Experimental investigation of a double pass converging finned wire mesh packed bed solar air heater

摘要

A double pass converging finned wire mesh packed bed solar air heater design is investigated experimentally. Double (Counter) pass of air is provided by forcing the air first through an upper channel which is formed between the lower glass cover and the absorber plate, then through the lower channel created between the absorber and the back plates. Whereas, solar air heater design consists of two glass covers on the top and converging fins in the lower channel. The double glazing reduces the thermal losses to surrounding while the converging fins strengthen the convective heat transfer to the air by increasing heat transfer area and the velocity of the air at a given mass flow rate. Periodic converging sections are provided in the lower channel by utilizing sixteen numbers of fins attached at an angle of about 11 degrees to the bottom and top of the absorber and back plates, respectively. In addition to the finned channel, ten layers of wiremesh screens confer 96% channel porosity in the second channel. Moreover, wire mesh offers high heat transfer area to the exiting jet of the air from the converging region as well as provides thermal energy storage. The maximum thermal and thermohydraulic efficiencies of the solar air heater are obtained as 93% and 80%, respectively, at a mass flow rate of 0.03 kg/s and about 0.023 kg/s, respectively. The best output of the solar air heater is the hot air at a temperature of 55 degrees C corresponding to the mass flow rate of 0.01 kg/s and solar radiation of about 823 W/m(2).