- The major types of centrifugal fan are radial, forward curved and backward curved.
Radial fans are industrial workhorses because of their high static pressures (up to 1400 mm WC) and ability to handle heavily contaminated airstreams. Because of their simple design, radial fans are well suited for high temperatures and medium blade tip speeds.
Forward-curved fans are used in clean environments and operate at lower temperatures. They are well suited for low tip speed and high-airflow work – they are best suited for moving large volumes of air against relatively low pressures.
Backward-inclined fans are more efficient than forward-curved fans. Backward- inclined fans reach their peak power consumption and then power demand drops off well within their useable airflow range. Backward-inclined fans are known as “non- overloading” because changes in static pressure do not overload the motor.
- The major types of axial flow fans are: tube axial, vane axial and propeller
Tube axial fans have a wheel inside a cylindrical housing, with a close clearance between blade and housing to improve airflow efficiency. The wheel turns faster than propeller fans, enabling operation under high-pressures 250 – 400 mm WC. The efficiency is up to 65%.
Vane axial fans are similar to tube axial, but with the addition of guide vanes that improve efficiency by directing and straightening the flow. As a result, they have a higher static pressure with less dependence on the duct static pressure. Such fans are used generally for pressures up to 500 mmWC. Vane axial are typically the most energy-efficient fans available and should be used whenever possible.
Propeller fans usually run at low speeds and moderate temperatures. They experience a large change in airflow with small changes in static pressure. They handle large volumes of air at low pressure or free delivery. Propeller fans are often used indoors as exhaust fans. Outdoor applications include air-cooled condensers and cooling towers. Efficiency is low – approximately 50% or less.
- Common Blower Types
Blowers can achieve much higher pressures than fans, as high as 1.20 kg/cm2. They are also used to produce negative pressures for industrial vacuum systems. Major types are centrifugal blower and positive-displacement blower.
Centrifugal blowers look more centrifugal pumps than fans. The impeller is typically gear-driven states as 15,000 rpm. In multi-stage blowers, air is accelerated as it passes through each impeller. In single-stage blower, air does not take many turns, and hence it is more efficient.