concept of exergy [3] and later with the concept of anergy. Each energy consists of two parts: exergy and anergy – one part (exergy) can convert into 134

other forms of energy and the other part (anergy) which is needed but not convertible into other forms of energy [4]. Because of these two terms, Zoran Rant is well known among the experts around the world. His other achievements are less known, but almost as important as his discussions about exergy and anergy. Scientific interests of Prof. Rant were focused on energy problems in process technique. Changing energy from one form to another, rational as much as possible was the main idea that he followed at all theoretical and practical research work. After the Second World War Zoran Rant was one of a handful of experts worldwide who overpowered the manufacturing process of soda and that is why he was called for technical assistance in many countries. At the 90th Anniversary of his birth (1994), Prof. Rant was presented in a special edition of “Zoran Rant - An Anthology”, published in Slovenian and English [5], as well as at the 100th Anniversary of his birth (2004) in the Journal of Mechanical Engineering [6], where also a lot of graphic material was published. In 1994, Faculty of Mechanical Engineering of the University of Ljubljana set him up a memorial in a faculty hall. Rant’s contribution to the development of thermodynamics and process technique was in Germany and around the world presented by Prof. Dr. Wolfgang Augustin. Rant’s personality and his work at the TU Braunschweig were presented by his first assistant, Dr. Jurgen Krey in his book “Geschichte der Verfahrenstechnik an der Technische Universität Braunschweig” (History of Process Technique at the Technical University of Braunschweig) within the collection “Zur Geschichte der Wissenschaften” (The History of Science) [7]. Prof. Rant was presented as a great expert and practitioner, a very propulsive director of the Institute for Process Engineering, respected university lecturer, an internationally wellknown scientist and a very popular colleague. By all these publications, Prof. Dr. Zoran Rant was very well presented to German and world audience. His scientific, pedagogic and professional bibliography is impressive, it includes 43 scientific papers, 9 scientific books, 7 scientific articles and 19 various publications. His most important publications were published in German language; important part of his work published in Slovene language was published in the Journal of Mechanical Engineering [7]. Some publications are in the Croatian language, individual works can be found in English, French, Spanish, Italian, Russian, Bulgarian and Czech language. Scientific, pedagogical and professional work of Prof. Rant can be divided into three major periods: • 1928-1946 expert and manager in Soda Factory Lukavac in Bosnia, • 1946-1962 a full professor of Technical machine sciences, University of Ljubljana, • 1962-1972 university lecturer of Process Engineering, Technische Universitat Braunschweig.

THE SODA FACTORY LUKAVAC (1928-1946) As a 24 years old engineer, Zoran Rant started to work in Solvay Soda Factory in Lukavac, Tuzla. The bases of the factory were built way back in 1893 with the name „Prva bosanska tvornica amonijačne sode“ (First Bosnian Ammonia Soda Factory). In 1908, the factory passed into hands of the Group „Solvay Werke“, who started to modernize its production and was re-directed to the new Solvay technological process. For young Zoran Rant was the modernization of production real engineering challenge. He started to work hard immediately and to educate. At the end of his career he became technical director of the factory. Until his death he remained closely connected with the production of soda in Lukavac, although the factory was nationalized after the World War II. The faith of the once globally known factory was not exactly glamorous. In 2006, just before the bankruptcy, Turkish company bought the factory and is now named „Sisecam Soda Lukavac“. In the seventeen years of service at the Solvay Zoran Rant had a chance to use his engineering knowledge and theoretical findings in practice. He started as the head of the construction office and eventually took the other important assignments, such as keeping the main manufacturing plant of soda and concern for the modernization and extension of the whole factory. In the General Directorate in Zürich he renewed the technical department and was responsible for their factories in Hungary, Romania and former Yugoslavia. He also met his future wife Mara Lakić at that factory. Prof. Rant was able to exploit the opportunities provided at perfectly organized Solvay, and to educate in both ways - practically as well as theoretically. At his theoretical work in the factory he came out with an idea of working ability of heat and internal energy. At his practical work he found a theme for his doctoral dissertation entitled “Energy Evaluation of the Procedure of Soda Production,” which is based precisely on the basis of working ability of heat, which he later called exergy heat. Dark clouds crowded over him and his young family with three children after the end of World War II. The new government accused Solvay Group at the end of 1945, co-accused at the court in Tuzla was also Zoran Rant. In prison, he met a well-known thermodynamics scientist, Prof. Franjo Bošnjaković, who was two years older. In prison they became friends and their friendship lasted for good. Many eminent persons intervened to free the two prominent defendants and Acad. Dr. h. c. Feliks Lobe (1894-1970), “father” of the Faculty of Mechanical Engineering, University of Ljubljana, assured him a new life. UNIVERSITY OF LJUBLJANA (1946-1962) On 1 April 1946, Zoran Rant became a full professor of Technical machine sciences at the Department of Mechanical Engineering at the Technical Faculty, University of Ljubljana, by the invitation of Prof. Lobe. He worked there by the autumn of 1962. Those were the years in which Prof. Rant matured, as an educator and as a scientist. Soon after adjusting for a university professor he

