# Topic: Re: Can you calculate the power required by an anchor impeller to mix a fluid of known viscosity and density?

posed by  Last edited: 5 September 2012 At 12:25pm
It is possible to calculate the power required by an anchor impeller to mix a fluid of known viscosity and density.&nbsp; The motor power is at least 110% of the calculated impeller power.&nbsp; The motor power may be 125% to 200% of the impeller power, depending on the accuracy and certainty of the fluid viscosity.&nbsp; The power calculation is probably easier than the explanation.&nbsp;The impeller power is calculated by the Power Calculation - Viscous.&nbsp; The viscosity and rotational speed come from the fluid properties and mixer operation, the viscous power number and impeller diameter will be explained further.&nbsp; The viscous power number is calculated first from just the geometry according to Anchor - Power Number Viscous.&nbsp; The tank diameter is the stated starting point for the calculation question.&nbsp; A typical anchor impeller has a diameter 90% to 95% of the tank diameter.&nbsp; The blade width is typically about 10% of the impeller diameter.&nbsp; The number of arms is almost always two.&nbsp; The height of the vertical blade may be about the same as the impeller diameter, but the power will depend on the liquid level, if it is less than the height of the anchor blade.&nbsp; The determination of these values depends on the mixer design and application.&nbsp;However, this viscous power number value previously calculated only applies for a Reynolds number less than 15.&nbsp; So the Reynolds number must be calculated according to Reynolds Number Evaluation w Definition.&nbsp; With the Reynolds number a correction factor, Correction Factor - Viscous Power, can be calculated depending on the range for the Reynolds number.&nbsp; That correction factor can be multiplied times the Anchor - Power Number Viscous previously calculated.&nbsp; The corrected viscous power number can be used along with the other dimensions and properties in the Power Calculation introduced at the beginning of the explanation.&nbsp;As a final comment - an anchor impeller is a poor selection as an impeller type because is provides almost no vertical, top to bottom, motion.&nbsp; It only provides motion at the vessel wall and usually has a long blend time with poor mixing results.&nbsp; Better impellers, such as a helical ribbon impeller, are recommended for viscous mixing applications.&nbsp; In some cases, a combination of an anchor and other impellers on separate shafts will provide adequate mixing.
The answers by this expert are based on the best available interpretation of the information provided.&nbsp; The consequences of the application of this information are the responsibility of the user.&nbsp; If clarification is needed, please submit a further question.
• RAGHU RAMAYYA KARUTURI Community Member 1 Post

#### Re: Can you calculate the power required by an anchor impeller to mix a fluid of known viscosity and density?

Last edited: 6 September 2012 at 1:35pm
How to calculate power of motor with 4 Nos of baffles(width is 10% of vessel diameter) and anchor sweep is 70% of vessel diameter?
• Dave Dickey Forum Moderator 324 Posts

#### Re: Can you calculate the power required by an anchor impeller to mix a fluid of known viscosity and density?

Last edited: 8 September 2012 at 12:00am