Exergy Analysis of Flat Plate Solar Air Heaters Having Obstacles and Filled with Wire Mesh Layers

Two new experimental studies are presented in this research for improving the convection heat transfer and efficiency of flat plate solar air heater (SAH). An exergetic analysis is applied for evaluating the efficiency of a flat plate (SAH) with and without porous media. It was specially designed, low height bed filled with aluminium wire mesh layers and four aluminium longitudinal obstacles that increase the air path flow through the bed and the area of the absorber plate. Six wire mesh layers as an alternative of absorber plate, the layers had an internal diameter of 0.31 cm and a cross-sectional area of 0.22 cm × 0.22 cm. The wire mesh layers and the obstacles, improve the heat transfer from the absorber mesh layers in the moving air inside the heater. The plotted exergetic efficiency curves are a function of solar intensity, ambient temperature, bed temperature and temperature rise parameter (T_o-T_i / I). These efficiency curves are in bed with and without porous media through different airflow rate. The results illustrate that the heater with porous media SAH is more efficient, from exergy point of view, then the heater without porous media. The maximum exegetic enhanced efficiency with and without porous media SAH in this study has been found to be 3.42 % and 5.16 %, respectively. These results correspond to the low airflow rate of 0.015 kg/s and 2.5 cm channel depth. A significant improvement in the exergetic efficiency discovered when comparing the proposed system with other conventional SAHs. (paper)