Thermal behavior of single energy pile in saline soil environments

Energy piles are increasingly applied in saline soil regions, yet the influence of salinity on their thermal performance is not sufficiently quantified. This study implements a salinity-dependent thermophysical property module—based on established correlations for thermal conductivity, density, and specific heat—within a three-dimensional numerical model of a single energy pile using COMSOL Multiphysics. Unlike conventional analyses that assume constant soil thermal properties, the model accounts for salinity-induced variations in thermal conductivity. Parametric simulations show that increasing salinity from 0 to 8.775 (g/ kg) raises soil thermal conductivity by 28.2% while reducing specific heat capacity, thereby accelerating temperature evolution in the surrounding soil and lowering pile temperature by 0.61 °C. Flow velocity optimization indicates that increasing flow rate beyond 0.684 m 3 /h yields negligible improvements in heat transfer due to the dominance of soil conduction resistance. Quantitative design guidelines are proposed to define allowable operational temperature ranges and recommended flow velocity intervals. This work provides a physically consistent, quantitatively calibrated approach to the thermal design of energy piles in saline environments.