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LECTURE NOTES ON BE 8252 BASIC CIVIL AND MECHANICAL ENGINEERING (ANNA UNIVERSITY R2017) II SEMESTER CONTENTS ❖ Syllabus ❖ Unitwise notes ❖ Questuion bank ❖ Questuion bank with answers
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LECTURE NOTES
ON
BE 8252 BASIC CIVIL AND MECHANICAL
ENGINEERING
(ANNA UNIVERSITY R2017)
II SEMESTER
CONTENTS
❖ Syllabus
❖ Unitwise notes
❖ Questuion bank
❖ Questuion bank with answers
BE8252 Basic Civil and Mechanical Engineering Syllabus Regulation 2017
A – OVERVIEW
UNITI SCOPE OF CIVIL AND MECHANICAL ENGINEERING
Overview of Civil Engineering - Civil Engineering contributions to the welfare of Society –
Specialized sub-disciplines in Civil Engineering – Structural, Construction, Geotechnical,
Environmental, Transportation and Water Resources Engineering.
Overview of Mechanical Engineering - Mechanical Engineering contributions to the welfare
of Society –Specialized sub-disciplines in Mechanical Engineering - Production,
Automobile, Energy Engineering - Interdisciplinary concepts in Civil and Mechanical
Engineering.
B – CIVIL ENGINEERING
UNIT II SURVEYING AND CIVIL ENGINEERING MATERIALS
Surveying: Objects – classification – principles – measurements of distances – angles –
leveling – determination of areas– contours - examples. Civil Engineering Materials: Bricks
– stones – sand – cement – concrete – steel - timber - modern materials
UNIT III BUILDING COMPONENTS AND STRUCTURES
Foundations: Types of foundations - Bearing capacity and settlement – Requirement of good
foundations.
Civil Engineering Structures: Brick masonry – stonemasonry – beams – columns – lintels –
roofing – flooring – plastering – floor area, carpet area and floor space index - Types of
Bridges and Dams – water supply - sources and quality of water - Rainwater harvesting -
introduction to high way and railway.
C – MECHANICAL ENGINEERING
UNIT IV INTERNAL COMBUSTION ENGINES AND POWER PLANTS
Classification of Power Plants - Internal combustion engines as automobile power plant –
Working principle of Petrol and Diesel Engines – Four stroke and two stroke cycles –
Comparison of four stroke and two stroke engines – Working principle of steam, Gas, Diesel,
Hydroelectric and Nuclear Power plants –- working principle of Boilers, Turbines,
Reciprocating Pumps (single acting and double acting) and Centrifugal Pumps
UNIT V REFRIGERATION AND AIR CONDITIONING SYSTEM
Terminology of Refrigeration and Air Conditioning. Principle of vapour compression and
absorption system–Layout of typical domestic refrigerator–Window and Split type room Air
conditioner.
Basic Civil and Mechanical Engineering Introduction
• Mechanical engineering is a discipline of engineering that applies the
principles of materials science and physics for analysis, design, manufacturing, and
maintenance of mechanical systems.
• It is the branch of engineering that involves the production and usage of heat
and mechanical power for the design, production, and operation of machines and
tools.
• It is one of the oldest and broadest engineering disciplines. This field of
engineering requires an understanding of core concepts including
mechanics,kinematics, thermodynamics, materials science and machine analysis.
• These core principles are used to design and analyze manufacturing
plants, industrial equipment and machinery, heating and cooling
systems, transport systems, aircraft, watercraft, robotics, medical devices etc.
• As a result of developments in the field of physics, Mechanical Engineering
science emerged in the 19th century and has continually evolved to incorporate
advancements in technology.
Mechanical Engineering Contribution to the Welfare of Society
• Mechanical Engineering turns science and technology into something
substantial and useful to society.
• It is applied in creating various structures, home appliances and other
infrastructures and equipment, which make human lives safe and convenient.
• Mechanical engineers design and oversee the manufacturing of many
products ranging front medical devices to new batteries.
• Power-producing machines such as electric generators, internal combustion
engines, and steam and gas turbines as well as power-using machines, such as
refrigeration and air-conditioning systems are designed by the Mechanical
engineers.
• Mechanical engineers design material-handling systems, such as conveyor
systems and automated transfer stations. They also design other machines inside
buildings, such as elevators and escalators.
Mechanical engineers typically perform the following activities :
•Analyze problems to see how mechanical and therni,t, devices migh t
help solve the problem.
•Design or redesign mechanical and thermal devices usinil analysis and
computer-aided design.
•Develop and test prototypes of devices they design.
•Analyze the test results and change the design as needed.
•Oversee the manufacturing process for the device.
Subdisciplines of Medhanical Engineering
•The field of mechanical engineering can be thought of as a
collection of many mechanical engineering science disciplines.
•With a brief explanation and the application of each. several of these
subdisciplines which are typically taught at the undergraduate level are
listed below :
2.3.1Mechanics
•In the most general sense, Mechanics is the study of forces and their
effect upon matter.
•Typically, engineering mechanics is used to analyze and predict the
acceleration and deformation (both elastic and plastic) of objects under
known forces (also called loads) or stresses.
•Sub disciplines of mechanics include the following points :
a)Statics : It is the study of non-moving bodies under known loads and
it shows how forces affect static bodies.
b)Dynamics : It is the study of forces which affect moving bodies.
Dynamics includes kinematics (about movement, velocity, and
acceleration) and kinetics (about forces and resulting acceler ations)•
c)Mechanics of materials : It is the study of different materials which
deform under various types of stress.
d)Fluid mechanics : It is the study of fluids which react to forces.
e)Kinematics : It is the study of the motion of bodies (objects) and
systems (groups of objects), while ignoring the forces that cause the
motion. Kinematics is often used in the design and analysis of
mechanisms.
• It the engineering project %WC the deign of a vehicle, statics might be
employed to design the frame of the vehicle, to order to nalume %here
the muses will be MOO intense
• Dynamics might be used when designing the car's engine. to evaluate
the forces in the pistons and cams as the engine cycles.
• Mechanics of materials might be used to choose appropriate materials
for the frame and engine.
• Fluid mechanics might be used to design a ventilation system for the
vehicle cc to design the mute system for the engine.
• structural analysis may be used in the office %sten designing pans, In
the field to analyze faded parts, or in labor-atones vhere parts might
undergo controlled fail tests
Structural Analysis
! • Structural analysis u the branch of mechanical engineering (and also civil
engineering) denoted to examining why and how objects fail and to fix the objects
and their performance.
Structural failures occur in two general modes: strum failure. and (=gut failure
Static structural failure occurs when, upon being loaded (basing a force applied)
the object being analyzed either breaks or is deformed plastically. depending on the
criterion for failure.
Fatigue failure occurs Wheal an object fails after a number of repeated loading and
tmloadmg cycles.
Fatigue failure occurs because of imperfections in the object. Fee example : A
microscopic crack on the surface of the object. for instance. will grow slightly with
each cycle (propagation) until the crack is large enough to cause ultimate failure.
Failure is not simply defined as when a part breaks, however; it is defined as when
a part does not operate as
intended.
Sane systems, such as the perforated top sections of some plastic bags. are
designed to break_ If these systems do not break, failure analysts might be
employed to
determine the cause.
Thermodynamics is an applied science used in sacral branches of engineering,
including mechanical and chemical engineering.
Engineering thermodynamics is concerned with changing energy from one form to
another. For example : Automotive engines convert chemical energy (enthalpy)
from the fuel into heat and then into mechanical vest that eventually turns the
wheels
Thermodynamics principles are used by mechanical engineers in the fields of heat
transfer, nano-machines, and energy conversion.
Mechanical engineers use thamo-smence to design engines and power plants,
hearing. ventilation. and air-conditioning (HVAC) systems. heat exchangers, heat
sinks. radiators, refrigeration, insulation.
Design and Drafting
• Drafting or technical drawing is the means by labial mechanical engineer design
products and create instructions for manufacturing pare.
• A technical drawing can be a computer model or hand-drawn schematic showing
all the dimensions necessary to manufacture a part, as well as assembly cola, a list
of required materials. and other pertinent
information.
• A mechanical engineer or skilled worker who aeon technical drawings may be
referred to as a drafter or
draftsman.
• Drafting has lustoncally been a two-dimensional Proecess. but computer-aided
design (CAD) programs now allow the designer to create in dime dimensions
•Growth of manufacturing is also referred to as an index of technology growth of
a country Manufacturing provides availability of finished goods fin. technology
application Large scale manufacturing also provides goods at affordable prices.
Importance of manufacturing towards socio-economic development :
•Manufacturing is the backbone of any economy.
•Manufacturing industry provides employment to hundreds of people.
•Before the Industrial Revolution, manufacturing was carried out in rural areas,
where household-based manufacturing was the trend.
•Later government policy and entrepreneurs organized a number of manufacturing
households into a single enterprise producing goods at larger scale.
•It led to development of industrialization and society.
Manufacturing provides an opportunity for establishment of allied industries.
It provides a boost to the service industry catering to the people employed.
•Manufacturing is considered as a wealth-producing sector of an economy.
•It provides important material support for national infrastructure and for national
defense.
Production Process
• Production process of a workpiece involves transforming a raw material from
its original state to a finished state by changing its shape or the properties of
the material in a series of steps.
• The design engineer should have complete knowledge of production processes.
• Actually, production process is the part of manufacturing process directly
concerned with the changes in dimensions, shapes and properties of raw
material. It is accomplished in definite sequence.
Classification of Production Processes
Instructions for manufacturing a part must be fed to the necessary machinery,
either manually, through programmed instructions, or through the use of a
computer-aided manufacturing (CAM)
• Optionally, an engineer may also manually manufacture a part using the
technical drawings, but this is becoming an increasing rarity, with the
advent of computerized numerically controlled (CNC) manufacturing.
• Engineers Primarily manually manufacture parts in the areas of applied
spray coatings, finishes.
• Drafting is used in nearly every subdiscipline of mechanical
engineering, and by many other branches of engineering and architecture.
• Three-dimensional models created by using CAD software are also
commonly used in finite element analysis (FEA) and computational fluid
dynamics (CFD).
Manufacturing
• Manufacturing comes from Latin words manus (hand) and factura (make).
• It is primarily by the application of tools (equipments) through a series of
processing steps (manufacturing process) to transform raw materials into
finished goods for the consumption of society.
• Manufacturing was primarily a handicraft activity involving human and
its skills.
• Now-a-days with increasing demand and cost competitiveness,
manufacturing has evolved as mass industrial production.
• Mass production (manufacturing) involves producing finished goods on
large scale.
