Effect of the base angle of an isosceles obtuse-angled trapezoidal duct of a solar air heater on fluid flow and thermal characteristics – an experimental and computational investigation

This article reports the fluid flow and thermal traits of an isosceles obtuse-angled trapezoidal solar air heater duct. Six duct variants are obtained by altering duct base angle (θ). The advantage of adopting an obtuse-angled trapezoidal duct over the other geometries is that three surfaces (top and two sides) of the duct can be exposed to solar radiation. Experiments are conducted for the duct with θ = 90°. Further investigations at other base angles are conducted with 3-D computational model. Based on the orientation of sun and time during a day, the intensity of solar radiation is not-steady. Towards this, three heat-flux variants are imposed on absorber plates. They are: top plate subjected to steady heat-flux; top plate subjected to unsteady heat-flux; three plates of duct subjected to unsteady heat-flux. By adopting obtuse-angled ducts (at θ = 150°) than rectangular duct, Nu_avg and ΔT_bulk can be increased by 94.3 and 103 %, respectively, at afternoon.