Centrifugal Fans
A key factor in many industrial applications is directional airflow, which is necessary for removing dust, gases, pollutants, and for the safety of workers. Though axial fans could do the job, they are not capable of providing the required directionality and control. In those conditions, the tool that is most efficient and provides the airflow characteristics needed for the application is a centrifugal fan. Unlike axial fans, centrifugal fans pull air in and change its angle of discharge, a process that increases the velocity and pressure of the air. This design allows for accurate control of the airflow pattern.
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Applications of Centrifugal Fans
The advantage of centrifugal fans is their ability to control the pressure, velocity, and direction of the airflow so that it can be applied to a specific location. This feature is essential for industrial operations that involve dust, gases, and contaminants.
Centrifugal Fan Design and Function
A centrifugal fan has a spiral casing that contains an impeller attached to the motor. Two ducts allow air to enter and exit the fan casing. One duct pulls air in while the other duct discharges the air. The tight, uniform construction of the fan increases the pressure of the airflow as it leaves the fan.
When a centrifugal fan is activated, the impeller pulls ambient air in through the inlet duct. The blades of the impeller catch the air and increase its velocity by their rapid rotation. The swirling airflow moves from the center of the impeller to its outer edges and is expelled through the outlet duct at higher pressure and speed.
Types of Centrifugal Fans
Centrifugal fans are classified by the types of blades on their impeller and the drive of their motor. The difference between the types of blades is determined by the air pressure they create.
Impeller blades can be divided into these four categories:
- Radial Fans
- These are used in industrial applications where there is a great deal of dust, gases, or humidity. Fans with radial blades produce high air pressure from a medium airflow.
- Airfoil Fans
- Has blades in the shape of an airfoil. They provide the highest efficiency and are used in chemical factories, power plants, and metal factories. Airfoil fans are capable of operating in high temperature environments that have harsh conditions.
- Forward Curved Fans
- The impeller of a forward curved fan looks like a squirrel cage. They generate the highest amount of airflow and are used in high temperature applications, such as furnaces, where dust or particles are in the air.
- Backward Curved Fans
- Have the same characteristics as airfoil fans, including the same efficiency. The backward curvature of the blades helps avoid dust and contaminant buildup. They are normally chosen for high pressure applications.
Types of Centrifugal Fan Drives
The two types of drives are direct and belt. The choice of which drive depends on the fan manufacture and how the fan will be used. Belt drives are the most common. Direct drive fans have the motor connected to the shaft of the impeller. They have a very compact design and are easy to maintain. Direct drive fans are smaller and have a low cost with exceptional efficiency. The more common belt driven fan has the motor connected to the shaft of the impeller by a pulley. They have greater flexibility and can match any set of airflow requirements. Belt driven fans are larger and have variable pitch motors.