Normally blade speed for a high speed disperser is targetted at 5200 fpm (feet per minute).
Blade Speed (tip speed), measures how far a point on the outer most edge of the disperser blade travels in a given amount of time. You may remember from early math classes that the circumference (perimeter) of a circle is equal to:
Circumference = Π × D
So if we take a 1 foot diameter (D) blade and turn it one complete revolution, a point on its edge would have travelled pi (Π) 3.14 feet. By multiplying by rpm (n) we get the Tip Speed formula:
TipSpeed = Π × D × n
where:
- Tip Speed - impeller tip speed (rpm)
- D - impeller diameter (ft)
- n - impeller rotation speed (fpm)
Disperser manufacturers target between 4000 and 6000 fpm (feet per minute) for the tip speed of their dispersers. As with blade diameter, there are advantages to varying the tip speed of these dispersion blades. Higher tip speeds may produce superior grinds in difficult to disperse products or counter insufficient flow in high viscosity batches. Lower speeds will reduce the vortex in low viscosity batches.
From an operator's perspective, one blade may function adequately in several different diameter tanks, resulting in less operator intervention.
Below are three Calculators addressing the most common uses of the tip speed equation.
- Tip Speed - calculating tip speed based on a know blade diameter and rpm.
- RPM - calculating rpm needed to develop a desired tip speed with a know blade diameter.
- Scale Up - Match the tip speed of one mixer to that of second disperser with differing blade sizes.