清华大学 高等化工传递过程原理 第10章porous.pptVIP

MassTransferinPorousStructures

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ThreemainresistanceswithintwophasesSchematicdiagramofadsorbentorcatalystparticledepictingthethreemaindiffusionresistances

Macropore50nmMesopore2~50nmMicropore2nmPoresizedistributionofzeolite-X,molecularsievecarbonandactivatedcarbon

Threetypesofdiffusionmechanismswithinapore

ThreeContributionstoTotalMassFluxFluxofthediffusingspecieswithinaporousmedium

Contributionsofbulk,KnudsonandsurfacediffusionfortransferofH2Sacrossacatalyticmembrane(350nmpores)carryingtheClausreaction:2H2S+SO2=3/8S8+2H2OH2Sfluxacrosmembrance

ThedustygasmodelThemostconvenientapproachtomodelingcombinedbulkandKnudsendiffusion

ThedustygasmodelAssumptions:ThedustconcentrationCn+1isspatiallyuniformThedustismotionless,sothatNn+1=0Themolarmassofthedustparticles

EffectiveMaxwell-StefanDiffusivitiesGeneralizationtonon-idealfluidmixtureEffectiveKnudsenDiffusivities

MatrixForm

ForidealmixturesForidealgaseousmixtures

Viscousflow

MembraneProcesses

Pressuregradientinporousmediumgaseousmixtures

三元气体混合物He(1)－Ne(2)－Ar(3)扩散通过一个惰性多孔膜。膜内的孔可以看作是平行圆柱孔，膜的空隙率为70％。试确定在100nm、200nm和300nm三种孔径条件下，三个组分的传质通量和方向。已知条件如下：上游压力P0＝210×103Pa，下游压力Pδ＝190×103Pa，温度T=300K，气体粘度μ＝22×10-6Pa·s，膜厚度δ=9.6×10-3m，膜两侧的组成为：x10=0.4x1δ=0.4x20=0.4x2δ=0.3x30=0.2x3δ=0.3组分在压力为100×103Pa和温度为300K的主体相气体中的二元Fick扩散系数为D12=1.068×10-4㎡/sD13=0.724×10-4㎡/sD23=0.316×10-4㎡/sProblem