UNIT-3: SOLAR ENERGY

Syllabus: Introduction to solar Energy, fundamentals of solar radiation & its measurement
aspect, Basic physics of semiconductors, Carrier transport, generation & recombination in
semiconductors, Semiconductor junction, metal-semicartductor junction & p-n junction,
Essential characteristics of solar photovoltaic devices, First Generation Solar Cells, 2 nd
Generation Solar Cells, 3rd Generation Solar Cells.
Solar energy: Sun is the fundamental source of all type of energy. The sun releases the enormous
amount of energy due to continuous nuclear fusion reaction taking place in it. It sends the energy in
the form of radiations at the rate of 3.7×1020 MW. However, the energy received by the earth is
about 1.85×1011 MW.
Solar energy is a clean, cheap and abundantly available renewable energy and it is also the most
important of the non-conventional sources energy because it is non-polluting and therefore helps in
decreasing the green house effect.
Solar energy can be used:
i. By direct conversion to a fuel by photosynthesis.
ii. By direct conversion to electricity by photovoltaic.
iii. By conversion to electricity via thermo-electric power system
The application of solar energy is 1. Heating and cooling residential buildings
2. Solar water heating
3. Solar drying of agricultural and chemical products.
4. Solar distillation of a small community scale
5. Salt production by evaporation of seawater
6. Solar cookers
7. Solar engines for water pumping
8. Food refrigeration
9. Bio conversion and wind energy and which are indirect source of solarenergy
10. Solar furnaces
11.Solar electric power generation by i) Solar ponds ii) Steam generators heated by rotating
reflectors iii) reflectors with lenses and pipes for fluid circulation
12. Solar photovoltaic cells which can be used for conversion of solar energy directly into electricity
(or) for water pumping in rural agriculture purposes.

Energy: Energy can be defined as the capacity of any object to do work. The study of various forms
of energy and its conversion from one form to another is called energy science. The applied part of
energy science useful to human beings is called the energy technology.
Indian and Global Energy Sources: Energy sources may be classified in to the following types:
1. Primary & Secondary energy sources
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2. Commercial & Non-commercial sources
3. Renewable & Non-renewable energy sources
4. Conventional and Non-conventional energy
Primary sources: Primary energy sources are those which are found or stored in nature. e.g. coal,
oil, natural gas and biomass like wood etc. Other primary energy sources are as found on earth are
nuclear energy from radioactive substances, geothermal energy, potential energy due to earth’s
gravity etc.
Secondary energy sources:
Secondary energy sources are usually converted from primary energy sources. e.g. the electricity
sources converted from oil, natural gas or coal etc.
Commercial & Non-commercial sources: Commercial energy sources are those which are
available in the market and can purchased at a definite price from the producing agencies. e.g.
electricity, coal, oil etc.
Non-commercial energy sources are those which are not available in commercial market for a
price. These are also called traditional fuels. e.g. agro waste, animal dung etc.
Renewable & Non-renewable energy sources: Renewable energy is energy obtained from the
sources that are essentially inexhaustible. Examples of renewable resources include wind power,
solar power, geothermal energy etc.
Non-renewable energy is the conventional fossil fuels such as coal, oil, gas etc. This form of energy
is exhaustible and likely to deplete with time.
Non-conventional Energy Sources Relevant to India: There is separate Ministry in the
Government of India to exclusively focus on this important area of power generation. National
Electricity Policy lays down that the state Electricity Regulators Commissions should prescribe a
proportion of power which should be produced and supplied to the grid through the non-
conventional sources.
The various non-conventional energy sources are as follows: 1. Solar energy 2. Wind energy 3.
Energy from biomass and biogas 4. Ocean thermal energy conversion 5. Tidal energy 6. Geothermal
energy 7. Hydrogen energy 8. Fuel cells 9. Magneto-hydro-dynamic generator 10. Thermionic
converter 11. Thermo-electric power
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Direct application of solar energy

1. Solar Space heating and cooling of residential buildings 2. Solar water heating
3. Solar drying of agricultural and animal products 4. Solar distillation
5. Salt production by evaporation of seawater or inland brines 6. Solar cookers 7. Solar pumping
8. Food refrigeration 9. Solar greenhouses 10. Solar furnaces 11. Solar electric Power generation
12. Solar photovoltaic cells
Need to develop Non-conventional Sources of Energy: 1. Conventional sources are energy are
reducing with phrase of time. e.g. oil is likely to last up to 2025 and coal another 200 years.
2. Conventional sources are one of the main causes of air pollution which is causing global warming
and climate change.
3. It causing reduction in agricultural production per capita.
4. Reduced fresh water supply
Solar Radiation: The solar radiations received by the earth’s surface depends on various factors,
like location, weather conditions, climate, absorption, reflection, scattering and attenuation by
aerosol, particulates present in the atmosphere. The solar radiation may be explained in two
categories:
1. Extraterrestrial Solar Radiation: The intensity of sun’s radiation outside the earth’s atmosphere
is called extraterrestrial radiation. It has no diffuse components. The radiations are measured as an
average earth-sun distance on a surface normal to radiation.
The energy flux is called solar radiation and may be defined as: “The energy received from the
sun per unit time on a unit area of surface, perpendicular to the direction of propagation of the
radiation at the earth’s mean distance from the sun outside the atmosphere.” It is denoted by
ISC and is estimated as 1367 W/m2.
1. The value of solar constant remains constant throughout the year.
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2. Its value changes with location. The extraterrestrial radiation observed on different days is known
as apparent extraterrestrial solar radiation (irradiance) and can be calculated on any day of year with
given equation

Spectral distribution of extraterrestrial solar radiation

Terrestrial Solar Radiation: The radiations receive on the earth surface is called the terrestrial
radiation and is nearly 70% of extraterrestrial solar radiation. Its maximum value on horizontal earth
surface is 1000 W/m2, because a large part of radiations are absorbed, reflected, attenuated back by
earth’s atmosphere.
(i) Direct or Beam Radiation (Ib): The radiation received on the earth’s surface directly without
change in direction and does not get absorbed, reflected and scattered while passing through
atmosphere.
(ii) Diffuse radiation (Id): The radiation received on earth surface at a location from all the
directions. This radiation changes the original direction after scattering, reflection in the atmosphere
as well as by ground surface. Its average value is nearly 20% in the morning hrs and decreases to 5-
10% of the total radiation during the clear day but increase in the hazy and cloudy conditions of sky.
(iii) Total or Global Radiation (It): The sum of beam and diffuse radiation intercepted at the
surface of the earth per unit area of location is called the total /global radiation or insolation:
It = Ib +Id
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Air Mass: It is a term used to assess the distance travelled by a beam radiation through the
atmosphere before reaching the location on the earth’s surface.
It is defined as the ratio of the path of the sun’s ray through the atmosphere to the length of the path
when the sun is directly over head or sun is at its zenith.
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Angle of latitude of a particular location: It is the vertical angle between the line joining that point
of location to the centre of the earth and its projection on an equatorial plane. It is 00 for a point on
the equator and ±900 for a point at the poles.
Declination angle (δ): It is the angle made between the line joining the sun to earth and its
projection on the equatorial plane. Due to the inclination of earth’s axis, the line joining the Sun and
Earth will not lie on the equatorial plane. It varies through the year from + 23.45 0 to -23.450

Hour angle (ω): It is the angle representing the position of the sun with respect to clock hour and
with reference to sun’s position at 12 noon. In other words it represents the angle through which the
earth must rotate so that the meridian at a point comes into alignment with sun’s rays. It is a constant
and equal to 150/hr.
Solar altitude angle (α): It shows a horizontal plane drawn at any place on earth. At any point the
line joining sun to the centre of this horizontal plane and the line joining the projection of sun and
the centre of the horizontal plane makes a vertical angle α, which is called the altitude angle.
Zenith angle (θZ): If a vertical line is drawn to this horizontal plane, at its centre, the line joining
sun and the centre of the plane will make an angle θZ with this vertical. This angle is called the
zenith angle.
Local solar time (LST): This is also called Local Apparent Time (LAT) td calculated using various
values of θZ. The time so calculated the Local Solar Time. This will vary from the actual clock time
by approximately 4 minutes. This variation changes with the month of the year.
Solar Constant (Isc): It is the rate at which energy is received from the sun on a unit area
perpendicular to the ray’s of the sun, at the mean distance of the earth from the sun. Based on the
measurements made up to 1970 a standard value of 1353 W/m 2 was adopted in 1971. However
based on subsequent measurements, a revised value of 1367 W/m 2 has been recommended. The
earth revolves around the sun in an elliptical orbit having a very small eccentricity and the sun at the
foci. Consequently, the distance between earth and sun varies a little through the year. Because of
this variation, the extra terrestrial flux also varies.

Solar Thermal Energy: The application of solar thermal energy ranges from solar cooker of 1 kW
to power plant of 200 MW. These systems are grouped into low temperature (< 150 0C), medium
temperature (1500 - 3000C) and high temperature (5000 – 10000C).
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Solar Cell: Solar Cells are solid electronic devices used to convert the electromagnetic energy of
solar radiation directly into direct current electricity. Thus a solar cell is a transducer which converts
the sun’s radiant energy directly into electricity and is basically a semiconductor diode capable of
developing a voltage of 0.5-1V and current density of 20-40 mA/cm2 depending on the materials
used and the sun light conditions. This makes the system far more convenient and compact
compared to thermal methods of solar energy conversion.

Solar Cell Materials: Solar cells are made of different materials and Silicon (Si) is one used in
nearly 90% applications. The choice of the materials depends on the energy gap, efficiency and cost.
The maximum efficiency of solar cell is achieved with the band energy of 1.12 eV – 2.3 eV. Other
commonly used Materials are Cadmium Telluride (CdTe), Gallium Arsenide (GaAs), Zinc Telluride
(ZnTe) etc
Performance Characteristic of Solar Cell: Performance characteristics of PV cell is dependent on
solar radiation, climate conditions etc. The cell is tested at standard test conditions of 1000 W/m 2
solar radiation and 25 0C cell temperature. The testing setup is shown in figure. When the circuit is
open, the flowing current is zero and this open circuit voltage (V oc) is nearly 0.6 V.

Photovoltaic module & Array: A typical silicon cell can produce upto 0.6 V and upto 6 Amp i.e.
equivalent to about 3 W power. The cell size varies from 1 cm to about 10 cm across. To increase
power output, cells are electrically connected in series and parallel to absorb as much light as
possible to produce desired voltages and current. A number of cells are combined to form a Module.
When modules are combined we get a Panel. Panels are combined to get an array

Photovoltaic Power Generation: The maximum possible output of a solar array is about 300
W/m2. Figure shown in next page shows the basic structure of a solar cell power plant. This scheme
is suitable for feeding a local load as also for feeding a grid. The photo voltaic array produces dc
power and this must be converted into ac power for local use and feeding into the grid. Some form of
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energy storage is invariably used so that at time of excess generation, the energy may be stored so
that it can be used at the time of low generation.

Solar Cell Power Plant: Depending on the method of utilization there can be two configurations: 1.
Stand alone system 2. Grid connected system

1. Stand alone system: This system having following characteristics:

(i)Operates autonomously and independently (ii) commonly used for backup power where
connecting to grids are very costly. (iii) Can be used to power DC loads and by the use of an inverter
it may used for AC loads also. (iv)Hybrid stand alone systems may include other power producing
devices also for backup.

Types of Stand alone systems:

1. Direct Coupled Stand alone system: In this the solar array is directly connected to the DC load.
There is no energy storage. It can be used only in sunshine hours. Basically uses for water supply
pumps for agricultural purpose.

2.Stand alone system with Battery storage: In this the PV array charges the battery and the battery
supplies DC power to the loads. There is no charge control and is susceptible to overcharge and over
discharge.
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3. Stand alone system with battery and charge control: This has got charge control for controlling
the charge / discharge

4.Stand alone system with AC and DC loads: This system can be used to power AC as well as DC
loads. It needs inverter in the circuit. In addition the main AC supply also may be used for charging
only in the case of emergency.

5. Hybrid Stand alone systems:

In such systems one or more sources in addition to the PV panels are used. Sources like stand by
engines, turbines, fuel cells etc may be used in conjunction with PV arrays which reduces the
dependency on any single source. This also reduces battery storage capacity and size of PV arrays.
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Grid Connected Systems: In this system the power generated by the PV array is fed to the grid or
to the AC load directly. At the time of excess power generation the requirement of the loads is
supplied to a commercial grid. The output from the inverter has to satisfy the norms of the quality of
the electrical standard so that it can match the grid system.

Devices used for measuring the solar radiations

Various devices are used for measuring the solar radiations. Some of them are as following
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1.Pyranometer 2. Pyrheliometer 3. Sunshine Recorder

1.Pyranometer: A Pyranometer is an instrument for measuring global or diffuse radiations.

Construction: It consists of following components:
i. Black Surface: These receive the beam as well as diffuse radiations. which rises heat.
ii. Glass Dome: It prevents the loss of radiation received by the black surface.
iii. Thermopile: It is a temperature sensor and consists of a number of thermocouples connected in
series to increase the sensitivity.
iv. Supporting Stand: It keeps the black surface in a proper position.
Working: Pyranometer is kept exposed to the sun and it starts receiving the radiations.
Pyranometer consists of a black surface which heats up when exposed to solar radiation. It’s
temperature increases until the rate of heat gain by solar radiation equals the rate of heat loss by
convection, conduction and radiation. The hot junctions of thermopile are attached to the black
surface, while the cold junctions are located under a guard plate so that they do not receive the
radiation directly. As a result an emf is generated. This emf which is usually in the range of 0 t0
10mv can be read, recorded or integrated over a period of time and is a measure of global radiation.
The Pyranometer can also be used for measurement of diffuse radiation. This is done by mounting
it at the center of a semi circular shading ring.

2.Pyrheliometer: It is a device used for measuring the beam or direct radiations.

Construction: It consists of following components

i. Receiver: It is in the shape of a hollow tube with reflecting surface inside.

ii. Absorber Plate: It consists of a blackened surface and it is placed at the bottom of the tube.
iii. Thermopile: It is a sensing element of temperature consisting of a group of thermopiles.
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Working:
1. The hollow receiver tube can be tilted about an axis perpendicular to its length.
2. Thus, the tube can be made to face the sun's radiation, thereby receive only the beam
radiation and no diffuse radiation can enter the tube
3. When the radiation falls on the absorber plate, it absorbs the radiation and it gets heat up,
so the temperature increases.
4. The rise in temperature is measured by measuring the thermo-emf of the thermopile.
Types of Pyrheliometer: (i)Angstrom Pyrheliometer (ii) Abbot silver disc Pyrheliometer
(iii)Eppley Pyrheliometer
3.Sunshine Recorder: It is a device used to measure the hour’s of bright sunshine in a day.
Construction: It consists of a glass sphere installed in a section n spherical metal bowl,
having grooves for holding a recorder card and the glass sphere for adjusting the focus of sun
rays to a point on card strip.

Working
1. Sun's beam is focused to a point by a spherical glass, which acts as a convex lens and graduated
paper strip is placed at the focal point.
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2. Due to the heating effect of the focused beam, a burn mark is produced on the paper and the
graduation on the paper is done as per the hours of the day.

Que. Calculate the angle declination on 6th of June, Assuming non leap year.

Que. If the angle of declination on a particular day was +18.250 which is the date assuming
leap year? Solution. We know that declination angle
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Que. Determine the solar insolation on march 22 assuming the solar constant Isc = 1353 W/m 2

Solution

Que. Calculate the day hours on may 02 and December 1 on a surface sloping southwards at
an angle of 400 at a place of 19007/ north latitude and 72.51 east longitude.

Solution
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Que. Calculate the hour angle at sunrise and sunset on june 10 and December 21 for a surface
inclined at 10 degree facing due to south. Surface is located at 17 0N and 750 E.
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Solar Radiance: The solar radiance is an instantaneous power density in units of kW/m2 The solar
radiance is strongly dependant on location and local weather. Solar radiance measurements consist
of global and/or direct radiation measurements taken periodically throughout the day. The
measurements are taken using either a pyranometer or a pyrheliometer.

