EXPERIMENTAL STUDY OF AEROTHERMAL PERFORMANCE IN RECTANGULAR DUCT WITH TRAPEZIUM RIBS
The present work is a detailed study of aerothermal performance and the underlying flow mechanism in a rectangular duct (4:1) roughened with Trapezium ribs placed transversely on the bottom wall. The rib height-to-hydraulic diameter ratio, the rib pitch-to-height ratio, and the Reynolds number based on duct hydraulic diameter are fixed at 0.125, 12 and 42500, respectively. The chamfering angle (α) is varied from 0 to 20° in a step of 5°. The forced convective heat transfer coefficient has been measured via transient Liquid Crystal Thermography technique, while reliable and detailed flow measurements have been made via Particle Image Velocimetry technique. The investigation focuses towards assessing the influence of altering chamfering angle on the local and the duct-averaged features of the heat transfer fields and friction factor. In particular, the flow mechanisms responsible for high or low heat transfer regions as well as for hot-spot formation in the vicinity of the ribs are identified and explained. Trapezium ribs ameliorate the heat transfer just behind the rib as compared to square ribs. The averaged heat transfer and friction factor measurements are compared along with the thermo-hydraulic performance. Trapezium rib with α = 5° turned out to be the most promising one with better thermo-hydraulic performance.