基于岩土轴向分层垂直地埋管换热模型分析

Numerical Approach to Evaluating Performance of Borehole Heat Exchanger in Multilayered Subsurface

当埋管周围岩土轴向分层热物性相差较大时,传统均匀介质模型忽略了岩土分层、热物性变化和地下水流动的综合影响,往往会带来偏差。本文通过对南京某一地埋管换热器现场实验,分析了岩土分层和地下水流动特性,建立了地埋管换热器岩土轴向分层数值模型,并进行验证分析。对比分析轴向数值模型与传统的有限长纯导热模型(FLS)和渗流有限长线热源模型MFLS均匀介质模型,结果表明:连续加热60 d后轴向分层模型的埋管出水温度比FLS模型低约0. 5℃,比MFLS模型高0. 3℃,且轴向分层模型不同深处温度响应差别较大。并对不同距离不同加热时间下,埋管轴向温度的分布特性进行了研究探讨。

The subsurface near the vertical borehole heat exchanger( BHE) contains different geological layers and thermal properties that are variable with depth. The stratified subsurface,variable thermal properties,and groundwater flow would make the heat transfer of BHE more complex. Thus,the traditional homogenous model inevitably leads to some problems for the design of BHE in a layered subsurface. In this study,through a borehole field test in Nanjing,a numerical model considering five strata was developed and verified. Comparing the numerical multilayered model with the traditional homogenous FLS and MFLS models shows that the outlet temperature of the numerical model is 0. 5 ℃ lower than the FLS model after 60 d of heating and 0. 3 ℃ higher than the MFLS model. This also indicates that the temperature response is different at different layers. Furthermore,the axial temperature profiles of different layers at different distances under different heating times are presented and explored.