Experimental investigation of local heat transfer in a square duct with various-shaped ribs

In the present study, experimental studies are carried out to investigate the heat transfer and friction characteristics in a square duct roughened by various-shaped ribs on one wall. The ribs are oriented transversely to the main stream in a periodic arrangement. Liquid crystal thermography is employed to measure the local and average heat transfer coefficient on the ribbed surface. The rib height-to-duct hydraulic diameter ratio is fixed at 0.1; the rib pitch-to-height ratio varies from 8 to 15 and the test Reynolds number spans from 8,000 to 20,000. The results show that the trapezoidal-shaped ribs with decreasing height in the flow direction (case C) provide the highest heat transfer enhancement factor and are likely to be used to suppress the local hot spot which usually occurs in the region just behind the ribs.