A comprehensive investigation has been carried out in this study to evaluate the thermal performance of conventional single-flow and double-flow solar air heaters. An analytical model was developed to describe the thermal behavior of the systems. The enhancement of thermal performance in a solar air heater is primarily achieved by increasing the rate of heat transfer. In a double-flow solar air heater, air flows simultaneously above and below the absorber plate, resulting in a larger effective heat-transfer area compared to a single-flow configuration, where air passes either over or under the absorber plate. Due to this increased heat-transfer surface, the double-flow system demonstrates superior performance. Furthermore, based on energy balance equations, the influence of mass flow rate fraction on the efficiency of the double-flow solar air heater has also been analytically examined.
Som Nath Saha (Sun,) studied this question.