Investigation of optical properties of Ag nanoparticle aggregates for enhanced solar photothermal conversion

In solar photothermal conversion technology, nanofluids are widely regarded for their high absorptive capacity and enhanced thermal conductivity. However, nanoparticle aggregation during preparation or dispersion significantly impacts the solar energy absorption properties of these fluids. This study investigates the optical properties of Ag nanoparticle aggregates dispersed in water, using the finite element method to model and compare the aggregates with independently dispersed nanoparticles. The influence of both the number of nanoparticles and their interparticle spacing on the optical properties of nanoparticle aggregates is further investigated. The results show that nanoparticle aggregates exhibit broader absorption bands and enhanced solar energy absorption, particularly with reduced nanoparticle spacing and increased aggregation. Furthermore, the study reveals the mechanisms behind these enhancements through analyses of scattering diagrams, electric field distributions, and resistive heat patterns. At a volume fraction of 10^-6 and a collector depth of 2 cm, the solar weighted absorption coefficient of the aggregates increased by 12.53% compared to independently dispersed nanoparticles. These findings suggest that nanoparticle aggregates hold significant potential for improving solar thermal conversion efficiency in direct absorption solar collectors.