Comparative Analysis of MgCl₂ (Salt PCM) and Aluminum (Metallic PCM) for Melting and Solidification Performance in Latent Heat Storage

Next-generation concentrated solar power systems require thermal energy storage technologies capable of reliable operation above 600 °C. This study numerically compares aluminum as a metallic phase change material (PCM) and MgCl₂ as a salt PCM (enhanced with perforated fins) in a shell-and-tube TES unit using liquid sodium as the heat transfer fluid. Simulations were carried out with the enthalpy-porosity method in ANSYS Fluent 2024R2. Contrary to assumptions in the literature, natural convection is not negligible during melting or solidification of aluminum, underlining the need to account for convection in metallic PCM modeling. Results further show that for aluminum, melting and solidification times are almost identical, with only a 7-minute difference, and the overall phase change is nearly twice as fast as MgCl₂. Moreover, the obtained outlet temperature profiles ensure suitable operating conditions for turbines, while the nearly constant heat flux trend approximates steady-state system behavior.