Importance of manufacturing towards technology
development :
• Manufacturing and technology development are complementary to
each other.
• Growth in manufacturing enables increased availability of finished goods and its
application in various sectors.
• such applications lead to technology development of the industry which is then
transferred to development of manufacturing technology.
1. Primary shaping processes
2. Deforming processes
3. Machining processes
4.Joining processes
5.Surface finishing processes
6.Material properties modification processes
Primary shaping processes
•Primary shaping is the production of a solid body from a molten state or
gaseous state or amorphous material (gases, liquids, powders, fibres, chips,
etc.).
•A primary shaping process contains a molten metal like cast iron which
poured into the hollow space (mould of desired shape). After solidification, it
attains the shape of hollow space. Some of the important primary shaping
processes is as follows:
1.Casting processes
2.Powder metallurgy processes
3.Processing of plastics
Deforming processes
• In deforming processes, a metal is in cold or hot condition, which is
deformed plastically into the desired shapes without changing its mass or
metal composition
• In deforming processes, no metal is removed; only it is deformed and
displaced
• This process makes use of suitable stresses like tension, compression, etc. to
cause plastic deformation.
• Some of the important deforming processes are as
Follows
1. Forging
2. Rolling
3. Sheet metal working
4. Extrusion
3. Machining processes
• In machining processes, the material is removed by providing suitable
relative motions between the work piece and tool, so as to generate the required
size and shape on the component.
• As the material is removed, these processes are also called as removing
processes.
Some of the important machining processes are as follows
1. Turning 2. Drilling
3. Milling 4. Shaping 5. Reaming
Joining Processes
• In these processes, two or more pieces of metal parts are joined together to
make a fatal component
• The joining process can be carried out by fusing, pressing rubbing. etc.
• Most of the processes require heat and pressure for joining of metal pieces.
• Some of the important joining processes arc as follows :
1. Welding 2. Soldering
3. Brazing 4. Screwing
S. Riveting 6. Adhesive bonding
Surface finishing processes
• These processes are used only to provide good surface finish or decorative or
protective coating on the metal surface of a work piece.
• During the process, dimensions of the part arc not changed, only a
negligible amount of metal is removed from the work piece
Some of the important surface finishing processes arc as follows
1. Honing 2. Lapping
3.Buffing 4. Plating
5. coating 6. Grinding
ROLE OF AUTOMOBILE INDUSTRY IN NATIONAL GROWTH
The Indian Automobile industry includes vivo-wheelers, trucks, cars, buses and three-
wheelers which play a crucial role in growth of the Indian economy. India has
emerged as Asia's fourth largest exporter of automobiles, behind Japan, South Korea
and Thailand.
•The Economic progress of this industry is indicated by the amount of goods and
services produced which give the capacity for transportation and boost the sale of
vehicles. There is a huge increase in automobile production with a catalyst effect by
indirectly increasing the demand for a number of raw materials like steel, rubber,
plastics, glass, paint, electronics and services.
•The well-developed Indian automotive industry fulfills this catalytic role by
producing a wide variety of vehicles like passenger cars, light, medium and heavy
commercial vehicles, multi-utility vehicles such as jeeps, scooters, motorcycles,
mopeds, three wheelers, tractors etc.
•It contributes about 4% to India's Gross Domestic
Product (GDP) and 5% to India's industrial production.
•Indian market before independence was seen as a market for imported vehicles while
assembling of cars manufactured by General Motors and other brands was the order
Indian automobile industry mainly focused on servicing, dealership, financing and
maintenance of vehicles. Later only after a decade from independence manufacturing
started
•India has become one of the international players in the automobile market. In the
year 2006-07, the Indian Automobile Industry produced 2.06 million four wheelers
and 9 million two and three wheelers.
•As of 2013, the Indian automobile industry had contributed to almost 7 % of the
country's GDP. During the time it provided 22 % of India's manufacturing GDP and
provided around 18 % of excise duties to the state exchequer. The Indian automobile
industry has also significantly increased the presence of the nation in international
markets with a year-on-year increase in exports of approximately 18 %.
Current Scenario in Indian Auto Industry
•India has become one of the international players in the automobile market. In the
year 2006-07, the Indian Automobile Industry produced 2.06 million four wheelers
and 9 million two and three wheelers -
•India ranks 2nd in the global two-wheeler market while 4th biggest commercial
vehicle market in the world. India is on rank 11 in the international passenger car
market. It ranks 5th pertaining to the number of bus and truck sold in the world.
•It is expected that the Automobile Industry in India would be the 7th largest
automobile market within the year 2016.
•The Indian Automobile industry is at present engaged in mergers and acquisitions on
the international scale.
•The automotive industry in India is one of the largest in the world with an annual
production of 23.96 million vehicles in FY 2015-16, following a growth of 2.57 %
over the last year. The automobile industry accounts for 7.1 % of the country's gross
domestic product.
•India is also a prominent auto exporter and has strong export growth expectations for
the near future. In FY 2014-15, automobile exports grew by 15 percent over the last
year.
In addition, several initiatives by the Government of India and the major automobile
players in the Indian market are expected to make India a leader in the Two Wheeler
and Four Wheeler market in the world by 2020
ENERGY ENGINEERING
•Energy is one of the basic inputs to the human lives. It has great impact on human
developments and their
Quality of life. Energy is required for national economical growth.
•The availability of electrical energy and its per capita consumption is regarded as an
index of national standard of living in the present day civilization.
•The flourishing power generation industry is a sign of growing gross national
products which reflects prosperity of the people.
•Energy has become synonymous with progress. The energy in the form of electricity
is most desired as it is easy to transport, easy to control, clean in its surroundings and
can be easily converted into heat or work as per requirements.
Global Scenario of Power Generation
•The development of future global energy demand is determined by following factors
:
1.Population development : The increase in population increases the number of people
consuming energy or use of energy services.
2.Economic development : GDP (Gross Domestic Product) is the most common
indicator of economic development. An increase in GDP indicates increase in energy
demand.
3.Energy intensity : It indicates the measure of how much energy required to produce
to meet the maximum demand.
Development of Global Energy Demand
•In coming years electricity demand is expected to increase disproportionately, with
domestic and industrial consumers. With the exploitation of efficiency measures,
however, an even increase can be avoided, leading to electricity demand of around
26000 TWh per annum in the year 2050. Compared to present scenario, efficiency
measures avoid the generation of about 13000 TWh per annum.
•This reduction in energy demand can be achieved in particular by introducing highly
efficient electronic
devices using the best available technology in all demand sectors
.
Material Science
Material is something that consists of matter. Mate r i a l s compr i se a wide
r ange o f meta l s and non-metals which must be operated upon to form
the finished product.
This end product may be an automobile, computer, bridge, so an
engineer must have an adequate knowledge of the properties and behavioral
characteristics of the materials.
Material Classification
Most engineering materials may be classified into the following types :
(a) Metals (b) Ceramics (c) Organics
(d) Composites (e)Semiconductors
•Metals are very important in the industrial application and play a major role in the
day-to-day life of human beings.
•There are many metal parts and objects, which are used in engineering
applications.
• The commonly used metal are as follows :
(i) Iron (ii) Aluminium
(iii) Copper (iv) Magnesium, etc.
(b) Ceramics :
•Ceramics generally consist of oxides, nitrides, carbides, silicates or borides of
various metals.
•Ceramic materials contain compounds of metallic and non-metallic elements such
as MgO, Si02, SiC, glasses etc.
•Ceramics are any inorganic, non-metallic solids, processed or used at high
temperatures.
•The commonly used ceramic materials are as follows :
(i) Sand (ii) Cement
(iii) Abrasives (iv) Glass
(v) Concrete (vi) Plaster, etc.
(C) Organic
•Organics are polymeric materials composed of carbo
compounds. (Polymers are solids composed of ion molecular chains).
•Organic materials may be natural, synthetic ( manufactured and based
chemically on carbon.
•The commonly used organics are as follows :
(i) Rubber (ii) Plastics
(iii) Lubricants (iv) Wood
(v) Textiles (vi) Fuels, etc.
(d) Composites :
•Composite materials consist of more than one materials
•For example, fibre-glass in which glass fibres are embedded within a
polymeric material.
(e) Semiconductors :
•Semiconductors have electrical properties that are intermediate between the
electrical conductors and insulators.
•The electrical characteristics of these materials are extremely sensitive to the
presence of minute concentrations of impurity atoms, of which concentrations
may be controlled over very special regions.
Importance of Materials :
•The importance of materials lies in the fact that they satisfy the engineering
requirements for making engineering components such as crankshaft, spanner,
etc.
•The materials selected for making components have such properties as they
will permit the component parts to perform their functions successfully when
they are in use.
•The materials satisfy the fabrication, service and economic requirements of
engineering.
•Materials can be easily fabricated as they have various properties such as
machinability, ductility, castability, heat treatability, weldability, etc.
•Materials help in providing proper service required if they are of proper
strength, wear resistant and corrosion resistant.
•Economically, minimum overall cost may be achieved by proper selection of
both technical and marketing
Interdisciplinary Concepts in Civil and Mechanical Engineering
• Mechanical engineering are concerned with the design, analysis, and
development of solutions to static and d y n a m i c l o a d b e a r i n g
s t r u c t u r e s , f o r m i n g a n d manufacturing of materials, conversion
of heat to mechanical work, the flow of fluids and heat in various media
etc, whereas the civil engineering is concerned with the design, and
development
construction projects, transportation, certain aspects of urban and rural
planning.
• Most structural engineers have a background in civil engineering. In a
certain construction, mechanical eng ineers dea l wi th p lumbing ,
HVAC (hea t ing , ventilation and air-conditioning) and miscellaneous
machinery, whereas structural engineers deal primarily
with significant load-bearing concrete and Metal structures.
• Mechanical engineers depend on structural engineers to design support structures for
air ducts, roof chillers, and miscellaneous other equipment. On the other hand,
structural engineers take into account weight of the equipment and mechanical
vibration and torques when consulting for the mechanical engineer.
Review Questions
1. What is mechanical engineering ?
2. What is the role of mechanical engineering to the welfare of
society ?
3. What are the different sub-disciplines in mechanical engineering
Explain any two.
4. State interdisciplinary concepts in Civil and Mechanical
Engineering.
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UNIT IV INTERNAL COMBUSTION ENGINE AND POWER PLANTS
QUESTIONS AND ANSWERS
PART A
1. How do you classify the hydro-electric power plants?
Classification of Hydro-Electric Power plants:
Hydel plants are classified according to the Head of Water under which they work.
1. High Head Power Plant: When the operating head of water exceeds 70 meters, the plant is known as High Head
Power Plant. Pelton turbine is the prime mover used.
