Effect of Nanoparticle Size on the Stability and Efficiency of Silver Nanofluids in Solar Thermal Systems

Silver nanofluids have emerged as promising candidates for advanced thermal and optical applications due to their excellent thermal conductivity and tunable optical properties. However, the influence of nanoparticle size on these properties remains inadequately explored. The objective is to determine the optimal nanoparticle size for enhanced thermal conductivity (TC), heat transfer coefficient (HTC), and optical absorption. Nanofluids were prepared and tested under controlled conditions using a transient hot-wire apparatus for TC and a closed-loop system for HTC. Results showed that 30 nm nanoparticles (nps) exhibited the highest TC (0.75 W/mK) and HTC (420 W/m² K), outperforming larger particles by 15 and 10%, respectively. Conversely, 50 nm nanoparticles demonstrated superior optical absorption efficiency due to red-shifted SPR peaks. The study underscores the importance of size optimization for specific applications and highlights RSM as a powerful tool for predicting optimal conditions. These findings pave the way for the tailored design of nanofluids in energy systems, with potential future research extending to hybrid nanofluids and advanced thermal systems.