Centrifugal air blower
Content
January 15, 2015
Heat Transfer Lab
Batch 3 - Roll Nos: 46 to 51
PERFORMANCE TEST ON CENTRIFUGAL AIR BLOWER
Shivangi Sharma, Shubham Maurya, Siddhartha S. Subbaraman,
Sreekanth M.N., Sudhanshu Kandpal, Sudehhendra R.
B.Tech IV semester
Department of Aerospace Engineering
Indian Institute of Space Science and Technology
ABSTRACT
The objective of this experiment is to carry out a performance test for a centrifugal blower. Performance test is done
to determine, under actual operating conditions, the volume flow
rate, power input and pressure rise across the blower. In this
experiment, the blower is made to operate under different loads
with the help of a control valve. The speed of the motor and the
static and dynamic pressure heads are measured using a tachometer and a manometer and input power using an energy meter. The
characteristics of the blower are plotted from which operating
conditions and efficiency can be determined.
INTRODUCTION
Centrifugal blowers are rotodynamic machines used for
moving air continuously against moderate pressures through ventilation and air conditioning systems. A centrifugal blower consists of a motor, impeller, and its body. As the electric motor rotates the impeller, air gets sucked in through the center of the eye
of the impeller. The rotation throws the air of the impeller blades
on to the volute casing which guides it to the outlet duct. After
the gas is thrown off, the pressure in the middle of the impeller
decreases. This causes air from outside to rush in to normalize
the pressure difference. This cycle is repeated to get a continuous transfer of air. The resistance offered by the casing and duct
causes a slight increase in pressure. Typical pressure ratio for
a blower ranges between 1.1 to 1.2 which distinguishes it from
fans and compressors.
NOMENCLATURE
a1 Area of venturi in m2
a2 Area of throat in m2
Cd Coefficient of discharge of venturimeter
hs Static head measured by manometer
Ha Head causing flow
Hd Dynamic head
Hs Static head
Hw Venturi head difference in manometer
lb Barometer reading in mm of Hg
K Enerhy meter constant
Pa Atmospheric Pressure
Q Discharge
R Characteristic gas constant
t time for 20 impulse
T Air Temperature in K
V Velocity of flow
ρa Density of air
ρw Density of water
η Efficiency
γa Specific weight of air
Impellers used in blowers are of three types: radial, forward
curved and backward curved. Radial blades are usually efficient,
handling low volumes at high pressures. They are typically used
for dirty airstream, high pressure, high temperature and corrosive applications. Forward curved blade handles a given amount
of air with the lowest speed of any centrifugal and are typically
employed in recirculation of hot air within a furnace after some
exhaust operation. Backward curved blades are the most efficient
and are employed in a wide variety of industrial fields like air
conditioning, ventilation, heating and clean room applications.
The efficiency of a blower depends on factors like fan volume,
static pressure head, fan speed, input power etc. The operating
conditions may be obtained from fan curves which in this experiment includes total head, efficiency and input power against air
discharge.
1
THEORY
A centrifugal blower is a machine for moving volumes
of a gas with moderate increase of pressure. In a centrifugal
blower,fluid enters axially in the center of the pump and is discharged radially, along the outer radius of the pump casing.
Generally, a centrifugal blower is based around a casing
filled with fluid. A special unit within the casing exerts fast rotary
motion that causes the fluid to spin, generating centrifugal force
that channels it through a discharge outlet. Discharged fluid creates a vacuum for atmospheric pressure to force more fluid out
of the casing. It is a continuous process, dependant mostly on
continued rotary motion and a constant supply of fluid. Most
centrifugal pumps rely on rotating impellers or vanes to provide
rotary motion, though the design and implementation of these
systems can vary according to capacity and project requirements.
According to Cengel and Cimbala [1] there are three types
of impellers that are usually used in blowers. They are
through the center and delivers the air through it periphery. Blowers are used to deliver air in large volume but at
low pressure. Impellers maybe forward, radial or backward
curved. Impellers maybe made up of sheet or casted.
