Максим Дмитриевич Попов

Relevance. The need to predict air convective movement in mine shafts in emergency modes of mine ventilation associated with the cessation of their forced ventilation. The occurrence of extended convective vortices in the shafts intensifies heat and smoke transfer in the event of a fire, and reduces as well the amount of natural draught, which poorly ventilates the mine after the fan is turned off. Knowledge of the conditions for the occurrence of thermal convection in shafts will allow for more accurate planning of measures to combat mine fires. Aim. To develop a methodology for assessing the convective stability of air in relation to the conditions of mine shafts. Objects. Mine shafts. Methods. Analytical and numerical modeling of convection occurrence and development in the mine shaft; comparative analysis of methods for estimating the convective stability of an unevenly heated medium in the gravitational field. Results. The authors have analyzed the methods for estimating air convective stability depending on the value of the vertical temperature gradient. It is shown that analytical methods of estimation in approximations of a compressible fluid in hydrodynamics, an ideal gas in meteorology, or by the sign of a vertical density gradient give results that differ significantly quantitatively. In order to identify the most adequate method of assessment in relation to mine conditions, the authors carried out numerical simulation of the convective air movement in the shaft at different values of its vertical temperature gradient. By calculation, it was established that the still air in the shaft when heated from below turns out to be even more stable than follows from the most optimistic estimate – the critical temperature gradient of the air is almost 5 times higher than the adiabatic one. The obvious reason for the result obtained is the stabilizing effect of viscosity forces, which increases many times over in the cramped conditions of mine shafts, preventing the development of convection, which occurs in a free atmosphere with much lower convective forces. Based on the results obtained, it is concluded that the meteorological criterion for assessing the convective stability of air in relation to the conditions of mine shafts is not suitable, since it is excessively rigid. Convection occurs at a vertical temperature gradient of ~ 46 °C/km, which is possible either when cold outside air enters the shaft or when there are heat sources in the shaft that heat the air more than the heat exchange with the surrounding rock mass.

Effective fire prevention in mine workings and tunnels requires a thorough theoretical analysis of the heat and mass transfer processes within these structures. This involves using established models to calculate non-isothermal air flow dynamics in long tunnels and mine workings. While the ventilation of tunnels has been extensively studied, significant challenges persist regarding mine ventilation systems, particularly due to their complex and branched topology. This study aimed to address these challenges and gaps in mine ventilation. We designed a laboratory bench to simulate an inclined mine working with a heat source (fire) and validated a mathematical model of heat and mass transfer in such settings. Using experimental measurements, we verified the model’s accuracy. It is important to note that our experimental and theoretical analyses focused solely on the thermal effects of a fire, without considering the release of harmful impurities. Using the validated model, we conducted multiparameter simulations to identify the conditions leading to the formation of a thermal slug in an inclined mine working and the subsequent reversal of air flow. The simulation data enabled us to determine the dependency of the critical heat release rate on the aerodynamic parameters of the mine working. Additionally, we evaluated the changes in average air density within a mine working at the critical heat release rate. These findings are crucial for the further development of a network-based method to analyze air flow stability in mine ventilation networks during fires.