Intermeshing Impellers

To create the mixer geometry, a cylindrical mesh is generated for the tank. Two other, completely independent meshes are defined for the blades. The three meshes are then combined into one. As the blades rotate, the transient flow pattern in the tank can be calculated and illustrated by the dispersion of tracer particles, as shown in the figure. As the total number of rotations increases, the tracer becomes more uniformly distributed. After six rotations, the dispersion of the tracer particles in the horizontal plane is satisfactory. Note, however, that the particles have moved little in the vertical direction. This is becanse the anchor impellers in use impart little or no axial momentum to the fluid. Twisted blades, which also impose an axial motion on the flow, might perform better to distribute the tracer throughout the vessel. The mesh superposition technique is well suited to study such systems. For other examples of flow in planetary mixers, see Tanguy et al. (1999) and Zhon et al. (2000). 

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Equipment for viscous mixing usually has a small clearance between impeller and vessel walls, a relatively small volume, and a high power per unit volume. Intermeshing blades or stators may be present to prevent material from cyhndering on the rotating impeller. 

Figure 5-28 Dispersion of a particle tracer in a vessel equipped with two intermeshing anchor impellers, calculated using the mesh superposition technique. After six full rotations, the particles are well dispersed on the horizontal plane where they were released.

For specifically difficult applications, special combinations of anchors/helixes and anchor/turbines can be used. For example, a helical ribbon impeller can be supported on an anchor for providing both top-to-bottom material movement and folding action. For dispersing powder into a viscous liquid, a high-speed dispersing disk is used in combination with the helix. Intermeshing cone helical ribbon impellers also exist for self-cleaning action and for viscous plastic masses, which may accumulate on the impeller blades. 

Intermeshing blades or stators to keep the material from cyUndering on the rotating impeller... 

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