考虑桩身热容的能量桩传热性能分析

Analysis of Heat Transfer Performance of Energy Pile Considering Heat Capacity of Pile Body

与传统垂直钻孔地埋热交换器相比,能量桩桩径较大,需考虑桩身热容对能量桩传热的影响。利用无限长线热源模型与无限长桩热源模型的解析解对不同桩身热容的能量桩在饱和黏土中的传热过程进行对比计算,分析桩身热容对能量桩传热性能的影响。当桩身为混凝土时,不同粗集料引起的热容差异对能量桩传热初期造成影响,桩径是影响能量桩传热的主要因素之一,而混凝土桩与钢桩的热容差异对能量桩传热的影响较大。分析表明,整个传热过程分为两个阶段,初期热源向桩内外传递的比例取决于桩身和桩周物质热扩散系数的相对值,桩身的热扩散系数相对越大,向桩内传递热量越快,桩外过余温度越低;当桩内温度达到均衡时,向桩内传递的热量取决于桩面处土体的温度以及桩身的热容。对于第一阶段,桩热源模型比线热源模型更能精细地描述能量桩的传热性能;对于第二阶段,两种模型的计算结果差别很小。

Compared with the traditional used vertical borehole ground heat exchanger,energy pile has a larger diameter.The effect of heat capacity of pile body on heat transfer needs to be considered.The analytical solutions of infinite line-source model and infinite pile-source model were used to compare the heat transfer process within energy piles of different heat capacities in saturated clay,so as to examine the influence of heat capacity on heat transfer performance.For pile bodies made of concrete,the heat capacity difference caused by the different types of coarse aggregate had an impact on initial heat transfer performance.The pile diameter was seen as one of the major factors affecting heat transfer.The heat capacity difference between concrete piles and steel piles had a larger impact on heat transfer performance.The results showed that the whole heat transfer process is divided into two phases.In the first phase,the speed of heat transfer from the source to the inside and outside of the pile depends on the relative value of the thermal diffusion coefficient of the pile body and soils around the pile.The larger the pile’s thermal diffusion coefficient is,the faster the heat transfer to the inside of the pile,the lower the excess temperature outside the pile is.When the temperature inside the pile reaches a balance,the amount of heat transferred to the inside of the pile depends on the temperature of the soil around the pile and the heat capacity of the pile body.For the first phase,the pile-source model is more precise than the line-source model in describing the heat transfer performance.For the second phase,the difference between the results of the two models is negligible.