A novel correlation for the direct determination of the discharging time of plate-based latent heat thermal energy storage systems

One of the key factors that currently limit the commercial deployment of latent heat thermal energy storage (LHTES) systems is their complex design procedure. The optimization of such kind of systems requires a compromise between the storage capacity and the charging/discharging power, and therefore, there is a need of modeling tools that allow their fast and accurate simulation. In light of this, a novel correlation that allows the straightforward determination of the discharging time of plate-based LHTES systems is developed in the present article. To approach this objective, an experimentally validated CFD model was used. Simulations with 3 commercial phase change materials (PCMs) were first employed to gain knowledge of the melting and solidification behavior of the system. Then, a theoretical formulation of the heat transfer problem involved was performed so as to identify those dimensionless numbers concerned in the process. Afterwards, 15 virtual PCMs were defined and CFD simulations were performed. The obtained discharging time results were adjusted by regression to get the exponents and coefficients of the dimensionless numbers involved in the correlation. Finally, to validate the correlation, simulations with five additional PCMs were carried out and their results were compared with those obtained from the correlation. By means of the obtained expression, the maximum plate thickness capable to provide a desired discharging power can be determined as a function of the properties of the PCM and the operation constraints of the application without the need of simulations. The technique eases the design process of this kind of systems and decreases the amount of time needed to size them from days/hours to minutes.