Magnetically mediated flow enhancement for controlled powder discharge of cohesive powders

A new flow enhancement system is developed for cohesive powders. It is based on the concept of multiple, point source, internal excitations. In this system, a mass of small permanent-magnetic particles are placed in the discharge zone of a hopper, and then an oscillating magnetic field is applied to excite these magnets. A screen is placed at the exit to keep the magnets within the hopper. The magnetic particles spin furiously, go though random collisions with each other, and agitate the mass of cohesive powder near the exit of the hopper. As a result, the internal structure of the cohesive powder is disrupted and the powder gets fluidized and demonstrates an Ž . increased flowability. This device, called the magnetically assisted powder flow MAPF system, has been investigated for discharging cohesive powder from a hopper. It is shown that this device is capable of a controlled powder discharge, which is a linear function of time. The effects of various parameters, such as the amount and size of the magnetic particles and the magnetic field strength on the discharge rate are investigated. The operating principle of this device is different from conventional flow enhancement devices such as pneumatic, vibrational, or mechanical systems because powder ‘‘fluidization’’ is generated through random motion of the magnetic particles within the powder, and the presence of the screen prevents flooding. Modeling of the motion of the magnetic particles under the influence of an oscillating field is considered to show how the spinning and random translations occur in such a system. Discrete element modeling of a system of magnetic particles is also carried out to show the effect of various parameters on fluidization. This system can be applied for other powder technology applications, for example, the measurement of angle of repose for cohesive powders. q 2000 Elsevier Science S.A. All rights reserved.