Advancements in CFD Analysis of Shell and Tube Heat Exchangers with Nanofluid and Twisted Tape Turbu by IRJET Journal

Advancements in CFD Analysis of Shell and Tube Heat Exchangers with Nanofluid and Twisted Tape Turbulators: Mechanisms and Performance Enhancement"

Sudhanshu Bhushan1, Dr. Ajay Singh2, Dr. Parag Mishra3

1 Scholar, Department of Mechanical Engineering, Radharaman Institute of Technology and Science, Bhopal, M.P., India

2Head and Prof., Department of Mechanical Engineering, Radharaman Institute of Technology and Science, Bhopal, M.P., India

3AssociateProfessor, Department of Mechanical Engineering, Radharaman Institute of Technology and Science, Bhopal, M.P., India ***

Abstract -

Efficiency in industrial processes heavily relies on heat exchanger performance. As industries strive for heightened energy efficiency, integrating innovative methods becomes imperative.ComputationalFluidDynamics(CFD)hasemerged as a potent tool for optimizing heat exchanger designs. This review focuses on employing CFD techniques to explore the integrationofnanofluidsandtwistedtapeturbulatorsinshell andtubeheatexchangerstoenhanceheattransferefficiency significantly.Nanofluids,comprisingnanoparticlesdispersed in base fluids, offer potential for augmented thermal conductivity and convective heat transfer due to unique nanoparticle properties. Similarly, twisted tape turbulators manipulate fluid flow patterns within tubes, intensifying convective heat transfer but simultaneously increasing pressure drop. By analyzing numerous studies, this paper distillsinsights,challenges,andopportunitiesarisingfromthis combined approach. It delineates nanofluids' capability in improving convective heat transfer coefficients while addressing issues like nanoparticle agglomeration. Additionally, it underscores the impact of twisted tape turbulators on fluid flow dynamics and heat transfer, highlighting the trade-offs between enhanced heat transfer and increased pressure drop. The review emphasizes the necessity for holistic approaches combining theory, experiments,andsimulationstopropelinnovationinefficient heat exchange across diverse industries. The synergy of nanofluids, twisted tape turbulators, and CFD simulations presents promising avenues for advancing heat exchanger technology towardsenhancedefficiency andperformance.

Key Words: CFD Analysis, Shell and Tube Heat Exchanger, Nanofluid, Twisted Tape Turbulator, Rate of HeatTransfer

1.INTRODUCTION

The efficiencyofheatexchangersplays a pivotal rolein numerous industrial processes, ranging from power

generationtochemicalprocessing.Asindustriescontinueto seek enhanced energy efficiency and performance, researchers and engineers have explored innovative methods to augment the heat transfer rates within these systems. In recent years, Computational Fluid Dynamics (CFD) has emerged as a powerful tool for analyzing and optimizing heat exchanger designs. This review paper focusesontheutilizationofCFDtechniquestoinvestigate theintegrationofnanofluidsandtwistedtapeturbulatorsin shell and tube heat exchangers, aiming to achieve remarkable improvements in heat transfer efficiency. Nanofluids,colloidalsuspensionscontainingnanoparticles dispersed in conventional base fluids, have attracted substantialattentionduetotheirpotentialtosubstantially enhancethermalconductivityandconvectiveheattransfer. The unique characteristics of nanoparticles, such as high surfaceareaanddistinctivethermalproperties,haveledto intriguing possibilities for improving heat exchanger performance. Through precise control of nanoparticle concentration and size, researchers have aimed to exploit these properties to achieve elevated heat transfer coefficientsandreducedtemperaturegradients.

