Centrifugal fan which is also called as squirrel cage fan because of its hamster wheel design is widely used to move air/gas continuously in industries and commercial applications. The speed of the air stream entering into the fan, is increased by the impeller thereby it gains kinetic energy and accelerates radially changing the direction by 90°. As these fans are capable of displacing constant volume of air/gas at increased speed, they are widely used in various process applications in industries such as in material handling, boiler applications, transporting gas or materials, ventilation and combustion, air circulation and in other HVAC systems.

1. Important parts of a Centrifugal fan
Neel Rao
Writer at Reitz India, a leading provider of
high quality fans, with thousands of
centrifugal fan & PA fan installations in
process industries
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2. Centrifugal fan which is also called as squirrel cage fan because of its hamster
wheel design is widely used to move air/gas continuously in industries and
commercial applications. The speed of the air stream entering into the fan, is
increased by the impeller thereby it gains kinetic energy and accelerates
radially changing the direction by 90°. As these fans are capable of displacing
constant volume of air/gas at increased speed, they are widely used in various
process applications in industries such as in material handling, boiler
applications, transporting gas or materials, ventilation and combustion, air
circulation and in other HVAC systems.
Apart from small accessories like bearings, couplings, hoods, guards, flanges,
isolators etc., centrifugal fan also contain some basic parts that play a major
role in system working and performance.
Some important parts of centrifugal fans are:
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3. Impeller:
Impeller is a rotating device consisting of number of fan blades mounted on a
hub with drive shaft that forces the air/gas in the desired direction with
increased pressure. In centrifugal fan, the air stream enters the impeller in an
axial direction, acquires acceleration due to centrifugal force as it flows
through the fan blades and gets discharged radially from the fan housing.
To meet the demands of large scale applications in industries, centrifugal fans
are custom designed as double inlet impeller and multistage impellers where
two or more single inlet impellers are mounted back to back on the same
shaft. Industries with large capacity plants which require high pressure airflow
use these types of fans in their process applications.
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4. Fan Blades:
Based on the blade configuration such as forward curved, backward curved,
radial, airfoil etc., centrifugal fans are divided into various types and differ in their
functionality. The efficiency and fan performance basically depends on the shape
of the blades that are mounted on a hub of the fan wheel. Some fans can handle
larger volumes of air with high static pressures where as some are meant for low
flow rates. Hence, it is important to select the centrifugal fan design that matches
with the required pressure and flow-rate of any industrial process, so that the
efficiency will be high for the given operating conditions.
Fan Housing:
Housing in a fan system improves efficiency as it reduces noise and acts as a
protection for moving parts like impeller, hub etc. In centrifugal fan, the air from
the inlet enters the impeller axially through fan housing, where it picks up the
acceleration and is radially sent out in 90° direction.
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5. The design of the housing has to be optimized so that it withstands the centrifugal
action of spinning of the air inside it.
Drive shaft:
It is a rotating device that holds the impeller & blades and determines the
speed of the fan wheel through various drive mechanisms like direct, belt or
variable. Shaft design depends on the installed impeller weight and the
velocity of the inlet gases.
 Direct: In direct driven fans, the fan speed is directly proportional to the
speed of the motor as the shaft is straightaway connected to the fan motor.
 Belt driven: In belt driven mechanism, the wheel shaft and the motor shaft
are connected by belt which is mounted on the sheave. These fans have
fixed wheel speed unless the belt gets misplaced from its position.
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6.  Variable: To get the desirable variable speed of the fans, variable driven
mechanisms use couplings to establish a connection between the motor
shaft and the wheel shaft. Some of the fan systems are equipped with
electronic variable speed drives that can automatically control the fan
speed at the desired level.
Inlet and outlet ducts:
Ducts that are attached at the fan inlet and outlet will affect the airflow
pattern and influence the performance of the fans. Ducts at the inlet
control the flow of air/gas by admitting only required amount of air
whereas ducts at the outlet impose a resistance to the air stream. Improper
inlet and outlet airflow conditions, and ducts with sharp cornered turns
result in inefficient fan operation, high system noise and poor performance
with undesired outputs.
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7. Dampers & Louvers:
Dampers and louvers are the plates or sheets inside the ducts which are used
to control or alternatively block the airflow at the inlet or outlet of a fan. The
main difference between them is damper blades are movable or adjustable
manually or automatically to control the volume or regulate the airflow
whereas louver blades are fixed and there is no control over the air moving
through them.
Centrifugal fans and blowers provide customized solutions to many industrial
processes and air pollution systems for ventilation, dust collection, drying &
cooling, exhausting gases, fume extraction, air recirculation, pollution control
etc. The amount of the airflow and the efficiency of the fan system will decide
which type of the fan has to be used in the industrial process.
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8. Reitz India, a global leader in fan technology, has served the needs of various
industries with thousands of centrifugal fan installations not only in India but
in Middle East, East Africa and South East Asian countries as well. Reitz has
incorporated latest technology in FD fan and PA fan design and fabrication to
provide energy efficient and cost effective solutions with high industrial
standards.
Thank you for spending your precious time in reading this article.
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