High temperature thermal energy storage an experimental study

Abstract
This experimental study deals with the thermal energy storage based on phase change effects of melting and vaporization in the storage medium. The phase change materials considered are chloride and fluoride salts having a melting point within the 600-1300°C temperature range. These salts are known to have extremely low thermal conductivity resulting in a substantially large heat exchanger surface embedded in the storage medium. Thermal performance enhancements of the storage systems can be obtained, however, by introducing an intermediate medium of high thermal conductivity to transfer heat from the salt to the heat exchanger. Liquid sodium Na has been selected for this purpose, on the analogy of pool boilers. The experimental results of this work have successfully demonstrated the effect of reflux evaporation - condensation heat transfer employed. It was shown that a storage system containing NaCl-Na could be operated for a prolonged time at a stable outlet working gas temperature of 780°C while the storage temperature was as high as 800°C. The factor that controlled the process of heat discharge was heat and mass transfer occurring on the NaCl-Na interface.