Performance augmentation of a double-coil heat exchanger: analyzing the impact of radial fin count and diameter ratio

The growing demand for high-efficiency, compact heat exchangers in various industrial applications necessitates innovative solutions for thermal performance enhancement. This study aims to numerically investigate the thermal-hydraulic performance of a shell-and-double-helical-coil heat exchanger by integrating annular fins on the shell side. We systematically explore the influence of two critical geometric parameters: the number of annular fins (120, 160, and 200) and the fin outer-to-inner diameter ratio (Do, fin/Di, fin, varied across 1.25, 1.50, and 1.75). A three-dimensional computational fluid dynamics (CFD) model was utilized to rigorously analyze the average convective heat transfer coefficient (h), Nusselt number (Nu), pressure drop (ΔP), and overall thermal performance (η) across a wide range of Reynolds numbers. The results demonstrate that the addition of annular fins significantly augments heat transfer due to enhanced fluid mixing and the generation of secondary flow structures. Specifically, the 200-fin configuration achieved a thermal performance (η) of approximately 2.1 at Re = 2000, representing a 110% improvement over the unfinned case. Furthermore, varying the fin diameter ratio revealed that the 1.75 ratio yielded the highest thermal performance, reaching approximately 2.2 at Re = 2000, a 120% enhancement over the unfinned coil. These findings underscore the critical role of fin geometry in improving the thermo-hydraulic performance of compact heat exchangers.