Analysis of Enhanced Heat Transfer Characteristics of Geothermal Coaxial and Finned Borehole Heat Exchanger

Abstract

Geothermal energy has been recognized as a reliable and continuous resource of renewable energy. In the past, numerous investigations have been conducted to increase the thermal performance of the coaxial borehole heat exchangers. Previous research efforts have focused on parametric studies, incorporated the use of vortex generators and multiple external chambers. While the effect of fins on various configurations, such as U-tube, spiral tubes and horizontal type heat exchangers have been studied, there is a lack of research on their impact on geothermal coaxial borehole heat exchangers. In this study the effect of longitudinal fins on coaxial borehole heat exchanger (CBHE) was evaluated using CFD software. Transient simulations were performed for the period of 24 hours for cooling operation at different flow rates i.e 4L/min and 8L/min. Fin lengths of 5mm, 10mm, 15mm and 20mm were evaluated to determine optimum fin length. At optimum fin length of 15mm, it was observed that heat transfer rate per unit length was increased by 18% at 4L/min and 22% in case of 8L/min flow rate which indicates the increase in CBHE efficiency. This research establishes a foundation for future investigations of finned ground heat exchangers which can contribute towards a sustainable and efficient energy solution.