Solar Insolation: The solar insolation is the total amount of solar energy received at a particular
location during a specified time period, often in units of kWh/(m 2 day). Solar insolation data is
commonly used for simple photovoltaic (PV) system design while solar radiance is used in more
complicated PV system. By knowing the insolation levels of a particular region we can determine
the size of solar collector that is required and how much energy it can produce.
Solar insolation can be measured using sunshine recorders. These Sunshine recorders measure the
number of hours in the day during which the sunshine is above a certain level.
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Solar Collectors: Solar collectors are used to collect the solar energy and convert the incident
radiations in thermal energy by absorbing them. This heat is absorbed by flowing fluid in the tube of
collector.
These are of two types: 1. Non concentrating collectors 2. Concentrating collectors
1.Non concentrating collectors: In these collectors the area of collector to intercept the solar
radiation is equal to the absorber plate and has concentration ratio of 1.
1. These can be categorized as
(a) Flat Plate Collectors (FPC) (b) Vacuum Tube Collectors (c) Unglazed Flat Plate Collectors

Flat Plate Collectors (FPC)

These are the most important part of any solar thermal energy system. It is simplest in design and
absorbs direct and diffuse radiations both and converts it into useful heat. It is suitable for heating to
temperature below 1000C.

Construction and Materials for Flat Plate Collectors: Material needed for flat plate collectors
can be classified into following groups:

Physical properties – tensile strength, density etc.

Thermal properties – thermal conductivity, heat capacity etc.

Environmental properties – corrosion resistant, degradation of material due to UV radiation,

moisture penetration etc.
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The materials generally used for various components of a flat plate collector are as given below:

(a) Absorber Plate and Tubes: These plates should have high tensile strength; high thermal
conductivity and it should be corrosion resistant (generally made of copper, aluminum, steel etc).
Generally black chrome, black copper oxides, black nickel etc are used for its coating to having high
absorptivity.

(b) Thermal Insulation: The material used for insulation should have low thermal conductivity,
stability at high temperature up to 2000C, non-corrosive. Insulating materials generally used are
mineral wool, rock wool, glass, thermo Cole, foam etc.

(c) Transparent Cover Plates: Cover plates must have high strength, high solar energy
transmittance and high durability against UV radiation. Usually plain glass plates or toughened of 4
to 5 mm thickness are used.

(d) Casing: This contains all the above components which is placed at an angle facing south at an
inclination to the horizontal equal to the latitude of the place plus 150. It is made of aluminum, steel
or fiber glass in rectangular shape.

(e) Selective Coating: This surface has high absorptivity of incoming solar radiation and low value
of emissivity. Selective surfaces are essential to reduce the heat losses from absorber plate and
increase the temperature of absorbing surface i.e. it should have high collector efficiency. Various
methods of these coatings which are employed are by electroplating, anodic oxidation, chemical
conversion etc. Generally Black chrome, black nickel, aluminum nitride etc are used for this
purpose.
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2. Concentrating collectors: These are the solar collectors where the radiation is focused either to a
point (focal point of the collector) or along a line (focal axis of the collector). Since the radiation is
focused, the η of concentrating collector is always greater than that of non-focusing or FPC. This is
because of the following reasons,

1) In case of focusing collector the area of the absorber is many times smaller than that of the area of
the collector. Where as in a non-concentrating type the area of the absorber equals area of the
collector. Hence here the loss of absorbed radiation is more compared to the concentrating type.

Classification of semiconductors
On the basis of band theory of solid conductor are classified in three
Categories
1. Conductor
2. Insulator
3. Semiconductor
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(i) Conductors are those substances through which electricity can pass easily, e.g., all metals are
conductors.
(ii) Insulators are those substances through which electricity cannot pass, e.g., wood. rubber, mica
etc.
(iii) Semiconductors are those substances whose conductivity lies between conductors and
insulators. e.g., germanium, silicon, carbon etc.
Energy Bands of Solids
1. Energy Band
In a crystal due to interatomic interaction valence electrons of one atom are shared by more than
one atom in the crystal. Now splitting of energy levels takes place. The collection of these closely
spaced energy levels els is called an energy band.
2. Valence Band
This energy band contains valence eelectrons. This band may be partially or completely filled with
electrons but never be empty. The electrons in this band are not capable of gaining energy from
external electric
ric field to take part in conduction of current.
3. Conduction Band
This band contains conduction electrons. This band is either empty or partially filled with electrons.
Electrons present in this band take part in the conduction of current.
4. Forbidden Band
This band is completely empty. The minimum energy required to shift an electron from valence band
to conduction band is called band gap (Eg). Energy gap for Ge is 0.72 eV and for Si it is 1.1 eV.

Types of Semiconductor:

(i) Intrinsic Semiconductor: A semiconductor in its pure state is called intrinsic semiconductor.

(ii) Extrinsic Semiconductor: A semiconductor doped with suitable impurity is called extrinsic
semiconductor.
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S. No. Intrinsic Semiconductor Extrinsic Semiconductor

1. It is a pure semiconductor with no impurity. It is an impure semiconductor i.e., pentavalent
or trivalent impurity is added.

2. The number of free electrons in the In an n-type semiconductor, free electrons far
conduction band is equal to the number of exceed the holes. In p-type semiconductor, it
holes in the valence band. is the reverse.
3. Its electrical conductivity is low. Its electrical conductivity is high.

4. Its electrical conductivity depends on the Its conductivity depends the temperature and
temperature alone. amount of doping.

It is used in electronic devices.

5. It is of no practical use.

On the basis of doped impurity extrinsic semiconductors are of two types

(i) n-type Semiconductor: Extrinsic semiconductor doped with pentavalent impurity like As,
Sb, Bi, etc in which negatively charged electrons works as charge carrier, is called n-type
semiconductor.

In n type Fermi level lies just below the conduction band.

(ii) p -type Semiconductor: Extrinsic semiconductor doped with trivalent impurity like Al,
B, etc, in which positively charged holes works as charge carriers, is called p-type
semiconductor. Every trivalent impurity atom have a tendency to accept one electron,
therefore it is called an acceptor atom.
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Metal-Semiconductor Junction: Metal-semiconductor (M-S) junction is a type of electrical
junction in which a metal comes in close contact with a semiconductor material. Metal
semiconductor (M-S) junctions can behave as either Schottky barriers or as Ohmic contacts
depending on the interface properties. The principle of forming different types of the metal-
semiconductor contact is the mismatch of the Fermi energy between metal and semiconductor
material which is due to the difference in work functions.
M-S Junction in Forward Bias: As a positive bias is applied to the metal, the Fermi energy of the
metal is lowered with respect to the Fermi energy in the semiconductor. This results in a smaller
potential drop across the semiconductor. The balance between diffusion and drift is disturbed and
more electrons will diffuse towards the metal than the number of electrons drifting into the
semiconductor. This leads to a positive current through the junction at a voltage comparable to the
built-in potential.
M.S Junctions in Reverse Bias: As a negative voltage is applied, the Fermi energy of the metal is
raised with respect to the Fermi energy in the semiconductor. The potential across the semiconductor
now increases, yielding a larger depletion region and a larger electric field at the interface. The
barrier which restricts the electrons to the metal is unchangedS 0 that barrier independent of the
applied voltage limits the flow of electron
Solar Photovoltaic System: It refers to a wide variety of solar electricity systems. This system use
solar array made of silicon to convert sunlight into electricity. Components other than PV array are
collectively known as balance system (BOS) which includes storage batteries, an electronic charge
controller and an inverter. Storage batteries with charge regulators are provided for back-up power
supply during periods of cloudy day and during nights. Batteries are charged during the day and
supply power to loads. The capacity of a battery is expressed in ampere-hours and each cell of the
lead-acid battery is of 2 volts. Batteries are installed with a microprocessor based charge regulator to
monitor the voltage and temperature. It also regulates the input and the output current to eliminate
overcharging and excessive discharge respectively. An inverter is provided for converting DC power
from battery or PV array to AC power. It needs to have an automatic switch-off in case the output
voltage from the array is too low or too high.
Principle of Solar Photovoltaic: It is a field of solar energy utilization by which solar radiation is
converted into electrical energy using a device called photovoltaic cell or solar cell. A solar cell is
made up of a semiconductor material like silicon (Si) or Gallium arsenide (GaSe).
In semiconductors, atoms carry four electrons in the outer valence orbit, some of which can be
dislodged to move freely in the materials, if Then, a semiconductor attains the property to conduct
the current. This is the basic principle on which the solar cell works and generates power.
Photovoltaic Effect: Photoelectric effect is the emission of electrons or other free carriers when light
hits a materials. When a solar cell is illuminated, electron-hole pairs are generated and electric
current I is obtained. I is the difference between the solar light generated current I L and the diode
dark current Id.
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V-I Characteristic of Photovoltaic (PV) Device:

The V-I characteristic of a PV device is a non-linear graph between current and voltage generated.

For different temperature levels, different graphs have been plotted. Maximum power points have
also been shown to represent the point at which maximum power can be drawn from a PV device.
These maximum power point constitute the maximum power line(MPL). MPL represents the path
tracked by maximum power point tracker (MPPT).

P-V Characteristic of Photovoltaic Device:P-V characteristic curve of a PV device is also a non-

linear curve plotted between power and voltage of a PV device. For different power densities in
W/m2,different graphs have been plotted between power and voltage of a PV module. The maximum
power point (MPP) constitute, the maximum power line. MPL is also non linear curve.
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Advantages of Solar Photovoltaic Systems:

1. No operational cost.
2. Low maintenance.
3. These systems are durable.
4. More flexibility is available in solar photovoltaic systems.
5. These systems are eco-friendly.
Disadvantages of Solar Photovoltaic Systems:
1. Low efficiency.
2.Weather dependent.
3.Installation cost is more.
First Generation Solar Cells: These cell consists of a large area, single crystal, single layer of p-n
junction diode, capable of generating usable electrical energy from light sources With the
Wavelengths of sunlight. These cells are typically made using a diffusion process with silicon
Wafers. These silicon wafer based solar cells are the dominant technology in the cells, accounting
for more than 86 % of terrestrial solar cell market.
Various types of First Generation Solar Cells:
(i)Monocrystallinc Silicon Cells: In monocrystalline silicon cells, silicon is doped with boron to
produce p-type semiconductor. Monocrystalline rods are extracted from silicon and then sawed into
thin plates or wafers. The upper layer of the wafers is doped with phosphorous to produce n-type
semiconductor. This becomes p-n junction. Maximum efficiency of these cells is 24%.
(ii)Polycrystalline Silicon Cells: In polycrvstalline cells, liquid silicon is poured into blocks that are
sawed into plates. During solidification of the material, crystal structures of varying sites are formed.
The size of crystallites mainly depends upon the cooling condition. If the molten silicon is cooled
very slowly, the crystallites of larger size are obtained. The silicon solar cells made from
polycrystalline silicon are low cost but low efficiency. Maximum efficiency of these cells is 17.8 %.
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(iii)Amorphous Silicon Cells: If a silicon film is deposited on glass or another substrate material,
this is so called amorphous or thin layer cell.
The layer thickness is less than 1 pm, so production costs are lower due to the low material costs.
However, the efficiency of amorphous cells is much lower than that Of the other cells. Because of
this, they are primarily used in low power equipment such as watches, pocket calculators etc.
Maximum efficiency of these cells is 13%.
Second Generation Solar Cells: These cells are based on the use of thin epitaxial deposits
semiconductors on lattice matched wafers.
There are two classes of epitaxial photovoltaic - space and terrestrial. Space cells typically have
higher efficiencies (28-30 %) in production but also have a higher cost per watt. Examples are
amorphous silicon, polycrystalline, micro crystalline cadmium telluride. second generation solar
cells now comprise a small segment of the terrestrial photovoltaic market, and approximately 90 %
of the space market.
Types of Second Generation Solar Cells:
(i)Copper Indium (Gallium) Diselenide (CIS) Cell: CIS has a direct band gap of 1.0 eV.
Incorporation of Ga into the CIS mixture increases the band gap beyond 1.1 eV. A heterogeneous
junction with Il-type Cd-S and p-type CIS is fabricated using thin-film technology. Its main
attraction is inexpensive preparation. It is more stable as compared to a Si cell in outdoor
applications and has efficiency of around 10%. However, exposure to elevated temperatures results
in loss of efficiency but light soaking restores it to original efficiency level.
(ii)Cadmium Telluride Cell: Cd-Te has a favorable direct band gap of 1.44 eV. Thin film
heterogeneous junction with n-type Cd-S and p-type Cd-Te is fabricated as

Here, a transparent conducting oxide layer is used instead of metallic contact at the top on the n side.
EVA(ethylene vinyl acetate) is used for encapsulation. Its efficiency is about 10 % and open circuit
cell voltage is around 0.8 V.
Third Generation Solar Cells: They arc proposed to be very different from the previous
semiconductor devices as they do not rely on a traditional p-n junction to separate photogenerated
charge carriers. For space applications quantum well devices (quantum dots, quantum ropes, etc.)
and devices incorporating carbon nanotubes are being studied with a potential for up to 45 %
production efficiency. For terrestrial applications, these new devices include photoelectrochemical
cells, polymer solar cells, nanocrystal solar cells, dye sensitized solar cells and are still in the
research phase.
Types of Third Generation Solar Cells:
 UNIT-3: SOLAR ENERGY
(i)Organic PV Cell: The solar cells based on organic semiconductor can provide a low cost
alternative for solar PV. The thickness of the active layer of organic solar cells is only 100nm thin,
which is about 1000 times thinner than the crystalline silicon solar cells, and it is about 10 times
thinner than the current inorganic thin film solar cells. In the low material consumption per solar cell
and the relatively simpler cell processing of organic semiconductors. There is a large potential for
low cost large area solar cells. Due to this reason, there is a considerable interest in devices. Their
principal advantage is that they are flexible and breaking, unlike Si, which is brittle. They are also
very light and cheap. They may be folded or cut into required sizes and can still be used.
(ii)Dye Sensitized Solar Cell (DSC): The DSC can be considered as a thin film solar cell device.
This technolgy is not yet commercialized but is on the verge of commercialization. The DSC solar
cells can be made flexible. It has a good potential for being a low cost solar cell technology. This is
mainly possible because of the large availability and low the ingredient material as well as due to the
low processing temperature. The DSC is a photoelectron chemical device. In its operation it involves
a photon, an electron and a chemical reaction. The operation of DSC is considered similar to that of
a photosynthesis process.
 Unit- 2 Nuclear Energy
Atomic Structure: Rutherford's  -scattering experiment established that the mass of atom is
concentrated with small positively charged region at the centre which is called 'nucleus'. Nuclei
are made up of proton and neutron. The number of protons in a nucleus (called the atomic
number or proton number) is represented by the symbol Z. The protons have a positive charge.
In order for the atom to have a neutral charge, the electrons need to balance it out with their
negative charge. The number of neutrons (neutron number) is represented by N. The total
number of neutrons and protons in a nucleus is called it's mass number A so A = Z + N.
Neutrons and proton, when described collectively are called nucleons.

Neutron: Neutron is a fundamental particle which is essential constituent of all nuclei except
that of hydrogen atom. It was discovered by Chadwick.
(1) The charge of neutron: It is neutral
(2) The mass of neutron: 1.6750  10–27 kg
(3) It's spin angular momentum : ½  h/2J s
(4) It's magnetic moment : 9.57 10–27 J/Tesla
(5) It's half life : 12 minutes
(6) Penetration power: High
(7) Types: Neutrons are of two type’s slow neutron and fast neutron; both are fully capable of
penetrating a nucleus and causing artificial disintegration.
Thermal neutrons: Fast neutrons can be converted into slow neutrons by certain materials
called moderator's (Paraffin wax, heavy water, graphite) when fast moving neutrons pass
through a moderator, they collide with the molecules of the moderator, as a result of this, the
energy of moving neutron decreases while that of the molecules of the moderator increases.
After sometime they both attains same energy. The neutrons are then in thermal equilibrium with
the molecules of the moderator and are called thermal neutrons.
Energy of thermal neutron is about 0.025 eV and speed is about 2.2 km/s.
Properties of Neutrons: 1.Neutrons are fundamental constituents of a nucleus.
Inside a nucleus, neutrons stay forever but as a projected particle outside it, it, exists
for a short time only.
2. In nuclei of heavier elements, the number of neutrons is greater than the number of
protons. It is this abundance of neutrons which makes the elements stable.
3. Since neutrons are uncharged particles, therefore these are neither affected by
external magnetic or electric fields nor by the presence of protons when they enter or
penetrate the nucleus.
4. Depending upon their speed, neutrons are put in two categories:
i.Fast neutrons, and
ii.Slow neutrons.
5. Both are fully capable of penetrating a nucleus and causing artificial disintegration in nucleus.
Nucleus contains two types of particles: Protons and neutrons
Nuclides are represented as; ZXA where X denotes the chemical symbol of the element.
Size of nucleus nuclear radius: Experimental results indicate that the nuclear radius is
proportional to A1/3, where A is the mass number of nucleus i.e.
1/3 –15
 R  R0 A , where R0 = 1.2  10 m = 1.2 fm.
R  A1 / 3

Heavier nuclei are bigger in size than lighter nuclei.

