Simulation and experiment of gas diffusion in a granular bed

Abstract The diffusion of gas through porous material is important to understand the physical processes underlying cometary activity. We study a rarefied (Knudsen regime) packed bed monodisperse spheres via experiments and numerical modelling, providing an absolute value coefficient compare it published analytical models. are designed be directly comparable simulations, by using precision steel beads, simple geometries, trade-off sample size between small boundary effects efficient computation. For direct comparison, determined in Direct Simulation Monte Carlo (DSMC) yielding good match with experiments. This model further-on used on microscopic scale, which cannot studied experiments, determine mean path molecules its distribution, against model. Scaling properties (particle size, porosity) (molecular mass, temperature) consistent As predicted these, results very sensitive porosity we find that tortuosity q(ϵ) depending linearly ϵ can well reconcile simulations. Mean paths close those described literature, but their distribution deviates from expectation for lengths. provided coefficients scaling laws applicable thermophysical models idealised material.