Eme Bharath a Notes

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PART A

UNIT I

ENERGY & STEAM

Energy: The capacity to do work is called Energy.The energy sources are available in various forms.

These sources are broadly classified as commercial or conventional energy

sources and non-commercial or non-conventional energy sources. Most of the

developed countries are highly dependent on conventional form of energy whereas,

for developing countries like India both forms of energy sources are needed.

Classification of Energy sources:

Energy sources may be mainly classified into two categories.1. Renewable Energy sources and

2. Non-Renewable Energy sources

1. Renewable Energy Sources:

Renewable energy sources are produced by nature and are inexhaustible.

These sources of energy does not get exhausted due to pronged usage i.e. they can be

renewed. Renewable energy sources include both direct solar radiation utilized by

solar collectors and cells and Indirect solar energy in the form of wind, hydropower,

ocean energy and sustainable biomass resources.

2. Non Renewable Energy Sources:

Non Renewable Energy sources are either available in nature or produced by

man artificially. They are exhaustible and non renewable. Conventional Energy

Sources like nuclear power and fossil files are non renewable.

Advantages and Disadvantages of Renewable Energy Sources:

Advantages:

1. They are produced by nature and considered as inexhaustible.

2. Except biogas they are pollution free and hence Eco-friendly.

3. If utilized properly in developing countries, they can save lot of foreign exchange

and generate employment opportunities.

4. Deployment is easy and rapid due to flexibility in their utilization.

5. They are economical when considered over a longer period.

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Disadvantages:

1. Their availability is intermittent (eg. Solar, Wind, tidal, hydro etc) and hence need

the assistance of non-renewable energy.

2. Complete commercialization is difficult on a larger scale.

3. Initial cost is high due to the newer technologies used which are still at preliminary

stages.

4. Sources are not evenly spread across the globe.

Conventional And Non Conventional Energy Sources:

The most of the energy needs comes mainly from fossil fuels such as coal,

petroleum and natural gas and hydel sources, which are relatively cheaper. Although

energy from nuclear fuels can be used, it is not being used in large scale due to its

inherent hazardous nature and high cost of generation of power from nuclear source.

Since the fossil fuels and hydel sources are in use over several decades, they are

called conventional energy sources.

Non-Conventional Energy Sources:

The rapid use of fossil fuels day has threatened exhausting of this source very

soon. The hydel source cannot be a major source of energy since, its availability is

limited to certain areas and also depends on the up predictable nature of the

hydrogical cycle. More over its cost of generation is very high due to high initial

investments and transmission problems.

So there comes a need for alternate inexhaustible energy sources to replace the

conventional sources. The other alternative energy sources that are tried for

harnessing are, solar energy, wind energy, total energy OTES, fuel cells, solid wastes,

hydrogen etc. These alternate inexhaustible sources of energy are called non-

conventional Energy Sources.

Conventional Energy Sources:

These are commercial forms of energy available. They include: -

1. Fossil fuels, which may be in Solid/liquid/gaseous form.

2. Water power or energy stored in Water

3. Nuclear Energy

About 92 % of the worlds total energy comes from coal, oil, gas and uranium

and hence there are the most commonly used commercial energy sources.



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1. Coal: -

It is the most common source of energy that is being used since

industrialization. Modern steam boilers burn coal in any of its forms as a primary

fuel. Different ranks of coal available are peat, lignite, bituminous and anthracite.

However coal has lower calorific value & its transportation is uneconomical. When

burnt it produces pollutants like CO & CO 2.

2. Oil:-

Almost 40 % of energy needs is met by oil alone with present consumption of

250,000 million tones of oil, it is estimated to last for only 100 years, unless more oil

is discovered. Major chunk of oil comes from petroleum.

3. Gas: -

Due to non-availability of ready market, gas is not completely and effectively

utilized and is burnt in huge quantities. Its transportation cost is much higher than oil.

Large reserves are estimated to be located in accessible areas.

1. Gases of fixed composition like acetylene, ethylene,

methane etc.,

Gaseous Fuels

2. Industrial gases like producer gas, coke oven gas etc.,

4. Agricultural and Organic Wastes: -

These include Sawdust, bagasse, garbage, animal dung, paddy husk, corn stem

etc, and accounting major energy consumption.

5. Water: -

It is one of the potential sources of energy meant exclusively for hydro-electric

power generation. Potential energy of water is utilized to convert into mechanical

energy by using Prime movers known as Hydraulic turbines. The operating cost of the

plant is cheaper compared to other types of power plants. It is the only renewable

non-depleting source of energy, which doesnt contribute to pollution.

6. Nuclear Power: -

The Controlled fission of heavier unstable atoms like U 235 (Thorium) and Pu239 (plutonium) liberates enormous amount of energy. The energy released by fission

of one Kg of U 235 is equivalent to the heat generated by burning 4500 tons of coal.

The heat generated during the nuclear fission reaction is used to produce steam in

Heat Exchangers, which is utilized to run the turbo-generators. The nuclear power contribution to the total power requirements of our country is very less (about 5%).



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In India presently there are 6 Nuclear power stations.

1. Tarapore Maharastra.

2. Rama Pratap Sagar Kota (Raj)

3. Kalpakkam Tamilnadu.

4. Narora.

5. Kakrapar Gujarat and

6. Kaiga Power Plant in Karwar.

The nuclear power plant has the following advantages and limitations: -

Advantages: -

1. They require lesser space compared to other conventional energy systems

2. They need small quantity of fuel, which can liberate enormous energy. There is no

problem of fuel handling and storing etc.,

3. There are no smoke and ash problems

4. They are independent of weather conditions

5. They are suitable for large power outputs

Disadvantages: -

1. Initial cost is high due to highly sophisticated costly shielding, moderator etc

2. They are not suitable for varying load conditions

3. Disposal of Radioactive waste is complicated

4. Careful Maintenance is essential

5. Trained and skilled persons are required to handle the Nuclear system.

Non-Conventional Energy Sources:

1. Solar Energy: -

Solar Energy has the greatest potential of all the sources of renewable energy,

which come to the earth from sun. This energy keeps the temperature of the earth

above that in colder space, causes wind currents in the ocean and in the atmosphere,

causes water cycle and generates photosynthesis in plants. The Solar energy reaching

the surface of the earth is 10 16 W where as the World wide power demand is about 1013W. Even if we use 5 % of this energy it is more than 50 times our requirement. Solar

energy can be tapped by using photovoltaic cell or by solar thermal heating.

1. Photovoltaic Cell: -

The Solar energy conversion devices which are used to convert

sunlight into Electricity by the use of photovoltaic effect are called solar cell. ASingle energy converter is known as a Solar cell or a Photovoltaic cell and a



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Combination of them is called a solar module or solar array. Photovoltaic cells are

made of Semiconductors (P and N type) that generate electricity when they absorb

light energy or photons. The photons absorb the free electrons at the outermost shell

of the atoms of semiconductors (like silicon with doping material, Cadnium sulphide

etc.,) and generate free electrical charges. These charges can be tapped by suitable

arrangements.

Fig. Gross Sectional diagram of a Silicon Cell

Fig shows a typical solar cell made up of a thin slice (0.2 to 0.5 m) of p typeSilicon Crystal which is diffused into n type dopant.

Note: Silicon when doped with phosphorus, arsenic or antimony, the silicon becomes

a n-type Semiconductor and when doped with boron, aluminium, indium or gallium, it

forms p-type semiconductor. If p-type Semiconductor is brought into intimate contact

with one of the n-type they form a p n or n p junction.

The n type silicon is made up of rectangular metallic grid and p type

silicon which is a collector completely covers the back metallic surface, An

antireflection coating of so (0.1 m thick) and a thin transparent Encapsulating sheetare also put on the top surface. When the sun rays fall on the surface of the cell, the

electrons are ejected by the photons which in tern or collected by the collector. Hence

electric current flows on load. A typical cell develops a voltage of 0.5 1V and a

current density of 20 40 mA/Cm 2.



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2. Solar pond: -

Solar pond is a mass of water collected in a large collection area to a shallow

depth of about 1 or 2 meters. It not only collects the solar energy from the sun but

also acts as a heat trap by storing the sensible heat.

Solar

Pond:

Fig. Shows Schematic diagram of a solar pond. It is about 1 to 2 m deep

coated with a thick durable plastic liner of low-density polyethylene (LDPE), high-

density polyethylene (HDEE) woven polyester yarn (XB 5) and hypalon reinforced

with nylon mesh.

