Computer modelling and experimental investigation of phase change hysteresis of PCMs: The state-of-the-art review

The present review provides an overview and critical analysis of recently published simulation approaches and experimental studies addressing the phase change hysteresis (PCH) and supercooling (SC) of phase change materials (PCMs). In terms of the enthalpy-temperature h(T) relationships for the solid-liquid phase changes, the PCH is a temperature delay of the h(T) curves between the melting and solidification process, while SC means that solidification does not start at the nominal solidification temperature and a lower temperature is needed for the nucleation to start. However, the PCH and SC are often neglected in the studies dealing with thermal energy storage in PCMs. Several studies indicate that experimental techniques and conditions can significantly influence the behaviour of PCMs, including the PCH and SC. Another issue is the difference in the behaviour of small samples, such as those used in the differential scanning calorimetry (DSC), and the behaviour of bulk PCM. As the DSC results are often used as inputs in simulations of systems with the bulk PCM, this issue is of high importance. Further, the entire amount of PCM does not always fully melt and solidify, and thus partial phase transitions are common in many real-life applications. Several modelling approaches have been proposed to address the PCH and SC of PCM. While simulations of complete phase change cycles are rather straightforward even with the PCH and SC involved, incomplete phase change cycles with partial phase transitions are much more challenging, and this issue has not yet been satisfactorily solved. The simulation techniques identified in the literature search were analysed, assessed, and compared to each other. The results indicate that there are only a few modelling approaches for partial phase transitions, and only some of them are reasonably validated with experimental data.