Network modeling of diffusion coefficients for porous media: I. Theory and model development

This study was conducted to investigate the macroscopic relative gas diffusion coefficient vs. air-filled porosity relationships (diffusion characteristic) of porous media using a network modelling approach. A cubic sphere-and-tube network model of porous media was adapted from petroleum engineering using Fick's law and the principle of conservation of mass to simulate one-dimensional, steady-state, isothermal, isobaric, molecular diffusion of a dilute binary gas in a nonadsorbing porous medium containing a single nonwetting fluid (air) and a single wetting fluid (water). The network model simulates hysteresis in air and water distributions in porous media for boundary drying and wetting curves of the soil water characteristic and demonstrates the effect of air-filled porosity, Henry's law liquid-gas partitioning coefficient, and ratio between gas- and liqiuid-phase diffusion rates, and pore geometry on the diffusion characteristic. -from Authors