考虑土壤分层的竖直埋管换热器传热特性研究

Heat Transfer Characteristics of Vertical Borehole Heat Exchanger based on Soil Stratification

建立柱热源的分层土壤地埋管传热模型,利用分层岩土热响应试验验证模型的准确性,并与均质土壤模型比较分析了不同工况下地埋管换热器的传热特性。结果表明:使用均质土壤模型分析地埋管换热器传热特性会低估该埋管系统的换热能力,在变进口流体温度、变进口流体流速和变管径工况下,用均质土壤模型估算的单位管长换热量及钻孔平均导热系数,比分层土壤模型估算值分别低7.00%和6.62%、6.20%和6.19%、6.57%和6.56%;由于分层土壤模型考虑了土壤热物性沿埋管轴向分布、土壤温度也呈分层非均匀分布的特点。分层土壤、均质土壤模型模拟的最大热作用半径基本相同,且随着模拟时间的延长,分层土壤模型模拟土壤温度场温度分布呈均匀化趋势。由此可见,分层土壤模型可更好的揭示土壤热特性、热传导及热分布规律,将其应用于不同实际工况的系统设计计算可为工程量和工程费用的合理估算提供支持。

The heat transfer model of buried pipes in stratified soils established based on column heat source,and the accuracy of the model was verified by stratified rock-soil thermal response test.The heat transfer characteristics of buried pipes under different working conditions were compared between heat transfer model and the homogeneous model.The results showed that the mean value model for analysis of heat transfer characteristics underestimated the heat transfer capacity of the buried pipe system.Under the conditions of variable inlet fluid temperature and velocity and variable pipe diameter,if the soil was regarded as a homogeneous whole,the maximal underestimates for heat transfer amount per unit pipe length and average thermal conductivity of boreholes were 7%and 6.62%,6.20%and6.19%,6.57%and 6.56%respectively.For the soil temperature field,due to the stratified characteristics of the soil thermalphysical properties along the axial direction of the buried pipes,the temperature distribution of the stratified model was also layered rather than homogeneous.The thermal influencing radius was larger at the depths of 30-35 m and 55-60 m,and the smallest at 38 m.But the maximal heat influencing radius between the two models was basically the same with the increase of the corresponding operating parameters under various working conditions.The soil temperature field distribution of the stratified model hads a homogenized trend.This showed that the stratified model could better reveals the actual stratified phenomenon of the soil.In the actual working conditions,the system engineering cost can be reduced to a certain extent by using the layered model for system design calculation.