Numerical and experimental investigation of a mini-concentrator based solar air heating system

The Compound Parabolic Concentrator (CPC) has been widely utilized in medium and low temperature solar applications. The FM-CPC, a miniature concentrator designed for full-sunlight collection, offers notable benefits including full-sunlight concentration, a compact structure, and low implementation costs. Consequently, a solar air heating system was constructed by integrating the FM-CPC with an evacuated tube of the expansion joint type. An integrated simulation model, encompassing the process from radiation concentration to heat collection, was developed using the Finite Volume Method (FVM) and its reliability was subsequently validated via outdoor experimental testing. The results indicate a maximum absolute error of 1.99 °C for the outlet temperature and 5.3% for the thermal efficiency between the simulated and experimental data, thereby confirming the reliability of the simulation model. Furthermore, leveraging the validated model, the impact of air velocity on collection efficiency was examined, elucidating how the expansion joint structure governs the airflow regime and convective heat transfer intensity. The researches show that at 0.7 m/s, the average convective heat transfer coefficient reached 4.77 W/(m2·°C), and the thermal efficiency of the system reached 53.5%. The expansion joint structure effectively intensified local turbulence, thereby enhancing the convective heat transfer coefficients across the wall surfaces.