Numerical and analytical analysis of groundwater influence on the pile geothermal heat exchanger with cast-in spiral coils

The effect of groundwater flow on the heat transfer performance of pile geothermal heat exchanger (PGHE) with spiral coils was simulated by a 3-D simulation model using finite element method. Different groundwater flow conditions were taken into consideration by applying different hydraulic gradients. Based on the moving ring-coils model and simulation results, an improved analytical model is developed by introducing a key parameter of effective dimensionless velocity. The calculation results shows that the improved model can better describe the heat transfer performance of PGHE with spiral coils. Both numerical and analytical results indicated that the groundwater flow has an enhancing effect on the heat transfer performance of the PGHE with spiral coils and can accelerate the heat transfer process into stability. When the groundwater flow mean velocity equal to 6.98E-06 m/s, the amount of heat exchange is higher than 26.72% than it of non-advection situation. The improved ring-coils analytical model can be used as a reliable tool for the design of pile geothermal heat exchanger with spiral coils under groundwater flow. (C) 2015 Elsevier Ltd. All rights reserved.