Summary: 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\(^\circ\) and 90\(^\circ\). The present turbulent results clearly showed the locally high heat transfer spots at several locations. The comparison between 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.