Gas-assisted control of arch stability in bulk material discharge

This study investigates the effect of gas velocity, direction, and configuration on arch formation and collapse during bulk granular material discharge through horizontal orifices. Experiments were conducted using cold quasi-2D (250 × 50 × 5 mm) and hot scale models (cylindrical shaft, D = 300 mm, H = 500 mm) with high-speed imaging (2000 fps, 1280 × 1024) across various materials. Uniform gas flow stabilizes arches, reducing the normalized mass flow rate Zt/Z₀ to 0.20 ± 0.03 at critical gas velocity ratios W₁/W₂≤20 and area ratios L₁/L₂≥0.37. Conversely, localized gas jets increase Zt/Z₀ to 1.45 ± 0.05. The scientific novelty lies in developing a unified torque-balance model that, for the first time, predicts critical counter-current gas velocities Wkr across different configurations within a ±28.9% error margin (n = 3, p < 0.05). These findings provide a quantitative basis for designing industrial systems such as shaft furnaces, pneumatic conveyors, and dosing units. Future work will focus on industrial-scale validation, extension to humid or adhesive materials, and complex geometries to further optimize gas-assisted flow control.