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International Journal of Electrical and Electronics Engineering Research (IJEEER) ISSN(P): 2250-155X; ISSN(E): 2278-943X Vol. 4, Issue 2, Apr 2014, 113-124 © TJPRC Pvt. Ltd.

EXPERIMENTAL AND ANALYTICAL STUDY OF ROOF HEAT EFFECT ON THE PERFORMANCE OF SOLAR DESALINATION SYSTEM K. RAJ THILAK1, R. KIRUTHIKA2 & M. SAKTHIVEL3 1,2 3

Department of EEE, Sri Eshwar College of Engineering, Chettipalaiyam, Tamil Nadu, India

Department of Mechanical Engineering, Info Institute of Engineering, Coimbatore, Tamil Nadu, India

ABSTRACT This paper presents a new approach to enhance the productivity of single basin solar stills especially during the nocturnal period; a heat recovery system (building roof heat) was coupled to the still. An exertion has been made to utilize the maximum amount of solar energy and to reduce the heat loss from the sides and the bottom of the still. The roof heat (copper tubes lay inside the roof) absorbs the excess heat energy from solar radiation during noon hours. An experimental as well as theoretical investigation is carried out. This device can be a suitable solution to solve drinking water problem. Mathematical models are developed to give the ability to estimate the expected performance of the system under given climatic conditions. The whole investigation is based mainly on experimental data under real usage conditions. To validate the proposed mathematical models, comparisons between experimental and theoretical results had been performed. Good agreement had been achieved. The study also showed that the daily production of still can be increased by reducing the depth of the water in the basin. These results indicate that the still productivity is increased by 17–20% and also the amount of heat penetrated inside the building through the roof can be reduced.

KEYWORDS: Single Basin Solar Still, Roof Heat, Glass Temperature INTRODUCTION The demand on fresh water is growing steadily and is becoming one of the worldwide challenges. Fresh water is a basic human need, and it is adversely affected by the pollution created by man-made products. Seawater comprises approximately 97.5% of global water resources, and the remaining 2.5% of fresh water is available in the earth surface in the form of deep wells and natural aqueducts. From that, less than 1% of the earth's fresh water is within human reach for drinking and agriculture purposes. It has been predicted that in many parts of the world, two thirds of humanity will face a shortage of drinking water by 2025 due to the poor quality of fresh water. The demand for fresh water is rapidly increasing, while supply has been decreasing over the decades. This is the right time for technology to take an important role and match the supply with demand for fresh water. Any technology developed by scientists is accepted only if the system is ecologically friendly and economically viable in the present conditions. Many technologies were invented for desalination purposes, and most do not satisfy the above considerations. Many types of renewable energy resources are available for the desalination of water but solar distillation has become more popular in recent years, particularly in rural areas. Solar distillation mimics nature’s hydrologic water cycle by purify water through evaporation as well as condensation. It is one of the most basic purification systems available today to get high quality of drinking water and can remove non-volatile contamination from almost any water source.

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K. Raj Thilak, R. Kiruthika & M. Sakthivel

