Air compressor working

1. AIR COMPRESSOR

2. COMPRESSOR
COMPRESSION
 process of increasing the pressure of air,
gas or vapour by reducing its volume
COMPRESSOR
 Device used to carryout compression
APPLICATIONS
Pneumatic brakes, Pneumatic drills
Pneumatic lifts, Spray painting
Shop cleaning, Injecting fuels in diesel engines
Refrigeration and air conditioning systems

3. CLASSIFICATION
Based on principle of operation
• Positive displacement compressor.
• Non-positive displacement compressors.
Based on the type of mechanism used for
compression
• Reciprocating type positive displacement
compressors
• Rotary type positive displacement
compressors.

4. Based on number of stages
• Single stage Compressor
• Multi stage air compressor
Based on Capacity of compressors
• Low (air delivery capacity of 0.15 m3/s or
less)
• Medium (air delivery capacity between 0.15
to 5 m3/s)
• High (air delivery capacity more than 5
m3/s)

5. Based on highest pressure developed
• Low (max pr. upto 1 bar)
• Medium (max pr. from 1 bar to 8 bar)
• High (max pr. from 8 to 10 bar)
• Super high (max pr. more than 10 bar)
Based on action
• Single acting
• Double acting

6. TECHNICAL TERMS
• Inlet pressure
– Absolute pressure of air at the inlet of a compressor
• Discharge pressure
– Absolute pr. of air at the outlet of a compressor
• Compression ratio or pressure ratio
– Ratio of discharge pressure to the inlet pressure
• Swept volume
– Volume of air sucked by the compressor during its
suction stroke
• Mean effective pressure
– Ratio between work done and swept volume
length
Stroke
L
bore,
cylinder
of
diameter
D
L
D
4
π
V 2
s 



7. SINGLE STAGE RECIPROCATING
AIR COMPRESSOR
INLET
DELIVERY
RESERVOIR
CLEARANCE
VOLUME
SWEPT
VOLUME

8. CLEARANCE SPACE AND
CLEARANCE VOLUME
• CLEARANCE SPACE
– Space between piston top and cylinder head
• CLEARANCE VOLUME
– Volume occupied clearance space

9. CLEARANCE VOLUME

10. • Compression of air in compressor may be
carried out following number of thermodynamic
processes
–Isothermal compression,
–Polytropic compressor
–Adiabatic compressor.
WORK DONE WITHOUT
CLEARANCE VOLUME

11. p-V DIAGRAM T-s DIAGRAM

12. WORKDONE DURING
ISOTHERMAL COMPRESSION
(pV=c)

13. Workdone=Area1-2-3-4-1
Workdone = Wcomp+Wdelivery-Wsuction






























1
2
2
1
1
2
2
2
1
1
1
1
2
2
2
1
1
1
p
p
V
V
p
p
mRT1
W
V
p
V
p
V
p
V
p
v
v
ln
V
p
W

14. WORKDONE DURING
POLYTROPIC COMPRESSION
PVn=c

15. Workdone=Area1-2-3-4-1
Workdone = Wcomp+Wdelivery-Wsuction
V
p
V
p
1
-
n
V
p
-
V
p
W 1
1
2
2
1
1
2
2



1
-
n
V
p
)
1
n
(
V
1)p
-
(n
V
p
-
V
p
W 1
1
2
2
1
1
2
2 




16. 1
-
n
V
p
V
np
V
p
-
V
np
V
p
-
V
p
W 1
1
1
1
2
2
2
2
1
1
2
2 



















1
T
T
mRT
1
-
n
n
)
T
(T
mR
1
-
n
n
W
)
mRT
(mRT
1
-
n
n
W
)
V
p
V
(p
1
-
n
n
W
1
-
n
V
np
V
np
W
1
2
1
1
2
1
2
1
1
2
2
1
1
2
2

17. n
1
n
1
2
1
2
process
polytropic
For










p
p
T
T





























1
p
p
V
p
1
-
n
n
W
1
T
T
mRT
1
-
n
n
W
1
1
2
1
1
1
2
1
n
n

18. WORKDONE DURING
ISENTROPIC COMPRESSION
(REVERSIBLE ADIABATIC)
C)
(pVγ


19. Workdone=Area1-2-3-4-1
Workdone = Wcomp+Wdelivery-Wsuction
V
p
V
p
1
-
V
p
-
V
p
W 1
1
2
2
1
1
2
2




1
-
V
p
)
1
(
V
1)p
-
(
V
p
-
V
p
W 1
1
2
2
1
1
2
2


 




