Latent Thermal Storage Using Sodium Hydroxide -Based Molten Salts: Demonstration of 30kWh-scale storage units

The present paper describes experimental results of the operation of 30kWh-scale molten salt latent thermal storage units using a eutectic of sodium hydroxide and sodium nitrate which is suitable for thermal storage around 250°C. The main problems of molten salt as a latent thermal storage material are its large volume change on phase change and its feasibility for use with structural materials. Using mild steel, two different U-tube storage units were built for testing heat transfer performance, structural feasibility and compatibility with the molten salt. From thorough and comprehensive material analyses after 1, 000 melting-freezing (charge-discharge) cycle tests, it was concluded that the present storage unit structure (horizontal U-tube and multiple-path type) and material selection were fairly feasible for a latent thermal storage unit with this particular molten salt.