Fundamental forces present in nature
Various fundamental forces present in nature are as follows:
1. Gravitational Force: It is the force of mutual attraction between any two objects by virtue
of their masses. It is a universal force as every object experiences this force due to every
other object in the universe.
2. Electromagnetic Force: It is the force between charged particles. Charges at rest have
electric attraction (between unlike charges) and repulsion (between like charges). Charges in
motion produce magnetic force. Together they are called electromagnetic force.
3. Strong Nuclear Force: It is the attractive force between protons and neutrons in a nucleus.
It is charge-independent and acts equally between a proton and a proton, a neutron and a
neutron, and a proton and a neutron.
4. Weak Nuclear Force: This force appears only in certain nuclear processes such as the P-
decay of a nucleus. In P-decay, the nucleus emits an electron and an uncharged particle called
neutrino.
Nuclear force: Nuclear forces are those forces which act between two are more nucleons` they
bind proton and neutrons into atomic nuclei.
Properties of nuclear forces are as follows:
1. Nuclear forces are attractive force and causes stability of the nucleus.. When the distance
between two nucleons is 10-14 m which is equal to the size of a nucleus, the nuclear force comes
into play as an attractive force.
2. Nuclear forces are charge independent.

3. Nuclear forces are short range forces. These do not exist at large distances greater than 10 –15
m.

4. Nuclear forces are spin dependent. The force between two nucleons having parallel spins is
stronger than the force existing between two nucleons having anti parallel spins.
5. Nuclear forces show saturation properties. A nucleon can interact only with those
nucleons which are its nearest neighbors.
6. Nuclear forces are the strongest forces in nature.

7. Nuclear forces are non-central force.

Nuclear forces are exchange forces

According to scientist Yukawa the nuclear force between the two nucleons is the result of the
exchange of particles called mesons between the nucleons.

Mesons are of three types – Positive  meson (  +), negative  meson (  –), neutral  meson
(0)

The force between neutron and proton is due to exchange of charged meson between them i.e.
 p     n, n  p   

The forces between a pair of neutrons or a pair of protons are the result of the exchange of
neutral meson (  o) between them i.e.
p  p' and n  n' 0

Thus exchange of  meson between nucleons keeps the nucleons bound together. It is
responsible for the nuclear forces.
Atomic mass unit (amu): The unit in which atomic and nuclear masses are measured is called
atomic mass unit (amu)
1 amu =1/12 th of mass of 6C12 atom = 1.66  10–27 kg
Masses of electron, proton and neutrons: Mass of electron (me) = 9.1  10–31 kg = 0.0005486 amu,
Mass of proton (mp) = 1.6726  10–27 kg = 1.007276 amu
Mass of neutron (mn) = 1.6750  10–27 kg = 1.00865 amu,
Mass of hydrogen atom (me + mp) = 1.6729  10–27 kg = 1.0078 amu
Mass-energy equivalence:
According to Einstein, mass and energy are inter convertible. The Einstein's mass energy relationship
is given by E  mc2 If m = 1 amu, c = 3  108 m/sec then E = 931 MeV i.e. 1 amu is equivalent to
931 MeV or 1 amu (or 1 u) = 931 MeV
Mass defect (m): It is found that the mass of a nucleus is always less than the sum of masses of it's
constituent nucleons in free state. This difference in masses is called mass defect. Hence mass defect
m = Sum of masses of nucleons – Mass of nucleus

 Zm p 
 (A  Z)mn  M

where mp = Mass of proton, mn = Mass of each neutron, me = Mass of each electron

M = Mass of nucleus, Z = Atomic number, A = Mass number
Binding energy (B.E.): The neutrons and protons in a stable nucleus are held together by
nuclear forces and energy is needed to pull them infinitely apart (or the same energy is
released during the formation of the nucleus). This energy is called the binding energy of the
nucleus. or
The binding energy of a nucleus may be defined as the energy equivalent to the mass
defect of the nucleus. If m is mass defect then according to Einstein's mass energy
relation
Binding energy = m  c2 = [{mpZ + mn(A – Z)} – M] c2 (This binding energy is expressed in joule, because
m is measured in kg)

If m is measured in amu then binding energy = m amu = [{mpZ + mn(A – Z)} – M] amu = m  931 MeV
Binding Energy Curve. It is the graph between binding energy per nucleon and total number
of nucleons (i.e. mass number A)

1. Some nuclei with mass number A < 20 have large binding energy per nucleon than their neighbour nuclei.
4 8 12 16
For example 2 He , 4 Be , 6 C , 8 O and 10 Ne 20 . These nuclei are more stable than their neighbours.

2. The binding energy per nucleon is maximum for nuclei of mass number A = 56 (26 Fe 56 ) . It's value is 8.8
MeV per nucleon.

3. For nuclei having A > 56, binding energy per nucleon gradually decreases for uranium (A = 238), the
value ofbinding energy per nucleon drops to 7.5 MeV.
4. When a heavy nucleus splits up into lighter nuclei, then binding energy per nucleon of lighter
nuclei is more than that of the original heavy nucleus. Thus a large amount of energy is liberated in
this process (nuclear fission).

5. When two very light nuclei combines to form a relatively heavy nucleus, then binding energy per
nucleon increases. Thus, energy is released in this process (nuclear fusion).
Binding energy per nucleon 6C12

Atomic weight of 6C12 atom= 12.000 amu

Mass of 6 proton = 1.00759x6= 6.04554amu

Mass of 6 neutrons =1.00898x6=6.05388amu

Mass of 6 electrons =0.00055x6 = O.0330 amu
Total = 12.10272amu
Mass defect = 12.10272 – 12.000 = 0.10272amu
1amu = 931 MeV
Total binding energy = 0.10272x931 = 95.91 MeV
Total binding energy per nucleon = 95.91 / 12 = 7.99MeV

Nuclear Reactions: The process by which the identity of a nucleus is changed when it is
bombarded by an energetic particle is called nuclear reaction. The general expression for the
nuclear reaction is as follows.

Here X and a are known as reactants and Y and b are known as products. This reaction is
known as (a, b) reaction and can be represented as X(a, b) Y
Q value or energy of nuclear reaction: The energy absorbed or released during nuclear
reaction is known as Q-value of nuclear reaction.
Q-value = (Mass of reactants – mass of products)c 2 Joules
= (Mass of reactants – mass of products) amu
If Q < 0, The nuclear reaction is known as endothermic. (The energy is absorbed in the
reaction)
If Q > 0, The nuclear reaction is known as exothermic (The energy is released in the reaction)
Nuclear fission: The process of splitting of a heavy nucleus into two lighter nuclei of
comparable masses (after bombardment with a energetic particle) with liberation of energy is
called nuclear fission.

The phenomenon of nuclear fission was discovered by scientist Ottohann and F. Strassman and
was explained by N. Bohr and J.A. Wheeler on the basis of liquid drop model of nucleus.
 U 235  0 n1 92 U 236  56 Ba 141  36 Kr 92  3 0 n1  Q
92

i.The energy released in U235 fission is about 200 MeV or 0.8 MeV per nucleon.
235
(ii) By fission of 92U , an average 2.5 neutrons are liberated. These neutrons are called fast
neutrons and their energy is about 2 MeV (for each). These fast neutrons can escape from the
reaction so as to proceed the chain reaction they are need to slow down.

(iii) Fission of U235 occurs by slow neutrons only (of energy about 1eV) or even by thermal
neutrons (of energy about 0.025 eV).

(iv)50 kg of U235 on fission will release 4 × 1015 J of energy. This is equivalence to 20,000
tones of TNT explosion. The nuclear bomb dropped at Hiroshima had this much explosion
power.

Nuclear Fusion:
In nuclear fusion two or more than two lighter nuclei combine to form a single heavy nucleus.
The mass of single nucleus so formed is less than the sum of the masses of parent nuclei. This
difference in mass results in the release of tremendous amount of energy.

1 H 2  1 H 2  1 H 3  1 H 1  4 MeV

1 H 3  1 H 2  2 He 4  0 n1  17 .6 MeV

or 1 H 2  1 H 2  2 He 4  24 MeV

For fusion high pressure ( 106 atm) and high temperature (of the order of 107 K to 108 K)
is required and so the reaction is called thermonuclear reaction.
Fusion energy is greater then fission energy fission of one uranium atom releases about
200 MeV of energy. But the fusion of a deutron (1 H 2 ) and triton (1 H 3 ) releases about 17.6
MeV of energy. However the energy released per nucleon in fission is about 0.85 MeV but that
in fusion is 4.4 MeV. So for the same mass of the fuel, the energy released in fusion is much
 larger than in fission.
Plasma: The temperature of the order of 108 K required for thermonuclear reactions leads to
the complete ionisation of the atom of light elements. The combination of base nuclei and
electron cloud is called plasma. The enormous gravitational field of the sun confines the
plasma in the interior of the sun.
The main problem to carryout nuclear fusion in the laboratory is to contain the plasma
at a temperature of 108K. No solid container can tolerate this much temperature. If this
problem of containing plasma is solved, then the large quantity of deuterium present in sea
water would be able to serve as in-exhaustible source of energy.
To achieve fusion in laboratory a device is used to confine the plasma, called
Tokamak.

Stellar Energy: Stellar energy is the energy obtained continuously from the sun and
the stars. Sun radiates energy at the rate of about 1026 joules per second. Scientist
Hans Bethe suggested that the fusion of hydrogen to form helium (thermo nuclear
reaction) is continuously taking place in the sun (or in the other stars) and it is the
source of sun's (star's) energy. The stellar energy is explained by two cycles .

Proton-proton cycle

1 H 1  1 H 1  1 H 2  1 e 0  Q1

1 H 2  1 H 1  2 He 3  Q2

2 He 3  2 He 3  2 He 4  21 H 1  Q3

4 1 H 1 2 He 4  2 1e
0
 2  26.7 MeV

Carbon-nitrogen cycle

1 H 1  6 C 12  7 N 13  Q1

7 N 13  6 C13  1 e
0

1 H 1  6 C13  7 N 14  Q2

1 H 1 7 N 14  8 O15  Q3

8 O15  7 N 15  1 e 0  Q4

1 H 1  7 N 15  6 C 12  2 He 4

4 1 H 1  2 He 4  2 1 e 0  24.7 MeV
About 90% of the mass of the sun consists of hydrogen and helium. Nuclear Bomb Based on uncontrolled
nuclear reactions

Atom bomb Hydrogen bomb

Based on fission process it involves the fission of U235 Based on fusion process. Mixture of deutron and
tritium is used in it
In this critical size is important There is no limit to critical size
Explosion is possible at normal temperature and High temperature and pressure are required
pressure
Less energy is released compared to hydrogen bomb More energy is released as compared to atom bomb so
it is more dangerous than atom bomb

Chain reaction: In nuclear fission, three neutrons are produced along with the release of large
energy. Under favourable conditions, these neutrons can cause further fission of other nuclei, producing
large number of neutrons. Thus a chain of nuclear fissions is established which continues until the
whole of the uranium is consumed.

or

In the chain reaction, the number of nuclei undergoing fission increases very fast. So, the
energy produced takes a tremendous magnitude very soon.

Difficulties in chain reaction (i) Absorption of neutrons by U238, the major part in natural
uranium is the isotope U238 (99.3%), the isotope U235 is very little (0.7%). It is found that U238
is fissionable with fast neutrons, whereas U235 is fissionable with slow neutrons. Due to the
large percentage of, U238 there is more possibility of collision of neutrons with U 238. It is found
that the neutrons get slowed on coliding with , U 238 as a result of it further fission of U238 is not
possible (Because they are slow and they are absorbed by U238). This stops the chain reaction.
 235
Removal : (i) To sustain chain reaction 92U is separated from the ordinary uranium.
Uranium so obtained is known as enriched uranium, which is fissionable with the fast and slow
neutrons and hence chain reaction can be sustained.

(ii) If neutrons are slowed down by any method to energy of about 0.3 eV, then the probability
of their absorption by U238 becomes very low, while the probability of their fissioning
U235becomes high. This job is done by moderators. Which reduce the speed of neutron rapidly
graphite and heavy water are the example of moderators.

(iii) Critical size: The neutrons emitted during fission are very fast and they travel a large
distance before being slowed down. If the size of the fissionable material is small, the neutrons
emitted will escape the fissionable material before they are slowed down. Hence chain reaction
cannot be sustained. Removal : The size of the fissionable material should be large than a
critical size. The chain reaction once started will remain steady, accelerate or retard depending
upon, a factor called neutron reproduction factor (k). It is defined as follows.

𝑟𝑎𝑡𝑒 𝑜𝑓 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑛𝑒𝑢𝑡𝑟𝑜𝑛

𝑘=
𝑟𝑎𝑡𝑒 𝑜𝑓 𝑙𝑜𝑠𝑠 𝑜𝑓 𝑛𝑒𝑢𝑡𝑟𝑜𝑛

1. if k = 1, the chain reaction will be steady. The size of the fissionable material used is said to
be the critical size and it's mass, the critical mass.
2. If k > 1, the chain reaction accelerates, resulting in an explosion. The size of the material in
this case is super critical. (Atom bomb)
3. If k < 1, the chain reaction gradually comes to a halt. The size of the material used us said to
be sub-critical.
Types of chain reaction: Chain reactions are of following two types

Controlled chain reaction Uncontrolled chain reaction

Controlled by artificial method No control over this type of nuclear reaction
All neurons are absorbed except one More than one neutron takes part into reaction
Reproduction factor k = 1 Reproduction factor k > 1
Energy liberated in this type of reaction is always less A large amount of energy is liberated in this type of
than explosive energy reaction
Chain reaction is the principle of nuclear reactors Uncontrolled chain reaction is the principle of
atombomb.
It's rate is slow Fast rate
Comparison of Nuclear Fission and Nuclear Fusion Process:

Nuclear Fission Nuclear Fusion

1. A heavy nucleus breaks up to form two Two nuclei combine to form a heavy
lighter nuclei. nucleus.

2. It involves a chain reaction. Chain reaction is not involved

3. Nuclear reaction residual problem is high. Residual problem is much less.

4. Amount of radioactive material in a Amount of radioactive material is less.

fission reactor is high.

5. Because of higher radioactive material, Because of lesser radioactive material,

health hazard is high in Case of accidents. health hazard is much less.

6. We have proper mechanisms to control Proper mechanisms to control fusion

fission reaction for generating electricity. reaction are yet to be developed.

7. Raw material is not easily available and is Raw material is comparatively cheap and
costly. easily available.

8. Disposal of nuclear waste is great Disposal of nuclear waste is not involved.

environment problem.
Nuclear Reactor: A nuclear reactor is a device in which nuclear fission can be carried out
through a sustained and a controlled chain reaction. It is also called an atomic pile. It is thus a
source of controlled energy which is utilised for many useful purposes.

Parts of nuclear reactor (i) Fissionable material (Fuel) : The fissionable material used in
the reactor is called the fuel of the reactor. Uranium isotope (U 235) Thorium isotope (Th232) and
Plutonium isotopes (Pu239, Pu240 and Pu241) are the most commonly used fuels in the reactor.

(ii) Moderator : Moderator is used to slow down the fast moving neutrons. Most commonly
used moderators are graphite and heavy water (D2O).

(iii) Control Material : Control material is used to control the chain reaction and to maintain a
stable rate of reaction. This material controls the number of neutrons available for the fission.
For example, cadmium rods are inserted into the core of the reactor because they can absorb
the neutrons. The neutrons available for fission are controlled by moving the cadmium rods in
or out of the core of the reactor.

