Prediction of coal mine goaf self-heating with fluid dynamics in porous media

Coal mine goaf self-heating due to exothermic coal oxidation has been recognized as a major threat to coal mine safety. To evaluate the risk of the coal mine goaf self-heating hazard, both gas distribution characteristics in goaf and heat transfer mechanisms in porous media must be studied. However, due to the difficulty of determining goaf permeability and the complexity of the overlaying strata caving characteristics, it is a considerable challenge to determine the thermal-fluid field coupling. Based on the volumetric average method in porous media, this work develops three numerical models for solving fluid dynamics and heat transfer in both longwall face and goaf. The Brinkman-Forchheimer-extended Darcy model is introduced to describe inertia and frictional forces in fluid phase exerted by solid phase. Temperature profile is highly dependent on and affects coal oxidation rate; therefore, governing equations for energy and oxygen mass equilibrium must be coupled. A twodimensional goaf permeability distribution model is established based on different caving conditions in goafs. Three scenarios are simulated and validated by field and experimental data, and it is observed that these models are capable of predicting gas flow pattern and temperature distribution.