分层渗流地层中竖直地埋管的换热计算模型

ANALYSIS MODEL FOR VERTICAL BOREHOLE HEAT EXCHANGER CONSIDERING THE LAYER-CHARACTERISTICS OF SOIL AND SEEPAGE

假定实际地层为水平分层且部分地层中有稳定的水平渗流,建立竖直地埋管换热器的计算模型。该模型采用解析和数值计算相结合的方法,采用一个迭代公式便能方便地得到任意时刻换热器和地层中的温度分布,且能直接用于变负荷条件下换热器工作性能的分析。应用该模型对一简单分层渗流地层中换热器的工作性能进行计算,结果表明:稳定的地下水渗流能有效增强换热器的工作性能;渗流层所对应孔壁的温度明显低于其他岩土层,且渗流层的单位深度换热量高于其他岩土层;渗流对换热器性能的影响需要一定时间才能反映出来,渗流速度越小所需时间越长。比较该模型与现有解析模型表明,现有解析模型中采用整个地层具有稳定渗流的假定高估了换热器的工作性能。

A new model for analyzing the vertical borehole heat exchanger （VBHE） was presented, which can take into account the layer-characteristics of soil and seepage. It combines the existed analytic solution and the differential method, using an iterative formula to obtain the temperature distribution in the soil and VBHE for anytime, and can be directly applied to analyze the performance of VBHE under dynamic thermal load. With this model, the performance of VBHE in layered soil and seepage was analyzed. The results indicated that the seepage can effectively enhance the performance of VBHE, but need a certain time to show it. The larger the seepage velocity, the shorter the time is. For the multilayer soil with seepage, in the seepage layer the temperature on the borehole wall are obviously lower than in the other layers, and as the passage of time the proportion of the heat exchanged through the seepage layer will increase. In the layered soil with seepage, the performance of the VBHE is much different from the one in the homogeneous soil with homogeneous seepage, as its efficiency is little higher than the latter in a short time, but much lower than the latter in a long time, which indicated that the latter as a assumption usually introduced by the existed analytic solution may overestimate the efficiency of the VBHE.