Comparative study of the effects of two types of ribs on thermal performance of solar air heaters

This paper aims to analyze fluid flow characteristics and heat transfer augmentation in the air duct of a solar air heater using CFD techniques. The air duct has a rectangular section, the top wall is the glazing and the bottom one is the absorber provided with transverse rectangular or squared ribs. The simulations are performed in the turbulent regime and RANS formulation is used to model the flow and resolve mass, momentum, and energy equations using Finite Volumes method. The air flow analysis shows that the velocity profile is not disturbed by the ribs outside the laminar sublayer. Heat transfer analysis based on the calculation of Nusselt Number, friction factor, and thermo-hydraulic performance highlights the heat transfer enhancement and no big friction losses are recorded. A comparative study between two rib shapes (square and rectangular) is performed, which shows better thermohydraulic performance of the rectangular ribs. (C) 2017 Sharif University of Technology. All rights reserved.