Power number
Encyclopedia
The power number Np 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:
with
Resistance force
In physics, resistance force is the force which an effort force must overcome in order to do work on an object via a simple machine. Resistance force, like most other forces, is measured in newtons or in pounds-force....
to the inertia force
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
.
The power-number has different specifications according to the field of application. E.g., for
stirrers the power number is defined as:
with
- P: powerPower (physics)In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
- ρ: fluidFluidIn physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
densityDensityThe mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight... - n: rotational speedRotational speedRotational speed tells how many complete rotations there are per time unit. It is therefore a cyclic frequency, measured in hertz in the SI System...
- d: diameterDiameterIn geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
of stirrer