Finite Element Analysis of Combined Energy Piles with Long and Short Heat Exchanger Tubes

To improve the heat exchange effect of energy piles in coastal areas, a new energy pile with a combination of long and short heat exchanger tubes is proposed. This technology combines the characteristics of implanted pile construction and arranges heat exchanger tubes of different lengths inside and outside the precast pipe pile, which can make full use of the geological conditions in coastal areas. Finite element analysis was applied for a project in a deep, soft soil ground to study the effectiveness of the new combined energy pile technology. The influences of the combined heat exchanger tubes and groundwater seepage conditions on the heat transfer and stress state of the energy pile were analyzed. The results show that the deformation and internal force of the pile body are closely related to temperature change. The temperature change is determined by heat transfer, which is closely related to the arrangement of heat exchanger tubes and underground water flow. With the increase of groundwater seepage velocity, the heat taken away by the heat exchanger tubes gradually increases; thus, the heat exchange between the heat exchanger tubes and the pile body decreases. The inner heat exchanger tube of the pile leads to an increase in heat exchange. However, as the length of the inner heat exchanger tube increases from 40 m to 80 m, the heat exchange decreases. The research results provide technical support for further development of the new energy pile technology.