羧基化MWCNT强化重力热管煤火移热研究OA

To improve the efficiency of the gravity heat pipe(TPCT)in extracting low-grade thermal energy from coal fire areas,carboxylated multi-walled carbon nanotubes(MWCNTs-COOH)were pre-pared by a mixed-acid liquid-phase oxidation method,and MWCNTs-COOH nanofluids were then pre-pared using a two-step method.Thermogravimetric analysis was conducted to evaluate the thermal sta-bility of the vacuum-dried nanofluids.Combined with zeta potential,contact angle,and thermal conduc-tivity tests,their dispersion stability,interfacial wettability,and thermal conductivity were systematically investigated.In addition,a self-built coal fire heat extraction test platform was used to analyze the tem-perature field distribution and heat transfer characteristics during thermal energy extraction.The results show that the MWCNTs-COOH nanofluid has excellent thermal stability,with a mass residual rate of up to 92%.The dispersion stability and thermal conductivity of the modified multi-walled carbon nano-tubes are significantly improved.The zeta potential of the carboxylated nanofluid reaches 45 mV,the contact angle is about 69°,and the increase in thermal conductivity rises steadily from 4.04%at 20℃to 4.32%at 100℃.Under a coal temperature field of 100℃,the maximum temperature reduction of the TPCT using the MWCNTs-COOH working fluid is 40.2℃,significantly higher than the 29.9℃obtained with the MWCNT working fluid,corresponding to a 24%improvement.The cumulative heat extraction of the TPCT using the MWCNTs-COOH working fluid over 24 h reaches 322.4 MJ,about 38.42%higher than the 232.9 MJ obtained with the MWCNT working fluid.These results provide a theoretical basis for engineering design and analysis of clean and efficient utilization of thermal energy from coal fires.