Supercooling of phase change materials: A review

Supercooling is a natural phenomenon that keeps a phase change material (PCM) in its liquid state at a temperature lower than its solidification temperature. In the field of thermal energy storage systems, entering in supercooled state is generally considered as a drawback, since it prevents the release of the latent heat. Conversely, when dealing with plants, animals or preservation processes, supercooling protects organs, tissues or blood from solidification that leads to damage or to death. This paper first reviews the most important applications and cases in which supercooling can take place and dramatically change the performance. Second, the paper discusses the factors affecting the occurrence and the degree of supercooling, such as cooling rate, PCM container characteristics, PCM thermal history, use of additives, etc. The paper includes a supercooling modeling section, which presents the main mathematical and numerical methods used to solve the challenges encountered by researchers. This review shows that to experimentally foster or reduce supercooling, most researchers tend to use similar methods such as controlling the cooling rate, changing container's characteristics or adding additives. The main challenge in supercooling modeling being its unstable and probabilistic nature, most authors tend to perform experimental measurements to obtain some key parameters, notably the supercooling degree, prior to the modeling. This strategy restricts the validity of the models to applications having the same conditions as the experiments. Nevertheless, this review offers the guidelines to select the appropriate experimental parameters and modeling strategies, depending on the specific and practical objectives of each application.