20. 1
-
V
p
V
p
V
p
-
V
p
V
p
-
V
p
W 1
1
1
1
2
2
2
2
1
1
2
2


 



















1
T
T
mRT
1
-
n
n
)
T
(T
mR
1
-
n
n
W
)
mRT
(mRT
1
-
W
)
V
p
V
(p
1
-
W
1
-
V
p
V
p
W
1
2
1
1
2
1
2
1
1
2
2
1
1
2
2








21. 
 1
1
2
1
2
process
isentropic
For










p
p
T
T





























1
p
p
V
p
1
-
W
1
T
T
mRT
1
-
W
1
1
2
1
1
1
2
1







22. WORK DONE WITH CLEARANCE
VOLUME

23. Workdone=Area1-2-3-4-1
=(Area1-2-A-B-1)-(Area 3-A-B-4-3)
Workdone = Workdone Workdone
during - during
compression expansion
3
2
4
1
1
4
3
4
4
1
1
2
1
1
p
p
,
p
p
1
p
p
V
p
1
-
n
n
-
1
p
p
V
p
1
-
n
n
W











































n
n
n
n

24. 3
2
4
1
1
1
2
4
1
1
1
2
1
1
p
p
,
p
p
1
p
p
V
p
1
-
n
n
1
p
p
V
p
1
-
n
n
W












































n
n
n
n










































1
p
p
)
V
-
(V
p
1
-
n
n
W
)
V
-
(V
1
p
p
p
1
-
n
n
W
n
1
n
1
2
4
1
1
4
1
n
1
n
1
2
1

25. /cycle
delivered
air
free
of
volume
Actual
V
-
V
V
1
p
p
V
p
1
-
n
n
W
1
p
p
)
V
-
(V
p
1
-
n
n
W
4
1
a
n
1
n
1
2
a
1
n
1
n
1
2
4
1
1

































































1
p
p
mRT
1
-
n
n
W
n
1
n
1
2
1

26. FREE AIR DELIVERY
• Volume of air delivered by an air compressor at
atmospheric temperature and pressure.
Delivered mass of air = Intake mass of sir
C

15
T
,
m
kN
101.325
p
volume)
clearance
(without
T
V
p
T
V
p
T
V
p
volume)
clearance
(with
T
)
V
(V
p
T
)
V
(V
p
T
V
p
f
2
f
2
2
2
1
1
1
f
f
f
2
3
2
2
1
4
1
1
f
f
f









27. VOLUMETRIC EFFICIENCY
cyclinder
of
volume
Stroke
cycle
/
air taken
free
of
Volume
ηvol 

28.  
s
c
4
c
s
s
c
4
s
s
s
s
4
1
vol
c
4
V
1
V
V
V
V
V
V
V
V
V
x
V
V
V
V
η
V
V
x






























 1
V
V
V
V
1
η
c
4
s
c
vol

29. n
n
n
p
p
V
V
V
p
V
p
1
4
3
3
4
4
4
3
3










n
c
c
p
p
V
V
p
p
p
p
V
V
1
1
2
4
2
3
1
4
3 ,
,











































 1
V
V
1
1
V
V
V
V
1
η
1
1
2
s
c
c
4
s
c
vol
n
p
p

30. s
c
V
V
C
ratio
Clearance 










































n
n
p
p
p
p
1
1
2
vol
1
1
2
vol
C
C
1
η
1
C
1
η

31. LIMITATIONS OF SINGLE
STAGE COMPRSSION
• Greater expansion of clearance air in the cylinder and
as a consequence, it decreases effective suction
volume (V1-V4) and there is a decrease in fresh air
induction
• With high delivery pressure, the delivery temperature
increases. It increases specific volume of air in the
cylinder, thus more compression work is required
• For high pressure ratio, the cylinder size would have
to be large, strong and heavy working parts will be
needed. It will increase balancing problem and high
torque fluctuation will require a heavier flywheel
installation.

