地源热泵中U型埋管传热过程的数值模拟

Numerical simulation on heat transfer process in U-bend ground heat exchanger of ground source heat pump

以钻孔壁为界将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,以构成完整的埋管传热模型.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,在考虑埋管流体温度的沿程变化及U型管2支间热干扰的基础上,基于能量平衡建立了钻孔内U型埋管的稳态传热模型.用所建U型埋管传热模型对地源热泵系统的运行特性进行了动态模拟,得出了埋管出口流体温度、钻孔瞬时壁温、单位埋管吸热量及热泵COP随运行时间的变化规律.所建埋管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.

The heat transfer region of vertical U-bend buried coil is divided into two parts at the boundary of borehole wall and the two parts are coupled by the temperature of borehole wall, 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 borehole by use of the variable heat flux cylindrical source model developed based on the classical constant heat flux cylindrical source theory. As for the region inside borehole, considering the variation of fluid temperature along the length and the heat interference between two adjacent legs, a steady heat transfer model is developed based on energy conservation. The dynamic simulation on the operation characteristic of ground source heat pump （GSHP） is conducted by use of the developed model, and the variation of exiting fluid temperature of U-bend buried coil, borehole wall transient temperature, absorbed heat flux of buried coil per length and coefficient of performance （COP） of heat pump with operation time are obtained. The developed buried coil model may provide reference for the system dynamic simulation, optimization design, and improvement of GSHP.