How Do You Calculate Torque for an Anchor Type Agitator Motor?

In summary: The motor has a soft start, but it is operated at constant RPM.Therefore, the idea is to get a worst-case scenario to design from.
  • #1
Nickf_Zar
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TL;DR Summary
Calculating the torque required for an agitator/scraper.
Hi All,

I must calculate the torque and for an agitator motor. An anchor type agitator/scraper, removing crust off the edge of a tank.

My instinct is the max or startup torque will be = (Moment of Inertia) x (Angular Acceleration) + (Drag force of the submerged impeller)* Max radius + (Frictional forces on the edge of the tank)* Max Radius

Tmax = ( I * α ) + [ ( Cd * A * ρ * V² * ½ ) + (µ * F) ] * D/2

• The motor has a soft start but is operated at constant RPM.
• The idea is to get a worst-case scenario to design from.
• Please suggest if you think this problem can be solved with a better solution.

I have very little experience with this type of stuff and would greatly the feedback.

My Questions to the community

• Is this analysis correct?
• What would be an acceptable coefficient of drag to use for a plate with cut-outs in it without doing an experiment
• What would be an acceptable coefficient of friction to use, for the solidified sealing compound attached to the walls?

Thank you
 

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  • #2
Nickf_Zar said:
I must calculate the torque and for an agitator motor. An anchor type agitator/scraper, removing crust off the edge of a tank.
If it's scraping crust, then it's a slow speed machine, and you can ignore the acceleration torque. Scraping crust is not a friction problem, it's a "cutting through the crust" problem. There are no published numbers for the force to do this, so you need to run some experiments. One possible experiment is to pull a hand scraper with a spring scale to directly measure the scraping force. Do your best to measure the worst case force, then add a substantial safety factor.
 
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  • #3
How the material could solidify if the agitator is constantly working?
Or it is the case that the agitator is only activated after the solidification occurs?
 

Related to How Do You Calculate Torque for an Anchor Type Agitator Motor?

What is agitator torque calculation?

Agitator torque calculation is the process of determining the amount of torque required to rotate an agitator in a mixing system. This calculation takes into account factors such as fluid viscosity, agitator speed, and impeller size to ensure efficient mixing.

Why is agitator torque calculation important?

Agitator torque calculation is important because it helps ensure that the agitator is able to properly mix the fluid in a tank or vessel. If the calculated torque is too low, the agitator may not be able to effectively mix the fluid. If the torque is too high, it can cause excessive wear and tear on the agitator and its components.

What factors are considered in agitator torque calculation?

The main factors considered in agitator torque calculation are fluid viscosity, agitator speed, impeller size, and tank dimensions. Other factors such as fluid density, agitator type, and baffle design may also be taken into account depending on the specific mixing system.

How is agitator torque calculated?

Agitator torque is typically calculated using the following formula: Torque = (fluid density x agitator speed^2 x impeller diameter^5) / (fluid viscosity x tank diameter^3). This formula takes into account the various factors that affect the torque required for efficient mixing.

What are some common challenges in agitator torque calculation?

Some common challenges in agitator torque calculation include accurately determining the fluid viscosity, accounting for non-Newtonian fluids, and considering the effects of multiple agitators or baffles in a mixing system. Additionally, variations in fluid properties or changes in the mixing process can also affect the accuracy of the calculated torque.

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