ended and successfully defended his doctoral dissertation (in spring 1950). In spite of unsettled and unjust accusations in the country, Rant has continued to help building “their” Factory of soda in Lukavac. In next few years he managed to quickly restore the factory that was defected in the maelstrom of war and also to increase its capacity. He prepared the specifications for building similar factories in Colombia, Argentina and Egypt. He actively assisted in the construction of soda factories in India and Brazil as well as in almost all the countries of Eastern Europe. He was also participating in the construction and renewal of several other factories in Slovenia. Besides his work at the faculty, he was dealing with modernization of compressor systems in the Slovenian coal mines and the reconstruction and designing of new cement plants. Despite of the poor and low-calorific coal, only available in the country, he managed to enlarge production of clinker to an enviable technical level. According to his specifications, two Slovenian limestone factories have been restored and fully mechanized. He has also helped in the construction of Slovenian thermoelectric plants and several small and large cooling towers. Rational changing of energy from one form to another was the thought that he was accompanied by almost all of his theoretical and practical research. His almost prophetic thoughts, which he wrote in 1957, are still worth reading [8]. “One can often hear that we are living in the era of technology, and yet it might be more correct to call this new period which mankind is really just entering an era of energy, as I have read somewhere. Energy is the motive power which gives the technology of today an honourable stamp: on the one hand it makes life easier for man and, at the same time, it makes the building of ever new gigantic technical works possible. The free use of energy and its application are a direct measure of the richness or poverty of nations. Energy is thus becoming the most precious and noble benefit – all of the world hungers for energy. The need for energy is, naturally, proportionally larger in less developed and underdeveloped countries than it is in the more and the most developed countries. The solving of energy problems is difficult, above all due to the limited energy sources and considerable financial means required to activate energy sources. We fight energy problems constantly and trouble our heads with the question of how and from where to provide the ever larger amounts of electrical energy needed for the economy and our homes.” As a university lecturer, Prof. Rant not only raised the level and improved the study of thermodynamics and process techniques to a level above average, but also knew how to attract young people to scientific work in these fields. He was a lively and a cheerful man who attracted every listener with his faith and optimism. He knew how to fill with enthusiasm students who decided to enrol in the studies under his mentorship, not only with interesting themes, but also with his personality. He was strict to himself and to others in reflecting on his pedagogic mission. Some of his thoughts he wrote in 1959 are still worthy of reflection [9]: “For a professor, thorough knowledge of the subject is only a part of his qualification. Only when a professor has a number of moral characteristics, combined with knowl-

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edge, does he gain authority among the audience. A professor should be the first and the best friend to a student, which naturally, should not be related to lower criteria in studies and examinations. A student should feel this friendship and there is no greater satisfaction for us professors than to have the trust of our students. Nothing is more pleasing to a mature man than to be in constant contact with young people and to give them something which will be of benefit to them throughout their lives. It is a great privilege enjoyed by few people.” And further: “A professor should also be a good pedagogue. It is a delicate question, since it is well known that pedagogical skills are not always connected with solid knowledge, and vice versa”. “Of course, for a university lecturer, scientific and professional education is more important than his pedagogic skills. Experience also shows that in time, it is possible to acquire at least a sufficient pedagogic ability on the basis of knowledge, but not vice versa.” He ends his thoughts as follows: “A professor should give his students more than he bare, and therefore dead, knowledge. That knowledge should be expressed with his personality and, in a way, bear his own stamp. A professor should present his lecture with enthusiasm, his personality and character should be given out to students. Professors and students, after selection, naturally, are inseparable whole and not two different sides. Problems in cooperation should not be discussed at all – with the correct attitude, they do not exist.” As a university lecturer he was able to attract learners, he radiated a real engineering enthusiasm in his lectures. He substantiated heavily understandable topics with examples from his own industrial practices and provided students an impression they are learning something they can well use in life. His lectures were carefully prepared, his exams were always written and oral and he was strict in the evaluation but he took enough time for each student. In sixteen years of academic career of Prof. Rant at the University, an independent Faculty of Mechanical Engineering has grown from the Department of Mechanical Engineering and Prof. Dr. Rant became its first dean. In 1959 he published the book “Verdampfen and Theorie und Praxis” (Evaporation in theory and practice), which was translated into several languages a nd has experienced several editions. He received the National Award ,,Boris Kidrič” for that book in 1960. We can also put the book “Thermodynamics” in this era, published in Slovene in 1963. The book was reprinted in 2001 and is still the most important Slovenian work from the field of thermodynamics. TECHNICAL UNIVERSITY OF BRAUNSCHWEIG (1962-1972) Zoran Rant left the Faculty of Mechanical Engineering in Ljubljana in October 1962 and accepted the invitation of the Technical University of Braunschweig to organize and to be the Chair of Process Technique. He became ordinarius at the TU Braunschweig and was named as the next director of the institute. Technical University of Braunschweig has a centuries-old tradition. In 1745, Collegium Carolinum was founded in Brunswick. It was college for students between high school and the university, which

