地下煤火燃烧面积广、持续时间长、热能储量大。考虑常规治理技术的局限性和巨大的热能资源，由热虹吸器与热电模块构成的煤火废热转化系统成为煤火治理与热能利用的有效方法。

为提高热能移取率，本文基于热虹吸器常规竖直结构，改变蒸发段角度和传热面积，设计新型弯曲井身结构，探索井身结构的变化对热虹吸器传热性能的影响。以相同热边界条件下每种热虹吸器的轴向壁温分布、传热效率、传热热阻以及等效对流换热系数作为判定依据，确定热虹吸器的最优结构。其次，以热虹吸器为基础增加热电模块构成煤火废热转化系统，设计冷却方式、热电器件覆盖率以及连接方式的不同组合，研究每种组合对热电模块发电性能的作用效果进而获得最佳组合设计。最后搭建煤火热能移取与利用实验台，将优化的煤火废热转化系统应用于实际煤堆，探究不同热源温度下系统对煤堆的移热降温效果和热电转换能力，主要研究成果如下：

以竖直结构为基准，比较两种工况（相同传热面积和相同埋深）下的弯曲结构对热虹吸器传热性能的影响可以发现：改变井身结构可以有效提高热虹吸器的传热能力。特别是相同埋深下角度为30°的热虹吸器，其最大传热效率可达81.84%，最小热阻为0.08 ℃/W，最大等效对流换热系数为945.96 W/m²/K。角度和传热面积对热虹吸器传热性能的贡献度为：传热面积>角度。角度与热虹吸器传热性能呈正相关，即改变角度可以有效提高热虹吸器的传热性能，且角度与传热面积协同作用时具有最优结构，而传热面积过大也会限制热虹吸器的传热，增加内部工质相变过程中的阻力。

热电模块的最佳组合方式为水冷冷却、串联连接方式、热电器件覆盖率为22.5%，获得系统开路电压6.82 V。水冷冷却可以大幅度提高热电器件冷热端温差，增强热电转换能力；串联时的开路电压与输出性能优于并联连接时的开路电压与输出性能；热电器件覆盖率的大小影响系统的传热过程，传热热阻随着覆盖率的增大而增大；当热电器件覆盖率为22.5%，系统热电转换性能最佳，热电转换效率可达0.35%。

由优化后热虹吸器与热电模块构成的煤火废热转化系统实际作用于煤堆中的降温效果显著，特别是底部和中部的煤堆温度大幅度下降，最大降温幅度和降温率可达203.60 ℃、68.45%。与底部和中部煤堆相比，上部煤堆的温度变化趋势出现差异的原因是由于煤堆的热扩散、煤火废热转化系统的移热作用以及上层煤堆与外部氧气发生复合反应产热的综合影响。与电加热方式提供的热源不同，煤堆热源所具有的时空非均匀特性对煤火废热转化系统的传热和发电增添了更多的不确定性和波动性。煤火废热转化系统在实验中的最大开路电压为4.36 V；增加外部负载后系统的最大输出功率为0.57 W，最佳匹配负载值为33 Ω；通过虚拟热源法计算得到系统的总移热量，进而获得系统实际应用于煤堆中的最大热电转换效率为0.32%。

Underground coal fires burn over a wide area, last for a long time, and have large thermal energy reserves. Considering the limitations of conventional treatment techniques and the huge thermal energy resources, a coal-fired waste heat conversion system consisting of a thermosyphon and thermoelectric module has become an effective method for coal fire treatment and thermal energy utilization.

To improve the heat transfer efficiency, this paper explored the effect of variations in geometrical structure on the heat transfer performance of the thermosyphon by designing new curved bodies based on the conventional vertical structure of the thermosyphon, changing the angle and heat transfer area. The axial wall temperature distribution, heat transfer efficiency, heat transfer thermal resistance, and equivalent convective heat transfer coefficient of each type of thermosyphon were employed as the basis for determining the optimum structure of the thermosyphon under the same boundary conditions. Secondly, a coal-fired waste heat conversion system was formed by adding thermoelectric module based on a thermosyphon. Different combinations of cooling methods, coverage rate of thermoelectric components, and connection methods were designed. The effect of each combination on the power generation performance of the thermoelectric module was investigated to obtain the best combination. Finally, a coal-fired thermal energy extraction and utilization experimental bench was built and the optimized coal-fired waste heat conversion system was applied to an actual coal pile to study the heat transfer effect and thermoelectric conversion capacity of the system on the coal pile at different heat source temperatures. The main research results are as follows:

Based on the vertical structure, comparing the influence of curved structures on the heat transfer performance of thermosyphon under two working conditions (same heat transfer area and same buried depth), it can be concluded that changing the well structure can effectively improve the heat transfer capacity of thermosyphon. The thermosyphon with the best heat transfer performance in the experiment is the one with an angle of 30° at the same burial depth, with a maximum heat transfer efficiency of 81.84%, a minimum thermal resistance of 0.08 °C/W, and a maximum equivalent convective heat transfer coefficient of 945.96 W/m²/K. The contribution of angle and heat transfer area to the heat transfer performance of a thermosyphon: heat transfer area > angle. The angle is positively correlated with the heat transfer performance of the thermosyphon, changing the angle can effectively enhance the heat transfer performance of the thermosyphon. The angle and the heat transfer area work in synergy to have the optimum structure, but too much heat transfer area can limit the heat transfer of the thermosyphon and increases the resistance during the phase change of the internal working medium.

The optimum combination of thermoelectric module with water cooling, series connection, and coverage rate 22.5% of thermoelectric components obtains an open-circuit voltage of 6.82 V. Water cooling could significantly increase the temperature difference between the hot and cold ends of the thermoelectric components, enhancing the thermoelectric conversion capability. The open-circuit voltage and output performance when selected for series connection is better than when connected in parallel. The coverage rate of the thermoelectric components affects the heat transfer process of the system, the heat transfer thermal resistance increases with increasing coverage rate; When the coverage rate of thermoelectric components is 22.5%, the system has the best thermoelectric conversion performance, with a thermoelectric conversion efficiency of 0.35%.

The actual effect of the coal-fired waste heat conversion system on the cooling effect in the coal pile is remarkable, especially the temperature at the bottom and middle of the coal pile dropped significantly, the maximum cooling range and cooling rate can reach 203.60 ℃ and 68.45%, respectively. Comparing to the bottom and middle piles, the difference in temperature trends in the upper pile is due to the comprehensive impact of thermal diffusion from the pile, heat transfer effect of the coal-fired waste heat conversion system, and heat production from the upper pile in a complex reaction with external oxygen. Unlike heat sources provided by electric heating, the spatial and temporal non-uniformity of coal pile heat sources add more uncertainty and volatility to the heat transfer and power generation of coal-fired waste heat conversion system. The maximum open circuit voltage of the coal-fired waste heat conversion system is 4.36 V in the experiment; The maximum output power of the system with added the best matched load value of 33 Ω is 0.57 W; The virtual heat source method is used to calculate the total extracted thermal energy of the system and then obtain a maximum thermoelectric conversion efficiency of 0.32% for the actual application of the system in the coal pile.

[1]张志军. “双碳”背景下我国地下煤火防治技术研究进展 [J]. 中国煤炭地质, 2023, 35(01): 39−42.

[2]金永飞, 郭军, 文虎, 等. 煤自燃高温贫氧氧化燃烧特性参数的实验研究 [J]. 煤炭学报, 2015, 40(03): 596−602.

[3]Heffern E, Coates D. Geologic history of natural coal-bed fires, Powder River basin, USA [J]. International Journal of Coal Geology, 2004, 59: 25−47.

[4]郑学召, 贾勇骁, 郭军, 等. 煤田火灾监测技术研究现状及展望 [J]. 工矿自动化, 2019, 45(05): 6−10.

[5]卢国栋. 大面积煤田火区范围圈划及燃烧机理研究 [D]. 北京: 中国矿业大学（北京）, 2010.

[6]曾强, 王德明, 蔡忠勇. 煤火研究与治理进展 [J]. 矿业安全与环保, 2011, 38(01): 72−75.

[7]朱红青, 袁杰, 赵金龙, 等. 地下煤火分布及探测技术现状研究 [J]. 工业安全与环保, 2019, 45(12): 28−32.

