Enhancing thermal efficiency of parabolic trough collectors using SiO2 nanofluids: a comparative study of particle size impact on solar energy harvesting

Solar energy technologies, particularly Parabolic Trough Solar Collectors (PTSCs), are crucial for efficient and scalable thermal applications in Concentrated Solar Power (CSP) plants. This study investigates the thermal efficiency of PTSCs utilizing silicon dioxide (SiO2) nanofluids with varying particle sizes (20 nm, 50 nm, and 100 nm) compared to deionized (DI) water as the heat transfer fluid (HTF). The objective is to enhance PTSC performance by improving the HTF's thermal properties by adding SiO2 nanoparticles. SiO2 nanofluids were synthesized using the sol-gel method and characterized for thermal conductivity, viscosity, and specific heat capacity. _The novelty of this study lies in the comprehensive analysis of the effects of nanoparticle size on PTSC efficiency, which offers practical insights for optimizing solar thermal systems. Experimental setups measured PTSC thermal efficiency under varying solar irradiation and ambient temperature conditions. The results showed a significant improvement in thermal efficiency when using SiO2 nanofluids, with the 20 nm nanoparticles exhibiting the highest enhancement of approximately 26% over DI water. The 50 nm and 100 nm nanoparticles showed 21% and 17% improvements, respectively. The increased efficiency is attributed to smaller nanoparticles' higher surface area-to-volume ratio, which enhances thermal conductivity and reduces boundary layer thickness. Additionally, thermal conductivity increases with temperature and decreases with nanoparticle size, while specific heat capacity decreases with temperature and nanoparticle size. SiO2 nanofluids, particularly those with smaller nanoparticles, significantly enhance the thermal performance of PTSCs. This study highlights the potential of nanofluids in solar thermal applications and provides a basis for further research on the long-term stability and economic viability of nanofluid-based HTFs.