基于不平衡系数对地埋管热短路的评价与分析

Research of Thermal Short-circuiting and its Influence on Vertical Single U-shape Ground Heat Exchangers

在热响应试验的基础上,通过FLUENT建立单U型竖直地埋管系统的三维非稳态数值模型。引入热短路不平衡系数作为评价热短路现象强弱的指标,分析了回填土导热系数、管内流速、系统井深和运行方式对地埋管热短路现象的影响。模拟结果表明,回填材料导热系数和系统井深与热短路不平衡系数成正比;流速与热短路不平衡系数成反比,而且对热短路现象强弱影响最大;采用间歇运行可以提升系统换热效率,但不能缓解热短路现象。

This paper uses the Fluent software to establish a 3-D equivalent rectangular numerical for vertical U-shape borehole heat exchangers（ BHEs）. And the result is verified by the thermal response test. Introduce thermal short-circuiting unbalance coefficient as the evaluation index of the strength of thermal short-circuiting. The influence on coefficient of thermal conductivity of Backfill material,depth of buried pipes,velocity in pipe,and system operation mode were analyzed. The result shows that,backfill material coefficient of thermal conductivity and the buried depth of pipe is proportional to thermal short-circuiting unbalance coefficient. The velocity in pipe is inversely proportional to thermal short-circuiting unbalance coefficient,and it is the biggest effect and strength of thermal short-circuiting phenomenon. Intermittent operation can improve the system efficiency of heat exchanging,but not because of easing thermal short-circuiting phenomenon.