FANS
What Is a Centrifugal Fan?
What Is a Centrifugal Fan?
A centrifugal fan is a type of industrial blower that utilizes spinning blades to accelerate and push air outward through ductwork or tubing. They are common in applications that function with dirty airstreams containing particulates and gases and for systems that operate at high temperatures. They are sturdy, quiet, and reliable and can operate over a wide range of conditions.
A central component of a centrifugal fan is a rotating wheel of curved blades called an impeller. The impeller is surrounded by a drum-shaped housing that houses the shaft and bearings. The hub of the wheel is mounted on an electric motor that rotates the wheels – usually using an AC induction motor. The rotational force of the motor generates centrifugal power to increase the kinetic energy of the gas particles close to the impellers and the kinetic energy of the particles farther from the impellers – resulting in higher airflow performance.
The fan housing may include features such as inlet and outlet cones, vanes, and scroll sections to further shape and guide the flow of air. The outer edge of the housing is typically shaped like a twisted ammonite shell without the spiral – a design called a volute casing. The curved funnel shape increases in area as it gets closer to the fan discharge port, which allows the fan to handle higher pressures.
Some fans use a single, fixed-speed motor that drives the entire impeller assembly. This provides greater efficiency than direct drive fans, but at a sacrifice in output compared to fan designs that have a separate electric motor for each individual impeller rotational speed. Some fans use a variable-speed electric motor that allows the operator to control the rotational speed of the motor based on the required system output – improving efficiency and increasing or decreasing the output accordingly.
Fans are rated in terms of their airflow capacity, which is measured in standard cubic feet per minute (SCFM). The rating is based on uniform procedures for testing housed fans under a variety of operating conditions. The procedure for determining an airflow rate is defined by the AMCA Standard 210, which defines exact test methods and conditions that should be used in order to compare the performance of different fans.
A common comparison between axial and centrifugal fans is that centrifugal fans are constant-volume devices while axial fans are positive-displacement machines. This difference is important because the horsepower required by a centrifugal fan will vary directly with variations in air/gas density, which can occur due to changes in incoming temperature and elevation above sea level (altitude).
Because centrifugal fans are designed for stable operation, any variation in output will significantly affect their reliability and useful life. This is why most fans are fitted with dampers on both the inlet and outlet sides of the fan to limit the amount of output that can be changed. Dampers are also used to adjust fan power consumption based on system requirements.
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