# Mixer Impeller Speed & Particle Velocity Discussion

• thegeant
In summary, the relationship between impeller speed (RPM) and particles velocity (bubbles) in a mixer can be approximated by calculating the distance the impeller moves for each revolution and considering any potential slip. Additionally, the efficiency of the impeller can also be affected by the angle of attack of its blades. Further clarification is needed on whether the bubbles are induced by cavitation or entrained from the surroundings. Studies on the terminal velocity of rising bubbles can be found in hydrodynamics literature.
thegeant
I would like to ask question and open a discussion about the relation between the impeller speed (RPM) of a mixer and particles velocity (bubbles). Thanks

If you think of an impeller/propeller as being like a wood screw screwed into some wood then you can calculate how far it should move for each revolution. From that and the rpm you can work out how fast it should move through the material...or how fast the material should move through it.

The above give a rough estimate of the maximium speed that an impeller/propeller can move material, however it could be less than that due to "slip".

If you think of a propeller blade as being like a wing then without slip the pitch of the blades would have zero angle of attack relative to the material they are moving through. Wings are generally more efficient at a slightly positive angle of attack.

I'm sure there are people out there who know more then me but that's my take on the issues.

thegeant said:
I would like to ask question and open a discussion about the relation between the impeller speed (RPM) of a mixer and particles velocity (bubbles). Thanks

thegeant, Welcome to Physics Forums!

Will you please be more specific? Are you referring to gas bubbles induced by cavitation of the impeller blades? Or are you referring to gas bubbles entrained from the surroundings by the impeller? The hydrodynamics literature normally contains studies of the terminal velocity of rising bubbles. Is this what you are asking about?

Cheers,
Bobbywhy

## 1. What is the purpose of controlling mixer impeller speed?

Mixer impeller speed is controlled to achieve desired particle velocity and mixing efficiency in a mixing process. It also ensures proper distribution of energy and shear forces within the mixing vessel.

## 2. How does mixer impeller speed affect particle velocity?

Mixer impeller speed directly affects particle velocity by generating shear forces and turbulence, which promote the movement and collision of particles. Higher impeller speeds result in higher particle velocities, while lower speeds generate lower velocities.

## 3. What factors influence the optimal mixer impeller speed?

The optimal mixer impeller speed is influenced by the properties of the particles being mixed (such as size, density, and shape), the desired mixing time, and the type of mixing vessel and impeller design.

## 4. How can I calculate the ideal mixer impeller speed for my mixing process?

The ideal mixer impeller speed can be calculated through various methods, such as empirical equations, computational fluid dynamics (CFD) simulations, or experimental trials. The best approach will depend on the specific characteristics of the mixing process and the available resources.

## 5. Can changing the mixer impeller speed improve mixing efficiency?

Yes, changing the mixer impeller speed can significantly improve mixing efficiency by promoting better particle movement and collision, reducing mixing time, and achieving better homogeneity in the final product. However, the optimal impeller speed will vary depending on the specific mixing process.

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