[en] An investigation of rib-roughened surface was undertaken to determine the effects of rib shape, angle of attack and pitch to height ratio on friction factor and heat-transfer results. A parallel plate geometry was used. Based on the law of the wall similarity and the application of the heat-momentum analogy developed by Dipprey and Sabersky, a general correlation for friction factor and heat transfer was developed to account for rib shape, spacing and angle of attack. Ribs at 45⁰ angle of attack were found to have superior heat transfer performance at a given friction power when compared to ribs at a 90⁰ angle of attack or when compared to sand-grain roughness. (author)