  The performance of a fan is usually estimated from hydrodynamical
considerations. The calculations are long and involved and the results are
expressed in terms of three affinity laws. In this work we use kinetic theory
to attack this problem. A hard sphere collision model is used, and subsequently
a correction to account for the flow behaviour of air is incorporated. Our
calculations prove the affinity laws and provide numerical estimates of the air
delivery, thrust and drag on a rotating fan.
