it is worth

1. E.M.E.

2. E.M.E.

3. Air Compressors
1. Introduction And Classification
2. Uses Of Compressed Air
3. Types of Air Compressors
4. Reciprocating Compressors
5. Operation And Work Done For Compressors
6. Power And Efficiencies Of Compressors
7. Multistage Reciprocating Compressors
8.Rotary Air Compressors
E.M.E.

4. E.M.E.
INTRODUCTION:-
 The machine which takes in air or any other
gas at low pressure and compresses it to high
pressure are called COPMORESSORS. Anda
compressors are used for increasing pressure
of air is called AIR COMPRESSORS.
 Generally, the compressors are driven by ele.
Motors, i.c. engines or gas turbines.


5. E.M.E.
Classification Of Compressor:-
 The compressors are classified as given bellow:-

6. E.M.E.
Classification Of Compressor:-
1. Method of compression
a) Reciprocating Compressors
b) Rotary compressors
c) Centrifugal Compressors
2. Delivery Pressure
a) Low Pressure:- up to 1.1 bar
b) Medium Pressure:- 1.1 to 8 bar
c) High Pressure:- 8 to 10 bar
d) Very High Pressure:- above 10 bar

7. E.M.E.
Classification Of Compressor:-
3. Principle Of Operation
a) Positive Displacement
b) Rotodynamic
4. The Number Of Stages
a) Single Stage Compressors:- Pressure up to 5 bar
b) Multistage Compressors:- pressure above 5 bar
5. The Number Of Cylinders
a) Single Cylinders
b) Multi Cylinders

8. E.M.E.
Classification Of Compressor:-
6. The Pressure Limits
a) Fans:- Pressure ratio 1 to 1.1
b) Blowers:- pressure ratio 1.1 to 2.5
c) Compressors:- pressure ratio above 2.5
7. Volume Of Air Delivered
a) Low Capacity:- volume flow rate up to 10푚3/min
b) Medium Capacity:-volume flow rate up to 10푚3/min to 300푚3/min
c) High Capacity:-volume flow rate above 300푚3/min

9. E.M.E.
Classification Of Compressor:-
A. The compressors compresses air by reciprocating action of piston
inside a cylinder is called Reciprocating compressors.
B. Air or gas compressed due to the rotation of blades inside a casing
similar to a rotary pump is called Rotary Compressors.
C. A machine in which compression of air to desired pressure is carried
out by rotating impeller as well as centrifugal action o air is called
Centrifugal Compressors.

10. E.M.E.
Classification Of Compressor:-
Reciprocating
compressors.
Rotary
Compressors
Centrifugal
Compressors

11. E.M.E.
Uses Of Compressed Air:-
• In refrigeration cycle.
• Operating pneumatic tools like drill, hammers,etc.
• Filling the air in automobile tyres.
• Increasing inlet pressure of I.C. engines.
• To operate air motor in mines where fire risk is more.
• Conveying the materials like sand and concrete along a pipe line.
• Operating blast furnaces.
• Operating air brakes used in buses, trucks, trains, etc.
• Spray paintings.

12. Reciprocating Compressors:-
 It consist of cylinder in which a piston
reciprocates.
 The piston is driven by crank through
connecting rod. The crank is mounted
in a crankcase.
 They operate automatically by
difference of pressure across valve.
 Reciprocating Compressors are widely
used for compressing air.
E.M.E.

13. Reciprocating Compressors:-
 It is assumed that in an ideal
compressors there is no clearance
volume.
 In actual compressor there is always
clearance volume. It is required
because of preventing striking of
piston, thermal expansion, maintaining
tolerance.
 Pv digrame for clearance
and non clearance
E.M.E.

14. Work For Compression:-
 The P-V diagram
of a single stage
compressor
without clearance
is shown in fig 1.1
 The P-V diagram
of a single stage
compressor with
clearance is shown
in fig 1.2
E.M.E.

15. Work For Compression:-
 Work done for without clearance:
i. If The Compression follows the low p푉훾 = consant
후
후−ퟏ
W=
풑ퟏ 푽ퟏ
풑ퟐ
풑ퟏ
휸−ퟏ
휸 − ퟏ .
ii. If The Compression follows the low p푉훾 = consant
풏
풏−ퟏ
W=
풑ퟏ 푽ퟏ
풑ퟐ
풑ퟏ
풏−ퟏ
풏 − ퟏ .
iii. If The Compression 푖푠 푖푠표푡ℎ푒푟푚푎푙 then W=pVlog푒
푝2
푝1
E.M.E.

