Thermal interaction of slender geothermal boreholes with creeping groundwater flows

Abstract

In the presence of groundwater flows, more compact and affordable geothermal heat exchangers can be constructed thanks to the increased heat transfer capabilities of the ground. To correctly design them, theoretical models for the thermal interaction of geothermal boreholes with aquifers are required. By using matched asymptotic expansion techniques, a new theoretical model for the case of creeping groundwater flows is developed in the present work. This new model improves by an order of magnitude the accuracy of the state of the art, leading to absolute (relative) errors below 0.03 (2.3%). Additionally, the mathematically-rigorous and physically-sound derivation of the proposed model allows, for the first time, the assessment of the theoretical and conceptual merits and limits of the state of the art.