Thermal performance enhancement of solar air heaters by using transverse ribs and determination of optimum arrangement of the ribs

In this paper, performance of a solar air heater has been investigated by using of transverse ribs. For this aim, the governing equations for fluid flow including mass, momentum and energy conservation laws have been solved by Fluent software. With respect to having turbulent flow in solar air heaters and noticeable portion of radiation in heat transfer, turbulence and radiation have been considered either and for finding best models for turbulence and radiation, results have been compared with previous experimental studies for solar air heater without ribs. Then effects of parameters such as existence of ribs, changing effective heat flux, geometry and arrangement of the ribs in different mass flow rates, have been studied by using of obtained best models. The results confirmed enhancement of thermal performance by using of transverse ribs and illustrated that wedge shaped ribs have the best thermal performance among the investigated geometries. In addition, optimum arrangement of the ribs is different for various Reynolds numbers. So that in low Reynolds numbers optimum gap between two adjacent ribs is more than it in high Reynolds numbers.