过程装备与控制工程专业英语翻译13

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1、ReadingMaterial13PrinciplesofMassTransfer1.GeneralRemarksSomeofthemosttypicalchemicalengineeringproblemslieinthefieldofmasstransfer.Adistinguishingmarkofchemicalengineerishisabilitytodesignandoperateequipmentinproductsisprepared,chemicalreactionstakeplace,andseparationsoftheresultingpro

2、ductsaremade.Thisabilityrestslargelyonaproficiencyinthescienceofmasstransfer.Applicationsoftheprinciplesofmomentumandheattransferarecommoninmanybranchesofengineering,buttheapplicationofmasstransferhastraditionallybeenlargelylimitedtochemicalengineering.Otherimportantapplicationsoccurinm

3、etallurgicalprocesses,inproblemsofhigh-speedflight,andinwastetreatmentandpollution-controlprocesses.Eddydiffusionisapparentinthedissipationofsmokefromasmokestack.Turbulencecausesmixingandtransferofthesmoketothesurroundingatmosphere.Incertainlocationswhereatmosphericturbulenceislacking,s

4、mokeoriginatingatthesurfaceoftheearthisdissipatedlargelybymoleculardiffusion.Thiscauseseriouspollutionproblemsbecausemassistransferredlessrapidlybymoleculardiffusionthanbyeddydiffusion.4.ConvectiveMass-TransferCoefficientsInthestudyofheattransferwefoundthatthesolutionofthedifferentialen

5、ergybalancewassometimescumbersomeorimpossible,anditwasconvenienttoexpresstherateofheatflowintermsofaconvectiveheat-transfercoefficientbyanequationlikeTheanalogoussituationinmasstransferishandledbyanequationofformThemassfluxNAismeasuredrelativetoasetofaxesfixedinplace.Thedrivingforceisth

6、edifferencebetweentheconversationatthephaseboundary(asolidsurfaceorafluidinterface)andtheconcentrationatsomearbitrarilydefinedpointinthefluidmedium.Theconvectivecoefficientmayapplytoforcedornaturalconverction;therearenomass-transfercounterpartsforboiling,condensation,orradiationheat-tra

7、nsfercoefficients,thevalueofisafunctionofthegeometryofthesystemandthevelocityandpropertiesofthefluid,justaswasthecoefficienth.3.EddyDiffusionJustasmomentumandenergycanbetransferredbythemotionoffiniteparcelsoffluid,somasscanbetransferred.Wehaveseenthattherateofthesetransferopera