2. Medium Head Plant: When the head of water ranges from 15 to 70 meters, then the power plant is known as Medium
Head Plant. It uses Francis turbine.
3. Low Head Plant: When the head is less than 15 meters, the plant is named as Low Head Plant. It uses Francis or
Kaplan turbine as prime mover.
2.What is surge tank? What do you meant by water hammer?
Surge tanks : Surge tanks are installed along the penstock (in between turbine and reservoir) to control or regulate the
sudden water overflow and to protect penstock from bursting. Surge tank reduces the pressure and avoids damage to
the penstock due to water hammer effect. There are possibilities of sudden increase or decrease in pressure, due to the
backflow of water if the load on the turbine is reduced. This is known as water hammer effect.
3. What are the factors to be considered while selecting the location of the hydro-electric power plant?
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Availability of water : Adequate water must be available with good head.
Cost and type of land : Land should be available at reasonable price. The bearing capacity of the land should be good
enough to withstand huge structures and
equipments.
Storage of water : A dam must be constructed to store large quantity of water in order to cope with variations of water
availability throughout the year.
Transportation facilities : The site should be accessible by rail and road for easy transportation of equipments and
machinery.
Pumped storage facilities : Pumping facilities to reuse the water should be possible.
4. What are the factors to be considered while selecting the location of the nuclear power plant?
Availability of water : Sufficient water must be available for cooling. Therefore, nuclear power plant must be situated
near a river or by the side of sea.
Distance from populated areas : Must be far away from populated areas as there may be radioactive particles in the
atmosphere, which are highly dangerous.
Disposal of waste : Waste produced is generally radioactive. Hence, it must be disposed properly to avoid health
hazards. Waste must be disposed in deep trench or in sea away from sea shore.
Transportation facilities : The site should be accessible by rail and road for easy transportation of equipment and
machinery.
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5. Define a pump. What are the applications of a pump? Write down the important specifications of a pump?
A pump is a machine that is used to raise or transfer fluids (liquids, slurries and gases). Pump is also used to maintain
constant flow rate or constant pressure. Pumps find applications in draining, collection and treatment of sewage,
irrigation, chemical industries, petroleum industries, medical fields, etc. Pumps are normally driven by an engine or a
motor. Pumps are commonly rated by horsepower. Important specifications for pump include maximum discharge
flow, maximum discharge pressure, inlet size and discharge size.
6. How do you Classify the pumps?
Pumps are broadly classified into positive displacement pumps and rotodynamic pumps.
7. What is positive displacement pump? Give example
In positive displacement pump, fluid is drawn or forced into a finite space and is then sealed by mechanical means.
Then, the fluid is forced out (discharged) and the cycle is repeated. A positive displacement pump is one in which a
definite volume of liquid is delivered for each cycle of pump operation regardless of the head against which the pump
is operating and the resistance to flow offered by the system. Reciprocating pump is a positive displacement pump.
Some positive displacement pumps like gear pump and vane pump use rotary action instead of reciprocating action.
8. What is rotodynamic pump? Give example
In rotodynamic pumps, there is free passage of fluid between the inlet and outlet without any intermittent sealing.
Centrifugal pump is a rotodynamic pump.
4
9. What is priming?
Priming : Before starting the centrifugal pump/reciprocating pump, priming is to be performed. Priming means filling
the suction pipe and the casing with water in the case of centrifugal pump - suction pipe and clearance volume of the
cylinder in the case of reciprocating pump, so that there is no air pocket left in the pump.
10. Define Reciprocating pump. How do you classify the same?
Reciprocating pump uses a piston and cylinder arrangement with suction and delivery valves integrated into the pump.
Reciprocating pump can be single acting (single suction and discharge strokes) or double acting (suction and discharge
in both the directions). There may be a single cylinder or multi-cylinder.
11. What are the uses of a reciprocating pump?
Uses of reciprocating pumps : In general, reciprocating pumps are best suited for small capacities and high heads.
Reciprocating pumps were used extensively in steam power plant as boiler feed water pump. Reciprocating pumps are
also frequently used in pneumatic and hydraulic systems for pumping highly viscous fluids including concrete and
heavy oils. Use of reciprocating pumps in oil drilling operations is very common.
12.What are the advantages of reciprocating pumps?
Reciprocating pumps are usually preferred due to their relatively compact design, high-viscosity performance and
ability to handle high differential pressure.
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13. What are the uses of centrifugal pumps?
Uses of centrifugal pumps : Centrifugal pumps are used widely in power plants. They are also used for plumbing,
Drainage and marine works. They find applications in residences, agriculture and industries such as petroleum, sugar,
paper, pharmaceutical, chemicals, etc. In general, centrifugal pumps are used for large discharges and low heads.
14. Define Centrifugal pump
A centrifugal pump is one of the simplest of rotodynamic pumps that uses centrifugal force to move the fluid into a
pipe. The operating cost of the centrifugal pumps is low when compared to other pumps. Centrifugal pumps are popular
for their high reliability and smooth operation.
15.Classify centrifugal pump and define each type.
Classification of centrifugal pump
a)Radial flow
b)Mixed flow
c)Axial flow
In the radial flow centrifugal pump, the pressure is developed wholly by centrifugal force. In mixed flow
centrifugal pump, the pressure is developed partly by centrifugal force and partly by the propelling action of the vanes
of the impeller on the liquid. In axial flow centrifugal pump, the pressure is developed by the propelling action of the
vanes of the impeller on the liquid.
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16. Define Multistage centrifugal pump.
A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may
be mounted on the same shaft or on different shafts. A multistage centrifugal pump helps to develop a high head and
discharge a large quantity of liquid. If a high head is to be developed, the impellers are mounted on the same shaft
(series) while for large quantity of discharge of liquid, the impellers are mounted on different shafts (parallel)
17. What are the Advantages of centrifugal pumps?
• Centrifugal pump is compact and simple to use.
• It is reliable.
• A centrifugal pump runs smoothly.
• It ensures smooth flow of general purpose fluids, pure water, sludge, sewage, slurry, high viscosity fluids, chemicals,
etc.
• Internal lubrication is not required for centrifugal pumps.
• Horizontal centrifugal pumps are easy to install and need less maintenance.
18. Compare between reciprocating and centrifugal pumps
Reciprocating pump
Centrifugal pump
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Occupies large space and heavy Compact and light
High initial cost and difficult to erect Low installation cost and easy to erect
Uneven flow Smooth flow
Low speed High speed
High maintenance cost Low maintenance cost
Low efficiency in low heads High efficiency in low heads
Problems arise due to valves and glands Easy to handle
Varying torque Smooth running
19. What is a turbine? How the energy conversion takes place inside it?
Turbine is a rotary engine that extracts energy from a working fluid flow such as steam, gas and water. A
working fluid possesses potential (pressure) energy and kinetic (velocity) energy. The turbine changes the potential and
kinetic energy of the working fluid into mechanical (rotational) energy and acts as a prime mover in any power plant.
The simplest turbine has a rotor assembly to which a shaft with wheels or curved blades is attached . By providing
multiple wheels, the efficiency of the turbine is increased. The turbines have a casing around the blades that contains
and controls the working fluid. The potential energy and kinetic energy from the nozzle when directed to the wheels or
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blades, rotate the wheel and the wheel in turn rotates the turbine shaft. The other end of the turbine shaft is coupled to
an electric generator which generates electricity. The different turbines are steam, gas and hydraulic turbines.
20. Define a Steam turbine. What are its uses and advantages?
Steam turbine is a machine which converts the pressure energy of steam into kinetic energy and then the kinetic energy
into mechanical energy (rotation of the turbine shaft). The main parts of the steam turbine are fixed nozzles, rotor, fixed
and moving blades, outer casing, etc. The rotor is a circular disc fixed to a horizontal shaft. On the periphery of the
rotor, a number of blades are fixed at uniform intervals (Fig. 1).
Use : Steam turbines are used for the generation of electricity in thermal and nuclear power plants.
The advantages of steam turbine are (i) reliability (ii) less floor space requirement (iii) less lubricating oil consumption
and (iv) minimum maintenance cost.
The steam turbine is broadly classified as impulse turbine and reaction turbine.
21. What is a Gas turbine? State its uses and fuel used in it and its classification.
Uses of gas turbine : Gas turbine is used to generate electricity in gas power plant. Gas turbines are also used in jet
aircrafts, ships, high speed cars, etc.
Fuels used in the gas turbine : Gas turbines use fuels such as natural gas, coal gas, gasoline, etc.
Gas turbines are classified as open and closed cycle gas turbines.
22. Define Hydraulic (water) turbines. How do you classify the same?
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Hydraulic turbines convert the potential energy of water into mechanical (rotational) energy usable in hydro-
electric power plants for the generation of electricity. The hydraulic turbines are broadly classified into two types
namely, impulse turbine and reaction turbine. The choice of the turbine is based on the head of water, quantity of water
flow and the quantity of electricity to be produced.
23. What do you meant by Clean Atomic Power by Nuclear Fusion?
Nuclear Fusion: Nuclear fusion technology is based on producing energy by uniting atoms, while nuclear fission
achieves this by splitting atoms. Nuclear fusion is the process by which light elements are combined to form a single
element with a release of energy. The two light elements fuse into a heavier element. Hydrogen nuclei are made to fuse
to form Helium nucleus. The difference in mass is converted into energy. Fusion reactors do not give out harmful
radiation.
A laboratory breakthrough has been achieved in U.S.A., in the area of nuclear fusion for the production of clean
atomic power without creating any environmental problem.
PART B
1. With the aid of a general layout, explain the working principle of different circuits of a thermal power plant.
Layout of a Modern Thermal Power Plant
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Fig. 1 shows the layout of a thermal power plant. It consists of four circuits. These are:
1. Coal and Ash Circuit 3. Feed Water and Steam Circuit
2. Air and Flue Gas Circuit 4. Cooling Water Circuit
1. Coal and Ash Circuit
Coal from the mines is stored in the Coal Storage Yard. It is transferred to the boiier furnace by means of coal
handling equipment like belt conveyor, bucket elevator, etc. Coal is burnt in the boiler furnace. Hot ash resulting from
the combustion of coal in the furnace is removed to the Ash Storage Yard by means of ash handling equipment.
Ash Disposal: Indian coal contains about 40% ash. A power plant of 100 MW capacity produces about 25 tonnes of hot
ash per hour. Hence, sufficient space near the power plant is essential to dispose such large quantities of hot ash.
2. Air and Flue Gas Circuit
Air is taken in from the atmosphere to Air Pre-heater. Air is heated in the air pre-heater by the heat of the flue
gases. The hot air from the air pre-heater is supplied to the furnace of the Boiler for combustion of coal.
