The micro-/nano-PCMs for thermal energy storage systems: A state of art review

With advancement in technology-nanotechnology, various thermal energy storage (TES) materials have been invented and modified with promising thermal transport properties. Solid-liquid phase change materials (PCMs) have been extensively used as TES materials for various energy applications due to their highly favourable thermal properties. The class of PCMs, organic phase change materials (OPCMs), has more potential and advantages over inorganic phase change materials (IPCMs), having high phase change enthalpy. However, OPCMs possess low thermal conductivity as well as density and suffer leakage during the melting phase. The encapsulation technologies (ie, micro and nano) of PCMs, with organic and inorganic materials, have a tendency to enhance the thermal conductivity, effective heat transfer, and leakage issues as TES materials. The encapsulation of PCMs involves several technologies to develop at both micro and nano levels, called micro-encapsulated PCMs (micro-PCM) and nano-encapsulated PCMs (nano-PCM), respectively. This study covers a wide range of preparation methods, thermal and morphological characteristics, stability, applications, and future perspective of micro-/nano-PCMs as TES materials. The potential applications, such as solar-to-thermal and electrical-to-thermal conversions, thermal management, building, textile, foam, medical industry of micro- and nano-PCMs, are reviewed critically. Finally, this review paper highlights the emerging future research paths of micro-/nano-PCMs for thermal energy storage.