Linear driving force model, for mass transfer

This solution is valid for plug flow assuming a linear driving force model for mass transfer. 

Unfortunately, because of the conplexity of the flow fields in most separators, reactors, and other devices where interfacial mass transfer occurs, solution of the Fickian diffusion equations for binary systems is not usually feasible. In these cases we typically use the empirical linear driving-force model for mass transfer that was briefly introduced in Section 1.3. This equation [a modification of Eq. ri-411 is... 

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