Adaptive thermal management and system-level design of magnesium hydride hydrogen storage for renewable energy systems

Magnesium hydride (MgH₂) is one of the most promising solid-state hydrogen storage materials owing to its high hydrogen-storage capacity, low cost, and excellent chemical stability. However, its inherently low thermal conductivity, strong Mg-H bonding, and high activation energy significantly restrict hydrogen desorption per-formance and limit its practical implementation in integrated renewable energy systems. This thesis presents a comprehensive numerical, thermal, and thermodynamic investigation aimed at improving the efficiency and engineering applicability of MgH₂-based hydrogen storage through three complementary research directions: temperature-dependent thermal conductivity modelling, transient thermal management using pulsed heating, and system-level integration with waste-heat recovery.

A unified finite-element modelling framework was developed in COMSOL Multiphysics to simulate the coupled heat transfer, hydrogen transport, and desorption kinetics within MgH₂ reactors. The numerical model was veri-fied through mesh-independence analysis and validated against published experimental measurements and es-tablished numerical studies, providing confidence in the predictive capability of the modelling framework. First, a temperature-dependent effective thermal conductivity model was developed using effective-medium theory and experimentally derived conductivity data. Compared with the conventional constant-conductivity ap-proach, incorporating λ(T) significantly improved the prediction of transient heat transfer, accelerated hydrogen desorption, reduced desorption time by up to nine minutes under slow-heating conditions, and produced more uniform temperature distributions within the hydride bed.

Second, a pulsed radial heat-flux strategy was introduced to enhance thermal management without employing internal heat exchangers. Optimized ON-OFF heating cycles reduced the overall desorption time by approxi-mately 25%, while simultaneously lowering energy consumption, suppressing excessive wall temperatures, and improving thermal utilization within the reactor. Finally, a coupled numerical-thermodynamic framework was developed to integrate reactor-scale desorption behavior with a proton exchange membrane fuel cell (PEMFC) and an Organic Rankine Cycle (ORC). The results demonstrate that the coordinated use of reactor waste heat improves overall system efficiency, reduces external heating requirements, and enhances hydrogen utilization in integrated renewable energy systems.

Overall, this research demonstrates that the coordinated optimization of material-property modelling, transient thermal management, and system-level energy integration offers an effective engineering strategy to improve the performance, efficiency, and practical deployment of MgH₂-based hydrogen storage technologies. The findings provide practical design guidelines for next-generation solid-state hydrogen storage reactors and contribute to the development of more efficient and sustainable hydrogen energy systems.