Cyclability of Thermochemical materials: Quantifying microstructural evolution and its impact on packed bed performance

Transitioning to sustainable energy systems requires reliable methods for storing and releasing energy from renewable sources. Among various storage technologies, thermochemical storage using salt hydrates offers distinct advantages, including high energy density and negligible long-term losses. However, the long-term stability of these materials under repeated hydration–dehydration cycles remains poorly understood. This thesis investigates the microstructural evolution of potassium carbonate and its impact on packed bed performance across multiple scales.
At the particle level, advanced imaging techniques such as micro-X-ray computed tomography (Micro-CT) are employed to characterize structural changes in grains subjected to repeated cycling. Results reveal significant variations in porosity, connectivity, and density arising from swelling and shrinkage during water uptake and release. These microstructural alterations are linked to the material’s capacity to retain performance over extended use.
Building on this, in-situ experimental methodologies are developed to monitor agglomeration and volume changes in real time under controlled cycling conditions. Micro-climate chambers and Micro-CT provide direct evidence of how mechanical stress and pressure accelerate agglomeration, offering new insights into mechanisms that degrade material stability in practical reactor environments.
At the reactor scale, Micro-CT analysis is extended to packed beds, quantifying changes in porosity distribution, grain size, and thermal conductivity both axially and radially. These results highlight how microstructural changes propagate to macroscopic effects such as non-uniform flow, increased pressure drop, and localized hot spots. To capture these processes, COMSOL Multiphysics simulations integrate experimental findings, comparing uncycled and cycled reactors. Cases incorporating spatially resolved porosity data demonstrate how agglomeration directly influences heat and mass transfer efficiency.
Overall, this work advances fundamental understanding of microstructural evolution in thermochemical storage materials. By linking particle-scale processes to reactor-scale performance, it establishes experimental and modeling frameworks that support the development of more durable, efficient salt hydrate systems for sustainable energy applications.