Numerical evaluations on the effects of thermal properties on the thermo-mechanical behaviour of a phase change concrete energy pile

Abstract

Energy pile is a kind of economic and efficient geothermal utilization technology that the ground heat exchanger (GHE) used in ground source heat pump (GSHP) is embedded into building pile foundation to realize heat exchange with surrounding soil. Adding phase change material (PCM) into the energy pile can not only reduce the temperature variation and thermal deformation range of energy pile, but also improve its energy storage and heat transfer performance. In this work, phase change concrete energy pile (PCCEP) is proposed by using PCM as a part of backfill material of energy pile. A three-dimensional numerical model is developed to find the influences of thermal properties of PCCEP on its thermo-mechanical behaviour. According to the model, the influences of thermal conductivity, phase change latent heat (PCLE) and phase change temperature (PCT) on the thermal performance and mechanical characteristics of PCCEP are numerically investigated. It can be seen that for improving heat transfer performance of PCCEP, the thermal conductivity should be increased, but from the perspective of reducing change of pile displacement, axial force and side friction resistance, the thermal conductivity should be reduced. Under heat release mode, lower PCT and larger PCLE contribute to the improvement of thermal performance of PCCEP, and accordingly the rise range of pile temperature, pile displacement change and pile thermal stress can all be reduced. The experimental validation on the model shows that the simulation values of pile wall middle temperature(PWMT) and pile top displacement are agreed well with the corresponding experimental results, the real-time relative error of PWMT and pile top displacement are respectively within 5.1 and 12%.