Experimental study on heat transfer characteristics in a ribbed channel with dimples, semi-spherical protrusions, or oval protrusions

Flow turbulators such as ribs, dimples, and protrusions induce high flow disturbance, and as a result, enhance the heat transfer coefficient. For higher heat transfer augmentation, two or more heat transfer enhancement methods can be applied simultaneously. For the present study, dimples or protrusions in various shapes were installed in a channel with angled ribs, and the effects of the protrusion configurations on the heat transfer coefficient and thermal performance were experimentally investigated. The heat transfer coefficient was measured using the transient IR camera technique. The tested Reynolds numbers based on the channel hydraulic diameter were 30,000, 50,000, and 70,000. The channel aspect ratio and the hydraulic diameter were 2 and 0.0533 m, respectively. Both the height and thickness of the ribs were 5 mm, and the rib installation angle was 60°. Both the semi-spherical and oval protrusions were tested for the rib-protrusion compound cases. For the cases with oval protrusions, three protrusion installation angles were considered. The results showed that the rib-dimple compound configuration achieved the best performance in terms of heat transfer augmentation, but the pressure drop was also the highest. Among the rib-protrusion compound configurations, those with low protrusions were more effective in terms of heat transfer augmentation. The heat transfer augmentation in the rib-oval protrusion compound configuration was strongly affected by the installation angle of the protrusion.