|Themes > Science > Physics > Fluid Dynamics > Flying the flag for fluid dynamics > Aerodynamics > Low-speed steady aerodynamics / hydrodynamics > All you need to know about fans > The Fan Laws|
Sometimes it may be necessary to determine the output of a given fan under other conditions of speed or density, or to convert the known performance of an air mover of one size to that of another geometrically similar unit of a different size. The fan laws permit this.
Geometrically similar fans can be characterized by the following four equations:
Volumetric Flowrate: G = KqND3
Mass Flow Rate: m· =Km ND3
Pressure: P = KpN2D2
Power: HP = KHPN3D5
From these relationships, it is possible to calculate a fan performance at a second condition. Table 1 is a summary of the fan law equations in a form useful for fan analysis.