Gravity-driven powder flow and the influence of external vibration on flow characteristics

The controlled and homogeneous flow of dry granular powders through hoppers is essential for applications, namely, packaging of food grains, fertilizers and additive manufacturing processes such as directed energy deposition for better product quality. One of the major issues encountered in the granular flows through hoppers is flow stagnation due to the well-known arching phenomenon. Vibration-assisted granular flow through hoppers is one of the mechanisms used for better mass flow control. In this work, the influence of external mechanical vibration on the powder flow is investigated experimentally and using discrete element simulations. First, the mass flow rate through the hopper increases with an increase in vibration amplitude and then decreases, signifying the existence of an optimal amplitude of vibration. The DEM simulations explained the underlying mechanisms for the existence of an optimal amplitude of vibration corresponding to the maximum mass flow rate. A range of vibration amplitudes from 0 mm to 3.5 mm is used to study the flow behaviour; the maximum flow of around 33 g/s to 35 g/s is observed for 0.75 mm to 1.25 mm vibration amplitude for the hopper-particle combination studied in this work. The work also reports the influence of vibration frequency, hopper, and particle dimension on the flow characteristics. The research facilitates the effective use of mechanical vibration to enhance powder flow that can further be extended to non-spherical and multi-material particles.