Discrete element simulation of free flowing grains in a four-bladed mixer

Brenda Remy, Johannes G. Khinast, Benjamin J. Glasser

Research output: Contribution to journalArticlepeer-review

133 Scopus citations

Abstract

Numerical simulations of granular flow in a cylindrical vessel agitated by a fourblade impeller were performed using the discrete element method. Velocity, density, and stress profiles within the mixer displayed a periodic behavior with a fluctuation frequency equal to that of the blade rotation. Blade orientation was found to affect flow patterns and mixing kinetics. For an obtuse blade pitch orientation, a threedimensional recirculation zone develops in-front of the blade due to formation of heaps where the blades are present. This flow pattern promotes vertical and radial mixing. No recirculation zone was observed when the blade orientation was changed to an acute blade pitch. The system's frictional characteristics are shown to strongly influence the granular behavior within the mixer. At low friction coefficients, the 3-D recirculation in front of the obtuse blade is not present reducing convective mixing. Higher friction coefficients lead to an increase in granular temperature which is associated with an increase in diffusive mixing. Normal and shear stresses were found to vary with mixer height with maximum values near the bottom plate. Additionally, a strong dependence between the magnitude of the shear stresses and the friction coefficient of the particles was found. The stress tensor characteristics indicate that the granular flow in our simulations occurs in the quasi-static regime. At the same time, the averaged pressure was found to vary linearly with bed height and could be predicted by a simple hydrostatic approximation.

Original languageEnglish (US)
Pages (from-to)2035-2048
Number of pages14
JournalAIChE Journal
Volume55
Issue number8
DOIs
StatePublished - Aug 2009

All Science Journal Classification (ASJC) codes

  • Biotechnology
  • Environmental Engineering
  • General Chemical Engineering

Keywords

  • Agitated dryer
  • Bladed mixer
  • DEM
  • Granular mixing
  • Quasi-static flows

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