High Shear Dispersing
Ordinary paddle or propeller type mixers operate in the 1000-2000 Feet/Minute (FPM) tip speed range.
High Shear disperser/mixers operate in the 4500-6000 Feet/Minute tip speed range.
FPM= RPM x impeller diameter in inches/12 x 3.14159.
High shear dispersing is needed when mixing immiscible liquids, or dry powders and liquids. Slow speed mixing of powders and liquids form lumps with dry centers coated with a wet outer layer. The high tip speed of the saw tooth Cowles style impeller, creates intense fluid shear which rips those lumps apart into individual particles or much smaller agglomerates, giving smooth texture to the mixture.
Additional shear, over and above a saw tooth style impeller, can be achieved with a Rotor-Stator device, which creates an intense shear zone between the tight tolerance rotor and stator.
An open saw tooth style impeller has a fluid shear zone that extends out about 1” from the impeller tips which are moving about 5000 FPM for shear gradient of about 5000 FPM/inch. The Rotor-Stator has a shear zone of about .040” between the rotor running about 2000 FPM and the stationary stator, for shear gradient of about 50,000 FPM/inch, ten times as much.
The Rotor-Stator attachment is useful for making some emulsions and dealing with very hard to wet powders.
Additional dispersion may be accomplished through bead or media milling. We don’t make true media milling equipment, though we do offer small batch media mill attachment for the CM-100 machine.
If you have any questions about the dispersing process or would like to discuss your mixing/dispersing equipment needs with an expert, call us at 928-567-2588 today.