Investigation of Absorber Plate Porosity effects on a Solar Air Heater Performance With Slatted Glass

In this research a flat plate solar air collector was investigated under direct solar radiation consisted of a slatted glass cover، perforated absorber aluminum sheets (porosity 0. 0177، 0. 0314 and absorber thickness of 2. 5 mm). The effect of porosity on absorber efficiency of collector was evaluated. Six levels of air mass flow rates (0. 0056 to 0. 0385 kg m-2 s-1) were adopted. Average solar energy was reported to be 1040 Wm-2. The experimental results show that thermal efficiency of collector increases by an increase in the porosity of the absorber. This improvement may be due to an increase in heat transfer surface area within the porous medium at higher air mass flux which yields a higher heat transfer coefficient. The absorber with lower porosity shows a better thermal efficiency at lower air mass flux because the air flows in the shorter path through the outlet air channel and may not able to cool the absorber effectively. In the minimum air flow rate، absorber efficiency with porosity 0. 0177 & 0. 0314 are 0. 31 & 0. 29 respectively whereas، at the maximum flow، efficiency shows an enormous change of 0. 83 and 0. 88 respectively. This solar air heater can be used for drying agricultural products، and etc.