Cost strategy-integrated geometry selection of phase change material macro-capsule for latent thermal energy storage

The commercial use of phase change material (PCM) based latent energy storage systems provides a reliable solution for balancing the intermittency of renewable energy sources with human energy demands. This study proposes a cost–performance-integrated strategy for selecting the optimal geometry of macro-encapsulated PCMs in latent thermal energy storage systems. Seven capsule shapes were numerically evaluated using the enthalpy–porosity method to determine their melting performance and material usage. Two new dimensionless indicators—dimensionless cost and dimensionless cost benefit—were introduced to quantify the trade-off between heat conduction efficiency and capsule material cost. The melting process of the capsules was analysed. The best shape capsule (cone on half ellipsoid) based on the dimensionless cost indicator analysis could save cost by 48.45 % compared to the traditionally selected best shape capsule (triangular prism) while increasing the melting time by 43.3 %. Compared to the option of a triangular prism shaped capsule, the dimensionless cost benefit indicator analysis indicates that a cone shaped capsule offers a cost saving of 28.4 %, while the melting time increases by only 13.8 %, which means that the mutually exclusive indicators of cost and performance are optimally balanced. Using these two new indicators for analysis can avoid unreasonable increases in shell volume ratio when optimizing capsule shapes and can assess the cost-to-performance ratio for rational applications. Filling the same capsule with different phase change materials can lead to variations in the analysis results. The proposed strategy offers a practical guideline for geometry selection, balancing thermal performance with economic considerations in PCM-based storage applications.