Modeling the Gas Diffusion Coefficient in Analogy to Electrical Conductivity Using a Capillary Model
2000
Weerts, Albrecht H. | Freijer, Jan I. | Bouten, Willem
A conceptual model that accounts for the influence of pore geometry is presented to model gas diffusion coefficients in soils as a function of water content. To model the diffusion coefficient of the gas phase, we rewrote the Mualem and Friedman bulk electrical conductivity model. The model was calibrated using measured soil water retention curves and gas diffusion coefficients of seven mineral soil horizons. The model with only one free parameter fitted the data of five horizons. The model failed to describe the data of two clayey surface horizons. Estimated gas tortuosity parameters were tested on measured hydraulic conductivity data of three of the soils studied. The use of the gas tortuosity parameter led to overestimation of the unsaturated hydraulic conductivity at low water contents. This systematic deviation suggests that the gas (non-wetting) tortuosity parameter is not equal to the hydraulic (wetting) tortuosity parameter, although a relationship is likely.
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