Numerical Study on the Thermal and Hydraulic Behavior in a Solar Air Collector Featuring Varying Baffle Lengths

Improved thermal performance in solar air collectors (SACs) can be achieved by incorporating baffles under the absorber surface. This study presents a detailed numerical study of a helical SAC to investigate the effect of baffle length and operating conditions on thermal–hydraulic performance. Three baffle lengths d ranges from 375 to 699 mm are analyzed. The computational model is developed in ANSYS Fluent 2021, including thermal radiation via the Discrete Ordinates model. A mesh independence analysis is performed to ensure reliability. Moreover, the model is validated against experimental data and empirical correlations, showing mean deviations of 4.6% for outlet temperature, 5.8% for the Nusselt number, and 1.8% for the friction factor. The results showed that geometry with d = 669 mm enhances turbulence, increases air residence time, and maximizes heat transfer. Additionally, at a mass flow rate (MFR) of 0.0175 kg/s, the outlet temperature reaches 57.2°C, and the pressure drop is reduced to 1000 Pa compared with 1532.9 Pa for d = 375 mm. Furthermore, thermal efficiency rises with MFR, reaching 56.3% for the longest baffles. The thermohydraulic performance parameter of d = 669 mm ranges from 1.275 to 1.37 for Re between 8400 and 14,700, indicating superior thermal–hydraulic performance.