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1、ConferenceonNewEnergyTechnologiesforEnvironmentalDevelopmentintheArabWorld,Cairo,EgyptHeatPipes:TheoryandOperationDr.Eng.MohammedM.El-KhayatNREA,P.O.Box4544MasakinDobatEl-Saff,El-HayEl-Sades,Nasrcity,Cairo,Egypt.e-mail:mohamed_elkhayat@hotmail.comAbstractOneofthemainobjectivesofthisstudyistoobt
2、ainanunderstandingofheatpipesandtheirroleinenergytransmission,especiallyinthefieldofsolarenergy.Heatpipesarehighlyefficientheattransferdevices,whichusethecontinuousevaporation/condensationofasuitableworkingfluidfortwo-phaseheattransportinaclosedsystem.Sincethelatentheatofvaporizationisverylarge
3、,heatpipestransportheatatsmalltemperaturedifference,withhighrates.Duetoavarietyofadvantagefeaturesthesedeviceshavefoundanumberofapplicationsbothinspaceandterrestrialtechnologies.Thetheoryofoperationandthecharacteristicsofdifferenttypesofheatpipesaredescribed,andtheirperformancelimitationsaredis
4、cussedandpresentedinthisstudy.Moreover,Adescriptionofusinghigh-temperaturenon-concentratingcollectorsisillustrated.KeyWords:Heatpipes,Compositewicks,Homogenouswicks,andEvacuatedsolarcollectors.1-IntroductionHistorically,thefirstapplicationofgravityheatpipeswasinboilersandbakeries,theso-calledPe
5、rkinstubewaswidelyusedinthe19thcentury.Thisisabare,thick-walledcarbonsteeltubefilledwithacertainamountofwater,about1/3ofthetotaltubevolume,andhermeticallysealed.Thelowertubeendwasheatedbyfluegases,theupperendextendedintotheboilerwhereitwasusedtogeneratesteam.In1938apatentwasgrantedintheUSAwhich
6、describesatubeincorporatingcapillarygroovestoaidliquiddistributionandhencevaporizationinboilers.ThefirstpatentofaheatpipeemployingacapillarywickforpumpingliquidagainstgravitywasappliedbyGauglerin1944asatwo-phaseheattransportdeviceforrefrigerators.Itwassupposedtoallowmovementoftheworkingfluidwit
7、houtpumpsandwithoutnaturalconvection,byutilizationofthecapillaryforcegeneratedbyacapillarywick,Asselman(1973)andGroll(1992).In1963thecapillarypumpingprinciplewasindependentlyre-inventedbyGroverandhisco-workersattheLosAlamosScienti
