Rotary compressors ppt

1. ROTARY COMPRESORS
UNIT -4 COMPRESSORS
S K Singh
Centre for Energy Studies
IIT Delhi
20-May-21

2. ROTARY COMPRESORS
CLASSIFICATION
POSITIVE DISCPLACEMENT
1. ROOTS BLOWER
2. VANE COMPRESSORS
3. SCREW COMPRESSORS
STEADY FLOW COMPRESSORS
1. CENTRIFUGAL COMPRESSORS
2. AXIAL FLOW COMPRESSORS
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3. RECIPROCATING AND ROTARY
COMPRESORS COMPARISON
RECIPROCATING
1. PRESSURE UPTO 1000
BAR
2. VOLUME FLOW RATE 3O
m3/min
3. SLOW SPEEDS
ROTARY
1. PRESSURE UPTO 10 BAR
BY MULTISTGE MAX 40
BAR
1. VOLUME FLOW RATE
1200 TO 4200 m3/min
2. HIGH SPEEDS 3000 RPM
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4. POSITIVE DISCPLACEMENT
1. ROOTS BLOWER/ VANE /SCREW COMPRESSORS
PRESSURE UPTO 4 BAR
VOLUME FLOW RATE 0.5 TO 1500 m3/min
2. CENTRIFUGAL COMPRESSORS
PRESSURE RATIO 4:1
VOLUME FLOW RATE 15 TO 1200 m3/min
3. AXIAL COMPRESSORS
per stage compression ratio = 1.2 to 1.3
No. of stages = 8 to 20
Total compression ratio = 20:1
Discharge pressure = 400 bar
Volume flow rate = 1200 m3/min to 42000m3/min
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5. ROOTS BLOWER
• The Roots type supercharger or Roots blower is a
positive displacement lobe pump which operates by
pumping a fluid with a pair of meshing lobes not unlike a
set of stretched gears. Fluid is trapped in pockets
surrounding the lobes and carried from the intake side to
the exhaust. It is frequently used as a supercharger in
engines, where it is driven directly from the engine's
crankshaft via a belt or, in a two-stroke diesel engine, by
spur gears.
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6. ROOTS BLOWER
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7. ROOTS BLOWER ANALYSIS

8. ROOTS BLOWER ANALYSIS
• Work required to drive the root blower with two lobes per
revolution
• W = V (P2-P1)
Note: V= 4V for 2 lobe rotor and 6V for 3 lobe rotor
• Volume of air compressed per minute (Va) = 4V*N [ for 2 lobe]
Where N = speed of blower in RPM
- ACTAUL POWER REQUIRED TO COMPRESS Va AIR in
m3/min = Pa = Va (P2-P1)
- IDEAL POWER REQUIRED TO COMPRESS Va AIR in
m3/min = Pi = (γ/ γ-1) P1 Va [(p2/P1)(γ-1/ γ) - 1]
(The same relation we’ve derived for reciprocating compressor in class )
- Root Efficiency = Ideal Power/Actual Power
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9. Root Blower Efficiency
- Root Efficiency = Ideal Power/Actual Power
= (γ/ γ-1) P1 Va [(p2/P1)(γ-1/ γ) - 1]
Va(P2-P1)
OR
ROOT EFFICIENCY = (γ/ γ-1) [(rp) )(γ-1/ γ) - 1]
[rp-1]
Where rp is the pressure ratio
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10. VANE BLOWER
• Mechanism:
• The rotor is bias rotated (as the follow diagram) with the
vane going in and out inside the slots. The vane are
compelled to attach the inside surface of casing, so that air
is absorbed from inlet and compressed out to the outlet
Applications:
* Wastewater treatment
* Air transportation
* Fish breeding aeration * Dust collection
* Vacuum packing * Vacuum absorption
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11. VANE BLOWER
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12. VANE BLOWER ANALYSIS
1
2
c
P1
Pc
P2
P
V
Pressure rise due to
back flow of air
Pressure rise due to
internal compression
Total pressure rise = Internal compression pressure rise + Back flow
W = W1-c + Wc-2
W = (γ/ γ-1) P1 V1 [(Pc/P1)(γ-1/ γ) - 1] + Vc (P2-PC)
Also P1V1γ = Pc Vc
γ
So, W = (γ/ γ-1) P1 V1 [(Pc/P1)(γ-1/ γ) - 1] + (P1/Pc)(1/ γ) V1 (P2-Pc)
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13. SCREW COMPRESSORS
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14. SCREW COMPRESSORS
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15. Steady flow compressors
1. centrifugal compressor
The centrifugal air compressor is a dynamic
compressor which depends on a rotating impeller to
compress the air
In order to do this efficiently, centrifugal
compressors must rotate at higher speeds than the
other types of compressors
These types of compressors are designed for higher
capacity because flow through the compressor is
continuous and oil free by design
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16. 20-May-21

17. Centrifugal compressors consist of three main
parts, as shown in Figure
•The first is a rotating impeller, which imparts
work to the gas by increasing its angular
momentum. The fluid static pressure and
absolute velocity (stationary frame of
reference) increase through the impeller
passage.
•The second component is the diffuser
section, often with vanes to increase the
effectiveness. The diffuser converts the kinetic
energy into the static pressure by decelerating
the fluid.
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18. • The third and final component is a volute or
collector, used for collecting the gas from
diffuser and delivering to the outlet pipe. A
volute has two functions: collection and
diffusion.
• The volute must collect and transport the
fluid to the downstream system. It also raises
the static pressure by converting kinetic
energy (ρu2) to potential energy (static
pressure).
• The latter function has performance benefits,
as the discharge pressure is increased.
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19. • Impeller rotates around 3000 rpm and produce
centrifugal head which causes air to flow from
surrounding to axially inside the impeller eye
• The air flows radially outwards into the impeller
blade
• When air flow from impeller eye to tip of impeller
blades, there is an increase in pressure and
temperature of air due to increased momentum
CENTRIFUGAL COMPRESSOR WORKING
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20. • Diffuser blades provide an increased area
of passage to the air which is passing
outward due to which K.E of air leaving the
impeller is reduced and its pressure
energy in increased.
• Due to increased area of volute casing the
pressure further rises in casing
CENTRIFUGAL COMPRESSOR WORKING
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21. Figure : Centrifugal compressor layout. (a) A cross-sectional
view, showing the impeller followed by a vaned diffuser, and a
volute. (b) An isometric view of the package.
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22. Impeller of compressor
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23. Examples of Application
• Vaned diffuser for centrifugal compressor
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24. 20-May-21

25. AXIAL FLOW COMPRESSOR
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26. AXIAL FLOW COMPRESSOR
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27. AXIAL FLOW COMPRESSOR
Air Flow – parallel to compressor axis Fixed blade receive
high velocity gas from preceding rotor blade and directs
the flow to the succeeding rows of rotor blades.
The gas space is restricted as staging progresses by
decreasing the radial distance between the rotor drum
and the casing and also by shortening the blades due to
reduction in volume.
Blades – made of aerofoil section to reduce friction
Pr ratio per stage = 1.06 to 1.2
No. of stages used around 5 to 14
Ultimate pressure ratio = 10:1
Flow rate around 30000 m3/min
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