Experimental study of impinging heat transfer along smooth or rib-roughened surfaces

The objective of this work is to examine the detailed heat transfer characteristics on either smooth or rib-roughened surfaces under arrays of impinging elliptic jets by using a liquid crystal thermograph technique. The impingement heat transfer performance for elliptic jet holes of five different aspect ratios, AR, and three jet-to-target spacing, Z = 1.5, 3 and 4.5 were tested at jet Reynolds numbers, Re = 1500, 3000 and 4500 with three different exit flow orientations. For rib-roughened surfaces, both continuous and broken angled-rib configurations were considered. Measured results show that, the mean heat transfer rates along a smooth surface with the elliptic jets of AR = 0.5 are the highest at Re = 3000 and 4500; while in the low-Re case of Re = 1500, the jet arrays with AR = 2 and 1 perform better than that with AR = 0.5. In addition, experimental results show that the local heat transfer rates over the ribbed surface are characterized by obvious periodic-type distributions. Compared to the results without ribs, the heat transfer over the rib-roughened surface may be enhanced or retarded. Whereas, among the test angled-rib arrangements, the best heat transfer performance is obtained with a surface with 45° V-shape ribs. The surface with continuous ribs provides a better heat transfer than that with broken ribs.