Air compressor efficiency with & Without clearance with all formulas. Elements of mechanical Engineering.

1. GEC DAHODGEC DAHOD
EVEN-SEM 2017
B.E. 1st
YEAR (C)
SUBJECT:- E.M.E.(2110006)
Topic:- “Air compressor efficiencies with and without
clearance”

2. Contents:Contents:
 Introduction
 Different Parameters
 Volumetric efficiency of compressor with clearance
 Volumetric efficiency of compressor with clearance
 Other Efficiencies

3. IntroductionIntroduction
 Definition:- Air compressor is a device which take in gas or vapour,
increase the pressure of it and deliver it at a high pressure.
 Compression requires Work to be done on the gas,
Compressor must be driven by some sort of Prime Mover
 Compressed air powers many different kinds of devices. It can be used
to push a piston, as in a jackhammer Compressed air provides torque
and rotation dental drill, small turbine shaft.
 power for pneumatic tools, such as drills, brushes, nut runners, riveting
guns and screwdrivers, dental drill, small turbine shaft.
 Before the study about efficiency we should know about parameters of
compressor efficiency.

4. P1
P2
V1V4
6 2
5 1
3
4
V3
Effective Swept Volume,
V1-V4
Swept Volume, V1-V4=Vs
Total Volume, V1
Clearance Volume,
V3=Vc
EXPANSION
COMPRESSION
CVP n
=
Different Parameters of Compressor:Different Parameters of Compressor:
 1) Clearance volume:- It is that volume which remains in the cylinder
after the piston has reached the end of its inward stroke.
 P-V diagram with clearance:-
 At condition (1) cylinder is full of with
intake air, having volume V1 and
pressure P1. At this point, the piston is
about to start its compression stroke.
The air is compressed polytropically
according to law . The pressure
increased from p1 to p2.
 At point 2, the delivery valve opens. In
the stroke 2 to 3, the compressed air is
delivered from the cylinder by
movement of the piston. Volume
decreases from V2 to V3 and gas
enters the receiver.
 At point 3, the piston has reached the
end of its inward stroke. The delivery of
the compressed air ceases at 3. V3 is
the clearance volume .
n
PV C=

5.  At this stage it is filled with compressed air at pressure P2 = P3 . As the piston
begin to intake stroke this residual compressed air will expand. This expansion
according to same polytrophic law. Pressure reduce from P3 to intake pressure P4..
Inlet valve begin open and permit the intake of fresh charge.
 Clearance volume is trapped between piston head and cylinder top. It is
represented either by VC or V3.
 Why small Clearance is required?
A) For a thermal expansion due to high temperature at the end of compression.
B) For maintaining machine tolerance.
C) For preventing pistion striking the cylinder head.
 Effect of clearance is to reduce the volume of the gas actually sucked in per
working cycle.
 2)Swept volume:- It is a volume equivalent to the piston displacement is known
as swept volume. It is represented by VS
 3)Effective swept volume:- For the remainder of the intake stroke a fresh
charge is taken into the cylinder is called effective swept volume(V1 - V4).

6. Volumetric efficiency of Compressor withVolumetric efficiency of Compressor with
clearance:clearance:
 Volumetric Efficiency :
The ratio of effective swept volume to the swept volume is called
volumetric clearance efficiency.
 Presence of Clearance Volume
 Volumetric Efficiency less than 1. ( 60 – 85 % )
 Volumetric Efficiency =
Effective Swept Volume
Swept Volume
V1 – V4
V1 – V3
=
Clearance Volume
Swept Volume
 Clearance Ratio =
Vc
Vs
= = γ ( 4 – 10 % )

7. ⇒↑ Pr. Ratio ↑ Effect of Clearance Volume
….Clearance air expansion through greater volume before intake
⇒
⇒
Cylinder bore and stroke is fixed.
Effective Swept Volume (V1 – V4) ↓ with ↑ Pr. Ratio
↓ Volumetric Efficiency⇒
⇒
P1
P2
V1V4
6 2
5 1
3
4
V3
Effective Swept Volume,
V1-V4
Swept Volume, V1-V3=Vs
Total Volume, V1
Clearance Volume,
V3=Vc
( ) ( )
( ) ( ) ( )
( ) ( )
( ) ( ) 3
4
31
3
31
3
3
3
31
4
31
3
31
4
31
3
31
4331
31
41
1
1
1
V
V
VV
V
VV
V
V
V
VV
V
VV
V
VV
V
VV
V
VV
VVVV
VV
VV
vol
•
−
−
−
+=
•
−
−
−
+=
−
−
−
+=
−
−+−
=
−
−
=η

8. 







−





•−=








−





−
−=






−
−
−=






−
−
+=
11
11
11
11
/1
4
3
/1
4
3
31
3
4
3
31
3
4
3
31
3
n
vol
n
vol
vol
vol
P
P
P
P
VV
V
V
V
VV
V
V
V
VV
V
γη
η
η
η
P1
P2
V1V4
6 2
5 1
3
4
V3
Effective Swept Volume,
V1-V4
Swept Volume, V1-V3=Vs
Total Volume, V1
Clearance Volume,
V3=Vc

9. Volumetric efficiency of Compressor withVolumetric efficiency of Compressor with
clearance:clearance:
Intake Pr.
P1
Delivery Pr.
P3 or Pd
22’ 2”
1
CVP n
=
4
3
Intermediate Pr.
P2 CVP =
Adiabatic
Isothermal
Volume
B
A
 4-1: Volume of air aspirated into
compressor at pressure P1 and
temperature T1
 1-2: Air is compressed according to
law of polytrophic process from
pressure P1 to P2 .
 2-3 Compressed air of volume V2
and pressure P2 with temperature
T2 is delivered from the
compressor.
 For Efficiency without clearance V3 = 0
 Swept volume = V1
 Volume of air compressed = V1
P-V Diagram:-
1 4
1
1
1
4
1
1
4
vol
V V
V
V
V
P
P
η
−
=
= −
 
= − ÷
 
Efficiency,

10. Other efficiencies:Other efficiencies:
Compressor Efficiency = Isothermal Power
Indicated Power
Isothermal Efficiency = Isothermal Work done
Actual work done
 Isothermal efficiency: It is a Ratio of isothermal work done to the actual
work done.
 Mechanical Efficiency : Ratio of mechanical output to mechanical input.
Mechanical Efficiency, ηmech = Indicated Power
Shaft Power

11.  Adiabatic Efficiency : Ratio of Power required to drive the Compressor;
compared with the area of the hypothetical Indicator Diagram; assuming
Adiabatic Compression.
CompressorthedrivetorequiredPowerBrake
P
P
VP
adiabatic
















−
−
=
−
γ
γ
γ
γ
η
1
1
2
11 1
1

12. Created by,
Suraj Biniwale
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