二区域U型埋管传热模型及其实验验证

TWO-REGION HEAT TRANSFER MODEL OF U-TUBE GROUND HEAT EXCHANGER AND ITS EXPERIMENT VALIDATION

以钻孔壁为界将垂直U型埋管的换热区域划分为钻孔内外两部分,并分别采用稳态与非稳态传热来分析求解.两区域模型间通过钻孔壁温耦合连接,从而构建了二区域U型埋管传热解析解模型.对于钻孔以外部分.采用变热流圆柱源模型来求解钻孔瞬时壁温.钻孔以内部分,基于元体能量平衡法建立了考虑埋管流体温度沿程变化及U型两支管间热干扰的钻孔内U型埋管传热模型.实验验证表明,该模型预测出的埋管出口温度值与实测值的变化趋势一致,预测相对误差在6%以内.所建二区域U型埋管传热模型可为地源热泵系统的动态模拟、优化设计及其改进提供参考.

A two-region vertical U-tube analytical solution model is developed firstly by dividing the heat transfer region of vertical U-bend buried coil into two parts at the boundary of borehole wall, and the two regions are coupled by the borehole wall temperature. Both steady and transient heat transfer method are used to analyze the heat transfer characteristics inside and outside borehole respectively. The transient borehole wall temperature is calculated for the soil region outside borehole by use of the variable heat flux cylindrical source model. As for the region inside borehole, considering the variation of fluid temperature along the length and the heat interference between two adjacent legs of U-tube, a steady-state heat transfer analytical solution model is developed based on element energy conservation. The experiment validation indicates that the calculated fluid exit temperatures of the GHE by the model are agreed well with the test data and the relative error is less than 6%. The developed U-bend GHE model may provide a reference for the system dynamic simulation, optimization design, and improvement of GSHP.