The Influence of Structural Heterogeneity of Layers of a Two-Layer Membrane on Diffusion Transfer

Abstract

The unidimensional diffusion transfer of a gas through a medium composed of two dissimilar layers has been studied. The heterogeneity of the layers was simulated by the dependences of diffusion coefficients on a spatial variable. Analytical expressions have been derived for the flux of a substance that diffuses through the medium at arbitrary dependences of the diffusion coefficients on the spatial variable. A generalized relation has been obtained for the permeability of the two-layer heterogeneous membrane. It has been found that the permeability of such a membrane may depend on the direction of the transfer. Mathematical simulation has been carried out for the transfer in the case of an exponential dependence of the diffusion coefficients on the spatial variable. The main parameters affecting the asymmetry of the transfer have been determined. It has been shown that the asymmetry effect may arise, provided that at least one of the diffusion coefficients depends on the spatial variable. It has been found that, at some values of the membrane heterogeneity parameters, the gas transfer occurs in the regime of a “diffused diode.”