In parallel, the deployment of twisted tape turbulators withinheatexchangertubeshasdemonstratedconsiderable promiseinaugmentingheat transfer rates.Twistedtapes, with their ability to induce swirl, vortices, and enhanced turbulence,cansignificantlyinfluencefluidflowdynamics and heat transfer characteristics. By altering the flow patterns within the tubes, these turbulators contribute to increasedconvectiveheattransfercoefficients,potentially leading to more efficient heat exchanger operation. The convergence of nanofluid-enhanced heat exchangers and twisted tape turbulators, coupled with the computational powerofCFDsimulations,hasprovideda platformforindepthinvestigationsintotheintricateinteractionsbetween fluiddynamicsandheattransfer.Thisreviewpaperaimsto criticallyanalyzethecollectivefindingsfromvariousstudies, shedding light on the underlying mechanisms driving enhanced heat transfer performance. Furthermore, the

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paper will address challenges and limitations inherent in these techniques, such as nanoparticle agglomeration and pressure drop penalties, which necessitate careful considerationduringdesignandoperation.Asthedemands for energy-efficient technologies grow, the insights presentedinthisreviewpaperholdsignificantimplications for both academia and industry. By synthesizing the advancements in CFD analysis of shell and tube heat exchangers integrated with nanofluids and twisted tape turbulators, this paper contributes to a deeper understandingofthecomplexphenomenaunderlyingheat transferaugmentation.Itservesasavaluableresourcefor researchers,engineers,andpractitionersseekingtooptimize heatexchangerdesignsandadvancethefrontiersofthermal engineering.

2. LITERATURE SURVEY

Different types of heat exchangers, such as plate heat exchangers, tube fin heat exchangers, plate fin heat exchangers, double-pipe concentric tube heat exchangers, regenerators, cooling towers, and shell & tube heat exchangersare in use. They are selectedand designedfor specificpurposesandheatingandcoolingapplications[1]. Inpassivetechniques,theheattransferrateisimprovedby using some modification techniques such as swirl flow devices,extendedsurfaces,coiledtubes,additivesforliquids andgases,displacedenhancementdevices,etc.Incompound techniques, heat transfer is improved by the right combinationofpartialactiveandpartialpassivetechniques [2]. Z. Said et al. (2019) investigated Shell-and Tube Heat Exchanger operating withCuO/H2O nanofluid toanalyses thestability,heattransferperformance,possiblereduction oftheeffectiveareaandthermosphysicalpropertieswith Nanoparticleconcentrationsof0.05,0.1and0.3vol%.They foundthatoverallheattransfercoefficientincreasedby7%, and the area was reduced by 6.81 % [3]. Mohammad HusseinBahmani(2018)investigatedparallelflowdouble pipe heat exchangers and counter flow double pipe heat exchangers to evaluate heat transfer characteristics at turbulent flow conditions of H2O/alumina nanofluid. His resultsshowedthatbyincreasingthenanoparticlevolume fraction and with an increase in Reynolds number (Re), enhancement of convection heat transfer coefficient and Nusseltnumbertakesplace.Themaximumrateofthermal efficiencyenhancementandaverageNusseltnumberare30 % and 32.7 %, respectively [4]. Baba et al. (2018) investigated a double-pipe heat exchanger having longitudinal fins experimentally to evaluate heat transfer characteristics.TheyusedFe3O4/H2Onanofluids(0–0.4% volume concentration) at Reynolds number (Re) 5300 to 49000.Theyfoundthatathighervolumeconcentrationof nanofluids,therewasan80to90%increaseinheattransfer rateforproposed(finned)heatexchangersascomparedto plain tube heat exchangers [5]. A. K. Gupta et al. (2021) evaluated the heat transfer characteristics of SiO2/H2O, Al2O3/H2O, and CNTs/H2O nanofluids for turbulent flow

