Centrifugal FansThe centrifugal fan was invented in 1832 by military engineer Lieutenant General Alexander Sablukov of the Russian Empire’s Imperial Russian Army. Often called blowers, centrifugal fans vary differently from axial fans. The pressure of an incoming airstream is increased by a fan wheel, a series of blades mounted on a circular hub. Centrifugal fans move air radially — the direction of the outward flowing air is changed, usually by 90°, from the direction of the incoming air.http://www.hongkefans.com/centrifugal-fan/