Numerical and experimental study of perforated-ring inserts for water-cooled tube heat transfer

Thermal losses in absorber tubes constrain the efficiency of water-cooled photovoltaic-thermal systems. This work presents an absorber tube fitted with perforated-ring inserts, coupling high-resolution Computational Fluid Dynamics (CFD) optimization with experimental thermohydraulic testing. CFD studies at a constant heat flux of 1000 W/m 2 and Reynolds numbers from 897 to 6505 were used to optimize perforation shape (circular, square, triangular), perforation number (3–7), ring inner diameter (3.1–7.1 mm), and ring arrangement (2–6 rings). The CFD-evaluated ring insert, including (circular geometry, 6 perforations per ring, 7.1 mm ring inner diameter, and 5 rings), was manufactured and experimentally evaluated. The results show the selected design increases the Thermal–Hydraulic Performance Factor (THPF) by 77.1%, demonstrating a marked enhancement in heat transfer performance. Experimental results showed good agreement with CFD simulations, with deviations limited to ± 3%. These results validate the use of perforated-ring inserts as an effective passive strategy to improve absorber-tube cooling in advanced PVT applications.