(Re2,000to10,000).Theyperformedcomputationalfluid dynamics(CFD)inaconcentrictubeheatexchanger.They considered1%,2%and3%volumeconcentrations.They found that23.72 %,20.71 %,and32.65% improvedheat transfer rates and a 26.83 %, 23.6 %, and 37.25 % improvementintheoverallheattransfercoefficientwitha3 %volumeconcentrationofAl2O3/H2Onanofluid,SiO2/H2O nanofluid,andCNTs/H2Onanofluidwhenequatedwithbase fluid, respectively [6]. In nanofluid, nanometer-sized particles,generallyhavinghighheattransfercharacteristics (metal oxides/carbides/CNTs), suspended in a base fluid, generallyhavinglowthermalconductivity(water/ethylene glycol/oil),formacolloidalsolution.Inpresentsituations, nanofluidhasbeenincorporatedsuccessfullytoenhancethe performance of solar devices [7]. A specially prepared mixtureofbasefluidandnanoparticlesiscallednanofluid. Nanofluid properties have a collective effect of base fluid propertiesandnanoparticleproperties[8].AdnanSözenet al.(2019)experimentedwithaplateheatexchangerwith1.5 wt%water-TiO2nanofluid.Theyuseatemperaturerangeof 40to50degreecelsiusandamassflowrateof3to7lpm. Theyresultedinan11%improvementinheattransferrate in experimental work [9]. Kumar & Chandrasekar (2019) performedcomputationalfluiddynamicanalysisondouble helical coiled tube heat exchanger with CNT/water nanofluids having 0.2, 0.4 and 0.6 % of volume concentrations.Theyresulted30%enhancementinNusselt numberwith0.6%volumeconcentrationofnanofluidwhile 11%ofpressuredropascomparedtowithoutnanofluids [10].Y.Phaindraaetal.(2018)experimentallyinvestigated heat transfer and flow characteristics of hybrid nanofluid (Al2O3 & Cu/Oil with a 0.1 % volume concentration) in a concentrictubeheatexchanger.Theresultshowsa10.34% average increase in Nusselt number for Al2O3 & Cu/Oil hybridnanofluidascomparedtopureoil[11]. M.Armstrong etal.(2020)organizedanexperimentalinvestigationintoa silver nano-coated double pipe heat exchanger to analyze heattransferperformanceusingthedisplacementreaction method.Theyobservedinnano-coatedsurfaceheattransfer increasedwiththeincreaseinmassflowratewitha95% enhancement as compared to bare copper pipe [12]. N. Parthibanetal.(2020)experimentallyinvestigatedtheheat transferperformanceofacounterflowheatexchangerwith SiO2 nanoparticles at different mass flow rates. Heat exchanger effectiveness and heat transfer rate were increasedwiththeuseofSiO2nanoparticles.Themassflow rate of 0.05 kg/s was found as the optimum for nanofluid [13]. L. Liu et al. (2021) evaluated the thermal energy storageperformanceofatubularheatexchangerusingPCM nano emulsion at charging and discharging temperature rangesof20–5°Cand5–15°Crespectively.Theyfoundthat PCMnanoemulsionhashighenergyreleaseefficiency(50% higher than water) and encouraging potential for airconditioningapplicationinbuildings[14]. M.E.Nakhchiet al. (2021) evaluated the heat transfer characteristics and thermalperformanceofadouble-pipeheatexchangerusing CuO/H2Onanofluids.Theyproposedanovelarrangement

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withperforatedcylindricalturbulators.Theyfoundthatfora proposed heat exchanger with a 1.5 % volume fraction of CuOnanofluids,thethermalperformancefactorwas1.931 higherascomparedtoasimpleheatexchangerarrangement [15]. S.Kaushiketal.(2021)performedcomputationaland experimental analysis for a concentric spiral tube heat exchangertoevaluateheattransferrates.Theyusedthree differentnanomaterials(Al2O3,ZnO,CuO)andtestedthem inturbulentflowconditions.Theyfoundoptimizedresults fortheReynoldsNumberrangeof4236–18540andaflow rate of 0.72 to 2.94 L/min [16]. C. J. Ho et al. (2022) experimentallyinvestigatedaconcentricdoubletubeductto analyses forced convection heat transfer (at laminar flow condition) with the use of Al2O3/PCM nanofluids. In this experimental setup,Al2O3/Waternanofluidisusedinthe outer tube and PCM Nanofluid in the inner tube. They discoveredthatatRe=1700,heattransferrateincreasesby 32%for1%Al2O3/H2Onanofluidand4.63%forphasechangenanofluid[17]. JShenglanetal.(2022)Innovative double-tube heat exchanger with staggered helical fins (DTHE-SHF) showcased notable advantages: substantial pressure drop reduction compared to traditional designs (DTHE-TSHF)andanenhancedcomprehensiveperformance by 10%–30%. Through numerical simulations and field synergy theory, the DTHE-SHF's optimized synergy angle between velocity and pressure fields contributed to improvedthermalefficiency[18].JBahrametal.(2022)The studyexploresconvectionheattransferinacountercurrent double-tubeheatexchangerwithvariousfinconfigurations using water-aluminum oxide and water-titanium dioxide nanofluidsatdifferentconcentrations.Comparedtowatertitaniumdioxide,water-aluminumoxidenanofluidexhibits superior convection heat transfer, with a 12% increase in coefficient at 6% concentration. Geometries with fins, especially the curved fin, show significantly improved efficiency (up to 85%) compared to finless designs, while maintaining lower pressure drops despite higher heat transfer coefficients. However, higher Reynolds numbers andnanofluid concentrationsresult in increasedpressure dropsinthisnovelgeometry[19].KDeshmukhetal.(2023) The study investigates TiN nanofluid's convective heat transferperformanceinaheatedUpipe,analyzingitsimpact atvariedconcentrationsandflowconditions.UtilizingTiN nanoparticles in water presents promising thermal propertiesforsolarapplications.Experimentalevaluations demonstrate increased heat transfer efficiency with TiN nanofluidconcentrationandReynoldsnumberrise,yielding a30.04%enhancementinNusseltnumberat0.1%volume concentration. Additionally, the study correlates data to estimateNusseltnumberandfrictionfactor,showinga2% pressure drop for enhanced heat transfer [20].