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had a good reputation already at that time. School has spread through the decades to Polytechnic, in 1878 in the Technical College and at the time of Prof. Rant received its present name: Technical University of Braunschweig. Chair of Process Engineering was founded in 1961 and was formed by dividing Chair for Thermal and Process Technique, headed by prof. Bošnjaković. When he left, his department divided into three chairs: the Thermodynamics, Heat and Combustion Technique and Process Engineering. The last one was handed to Prof. Rant and in the school year 1962/63 he started with four-hour weekly lecture “Process Engineering”. Lectures, which were attended by 70 students, were resumed in the summer semester. In the winter semester prof. Rant also had lectures of the subject under the common title “Exergy”. In the following years he also lectured some other related subjects. Despite the lack of space, was the first assistant called already in October 1962, the second one in early 1963 and the third one in October 1963. At the same time, Rant was trying to start a new investment – building of a new Institute for Process Engineering. He was successful with that, as the building process started in November 1964 and in September 1966, a new four floor building with 2000 m2 of working space was ready to use. As the director of the Institute, Prof. Rant also took care for all subsidiary plants: for ensuring technological steam, demineralized water, cooling water and air compressor. Part of the Institute was also a large open area for experiments that could not be carried out in a building. In this era Prof. Rant reached his peak as a consultant, educator and scientist. He has published a series of important articles. In 1968 he wrote the book “Die Erzeugung von Soda nach dem Solvay-Verfahren” (Soda Production according to the Solway Method), made the new Chair for Process Engineering and built a large new institute. Besides memberships in a variety of reputable professional associations, he became a corresponding member of the Slovenian Academy of Sciences and Arts, where he was proposed by Acad. Dr. h. c. Feliks Lobe. In 1970, he received the medal named “Johann-Joseph-Rittervon-Prechtl-Medaille” by the Vienna University, which is meant for its most respected graduates and in 1971, less than a year before his death, the medal “Arnold-EuckenMedaille” by the German Association for Process Engineering, which is being presented only every two years. Exergy and anergy were the most important thermodynamic topics in Germany from 1961 to 1966. The introduction of the two concepts, proposed by Prof. Rant caused a strong reaction at the beginning and divided experts into supporters and opponents of these concepts. Basics and the use of exergy and anergy were discussed in numerous articles and several consultations. On the German Engineering Consulting in Münich in 1964, prepared by the Society of German Engineers VDI, were presented several papers on exergy and anergy. Both concepts were quickly spread throughout Eastern and Northern Europe; but they were not that popular in Western Europe and in the US. A resistance to the introduction of the concept of exergy was present also in Germany. The opponents argued that the introduction of a new term was redundant.

After the end of the thermodynamic colloquiums, annually organized by the Section Energy Technology VDI, several professors joined closed debate on Exergy in the years 1965 and 1966. Opinions were divided. Zoran Rant, Hans Dieter Baehr and other defenders of the concept were not able to convince opponents and therefore these meetings no longer continued after 1966. For this reason, in the next ten years at the Colloquium no one dared to lecture on Exergy. Zoran Rant was no longer alive when Americans accepted exergy – because of the two oil crises in 1973 and 1979. “Second law analysis” has become an important headword in the United States at that time. Exergy has been discussed again, not considering European development and principles of Zoran Rant. “Professor Rant would certainly look forward to the fact that Americans did not only rediscover our knowledge, but also repeated our mistakes”, concludes his interpretation Hans Dieter Baehr. Prof. Rant remained connected with the Faculty of Mechanical Engineering in Ljubljana even after his departure to Braunschweig. Despite many commitments he still found time to give cyclical lectures to students in Ljubljana and in other education centres in former Yugoslavia on thermodynamics, control technique and thermal process engineering. Prof. Rant was perfectly combining his features in excellent techniques, as a practical expert and a very good teacher. Zoran Rant wrote a request for retirement exactly on his 67th birthday, on 14 September 1971. He did not live long enough to retire as he died of a heart attack in Münich, 12 February 1972. Originally, he was buried in a family tomb in Ljubljana. Later, at the request of his wife, who he deeply respected all his life, Zoran Rant was reburied. Now he rests in the cemetery in Piran, together with the oldest daughter Metka and his wife Mara. PROF. ZORAN RANT – A MAN Rant was a man of principles and positive life philosophy: responsibility and duty were typical for his character and self-confidence and modesty for his personality. He was workaholic but his family was always the most important in his life. He was very attentive, not only towards his wife and three daughters, but also towards other relatives and friends. Rant was very sociable and always an excellent and humorous co-speaker. At larger gatherings, which were in Braunschweig almost always joined with related institutes, were his speeches something special. It almost became a rule that his speech was full of jokes and humour, calling it “Rant Rede” (Rant’s speech). That put him at the centre of attention. There were always some anecdotes about him circulating among colleagues and students at home and in Germany. After World War II there were not many university lecturers who would have a PhD on the technical field. On the question why he has a doctorate, he explained that this is just because of his signing. As Ing. Rant someone might read it wrong and call him Professor Ignorant. As the director of the institute he had a very modern way of management, even for now days. He had a lot of confidence to his colleagues, they had to make decisions

