Enhancing turbulent heat transfer and flow characteristics in ribbed channels with periodic slits: A comparative study of transverse, inclined, and V-shaped configurations

In this study, we experimentally investigate the turbulent heat transfer characteristics of rectangular channels equipped with miniature transverse, inclined, and V-shaped ribs, each incorporating various types of periodical slits. These slits, located between the lower wall of the rib and the bottom wall of the channel, create different slit channels (confusor, diffusor, and constant cross-section). The rib blockage ratio and the pitch to rib height ratio were kept at 0.032 and 10, respectively. To measure the local heat transfer characteristics on the bottom ribbed wall at Reynolds numbers varying from 40,000 to 120,000, the transient thermochromic liquid crystal (TLC) method was employed. In addition, the k-ω SST turbulence model was used to simulate the spatial turbulent flow behaviours in rectangular channels with slit ribs to reveal the heat transfer mechanism. The results indicate that the configuration of miniature ribs, along with the type and position of slits, significantly affects the heat transfer and friction loss of the rectangular channel. Opening periodical slits on the ribs reduces the pressure drop of the ribbed channel while exerting various influences on heat transfer performance due to complex vortex structures induced by the ribs and slits, which affect the secondary flow intensity. The highest average augmentation Nusselt number and thermal-hydraulic performance (THP) were observed in channels with V-shaped solid ribs, achieving values up to 2.5 and 1.7 at Re = 40,000. Lastly, we established experimental correlations for the overall averaged Nusselt number and friction characteristics specific to the slit ribbed channels.