Sodium Nitrate for High Temperature Latent Heat Storage

In this paper the results of material investigations of sodium nitrate (NaNO3) with a melting temperature of 306 °C as a phase change material (PCM) are presented. The thermal stability was examined by long duration oven tests. In these experiments the nitrite formation was monitored. Although some nitrite formation in the melt was detected, results show that the thermal stability of NaNO3 is sufficient for PCM applications. The compatibility of graphite foil and molten NaNO3 was also examined. Results show that the molten NaNO3 oxidizes graphite. Measurements on thermophysical properties of NaNO3 are also reported. These properties include the thermal diffusivity by the laser flash method and the heat capacity by a heat flux differential scanning calorimeter. Reliable temperature dependent thermophysical values of the density, heat capacity, diffusivity and conductivity are identified. Results show that there is a lack of consistent conductivity and diffusivity data in the solid phase.