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Turbo Machine
is defined as adevice that extracts energy from a
continuously
flowing fluid by the dynamicaction of one or more rotatingelements .
The prefix turbo is a Latin wordmeaning spin or whirl implying
that turbo machines rotate in
some way.
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TypesofTurbines
1. Steam Turbines
2. Gas Turbines (Combustion Turbines)
3. Water (Hydraulic) Turbines
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Steam Turbines
A steam turbineis mainly used as an ideal prime moverin which heat energy is transformed into mechanicalenergy in the form of rotary motion.
A steam turbineis used in
1. Electric power generation in thermal power plants.
2. Steam power plants.
3. To propel the ships, submarines.
In steam turbines, the heat energyof the steam is firstconverted into kinetic (velocity) energywhich in turn istransformed into mechanical energy of rotation andthen drives the generator for the power generation.
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Based on action of steam or type of
expansion:1. Impulse or velocity or De Laval turbine
2. Reaction or pressure or Parsons turbine
3. Combination turbineBased on number of stages:
1. Single stage turbine 2. Multi-stage turbine
Based on type of steam flow:1. Axial flow turbine 2. Radial flow turbine
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. The steam is made tofall in its pressure by
expanding in a nozzle.Due to this fall inpressure, a certainamount of heat energyis converted into kineticenergy, which sets thesteam to flow with a
greater velocity.
The rapidly moving particles of the steam enterthe rotating part of the turbine, where itundergoes a change in the direction of motion,which gives rise to achange of momentum and
therefore a force. This constitutes the drivingSrinivas School of Engineering, Mukka 8
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Impulse Turbines (De Laval
Turbine)
In this type of turbine, steam is initially
expanded in a nozzle from high pressure tolow pressure. High velocity jet of steamcoming out of the nozzle is made to glide
over a curved vane, calledBlade
.
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The jet of steam gliding over the blade getsdeflected very closely to surface. This causes
the particles of steam to suffer a change in thedirection of motion, which gives rise to a changeof momentumand therefore a force, which will becentrifugalin nature.
Resultantof all these centrifugal forces actingon the entire curved surface of the blade causes
it to move.
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NOZZLE
EXHAUSTSTEAM
TURBINESHAFT
MOVINGBLADES
HIGH PRESSURESTEAM
Schematic of Impulse Turbine
VL
PH
Q
PL
VH
R
C
B
Nozzle
RotorBlades
VelocityVariation
PressureVariation
Pressure-Velocity diagram in ImpulseTurbine
A
P
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Principle of working -
In this type of turbine,the high pressure steamdoes not initially expandin the nozzle as in thecase of impulse turbine,but instead directlypasses onto the moving
blades.
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Blade shapes of reaction turbinesare designed in such a way that thesteam flowing between the blades
will be subjected to the nozzle effect.Hence, the pressure of the steamdrops continuously as it flows overthe blades causing, simultaneousincrease in the velocity of thesteam.
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Reaction force:
is due to the change inmomentum relativevelocity of the steamwhile passing over theblade passage.
Centrifugal force:
is the force acting on theblade due to change in
radius of steam enteringand leaving the turbine.
Resultant force:
is the resultant of
Reaction force andCentrifugal force. Srinivas School of Engineering, Mukka 15
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Fixed BladeMoving Blade
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Impulse Turbine Reaction Turbine
The steam expands(pressure drops)completely in nozzles or inthe fixed blades
The steam expands bothin the fixed and movingblades continuously as itflows over them
The blades havesymmetrical profile ofuniform section
The blades haveconverging (aerofoil)profile
The steam pressure while
passing over the bladesremains constant
The steam pressure while
passing over the bladesgradually drops
Because of large initialpressure drop, the steamand turbine speeds are
Because of gradualpressure drop, the steamand turbine speeds areSrinivas School of Engineering, Mukka 17
Difference between Impulse & Reaction Turbines
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Impulse Turbine Reaction Turbine
Power is obtained onlydue to the impulsiveforce of the incomingsteam
Power is obtained due toimpulsive force ofincoming steam as wellas reaction of exit steam
Suitable for smallcapacity of powergeneration & occupiesless space per unit
power
Suitable for medium &high capacity powergeneration and occupiesmore space per unit
powerEfficiency is lesser Efficiency is higher
Compounding isnecessary to reducespeed
Compounding is notnecessary
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Compounding of Impulse TurbinesAs the complete expansion of steam takes in one stage
(i.e., the entire pressure drop from high pressure to low pressuretakes place in only one set of nozzles), the turbine rotorrotates at very high speed of about 30,000 rpm (K.E. isfully absorbed).
High speed poses number of technical difficulties likedestruction of machine by the large centrifugal forcesdeveloped, increase in vibrations, quick overheating of
blades, impossibility of direct coupling to othermachines, etc.
To overcome the above difficulties, the expansion ofsteam is performed in several stages.
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Utilization of thehigh pressureenergy of thesteam byexpanding it in
successive stagesis calledCompounding.
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Velocity compounding
Comprise of nozzles and two or more
rows of moving blades arranged in
series. In between two rows of movingblades, one set of guide (fixed) blades are
suitably arranged.
