有渗流时埋管换热器传热模型

Study on heat transfer model of underground heat exchangers with groundwater advection

为研究地下水渗流对埋管换热器传热的影响,以移动热源的格林函数为基础,通过引入虚拟热汇,由叠加原理建立热渗耦合作用下的有限长线热源模型.将此模型与有渗流无限长线热源模型和无渗流有限长线热源模型作了对比,比较结果表明该模型计算有渗流时埋管换热器的传热更加合理.针对地下水渗流流速和土壤热物性等对传热影响的分析,表明地下水渗流导致土壤温度场发生变形,渗流速度越大,钻孔壁中点温度越快达到稳态,且稳态过余温度越低;土壤密度和比热越大,土壤导热系数越小,则土壤温度场变形越大.

In order to study the influence of groundwater advection on performance of underground heat exchangers, based on the Green＇s function of moving heat source and by introducing a virtual heat sink, a finite line-source model under coupled thermal conduction and groundwater advection conditions was established through the superposition principle . Comparisons with the infinite line-source model with groundwater advection and the finite line-source model without groundwater adveetion indicate that the developed model is more appropriate to calculate heat transfer of underground heat exchangers with groundwater advection. The influence of groundwater flow velocity and soil thermal properties on heat transfer was analyzed. The analysis result shows that groundwater advection causes the deformation of the soil temperature field, and the greater the advection velocity is, the faster the midpoint temperature of borehole wall reaches steady state, and the lower the steady-state temperature is. It is also indicated that the soil temperature field will get larger deformation accordingly as the density and specific heat of the soil increase or its thermal conductivity decreases.