V.Chuwattanakul et al. (2023) In this experimental investigation, broken V-ribbed twisted tapes (B-VRT) significantlyenhancedheattransferinaheatexchangertube through increased mixing via longitudinal vortices and swirling flow. The B-VRT with a 45° rib attack angle outperformed other configurations, offering up to 31.9%

higherNusseltnumberscomparedtotypicaltwistedtapes (TT) across a Reynolds number range of 6,000 to 20,000. Correlationsdevelopedforheattransfer(Nu),pressuredrop (f), and aerothermal performance (APF) showed accurate predictionswithin±4%to±5.4%deviations[21].CSunetal. (2023)Thisstudyintroducesanovelapproachfordesigning perforated twisted tapes (PTTs) through parametric modelingandoptimization,enhancingheattransferinflow channels. Utilizing multi-objective optimization and computational fluid dynamics, the method achieves significant reductions in average and root mean square temperatures by up to 5.46% and 72.64%, respectively, while reducing friction factors by 57.35%. The half-width PTTsexhibitsuperiorperformance,showcasingpotentialfor creating highly efficient convective heat transfer devices withexpandeddesignpossibilities[22].YHongetal.(2023) Thisstudydevisedathermalenhancementtechnologyusing spiralcorrugatedtubesandmultipletwistedtapesforliquidgas heat exchange in waste heat recovery scenarios. Numerical investigations revealed that incorporating multipletwistedtapeshomogenizedflowfields,increased heattransfer,andreducedfriction.Surfaceperforationson the twisted tapes further improved overall efficiency by around 7.9%, offering a promising waste heat recovery solution[23].KRohitetal.(2023)Theresearchdelvesinto optimizing solar water heating systems (SWHS) by integratingperforateddeltaobstacles,studyingtheirimpact on friction factor, Nusselt number, and thermo-hydraulic performance. The study identified the most efficient configuration(Reynolds number= 1200,angleofattack = 45°, pitch ratio = 1) using an AHP-ARAS hybrid decisionmaking approach, offering robustness through sensitivity analysisandvalidation[24].

3. MATHEMATICAL EQUATIONS

3.1.

Nusselt Number (Nu) Calculations

TheNusseltnumberrepresentstheratioofconvectiveheat transfer to conductive heat transfer and is often used to quantifyheattransferenhancement.

Forforcedconvection:=Nu=h⋅Dh/K

Where:

h=Convectiveheattransfercoefficient

Dh=Hydraulicdiameterofthetube

k=Thermalconductivityofthefluid

3.2.

Heat Transfer Coefficient (h) Calculation:

The convective heat transfer coefficient is a crucial parameterinheatexchangeranalysis.

