Numerical Modeling of Fluid Flow and Thermal Behavior in Geothermal Heat Exchangers

Abstract

Geothermal heat exchangers are highly dependent on the local heat exchange capacity and ground thermal properties. The ability to simulate performance and testing of geothermal heat exchangers is limited. Therefore thermal conductivity tests are usually required for correct sizing of geothermal heat exchange systems. To better understand these tests in relation to energy piles, a 3D finite element model was created using the COMSOL software to simulate the thermal conductivity test of a 12inch (30cm) energy pile. The finite element simulation was created and validated using experimental data to expand the comparisons made between geothermal boreholes and energy piles. In this study, the numerical finite element model has been recreated using the commercial computational fluid dynamics (CFD) software ANSYS which incorporates fluid flow effects. Confirming that the CFD model can accurately model the thermal conductivity test provides an additional tool that will be valuable in modeling geothermal heat exchangers. Results show that parametric variations in terms of fluid flow rate and fluid selection are easier to evaluate using the CFD model compared to the finite element model. Results are also compared with discrete thermal conductivity measurements obtained from real geothermal heat exchangers.