Mixing Principle: Turbulent Hydraulic Shear

     Fig A.  FDM rotor                Fig. B   Flowpath through      Fig C.  Detail showing hydraulic
               and stator                         an FDM mixer                      action in rotor cavities 

FDM is a concentric rotor-stator system with indentations or cavities machines into the rotor and stator surfaces (Fig. A).  The rotor and stator are based on a stepped conical form so that the diameter of the cone increases from inlet to outlet.  This increasing diameter provides a centrifugal pumping effect.  The cavities in the rotor and stator are typically spherical segments which are open on both vertical and horizontal faces.

Fluid moving from inlet to outlet through the mixing head (Fig. B), is driven both axially and radially by the pumping and rotational forces generated by the rotor component.  As fluid enters the mixing head, it fills the first paired rotor-stator row of cavities. The motion of the rotor initiates spin in the fluid and the direction of spin in the rotor cavities is opposite to that in the stator cavities. The fluid vortices formed by this action (Fig. C) collide with one another, imparting hydraulic shear. It is this shearing action that transfers energy to the fluid for particle and droplet size reduction. An additional effect of the contra-vortex motion of the fluid is intimate microscopic-scale blending. This helps with rapid and complete powder dispersion in liquids.

Benefits
This unique high shear mixing mechanism has several additional benefits when compared to conventional blade/screen type shearing mixers:

• the rotor-stator gap is relatively unimportant - tight clearances can be avoided
   

• the energy transfer primarily results from fluid shearing on itself, so particles contained within the fluid are impacted against each other rather than against the mixer surface.  This gives improved particle size reduction and reduces the amount of wear on the mixer surfaces.
   

• all of the material going through the mixer is forced to participate in the high shear action, giving much more consistent results per pass when compared to conventional machines where much of the fluid may bypass the high shear zone.