10-05-2012, 05:04 PM
FANS AND BLOWERS
[attachment=21813]
Introduction
Fans and blowers provide air for ventilation and industrial process requirements. Fans generate
a pressure to move air (or gases) against a resistance caused by ducts, dampers, or other components
in a fan system. The fan rotor receives energy from a rotating shaft and transmits it to
the air.
Fan Types
Fan and blower selection depends on the volume flow
rate, pressure, type of material handled, space limitations,
and efficiency. Fan efficiencies differ from
design to design and also by types.
Common Blower Types
Blowers can achieve much higher pressures than fans, as high as 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 like centrifugal pumps than fans. The impeller is typically
gear-driven and rotates as fast 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.
Fan Characteristics
Fan characteristics can be represented in form of fan curve(s). The fan curve is a performance
curve for the particular fan under a specific set of conditions. The fan curve is a graphical representation
of a number of inter-related parameters. Typically a curve will be developed for a
given set of conditions usually including: fan volume, system static pressure, fan speed, and
brake horsepower required to drive the fan under the stated conditions. Some fan curves will
also include an efficiency curve so that a system designer will know where on that curve the fan
will be operating under the chosen conditions (see Figure 5.6). In the many curves shown in the
Figure, the curve static pressure (SP) vs. flow is especially important.
[attachment=21813]
Introduction
Fans and blowers provide air for ventilation and industrial process requirements. Fans generate
a pressure to move air (or gases) against a resistance caused by ducts, dampers, or other components
in a fan system. The fan rotor receives energy from a rotating shaft and transmits it to
the air.
Fan Types
Fan and blower selection depends on the volume flow
rate, pressure, type of material handled, space limitations,
and efficiency. Fan efficiencies differ from
design to design and also by types.
Common Blower Types
Blowers can achieve much higher pressures than fans, as high as 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 like centrifugal pumps than fans. The impeller is typically
gear-driven and rotates as fast 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.
Fan Characteristics
Fan characteristics can be represented in form of fan curve(s). The fan curve is a performance
curve for the particular fan under a specific set of conditions. The fan curve is a graphical representation
of a number of inter-related parameters. Typically a curve will be developed for a
given set of conditions usually including: fan volume, system static pressure, fan speed, and
brake horsepower required to drive the fan under the stated conditions. Some fan curves will
also include an efficiency curve so that a system designer will know where on that curve the fan
will be operating under the chosen conditions (see Figure 5.6). In the many curves shown in the
Figure, the curve static pressure (SP) vs. flow is especially important.