Design and testing of a locally made loop-type the

TechnicalnoteDesignandtestingofalocallymadeloop-typethermosyphonicheatsinkforstove-topthermoelectricgeneratorsR.Y.Nuwayhid*,R.HamadeDepartmentofMechanicalEngineering,FacultyofEngineeringandArchitecture,AmericanUniversityofBeirut,RiadElSolh1107-2020,Beirut,LebanonReceived16July2004;accepted18September2004Availableonline23November2004AbstractTheperformanceofathermoelectricgenerator,amongotheraspects,dependsontheuseofaneffectiveheatsink.Whileforcedcoolingusingeitherairorwater(orothercoolants)isefficient,itisparasiticonthegeneratedpowerand/orbulkyandinconvenient.Heatpipesareknowntobehighlyeffectiveheattransportdevices.Coupledtoathermoelectricgenerator,thesecanbeusedtogiveacceptablepoweroutput.Basingthecoolingonwatergiveslow-cost,simplicity,safety,togetherwithgoodperformance.Inthiswork,thedesignandgeneralperformanceofasmallsingle-modulethermoelectricgeneratorconfiguredforastovetopwaste-heatapplicationandcoupledtoalocally-madethermosyphonicloop-typeheatsinkwasundertaken.Developmentandperformancecctestinggavemixedresultsandfurthernumericalandexperimentalstudyisunderway.q2004ElsevierLtd.Allrightsreserved.Keywords:Thermoelectricgenerator;Thermosyphonicheatsink;Stovetop1.IntroductionThermoelectricpowergenerationhasbeeninexistenceforover100years.Theefficiencyofconversionhasnotmanagedtoexceedabout10%fortemperaturerangesof0960-1481/$-seefrontmatterq2004ElsevierLtd.Allrightsreserved.doi:10.1016/j.renene.2004.09.008RenewableEnergy30(2005)1101–1116*Correspondingauthor.Fax:C9611744462.E-mailaddress:[e-mail](R.Y.Nuwayhid).practicalinterest.Thus,powergenerationapplicationshavebeenlimitedtospecialdeepspaceprobes(Pioneer,etc.)whichuseradioisotopeheatsourcesandgeneraterelativelylowpowersufficientforthetaskathand.TheotherapplicationisinremotepowerforPolarRegions,petroleumplatformsorothersimilarinstances.Thesesystemsusefossilfuelheatsources,andconsideringweatherandotherfactors,mayhaveamarginaladvantageoverpowergeneratingusingothermethodssuchasphotovoltaics.NomenclatureCffrictioncoefficientCpliquidspecificheatDxgridsize[m]ggravitationalacceleration[msK2]hheattransfercoefficient[WmK2KK1]hfglatentheatofvaporization[kJkgK1]Hpdepthoftheliquidpool[m]Klliquidthermalconductivity[WmK1KK1]Llengthofthethermosyphon[m]mcmassflowrateofcondensercoolingwater[kgsK1]Ppressure[Pa]q00wallheatflux[WmK2]Rinnerradiusofthethermosyphon[m]rvaporcoreradius[m]ReReynoldsnumber,4G/mTtemperature[K]uvelocity[msK1]Vvaporcondensationvelocity[msK1]xaxialdistancefromthetopendofthermosyphon[m]Greeksymbolsdliquidfilmthickness[m]mdynamicviscosity[NsmK2]rdensity[kgmK3]fphasechangecorrectionfactorSubscriptsaadiabaticregionatmatmosphericconditionsccondenserregioneevaporatorregionlliquidphasepliquidpoolsurfaceSsaturationwtubewallvvaporphaseR.Y.Nuwayhid,R.Hamade/RenewableEnergy30(2005)1101–11161102Ontheotherhand,Rowe[1]hasarguedthatwhentheenergyinputisofthewasteheattype,thereisacasefortheuseofthermoelectricconversion.Insuchacase,powerratherthanefficiencyistheprimarycriterion.Onesituationwhereawasteheatapplicationexistsisruraldomesticwinterheatingstoves(diesel,woodorsimilar).Thegenerationofthermoelectricpowerfromsuchstoveshasbeenstudiedundersuchsituations.Kilanderetal.[2]consideredthecaseoftheNordiccountrysideinNorthernSwedenwherenoelectricgridexists;whileNuwayhidetal.[3]assessedthecaseofruralLebanonwheretheelectricsupplyisgenerallyunreliableandruralstovesareincommonusedinwinter.Inthecaseofdomesticstoves,thehotsidetemperatureofathermoelectricgenerator(TEG)maybeconsideredconstantonaverage(fluctuationespeciallywhenconsideringwood-fedstovesmaybesignificant).Inthecomingsection,itwillbeshownthatpowerisproportionaltothesquareofthetemperaturedifferenceacrossthethermoelectricmodule.Thus,thetaskbecomestominimizethecoldsidetemperature.Typically,thestovetoptemperaturewouldbearound200–2308C(about500K).Considering,asaworstcase,anaverageambienttemperatureof20–238C(293–296K),itbecomesclearthatwithsuchanapplication,atemperaturedifferenceofabout200Kisthelimit.ItisquiteinterestingtonotethatthisapplicationappearstomatchtherangeatwhichBismuthTelluride(Bi2Te3)performsverywell[4].Basedontheabove,thetaskofdecreasingthecoldsidetemperaturebecomesaheatsinkproblem.Heatsinksforthermoelectricgeneratorscanbebasedeitheronnaturalconvectiontotheambientoronforcedcooling.Thesimplestdesignisasimplefinnedheatsink,butinthisstovetopsituationitwouldnotbecapableofremovingadequateheat.Addingabrushlessfanisthefirstimprovementthatcomestomind.Whilethisaffordsacompactandlightweightsolution,thefanhastobepoweredbyparasiticallydrawingfromthegeneratedpower.Atthisstage,andbecauseofwater’ssuperiorheattransportproperties,forcedwater-coolingcomestomind,butonceagain,parasiticpumpingpowerisrequired.Thisleadstotheconsiderationofnaturalcoolingusingwater(thealternativeistouseanair-coolednaturalconvectionsystembutthiswouldleadtoaverylargesystem).Forcompactness’sake,aclosed-loop,water-based,naturalcirculationheat-pipe-typesystemisselectedforbuildingandtesting.Inthiswork,aftersomeintroductiontothermoelectricity,he