水平螺旋型地埋管换热器换热特性的数值模拟与试验验证

Numerical Simulation and Experimental Validation on Heat Exchange Characteristics of Horizontal Slinky Coil Ground Heat Exchanger

基于有限差分法建立了水平螺旋型地埋管换热器的传热数学模型,分析了地下水渗流速度、地下水位、土壤孔隙率、土壤类型对其换热量及其周围土壤温度分布的影响,结果表明:随地下水渗流速度增加,埋管换热器周围土壤温度降低速率增加,从而可提高其换热性能;当地下水位在4.2 m以上时,地下水位越浅,带走换热器周围土壤的热量越多,换热器周围土壤温度越低;当地下水位在4.2 m以下时,地下水渗流对换热器换热量影响较小;随孔隙率增加,埋管内水温下降速率增大,埋管换热量增加。此外,土壤类型对土壤温度变化影响较大,热扩散系数高有利于土壤中热量的扩散,比热容高有利于降低土壤温度上升速率和幅度,砂岩由于其比热容和热扩散系数高,最有利于换热器运行,而黏土是最不利于换热。试验验证表明:所建水平螺旋型埋管模型预测出的换热量与对应试验值吻合较好,其最大与平均相对误差分别为9.1%与3.3%。

A heat transfer mathematical model of the horizontal slinky coil GHE was developed by the finite difference method. Based on the numerical solution of the model,the effects of groundwater advection velocity,groundwater table,soil porosity and soil type on the heat exchange rate and soil temperature distribution surrounding the horizontal slinky coil GHE were analyzed. The results show that with the increase of groundwater advection velocity,the dropping rate of temperature of soil surrounding the coil pipe increases,and thus the heat exchange performance of slinky coil GHE is improved. When the groundwater table is above 4.2 m,the more shallow the water table is,the more heat is taken away by groundwater flow,and the lower the soil temperature around the coil pipe is. When the groundwater table is below 4.2 m,the effect of groundwater advection on heat exchange rate of GHE is very small. With the increase of the porosity,the water temperature dropping rate increases,and the heat transfer rate increases. In addition,soil type has greater influence on the soil temperature variations. A high thermal diffusivity is beneficial to the diffusion of heat in the soil,a high thermal capacity is favorable to reducing the soil temperature rise rate and amplitude. The sandstone,due to its high specific heat capacity and thermal diffusion coefficient,is the most conducive to operation of the soil heat exchanger,whereas the clay is most unfavorable to heat transfer. The experimental validation shows that the heat exchange rate predicted by the model is in good agreement with the corresponding experimental values,and the maximum and average relative errors are 9.1% and 3.3%,respectively.