Numerical investigation of aluminum-silicon solidification in a novel high temperature latent heat thermal energy storage system

Energy storage plays a critical role in facilitating the integration of intermittent renewable energy sources into contemporary energy systems. This study presents a comprehensive numerical investigation of the solidification process of an Aluminum-Silicon (88Al–12Si) metal alloy phase change material (PCM) in a state-of-the-art latent heat thermal energy storage (LHTES) system, utilizing liquid sodium as heat transfer fluid (HTF). A three-dimensional (3-D) computational fluid dynamics (CFD) model using the time-dependent enthalpy-porosity method is developed to predict temperature distributions, PCM melt fraction, heat flux, and Nusselt number at the HTF-PCM tank interface. The HTF outlet temperature is found to be within ±5 °C (1 %) of corresponding experimental data. Using the validated CFD model, the effects of HTF selection, inlet velocity, and inlet temperature on PCM solidification are analyzed. Heat transfer within the PCM is found to be predominantly diffusion driven. The modeled LHTES system discharge efficiency is evaluated at 93.5 %, primarily due to the high thermal conductivity of the 88Al–12Si PCM, which enables the use of a simple geometric design without additional heat transfer enhancement apparatus. Relative to the existing reference system prototype design, potential reduction of up to 61 % in solidification time and enhancement of the thermohydraulic performance by a factor of 3.4 may be obtained using a reduced HTF inlet temperature (i.e., 400 °C instead of 527 °C). The results also suggest further thermofluid improvements using lithium or gallium as HTFs.