CFD Simulations and Experimental Investigation of a Flat-Plate Solar Air Heater at Different Positions of Inlet and Outlet

Abstract

In this study, the effects of the positions of inlet and outlet in a single-flow flat plate rectangular box active solar air heater due to convective heat transfer were designed, constructed, theoretically investigated using CFD fluid flow (fluent) software, and experimentally examined. The internal dimensions of the solar air heater are length and width of 100 cm and 50 cm, respectively, and the air gap between absorber plate and glazing glass is 9 cm. The solar air heaters are constructed with 18 mm thickness plywood, 4 mm thickness glazing glass, and 1 mm thickness aluminium sheet metal. Except for the glazing glass, other construction materials are painted black to absorb solar radiation. The positions of the inlet and outlet depend on the fraction of the width of the solar air heater. Based on the three-day average outlet temperature of the solar air heaters, solar air heater B has the highest average outlet temperature compared with other active solar air heaters and ambient air temperatures. Based on the three-day average outlet temperature of solar air heaters and ambient air temperatures, the active solar air heater B outlet temperature is 33.83 percent greater than the ambient air average temperature. The average outlet temperature of the air in passive solar air heaters increased by 17% and 4.43% compared to ambient air and active solar air heaters outlet air temperatures, respectively, due to the speed of the air in the solar air heater. The uncertainty of the instruments to measure the temperature of the air is $\pm$ 0.289°C, and the uncertainty of the solar air heater is $\pm$ 0.462°C. A higher average air outlet temperature was achieved in March at a tilt angle of 12° at a latitude of 8.89°. The negative tilt angle in May at a latitude of 8.89° indicates the south-facing orientation of solar air heaters is better. The passive solar air heater and ambient air temperature have a higher air temperature fluctuation than the active solar air collector.