2015-Optimization-of-Low-Wattage-Thermosyphon-by-T

JournalofAeronautics,AstronauticsandAviation,Vol.47,No.2pp.101-106(2015)101DOI:10.6125/15-0202-833OptimizationofLowWattageThermosyphonbyTaguchiMethodandNumericalSimulation*Che-yinLee**1,Hsin-hengHuang2,Shih-mingLee2andKwanOuyang31DepartmentofMechanicalandElectro-MechanicalEngineering,TamkangUniversityNo.151,YingzhuanRd.,TamsuiDist.,NewTaipeiCity25137,Taiwan,R.O.C.2DepartmentofAerospaceEngineering,TamkangUniversityNo.151,YingzhuanRd.,TamsuiDist.,NewTaipeiCity25137,Taiwan,R.O.C.3DepartmentofMarineEngineering,TaipeiCollegeofMaritimeTechnologyNo.150,Sec.3,BinhaiRd.,TamsuiDist.,NewTaipeiCity25172,Taiwan,R.O.C.ABSTRACTThisstudyusednumericalsimulationandTaguchimethodtoanalyzetheinfluenceofdifferentfactors,includingvacuumdegree,fillratioandaspectratioandinclinedangle,ontheheattransfercharacteristicsoflow-wattthermosyphoninnaturalconvection.Themassandenergysourcetermswereaddedinthecontinuityandenergyequationtosimulatetheexchangesbetweenvaporandliquidphases.Thecomparisonanalysisofcomputedresultandexperimentdatashowedthatthenumericalmodelusedinthisstudyisappropriatetotheanalysisofphysicalmechanismandheattransferpropertyofthermosyphon.Theresultsconcludedthatinclinedthermosyphonhasbetterthermalperformance.BasedonTaguchimethodfindthatThebestfillratiowas90%whenthevacuumdegreewas35torr,theaspectratiowas9.8andtheinclinedanglewas45degree.Keywords:HeatPipe,NumericalSimulation,Thermosyphon,TaguchiMethod,InclinedAngle*Manuscriptreceived,February2,2015,finalrevision,April27,2015**Towhomcorrespondenceshouldbeaddressed,E-mail:[e-mail]s,theearth'sfossilenergyisconsumedrapidly,resultinginenergypoverty.Therefore,thedevelopmentofalternativeenergyhasbecomethekeypointoflateyears.Amongthepresentalternativeenergysources,solarpowergeneration[1]andgeothermalpowergenerationarepopularalternativeenergy.However,theequipmentareexpensiveandthegeneratingefficiencyislimited,sothatusingthelow-costthermosyphonwithsimplestructure[2]toincreaseefficiencyandreducecostbecomesthemainstream.Thethermosyphonisextensivelyusedforfrozensoilpreservation[3],snowthawingandtunnelanti-freezingforitshighthermalconductivityinrecentyears.ThethermosyphonwasfirstproposedbySchmidt[4]in1951,whosuggestedthatevenifthetemperaturedifferencebetweentheevaporationzoneandcondensationzonewassmall,theheattransferefficiencywasstillhigh.Furtherdiscussionsweremadeontheheattransferperformanceandapplicationofthermosyphon.In1983,Imuraetal.[5]usedworkingfluidwater,ethanolandtrichlorotrifluoroethanetryingtocorrectexperimentaldata,andestablishedthecriticalheatfluxequationofclosedtwo-phasethermosyphon.Thefindingsshowedthattheinnerpipediameter,heatingrange,workingfluid,loadingandvacuumdegreeofthermosyphonwereimportantfactorsinfluencingthecriticalheatflux.In1990,Terdtoonetal.[6]useddifferentfillratiosandinclinedanglestoexperimentallydiscusstheinfluenceontheheattransfercharacteristicsofthermosyphon.Theexperimentalresultsshowedthatthefillratiohadsignificantinfluenceontheheattransfercharacteristics,andinclinedplacementhadbetterheattransfereffectthanverticalplacement.ThemaximumheattransfercapacityoccurredwhentheinclinedangleChe-yinLeeHsin-hengHuangShih-mingLeeKwanOuyang102was45°andthefillratiowas50%.In2005,Noie[7]exploredthreefactorsthatwouldinfluenceverticalclosedtwo-phasethermosyphon.Thethreefactorsincludedtheinputheattransfercapacity,workingfluidfillratio,evaporationendlengthratio(A.R.:AspectRatioistheratioofevaporationendlengthtointernaldiameterofpipe).Thedeionizedwaterwasusedasworkingfluid.Theexperimentalresultshowedthatatdifferentevaporationendlengths,themaximumheattransfercapacityoccurredatdifferentfillratios.Themaximumheattransfercapacityofevaporationendlengthratio11.8occurredwhenthefillratiowas60%.Themaximumheattransfercapacityofevaporationendlengthratios7.45and9.8occurredwhenthefillratiowas90%and30%respectively.Asthethermosyphonisusedextensively,thisstudyusedTaguchiMethod[8]toanalyzefourfactorsinfluencingthethermosyphonefficiency.Thefourfactorsincludedthreevacuumdegrees(Vacuum=35,55,75torr),threeaspectratios(A.R.=7.45,9.8,11.8),threefillratios,namelythevolumeratioofliquid(F.R.=30%,60%,90%)andthreeinclinedangles(I.A.=45,60,90degree).Theworkingfluidwaspurewater.ThefourfactorsandTaguchiMethodwereusedtoanalyzetheoptimumapplicationconditionsofthermosyphon,soastoimprovethethermosyphonperformance.II.THEORIESANDEQUATIONS2.1SimulationmodelTheexperimentalmodelofS.H.Noie[9]isshowninFigure1,theoveralllengthis980mm;theoutsidediameteris32mm;thewallthicknessis3.5mm;thecondensationsectionlengthisfixedat380mm,theaspectratio(A.R.)isdefinedasevaporatorlength/insidediameterof7.45(evaporatorlength238mm;insulationsectionlength362mm),9.8(evaporatorlength314mm;insulationsectionlength286mm)and11.8(evaporatorlength377mm;insulationsectionlength223mm)respectively.Figure1DetailsofthermosyphonA.R.=7.45,9.8,11.82.2AssumedconditionThefundamentalassumptionsforsimulationinclude:1.Steady-stateheattransfer.2.Thefluidflowfieldinsideheatpipeislaminarflow.3.Thevaporissaturatedvapor.4.Undergr