Elements of Mechanical EngineeringAir Compressors

Created by,

Devang Pandit(130110120025)Yash Pandya(130110120026)Akash Pansuriya(130110120027)Tanuj Parikh(130110120028)

Topics To be Covered

• Introduction• Uses if Compressed air• Reciprocating compressors• Operation of a compressor• Work for compression• Power required• Reciprocating compressor efficiencies• Multistage reciprocating compressors• Rotary Compressors• Comparison between reciprocating and rotodynamic

Compressors

Introduction

• The machine which takes in Air or any other gas at lower pressure and compresses it to high pressure are called compressors

• Compressors are power Consuming machine

• They are also considered as reversed heat engine

• A compressor is used for increasing the pressure of air is called air compressor

Classification of Compressors

Compressors are Classified According to:

(1) Method of Compression:

(a)reciprocating Compressors:

--Compressies air by Reciprocating Action of piston inside a cylinder.

--Suitable for producing high pressure

(b) Rotary Compressors: Air is compress due to rotation of impeller or blade inside a casing similar to a rotary pump

(c)centrifugal compressor:

--Compression of air to desired pressure is cariied out by centrifugal force

--suitable for medium pressure

(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

(3) Principle Of operation

(a)Positive displacement:Pressure of air is increased by reducing volume.

--These are capable to produce high pressure with low volume flow rate

(b) Rotodynamic or steady flow Compressor : Compreeson of air cariied out by rotetingelement imparting velocity to the flowing air and developed desired pressure.

(4) The number of Stages:--Single stage – pressure upto 5 bar--Multistage –pressure above 5 bar

(5) The number of cylinder:--Single cylinder -- Multicylinder

(6)The pressure Limit--Fans – pressure ration upto 1 to 1.1--blowers- pressure ratio 1.1 to 2.5--Compressors – pressure ratio above 2.5

(7) Volume Of air delivered

-(a) Low capacity- Volume flow rate up to 10m3/min

(b)Medium Capacity – Volume flow rate 10m3/min to 300m3/min

(c) high Capacity – Volume flow rate above 300m3/min

Uses of Compressed Air

• In refrigeration Cycle• Operating Pneumatic tools like drill , hammers ,

rivetting machine etc• Filling the air in automobile tyres• Spray painting• Increasing inlet pressure of I.C engine• To operate air moter in mines where fire risks are more• Pumping of water• Gas turbine plant• For sand blasting• Operating blast furnaces

Reciprocating Compressors

It is widely used forCompressingAir and satisfactory for all ranges of pressure

Consist of the cylinder in which a piston reciprocates

The piston Is driven by Rod

The crank is monted in a crankcase

Operation Of a compressor

• (1) Operation without clearance:

Operation Of a Compressor

(2) Operation with Clearance:

1-2 Compression process

2-3 delivery process

3-4 Expansion process

4-1 Suction process

Multistage Reciprocating Compressure

• There are several disadvantages to compress the air at a high pressure in a single cylinder.

• In single stage Compresseor If the ration of pressure increase the volumatic efficiency decrease

**The Following problem With single Stage Compression:

--The higher the delivery pressure, the higher will be delivery temperature

--the increase in temperature of air causes reduction in density of air ,hence the mass flow through compressor decreases

--The operation at high pressure and temperature will need heavy working parts

``In low pressure cylinder air s compressed adiabatically from 1 to 2

The Compressed air is passed through intercooler-1 wher it is cooled down from 2-2’

• The air is compressed adiabaticlly from 2-3’

• The Compressed air is cooled down from 3-3’

• Finally air enters into high pressure cylinder for getting higher pressure

**Advantages OF Multistage compressor**--Volumetric efficiency is increased due to the

smaller pressure range as the efforts of expansion of air in the clearance volume is less

--Due to smaller working tempreture better lubricating effect is provided

--In a multi stage Compressor the low pressure cylinder is lighter

--There is less amount of leakage problems due to less pressure differace for each stage

Advantages of multistage compressor:--without intercooling the curve of compression will

follow the path (1-4), hence the saving in work-- Volumetric efficency is increased due to smaller

pressure range--less shaft power is requred for a given pressure ratio

due to the saving in work input--Due to smaller working tempreratur, better lubricating

effect is provided-- better mechanical balance and smoother torque angle

diagram is obtained

Comparison between Reciprocating and Rotodynamic Compressors

Reciprocating Compressors

• Maximum delivery pressure can be achieved as high as 1000 bar

• These are suitable for low discharge and high pressure application

• Air discharge is not continuous

• These compressors require complicated lubrication system

• Rotational speed is low

Rotodynamic compressors

• Maximum delivery pressure is up to 10 bar by multistaging up 40 bar

• These are suitable for high discharge and low pressure application

• Air discharge is continuous

• Simple lubrication syste, is required

• Rotational speed is high

• Size of this compressor is larger than rotary compressor for same discharge

• Due to reciprocating parts balancing is the major problem

• Maintenance cost is more

• Efficiency is less than 100%

• Running cost is more

• Size of this compressors is smaller than reciprocating compressor for same discharge

• There is no reciprocating parts, balancing is not problem

• Maintenance cost is less

• Efficiency is nearly 100%

• Running cost is less