and take responsibility. He knew that they can make their own decisions and know where the limits of their competence are. In the first years of his work in Braunschweig he preferred colleagues who had proven themselves with industry practice. He took care that they were all equally burdened with teaching and other administrative tasks, regardless of what financial sources were they paid from. He took over presenting of the Institute towards ministry, university administration, etc. and left most of the Institute cases to the assistants. He was closely monitoring scientific research work of his colleagues. He found time for all the problems they had, including personal. He was a man of unusual character who almost always succeeded to gain surroundings for his ideas with his positive philosophy. He was persistent and propulsive in his ideas, he could not hear “no” and if necessary, he used “sports negotiations”, as he liked to say. He was using all possible tricks: persuasion, charm, persistence and some other tricks. He had many tactics. He was sure that it is necessary to find weak points of the co-speaker. If you can not immediately succeed, it is necessary to withdraw two steps back, two further away and then back on. Or, behave stupid and provide the facts in the meantime. If necessary, apologize or ask for help, so that the error does not occur any more. Iva Zozoly, granddaughter of Zoran Rant, is remembering her grandfather: “Zoran Rant was born in the early 20th century and was really a child of that time - even figuratively. It was a time when people believed in the unlimited power of progress, when it seemed that science can give answers to all the problems of mankind and that progress can only improve the world. In such an atmosphere as a young man in 20-ies of the 20th century, he enthused himself for the Mechanical Engineering and remained faithful to that passion till the end of his life. References [1] Energie und Exergie. Die Anwendung des Exergiebegriffes in der Energietechnik, Düsseldorf, VDI Verlag 1965 [2] H. D. Baehr: Exergie und Anergie. Zoran Rant – An Anthology, Ljubljana 1994 [3] Rant, Z.: Exergie, ein neues Wort für »technische Arbeitsfähigkeit«, Forschung auf dem Gebiet des Ingenieurwesens (22) 1956/1, str. 36-37. [4] Z. Rant: Exergie und Anergie. Wissenschaftliche Zeitschrift der TU Dresden (3) 1964/4, str. 11451149. [5] M. Tuma (urednik): Zoran Rant – An Anthology, Ljubljana 1994 [6] A. Alujevič (urednik): Journal of Mechanical Engineering (50), Ljubljana 2004, št. 9 [7] W. Augustin (urednik): Geschichte der Verfahrenstechnik an der Technischen Universität Braunschweig, knjižna zbirka »Zur Geschichte der Wissenschaften«, Braunschweig 2001 [8] Z. Rant: Termoelektrarna Šoštanj (v slovenščini), Journal of Mechanical Engineering (50), 1957, št. 4/5, str. 79-82 [9] Z. Rant: Nekaj besed k študiju na oddelku za strojništvo (v slovenščini), Strojniški zbornik, Ljubljana 1959, str. 17-24

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Study programme

The Faculty of Mechanical Engineering (FME) is the principal institution of higher education in the Republic of Slovenia. Being fully aware of the given responsibility it provides, by performing education on all three study levels (undergraduate, master’s and doctor’s studies), leading its own research and disseminating the acquired new knowledge, the conditions for an improved competitive position of the Slovenian economy in the globalised world markets. The FME carries out education in mechanical engineering for over 90 years. Recently, the old study programmes have been updated in accordance with the Bologna reform guide lines. The fundamental objective of all those study programmes is to educate the graduates of mechanical engineering, adequately qualifying them, depending on the level of a study programme, for applied and development work, as well as for independent research creating so new knowledge both in the area of mechanical engineering disciplines and in the fields that require interdisciplinary networking. In its activities, while striving to ensure knowledge comparable on the European level and employability of the graduates the FME is abiding by the criteria of sustainable development and environmental protection all the time. The study programmes’ curricula are conceived both on respecting the Bologna reform premises on one hand and including, depending on the level of education, a corresponding upgrading of the fundamental knowledge, on the other hand. The acquired knowledge, skills and competences will allow students, through the action of students’ mobility and credit-based certificate of performed study duties, to move between study programmes, thus optimizing their personal education in accordance with their professional preferences. Enriched by such international experience the students will enter, when graduated, the labour market competently. BACHELOR OF SCIENCE IN MECHANICAL ENGINEERING, RESEARCH & DEVELOPMENT PROGRAMME The primary objective of this undergraduate university study programme, which addresses mostly that part of the secondary-school population attending high-school (gymnasium) education, is to provide the qualification of a professional, who will be able to solve complex research and development problems and tasks in the area of me138

