Diffusion Mechanism of Porous Gases in Coal Seams

Diffusion modes and micro mechanism of gases in coal were analyzed. It is pointed out that in coal seams there are the following diffusion modes: Fick diffusion, Knudsen diffusion, transitional diffusion, surface diffusion and crystal diffusion. Moreover, the movement and diffusion processes of gas in coal seams during the drainage were described. The effect rules of pressure and temperature on the mean molecule free path of gas were discussed in microcosm according to molecule dynamics. Besides, the micro mechanism of enhancing the diffusion ability of porous gases by increasing pressure and temperature was explained. On the basis of the relationship between the diffusion coefficients and the mean free path of gas molecules, it is found that the macro parameters of gas diffusion is determined all by the micro parameters of gas molecules.