a critical review of convective heat transfer of n

RenewableandSustainableEnergyReviews11(2007)797–817AcriticalreviewofconvectiveheattransferofnanofluidsWeerapunDaungthongsuk,SomchaiWongwisesFluidMechanics,ThermalEngineeringandMultiphaseFlowResearchLaboratory(FUTURE),DepartmentofMechanicalEngineering,KingMongkut’sUniversityofTechnologyThonburi,Bangmod,Bangkok10140,ThailandReceived3May2005;accepted1June2005AbstractAnanofluidisasuspensionofultrafineparticlesinaconventionalbasefluidwhichtremendouslyenhancestheheattransfercharacteristicsoftheoriginalfluid.Furthermore,nanofluidsareexpectedtobeideallysuitedinpracticalapplicationsastheiruseincurslittleornopenaltyinpressuredropbecausethenanoparticlesareultrafine,therefore,appearingtobehavemorelikeasingle-phasefluidthanasolid–liquidmixture.Aboutadecadeago,severalpublishedarticlesfocusedonmeasuringanddeterminingtheeffectivethermalconductivityofnanofluids,somealsoevaluatedtheeffectiveviscosity.Thereareonlyafewpublishedarticlesonderivingtheforcedconvectiveheattransferofnanofluids.Thepurposeofthisarticleistosummarizethepublishedsubjectsrespecttotheforcedconvectiveheattransferofthenanofluidsbothofexperimentalandnumericalinvestigation.r2006ElsevierLtd.Allrightsreserved.Keywords:Nanofluids;Ultrafine;Effectivethermalconductivity;Effectiveviscosity;ForcedconvectiveheattransferContents1.Introduction.......................................................7982.Experimentalapproach...............................................7983.Mathematicalapproach...............................................8054.Conclusion........................................................816ARTICLEINPRESS:10.1016/j.rser.2005.06.005Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](S.Wongwises).Acknowledgements......................................................816References............................................................8161.IntroductionImprovementstomakeheattransferequipmentmoreenergyefficientwouldneedtofocusonminiaturizationontheonehandandanastronomicalincreaseinheatfluxontheother.Heattransferfluidssuchaswater,mineraloilandethyleneglycolplayavitalroleinmanyindustrialprocesses,includingpowergeneration,chemicalprocesses,heatingorcoolingprocesses,andmicroelectronics.Thepoorheattransferpropertiesofthesecommonfluidscomparedtomostsolidsisaprimaryobstacletothehighcompactnessandeffectivenessofheatexchangers.Theessentialinitiativeistoseekthesolidparticleshavingthermalconductivitiesseveralhundredsoftimeshigherthanthoseofconventionalfluids.Aninnovativeideaistosuspendultrafinesolidparticlesinthefluidforimprovingthethermalconductivityofafluid.Manytypesofparticle,suchasmetallic,non-metallicandpolymeric,canbeaddedintofluidstoformslurries.However,theusualslurries,withsuspendedparticlesintheorderofmillimetersorevenmicrometersmaycausesomesevereproblems.Theabrasiveactionoftheparticlescausesthecloggingofflowchannels,erosionofpipelinesandtheirmomentumtransfersintoanincreaseinpressuredropinpracticalapplications.Furthermore,theyoftensufferfrominstabilityandrheologicalproblems.Inparticular,theparticlestendtosettlerapidly.Thus,althoughtheslurriesgivebetterthermalconductivities,theyarenotpractical.TheuseofparticlesofnanometerdimensionwasfirstcontinuouslystudiedbyaresearchgroupattheArgonneNationalLaboratoryaroundadecadeago.Choi[1]wasprobablythefirstonewhocalledthefluidswithparticlesofnanometerdimensions‘nano-fluids’.Comparedwithsuspendedparticlesofmillimeter-or-micrometerdimensions,nanofluidsshowbetterstabilityandrheologicalproperties,dramaticallyhigherthermalconductiv-ities,andnopenaltyinpressuredrop.Severalpublishedliteraturehavemainlyfocusedonthepredictionandmeasurementtechniquesinordertoevaluatethethermalconductivityofnanofluid.Recently,TrisaksriandWongwises[2]reviewedtheliteratureonthegeneralheattransfercharacteristicsofnanofluids.Itwasfoundthatonlyafewpapershavediscussedontheconvectiveheattransferofnanofluids.Thepurposeofthisarticleistoreviewtheliteraturementioningconvectiveheattransferofnanofluids,includingtheexperimentalandtheoreticalinvestigations.2.ExperimentalapproachAseveralyearsago,thenanofluidhasbeenfoundtobeanattractiveheattransportfluids.Ithasexhibitedasignificantpotentialforheattransferaugmentationrelativetotheconventionalpurefluids.Ithasbeenexpectedtobesuitablefortheengineeringapplicationwithoutsevereproblemsinpipelineandwithlittleornopenaltyinpressuredrop.However,theearlierresearchesrevealedthatmoststudiesofthetransportpropertiesofthenanofluidwerefocusedonthethermalconductivity.Theconvectiveheattransferofnanofluidshasreceivedcomparativelylittleattentioninliterature.Therearefewpublicationsdealingwiththeconvectiveheattransferofnanofluids.Themostproductivestudieshavebeencontinuouslycarriedoutbythefollowingresearchers.ARTICLEINPRESSW.Daungthongsuk,S.Wongwises/RenewableandSustainableEnergyReviews11(2007)797–817798ARTICLEINPRESSNomenclatureAcrosssectionarea,m2Cconcentrationofliquidsolution,kgw/kgsolCpspecificheat,J/kgKdnanoparitclediameter,mDinnerdiametero