The research on ring-coil heat transfer models of pile foundation ground heat exchangers in the case of groundwater seepage

This paper presents a mathematical model for describing heat transfer around the pile foundation ground heat exchangers (GHEs) when seepage of groundwater imposes an effect on the heat exchange process. The corresponding analytical solutions on temperature response are acquired based on combined heat transfer case; the model take the spiral coils arrangement and their pitches inside piles into consideration and identify the differences between the new models and those former models which did not treat spiral tube as a series of separate coils along the z-axial direction. The influence exerted on temperature response by every parameter was investigated. Two cases were compared, i.e. pure conduction and combined heat transfer including both conduction and convection. The relevant calculations prove that the heat transfer efficiency between pile foundation GHEs and the surrounding underground medium can be improved especially when some parameters attain a certain extent. The research on new models can help boost the development of energy pile technology.