8.3.1 Molecular diffusion in binary mixtures 8< Diffusion in a direction扩散方向 Diffusion in a direction is perpendicular to the interface between the phases and at a definite location in the equipment 9 Steady state Steady state is assumed, and the concentrations at any point do not change with time
8. Diffusion in a direction 扩散方向 Diffusion in a direction is perpendicular to the interface between the phases and at a definite location in the equipment. 9. Steady state Steady state is assumed, and the concentrations at any point do not change with time. 8.3.1 Molecular diffusion in binary mixtures
c8.3. 1 Molecular diffusion in binary mixtures Fick's first law of diffusion for a binary mixture (P51)(双组份扩散时的费克第一定律) 1 What's Fick's first law ∵分子扩散的实质是分子的微观随机运动。 对于一定温度和压力下的一维定态扩散,其统计 规律可用宏观的方式表达。这就是费克定律: d =-D △B (8-9) Where: Ja the diffusion flux of component A IA moles/per unit area per unit time IA moles/ms
二. Fick’s first law of diffusion for a binary mixture (P514)（双组份扩散时的费克第一定律） 1. What’s Fick’s first law ? ∵分子扩散的实质是分子的微观随机运动。 ∴对于一定温度和压力下的一维定态扩散，其统计 规律可用宏观的方式表达。这就是费克定律： Where: JA= the diffusion flux of component A; [A moles/per unit area per unit time] ～ [A moles/m2·s] 8.3.1 Molecular diffusion in binary mixtures ( ) A A AB dC = - 8 - 9 J D dZ
8.3.1 Molecular diffusion in binary mixtures dca/dF the concentration gradient of component a diffusing in a direction, [(mol/m )/ml DAR=Diffusivity of component A in component B, m/s I Reference to(8-9), a similar equation for component B: do JB- DBa dz B(8-1) For binary mixture DAB=DBA-D Then J=-J B (8-13)
dCA/dz= the concentration gradient of component A diffusing in a direction， [(mol/m3 )/m] DAB=Diffusivity of component A in component B，[m2 /s ] Reference to（8-9）, a similar equation for component B: ∵ For binary mixture DAB=DBA=D Then JA=－JB （8-13） 8.3.1 Molecular diffusion in binary mixtures ( ) B B BA dC = - 8 -11 dZ J D
8.3.1 Molecular diffusion in binary mixtures 2.“现象定律 That's phenomena law. 上学期已经学过两个基本定律: 牛顿粘性定律: 气 Newton's la aw ot viscos Molecular momentum transport 傅立叶定律:a cFourier's law of heat conduction c Molecular energy transport Comparison to those three formulas ()传递的物理量:动量,热量,质量 momentum, energy, and mass
2. “现象定律” ～ That’s phenomena law. 上学期已经学过两个基本定律： 牛顿粘性定律: ～Newton’s law of viscosity ～ Molecular momentum transport 傅立叶定律: ～Fourier’s law of heat conduction ～ Molecular energy transport Comparison to those three formulas: ⑴ 传递的物理量：动量，热量，质量 ～momentum, energy, and mass 8.3.1 Molecular diffusion in binary mixtures du τ μ ＝－ dy dt q = k － dy
18.3.1 Molecular diffusion in binary mixtures (2)均为传递通量:(传递的物理量)/m2s 大小( Magnitudes):与对应强度因素梯度成正比。 方向( Directions):沿着浓度减小的方向传递。 (3)各式中的系数仅为状态函数,即是TP和组成的函 数,而于流动无关。 又统一称这三个定律为 “现象定律”~That' s phenomena law 大家在学习质量传递时,完全可以与前面所学过的动 量、热量传递进行类比
⑵ 均为传递通量：（传递的物理量）/m2·s 大小 (Magnitudes) : 与对应强度因素梯 度成正比。 方向（Directions) : 沿着浓度减小的方向传递。 ⑶ 各式中的系数仅为状态函数，即是T,P和组成的函 数，而于流动无关。 ∴又统一称这三个定律为 “现象定律” ～ That’s phenomena law. ∴大家在学习质量传递时，完全可以与前面所学过的动 量、热量传递进行类比。 8.3.1 Molecular diffusion in binary mixtures