The flue gases after combustion in the furnace, pass around the boiler tubes to generate steam. The flue gases
then flow through an Economizer and the Air Pre-heater. Finally, the flue gases are exhausted to the atmosphere
through the Chimney. By this method, the heat of the flue gases which would have been wasted otherwise is used
effectively in both the economizer and the air pre-heater. Thus, the overall efficiency of the power plant is improved.
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Air Pollution: The pollution of the surrounding atmosphere is caused by the emission of the objectionable gases and
dust through the chimney. The air pollution causes nuisance to people surrounding the plant. In fact, air pollution is a
health hazard.
3. Feed Water and Steam Circuit
The high pressure steam generated in the boiler is supplied to the Steam Turbine. Work is done by the expansion
of steam in the turbine. Hence, the pressure of steam is reduced. The expanded steam then passed to the Condenser,
where it is condensed to water by cooling. The condensate (i.e., condensed water) leaving the condenser is first heated
in a L.P. Water Heater by using the steam taken from the low pressure extraction point of the turbine.
Some of the steam and water is lost passing through different components of the system. Therefore, feed water is
supplied from external source to compensate this loss. The external water is used as a make-up to the feed water
system.
The feed water supplied from external source is passed through a purifying plant to reduce the dissolved salts.
Purification is necessary to avoid the scaling of the boiler tubes.
Again, steam taken from the high pressure extraction point of the turbine is used for heating the feed water in the
H.P. Water Heater. The hot feed water is passing through the economizer, where it is further heated by the flue gases.
The feed water which is sufficiently heated by the feed water heaters as well as economizer is fed into the boiler.
4. Cooling Water Circuit
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The condenser condenses the exhaust steam from the turbine to water by cooling. The volume occupied by the
condensate is very much less than that of the low pressure steam. Thus, the pressure of the condensate reduces to
vacuum. When the exhaust steam is passed to the condenser, its pressure automatically drops to vacuum that is existing
in the condenser.
Hence, the steam in the turbine expands to vacuum condenser pressure, instead of to atmospheric pressure. This
increase in the amount of pressure drop in the turbine increases the amount of work done. Thus, the efficiency of the
plant is improved.
Abundant quantity of cooling water (called coolant) is required for condensing the steam in the condenser. The
condensed water is reused in the cycle.
Water circulating through the condenser may be taken from various sources such as river or lake, provided
adequate water supply is available from the river or lake throughout the year. If adequate quantity of water is not
available at the plant site, the hot coolant from the condenser is cooled in the Cooling Tower and re-circulated again.
Cooling Tower: The hot coolant passes on to the top of the cooling tower from where it is sprayed through
nozzles. It is cooled by a current of cold air entering along the periphery of the tower from the bottom and traveling in
the upward direction. The hot coolant giving up its heat to the air, becomes cool and is collected at the bottom of the
tower. This cold water is once again circulated by the coolant pump to the condenser.
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2. State the advantages and disadvantages of steam/thermal power plant compared to hydel and nuclear power
plants.
Advantages
1. Initial Cost is low compared with hydel power plant.
2. The thermal power plant can be located near the load center. Therefore, the transmission cost and transmission losses
are considerably reduced.
3. The generation of power is not dependent on the nature’s mercy like hydel plant.
4. The construction, erection and commissioning of thermal plant requires less period of time than a hydel plant.
Disadvantages
1. The fuel (coal) needed may be exhausted by gradual use.
2. Efficiency of the power plant decreases with time.
3. Its part load efficiency decreases very rapidly with decreasing load.
4. Transportation of fuel is difficult, if the plant is located away from the coal mines.
5. Power generation cost is considerably high compared with hydel plant.
6. Air pollution causes smoke in the surrounding atmosphere.
7. Life of the thermal power plant is hardly about a few decades compared with the life of the hydel power plant (i.e.,
about a few centuries).
3. Give a schematic layout of a storage type hydro-electric power plant and explain the function of each
component of the plant.
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General Arrangement of a Hydro-Electric Power Plant
Fig. 2 shows the schematic representation of a Hydro-Electric Power Plant.
1. Water Reservoir: Continuous availability of water is the basic necessity for a hydroelectric plant. Water collected
from catchment area during rainy season is stored in the reservoir. The main purpose of the reservoir is to store the
water during rainy season and supply the same during dry season.
Water surface in the storage reservoir is known as Head Race Level.
Capacity of the reservoir depends upon the catchment area and rainfall at that place. The water head available for
power generation depends on the reservoir height.
2. Dam: The function of a Dam is to increase the height of water level behind it, which ultimately increases the
reservoir capacity.
Spillway: During rainy season, water after a certain safe level in the reservoir overflows through spillway without
allowing the increase in water level in the reservoir.
3. Penstock Pipe: Penstock Pipe is used to bring water from the dam to the hydraulic turbine. Penstock pipes are made
up of steel or reinforced concrete. The turbine is installed at a lower leve from the dam.
Penstock is provided with a Gate Valve at the inlet to completely close the water supply. It has a Control Valve to
control the water flow rate into the turbine.
4. Surge Tank: There may be sudden increase of pressure in the penstock pipe due to sudden backflow of water, as
load on the turbine is reduced. The sudden rise of pressure in the penstock pipe is known as Water Hammer.
The Surge Tank is introduced between the dam and the turbine to reduce the sudden rise of pressure in the
penstock. Otherwise, penstock pipe will be damaged by the water hammer effect.
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5. Water Turbine: Water Turbine is also known as Hydraulic Turbine. Water through the penstock pipe enters into the
turbine through a control valve. Prime movers which are in common use are Pelton Turbine, Francis Turbine and
Kaplan Turbine.
The potential energy of water entering the turbine is converted into mechanical energy.
The mechanical energy available at the turbine shaft is used to run the electric generator. The water is then
discharged through the Draft Tube.
6. Draft Tube: Draft Tube is connected to the outlet of the turbine. It converts the kinetic energy available in the water
into pressure energy in the diverging portion. Thus, it maintains a pressure of just above atmospheric at the end of the
draft tube to move the water into the tail race. Water from the tail race is released for irrigation Pu rpose S.
7. Tail Race Level: Tail Race is a water path to lead the water discharged from the turbine to the river or canal. The
water held in the tail race is called Tail Race Water Level.
8. Power House: The Power House accommodates the water turbine, generator, transformer and control room. The
function of the step-up transformer is to raise the voltage generated at the generator terminal before transmitting the
power to the consumers.
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4. State the merits and demerits of hydro-electric power plant
Merits of Hydro-Electric Power Plant
1. Water is a renewable source of energy. Water which is the operating fluid, is neither consumed nor converted into
something else.
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2. Water is the cheapest source of energy, because it exists as a free gift of nature. The fuels needed for the thermal,
diesel and nuclear plants are exhaustible and expensive.
3. There is no ash disposal problem as in the case of thermal power plant.
4. Hydro-plant does not pose the problem of air pollution as in the case of thermal plant or radiation hazards as in the
case of nuclear plant.
5. Variable loads do not affect the efficiency in the case of a hydro-plant.
6. Life of hydro-plant is very long (a few centuries) compared with thermal plant (a few decades). This is because the
hydro-plants operate at atmospheric temperature, whereas thermal plants operate at very high temperatures (about 500
to 800°C).
7. Hydro-plant provides additional benefits like irrigation, flood control, fishery and
recreation.
8. The water storage of hydro-plant can also be used for domestic water supply.
9. Auxiliaries needed for hydro-plant are less compared to thermal plant of equal capacity.
10. It requires less supervising staff.
11. Maintenance cost is low.
Demerits of Hydro-Electric Power Plant
1. Hydro-plants are situated away from the load centers. Hence, long transmission lines required for delivery of power,
This increases the cost of transmission lines and transmission losses. But, a thermal plant can be located near the load
center, thereby transmission cost and transmission losses are considerably reduced.
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2. The power produced by hydro-plant depends upon the quantity of water which in turn dependent upon the rainfall.
The dry year affects the hydro-power generation considerably.
3. Initial cost of the plant is high.
4. Erection of hydro-plant (construction of dam, etc.) usually takes long period of time.
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5. Explain the working principle of a nuclear power plant.
Main Components of Nuclear Power Plant (Fig. 4)
1. Nuclear Reactor
A Nuclear Reactor may be regarded as a substitute for the boiler furnace of a thermal power plant. Heat is
produced in the reactor due to nuclear fission of the fuel U35.
Types of Reactors
i) Pressurized Water Reactor (P. W.R) shown in Fig. 4.
[Advantages: It is compact. Normal turbine maintenance techniques can be
used, as the steam is not contaminated by radiation
ii) Boiling Water Reactor (B.W.R)
iii) Heavy Water-Cooled Reactor,
iv) Gas Cooled Reactor
Pressurized Water Reactor: It has primary and secondary circuits.
In the primary circuit, the pressurizing tank maintains a constant high pressure in the water in the range of 1 50 bar.
Electrical heating coil in the pressuriser boils the water to form steam. The steam is collected in the dome and it
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pressurizes the entire coolant circuit before starting the reactor. The coolant circuit pressure is maintained at a higher
level than that of the steam circuit to maintain the coolant at liquid state.
The coolant water in the primary circuit gets heated by absorbing the fission energy in the reactor core. Coolant
pump supplies coolant water to the reactor.
Radiation Hazards and Shieldings: The water becomes radio-active in passing through the reactor. Hence, the
reactor is a source of intense radio-activity. These radiations are very harmful to human life. It requires strong control
to ensure that this radioactivity is not released into the atmosphere to avoid atmospheric pollution.
A thick concrete shielding is provided to prevent the escape of these radiations to atmosphere. Thermal shielding
reduces the heat loss in the reactor.
2. Steam Generator
The heat liberated in the reactor is taken up by the coolant circulating through the core. The purpose of the
coolant is to transfer the heat generated in the reactor core and use it for steam generation. Ordinary water or heavy
water is a common coolant.
3. Hot coolant
Hot coolant water leaves the reactor at the top. It flows into the steam generator (boiler) in the secondary circuit
and transfers the heat to the feed water in the steam generator. The feed water evaporates to become steam. Feed Pump
supplied feed water to the steam generator.
4. Turbine
The steam produced in the steam generator is passed to the turbine. Work is done by the expansion of steam in
the turbine.
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5. Condenser:
The exhaust steam from the turbine flows to the condenser where cooling water is circulated. The exhaust steam
is condensed to water in the condenser by cooling. The condensate is pumped again into the steam generator by the
feed pump.
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6. State the advantages and disadvantages of Nuclear power plant.