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For internal flow (Dittus-Boelter equation):

Nu=0.023⋅Re0.8⋅Pr0.3

ℎ=k⋅Nu/Dh

Where:

Re=Reynoldsnumber

Pr=Prandtlnumber

3.3. Reynolds Number (Re) Calculation:

The Reynolds number helps characterize the flow regime withinthetubes.

Re=ρ⋅V⋅Dh/μ

Where:ρ=Densityofthefluid

V=Velocityofthefluid

μ=Dynamicviscosityofthefluid

3.4. Pressure Drop:

Pressure drop is a critical consideration, especially when turbulatorsareemployed.

Forflowthroughtubeswithtwistedtapeturbulators:ΔP=f⋅L

⋅ρ⋅V2/(2.Dh)

Where:

f=Frictionfactor

L=Lengthofthetubesegment

3.5. Concentration of Nanoparticles:

Inthecaseofnanofluids,theconcentrationofnanoparticles canberepresentedbyasimpleequation.

Cnanoparticles=mnanoparticles/Vbasefluid

Where:

mnanoparticles=Massofnanoparticles

Vbasefluid=Volumeofthebasefluid

3.6. Effective Thermal Conductivity of Nanofluids:

Theeffectivethermalconductivity(keff)ofnanofluidstakes intoaccounttheincreasedconductivityduetonanoparticles.

keff=kbasefluid⋅(1+2.5⋅Cnanoparticles)

Where:

kbasefluid=Thermalconductivityofthebasefluid

These equations provide a glimpse into the mathematical aspects of analyzing shell and tube heat exchangers with nanofluids and twisted tape turbulators. However, dependingonthespecificmodelingandassumptions,more intricateequationsandnumericalmethodscanbeemployed in CFD simulations to capture the complex fluid flow and heattransferphenomena.

4. CFD (FLUID FLOW FLUENT)

CFDSimulationforFluidFlowAnalysiswithANSYSFluent CFD simulations have become a cornerstone in the analysis and optimization of heat exchangers due to their abilitytocapturecomplexfluidflowpatterns,temperature distributions, and heat transfer characteristics. ANSYS Fluent, a widely used CFD software, offers a versatile platformforconductingdetailedsimulationsthataidinthe understanding and enhancement of heat exchanger performance.

4.1. Geometry and Meshing:

The first step in a CFD simulation involves creating a representative 3D geometry of the shell and tube heat exchanger,incorporatingdetailssuchastubelayout,baffles, andtwistedtapeturbulators.ANSYSFluentsupportsvarious meshingtechniques,includingstructuredandunstructured grids, which discretize the geometry into smaller computationalelements.Anappropriatelyrefinedmeshnear theheattransfersurfacesandturbulatorregionsisessential tocapturegradientsaccurately.

4.2. Boundary Conditions:

Defining accurate boundary conditions is crucial for a reliable simulation. Inlet and outlet conditions, such as velocity profiles and temperature distributions, need to mirrorreal-worldscenarios.Fornanofluidsimulations,inlet conditions should account for the concentration of nanoparticles. ANSYS Fluent provides user-friendly interfacestoinputtheseconditions.

4.3. Fluid Properties and Turbulence Modeling:

Accuraterepresentationoffluidpropertiesisvital.ANSYS Fluentsupportsvariousfluidpropertymodelsfornanofluids and base fluids. Additionally, turbulence models like the Reynolds-AveragedNavier-Stokes(RANS)equationscoupled with appropriate turbulence models (k-epsilon, k-omega, etc.)areusedtocapturetheeffectsofturbulenceinducedby twistedtapeturbulators.

4.4. Nanofluid Modeling:

To simulate the behavior of nanofluids, ANSYS Fluent enables the inclusion of additional phases representing nanoparticlesdispersedwithinthebasefluid.Thisrequires definingthe propertiesand behaviorofthe nanoparticles, including thermal conductivity, density, and dispersion characteristics.

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4.5. Twisted Tape Turbulators:

For twisted tape turbulators, the geometry of the tapes can be incorporated into the simulation model. ANSYS Fluent's capability to handle moving geometries can simulate the swirl induced by the twisted tapes, which influencesfluidflowpatternsandheattransfer.

