双U型埋管地热换热器的传热模型

A heat transfer model for double U-tube geothermal heat exchangers

合理地分析地热换热器中的传热过程是保证地源热泵空调系统经济可靠地运行和降低其初投资的要求 ,因而确定钻孔内热阻对于设计地源热泵空调系统中的地热换热器具有重要的意义。本文采用准三维模型对于对称布置的双U型埋管地热换热器钻孔内的传热情况进行了分析研究。在考虑各支管间的“热短路”的条件下 ,导出了循环流体在各个支管内沿钻孔深度方向上温度变化的解析表达式 ,进而确定了双U型埋管地热换热器钻孔内的热阻。

The ground source heat pump (GSHP) system features its ground heat exchanger (GHE), which contributes to a substantial portion of ist initial cost. It is crucial to determine the thermal resistance with higher accuracy for cost efficient applications of GSHPs. The heat transfer process inside a borehole with symmetrically disposed double U tubes has been analyzed based on a quasi three dimensional model. Taking the impacts of the thermal ″short circuiting″ among the legs of the U tubes into account, an analytical expression for the temperature profile of the circulating fluid along the depth of the borehole has been obtained.Consequently, the thermal resistance of the borehole with double U tubes in GHEs has been worked out. Thus, this model provides a solid foundation for further quantitative analysis of the complications affecting the performance of the double U tube ground heat exchangers.