化工傳遞過(guò)程原理課件：第一 (II) Basic Concepts_344404490

1、Basic Concepts: Fluxes, Driving Forces, Constitutive Equations and Transport PropertiesBulk Movement Convective transport Convective FluxSmall scale molecular displacement Molecular(or Diffusive) transport Molecular (or Diffusive) FluxTotal Flux= Convective Flux+ Molecular FluxVelocity and reference

2、 velocity of a mixtureVelocity relative to the mixture: diffusive velocity1vvnaiiia11nnMiiiiiixvvvvaiv - viv - vMiv - vGradientEnergy flux Flux of species iTemperatureConcentration of specie iConcentration of species jElectrical potentialPressure.Conduction (Fourier)Diffusion-thermo effect (Dufour)T

3、hermal diffusion(Soret)Binary Diffusion (Fick)Multicomponent diffusion (Maxwell-Stefan)Ion migration (M-S)Pressure diffusion (M-S)Molecular Flux = f (Transport Properties, Gradients)Dominant gradient : Primary transport propertyOther gradients : Secondary transport properties Constitutive Equations

4、for Molecular Transport Classic Constitutive Equations :Molecular Flux = -Transport PropertyGradient （dominant)Heat Transport-Fouriers Law of Conduction Momentum Transport- Newtons Law of ViscosityMass TransportFicks Law of DiffusionyTkqTkqyyynqeennqn if)(nqxyzn=eyqTkqHeat ConductionT qFor isotropic

5、 materialsFor anisotropic materialsStress and Momentum Fluxxyxdvdy T vvns(n)xyzn=eysns1s2s(n)yzyxyy( ) ( )()xxxyxzyxyyyzzxzyzzyyxxyyyyzzs nn s ns eeee xxyvev iiiiiCnNvthe molar flux of species irelative to fixed coordinatesthe mass flux of species irelative to fixed coordinatesthe velocity of specie

6、s irelative to fixed coordinatesthe mole concentration of species ithe mass concentration of species iniiiMniiix11,vvvv11,iiiiiinnttiiiiCCxCCDiffusion of Chemical SpeciesThe mass-average velocity and the molar-average velocity mass fraction mole fractionDiffusion of Chemical SpeciesDefinitions of fl

7、uxes:Reference velocity Molar units Mass units 0 Ni ni v Ji ji vM JiM jiM1111,0,0nnMMMMiiiiiiiiinnMMiiiiiiiiiCCCNvJvJNvJnvjvjnvjFlux relationshipsvvaaiiij10naiiiiajJvvaaiiiC1J0naiiiiax1vvnaiiia11niiaTransformations between Species Fluxes( )()nMN()()aajMJ ,1,2,1i kn,1,2,1i knaabbjAjabknkikikiknkaa bA

8、baabbJBJabknkikikiknkaa bBxxb xFicks law for binary mixtures of A and B ABABAAAAMMAAABDDMCM DAReference Velocity Mass units Molar units- vj- J vj-MAAABAxCDx J-Transport coefficients (Diffusivities) Classic constitutive equations:Molecular Flux = -(Diffusivity) (Concentration Gradient)()yppkqC TyC AA

9、yABCJDy xyxdvdy Prandtl number Schmidt number Lewis numberPrpCkABABScDDPrABScLeDMagnitudes of Transport CoefficientsViscosity 10-610-510-410-310-210-1100GasesLiquidsViscosity (Pas)Magnitudes of Transport CoefficientsThermal conductivity10-310-210-1100101102103GasesNonmetallicLiquidsThermal Conductivity (W m-1 K-1)LiquidMetalsNonmetallicSolidsSolidM