A numerical study on enhancing heat transfer within helical coils using twisted tape inserts

This numerical study investigates two key methods for enhancing the thermo-hydraulic performance of a shell-and-tube heat exchanger (SCTHE). The first method involves a geometrical modification by adding a varying number of external helical fins, and the second method explores the influence of different cold-fluid inlet flow orientations. Three distinct finned configurations, featuring two, three, and four external spiral fins (TWESF, THESF, and FOESF, respectively) were modeled and compared to a plain unfinned coil. Additionally, the study analyzed the most efficient finned design under four separate flow inlet conditions: Horizontal Counter-Flow (HCF), Horizontal Parallel-Flow (HPF), Vertical Counter-Flow (VCF), and Vertical Parallel-Flow (VPF). The presence of external fins significantly improved both flow mixing and heat transfer rates. At a Reynolds number (Re) of 2000, the FOESF design exhibited the highest thermal performance, showing a 77 % efficiency gain over the unfinned coil. Furthermore, the analysis of fluid inlet configurations demonstrated that flow direction has a profound effect on performance. The HCF and VCF arrangements delivered notable efficiency improvements of 95 % and 77 % respectively over a simple helical coil. The study also confirms that increasing fluid velocity intensifies swirling vortices, leading to a substantial increase in the Nusselt number. This research validates that a combination of optimized fin geometry and strategic fluid inlet orientation can serve as a powerful approach to developing high-performance SCTHEs. The findings provide critical insights for the design of more efficient and compact heat exchange systems in various industrial applications.