chanical engineering efficiently and creatively. As we are aware that it takes more than three years, which is the duration time of this undergraduate programme, to achieve this goal entirely, we have taken as the starting point for this phase of study the emphasised building up of a strong fundamental and rather basic professional knowledge. This enables the programme’s graduates to make their acquaintance with and understand a wide range of mechanical engineering problems and to obtain, at the same time, a large amount of interdisciplinary knowledge. Considering that the programme is conceived intentionally as a programme, which is to be followed by a corresponding master’s programme, the employment opportunities for the graduates will certainly be, despite equipped with a broader knowledge from the area of mechanical engineering, substantially scarce. The main goal of the programme is clearly, considering the established comprehension of the impact an integrated and interdisciplinary approach has on solving the most challenging problems in modern mechanical engineering, to encourage most of the graduates to continue their education on the masters’ level with the research and development-oriented study emphasized. MASTER OF SCIENCE IN MECHANICAL ENGINEERING, RESEARCH & DEVELOPMENT PROGRAMME The master’s study programme is in its substance a continuation and an upgrade to the three-year undergraduate programmes in mechanical engineering (both programmes, specified in this table in the columns aside, apply jointly with the actual master’s programme for the accreditation following cluster procedure) and the topics addressed therein. Considering advanced topics the programme is clearly oriented, in the spirit of the Bologna reform, into specific professional fields of mechanical engineering individually. By introducing at the same time in the programme new interdisciplinary fields of study and including related topics, we follow the needs and demands of current economic and social development. This context also provides the justification for the introduced Engineering pedagogy study field, with which the FME assumes the responsibility to ensure a higher level of quality and efficiency in the education of technical profiles involved in teaching the mechanical engineering courses

and general technical courses in upper secondary schools. The primary goal of the master’s study programme is to educate graduates, giving them a full qualification to conduct independent interdisciplinary research and development projects and to design, manage and realize applied projects. To achieve this, we rely firstly on the sound theoretical knowledge the students have acquired in their undergraduate study about individual physical phenomena and their practical effect, and secondly on the way how we will empower intense research and development oriented study assisted with adequate methodological approaches. The fundamental objectives followed by the programme in the Engineering pedagogy field focus on ensuring competences and skills for autonomous work in the secondary education and teaching. Based on modern didactics theories the graduates develop the potential of evaluating one’s own practice and creating innovative solutions in the school practice.

PhD PROGRAMME

The primary goal of this higher professional study programme, which addresses mainly that part of the secondary-school population not attending high-school (gymnasium) education, is to provide fair fundamental education in the field of mechanical engineering and sufficient applied knowledge in a narrower professional field of study selected by the student. The acquired knowledge, skills and competences, will enable the graduates for immediate employment in the enterprise sector. They will be able, being in possession of fundamental engineering knowledge upgraded adequately with applied mechanical engineering know-how, to integrate into the processes of management and maintenance of production, as well as into the project design and technological work involving also creative applied development of new, technically more demanding products with a higher value added.

RESEARCH & DEVELOPMENT PROGRAMME

PROGRAMME ENTRANCE

MECHATRONICS

PRODUCTION, ENGINEERING

BACHELOR OF APPLIED SCIENCE IN MECHANICAL ENGINEERING

ENGINEERING DESIGN, MACHINE OPERATION AND MAINTENANCE

BACHELOR OF SCIENCE IN MECHANICAL ENGINEERING

POWER, PROCESS AND ENVIRONMENTAL ENGINEERING

RESEARCH & DEVELOPMENT PROGRAMME

AVIATION

MECHATRONICS AND LASER TECHNOLOGY

MACHINE DESIGN AND MECHANICS

PRODUCTION ENGINEERING

JOB POWER AND PROCESS ENGINEERING

MASTER OF SCIENCE IN MECHANICAL ENGINEERING

BACHELOR OF APPLIED SCIENCE IN MECHANICAL ENGINEERING, PROJECT ORIENTED APPLIED PROGARMME

PROJECT ORIENTED APPLIED PROGRAME

PROGRAMME ENTRANCE

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Graduated students in 2015 Graduated students according to masters study program or previous university degree program at DEE in 2015

LABORATORY FOR HEAT AND POWER Mentor

Student

Dregree

Prof.Dr. Mihael Sekavčnik

Rok Čepon

MSc

Jaka Grošelj

MSc

Klemen Spruk

Univ.Dipl.

Assoc.Prof.Dr. Andrej Senegačnik

Dušan Pirman

MSc

Gregor Lukežič

MSc

Assist.Prof.Dr. Mitja Mori

Grega Štern

MSc

Mentor

Student

Dregree

Prof.Dr. Branko Širok

Jaka Gortnar

MSc

Damjan Zajc

MSc

Alja Puhek

Univ.Dipl.