The water in the pond is made dense at the bottom part by adding salts like

sodium chloride., sodium nitrate etc, The concentration of salt varies from 20 to 30

percent at the bottom to almost zero at the top layer. However salt concentration

gradient will disappear over a period of time. In order to maintain it, fresh water is

added at the top of the pond and slightly Saline water is run off. At the same time

concentrated brine is added at the bottom of the pond. Because of low conductivity of

saline water, it acts as an insulator and allows a high temperature of about 90 0 C to

100 o C to develop at the bottom layers. Thus part of the Solar Radiation is absorbed

by the water at the top surface of the pond while most of the solar radiation, is

absorbed by concentrated Saline water at the bottom. This heat can be utilized for

various purposes.

Application: - 1) Heating and cooling of Buildings. 2) Production of power 3) Heat

for biomass Conversion.



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2. Wind Energy: -

Wind Energy can be economically used for the generation of electrical energy.

Winds are caused from two main factors.

1. Heating and cooling of the atmosphere, which generates convection currents.

Heating is caused by the absorption of solar energy on the Earths surface and in the

atmosphere.

2. The rotation of the earth with respect to atmosphere, and its motion around sun.

The energy available in the winds over the earths surface is estimated to be

1.6 10 7 MW which is almost the same as the present day energy consumption. Thewind energy can be utilized to run windmill, which in turn is to drive the generators.

Due to pressure differential existing between any two places on earth air

moves at high speed. This pressure differential is caused due to earths rotation and

by uneven heating of the earth by the sun. The Kinetic energy of air can be utilized to

generate electric power or to perform a specific work.

Application of Wind Energy: -

Wind Mills: -

A Windmill converts the Kinetic energy of moving air into mechanical rotary

motion that can be either used directly to run a machine/pump or to run a generator to

produce electricity.

Fig. Wind Mill.

Fig. Shows a typical wind mill where water can be pumped out for irrigation

and drinking purpose. Here, the rotational motion of the wheel can be either

translated into rotary motion (to generate electricity) or reciprocating motion (to drive

the pump). The major disadvantage of wind energy is that it is not constant and

steady, which makes the plant design complicated.



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3. Energy from Biomass and Biogas: -

The process by which green plants harness (utilize) the energy of the sun and

build or produce organic compounds from carbon dioxide and water is called

photosynthesis. Biomass is the Organic matter, which is produced in nature through

photosynthesis. In the presence of solar radiation, water and carbon dioxide are

converted into organic material, CH 2O.

Solar Energy

H2O + CO 2 CH 2O + O 2

CH 2O is stable at low temperature but breaks at higher temperature releasing

heat equal to 469 KJ /mole. It is possible to produce large amount of carbohydrate by

growing plants like algae in plastic tubes or ponds. The algae could be harvested,

dried and burned for production of heat that could be converted into electricity by

conventional methods. The biomass can be either used directly by burning or can be

processed further to produce more convenient liquid or gaseous fuels.

There are three sources for biomass energy conversion.

1. Biomass in its traditional solid mass like wood and agricultural wastes which are

burnt directly to get energy.

2. Biomass in its non-traditional form in which biomass is converted into ethamol,

methanol which are used as liquid fuels in engines.

3. Biomass in fermented form in which biomass like animal wastes and aquation

plants are fermented an aerobically to obtain a gaseous fuel called biogas which

contains 55 to 65 % methane, 30 40 % CO 2 and rest as impurities like H 2, H 2S and

some N 2.

4. Energy From Oceans: -

A large amount of solar energy is collected and stored in oceans. The surface

pf water acts as a collector for solar heat, while the upper layer of the sea constitutes

infinite heat storage reservoir.

Rotation of the earth causes the cold water coming from the direction of the

poles to flow slowly along the ocean base towards the tropics. In the tropical region,

the cold-water density decreases. The water warmed in this manner, flows at the

surface in another current towards the Polar Regions. The cycle is repeated as the

water-cools and starts a return trip towards the tropics.



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The heat contained in the oceans could be converted in to electricity due to the

temperature difference (20 25 K) between the warm surface waters of the tropical

oceans and the colder waters in the depths. This is the basic idea of OTEC systems.

The surface water, which is at higher temperature, could be used to heat some low

boiling point organic fluid, the vapours of which would run a heat engine. The

amount of energy available from OTEC is enormous, and is replenished continuously.

The concept of OTEC is based on the utilization of the temperature difference

existing between the surface of the sea and deep water. In the tropics, the ocean

surface temperature often exceeds 25 oC, while 1 Km below the temperature is not

higher than 10 o C. Water density decreases with an increase in temperature (about

3.98 oC where the pure water density is maximum, decreasing again below this

temperature, the reason ice floats). Thus there will be no thermal convection currents

between the warm lighter water at the top and deep cooler heavier water. Thermal

conduction heat transfer is too low across larger depths. As mixing is retarded,

warmer water stays at the top and cool water stays at the bottom.

Thus OTEC plant operates between two infinite heat reservoirs, a heat source

at about 27 oC & a heat sink some 1 km below water surface at 4 oC

The Carnot efficiency given by,

.077.030023

)27327(427 ==+

== H

C H C T

T T

Disadvantages: -

1. Efficiency is extremely low and hence the system needs extremely large power

plant heat exchangers and components.

2. Even though there is no fuel cost, the cost is very high and hence unit power cost is

higher.

3. Involves developmental problems and uncertainties of market penetration.

5. Tidal Energy: -

Tide is a periodic rise and fall of the water level of sea, which are carried by

the action of the sun and moon on the water of the Earth.

The Energy can be tapped from costal waters by building dams that entrap

water at high tide and release it at low tide back to the sea. Power can be obtained by

turbines from both in and out flows of water. Though the amount of energy availableis very large, but only in a few parts of the world.



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The tides are rhythmic but not constant. Their occurrence is due to a balance

of forces, mainly gravitational force of the moon and sun to some extent balancing the

centrifugal force on water due to earth rotation.

The result in rhythmic rise and fall of water. The tidal R is given by.

R = Water elevation at high tide Water elevation at low tide.

This range is maximum during new and full moons and is known as spring

tide and neap tide. This period rise and fall of water above the mean sea level is called

flood tide (High tide) and when the water is below the mean sea level it is known as

Ebb tide (Low tide).

To harness tides, a dam is built across the mouth of the bay with large gates

and low head hydranlic reversible turbines. A tidal basin formed thus gets separated

from the sea, by dam. There always exists a difference between the water levels on

either side of the dam during low tides and high tides. Thus the reversible water

turbine runs continuously producing power by using the generator connected to it.

Fig. Shows a single pool dial system having one pool or basin behind a dam

that is filled from the ocean at high tide and emptied to it at low tide. Both filling and

emptying takes place during short time period. Filling takes place when the ocean is

at high tide and pool is at low tide level, whereas, emptying takes place when the

ocean is at low tide and pool is at high tide level. The flow of water in both directions

is used to drive a number of reversible water turbines, each driving an electrical

generator.

4.Fig single Pool tidal System

6. Geothermal Energy: -

Geothermal energy is the heat transported from the interior of the earth, by the

hot magma near the surface, which causes active volcanoes and hot springs and

geyser where water exists. It also causes the steam to vent through the fissures. This



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is the energy, which comes from within the Earths crust. In some locations of the

earth, the steam and hot water comes naturally to the surface. For large scale use,

bore holes are normally sunk with depth up to 1000 m releasing stem and water at

temperatures up to 200 to 300 o C and pressures up to 3000 KN/m 2. Generally there

are two methods to generate power using GTE.

Method 1:

In this method the heat energy is transferred to a working fluid, which operates

the power cycle. It is found that molten interior moss of the earth vents to the surface

through fissures at temperatures ramging between 450 o C to 550 o C.

Method 2:

In this method the hot geothermal water and / or steam is used to operate the

turbines directly from the wellhead. Steam is transmitted by using pipes of 1 m

diameter over distances up to 3000 m to the power plant. In this system water

separates are used to separate moisture and solid particles from steam.

Fig. A Typical Geothermal Field

Fig. Shows a typical Geothermal field. The hot magma near the surface

(A) Solidifies into Igneous Rocks.

(B) The heat of magma is conducted up to this igneous rock. Ground water that finds

its way down to this rock through fissures (a split or cleavage) in it will be heated by

the heat of the rock or by mixing with hot gases and steam emitting from the magma.

The heated water rises convectively upwards into a porous and permeable reservoir .

(C) Above the igneous rock, which is caped by an impermeable solid rock.

(D) That traps the hot water in the reservoir. The solid rock has fissures.

(E) That acts as vents of the giant underground boiler. Viz. in the form of geysers,fumaroles.



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(F) Or hot springs.

(G) A Well

(H) Taps steam from the fissure for use in a Geothermal Power plant.

