A review of performance investigation and enhancement of shell and tube thermal energy storage device containing molten salt based phase change materials for medium and high temperature applications

Phase change material (PCM) based latent heat thermal energy storage (LHTES) has a significant role to play in conserving and efficient utilising energy, dealing with mismatch between demand and supply, and enhancing performance of energy systems. Successful utilization of a PCM usually depends on the development of the device which provides encapsulation for PCM and container for heat transfer fluid (HTF). Shell and tube type of LHTES device is considered as one of the most popular devices for commercial and industrial applications due to its simple design and high specific heat transfer areas. However, the performance of shell and tube device is limited by the poor thermal conductivity and some other inherent issues of PCMs and HTFs employed. This paper reviews various heat transfer and performance enhancement techniques proposed in the literature with the focus on the features and implementation of those techniques on the shell and tube device containing molten salt based PCMs for medium and high temperature thermal energy storage applications. The aims are to provide necessary information on limitations and design considerations of each technique and to promote further research on this type of device. In the paper, the current state of the art development in molten salt based PCMs that suitable for medium and high temperature applications with range over 200–1000 °C is first reviewed. And then, the experimental and numerical investigations on the heat transfer performance of shell and tube LHTES device containing molten salt PCMs are reviewed. Further, emphasis of the work has been placed on the performance enhancement techniques from the salt side such as the use of fins and extended surface, employing cascade salts, impregnation of porous matrix, and using the form-stable composite PCMs. The enhanced techniques from the HTF side by using for example different tube structures to increase heat transfer surface area and internals fins to create the turbulence are also discussed. Finally, the applications of such molten salt based devices in power generation are highlighted.