Determination of the effects of using different rocks as filling materials on efficiency in air heated solar collectors

Within the scope of the study, the systems used in applications such as agricultural product drying, space and greenhouse heating, known as air solar collectors, are discussed. It is aimed to increase the thermal efficiency of air solar collectors by using different filling materials. In the studies carried out under laboratory conditions, 6 different variations, 1 unfilled and 5 different rock types (limra, marble, travertine, limestone and dolomitic limestone) were examined. An equal number (45) of rectangular prism-shaped stones measuring 5.1x5.1x2.1 cm were used. The solar collector, which is made of galvanized sheet material, has dimensions of 110×80×10 cm. Air was sent to the system with the help of a radial fan. Artificial solar radiation is provided by a simulator with 30 halogen lamps, each of which has a power of 330 W, with a radiation intensity of 1000 W/m2 and an incidence angle of 0º. In the first 2.5 hours of the experiment, the simulator and the fan worked together, then the fan worked alone for 2 more hours until the collector absorber surface temperature approached the ambient temperature. The areal flow rate of the air sent to the test system is 4.51 kg/min. It is kept constant at m2. The yields of all the filling materials used in the experiment are higher than the unfilled application. In the trials, the highest efficiency was determined with 72.4% in the application using travertine as filling material.