Advantages of Nuclear Power Plant
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1. Nuclear plant can be easily adopted where water and coal resources are not available.
2. It requires very small quantity of fuel. Hence fuel transportation cost is less.
3. Space requirement is less compared to other power plants of equal capacity.
4. It is not affected by adverse weather conditions.
5. Fuel storage facilities are not needed as in the case of the thermal power plant.
6. Nuclear plants will conserve the fossil fuels (coal, petroleum) for other energy needs.
7. Number of workmen required at nuclear plant is far less than thermal plant.
8. It does not require large quantity of water.
Disadvantages of Nuclear Power Plant
1. Radio-active wastes, if not disposed very carefully, have adverse effect on the health of workmen and the population
surrounding the plant.
2. Nuclear plant is not suited for varying load conditions.
3. It requires well-trained personnel.
4. It requires high initial cost compared to hydro or thermal power plants.
7. With a very neat layout explain the working principle of Diesel power plant
1. Diesel Engine: Diesel Engine is also known as Compression Ignition Engine. It is classified as two stroke engine
and four stroke engines. In diesel engine, air admitted into the cylinder is compressed, the compression ratio being 12
to 20.
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At the end of compression stroke, the fuel is injected. It burns and the burning gases expand and do work on the piston.
The engine is directly coupled to the generator. The gases are then exhausted from the cylinder to atmosphere.
2. Engine Starting System: This includes Air Compressor and Starting Air Tank. function of this system is to start the
engine from cold by supplying compressed air.
3. FuelSystem: Pump draws diesel from the Fuel Storage Tank and supplies it to the small
Day Tank through the filter. Day tank supplies the daily fuel need of the engine. The
day tank is usually placed high so that diesel flows to engine under gravity.
Diesel is again filtered before being injected into the engine by the Fuel Injection Pump.
The fuel is supplied to the engine according to the load on the plant.
4. Air Intake System: Air filters are used to remove dust from the incoming atmospheric air. Air filters may be of dry
type, which is made up of felt, wool or cloth. In oil bath type of filters, the air is swept over a bath of oil so that dust
particles get coated.
5. Exhaust System: In the exhaust system, Silencer (Muffler) is provided to reduce the noise produced by the engine.
6. Engine Cooling System: The temperature of burning gases in the engine cylinder is of the order of 1500°C to
2000°C. Water is circulated inside the engine to keep the temperature at a reasonable level. The hot water from the
engine is cooled in a Spray Tank and re-circulated using pumps.
7. Engine Lubricating System: Lubrication is essential to reduce friction and wear of the engine parts such as cylinder
walls and piston. Engine Lubricating System includes Lubricating Oil Cooler and oil pump. [Oil pump is not shown.]
Lubricating oil which gets heated due to the friction of the moving parts is cooled before re-circulation.
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8. State the advantages and disadvantages of Diesel power plant.
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Advantages of Diesel Engine Power Plant
1. Plant layout is simple. Hence, it can be quickly installed and commissioned, while the erection and starting of a
steam power plant or hydro-plant takes a fairly long time.
2. Quick starting and easy pick-up of loads are possible in a very short time.
3. Location of the plant is near the load center.
4. The load operation is easy and requires minimum labour.
5. Efficiency at part loads does not fall so much as that of a steam plant.
6. Fuel handling is easier and no problem of ash disposal exists.
7. The plant is smaller in size than steam power plant for the same capacity.
8. Diesel plants operate at high overall efficiency than steam plants.
Disadvantages of Diesel Engine Power Plant
I. Plant capacity is limited to about 50MW of power.
2. Diesel fuel is much more expensive than coal.
3. The maintenance and lubrication costs are high.
4. Diesel engines are not guaranteed for operation under continuous overloads, while steam turbines can work under
25% of overload continuously.
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9. Write down the Applications of diesel power plant
1. Diesel power plants in the range of 2 to 50 MW capacity are used as central stations for small or medium power
supplies.
2. They can be used as standby plants to hydro-electric power plants and steam power plants for emergency service.
3. They can be used as peak load plants in combination with thermal or hydro-plants.
4. They are quite suitable for mobile power generation and are widely used in transportation systems such as
automobiles, railways, air planes and ships.
5. Nowadays power cut has, become a regular feature for industries. The only solution to tide over this difficulty is to
install diesel-generating sets.
10. Explain the working principle of gas power plant(combined cycle) with neat diagram
Working principle of gas power plant (combined cycle)
Gas power plant is expensive to operate. Therefore, it is usually installed with steam power plant in closed
combined cycle. Fig. 1 shows a schematic diagram of the closed combined cycle gas power plant, which has a
combination of gas turbine and steam turbine. The combined cycle gas power plant consists of air compressor, gas
turbine, heat recovery steam generator, steam boiler, steam turbine, steam condenser and generators.
Combustion and generation of electricity : The gas turbine draws clean air through suitable air filter from the
atmosphere with the help of a compressor. Due to the compression, the pressure of the air is increased. Then, the
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compressed air is passed to a combustion chamber along with fuel (natural gas). The air-fuel mixture is ignited at high
pressure in the combustion chamber and as a result, combustion takes place. The generated hot gas of combustion is
passed through the gas turbine. As a result, the hot gases expand and the turbine blades connected to the turbine shaft
are rotated. The turbine shaft, which is coupled to the shaft of the electrical generator at the other end also rotates and
drives the electrical generator. A portion of the energy developed by the hot gases passing through the gas turbine is
used to run the compressor.
The residual hot gases from gas turbine are passed through a heat exchanger (heat recovery steam generator),
which produces steam with high pressure with a help of steam boiler. The steam is allowed to expand in the steam
turbine when it passes through the turbine blades and thus the shaft of the steam turbine is rotated. The steam turbine
shaft is coupled to the shaft of the generator, which also generates electricity. Gas turbine and steam turbine
combination enables increased power generation.
Transmission and distribution : The generated electricity from both gas and steam turbines is fed to the step-up
transformer where its voltage is increased. Then, the electricity is conveyed through transmission lines for distribution.
Condensation of steam : The gas power plant incorporates condensation process also which increases the efficiency of
the power plant.
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11. State the merits and demerits of gas power plant.
Merits of gas power plant
• Natural gas is readily available.
• Setting-up cost can be reduced if the plant is installed near the fuel source.
• Less gas storage cost and space occupied is also less.
• Design and construction of gas power plant are simpler than those of a thermal power plant.
• Much smaller in size compared to the steam power plant of same capacity.
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• Low operating cost.
• Less water consumption.
• Low maintenance cost.
• Can be started quickly and can be put on load in a very shorter time.
• No stand-by losses.
• Cheaper fuels like natural gas, kerosene and benzene are used.
Demerits of gas power plant
• Two-thirds of generated power is used for driving the compressor.
• Gas turbine has low thermal efficiency.
• Turbine blades have to be cooled by special cooling methods.
* Has starting problem.
• Efficient only in a combined cycle configuration.
• Temperature of combustion chamber is too high thereby resulting in a shorter life.
12. Explain the working principle of reciprocating pump(single acting & double acting)
Working principle of reciprocating pump
The reciprocating pump consists of a piston that reciprocates in a cylinder with a suction port and a delivery port
as shown in Fig. 1. Check valve (one way valve) in the suction and delivery ports allow flow in only one direction.
During the suction stroke (Fig. 1 a), the piston moves to the left, causing the check valve in the suction line between the
tank and the pump cylinder to open and admit water from the tank/well to the cylinder. During the discharge stroke
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(Fig. 1 b), the piston moves to the right, closes the check valve in the suction line and opens the check valve in the
delivery line. The volume of liquid moved by the pump in one cycle (one suction stroke and one discharge stroke) is
equal to the change in the liquid volume of the cylinder as the piston moves from its farthest left position to its farthest
right position.
Types of reciprocating pump
Reciprocating pumps are broadly classified as single-acting and double-acting.
Single acting reciprocating pump : Fig.2 shows a simple arrangement of single- acting reciprocating pump. The
pumping unit consists of the piston, cylinder (bi-housing body), valves, oil seal, sleeve, compression ring, piston rod,
suction and delivery pipes (ports). The pump works on the principle of reciprocation of the piston in the cylinder. The
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basic principle of operation is the creation of vacuum resulting in suction and compression of water resulting in
discharge. In a single-acting pump, the liquid is filled in the cylinder in only one direction during suction stroke
(Fig.2a).
Then, the liquid is forced out of the cylinder during the return stroke called the discharge stroke (Fig. 2b).
Double acting reciprocating pump : In double acting pump, each cycle consists of two strokes. Both the strokes are
effective and hence, it is known as a double-acting reciprocating pump. Fig. 3 shows a simple arrangement of double-
acting reciprocating pump. In a double-acting pump, liquid is filled at one end and discharged at the other end of the
cylinder during the forward stroke (Fig. 3a). On the return stroke, the end of the cylinder just emptied is filled and the
end just filled is emptied (Fig. 3b).
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13. Explain the Working principle of centrifugal pump with neat sketch.
A centrifugal pump works on the principle of conversion of the mechanical (rotational) energy of an electric
motor or engine into kinetic energy and then into pressure energy of fluid that is being pumped. A centrifugal pump has
two main components (i) a rotating component comprising an impeller and a shaft (ii) stationary component comprising
a volute (casing), suction pipe and delivery pipe. Fig. 5 shows the sectional view of a typical centrifugal pump. The
impeller converts mechanical (rotation) energy into kinetic energy that provides the centrifugal acceleration to the fluid.
The volute (casing) converts the kinetic energy into pressure.
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Conversion of kinetic energy into pressure head : The rotation of the pump impeller imparts kinetic energy to the fluid
drawn into the suction pipe and then into impeller eye (centre of the impeller). When the impeller rotates, it spins the
liquid and provides centrifugal acceleration. As the liquid leaves the eye of the impeller, a low pressure area is created
causing more liquid to flow towards the eye. The curved impeller blades push the liquid in a tangential and radial
direction by the centrifugal force. As the fluid exits the impeller, the kinetic (velocity) energy of the fluid is converted
into pressure (head) due to change in area when the fluid moves to the volute section. The volute forces the liquid to
discharge from the pump.
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The head (pressure in terms of height of liquid) developed is approximately equal to the velocity energy at the
periphery of the impeller.
14. Explain the Day-to-day operation of centrifugal pump
Fig.6 shows a centrifugal pump. Priming cock is opened and water is poured till all the air bubbles escape and the
pump is filled with water. Now, the motor can be switched on. The foot valve forms the bottommost part of the suction
pipe. It is a one-way non-return valve which allows water only in upward direction. The foot valve is fitted with a
strainer that prevents the entry of any solid particles into the suction pipe. The bottom portion of the suction pipe is
immersed in water. The pumping should be stopped when the water level is just above the foot valve. Otherwise, air
particles will enter the suction pipe and cause air locking. Once air locking occurs, pump will not deliver water unless
priming is done.
