岩土分层对中深层U型对接井换热性能的影响

Effect of rock-soil stratification on the heat transfer performance of U-shaped butted well in medium-deep layers

中深层U型对接式换热井出水温度高、取热能力大、井内流动阻力小,是理想的中深层地热能换热形式。基于热阻串联理论,建立了中深层U型对接式换热井地下换热的分层解析计算模型,并采用实测结果进行了验证。在建立解析模型的基础上,选取关中盆地作为研究区域,分析了地下3000 m以浅深度范围内的岩土导热系数和体积比热分层变化对中深层U型对接式换热井整个采暖期内出水温度和取热量的影响。结果表明:岩土导热系数分层对地下换热特性有较大影响,根据平均导热系数计算会高估井口出水温度和取热量,偏差值介于6%~15%;岩土体积比热分层对地下换热特性影响较小。在中深层U型对接式换热井的设计和传热性能分析中,应考虑地下分层的影响,建议分层数量不低于8层。

The medium-deep geothermal exchanger featuring a U-shaped pipe configuration presents an optimal solution for geothermal energy heat exchange due to its capability to deliver higher temperature water,achieve greater heat extraction rates,and maintain minimal flow resistance.A layered analytical model for such exchanger is established based on the theory of thermal resistance in series methods.Experimental results are employed to validate the accuracy of this layered analytical model.By focusing on the Guanzhong Basin in Shaanxi Province as the focal point of research,the model investigates the influence of subterranean stratification in thermal conductivity and volumetric specific heat on the outlet water temperature and heat extraction rate throughout an entire heating period for a 3000 m deep geothermal exchanger with U-shaped pipe.The findings reveal that the underground thermal conductivity stratification has a significant impact on the heat transfer performance.A simplistic approach using average thermal conductivity,as opposed to a detailed accounting of layered conductivities,results in an overestimation of outlet water temperature and heat extraction rate by approximately 6%to 15%.However,specific heat stratification exerts minimal influence on the subterranean heat transfer dynamics.This underscores the importance of considering the effects of underground thermal property stratification in the design and analysis of the heat transfer performance of a medium-deep geothermal exchanger with U-shaped pipe.For precise modeling and results,it is recommended to segment the underground area into at least eight distinct layers.