Powder Mixing and Segregation

Publication Reference: 
33-08
Author Last Name: 
Muzzio
Authors: 
Fernando J Muzzio and Troy Shinbrot
Report Type: 
FRR
Research Area: 
Powder Flow
Publication Year: 
2001
Publication Month: 
05
Country: 
United States

We describe specific progress in our understanding of granular segregation in granular and powder processing equipment of industrial importance. We have found several new results of apparent practical importance for the blending of solids.

We have:

· Established that in some applications segregation patterns shut down above a specific particle size ratio. Velocimetry measurements indicate that this cut-off occurs when larger particles sink into the cascading layer, at which point they become unable to overtake their smaller neighbors.

· Determined that segregation in tumbling blenders scales according to two distinct scaling relations depending on tumbling regime.

· Confirmed that small amounts of cohesion are sufficient to significantly inhibit segregation. When cohesion is introduced by increasing the moisture content of a blend, the amount of moisture needed to effectively mitigate segregation decreases with particle size.

· Quantitatively evaluated the effects of intensifier bars on preblending of cohesive blends of common industrial powders.

· Determined that there exist a robust and reproducible set of segregation patterns that can be found across a wide range of blender sizes and geometries and across a wide scale of particle sizes.

These segregational states can actually be accentuated by traditional strategies for improving mixing by introducing cross-flows. Moreover, the dominant segregation pattern seen at high fill levels and tumbling speeds is the pattern exhibiting the most extreme segregation throughout the highest volume of the blend.

• Developed accurate models for the development of segregation patterns based on velocity histories of cascading particles that successfully predict segregation outcomes in a several different classes of 3D blenders. These results are of direct practical importance and call for validation at all feasible scales.