Suction head is the distance between the centre of the impeller eye and the water level in the sump or well.
Suction head varies with the water level in the well. The distance between the impeller eye and the point of delivery of
water is called delivery head. Thus, total head = suction head + delivery head.
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37
15. Explain the working principle of impulse and reaction turbine:
Working principle of an impulse turbine : An impulse turbine is also known as velocity turbine. Fig. 1(a) shows the
working of a simple impulse turbine. The high pressure steam from the boiler is sent through the fixed nozzles. The
steam is allowed to expand at the end of the nozzle at high velocity in the form of jet. The jet strikes the blades of the
steam turbine thus developing an impulse force that rotates the rotor of the turbine.
Fig. 1(b) shows the variation of steam pressure and steam velocity across nozzle and blade of an impulse turbine.
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39
Working principle of a reaction turbine : The reaction turbine applies the principle of both impulse and reaction force.
In other words, the driving force is partly impulsive force and partly reaction force. Fig.2(a) shows the working of a
simple reaction turbine. In the reaction turbine, there is no nozzle. However, both fixed blades and moving blades
behave as nozzles. The kinetic energy in the reaction turbine is available in the form of change in momentum of steam
(impulse) that occurs in the fixed blades and the reaction that is developed by the expanding steam in the moving
blades.
Thus, a combination of impulsive force and reaction force causes the rotation of the shaft of the reaction turbine. The
shaft of the turbine is coupled to a generator that generates electricity.
Fig.2(b) shows the variation of steam pressure and steam velocity across the fixed blades and moving blades of a
reaction turbine.
16 . Compare the impulse and reaction turbine
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17. Explain the Working principle of open cycle gas turbine:
In open cycle gas turbine (Fig.3), the air compressor sucks air from the atmosphere and compresses it to high
pressure. In the combustion chamber, the compressed air-fuel mixture is ignited (burnt) and high pressure and high
velocity gas is produced. The high pressure and high velocity gas is allowed to expand in the gas turbine. The turbine
has fixed and moving blades. The stationary blades guide the gases towards the moving blades that rotate the shaft of
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the turbine. The shaft of the turbine is in turn coupled to a generator that generates electricity. Part of the gas turbine
power is also used for driving the compressor. In the open cycle, the working fluid (air and fuel mixture) must be
replaced continuously as they are finally exhausted into the atmosphere.
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18. Explain the Working principle of closed cycle gas turbine :
In a closed cycle gas turbine (Fig.4), the same working fluid (air-fuel mixture) is continually circulated and used.
The compressed air from the compressor is heated in the heat exchanger using external sources such as oil, coal, etc. In
the combustion chamber, the compressed air-fuel mixture (working fluid) is ignited (burnt) and high pressure and high
velocity gas is produced. Then, the burnt working fluid is expanded through the turbine blades rapidly causing rotation
of the turbine blades and the turbine shaft. The turbine shaft is in turn coupled to a generator that generates electricity.
The exhaust working fluid (in wet condition) is cooled in a pre-cooler before it is directed to the compressor again.
Since same working fluid is used in closed cycle gas turbine, there is less chance of corrosion of turbine blades and
hence there is no need for internal cleaning. The efficiency of the closed cycle gas turbine is higher than that of the
open cycle gas turbine.
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19. Explain the working principle of pelton turbine:
Impulse turbine - Pelton turbine
Pelton turbine is a type of impulse turbine named after Pelton who invented it. Pelton turbines are suited to high heads
(normally more than 300 meters) and low water flows.
Working principle of Pelton turbine: Fig.5 shows the working of a Pelton turbine. The water is allowed to flow through
a pipe (penstock) down a hillside. At the lower end of the pipe, the water is passed through a nozzle. The water coming
out of the nozzle in the form of jet strikes the spoon-shaped buckets or cups arranged on the periphery of a runner
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mounted on the shaft of the turbine with very high velocity. The buckets are designed in such a way that when the
water strikes the bucket, an impulse force is developed at the centre of the bucket. This force causes the runner to rotate
and thus making the shaft of the turbine to rotate. The shaft of the turbine is coupled to a generator that generates
electricity. The rotation of the shaft is controlled by adjusting the flow of water to the buckets. In order to stop rotation
of the turbine wheel, a valve (spear rod) is used to shut off the water completely. After impinging on the buckets, the
water flows into the tail-race. Pelton turbines can be operated at 90 % efficiency.
Precaution : Pelton wheel should be erected at such a level that the buckets do not touch the tail-race water when the
wheel rotates.
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20. Explain the working principle of Kaplan and Francis turbine
Reaction turbine — (i) Kaplan turbine
Kaplan turbine is a type of reaction turbine developed by Kaplan. Kaplan turbines are widely used for low heads
(usually less than 30 meters) and high flows (large discharge). The Kaplan turbine is an inward flow reaction turbine,
which means that the working fluid (water) changes its pressure as it moves through the turbine and gives up its energy.
The fluid flow is both radial and axial.
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Working principle of Kaplan turbine : The Kaplan turbine has a propeller resembling a marine propeller or airplane
propeller that has adjustable (movable) blades (Fig.7). The Kaplan turbine is completely immersed in water. The
turbine blades are rotated by the pressure of water. The guide vanes (wicket gates) help to regulate the amount of water
approaching the blades. The guide vanes could also be turned off or automatically adjusted to any angle suited to that
of the blades to enable Kaplan turbine work efficiently at different workloads. The adjustable runner blades enable high
efficiency even with variation of flow conditions or load.
As the water passes through the runner and over the curved surfaces, it causes rotation of the runner. The rotational
motion (mechanical energy) is transmitted by a shaft to a generator that generates electricity.
The outlet of the Kaplan turbine consists of a specially shaped draft tube that reduces the velocity of water. Draft tube
also helps in recovering the kinetic energy. The draft tube must be immersed in water to at least one metre below the
lowest tail-race level.
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48
Reaction turbine — (ii) Francis turbine
Francis turbine is a type of inward flow reaction turbine (combination of both radial and axial flow) developed by
Francis. Francis turbine is designed for a wide range of heads (3-600 meters) and flows. Fig.8 shows a photograph of
the blades of a typical Francis turbine. A Francis turbine is normally located at the base of a dam prefer
between the high pressure water source and the low pressure water exit.
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REVIEW QUESTIONS
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PART A
1. Define the term: Prime mover.
2. ‘Energy exists in various forms.’ State any four forms of energy.
3. Give examples for conventional and non-conventional sources of energy.
4. Give examples for renewable and non-renewable sources of energy.
5. Name any two coal handling equipment in a thermal power plant.
6. What are the two major problems associated with the thermal power plant.
7. State any two significant advantages of a thermal power plant.
8. The power transmission losses are minimum for thermal power plant-How?
9. Explain briefly the phenomenon of water hammer.
10. How do you classify the hydro-electric power plants?
11. What are the components of a nuclear reactor?
12. State the function of the pressuriser in a nuclear reactor.
13. Name any two types of nuclear reactors.
14. State any two applications of the diesel power plant.
15. State any two applications of the gas turbine power plant.
16. Distinguish between open cycle and closed cycle systems of a gas turbine.
17. Name any two fuels used in the gas turbine.
18. What are the alternate sources of energy to fossil fuels?
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19. State any three applications of solar energy.
20. Explain briefly how wind is caused?
21. What are the applications of solar cells?
22. What are desirable locations of wind mills?
23. What are the two different uses of steam produced in the boiler?
24. Where do you use process system?
25. State any two primary requirements of a boiler?
26. How do you classify boilers?
27. State any two salient features of Cochran boiler.
28. What is the function of baffles in Babcock and Wilcox boiler?
29. What do you understand by natural circulation?
30. State the functions of:
i) Safety Valve iii) Fusible plug
ii) Stop Valve iv) Blow-off Cock
31. State any two advantages of high pressure boilers.
32. What do you understand by forced circulation?
33. How do you classify prime movers?
34. Define the terms: Impulse and Reaction.
35. Draw the pressure velocity diagram of a single stage impulse turbine.
36. Mention any two applications of gas turbine.
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37. Name any two fuels used in a gas turbine.
38. How do you classify gas turbines?
39. State the basic difference between the open cycle and closed cycle gas turbines.
40. Define the terms: Hydraulic prime mover, Axial flow turbine, Tangential flow turbine, Impulse turbine and
Reaction turbine.
41. How do you classify hydraulic turbines according to the type of energy at inlet?
42. How do you classify hydraulic turbines according to the head at the inlet?
43. What is a pump?
44. What do you mean by pumping?
45. Mention any two important uses of pumps.
46. What is the function of non-return valve in a reciprocating pump?
47. Pump industry attaches more emphasis on high reliability than on efficiency. Why?
48. When can the slip, in a reciprocating pump, be negative?
49. Name the different types of casings for the impeller of a centrifugal pump.
50. Under what headings the centrifugal pumps are classified?
51. How do you classify pumps?
52. Explain the function of spiral casing for a centrifugal pump.
53. Define positive displacement pump. Give an example.
54. Define rotodynamic pump. Give an example.
55. Define the terms: Reciprocating pump, Centrifugal pump, Priming and NPSH.
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56. State any two applications of reciprocating pumps.
57. How do you classify reciprocating pumps?
58. Define the term: Specific speed of a centrifugal pump.
59. Write the equation for the discharge through a single acting reciprocating pump.
60. Name the types of impellers used in centrifugal pumps.
61. Why is priming necessary in a centrifugal pump?
PART B
1. Discuss the various renewable and non-renewable sources of energy in detail.
2. Compare the various sources of energy, highlighting important characteristics.
3. List the advantages and disadvantages of renewable energy resources.
4. With the aid of a general layout, explain the working of different circuits of a thermal power plant.
5. Sketch and describe the schematic arrangement of a modern steam power station and detail the various heat saving
devices used.
6. Give a schematic layout of a storage type hydro-electric power plant and explain the function of each component of
the plant.
7. State the advantages and disadvantages of hydro-electric power plant compared to thermal and nuclear power plants.
8. Explain the working principle of a nuclear power plant. Draw a neat diagram of a nuclear plant and explain how it is
different from conventional thermal power plant.
9. a) Sketch schematically the arrangement of a diesel power plant for electric power generation and explain the
functions of its main components.
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b) What are the applications of the diesel power plants?
