A Comparison of Gas Diffusivity Models for Unsaturated Porous Media

Abstract

Abstract The effective gas diffusivity in a porous medium decreases rapidly with increasing water content. Comparisons are made between experimental diffusivity data for different materials at various moisture contents, and estimation methods from the literature. The estimation methods proposed by R.J. Millington and R.C. Shearer in 1971 give the best predictions of the effective diffusivity. The methods are extended here to account for the contribution of diffusion in the water‐filled pores. The method for aggregated media should be used for undisturbed clayey soils, and the method for nonaggregated media may be used for sandy soils and for other materials that are not aggregated, e.g., laboratory packed clayey soils. The experimental data show that very low effective diffusivities may be obtained in practice in soils with high moisture content.