Coupled multiphysics modelling and cyclic durability validation of packed-bed thermal energy storage systems

Packed-bed thermal energy storage systems subjected to repeated thermal cycling may experience progressive thermo-mechanical degradation due to the coupled interaction among heat transfer, granular mechanics and structural constraints, posing a risk of collapse. This issue is conventionally addressed through simulation because the thermo-mechanical phenomenon evolves very slowly, making experimental campaigns impractically long and costly. However, conventional modelling approaches often neglect bidirectional interactions between fluid flow, particle-scale contact mechanics and structural deformation, limiting their predictive capability for long-term operation. This work presents an experimentally validated coupled multiphysics modelling approach for the thermo-mechanical analysis of packed bed TES systems under cyclic operation. The methodology integrates fluid-particle heat transfer, discrete element modelling of granular contacts and structural response of the containment vessel within a consistent coupling strategy enabling both one-way and two-way interactions. The model captures thermal expansion mismatch, contact force evolution and stress redistribution within the granular bed and the surrounding structure. The numerical framework is validated against an accelerated experimental campaign comprising 520 thermal cycles, including post-mortem inspection and X-ray tomography to assess internal damage and particle rearrangement. The results demonstrate that coupled interactions significantly influence stress amplification and ratcheting effects, as captured by the validated framework at the laboratory scale. The two-way coupling is shown to alter the evolution of contact forces and wall stresses under cyclic loading. The proposed modelling strategy provides a predictive tool for assessing long-term thermo-mechanical durability of industrial packed bed TES systems and supports improved design criteria for cyclic high temperature applications.