Analytical modelling of PCM supercooling including recalescence for complete and partial heating/cooling cycles

Phase change material (PCM) experiencing supercooling and phase change hysteresis are widely reported in the literature. However, only few studies model analytically such PCM, and they mostly focus on either supercooling or phase change hysteresis, but rarely on both phenomena. Moreover, partial phase change cycles, with an incomplete melting or solidification, are rarely considered even if these processes occur frequently in latent heat thermal energy storage (LHTES) systems. The objective of this study is to model analytically the thermal behaviour of a PCM experiencing supercooling and phase change hysteresis, for complete and partial phase change cycles. The developed method, based on a heat source term, enables to model the recalescence process during the solidification. Currently rarely considered, the influence of the cooling rate on the supercooling degree and the recalescence process is evaluated with a phenomenological approach. For partial cycles, the different behavior between heating and cooling is modelled with the hysteresis model curve scale already validated in literature. The experimental validation is carried out on a PCM brick sample, monitoring both the heat flux and the PCM temperature, which enables to characterize a greater mass of PCM compared to direct scanning calorimeter (DSC) analysis. The selected PCM undergoing supercooling during solidification is PEG6000, a polymer suitable for domestic hot water (DHW) storage. Results show a good agreement between experimental and numerical results for complete heating and cooling cycles. The behavior laws used to model the solidification with the supercooling and recalescence processes are validated for the cooling rate range tested. The modelling is also satisfactory concerning the experiments on partial solidification for different temperature plateaus. However, the model fails to correctly represent the thermal behavior for a cooling process after a partial melting of the PCM. To conclude, the developed model enables to represent accurately the thermal behaviour of a PCM experiencing supercooling and phase change hysteresis for most of the phase change processes studied. Investigations on the thermal conditions influencing the crystalline structure and the effect on the phase change dynamic are suggested to improve supercooling modelling. The developed model needs to be validated for PCM having a higher supercooling degree, such as sugar alcohols or salt hydrates.

Automated summary

This study aims to analytically model the thermal behavior of a PCM experiencing supercooling and phase change hysteresis, for both complete and partial phase change cycles. The developed method relies on a heat source term to model the recalescence process during solidification.