Power number

The power number N_p (also known as Newton number) is a dimensionless number relating the resistance force to the inertia force. In engineering, this number, along with the Reynolds number, is one of the most widely employed dimensionless numbers.

The power-number has different specifications according to the field of application. E.g., for stirrers the power number is defined as:

<math> N_{p} = {M_{t}\over \rho n^{3} d^{5}} <math>

with

• M_t: torque
• ρ: fluid density
• n: rotational speed
• d: diameter of stirrer