煤火导致的安全和环境问题突出，开发高效的煤火热能移取技术对于实现火灾控制具有重要意义。基于汽液相变传热的重力热管具有传热系数高、安全可靠等优点，但存在煤岩体低导热性和热扩散性导致的地层侧热阻大、移热效率受限的问题，且煤火重力热管火区实际应用性能试验和场地尺度优化预测研究不足，有必要开展煤火重力热管性能强化及火区移热降温性能研究。为此，本文设计弯曲型重力热管结构，开展了相关的实验研究和数值模拟。主要研究工作及结果如下：

（1）从管型改进降低地层侧热阻的角度出发，设计弯曲型重力热管结构，对比研究了蒸发段热源功率60 W、充液率30%工况条件下，常规竖直型、斜插直管型和L型弯曲重力热管的传热特性，分析了传热面积和弯曲角度的影响效应，发现增大传热面积，斜插直管重力热管传热效率降低，而弯曲型为先增再减，角度从30°增加到60°时，弯曲型热管传热效率呈先增再减的趋势，但整体要低于常规型，而斜插直管热管的变化趋势则为先减后增；在所测定的实验工况范围内，相同埋深深度下弯曲角度为30°的弯曲型重力热管传热性能最优，传热效率为73.09%，传热热阻为0.37 ℃/W。采用响应面法对弯曲型重力热管的热源功率、充液率、弯曲角度条件下的传热特性进行了定量分析，发现重力热管传热性能的参数敏感性排序为：热源功率 > 充液率 > 角度；三者对热阻的影响存在差异，随着功率增加，热阻呈现出减小速率由快至慢的变化规律，弯曲角度与热阻成正比关系，充液率与热阻呈现出先减小后增加的变化趋势，获得了重力热管等效导热系数数学表征。

（2）针对所得到的最佳管型开展煤火重力热管热能移取实验研究，建立了基于等效导热系数数学表征的煤火重力热管移热降温耦合传热数值模型，研究表明重力热管对煤堆的降温效果显著，对下层的降温效果更为明显，布置间距为40 cm时，降温30 h后平均降温幅度为150.9℃，最高可达173.2℃；在相同工况下，随着煤堆深度减小，降温幅度和降温率均逐渐减小，下层和上层降温幅度平均差值为170.2℃。减小重力热管布置间距后，可有效提高降温幅度，但间距从40 cm减小至20 cm后，对煤堆整体的降温效果减弱，最大差值为75.1℃；数值模拟与实验结果吻合良好，下层和上层平均误差和最大误差分别为0.42%和2.27%，可为煤火重力热管移热降温性能研究提供预测方法；热管布置间距为核心影响半径之和时对煤堆的移热降温效果最佳。

（3）开展煤田火区重力热管热能移取现场应用试验，发现在实际火区应用中，热能移取系统的单孔降温效果随着深度增加呈现先增加后降低的变化趋势，弯曲型重力热管降温效果相较于竖直型持续时间更长，表明弯曲构型强化了重力热管的移热性能；为进一步分析预测管群作用于火区的长周期降温移热性能演化特征，建立了煤田火区重力热管管群移热降温非稳态热-流-化耦合数值模型，模拟结果表明重力热管管群降温效果明显，初期靠近热管蒸发段上部的岩石有升温趋势；重力热管的影响半径有限，不同布置间距对降温效果影响显著，布置间距4 m时深度16 m处岩层平均降温幅度比2 m间距时低34.9℃。

The safety and environment problems caused by coal fire are prominent. It is of great significance to develop efficient coal fire heat extraction and cooling technology for fire control. The gravity heat pipe based on vapor-liquid phase change heat transfer has the advantages of high heat transfer coefficient, safety and reliability, but the problems of large thermal resistance at formation side and limited heat transfer efficiency caused by low thermal conductivity and thermal diffusivity of coal and rock mass are profound. Moreover, the actual application performance test and site scale performance prediction for heat extraction-cooling performance of coal fire gravity heat pipe are insufficient. It is necessary to investigate the heat transfer enhancement for gravity heat pipe used for coal fires, and the practical field test and long-term prediction investigation on heat extraction and cooling performance in the fire zone. For this purpose, the structure of curved gravity heat pipe was designed in this paper, and carries out the relevant experimental research and numerical simulation. The main research work and results are as follows:

