A critical review on artificial roughness provided in rectangular solar air heater duct

Applications of artificial roughness on the underside of absorber plate in solar air heater duct have been widely used to improve heat transfer with moderate increase of friction factor. The design of the roughness shape and arrangement is most important to optimize the roughened surfaces. The roughness parameters and ribs arrangement are responsible to alter the flow structure and heat transfer mechanisms are mainly governed by flow structure. The critical reviews on various artificial roughness elements available in literature have been conducted and the effects of the roughness patterns are discussed. The Nusselt number and friction factor correlations for various roughness elements have been summarized. A comparison study of thermohydraulic performance of different roughness elements has also been reported to understand the results of applications of artificial roughness.