地源热泵U型管地下换热器的准三维模型

Pseudo 3D model of ground heat exchanger for GSHP

为了模拟地源热泵U型管地下换热器的运行工况 ,通过耦合不同方向的低维模型 ,在换热器进水口的边界处引入换热功率函数作为边界条件 ,求和平均管壁各点到区域中心的距离来计算线热源到区域中心的距离 ,从而建立一准三维传热模型 ,并运用有限体积法求解。模拟结果与试验结果的最大相对误差为 3 4 8% ,平均相对误差 1 33% ,精度满足工程要求 ,而且随着运行时间的推移 ,相对误差呈减小趋势。运用该模型模拟得到的U型管管内流体温度分布情况表明 ,钻孔深度为 4 0m时 ,进水支管与出水支管的温升比为 1 34;钻孔深度为 80和 12 0m时该比值分别为 1 90和 2 77,而出水支管的温升几乎相同 :说明增加钻孔深度会加剧U型管 2支管之间的热短路。

In order to simulate the behavior of the U-tube ground heat exchanger (GHE) used in ground source heat pump (GSHP), a pseudo 3D model was developed which was based on coupling two less dimensional models. A heat exchange power function was introduced as the boundary condition for the inlet of the U-tube. The distance between the heat source and the center of the field was simplified by calculating a mean distance between them. Finite-volume-method was used to solve the control equations. The maximum and mean relative error between numerical and experimental results were only 3.48% and 1.33% respectively. According to the numerical results, with a 40m depth borehole the specific value between inlet and outlet temperature is 1.34; with 80m and 120m depth this value were 1.90 and 2.77 separately, and the difference temperature caused by the outlet tube is minor. This came the conclusion that extra borehole depth aggravates heat short circut between the 2 legs of the U-tube.