Heating of single nanoparticles, their assemblies and ambient medium by solar radiation

Abstract

Absorption of solar radiation by nanoparticles and their heating are applied in light-to-heat conversion, in solar thermal devices, photocatalysis, solar cells, etc. The purpose of this investigation is the modeling of the heating dynamics of single homogeneous and core–shell nanoparticles, their assemblies and surrounding medium (fluid) by solar radiation allowing to select their parameters for effective applications. The properties of homogeneous metallic (titanium Ti and aurum Au) nanoparticles and titanium core–its oxide shell (Ti–TiO2) nanoparticles with the radii in the range 25–125 nm have been investigated for the spectral interval 200–2500 nm of solar radiation. Novel temporal dependencies of the temperatures of single nanoparticles, their assemblies and ambient medium under solar irradiation have been investigated. The influence of the concentrations, sizes and other parameters of nanoparticles on dynamics and the results of solar heating have been established. Metallic Ti and core–shell Ti–TiO2 nanoparticles with the radii in the range 75–125 nm and maximal values of energetic \( q_{0} r_{0}^{2} \), \( q_{1} r_{1}^{2} \) and optical P1 ≥ 1 parameters can be used for effective absorption of solar radiation and heating of nanoparticles and nanofluids in the spectral interval 200–1100 nm in volumetric water absorber and in the spectral interval 1100–2500 nm in surface absorbing layer of water. Presented results can be used for increase in efficiency of solar absorption by nanofluids and can be applied for the development of novel working nanofluids and their heating in solar collectors. Selection of suitable nanoparticles and nanofluids for effective absorption of solar radiation and their heating includes the choice of nanoparticles structure (homogeneous, core–shell, etc.), material (metal, oxide, etc.), size (their radii, thicknesses of shells), their concentrations and the simultaneous use of appropriate values of parameters realizing effective heating of nanoparticles and surrounding medium. These results are highlighting the importance of the use of established remarkable approaches that can improve current solar thermal technologies in near future.