Periodic capillary models of diffusion in porous solids

Abstract

Periodic capillary networks are proposed as models for describing diffusion in porous solids. The capillary network is analyzed by means of the nodal concentration equations for a single unit cell and expressions are derived for the diffusional flux in terms of the macroscopic concentration gradient. Conditions for isotropy are derived and the validity of the smooth field assumption is discussed. The theory is illustrated with a macropore-micropore model of porous catalyst pellets and comparisons are made with an earlier capillary model.

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