Flow and diffusion of gases in capillaries and porous media

The methods and results of the treatment of flow and diffusion phenomena in the rarefied gas mixture flowing in a capillary or a porous medium are discussed. The interior flow of a gas mixture at all Knudsen numbers is analyzed by means of the “dusty gas model” and the exact kinetic theory. The problems of the free-molecular diffusion, the diffusion in a viscous flow and the viscous slip, diffusion slip and thermal creep at small Knudsen numbers are considered. The comparison of the results for the “dusty gas model”, moment-transfer arguments and exact kinetic theory allows us to establish the range of validity of different methods and practical application of the theoretical expressions. Some kinetic effects (diffusion-pressure effect, separation effect, thermomolecular pressure difference) are analysed.