Asymmetrical diffusion across a porous medium-homogeneous fluid interface

Interfaces formed by a homogeneous fluid and a porous media are commonly found in nature and applications. This work uses Brownian motion simulations for exploring the effects of the interface in the diffusion transport of passive particles. The results revealed that the diffusion transport is asymmetric in the sense that particles migrate faster in the porous medium-to-homogeneous fluid interface than in the opposite direction. Besides, such asymmetry is stronger as the porosity decreases. Macroscopic model using volume averaging methods showed that the asymmetrical diffusion effect is induced by sharp transitions in porosity and effective diffusivity in a vicinity of the interface.