Effect of the absorber surface roughness on the performance of a solar air collector: An experimental investigation

Solar air collectors (SAC) convert the available solar energy into useful thermal energy for different heating applications such as drying, space heating, hot water etc. The study aims to enhance the thermal performance of a flat plate SAC by modifying the absorber surface. The experimental performance of two variant SACs (a sand coated absorber to increase surface roughness and a conventional plain absorber) was compared under controlled laboratory conditions The experimental tests were performed under a solar simulator for radiation levels of 400, 600, and 800 W/m ² and variable air mass flow rate ranging from 0.01 to 0.02 kg/s/m ². Results indicated that increasing the air flow rate by 90% enhanced the thermal efficiency on a plain absorber SAC by almost 68%, and the rate of increase was higher for the sand coated absorber. SAC with the sand coated absorber provided additional surface area resulting in an increase in the effective heat transfer. The thermal efficiency of the collector was improved by up to 17% for the sand coated absorber compared to the plain absorber. The absolute thermal efficiency of the SAC varied from 19% to 41% under the different tests conditions.