A timeline of the phase-change problem for latent thermal energy storage systems: A review of theoretical approaches from the 1970′s to 2022

Latent thermal energy storage, employing phase-change materials, has been traditionally researched in several areas such solar energy, refrigeration, and electronic cooling, but less conventional applications, e.g. cancer therapy, are also emerging. In this review, theoretical studies categorized in a wide range of subjects are critically discussed. Some topics commonly found in the literature are analyzed, including (not limited to) intensification techniques of heat transfer and numerical methods. Nevertheless, less reported matters are also discussed, such the development of correlations and the utilization of non-conventional techniques to enhance heat transfer. Besides, this work is arranged in a timeline, so that the origins of each topic are tracked and followed along the years to better identify the incremental and disruptive contributions. As an example, first attempts to compare different algorithms to solve phase-change problems, were identified in the 1990′s. To cite more significant advancements, the 2000′s was marked by the first use of artificial neural networks and by the birth of nano-enhanced phase-change materials. Lastly, research gaps and prominent research fields are pointed out as the consequence of mapping the state of the art. A sample of identified gaps are the: (i) investigation on the Newtonian behavior of nano-enhanced phase-change materials in the liquid state, (ii) better investigation on the porosity constant values, for the same phase-change material under different conditions. On the other hand, some promising fields revealed were the development of correlations to predict several parameters and the investigation of non-conventional techniques, e.g. magnetic fields and ultrasound. Latent thermal energy storage was found to possess some well understood behaviors for a ready implementation in commercial scales, but also presents a wide range of areas for continuous research and development.