Thermal-Hydraulic and Hydrodynamic Analysis of Twisted Fins in a Double-Pipe Heat Exchanger

Abstract

This paper examined the integration of twisted fins (TF) on the inner wall of the outer pipe in a double-pipe heat exchanger (DPHE) to enhance thermal-hydraulic performance. The influence of varying twist angles within the turbulent flow regime on heat transfer and pressure drop is evaluated to identify an optimal configuration for energy efficiency. Simulations conducted using ANSYS Fluent, employing the SST k-ω viscous model to simulate the effects of swirling flows and vortex interactions induced by TF and the COUPLED algorithm to solve the Navier-Stokes equations. Results show that TF significantly enhances heat transfer by improving fluid mixing and disrupting thermal boundary layers but increases pressure drop due to higher turbulence and friction. Elevated turbulent kinetic energy (TKE) associated with swirling flows and vortices is identified as the primary mechanism for heat transfer enhancement, intensifying with increasing twist angle. However, for twist angles above 40°, the rate of heat transfer improvement diminishes, indicating diminishing returns. The most significant overall improvement occurs in the transition from 30° twisted fin (TF30) to 40° twisted fin (TF40), with a 15.80% increase in Nusselt number and a 14.93% increase in friction factor. Performance evaluation criteria (PEC) values show that all TF configurations achieve PEC > 1, indicating that the Nusselt number improvement outweighs the friction factor increase. TF40 achieves the highest average PEC of 1.305, establishing it as the optimal configuration for energy management. These findings demonstrate the effectiveness of TF in improving DPHE efficiency, highlighting their potential for future heat exchanger applications.