Performance research on a high-efficiency coaxial heat exchanger for medium-deep geothermal energy utilization

Purpose The extraction and application of renewable energy are significant for breaking through traditional energy structures. Geothermal energy is an illustrated clean and renewable energy source that possesses enormous reserves, wide distribution and safety and stability. The purpose of this study is to improve the internal tube structure of smooth coaxial heat exchangers and innovatively proposes spiral finned and double slanted finned structures for the improvement of convective thermal energy transport inside the pipeline. Design/methodology/approach The computational fluid dynamics (CFD) numerical research investigates the impacts of three different internal tube structures on the exit temperature of the heater system, the energy extraction power and the surrounding soil temperature field, and analyzes the enhanced energy transport performance of the new coaxial thermal exchangers. Findings The outcomes illustrate that the spiral finned coaxial thermal energy exchanger demonstrated superior convective energy transport enhancement through comparative analysis under different conditions. Subsequently, the study explores the different effects of inner tube diameter, pitch and fin height of spiral finned heat exchanger on its heat transfer performance. The better efficiency inner tube structure increases the thermal energy extraction intensity by 4.49% in comparison with the smooth one. Under equal extraction conditions, the heat exchanger can obtain more geothermal energy by choosing soil heat sources with a larger temperature gradient. When the local temperature gradient rises between 0.025 and 0.045 K/m, the thermal energy extraction power can be increased by 66.7%. Originality/value The present study provides theoretical support for improving the thermal energy extraction efficacy of a novel coaxial heater system in practical applications.