Determining the phase change characteristics of lauric acid to realise its optimum performance in latent thermal energy storage

Abstract
This study presents the results of a simulation of heat charging during melting and heat discharging during the solidification of an organic phase change material (PCM) of lauric acid with a spherical geometry. Simulations were performed using ANSYS Fluent software with six shell diameters (5, 15, 30, 45, 60, and 75 mm) and three Stefan numbers (0.217, 0.345, and 0.472). The heat transfer mechanism inside the shell was studied based on liquid fraction contours and velocity vector diagrams. Melting is dominated by convection, whereas conduction is the dominant solidification mechanism. The convection intensity increased with an increase in the shell size up to a shell diameter of 30 mm with an increase in the Stefan number. The size effect on the melting and solidification times fit well with the Chvorinov model used for metal casting. The specific melting/solidification time, as defined by the time required for melting/solidifying a unit mass of PCM, decreases with increasing shell size until it becomes nearly constant for shell diameters above 30 mm and then decreases with an increasing Stefan number. We propose a method for determining the crossover between conduction and convection heat transfers based on the vertical temperature distribution inside the shell. A comprehensive understanding of heat transfer during the phase change of lauric acid, including heat transfer crossover, is crucial for its technical design as a latent thermal energy storage (TES) material and for the application of appropriate strategies to control the heat transfer rate in various scenarios.