Solar still is a one kind of solar distillation system in which brackish or impure water converted into drinkable water. Solar stills are economically better than any other water purifying system but the only disadvantage is its low productivity that is the amount of distillate is very low. In order to increase the efficiency of the solar still a number of changes in the design are suggested by various researchers. One of the solutions to increase the productivity or output of a solar still is adding a heat recovery system (roof heat) to the still. Ben Bacha H. et al. [1] investigate the behaviour of a Desalination unit coupled with solar collectors and a storage tank by a series of modelling and simulation to increase productivity of the desalination unit. In this paper, mathematical models were carried out and used for simulation of three different configurations solar hot water systems. He concluded that the modelling and simulation results achieved showed that a divided hot water tank with internal heat exchanger increasing considerably the production of distilled water than those obtained with the others configurations. Abdallah S. et al. [2] developed and tested the sun tracking system for productivity enhancement of solar still. A computerized sun tracking device was used for rotating the solar still with the movement of the sun. A comparison between fixed and sun tracked solar stills showed that the use of sun tracking increased the productivity for around 22%, due to the increase of overall efficiency by 2%. It can be concluded that the sun tracking is more effective than fixed system and it is capable of enhancing the productivity. Badran O.O. et al. [3] experimental Investigation to study the effect of coupling a flat plate solar collector on the productivity of solar stills was carried out. Comparison of the output between coupled and stand alone still was studied. It was found that the productivity of the coupled still is found to be 36% higher than the still alone. He concluded that, the present still design leads to higher distilled water output due to higher basin water temperature. El-Sebaii A. A. et al. [4] conducted Thermal performance of an active single basin solar still (ASBS) coupled to shallow solar pond (SSP) to enhance the productivity of still especially during the night time. An analytical model and numerical calculation were carried out for the various elements of the system. From the obtained results, it is concluded that the daily productivity Pd of the ASBS with the SSP is found to be higher than that of the still alone. The daily efficiency of the ASBS with the SSP is higher than that obtained without the SSP by 54.98%. Farshad Farshchi Tabrizi et al. [5] designed and investigated experimental the study of an integrated basin solar still with a sandy heat reservoir. Integrated heat reservoir causes to have significantly higher solar still productivity during nights and cloudy days. Also, as the heat reservoir integrated with the solar still, it does not need pumping systems and operators for the night mode usage. Also, the analysis of the input brackish water, desalinated water and the output salty water is reported. He attained that the implementation of a sandy heat reservoir to a basin solar still enhances the daily productivity. Kabeel A. E. et al. [6] experimental as well as theoretical investigation of modified stepped solar still were carried out to improve the performance of still. Preheating the feed water of the stepped still has a slight effect on enhancing the productivity, but the efficiency of the system decreases approximately to the half. The daily efficiency and the estimated cost

per

liter

of

distillate

for

stepped

and

conventional

solar

stills

are

approximately

53%–0.039$.

Kalidasa Murugavel K. et al. [7] conducted experiments on a double slope simulation type solar still with thin layer of water in the basin. He stated that for maintaining thin layer of water basin, the water was spread throughout the basin by some kind of wick or porous materials. In this work, experimental results of still yield by using wick materials, light cotton cloth, light jute cloth and sponge sheet of small thickness and porous materials like washed natural rock of small sizes were compared. He concluded that the still with black light cotton cloth as spread material is found to be more productive. Impact Factor (JCC): 5.9638

Index Copernicus Value (ICV): 3.0


115

Experimental and Analytical Study of Roof Heat Effect on the Performance of Solar Desalination System

Madhlopa A. et al. [8] developed and tested a passive solar still with separate condenser. The system has one basin (basin 1) in the evaporation chamber and two other basins (2 and 3) in the condenser chamber, with a glass cover over the evaporator basin and an opaque condensing cover over basin 3. The top part of the condensing cover is shielded from solar radiation to keep the cover relatively cool. The performance of the system is evaluated and compared with that of a conventional solar still under the same meteorological conditions. Results show that the distillate productivity of the present still is 62% higher than that of the conventional type. Rattanapol Panomwan Na Ayuthaya et al. [9] investigated experimentally the thermal performance of an ethanol solar still with fin plate to increase productivity. The test still contained a horizontal evaporating surface and a condensing surface inclined 14° to a horizontal. Various concentrations of ethanol-water solution were employed for this experiment. Accordingly, a mathematical model was developed based on the Spalding theory of convection and the Fick’s law of diffusion. He found that the productivity of the modified solar still was increased by 15.5%, Compared to that of a conventional

still.

Condition

of

high

concentration

output

and

high

productivity

was

investigated.

Torchia - Nuneza J.C. et al. [10] steady-state and transient theoretical exergy analysis of a solar still, focused on the exergy destruction in the components of the still: collector plate, brine and glass cover. The analytical approach states an energy balance for each component. The energy balances are solved to find temperatures of each component; these temperatures are used to compute energy and exergy flows. Results in the steady-state regime show that the irreversibilities produced in the collector account for the largest exergy destruction, up to 615W/m2 for a 935W/m2 solar exergy input, whereas irreversibility rates in the brine and in the glass cover can be neglected Vijaykumar K.C.K. et al. [11] constructed and tested performance of hollow clay tile (HCT) laid reinforced cement concrete (RCC) roof for tropical summer climates. He proposed a new concept wherein hollow clay tiles (HCT) are laid over RCC instead of WC. When compared with conventional WC roof. When air is allowed to flow through the hollow passages, the air flow is found to take care of all variations in the outside climate and solar radiation, thus providing almost uniform roof bottom surface temperature. Ravikumar M. et al. [12] analysis of heat transfer in PCM filled RCC roof for thermal management. A transient numerical procedure is developed. The simulation is carried out on 365 days of year for these three roofs. He concludes that on yearly basis, about 56% reduction in heat transmission into the room is obtained with PCM roof when compared to the conventional weathering coarse laid roof. Runsheng Tang et al. [13] experimentally investigated and analysis on a thermal performance of an improved roof pond for cooling buildings. The model is based on the newly proposed empirical correlation of water evaporation rate from a wetted surface to the ambient air proposed by the authors, and takes into account the response of buildings as a whole to evaporative cooling. Results by simulations show that, regardless of the type of buildings the technique is applied to, RPWGB has a better cooling performance in terms of the indoor air temperature and heat flux through the roof into pond as compared to a roof covered with wetted gunny bags, which had been widely considered to be one of the most efficient roof cooling techniques.

