Analysis of multicomponent diffusion in pore networks

Abstract

Diffusion flux models are developed for isobaric diffusion of a multicomponent gas mixture in pore networks of distributed pore size and length constructed by arranging pore segments around the bonds of a lattice of constant coordination number. Eigenvalue-eigevector analysis is used to decompose the dusty-gas model equations, written for each pore segment in the network, into a set of independent single-species diffusion problems, each of which is then treated by combining the effective medium theory for resistor networks with the smooth field approximation (Burganos and Sotirchos, 1987). Results for a ternary mixture diffusing in a porous slab show that direct application of the smooth field approximation underestimates significantly the mass transport resistance.

Multicomponent diffusion and convection in capillary structures

“…Another alternative is to use the Feng and Stewart model for nonisobaric diffusion, which is obtained by integrating the nonisobaric dusty-gas equations for a single pore over the pore sizes and pore orientations, assuming smooth microscopic concentration and pressure fields. The extension of the eigenanalysis procedure of Sotirchos and Burganos (1988) to the more general problem of multicomponent diffusion under nonisobaric conditions is the subject of my paper. A general method for developing flux models for nonisobaric multicomponent diffusion is presented.…”

“…The special structure of the multicomponent flux expressions derived by Sotirchos and Burganos (1988) made possible their direct comparison with the "two-parameter" dusty-gas model for isobaric diffusion in porous media which makes use of effective, concentration-independent diffusion coefficients for binary and Knudsen diffusion. The comparison showed that the rigorous multicomponent flux model could be approximated satisfactorily by the "two-parameter'' dusty-gas model provided that the same averaging procedure was used to obtain the effective diffusion coefficients of the n auxiliary species (appearing in the rigorous model) and the effective binary and Knudsen diffusion coefficients (appearing in the "two-parameter" flux model).…”

“…In a previous article (Sotirchos and Burganos, 1988), the problem of multicomponent diffusion of gases in pore networks under isobaric conditions was investigated. The capillary structures considered in that study were visualized as consisting of cylindrical pore segments arranged around the bonds of a twoor three-dimensional lattice, with two-dimensional capillary structures understood as embedded in a slice of the porous medium.…”

“…A general method for developing flux models for nonisobaric multicomponent diffusion is presented. The method is employed to construct flux models using the SFA and EMT-SFA procedures introduced in previous papers (Burganos and Sotirchos, 1987;Sotirchos and Burganos, 1988), which are then compared with the corresponding "three-parameter'' dusty-gas models.…”

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A previously developed method (Sotirchos and Burganos, 1988) for studying isobaric multicomponent diffusion in a class of capillary networks is extended for application to the problem of convection and diffusion of gaseous mixtures in porous media. The method is used to develop flux models for nonisobaric transport in capillary structures, which are then compared with corresponding "three-parameter'' dustygas models.

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