Thermal Performance Investigation of Single-Pass Tubular Solar Air Heater for Different Duct Heights

Solar air heaters play a significant role in addressing global food loss challenges caused by overproduction, underproduction, limited availability, and inefficiencies in distribution and supply chains. These systems are widely utilized for drying applications, industrial heating, and various thermal energy processes. This study focuses on a comparative experimental analysis of single-pass tubular solar air heater (SP-TSAH) and flat plate solar air heater (FP-SAH) designs. It investigates the effect of four different duct heights: 60, 70, 80, and 90 mm, under varying air mass flow rates of 0.004, 0.007, and 0.01 kg/s, aiming to determine the most effective duct height based on thermal efficiency and outlet air temperature. The experiments, conducted between April and May 2024, involved tubular absorbers with a diameter of 38 mm and a pitch of 43 mm. Results revealed that the single-pass tubular solar air heater design achieved the highest outlet temperature of 86.7°C and an average temperature of 73.8°C at a duct height of 60 mm with an airflow rate of 0.004 kg/s. At a higher airflow rate of 0.01 kg/s, the same configuration yielded peak and average thermal efficiencies of 42.6% and 35.8%, respectively. In contrast, the flat plate solar air heaters reached maximum and average efficiencies of 37.2% and 29.6% at the same duct height. While the 90 mm duct height showed a notable efficiency improvement of 59.5% at the lowest airflow rate, the 60 mm configuration consistently offered the best thermal performance across both solar air heater types regarding outlet temperature and energy efficiency.