Recent advances on thermal conductivity enhancement of phase change materials for energy storage system: A review

Phase change materials (PCMs) possess very high heat storage capacity and are capable of maintaining a constant temperature during phase change, which makes them most prominent candidates for solar energy storage systems, heating, and cooling systems. The low thermal conductivity of PCM results in slow heat transfer and low heat storage and release rate, which is a major drawback for their practical applications. This review focuses on the enhancement of thermal conductivity by the introduction of highly thermally conductive metallic and carbon-based nanoparticles, metallic foams, expanded graphite and encapsulation of PCM. Carbon-based nanoparticles including carbon fiber, carbon nanotubes, and graphene show better performance than metal-based nanoparticles due to lower density and better dispersion. The thermal conductivity of the composite phase change material (CPCM) depends on the shape, size, aspect ratio and concentration of nanoparticles. The thermal conductivity of CPCM increases by increasing concentration and aspect ratio of the additive. Metallic foam and expanded graphite possess high thermal conductivity and good thermo-physical properties and also prevent leakage of PCM during phase change. The porosity of foam has a huge impact on thermal conductivity than pore size. Encapsulated PCM has well-enhanced thermal conductivity and long-lifetime due to the high thermal conductive shell which also protects the PCM from direct contact with the environment.