Experimental comparison of thermal efficiency of two different types of air solar collectors

In the Black Sea region, due to the low number of sunny days and the short duration of sunlight, there is a need for the development of solar collectors that can efficiently capture sunlight and convert it into heat. In this thesis study, air-type solar collectors with flat and partially cylindrical channel designs were manufactured in order to compare their thermal efficiencies. Experiments were conducted at four different air velocities to determine the effect of channel geometry on the amount of absorbed energy and collector efficiency. With the increase in air velocity, the collector outlet temperature has decreased. For the partially cylindrical channel geometry, the outlet temperature of the air is on average 13% higher than that of the flat channel geometry at four applied velocities. As the air velocity increases, the outlet temperature of the partially cylindrical collector approaches that of the flat collector. When the radiation value is high, the difference between the outlet temperatures of the partially cylindrical and flat collector with increasing air velocity is maximum at 19.7%, whereas as the radiation value decreases, this difference decreases to 3%. The thermal efficiencies of flat collectors vary according to radiation values. The lowest thermal efficiency is approximately 35% at 0.5 m/s, while the highest thermal efficiency is calculated to be 85% at an air velocity of 3 m/s. Conversely, for partially cylindrical collectors, the lowest thermal efficiency is realized at approximately 34% at 0.5 m/s, with the highest thermal efficiency at 83% at an air velocity of 3 m/s. At an air velocity of 2 m/s, the partially cylindrical collector is on average 8% more efficient than the flat collector, while at other velocities, the flat collector is on average 2% more efficient than the partially cylindrical collector. The lowest useful energy output is calculated to be an average of 319 W (flat) and 385 W (partially cylindrical) at an air velocity of 0.5 m/s, while the maximum useful energy output is calculated to be an average of 516 W (flat) and 656 W (partially cylindrical) at an air velocity of 3 m/s. The use of partially cylindrical cross-sectional air-type solar collectors is more suitable for meeting high-temperature demand compared to flat collectors