Assessment of the energy storage potential of NaNO3 aided by alumina nanoparticles using discharge kinetics

Abstract

Sodium nitrate (NaNO₃) is a phase change material (PCM) with high melting temperature and latent heat but has a relatively lower thermal conductivity. Alumina (Al₂O₃) nanoparticles were added to NaNO₃ using ball milling to prepare Al₂O₃-NaNO₃ nanocomposite. The effect of alumina nanoparticle concentration (up to 2 wt%) on phase change transition characteristics and thermal conductivity was investigated. Experiments on the discharge of stored latent heat were performed for NaNO₃ and Al₂O₃-NaNO₃ nanocomposite with well-agitated Therminol-55 and air under forced convection as the two heat transfer fluids. Enhancements in thermal conductivity and specific heat were observed with Al₂O₃ nanoparticles’ addition. The loss in latent heat was attributed to the solid nanoparticles present in the nanocomposite. The Al₂O₃-NaNO₃ nanocomposite containing Al₂O₃ at the concentration of 1 wt% resulted in a 15 % reduction in solidification time, 11.9 % & 25.1 % enhancements in the PCM side heat transfer coefficient for latent heat recovery using Therminol-55 and air as the coolants, respectively. The corresponding enhancements in the PCM side heat transfer coefficient for solid phase sensible heat recovery using Therminol-55 and air as the coolants were 21.4 % & 198 %, respectively. These results indicate that Al₂O₃-NaNO₃ nanocomposite can offer significant improvement in the heat transfer performance for about 500 cycles before the latent heat loss becomes significant.