Mechanical Engineering Study materials & Science & Technology

Hello Friends,Now I am going to explain about the two new Concept that is Stress and Strain.In Engineering field stress and strain have different meanings that you should know about this.In Engineering field stress and strain are basically seen in Materials, structures,dams,bridges,trusses etc.It is very important topics because if you are a Mechanical Engineer and if you want to become future Design Engeer then you should know about this.Now Let's start?

Stress:-

According to it's defination ,The internal resisting force acting per unit area, offered by a body against deformation is known as Stress.The force which cause or produced stress called load or external force.
Mathematically it can be written as:
Where force(F)= External force or Load
             Area(A)=Cross-sectional area

S.I units of Stress,here Force is expressed in Newton's (written as N) and area is expressed as m^2 (metre sq.)

Now we should Know about the types of Stress for better understanding of these concepts:
Stress is basically of three types:

1. Tensile Stress
2. Compressive Stress
3. Shear Stress

Single stage Centrifugal Compressor

These type of compressors are considered to have an overhung impeller arrangements.

Multistage centrifugal Compressor

Multistage centrifugal Compressor consist of one to ten impellers and it can be arranged in a variety of low path configuration throughout each and every stage the temperature and Compression ratio are resume to be constant because the act of Compression heats up the gas there is a limit to how much gas pressure can be raised up across any given compression stage.
          Higher and Higher pressure can be achieved by placing multiple stages of Compression in series that is having the discharge of one stage of Compression feed the intake of the next stage an so on.
                              Multistaging is the term used whenever multiple stages are used to meet the pressure requirement of given application.
                  If the temperature from the one compression stage is predicted to get excessive then interstage cooling is required to drop the gas temperature to a safe level before entering to the next stage.
And problems with interstage cooling system can result in loss of flow, pressure, capability and in surging.

               Multistage centrifugal Compressor
   


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Working principle of Centrifugal Compressor:-

The centrifugal Compressor increases the pressure air by first creating a very high velocity and then some amount of kinetic energy of moving air into high static pressure by Centrifugal force.

Constructionand and Working:-

• A Single stage centrifugal Compressor consist of an impeller to which a number of curved vanes are fitted symmetrically.
• The impeller rotates it pushes the air from the centre of the impeller to it's periphery by centrifugal force.
• The high speed of impeller leaves the air with high velocity at vane tips of the impeller.
• The kinetic energy thus attained at the impeller outlet is converted into pressure energy,when the high velocity air passes over the diffuser.
• The diffuser is normally a vane less pipe as it permits more efficient part load operation.
• The volute casing collects the air from the diffuser and it further converts kinetic energy into pressure energy it leaves the compressed air to outlet.

Centrifugal Compressor

A Centrifugal Compressor is a radial flow rotodynamic fluid machine that uses mostly air as the Working fluid and utilizes the mechanical energy imparted to the machine From outside to increase the total internal energy of the fluid mainly in the form of increased static pressure head.
                          The Compression principle of Centrifugal Compressor is quite different from that of Reciprocating or rotary type Compressor.
                       When the air passes through the rotating impeller it experiences force or work which is performed by centrifugal force.the work input takes place as increase in pressure and velocity or speed of the air flow through the impeller.the diffuser is actually a fixed or static components that exert air flow when it leaves the impeller.
This loss in velocity eventually results in additional increase of pressure the impeller and diffuser contribute 65% and 35% of the total pressure developed in the Compressor.
                  Each stage of the part takes place overall the Compressor unit.the depending upon the pressure in the application a number of stages can be arranged in a series to achieve a higher pressure.this type of multistage application is often used in the oil and gas industry.
                 Image source- mechaniclove.com
                                          By google.com


Why Centrifugal Compressor used mostly in industry?

Because of the following reasons centrifugal Compressor mostly used in industry:-

• Oil free air
• High reliability
• Lowest Cost operation
• Easy operation 
• Easy maintenance
• Simple installation
• High Life expectancy
• Less foundation, piping and spacecraft
• Best Specific power consumption efficiency.

Advantages

• Rotary screw Compressor is used basically for continuous supply of air.
• It gives high pressure upto 90 bar.
• It gives high power upto 500 hp.
• It gives oil free air output after comple compression.

Rotary vane compressor

Rotary vane compressor utilize one of the oldest Compressor technologies.they consists rotor with a number of blades inserted in radials slots in the rotor.
The rotor is mounted offset in a larger housing that is either circular or a more complex shape.As the rotors turns,blades slide in and out of the slots keeping contact with the outer wall of the housing.thus a series of decreasing volume is created by rotating blades.they can be either stationary or portable,can be single or multistage and can be driven by electric motors or internal combustion engines.they are well suited to electric motor drive.

                    Image source-pumpschool by Google.com

Principle:-

• It is based on the principle of backflow of air. at first air is compressed and then by using backflow of air.