EXPERIMENTAL SET-UP The Schematic diagram of single basin solar still is designed as shown in Figure 1, which is modified by adding heat recovery system (roof heat) to the still. The solar still consists of the following components glass cover, basin, aluminium channel to collect condensate, wooden frame and insulation (saw dust) material.

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116

K. Raj Thilak, R. Kiruthika & M. Sakthivel

The Still has a rectangular basin having an area of 1m x 0.5m made by bending a mild steel of 2mm thickness and assembled by soldering. The inner surfaces of the basin facing the sun are painted black for maximum absorption of solar radiation. The bottom and side walls of the basin are insulated with saw dust (thermal conductivity = 0.069 Wm-1K-1) of 40mm thick. The insulated basin is kept in a wooden frame of trapezoidal shape; two of its parallel sides are rectangular in shape while the other two parallel sides are trapezoidal as shown in Figure 1

Figure 1: Schematic Diagram for the Solar Still with Roof Heat The still cover is made of 0.004m thick ordinary glass and kept on the wooden frame at an inclined position at an angle of 25° with respect to the horizontal. An aluminium channel is attached to the lower end of the glass cover to collect the condensed water (yield) which slides from the inner surface of the glass cover and that condensed water is taken outside using a funnel arrangement and collected in a measured jar. Holes are made in the sides of the still frame for feeding raw saline water, and a tap is provided to drain the saline water. Calibrated Ni Cr–Ni thermocouples, connected to a multichannel temperature recorder are inserted through the holes provided in the sides of the still and fixed at different points to measure the temperatures of different parts of the still like basin, water, vapour–air space, inner and outer surfaces of the glass and ambient temperature. To keep the whole system vapour tight, silicon rubber is used as a sealant because it remains elastic for quite a long time. The global solar radiation on a horizontal surface is measured using a solarimeter. This instrument is analog type, can measure in the range 1–100mWcm-2 solar intensity with an accuracy of 2mWcm-2. A plastic beaker of 2 L capacity is used to measure the hourly yield. The still is placed along the east-west direction and inclined glass cover surface is facing south to intercept maximum solar radiation. In the single basin solar still, experiments have been carried out to find the effect of water depth or quality of saline water in the still productivity and to find the optimum depth (quantity) of saline water at which the still yield will be maximum. Then the same still is coupled with heat recovery system (roof heat) to utilize the energy during nocturnal period. Roof structure has a rectangular area of 1m x 1m made by concrete material of 60 mm thickness. Copper tube of length 47.3m lay inside the roof structure at the depth of 40 mm. Experiments have been carried out under the same climate condition to find the effect of roof heat in the still productivity.

Impact Factor (JCC): 5.9638

Index Copernicus Value (ICV): 3.0


Experimental and Analytical Study of Roof Heat Effect on the Performance of Solar Desalination System

117

MATHEMATICAL MODELLING Mathematical equation that describes the performance of each component of the system for the still and the roof are presented. The method of solving these sets of equations to predict the system performance is presented. Energy balance equations for each component of the system. •

Energy Balance for the Glass Cover The rate of energy absorbed by the glass cover out of solar radiation strikes on it and rate of energy received from

water surface by radiation, convection and evaporation is equal to the rate of energy lost to atmosphere from glass cover by convection and radiation.

