Turbo Machines Course: Steam Turbines Classification and Working Principle

TURBO MACHINES
Course Code 18ME54 CIE Marks 40
Teaching Hours / Week (L:T:P) 3:0:0 SEE Marks 60
Credits 03 Exam Hours 03
[AS PER CHOICE BASED CREDIT SYSTEM (CBCS) SCHEME]
SEMESTER – V
Dr. Mohammed Imran
B. E. IN MECHANICAL ENGINEERING

Course Objectives
 Understand typical design of Turbo machine, their working principle,
application and thermodynamics process involved.
 Study the conversion of fluid energy to mechanical energy in Turbo
machine with utilization factor and degree of reaction.
 Analyse various designs of steam turbine and their working
principle.
 Study the various designs of hydraulic turbine based on the working
principle.
 Understand the various aspects in design of power absorbing
machine.
Dr. Mohammed Imran

Course outcomes
On completion of the course the student will be able to
CO1: Model studies and thermodynamics analysis of turbomachines.
CO2: Analyse the energy transfer in Turbo machine with degree of reaction
and utilisation factor.
and utilisation factor.
CO3: Classify, analyse and understand various type of steam turbine.
CO4: Classify, analyse and understand various type of hydraulic turbine.
CO5: Understand the concept of radial power absorbing machine and the
problems involved during its operation.
Dr. Mohammed Imran

Module-3
 Steam Turbines:
 Classification,
 Single Stage Impulse Turbine,
 Condition For Maximum Blade Efficiency,
 Stage Efficiency,
 Need And Methods Of Compounding,
 Need And Methods Of Compounding,
 Multi-stage Impulse Turbine,
 Expression For Maximum Utilization Factor,
 Numerical Problems.
 Reaction turbine
 Parsons’s Turbine,
 Condition For Maximum Utilization Factor,
 Reaction Staging.
 Numerical Problems.
10 Hours
Dr. Mohammed Imran

Text Books:
 An Introduction to Energy
Conversion, Volume III,
Turbo machinery, V.
Kadambi and Manohar
Prasad , New Age
International Publishers,
reprint 2008.
Dr. Mohammed Imran
International Publishers,
reprint 2008.
 Turbo Machines, B.U.Pai ,
Wiley India Pvt, Ltd , 1st
Edition.
 Turbo machines, M. S.
Govindegowda and A. M.
Nagaraj , M. M.
Publications, 7Th Ed, 2012

Reference Books:
Dr. Mohammed Imran

MODULE-3 PART – A
STEAM TURBINES
SEMESTER – V
Dr. Mohammed Imran

Module-3
1. Steam Turbines
 A steam turbine is a key unit in a steam power plant
from which we get power .
 A steam turbine is a turbo machine and a prime mover
in which energy of stem is transformed into kinetic
energy and this kinetic energy is then transformed into
mechanical energy of rotation of shaft of turbine.
mechanical energy of rotation of shaft of turbine.
 The modern steam turbine was invented in 1884 by Sir
Charles Parsons, whose first model was connected to a
dynamo that generated 7.5 kW (10 hp) of electricity.
 The Parsons turbine also turned out to be easy to scale
up. Parsons had the satisfaction of seeing his invention
adopted for all major world power stations, and the
size of generators had increased from his first 7.5 kW
set up to units of 500MW capacity.
Dr. Mohammed Imran

Module-3
2. TURBINES
A turbine is a rotary engine that extracts energy from a fluid flow. The simplest
turbine will have one moving part, a rotor assembly with blades attached to it,
moving fluid acts on the blades or the blades react to the flow so that they rotate
and impact energy to the rotor. High pressure & low velocity steam
Major parts of turbine
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Module-3
2. TURBINES
Part Description
Nozzle
 It is the passage of varying cross-section through which fluid flows
(Ex: Converging Divergent nozzle.).
 It is used to increase or decrease the velocity and pressure of the fluid.
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Blades
 This should be made for a turbine in the form of curved plates
 It is fixed on circumference of a revolving wheel called rotor or
runner
Runner
It is the circular wheel with a series of evenly spaced blades is fixed
around its periphery.
Turbine casing
The casing prevents the splashing of the water and it also helps to
discharge the water into the tail race.

Module-3
2.1 Steam Turbines:
It is defined as a prime mover in which the heat energy of the
steam is transformed in to mechanical energy directly in the form
of rotary motion.
Dr. Mohammed Imran

Module-3
2.2 Steam Turbines Classification
1. According to action of steam
a) Impulse turbine
b) Reaction turbine
c) Combination of both
2. According to direction of flow:
a) Axial flow turbine
4. According to method of governing:
a) Throttle governing turbine.
b) Nozzle governing turbine.
c) By pass governing turbine.
5. According to usage in industry:
Classification of steam turbines may be done as following:
a) Axial flow turbine
b) Radial flow turbine
3. According to number of stages
a) Single stage turbines
b) Multi stage turbine
4. According to steam pressure at
inlet of Turbine:
a) Low pressure turbine
b) Medium pressure turbine.
c) High pressure turbine
d) Super critical pressure turbine.
Dr. Mohammed Imran
5. According to usage in industry:
a) Stationary turbine with constant speed.
b) Stationary turbine with variable speed.
c) Non stationary turbines.
The common types of steam turbine are
(1) Impulse Turbine, and (2) Reaction Turbine.
The main difference between these two turbines
lies in the way of expanding the steam while it
moves through them

