Multi-scale numerical simulation of gas flow field in goaf and thermal evaporation effect analysis

Air leakage in goaf is one of the main reasons for spontaneous combustion of residual coal. However, under different research scales, the gas flow in goaf follows different laws. In this paper, the velocity and pressure distribution of steady-state flow field in free flow domain and porous media domain in goaf are studied by using multi-scale correlation analysis method from macro scale and meso scale respectively. The heat flow moisture multi-field coupling model is constructed, and on this basis, the change of moisture in coal under the influence of gas flow and thermal evaporation is simulated by using multi-physical field simulation software. The results show that the moisture content in coal will gradually decrease under the effect of thermal evaporation, which is consistent with the results of thermogravimetric experiment. The concentration of water vapor on the leeward side is higher affected by the flow field. In addition, under the influence of evaporation and heat absorption, the temperature distribution of coal body will change continuously, and the internal temperature of coal body near the leeward side decreases slowly.