Heat transfer augmentation in solar air heater using delta-shaped obstacles mounted on the absorber plate

An experimental investigation has been carried out to study the heat transfer augmentations by using delta-shaped obstacles mounted on the absorber surface of an air heater duct with an aspect ratio 6:1 resembling the conditions close to solar air heaters. The experiment encompasses the Reynolds number ranging from 3400 to 28,000, obstacle longitudinal pitch (P-l/e) varying from 3 2 to 11/2 and relative obstacle height (e/H) varying from 0.50 to 0.75, while relative obstacle transverse pitch (P-t/b) = 7/3 and the angle of attack of flow on obstacle = 90(circle) are kept constant during the whole experimentation. The maximum heat transfer augmented by using an obstacle-mounted duct was 3.6 times higher compared with a smooth duct under similar geometrical and flow conditions. A numerical analysis using FLUENT software has also been done for further observation of heat transfer behaviour near the obstacles.