Enhancing thermal-hydraulic performance in curved pipes through optimal radial fin placement: A numerical investigation

Increasing heat transfer in straight pipes, particularly in applications like heat exchangers, can be achieved by incorporating fins into the pipe wall. However, in curved pipes, the presence of more intricate flows resulting from centrifugal forces can alter this effect. The current study investigates how both the height and angular position of radial fins simultaneously influence the flow patterns within curved pipes. Adjusting the placement of radial fins is identified as a cost-effective and strategic approach to improve both the hydrodynamic and thermal efficiency in curved pipe systems. The numerical analysis focuses on studying laminar, incompressible flow in curved tubes with radial fins. The mass, momentum, and energy conservation equations in toroidal coordinates were discretized with the second-order finite difference method on a staggered grid, followed by their solution through the projection algorithm. The results indicate that adapting the angular position of the fins improves the thermal-hydraulic performance by 51.8%, 48.4%, 36.3%, and 20.6% for one to four fins, respectively. These changes are closely related to the behavior of the secondary flows. Furthermore, altering the height of the fins reveals that for three fins within the tube, the most optimal fin height is half of the tube radius. In other cases, a fin height equal to 0.7 multiplied by the tube radius provides the highest performance. From the numerical results, it is found that the primary factor affecting the heat transfer rate in curved pipes is the strength of secondary motions, while the generation of friction is influenced only by the axial velocity.