Date of Award

Fall 2001

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

Jay N. Meegoda

Fourth Advisor

Chao Zhu

Fifth Advisor

Moinuddin Malik

Abstract

In the study of granular materials, two major topics of importance are powder flow enhancement mechanisms and the flow characterization. This dissertation is involved with both of these topics. With respect to the powder flow enhancement, this study involves investigation of two types of flow enhancement methods. The first flow enhancement method examined is a novel method called the Magnetically Assisted Powder Flow (MAPF) method. In the MAPF, small magnetic particles and powders are placed in a test hopper. A mesh is placed at the bottom of the hopper to hold the magnetic particles while the powder is discharged through the mesh. It is shown that this method may be used for controlled discharge of cohesive powders and hence may be used also for cohesive powder flow characterization. Therefore this technique is utilized for the angle of repose (AOR) measurements, which is the most convenient and popular method used in industry for powder characterization. It is found that many factors affect the results obtained for AOR, including the technique of measurement. The AOR measurement through MAPF method is developed and the effects of various variables including the dropping height, mass of the powder used in the hopper, magnetic field strength, hopper position in the magnetic field, mass of magnetic particles hopper outlet area and mesh size are evaluated. This novel AOR measurement method is found to be more reliable and easier to use.

The second flow enhancement method examined is the use of vibration, which is currently a commonly applied industrial method to enhance powder flow. However, it is well known that vibration causes segregation due to the difference in particle size or density and thus causes certain adverse effects on products. In order to understand the mechanisms of segregation in vibrating systems, a systematic study of vibrated hoppers with mono-disperse as well as binary system of particles is carried out. This includes physical experiments as well a computer model using the Discrete Element Method (DEM) to simulate the model system. The first part of the study involves hoppers with the outlet closed, and includes experiments and simulations. The effects of various system parameters are investigated and several important regimes of behavior are identified based on the state diagram of dimensionless amplitude and frequency of applied vibrations. A plausible explanation through the experimental and simulation results is given for one of the most interesting regimes, where the hopper surface is inclined (i.e. forms a heap). It is shown that this occurs due to the existence of lateral (i.e. horizontal) vibration mode.

For the binary system, mixtures of equal-density glass at different size ratios are vibrated and behavior is characterized as a function of the vibration amplitude. Experiments are also conducted on funnel and mass flow hoppers with outlet open, and the segregation upon discharge is measured for various operating conditions as well as hopper geometries. It is found that the segregation upon discharge varies depending on the operating conditions and flow pattern in the bed.

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