Air compressors:- One of the important device used to compress air at high pressure.
The presentation contains a detailed information about air compressors, classification of air compressors, reciprocating air compressors, rotary type, multistage/ single stage compressors. advantages and lastly application/ uses of air compressors.
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1. Air Compressor
Active Learning Assessment
Elements of Mechanical Engineering(2110006)
Semester:1
Made by: Burhanuddin Kapadia
Enrollment Number: 170120119026/201719000028
Class: ME H2
Submitted to: Prof. Shubham Sarthi
GANDHINAGAR INSTITUTE OF TECHNOLOGY
Approved by AICTE and Affiliated to GTU
Khatraj - Kalol Road, Vil. MotiBhoyan, Tal.Kalol, Dist. Gandhinagar-382721
2. Outline
• Introduction
• Classification
• Reciprocating Compressor
i. Single acting
• Working
i. Compression without clearance
ii. Compression with clearance
• Power Required
• Reciprocating Compressor efficiency
• Multi stage reciprocating compressor
• Advantages of multi stage reciprocating compressor
• Rotary Compressor
• Application/Uses
• Reference
3. Introduction
• The machine which takes in air at low pressure and compresses it to high
pressure with the help of some suitable arrangement are called air compressors.
• According to 2nd law of thermodynamics it is only possible when work is done on
the system.
• Generally, the compressors are driven by electric motors, I.C engine or gas
turbine.
• A compressor which is used for increasing the pressure of air is called as air
compressor.
4. Delivery
Pressure
Methods of
compression
Pressure
Limits
Number Of
Cylinders
Volume Of
air
Delivered
Fluid to be
Compressed
Reciprocating
Rotary
Centrifugal
Low Pressure (up to 1.1 bar)
Medium Pressure (1.1 – 8 bar)
High Pressure (8-10 bar)
Very High Pressure (above 10 bar)
Positive DisplacementRotodynamic
Single Stage (up to 5 bar)
Multi Stage ( above 5 bar)
Single Multi
Fans (1-1.1)
Blower ( 1.1-2.5)
Compressor ( <2.5)
Low Capacity
(10 m³/min)
Medium Capacity
(10 m³/min-300
m³/min)
High Capacity
(<300 m³/min)
Air
Gas
Vapour
• Classification
5. Reciprocating Compressor
• is a positive-displacement compressor that uses pistons driven by a crankshaft to
deliver gases at high pressure.
• sizes up to 25 hp.
• used for light-duty applications
• Has low mass flow rate (kg/s) and high pressure ratio
• Applications include oil refineries, gas pipelines, chemical plants, natural gas
processing plants and refrigeration plants.
Reciprocating
Single
Cylinder
Double
Cylinder
Single
Acting
Double
Acting
7. Working
• Generally, an air compressor takes in air at atm, compresses at high pressure then
deliver it to storage tank.
• From storage tank to gets supplied to different uses through pipe.
• Going technical, working for compression is based on two types :-
a) Compression without clearance
b) Compression with clearance
8. Compression without clearance
• Consider a single stage reciprocating air compressor without clearance volume
delivering air from one side of the piston only.
• Let, P1 = Initial pressure of air
V1 = Initial volume of air
T1 = Initial temperature of air
P2, V 2, T2 = Corresponding values for the final
r = Pressure ratio (i.e. P 2 / P 1)
• Hence the net work done, during adiabatic
process will be: swept volume
A)𝑊 =
𝛾
γ−1
𝑝1𝑉1
𝑝2
𝑝1
𝛾−1
𝛾
− 1
Isothermal 𝑝𝑉 = 𝐶
adiabatic 𝑝𝑉 𝛾 = 𝐶
Polytrophic 𝑝𝑉 𝑛 = 𝐶
1
p
p2
p1
V
4
22’2”3
V1
9. Compression without clearance
B) Work done if compression is polytrophic,
Replacing𝛾 = 𝑛,
𝑊 =
𝑛
𝑛 − 1
𝑝1𝑉1
𝑝2
𝑝1
𝑛−1
𝑛
− 1
C) If compression is isothermal,
𝑊 = 𝑝1𝑉1 log 𝑒
𝑝2
𝑝1
= 𝑝2𝑉2 log 𝑒
𝑝2
𝑝1
= 𝑝𝑉 log 𝑒(
𝑝2
𝑝1
)
10. Compression with clearance
• Consider a single stage reciprocating air compressor with clearance volume delivering
air from one side of the piston only.
