Numerical characterization of the dynamic high-temperature zone under the coupling effects of air supply, gas drainage and nitrogen injection

The dynamics localization of high-temperature zones inside the gob has proven particularly difficult without direct observation. Although oxidation zones have been identified using air leakage velocity and oxygen concentration in gob, such techniques are insufficient for helping to determine the exactly distribution of high-temperature zone. This study utilizes Computational Fluid Dynamics (CFD) and proposes a time-series cumulative model to simulate air-leakage flow fields, gas concentrations, and the high-temperature zones in gob during dynamic advancing. Under the coupling effects of air supply, gas drainage and nitrogen injection, triangular characteristics have been creatively used to simplify the location of the high-temperature zone in gob for investigation. The high-temperature zone can be ascertained by the vertex A as well as the length on the air inlet side. As the air-supply volume increased, the high-temperature zone transitioned from acute to obtuse triangular forms, with vertex A moving at a rate of 0.04m/(m 3 /min) and angle α rising at 0.02 o /(m 3 /min). Gas drainage volumes have limited impact on vertex A and the angle α, which remain stable at roughly x =45m and α=88 o . Only 6% of the gob experiences a temperature rise of 25–40°C with a nitrogen injection volume of 16m 3 /h. The triangle simplification approach in high temperature zones and the time-series model suggested in this work may be used to assess the combined disaster risk of coal spontaneous combustion in dynamic advancing.