Estimation of Binary Mass Transfer Coefficients

Binary mass transfer data usually are correlated in terms of dimensionless groups, such as the Sherwood number, 

Dimensional analysis suggests that the Sherwood number be a function of the Reynolds number (Re = ud/r) and Schmidt number. Sc (Sherwood et al., 1975) 

There are a great many correlations available in the literature for estimating binary mass transfer coefficients. It is beyond the scope of this book to review these correlations in detail [the reader is referred to the text by Sherwood et al. (1975) for more information]. For present purposes it suffices to cite only a couple of examples of useful empirical expressions. Other correlations are discussed in Sections 12.1.5 and 12.3.3. 

The Gilliland-Sherwood correlation for gas-phase binary mass transfer in a wetted wall column is 

An apparent weakness of the film model is that it suggests that the mass transfer coefficient is directly proportional to the diffusion coefficient raised to the first power. This result is in conflict with most experimental data, as well as with more elaborate models of mass transfer [surface renewal theory considered in the next chapter, e.g., or boundary layer theory (Bird et al., I960)]. However, if we substitute the film theory expression for the mass transfer coefficient (Eq. 8.2.12) into Eq. 8.8.1 for the Sherwood number we find 

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