Experimental study of the gas concentration boundary condition for diffusion through the coal particle

Gas diffusion law for coal particles has been researched by many authors due to theoretical and practical significance to gas emission prediction and coal and gas outburst prevention. But its definition remains fuzzy for indeterminacy of the concentration boundary condition that mainly depends on the change rules of external gas pressure and temperature of the coal particles during the desorption process. In this paper, reliable data of the external gas pressure and temperature are obtained by using a self-developed experimental setup of which the most remarkable characteristic is the application of a specially-made real time data acquisition system capable of recording data at very short time intervals (several milliseconds). Experimental results showed that after the opening of pneumatic valve gas pressure decreased nonlinearly with increasing time, and gas pressure had exponent relation to time. Gas temperature decreased rapidly at first, then increased with a decreasing speed, and finally reached a constant. The final gas temperature did not rise to the initial equilibrium value. With increase of the equilibrium gas pressure, the lowest gas temperature decreased, and the temperature difference between the equilibrium gas temperature and the lowest gas temperature increased gradually. Based on the tested change rules of gas pressure and temperature, the concentration boundary condition is achieved.