Three-dimensional thermomechanical modeling of geothermal energy piles with U-tube heat exchangers of different cross-sectional shapes
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Date
2025
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Abstract
This study explores the thermomechanical performance of a three-dimensional (3D) geothermal
energy pile (GEP) system, emphasizing the optimization of heat exchanger (HE) geometry to
improve both thermal efficiency and structural integrity. As GEPs offer a promising avenue for
integrating renewable geothermal energy into building foundations, their design must balance
energy performance with mechanical stability. A finite volume-based numerical model is developed,
employing
second-order
spatial
and
temporal
discretization
and
the
Pressure-Implicit
with
Splitting
of Operators (PISO) algorithm for pressure–velocity coupling. A segregated solution
strategy with under-relaxation is used to ensure numerical stability and convergence. The model
simulates a concrete-encased U-shaped HE embedded in clayey soil, with three cross-sectional
geometries: circular, square, and triangular. Simulation outcomes are validated against analytical
predictions and benchmarked with experimental and numerical data from the literature.
Among the tested geometries, the triangular HE demonstrates superior thermal and structural
performance under both mechanical and thermomechanical loading conditions. Compared to the
circular configuration, the triangular U-pipe enhances cooling efficiency by reducing outlet
temperature by 1.2 % and increasing heat extraction by 8.6 %. In heating mode, it raises the
outlet temperature by 0.6 % but lowers the heat transfer rate by 4.8 %, underscoring the need for
season-specific or hybrid designs. Thermomechanically, the triangular configuration exhibits the
highest axial compressive stress in summer, increasing by 6.36 %, while in winter, it shows a 4.75