Steady-state equimolal counterdiffusion

Pick s law for steady-state equimolal counterdiffusion is then expression by Eq. (44)... 

Steady-State Equimolal Counterdiffusion and Unimolal Unidirectional Diffusion... 

For the reaction A B, reaction and diffusion (at steady state) in a pore would require equimolal counterdiffusion that is, Ng = — Then a = 0, and the effective diffusivity is... 

There are several types of situations covered by Eq, (21.16). The simplest case is zero convective flow and equimolal counterdiffusion of A and B, as occurs in the diffusive mixing of two gases. This is also the case for the diffusion of A and B in the vapor phase for distillations that have constant molal overflow. The second common case is the diffusion of only one component of the mixture, where the convective flow is caused by the diffusion of that component. Examples include evaporation of a liquid with diffusion of the vapor from the interface into a gas stream and condensation of a vapor in the presence of a noncondensable gas. Many examples of gas absorption also involve diffusion of only one component, which creates a convective flow toward the interface. These two types of mass transfer in gases are treated in the following sections for the simple case of steady-state mass transfer through a stagnant gas layer or film of known thickness. The effects of transient diffusion and laminar or turbulent flow are taken up later. 

Equimolar counterdiffusion. Starting with the general equation (6.2-14), we can obtain for equimolal counterdiffusion where = —Ng, an equation similar to Eq. (6.1-11) for gases at steady state. 

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