Coupling effect of operational factors on heat extraction from a coal pile using a two-phase closed thermosyphon

Thermal extraction from a coal fire by using a two-phase closed thermosyphon (TPCT) is a clean and sustainable approach to govern coal spontaneous combustion (CSC). However, investigations into the elimination of coupling effects and the optimal design of the primary operational variables of TPCTs for effective prevention and control of coal fires are lacking. Through orthogonal experiments, this study examined the influence of the major factors of nanoliquid as liquid working medium, filling percentage, and aspect ratio on TPCT heat transfer. Analysis of variance (ANOVA) was performed to obtain the optimal combination of variables. The results indicated that when the coal temperature was 100 degrees C, the highest heat transfer performance of TPCTs among all experimental test cases was achieved which utilising CuO-H2O as the liquid working fluid, a 25% filling percentage, and an aspect ratio of 15. The optimal combination of variables obtained using ANOVA constituted a CuO-H2O liquid working medium, a filling percentage of 15%, and an aspect ratio of 15. Subsequent numerical predictions indicated a 74.9% increase in the heat transfer performance of TPCT with the aforementioned combination of ANOVA-based variables compared with the experimental combinations. (C) 2021 Elsevier Ltd. All rights reserved.