双U型地埋管换热器换热性能试验研究

双U型地埋管换热器(DUBTHE)在实际应用中易出现管路交叉，引起热短路，造成换热性能降低，直接影响浅层地源热泵系统的运行效率。以西安某浅层地源热泵项目为工程背景，基于无限长线热源理论和斜率法，通过现场岩土热响应试验、不同测温法测温试验，研究了岩土初始平均温度、导热系数和体积热容，及管卡间距对DUBTHE换热性能的影响。结果表明：多点式测温线缆测得的岩土初始平均温度为17.08℃，更接近实际地层温度。该地层的岩土综合导热系数和综合体积热容分别为1.65 W/(m·K)、2.81×10⁶ J/(m³·K)。DN25 DUBTHE的夏、冬季单位延米换热量随着管卡间距减小而增加，且增速随管卡间距的减小先增大后减小。当管卡间距分别为1、2、3、4 m时，DN25 DUBTHE的夏季单位延米换热量较无管卡分别提高了21.03%、19.48%、15.16%、3.92%;DN25 DUBTHE的冬季单位延米换热量较无管卡分别提高了20.83%、19.48%、14.94%、3.79%。工程中最优的管卡布置方式为2 m或3 m管卡间距的DN25 DUBTHE。...

Experimental study on heat transfer performance of double U-shaped buried tube heat exchanger

Double U-shaped buried tube heat exchanger (DUBTHE) are prone to pipe crossing and thermal short-circuiting in the practical applications, resulting in the reduced heat transfer performance and directly affecting the operational efficiency of shallow geothermal heat pump system. Based on the initial line thermal average temperature, thermal conductivity theory and slope method, and taking a shallow geothermal heat pump project in Xi'an as the engineering background. Then, this study investigate the effects of initial average temperature, thermal conductivity and volumetric heat capacity of rock-soil, and tube clamp spacing on the heat transfer performance of DUBTHE through field geotechnical thermal response testing and different temperature measurement methods. The results show that the initial average temperature of rock-soil measured by the multi-point temperature measurement cable is 17.08℃, which is closer to the actual formation temperature. Besides, the comprehensive thermal conductivity and volumetric heat capacity of rock-soil in the formation are 1.65 W/(m·K) and 2.81×106 J/(m3·K), respectively. In addition, the heat exchange per linear meter of DN25 DUBTHE in summer and winter increases with the decreasing tube clamp spacing, with the acceleration increasing firstly and then decreasing with the decreasing tube clamp spacing. Definitely, the heat exchange per linear meter of DN25 DUBTHE in summer is increased by 21.03%, 19.48%, 15.16% and 3.92% respectively compared with that without tube clamp, and that in winter is increased by 20.83%, 19.48%, 14.94% and 3.79%, respectively, in case that the tube clamp spacing is 1 2, 3, and 4 m. DN25 DUBTHE with a tube clamp spacing of 2 m or 3 m is the optimal arrangement in the project. Therefore, the results could provide experience and data support for the optimal design of shallow ground source heat pump systems in Guanzhong area.