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 the 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. The design allows for accurate control of the airflow pattern.
What is a Centrifugal Fan?
A centrifugal fan has a spiral casing that contains an
impeller that is 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.
The advantage of centrifugal fans is their ability to
control the pressure, velocity, and direction of the airflow such that it can
be applied to a specific location. This feature is essential for industrial
operations that involve dust, gases, and contaminants.
Types of Centrifugal Fans
Centrifugal fans are classified by the types of blades on
their impeller and the drive of their motor. Impeller blades can be divided
into four categories – airfoil, backward curved, forward curved, and radial.
The difference between the types of blades is determined by the air pressure
Radial blades 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.
An airfoil fan 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.
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 there is dust or particles in
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 dive 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.