Power Number definition

For improved performance it’s good to be aware of PN

For a specific vessel with specific internals (like baffles, deep tubes, sensors) the Power Number of the specific rotor at a specified rotational speed, in a liquid with known density, can be calculated with knowledge about the consumed rotor power measured in Watt.

Watt = Power Number x Density x Agitator speed3 x Rotor Diameter5

Rotor power as Watt consumption is though difficult to measure. Scientific articles don’t suggest an easy way to measure Watt consumption. Often, it requires the measurement of the torque at the rotor shaft. Use Perseus to measure Watt and get the Power Number instantly.

CerCell offer 650 different impellers each with a name code: principal type, diameter in mm, number of blades, blade angle in degree, direction (Left or Right).

Typical values of impeller 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

CerCell offer 150 different turbines with a specific name code: principal type, diameter in mm, number of blades, blade angle in degree, direction (Left or Right).

Typical values of turbine Power Number (Np) are:

  • Turbines as shown on drawings above: 2.5 – 6.5

We further suggest looking into:

  • Check out the online calculator
  • How to measure Power Numbers with Perseus
  • Check out SUB impellers available
  • Check out SUF turbines available
  • Glossary