基于内外场合算的垂直埋管换热器传热模型

UNIFIED HEAT TRANSFER MODEL OF VERTICAL U-TUBE HEAT EXCHANGERS FOR GROUND SOURCE HEAT PUMP SYSTEM

该文建立了垂直地埋管换热器传热理论模型,该模型能考虑钻孔内比热容和地埋管内循环液体沿竖直方向的对流换热。基于该理论模型编制了相应的计算软件,分析了竖直地埋管换热器钻孔内材料参数对其换热效率的影响。计算结果表明:当钻孔内回填料的导热系数较大、U形管两臂较近时,两臂之间会发生明显的热短路现象;U形管两臂间距越大,换热效率越高;U形管管径越大,换热效率越高;回填料的比热容对地埋管的换热效率在短期内有一定影响,当地埋管地源热泵系统长期运行时,回填料比热容的影响可以忽略;钻孔内回填料的导热系数对地埋管的换热效率有较大影响,当其小于岩土层导热系数时,地埋管的换热效率会随回填料导热系数的增大而较快提高;但当其大于岩土层导热系数时,由于两臂间的热短路增强,地埋管的换热效率随回填料导热系数的增加而趋于平缓。

A theoretical model of U-tube heat exchangers for a ground source heat pump(GSHP) system was established by taking into account the specific heat of backfill grouting and the vertical heat convection of flow inside a U tube. The influence of the parametric, such as the thermal properties of backfill grouting, the arm distance and the diameter of a U-tube, upon the efficiency of the thermal conversion of a U-tube was analyzed. The calculated results show that the heat cutting-out between the two arms of the U-tube would occur when they are closed. The bigger of the distance of the arms and the diameter of the U-tube, the higher efficiency of the thermal conversion would be obtained. The specific heat of the backfill grouting can influence the efficiency of the thermal conversion of the U-tube in a shorter operation time period, which could be ignore in a longer operation time period. The thermal conductivity of backfill grouting could influence the efficiency of the U-tube significantly. When the thermal conductivity of backfill grouting is bigger than that of soil, the efficiency of a U-tube would increase rapidly. When it is less than the thermal conductivity of soil, the change will become slow due to the cutting-out of heat.