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1、Chapter–4ConvectiveMassTransfer4.1Introduction4.2ConvectiveMassTransfercoefficient4.3Significantparametersinconvectivemasstransfer4.4TheapplicationofdimensionalanalysistoMassTransfer4.4.1Transferintoastreamflowingunderforcedconvection4.4.2Transferintoaphasewhosemotionisduetonaturalconvection4.5Analo

2、giesamongmass,heat,andmomentumtransfer4.5.1Reynoldsanalogy4.5.2Chilton–Colburnanalogy4.6Convectivemasstransfercorrelations4.6.1Forflowaroundflatplat4.6.2Forflowaroundsinglesphere4.6.3Forflowaroundsinglecylinder4.6.4Forflowthroughpipes4.7Masstransferbetweenphases4.8Simultaneousheatandmasstransfer4.8.

3、1Condensationofvapouroncoldsurface4.8.2Wetbulbthermometer4.1IntroductionOurdiscussionofmasstransferinthepreviouschapterwaslimitedtomoleculardiffusion,whichisaprocessresultingfromaconcentrationgradient.Insysteminvolvingliquidsorgases,however,itisverydifficulttoeliminateconvectionfromtheoverallmass-tr

4、ansferprocess.Masstransferbyconvectioninvolvesthetransportofmaterialbetweenaboundarysurface(suchassolidorliquidsurface)andamovingfluidorbetweentworelativelyimmiscible,movingfluids.Therearetwodifferentcasesofconvectivemasstransfer:1.Masstransfertakesplaceonlyinasinglephaseeithertoorfromaphaseboundary

5、,asinsublimationofnaphthalene(solidform)intothemovingair.2.Masstransfertakesplaceinthetwocontactingphasesasinextractionandabsorption.Inthefirstfewsectionwewillseeequationgoverningconvectivemasstransferinasinglefluidphase.4.2ConvectiveMassTransferCoefficient24Inthestudyofconvectiveheattransfer,thehea

6、tfluxisconnectedtoheattransfercoefficientas--------------------(4.1)Theanalogoussituationinmasstransferishandledbyanequationoftheform--------------------(4.2)ThemolarfluxNAismeasuredrelativetoasetofaxesfixedinspace.Thedrivingforceisthedifferencebetweentheconcentrationatthephaseboundary,CAS(asolidsur

7、faceorafluidinterface)andtheconcentrationatsomearbitrarilydefinedpointinthefluidmedium,CA.TheconvectivemasstransfercoefficientkCisafunctionofgeometryofthesystemandthevelocityandpropertiesofthefluidsim