Ultra-thin perforated unglazed solar air collector for enhanced thermal efficiency and operational performance: Experimental and numerical analysis

This study proposes a compact ultra-thin perforated unglazed solar air collector (UPSAC) which could make full use of impinging jet for enhanced heat transfer, addressing efficiency limitations and usage restrictions of conventional unglazed solar air collectors. This paper experimentally investigates the temperature distribution and thermal efficiency of the UPSAC under various radiation intensities, mass flow rates, and ambient temperatures using an indoor solar simulator system. The proposed system can achieve a peak thermal efficiency of 75.05 % (average efficiency of 59.49 %) at 400 W/m2 and 15 °C, outperforming most of the existing unglazed systems. The back air intake mode, where microjets can directly impact the absorber plate, resulted in a 33.46 % reduction in absorber temperature and a 39.05 % increase in the outlet temperature when compared to the front air intake mode. And further numerical simulations explain the improvement for better thermal uniformity under the back air intake mode. Economically and ecologically, the UPSAC system can achieve an energy payback period of 0.53 years and an annual carbon reduction of 332.70 kg. The UPSAC has the potential to serve as an innovative building envelope, providing auxiliary heating during winter and thermal insulation during summer, thereby reducing energy consumption.