• Let, P1 = Suction pressure
V1 = Initial volume of air
T1 = Initial temperature of air
P2,V 2, T2 = Delivery change in valve
r = Pressure ratio (i.e. P 2 / P 1)
P1=P4 & P2=P3
• Work done during adiabatic cycle :-
𝑊 =
𝑛
𝑛 − 1
𝑝1 𝑉1 − 𝑉4
𝑝2
𝑝1
𝑛−1
𝑛
− 1
J
cycle
Can also be written as 𝑊 =
𝑛
𝑛−1
𝑚𝑎𝑑 𝑅𝑇1
𝑝2
𝑝1
𝑛−1
𝑛
− 1
J
cycle
11. Power Required
• Power required to compress air is called indicated power(IP)
∴ 𝑰𝑷 =
(𝑾𝒐𝒓𝒌 𝒅𝒐𝒏𝒆)/𝒎𝒊𝒏
𝟔𝟎∗𝟏𝟎𝟎𝟎
𝒌𝑾 or ∴ 𝑰𝑷 =
𝑷𝒎𝑳𝑨𝒏
𝟔𝟎𝟎𝟎𝟎
𝒌𝑾
• Power required to drive the compressor is called brake power(BP)
∴ 𝑩𝑷 =
𝟐𝝅𝑵𝑻
𝟔𝟎𝟎𝟎𝟎
(BP>IP)
• Mean effective pressure of compressor (𝑃𝑚)
∴ 𝑷𝒎 =
𝒏
𝒏 − 𝟏
𝒑𝟏 𝑽𝟏 − 𝑽𝟒 ∗
𝒑𝟐
𝒑𝟏
𝒏−𝟏
𝒏
− 𝟏
12. Reciprocating compressor efficiency
• The ratio of indicated power to brake power gives mechanical efficiency
𝜂 𝑚 =
𝐼𝑃
𝐵𝑃
• The ratio of isothermal work to indicated work gives isothermal efficiency
𝜂𝑖𝑠𝑜 =
𝑝1𝑉1log 𝑒(
𝑝2
𝑝1
)
𝑛
𝑛 − 1
𝑝1𝑉1
𝑝2
𝑝1
𝑛−1
𝑛
− 1
• The ratio of swept effective volume to swept volume of cylinder is called
volumetric efficiency
𝜂 𝑣 = 1 − 𝐶
𝑝2
𝑝1
1
𝑛
− 1
13. Multistage Reciprocating Compressor
• High delivery pressure=high temperature, leads to more volume of air
• Temperature increases reduces the density of air hence mass flow decreases
• High temperature will need heavy working parts hence more cost and less work
• To overcome this problems of single stage , multistage cylinder came into use
• Multi-stage compressors feature a series of cylinders, each of a different
diameter.
• In a two-stage compressor, air is forced into chamber where it is pressurized to
the required extent.
• In a three-stage compressor, an cycle of compression and cooling occurs before
this.
14. Multistage Reciprocating Compressor
• An intercooler, is an air-to-air or air-to-liquid heat
exchange device used on turbocharged and
supercharged.
• When air is compressed, its temperature increases.
• Between each compression stage, the air passes
through a heat exchanger, where it is cooled.
15. Advantages of multistage Compressor
• By intercooling , more work done in less input
• Volumetric efficiency is increased
• Less working temperature , hence better fuel consumptions
• Better mechanical balance and smoother torque angle is obtained
16. Rotary Compressor
• A rotary-screw compressor is positive-displacement mechanism.
• Air enters a sealed chamber where it is trapped between two contra-rotating
rotors.
• they reduce the volume of trapped air and deliver it compressed to the proper
pressure level.
• high mass rate but low pressure ratio.
18. Rotary Compressor
• Positive displacement compressors draw in and capture a volume of air in a
chamber, then reduce the volume of the chamber to compress the air.
• Axial compressors use a series of turbine blades, similar in appearance to a jet
engine, to force air into a smaller and smaller area.
• Centrifugal compressors are often used in sizes ranging from about 150 hp up to
over 10,000 hp.
• Rotary screw compressors in sizes from small (in cars) up to 500-600 hp are very
popular because of their high reliability and low maintenance requirements.
• Centrifugal compressors draw in air to the center of an impeller, and then
accelerate it outward toward its perimeter.
• Centrifugal compressors used for manufacturing are water-cooled and use two or
three stages of compression
19. Applications
• Small & medium size business
• Industrial use
• Agricultural/Farming
• Manufacturing
• Dry cleaning
• Pharmaceuticals
• Food/Beverages
• Commercial use
20. Uses
• Manufacturing of acids& chemicals
• Food processing
• Spraying paints & insecticides
• Construction
• Operating air brakes
• Operating elevators& also in doors
• Glass blowing
21. Reference
• https://en.wikipedia.org/wiki/Air_compressor
• http://www.popularmechanics.com/home/how-to/a151/how-air-compressors-
work/
• Basic of Mechanical Engineering – Pravin Kumar
• http://www.tpub.com/fireman/102.htm
• http://www.brighthubengineering.com/hvac/64884-different-types-of-air-
compressors/
• Elements Of Mechanical Engineering - Dr. N.M Bhatt
• https://www.quincycompressor.com/products/2-and-3-stage-air-compressors/
• https://www.google.co.in/search?q=application+of+an+air+compressor&source=l
nms&tbm=isch&sa=X&ved=0ahUKEwil9IaXtLfXAhWBOo8KHTJhDiEQ_AUICygC&bi
w=1366&bih=651
