深层埋管式能源桩换热性能影响因素分析

Analysis on Factors Influencing Heat Transfer Performance of Energy Pile with Deeply Penetrating Heat Exchanger

提出一种新型的能源桩换热管型式,即深层埋管式能源桩。利用Comsol Multiphysics建立三维方法模拟桩体−土体传热,一维方法模拟管内水动态传热传质的数值模型,考虑了土体温度随深度的变化,模拟出口水温随时间的变化规律并计算换热量,比较深层埋管式与传统的1-U型、1-W型能源桩的换热量,分析了桩径、桩体导热系数、桩体密度、桩体比热容等不同参数对新型深层埋管式能源桩换热量的影响。模拟结果表明:以运行50 h为例,深层埋管式的总体换热量比1-U型、1-W型分别高122%、54%;而对于单位管长换热量,深层埋管式比1-U型、1-W型分别高9%、50%,桩径从0.5 m增加到1 m,换热量增加14.3%;桩体导热系数从1.2 W/(m·K)增大至2.5 W/(m·K),换热量增加9.6%;桩体密度从1800 kg/m^3增大到2600 kg/m^3,换热量增大0.8%;桩体比热容从637 J/(kg·K)增大到1037 J/(kg·K),换热量增大1.1%。因此深层埋管式的热性能优于传统1-U型和1-W型,在满足能源桩力学性能的前提下,为了提高深层埋管式能源桩换热性能,可以适当增大桩径。对于桩体材料的选择,应该选择导热系数较高的材料。密度和比热容对换热量的提升影响不大。

A novel heat exchanger configuration—the deeply penetrating 1-U-shape configuration for energy pile was presented in this paper.Comsol Multiphysics was utilized to simulate a model of three-dimensional dynamic heat transfer for soil and concrete pile and a one-dimensional dynamic heat and mass transfer for water in the tube.The variations of outlet water temperature with time and heat transfer rate were simulated.Heat transfer performance of energy pile with the proposed configuration was compared with the traditional 1-U-shape and 1-W-shape configurations.Parametric analysis was performed to investigate the effects of several important parameters(i.e.,the pile diameter,the pile thermal conductivity,the pile density,and the pile heat capacity)on the heat transfer performance of energy pile with the proposed configuration.Simulation results showed that after 50 h of operation,the total heat transfer rate for deeply penetrating 1-U shape was 122%and 54%higher than that for 1-U shape and 1-W shape,respectively.In terms of the heat transfer rate per unit length of tube,the value for deeply penetrating 1-U shape was 9%and 50%higher than that for 1-U shape and 1-W shape,respectively.The heat transfer rate indicated a maximum increase of 14.3%when pile diameter increased from 0.5 m to 1 m,an increase of 9.6%when thermal conductivity increased from 1.2 W/(m·K)to 2.5 W/(m·K),an increase of 0.8%when density increased from 1800 kg/m^3 to 2600 kg/m^3,and an increase of 1.1%when heat capacity increased from 637 J/(kg·K)to 1037 J/(kg·K).Therefore,energy pile with deeply penetrating 1-U-shape configuration showed superior heat exchange efficiency compared with the traditional 1-U-shape and 1-W-shape configurations.In order to improve the heat transfer performance of energy pile with deeply penetrating 1-U-shape heat exchanger,the pile diameter can be appropriately increased.For the selection of pile materials,the materials with high thermal conductivity should be selected.Materials with high density and specific heat capacity have little impact on the improvement of heat transfer efficiency.