(28b) The Stress, Orientation, Displacement Deviation, and Solid Fraction Predictions from a Modified Attrition Cell Containing Needle-Shaped Particles

Authors: 
Kumar, R., Purdue
Sarkar, A., Worldwide Research and Development, Pfizer Inc.
Ketterhagen, W. R., Pfizer Worldwide Research and Development
Hancock, B. C., Pfizer Worldwide Research and Development
Curtis, J. S., UC Davis
Wassgren, C. R., Purdue University
A discrete element model (DEM) is used to predict the stress distribution, the orientation distribution, the displacement deviation, and the solid fraction in a modified attrition cell containing needle-shaped particles. The effects of particle aspect ratio, particle-particle friction coefficient, agitation blade height, pressure on the top plate, and particle-wall friction coefficient were investigated in this study. Prior studies have shown that particle breakage in an attrition cell mainly occurs at the base of the cell and in front of the blades near the cell circumference. Therefore, instead of simulating the entire attrition cell, a smaller control volume in the form of a periodic box containing an agitation blade is used in this study. Average particle stresses increase with an increase in particle aspect ratio, particle-particle friction coefficient, pressure on the top plate, and agitation blade height, indicating a higher probability of particle breakage. Particles orientation distributions indicate that as particle aspect ratio increases, particles orient such that their major axes are nearly aligned with the flow streamlines. Time-averaged displacement deviation, which is a measure of particle mixing, increases with increasing agitation blade height and decreases with increasing particle-particle friction coefficient. Increasing particle aspect ratio increases displacement deviation for smaller aspect ratios but displacement deviation becomes approximately constant for larger aspect ratios. Other factors such as, particle-wall friction coefficient and top plate pressure do not have any significant effect on either particle orientation or displacement deviation.