渗流分层岩土中管群换热器钻孔内外耦合换热分析

Heat Transfer Analysis of Multiple Borehole Heat Exchangers in Layered Soil With Groundwater Advection Using Coupled Heat Transfer Model

基于移动有限长线热源模型和钻孔内的准三维模型,建立了渗流条件下分层管群换热器钻孔内外耦合传热的解析模型。比较了不同运行时间下分层和均质岩土中钻孔壁面的温度分布及地埋管换热器的出口温度。在不同钻孔位置、不同热流密度和不同渗流速度下,研究了不同周向位置和深度方向的钻孔壁面温度下所对应的地埋管出口温度。结果表明:对于渗流条件下的分层管群解析模型,如果将分层岩土视为均质岩土,将会导致边缘中间钻孔埋管出口温度产生6.8%偏差。钻孔壁面温度的选取应同时考虑钻孔周向位置和深度方向二重积分的平均值。越靠近管群上游,热流密度和渗流速度越大的钻孔,在不同周向位置的钻孔壁面温度下,地埋管换热器的出口温度相差越大。

An analytical model of coupled heat transfer inside and outside the borehole for multiple layer multiple Borehole Heat Exchangers(BHEs) considering groundwater advection is proposed based on the Moving finite Line Source(MFLS) model and quasi three-dimensional model in borehole.The borehole wall temperature distribution and the outlet temperature of BHEs in layered and homogeneous soil under different operation time are compared. The outlet temperature for BHEs under the borehole wall temperature at different circumferential positions and depth directions is investigated in case of different borehole positions, heat flux and advection velocities. Also, the effect of advection velocity and thermal diffusivity on soil temperature distribution in the neighborhood of multiple BHEs is studied. The results show that for the analytical model of multiple layer multiple BHEs under advection action, treating the stratified rock as homogeneous would result in a 6.8%deviation in the edge middle BHE outlet temperature. The borehole wall temperature should be selected by taking into account both the average value of double integration of the circumferential position of the borehole and the borehole depth direction. The closer to the upstream of multiple BHEs, the greater the heat flux and advection velocity, and the greater the difference of the outlet temperature for BHEs under the borehole wall temperature at different circumferential positions.