Enhancing the thermal performance of an evacuated tube solar collector using CuO nanofluids

With the growing adoption of Evacuated Tube Solar Collectors (ETSCs), enhancing their thermal performance remains a critical challenge. Nanofluids have shown strong potential to enhance heat transfer, yet the optimal nanoparticle input parameters for maximizing collector efficiency remain poorly understood. This study investigates the use of CuO/50:50 ethylene glycol–water (EG–water) nanofluids to improve heat transfer and thermal efficiency in ETSCs through a novel and comprehensive experimental, computational and parametric optimization approach. Baseline experiments with 50:50 EG–water provide validation for a Computational Fluid Dynamics (CFD) model, which is then simulated with CuO nanofluids to investigate how variations in Reynolds number, nanoparticle volume concentration and irradiance affect ETSC thermal performance. The results demonstrate that a 5% CuO nanoparticle volume concentration enhances the Nusselt number by 34% and improves collector thermal efficiency by 13.5%, albeit with a 21% increase in skin friction coefficient. The optimal operating conditions occur at Re = 850, ϕ = 5%, I = 1000 W/m2 and T 1 = 268 K, yielding a high Nusselt number of 62.6 and a low skin friction coefficient of 0.0359. These findings demonstrate the strong potential of employing CuO nanofluids in ETSCs to enhance their thermal performance.