Module-3
2.3 Steam Turbines Classification
The common types of steam turbine are (1) Impulse Turbine, and (2)
Reaction Turbine. The main difference between these two turbines lies in
the way of expanding the steam while it moves through them,
Another type of classification is based on “staging” arrangements, that is,
turbines are either single-stage or multi-stage. Turbines are also named
after the persons who designed such arrangements:
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after the persons who designed such arrangements:
 De Laval turbine, named after its designer, Gustafe de Laval;
 Curtis turbine, named after its designer, Charles Curtis;
 Parsons turbine, named after its designer, Charles Parson and
 Rateau turbine, named after its designer, Auguste Rateau.

Module-3
2.4 Simple impulse Turbine
Principle of impulse turbine:
 This turbine works on the principle of impulse. Where the kinetic
energy is the jet of steam is used to exert a force on a set of
moving blades. It working based on Newton’s second law of
motion; the rate of change of momentum is proportional to the
imposed force and goes in the direction of the force.
Working Impulse Steam turbine:
 An impulse turbine requires high head with low rate of flow.
 The turbine consists of a series of curved blades fixed on the
 The turbine consists of a series of curved blades fixed on the
circumference of a single wheel called rotor which in turn is
connected to a shaft
 The high pressure and low velocity steam generated in the
boiler is used as a working fluid. The working fluid contains
potential energy and kinetic energy
 Before reaching the turbine the fluid’s potential energy gets
changed to kinetic energy by accelerating the fluid through a
nozzle
 The high velocity steam leaving the nozzle is directed towards
the moving blades of the turbine
 The steam flowing over the blades undergoes a change in its
velocity and direction thereby resulting in change of
momentum called impulse force.
 This resulting impulse force pushes the blade in the same
direction
 Example: Delaval’s Turbine
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Fig: Impulse turbine

Module-3
2.4 Simple impulse Turbine
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Module-3
2.5 Simple Reaction Turbine
Reaction turbines(Parson’s Turbine):
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Module-3
Principle of reaction turbine:
This turbine work on
the principle of
reaction, that is a
backward force
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backward force
developed opposite
to the action of the jet
of steam. It working
based on Newton’s
third law of motion,
which stat that for the
every action, there
must be an equal and
opposite reaction.

Module-3
Working Reaction turbine:
Constriction of Reaction turbine
• A reaction turbine requires low head with high rate of flow.
• The turbine runs by the reactive force of the jet of steam rather than the direct push or
impulse as in case of impulse turbine.
• It consists of several alternate rows of fixed and moving blades.
• The fixed blades are fastened to a stationary casing, while the moving blades are
Dr. Mohammed Imran
• The fixed blades are fastened to a stationary casing, while the moving blades are
mounted on the periphery of a rotating wheel called rotor which in turn is connected to a
shaft.
• In reaction turbine the shape and the cross-section of moving and fixed blades are
designed such that it acts as a nozzle.
Operation of reaction turbine:
• The high pressure, low velocity steam generated in a boiler first passes over the fixed
blade
• The fixed blade acts as a nozzle where the steam gets expanded to a low pressure and
high velocity and it also guides the steam onto the moving blades where it undergoes a
change in its velocity and direction thereby resulting in impulse force
• The kinetic energy of the steam is converted into mechanical energy by the rotation of the
rotor and when the steam leaves the moving blade, a reactive force is set up and same set
of operation should be repeated in next stage of turbine.

Module-3
2.6 Difference between Impulse and Reaction Turbines:
Sl.
No.
Description Impulse turbine Reaction turbine
1 Driving force
Is due to the impulsive force of the
steam
Is due to both impulsive force of the
incoming steam and reactive force of
the outgoing steam
2
Pressure of Remains constant at both inlet and
Decreases from inlet to the exit
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2
steam exit of the turbine
Decreases from inlet to the exit
3 Blades Have symmetrical profile Have asymmetrical profile
4 Working
Works on principle of Newton’s 2nd
Law
Works on principle of Newton’s 3rd
Law
5 Compounding Requires compounding Does not require compounding
6 Space Occupies less space Occupies more space
7 Application Used in small capacity power plants
Used in medium and large capacity
power plants

Module-3
2.8 Compounding:
Necessity/ Needs : It is the method of reducing the speed of
the turbine to practical limits. In the impulse turbine, steam
expands completely in the nozzle resulting in a very high
velocity jet of steam(may be 150 m/s). If this high velocity
steam is made to impinge on the moving blades, it produces
rotor speed of about 30,000 rpm which will be too high to be
used for practical purpose. Hence in order to achieve this, more
rotor speed of about 30,000 rpm which will be too high to be
used for practical purpose. Hence in order to achieve this, more
than one set of nozzle, blade and rotors are used in order to
reduce the velocity and pressure of the steam.
Classification of Compounding:
 Velocity compounding
 Pressure compounding
 Pressure and velocity compounding
Dr. Mohammed Imran

