Experimental Study of Detailed Heat Transfer and Fluid Flow Characteristics in a Rectangular Duct With Solid and Slitted Pentagonal Ribs

Rib turbulator is the most effective, economically feasible, and rigorously studied tool to increase thermal performance because of its fundamental nature and due to the vast field of industrial applications. The rib turbulator results in heat transfer enhancement with additional pressure penalties, and thus encourages the researcher and designers towards selecting an efficacious rib configuration. The present work is a study towards detailed heat transfer and flow field characteristics inside a rectangular duct roughened by solid as well as ventilated pentagonal ribs placed transversely on the bottom wall. The rib height-to-hydraulic diameter ratio, the rib pitch-to-height ratio, the open area ratio, and the Reynolds number based on duct hydraulic diameter fixed during experiments are 0.125, 12, 25%, and 42500, respectively. The heat transfer coefficient (HTC) distribution was mapped by using transient Liquid Crystal Thermography (LCT) technique, while detailed flow measurements were made by using Particle Image Velocimetry (PIV) technique. The investigation focuses towards assessing the influence of three different rib configurations named as solid pentagonal ribs, pentagonal rib with parallel slit, and pentagonal rib with inclined slit, on the local heat transfer fields as well as flow characteristics. The flow mechanisms responsible for high or low heat transfer regions as well as for hot-spot formation in the wake of the ribs are identified and explained. The overall heat transfer and friction factor measurements are observed along with the thermohydraulic performance. Results show that the solid pentagonal ribs are superior to slitted ribs from both heat transfer augmentation and thermo-hydraulic performance perspective. Additionally, the slitted pentagonal ribs significantly control the small-scale vortices present at the leeward corner of the solid pentagonal ribs and eventually facilitates in preventing the hot spots formation with reduced pressure penalty.