Performance enhancement of PV/T systems through geometric modification of spiral–tube absorbers: a 3D CFD analysis

The growing global energy demand and the temperature-dependent performance degradation of photovoltaic (PV) systems have intensified the need for advanced thermal management strategies capable of simultaneously improving electrical output and heat recovery. In this study, a high-fidelity three-dimensional computational fluid dynamics (CFD) model is developed to investigate the thermo-hydraulic behavior of a photovoltaic–thermal (PV/T) module integrated with spiral-tube heat exchangers and filled with Ternary nanofluid coolants (Cu-Al 2 O 3 -ZnO). The geometric parameters considered are the length of the cooling tubes (S = 3–6 m), the number of bends (N = 5–11), the flow arrangement (single and double path), the Reynolds number (200–800), and the temperature of the coolant (307–315 K). The results indicate that the optimal configuration occurs at S = 6 m and N = 5. Increasing the spacing S from 3 m to 6 m reduces the panel bottom surface temperature and improves thermal performance, with temperature reductions of 0.53%, 0.4%, 0.37%, and 0.34% for N = 5, 7, 9, and 11, respectively. The highest thermal efficiency is obtained at S = 6 m, where efficiency increases from about 4% (S = 3 m) to nearly 6%, corresponding to improvements of 55.8%, 47.6%, 46.3%, and 42.5% for N = 5, 7, 9, and 11. The double–path configuration further enhances performance, increasing thermal efficiency from 6.62% to 9.14% (about 38% improvement). Reynolds number also significantly affects thermal behavior; thermal efficiency rises from 5.5% at Re = 200 to 10.64% at Re = 800, while electrical efficiency changes slightly from 10% to 10.26%. In addition, lowering the inlet temperature from 315 K to 307 K increases thermal efficiency by about 50%. Overall, the double–path PV/T system with S = 6 m and N = 5 provides the best thermal performance and the most uniform panel temperature. Co-optimizing spiral tube geometry and nanofluid properties effectively creates high-performance PV/T modules, ensuring superior thermal management and longevity.