The heat flux from the Earths interior through the surface is 9.5 1020

3 /Yr.Difference between Conventional and Non Conventional sources of Energy:

S.No Conventional Sources of Energy Non-Conventional Sources

of Energy1 Conventional sources of energy are all

depleting type in nature except Hydel

Energy.

They are non-depletable,

and thus they are called

renewable types.2 Generally they cause enormous

Environmental Pollution (Except hydel power).

They are non-polluting type

except Geothermal &Biomass Energy.

3 Conventional sources are available for

utilization after incurring heavy investments

They are available free of

cost (generally).4 The relative abumdancy of availability does

not exist when compared with NCES.

The Relative abundancy of

availability of NCES is very

high compared to

conventional sources.

5 They are more efficiently convertible intouseful from of energy as compared with

NCES because energy release per unit

volume of C.E.S is very high.

It is less efficient comparedto C.E.S.

6 For utilization, Initial costs are very high,

but are cheaper as for as running costs are

concerned.

Here Initial costs are very

less and are generally

maintenance free Ex: Wind,

Solar & bio-gas.



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BOILERS

STEAM AND ITS PROPERTIES

Pure Substances:

It is a substance, which has one chemical composition (or) structure but iscapable of existing in more than one phase.

Steam: Water existing in Vapour phase. It is used in various process industries for

heating purpose and also for power generation in steam power plants. It is a working

fluid in steam engines steam turbine.

Phase Transformation:

Melting (or) fusion of Ice: It is the transformation of solid phase (ice) to liquid phase

(water)

Freezing (or) solidification: It is the transformation of liquid phase to solid phase

Vaporization: It is the transformation of Liquid to vapour phase.

Condensation: It is the transformation of Vapour to liquid.

Sublimation: It is the transformation of Solid to vapour.

Fig : Phase transformation at constant pressure

One Kg of Water at 0 oC is taken in a cylinder with a freely moving, frictionless

piston. A Wt W placed on the piston extents constant pressure p on water inside

the cylinder as shown in fig (a). Volume occupied by water is V. The condition of

water represented by point 1 in T h diameter. Heat is supplied to the cylinder and

temperature of water increases slowly and steadily fill it reaches the boiling



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temperature. That is represented by Point 2. At this condition volume of water is

slightly increases to V f .

The temperature at which water starts boiling is known as saturation

temperature of water. (T s). The amount of heat absorbed by the water to heat it from

freezing point is boiling point is known as sensible heat denoted by h f . The sensible

heat is also known as total heat of water. If the heating of water is continued, there

will be no further rise in temperature of water but evaporation of water takes place at

(T s). Now water exists as a two-phase mixture of saturated liquid and vapour

occupying volume Vfg. Steam, having small water particles held in suspension such

steam is known as Wet steam.

Fig : Formation of steam on temperature- enthalpy diagram

Temperature

Tsup 4

Degree of Superheat

2 p = c

Ts 3

P=c

T1=0 0c Enthal py

Sensible heat Latent Heat Super Heat

H f hfg

hg

hsup



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If the heating of water is continued further, there will be no more water

particles and steam becomes completely dry. That represented by Point 3. The

volume occupied by the dry steam Vg, Pressure and temperature is constant in 2 3.

The amount of heat utilized to evaporate unit mass of water at saturation temperature

Ts to unit mass of dry saturated stem at constant temperature Ts and given pressure

p is known as latent heat of evaporation. Process of heating dry steam above its sat

temperature Ts is known as super heating and the temperature of steam above its

saturation temperature is known as super heat temperature (Ts) The volume occupied

by super heated steam is Vsup.The amount of heat required to miss the temperature of

dry steam above the saturation temperature (Ts) is known as enthalphy of superheated

steam (hsup).Degree of super heat Difference between the super heated

temperature and saturation temperature of steam.

= Tsup - Ts.

Wet Steam:

Two phase mixture which contains partly vapour (steam) and partly liquid

(water) at saturation temperature (Ts) and given Pressure.

Dryness Fraction:

Fraction of the steam that is in the vapour form. Dryness fraction (x) = Mass

of dry steam / Mass of wet steam.

= Mg/ mw = mg / mf + mg

Mass of suspended Mass of dry steam

water particles.

Dry saturated steam / Dry steam:

Steam without suspended water particles in it at the saturation temperature of

water (Ts) and at a given pressure. Dryness fraction of dry stem is unity.

Super heated Steam:

Steam which is heated above its saturation temperature (Ts) and a given

pressure. Dryness fraction will give the quality of the steam. If the quality of steam is

60 % dry, 1 Kg of steam contains 0.6 Kg of dry steam and 0.4 kg of water particles.

Heat absorbed by water during the transformation of water to steam is called latent

heat.

Advantages of Super heated steam:



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1. It has high content (or) heat energy at a given pressure than wet steam (or) dry

saturated steam of same mass. Hence it is used for power generation in steam power

plants.

2. Superheated steam doesnt contain any water particles in suspension. The erosion

and corrosion of the steam turbine blades is eliminated. So we can improve the

efficiency of the turbine blades.

3. Overall thermal efficiency of the plant increases by the use of superheat steam.

Super heater tube high heat resistant alloy steel.

Disadvantages Production cost of super heated steam is high.

Specific volume of steam:

Volume occupied by unit mass of steam at a given pressure and temperature.Specific volume of wet steam:

1 Kg of Wet steam x dryness fraction of steam. Wet steam contains x kgof dry stem and (1 x) kg of water vapour.

V f special volume of saturated water

Vg special volume of dry steam.

Specific volume wet steam V = x V g + (1 x) V f

If V f is very small, so it is neglected.V = x V g. m 3/kg

Volume occupied by wet steam in a unit mass of wet steam at a given

pressure.

Specific volume of dry saturated steam:

Volume occupied by unit mass of dry steam at a given pressure and

temperature. Specific volume of super heated steam: When the steam is super heated,

the steam obeys gas laws. Volume occupied by unit mass of super heated steam at asuperheat temperature and given pressure.

g

g

T

V

T

V =

sup

sup(charles law) Volume of given mass of gas is directly

proportional to the temperature when the pressure remains constant.

Vsup = T sup Vg/Tg in m 3/kg.V/T = constant [when pressure is constant]

Enthalphy of Steam:

Amount of heat energy contained in a given unit mass of steam.

h = u + pv



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Sum of internal energy of steam and product of pressure and volume.

h = u + pv

Differentiate, dh = du + pdv + vdp

dh = dq + vdp [1 st law of td, dq = du + pdv]

At constant pressure, dp = 0.

dh = dq

At constant pressure change in enthalphy is equal to the amount of heat added.

Enthalphy of Wet Steam:

Amount of heat required to convert unit mass of water at freezing point into

wet steam of given dryness fraction at constant pressure.

h = hf + x hfg kJ/kg

Enthalpy of dry saturated steam:

The amount of heat required to convert unit mass of water at freezing point

into dry saturated steam at its sat temperature.

hg = h f + h fg

Enthalphy of Superheated Steam:

The amount of heat required to convert unit mass of water at freezing point

into superheated steam at superheated temperature constant pressure.

hsup = (h f + h fg) + C ps (T sup T s)

h sup = h g + C ps (T sup T s)

C ps Special heat of superheated steam 2.25 Kj/kg.

Latent Heat:

Amount of heat required to effect phase transition in a given unit mass of

substance at constant pressure.

External Work during Evaporation:

The latent heat absorbed during the evaporation by steam is utilized not only

for phase change but also to do external work due to large in volume. Due to

increased volume (V f to V g) the piston inside the cylinder move upwards. External

work of evaporation is the amount external work due to large increase in volume

water changes into steam.

For wet Steam, External work = x P vg KJ/kg

Dry saturated steam, External work = P vg KJ/kg

Super heated steam, External work = PV sup KJ/Kg.



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Internal energy of Steam:

Difference between the enthalpy of steam and external work of evaporation.

For wet steam, Internal energy u = h f + x h fg x P Vg KJ /kg.

Dry steam , Internal energy u = hg PVg

Superheated steam, Internal energy u = h sup P vsy.

Steam Problems

h i specific enthalpy of saturated solid

hf specific enthalpy of liquid at saturated temperature.

hg specific enthalpy of vapour at saturated temperature.

hfg specific enthalpy change from liquid to vapour at saturated temperature

(or) Enthly of vaporisation

h sup specific enthalpy of superheated vapour

V i specific volume of the solid phase at freezing

V f specific volume of liquid at saturated temperature.

U f specific internal energy of liquid at saturated temperature.Ts Temperature at saturated of liquid and vapour and during vaporizations.

Ps Pressure at saturated of liquid and vapour and during vaporizations.

Psup Pressure of superheated vapour.

T sup Temperature of super heated vapour.

P i Pressure at freezing (or) during solidification.

