Composition dependence of the viscosity of dense gas mixtures

We present a method for the computation of the composition dependence of the viscosity of a dense gas mixture. This method uses the (modified) Enskog theory formula for the viscosity of a dense mixture of rigid-sphere gases, as obtained by Thorne, and assumes that this formula can be applied to real gas mixtures provided one replaces the purely rigid sphere quantities in the Enskog theory by suitably chosen real gas quantities. In order to compute the composition dependence of a mixture one needs: (a) the viscosities of the pure component gases at the same molar density as the mixture; (b) the low-density viscosities of the pure component gases; (c) one low-density value of the mixture viscosity; (d) the second virial coefficient and its temperature derivative for each component pure gas; and (e) in some cases, the equations of state of the pure components. No dense mixture data are required. Many of the low-density and equation-of-state quantities can be obtained with sufficient accuracy from existing correlation schemes. The technique has been applied to three binary systems for which accurate measurements exist: He-Ar, Ne-Ar, and H₂-CH₄. There is agreement to about 1% up to densities 0.7 of the critical, and to about 5% for densities up to 1.8 times the critical for H₂-CH₄. The multicomponent generalization is also given but experimental data for comparison are lacking.