A numerical study on enhancing heat transfer within helical coils using twisted tape inserts
Sara Jumah Flayh, Eman H. Ismail, Karrar Saeed Mohammed, Hussein Ali Abdulhussein, Seyed Hossein Hashemi Karouei, Dheyaa J. Jasim
Abstract
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.