Date of Award

Fall 2002

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering - (Ph.D.)

Department

Mechanical Engineering

First Advisor

Rajesh N. Dave

Second Advisor

Ian Sanford Fischer

Third Advisor

I. Joga Rao

Fourth Advisor

Chao Zhu

Fifth Advisor

Robert Pfeffer

Abstract

Dry particle coating is an emerging field in the industries that deal with particulate products and powder processing. Compared to the widely reported experimental studies of the dry particle coating, the theoretical modeling of such processes is found to be less comprehensive. The work presented in this thesis is an attempt to fill this gap.

The first part of the dissertation aims at the numerical investigation of the hybridization system (Nara Machinery, Tokyo, Japan). The flow behavior of different materials processed in this device is analyzed using three-dimensional Discrete Element Method (DEM) as well as the computational fluid dynamics (CFD) models. The particulate motion is directly simulated using the D EM c ode, which incorporates the effect of the fluid drag force, computed through the CFD models. The diagnostic investigation includes various aspects pertinent to the effectiveness of the hybridizer system in the coating process. Inter-particle collisions and particle-wall collisions as well as the normal and tangential forces between the particles are estimated which play an important role in the surface modification process of a powder. Experimentally measured velocities in the mixing chamber are in good agreement with the computed velocities. CFD results show that the flow field is not significantly affected as the volume fraction of particles is varied from 3 to 10 percent. Overall, it is found that the combined DEM-CFD model appears to be an adequate approximation of the behavior of the fluid-particle system in the hybridizer.

The experimental part of this dissertation presents an investigation of different powder processing devices such as the Hybridizer, Mechanofusion and Magnetically Assisted Impaction Coating (MAIC) devices for a specific application of improving the humidity resistance of the ground magnesium powder through the dry particle coating technique. It is shown that coating by wax (1 percent by weight) is sufficient to increase the humidity resistance of ground magnesium to a level almost as good as the atomized magnesium powder.

The last part of the dissertation deals with a related, yet different type of numerical study, carried out using the DEM approach, of the granular flows and mixing behavior in the oscillating sectorial containers. Mixing patterns are observed for a wide range of frequencies of oscillation as well as different operating conditions such as the powder loading, the coefficient of friction, and the coefficient of restitution. It is observed that the flow patterns follow a particular trend and there exists a critical frequency at which the mixing rate is very small.

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