Significance of pressure gradients in porous materials: Part I. Diffusion and flow in fine capillaries

Abstract

Abstract Equations are derived for the effect of a total pressure gradient on flow and diffusion of a binary gas system in a fine capillary. The results apply over the pressure and pore radius regimes from Knudsen flow to Poiseuille flow. Application of the equations to a pure component leads to an expression for the permeability which predicts the observed minimum flow in the slip‐flow region. This expression agrees well with Knudsen's data for carbon dioxide and for new measurements for nitrogen in a glass capillary (radius = 0.01244 cm.).