(208f) Sphero-Cylindrical Particle Stresses in a Vertical Axis Mixer

A discrete element method model is used to examine the stresses in sphero-cylindrical particles agitated in a vertical axis mixer. The model is validated against experimental measurements of the rotating shaft torque.  Using this model, the effects of particle aspect ratio from one to approximately nine, on blade torque, flow patterns, and average particle internal stress are investigated. Increasing particle aspect ratio generally decreases the flow rate of particles over the blade and increases the height of the heap in front of the blade. The mean particle hydrostatic and Mises stresses are found to increase with increasing bed depths ranging from one to two times the blade height and impeller speeds from 0 to 90 rpm.  The stress distributions also appear to follow two different exponential distributions, depending on the stress magnitude.  Increasing the particle aspect ratio increases the mean Mises stress due to an increase in the bed height in front of the mixer blade, as well as due to the interference of particles as they flow past one another.  Increasing either the inter-particle friction coefficient from 0.11 up to 0.66 or the particle elastic modulus from 1 MPa up to 100 MPa results in larger internal stresses.  However, increasing the particle-drum friction coefficient from 0.17 up to 0.68 has a much weaker influence.