A perspective on Phase Change Material encapsulation: Guidance for encapsulation design methodology from low to high-temperature thermal energy storage applications

Encapsulation is one of the strategies that researchers have explored to improve the thermal performance of Thermal Energy Storage systems. Encapsulation can tackle some of the challenges that are currently hindering Phase Change Material utilisation. Encapsulation provides a protective layer that avoids the PCM from being in contact with the environment (in some cases the chemical stability of the PCM is affected by the environmental conditions), prevents corrosion of TES system components, and helps to control the volume change during the phase change. Although in the literature there are reviews about PCM encapsulation, no guidance about how to properly select one depending on the final application can be found. In this paper, encapsulation has been categorized depending on the nature of the shell material into ceramic, metallic or polymeric capsules, and their encapsulation method into macro, micro or nano encapsulation techniques. Then, a thorough review of the different encapsulation techniques of PCMs, from low to high-temperature applications, has been carried out. The assessment of TES encapsulation methods has been used as the starting point for the creation of a flowchart that aims to give the research community a path to properly select and validate the encapsulation material and method depending on different application variables such as working temperature and PCM nature.