Determination of the Binary Diffusion Coefficients and Interaction Viscosities of the Systems Carbon Dioxide–Nitrogen and Ethane–Methane in the Dilute Gas Phase from Accurate Experimental Viscosity Data Using the Kinetic Theory of Gases

Abstract

The results of viscosity measurements at moderate densities on the two gaseous mixtures carbon dioxide–nitrogen and ethane–methane including the pure gases between 253.15 K and 473.15 K, originally performed by Humberg et al. at Ruhr University Bochum, Germany, using a rotating-cylinder viscometer between 0.1 MPa and 2.0 MPa, were employed to determine the interaction viscosity, eta _{12}^{(0)}, and the product of molar density and diffusion coefficient, (rho D_{12})^{(0)}, each in the limit of zero density. The isothermal viscosity data were evaluated by those authors with density series restricted to the second order at most to derive the zero-density viscosities and initial density viscosity coefficients, eta _textrm{mix}^{(0)} and eta _textrm{mix}^{(1)}, for the mixtures, as well as, eta _i^{(0)} and eta _i^{(1)} (i=1,2), respectively, for the pure gases. Humberg et al. have already compared their eta _textrm{mix}^{(0)} and eta _i^{(0)} data for carbon dioxide–nitrogen and ethane–methane with corresponding viscosity values theoretically computed for the nonspherical potentials of the intermolecular interaction. Now we employed eta _textrm{mix}^{(0)} and eta _textrm{mix}^{(1)} as well as eta _i^{(0)} and eta _i^{(1)} in two procedures to derive eta _{12}^{(0)} values. For this, we needed A_{12}^* values (ratio between effective cross-sections of viscosity and diffusion). But the second procedure applying the initial density viscosity coefficients eta _textrm{mix}^{(1)} and eta _i^{(1)} failed to yield reasonable eta _{12}^{(0)} values. The first procedure should provide the best results when it is possible to use A_{12}^* values computed for the nonspherical potential. The effect is comparatively small if eta _{12}^{(0)} is determined. But if (rho D_{12})^{(0)} is calculated from eta _{12}^{(0)} using A_{12}^* values for the nonspherical potential, the impact is several percent. Moreover, the experimentally based eta _{12}^{(0)} and (rho D_{12})^{(0)} data agree with theoretically calculated values for the nonspherical potentials.