Fabrication of heat storage pellets composed of microencapsulated phase change material for high-temperature applications

Abstract

Latent heat storage using a metallic phase change material (PCM) is an attractive option for high-temperature thermal energy storage. However, there are serious technical barriers to applying a metallic PCM to practical applications, mainly caused by its high corrosivity. This study reports the fabrication of a pellet-type PCM composite, mainly composed of a microencapsulated metallic PCM, as a potentially viable solution to this issue. This microencapsulated PCM (MEPCM) has a core composed of Al-25 mass% Si, which acts as a PCM. Its shell is composed of Al2O3 (or a precursor of Al2O3), and grass frit was used as a sinter agent. The composites were fabricated by mixing the MEPCM with a sintering agent, pelletizing, and sintering. The PCM composites exhibited a melting point of ~577 °C and a latent heat of 108–122 J g−1. The thermal conductivities of the PCM composites were in the range of 2.16–3.20 W m−1 K−1. The cycling performance demonstrated the good durability of the composites. There were no significant changes in the shape and chemical composition of the pellets, even after 300 cycles of melting and freezing tests. These results indicate that the concept of pellet-type composites using MEPCM developed in this study will overcome the technical barriers to utilizing metallic PCMs. Thermal energy storage structures in various shapes could be fabricated via the method for fabricating PCM composites proposed in this study. This concept therefore shows substantial promise for application in high-temperature thermal energy storage systems.