Entry Region Heat Transfer Augmentation With Pins, Fins, and Turbulators in Circular Channels

Abstract

Entry region heat transfer is known to provide significantly higher heat transfer than fully developed conditions. Utilizing entry region heat transfer would provide an additional heat sink at the inlet of an aircraft engine before the fan, but requires further investigation of the convective heat transfer augmentation and downstream boundary layer impacts. The addition of near-wall heat transfer augmentation features only in the entry region at high Reynolds numbers is uncommon. Thus, heat transfer enhancement comparing small features in the entrance region of a circular channel and the effect on the downstream boundary layer has not been investigated. This study investigates three heat transfer augmentation features: pins, fins, and turbulators, mounted on the wall at the inlet of a circular channel. Two boundary layer probes, one mounted immediately after the augmentation features and one located three diameters downstream of the features, are used to evaluate the growth of the boundary layer due to the features. The convective heat transfer is evaluated using a constant heat flux surface with surface temperature measurements using infrared thermography. All features are evaluated at Reynolds numbers ranging from 1.0 × 105 to 5.0 × 105. Each type of geometry is capable of producing augmented heat transfer relative to a smooth entry region, with the maximum overall heat transfer coefficient augmentation of 2.8 compared to a smooth entry region. Fin arrays produced the lowest average total pressure losses, doubling the losses compared to a smooth channel. Overall, the fin arrays also provided the highest overall heat transfer coefficient performance with minimal total pressure boundary layer losses, but also exhibited a sensitivity to Reynolds number.