10. a) Discuss the factors which go in favour of gas turbine power plant compared to other types of power plants.
b) Explain the essential features and their functions of a gas turbine power plant with a neat diagram.
11. Write brief notes on the following:
i) Classification of hydro-plants
ii) Clean atomic power using nuclear fusion
12. State the advantages and disadvantages of a hydel power plant.
13. State the advantages and disadvantages of the diesel power plant.
14. State the advantages and disadvantages of a gas turbine plant.
15. Enumerate the various types of steam generators.
16. Explain, with a neat sketch, the working of a Cochran boiler.
17. Sketch and describe the working principle of a locomotive boiler.
18. With the aid of neat sketches, explain the constructional features and functioning of a Lancashire boiler.
19. Give an outline sketch showing the arrangement of water tubes and furnace of a Babcock and Wilcox boiler.
Indicate on it the path of the flue gases and water circulation. Show the positions of superheater, fusible plug and blow-
off cock. Mention the function of each.
20. Explain, with the help of a diagram, the construction and working of a fire tube boiler.
21. Distinguish between fire tube boilers and water tube boilers.
22. Name the important boiler mountings and briefly explain their functions.
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23. Describe, with a neat sketch, a water level indicator. Explain how the flow of steam and water is automatically
stopped when the glass tube breaks.
24. What is the purpose of a fusible plug? Explain.
25. Define a High Pressure Boiler. Mention the advantages of high pressure boilers.
26. Explain the working principle of La-Mont High Pressure Boiler with a neat sketch.
27. Discuss the working and the salient features of Benson Boiler with a neat sketch.
28. Discuss the concept of cogeneration. Explain topping cycle system.
29. Explain the bottoming cycle system of cogeneration with a suitable sketch.
30. What are the benefits and applications of cogeneration.
31. With the help of a neat sketch, explain the principle of a single stage impulse turbine.
32. Sketch and explain a velocity compounding impulse turbine. Give the pressure
velocity diagram.
33. Sketch and explain a pressure compounding impulse turbine. Give the pressure
velocity diagram.
34. Explain the principle of reaction turbine. Explain the constructional features and
working of Parson’s reaction turbine.
35. Distinguish between impulse and reaction steam turbines.
36. With the help of a neat sketch, explain the working of open cycle gas turbine.
37. What are the advantages and disadvantages of open cycle gas turbine.
38. With the help of a neat sketch, explain the working of closed cycle gas turbine.
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39. What are the advantages and disadvantages of closed cycle gas turbine.
40. With the help of a neat sketch, explain the working principle of Pelton wheel.
41. Explain the constructional features and working of a Francis turbine.
42. Sketch and explain the working of a low head reaction turbine.
43. What is a reciprocating pump?
44. Why is a reciprocating pump called Positive Displacement Pump?
45. Describe the working of a single stage reciprocating pump with a neat sketch.
46. How do you classify the reciprocating pumps?
47. Differentiate:
A] Between a single acting and double acting reciprocating pump.
B] Between a single cylinder and double cylinder reciprocating pump.
48. What is a centrifugal pump? On what principle does it work?
49. Explain the working of a single stage centrifugal pump with sketches.
50. Differentiate between volute casing and vortex casing for the centrifugal pump.
51. What do you understand by the term ‘Multi-stage Pump’? Explain clearly the difference between a single stage and
a multi-stage centrifugal pump.
52. State the differences between a closed, semi-closed and open impeller.
53. Define the terms: Suction head, Delivery head, Static head and Mechanical efficiency.
54. Differentiate between volute casing and diffuser casing with suitable sketches.
55. What is priming? Why is it necessary?
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56. Define cavitation. What are its causes?
57. What are the effects of cavitation? Give the necessary precautions against cavitation.
IC ENGINES AND BOILERS PART A 1. Define the following terms: i) Cylinder bore ii) Stroke or stroke length iii) TDC iv) BDC v) Compression ratio vi) Stroke volume or swept volume or displacement volume vii)Clearance volume viii)Air-fuel ratio ix) IHP x) BHP xi)FHP xii)Thermal effiency xiii) Mechanical efficiency 1. Cylinder Bore: The inside diameter of the engine cylinder is known as Cylinder bore. 2. Stroke or Stroke Length: It is the linear distance through which the piston moves inside the cylinder during one stroke. In other words, stroke length is the distance between the extreme upper and lower positions of the piston. Numerically, the stroke length is equal to twice the crank radius. 3. Top Dead Center (TDC) or Inner Dead Center (IDC): Top Dead Center (TDC) in the vertical engine is the extreme position of the piston on the top of the cylinder (head side). At this position, piston motion reverses direction and the cylinder volume is at a minimum. In the case of horizontal engine, this position is known as Inner Dead Center (IDC). At TDC or IDC, the crank angle is zero. 4. Bottom Dead Center (BDC) or Outer Dead Center (ODC): Bottom Dead Center (BDC) in vertical engine indicates the extreme position at the bottom of the cylinder. At this position, the piston motion reverses direction and the cylinder volume is at a maxim urn. In the case of horizontal engine, this position is known Outer Dead Center (ODC). At BDC or ODC, the crank angle is 180°. 5. Compression Ratio: It is a ratio of the volume when the piston is at bottom dead center to the volume when the piston is at top dead center.
Compression Ratio = Maximum cylinder volume/ Minimum cylinder volume 6. Stroke Volume or Swept Volume or Displacement Volume: It is the volume generated by piston movement in one stroke from one dead center to other. Swept Volume= pie* D*D/4 x L ( D = cylinder bore and L = piston stroke length ) 7. Clearance Volume: The volume contained in the cylinder above the top of the piston, when the piston is at TDC is called Clearance Volume. Thus, when the piston is at BDC, total volume = Swept Volume + Clearance Volume. 8. Air-Fuel Ratio: This is expressed as a ratio of the mass of air to the mass of the fuel. 9. Indicated Horse Power (I.H.P.): It is the power produced within the engine cylinder. It is called indicated power as it can be measured with the help of an Indicator. Indicator is an instrument that draws pressure-volume diagram for the engine. 10. Brake Horse Power (B.H.P.): This is the net output of an engine. It is called Brake Power, since it can be measured by absorbing the power with a brake system. (The brake system consists of a brake pulley mounted on the engine shaft.) 11.. Friction Horse Power (F.H.P.): It is the difference between I.H.P. and B.H.P. This is the power absorbed by the moving parts of the engine (piston bearings, etc.,). 12. Thermal Efficiency: It is the ratio of work done inside the engine cylinder (I.H.P.) to the fuel energy supplied to the engine. 13. Mechanical Efficiency: Mechanical Efficiency of an IC. engine is defined as the ratio of power delivered (B.H.P.) to the power provided to the piston (I.H.P.). 2. Name some of the BOILER MOUNTINGS? For the safe operation, satisfactory functioning, efficient working and easy maintenance of the boilers, Boiler Mountings are provided as per the Indian Boiler Act. These include: 1. Water Gauge (Water Level Indicator) 2. Pressure Gauge 3. Safety Valves (A) Spring Loaded Safety Valve (B) High Steam Low Water Safety Valve
4. Fusible Plug 5. Feed Check Valve 6. Stop Valve 7. Blow-off Cock 3. Define the function of the following engine parts i) Engine cylinder ii) Cylinder head iii) Piston iv) Piston rings v) Piston pin vi) Connecting rod vii) Valves viii) Crank and crank shaft ix) crank case x) Flywheel 1. Engine Cylinder: The heart of the engine is the cylinder in which fuel is burnt and power is developed. The cylinder allows the piston to move to and fro. Combustion of fuel takes place inside the cylinder. The cylinder has to withstand a high pressure (more than 500 N / sq.cm.) and temperature (around 1500°C to 2000°C). 2. Cylinder Head: The cylinder is closed by the cylinder head at one end and the other end is covered by the moving piston. The cylinder head contains inlet and exhaust valves for admitting fresh charge and for exhausting the burnt gases. In petrol engines, the cylinder head also contains a spark plug for igniting the fuel mixture. But in diesel engines, the cylinder head contains nozzle for injecting the into the cylinder. 3. Piston: Piston is sliding within the cylinder. This sliding movement changes volume of the cylinder and provides the combustion space. The space formed bet the cylinder head and top of the piston during the process of combustion is known as Combustion Chamber. Piston transmits the force exerted by the burning of the charge the connecting rod. 4. Piston Rings: Piston rings are circular rings used to maintain a pressure tight seal between the moving piston and the cylinder wall. 5. Piston Pin (also known as Gudgeon Pin): A Piston Pin (Gudgeon Pin ) connects piston to the small end of the connecting rod.
6. Connecting Rod: As the name suggests, the connecting rod connects the piston with the crank. It is attached to the piston by piston pin. It converts the up and down motion (reciprocating motion) of the piston to a rotary motion of the crankshaft. 7. Valves: Valves are needed to let the air and fuel into the cylinder (Intake Valve) and also to let out the burnt or spent gases after they have done their work (Exhaust Valve). Valves are operated by cams, rotated by a camshaft, driven by the crankshaft. [However, two stroke cycle engines have only ports at the cylinder walls and have no valves.] 8. Crank and Crankshaft: Crank is a lever. It is connected to the end of the connecting rod by a pin joint. Its other end is connected to a shaft called Crankshaft. It is the rotating member of the engine. Its function is to convert the reciprocating motion of the piston into a rotary motion with the help of the connecting rod. 9. Crank Case: The main body of the engine which contains the crank and crankshaft is known as Crank Case. It serves as sump for the lubricating oil. 10. Flywheel: It is a heavy wheel, mounted on the crankshaft. Its function is to store the excess energy during power stroke of the engine and help the movement of the piston during the remaining idle strokes, thus maintaining uniform rotation (speed) of the crankshaft.
