Abstract
Reliable discharge of bulk granular materials is essential for the efficient operation of shaft furnaces, pneumatic conveying systems, and industrial dosing equipment, where uncontrolled arch formation can lead to flow instability and blockage. 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 Wt/W0 to 0.20 ± 0.03 at critical gas velocity ratios V1/V2≤20 and area ratios L1/L2≥0.37. Conversely, localized gas jets increase Wt/W0 to 1.45 ± 0.05. The scientific novelty lies in the development of a unified torque-balance model that, for the first time, predicts critical counter-current gas velocities Vkr across different operating configurations with an error not exceeding ±28.9% (n = 3, p < 0.05). Three characteristic discharge regimes—continuous flow, pulsating discharge, and blockage-dominated flow—were identified and related to the stability of dynamically unstable arch structures. These findings provide a quantitative basis for the design and optimization of industrial systems such as shaft furnaces, pneumatic conveyors, and dosing units. Future work will focus on industrial-scale validation, extension to humid or cohesive materials, and investigation of more complex flow geometries to further improve gas-assisted flow control.