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Calculating the Agitator Torque For Adhesive Production

Q: We are trying to calculate the agitator torque for adhesive production. What size electrical motor and gearbox is required to drive this agitator? How about with a hydraulic drive?

Here are the specs:

ID of reactor is 1,250 mm
Height of reactor is 2,360 mm
Rod diameter is 80 mm
Agitator has two 45-degree pitched blades
Length of blade is 530 mm
Diameter of agitator with blade is 1,140 mm
Material viscosity is 100,000 cp
Require speed is variable from 30 to 100 rpm
Density of material is 1250 kg/m³

A:

Although this design is unusual, including both the impellers and baffles, it may be able to mix 100,000 cp adhesive, so long as the material is not too visco-elastic.

No way do you want to run this mixer at 120 rpm, not even in water.  In polymer, the power required is 112 kW with 28,700 N.m torque.  You would effectively boil or decompose any adhesive in a mater of minutes.  Even in water at 120 rpm, this mixer would require a 56 kW motor with similar results.  The maximum speed and power that the shaft could tolerate, even with the steady bearing is about 70 rpm, which would require a 37 kW motor and 9,600 N.m of torque.  A higher torque would break the shaft.
 
A practical and effective design would run at 37 rpm and require an 11 kW motor with 2,870 N.m of torque.  A lower speed may be as effective or more effective at high viscosity.  Some materials need time to flow after the impeller blade passes through the material.  Whether you use an electric motor or hydraulic drive, the power required by the impellers remains the same.
 

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