I ( t ) A gl + U ows gl ( Tws − Tgl ) = ( h c gl-a + h r gl-a )( Tgl − Ta ) U o ws-gl = ( h c ws-gl + h eva ws-gl + h r ws-gl ) •

Energy Balance for the Basin The rate of energy absorbed by the basin out of solar radiation strikes on it is equal to the rate of heat from basin

to water by convection and rate of heat lost from basin to atmosphere through bottom and sides of the still by conduction and convection.

I ( t ) A b = h c b-ws ( Tb − Tws ) + U o b-a ( Tb − Ta ) U o b-a •

 1 L L 1  = + ins + sd +   h c b-ws K ins K sd h c b-a 

−1

Energy Balance for the Water Mass in the Still The rate of energy absorbed by the water out of solar radiation strikes on water and rate of heat energy absorbed

by water from basin by convection is equal to the rate of energy stored in water due to its specific heat and rate of heat loss from water to glass cover by radiation, convection and evaporation.

I ( t ) A w + h c b-w ( Tb − Tw ) = M ws C P ws

dTws + U o ws-gl ( Tws − Tgl ) dt

(3)

U o ws-gl = ( h c ws-gl + h eva ws-gl + h r ws-gl ) •

Energy Balance for the Concrete The rate of energy absorbed by the concrete out of solar radiation strikes on it is equal to the rate of energy stored

in concrete due to its specific heat and rate of heat from concrete to water by convection.

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118

K. Raj Thilak, R. Kiruthika & M. Sakthivel

I ( t ) A c = M c Cpc

dTc ( Tc − Twc ) + r dt ln 2 r1 1 + 2π K c h c c-w 2π r1

(4)

Energy Balance for the Water Mass in the Roof The rate of heat from concrete to water by convection is equal to the rate of energy stored in water due to its

specific heat.

( Tc − Twr ) r2 r1 1 + 2π k c h c wr 2π r1

= M wr Cpwr

ln

dTwr dt (5)

The absorptances of the system components are given by

A gl = (1 − γ gl ) α gl

(6)

A ws = (1 − γ gl )(1 − α gl ) α ws

(7)

A b = (1 − γ gl )(1 − α gl ) (1 − α ws ) α b

(8)

A c = (1 − γ c ) α c

(9)

The above equations can be re-arranged as follows: Equations (1) and (6) can be re-arranged as

  1 Tgl =   U + U ogl − a ow − gl    I ( t ) A gl + U ogl−a Ta + U ow −gl Tw 

(10)

Equations (2) and (7) can be re-arrange as

  1 Tb =    h cb− ws + U ob−a   I ( t ) A b + h cb − ws Tws + U ob −a Ta 

(11)

Equations (3) and (8) can be re-arrange as

Impact Factor (JCC): 5.9638

Index Copernicus Value (ICV): 3.0


Experimental and Analytical Study of Roof Heat Effect on the Performance of Solar Desalination System

119

dTws ( U o ws-gl + h c b-ws ) + Tws dt M ws C P ws =

1  I ( t ) A ws + h cb− ws Tb + U ows −glTgl  M ws Cpws 

(12)

It is similar to the differential equation format of

dTws + a 0 Tws = c 0 dt Where

(U

o ws-gl

+ h c b-ws )

M ws CP ws

= a0 and

1  I ( t ) A ws + h cb − ws Tb + U ows −glTgl  = c0 M ws Cpws 

Then the solution for equation (12) is

Twsi +1 =

(

)

C0 1 − e - a 0 t + Twsi e − a 0 t a0

(13)

Equation (4) and (9) can be re-arrange as

 2 πΚ c h c c-w r1  r2  ln h c c-w r1 + Κ c d Tc  r1 +  dt M c C pc    I (t )A c + =

   T  c   

T w 2 π Κ c h c c -w r1 r ln 2 h c c -w r1 + Κ c r1 M c C pc

(14)

Where

 2 π Κ c h c c -w r1  r  ln 2 h c c-w r1 + Κ c r1   M c C pc   

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    = a 1    

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120

K. Raj Thilak, R. Kiruthika & M. Sakthivel

I(t )A c +

T w 2 πΚ c h c c-w r1 r ln 2 h c c-w r1 + Κ c r1 = C1 M c C pc

Then the solution for equation (14) is

Tci +1 =

(

)

C1 1 − e - a1t + Tci e − a1t a1

(15)

