Alternative Forms of the Generalized Ficks Law

There are three forms of the generalized Fick s law in common use  

Molar flux with respect to molar average velocity. 

Mass flux with respect to mass average velocity. 

For binary systems all matrices contain just a single element and Eqs. 3.2.5-3.2.7 reduce to Eqs. 3.1.1, 3.1.6, and 3.1.4, respectively. As noted earlier, the three binary coefficients, , P°, and are equal (Bird et al., 1960). For the general multicomponent case, the three matrices defined above are, in general, different from one another (as indicated in the next section). Cullinan (1965) has shown that the eigenvalues of [ ], [Z)°], and are, 

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