Guide (fixed) blades are fixed to casingand are stationary.
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Velocity Compounding (Curtis Impulse Turbine)
N NozzleM Moving BladeF Fixed Blade
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Pressure compounding
Consists of two stage of nozzles followed bytwo rows of moving blades.
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Pressure Compounding
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Pressure-Velocity Compounding
(Combined Impulse Turbine)
Total pressure drop is divided into two stages & the total
velocity obtained in each stage is also compounded
A Axial clearance, N Nozzle, M Moving Blade, F Fixed BladePi and Pe Pressure at inlet & exit, Vi and Ve - Velocity at inlet & exit
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A Gas turbineuses the hot gases ofcombustion directly to produce themechanical power.
Fuels used - Kerosene, coal, coal gas,bunker oil, gasoline, producer gas, etc.,
Classification:1. Open cycle gas turbine
2. Closed cycle gas turbine
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ApplicationsGas turbines are used in:
Electric power generation plants
Steel, oil and chemical industries
Aircrafts, Ship propulsion
Turbo jet and turbo-propeller engineslike rockets, missiles, space ships etc.,
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Open cycle gas turbine:
The entire flow of the working
substance comes from atmosphere andis returned to the atmosphere back ineach cycle.
Closed cycle gas turbine:The flow of the working substance ofspecified mass is confined within the cyclic
path. ( Air or Helium is the workingsubstance)
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COMPRESSOR:
draws in air and compress it before it is
fed into combustion chamber COMBUSTOR:
fuel is added to the compressed air and
burnt to produce high velocity exhaustgas
TURBINE:
extracts energy from exhaust gasSrinivas School of Engineering, Mukka 31
Open cycle gas turbine
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Open cycle Closed cycle
Lesser thermal efficiency Higher
Loss of working fluid No loss of workingfluid
Bigger in size SmallerBig compressor is needed Smaller one is
sufficient
Possibility of corrosion of blades
and rotor
Free from corrosion
Economical Not economical
Exhaust gases from turbine exit toatmosphere
Fed back into thecycle
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Difference between open & closed cycle turbine
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PharmaceuticalPharmaceuticalPharmaceuticalPharmaceutical
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HospitalsHospitalsHospitalsHospitals
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Pulp and PaperPulp and PaperPulp and PaperPulp and Paper
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It is aprime mover, which converts hydropower (energy of water) into mechanical
energy and further into hydro-electric power.
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Cl ifi i f W T bi
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Classification of Water TurbinesBased on action of water:
1. Impulse turbine
pelton wheel.2. Reaction turbine francis and kaplan.
Based on name of originator:1. Pelton turbine or Pelton wheel
2. Francis turbine3. Kaplan turbine
Based on head of water:1. Low head turbine
2. Medium head turbine
3. High head turbine
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Pelton Turbine(Pelton Wheel or Free Jet Turbine)
High head, tangential flow, horizontal shaft,
impulse turbine
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PELTON TURBINE
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Srinivas School of Engineering, Mukka 47Pelton Turbine Runner
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Only a part of the pressure energy ofthe water is converted into K.E. and
the rest remains as pressure head.
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Fi t th t t th id
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First, the water passes to the guidevaneswhich guide or deflect the water to
enter the blades, calledmoving blades,mounted on the turbine wheel, withoutshock.
The water from theguide bladesaredeflected on to themoving blades, whereits part of thepressure energy is
converted intoK.E., which will be
absorbed by the turbine wheel. Thewater leaving the moving blades willbe at a low pressure.
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The difference in pressure between the
entrance and the exit of the moving blades iscalled Reaction pressure, which acts onmoving blades of the turbine wheel and sets
up the turbine wheel into rotation in theopposite direction.
Examples:Francis turbine, Kaplan turbine,Propeller turbine, Thompson turbine, Bulbturbine.
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Francis TurbineMixed flow, medium head reaction
turbine.
Consists of a spiral casingenclosing anumber of stationary guide bladesfixed all
round the circumference of an inner ringof moving blades (vanes) forming therunner, which is keyed to the turbineshaft.
Radial entry of water along the peripheryof the runnerand discharge at the centerof the runner at low pressure through the
diverging conical tube called draft tube.Srinivas School of Engineering, Mukka 52
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Srinivas School of Engineering, Mukka 53FRANCIS TURBINE
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Francis Inlet Scroll, Grand Coulee Dam
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Francis Runner,Grand Coulee Dam
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FRANCIS TURBINE & GENERATOR
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Kaplan TurbineAxial flow, low head.
Similar to Francis turbine except therunner and draft tube.
The runner(BossorHub) resembles withthe propeller of the ship, hence sometimes it is called as Propeller turbine.
Water flows parallel to the axis of theshaft.
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Srinivas School of Engineering, Mukka 59KAPLAN TURBINE
(SCROLL CASING)
(GUIDE VANE)
(RUNNER VANE)
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Vertical Kaplan Turbine(Courtesy: VERBUND-Austrian Hydro Power)
Propeller Turbine Runner
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Propeller Turbine Runner
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