T i Temperature freezing (or) during solidification.

1. Steam at 1 MPa is used in a process industry for heating purpose. Determine

the enthalpy of steam assuming (i) Steam is wet with 10 % moisture contained in it.

(ii) Steam is dry saturated (iii) Steam is superheated to 520 K. Assume

Cps = 2.3 KJ/kg K

Given data:

T sup = 520 ok

1 Mpa = 1 10 6 pa = 10 10 5 N/m 2 (1 pa = 1 N/m 2)



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= 10 bar (1 bar = 10 5 N/m 2)

From the steam tables at 10 bar,

Ts = 179.9 oC; h f = 762.8 KJ/kg; h fg = 2015.3 KJ/kg.

(i) Steam is Wet:

Steam contains 10 % moisture, so 90 % dry.

Hence x = 0.9

Enthalpy of wet steam h = h f + x f g.

= 762.8 + (0.9) 2015.3

= 2576. 57 KJ/kg.

(ii) Enthalpy of dry saturated steam:

hg = h f + h fg (x - 1)

= 762.8 + 2015.3

= 2778.1 KJ/kg.

(iii) Enthalpy of superheated steam:

h sup = h g + C ps (T sup T s)

= 2778.1 + 2.3 (520 [179.9 + 273])

= 2932.43 KJ/kg.

2. The enthalpy of 1 Kg of steam at 8 bar pressure is 2373.5 KJ/kg. Find the

condition of the steam.

From steam tables at 8 bar,

hf = 721.1 KJ/kg ; h fg = 2048.0 Kj/kg.

H = h f + x h fy.

20481.7215.2373 ==

fg

f

h

hh x

x = 0.8

i.e., the steam is 80 % dry.

3. Find the special volume and enthalpy of 1 Kg of steam at 0.8 Mpa. a) When

the dryness fraction is 0.9. b) When the steam is super heated to a temperature of

300 oC. The specific heat of superheated steam is 2.25 KJ/KgK.

Given data:

Pressure = 0.8 Mpa = 0.8 10 6 Pa = 8 bar.

X = 0.9 T sup = 300 oC = 573 o K

CPs = 2.25 KJ/kg o-k



20/159

From steam tables at 8 bar,

Ts = 170.4 oC

hf = 721.1 KJ/kg hfg = 2048 KJ/kg.

V f = 0.001115 m 3/kg V g = 0.240 m 3 /kg.

a) Enthalpy of Wet Steam h g = h f + xh f g

= 721.1 + (0.9)2048

hg = 2564.3 KJ/kg

Specific volume of wet steam V = XV g = 0.9 0.240

V = 0.216 m 3 /kg.

b) Steam is superheated.

Enthalpy superheated steam h sup = h g + C ps (T sup T s)

= 2564.3 + 2.25 (300 170.4)

hsup = 2855.9 KJ/kg.

Specific volume of superheated steam V sup = V g S

Sup

T

T (T s = T g)

= 0.24 4.170

300

V sup = 0.422 m 3/kg.

4. By actual measurement the enthalpy of saturated steam at 190 oC is 2500

KJ/kg. What is the quality of the steam? If 500 KJ/kg of heat is added at constant

pressure, what is the final state of the steam?

Given data:

h = 2500 KJ/kg.

Ts = 190 oC.

From steam tables at 190 oC,

P = 12.544 bar, V g = 0.15654m 3/kg.hf = 807.62 KJ/kg h fg = 1978.8 KJ/kg, h g = 2786.4 KJ/kg.

Quality of the steam:

h = h f + x h fg

855.08.1978

62.8072500 === fg

f

h

hh x

so the steam is 85.5 % dry

When 500 KJ/kg of heat is added at constant pressureSo, Enthalpy h 1 = 2500 + 500 = 3000 KJ/kg.



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h1 > h g (3000 > 2786.4)

Due to addition of additional heat, enthalpy will rise.

That enthalpy is more than the enthalpy of steam at saturated temperature.

So the steam is superheated.

hsup = h g +C ps (T sup T s)

3000 = 2786.4 + 2.3 (T sup - 190)

Tsup = 282.86 oC

5. A steam initially will be at 9 bar and dryness 0.98. Find the final quality and

temperature of the steam at each of the following operations.When the steam losses

50 KJ/kg at constant pressure. When the steam receives 100 KJ/kg at constant

pressure

From the steam table at 9 bar,

Ts = 175.4 oC, Vg = 0.215 m 3/kg , h f = 742.8 KJ/kg; h fg = 2031.1 KJ/kg, h g = 2773.9

Enthalpy of Wet steam h g = h f + x h fg

= 742.8 + (0.98) 2031.1

hg = 2733.27 KJ/kg.

(i) When the steam losses 50 KJ/kg at constant Pressure

h = h g 50 = 2733.27 50 = 2683.27 KJ/kg.

h = h f + x h fg

1.20318.74227.2683 ==

fg

f

h

hh x

x = 0.955.

(ii) When the steam receives 100 KJ/kg at constant pressure.

Enhalphy of steam h = 2733.27 + 100

= 2833.27 KJ/kg. h = h f + x h fg

1.20318.74227.2833 ==

fg

f

hhh x = 1.02.

h > h g, so the steam is superheated.

hsup = h g + C p (T sup T s)

2833.27 = 2773.9 + 2.25 ( T sup 175.4)

Tsup = 201.78 oC

Properties Wet Steam Dry Saturated Steam Superheated SteamSpecific volume in

m3/kg.

V = XV g V = V gV sup = V g sT

T sup



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Enthalpy in KJ/kg h = h f + xh fg hg = h f + h fg hsup = h g + C ps (T sup

Ts)Internal energy in

KJ/kg

U = h f + xh fg xvgP V g = h g -PV g U sup = h sup PV sup

External work of vaporization in KJ.

X pVg PV g PV sup

Steam Boilers

It is also known as steam generator. It is a closed vessel in which water is

converted into steam above atmospheric pressure by the application of heat.

Functions:

The steam is used for driving prime movers like steam engine (It is a form of

heat engine where heat energy is converted into mechanical work. It is used as a prime mover for locomotives & ships], Steam Turbine for Power Generation. It is also

used for producing process steam as in the case of textile industries for sizing,

bleaching etc. (or) other industries like paper, sugar and chemical industries.

Primary requirements of Boiler:

1. Water must be safely contained

2. Steam must be delivered safely at the required temperature & pressure and at the

required rate

3. Maximum heat produced by the fuel in the furnace should be utilized for economy.

4. It should be accessible for inspection.

Types of Boilers:

(i) According to the flow of water & hot gases:

(a) Fire tube Boiler: Hot gases pass through the tubes which are surrounded with

water.

Ex: Cornish One large tube surrounded by water.

Lancashire Two large Tubes surrounded by water.

Vertical Coehran (or) Locomotive many smaller tubes surrounded by water.

(b) Water tube Boiler: Water circulates through a large number of tubes and hot gases

pass around them.

Ex: Bobcock & Wilcox boiler, Striling boiler.

(ii) According to the axis of the shell:

Horizontal & Vertical boiler (axis of the shell will be in vertical)

(iii) According to location (or) position of the furnace:



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(a) Externally Fired Boilers: Furnace place outside the shell. Most of the water tube

boilers.

(b) Internally fired boiler Furnace is placed inside the shell. Most of the fire tube

boilers.(iv) According to the method of water circulation:

(a) Natural Circulation boiler Water is circulated by natural convection currents,

which are setup due to the temperature difference.

Ex: Lancashire, Babcock & Wilcox.

(b) Forced Circulation boiler Water is circulated with the help of a pump driven by

motor. High pressure cap boiler.

Ex: Lamont, Velox, Benson.(v) According to the Application:

(a) Stationary boilers It is installed permanently on a land installation.

Most of the industrial & power generation boiler.

(b) Mobile boiler These boilers are move from one place to the other place.

Ex: Locomotive & marine boiler.

(vi) According to the heat source:

(a) The combustion of fuel in solid, liquid (or) gaseous form(b) By products of other chemical process

(c) Electrical energy

(d) Nuclear energy

(vii) According to Steam Pressure Low, high, medium pressure boilers.

0.5 atm.pressure 30-200 atm pressure. 5-30 atm pressure

Lancashire Boiler:It is a stationary, horizontal, straight tube, internally fixed, natural circulation,

fire tube boiler. The size of the boiler is approximately 7 9 m in length and 2 3 m

in diameter. Boiler can generate steam at the rate of 8.5 tones hr at a pr of 25 bar.



24/159

Fig:

It consists:1. Cylindrical Shell: It is placed in horizontal position. It is filled about of its

volume by water submerging the fuel tubes.

