Nitrate based nanocomposite thermal storage materials: Understanding the enhancement of thermophysical properties in thermal energy storage

Abstract

Molten salt is considered to be a significant medium of thermal energy storage (TES) used for concentrating solar power (CSP). Reasonably improving its thermophysical properties can realize the efficient utilization of solar energy. To investigate the effect of nanoparticle-doped molten salt, adding two size nano-alumina (NA, NA1 and NA2) with different content to solar salt (SS, with 60:40 ratio) by high temperature melting method. The using temperature zone had been broadened. For the same system, the specific heat (cp) of the solid was higher than that of the liquid. The maximum cp values in liquid of both systems appeared at the NA content of 0.5 wt%, corresponding to 1.71 J g−1K−1 and 1.84 J g−1K−1, respectively, which increased by 9.62% and 17.95% compared with the pure SS. Due to the high specific surface areas of NA1 and NA2, which were 151.3 m2 g−1 and 177.04 m2 g−1, respectively. And the higher surface tension (γ) of NA2-SS, which had a higher surface energy to improve the cp nanocomposites. The thermal conductivity (λ) increased with the content of NAs, increasing by 2.27% and 4.28%, respectively when the content of two NAs was 0.5 wt%. The content of NAs had little effect on viscosity (η). As a nitrate-based nanocomposite thermal storage material, it has great application prospects in TES, owing to its high cp and λ, widened operating temperature range and reliability.