(iv)Coolant: Coolant is a cooling material which removes the heat generated due to fission
in the reactor. Commonly used coolants are water, CO2 nitrogen etc.

(v) Protective shield: A protective shield in the form a concrete thick wall surrounds the
core of the reactor to save the persons working around the reactor from the hazardous
radiations.

Note : It may be noted that Plutonium is the best fuel as compared to other fissionable
material. It is because fission in Plutonium can be initiated by both slow and fast
neutrons. Moreover it can be obtained from U238 .
 Nuclear reactor is firstly devised by fermi. Apsara was the first Indian nuclear reactor.

Uses of nuclear reactor (i) In electric power generation (ii) To produce radioactive isotopes
for their use in medical science, agriculture and industry. (iii) In manufacturing of PU 239
which is used in atom bomb. (iv) They are used to produce neutron beam of high intensity
which is used in the treatment of cancer and nuclear research.

Note: A type of reactor that can produce more fissile fuel than it consumes is the breeder
reactor.

Radioactivity

The phenomenon of spontaneous emission of radiations by heavy elements is called

radioactivity. The elements which show this phenomenon are called radioactive elements.

1. Radioactivity was discovered by Henery Becquerel in uranium salt in the year 1896.
2. After the discovery of radioactivity in uranium, Piere Curie and Madame Curie discovered a
new radioactive element called radium (which is 106 times more radioactive than uranium)
3. Some examples of radioactive substances are: Uranium, Radium, Thorium, Polonium,
Neptunium etc.
4. Radioactivity of a sample cannot be controlled by any physical (pressure, temperature, electric or
magnetic field) or chemical changes.
5. All the elements with atomic number (Z ) > 82 are naturally radioactive.
6. The conversion of lighter elements into radioactive elements by the bombardment of fast
moving particles is called artificial or induced radioactivity.
7. Radioactivity is a nuclear event and not atomic. Hence electronic configuration of atom doesn’t
have any relationship with radioactivity.
Nuclear radiatons: According to Rutherford's experiment when a sample of radioactive substance is
put in a lead box and allow the emission of radiation through a small hole only. When the radiation enters
into the external electric field, they splits into three parts

(i) Radiations which deflects towards negative plate are called -rays (stream of positively charged particles)
(ii) Radiations which deflects towards positive plate are called  particles (stream of negatively charged particles)
(iii) Radiations which are undeflected called -rays. (E.M. waves or photons)
Note: Exactly same results were obtained when these radiations were subjected to magnetic field.

No radioactive substance emits both  and  particles simultaneously. Also -rays are emitted after the
emission of  or -particles.
-particles are not orbital electrons they come from nucleus. The neutron in the nucleus decays into
proton and an electron. This electron is emitted out of the nucleus in the form of -rays.

Properties of  and  -rays

Features - particles  - particles  - rays

1. Identity Helium nucleus or Fast moving electron Photons (E.M. waves)
doubly ionised helium 0
( or  )
–

atom (2He4)
2. Charge + 2e –e Zero
3. Mass 4 mp (mp = mass of 4 mp me Massless
proton = 1.87  10–27
4. Speed  107 m/s 1% to 99% of speed of light Speed of light
5. Range of kinetic energy 4 MeV to 9 MeV All possible values between Between a minimum
a minimum certain value to value to 2.23 MeV
1.2 MeV
6. Penetration power (, , 1 100 10,000
) (Stopped by a paper) (100 times of ) (100 times of  upto 30
cm of iron (or Pb) sheet
7. Ionisation power ( >  > ) 10,000 100 1
8. Effect of electric or Deflected Deflected Not deflected
magnetic field
9. Energy spectrum Line and discrete Continuous Line and discrete
10. Mutual interaction with Produces heat Produces heat Produces, photo-electric
matter effect, Compton effect,
pair production
11. Equation of decay 
 dec ay
XA A 0
Z X A  Z Z 1 Y  1 e   z X A  z X a  
A4 n
Z 2 Y  2 He 4 X A



 A
Z Z' X

Various types of radioactive decay:

 Alpha Decay:- particles are helium nuclei, each consisting of two protons and two neutrons
and are commonly emitted by the heavier radioactive nuclei.
The decay of Pu239 into fissionable U235 and (2He4) particles is an example of a-decay.
239 235
94Pu 92U + 2He4
Beta () Decay: It is negatively charged particle which is due to the emission of neutrino (A) and
y radiation. Example of decay,

82 + _1e0
Gamma()Decay:  Particles are electromagnetic radiation of extremely short Wavelength and
very high frequency resulting in high energy.  Rays originate from the nucleus while X-rays
from the atom
Positron Decay: Positron decay is caused when the radioactive nucleus contains an excess of
protons. Example

7 (positron)

Law of radioactive disintegration: According to Rutherford and Soddy law for radioactive
decay is as follows. "At any instant the rate of decay of radioactive atoms is proportional to the
number of atoms present at that instant" i.e.

𝑑𝑁 𝑑𝑁 𝑑𝑁
− ∝N ⟹ − = λN ⟹ = −λ dt
dt dt N

On integrating [logN] = −λt ⟹ log = −λt

N = No e

where N = Number of atoms remains undecayed after time t, N0 = Number of atoms present
initially (i.e. at t = 0), at time t = 0, N0 – N = Number of disintegrated nucleus in time t.
This shows that radioactive decay follow exponential law.

Activity: It is defined as the rate of disintegration (or count rate) of the substance (or the
number of atoms of any material decaying per second) i.e.
𝑑𝑁
A=− ∝N
dt

A = Ao e

where A0 = Activity of t = 0, A = Activity after time t

Units of activity (Radioactivity): It's units are Becqueral (Bq), Curie

(Ci) and Rutherford (Rd)

Half life (T1/2): Time interval in which the mass of a radioactive substance or the number of it's
atom reduces to half of it's initial value is called the half life of the substance.

If N = No / 2 then t = T1/2
.
N = No e = No e / ⟹T / = =
 Mean (or average) life (  ): The time for which a radioactive material remains active is

defined as mean (average) life of that material.

𝑠𝑢𝑚𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑙𝑖𝑣𝑒𝑠 𝑜𝑓 𝑎𝑙𝑙 𝑎𝑡𝑜𝑚 1

𝛕= =
𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑎𝑡𝑜𝑚 λ

0.693 0.693
since T / = so λ =
λ T/

1 T/
= = 1.44 T / ⟹ 𝛕 = 1.44 T /
λ 0.693

Nuclear power plant:

The Power Plant which uses nuclear energy of radioactive material (Uranium or Thorium)
converted into Electrical Energy is known as Nuclear Power Plant.

Basic principal of nuclear power plant: Every power plant has its own basic principal, on the
basis of this the plant works. The Basic Principal of Nuclear Power Plant is given below:

Nuclear energy →Heat energy →Kinetic energy→ electrical energy

As we know that, the freely moving neutrons bombarded with radioactive material (U 235 or
Th232) the heat energy produced, with the help of this heat energy & water a steam produced at
high pressure & temperature. High pressure steam passes towards turbine where KE is
converted to ME. We know that, turbine & generator are mechanically coupled through this
combination an Electrical Energy is produced in Nuclear Power Plant.

Factors governing selection of site for the nuclear power plant

1. Availability of water: sufficient supply of neutral water is obvious for generating steam &
cooling purposes in nuclear power station.

2. Disposal of Waste: The wastes of nuclear power station are radioactive and may cause
severe health hazards. Because of this, special care to be taken during disposal of wastes of
nuclear power plant. The wastes must be buried in sufficient deep from earth level or these
must be disposed off in sea quite away from the sea share.
3. Distance from Populated Area: As there is always a probability of radioactivity, it is
always preferable to locate a nuclear station sufficiently away from populated area.

4. Transportation Facilities: During commissioning period, heavy equipment to be erected,

which to be transported from manufacturer site.So good railways and road ways availabilities
are required.

5. Skilled Person Requirement: For availability of skilled manpower to run & handle the
plant also good public transport should also be present at the site.

6. Near to Load Centre: As we know that generating stations are far away from thickly
populated area, so to reduce the transmission & distribution losses the plant should located near
to load centre.

7. Storage of Nuclear Material: the nuclear materials are radioactive, which are dangerous to
health to overcome this drawback a separate arrangement provided for storage of material.

8. Geographical Condition: the radioactive material are very dangerous to human health & all
living organisms, if due to earthquake chances occurs to blast the reactors to avoided this the
area should be free from earthquake

Main parts & explanation of nuclear reactor: 1. Nuclear Fuels. 2. Moderator. 3. Control
rods. 4. Reflectors 5. Shielding 6. Reactor vessel 7. Heat Exchanger 8. Coolant 9. Turbine, 10.
Condenser, 11. Cooling Tower,12. Water Treatment Chamber.

1. Nuclear Fuels: In Nuclear Power Plant for the Production of heat energy Uranium,
thorium & plutonium fuels are used.

Atomic Number: 92 Melting Point: 1408 K (1135°C or 2075°F) Boiling Point: 4404 K
(4131°C or 7468°F) Uranium is a very important element because it provides us with
nuclear fuel used to generate electricity in nuclear power stations. Naturally occurring
uranium consists of 99% uranium-238 and 1% uranium-235. Uranium-235 is the only
natural occurring fissionable fuel (a fuel that can sustain a chain reaction).
Enriched uranium: The Process used to increase the percentage of 235-U is known as
enrichment. This will help us to maintain chain reaction. Normally it contains higher
percentages (3 to 4%) of 235-U.

Plutonium: Due to the absorption of neutrons without fusion in & the plutonium is formed.
Atomic Number: 94, Melting point: 641 °C, Boiling point: 3232 °C

2. Moderator: In nuclear power plant, moderator is a device, of rod shaped. Moderator is

placed near the nuclear fuel rod. The main function of moderator in nuclear power plant
is reduce the speed of neutrons (neutron at slower speed is required to produce fission)
& increases the fission processes. Moderator rod is made up of graphite or heavy water
or beryllium material.

3. Control Rods: In nuclear power plant, the control rods are placed in between nuclear
fuel rod, moderator and then control rod. These control rods are operated either
automatically or manually.(To start or stop the chain reaction). In nuclear power plant
the main function of control rod is to control the chain reaction. If the control rod is
inserted then it absorbs the freely moving neutrons & stop the chain reaction, if it is no
inserted chain reaction is in process, means chain reaction continued. The steady rate or
 to stop the chain reaction is maintained through control rods. The control rods are made
up of cadmium, boron (alloyed with steel or aluminum).

4. Reflector: Before shielding, the reflector is placed. The reflector is used to surround the
reactor core. The reflector will also help to bounce the escaping neutrons back to the
reactor core & it conserve the nuclear fuel.

5. Shielding: Shielding is the also important part of nuclear power plant, shielding is in
other words protecting. In nuclear reactor, first one is nuclear fuel rod then moderator,
control rod & reflector. Through this shielding is provided. When the chain reaction
starts, heat energy start to produce. During this period lots of radiation or rays are
produced, these are very harmful; to avoid this shielding is provided in reactor.

6. Reactor vessel: After shielding the next layer is a reactor vessel. This vessel encloses
reactor core, reflector, shielding. It is used to protect complete nuclear reactor. Few holes
are provided in the top portion of reactor vessel to insert control rods & at lower side of this
vessel fuel & moderator assembly are placed.

7. Heat Exchanger: The main function of heat exchanger in nuclear power plant is the
boiled the cold water and produces steam at high temperature & pressure. Heat exchanger
is used in nuclear power plant, to exchange the heat i.e. it consists of one input to feed the
cold water & output to flow of hot steam. The heat exchanger receives the heat from
reactor, this heat is continuously circulated through pipe, before it is re-entered to the
reactor it is filter. By using this heat a heat exchanger boils the cold water produces steam
at high temperature & Pressure. Further this steam passes to the steam turbine for
generation of electrical power.

8. Coolant: The coolant becomes a cold metal. In coolant the gases are used like carbon
dioxide, air, hydrogen etc. the heats from the heat exchanger are re-circulated to the reactor
through pump after filtration. During filtrations the unwanted impurities in the coolant are
removed.

9. Turbine: We know that, the turbine is a mechanical device and it is mechanically

coupled with alternator. In case of nuclear power plant turbine receives steam from heat
exchange at high pressure, and it rotates at high speed then alternator also rotates, this way
electrical power produced. The exhaust steam from turbine passes to condenser for further
use.

10. Condenser: The condenser receives an exhaust hot steam from turbine; with the help of
water it is cooled. Water taken from available water sources e.g. river and is filtered in
water treatment plant. This water is re-circulated to heat exchanger through feed water
heater & Pump.

11. Cooling Tower: The cooling towers are used to convert the hot water or steam
exhausted from turbine into normal water. That is, its temperature decreases at normal
temperature.

12. Water treatment chamber: The water treatment chamber provides filter water to the
cooling tower, condenser through available water source. It also reduces unwanted
impurities in the stored water.

Types of Nuclear Reactor: The nuclear reactors are classified into four types.

1. Pressurized Water Reactor (PWR). 2. Boiling Water Reactor (BWR). 3. Advanced Gas
Cooled Reactor (AGCR). 4. Fast Breeder Reactor (FBR).

Pressurized Water Reactor (PWR): In PWR the enriched uranium fuel is used.

Construction and Working of Pressurized Water Reactor:

1. Before starting the reactor, water in the pressurizer is boiled and converted into steam by
an electric heating coil. In order to prevent the boiling of water in the core, it is kept
under the pressure of about 130-150 bar.
2. It helps in absorbing the heat by water in the liquid state in the reactor. The heat energy
absorbed by the water in the reactor is used for converting the water into steam in the
heat exchanger.
3. This steam is used in a conventional way in the steam power plant cycle. Thus, power is
not only generated through the reactor but also through the steam power plant.
4. The condenser condenses hot steam from the steam power plant and cools it down.
 5. The water coolant from the heat exchanger is recirculated to the reactor with the help of
the coolant pump.
6. These power plants are compact and their cost is reduced since it uses water as a coolant
as well as moderator. However, high pressure in the primary circuit of water-absorbing
heat in the reactor requires a stronger shell which increases its cost.
7. In these reactors, the water flowing through the reactor becomes radioactive.
8. Therefore this primary circuit must be heavily shielded to protect the operators.

Merits of PWR:

1. Water used in reactor is cheap and easily available.

2. The reactor-is compact and power density is high.
3. Fission products remain contained in the reactor and are not circulated.
4. A small number of control rods are required.

Demerits of PWR: 1.Capital cost is as high primary circuit requires strong pressure vessel.
2. In the secondary circuit the thermodynamic efficiency of this plant is quite low.
3. Fuel suffers radiation damage and, therefore its reprocessing is difficult.
4. Severe corrosion problems.
5.The plant needs to be shut down for fuel charging.
Boiling Water Reactor (BWR): Boiled Water Reactor uses enriched uranium as fuel. These
reactors do not need heat exchangers as needed in Pressurized Water Reactor (PWR) since water
is directly converted into saturated steam at about 285-degree centigrade at 70 bar pressure. For
the above reasons, this system is also called a Direct cycle Boiled Water Reactor power plant.
The feed water circulated in the reactor is converted into saturated vapor or steam by transfer of
heat energy released in the reactor core in the fission process. This steam is supplied to the steam
turbine in a conventional power plant working on the cycle. Thus, the mechanical power
developed by the turbine is converted into electrical energy by the generator. The exhaust of the
steam from the turbine is condensed into the condenser. The condensate is returned to the reactor
as feedwater by the feedwater pump.