2. Steam Space: The space above the water level serves for steam separation and

storage.

3. Furnace Tubes, Bottom flue and side flues: Two large internal furnace tubes

extend from one end to the other end f the shell. One bottom flue and 2 side flues are

formed by brick setting.4. Grate:

It is provided at the front end of the main flue tubes. Coal is fed to the grate

through the fire hole. It is suitable for stationary boiler because it cannot withstand

jerks/vibration of mobile boilers. It is not suitable for high pressure boiler because

heavy weight is required to balance the steam pressure.

5. Fire Bridge:



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It is provided at the end of the grate to prevent the flow of coal and ash

particles into the interior of furnace tubes. Otherwise the coal & ash particles carried

with gases from deposits on the interior of the tubes & prevents the heat transfer.

6. Dampers:

It is in the form of sliding doors are placed at the end of side flues to control

the flow of gases from side flues to the Chimney flue.

7. Steam Collecting pipe/ Antipriming pipe/ Dry pipe:

It is in the top of the steam space of the boiler. It is horizontal and closed at its

ends. It collects steam from different parts of the boiler and leads to the steam stop

value. When the steam leaves water, it takes some water particles also. The amount

of water is heavier than the steam hence it tends to fall down steam goes up and water

attempts to fall back.

8. Blow off Cock:

- It is used for the removal of mud & sediments

- To empty the water in the boiler during inspection.

9. High steam & low safety valve:

It having 2 valves.

(i) When the steam exceeds above the working pressure.

(ii) When the water level falls below the normal level. During that time it will

give some sound.

10. Man hole:

It is used for cleaning & inspection purpose.

Diameter should not less than 40 Cm.

Normally it is in oval shape.

11. Fusible Plug:

To protect the fire tube burning due to excessive heating.

Working:

The flue gases are formed due to the combustion of fuel on the furnace grate

move along the main flue tubes from front end to rear end. As a result of this first run

of flue gases, heat of combustion is transferred to water present in the boiler drum.

After approaching the rear end, flue gases are deflected by the rear-enclosed chamber

and enter the bottom central flue tube. During this second run, water present in the

bottom portion of the flue tube gets heated by the flue gases. Temperature of water further increases. After traveling bottom central flue tube, flue gases reach the front



26/159

end and divided into the side flues tubes. During this 3 rd run, hot flue gases contact the

two sides of the boilers shell. Heat is transferred from the flue gases to the boiler

shell. After the 3rd run, the flue gases will enter to the Chimney. Steam is formed due

to this heat transfer and occupies the steam space. Then it is passed to the super heater

for forming the superheated steam.

Babcock and Wilcox Boiler:

Fig:

It is a land type (or) stationary, horizontal straight tube, externally fixed,

natural circulation water tube boiler.

- It is suitable for all types of boiler.

- Normal working pressure 12 to 18 bar and in certain cases it can raise

steam to pressure as high as 40 to 42 bar.

- Steaming rates range between 2 to 20 tones/hr.



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It consists of

1. Steam and Water Drum:

The drum is placed horizontally and half of the volume filled by water.

Size 8 m length & 2 m diameter.2. Water Tubes:

It lies in between drum & furnaces, in an inclined position (angle of 10 o to 15 o)

to promote water circulation. These tubes are connected to the uptake leader & down

comes.

3. Uptake header & Down Comer: Drum is connected at one and to the uptake

header by short tubes and at the other end to the down comer by long tubes.

4. Grate furnace: Hot flue gases are forming in this zone.

5. Baffles: The fire brick baffles, two in number, it provided to deflect the hot flue

gases.

6. Super heater: Saturated steam from the drawn passes through the super heater

tubes where the steam gets superheated. It lies in between drum & water tubes.

7. Mud Box: The Sediments of water collected here.

8. Inspection Doors: For cleaning and inspection of boiler.

Working:

Coal is fed to the grate through the fire door and is burnt.

Flow of Flue Gases:

Hot flue gases rise upward and pass across the left side proton of the water

tubes. The baffles deflect the flue gases and hence the Flue Gases travel in a zig-zag

manner (hot gases are deflected by the baffles to move in the upward direction, then

downward again upward direction). Over the water tubes and along the super heater.

The flue gases finally escape through the Chimney.

Water Circulation:

Due to the heat, water density being decreased rises into the drum through the

uptake header steam being lighter is collected in the upper part of the drum. A

continuous circulation of water from the drum to the water tubes and water tubes to

the drum is maintained.

Super Heating:

Steam is taken from the steam space of the drum through a tube to the super

heater. Steam is superheated as it receives the additional heat.



28/159

Salient Features:

- Overall efficiency is high compare than fire tube boiler.

- Defective tubes can be replaced easily.

- All the components are accessible for inspection even during the operation

- Steam generation capacity & operating pressure is high compare than other

boiler.

- Water tubes are kept inclined at an angle of 10 o 15 o to promote water

circulation

Advantages of Water Tube Boiler over Fire Tube Boiler:

1. Steam can be generated at very high pressure

2. Rate of evaporation and heating surface is more due to the large no.of small

diameter tubes.

3. The hot gases flow almost at right angles to the direction of water flow. Hence

maximum amount of heat is transferred to water.

4. Furnace can be altered easily because it present outside of the shell.

5. Boiler cannot be shutdown immediately.

6. Water circulation is cyclic i.e., from boiler drum to water tubes and again to boiler

drum

7. Cleaning, repairing, inspection is very easy

8. Bursting one (or) two tubes does not affect the boiler. So we can called as safety

boilers

9. The different parts of a water tube boiler can be separated. Hence it is easier to

transport

10. It is suitable for steam power plants

Disadvantages of Water Tube Boiler over Fire Tube Boiler:

1. Maintenance cost is high

2. Even small scaling sediments of water will make over heating the boiler & burst the

tube

3. Not used for mobile purposes

4. Water level must be watched very carefully

Boiler Mountings:

It is a external fittings which are required to ensure safe operation of the

boiler.



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1. Water level indicator:

To indicate the level of water inside the boiler drum at any given instant.

- 2 Water ganges are fitted at front of the boiler drum

It warns the operator if the water level goes below a fixed mark, so that

corrective action may be taken in tome to avoid any accident.

Fig:

The Water and steam cocks are opened and drain cock (C 3) is closed.

The steam enters from the upper metal tube M1 into the glass tube and water

enters from the lower metal tube M2 into the glass tube. Hence, water stands in the

glass tube at the same level as in the boiler.

2. Pressure gange [Bourdan Type]

Fig:

To indicate the steam pressure of the boiler.



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When steam efforts the elliptical tube (S), the tube section tries to become.

Circular, which causes the other end of the tube to move outward. The movement of

the closed end of the tube is transmitted and magnified by the link and the toothed

sector. The magnitude of the movement of the sector is indicated by the pointer on the

scale.

3. Safety Valve:

To maintain a constant safe pressure inside the boiler. When the pressure

inside the boiler increases, the excess steam will escape to the atmosphere through the

value automatically.

(a) Dead Weight safety valve:

Fig:

Valve is made up of gunmetal to prevent from rusting. V restricts on seat (S)

and fixed on the top of the Pipe (P).P has a flange (F) for firing at the tope of the

boiler shell.

P Steam Pipe

C Weight Carrier (It carries cost iron rings)

The total weight must be sufficient to keep the valve on its seat against the

normal working pressure. When the steam pressure exceeds the normal working pressure, it lifts the valve with its weight. The excess steam escape through the pipe

to the atmosphere, until the pressure reaches its normal value.

b) Lever safety value:



31/159

Heavy dead weight is replaced by a lever with a smaller weight used in

stationary boiler. The thrust of the lever with its weight is transmitted to the valve by

the strut. When the steam pressure exceeds the safe limit, the upward thrust of steam

lifts the valve from its seat and the lever with its weight. The required weight W at

the end of the lever for maintaining the pressure P in the boiler is obtained by taking

moments about the hinged pressure.

PaL 1 = WL 2

a Area of the valve exposed to steam

L1 Distance of the valve centre from the hinged point.

L2 Distance of the valve centre of the Weight to the hinged point.

C) Spring Loaded safety Value:

It is loaded with a spring instead of weights.

- 2 C.I body having two branch pipes P 1 and P 2.

- 2 Valves are placed over the seating.

Fig:



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The lever is attached to a spring at its middle. The spring pulls the lever in

downward direction. The lower end of the spring is attached to the value body

through the specific. Thus the values are half fight to their seats by the spring force.

When the steam pressure exceeds the working pressure, the value will open against

the action of spring.

- Due to the spring action it can withstand all kinds of jerks/vibration load, so

it is used the Mobile Boilers. (Locomotive & Marine).

d) High steam & Low Water safety valve.

