Diffusion of rarefied gas mixtures in a circular tube under the existence of pressure gradients

Abstract

A simple and general expression for nonuniform pressure diffusion of a binary mixture in a circular tube is obtained by applying locally uniform distributions of molecular velocity plus a new physical model on the molecular transport of momentum in the Knudsen layer, which is derived from the momentum balance considerations including the influence of wall interactions of molecules, to Maxwell’s transport equation. The theory predicts some striking phenomena, the Kramers–Kistemaker pressure effect, the Hoogschagen flux ratio, Knudsen minimum, and so on. In order to check the validity of the theory, the flux of a component gas in the Stefan tube and the pressure difference which accompanies it are determined experimentally for Hg-He and Hg-Ar mixtures and found to be in good agreement with those predicted from theory.