Thermal energy storage in supercooled salt mixtures

Abstract

Mixtures of the two salts NaC 2H 3O 2.3H 2O and Na 2S 2O 3.5H 2O have been found to form supercooled melts which do not crystallize spontaneously even at temperatures below −10°C. The hydrated salts form a eutectic at a mole fraction of Na 2S 2O 3.5H 2O of 0.585 with a melting temperature of 40.8°C, and crystallization of the mixture by seeding results in a temperature rise to about 40°C even if the initial temperature was −20°C or below. The thermal energy storage capacity for supercooled 3:2, 1:1 and 2:3 molar mixtures of NaC 2H 3O 2.3H 2O and Na 2S 2O 3.5H 2O have been determined as a function of temperature, and a maximum storage capacity of 224 kJ kg −1 was observed for the 3:2 mixture at 39°C. The advantages of these supercooled salt mixtures as thermal energy storage media are discussed.