4. Fusible Plug:

To put off the fire in the fusible of the boiler when the water level falls below

an unsafe level. To avoid explosion which may takes place due to overheating of

tubes and the shell.

During the normal operation, the fusible plug is submerged in water which

keeps the temperature of the fusible metal below its melting pressure. But when the

water level below the top of the fusible plug, it is uncovered by the water. Fusible

plug melt by the heat of the furnance. Thus the Cu plug drops down and is held within

the gunmetal body by the ribs. The opening so made allows the steam rush into the

furnance and extinguish the fire. Thus damage to the firebox which could burn up, is

avoided.5) Steam Stop Value/ Junction Value: To shut of the steam flow (or) to regulate the

steam flow as per the requirement.

6) Feed Check Value: To regulate the flow of water to the boiler drum. It having 2

valves. One for to regulate the flow of water and another for prevents water rushing

back from the boiler.

7) Slow down valve (or) Cock: To remove the sediments collected at the bottom of

the boiler drum from time to time.



33/159

Boiler Accessories:

Boiler accessories are the appliances required for the effective, efficient and

economic operation of a Boiler.

1. Economizer:

To heat the feed water by utilizing the heat in the exhaust flue gases before

leaving the Chimney.

Water Out.

Flue Gases

Water in

It consists large no.of Vertical C.I pipes, which are connected to bigger

horizontal pipes at its both ends. Feed Water goes into the economizer from bottom

horizontal pipe. Hot flue gases are passed over the tubes and the floor is maintained in

opposite direction to that of flow of water. Cross flow provides a better heat transfer

between exhaust gases and feed water.

2. Super heater: Function of the super heater is to increase the temperature of steam

above its saturation temperature.

3. Air preheated: Function of the air heater is to recover the heat of a portion of

exhaust flue gases between the flue gases enter the chimney.

4. Feed Water pump: Function of the feed pump is to pump water at high pressure

to the water space of the boiler drum.

5. Pressure Reducing Valve: Function of the pressure reducing valve is to maintain

constant pressure on the delivery side of the valve, with the fluctuating boiler

pressure.

6. Steam trap: The function of steam trap is to drain off water resulting from the

partial condensation of steam in the steam pipe lines and jackets without allowing the

steal to escape through it.

7. Steam Separator: Function of the steam separator is to separate the water

particles in suspension that are carried by the steam coming from the boiler.



34/159

UNIT - II

TURBINES

Steam: It is pure substance. It is nothing but water existing in vapour phase.

Pure Substance: It has a homogeneous and invariable chemical composition,

irrespective of the phase (or) phases n which they exists. Ex: ice, water and steam.

Enthalpy: Amount f heat energy contained in a given unit mass of steam.

h = u + PV

Boyles Law: The volume of given mass of a perfect gas varies inversely as the

absolute pressure. When temperature is constant.

V 1/P (or) PV = constant f T is constant.

Prime Movers :

Prime Movers are devices which convert the energy from a natural source into

mechanical work.

Steam turbine

(1) Thermal Prime Movers IC engine

Gas turbine

(2) Hydralic Prime Movers Potential energy and kinetic energy of water isconverted into mechanical work.

IC Engine It is a heat engine in which may the heat energy of a fuel is converted

mechanical energy by combustion process (Conversion of chemical energy into heat

energy) inside the engine cylinder.

STEAM TURBINE

It is a prime mover used to convert heat energy of steam into mechanical

energy (mechanical rotary motion). It is used in thermal power plants to drive the

alternators. Steam turbines are directly coupled to the generators, pumps,

Compressors.

It is used in textile and sugar industry machines.



35/159

Expansion of steam in a convergent divergent nozzle:

Entry Exit

high enthalpy low enthalpy low pressure high velocity

high pressure

low Velocity

Convergent part Throat Divergent part

Steam nozzle is a passage of varying cross section by means of which the heat

energy of steam is converted Kinetic energy. Due to expansion of steam in nozzle, the

volume will increase and pressure, enthalphy will decrease.

Classification of Steam Turbine:

It depends on whether the drop in pressure of the steam due to its expansion

takes place before it passes on to the moving blades (or) while moving on the blades

itself and also type of propelling force.

(i) Impulse Turbine

(ii) Reaction Turbine

Impulse Steam Turbine:

Fig:



36/159

Arrangement of Blades and Nozzle:

Fig:

Variation of Pressure and Velocity (or) Impulse turbine stage:

Fig:

Blade Profile:

The Steam expansion in the nozzle causes a pressure drop & enormous

increase in steam velocity (about 1000 m/s) at the nozzle. High velocity steam coming

out from the nozzle strikes the blades fixed on the periphery of the rotor. So the

steam velocity decreases continuously. The high velocity jet posses over the curved



37/159

blades, and gets deflected because of the shape of the blades. The change in the

direction of motion of the steam jet results in a change of momentum (mass

velocity) and hence a force direction normal to the blade surface i.e and Impulse

(force Time ) force. The stem jet when moves over the curved surface of the blades,exerts pressure on the blades due to Centrifugal action. Resultant of all these

centrifugal pressure and effects of change of velocity is the motive force, which

causes the turbine to move. In velocity, pressure variation, due to expansion pressure

drop will occur. After expansion the pressure remains constant in the moving blades.

In nozzle part volume exit at higher volume. It will drop in moving blades because

the moving blades absorb the Kinetic energy. However the final velocity is much

higher than the initial velocity.Ex: Peltan, De lavel, Curits, Rateav Turbine.

Reaction Turbine:

In this turbine steam is expanded in a set of moving and fixed blades, No

nozzle provided here. It consists of rows of equal no. of fixed and moving blades.

The moving blades are attached to the turbine motor and fixed blades are attached to

the turbine casing. Minimum gap is maintained in between the fixed and moving

blades.

Fig: Blade Profile:

Fig: Impulse reaction turbine stage:



38/159

The fixed blade acts as a nozzle. The steam is admitted from casing through

the whole of circumference. In the first row of fixed blades, the pressure drop will

occur and velocity will increase. Next it will enter to the moving blades, due to charge

of momentum the velocity will decrease and continuous pressure drop also occur.

Here the driving force is a combination of impulse and reaction force.

Ex: Kaplan, Francis turbine,

Casing Material C.I

Blade Material C.I, S.S, Cast steel bronze.

Sl.No. Impulse Turbine Reaction Turbine

1. Steam expands in the nozzle. Steam expands partially in

the fixed blades and partially

in the moving blade.2. Pressure remains constant during flow through

its blades passage.

Pressure of steam is not

constant during its flow

through moving & fixed

blade passage.3. Steam flow over the blade is uniform due to

symmetrical blade profile.

Steam flow over the blade

varies due to aerofoil section

(Unsymmetrical) blade

profile.4. Due to complete pressure drop in the nozzle,

the steam velocity and rotor speed are very

high, resulting in centrifugal stresses acting on

the blades. This may result in blade failure.

Pressure drop occurs in fixed

blades partially, so the steam

velocity and rotor speed are

not high. Hence stress

developed are less.5. Speed of turbine is very high and hence

requires compounding.

Speed of turbine is low.

Does not require

compounding.6. Turbine is compact less space. It is bigger. So requires more

space.7. It is used in small capacity power plant. Medium and large capacity

power plants.

Advantages of Steam turbines over other prime movers:

1. No reciprocating parts. So no wear will occur. Hence its durability



39/159

2. No sliding parts so less lubrication is sufficient

3. Due to direct rotary motion, steam turbines produce uniform torque. It reduces

shock loads and hence vibrations are minimum

4. More compact

5. Less maintenance

6. More economical with respect to their construction and operation

7. Very high thermal efficiency and mechanical efficiency

8. Balancing of masses is easier as turbine contains rotating masses

9. It is used in large power plants

10. It is used to drive high speed generators, compressors

Parsons turbine:

The power obtained mainly by an impulsive force of the incoming steam and

small reactive force of the outgoing steam. This consists of a rotor of a varying

diameter. Moving blades are fixed on the rotor. Diameter of the casing also varies.

Fixed blades are attached to the casing. Steam is admitted to the first set of moving

blades through nozzles. The blades receive the impulsive force of the incoming steam.

Then it goes to fixed blades which act as nozzles. Thus steam flows alternatively

through moving and fixed blades.

Compounding of Steam Turbines:

If the entire pressure drop occur in the nozzle, so very high level is come out

from the nozzle. Steam Turbine speed is directly proportional to the velocity speed.

We are getting 30,000 rpm in turbine. Due to this very higher speed, large centrifugal

forces acting in the blade so blade will get failure and increase in vibration, quick

overheating of the bearings, impossibility of direct coupling to the other machines

these types of technical problems are came. This much amount higher speed wont

help practical purpose. The normal velocity force is 400 m/s. We are

reducing/controlling the rotor speed is called compounding.

