Multi-component gas transport in micro-porous domains: Multidimensional simulation at the macroscale

For decades, models based on the Maxwell–Stefan diffusion equations have been used to predict mass transfer of multi-component gases in porous media. However, the validity of these models is restricted to transport processes that are dominated by diffusion and wall-friction. Therefore, a new computational model is presented, which is based on a comprehensive theory of multi-component gas transport. It comprises conservation equations of mass and momentum for each species contained in the gas mixture together with an energy balance for the mixture. The model is intended to be used for investigations on the macroscopic scale. Thus, the local volume averaging technique is applied and friction coefficients, which encompass the full range of Knudsen numbers, are used to describe the drag forces exerted by the pore structure. In the volume averaged energy equation the gas and solid phases are considered a pseudo-homogeneous medium. The resulting set of highly coupled transport equations is implemented in a commercial computational fluid dynamics program. For validation purposes, the mass transfer model is first used to simulate the isothermal diffusion problem in a Loschmidt tube. Then, the simultaneous mass and heat transfer in a porous duct with cooled walls is investigated. In both cases, the numerical results are in very good agreement with experimental data.