KINETIC-THEORY CALCULATIONS OF PRESSURE EFFECTS OF DIFFUSION

The pressure effects of diffusion in an isothermal capillary tube are calculated. The linearized Boltzmann equation, the third-order Gross-Jackson model for the collision term, and Maxwell's diffuse-specular boundary condition at the wall are used to compute the dimensionless component mean velocities for binary mixtures using numerical methods. The pressure effects are obtained by mass conservation. With the accommodation coefficients as parameters, the calculations reproduce the experimental data for the systems of nitrogen-hydrogen, argon-nitrogen, and carbon dioxide-argon quantitatively and the sign change in pressure effects observed for the system of ethylene-neon. Independent assignment of the accommodation coefficients is required for a predictive theory.