[8]Song Z, Kuenzer C. Coal fires in China over the last decade: A comprehensive review [J]. International Journal of Coal Geology, 2014, 133: 72−99.

[9]曹代勇, 时孝磊, 樊新杰, 等. 煤田火区环境效应分析 [J]. 中国矿业, 2007(07): 40−42.

[10]武建军, 蒋卫国, 刘晓晨, 等. 地下煤火探测、监测与灭火技术研究进展 [J]. 煤炭学报, 2009, 34(12): 1669−1674.

[11]邓军, 肖旸, 张辛亥, 等. 煤火灾害防治技术的研究与应用 [J]. 煤矿安全, 2012, 43(S1): 58−61.

[12]梁运涛, 侯贤军, 罗海珠, 等. 我国煤矿火灾防治现状及发展对策 [J]. 煤炭科学技术, 2016, 44(06): 1−6.

[13]齐俊德. 宁夏煤田火灾的危害及综合治理研究 [J]. 能源环境保护, 2007(02): 36−39.

[14]建信. 我国破解地下煤火防治难题 [J]. 建井技术, 2018, 39(02): 9.

[15]任小坤, 唐守胜, 孙郁, 等. 地下煤火热能利用分析 [J]. 煤矿安全, 2017, 48(09): 160−162.

[16]於仲义. 土壤源热泵垂直地埋管换热器传热特性研究 [D]. 武汉: 华中科技大学, 2008.

[17]MIT-led interdisciplinary panel. The Future of Geo-thermal Energy-Impact of Enhanced Geothermal Systems (EGS) on the United States in the 21st Century [R]. Idaho: Idaho National Laboratory, 2006: 1−16．

[18]仲晓星, 汤研, 田绪沛. 大面积煤田火区热能的提取与转换方法 [J]. 煤矿安全, 2016, 47(10): 161−164.

[19]徐礼华. 煤垛热管降温的实验研究 [J]. 能源研究与利用, 1991(02): 11−15.

[20]邓军, 李贝, 马砺. 用热棒技术强化煤堆降温幅度试验 [J]. 中国安全科学学报, 2015, 25(06): 62−67.

[21]张亚平, 王建国, 姬长发, 等. 热管抑制煤自燃的降温效应分析 [J]. 煤炭工程, 2017, 49(02): 100−102.

[22]李贝, 高伟, 邓军, 等. 基于热棒防灭火技术的煤自燃区域热迁移特征 [J]. 中南大学学报(自然科学版), 2020, 51(04): 1135−1144.

[23]张柏林, 房淑华. 重力热管在猫儿沟露天矿排土场深部积温治理的应用 [J]. 能源研究与利用, 2021, (01): 44−46.

[24]李文胜, 李建勋, 刘旭东, 等. 利用低温热管技术防止圆形封闭煤场煤堆自燃 [J]. 制冷与空调(四川), 2018, 32(03): 251−255.

[25]Xu Z, Zhang Y, Li B, et al. Heat performances of a thermosyphon as affected by evaporator wettability and filling ratio [J]. Applied Thermal Engineering, 2018, 129: 665−673.

[26]Choi S. Enhancing thermal conductivity of fluids with nanoparticles, developments and applications of non-Newtonian flows [J]. 1995.

[27]Buschmann M, Franzke U. Improvement of thermosyphon performance by employing nanofluid [J]. International Journal of Refrigeration, 2014, 40: 416−428.

[28]Grab T, Gross U, Franzke U, et al. Operation performance of thermosyphons employing titania and gold nanofluids, International Journal of Thermal Sciences, 2014, 86: 352−364.

[29]Ghorabaee H, Emami S, Moosakazemi F, et al. The use of nanofluids in thermosyphon heat pipe: A comprehensive review [J]. Powder Technology, 2021, 394: 250−269.

[30]Sarafraz M, Hormozi F, Experimental study on the thermal performance and efficiency of a copper made thermosyphon heat pipe charged with alumina-glycol based nanofluids [J]. Powder Technololy, 2014, 266: 378−387.

[31]Noie S. Heat transfer characteristics of a two-phase closed thermosyphon [J]. Applied Thermal Engineering, 2005, 25(4): 495−506.

