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Power consumption equation

Q: I would like to know the formula for calculating power consumption for an agitator and grinding mill. I have all the process data information for this equipment, but I don’t know how to calculate approximate power from the data.

A: Mixer Power

Power = Power Number x Density x Rotational Speed³ x Impeller Diameter⁵

for common engineering units:

Power (P) - horsepower

Power Number (Np) - dimensionless quantity depending on impeller

geometry - a constant for turbulent conditions and geometric

similarity - need to know geometry of impeller for value (typical values between 0.3 and 6.0)

Density (sp.gr.) - specific gravity w/respect to water

Rotational Speed (N) – rpm

Impeller Diameter (D) – inches

Viscosity is not a factor for turbulent conditions

P = Np x (sp.gr.) x N³ x D⁵/1.524x10¹³