# Power Number

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

## Power Number

Power number ( $$N_p$$ ) (dimensionless number) is proportional to drag force and inertial force and is used in momentum transfer and power consumption by fans, mixers and pump impellers at a specified rotational speed.

### Power Number FORMULA

$$\large{ N_p = \frac {k_dP} {N^3\rho l^5} }$$

Where:

$$\large{ N_p }$$ = Power number

$$\large{ k_d }$$ =  dimensional constant

$$\large{ P }$$ = power

$$\large{ N }$$ = rate of rotation

$$\large{ \rho }$$  (Greek symbol rho) = density

$$\large{ l }$$ = characteristic length

Tags: Equations for Power