Alternative Heat Transfer Enhancement Techniques for Latent Heat Thermal Energy Storage System: A Review

Various enhancement techniques are proposed in the literature to alleviate heat transfer issues arising from the low thermal conductivity of the phase change materials (PCM) in latent heat thermal energy storage systems (LHTESS). The identified techniques include employment of fins, insertion of metal structures, addition of high conductivity micro/nanoparticles, micro-encapsulation, macro-encapsulation and cascaded PCMs arrangement. However, these conventional techniques tend to reduce the storage capacity as they generally add additional components/materials into the storage medium. On the other hand, if techniques such as direct contact heat exchange, ultrasonic vibration, electrohydrodynamics and movable PCM are employed, the storage volume would remain unaffected. Hence, the said techniques seem to have gained importance in PCM research in recent times. Although several review papers elaborating conventional techniques are available, none can be found on the aforementioned alternative class. Driven by the current scenario, this review paper intends to summarize past research on alternative heat transfer enhancement techniques employed for LHTESS. The critical analysis of the potential of each technique in enhancing the phase change heat transfer rate and their practical applicability are presented. Further, the present review evaluates relative merits/demerits and challenges/issues/limitations of these techniques to provide guidelines for future research.