Heat transfer enhancement of nano-fluids

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1、InternationalJournalofHeatandFluidFlow21(2000)58±64www.elsevier.com/locate/ijhHeattransferenhancementofnano¯uidsYiminXuan*,QiangLiSchoolofPowerEngineering,NanjingUniversityofScienceandTechnology,Nanjing210094,People'sRepublicofChinaReceived5February1999;accepted1September19

2、99AbstractThispaperpresentsaprocedureforpreparinganano¯uidwhichisasuspensionconsistingofnanophasepowdersandabaseliquid.Bymeansoftheprocedure,somesamplenano¯uidsareprepared.TheirTEMphotographsaregiventoillustratethestabilityandevennessofsuspension.Thetheoreticalstudyofthethe

3、rmalconductivityofnano¯uidsisintroduced.Thehot-wireapparatusisusedtomeasurethethermalconductivityofnano¯uidswithsuspendedcoppernanophasepowders.Somefactorssuchasthevolumefraction,dimensions,shapesandpropertiesofthenanoparticlesarediscussed.Atheoreticalmodelisproposedtodescr

4、ibeheattransferperformanceofthenano¯uid¯owinginatube,withaccountingfordispersionofsolidparticles.Ó2000ElsevierScienceInc.Allrightsreserved.Keywords:Nano¯uid;Enhancedheattransfer;Thehot-wireapparatus;DispersionNotationSubscriptseeectiveAqcross-sectionareaf¯uidathermaldiusivi

5、typparticlecpspeci®cheatxx-directionCconstantrr-directiondaveragediameterDthermaldispersioncoecientfFanningfrictionfactorhconvectiveheattransfercoecientkthermalconductivity1.IntroductionmnumberoftheparticlesperunitvolumenparticleempiricalshapefactorLowthermalconductivityof

6、process¯uidhindershighNulocalNusseltnumbercompactnessandeectivenessofheatexchangers,althoughaPePecletnumbervarietyoftechniquesisappliedtoenhanceheattransfer.Im-PrPrandtlnumberprovementofthethermalpropertiesofenergytransmissionqheat¯uxperunitlength¯uidsmaybecomeatrickofaugme

7、ntingheattransfer.AnrradialvariableinnovativewayofimprovingthethermalconductivitiesofRinnerradiusofthetube¯uidsistosuspendsmallsolidparticlesinthe¯uids.VariousReReynoldsnumbertypesofpowderssuchasmetallic,non-metallicandpolymericxaxialvariableparticlescanbeaddedinto¯uidstofo

8、rmslurries.Thethermalttimeconductivitiesof¯uidswithsuspendedparticlesareexpectedTt