16. Work For Compression:-
 Work done for with clearance:
i. If The Compression follows the low p푉훾 = consant
풏
풏−ퟏ
W=
풑ퟏ( 푽ퟏ−푽ퟒ
풑ퟐ
풑ퟏ
풏−ퟏ
풏 − ퟏ .
E.M.E.

17. Power Required:-
1. Indicated Power:-The power required to compress
the air is called indicated power.
I.P.=
푝푚퐿퐴푛
60000
푘푊
2. Brake Power:- The power required to drive the
compressor is called brake power.
2휋푁푇
60000
B.P.=
E.M.E.

18. Efficiencies:-
1. Mechanical Efficiency(훈푚):-The ratio of indicated
power to the Brake power of compressor.
훈푚 =
I.P.
B.P.
2. Isothermal Efficiency(훈푖푠표):-The ratio of Isothermal
work to indicated work
훈푖푠표 =
푝1푉1 log푒
푝2
푝1
풏
풏−ퟏ
풑ퟏ 푽ퟏ
풑ퟐ
풑ퟏ
풏−ퟏ
풏
−ퟏ
E.M.E.

19. Efficiencies:-
3. Volumetric Efficiency(훈푣):-The ratio of effective
swept volume to swept volume of cylinder.
훈푣 = ퟏ − 푪
풑ퟐ
풑ퟏ
ퟏ
풏 − ퟏ .
 Free Air Delivery:-The free air delivery is the volume
of air delivered by the compressors when reduce to
intake air and pressure.
E.M.E.

20. Free Air Delivery (FAD):-
 The free air delivery is the volume of air delivered by
the compressor when reduced to intake temperature
and pressure.
 The free air volume is less then the compressor
swept volume because:
A. The presence of clearances volume
B. The throttling of air when its passes through the
inlet and outlet vessel
C. Heating of incoming air
D. leakage
E.M.E.

21. Multistage Reciprocating Compressor:-
 Multistage Reciprocating
Compressor
 To eliminate limitations of single
stage compressor
 To increase efficiency
 PV diagram for multistage
compressor is
E.M.E.

22. Rotary Compressors:-
 The rotary compressor may be classified as
E.M.E.

23. Rotodynamic compressor:-
There is two type of rotodynamic compressor
1. Centrifugal compressor
2. Axial flow compressor
E.M.E.

24. Centrifugal compressor:-
 It consists of a rotating element
called impeller and volute casing.
 Impeller rotates at 30000 RPM
 Impeller produce centrifugal
force and rotate at hi speed
 Suitable for large flow rate
 Pressure ratio up to 12 can be
obtained
E.M.E.

25. Axial Flow Compressor:-
 Air flow parallel to the axis
 It consists fixed blades and rotor
attached with moving blade
 It rotates at 10000-30000 rpm
 Pressure ratio of 10:1 can be
achieved
E.M.E.

26. Positive Displacement Compressor:-
 Volume of air is positively
displaced
 It has two type
1. Roots blowers
2. Vane type compressor
E.M.E.

27. Roots blower:-
 It consist of two lobe, fixed casing
which contains two shaft fitted with
two lobe.
 The profile of rotor is involute type.
 P-V diagram is shown here
 Total volume delivered per revolution
for two lobes rotor is 4V
 Work done per revolution is equal to
4V(푝2 − 푝1).
E.M.E.

28. Roots blower:-
 It consist of two lobe, fixed casing
which contains two shaft fitted with
two lobe.
 The profile of rotor is involute type.
 P-V diagram is shown here
 Total volume delivered per revolution
for two lobes rotor is 4V
 Work done per revolution is equal to
4V(푝2 − 푝1).
E.M.E.

29. Comparison of reciprocating-rotodynamic comp.:-
Reciprocating Compressor Rotodynamic Compressors
1.Max. delivery pressure up to 1000 bar 1.Max. delivery pressure up to 40 bar
2.Suitable for low discharge high pressure 2.Suitable for high discharge low pressure
3.Air discharge is not continuous, so a receiver is
needed
3.Air discharge is continuous, so receiver is not
needed
4.It requires complicated lubrication system 4.Simple lubrication system is required
5.Size of compressor is larger than rotary
compressor for same discharge
5.Size of compressor is smaller than
reciprocating compressor for same discharge
6.Due to reciprocating parts balancing is the
major problem
6.No reciprocating part, so balancing is not a
problem
7.Maintenance cost is more 7.Maintenance cost is less
8.Due to clearance volumetric efficiency is
<100%
8.No clearance so volumetric efficiency is 100%
9.Running cost is more 9.Running cost is less.
E.M.E.

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E.M.E.