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This study presents the geometrical optimization of a solar air heater. A reasonable working range of geometrical parameters: length 1-3 m, width 0.1-0.5 m, and height 0.005-0.05 m (or aspect ratio 1-20) are investigated as per general applications and installation-constraints. The effect of these geometrical parameters on thermal (heat flux and outlet air temperature) and hydraulic (air velocity, mass flow rate, pressure loss and pumping power, and Bejan number) parameters are theoretically studied. Later, a numerical investigation is carried out with an optimum geometry of SAH-duct (length 2.44 mm and width 0.3 m), for aspect ratio 4-18 and Re 3000-15000. An experimental study is also done to validate numerical results. The heat transfer and frictional loss do not show a significant change in the values for the aspect ratio 8-12.

An asymmetrically heated (only one side of the duct is heated) solar air heater duct is numerically investigated using openFOAM to study the effect of passive turbulators (suspended cylinders) installed within the boundary layer close to the absorber plate to enhance heat transfer from it. Vortex flow is created behind the suspended cylinders, which disturbs the boundary layer and causes mixing of hot stream lines near the surface with relatively cold stream away from the absorber plate. Diameter of the suspended cylinders and its distance from the absorber plate is varied to study its effect on wall temperature of absorber plate in the turbulent flow regime.

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