Advantages of Boiled Water Reactor

1. It eliminates the use of a heat exchanger, pressurizer, circulating pump, and piping.
Therefore, the system is simple and cheap.
2. The efficiency of the system is high.
3. The use of a low-pressure reactor further reduces the cost of the plant.
Disadvantages of Boiled Water Reactor
1. It cannot meet sudden changes in load on the plant.
 2. It has the possibility of radioactive contamination of the steam turbine.
3. The system requires extensive safety devices against radioactive radiation which are
costly.
Advantages of Nuclear Power Station:

1. A nuclear power station occupies much smaller space compared to other conventional power
station of same capacity.
2. This station does not require plenty of water; hence it is not essential to construct plant near
natural source of water.
3. This also does not required huge quantity of fuel; for e.g. 1 kg of uranium produces a heat
which is equivalent to 4300 tonnes of coal.
4. It is possible to locate the plant near to load center
5. If bulk power is produced it is economical.
6. Clean operation, no ash is produced.
7. Area required is very less.
8. Independent of geographical conditions.
9. Saving of natural resources such as coal, oil, gas etc.
Disadvantages of Nuclear Power Plant
1. The fuel is not easily available and it is very costly.
2. Initial cost for constructing nuclear power station is quite high.
3. Erection and commissioning of this plant is much complicated.
4. The fission by products is radioactive in nature, and it may cause high radioactive pollution.
5. The maintenance cost is higher and the man power required to run a nuclear power
plant is quite higher since specialty trained people are required.
6. Sudden fluctuation of load cannot be met up efficiently by nuclear plant.
7. It is very big problem for disposal of this by products. It can only be disposed deep
inside ground or in a sea away from sea share.
8. Enrichment technology is essential for fuel processing & fabrication.
9. Maintenance cost is very high.
10. Waste disposal is problematic.
11. For variable load it is not suitable.
12. Construction is complicated.
Pressurized heavy water reactor (PHWR)
1.A pressurized heavy water reactor (PHWR) is a nuclear power reactor commonly using
enriched natural uranium as its fuel that uses heavy' water (deuterium oxide D2O) as its coolant
and moderator.

2.The heavy water coolant is kept under pressure, allowing it to be heated to higher temperatures
without boiling much as in a typical pressurized water reactor.

3.While heavy water is significantly more expensive than ordinary light water, it yields greatly
enhanced neutron economy, allowing the reactor to operate without fuel enrichment facilities
and generally enhancing the ability of the reactor to efficiently make use of alternate fuel cycle.
4.The CANDU reactor is the first and most, widely used heavy water reactor.

Advantages
1.The use of heavy water as the moderator is the key to the PHWR (pressurized heavy water
reactor) system, enabling the use of natural uranium as the fuel (in the form of ceramic UO 2),
which means that it can be operated without expensive uranium enrichment facilities.
 2. The mechanical arrangement of the PHWR, which places most of the moderator at lower
temperatures, is particularly efficient because the resulting thermal neutrons have lower energies
after successive passes through a moderator roughly equals the temperature of the moderator)
than in traditional designs, where the moderator normally is much hotter.

Disadvantages

Pressurised heavy-water reactors do have some drawbacks. Heavy water generally costs
hundreds of dollars per kilogram, though this is a trade-off against reduced fuel costs. The
reduced energy content of natural uranium as compared to enriched uranium necessitates more
frequent replacement of fuel, this is normally accomplished by use of an on-power refuelling
system. The increased rate of fuel movement through the reactor also results in higher volumes
of spent fuel than in LWRs employing enriched uranium. Since enriched uranium fuel
accumulates a lower density of fission products than enriched uranium fuel, however, it
generates less heat, allowing more compact storage.[

Nuclear fuel cycle with block diagram

1. The nuclear fuel cycle is the series of industrial processes which involves the production of
electricity from uranium in nuclear power reactors.
2. Fuel removed from a reactor, after it has reached the end of its useful life, can be reprocessed so
that most is recycled for new fuel.
3. The various activities associated with the production of electricity from nuclear reactions are
referred to collectively as the nuclear fuel cycle.
4. The nuclear fuel cycle starts with the mining of uranium and ends with the disposal of nuclear
waste. With the reprocessing of used fuel as an option for nuclear energy, the stages form true
cycle.
5. To prepare uranium for use in a nuclear reactor, it undergoes the steps of mining and milling,
conversion, enrichment and fuel fabrication. These steps make up the front end of the nuclear
fuel cycle.

6. After uranium has spent about three years in a reactor to produce electricity, the used fuel may
undergo a further series of steps including temporary storage, reprocessing, and recycling before
wastes are disposed. Collectively these steps are known as the back end of the fuel cycle.
 Safety measures for nuclear power plants are as follows

1. A nuclear power plant should be constructed away from human habitation. An exclusion
zone of 106 km radius around the plant should be provided where no public habitation is
permitted.
2. The materials to be used for the construction of a nuclear power plant should be of required
standards.
3. Waste water from nuclear power plant should be purified.
4. The nuclear power plant must be provided with such a safety system which should safely
shut down the plant as and when necessity arises.

5. There must be periodic checks to ensure that radioactivity does no t exceed the permissible
value in the environment.

6. While disposing off the wastes from the nuclear plants it should ensured that there is no
pollution of water of river or sea where these wastes are disposed.
 Energy Science and Engineering
Subject Code: KOE033/043
Unit-I Energy and its Usage
Units and scales of energy use, Mechanical energy and transport, Heat energy: Conversion between heat and
mechanical energy, Electromagnetic energy: Storage, conversion, transmission and radiation, Introduction to the
quantum, energy quantization, Energy in chemical systems and processes, flow of CO2, Entropy and temperature,
carnot and Stirling heat engines, Phase change energy conversion, refrigeration and heat pumps, Internal
combustion engines, Steam and gas power cycles, the physics of power plants. Solid-state phenomena including
photo, thermal and electrical aspects.
Unit-II Nuclear Energy

Fundamental forces in the universe, Quantum mechanics relevant for nuclear physics, Nuclear forces, energy
scales and structure, Nuclear binding energy systematics, reactions and decays, Nuclear fusion, Nuclear fission
and fission reactor physics, Nuclear fission reactor design, safety, operation and fuel cycles.

Unit-III Solar Energy

Introduction to solar energy, fundamentals of solar radiation and its measurement aspects, Basic physics of
semiconductors, Carrier transport, generation and recombination in semiconductors, Semiconductor junctions:
metal-semiconductor junction & p-n junction, Essential characteristics of solar photovoltaic devices, First
Generation Solar Cells, Second Generation Solar Cells, Third Generation Solar Cells.

Unit-IV Conventional & non-conventional energy source

Biological energy sources and fossil fuels, Fluid dynamics and power in the wind, available resources, fluids,
viscosity, types of fluid flow, lift, Wind turbine dynamics and design, wind farms, Geothermal power and ocean
thermal energy conversion, Tidal/wave/hydro power.

Unit-V Systems and Synthesis

Overview of World Energy Scenario, Nuclear radiation, fuel cycles, waste and proliferation, Climate change,
Energy storage, Energy conservation. Engineering for Energy conservation: Concept of Green Building and Green
Architecture; Green building concepts, LEED ratings; Identification of energy related enterprises that represent the
breath of the industry and prioritizing these as candidates; Embodied energy analysis and use as capacity
consumption
 UNIT-1 Energy and Its Usage

Energy is defined as the ability to do work. Energy comes in various forms. Here are 10 common types of energy
and examples of them. Energy is a scalar quantity

1. Mechanical Energy-Mechanical energy is energy that results from movement or the location of an object.
Mechanical energy is the sum of kinetic energy and potential energy. Examples: An object possessing mechanical
energy has both kinetic and potential energy, although the energy of one of the forms may be equal to zero. A
moving car has kinetic energy. If you move the car up a mountain, it has kinetic and potential energy. A book
sitting on a table has potential energy.

2. Thermal Energy-Thermal energy or heat energy reflects the temperature difference between two systems.
Example: A cup of hot coffee has thermal energy. You generate heat and have thermal energy with respect to your
environment.

3. Nuclear Energy-Nuclear energy is energy resulting from changes in the atomic nuclei or from nuclear
reactions. Example: Nuclear fission, nuclear fusion, and nuclear decay are examples of nuclear energy. An atomic
detonation or powers from a nuclear plant are specific examples of this type of energy.

4. Chemical Energy-Chemical energy results from chemical reactions between atoms or molecules. There are
different types of chemical energy, such as electrochemical energy and chemical luminescence. Example: A good
example of chemical energy is an electrochemical cell or battery.

5. Electromagnetic Energy-Electromagnetic energy (or radiant energy) is energy from light or electromagnetic
waves. Example: Any form of light has electromagnetic energy, including parts of the spectrum we can't see.
Radio, gamma rays, x-rays, microwaves, and ultraviolet light are some examples of electromagnetic energy.

6. Sonic Energy-Sonic energy is the energy of sound waves. Sound waves travel through the air or another
medium. Example: A sonic boom, a song played on a stereo, your voice.

7-Gravitational Energy-Energy associated with gravity involves the attraction between two objects based on their
mass. It can serve as a basis for mechanical energy, such as the potential energy of an object placed on a shelf or
the kinetic energy of the Moon in orbit around the Earth. Example: Gravitational energy holds the atmosphere to
the Earth.

8. Kinetic Energy-Kinetic energy is the energy of motion of a body. It ranges from 0 to a positive value. Example:
An example is a child swinging on a swing. No matter whether the swing is moving forward or backward, the
value of the kinetic energy is never negative.

9. Potential Energy-Potential energy is the energy of an object's position. Example: When a child swinging on a
swing reaches the top of the arc, she has maximum potential energy. When she is closest to the ground, her
potential energy is at its minimum (0). Another example is throwing a ball into the air. At the highest point, the
potential energy is greatest. As the ball rises or falls it has a combination of potential and kinetic energy.
10. Ionization Energy-Ionization energy is the form of energy that binds electrons to the nucleus of its atom, ion,
or molecule. Example: The first ionization energy of an atom is the energy needed to remove one electron
completely. The second ionization energy is energy to remove a second electron and is greater than that required to
remove the first electron.

High Grade Energy: Electrical and chemical energy are high-grade energy, because the energy is concentrated in
a small space. Even a small amount of electrical and chemical energy can do a great amount of work. The
molecules or particles that store these forms of energy are highly ordered and com- pact and thus considered as
high grade energy. High-grade energy like electricity is better used for high grade applications like melting of
metals rather than simply heating of water.

Low-Grade Energy: Heat is low-grade energy. Heat can still be used to do work(example of a heater boiling
water), but it rapidly dissipates. The molecules, in which this kind of energy is stored (air and water molecules),
are more randomly distributed than the molecules of carbon in a coal.

Units and Scales of energy use: The units of energy are very wide. The usage of units varies with country,
industry sector, systems such as FPS, CGS, MKS and SI, and also with generations of earlier period using FPS and
recent generations using MKS. Even technology/equipment suppliers adopt units that are different from the one
being used by the user of that technology/equipment.

Energy Units and Conversions (What are three examples of units used for energy?) AKTU 2019-20 (2 marks)

Joule (J) is the MKS unit of energy

1 kilowatt-hour is the energy of one kilowatt power flowing for one hour. (E = P t).

1 kilowatt-hour (kWh) = 3.6 x 106 J = 3.6 Mega Joules. (The energy unit used for electricity)

1 calorie of heat is the amount needed to raise 1 gram of water 1 degree Centigrade.

1 calorie (cal) = 4.18 joule (The Calories in food ratings are actually kilocalories.) Food energy is measured in
calories or kilocalories

A BTU (British Thermal Unit) is the amount of heat necessary to raise one pound of water by 1 degree Farenheit
(F).

1 British Thermal Unit (BTU) = 1055 J (The Mechanical Equivalent of Heat Relation)

1 BTU = 252 cal = 1.055 kJ

1 Quad = 1015 BTU (World energy usage is about 300 Quads/year, US is about 100 Quads/year in 1996)

1 Therm = 100,000 BTU (One Therm is equal to about 105.5 megajoules.)

1,000 kWh = 3.41 million BTU

In physics and chemistry, convenient, units is electron volts (eV)= 1.6x10-19 joule. The Hartree (the atomic unit of
energy) is commonly used in calculations.

In Explosions A gram of TNT releases 980–1100 calories upon explosion. 1 gram TNT = 4184 J.

Power Conversion: 1 horsepower (hp) = 745.7 watts

Gas Volume to Energy Conversion

1. One thousand cubic feet of gas (Mcf) -> 1.027 million BTU = 1.083 billion J = 301 kWh

2. One therm = 100,000 BTU = 105.5 MJ = 29.3 kWh

Energy Content of Fuels Coal

Coal 25 million BTU/ton

Crude Oil 5.6 million BTU/barrel Oil

Oil 5.78 million BTU/barrel = 1700 kWh / barrel

Gasoline 5.6 million BTU/barrel (a barrel is 42 gallons) = 1.33 therms / gallon

Natural gas liquids 4.2 million BTU/barrel

Natural gas 1030 BTU/cubic foot

In Australia, natural gas is sold in Cubic Meters (1m3 = 38 megajoules). In the most of the world, natural gas is
sold in gigajoules.

Various scales of energy their uses are as follows :

1. Milli (10-3) Milli refers to something that is in the 10-3 range.

Uses : A typical scientific calculator uses power in the scale of 0.1 milliWatt.
2. Micro (10-6) : Micro refers to something that is in the 10-6 range.
Uses : In measuring instrument in the fields of science and engineering.
3. Kilo (103) : Kilo refers to something that is in the 103 range.
Uses : In solar panels and batteries in Hubble space telescope
4. Nano (10-9) : Nano refers to something that is in the 10-9 range.
Uses: Electron micrograph is an example of instrument using 10-9 range.
5. Pico (10-12): Pico refers to something that is in the 10-12 range.
Uses: High precisian power supply used in laboratories to make very precise measurements of current,
voltage and resistance of specific samples.
6. Femto (10-15): Femto refers to something that is in the 10-15 range.
Uses: Certain specialized medical facilities, have a certain lasers referred to as Femtoseeond lasers.
 So, Femtosecond lasers are laser which are on' for of a second and then they go 'off'.
7. Mega (106): Mega refers to something that is in the 106range.
Uses: Used in large vehicles like submarines.
8. Giga (109): Giga refers to something that is in the 109 range.

9. Uses: Modern day mobile phones have built in storage, which a, the order of 16 GB, 64 GB which mean
mobile phone store several gigabyte.

10. Tera (1012): Tera refers to something that is in the 1012 range

Uses : Cameras and computers today uses hard disks in the scale.

11. Peta (1015) : Peta refers to something that is in the 1015 range.
Uses : Today's supercomputers operate in hundreds of petaflops.
12. Exa (1018) : Exa refers to something that is in the 1018 range.
Uses : 1018 is a kind of a quantity that is indicated with prefixna, world today uses energy in the range of
500 exajoules.
13. Zetta (1021) : Zetta refers to something that is in the 1021 range

Uses : In 2010 humanity is said to have crossed the 1 zetta byte mar! terms of data created and stored
overall. And we might be ctos: 7 zetta byte mark by 2020.

14. Yotta (1024) : Yotta refers to something that is in 1024 range. Uses: We can understand this scale when
we compare something in the scale of the galaxies and universe.
Mechanical energy and transport: Mechanical energy can be converted into heat, and heat can be converted
into some mechanical energy. Mechanical energy is the sum of potential energy and kinetic energy i.e
Mechanical energy = potential energy (mgh) + kinetic energy (1/2 mv2)
Many devices are used to convert mechanical energy to other forms of energy, e.g. an electric motor converts
electrical energy to mechanical energy, an electric generator converts mechanical energy into electrical energy and
a heat engine converts heat energy to mechanical energy. For example: satellite

Mechanical energy of the satellite-Earth system is given by = U+ K

Kinetic energy: The kinetic energy of a body is the energy that is possessed due to its motion. Let us consider a
particle is at rest when a force is applied on it so it moves with distance d and velocity become v.

Initial velocity = 0, Final velocity = v, Displacement = S

work done = F x S = ma x S ----(1)

using third equation of motion v2 = u2 + 2aS

v2 = 0 + 2aS → aS = v2/2

putting in equation 1 we get, w = ½ mv2

Transport phenomenon

A transport phenomenon is the subject which deals with the movement of different physical quantities
in any chemical or mechanical process and describes the basic principles and law of transport. It also describes the
relations and similarities among different types of transport that may occur in any system. Transport in a chemical
or mechanical process can be classified into three types:

(i)Momentum Transport: Momentum transport deals with the transport of momentum in fluids and is also
known as fluid dynamics

(ii)Energy Transport: Energy transport deals with the transport of different forms of energy in a system and is
also known as heat transfer.
 (iii)Mass Transport: Mass transport deals with the transport of various chemical species themselves

Conversion of mechanical work into heat (Joule Law)

Whenever heat is converted into mechanical work or mechanical work is converted into heat, then the ratio of
work done to heat produced always remains constant.
W  Q or W = JQ

This is Joule’s law and J is called mechanical equivalent of heat.