In similar way equation (5) can be re-arranged

d Tw r dt

 2 π Κ c h c w r r1  r2  ln h c w r r1 + Κ c r1 +   M w r C pw r   

  T 2πΚ h c c c -w r1 TC  w r  ln 2 h c c -w r1 + Κ c  r1  = M w r C pw r

   T  wr   

      (16)

Where

 2 π Κ c h c w r r1  r  ln 2 h c w r r1 + Κ r1   M wr C pwr   

c

    = a 2    

  T 2 πΚ h c c c-w r1 TC  w  ln r2 h  r c c-w r1 + Κ c  1 M wr C pwr

      =c 2

Then solution for equation (16) is

Twri +1 =

(

)

C2 1 − e - a 2 t + Twri e − a 2 t a2

(17)

The radiation and thermo physical data used in equations are given in table 1.

Impact Factor (JCC): 5.9638

Index Copernicus Value (ICV): 3.0


Experimental and Analytical Study of Roof Heat Effect on the Performance of Solar Desalination System

121

Table 1

Numerical Calculation A computer program has been developed for the solution of the above-said nonlinear equations (10), (11), (13), (15) and (17). The input parameters to the program include climatic, design and operational parameters were taken from the measured values. The relevant thermo physical parameters were taken from Table 1 Numerical calculations are initiated assuming the temperatures of different elements of the still to be equal to the ambient temperature at t=0. Using known initial values for different temperatures, different internal and external heat transfer coefficients are calculated. Using these values along with climatic parameters, Tgl, Tb, Tws, Tc and Twr are calculated from Equations (10), (11), (13), (15) and (17) respectively, for a time interval of 1 min. A time step of 1 min is used in the simulation. After knowing the hourly variation of Tgl, Tb, Twc, Tc and Twr, the hourly yield per unit area can be evaluated as given below

m=

h eva w gl ( Tw − Tgl ) x3600 h fg

kg m −2 h −1 (18)

Where hfg is the latent heat of evaporation (J kg-1) which can be taken from the steam table for the hourly average temperature of water. The procedure is repeated with the new values of Tgl, Tb, Tws, Tc and Twr for additional time intervals

NUMERICAL RESULTS AND DISCUSSIONS The different design and climate parameters used in this study are reported in table 1. In the conventional still, experiments are conducted for different depths of saline water (different quantity) per m2 area of the basin to get the optimum quantity of saline water. Experimental results are given in table 2

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122

K. Raj Thilak, R. Kiruthika & M. Sakthivel

Table 2: Experimental Observations in the Conventional Still for Different Depth (Quantity) of Saline Water 20 mm Depth of Saline Water 30 mm Depth of Saline Water (30 kg) (20 kg ) Temp of Still Temp of Still Temp of Temp of Water Time h Glass Cover Output Glass Cover Output ° ° Water Tws C Tws C tgl °C kg / m2 Tgl °C kg / m2 9.00 33.30 35.20 0.00 33.50 36.20 0.00 10.00 39.20 40.50 0.00 41.10 46.80 0.02 11.00 54.60 52.70 0.16 57.70 58.80 0.20 12.00 69.60 59.70 0.40 65.80 63.60 0.40 13.00 71.70 62.70 1.10 75.40 69.60 0.95 14.00 74.70 65.00 1.40 75.30 70.20 1.50 15.00 71.80 64.20 1.80 74.10 68.20 1.95 16.00 63.70 56.30 2.00 70.90 67.10 2.25 17.00 58.10 53.60 2.30 64.10 58.30 2.45 18.00 50.30 45.40 2.65 55.40 48.60 2.95 19.00 40.00 35.00 2.80 3.35

40 mm Depth of Saline Water (40 kg) Temp of Water Tws °C 32.90 42.30 55.70 62.00 72.10 70.90 68.70 67.90 62.20 58.20 40.60

Still Temp of Glass Output ° Cover Tgl C kg / m2 34.70 0.00 50.50 0.00 61.50 0.10 61.40 0.30 68.70 0.80 66.80 1.20 64.60 1.55 61.70 1.75 56.10 1.95 46.80 2.65 35.20 3.05

Solar Intensity I W/m2 240 475 680 840 740 660 620 520 320 0 0

Figure 2: Variation of Still Output for Different Depths of Saline Water in Conventional Still Experiments are conducted by covering a wide range of parameters such as temperature of water, temperature of glass cover, hourly yield, temperature difference between water and glass cover. At this particular condition, experiments were conducted for a number of days so that analysis and comparison could be done fairly under the same climatic condition and to get concurrent results. The effects of depth (quantity) of saline water in the conventional still have been analysed. Figure 2 shows the variation of still yield with time. It is found that for a certain lower depth (20 mm) of saline water, the yield per day is low and increases with depth and again starts decreasing beyond certain depth of saline water. It is predicted that for a particular depth of water (30 mm), yield per day is maximum. It is obvious that the still output is optimized at 30mm depth of saline water.

