Evaluation of the performance of an improved solar air heater with S shaped ribs with gap

Compared with liquid solar collectors, the thermal efficiency of solar air heaters is generally low. To improve the thermal efficiency of a solar air collector, an improved solar air heater with s-shaped ribs with gaps is proposed; the solar air heater can enhance the heat transfer between air and heat absorber plate sufficiently. At the same time, to reduce the flow resistance of air, a gap of certain width was created on the ribs. In this study, the results of an experimental investigation on collector efficiency and pressure drop in a solar air heater with multiple s-shaped ribs with gaps as the roughness element are presented. The main factors including the rib geometry size, namely, the rib spacing, rib width, rib clearance width, channel height, solar radiation intensity, air mass flow rate were evaluated. The effects of these factors on the heat efficiency of solar air heater and the temperature difference between inlet and outlet were analyzed. Compared with a smooth plate, the thermal efficiency of solar air heater with artificial roughness was improved by 13% to 48% under different conditions. However, the work section pressure drop of this new solar air heater is within the range of 15.8-30 Pa. These experimental results are important for the application of this improved solar air heater.