Comparison study of molten salts and metal PCM and simulation of a latent packed-bed thermal energy storage system

"High-temperature renewable and industrial heat applications require efficient and compact solutions to address their inherent intermittency. Latent heat thermal energy storage is one such solution, acting as a buffer between supply and demand. Compared to conventional sensible storage systems, latent heat thermal energy storage systems based on encapsulated phase change materials offer higher energy density and improved outlet temperature stability. However, the technological maturity of high-temperature applications remains low, and optimal material combinations still need to be identified and demonstrated. In this work, the thermal behaviour of a high-temperature latent packed-bed thermal energy storage system is investigated. An existing one-dimensional two-phase MATLAB model based on the finite volume method is further developed, using a previous reference model, to simulate a packed-bed thermal storage system with phase change material capsules. In this model, intra-particle heat conduction is considered and the phase transition is represented using the effective heat capacity method and natural convection inside the capsule. It is validated against experimental data from the literature. The analysis also includes an estimate of material and facility costs. The parametric study includes three heat transfer fluids: liquid sodium, lead and halide salts, as well as three inorganic phase change materials, AlSi12 and chloride salts, with ceramic shell materials, Al2O3, MgO and ZrSiO4. The effect of geometric and operational parameters, such as void fraction, capsule diameter, mass flow rate, height-to-diameter ratio and shell thickness, is also evaluated using thermal key performance indicators. Finally, the selected LHTES configuration is compared to a sensible packed-bed using Al2O3 ceramic solid filler. The results indicate that the combination of liquid sodium, AlSi12, and Al2O3 provides the best overall performance among the cases studied, with longer utilization time, higher efficiency, and a smaller required storage tank".