FLOW AND DIFFUSION OF GASES IN CAPILLARIES AND POROUS-MEDIA

The methods and results of the treatment of flow and diffusion phenome na in the rarefied gas mixture flowing in a capillary or a porous medi um are discussed. The interior flow of a gas mixture at all Knudsen nu mbers is analyzed by means of the ''dusty gas model'' and the exact ki netic theory. The problems of the free-molecular diffusion, the diffus ion 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 exa ct kinetic theory allows us to establish the range of validity of diff erent methods and practical application of the theoretical expressions . Some kinetic effects (diffusion-pressure effect, separation effect, thermomolecular pressure difference) are analysed.