From W = JQ if Q = 1 then J = W. Hence the amount of work done necessary to produce unit amount of heat is
defined as the mechanical equivalent of heat. J is neither a constant, nor a physical quantity rather it is a
conversion factor which used to convert Joule or erg into calorie or kilo calories vice-versa.

When water in a stream falls from height h, then its potential energy is converted into heat and temperature of
water rises slightly.

From W = JQ

mgh = J ms t [where m = Mass, s = Specific heat of water]

# The kinetic energy of a bullet fired from a gun gets converted into heat on striking the target. By this
heat the temperature of bullet increases by t.

From W = JQ so ½ mv2 = J m s t

[where m = Mass, v = Velocity of the bullet, s = specific heat

Heat: Heat is a form of energy called thermal energy which flows from a higher temperature
body to a lower temperature body when they are placed in contact. Heat or thermal energy of a
body is the sum of kinetic energies of all its constituent particles, on account of translational,
vibrational and rotational motion.

The SI unit of heat energy is joule (J). The practical unit of heat energy is calorie. 1 cal = 4.18 J

Specific Heat: The amount of heat required to raise the temperature of unit mass the substance
through 1°C is called its specific heat. It is denoted by c or s.

Its SI unit is joule/kilogram-°C'(J/kg-°C). Their dimension is [L2T-2θ-1].

The specific heat of water is 4200 J kg-1°C-1 or 1 cal g-1 C-1, which high compared with most
other substances.

Gases have two types of specific heat

1. The specific heat capacity at constant volume (Cv). 2. The specific heat capacity at constant
pressure (Cp). Specific heat at constant pressure (Cp) is greater than specific heat constant
volume (Cv), i.e., Cp > CV .

For molar specific heats Cp – CV = R where R = gas constant and this relation is called Mayer’s
formula. The ratio of two principal specific heats of a gas is represented by γ.

Amount of heat energy required to change the temperature of any substance is given by

Q = mcΔt where, m = mass of the substance, c = specific heat of the

substance and Δt = change in temperature.

Latent Heat: The heat energy absorbed or released at constant temperature per unit mass for
change of state is called latent heat.

Heat energy absorbed or released during change of state is given by Q = mL where m = mass of
the substance and L = latent heat.

Its unit is cal/g or J/kg and its dimension is [L2T-2].

For water at its normal boiling point or condensation temperature (100°C), the latent heat of
vaporisation is L = 540 cal/g = 40.8 kJ/ mol = 2260 kJ/kg

For water at its normal freezing temperature or melting point (0°C), the latent heat of fusion is

L = 80 cal/ g = 60 kJ/mol = 336 kJ/kg

It is more painful to get burnt by steam rather than by boiling was 100°C gets converted to water
at 100°C, and then it gives out 536 heat. So, it is clear that steam at 100°C has more heat than
water 100°C (i.e., boiling of water).

After snow falls, the temperature of the atmosphere becomes very cold this is because the snow
absorbs the heat from the atmosphere to down. So, in the mountains, when snow falls, one does
not feel too but when ice melts, he feels too cold.

There is more shivering effect of ice cream on teeth as compare that of water (obtained from
ice). This is because when ice cream down, it absorbs large amount of heat from teeth.

Melting: Conversion of solid into liquid state at constant temperature is melting.

Evaporation: Conversion of liquid into vapour at all temperatures (even below boiling point) is
called evaporation.

Boiling: When a liquid is heated gradually, at a particular temperature saturated vapour pressure
of the liquid becomes equal to atmospheric pressure, now bubbles of vapour rise to the surface d
liquid. This process is called boiling of the liquid. The temperature, at which a liquid boils, is
called boiling point. The boiling point of water increases with increase in pre sure decreases with
decrease in pressure.

Sublimation: The conversion of a solid into vapour state is called sublimation.

Electromagnetic energy: electromagnetic energy is a form of energy that is reflected or

emitted from an object in the form of electrical and magnetic waves that can travel in space with
speed of light. Example: Radio Waves, Radar waves, Heat (infrared radiation), Ultraviolet Light
(This is what causes Sunburns), X-rays Short waves, Microwaves, Gamma Rays. Sunlight is also
a form of electromagnetic energy.
Electromagnetic radiation is created when an atomic particle, such as an electron is accelerated
by a potential V produced electric
ectric field. The movement produces oscillating electric and
magnetic fields. The movement produces oscillating electric and magnetic fields, which travels
at right angles to each other in a bundle of light energy called a photon. Photons travel in
harmonicc waves at the fastest speed possible in the universe. The transfer of energy by an
electromagnetic wave is at right angles to both electric and magnetic components of the wave
vibration and its rate is proportional to the vector product of their amplitud
amplitudes
es which is called
pointing vector.

Electromagnetic storage in LC circuit

LC circuits are circuits that contain inductors and capacitors. Therefore, we see that the energy
stored within an LC circuit oscillates back and forth between the electric fields of the capacitor
and the magnetic field of the inductor. This oscillation is known as electromagnetic oscillation.

The energy stored on a capacitor is U = ½ CV2

Energy in an Inductor:: When a electric current is flowing in an inductor, there is energy stored
in the magnetic field. Considering a pure inductor L, the instantaneous power which must be
supplied to initiate the current in the inductor is

Power P = Vi = Li di/ dt
 𝒅𝑰 𝟏
Energy store = ∫ 𝑷𝒅𝒕 = ∫ 𝑳𝒊 𝒅𝒕 = 𝑳𝒊𝟐
𝒅𝒕 𝟐

Electromagnetic storage device

1. Capacitor 2 Superconducting magnetic energy storage (SMES):

2. Superconducting magnetic energy storage (SMES): Superconducting magnetic energy

storage (SMES) systems store energy in a magnetic field created by the flow of direct current
through a superconducting coil. A SMES system comprises a superconducting coil in a
cryogenic enclosure. An electronic converter to match the DC power in the coil to the AC on the
grid and an electronic switch to control the flow of current into and out of the coil. The
superconducting coil is charged by applying a DC voltage which causes the current through the
coil to increase. the current reaches its working value an electronic switch isolates the DC supply
and short-circuits the coil. Because the coil has zero resistance the current continues to circulate
without losses and with no heat generation. To release the stored energy, the sv is opened and
the coil discharges through the converter, yielding AC power which can be fed to the grid. Their
primary advantage compared to other types of energy storage is their very short reaction time
and ability to provide high power for short periods. Because they can be switched on with
virtually no time delay, SMES systems can counteract abrupt changes in demand for
applications where even the shortest interruptions are unacceptable.

Storage, conversion, transmission and radiation

Electromagnetic energy can be stored in the form of an electric field or a magnetic field, the
latter typically generated by a current-carrying coil. Practical electrical energy storage
technologies include electrical double-layer capacitors (EDLCs or ultra capacitors) and
superconducting magnetic energy storage (SMES)

Magnetic reconnection is a fundamental process of electromagnetic energy conversion into

kinetic energy and heat that operates in the solar corona, astrophysical accretion disks, active
galactic nuclei, and planetary magnetospheres
Electromagnetic spectrum

At the time Maxwell predicted the existence of electromagnetic waves, the only familiar
electromagnetic waves were the visible light waves. The existence of ultraviolet and infrared
waves was barely established. By the end of the nineteenth century, X-rays and gamma rays had
also been discovered. We now know that, electromagnetic waves include visible light waves, X-
rays, gamma rays, radio waves, and microwaves, ultraviolet and infrared waves. The
classification of em waves according to frequency is the electromagnetic spectrum. There is no
sharp division between one kind of wave and the next. The classification is based roughly on
how the waves are produced and /or detected.

Gamma rays: They were discovered by Becquerel and Curie in 1896. Their wavelength is of
the order of 10-14m to 10_10m. The main sources are the natural and artificial radioactive
substances. These rays affect the photographic plate. These rays are mainly used in the treatment
of cancer disease.

X-rays: They were discovered by Roentgen in 1895. Their wavelength is of the order of 10-12m
to 10-8m. X-rays are produced, when highly energetic cathode rays are stopped by a metal target
of high melting point. They affect the photographic plate and can penetrate through the
transparent materials. They are mainly used in detecting the fracture of bones, hidden bullet,
needle, costly material etc., inside the body, and also used in the study of crystal structure.

Ultraviolet Rays: They were discovered by Ritter in 1801. Their wavelength is of the
order 109 m to 4 x 10-7m. In the radiations received from sun, major part is that of the ultraviolet
radiation. Its other sources are the electric discharge tube, carbon arc etc. These radiations are
mainly used in excitation of photoelectric effect and to kill the bacteria of many diseases.

Visible Light: This was first studied in 1666 by Newton. The radiations in the range of
wavelength from 4x10-7 m to7x10-7 m fall in the visible region.
The wavelength of the light of violet colour is the shortest, and that of red colour is the longest.
Visible light is obtained from the glowing bodies, while they are white hot. The light obtained
from the electric bulbs, sodium lamp, fluorescent tube is the visible light.

Thermal or Infrared Waves: They were discovered by Herchell in 1800. Their wavelength is
of the order of 7 x 10-7 m to 10-3 m. A body on being heated emits out the infrared waves. These
radiations have the maximum heating effect. The glass absorbs these radiations, therefore for the
study of these radiations, rock salt prism is used instead of a glass prism. These waves are
mainly used for therapeutic purpose by the doctors, because of their heating effect.

Microwaves:They were discovered by Hertz in 1888. Their wavelength is in the range of

nearly 10-4 m to m. These waves are produced by the spark discharge or magnetron valve. They
are detected by the crystal or semiconductor detector. These waves are used mainly in radar and
long distance communication.

Radio waves: They were first discovered in 1895 by Marconi. Their wavelength is in the range
of 0.1m to 105m. They can be obtained by the flow of high frequency alternating current in an
electric conductor. These waves are detected by the tank circuit in a radio receiver or
transmitter.

Applications of Electromagnetic Spectrum:The different regions of the total electromagnetic

spectrum have been put to the following uses
 1. Radiowaves are used in radar and radio broadcasting.
2. Microwaves are used in long distance wireless communications via satellites.
3. Infrared, visible and ultraviolet radiations are used to know the structure of molecules.
4. Diffraction of X-rays by crystals, gives the details of the structure of crystals.
5. The bones are opaque to X-rays but flesh is transparent. X-ray pictures of a human body
are used in medical diagnosis of fractures and cracks of bones.
6. The γ – rays are used in the study of the structure of the nuclei of atoms.
Energy Quantization: Any atom or molecule can only have certain fixed energies, energy is
quantized and an atom or molecule can exist only in certain discrete levels. Since, the minimum
energy is ½hv the molecule is always vibrating. It is never at rest. It has zero point energy,
which must be allowed for many applications.
propagation and the direction of magnetic field. Therefore, the electric field component along
the z-axis is obtained as Ez = 60 sin (0.5 × 103 x + 1.5 × 1011 t) V/m

Que. What is the importance of Quantum mechanics? (AKTU 2021)

Quantum mechanics is an important tool to understand at the theoretical level the electronic
structure of chemical compounds and the mechanism, thermodynamics, and kinetics of chemical
reactions.
Wave Particle Duality : According to Einstein, the energy of light is concentrated in small
bundles called photon. Hence, light behaves as a wave on one hand and as a particle on the other
hand. This nature of light is known as dual nature, while this property of light is known as wave
particle duality.
Wave Function and its Significance: The wave function ψ is described as mathematical
function whose variation builds up matter waves. IψI2 defines the probability density of finding
the particle within the given confined limits.
Quantization: The process of restricting the possible values of a physical quantity to a set of
discrete values is called quantization.

de Broglie's waves or matter waves: When a material particle moves in a medium, a group of
waves is associated with it due to which it shows the wave particle duality. These waves are
known as matter waves or de Broglie waves.

According to de Broglie's concept, each material particle in motion behaves as waves,

having wavelength associated with moving particle of momentum p.

Properties of Matter Waves:

1.The de-Broglie wave length of a wave associated with a fast moving particle is less than the
wavelength associated with a slow moving particle.

2.The de-Broglie wave length of a wave associated with a particle at rest is infinite matter waves
is valid only when the material particles are in motion.

3.The de-Broglie wavelength does not depend upon the charge of the particle.

4.The velocity of a matter wave is greater than the velocity of electromagnetic wave

5.The velocity of matter wave depends upon the velocity of the material particle.

6.The wave and particle aspects of matter never appear simultaneously in the same experiment.
Schrodinger's Wave Equation: This wave equation is a fundamental equation in quantum
mechanics and describes the variation of wave function in space and time.
Temperature: Temperature of a body is the degree of hotness or coldness of the body. A device
which is used to measure the temperature is called a thermometer.

Branch of Physics dealing with production and measurement temperature close to 0 K is known
as cryagenics, while that deal with the measurement of very high temperature is called
pyrometer. Temperature of the core of the sun is 107 K while that of its surface 6000 K.

NTP or STP implies 273.15 K (0°C = 32°F).

Different Scale of Temperature

1. Celsius Scale: In this scale of temperature, the melting point ice is taken as 0°C and the
boiling point of water as 100°C and space between these two points is divided into 100 equal
parts

2. Fahrenheit Scale: In this scale of temperature, the melt point of ice is taken as 32°F and the
boiling point of water as 211 and the space between these two points is divided into 180 equal
parts.

3. Kelvin Scale: In this scale of temperature, the melting pouxl ice is taken as 273 K and the
boiling point of water as 373 K the space between these two points is divided into 100 equal
parts.

𝐶 𝐹 − 32 𝐾 − 273 𝑅
= = =
100 180 100 80

or
𝐶 𝐹 − 32 𝐾 − 273 𝑅
= = =
5 9 5 4

Thermodynamic System: An assembly of an extremely large number of particles whose state

can be expressed in terms of pressure, volume and temperature, is called thermodynamic system.

Thermodynamic system is classified into the following three systems

(i) Open System: It exchange both energy and matter with surrounding.

(ii) Closed System: It exchanges only energy (not matter) with surroundings.

(iii) Isolated System: It exchanges neither energy nor matter with the surrounding.

Thermodynamic equilibrium: A system is in thermodynamic equilibrium if the temperature

and pressure at all points are same; there should be no velocity gradient; the chemical
equilibrium is also necessary. Thus, for attaining a state of thermodynamic equilibrium the
following three types of equilibrium states must be achieved:
1. Thermal equilibrium The temperature of the system does not change with time and has same
value at all points of the system.

2. Mechanical equilibrium There are no unbalanced forces within the system or between the
surroundings. The pressure in the system is same at all points and does not change with respect
to time.

3. Chemical equilibrium No chemical reaction takes place in the system and the chemical
composition which is same throughout the system does not vary with time.

Internal energy (∆U): The total energy possessed by any system due to molecular motion
and molecular configuration, is called its internal energy. It is the heat energy stored in a gas.
If a certain amount of heat is supplied to a gas the result is that temperature of gas may increase
or volume of gas may increase thereby doing some external work or both temperature and
volume may increase; but it will be decided by the conditions under which the gas is supplied
heat. If during heating of the gas the temperature increases its internal energy will also increase.
Joule’s law of internal energy states that internal energy of a perfect gas is a function of
temperature only. In other words, internal energy of a gas is dependent on the temperature
change only and is not affected by the change in pressure and volume.

Zeroth Law of Thermodynamics: According to this law, two systems in thermal equilibrium
with a third system separately are in thermal equilibrium with each other. Thus, if A and B are
separately in equilibrium with C, that is if TA = TC and TB = TC, then this implies that TA = TB
i.e., the systems A and B are also in thermal equilibrium.

First Law of Thermodynamics: Heat given to a thermodynamic system (ΔQ) is partially

utilized in doing work (ΔW) against the surrounding and the remaining part increases the internal
energy (ΔU) of the system. Therefore, ΔQ = ΔU + ΔW

First law of thermodynamics is the principle conservation of energy

For isothermal process, change in internal energy is zero (ΔU = 0). Therefore, ΔQ = ΔW

For adiabatic process, no exchange of heat takes place, i.e., ΔQ = O. Therefore, ΔU = – ΔW

In adiabatic process, if gas expands, its internal energy and hence, temperature decreases and
vice-versa.