Assoc.Prof.Dr. Matevž Dular

Miha Pogačar

MSc

Darjan Podbevšek

MSc

Pablo Gutiérrez Ruiz

MSc

Assoc.Prof.Dr. Marko Hočevar

Nejc Draksler

Univ.Dipl.

LABORATORY FOR HYDRAULIC TURBOMACHINERY

LABORATORY FOR INTERNAL COMBUSTION ENGINES AND E-MOBILITY

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Mentor

Student

Dregree

Assoc.Prof.Dr. Tomaž Katrašnik

Jure Voglar

MSc

Darvor Rašić

MSc

STUDY PROGRAMME YEARBOOK 2016

Mentor Prof.Dr. Mihael Sekavčnik

Mentor Assoc. Prof. Dr. Andrej Senegačnik

Rok ČEPON Title: Energy system for utilization of internal calorific energy of seawater as heat source and heat sink Abstract: This study presents an energy system for utilization of internal calorific energy of seawater for heating and cooling of a hotel on Slovenian shore as an alternative to the classical energy systems. New system was designed and evaluated through environmental and economic aspect. A numerical model of the energy system was developed, based on energy and mass balances. Some typical stationary operating conditions were simulated. Results gained with numerical simulations were used to calculate energy system’s operational costs and its environmental impact. The results show that running cost as well as carbon dioxide emissions of the new energy system is much lower than it was with the previous system.

Dušan Pirman Title: Boiling in wood chips fired membrane wall constructed furnace Abstract: Properties of an industrial steam boiler are presented in this thesis. Boiler generates superheated steam and is fueled by fresh wood chips with high water percentage. We presented energy balance of the boiler, considering each heat exchanger separately. Discussion over thermosyphonic water and steam cycle for boiling water in vertical membrane walls is held. We analyzed boilers thermal output by thermovision with which we identified weakly insulated areas. We made diagram - Hd, td for flue gases and energy balance calculation of boiler.

Jaka GROŠELJ Title: Joule supercritical carbon dioxide cycle Abstract: In this Master thesis we were exploring closed thermodynamical Joule power cycle with supercritical carbon dioxide (sCO2) as a working medium. We compered this power cycle with theoretical ones and also with traditional power cycle like Rankine and open Joule power cycle. We made computer model for calculating thermodynamical properties for carbon dioxide at supercritical pressure and temperature. With use of these computer models we did calculations of two most common cycles design. Two most common power cycles are: simple sCO2 and cycle with recompression. We did sensitivity analysis of most delicate parameters which affect power cycle efficiency and comparison with traditional power cycles. Results of analysis showed good matching with literature and showed that power cycle with sCO2 has no superior advantages over traditional ones, considering whole energy transformations. Klemen SPRUK Title: Use of micro-steam turbine in CHP system with wood biomass Abstract: In the diploma thesis we have reviewed the theoretical possibilities of combined heat and power (CHP) generation using wood biomass. We focused on the CHP system with micro steam turbine and wood biomass fired boiler. Program IPSEpro was used to model the whole system. We compared the results of thermodynamical calculations with data from praxis and used them for systems economic evaluation, based on the levelized cost of electricity and net present value. The results of thermodynamic and economic calculations show, that with the predicted values the system is economically efficient and that the investment is most sensitive to the amount of support gathered for the generated electricity.

Gregor Lukežič Title: Exraction of natural gas using hydraluic fracturing methode Abstract: This work contains a detailed description of the hydraulic fracturing method. From the available data, all additives which are added to the water for the proper conduct of the process are analyzed. All threats and dangers that the additives represent to the environment are objectively estimated. On this basis is provided a general assessment of the environmental acceptability of certain additives and the acceptability of the overall method. In the conclusion is an assessment of the potential environmental impacts which can be caused of using of the hydraulic fracturing method on gas bearing field in Slovenia, nearby Lendava.

Mentor Assist.Prof.Dr. Mitja Mori Grega ŠTERN Title: Life-cycle assessment of uninterruptible power supply system based on fuel cells Abstract: In this master’s thesis, environmental analysis of 3kW uninterruptible power supply system based on fuel cells, was made. Presented system was designed and developed as part of an international project called FluMaBack. The presentation included system’s structure, comparison with existing systems and theoretical basics of life-cycle assessment method. Based on relevant literature and existing research, quantitative data were acquired and used for making complete numerical life-cycle model in software tool GaBi 6. Results revealed that use phase (hydrogen production) has the greatest environmental impacts. Energy and environmental comparison with existing system showed that using fuel cells for powering uninterruptible power supply systems is very suitable.

