In this paper, results of an experimental investigation on heat transfer and friction in a rectangular duct roughened with discrete multi v-shaped rib on one of its broad wall are presented. The discretizing of multi v-shaped rib is done by providing small symmetrical gap equal to rib height in both legs of multi v-rib. The artificially roughened duct was investigated having width to height ratio (W/H) of 12, relative width ratio (W/w) of 6, relative roughness pitch (P/e) of 10, relative roughness height (e/Dh) of 0.0433, angle of attack (α) of 60°, and relative gap distance (Gd/Lv) of 0.55. The relative gap width (g/e) was varied from 0.5 to 1.5. The heat transfer and friction factor results obtained experimentally were compared with those of smooth duct under similar experimental conditions. It is seen that there is a significant change in Nusselt number and friction factor as a result of providing discrete multi v-shape ribs. The enhancement in Nusselt number is found to be 6.32 times (that of smooth surface) for discrete multi v-shaped rib with relative gap width of 1.0. It is also found that the duct having this roughness geometry results in best thermo-hydraulic performance in comparison to other geometries under similar operating conditions.

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