For isochoric process, work done is zero, i.e., ΔW = 0, therefore ΔQ = ΔU

Thermodynamic Processes: A thermodynamic process is said to take place when some

changes’ occur in the state of a thermodynamic system i.e., the thermodynamic parameters of the
system change with time.

(i) Isothermal Process: when a process taking place in a thermodynamic system at constant
temperature is called an isothermal process. Isothermal processes are very slow processes.

These process follows Boyle’s law, according to which PV = constant

Since dU = nCvdT as dT = 0 so dU = 0, i.e., internal energy is constant.

From first law of thermodynamic dQ = dW, i.e., heat given to the system is equal to the work
done by system surroundings.

Work done W = μRT log (V2 / V1) = 2.3026μRT logl0 (V2 / V1) where, μ = number of moles, R
= ideal gas constant, T = absolute temperature and V1 V2 are initial volumes and final volume`
Examples (a) Melting process is an isothermal change, because temperature of a substance
remains constant during melting.
(b) Boiling process is also an isothermal operation.
Adiabatic Process: A process taking place in a thermodynamic system for which there is no
exchange of heat between the system and its surroundings. Adiabatic processes are very fast
processes. This process follows Poisson’s law, according to which

𝑇ϒ
𝑃𝑉 ϒ = 𝑇𝑉 ϒ = = constant
𝑃ϒ
Since dQ = nCdT, Cadi = 0 as dQ = 0, i.e., molar heat capacity for adiabatic process is zero.
From first law, 0 = ΔU + ΔW hence dU = – dW, i.e., work done by the system is equal to
decrease in internal energy. When a system expands adiabatically, work done is positive and
hence internal energy decrease, i.e., the system cools down and vice-versa.

Work done in an adiabatic process is W = 𝑊 = (𝑇1 − 𝑇2)

ϒ

Examples (a) Sudden compression or expansion of a gas in a container with perfectly non-
conducting wall.
(b) Sudden bursting of the tube of a bicycle tyre.
(c) Propagation of sound waves in air and other gases.
Isobaric Process: A process taking place in a thermodynamic system at constant pressure is
called an isobaric process.
Molar heat capacity of the process is Cp and dQ = nCpdT.
Internal energy dU = nCv dT
From the first law of thermodynamics dQ = dU + dW dW = pdV = nRdT
Process equation is V / T = constant. Hence P- V curve is a straight line parallel to volume axis.
Isochoric Process: A process taking place in a thermodynamics system at constant volume is
called an isochoric process.
dQ = nCvdT, molar heat capacity for isochoric process is Cv.
Volume is constant, so dW = 0,
Process equation is P / T = constant. P- V curve is a straight line parallel to pressure axis.
Cyclic Process: When a thermodynamic system returns to initial state after passing through
several states, then it is called cyclic process. Efficiency of the cycle is given by

𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒
𝜂=
Heat supplied

Work done by the cycle can be computed from area enclosed cycle on P- V curve.
Second Law of Thermodynamics: The second law of thermodynamics gives a fundamental
limitation to the efficiency of a heat engine and the coefficient of performance of a refrigerator.
It says that efficiency of a heat engine can never be unity (or 100%). This implies that heat
released to the cold reservoir can never be made zero.

Kelvin’s Statement: It is impossible to obtain a continuous supply of work from a body by

cooling it to a temperature below the coldest of its surroundings.

Clausius’ Statement: It is impossible to transfer heat from a lower temperature body to a higher
temperature body without use of an extemal agency.
Planck’s Statement: It is impossible to construct a heat engine that will convert heat completely
into work. All these statements are equivalent as one can be obtained from the other.

Equivalence of Clausius Statement to the Kelvin-Planck Statement: Consider a higher

temperature reservoir T1 and low temperature reservoir T2. Fig. shows a heat pump which
requires no work and transfers an amount of Q2 from a low temperature to a higher temperature
reservoir (in violation of the Clausius statement). Let an amount of heat Q1 (greater than Q2) be
transferred from high temperature reservoir to heat engine which develops a net work, W = Q 1 –
Q2 and rejects Q2 to the low temperature reservoir. Since there is no heat interaction with the low
temperature, it can be eliminated. The combined system of the heat engine and heat pump acts
then like a heat engine exchanging heat with a single reservoir, which is the violation of the
Kelvin-Planck statement.

Entropy: Entropy is the measure of a system's thermal energy per unit temperature that is
unavailable for doing useful work. Because work is obtained from ordered molecular motion, the
amount of entropy is also a measure of the molecular disorder, or randomness, of a system.
 The Second Law of Thermodynamics states that the state of entropy of the entire universe is an
isolated system. Entropy in the universe can never be negative.

When a small amount of heat dQ is added to a substance at temperature T, without changing its
temperature appreciably, the entropy of the substance is given by

dS = dQ/ T Joules per Kelvin

The term dQ/ T is called entropy and its change from state 1 to state 2 during reversible process
is given as,

When heat is removed, the entropy decreases, when heat is added the entropy increases.

The entropy of any substance is a function of the condition of the substance. It is a physical
property of the substance. For an ideal gas it is a function of its temperature and volume, and for
a solid and liquid it is a function of its temperature and internal structure. The entropy is
independent of the past history of the.

Principle of entropy: According to this principle, entropy of an isolated system cither

increases or in the limit remains constant.
An isolated system does not undergo any energy interaction (i .e., work or heat energy) with
its surroundings, and the total energy of all the possible states remains constant. Therefore for
an isolated system, dQ=0

(ds)Isolated ≥ 0

(i)If the process is reversible, (ds) Isolated = 0

(ii) if the process is irreversible (ds)Isolated > 0

From above we see that the entropy of an isolated system can never decrease. It always
increases with every irreversible process and remains constant during a reversible process. This
is called principle of entropy Increase.
Reversible process : A reversible process is one which can be reversed in such a way that all
changes occurring in the direct process are exactly repeated in the opposite order and inverse
sense and no change is left in any of the bodies taking part in the process or in the surroundings.

For example if heat is absorbed in the direct process, the same amount of heat should be given
out in the reverse process, if work is done on the working substance in the direct process then the
same amount of work should be done by the working substance in the reverse process.

The conditions for reversibility are

(i) There must be complete absence of dissipative forces such as friction, viscosity, electric
resistance etc.
(ii) The direct and reverse processes must take place infinitely slowly.
(iii) The temperature of the system must not differ appreciably from its surroundings.
Some examples of reversible process are

(a) All isothermal and adiabatic changes are reversible if they are performed very slowly.

(b) When a certain amount of heat is absorbed by ice, it melts. If the same amount of heat is
removed from it, the water formed in the direct process will be converted into ice.

(c) An extremely slow extension or contraction of a spring without setting up oscillations.

(d) When a perfectly elastic ball falls from some height on a perfectly elastic horizontal plane,
the ball rises to the initial height.

(e) If the resistance of a thermocouple is negligible there will be no heat produced due to
Joule’s heating effect. In such a case heating or cooling is reversible. At a junction where a
cooling effect is produced due to Peltier effect when current flows in one direction and equal
heating effect is produced when the current is reversed.

(f) Very slow evaporation or condensation. It should be remembered that the conditions
mentioned for a reversible process can never be realised in practice. Hence, a reversible process
is only an ideal concept. In actual process, there is always loss of heat due to friction,
conduction, radiation etc.
Irreversible process: Any process which is not reversible exactly is an irreversible process. All
natural processes such as conduction, radiation, radioactive decay etc. are irreversible. All
practical processes such as free expansion, Joule-Thomson expansion, electrical heating of a
wire are also irreversible. Some examples of irreversible processes are given below

(i) When a steel ball is allowed to fall on an inelastic lead sheet, its kinetic energy changes
into heat energy by friction. The heat energy raises the temperature of lead sheet. No
reverse transformation of heat energy occurs.
(ii) (ii) The sudden and fast stretching of a spring may produce vibrations in it. Now a part
of the energy is dissipated. This is the case of irreversible process.
(iii) Sudden expansion or contraction and rapid evaporation or condensations are examples
of irreversible processes.
(iv) Produced by the passage of an electric current through a resistance is irreversible.
(v) Heat transfer between bodies at different temperatures is also irreversible.
(vi) Joule-Thomson effect is irreversible because on reversing the flow of gas a similar
cooling or heating effect is not observed.
Heat reservoir or thermal energy reservoir: It is defined as the source of infinite heat energy
and a finite amount of heat absorbed or heat rejected from the heat reservoir will not have any
effect on its temperature i.e., heat reservoir is maintained at a constant temperature.

Source: 1.Thermal reservoir which supplies heat to a system is known as source.

2. This is at high temperature, e.g., boiler furnace, combustion chamber. nuclear reactor etc

Sink: 1. Thermal reservoir which absorbs heat from a system is known as sink.
2. This is at low temperature, e.g., ocean, river, atmospheric air.

Carnot Engine & Carnot cycle: It is a theoretical engine which works on the Carnot cycle. The
cycle was first suggested by a French engineer Sadi Carnot in 1824 which works on reversible
cycle and is known as Carnot cycle. Any fluid may be used to operate the Carnot cycle which is
performed in an engine cylinder the head of which is supposed alternatively to be perfect
conductor or a perfect insulator of a heat. Heat is caused to flow into the cylinder by the
application of high temperature energy source to the cylinder head during expansion, and to flow
from the cylinder by the application of a lower temperature energy source to the head during
compression.
The assumptions made for describing the working of the Carnot engine are as follows:

(i) The piston moving in a cylinder does not develop any friction during motion.

(ii) The walls of piston and cylinder are considered as perfect insulators of heat.

(iii)The cylinder head is so arranged that it can be a perfect heat conductor or perfect heat
insulator. (iv) The transfer of heat does not affect the temperature of source or sink.

(v) Working medium is a perfect gas and has constant specific heat.

(vi)Compression and expansion are reversible.

Following are the four stages of Carnot cycle:

Stage 1. (Process 1-2). Hot energy source is applied. Heat Q1 is taken in while the fluid expands
isothermally and reversibly at constant high temperature T1.
Stage 2. (Process 2-3). The cylinder becomes a perfect insulator so that no heat flow takes place.
The fluid expands adiabatically and reversibly whilst temperature falls from T1 to T2.

Stage 3. (Process 3-4). Cold energy source is applied. Heat Q2 flows from the fluid whilst it is
compressed isothermally and reversibly at constant lower temperature T2.

Stage 4. (Process 4-1). Cylinder head becomes a perfect insulator so that no heat flow occurs.
The compression is continued adiabatically and reversibly during which temperature is raised
from T2 to T1. The work delivered from the system during the cycle is represented by the
enclosed area of the cycle. Again for a closed cycle, according to first law of the
thermodynamics the work obtained is equal to the difference between the heat supplied by the
source (Q1) and the heat rejected to the sink (Q2).
OR 𝜂 =1−

Note : The efficiency of an actual engine is much lesser than that of an ideal engine. Actually the
practical efficiency of steam engine is about (8-15)% while that of a petrol engine is 40%. The
efficiency of a diesel engine is maximum and is about (50-55)%.

Carnot theorem: The efficiency of Carnot’s heat engine depends only on the temperature of
source (T1) and temperature of sink (T2), i.e

𝑇2
𝜂 =1−
T1

Carnot stated that “no heat engine working between two given temperatures of source and
sink can be more efficient than a perfectly reversible engine (Carnot engine) working
between the same two temperatures”. Carnot's reversible engine working between two given
temperatures is considered to be the most efficient engine

Carnot vapour power cycle with T-S diagram.

It is an ideal cycle having highest thermodynamic efficiency. Carnot cycle is shown in Fig.
Various processes of Carnot cycle are as follows:
Process 1-2: It is reversible isothermal heat addition process in the boiler.

Process 2-3: It is reversible adiabatic expansion process in steam turbine.

Process 3-4: It is reversible isothermal heat rejection process in the condenser.

Process 4-1: It is reversible adiabatic compression process or pumping process in feed water
pump.

Efficiency :

𝑡ℎ𝑒𝑟𝑚𝑎𝑙 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 𝜂 = = =1−

W3 Means work done in process 3 to 4 so W3 = Q34 and W1= Q12

𝑄34
𝜂 = 1−
Q12

Assuming entropy at point 1, 2, 3, 4 is S1, S2, S3, S4

𝑄34 = 𝑇 𝑑𝑆 = 𝑇2(𝑆4 − 𝑆3) = 𝑇(𝑆3 − 𝑆4)𝑑𝑢𝑒 𝑡𝑜 𝑐𝑜𝑝𝑟𝑒𝑠𝑠𝑖𝑜𝑛 𝑎𝑛𝑑 𝑄12 = 𝑇1 𝑑𝑆

= 𝑇(𝑆2 − 𝑆1)

From fig S1=S4 and S2= S3

 ( )
𝜂 =1− ( )
so it becomes

𝑇2(𝑆3 − 𝑆4)
𝜂 =1−
𝑇1(𝑆3 − 𝑆4)

𝑇2
𝜂 =1−
T1

Stirling Engine : It is a heat engine which is operated by a cyclic compression and expansion of
air or other gas at different temperatures such that there is a net conversion of heat energy to
mechanical work. It works on Stirling cycle.

Stirling cycle: Stirling cycle consists of two isothermal and two constant volume processes. It is
externally reversible cycle. Heat rejection and heat addition takes place at constant volume. This
cycle has mean effective pressure greater than Carnot cycle. But efficiency in ideal case equal to
the Carnot cycle.

From Fig. 1. it is clear that amount of heat addition and rejection during constant volume
process is same. In practical use Stirling cycle incorporated with a heat exchanger which
absorb the heat rejected during constant volume process and supplies back to the cycle in
heat addition during constant volume. So amount of heat transfer through heat exchanger
absorb heat and heat supplied back to cycle is same. But efficiency of heat exchanger is not
100%. So efficiency of Stirling cycle will be less than the Carnot cycle.
Refrigeration : Refrigeration means the cooling or removal of heat from a system. It is science
of producing and maintaining temperatures below the of the surrounding atmosphere i.e ,
removal of heat from a substance under controlled conditions.
The equipment employed to maintain the system at a low temperature is termed as
refrigerating system and the system which is kept at lower temperature is called refrigerated
system.

TYPES OF REFRIGERATION

Refrigeration is classified as based on working substance used

i.Air refrigeration system (Bell-Coleman cycle)

ii. Water refrigeration system

iii. Ice refrigeration system

iv. Refrigeration by special fluid

Refrigeration effect:

The rate at which the heat is absorbed in a cycle of from the interior space to be cooled is
called refrigeration effect. It is defined as the quantity of heat removed to the time taken. It is
also called as the capacity of a refrigerator.

The standard unit of refrigeration is ton refrigeration or simply ton denoted by TR.

Refrigerator: A refrigerator or heat pump is basically a heat engine run in reverse direction.
It operates as a reversed heat engine. Its duty is to extract heat as much as possible from cold
body and deliver the same to high temperature body/surroundings. It essentially consists of
three parts:
1.Source : At higher temperature T1
2.Sink : At lower temperature T2
3.Working substance : It is called refrigerant liquid ammonia as a working substance. The
working substance takes heat Q2 from a sink (contents of refrigerator) at lower temperature,
has a net amount of work done W on it by an external agent (usually compressor of
refrigerator) and gives out a larger amount of heat Q1 to a hot body at temperature T1 (usually
atmosphere). Thus, it transfers heat from a cold to a hot body at the expense of mechanical
energy supplied to it by an external agent. The cold body is thus cooled more and more.
The performance of a refrigerator is expressed by means of “coefficient of performance”,
which is defined as the ratio of the heat extracted from the cold body to the work needed to
transfer it to the hot body.

Coefficient of performance, (COP)ref = =

From the first law of thermodynamics, ΔQ = W so Q1 - Q2=W

Hence (COP)ref =

A perfect refrigerator is one which transfers heat from cold to hot body without doing work
i.e. W = 0 so that Q2Q1 and hence (COP)ref 

Applications of Refrigeration:
1. Making of ice.
2.It is used in transportation [cod at a required temperature.
3.It is used in industrial and comfort air conditioning.
4.It is in processing food products and beverages.
Heat pump: A heat pump is a reversed heat engine. It receives heat from a low temperature
reservoir and rejects it to a high temperature reservoir. This transfer of heat from n low
temperature body high temperature one is none spontaneous process and that calls for the help of
external work which is supplied to the heat pump. A heat pump extracts Q2 amount of heat from
the low temperature T2 and deliver Q1 amount of heat to the high temperature by consuming W
amount of external work.

