# Power Number

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Power number, abbreviated as $$N_p$$, is a dimensionless number that represents the proportional  drag force and inertial force. It is used in momentum transfer and power consumption by fans, mixers and pump impellers at a specified rotational speed. The calculation and formula for the Power Number are shown below.  Note: it may be referenced as the Newton Number.

 $$\large{ N_p = \frac {P}{\rho \; n^3 \; d^5} }$$          Where: $$\large{ N_p }$$ = Power number $$\large{ \rho }$$  (Greek symbol rho) = density of fluid $$\large{ d }$$ =  diameter of stirrer $$\large{ P }$$ = power $$\large{ n }$$ = rotational speed

Tags: Equations for Power