Jet impingement on a rib-roughened wall inside semi-confined channel

• Assessing combination of jet impingement and rib-roughened convection in wall-jet zone.
• Identifying rib configuration on heat transfer enhancement and discharge coefficient.
• The inverted V-shaped rib seems advantageous on convective heat transfer enhancement.
• Rib-roughened channel enhances convective heat transfer up 30% in wall-jet region.
• Discharge coefficient of rib-roughened channel is decreased 2%–10%.

Convective heat transfer on the rib-roughened wall impinged by a row of air jets inside semi-confined channel was experimentally investigated. Four rows of transverse ribs were arranged in the wall-jet zone downstream from the impinging jet stagnation to enhance heat transfer. Three typical rib configurations, including orthogonal ribs, V-shaped ribs and inverted V-shaped ribs, were considered under different non-dimensional jet-to-target distances ranging from 1 to 3 diameters and impinging jet Reynolds numbers ranging from 6000 to 30,000. The results show that the rib-roughened wall enhances the convective heat transfer up to 30% in the ribbed region by comparison with the smooth wall under the same jet Reynolds number. Among three rib configurations, the inverted V-shaped rib seems to be advantageous on the convective heat transfer enhancement, especially at lower jet-to-target spacing. The ribs on the impinging target do provide stronger convective heat transfer in the wall-jet region, but at greater expense of pressure drop inside the channel. At the jet-to-target spacing ratio of 1, the flow coefficient of the rib-roughened channel is decreased 5%–10% in related to the smooth channel.