（1）The structure of curved gravity heat pipe was designed from the perspective of improving the pipe configuration to reduce the thermal resistance at formation side. The heat transfer characteristics of conventional vertical, oblique and L-shaped curved gravity heat pipes under the condition of heat source power of 60 W in evaporation section and liquid filling rate of 30% were compared, and the effects of heat transfer area and bending angle were analyzed. It was found that the heat transfer efficiency of oblique and straight gravity heat pipes decreased with the increase of heat transfer area, while that of curved gravity heat pipes increased first and then decreased. When the angle increases from 30° to 60°, the heat transfer efficiency of the curved heat pipe increases first and then decreases, but the overall trend is lower than that of the conventional heat pipe, while the changing trend of the inclined straight tube heat pipe decreases first and then increases. In the measured range of experimental conditions, the curved gravity heat pipe with a bending angle of 30° under the same burial depth has the best heat transfer performance, heat transfer efficiency is 73.09%, and heat transfer resistance is 0.37 ℃/W. The heat transfer characteristics of curved gravity heat pipes under the condition of heat source power, liquid filling rate and bending angle were quantitatively analyzed by response surface method. It was found that the parameter sensitivity of heat source power > liquid filling rate > curving angle. The influence of the three factors on thermal resistance of gravity heat pipe is different. With the increase of input power, the thermal resistance decreases fast initially and then become slowly, the bending angle is proportional to the thermal resistance, the liquid filling rate and thermal resistance decrease first and then increase, and the correlation of equivalent thermal conductivity of gravity heat pipe is obtained.

（2）An experimental investigation on heat transfer of coal gravity heat pipe was carried out according to the best tube type obtained, and a numerical model of conjugated heat transfer of coalfire-used gravity heat pipe based on the mathematical correlation of equivalent thermal conductivity was established. The research shows that gravity heat pipe has a significant cooling effect on coal pile, and the cooling effect at the lower layer is most obvious. When the layout spacing is 40 cm, the average cooling range after 30 h is 150.9℃, with a maximum of 173.2℃. Under the same working condition, as the depth of coal pile decreases, the cooling amplitude and cooling rate decrease gradually, and the average difference between the lower layer and the upper layer is 170.2℃. When the spacing of the gravity heat pipe is reduced, the cooling range can be effectively improved, but when the spacing is reduced from 40 cm to 20 cm, the overall cooling effect on the coal pile is reduced, and the maximum difference is 75.1℃. The average error and maximum error of the lower and upper layers between the numerical model and the experiment are 0.42% and 2.27% respectively. The conjugated model based on mathematical correlation of equivalent thermal conductivity of the gravity heat pipe, can provide a prediction method for the following numerical prediction of heat extraction and cooling performance of gravity heat pipes in coal fire zones. Moreover, it can be concluded that when the heat pipe spacing is the sum of core influence radii, the heat transfer cooling effect of coal pile is the best.

（3）The field test of gravity heat pipe in coal fire area is carried out. It is found that the cooling effect of single-borehole gravity heat pipe system increases first and then decreases with the increase of burial depth in actual fire area. The cooling effect of the curved gravity heat pipe lasts longer, indicating that the curved pipe configuration strengthens the heat transfer performance of gravity heat pipe. To further predict and analyze the evolution characteristics of long-period heat extraction performance of gravity heat pipe groups acting on the coal fire area, the unsteady thermal-fluid-chemical coupling numerical model was established. The simulation results show that the cooling effect of the gravity heat pipe groups is obvious, and the rocks near the upper part of the evaporation section of the heat pipe initially have a temperature increasing trend. The layout spacing has a significant effect on the cooling effect. When the layout spacing is 4 m, the average cooling amplitude at the depth of 16 m is 34.9℃ lower than that at the spacing of 2 m.