Generalization to Other Geometries

For diffusion in cylindrical or spherical geometries the one-dimensional, steady-state form of Eq. 1.3.10 simplifies to 

A very important practical application of the above film model is to determine the external mass transfer resistance to catalyst particles (Example 8.2.2). 

Estimate the rates of mass transfer in the distillation of the system methanol(l)-ethanol(2) under the following conditions  

SOLUTION The first step is to calculate the molar density from the ideal gas law 

It is common (but not necessarily accurate—see Section 11.5) to assume equimolar counterdiffusion in distillation. Thus, = 0 and the flux of methanol is obtained directly from Eq. 8.2.17 as 

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