2. Manometer is an instrument that uses a column of liquid to measure pressure difference. The readings from the
manometer are taken for static and venturi head across the
venturi. [2]
3. Specifications of the experimental setup
Power of motor 5 HP (3.75 kW)
Speed 2880 rpm
Pipe Diameter 100 mm
Throat Diameter 60 mm
Arm Length 230 mm
1. Backward inclined blade are slightly inclined towards the
back and is the most efficient of the three because fluid flows
into and out of the blade passage with least amount of turning and slip. The pressure rise is intermediate between the
other two impellers.
2. Radial blades have the simplest design and produces the
highest pressure rise but the pressure rise decreases rapidly
after the point of highest efficiency.
3. Forward-inclined blades produce a pressure rise that is almost constant but that is lower than the other two impellers.
Forward inclined impellers usually have more blades than
the other, but the blades are smaller. These impellers usually have the least efficiency of the three.
By comparing the input energy and the energy output, the
efficiency of the system can be found out.
Atmospheric pressure,Pa = 132.95xlb
Pa
Density,ρa = RT
Head across veturi meter,Ha = Hw ρρwa
Figure 1.
√
2gHa
a1 −a22
Velocity in pipe,V= QA
Static head,Hs = hs ρρwa
A centrifugal air blower
a1 a2
Discherge,Q= Cd √
2
Dynamic pressure head,Hd =
Total head,H=Hs + Hd
Output= ρa gQHW
Input= 45000
t W
out putx100
Efficiency= input
V2
2g
PROCEDURE
1. The centrifugal blower is started at a position when the valve
is closed, that is, at no load condition.
2. Then the valve is fully opened to get the full open condition.
3. Readings are noted for rotation speed of the blower in RPM,
time taken for twenty impulses from the electronic devices
installed on the blower. Tachometer is used for measuring
RPM.
4. Venturi and static head are noted from the given manometer
by opening and closing of the appropriate valves.
APPARATUS
1. Blower test rig Blower consists of motor, impeller and its
body. Motor rotates the impeller and impeller sucks the air
2
3
2932
2917
2913
2903
2891
2884
2.4
2.7
3
3.3
3.5
DISCUSSIONS
REFERENCES
[1] Yunus A. Cengel, John M. Cimbala 2013 Fluid Mechanics
: Fundamentals and Applications McGraw Hill Education
[2] http://en.wikipedia.org/wiki/Centrifugal-fan
14.06
14.97
16.25
17.88
20.22
22.31
0.13
0.22
0.23
0.41
0.45
0.49
hs
0.89
0.70
0.48
0.30
0.19
0.06
Hw
Ha
308 1.12 796.28
308 1.12 620.61
307 1.13 422.18
306 1.13 264.88
306 1.13 165.66
305 1.13 52.10
T(K) ρ
Typical characteristic for backward vane type blower
t(sec)
0.34
0.30
0.25
0.20
0.16
0.09
Q(m3 /s)
115.03
197.06
202.64
360.56
400.43
432.67
Hs
43.41
38.32
31.61
25.04
19.80
11.10
V(m/s)
96.04
74.85
50.92
31.95
19.98
6.28
Hd
211.06
271.91
253.56
392.51
420.41
438.95
H=Hs +Hd
OBSERVATION TABLE
RESULTS
1.
1.9
Speed (rpm)
Figure 2.
Load (kgf)
791.64
900.37
694.74
854.64
723.92
425.26
Output (W)
3200.57
3006.01
2769.23
2516.78
2225.52
2017.03
Input (W)
5. The delivery valve is gradually closed and the procedure
is repeated to get readings for the various positions of the
valve.
