In the present study, the thermal and hydraulic characteristics of a rectangular duct with aspect ratio of 1/8 roughened by broken V-shaped ribs pointing upstream are investigated experimentally using Liquid Crystal Thermography (LCT) and Particle Image Velocimetry (PIV). The heat transfer distributions on the roughened wall were evaluated using liquid crystal images. It was found that the heat transfer coefficient had a spanwise variation on the ribbed wall, with high heat transfer coefficient at the upstream end of the rib and low value at the other end, similar to the continuous V-shaped ribs. However, the heat transfer distribution in the case of broken V-shaped ribs was observed more uniform, with local maxima due to the gap flow. In addition, the saw-tooth fashion of heat transfer distribution was also observed along the streamwise direction. The isothermal flow field measurements were obtained by PIV to catch the flow structures introduced by the ribs. The spanwise profile of the main flow velocity was found altered, and a complicated secondary flow was detected over the cross section. This flow phenomenon was caused by the ribs and the gaps between ribs.

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