Effects of heat exchange fluid characteristics and pipe configuration on the ultimate bearing capacity of energy piles

Abstract

This paper examines the ultimate bearing capacity of energy piles in sandy and clayey soils by conducting numerical modeling under different thermal loads, fluid-pipe configurations and fluid characteristics. Accordingly, U and W-shaped fluid-pipes with different diameters were simulated using ANSYS-FLUENT software, under different inlet flow rates, fluid temperatures and ground temperatures. Moreover, a semi-empirical analytical solution is proposed for predicting the outlet temperature for different pipe configurations. Then, the energy piles were modeled using ABAQUS FE-software, and the effect of temperature distribution in U, double-U and W-shaped pipes on the ultimate bearing capacity was studied, in heating/cooling conditions. Both numerical simulations and the analytical solution were validated against experimental data. Results showed that under constant flow rate, initial inlet temperature and pipe diameter, the differences between the inlet and outlet temperature of the heat exchange fluid in the U-shaped pipes was less than that obtained for the W-shaped pipes. Also, for constant inlet temperature and pipe diameter, the temperature difference decreased when the inlet flow rate increased. It was found that under constant thermal loading conditions, the changes in the ultimate bearing capacity were higher in piles with double U-shaped pipes, followed by U-shaped pipes, and lowest for W-shaped pipes.