4.6. Solution and post-processing:

Aftersettingupthesimulation,ANSYSFluentsolvesthe governing equations numerically using iterative methods. The simulation results provide detailed insights into flow patterns,temperatureprofiles,pressuredistributions,and heattransferrateswithintheheatexchanger.Theseresults canbevisualizedusingcontourplots,vectors,streamlines, and other graphical representations provided by the software.

4.7. Validation and Optimization:

It'scrucialtovalidatetheCFDsimulationresultsagainst experimentaldataoranalyticalsolutions.Oncevalidated,the simulation can be used to perform parametric studies, investigatingtheeffectsofvariousparameterslikenanofluid concentration, turbulator design, flow rates, and more on heatexchangerperformance.

Inconclusion,ANSYSFluentservesasapowerfultoolfor simulatingfluidflowwithinshellandtubeheatexchangers integratedwithnanofluidandtwistedtapeturbulators.The software's capabilities in handling complex geometries, boundaryconditions,turbulencemodeling,andmultiphase flows enable researchers and engineers to gain valuable insights into heat transfer enhancement mechanisms, optimizing designs, and ultimately contributing to the advancementofthermalengineering.

5. CFD QUATIONS

5.1. Navier-Stokes Equation:

Thefundamentalequationsdescribingfluidflowbehavior used in CFD simulations for fluid flow analysis in heat exchangersusingsoftwarelikeANSYSFluent:

∂ρ+∇⋅(ρV)=0

∂(ρV)/∂t+∇⋅(ρV⊗V)=−∇P+μ∇2V+ρg

Where:

ρ=Density

V=Velocityvector

P=Pressure

μ=Dynamicviscosity

g=Gravitationalacceleration

5.2. Energy Equations:

Theequationforenergyconservationtoaccountfor temperaturevariations:

∂(ρcpT)/∂t+∇⋅(ρcpTV)=∇⋅(k∇T)

Where:

cp=Specificheatatconstantpressure

T=Temperature

k=Thermalconductivity

5.3. Turbulence Model:

Forsimulatingturbulentflows,variousturbulencemodels canbeused,suchasthek-epsilonork-omegamodels.These modelsinvolveadditionaltransportequationsforturbulent kineticenergy(k)anditsdissipationrate(ε).

k-epsilonmodel:∂(ρk)/∂t+∇⋅(ρkV)=∇⋅[(μ+μt)∇k]+ρε−ρε0

Where:

k=Turbulentkineticenergy

ε=Turbulentdissipationrate

μt=Turbulentviscosity

ε0=Turbulentdissipationrateduetobuoyancyeffects

5.4. Species Transport Equation (For Nanofluid):

If simulating nanofluid behavior, a species transport equationfornanoparticles'concentration(Cnanoparticles) canbeadded.

∂(ρCnanoparticles)/∂t+∇⋅(ρCnanoparticles V)=∇⋅(ρD∇Cnanoparticles)

Where:

Cnanoparticles=Nanoparticleconcentration

D=Diffusivityofnanoparticles

6. CONCLUSIONS

Inthepursuitofenhancingheatexchangerefficiency,the integration of Computational Fluid Dynamics (CFD) simulations has proven invaluable in uncovering the intricate mechanisms that govern heat transfer augmentation. This review paper delved into the convergenceoftwoinnovativetechniques:theutilizationof nanofluidsandtheincorporationoftwistedtapeturbulators withinshellandtubeheatexchangers.Throughameticulous examinationofnumerousstudies,thispaperaimedtodistill the collective insights, challenges, and opportunities presentedbythissynergisticapproach.

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Thereviewhighlightsthepotentialofnanofluidsandtwisted tapeturbulatorsinenhancingheattransferrateswithinheat exchangers. Nanofluids offer improved convective heat transfer coefficients but face challenges like nanoparticle agglomeration. Twisted tape turbulators manipulate fluid flowforbetterheattransferbutincreasepressuredrop.CFD simulations,notablyANSYSFluent,havebeeninstrumental inunderstandingthesephenomena.Thereviewemphasizes the need for combined theoretical, experimental, and simulation-basedapproachestodriveinnovationinefficient heatexchangefordiverseindustrialapplications.

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