Abstract:
In this study, the thermal performances of single-and counter-flow solar air heaters with a normal cover and with quarter-and half-perforated covers were investigated experimentally. In this work, on two of the perforated covers, the holes were made in the first quarter at the top side of the covers. As for the other two covers, half of the cover area on the top side was perforated. The hole diameter, D, was 0.3 cm. The holes in the covers had a centre-to-centre distance of 20D (6 cm) or 10D (3 cm). It was found that the efficiency of the air heater with the quarter-perforated cover was slightly higher than that of the one with the half-perforated cover for both single-and counter-flow collectors. The average efficiencies of the double-pass solar collector with 20D and 10D quarter-perforated covers were 51.38% and 54.76%, respectively, and the ones for the collector with 20D and 10D half-perforated covers were 48.21% and 51.17%, respectively, at mass flow rate of 0.032 kg/ s. At the same mass flow rate, the average efficiency of the double-pass air heater with normal cover was 50.92%.
