# Power Number

Written by Jerry Ratzlaff. Posted in Dimensionless Numbers

Power number is a dimensionless number proportional to drag force and inertial force and is used in momentum transfer and power consumption by agitators, fans, pumps, etc.

## FORMULA

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

Where:

$$N_p$$ = Power number

$$k_d$$ =  dimensional constant

$$P$$ = power

$$N$$ = rate of rotation

$$\rho$$ (Greek symbol rho) = density

$$l$$ = characteristic length