Centrifugal fan

A centrifugal fan is a mechanical device for moving air or other gases from the rotating inlet, in a direction perpendicular to the axis of rotation of the fan, to an outlet. Centrifugal fans often contain a ducted housing to direct outgoing air in a specific direction or across an electronic device's heat sink; such a fan is also called a blower, blower fan, turbo fan or squirrel-cage fan (because it resembles a hamster wheel). Tiny ones used in computers are sometimes called biscuit blowers. They are typically used in ducted applications to either push or pull air through ductwork or a heat exchanger; similar to impellers. Centrifugal fans can provide similar air movement from a smaller fan package, and overcome higher resistance in air streams than a comparably sized axial fans.

Centrifugal fans use the kinetic energy of the impellers to move the air stream, which in turn moves against the resistance caused by ducts, dampers and other components. Centrifugal fans displace air radially, changing the direction (typically by 90°) of the airflow. They are sturdy, quiet, reliable, and capable of operating over a wide range of speeds.

Centrifugal fans are, like axial fans, constant-volume devices, meaning that at a constant fan speed, such device moves a constant volume of air rather than a constant mass. This means that at a constant fan speed the air velocity and volume in a system is static, but the mass of air flowing will vary based on the density of the air. Variations in density can be caused by changes in incoming air temperature and elevation above sea level, making these fans unsuitable for applications where a constant mass of air is required to be provided.

Centrifugal fans are not positive-displacement devices that have certain advantages and disadvantages when contrasted with positive-displacement blowers: centrifugal fans are more efficient, whereas positive-displacement blowers typically have a lower capital cost, and are capable of achieving much higher compression ratios. In comparison to axial fans for residential, industrial, and commercial applications, axial fans typically can operate at higher volumes and lower static pressures, and have higher efficiency. Therefore axial fans are usually used for high volume air movement, such as warehouse exhaust or room circulation, while centrifugal fans are used to move air in ducted applications such as a house or typical office environment.

The centrifugal fan has a drum shape composed of a number of fan blades mounted around a hub. As shown in the animated figure, the hub turns on a driveshaft mounted in bearings in the fan housing. The gas enters from the side of the fan wheel, turns 90 degrees and accelerates due to centrifugal force as it flows over the fan blades and exits the fan housing.