Modelling free-flowing sodium borohydride in the dense flow regime using DEM

Abstract

Sodium borohydride (NaBH₄) is a promising hydrogen carrier for maritime applications due to its high gravimetric and volumetric energy densities compared to compressed or liquefied hydrogen. As a solid granular material, NaBH₄ can be stored under atmospheric pressure and room temperature, eliminating the need for extreme pressures, or cryogenic conditions. Although NaBH₄ is hygroscopic and can become cohesive when exposed to humid environments, when stored and handled sufficiently dry it remains free-flowing, which is essential for reliable conveying, storage, and discharge operations. Designing equipment for these processes requires an accurate understanding of NaBH₄’s free-flowing behaviour, motivating the need for modelling tools. To address this, we model granular, free-flowing NaBH₄ using the Discrete Element Method. Granular flow behaviour depends strongly on the flow regime—defined by the applied shear and confining pressure through the inertial number—and practical handling systems typically operate in the dense flow regime; consequently, this study focuses on dense-flow conditions. A standard calibration–verification–validation methodology is applied, using a ledge test and rotating drum for calibration and verification, and an inclined surface test for validation. In parallel, we evaluate the inertial number across all setups using a velocity-based approach to characterise both the global flow regime and locally occurring flow regimes within the flowing layer. Rather than assigning a single characteristic value per setup, we demonstrate that distinct segments exhibit different inertial numbers, indicating that the inertial number is spatially dependent.