Thermal interaction of geothermal boreholes with groundwater flows at peclet numbers of order unity

M. Hermanns, J. Rico

10th Thermal and Fluids Engineering Conference - TFEC 2025, Washington (United States of America). 09-12 March 2025

Summary:

The presence of aquifers significantly affects the thermal response of geothermal boreholes. Consequently, theoretical models used in the design and sizing of geothermal heat exchangers must account for their presence. Existing models in the literature are effective for creeping groundwater flows, where heat convection close to the borehole is weak compared to heat conduction and the resulting Peclet number is small compared to unity. But strong groundwater flows, with Peclet numbers of order unity and beyond, are also present in real-world applications, such as in high-permeability soils or when energy piles are involved. In these cases, current models fail to correctly account for the flow field in the vicinity of the boreholes, leading to unsatisfactory results or the need of empirical tuning parameters. By using asymptotic expansion techniques, a new theoretical model for the thermal interaction of geothermal boreholes with strong groundwater flows has been developed. It is physically sound, mathematically rigorous, and free of tuning parameters. Comparisons with detailed numerical simulations demonstrate the models’ promising performance and accuracy. Furthermore, the developed model is applicable to other heat transfer problems involving circular cylinders and potential or Darcy flows, thereby extending its relevance beyond the field of low-temperature geothermal energy.

Spanish layman's summary:

Los acuíferos afectan la eficiencia de los pozos geotérmicos. Los modelos existentes son adecuados para flujos lentos, pero fallan para números de Peclet cercanos a la unidad. Este modelo funciona bien en dicho rango y se puede aplicar en geotermia y en otros problemas de transferencia de calor.

English layman's summary:

Aquifers affects geothermal boreholes' efficiency. Existing theoretical models work well for creeping flows but struggle with Peclet number of order unity. This new model fills the gap in the literature and not only can be applied to geothermal systems but also for other heat transfer problems.

Keywords: HVAC systems, geothermal heat exchangers, geothermal boreholes, groundwater flows, asymptotic solution

Publication date: 2025-03-09.

Citation:
M. Hermanns, J. Rico, Thermal interaction of geothermal boreholes with groundwater flows at peclet numbers of order unity, 10th Thermal and Fluids Engineering Conference - TFEC 2025, Washington (United States of America). 09-12 March 2025.