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ID:34174813
大小:63.00 KB
页数:7页
时间:2019-03-04
《mass transfer in bioreactors - dcu生物反应器的传质单元》由会员上传分享,免费在线阅读,更多相关内容在应用文档-天天文库。
1、MassTransferinBioreactorsMasstransferoccursinmixturescontaininglocalconcentrationvariablesMTplaysavitalroleinmanyreactionsystemsIf,forexample,themasstransferofOxygenfromthebubblesinthefermentationbrothisslow,thentherateofcellmetabolismcanbecomedependantont
2、herateofoxygensupplyfromthegasphase.SowhatdrivesMT?Moleculardiffusionisthemovementofmoleculesofagivensubstancefromanareaofhighconcentrationofthatgivencompoundtooneoflowerconcentration.Thetermconcentrationgradientisusedtodescribethisdifferenceinconcentratio
3、nandmoleculeswillmoveinadirectionwhichwilleventuallydestroythegradientWhathappensinGas-LiquidMassTransferGLMTisunusualasmoleculeshavetomovebetweendifferentphases(i.e.thegasphasetotheliquidphase)acrossaboundaryorinterface.Filmtheoryattemptstoexplaintheproce
4、ssofdiffusionof,letssay,Oxygenfromthebubblesinthebrothtothebulkliquidphase.LetusconsiderthemasstransferofOxygenfromgastoliquidacrossthebubbleinterface.Oxygenisinmuchhigherconcentrationinthebubble(21%ofthevolumeoftheairisOxygen)alsoOxygenissparinglysolublei
5、naqueoussolutions.ThereforeaconsiderabledrivingforceexiststomoveO2fromgastoliquid.Accordingtothefilmtheory,theturbulenceineachfluiddiesawayasyouapproachtheinterface.Athinfilmofstagnantfluidliesoneachsideoftheinterface.TheonlywaythroughfortheOxygenismolecul
6、ardiffusion(normallyingassesorliquidswehaveconvectivemasstransfer)Theconcentrationofanycompoundattheinterfacediffersacrosstheinterface,eventhoughthefluidsatethersideoftheinterfacearesupposedtobeinequilibrium.Thisissimplyduetothemoleculesrelativesolubilityi
7、neachphase.Asyoumoveawayfromtheinterface,ineitherdirection,theconcentrationofthemoleculereturnstothebulkliquidconcentrationwhichisregulatedthroughconvectivemasstransfer.CAGiCALiCALCAGGas-phasefilmresistanceLiquid-phasefilmresistanceBulkgasphaseBulkliquidph
8、aseFilmtheorydiagramreproducedfromDoran-Figure9.5ConvectiveMassTransferDefinition:Masstransferoccurringunderthepresenceofbulkfluidmotion.RateofMTisdirectlyproportionaltothedrivingforcefortransfer,andtheareaav
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