Compounding Method of reducing blade speed for a given overall pressure drop.

(i) Velocity Compounding:

Fig:



40/159

- One set of nozzles and two (or) more moving blades.

- There is a row of fixed blades in between two moving blades.

- Function of fixed blades is only to direct the steam coming from first

moving row to the next moving row.

There are also known as Guide Blades.

ii. Pressure Compounding:

Fig:

One row of fixed blades (works as nozzles) at the entry of each row of moving

blades. Total pressure drop of the steam does not take place in a single nozzle but isdivided among all the rows of fixed blades, which works as nozzle.



41/159

Due to pressure compounding, smaller transformation of heat energy into Kinetic

energy takes place. Hence steam velocities become much lower and reduce volume

of blade and rotational speeds.

3. Pressure and velocity Compounded Steam Turbine:

Combination of both pressure and volume compounding. Pressure is divided

into a no.of stages as done in pressure compounding and velocity obtained in each

stage is also absorbed in several stages.

It is used in Curtis Turbine.

Drawing is a Combination of both pressure and velocity compounded steam

turbine.

WATER TURBINES

Hydraulic Prime movers is a mechanical device, which converts the potential

Energy of Water into mechanical energy.

Types of Water Turbines: - The various types of hydraulic turbines are given below:

(a) Classification according to the type of energy at inlet: -

(i) Impulse Turbine Ex: Pelton Wheel.

(ii) Reaction Turbine Ex: Francis & Kaplan Turbines.

(b) Classification according to the direction of Fluid flow:

(i) Tangential flow Turbine: The Water flows along the tangent to the

runner or the wheel. Ex: Pelton Wheel.

(ii) Radial flow Turbines: The water flows in the radial direction through

the runner. Radial flow turbines are divided into inward flow turbines and

outward flow turbines.



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(iii) Axial flow Turbines: The water flows through the runner

parallel to the axis of the turbine. Ex: Kaplan Turbine.

(c) Classification according to the head at the inlet of the Turbine :

(i) High head turbine (>250 m) Pelton Wheel.

(ii) Medium head turbine (60 250 m) : Francis turbine Inward radial

flow reaction turbine.

(iii) Low head turbine (


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(i) A nozzle is a gradually tapering small opening at the end of a pipe. Its purpose isto convert a high pressure-low velocity water head into a low pressure high velocity

water jet. One or more jets can be used. A jet is located such that it directs the high

velocity water stream directly on the bucket, tangential to the runner.

(ii) The runner fixed with buckets (vanes) is a rotating part of the turbine. Buckets

with a concave shape, help in transferring energy from the high velocity jet to the

Runner. Runner converts the impact energy of water jets into Rotary motion of the

turbine.(iii) Casing is provided all around the runner to prevent splashing of water, to direct

the used water to the tailrace and to act as a Safety Guard.

(iv) Breaking jet is located to act in a direction opposite to that of main jet, on the

vanes. Since water impinges at a very high velocity. The stoppage of water supply

does not immediately stop the runner. The breaking jet is activated to stop the runner

for maintenance and in emergencies.

The velocity of water jet is controlled by a spear by controlling the amount of

water entering the jet.

Working: -

A Pelton Wheel uses a high velocity jet impinging on its buckets. Water from

a high pressure head is converted into high velocity head at the jet. In doing so the

potential energy of water at a high level (like in a dam) is converted into K.E. The

high velocity stream of water which in turn is converted into Rotary motion

(Mechanical Energy) and utilized to run electric generators.



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Fig: Francis Turbine

Construction:

Francis turbine is a reaction turbine. The construction of Francis turbine is as

shown in fig. The Components of a Francis Turbine are as follows:

(i) Spiral Ring

(ii) Guide Mechanism

(iii) Turbine Runner

(iv) Draft Tube(i) It is a Radial flow turbine, for which a suitable casing is essential. The casing has

a circular cross section, whose area reduces gradually as it goes around as shown in

fig. Hence it is termed spiral casing such a casing helps in maintaining the pressure

head constant around the runner.

(ii) A Guide mechanism, Comprises fixed varies (whose direction can be adjusted

externally) held between two rings, which in turn is held in the casing. The guide

vanes help to allow the water to flow correctly over the moving vanes, and smoothly

enters the runner without shock.

(iii) The Turbine runner with blades, converts the pressure energy into mechanical

energy. The blades are designed so as to provide smooth flow of the water and to

convert maximum energy into useful work.

(iv) A Draft tube connects the turbine runner outlet to the tail race and is kept

submerged in the water. The function of draft tube is to increase the effective water

head and to improve the turbine efficiency.



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Principle of Operation:

The Francis turbine is a radial inward flow reaction turbine. In operation, the

high-pressure water enters the turbine wheel through the casing from the periphery

and flows inward through the guide vanes then over the runner blades. It exists

axially from the direct the water onto the runner blades. The water under high

pressure exerts pressure on the moving blades as it flows through them, which causes

the wheel to rotate. Thus, the pressure energy of water gets converted into

mechanical energy in this turbine.

Fig: Kaplan Turbine

Construction: Kaplan turbine also called a propeller turbine, is an axial flow reaction

turbine. The construction of Kaplan turbine is illustrated as shown in the fig. The

turbine runner resembles the propeller in construction. It is placed vertically down as

shown in fig (a). The runner also called as the hub or the bores, is an extension so as

to allow smooth flow of the exit water. The vanes are fixed on the runner. The shaft

is held in axial thrust bearings. A suitable spiral casing and draft tube are provided to

utilize the available pressure energy efficiently. The casing has a gradually reducing

cross section similar to the Francis turbine.

Operation: - The water enters the casing, all round the runner. Then the water is

guided towards the axis of the runner, which then takes the axial path as shown in fig

(b). The pressure head of the water thus strikes the blades axially and transfers energy

to it. As the water flows over the vanes, the pressure head is converted into rotary

motion of the turbine runner. A Kaplan turbine is most suitable for low head and

large quantity of water.



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Gas Turbines

Gas turbines are widely used as power plants of aircrafts. They are also used

as auxillary power generating units in aircrafts. Many electric power plants for supplying energy to industries and domestic purpose use gas turbines as prime

movers. Gas turbines are similar to steam turbines, except that they use the thermal

energy released by the combustion of fossil fuels like pulverized coal, gaseous fuels

and liquid fuels.

Gas turbines in aircraft engines used high quality liquid fuels (aviation fuel).

Gas turbines are operated in multiple stages to make use of the maximum energy of

combustion.

Features of Gas Turbines:

1. They are compact and have high power to weight ratio (A 100 kg gas turbine with a

generator can produce about 100 kw power like in those used in auxiliary power unit

in aircraft).

2. They can use all the 3 kinds of fuels like solid (Pulverised) liquid and gaseous fuels

3. They are easy to start and a quick cold start

4. They can meet Peak load demands in power plants

5. They are reliable, economical to operate and maintain

Components of Gas Turbine: -

There are four important components of a gas turbine system:

1. Compressor and Inter Coolers: -

The Compressors used may be either reciprocating or rotary type. Because the

reciprocating compressors have frictional problems, low speed and low air capacity

they are not generally used, where as the rotary compressors have larger capacities,

can run at high speeds with no frictional problems, hence which are preferred more

for gas turbine plants. Centrifugal and axial; flow type of compressors are used.

Inter coolers are used in between the stages of compression. Generally

multistage compressors are used to get higher-pressure ratios. The compressed air

from one stage is cooled to its initial temperature (theoretically) before entering the

next stage. This increases the efficiency. A water-cooled, gross flow inter cooler is

generally used.



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2. Combustion Chamber: -

This is the most important component of the system where heat energy is

released by burning fuels. Since the gas turbine system is continuous one it is

required to burn large quantities of fuel with large volume of air. In gas turbine the air

fuel ratio is as high as 100: 1, which is too thin for continuous combustion. This

necessitates a combustion chamber to allow only a part of the flowing high pressure

air for combustion and figs shows the schematic representation of a gas turbine

working on open cycle, generally using Brayton Cycle.

In this cycle the atmospheric air, compressed and mixed with burnt gases acts

as the working medium. In Operation the atmospheric air is drawn in by the

compressible and compressed isentropically to a higher-pressure usually axial flow

compressors are used for this purpose. The compressed air then flows to the

combustion chamber, where the fuel is burnt at constant pressure to increase the

temperature of the working fluid i.e. the compressed air. The hot gases are then

expanded isentropically in a gas turbine. The expanded hot gases are finally

discharged at initial pressure to the atmosphere. This process of compressing

atmospheric air, burning fuel, expanding in turbine and discharging gases to the

atmosphere continues in cycles. This cycle is known as Open cycle. Since the gases

are finally discharged to atmosphere rest to mix with the products of the combustion.

