Heat transfer in a rib-roughened duct was numerically simulated by using the second-order finite difference method in coordinates fitted to transverse or angled ribs. Turbulent and laminar cases of which Reynolds numbers were 350 and 50, respectively, were computed for rib angles of 60 degrees and 90 degrees, The present turbulent results clearly showed the locally high heat transfer spots at several locations. The comparison between the laminar and turbulent results showed clear differences in heat transfer distribution because the higher momentum fluid of the turbulent case was more disturbed by the ribs as compared to the laminar case. (C) 2001 Elsevier Science Ltd. All rights reserved.