An infrared imaging system is used to measure detailed distributions of local heat transfer coefficient from rectangular channels with two opposite wide walls roughened by 45 degrees staggered ribs of twenty test cases. Nusselt number (Nu) contours over the ribbed surfaces are presented for five sets of channels with an identical rib-floor configuration, but different channel-heights where the complex NU distributions without bleed and then with bleeds from the scanned rib-floor or from the ribbed wall opposite to the scanned rib-floor or from the smooth sidewall are analyzed to examine the synergetic effects of variable channel-heights and different bleed conditions on heat transfer. Spatially averaged heat transfer results for the entire set of test channels are generated with the thermal performance factors compared to establish the heat transfer correlations with applications to the design of coolant channels in a gas turbine blade. (c) 2007 Elsevier Ltd. All rights reserved.