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, 𝜂^(0)_12 , and the product of molar density and diffusion coefficient, (𝜌D_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, 𝜂^(0)_mix and 𝜂^(1)_mix, for the mixtures, as well as, 𝜂^(0)_i and 𝜂^(1)_i ( i= 1, 2 ), respectively, for the pure gases. Humberg et al. have already compared their 𝜂^(0)_mix and 𝜂^(0)_i 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 𝜂^(0)_mix and 𝜂^(1)_mix as well as 𝜂^(0)_i and 𝜂^(1)_i in two procedures to derive 𝜂^(0)_12 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 𝜂^(1)_mix and 𝜂^(1)_i failed to yield reasonable 𝜂^(0)_12 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 𝜂^(0)_12 is determined. But if (𝜌D_12)^(0) is calculated from 𝜂^(0)_12 using A^∗_12 values for the nonspherical potential, the impact is several percent. Moreover, the experimentally based 𝜂^(0)_12 and (𝜌D_12)^(0) data agree with theoretically calculated values for the nonspherical potentials.