Numerical investigation of mixing and orientation of non-spherical particles in a model type fluidized bed

• Mixing in a fluidized bed is studied by the DEM/CFD for complex shaped particles.
• Results are very rich in details.
• Weakly elongated particles reveal the tendency to mix quicker than spheres.
• The representation accuracy has strong influence on the particle mixing.
• Elongated particles tend to align parallel/perpendicular to the vessel walls.

A numerical investigation of mixing in a model type fluidized bed is performed based on the three-dimensional discrete element method coupled with computational fluid dynamics (CFD). Particle motion is represented by the discrete element approach applying clustered spheres as well as polyhedrons for the particle shape representation. On the CFD-side fluid flow around individual particles is not resolved, but averaged over cells larger than the particles. Various elongated particle shapes are considered including cylinders, plates and cuboids. Comparisons to spherical particles are made. Thereby, the main focuses are mixing which is assessed by the Lacey index, bed height progression and averaged particle orientation. The investigated particle/fluid systems are rich in detail. Large deviations are obtained for the different particle shapes considered. Mixing as well as bed height progression is also strongly influenced by the particle shape. Especially the shape representation accuracy has strong influence on the results as mass and projection area get altered. Significant variations can be obtained for the preferred particle orientations taken up in regions close to the vessel walls in contrast to the interior of a fluidized bed which clearly limits the ability to evaluate processes inside fluidized beds based on visual observations from the exterior only.

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