Heat transfer enhancement of high temperature thermal energy storage using metal foams and expanded graphite

Latent heat storage (LHS) can theoretically provide large heat storage density and significantly reduce the storage material volume by using the material’s fusion heat, Δh_m. Phase change materials (PCMs) commonly suffer from low thermal conductivities, being around 0.4 W m⁻¹ K⁻¹ for inorganic salts, which prolong the charging and discharging period. The problem of low thermal conductivity is a major issue that needs to be addressed for high temperature thermal energy storage systems. Since porous materials have high thermal conductivities and high surface areas, they can be used to form composites with PCMs to significantly enhance heat transfer. In this paper, the feasibility of using metal foams and expanded graphite to enhance the heat transfer capability of PCMs in high temperature thermal energy storage systems is investigated. The results show that heat transfer can be significantly enhanced by both metal foams and expanded graphite, thereby reducing the charging and discharging period. Furthermore, the overall performance of metal foams is superior to that of expanded graphite.