Numerical evaluation of inclined heat pipes on suppressing spontaneous coal combustion

Suppressing spontaneous coal combustion with heat pipe (HP) is an effect fire fighting method in practice. To improve the heat transfer capacity of HPs in coal piles as much as possible, this work explores the optimal inclination angle of HPs to remove heat in the coal stockpiles. Based on the theory of fluid mechanics and heat transfer, a physical-mathematical model of coal-HP-air was established, and the spontaneous combustion process of coal piles and the effect of HPs at four inclination angles ( θ ) of 30°, 45°, 60°, and 90° on the spontaneous combustion of coal piles were studied. The results show that the presence of HPs can change the heat conduction path in a coal pile and help the coal pile to dissipate heat in time, and this process makes the temperature contours on both the windward side and the leeward side deform and exhibits a ‘saddle’-like cooling mode at the periphery of the HPs. As θ of the HPs increases, the area (Δ S ) by which the spontaneous combustion danger zone (SCDZ) is decreased first increases and then decreases, and the maximum temperature ( T max ) drop values (Δ T ) first increases and then decreases. Moreover, the thermal performance of the HPs at inclination angle of 60° is found to be higher than other tested inclination angles. When θ = 60°, the heat is largely removed, and the integrity of the SCDZ is destroyed, so that Δ S is 11.106 m 2 , Δ T is 13.1 °C, and the natural ignition period is extended by approximately 25 days. Consequently, this study provides a reference for the design and optimization of coal fire fighting engineering with HP application in the future.