A Comprehensive Review of Salt Hydrates as Phase Change Materials (PCMs)
Navin Kumar and Debjyoti Banerjee
National energy policies are often guided by a desire to reduce the environmental impacts of fossil fuels, especially for thermal management during power production and transportation systems. In these situations, technology development involving thermal energy storage (TES) platforms and associated materials play a significant role in enhancing the reliability and efficiency of thermal systems. In particular, phase change materials (PCMs) have attracted significant attention for TES in the last twenty years.
PCMs primarily leverage latent heat energy during phase transformation processes in order to minimize material usage and reduce form factors for thermal energy storage (TES) platforms. However, several impediments need to be resolved for wider deployment of PCMs in commercial applications. Significant improvements in the performance of PCMs is desired, especially, for improving the efficacy of the transport mechanisms, both at the micro and macro-scales.
Innovative approaches in materials research has produced reports in the literature on the development of novel PCMs. However, the price of innovation is often the higher uncertainty associated with the different ways the reliability of such materials could be compromised in commercial applications. Hence, the advances in materials research needs to be complemented by thermo-fluidic testing and validation, in order to ascertain the reliability of the PCMs. It is desired that the testing and validation tasks be performed to mimic the operational conditions (e.g., rapid thermo-cycling involving repeated melting and solidification for a “large” number of cycles and for large sample size or batch sizes). This can help to estimate the reliability of the thermal systems as well as the physical and chemical stability of these PCM samples in scenarios mimicking real application conditions.
The advantages and challenges associated with the deployment of inorganic PCMs for thermal systems is explored in this review, with an emphasis on the transport mechanisms that modulate the performance of the PCM samples at the micro level; while primarily focusing on the thermodynamic and material transport properties, transport (i.e., involving static, transient and kinetics considerations).
Keywords: Phase Change Materials, Salt Hydrates, Nucleation, Phase Segregation, Thermal Stability,