Experimental Investigation of Solar Air Heaters with Different Absorber Plates

Two solar air heaters are experimentally investigated in outdoor conditions in Amman, Jordan. One heater is integrated with a selective-coated absorber plate, and the other is integrated with a black-painted absorber plate. The two types of absorber plates are obtained from local solar water heater manufacturers. The two air heaters are tested on a clear sunny day. Contrary to what is reported in the literature, the results show that the air heater with a black-painted absorber plate has a better thermal performance than the air heater with a selective-coated absorber plate. The daily average efficiencies are 45.7 % and 42.2 % for solar air heaters with black-painted and selective-coated absorber plates, respectively. This is attributed to the fact that the emissivity of black-painted surfaces is much larger than the emissivity of the top and bottom of the selective-coating system, resulting in higher efficiency and a higher amount of energy being transferred to moving air in the solar heater with black painting on the absorber plate. In addition, the black-painted absorber is painted from top (facing sun) and bottom (in contact with moving air) sides, while the selective-coated absorber has coating only on top side and the bottom side is left without coating.