Optical properties of solar-absorbing oxide particles suspended in a molten salt heat transfer fluid

Abstract

The optical absorption properties of a high temperature molten salt heat transfer fluid were measured from 0.35 to 2.5 μm using both hemispherical transmission and reflection techniques. This fluid has application as a direct-absorbing working fluid in a high temperature central receiver solar energy facility. To enhance its solar absorption, particulate metallic oxides of Co or Cu were introduced into the fluid. Absorption spectra of these oxide particle suspensions in the molten salt were determined as a function of dopant concentration ranging from 0 to 0.1 wt% metal nitrate added to the molten salt. The solar-averaged absorption in a fixed layer thickness was calculated for various concentrations of the fluid-particle mixtures. The fluid without oxide particles absorbs approximately 8 per cent of the solar spectrum per cm of path length. Addition of 0.1 wt% of Co(NO 3) 2·6H 2O increases this absorption to approximately 90 per cent per cm.