竖直双U地埋蓄热井在不同运行条件下的换热特性

Heat Exchange Characteristics of Vertical Double U-tube Borehole Thermal Storage System with Different Operation Conditions

提出了简化双U地埋井三维模型建立和网格划分方法,在不同进口温度、流体流速和运行时间等影响因素下对蓄热井短期蓄热进行了瞬态模拟。根据模拟结果对比分析了不同条件下蓄热井换热性能和土壤热扩散特性,探讨了系统最佳进口温度、流速以及蓄热方式。结果表明:进口温度为40℃和50℃时换热量远高于进口温度为30℃时的换热量,流速为0. 1 m/s时的换热量远小于0. 3、0. 5m/s时的换热量,并且此两组流速对应的换热量相差不大。在径向方向上,靠近U管表面处土壤温度在换热初期急剧上升,离中心0. 5～1 m远处土壤受换热影响极其小。经分析得出,蓄热井最佳进口温度、流体流速和井间距为40～50℃、0. 3 m/s和1. 5～2 m,且结合合理的间歇蓄热方式也是提高换热量的关键。

A modeling and meshing method of 3D vertical double U- tube borehole heat exchanger was presented, transient simulation of short term therntal storage was carried out under different influential factors, including inlet temperature, fluid velocities and operation time. Heat exchange performance and soil temperature diffusive characteristic were comparatively analyzed according to the simulation result, and better inlet temperature and velocity were discussed simultaneously. Results show that, the heat exchange rate with respect to inlet temperature 40 ℃ and 50 ℃ is larger than that at inlet temperature 30 ℃ , and fluid velocity 0. 1 m/s far less than 0. 3, 0. 5 m/s. However the heat exchange rate with respect to 0. 3, 0. 5 m/s is very close. The radial temperature steep rise nearly heat source and has little effect far away from 1. 5 m. Taking thermal storage performance and economy into consideration, recommended inlet temperature and flow velocity and borehole distance are 40-50 ℃ , 0. 3 m/s, 1. 5N2 m respectively. Meanwhile, intermittent operation mode is recommend to improve heat exchange.