Thermal extraction from a low-temperature stage of coal pile spontaneous combustion by two-phase closed thermosyphon

Abstract

A two-phase closed thermosyphon (TPCT) with a CuO–H2O nanofluid was used to effectively harness the internal accumulation of thermal energy from a coal pile, formerly subject to the risk of spontaneous combustion. The heat transfer effect of different insertion ratios of the TPCT (evaporation section:condensation section = 1:3, 1:2, and 2:3) and inclination angles (30°, 45°, 60°, and 90°) was investigated for bituminous coal. The results indicated that the heat transfer effect of the insertion ratio, in descending order of preference, was 2:3 > 1:2 > 1:3. When the TPCT insertion ratio was 2:3, the maximum temperature difference was up to 37.7 °C. The heat transfer effects of the TPCT were strengthened when it was inserted at a given angle. In decreasing order of effectiveness, the tested inclination angles showed the following order of preference: 60° > 30° > 45° > 90°. Therefore, 60° was the optimal insertion angle. In general, TPCT has the optimal transfer effects when the insertion ratio is 2:3 and the inclination angle is 60°.