Axial and Centrifugal Ventilation Fans

By: Chicago Blower

Axial fans blow air across the axis of the fan, linearly, hence their name. This type of fan is used in a wide variety of applications, ranging from small cooling fans for electronics to the giant fans used in wind tunnels.

A variable pitch balde in axial fan blower is used where precise control of static pressure within supply ducts is required. The fan wheel will spin at a constant RPM. The blades follow the control pitch hub. As the hub moves toward the rotor the blades increase their angle of attack and an increase in flow results.

Some examples of axial fans are:

Table fan - Basic elements of a typical table fan include the fan blade, base, armature and lead wires, motor, blade guard, motor housing, oscillator gearbox, and oscillator shaft. The oscillator is a mechanism that motions the fan from side to side. The axle comes out on both ends of the motor, one end of the axle is attached to the blade and the other is attached to the oscillator gearbox. The motor case joins to the gearbox to contain the rotor and stator. The oscillator shaft combines to the weighted base and the gearbox. A motor housing covers the oscillator mechanism. The blade guard joins to the motor case for safety.

Electro-mechanical fans - among collectors, are rated according to their condition, size, age, and number of blades. Four-blade designs are the most common. Five-blade or six-blade designs are rare. The materials from which the components are made, such as brass, are important factors in fan desirability.

Ceiling fan with light. Ceiling fan - A fan suspended from the ceiling of a room is a ceiling fan.

In automobiles, a mechanical fan provides engine cooling and prevents the engine from overheating by blowing or sucking air through a coolant-filled radiator. It can be driven with a belt and pulley off the engine's crankshaft or an electric fan switched on/off by a thermostatic switch.

In centrifugal fan, as opposed to axial flow fan, the air is moving perpendicularly to the fan shaft. Often called a "squirrel cage" (due to its similarity in appearance to exercise wheels for pet rodents), the centrifugal fan has a moving component (called an impeller) that consists of a central shaft about which a set of blades, or ribs, are positioned. Centrifugal fans blow air at right angles to the intake of the fan, and spin the air outwards to the outlet (by deflection and centrifugal force). The impeller rotates, causing air to enter the fan near the shaft and move perpendicularly from the shaft to the opening in the scroll-shaped fan casing. A centrifugal fan produces more pressure for a given air volume, and is used where this is desirable such as in leaf blowers, hair driers, air mattress inflators, inflatable structures, and various industrial purposes. They are typically noisier than comparable axial fans.

A mixed flow fan - is an air moving device in between axial flow fan and centrifugal fan. Mixed Flow fans are an excellent choice for return air, supply, or general ventilation applications where low sound is critical. As compared to similarly sized tubular centrifugals and vane axials, a mixed flow fan will be 5-20 dB quieter! In addition, the mixed flow wheel is extremely efficient and will cut down on operating expenses.

For additional information please refer to

Oleg Tchetchel
Ventilation HVAC Engineer
CBC Canada Co.

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Oleg Tchetchel Ventilation HVAC Engineer CBC Canada Co.

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