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Mentor Prof.Dr. Branko Širok Jaka GORTNAR Title: Adhesion of dust to the fan rotor ofvacuum cleaner unit Abstract: Problems of adhesion of dust on the rotor radial fans that are installed in the vacuum cleaner unitsin various technical applications cleaning in dusty atmosphere, is big. The most common way of solving this problem isremoving dust particles before they are sucked into the rotor. The solution can be approached with the transformation of the rotor with the aim of reducing the adhesion of dust in the rotor. Adhesion of dust on the surface of the rotor is primarily due to flow conditions in the flow tract rotor. We have approached the problem with the experiment. We have done experimental adhesion of dust on the rotor, so that we determine the main areas of adhesion of dust in the rotor blade. By measuring the thickness of dustwe determined the shape of the flow tract smeared rotor.We have constructed andproduced a new form of rotor blades, so that we could determine the integral characteristics of the smeared rotor. We determined the correlation between the mass of dust on the blades of the dust in the air flow, at constant concentration. With CFD simulationsanalyzed the impact of thickness of dust on the blades on the integral air characteristics. Using computational fluid dynamics and analysis of the flow conditions of the air on the blade, we have tried to identify the reasons for the adherence of dust at the points of the maximum thickness. We constructed a new rotor, in which the adhesion of dust is almost completely eliminated. Damjan ZAJC Title: Fibre transport in the air flow and primary layer formation on the perforated grid Abstract: The purpose of this task is to carry out measurements and a kinematic analysis of the air flow in a vertical pipe of an experimental station. The whole problem of mineral wool production is based on the appropriate formation of a primary layer, while in order to identify the structure it is of primary importance to make the inventory of kinematics of the velocity field in the area of fiber transport. It is also necessary to detect the interaction of the air flow with the emerging fibers and then to complete basic visualization of the formation of the primary layer on a perforated surface. The purpose of this visualization is primarily to extract, out of time-dependent images, the basic physical picture of the primary layer formation through which we can, by changing individual parameters on the experimental station, optimize the formation of the latter. The entire experimental system must meet the requirements and conditions of different local and time scales so that the questions upon integral characteristics of the velocity field and local events in some parts of the station could be answered. Alja PUHEK Title: Effect of secondary flow on wing surface flow characteristics Abstract: The thesis represents an experimental study of the effect of secondary air flow on velocity field near 142

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the airfoil surface. Basic theory of wing, boundary layer control, statistical methods and visualization is presented. Experiment conducted is based on boundary layer control by blowing jet of secondary flow of air on the trailing edge of the profile. Separation points and angle of attack on leading edge are verified. As inlet variables, external flow over the wing, internal flow on trailing edge and angle of attack are controlled. Study is based on the use of computer-aided visualization. Separation point for each measurement is defined in ADM-Flow software. Angles of attack and stagnation points on the leading edge are defined statistically. Connection between leading edge velocity field, as well as separation point, and integral parameters: Reynolds number, angle of attack and ratio of secondary and primary flow, is presented. Finally, the effect of secondary flow on the change of angle of attack and separation point is presented.

Mentor Assoc.Prof.Dr. Matevž Dular Miha POGAČAR Title: Cavitation as a method for ensuring microbiological stability of wine Abstract: The term cavitation describes the phenomenon and behaviour of vapour bubbles in a liquid: the phase change from liquid to vapour and vice versa. Given appropriate conditions, local pressure drops inside the cavitating ow field occur at approximately constant temperature. The effects of cavitation are mostly undesired, however in some cases it may prove crucial for enabling or improving certain processes. Unwanted effects of cavitation include surface erosion, excessive noise generation and hydrodynamic pressure losses. On the other hand cavitation is being successfully implemented in medical applications, for cleaning of submerged contaminated surfaces and for optimization of certain processes. In the proposed master thesis, we investigated the possible use of hydrodynamic cavitation as a means of interrupting fermentation in wine musts and young wines. The interruption would occur at a certain sugar level of the must in order to reach a microbiologically stable wine before the bottling process. We also investigated the suitability of different cavitation regimes in terms of microbiological decontamination and sensorical properties of wine. The results of the thesis will serve as validation of hydrodynamic cavitation as an alternative technology in food processing, as well as its implementation in the real world wine production. Darjan PODBEVŠEK Title: Development of temperature and pressure sensitive nano probes for applications in confocal microscopy Abstract: Microchannels are often used in the study of fluid dynamics. With the aid of fluorescent microscopy the physical parameters in a flow can be determined at any chosen point. With the addition of nano probes into the observed fluid the confocal microscope makes possible two or three dimensional mapping of the parameters in the microchannel. In this master thesis we investigated a new family of luminescent substances, which could serve as fluorophores in the nano probes. The samples were