32. MULTI STAGE RECIPROCATING
AIR COMPRESSOR WITH
INTERCOOLING

33. p-V DIAGRAM

34. PURPOSE OF INTERCOOLER
• Inter cooler is a heat exchanger
• Provided after LP cylinder ,that reduces the
temperature of the air delivered by LP cylinder
at constant pressure so that the amount of work
required to compress air in next(HP cylinder)
stage is less ,hence the efficiency of
compressor is increased.

35. ASSSUMPTIONS MADE IN
MULTISTAGE AIR COMPRESSOR
• Suction and delivery pressure remains
constant during each stage
• Index of compression is same in each
stage
• The mass of air handled by the low and
high pressure cylinders are same
• There is no pressure drop in the
intercooler

36. COMPLETE OR PERFECT
INTERCOOLING
p-V DIAGRAM
T-s DIAGRAM
Volume Entropy

37. INCOMPLETE OR IMPERFECT
INTERCOOLING
p-V DIAGRAM T-s DIAGRAM

38. WORK DONE WITH
INTERCOOLER
• p1V1T1- pressure, volume and temperature of air
entering the low pressure (LP) cylinder
• p2V2T2- pressure, volume and temperature of air
entering the high pressure (HP) cylinder
• p3- final delivery pressure of air
• n-polytropic index of both the cylinder

39. Total work input
= Work input for LP compressor+
Work input for HP compressor










































1
p
p
V
p
1
-
n
n
1
p
p
V
p
1
-
n
n
W
1
2
3
2
2
1
1
2
1
1
n
n
n
n
When the intercoling is perfect p1V1=p2V2
2
p
p
p
p
V
p
1
-
n
n
W
1
2
3
1
1
2
1
1































n
n
n
n

40. CONDITION FOR MINIMUM
WORK INPUT
2
p
p
p
p
V
p
1
-
n
n
W
1
2
3
1
1
2
1
1































n
n
n
n
Differentiating w.r.t p2 and equating to zero
0
dp
dw
2


41. )
K(constant
1
-
n
n
let
0
2
p
p
p
p
V
p
1
-
n
n
dp
d
1
2
3
1
1
2
1
1
2










































n
n
n
n
0
2
p
p
p
p
V
Kp
dp
d
2
3
1
2
1
1
2



































K
K

42.    
       
        1
-
K
-
2
K
3
1
K
2
K
-
1
1
-
K
-
2
K
3
1
K
2
K
-
1
1
-
K
-
1
-
K
-
2
K
3
1
K
2
K
1
1
1
K
2
3
K
1
2
2
1
1
p
p
p
p
0
p
p
K
p
p
K
0
p
1
K)
(
p
p
K
p
1
V
Kp
0
2
p
p
p
p
dp
d
V
Kp





























































43.  
 
 
 
     
3
1
2
3
1
2
2
K
1
K
3
2K
2
K
-
1
K
3
1
-
K
-
2
1
K
2
p
p
p
p
p
p
p
p
p
p
p
p
p






44. MINIMUM WORK INPUT
2
p
p
p
p
V
p
1
-
n
n
W
1
2
3
1
1
2
1
1































n
n
n
n
3
1
2 p
p
p
if
minimum
is
input
Work


45. 2
3
2
1
1
3
1
2
2
1
3
1
2
1
2
2
1
2
2
2
1
2
3
1
2
3
1
2
2
p
p
p
p
p
p
p
p
p
p
p
p
p
p
by
)
1
(
p
p
p
p
p
p
p




































46. 2
p
p
2
V
p
1
-
n
n
W
2
p
p
p
p
V
p
1
-
n
n
W
2
1
1
3
1
1
2
1
1
3
2
1
1
3
1
1




















































n
n
n
n
n
n





















1
p
p
V
p
1
-
n
2n
W
2
1
1
3
1
1
n
n

47. 










































1
p
p
V
p
1
-
n
xn
W
stages
of
number
For x
1
p
p
V
p
1
-
n
3n
W
compressor
air
stage
3
For
xn
1
n
1
1
x
1
1
3n
1
n
1
4
1
1

48. ADVANATGES OF MULTISTAGE
AIR COMPRESSOR
• Work done per kg of air reduced with
intercooler as compared to single stage
compression for the same delivery pressure
• Better mechanical balance can be achieved

49. • Volumetric efficiency is improved by increasing
number of stages
• It gives more uniform torque and hence a
smaller flywheel is required
• Lower operating temperature permits the use of
cheaper materials for construction
• Better lubrication due to the lesser working
temperature
• Lighter cylinders