[32]Amatachaya P, Srimuang W. Comparative heat transfer characteristics of a flat two-phase closed thermosyphon (FTPCT) and a conventional two-phase closed thermosyphon (CTPCT) [J]. International Communications in Heat and Mass Transfer, 2010, 37(3): 293−298.

[33]杜斌, 董华, 张敬奎, 等. 重力热管单线内螺纹分布强化换热实验研究 [J]. 热能动力工程, 2017, 32(06): 12−16.

[34]战洪仁, 张倩倩, 史胜, 等. 带有内螺纹的重力热管仿真模拟研究 [J]. 沈阳化工大学学报, 2020, 34(04): 352−357.

[35]Naresh Y, Balaji C. Experimental investigations of heat transfer from an internally finned two phase closed thermosyphon [J]. Applied Thermal Engineering, 2017, 112: 1658−1666.

[36]尹岚. 煤火热能热棒提取与温差发电利用实验研究 [D]. 西安: 西安科技大学, 2019.

[37]孟曦. 煤火重力热管提热性能优化及预测研究 [D]. 西安: 西安科技大学, 2021.

[38]Payakaruk T, Terdtoon P, Ritthidech S. Correlations to predict heat transfer characteristics of an inclined closed two-phase thermosyphon at normal operating conditions [J]. Applied Thermal Engineering, 2000, 20(9):781−790.

[39]Hahne E, Gross U. The influence of the inclination angle on the performance of a closed two-phase thermosyphon [J]. Journal of Heat Recovery Systems, 1981 ,1(4):125−136.

[40]Noie S, Sarmasti E, Khoshnoodi M. Effect of inclination angle and filling ratio on thermal performance of a two-phase closed thermosyphon under normal operating conditions [J]. Heat Transfer Engineering, 2007, 28(4): 365−371.

[41]Xiao Y, Zhong K, Tian J, et al. Thermal extraction from a low-temperature stage of coal pile spontaneous combustion by two-phase closed thermosyphon [J]. Journal of Thermal Analysis and Calorimetry, 2021, 144(2): 587−597.

[42]Reji A, Kumaresan G, Sarathi A, et al. Performance analysis of thermosyphon heat pipe using aluminum oxide nanofluid under various angles of inclination [J]. Materials Today: Proceedings, 2021, 45: 1211−1216.

[43]姜峰, 景文玥, 齐国鹏, 等. 蒸发段可变的三相闭式重力热管的传热性能 [J]. 天津大学学报(自然科学与工程技术版), 2021, 54(07): 661−671.

[44]张正芳, 马同泽, 陈焕倬. 两相闭式热虹吸管加热段内的传热特性 [J]. 工程热物理学报, 1990, 11(03): 319−322.

[45]蒋方明, 黄文博, 曹文炅. 干热岩热能的热管开采方案及其技术可行性研究 [J]. 新能源进展, 2017, 5(06): 426−434.

[46]Pei W, Zhang M, Yan Z, et al. Numerical evaluation of the cooling performance of a composite L-shaped two-phase closed thermosyphon (LTPCT) technique in permafrost regions [J]. Solar Energy, 2019, 177: 22−31.

[47]Hou Y, Wu Q, Dong J, et al. Numerical simulation of efficient cooling by coupled RR and TCPT on railway embankments in permafrost regions [J]. Applied Thermal Engineering, 2018, 133: 351−360.

[48]Luo X, Yu Q, Ma Q, et al. Evaluation on the stability of expressway embankment combined with L-shaped thermosyphons and insulation boards in warm and ice-rich permafrost regions [J]. Transportation Geotechnics, 2021, 30: 100633.

[49]Zhang M, Lai Y, Wu Q, et al. A full-scale field experiment to evaluate the cooling performance of a novel composite embankment in permafrost regions [J]. International Journal of Heat and Mass Transfer, 2016, 95: 1047−1056.

[50]赵新兵. 热电材料与温差发电技术 [J]. 现代物理知识, 2013, 25(03): 40−44.

[51]Kim S, Won B, Rhi S, et al. Thermoelectric Power Generation System for Future Hybrid Vehicles Using Hot Exhaust Gas [J]. Journal of Electronic Materials, 2011, 40(5): 778−783.