exposed to different pressures and temperatures while performing a spectroscopy analysis. The analysis of the spectral response at the specific parameters allowed us to determine the most likely source of the peaks in the emission spectra and allow future engineering of such substance. We also evaluated the substances suitability for use in the nano probes. Such nano probes could eventually allow us to produce a three dimensional point by point measurement of temperature and pressure in the microchannel flow in a single acquisition. Pablo GUTIÉRREZ RUIZ Title: Relationship between pressure oscillations and cavitation erosion Abstract: The cavitation phenomenon, which is characterized by the formation and condensation of vapour bubbles, is often observed in hydraulic machines, where it causes vibrations that increase hydrodynamic drag, changes in the kinematics of the flow, noise, heat and light effects, and cavitation erosion. The mechanism of cavitation damage is, despite a significant amount of work in the past years, still not completely clear. One of the commonly used ways to evaluate the potential of cavitation to initiate damage is to measure pressure amplitudes via hydrophone. This method is, however, still poorly investigated. In the scope of the MSc thesis, we designed a test-rig for acoustic cavitation. We then measured the pressure oscillations at different conditions (water levels, hydrophone position and submergence). One the other side, we measured the cavitation aggressiveness by counting pits in a thin aluminium foil which was exposed to cavitation. In the final part of the work, we related the pressure amplitudes with the extent of the damage sustained by the aluminium foil.

Mentor Assoc.Prof.Dr. Marko Hočevar Nejc DRAKSLER Title: Design of guide vane for axial fan of air assisted sprayer for fruit orchards Abstract: This thesis represents the design of guide vane for axial fan for improving the aerodynamic properties of phytopharmaceutical agents air assisted sprayers and measurement results. The purpose of the work is to ensure an adequate flow of air, depending on the properties of the tree crown. Design and measurements were conducted at the Agricultural Institute of Slovenia, under the supervision of the Laboratory of Water and Turbine Machines. Measurements were carried out on the air assisted sprayer, of which is spraying optimized, intended for the effective application of the spray on plants. In the first part of the thesis, we designed guide vane of axial fan for the air assisted sprayer. Based on the measurements, we determined if it is possible to improve the functioning of the axial fan for the air assisted sprayer with the installation of guide vanes in front of it. In the second part of the thesis, we installed the designed guide van on the air assisted sprayer. We have carried out: measurements of the speed of output of the air flow at the exit of the sprayer, measurements with a visual method, measurements of velocity vectors of air flow with five hole probe, which were carried out in a number of

planes, that is, before the guide vane, between the guide vane and the axial fan and at the output of the axial fan in a number of working points and measurements of velocity vectors behind the fan, across the entire surface plane behind the fan. In conclusion, we evaluated the results of measurements and made suggestions for improved technological solution of upgrade of the guide vane.

Mentor Assoc.Prof.Dr. Tomaž Katrašnik Jure VOGLAR Title: Method for determination of location of top dead center form measured in-cylider pressure Abstract: Finding the correct Top Dead Center (TDC) offset for an internal combustion engine is harder than it seems. Thermodynamic TDC offset estimation is specialy demanding when dealing with engines where ignition occurs before reching TDC. That kind of problem is treated in this thesis. Thermodynamic approach with polytropic process assumptions was used to determine TDC offset. We focused on compression of gas mixture in cylinder before start of combustion. Calculations using several different methods were made by using numerical computing environment Matlab. All methods used least squares approximation method to find best fit between measured pressure trace and polytropic mathematical model. We wrote souce codes based on two basic assumptions. First assumption was based on unchanging polytropic exponent during process, while second assumption took into account changing of its value. Because value of polytropic exponent during real compression process is changing, one of the source codes using assumption of changing polytropic exponent proved itself as the most suitable based on tests. This source code calculated values of polytropic exponent using energy transfer ratio. Davor RAŠIĆ Title: Methodology for processing measured pressure trace in the cylinder of a diesel internal combustion engine Abstract: The objective of the thesis was to design, implement and validate a proposed methodology for processing of the pressure trace, measured in the cylinder of a diesel internal combustion engine. For this purpose, an analysis of the contributions of motoring, combustion, pressure oscillations in the combustion chamber and noise to the overall pressure trace was performed. The results of this analysis were validated using the short time Fourier transformation. This data was further used to determine the most appropriate FIR filter parameters. The most widely used method of estimation of the FIR filter order was used, but despite its presumable high effectiveness it did not prove its applicability for highly accurate analyses of in-cylinder processes. Consequently, a new and improved method of determination of the FIR filter order was proposed. Developed filters were validated with spectral analysis, the calculation of the rate of heat release and mass fraction burned.

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Dr. Martin Petkovšek Janez Koselj Marko Peternelj Igor Mele Assistant Boštjan Jurjevčič Assoc.Prof.Dr. Marko Hočevar Aleš Malneršič Assistant Dr. Samuel Rodman Oprešnik Assistant Dr. Lovrenc Novak Assistant Dr. Benjamin Bizjan Urban Žvar Baškovič Rok Vihar Assistant Dr. Boštjan Drobnič Assistant Tine Seljak Assistant Dr. Igor Kuštrin Rok Stropnik Ambrož Kregar Andrej Lotrič Tadej Stepišnik Perdih Assistant Dr. Gregor Tavčar Prof.Dr. Mihael Sekavčnik Assoc.Prof.Dr. Andrej Senegačnik Assoc.Prof.Dr. Tomaž Katrašnik Prof.Dr. Branko Širok Secretary Darja Jeločnik

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