Epsomite (MgSO4⋅7H2O) particle-bed heat absorption: Dehydration solid-phase metamorphosis including caking under heated air flow

Hydrated salts such as Epsomite ( MgSO 4 ⋅ 7 H 2 O ) offer high volumetric heat storage capacity, making them potential solutions for thermochemical energy storage (TES) and EV battery thermal runaway. However, their low effective thermal conductivity and caking (agglomeration) effect during dehydration present challenges. In this study, a packed bed of Epsomite particles is used to cool down high-temperature airflow (up to 450 °C); the permeability and reaction progress are measured, and X-ray microscopy (XRM) is used to directly visualize, for the first time, the internal structural metamorphoses of dehydrating salt-hydrate particles. Computational fluid dynamics (CFD) simulations reveal that the dehydration process is governed by a reaction completion–dependent activation energy Δ E a ( α ) , increasing with the dehydration level. Ab initio calculations attribute this behavior to the progressive breaking of Mg O covalent bonds. Structural evolution during dehydration includes intraparticle pore formation and shell transformation. Under constant high-temperature heating, local vapor condensation leads to the formation of pore water and dissolution of the particle shell, introducing recrystallization and particle caking that reduce bed permeability. In contrast, staged heating (100 °C → 150 ° C → 415 °C) prevents caking by moderating vapor release and diffusion, resulting in complete dehydration and increased permeability through particle shrinkage and channel formation. • Demonstration of using Epsomite powder bed for cooling via permeating heated airflow. • Mechanism of dehydration solid-phase transformations and their role in permeability loss. • Strategy for staged heating to prevent permeability loss. • Integration of multiscale (DFT, XRM, CFD) theoretical and experimental analyses.