This document discusses different types of air compressors. It describes reciprocating compressors which use pistons driven by crankshafts to compress air in cylinders. It also describes rotary compressors like centrifugal compressors which use rapidly spinning impellers to accelerate and compress air, and axial compressors which use alternating rows of fixed and moving blades to compress air. The document also discusses positive displacement compressors like roots blowers which use interleaving lobes to trap and compress air, and vane compressors which use sliding vanes and an eccentric rotor to vary chamber volumes and compress air.

1. AIR COMPRESSORS
Elements Of Mechincal Engineering
Electrical

2. Group members Enrollment
number

3. INDEX
1.1 Introduction
1.2 Uses of Compressed air
1.3 Reciprocating compressors
1.4 Operation of a compressors
1.5 Work of compression
1.6 Power required
1.7 Reciprocating compressor efficiencies
1.8 Multistage reciprocating compressors
1.9 Rotary compressors

4. Introduction
• The machine which takes in air or any other gas
at low pressure and compresses it to high
pressure are called compressors.
• They are power consuming machines in which
mechanical work is converted into the pressure
head of air or gas.
• They are also considered as reversed heat
engine.
• Generally, the compressors are driven by electric
motors, I.C. engine or gas turbines.
• A compressor is used for increasing the pressure
of air is called aircompressor.

5. Classification of compressors
(1) Method of compression
• Reciprocating compressors:.
• Rotary compressors:
• Centrifugal compressors
(2) Delivery pressure
• Low pressure
• Medium pressure
• High pressure
• Very high pressure

6. (3) Principal of operation
 Positive of displacement
 Rotodynamic or steady flow compressor
(4) The numberof stages
 Single stage compressor - pressure up to 5 bar
 Multistage compressor - pressure above 5 bar
(5) The numberof cylinder
 Single cylinder
 Multi cylinder

7. (6) Volume of airdelivered
• Low capacity
• Medium capacity
• High capacity
(7) Fluid to be compressed
• Air compressor
• Gas compressor
• Vapour compressor

8. Uses of compressed air
 In refrigeration cycle
 Operation tools like drill hammers etc.
 Filling the air in automobile tyres
 Spray painting
 Increasing inlet pressure of I.C. engine
 To operate air motor I mines where fire risk are more
 Pumping water
 Gas turbine power plant
 Conveying the materials like sand and concrete along
a pipe line
 For sand blasting
 Operating blast furnace
 Operating air brakes used in buses truck trains etc.

9. Reciprocating compressor
 A single stage reciprocating compressor. It used for
compressing air and it is satisfactory for all ranges of
pressure it consist of the cylinder in which a piston
reciprocates the piston is driven by crank through connecting
rod .the crank is mounted in a crank case. the value are
generally pressure differential type.

10. Workforcompression
(1) Compression without clearance
W = p1 V1 (p2/p1) = p2 V2 loge(p2/p1) = pV loge
(p2/P1)
(2) Compression with clearance
W = n/n-1 mad RT1 p2/p1 n-1/n – 1 J/cycle

11. Powerrequired
(1) Indicated Power:
I.P. = pmLAn KW
60000
(2) Brake power:
B.P.= 2NT
60,000

12. Reciprocating compressor
efficiencies
(1) Mechanical efficiency
ῃ= I.P/B.P
(2) Isothermal efficiency
ῃiso = p1 V1 loge (p2/P1)
[ (n/n-1) p1V1 (p2/p1)n-1/n -1}]
(3) Volumetric efficiency
ῃ = 1- C [(p2/p1)1/n -1)]

13. Multistage reciprocating
compressor
 There are several disadvantages to compress
the air at a high pressure in a single cylinder
the air is compressed by more than one
cylinder in series in a single stage compressor
if the pressure ratio is increased the volumetric
efficiency decrease .by the equation when the
pressure ratio is p2/p1=[1+1/c]n

14. Advantages of multistage
compressor
• Without inter cooling the curve of compression
will follow the path hence the saving work
input due to inter cooling .
• Volumetric efficiency is increased due to the
smaller pressure range as the effect of
expansion of air in the clearance volume is
less
• Less shaft power is required for a given
pressure ratio due to the saving in work input

15.  Due to smaller working temperature better
lubricating effect is provided
 Better mechanical balance and smoother
torque – angel diagram is obtained
 In multistage compressor the low pressure
cylinder is lighter
 There is less leakage problems due to less
pressure difference for each stage

16. Rotary compressor

17. (1) Centrifugal compressor
• A general arrangement of this compressor is
similar to a centrifugal pump Fig. shows main
components of a centrifugal compressor It
consist of a rotating elements called impeller and
a volute casing impeller rotates at a very high
speed may be up to 30,000 RPM The air enter
into the compressor through the
suction eye of the impeller. due to the
rotation of the impeller at a high
velocity.

18. • Then air with high velocity enter into a
diffuser ring. the diffuser blade of the
diffuser ring are so shaped that these
provided an increased area of passage to
the air which is passing outward due to
which the velocity of air leaving the impeller
is reduced and its pressure is increased the
high pressure air then flows to the divergent
passage of volute casing the velocity air is
further reduced due to increased cross
sectional area of volute casing causing very
small rise in pressure from the casing the
compressor air leads to exit pipe and finally

19. (2) Axial Flow compressor
• It consists of a casing fitted with several rows of fixed
blades and rotor attached with several rows of
moving blades.
• The fixed and moving blades are placed on alternate
rows the function of the fixed blades is to receive the
high velocity air from the moving blades.
• Axial flow compressor is also a high speed machine
and speed may even vary from 10,000 to 30,000
RPM. Pressure ratio of 10:1 can be achieved.

20. Positive Displacement
Compressors

21. (1) Roots Blowers
• The roots blower consists of two lobe For
higher pressure ratio three and four lobes may
be used here the pressure of air delivered is
slightly above the atmosphere.
• The machine consists of a fixed casing two
shafts fitted with two lobe rotors one of the
rotor is driven by electric motor or other prime
movers and other is driven through the gears
from first.

22. • The air is drawn through the inlet pipe due to
rotation of due rotors. the volume of air is
entrapped between one rotor and casing for a
very short interval due to rotation of lobe
trapped air is carried to the discharge side
continued rotation of rotors open the trapped
space to the discharge port. the air is pushed to
the receiver due to the continued rotation of
rotors.

23. (2) Vane type compressoror
Blower
• This type of compressor is shown inn fig. The
compressor is consists of rotor drum mounted
eccentrically in the cylindrical casing. The rotor is
provided with vanes in the slots. These vanes or
blades are made from non-metallic material usually
fiber or carbon.
• The vanes can slide in and out in the slots. The volume
between two vanes keeps on
changing due to eccentric motion
of the rotor. The rotation of the
rotor causes space to be created
between the vanes,the rotor and
casing.The space is connected to
suction pipe so that air enters into
the created space and filled.

24. • A volume V1 of air trapped between the vanes and casing. With
the rotation of rotor of rotor, air gets compressed due to reduction of
space towards delivery side.
• The fluid volume reduces to V2,when it communicates with the
delivery side. Since the receiver pressure is higher than the
compressed air between the vanes, the back flow of air from the
receiver will take place.
• Due to rotation of vanes air is delivered to the receiver. In this type
of compressor. the total pressure rise is partially due to internal
compression between the vanes and partially due to back flow of air
from receiver.
• This type of compressor can produce a pressure ratio up to 6 per
stage