不同埋管形式能量桩换热性能与承载性能的对比研究

目前对能量桩热-力学特性的研究大多数针对U形埋管桩基,对螺旋形埋管能量桩的研究多集中在换热性能方面。为探究不同埋管形式导致的能量桩热-力学效应的差异,首先建立了并联双螺旋形、双螺旋形及W形埋管能量桩的三维数值仿真模型,以数值仿真软件COMSOL Multiphysics对现场试验的仿真复现验证了模型的可靠性。之后,对3种埋管形式能量桩吸放热过程中的热、力学行为进行了模拟,分析了其换热性能(出口水温、单位管长换热量)、桩心温度变化及附加温度荷载、轴力及桩身位移等。结果表明:双螺旋形埋管换热效果较好,有利于提高热泵系统性能;W形埋管能量桩桩体温度、附加温度荷载较其他两种大。

Exploration of the thermo-mechanical features of energy piles in regard to the different types of buried pipes

The present paper intends to establish a 3-D numerical simulation model for testing energy piles in the form of underground burial with double spiral coils in 3 forms,i. e. in parallel,in series and in the letter W-shaped form. The purpose of our simulation below is to reproduce a field status in-situ of the thermo-mechanical energy piles to see the difference of its thermo-mechanical effects to be caused by the said forms. And,then,the simulation has also been done to test the thermo-mechanical behaviors in heat absorption and release process of the said energy piles beneath-buried via a numerical simulation software known as COMSOL. Hence,the heat transfer performance can be analyzed multiphysically through comparison with the outlet water temperature,the heat transfer per unit pipe length,and the temperature changes of the pile shaft and the soil layer. The results of the above tests may reveal that the energy pile buried in series in the double spiral coils may enjoy better heat transfer feature,which can also be further improved to be advantageous in function of heat-pumping. In addition,the total heat transfer volume of the energy piles buried with the double spiral coils in parallel can be made to reach its greatest efficiency,whereas the single pipe length heat transfer fails to. However,the temperature of the energy piles buried with the double spiral coils installed in series tends to change most slowly,which is more favorable for and conducive to the heat exchange between the pile and the soil ground. This is because the temperature of the soil and the additional temperature of the energy pile load buried in the W-shaped pipe can be greater than those of any other 2 kinds of energy piles,and,this may,in turn,lead to tension between the axial-oriented force of the piles and therefore reduce the additional temperature load in winter days,thus eventually lower the tensile strength of the concrete in other seasons. Such a kind of tension can also be reduced by the axial force at the end of the energy pile buried with W-shaped pipe. Therefore,necessary attention should also be paid to the axial tension at the end of the pile while the energy pile is in design and making.