Power number

This article is about the dimensionless number in fluid mechanics. For the arithmetical and algebraic operation of repeated multiplication, see Exponentiation. For the maximum number of spheres touching a common sphere sometimes referred to as the Newton number, see Kissing number.

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