1. BASICS OF MECHANICAL ENGINEERING

2. TURBINES Steam turbines Gas turbines Water turbines Classification
Principle of operation of impulse and reaction turbines
Delaval’s turbine
Parsons’s turbine
Compunding of impulse turbine
Gas turbines
Working principles and operations of open cycle and closed cycle gas turbine
Water turbines
Principle of operations of Pelton wheel
Francis turbine
Kaplan turbine

3. STEAM TURBINES
Prime mover – Is a self moving device which converts available natural source of energy into mechanical energy of motion to drive the other machines.
Steam turbine is a prime mover
Converts heat energy of steam into mechanical energy in the form of rotary motion.

4. STEAM TURBINES Steam turbines are mainly used in Thermal power plants
Heat energy of steam --> Kinetic energy --> mechanical energy of rotation
(Nozzle) (Turbine)
Steam turbines are mainly used in
Thermal power plants
Ships
Gas compressors
Textile and sugar industries

5. STEAM TURBINES Propelling force in the steam turbine
Steam is caused to fall in its pressure by expanding in a nozzle
Due to fall in pressure a certain amount of heat energy is converted into KE
The rapidly moving particles of steam enter the rotating part of the turbine
Where it undergoes change in direction of motion
Which gives rise to a change of momentum and therefore a force.
This constitutes the driving force of the turbine

6. STEAM TURBINES Expansion of steam in the nozzle
A high velocity jet of steam is produced by expanding a high pressure steam in a convergent divergent nozzle as shown in fig.
As steam passes between the entry and throat, it expands to a low pressure.
Due to this expansion in this portion of the nozzle the enthalpy of the steam is reduced
This loss in enthalpy of the steam must therefore be equal to the increase in the velocity of the steam.
The divergent portion is provided to complete any remaining expansion.

7. De Laval Turbine (Impulse turbine) Parson’s Turbine (Reaction turbine)
STEAM TURBINES
Classification of steam turbines
Depending on the drop in pressure due to the expansion of the steam that take place either before it is passed on to the turbine wheel or on the turbine wheel itself and the nature of the resulting propelling force
The steam turbines are classified into
De Laval Turbine (Impulse turbine)
Parson’s Turbine (Reaction turbine)

8. In this type of turbine the steam is initially expanded in a nozzle
STEAM TURBINES
De Laval Turbine (Impulse turbine)
In this type of turbine the steam is initially expanded in a nozzle
The high velocity jet of steam coming out of the nozzle is made to glide over a curved vane called blade.
From fig we found that the jet of steam gliding over the blade gets deflected
This causes the particle of steam to suffer a change in direction of motion which gives rise to change in momentum and therefore a force.
The resultant of these forces acting on entire curved surface of blade causes it to move.
When a number of such blades are fitted on the circumference of a revolving wheel, called rotor as shown in fig. they will be moved by the action of steam.

9. Pressure velocity changes in impulse turbine
STEAM TURBINES
Impulse turbine
Pressure velocity changes in impulse turbine

10. Parson’s turbine (Reaction turbine)
STEAM TURBINES
Parson’s turbine (Reaction turbine)
In this type of turbine the high pressure steam does not initially expand in the nozzle as in the case of impulse turbine, but instead directly passes onto the moving blades.
The blades are designed in such a way that the steam flowing between the blades will be subjected to the nozzle effect
Fig
The increase in velocity of the steam flowing over the blades develops a force

11. Pressure – velocity changes in reaction turbine
STEAM TURBINES
Reaction turbine
Pressure – velocity changes in reaction turbine
The actual reaction turbine consists of a number of rows of moving blades fitted on the different rotors keyed to the turbine shaft with alternate rings of fixed blades rigidly fixed to the casing of the turbine.
Both fixed and moving blades are designed in the shape of the nozzles
Therefore the expansion of the steam takes place both in fixed and moving blades

12. Comparison between impulse and reaction steam turbine
STEAM TURBINES
Comparison between impulse and reaction steam turbine
Impulse turbine
Reaction turbine 1
The steam completely expands from high pressure to low pressure in the nozzle before it enters the moving blades
The high pressure steam continuously expands successively in both the fixed and moving blades 2
Because of the large pressure drop in the nozzle, the steam speed and as well as the rotor speeds are high
Due to smaller pressure drop over both fixed and moving blades, both the steam speed and rotor speed are low 3
Occupies less space per unit power
Occupies more space for the unit power 4
Suitable for small power generation prime movers
Suitable for medium and high power generation prime movers 5
Due to high rotor speeds compounding is required to reduce the speed
The speeds are relatively less and hence no compounding is required