Coefficient of performance, (COP)HP = =

From the first law of thermodynamics, ΔQ = W so Q1 - Q2=W

Hence (COP)HP =

Heat engine:
A heat engine is a device which transforms the chemical energy of a fuel into thermal energy
and uses this energy to produce mechanical work continuously through a cyclic process.
The essential parts of a heat engine are
Source: It is a reservoir of heat at high temperature and infinite thermal capacity. Any
amount of heat can be extracted from it.
Working substance: Steam, petrol etc.
Sink : It is a reservoir of heat at low temperature and infinite thermal capacity. Any amount of
heat can be given to the sink.

The working substance absorbs heat Q1 from the source, does an amount of work W, returns the
remaining amount of heat to the sink at T2 temperature and comes back to its original state and
there occurs no change in its internal energy. By repeating the same cycle over and over again,
work is continuously obtained.

The performance of heat engine is expressed by means of “efficiency ” which is defined as the
ratio of useful work obtained from the engine to the heat supplied to it.

or 𝜂 = 1 −

A perfect heat engine is one which converts all heat into work i.e. Q1  W so that Q2 = 0 and
hence

=1. But practically efficiency of an engine is always less than 1

Heat engine is classified into two types-

(a)External combustion engine (b) internal combustion engine

Comparison between external combustion engine and internal combustion engine:

S. No. External combustion engine Internal combustion engine

1. Combustion of air-fuel is outside the engine Combustion of air-fuel is inside the engine
cylinder (in a boiler)
cylinder (in a boiler)

2. The engines are running smoothly and silently Very noisy operated engine

due to outside combustion

3. Higher ratio of weight and bulk to output It is light and compact due to lower ratio of

due to presence of auxiliary apparatus like weight and bulk to output.

boiler and condenser. Hence it is heavy

and cumbersome.

4. Working pressure and temperature inside Working pressure and temperature inside

the engine cylinder is low; hence ordinary the engine cylinder is very much high
alloys are
hence special alloys are used
used for the manufacture of engine cylinder
and

its parts.

5. It can use cheaper fuels including solid High grade fuels are used with proper filtration

6. Lower efficiency about 15-20% Higher efficiency about 35-40%

7. Higher requirement of water for dissipation of Lesser requirement of water

energy through cooling system

8. High starting torque IC engines are not self-starting

External combustion engine: In this engine, the products of combustion of air and fuel transfer
heat to a second fluid which is the working fluid of the cycle.

Examples: In the steam engine or a steam turbine plant, the heat of combustion is employed to
generate steam which is used in a piston engine (reciprocating type engine) or a turbine (rotary
type engine) for useful work.

In a closed cycle gas turbine, the heat of combustion in an external furnace is transferred to gas,
usually air which the working fluid of the cycle.

Internal combustion engine (IC Engines): The engines in which the combustion of air and
fuels takes place inside the engine or within the cylinder are known as internal combustion
engines.
Types of Internal combustion engine (IC Engines)

It can be classified into the following types:

1. According to the basic engine design

(a) Reciprocating engine (Use of cylinder piston arrangement),

(b) Rotary engine (Use of turbine)

2. According to the working cycle- (a) Otto cycle (constant volume cycle) engine, (b) diesel
cycle (constant pressure cycle) engine, (c) dual combustion cycle (semi diesel cycle) engine.

3. According to the number of strokes per cycle-

(a) Four stroke and (b) Two stroke engine

4. According to the type of fuel used-

(a) Petrol engine or gasoline engine,

(b) Diesel engine,

(c) Gas engine (CNG, LPG)

(d) Alcohol engine (ethanol, methanol etc)

5. According to the fuel supply and mixture preparation-

(a) Carburetted type (fuel supplied through the carburettor)

(b) Injection type (fuel injected into inlet ports or inlet manifold, fuel injected into the cylinder
just before ignition).

6. According to the method of igniting the fuel-( Ignition)

(a) Spark ignition engine (SI engine),

(b) compression ignition engine(CI engine) and

(c) hot spot ignition engine

7. According to the number of cylinder- (a) Single cylinder and (b) multi-cylinder engine

8. According to Method of cooling- (i) water cooled engine (ii) air cooled engine

9. According to Speed of the engine- Slow speed, medium speed and high speed engine

10. According to Cylinder arrangement-Vertical engines, horizontal engines, inline engines,

V-type engines, radial engines, opposed cylinder or piston engines.

11. According to Valve or port design and location- Overhead (I head), side valve (L head); in
two stroke engines: cross scavenging, loop scavenging, uniflow scavenging.

12. According to Method governing- Hit and miss governed engines, quantitatively governed
engines and qualitatively governed engine.

13. According to Application- Automotive engines for land transport, marine engines for
propulsion of ships, aircraft engines for aircraft propulsion, industrial engines, and prime movers
for electrical generators.

Internal combustion engine (IC Engines): Main components of IC engines are

1. Cylinder. It is one of the most important part of the engine, in which the piston movesto and
 fro in order to develop power. Generally, the engine cylinder has to withstand a high
pressure (more than 50 bar) and temperature (more than 2000°C).
2. Cylinder head: It is fitted on one end of the cylinder, and acts as a cover to close the
cylinder bore. Generally, the cylinder head contains inlet and exit valves for admitting fresh
charge and exhausting the burnt gases. In petrol engines, the cylinder head also contains a
spark plug for igniting the fuel-air mixture, towards the end of compression stroke. But in
diesel engines, the cylinder head contains nozzle (i.e. fuel valve) for injecting the fuel into
the cylinder.
3. Piston: It is considered as the heart of an I.C. engine, whose main function is to transmit the
force exel1ed by the burning of charge to the connecting rod. The pistons are generally made
of aluminium alloys which are light in weight.
4. Piston rings: These are circular rings and made of special steel alloys which retain elastic
properties even at high temperatures. The piston rings are housed in the circumferential
grooves provided on the outer surface of the piston. Generally, there are two sets of rings
mounted for the piston.
5. Connecting rod: It is a link between the piston and crankshaft, whose main function is to
transmit force from the piston to the crankshaft.
6. Crankshaft: It is considered as the backbone of an I.C. engine whose function is to convert
the reciprocating motion of the piston into the rotary motion with the help of connecting rod.
This shaft contains one or more eccentric portions called cranks.
7. Crank case: It is a cast iron case, which holds the cylinder and crankshaft of an I.C. engine.
It also serves as a sump for the lubricating oil. The lower portion of the crank case is known
as bed plate, which is fixed with the help of bolts.
8. Flywheel: It is a big wheel, mounted on the crankshaft, whose function is to maintain its
speed constant. It is done by storing excess energy during the power stroke, which is
returned during other strokes.

Terminology used in IC engine:

1.Cylinder Bore: It is the nominal inner diameter of the working cylinder It is represented by D.

2.Piston Area : It is the area of a circle of diameter equal to the cylinder bore.
3.Stroke : The distance travelled by piston from top dead centre to bottom dead centre is known
as stroke.

4. Bottom Dead Centre (BDC): It is the dead centre when the piston nearest to the crankshaft
or lowest position of the piston towards crank end side of cylinder.

5. Top Dead Centre (TDC): It is the dead centre when the piston farthest from the crankshaft or
top most position of the piston towards cover end side of cylinder.

6. Displacement Volume (or Piston Swept Volume) :

This is the volume swept by the piston moving from one dead centre to other. It is calculated as
the product of piston area and stroke.
vs = Piston area (A) x Stroke (L)

= 𝐷 L

7.Clearance Volume : The volume contained in the cylinder above top of the piston when the
piston is at top dead centre is called Clearance volume.

8. Cylinder Volume : The sum of swept volume and clearance volume is known as Cylinder
volume. V = Vs + Vc
9. Compression Ratio r: This is defined as the ratio of the volume at the beginning of
compression to the volume at the end of compression.

Vs + Vc Vs
r= =1+
Vc Vc
Working of internal combustion:

Working of internal combustion four stroke spark ignition engine is as follows :

Suction Stroke :
1.Suction stroke starts when the piston is at top dead centre position and about to move toward
bottom dead centre.

2.During this stroke, inlet valve is open and outlet valve is closed.

3.Due to the suction created by downward motion of the piston, charge consists of mixture of
air and fuel drawn into the cylinder.

4.At the end of suction stroke, both the inlet and outlet valves are closed.
 Compression Stroke:
1. The fresh charge taken into the cylinder during the suction stroke is compressed during the
return stroke of the piston.

2. In this stroke both the inlet and outlet valves remain closed. Just before end of the
compression stroke, mixture of air ignited with the help of spark plug.

3. Burning takes place when the piston is almost at top dead center.

5. During the burning process chemical energy of the charge is converted into sensible energy

and producing a temperature rise of about 20000c and pressure is also increased.

Expansion or Working Stroke:

1. Due to high pressure burnt gages forces the piston toward the dead centre so power is obtain
during this stroke.

2. Both pressure and temperature decreases during this stroke. In this stroke, both the valves
remain closed.

Exhaust Stroke: In this stroke Inlet valve is dosed and outlet valve is open. Piston moving from
bottom dead centre to top dead centre and burn gases sweep out from the cylinder.

Comparisons between SI engine and CI engine

S. No. Description Spark ignition engine (SI engine) Compression ignition engine(CI engine)
1. Basic cycle Otto cycle Diesel cycle
2. Fuel used Gasoline (petrol) Diesel
3. Ignition Spark plug is used. Self ignition due to high pressure and
temperature caused by compression of
4. Compression ratio 6 to 10 14 to 22
5. Weight Lighter Heavier
6. Speed High speed Low speed
7. Efficiency Lower efficiency due to low Higher efficiency due to high compression
compression ratio. ratio.

DEFINITION OF A CYCLE: A cycle is defined as a repeated series of operations occurring

in a certain order. It may be repeated by repeating the processes in the same order. The cycle
may be of imaginary perfect engine or actual engine. The former is called ideal cycle and the
latter actual cycle. In ideal cycle all accidental heat losses are prevented and the working
substance is assumed to behave like a perfect working substance.

Steam Power cycles: These are the cycles which uses steam as their working fluid. Rankine
cycle is the example of steam power cycle.

Rankine cycle: These are the cycle which uses steam as their working fluid. Rankine cycle is
the example of steam power cycle. Rankine cycle is the theoretical steam cycle on which turbine
works. Rankine cycle is shown in Fig. It consists of following processes:

Process 1-2 : Adiabatic expansion (in turbine).

Process 2-3 : Isobaric heat release (in condenser).
Process 3-4 : Adiabatic pumping (in pump).
Process 4-1 : Isobaric heat addition (in boiler).

Fig. T-s diagram of Rankine cycle

Gas Power Cycles: These are the cycles which use air or gas as their working fluid.

Otto cycle, Diesel cycle, Brayton cycles are the examples of gas power cycles.

Brayton Cycle : It is a theoretical cycle for gas turbines and also known as constant pressure
cycle for a perfect gas. The basic components of a Brayton cycle are shown in Fig.

There occur two isentropic processes and two constant pressure processes. Compression and
expansion of working fluid is done by isentropic process while addition and rejection of heat is
done at constant pressure. Brayton cycle P-V& T-s diagram respectively is
Brayton cycle shows has two adiabatic and two constant pressure processes:
Process 1-2 adiabatic compression
Process 2-3: Constant pressure heat addition
Process 3-4: Adiabatic expansion
Process 4-1: Constant pressure heat rejection

Now, Work done/ cycle = Heat added/cycle —Heat rejected/cycle

Heat added in (process 2-3) Q2-3 = m Cp (T3-T2)

Heat rejected in( process 4-1)Q4-1= m Cp (T4-T1)

Work done / cycle = = m Cp (T3-T2)- m Cp (T4-T1)

Efficiency of Brayton Cycle:

work done per cycle m Cp (T3 − T2) − m Cp (T4 − T1)

𝜂= =
heat addition per cycle m Cp (T3 − T2)

(T4 − T1)
𝜂 =1−
(T3 − T2)

ϒ 1
ϒ
T2 P2 ϒ
From process 1-2, = = 𝒓𝒑 = T1 (rp) ϒ where p2 / p1 is called pressure ratio rp.
T1 P1

ϒ
In process 3-4, 𝑻𝟑 = T4 (rp) ϒ

Hence
 (T4 − T1) 1
𝜂 =1− ϒ ϒ =1− ϒ
T4 (rp) ϒ − T1 (rp) ϒ (rp) ϒ
Diesel cycle- Thermodynamic cycle for low speed CI/diesel engine -Reversible adiabatic
compression and expansion process -Constant pressure heat addition (combustion) and heat
rejection process (exhaust) following figure show the diesel cycle.
For same compression ratio and same heat input
Problem 1: A heat engine receives heat at the rate of 1500 kJ/min and gives an output of 8.2
kW. Determine: (i) The thermal efficiency (ii) The rate of heat rejection.
Problem6. An ice tray contains 500 g of water. Calculate the change in entropy of the water
as it freezes completely and slowly at 00C.

Solution: The water freezes at 0 oC = 273 K. ΔS = ΔQ/T

ΔQ = -mL, m = mass of water, L = latent heat of fusion = 333000 J/kg.

ΔS = -(0.5 kg)(333000J /kg)/273 K = -610 J/K.

FUELS &FUEL INJECTION

In IC engines, the chemical energy contained in the fuel is converted into mechanical power by
burning (oxidizing) the fuel inside the combustion chamber of the engine.

Fuels suitable for fast chemical reaction have to be used in IC engines, they are following types-

(a) Hydrocarbons fuels derived from the crude petroleum by proper refining process such as
thermal and catalytic cracking method, polymerisation, alkylation, isomerisation, reforming and
blending.
 (b) Alternative fuels such as-Alcohols (methanol, ethanol)

Natural gas (methane)

LPG (propane, butane)

Hydrogen

Factors for designing a power plant: Following factors should consider while designing a
power plant:

1. Availability of cooling water (if coaling towers are used the possibility of adequate maake
up water)
2. Availability of fuel (water, rail or pipe connection to the fuel source, and the cost of fuel
transport).

3. Distance from the centre o gravity of load demand.

4. Cost of land including space for extension, maintenance, and workshop and storage yard.
5. Main wind direction and water current in cooling Water source (sea, lake or river) in order to
air and Water pollution. and other ecological considerations.
6. Character of soil.
7. With coal fired stations, disposal of ash.
8. If the plant is erected far from town, accommodation for staff.
9. Rail and road connection.
10. Security condition.
Power plant: A power plant may be defined as a machine or assembly of equipment that
generates and delivers a flow of mechanical or electrical energy. The main equipment for the
generation of electric power is generator. When coupling it to a prime mover runs the generator,
the electricity is generated.

The major power plants are,

1. Steam power plant 2. Diesel power plant 3. Gas turbine power plant 4. Nuclear power plant

5. Hydro electric power plant`

The Steam Power Plant, Diesel Power Plant, Gas Turbine Power Plant and Nuclear Power Plants
are called THERMAL POWER PLANT, because these convert heat into electric energy.

Steam is the most common working fluid used in steam/Thermal power plant because of its
many desirable characteristics, such as low cost, availability and high enthalpy of vaporization

Site selection: Selection of site of any power plant plays an important role in the economy of the
station. Site selection is based on various important factors, some of which for thermal power
plant is given as:
(a)Cost of land: Cost of land should be reasonable and further extensions, if necessary should
be possible.
(b)Nature of land: The type of the land selected as site should have good bearing
capability to withstand the load of the plant.
(c)Availability of fuel: Thermal power stations requires huge amount of fuel per day. Therefore
it is necessary that the location of the plant should in such that the fuel may available at low
cost and it should be easy to deliver fuel from coal fields at a low transportation charges
and within time.
(d)Availability of water: Thermal (steam) power plants requires large amount of water
because water is used as working fluid which is respectively evaporated and condensed.
Abundant quantity of cooling water for condenser should also available and its large amount is
required for ash handling. It is therefore, necessary to locate the power plant near water body.
(e)Easy transportation facility: It is also a very important consideration. It is always
necessary to have easy transportation by which transportation of fuel and heavy
machinery becomes an easy task.
(f)Waste disposal facility: It is an important factor because proper disposal of waste products is
very important, since they affects environment and may create serious problems.