Binary Mixtures—Low Pressure—Nonpolar Components

Binary Mixtures—Low Pressure—Nonpolar Components Many evaluations of correlations are available [Elliott and Watts, Can. J Chem., 50,31 (1972) Lugg, And. Chem., 40,1072 (1968) Marrero and Mason, AlChE J., 19, 498 (1973)]. The differences in accuracy of the correlations are minor, and thus the major concern is ease of calculation. The Fuller-Schettler-Giddings equation is usually the simplest correlation to use and is recommended by Poling et al. 

Chapman-Enskog (Bird et al.) and Wilke and Lee [31 ] The inherent assumptions of these equations are quite restrictive (i.e., low density, spherical atoms), and the intrinsic potential function is empirical. Despite that, they provide good estimates of for many polyatomic gases and gas mixtures, up to about 1000 K and a maximum of 70 atm. The latter constraint is because observations for many gases indicate that DABP is constant up to 70 atm. 

TABLE 5-9 Rules of Thumb for Diffusivities (See Cussler, Poling et aL, Schwartzberg and Chao) 

Liquid io-9 10- io-8-io-10 10 4-10 Approximate correlations exist, generally within 25% 

Liquid occluded in solid matrix KT10 10-6 10-8-10-12 10-4-10-8 Hard cell walls Deff/D = 0.1 to 0.2. Soft cell walls De /Di = 0.3 to 0.9 

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Binary Mixtures—Low Pressure—Polar Components The Brokaw correlation was based on the Chapman-Enskog equation, but 0 g and were evaluated with a modified Stockmayer potential for polar molecules. Hence, slightly different symbols are used. That potential model reduces to the Lennard-Jones 6-12 potential for interactions between nonpolar molecules. As a result, the method should yield accurate predictions for polar as well as nonpolar gas mixtures. Brokaw presented data for 9 relatively polar pairs along with the prediction. The agreement was good an average absolute error of 6.4 percent, considering the complexity of some of... 

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