For improved cultivation it’s good to be aware of Np
Power Number is a dimensionless parameter used for estimating the power consumed by the rotor/agitating rotor / delivered to the media.
For a standard cylindrical vessel geometry, the power consumed by the rotor/impeller(s) at a specified rotational speed, for a liquid with known density, can be determined from the Power Number correlation.
Power = Power Number x Density x Agitator speed3 x Impeller Diameter5
P = Np ρ n3 Da5
P = Impeller power, Watt
Np = Power Number
ρ = Density of liquid, kg/m3
n3 = Rotor/agitator speed measured in revolutions / second
Da5 = Rotor/impeller diameters in meters
Calculated Power Number data for different type of rotors / impellers, under a give set of conditions are documented in various technical literature. Typical values of Power Number (Np) are:
- Axial flow impellers, such as marine, helical : 0,25 to 0,75
- Mixed flow impellers, such as kidney, pitch: 0,75 to 2,0
Power Number decreases with an increase in Reynolds number.
See also Glossary
Experimental results can be downloaded here.