Particle Motion Modeling for Particle Size Distributions in Blade Geometries, 2003 Advanced Coating Fundamentals Symposium Proceedings

For several years it has been seen that narrow particle size distributions tend to need to be run at lower solids than broad particle size distributions. In addition, some pigments tend to be associated with build up on blades during coating, while others can be linked to rapid blade wear. Little detailed understanding of the mechanisms behind these issues has been reported in the literature.

An improved Stokesian Dynamics technique is used to describe the motion of several thousand particles in the entrance region of a blade. The new technique uses some storage and time saving methods, allowing for an increase in number of particles to be run in the simulation on a personal computer. Any particle size distribution can be input into the model, but the method is limited to spherical particles. This method represents an improvement over past work. Boundary roughness can be included by using boundary particles in fixed locations.

In all cases, an accumulation of fine particles is seen in the stagnation region and along boundaries. This agrees with the work of Toivakka and Eklund (1996) for flow in a pipe. If a significant number of these small particles are latex, the forces on these particles could cause a buildup of solid material on the back side of the blade. There is also an accumulation of fine particles along the surface of the blade. This result may point to the coating layer being either latex or colloidal fraction rich at the exit of the blade. The average blade forces are different between different particle size distributions, but these differences are not large.