Heat transfer and pressure loss characteristics of a high aspect ratio duct are measured under both, jet impingement and channel flow conditions, respectively. For both cases, roughness elements in consideration are staggered and inline axial ribs. The spacing (P) to height (e) ratios studied are P/e = 2 and P/e = 4; the rib height (e) to channel height (H) ratio is 0.125. Also studied is an aluminum foam roughness with a porosity of 92% and a height to channel height ratio of 0.15. Reynolds numbers considered for the channel flow case (based on the hydraulic diameter) range from 10.000 to 40,000. Reynolds numbers for the jet impingement case (based on the hole diameter) range from 5,000 to 20,000. Tests are performed using the copper plate regional average method. Results show a 50-90% increase in heat transfer due to the use of axial ribs in both, impingement and channel flow cases. The porous foam shows a more significant increase in heat transfer coefficient for both channel flow and impingement cases. (C) 2010 Elsevier Ltd. All rights reserved.