6. Finally the valve is closed and the readings are taken.
7. After completing the experiment the blower is switched off.
0.25
0.30
0.25
0.34
0.33
0.21
η
Heat Transfer Lab
Batch 3 - Roll Nos: 46 to 51
PERFORMANCE TEST ON CENTRIFUGAL AIR BLOWER
Shivangi Sharma, Shubham Maurya, Siddhartha S. Subbaraman,
Sreekanth M.N., Sudhanshu Kandpal, Sudehhendra R.
B.Tech IV semester
Department of Aerospace Engineering
Indian Institute of Space Science and Technology
ABSTRACT
The objective of this experiment is to carry out a performance test for a centrifugal blower. Performance test is done
to determine, under actual operating conditions, the volume flow
rate, power input and pressure rise across the blower. In this
experiment, the blower is made to operate under different loads
with the help of a control valve. The speed of the motor and the
static and dynamic pressure heads are measured using a tachometer and a manometer and input power using an energy meter. The
characteristics of the blower are plotted from which operating
conditions and efficiency can be determined.
INTRODUCTION
Centrifugal blowers are rotodynamic machines used for
moving air continuously against moderate pressures through ventilation and air conditioning systems. A centrifugal blower consists of a motor, impeller, and its body. As the electric motor rotates the impeller, air gets sucked in through the center of the eye
of the impeller. The rotation throws the air of the impeller blades
on to the volute casing which guides it to the outlet duct. After
the gas is thrown off, the pressure in the middle of the impeller
decreases. This causes air from outside to rush in to normalize
the pressure difference. This cycle is repeated to get a continuous transfer of air. The resistance offered by the casing and duct
causes a slight increase in pressure. Typical pressure ratio for
a blower ranges between 1.1 to 1.2 which distinguishes it from
fans and compressors.
NOMENCLATURE
a1 Area of venturi in m2
a2 Area of throat in m2
Cd Coefficient of discharge of venturimeter
hs Static head measured by manometer
Ha Head causing flow
Hd Dynamic head
Hs Static head
Hw Venturi head difference in manometer
lb Barometer reading in mm of Hg
K Enerhy meter constant
Pa Atmospheric Pressure
Q Discharge
R Characteristic gas constant
t time for 20 impulse
T Air Temperature in K
V Velocity of flow
ρa Density of air
ρw Density of water
η Efficiency
γa Specific weight of air
Impellers used in blowers are of three types: radial, forward
curved and backward curved. Radial blades are usually efficient,
handling low volumes at high pressures. They are typically used
for dirty airstream, high pressure, high temperature and corrosive applications. Forward curved blade handles a given amount
of air with the lowest speed of any centrifugal and are typically
employed in recirculation of hot air within a furnace after some
exhaust operation. Backward curved blades are the most efficient
and are employed in a wide variety of industrial fields like air
conditioning, ventilation, heating and clean room applications.
The efficiency of a blower depends on factors like fan volume,
static pressure head, fan speed, input power etc. The operating
conditions may be obtained from fan curves which in this experiment includes total head, efficiency and input power against air
discharge.
1
THEORY
A centrifugal blower is a machine for moving volumes
of a gas with moderate increase of pressure. In a centrifugal
blower,fluid enters axially in the center of the pump and is discharged radially, along the outer radius of the pump casing.
Generally, a centrifugal blower is based around a casing
filled with fluid. A special unit within the casing exerts fast rotary
motion that causes the fluid to spin, generating centrifugal force
that channels it through a discharge outlet. Discharged fluid creates a vacuum for atmospheric pressure to force more fluid out
of the casing. It is a continuous process, dependant mostly on
continued rotary motion and a constant supply of fluid. Most
centrifugal pumps rely on rotating impellers or vanes to provide
rotary motion, though the design and implementation of these
systems can vary according to capacity and project requirements.
According to Cengel and Cimbala [1] there are three types
of impellers that are usually used in blowers. They are
through the center and delivers the air through it periphery. Blowers are used to deliver air in large volume but at
low pressure. Impellers maybe forward, radial or backward
curved. Impellers maybe made up of sheet or casted.
