A Review On Methods Of Preventing Super Cooling In Phase Change Materials (PCMs)

A phase change material (PCM) is a substance which releases/absorbs sufficient latent heat of fusion at phase transition to provide useful heating/cooling. Hence, they act as excellent energy storage devices. In most of the PCMs, the phase transition happens at the solid-liquid interface. Hence, the phase transition temperature will be the melting point of the PCM. For a PCM to work efficiently, the difference between the melting temperature and solidification temperature should be as low as possible. However, in most of the PCMs, it is observed that solidification starts at a temperature much below the melting point. This phenomenon, known as sub-cooling, leads to significant loss in the storage/retrieval of latent energy which is undesirable. This paper reviews the various methods that has been investigated to overcome the problems associated with sub-cooling. The various methods discussed include - addition of appropriate nucleating agents of similar crystal structure as that of the PCM, cold finger technique and application of surface roughness on the walls containing the PCM, ultrasonic irradiation, application of dynamic pressure, cavitation and electrical means. Experiments conducted by researchers and their corresponding results have been discussed.