Numerical simulation of gas drainage in gob considering temperature change

Considering the air leakage of the gas drainage face in the gob, which causes the oxidation and heating of the remaining coal in the gob,based on Darcy’s law of seepage, Fick’s law of diffusion and Fourier’s law of heat conduction, combined with the mass conservation equation and the energy conservation equation, a multi-field coupled two-dimensional mathematical model of gas extraction in the gob was put forward. This model includes gas concentration field, oxygen concentration field, solid temperature field and gas temperature field and the interaction of these fields considering temperature changing. The finite volume method and Microsoft Visual Basic platform were used to discretize the multi-field coupling of gas drainage in the gob considering temperature changes. A three-dimensional mathematical model, a computer solution program based on Microsoft Visual Basic, and Tecplot software were used to visualize the solution results. The pressure, gas concentration, oxygen concentration, solid temperature and gas temperature distribution in the gob before and after gas drainage were studied. The results show that: before gas drainage, there is an obvious gas high pressure area near the lower corner of the gob and gradually decreases to the surroundings, and an obvious gas low pressure area near the upper corner and gradually increases to the surroundings; the gas concentration gradually decreases from the lower corner to the upper corner, and the gas concentration in the depths of the gob is higher than that near the working face, up to 16.0%; the oxygen concentration near the lower corner of the gob is higher, reaching 7.0%, and the oxygen concentration gradually decreases from the lower corner to the upper corner; there is an obvious solid and gas high temperature area on the side of the gob that leaks into the wind, and the temperature gradually decreasesfrom here to the surroundings. After the gas is drained, a gas low-pressure area is formed at the drainage point, and the gas pressure changes slowly in the depth direction of the gob; the gas concentration in the upper corner of the gob is greatly reduced whilethe gas in the deep part of the gob is less affected by drainage; the oxygen concentration in the shallow part (0～100 m) of the gob increases, and the oxygen concentration in the deep part (100～300 m) of the gobremains basically unchanged; the high temperature area is still formed on the side where the gob leaks into the wind, but the range of the high temperature zone has been expanded,the maximum solid and gas temperatures in the gob are 2 ℃ higher than before gas drainage.