Influence of local perforations on heat transfer enhancement in inclined rib turbulators

The present study numerically investigates the influence of tailored local perforations on swirling flows and their influence on heat transfer enhancement in the rib turbulators. Numerical simulations are conducted for various rib inclination angles and perforation positions. The results indicate that ribs inclined at 60° and 30° increase the normalized Nusselt number by approximately 23.2 % and 17.0 %, respectively, and improve the overall thermal performance factor by 11.9 % and 24.5 %, compared to conventional 90° inclined ribs. To further enhance heat transfer performance, ten perforations are applied in parallel with the flow direction at one end of each inclined rib, targeting the local swirling flow. These perforated configurations enhance turbulent mixing and strengthen the vortex structures, improving heat transfer over the bottom surface. For the 60° and 30° inclined ribs, the local perforations increase the normalized Nusselt number by 5.1 % and 4.4 %, respectively, while reducing the normalized friction loss by 1.5 % and 5.7 %, resulting in overall thermal performance improvements of 5.6 % and 6.5 %. In contrast, when perforations are applied at both ends of the 30° inclined ribs, the secondary flow is disrupted, leading to a localized reduction in heat transfer. This configuration yields an approximately 9.2 % lower overall thermal performance factor than the case with ten perforations positioned only at the left end of the 30° inclined ribs.