Numerical analysis and optimization of metal foam layout in metal hydride reactors for enhanced hydrogen absorption performance

High thermal conductivity materials (HTCM) such as metal foam are widely utilized to enhance heat transfer and reaction kinetics in metal hydride (MH) hydrogen storage reactors. However, the spatiotemporal heat transfer bottlenecks within MH beds lack detailed investigation, leading to suboptimal HTCM layouts and restricted heat transfer performance. In this study, spatiotemporal heat transfer characteristics within MH beds during hydrogen absorption are analyzed in detail, and fundamental layout principles for metal foam are established to enhance heat transfer. Subsequently, the synergistic effects of these principles are examined, and the optimal metal foam layout is determined using a genetic algorithm. The numerical results reveal significant delays in reaction heat dissipation within radial extension regions of the MH bed, attributed to longer heat transfer distances. This issue can be mitigated by radially shrinking the metal foam, reducing the absorption time by 5.5%. Since more heat is transferred through near tube regions during hydrogen absorption, a radial gradient distribution of metal foam porosity yields a 10.3% improvement in absorption rate. Additionally, the heat transfer in axial extension regions is markedly weakened due to higher fluid temperature. This limitation is addressed by an axial gradient distribution of metal foam porosity, reducing the absorption time by 5.8%. Overall, radial gradient porosity is the most effective method, while the radial shrinkage principle becomes a promising alternative when manufacturing conditions are restricted. Furthermore, the optimal metal foam layout, derived from the synergistic application of three layout principles, reduces absorption time by 12.6% compared to the uniform layout.