Numerical modeling of high-velocity groundwater flow influence on the thermal-hydraulic characteristics and energy extraction from energy piles

This study investigates the potential for energy extraction from energy piles under high-velocity groundwater flow, considering different soil thermodynamic properties, pile characteristics, heat-exchange pipe shapes, and thermo-hydraulic parameters. Accordingly, finite element numerical modeling was employed along with Brinkman's equation, which was then verified using three sets of previously published data. The utilization of Brinkman's equation has revealed notable differences from the traditional Darcy's law approach, particularly regarding soil thermodynamic properties. The key findings indicate that groundwater flow has minimal impact on energy output per pile length (Q/Lep) until 10-7 m/s, after which Q/Lep increases significantly up to 10-3 m/s with no further effect. The influence of soil thermodynamic characteristics on Q/Lep decreases with increasing groundwater velocity, and Brinkman's equation is recommended for analyzing flows above 10-7m/s, especially in soils with low thermodynamic properties. Low-velocity flows with high soil permeability can disrupt horizontal groundwater flow and impact energy extraction, while mixed convection minimizes the difference in energy received between the 2nd and 180th days and increases the slope of the Q/Lep diagrams. This research offers valuable insights into the complexities of energy extraction from energy piles, emphasizing the importance of considering groundwater flow and various design factors for accurate evaluations.