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 the fluid

\(\large{ d }\) =  diameter of stirrer

\(\large{ P }\) = power

\(\large{ n }\) = rotational speed

Tags: Equations for Power