13. GAS TURBINES
Steam turbine:
Heat obtained from combustion of fuel --> to generate steam-->steam turbine
Gas turbine
Hot gases of combustion --> to turbine
A gas turbine essentially consists of a combustion chamber in which a liquid fuel is burnt in presence of air supplied by a compressor.
The air compressor sucks the air from the atmosphere and compresses it, there by increasing its pressure
In combustion chamber compressed air combines with fuel and the resulting mixture is burnt.
The burning gases at very high pressures expands rapidly and made to pass over the rings of moving blades mounted on the turbine shaft
(kinetic energy is absorbed by the moving blades imparting rotary motion)

15. GAS TURBINES Principle of operation of closed cycle gas turbine Fig---
It consists of a compressor, a heater, a cooler and the gas turbine.
Fig---
Both compressor and turbine are mounted on same shaft

16. GAS TURBINES Principle of operation of open cycle gas turbine
It consists of a compressor, combustion chamber and the gas turbine.
Fig ---
The gas turbine and compressor are mounted on same shaft

17. Differences between closed and open cycle gas turbine
GAS TURBINES
Differences between closed and open cycle gas turbine
Closed cycle
Open cycle 1
Working substance is continuously re- circulated
Working substance is continuously replaced in every cycle 2
Any fluid may be used as the working substance
The working substance comprises of the mixture of air and the products of combustion of fuel 3
There is only heat and work transfer takes place between the system and surrounding
There is mass transfer taking place in addition to heat and work transfer between system and surrounding 4
There is no loss of working substance
In every cycle fresh air is drawn

18. WATER TURBINES
Water turbines are the machines that convert the kinetic and potential energies possessed by water into mechanical rotary motion
Water turbines are the prime movers which when coupled to an electric generator produces electric power.
Hydro electric power can be developed whenever continuously flowing high pressure water is available
Water is carried out from water reservoirs to turbine stations through large pipes called penstocks and in the turbines its hydraulic energy is converted into mechanical energy

19. Based on the type of hydraulic action water turbines are classified as
Classification of water turbines
Based on the type of hydraulic action water turbines are classified as
Impulse turbine Ex: Pelton wheel
Reaction turbine Ex: Francis turbine, Kaplan turbine
Impulse water turbine
In an impulse water turbine the whole pressure energy of the water is converted into the kinetic energy in nozzles before it is passed on to the turbine wheel
An impulse turbine requires high head and low discharge at the inlet of the turbine

20. WATER TURBINES
Impulse water turbine
PELTON WHEEL

21. Reaction water turbine
WATER TURBINES
Reaction water turbine
The water supplied to the reaction turbine posses both pressure as well as kinetic energies
First the water passes to the guided blades which guide or deflect the water to enter moving blades
When water flows over moving blades, part of the pressure energy is converted into the kinetic energy which will be absorbed by the turbine wheel.
The water leaving the moving blades will be at a low pressure.
The difference in pressure between entrance and exit of moving blades is called the reaction pressure.
A reaction turbine requires low head with high rate of flow.

22. Difference between impulse and reaction water turbines
Impulse water turbine
Reaction water turbine 1
The whole of the pressure energy is converted into kinetic energy before it is passed on to the turbine wheel
The water flows with both pressure and kinetic energies over the moving blades 2
The impulse force of the jet sets up the rotation of the turbine wheel
The reaction pressure sets up the rotation of the turbine wheel 3
The water may be admitted over a portion of the circumference of the wheel
The water must be admitted over the whole of the circumference of the wheel 4
The water discharges from the turbine wheel to the tail race
Water discharges from the turbine into a draft tube from which it discharges finally into tail race.

23. WATER TURBINES FRANCIS TURBINE
Is the medium head reaction turbine in which water flows radially inwards
Fig --

24. WATER TURBINES KAPLAN TURBINE
The Kaplan turbine is a low head reaction turbine in which water flows axially