Investigation of the Internal Pressure Exerted by a LaNi₅ Bed on a Vertical Cylindrical Vessel and Its Packing Fraction Distribution during Cyclic Hydrogen Ab/Desorption

Considering a vertical cylindrical vessel filled with LaNi 5, this study investigated the effect of cyclic hydrogen ab/desorption on the swelling pressure, i.e., the mechanical pressure exerted by LaNi 5 on the vessel, its packing fraction distribution, and the relationship between the swelling pressure and local packing fraction. The swelling pressure tended to increase close to the bottom of the vessel with increasing number of hydrogen ab/desorption cycles. In addition, it converged with the number of hydrogen ab/desorption cycles and did not increase after the 20th cycle. The packing fraction of the LaNi 5 bed was denser and closer to the bottom of the vessel. The packing fraction near the bottom increased with increasing number of hydrogen ab/desorption cycles. Almost no swelling pressure developed during the first hydrogen absorption although the packing fractions were high in some regions. Conversely, after cyclic hydrogen ab/desorption, the swelling pressure developed and increased exponentially with increasing local packing fraction. The swelling pressure appeared only in the LaNi 5 bed region where the local packing fraction exceeded 0.61 during hydrogen absorption. The obtained results are essential for preventing the deformation of LaNi 5 vessels for safe hydrogen storage.