Experimental Investigation of Natural Convection from Pinned Plate Solar Absorber

Solar collector consists of a solar absorber which absorbs heat from short wave solar radiation and transfers the heat to the working fluid for storage or use. Instead of merely a normal flat plate, staggered pinned plate absorbers with different surface roughness – 2 mm, 3mm and 4 mm height are introduced in this project. The main interest is on the effect of turbulence of absorber plates on the natural convection heat transfer process of the air heating solar collectors. The paper investigates the effect of inclination angle and absorber types on the heat transfer, solar insolation, air outlet temperature and velocity, etc. It involves series of experimental works conducted on 4 solar collector test rigs simultaneously that were ran at 10°, 30°, 50°, 70° and 90° inclination angles. For each configuration, the experiments are repeated for four consecutive days. Readings were recorded at two hours intervals from 8am until 6pm for data collection of the investigated parameters. Solar insolation is higher for system at lower inclination angle yet for convective heat transfer coefficient; it is optimum at 50° inclination angle which best at 45°. Solar collectors with pinned plate absorbers are noticeably provides better outlet temperature and heat transfer rate than a normal flat plate absorber where the 2mm is the best pursued by 3mm and 4mm pinned absorbers. The boundary layer is disturbed in channel with pinned plate thus the effect of added turbulent enhance the heat transfer. The overall system at all configurations possesses a mixed convection, turbulent flow behavior thus invalid the claims of natural convection.