Power number

For Newton number, see also Kissing number in the sphere packing problem.

The power number N_p (also known as Newton number) is a commonly used dimensionless number relating the resistance force to the inertia force.

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

$N_{\mathrm{p}}=\frac{P}{\rho n^3{D}^5}$

with

• P: power
• ρ: fluid density
• n: rotational speed in revolutions per second
• D: diameter of stirrer