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页数:7页
时间:2018-08-10
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1、内蒙古工业大学本科毕业设计说明书PrinciplesofMassTransfer1.GeneralRemarksSomeofthemosttypicalchemicalengineeringproblemslieinthefieldofmasstransfer.Adistinguishingmarkofthechemicalengineerishisabilitytodesignandoperateequipmentinwhichreactantsareprepared,chemicalreactionstakeplace,andsep
2、arationsoftheresultingproductsaremade.Thisabilityrestslargelyonaproficiencyinthescienceofmasstransfer.Applicationsoftheprinciplesofmomentumandheattransferarecommoninmanybranchesofengineering,buttheapplicationofmasstransferhastraditionallybeenlargelylimitedtochemicalengin
3、eering.Otherimportantapplicationsoccurinmetallurgicalprocesses,inproblemsofhigh-speedflight,andinwastetreatmentandpollution-controlprocesses.Bymasstransferismeantthetendencyofacomponentinamixturetotravelfromaregionofhighconcentrationtooneoflowconcentration.Forexample,ifa
4、nopentesttubewithsomewaterinthebottomisplacedinaroominwhichtheairisrelativelydry,watervaporwilldiffuseoutthroughthecolumnofairinthetesttube.Thereisamasstransferofwaterfromaplacewhereitsconcentrationishigh(justabovetheliquidsurface)toaplacewhereitsconcentrationislow(atthe
5、outletofthetube).Ifthegasmixtureinthetubeisstagnant,thetransferoccursbymoleculardiffusion.Ifthereisabulkmixingofthelayersofgasinthetubebymechanicalstirringorbecauseofadensitygradient,masstransferoccursprimarilybythemechanismofforcedornaturalconvection.Thesemechanismsarea
6、nalogoustothetransferofheatbyconductionandbyconvection;thereis,however,nocounterpartinmasstransferforthermalradiation.Theanalogybetweenmomentumandenergytransferhasalreadybeenstudiedinsomedetail,anditisnowpossibletoextendtheanalogytoincludemasstransfer.Indiscussingthefund
7、amentalsofmasstransferweshallconsidermainlybinarymixtures,althoughmulticomponentmixturesareimportantinindustrialapplications.Someofthesemorecomplicatedsituationswillbediscussedafterthebasicprincipleshavebeenillustratedintermsofbinarymixtures,7内蒙古工业大学本科毕业设计说明书2.MolecularD
8、iffusionMoleculardiffusionoccursinagasasaresultoftherandommotionofthemolecules.Thismotionissometimesref
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