CONCLUSIONS An experimental work has been conducted to enhance the productivity of the single basin solar still, the still has been integrated with a heat recovery system (roof heat). This study mainly deals with the effect of parameters on the performance of the still and to optimize the performance. From the obtained results, it is concluded that the daily productivity of the single basin solar still with the roof heat is found to be higher than that of the still alone. Maximum efficiency of the still with the roof heat is found to be 52% which is 8% higher than the conventional still efficiency.

Impact Factor (JCC): 5.9638

Index Copernicus Value (ICV): 3.0


123

Experimental and Analytical Study of Roof Heat Effect on the Performance of Solar Desalination System

Therefore, the considered single basin solar still offers a suitable solution to the fresh water problems faced by the people living in remote and rural areas in the world especially in developing countries.

ACKNOWLEDGEMENTS The author would like to thank the guide for providing the guidance for doing this project.

REFERENCES 1.

S. Abdallaha and O.O. Badran, “Sun tracking system for productivity enhancement of solar still”, Desalination, vol.220, pp.669–676, 2008.

2.

O.O. Badran and H.A. Al-Tahaineh, “The effect of coupling a flat-plate collector on the solar still productivity”, Desalination, vol.183 pp.137–142, 2005

3.

H. Ben Bacha, T. Dammak, A.A. Ben Abdalah, A.Y.Maalej and H. Ben Dhia, “Desalination unit coupled with solar collectors and a storage tank: modelling and simulation”, Desalination, vol.206 pp.341–352, 2007.

4.

A. El-Sebaii, S. Aboul-Enein, M.R.I. Ramadan and A. M. Khallaf, “Thermal performance of an active single basin solar still (ASBS) coupled to shallow solar pond (SSP)”, Desalination, vol.280 pp.183–190, 2011

5.

Farshad Farshchi Tabrizi, Ashkan Zolfaghari Sharak., “Experimental study of an integrated basin solar still with a sandy heat reservoir”, Desalination, vol.253 pp.195–199, 2010

6.

A.E. Kabeel, A. Khali, Z.M. Omara and M.M. Younes, “Theoretical and experimental parametric study of modified stepped solar still”, Desalination, vol.289 pp.12–20, 2012.

7.

K. Kalidasa Murugavel and K. Srithar, “Performance study on basin type double slope solar still with different wick materials and minimum mass of water”, Renewable Energy, vol.36 pp.612-620, 2011.

8.

A.Madhlopa and C. Johnstone, “Numerical study of a passive solar still with separate condenser”, Renewable Energy, vol.34 pp.1668–1677, 2009.

9.

Rattanapol Panomwan Na Ayuthaya, Pichai Namprakai and Wirut Ampun., “The thermal performance of an ethanol solar still with fin plate to increase productivity”, Renewable Energy, vol.33 pp.1-8, 2012

10. M. Ravikumar and P.S. Srinivasan, “Heat Transfer Analysis in PCM Filled RCC Roof for Thermal Management”, ARPN Journal of Engineering and Applied Sciences, vol.7 pp.1819-6608, 2012 11. Runsheng Tanga and Y. Etzion, “On thermal performance of an improved roof pond for cooling buildings”, Building and Environment, vol.39 pp.201 – 209, 2004 12. J.C. Torchia-Nuneza, M.A. Porta-Gandarab, and J.G. Cervantes-de Gortaria, “Exergy analysis of a passive solar still”, Renewable Energy, vol.33 pp.608–616, 2008 13. K.C.K. Vijaykumar, P.S.S. Srinivasan, and S. Dhandapani, “A performance of hollow clay tile (HCT) laid reinforced cement concrete (RCC) roof for tropical summer climates”, Energy and Buildings, vol.39 pp. 886–892, 2007

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13 k raj thilak ijeeer  

This paper presents a new approach to enhance the productivity of single basin solar stills especially during the nocturnal period; a heat r...

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