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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

37

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.


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.


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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