Experimental and Numerical Evaluation of the Impact of Hemi‐Circular Fins Number on Thermal Performances of a Double‐Pass Solar Air Heater

ABSTRACT Solar air heaters often suffer from limited thermal performance due to weak turbulence and low convective heat transfer inside the duct. To overcome this limitation, an experimental and numerical investigation was carried out on a double‐pass solar air heater (DPSAH). The system was equipped with hemi‐circular fins (HCF) attached to the absorber plate to increase the heat‐transfer surface and enhance flow mixing. Several configurations were analyzed and compared with a conventional SAH. Experimental tests were performed under real climatic conditions in the Gabès region, Tunisia. In addition, a numerical model was developed using ANSYS Fluent to simulate heat transfer and fluid‐flow behavior. Furthermore, the k–ε turbulence model and the discrete ordinates (DO) radiation model were adopted. Thus, the numerical predictions showed good agreement with the experimental results with an average deviation of 4%. Subsequently, five configurations, arranged as 3 × 3, 4 × 3, 3 × 4, 4 × 4, and 4 × 5, were investigated. The results demonstrated that the maximum outlet air temperature reached 80°C for the configuration 4 × 5 fins, while it remained below 73.5°C for the smooth duct. The thermal efficiency increased from 68% for the smooth duct to a maximum of 81% for the 4 × 5 configuration. The thermohydraulic efficiency also improved, reaching 76.1% in the configuration with 4 × 5 fins compared to 67.7% for the smooth case. However, the pressure drop increased to 325 Pa for the 4 × 5 arrangement, while it remained below 4 Pa for the smooth duct. Ultimately, HCF fins provide a simple and effective enhancement of DPSAH efficiency.