An experimental investigation of composite phase change materials of ternary nitrate and expanded graphite for medium-temperature thermal energy storage

Utilization of KNO3-LiNO3-Ca(NO3)(2)/expanded graphite (EG) as composite phase change materials (PCMs) for medium-temperature thermal energy storage was investigated in this paper. The thermo-physical properties of KNO3-LiNO3-Ca(NO3)(2) with different proportions were investigated. EG was employed as an additive to enhance thermal conductivity of PCMs as it has high thermal conductivity and excellent thermo-chemical stability. Thermo-physical parameters such as phase transition temperature, latent heat of fusion, thermal conductivity and decomposition temperature were measured experimentally. The results showed that the phase transition temperature of this ternary nitrate (60.2 wt% KNO3-29.9 wt% LiNO3-9.9 wt% Ca(NO3)(2)) is lower than that of Solar Salt and Hitec Salt. The composites with more EG have higher thermal conductivity. However, the addition of EG reduces their decomposition temperature. Furthermore, the corrosion experiments with six types of metal samples embedded in liquid ternary nitrate at 480 degrees C for 1500 h were delivered to investigate their chemical stability. Moreover, the PCMs have good long-term high temperature stability during the process. The results of this work confirmed the great potentials of KNO3-LiNO3-Ca(NO3)(2)/EG as composite PCMs that can be applied for industrial waste heat energy recovery applications, the solar power generation system and medium-temperature thermal energy storage.