[52]李海涛. 基于热管和温差发电的船舶缸套水余热利用研究 [D]. 大连: 大连海事大学, 2016.

[53]黄永胜, 徐道春, 李文彬, 等. 基于塞贝克效应的森林土壤温差发电 [J]. 森林与环境学报, 2018, 38(01): 84−90.

[54]丁奕文, 陈舜嘉, 张程宾. 热管式温差发电研究综述 [J]. 建筑热能通风空调, 2018, 37(12): 47−51.

[55]沈海青, 林龙. 推动超导热管和温差发电技术的广泛应用 [J]. 变压器, 2020, 57(08): 89.

[56]周福宝, 邓进昌, 史波波, 等. 煤田火区热能开发与生态利用研究进展 [J]. 中国科学基金, 2021, 35(06): 871−877.

[57]Pourkiaei M, Ahmadi M, Sadeghzadeh M, et al. Thermoelectric cooler and thermoelectric generator devices: A review of present and potential applications, modeling and materials [J]. Energy, 2019, 186: 115849.

[58]Venkatasubramanian R, Silvola E, Colpitts T, et al. Thin-film thermoelectric devices with high room–temperature figures of merit [J]. Nature, 2001, 413(6856): 597−602.

[59]Harman T, Taylor P, Walsh M, et al. Quantum dot superlattice thermoelectric materials and devices [J]. Science, 2002, 297(5590): 2229−2232.

[60]Funahashi R, Ikuta H, Takeuchi T, et al. An oxide single crystal with high thermoelectric performance in air [J]. Japanese journal of applied physics, 2000, 39(11B): L1127−L1129.

[61]Poudel B, Hao Q, Ma Y, et al. High-thermoelectric performance of nanostructured bismuth antimony telluride bulk alloys [J]. Science, 2008, 320(5876): 634−638.

[62]Xiao F, Hangarter C, Yoo B, et al. Recent progress in electrodeposition of thermoelectric thin films and nanostructures [J]. Electrochimica Acta, 2008, 53(28): 8103−8117.

[63]Shittu S, Li G, Zhao X, et al. Review of thermoelectric geometry and structure optimization for performance enhancement [J]. Applied Energy, 2020, 268: 115075.

[64]Bell. L. Cooling, heating, generating power, and recovering waste heat with thermoelectric system [J]. Science, 2008, 321(5895): 1457−1461.

[65]Ono. K, Suzuki. R. Thermoelectric power generation: Converting low-grade heat into electricity [J]. JOM, 1998, 50(12): 49−51.

[66]王春燕, 厉彦忠, 郑江. 多级温差发电器串并联分析模型 [J]. 制冷学报, 2016, 37(01): 106−113.

[67]Zhao Y, Fan Y, Li W, et al. Experimental investigation of heat pipe thermoelectric generator [J]. Energy conversion and management, 2022, 252: 115123.

[68]Elghool A, Basrawi F, Ibrahim T, et al. A review on heat sink for thermo-electric power generation: Classifications and parameters affecting performance [J]. Energy Conversion and Management, 2017, 134: 260−277.

[69]苏贺涛. 基于重力热管换热的地下煤火治理与应用研究 [D]. 徐州: 中国矿业大学, 2018.

[70]唐志伟, 俞昌铭, 马重芳. 热管性能评价准则探讨 [J]. 北京工业大学学报, 2003，29(01): 55−58.

[71]Kline S, McClintock F. Describing uncertainties in single-sample experiment [J]. Mechanical Engineering, 1953, 75: 3−8.

[72]Alegria P, Catalan L, Araiz M, et al. Experimental development of a novel thermoelectric generator without moving parts to harness shallow hot dry rock fields [J]. Applied Thermal Engineering, 2021, 200: 117619.

[73]权欣. 热管抑制煤自燃联合温差发电的实验研究 [D]. 西安: 西安科技大学, 2021.

[74]曾和义, 刁乃仁, 方肇洪. 地源热泵竖直埋管的有限长线热源模型 [J]. 热能动力工程, 2003, 18(104): 166−170.

[75]陈卫翠, 崔萍, 方肇洪. 倾斜埋管地热换热器稳态温度场分析 [J]. 山东建筑工程学院学报, 2005, 20(5): 30−34.