A theoretical investigation of the optical properties of metal nanoparticles in water for photo thermal conversion enhancement

Highlights: • We simulate the absorption and scattering of solid metal nanoparticles in water. • The results agree well with available experimental results in literature. • Despite low efficiency, aluminum absorb across a large wavelength range in the VIS. • Combining materials and geometries can yield wide range, high efficiency absorption. - Abstract: Nanofluids are used in photo thermal absorbers such as direct absorption solar collectors (DASC) to improve the absorption and heat transfer. A range of experimental studies have investigated the photo thermal conversion in nanofluids based on metal nanoparticles. The photo thermal conversion efficiency depends mainly on the ability of the metal nanoparticle based nanofluid to absorb light which in turn is governed by the particle localized surface plasmon resonance (LSPR). In this article we investigate the optical properties of metal nanoparticles in water, and based on this we judge their suitability for use in water based nanofluids. We simulate the optical properties and provide an overview of the absorption, scattering and extinction properties of solid and spherical aluminum, silver, copper and gold nanoparticles suspended in water. We study nanoparticle diameters between 20 and 140 nm for the wavelength range 300–1350 nm (200–1250 nm for aluminum). We compare our simulation results with the available experimental results presented in the literature, and find good agreement.