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论文类型：会议论文

发表时间：2021-01-25

页面范围：393-400

关键字：Coal mine environment; Gob; Flow distribution; Temperature distribution; Porous media; Thermal hazard

摘要：Flow and temperature distribution in underground coal mines leading to significant attention is not just because miners require suitable environment for labor works but more importantly the task to prevent thermal hazard from coal oxidation. If heat generated by low-temperature oxidation and geothermal source is not adequately dissipated, it results in net temperature increase in coal mass and may ignite combustion of burnable gases and even explosion. The extremely prone region for thermal hazard is coal mine gobs, which are in fact porous media composed by uncollected coal and collapsed rock fragments after mining. Air leakage from the tunnel-like working face into gobs on one hand dilutes the combustible gases but on the other hand also accelerates oxidation with continuous supply of oxygen. It is therefore very critical to understand flow and temperature distribution in coal mine gobs so it can assist to optimize ventilation to prevent thermal hazard. However, the inaccessible nature and possible collapse in gobs makes in situ measurement of thermal conditions nearly infeasible, so numerical modeling remains a very attractive option.
   Based on the volumetric average method of thermo-fluid theories in porous media, this investigation develops a new two-dimensional model for flow and temperature distribution in both mining faces (similar to tunnels) and gobs, by applying a vorticity-stream function approach. Since gob flows are mixed types with laminar, turbulent, and transient flows, the Brinkman-Forchheimer-exteiided Darcy model is incorporated into the Navier-Stokes (N-S) equations to approximate the contribution of viscous forces. Temperature distribution in gobs is highly dependent on coal oxidation and however temperature determines coal oxidation rate, so governing equations of energy and oxygen content are coupled and solved simultaneously.
   The numerical model was first tested for a natural convection flow in a two-dimensional enclosure with boundary conditions well prescribed in lab and then applied to simulate a typical U-type gob in China. The model is found being capable to provide flow, oxygen and temperature distribution in good agreement with measurement data. The simulation results reveal that an asymmetric airflow distribution is formed in them gob and high temperature gradients are mainly concentrated to the regions right behind the working face. The most risky location for thermal hazard is on the mid-line of the gob away from the working face with tens of meters. Such spot should be drawn full attention for possible spontaneous combustion to assure mine safety.