Experimental investigation of thermal performance of a solar air heater with perforated obstacles on an absorber plate

The thermal performance of solar air heaters can be significantly enhanced by modifying their design to overcome the limitations posed by the thermo-physical properties of air. In this experimental study, the impact of perforated obstacles with varying hole diameters (2, 3, 4, 5, and 6 cm) placed on the absorber plate of a solar air heater was investigated. The primary objective of this study is to experimentally assess the influence of different perforated obstacle configurations on thermal efficiency, effective efficiency, and pressure drop in a solar air heater, thereby identifying the most effective design for optimizing overall system performance. Tests were conducted in Fez city under two mass flow rates (0.025 and 0.039 kg/s). The results indicated a substantial improvement in thermal efficiency and heat exchange due to the turbulence created by the obstacles. At the higher flow rate (0.039 kg/s), the collector under Type V obstacles (hole diameter: 2 cm) achieved a maximum thermal efficiency of 85%, whereas at the lower flow rate (0.025 kg/s), the same obstacle type yielded a thermal efficiency of 69.5%. These values represent increases of 36% and 33%, respectively, compared to a simple collector. Effective efficiency, which considers the pressure drop in the channel, was also analyzed. At 0.039 kg/s, Type V obstacles exhibited an effective efficiency of 36%, while at 0.025 kg/s, the effective efficiency was 33.85%. Despite the increased pressure drop with smaller hole sizes, the enhanced heat transfer and temperature difference ensured an overall improvement in system performance. This study demonstrates that perforated obstacles are a viable method to optimize heat transfer and airflow dynamics in solar air heaters.