# FAN CALCULATOR. AFFINITY LAWS

This calculator provides information about how some paramenter of a fan changes when other are modifiedre. You can use any measurement unit, as long as you use always the same. Calculated data is shown in a shaded box.

## Rotational Speed - Volumetric flow

Volumetric flow is proportional to the rotational speed:

Known
conditions
Calculate
(Select)
r.p.m.
Caudal

This simple equation is very useful. For instance, it can show that if air temperature changes the fan will have the same volumetric flow rate, even if the density has changed.

## Pressure - Rotational speed

The pressure developed by a fan increases by the square of the speed and it also changes proportionally to the density. If we consider air at the same pressure, temperature, and relative humidity then the density does not change, so you can check the following option in order to avoid entering density value.

Density does not change

Known
conditions
Calculate
(Select)
Density [ρ]
r.p.m. [N]
Pressure [p]

## Power - Speed

Absorbed power from a fan varies directly by the cube of speed. This means that for small change in rotational speed the power changes a lot. For instance, if we reduce the speed by 20% we will have approximately half the power.

Density does not change

Known
conditions
Calculate
(Select)
Density [ρ]
r.p.m. [N]
Power [Pw]

## Fan tip speed

 Diameter (m) r.p.m. Speed (m/s)