Artificial roughness up to laminar sub-layer to enhance heat transfer coefficient is used in various applications like gas turbine blade cooling channels, heat exchangers, nuclear reactors, and solar air heaters. Several experimental studies in this area have been carried out but very few attempts of numerical investigation have been made so far due to complexity of flow pattern and computational limitations. In this case study, an attempt is made to predict numerically the details of both the velocity and temperature fields responsible for heat transfer enhancement. The presence of rib may enhance heat transfer because of interruption of the viscous sub layer, which yields flow turbulence, separation and reattachment leading to a higher heat transfer coefficient. The enhancement of heat transfer by flow separation and reattachment caused by ribs is significantly higher compared to that by the increased heat transfer area due to ribs (fin-effect).
Several research papers with different types of roughness have been examined by researchers in the past. This academic study highlights a sample casework involving rectangular ribs and the effect on Nusselt number (highlighting higher heat transfer) in comparative with smooth duct.