2. Manometer is an instrument that uses a column of liquid to measure pressure difference. The readings from the
manometer are taken for static and venturi head across the
venturi. [2]
3. Specifications of the experimental setup
Power of motor 5 HP (3.75 kW)
Speed 2880 rpm
Pipe Diameter 100 mm
Throat Diameter 60 mm
Arm Length 230 mm
1. Backward inclined blade are slightly inclined towards the
back and is the most efficient of the three because fluid flows
into and out of the blade passage with least amount of turning and slip. The pressure rise is intermediate between the
other two impellers.
2. Radial blades have the simplest design and produces the
highest pressure rise but the pressure rise decreases rapidly
after the point of highest efficiency.
3. Forward-inclined blades produce a pressure rise that is almost constant but that is lower than the other two impellers.
Forward inclined impellers usually have more blades than
the other, but the blades are smaller. These impellers usually have the least efficiency of the three.
By comparing the input energy and the energy output, the
efficiency of the system can be found out.
Atmospheric pressure,Pa = 132.95xlb
Pa
Density,ρa = RT
Head across veturi meter,Ha = Hw ρρwa
Figure 1.
√
2gHa
a1 −a22
Velocity in pipe,V= QA
Static head,Hs = hs ρρwa
A centrifugal air blower
a1 a2
Discherge,Q= Cd √
2
Dynamic pressure head,Hd =
Total head,H=Hs + Hd
Output= ρa gQHW
Input= 45000
t W
out putx100
Efficiency= input
V2
2g
PROCEDURE
1. The centrifugal blower is started at a position when the valve
is closed, that is, at no load condition.
2. Then the valve is fully opened to get the full open condition.
3. Readings are noted for rotation speed of the blower in RPM,
time taken for twenty impulses from the electronic devices
installed on the blower. Tachometer is used for measuring
RPM.
4. Venturi and static head are noted from the given manometer
by opening and closing of the appropriate valves.
APPARATUS
1. Blower test rig Blower consists of motor, impeller and its
body. Motor rotates the impeller and impeller sucks the air
2
3
2932
2917
2913
2903
2891
2884
2.4
2.7
3
3.3
3.5
DISCUSSIONS
REFERENCES
[1] Yunus A. Cengel, John M. Cimbala 2013 Fluid Mechanics
: Fundamentals and Applications McGraw Hill Education
[2] http://en.wikipedia.org/wiki/Centrifugal-fan
14.06
14.97
16.25
17.88
20.22
22.31
0.13
0.22
0.23
0.41
0.45
0.49
hs
0.89
0.70
0.48
0.30
0.19
0.06
Hw
Ha
308 1.12 796.28
308 1.12 620.61
307 1.13 422.18
306 1.13 264.88
306 1.13 165.66
305 1.13 52.10
T(K) ρ
Typical characteristic for backward vane type blower
t(sec)
0.34
0.30
0.25
0.20
0.16
0.09
Q(m3 /s)
115.03
197.06
202.64
360.56
400.43
432.67
Hs
43.41
38.32
31.61
25.04
19.80
11.10
V(m/s)
96.04
74.85
50.92
31.95
19.98
6.28
Hd
211.06
271.91
253.56
392.51
420.41
438.95
H=Hs +Hd
OBSERVATION TABLE
RESULTS
1.
1.9
Speed (rpm)
Figure 2.
Load (kgf)
791.64
900.37
694.74
854.64
723.92
425.26
Output (W)
3200.57
3006.01
2769.23
2516.78
2225.52
2017.03
Input (W)
5. The delivery valve is gradually closed and the procedure
is repeated to get readings for the various positions of the
valve.
6. Finally the valve is closed and the readings are taken.
7. After completing the experiment the blower is switched off.
0.25
0.30
0.25
0.34
0.33
0.21
η
