Performance Evaluation of a Packed Bed Latent Thermal Storage System Using Superellipsoidal PCM Capsules

Two crucial yet opposing design criteria govern the performance of packed bed latent thermal energy storage systems (PBLTESS): energy storage capacity and thermal power. While the former depends on the packing density of the phase change material (PCM) capsules forming the packed bed, the latter is influenced by the surface-area-to-volume ratio (SVR) of these capsules. This study introduces novel superellipsoidal geometries for PCM capsules to address both these factors and quantifies the impact of design parameters on both mentioned performance criteria. First, by using discrete element method (DEM) simulations, we performed virtual bed filling experiments and generated packed beds from 116 superellipsoidal designs with similar volume. These simulations revealed a maximum packing density of 65.2%—significantly higher than conventional spherical capsule designs. Validation through bed filling experiments using 3D-printed superellipsoids confirmed the results of the DEM simulations, with an average deviation of less than 5%. Additionally, the SVR of each superellipsoidal design was determined through CAD analyses. Subsequently, six superellipsoidal designs as well as a spherical design were selected for further investigation using a 1D PBLTESS model to simulate charging and discharging. With up to 85% higher storage capacity (due to increased packing density) and up to 50% higher thermal power (resulting from enhanced heat transfer), the superellipsoidal geometries clearly outperformed the spherical design.