Also the velocity of incoming air in the combustion chamber is very high, it is not



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possible to have a stabilized flame with ordinary burners. Hence the combustion

system must involve a flame stabilization technique.

3. Gas Turbine: -

Generally axial flow turbines are used, which are reaction turbines. Impulse

turbine can also be sued. The turbine will have more than two stages, which helps to

expand gases in more stages thereby reducing the stresses in the blades. The blades

over which high temperature and high velocity gases pass, are subjected to high

stresses. They are made of high strength corrosion resistant steels. Blades are

provided with air-cooling arrangement.

4. Heat Exchanger: -

Heat Exchanger are used to add heat energy to the air entering the combustion

chamber and extract heat from the hot air coming out of the turbine in case of a closed

cycle. The compressed air is heated by using the exhaust gases which carry heat

energy after expansion (in open cycle) or after heating the working medium i.e air in

case of a closed cycle. This regenerative heating improves the plant efficiency. Part

of the power developed by the gas turbine is used to run the Compressor.

Fig: Closed Cycle gas Turbine

Fig shows the schematic diagram of closed cycle gas turbine. This is known

as closed cycle since the same working fluid is recirculated after every cycle and not

let to atmosphere as in an open cycle. In this cycle atmospheric air or some other stable gas like Argon, Helium, Nitrogen, CO 2 etc., is used as the working fluid. In



49/159

operation initially atmospheric air is drawn/ or any other stable gases which ever is

used as working medium and compressed is geotropically top higher pressures.

The working fluid then passes through the combustion chamber where heat is

added to the working fluid, by the combustion of the fuel. The working fluid will not

directly come in contact with the products of combustion instead heat is transferred

using a heat exchanger. The products of combustion after heating the working fluid

are used to preheat the compressed air or directly discharged to atmosphere. The hot

high-pressure fluid is then isentropically expanded in gas turbine. The expanded

working fluid is then passed through a water cooler to bring down its temperature to

its initial temperature, which is then recirculated for compression, heating an

expansion. The cycle repeats with the same working fluid.



50/159

UNIT - III

Internal Combustion Engines

Heat Engine:

It is a device, which uses chemical energy of fuel, which is transformed into

thermal energy by combustion and uses this energy to do mechanical work.

Heat Engine

External Combustion engine Internal Combustion engineCombustion of fuel takes place Combustion of fuel takes place inside the

outside the working cylinders working cylinders.

Ex: Steam engines & Steam turbine Ex: Petrol engine, Diesel engine.

IC Engine advantage over EC engine (Steam Engine)

1. IC engine thermal efficiency (30 to 35 %) is much higher than steam engine (15 to

25%)2. Higher mechanical efficiency

3.More compact

4. Power developed by the IC engine per Kg weight of engine is higher so it is lighter

& occupies less space.

5. It can be started quickly

Classification of IC Engine:

1. According to the type of fuel used:

a) Gas engine Gaseous fuels like natural gas product gas, coal gas.

b) Petrol engine Volatile liquid fuel is used

- Paraffin/ Kerosene also be used

- Air fuel mixture ignited by electric spark

-Carburetor is used for to accurate supply of fuel

c) Diesel engine Heavy liquid fuels, which cannot easily vapourise air used in

diesel engine- Oil is injected by means of injectors



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2. No. of Stroke:

1. Four Stroke Engine: If an engine requires four strokes of the Piston (or) 2

revolution of the Crankshaft (flywheel) to complete the cycle. Both SI & CI engines

work on this principle.

2. Two Stroke Engine: If an engine requires 2 strokes of the piston (or) one revolution

of the crankshaft (flywheel) to complete the cycle. Both S.I & CI engines work on

this principle.

3. No. of Cylinders:

a) Single cylinder engines: If only one cylinder is used to develop power, power

developed in this engine is less and the engine is commonly used in 2 wheelers.

b) Multi cylinder engines: If more than one cylinder are used. Power developed in

this engine is more than single cylinder engine.

4. According to cycle:

a) Otto Cycle Engine:

Combustion of fuel takes place at constant volume.

- All gasoline & gas engines

- It is called as SI engines

b) Diesel Cycle Engine:

Combustion of fuel takes place at constant pressure

- Diesel engine

- It is called as CI engine

c) Dual combustion cycle engine: Combustion of fuel takes place partly at constant

volume and partly at constant pressure.

- All high speed diesel engine

- It is called as limited pressure cycle (or) mixed cycle engine.

5. According to the Speed:

a) Low speed engine Engine speed < 400 rpm.

b) Medium speed engine Engine speed is in between 400 & 900 rpm.

c) High speed engine Engine speed > 900 rpm.

6. Cooling System:

a) Air Cooled Engine: If engine is cooled by naturally/ Artificially by air.



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b) Water Cooled Engine: If engine is cooled using water.

* The temperature of IC engine is very high (2000 oC) as the combustion takes place

inside the cylinder. So cooling arrangement is necessary to prevent the overheating of

the cylinder.

7. According to the fuel supply:

a) Carbureted engines: Carburetor is atomize, vaporize, distributes metered

amount of fuel. All SI engines fitted with carburetor.

b) Injection type engine: A fuel injector is used to inject the fuel at very high

pressure just before the ignition. All CI engines are fitted with fuel injectors.

8. Based on the method of ignition:

a) Coil ignition system engine: Induction coil & battery that provides low

tension current.

b) Magneto-ignition system engine: Here magneto is used instead of battery.

Primary coils of a few turns and secondary coils of a large no. of turns are

wound across the armature of the magneto (or) generator.

9. Based on the engine Design:

a) Reciprocating engine Piston reciprocates inside of the cylinder.

b) Rotary engine Instead of piston, 3 sided rotor operates inside a chamber.

10. Based on the Arrangement of the Cylinder:

a) Vertical Cylinder Cylinder position is vertical. Ex: Scooter & motor cycleengines.

b) Horizontal Cylinder Cylinder position is horizontal

c) Inline engine It has only one cylinder block. All the cylinders are linearlyarranged. Ex: Car & Bus.

d) Radial Engine: Engine has more than two cylinders arranged radially andspaced equally around the crankshaft.

It is used in aircraft engine.

e) V-Engines: Combination of two in-line engines with two cylinder blocks.

- Heavier automobiles

f) Opposed cylinder engines: Engine has 2 cylinder blocks located an the opposite

sides of the crankshaft but in the same plane.

g) Opposed Piston engines: It has a single cylinder block with 2 pistons and 2

crankshafts.



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10. According to the method of governing used:

a) Quantity governing method: The quantity of mixture of air & fuel is changed

maintaining air-fuel ratio of the mixture constant.

- Petrol engine

b) Quality governing method: Quantity of fuel supplied is changed as per the required

and the air fuel ratio cannot remain constant.

- Diesel engine.

Fig: IC Engine Parts

IC engine must have certain basic components to accomplish motion.

1. Engine Cylinder:

It is a round sleeve into which a close fitting piston can slide in and out to

make strokes. The cylinder is closed by the cylinder head at one end and the moving

piston covers the other end. The Cylinder head contains the provisions for placing

inlet and exhaust valves. Combustion of fuel takes place inside the cylinder.

2. Piston:

It is connected to a mechanism which controls its sliding with in the cylinder.

The movement of the piston changes the volume of the cylinder and provides the

combustion space. Material Al alloy (Due to light weight)

Piston rings To maintain sufficient lubricating oil on cylinder walls.

Throughout entire length of the piston travel.



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It is used to maintain a pressure tight seal between the moving piston and the

cylinder wall. It conducts heat away from the piston head and prevent oil from

entering the combustion chamber.

Material fine grained alloy C.I containing Si & Mg. It has good heat & wear resisting qualities.

4. Piston Pin/ Gudgeon Pin: It connects the piston to the upper end of the

connecting rod. It is made up of low carbon case hardened steel.

5. Valves: To admit the air (and/or) fuel into the cylinder and to remove the burnt

gases after they have done their work. 2 stroke cycle engines have only ports at the

cylinder walls and have no valves.

6. Connecting rod: It is attached to the piston-by-piston pin. It converts the up &

down motion of the piston to a rotary motion of a crankshaft. It is made up of

forging of steel (or) Malleable C.I, spheroidal C.I.

7. Crank Shaft: It receives power from piston and connecting rod and transmits this

power to the drive. It is made up of Cast steel (C, Ch, Si, Mg, C, P, S), spheroidal

graphite C.I.

8. Crank Case: It is a C.I c

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