Centrifugal Fan Homepage

Question: Explain the operation of centrifugal fan.how the pressure increases in fan.?

(Posted by: bazoomba on 2006-02-15 03:38:53)

Posted by: phi071237 on 2006-02-15, 03:43:58

The air at the path of the rotating blade of the fan is forced to flow. pressure is directly proportional to the speed of the fan blade

Posted by: Kes on 2006-02-15, 05:26:06

As shown in the link, a centrifugal fan has a set of fan blades arranged on the surface of an imaginary cylinder that direct air flow out of the fan in a radial direction. When the fan rotates, the inside edges of the fan blades "scrape " air into the blades and the spinning effect throws the air outward much like spinning a bucket full of water, with a hole in the bottom, on a rope. Thus the pressure is lowered inside the fan causing more flow to enter the fan and the pressure increases at the outlet side causing the air to flow away from the fan, perhaps through an air duct. Interestingly though, air will flow in the same direction even if you reverse te motor because of the centrifugal forces, but the blades (vanes) are shaped to maximized efficiency only in the correct (designed) direction.

Posted by: jabbadahuthut on 2006-02-15, 21:56:53

There is a fundamental formula in turbomachinery that computes the work done on a flow of fluid by a rotating bladed disk (axial or centrifugal), and then relates the work to the pressure rise. It shows that the work and pressure head are determined by the "wheel speed " and "turning " done by the blades. Wheel speed can be thought of as rotational speed. Turning is the angle that the fluid flow is turned by as the blades do work on the fluid. Intuitively, this makes sense: To get more pressure rise either increase the speed of rotation or increase the pitch of the blades. This works only up to a certain point however, and eventually the fluid flow breaks down and the fluid "stalls " over the blades, and then the fan/ pump become very inefficient. WHat this means is that you have to put a lot for work into driving the fan/ pump/ compressor than it is able to do on the fluid and convert into useful pressure rise.