Module-3
2.8.1 Velocity compounding (Curtis stages ):
It is the method in which the kinetic energy of the steam is made to drop down gradually by
allowing the steam to pass through two or more rows of moving blades so that the rotor speed
is brought down to the practical limits.
 It consists of alternate rows of
moving blades and fixed blades
 The steam from the nozzle will be
Dr. Mohammed Imran
 The steam from the nozzle will be
expanded completely to a high
velocity
 It is then passed over the first ring of
moving blades where some portion
of kinetic energy gets absorbed
Fig: velocity compounding impulse turbine.
 The jet of steam is then passed on to the fixed blades and onto the second ring of moving blades where
further drop in the velocity takes place. i.e. gradually decrease in velocity.
 Pressure is constant from first ring of moving blades two second ring of moving blades.

 It consists of a number of simple
impulse turbines in series mounted on a
common shaft
 The exit steam from one turbine is made
Module-3
2.8.2 Pressure compounding (Rateau stages) :
 Pressure compounding: It is the method in which the pressure of the steam drops in a
number of stages rather than in a single set of nozzle.
 The exit steam from one turbine is made
to enter the nozzle of the next turbine
 The high velocity jet of steam is
directed onto the first ring of moving
blades where it enters the second ring of
nozzle and the pressure gets reduce
further
 The process is repeated in the
remaining rings until the whole of the
pressure has been reduced
Fig: Pressure compounding impulse turbine
Dr. Mohammed Imran

Module-3
2.8.3 Pressure and velocity compounding (Combination stages ):
 It is the combination of both
compounding type and has the
advantages of both types.
 In this type, we reduce the pressure of
the steam jet in multiple steps just
like in the case of pressure
compounding.
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compounding.
 After that we reduce the velocity of
the steam jet by passing it through
moving blades and then to reverse the
direction, we use fixed blades just
like in case of velocity.
 One thing is important here is that we
need to use large size stages as the
pressure of the steam reduces.
Figure pressure –velocity compounded impulse turbine
 This type of compounding allows us to extract energy in limited number of stages efficiently. The
arrangement of the blades is shown

Module-3
3. Analysis of Single Stage Impulse Turbine
3.1 Velocity diagram
 We should be able to calculate the propelling force applied
to the turbine rotor.
 We can estimate work done and hence power.
 Since the force is due to change of momentum mainly caused
 Since the force is due to change of momentum mainly caused
by change in direction of flow of steam, it is essential to draw
velocity diagram that shows how velocity of the steam varies
during its passage through the blades.
 Velocity is vector quantity as it has magnitude and direction.
 So we can represent velocity by a straight line and its length
indicates its magnitude and direction is indicated by direction
of line with reference to some fixed direction.
Dr. Mohammed Imran

Module-3
3.1 Velocity diagram Delaval Impulse Turbine
Dr. Mohammed Imran Fig Velocity diagram Delaval Impulse Turbine

Module-3
3.1 Velocity diagram Delaval Impulse Turbine
Dr. Mohammed Imran

Module-3
3.2 Combined Velocity diagram Delaval Impulse Turbine
To make the solution of problems connected with turbine easier, the inlet and
outlet triangles are combined by superimposing one over the other
Dr. Mohammed Imran

Module-3
3.3 Effect of friction on combined Velocity diagram
 If blade possess roughness, some
friction will be produced will be
during steam flow over the blade.
 The effect of this friction is to
reduce the relative velocity of
steam as it passes over the blade.
 The friction coefficient of the blade is given by where K1 is also called as
blade velocity coefficient.
 Combined velocity diagram with blade friction shown in fig above.
 The energy lost in friction = ½ m[Vr1
2 –Vr2
2]
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Fig: Combined velocity diagram with blade friction
steam as it passes over the blade.
In general a loss of 10 to 15% in
the relative velocity occurs due to
friction in the blades.

Module-3
3.4 Steam turbine efficiencies
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Module-3
3.5 Condition for Maximum efficiency for a single stage
impulse turbine (Delaval)
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Module-3
Condition for Maximum efficiency for a single stage
--(1)
--(2)
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--(2)
--(4)
--(5)
--(6)
Eq (2) 
--(3)

Module-3
3.5 Condition for Maximum efficiency for a single stage
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--(7)

3.6 Blade Speed
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3.7 Combined Velocity diagram for a two stage
Impulse Turbine (Curtis turbine )
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3.8 Condition for maximum efficiency for multi
stage Impulse Turbine
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MODULE-3 PART – B
REACTION TURBINE
SEMESTER – V
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Module-3
4. Velocity triangle for Reaction Turbine (Parson Turbine),
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Module-3
5. Degree of Reaction
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Module-3
6. Condition for maximum efficiency of a reaction turbine
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Module-3
7. Reheat Factor
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9. Reheat in steam turbines
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10. Bleeding is steam turbine
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Turbo Machines Course: Steam Turbines Classification and Working Principle

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