Instrument for ceramic particle dispersion II: Computational fluid dynamics analysis

A planetary-type mixer using a container equipped with stainless steel mesh has been developed. For various slurries (Al₂O₃ in water), each modeled as Newtonian fluid, the shear stress was calculated using computational fluid dynamics (CFD) under various mixing conditions and with different equipment properties. The meshed-geometry included more than 100,000 nodes with hexahedral cells in one zone, with quadrilateral cells in the remaining zones. The fluid viscosity, rotation rate, and mesh opening affected the maximum shear stress. The shear stress increased concomitantly with increasing fluid viscosity. The container rotation rate and the maximum shear stress share a proportional relation. For a fluid with 9.2 mPa s, the shear stress was 134 Pa or more for a 0.81 mm and larger mesh opening, as observed at the bottom of the container. Mesh having an opening smaller than 0.81 mm generated high shear stress on the mesh surface. The maximum shear stress increased with decreasing mesh opening size. The particle size distributions of the Al₂O₃ particles in the slurries after treatment by the mixer were estimated under conditions similar to those of the calculations. Results show peaks in the particle size distributions of the Al₂O₃ particles in the slurries before treatment at 0.2 and 2-70 μm because of the primary particle size and agglomerates. The amounts of the agglomerate decreased concomitantly with the decreased mesh opening size. When slurries pass through the small mesh openings, high shear stress is generated. That achieves the good dispersion of the sub-micron sized Al₂O₃ particles in the slurry.