Magnetically mediated flow enhancement for controlled powder discharge of cohesive powders

A new flow enhancement system is developed for cohesive powders. It is base d on the concept of multiple, point source, internal excitations. In this s ystem, a mass of small permanent-magnetic particles are placed in the disch arge 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 w ithin the hopper. The magnetic particles spin furiously, go though random c ollisions 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 po wder is disrupted and the powder gets fluidized and demonstrates an increas ed 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 disc harge, which is a linear function of time. The effects of various parameter s, such as the amount and size of the magnetic particles and the magnetic f ield strength on the discharge rate are investigated. The operating princip le of this device is different from conventional flow enhancement devices s uch as pneumatic, vibrational, or mechanical systems because powder "fluidi zation" 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 particl es is also carried out to show the effect of various parameters on fluidiza tion. This system can be applied for other powder technology applications, for example, the measurement of angle of repose for cohesive powders. (C) 2 000 Elsevier Science S.A. All rights reserved.