Gas Diffusion Model through Coal Particles and Parameters Calculation

The micro-mechanism of gas diffusion in coal was analyzed. The process of gas diffusion through coal particles and the mathematical physical model under the third kind boundary condition was determined to obtain the rules of gas diffusion through coal particles of different sizes. The analytical solution of the equation was obtained by the method of mathematical physics. The parameters of analytical solutions and the implications of parameters were analyzed. The results show that in coal body there are three kinds of diffusion modes: Fick diffusion, Knudsen diffusion, transitional diffusion, surface diffusion and crystal diffusion. The mathematical and physical model of methane diffusion under the third boundary condition was built. According to the analytical results, Biot criterion (Bi) and Fourier criterion (F-0) of mass transfer can represent and reflect the features of gas diffusion field of coal particles. Moreover, the measurement method of gas diffusion coefficient and surface mass transfer coefficient are introduced and an example of measurement is given. Also, the ultimate diffusion volume was gotten by applying the theory and model. The achievement can provide the support to prevent disasters related to methane in coal mines.