Performance Analysis Of Solar Air Heater By Extended Heat Transfer Surfaces

摘要

The power from the sun intercepted by the earth is approximately 1.8 x 10 MW, which is many thousands of times larger than the present consumption rate on the earth of all commercial energy sources. Thus, in principle, solar energy could supply all the present and future energy needs of the world on a continuing basis. This makes it one of the most promising of the unconventional energy sources. In this study, the effect of longitudinal fins on heat absorbing media in air type solar collector is studied experimentally. In the solar air heater, the value of the heat transfer coefficient between the absorber plate and the air is low and this result in a lower efficiency ranging 40% to 50%, to overcome this problem, the surfaces are sometimes roughened or longitudinal fins are provided in the air flow passages. The addition of continuous longitudinal fins to the upper or bottom side of the absorber plate improves the heat transfer rate. This is desirable because it increases the overall efficiency of the air heater. Heat transfer is strongly base upon the area of contact of sun radiations, by using this criteria the maximum total radiation is collected and is used to heat the air by solar energy. By changing the collector tilt angle for at least three positions (as above 5"C and 10"C to the latitude angle) and checked the performance of the air heater, also the effect of varying air mass flow rate on the heat transfer is studied. It is found that effective heat transfer coefficient is maximum for the smallest pitch of the longitudinal fins, in addition the friction factor and pressure drops are found lowest with largest Reynolds number.