ISOBAR1C DIFFUSION OF GASES IN PACKED BEDS OF FINE PARTICLES

Abstract

Diffusion of gases through packed beds of particles under uniform total pressure is studied analytically by using the rigorous kinetic theory of gases with the two-sided Maxwellian velocity distribution functions and Maxwell''s transport equation. Attention is paid to the solid parts of the packed beds, although most investigators have concentrated on the space structures to obtain a pore model. With some abbreviations the present results are quite similar to those of Evans et al., which were derived from the macroscopic multicomponent diffusion equation by considering the particles as giant molecules. But in the Knudsen diffusion region their results are about 2.4 times larger than the authors'' or the experimental results. The present treatment is considered to be more adequate and general than that of Evans et al. and others. To obtain experimental confirmation of the analytical results a simple method for measurement of the effective diffusivities and flow permeabilities of gases through porous media is proposed by using the wellknown relation, -N_A/N_B=(M_B/M_A)^1/2, which is also derived from the present treatment. The experimental results by this method are in relatively good agreement with the analytical ones obtained here. This is perhaps the first direct experimental confirmation of the dependency of the mean effective diffusivities of gases through porous media on composition.