Non-renewable energy sources met the world's energy demand for a long time, but they also led to an increase in global warming. Hydrogen is seen as the potential future fuel due to its abundant availability and environmentally friendly combustion properties. An essential aspect of the hydrogen economy is its storage. Solid-state hydrogen storage using metal hydrides (MHs) has proven superior to gaseous and liquid storage methods because MHs offer a high gravimetric energy density and enhanced safety. However, the hydrogen absorption process in MH is exothermic, necessitating a robust heat management system.

The current numerical analysis focuses on the absorption of 30 g of hydrogen in magnesium MH. The reactor setup includes a hydrogen supply tube along with inner and outer cylinders filled with MH and phase change material (PCM), respectively. Sodium nitrate (NaNO3) is utilized as a PCM due to its better heat storage properties. It effectively stores the reaction heat generated during the absorption, allowing for its reuse during desorption. A validated mathematical model is proposed to study the impact of buoyancy resulting from convection currents on storage performance. The convection currents are solved using the Navier-Stokes equations with the Boussinesq approximation. An iterative method is utilized to determine the exact amount of PCM required by considering both sensible and latent heat. Due to the low thermal conductivity of MH and PCM, circular copper fins are added to enhance heat transfer. A novel approach is introduced to estimate the fin efficiency (ηf) using temperature profiles of both MH and fins. A new parameter called the fin factor is proposed, which proves to be more effective in optimizing the number of fins compared to ηf. To evaluate the overall performance of the system relative to its weight, the performance evaluation criterion (PEC) is discussed. PEC shows that the system with more fins is not always better compared to fewer fins. The study also investigates the influence of hydrogen supply pressure and initial temperature on the system's performance parameters.