Semester

Summer

Date of Graduation

2006

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Richard Turton.

Abstract

Particle shape is a very important factor affecting the accuracy of discrete element modeling (DEM) simulations. Therefore, the purpose of this study is to determine its effect on the dynamic behavior of tablet movement in a rotating drum. First, the shape of typical standard round tablets was represented using the intersection of three convex spherical surfaces. Contact algorithms for Tablet-Flat Surface, Tablet-Curved Surface and Tablet-Tablet were developed based on the geometry of this representation of the tablets' shape. Good agreement was obtained between the simulation results for the collision of two tablets and those obtained from experiments. In addition, simulation results for the collision of two tablets using multi-sphere representations showed that the dynamic behavior of the tablet was very different from any of the multi-sphere representations.;A study of the effect of liquid bridging between two tablets on the dynamic behavior of tablets indicated that the capillary force can be ignored compared to the viscous forces caused by the liquid bridge, especially for liquids with high viscosity. Additionally, there was a linear relationship between limiting separation distance and viscosity of the liquid. The order of magnitude of the limiting separation distance in the liquid force model is about 1 mm.;For the multi-particle DEM simulations using spheres in rotating drums, the simulations reached steady state after approximately 6 s of pan rotation. A study of the influence of particle size and the radius of the drum on the surface velocity of particles along the inclined surface showed that the surface velocity of particles was inversely proportional to the square root of the diameter of the particles, and the surface velocity of particles is proportional to the square of the radius of the drum. In addition, the fractional fill volume in the 29 cm drum should be larger than 0.25 to obtain a velocity profile consistent with larger equipment.;Comparison of the surface velocity profiles from multi-particle simulations using tablets with that from multi-particle simulations using spheres showed that the surface velocity of tablets was much larger than that for spherical particles. It was also found that simulation results for batches of 1500 tablets and spheres in a rotating drum showed that the computational time for tablet simulations was about 60 times longer than that for spherical particle simulations.

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