4. What are the primary requirements of a good boiler?
The primary requirements of a boiler are as follows: - Steam must be delivered at the required temperature, pressure and at the required rate. - Maximum heat produced by the fuel in the furnace should be utilized for economy. - The boiler should be easily accessible for maintenance and inspection. - It should rapidly meet the changes in load. 5. Classify the boilers based on different characteristics Boilers can be classified as follows: 1. According to the Flow of Water and Hot Gases — Fire Tube (or Smoke Tube) Boiler and Water Tube Boiler. In Fire Tube Boilers, hot gases pass through tubes which are surrounded with water. Examples: Cochran, Lancashire and Locomotive boilers. There may be single tube as in the case of Lancashire boiler or there may be a bank of tubes as in a Locomotive boiler. In Water Tube Boilers, water circulates through a large number of tubes and hot gases pass around them. Example: Babcock and Wilcox Boiler. 2. According to the Axis of the Shell — Vertical and Horizontal Boilers. 3. According to the Application — Stationary and Mobile Boilers. A Stationary Boiler is one which is installed permanently on a land installation. Examples: Cochran, etc. A Marine Boiler is a mobile boiler meant for ocean cargo and passenger ships with an inherent fast steaming capacity. 4. According to Steam Pressure — Low, Medium and High Pressure Boilers. 6. What do you mean by a high pressure boiler? For pressures less than 140 bar, the natural circulation boilers are suitable. For pressures higher than 140 bar and in the supercritical range, i.e., around 221 bar and temperature 375°C, forced circulation boilers are used. Forced circulation boilers are also known as High Pressure Boilers. Water tube boilers are generally preferred for high pressure and high output. But, fire tube boilers are used for low pressure and low output. PART B
1. Explain the working of a four stroke petrol engine with the help of PV diagram.
Petrol Engine is also known as Spark Ignition (SI.) Engine. Four Stroke Petrol Engine requires four strokes of the piston to complete one cycle of operation in the engine cylinder.
See Fig. 2. It consists of a cylinder. Its one end is fitted with a cover and the other end left open. The cover is provided with inlet and exhaust apertures. These apertures are opened and closed by inlet and exhaust valves. A spark plug initiates the ignition of the fuel. The piston reciprocates inside the cylinder. The connecting rod and crank convert the reciprocating motion of the piston into rotary motion.
The petrol engine works on the principle of Otto Cycle, also known as Constant Volume Cycle. Fig. 3 shows the Pressure Velocity Diagram of Theoretical Otto Cycle. 1. Suction Stroke: Fig. 2(a)
During suction stroke, the Inlet valve (1) opens and air and fuel (petrol) mixture (charge) is sucked into the cylinder. The piston moves downward from Top Dead Center (TDC) till it reaches Bottom Dead Center (BDC). During suction stroke the Exhaust value (E) is closed. See Fig. 3. Suction stroke is theoretically represented by the horizontal line 1-2 in the PV Diagram. The drawal of air-fuel mixture is taking place at atmospheric pressure. 2. Compression Stroke: Fig. 2(b)
During this stroke, both the inlet and exhaust valves are closed. The air-fuel mixture is compressed as the piston moves upwards from BDC to TDC. The compression ratio in petrol engines varies from 7 to 10. As a result of compression, pressure and temperature of the charge are increased to 15-20 bar and 400°C respectively. See Fig. 3. The process of compression is theoretically represented by the curve 2-3 in the PV Diagram.
Shortly before the piston reaches TDC, the charge is ignited by means of a Spark Plug. It suddenly increases the pressure and temperature of the products of combustion, the volume remains constant.
During the burning process, the chemical energy of the fuel is converted into heat energy, producing a temperature rise of about 2000° C. See Fig. 3. This constant volume combustion process is theoretically represented by the vertical line 3-4 in the PV Diagram.
3. Expansion or Power or Working Stroke: Fig. 2(c) During this stroke, both the valves remain closed. Due to the rise in
pressure, piston is pushed down with a great force. The hot burnt gases expand pushing the piston from TDC to BDC. It is also called Working Stroke as work is done by the expansion of hot gases. See Fig. 3. The expansion stroke is theoretically represented by the curve 4-5 in PV Diagram. At or near the end of the expansion the exhaust valve opens to release the gases to the atmosphere. This suddenly brings down the Cylinder to atmospheric pressure. This drop in pressure at constant volume is theoretically represented by the vertical line 5-2 in the PV Diagram as shown in Fig. 3. Exhaust Stroke: Fig. 2(d) During this stroke, the exhaust valve opens, as moves from BDC to TDC. This movement of the piston pushes out the exhaust gases from the cylinder. The exhaust gases are exhausted through the exhaust valve into the atmosphere. See Fig. 3. The exhaust stroke is theoretically represented by the horizontal line 2-l in the PV Diagram. Uses: Four stroke petrol engines have higher load carrying capacities than two stroke petrol engines. Hence, they are used in high power high speed motor cycles and passenger cars.
2. Explain the working of a four stroke diesel engine with the help of PV diagram. The basic construction of a four stroke cycle diesel engine is the same as that of four stroke cycle petrol engine, except that instead of a spark plug, a fuel injector is mounted in its place. A fuel pump supplies diesel to the injector at higher pressure. Dr. Rudalf Diesel invented the Diesel Engine. It is also known as Compression Ignition (CI.) Engine, since ignition takes place due to the high temperature produced during the compression of air in engine cylinder. Liquid fuel, i.e., diesel, which cannot be vapourized, is injected into the cylinder in the form of fine spray using fuel pump and injector. Diesel engine works on the principle of Theoretical Diesel Cycle, also known as Constant Pressure Heat Addition Cycle. Fig. 5 shows the Pressure Velocity Diagram of the same. The ideal sequence of operation for the four stroke C.1. engine is explained as follows: 1. Suction Stroke: Fig. 4(a) During suction stroke, inlet valve (I) opens and exhaust valve (E) remains closed. The piston travels downwards from TDC. Air is drawn in, from outside to fill the cylinder through inlet valve till the piston reaches BDC. The air taken in is at atmospheric pressure. Suction stroke is theoretically represented by the horizontal line AB in the PV Diagram in Fig. 5. 2. Compression Stroke: Fig. 4(b)
At the end of the suction stroke, both the inlet and the exhaust valves remain closed. The piston moves upwards from BDC to TDC. The air sucked in during suction stroke is compressed to a high pressure (35- 40 bar) and temperature with a decrease in volume. These two strokes, viz., suction stroke and compression stroke complete one revolution of the crankshaft. The compression stroke is theoretically represented by the curve BC in Fig. 5. 3. Expansion or Power or Working Stroke: Fig. 4(c) Just before the beginning of this stroke, fuel (diesel) is Injected in the form of fine spray in the cylinder through the Fuel Injector. At this moment, the fuel is ignited by temperature of the hot compressed air and it starts burning at constant pressure.Due to the high compression ratio of 16 to 20, the temperature at the end compression stroke is more than 550°C. This temperature is sufficient to ignite the fuel injected into the combustion chamber. The fuel is continuously injected for 20% of expansion stroke. The ignited air-fuel mixture expands and forces the piston downwards from TDC to BDC. During this constant pressure expansion stroke, both the valves remain closed. See Fig. 5. This constant pressure expansion with simultaneous combustion theoretically represented by the horizontal line CD in the PV Diagram. The piston is forced further during the remaining part of the expansion stroke due the expansion of the burnt gases. [The linear motion of the piston causes the piston produce the mechanical work during this stroke.] As the piston moves, the pressure of the hot gases gradually decreases. The expansion of the burnt gases is theoretically represented by the curve DE in the PV Diagram as in Fig. 5. At the end of the outstroke, the exhaust valve opens. Some of the burnt gases escape into the atmosphere from the cylinder through the exhaust outlet at constant volume. This is theoretically represented by the vertical line EB. 4. Exhaust Stroke: Fig. 4(d) During the exhaust stroke, the inlet valve is closed and the exhaust valve is opened. The piston is on its upstroke from BDC to TDC, forcing the burnt gases out of the cylinder through the exhaust valve. See Fig. 5. The exhaust stroke is theoretically represented by the horizontal line BA. Expansion and exhaust stroke complete one revolution of the crankshaft. This completes the cycle and the engine cylinder is ready to suck the fresh air once again.
Uses: They are used in heavy-duty transport vehicles such as trucks, tractors, bulldozers. etc., power generation, industrial and marine applications.
3. Draw and explain the sequence of operations of a two stroke cycle petrol engine. Scavenging In the two-stroke petrol engine, the exhaust gases are removed from the cylinder with the help of fresh compressed charge. This process of removing exhaust gases is called Scavenging. A specific shape is given to the piston,
called deflector. The deflector helps to prevent the loss of incoming charge and helps for exhausting the hot gases effectively. It will be easier to describe the cycle beginning at the point when the piston reaches TDC at the end of the compression stroke. In the two-stroke petrol engine, the draw of petrol-air mixture into the cylinder will not take place in a separate stroke. Therefore, the method of draw of petrol-air mixture should be understood properly. First Stroke Fig. 7(a) shows the position of the piston at the end of compression. The spark is produced by the spark plug as the piston reaches TDC. The pressure and temperature of the gases are increased and hence the gases push the piston downwards producing the power stroke. Refer Fig. 7(b). When the piston opens the exhaust port during the downward stroke, burnt gases leave the cylinder through the exhaust port. Refer Fig. 7(c). A little later, the piston uncovers the transfer port and the crank case is directly connected to the cylinder through the transfer port. The downward stroke of the piston compresses the charge in the crank case by the underside of the piston. Scavenging: In the above position of the piston, the compressed mixture of petrol and air is transferred through the transfer port to the upper part of the cylinder. The exhaust gases are pushed out, with the help of compressed charge. This is known as Scavenging. Scavenging is continued until the piston reaches BDC. Second Stroke As the piston moves upwards, it covers the transfer port. Hence, flow of charge into the cylinder is stopped. The upward motion of the piston lowers the pressure in the crank case below atmosphere and fresh air is induced in the crank case through the inlet port as it is uncovered. A little later, the piston covers the exhaust port and actual compression of the charge starts as shown in Fig. 7(d). The compression is continued until the piston reaches TDC. The ratio of compression ranges from 1:7 to 1:10. The cycle is thus completed within two strokes. Note: The two-stroke engine requires only two strokes of the piston to complete one cycle of operation. The crankshaft makes only one revolution to complete one cycle. Power is developed in every revolution of the crankshaft. Uses: Two-stroke petrol engines are used in mopeds, scooters, motorcycles, because they at high speeds with moderate power outputs.
4. Draw and explain the sequence of operations of a two stroke cycle diesel engine. Refer Fig. 8. In two-stroke diesel engine, the draw of pure air into the cylinder will not take place in a separate stroke. First Stroke Fig. (a) shows the position of the piston at the end of compression. Diesel is injected using fuel injector just before completing the compression. It starts burning. The high pressure, high temperature gases push the piston downwards, producing the power stroke. As & piston moves little down, the supply of diesel stops. Refer Fig. (b). In this, the piston uncovers the exhaust port during the downward stroke. Hence the burnt gases leave the cylinder through the exhaust port. Refer Fig. (c). A little later, the piston uncovers the transfer port as shown. Now the crank case is directly connected to the cylinder through the transfer port. Air in crank case is compressed by underside of the piston and the compressed air is transferred to the cylinder through transfer port. The exhaust gases are pushed out with the help of fresh air until the piston reaches BDC (similar to two stroke petrol engine). Second Stroke
The piston moves upwards. It first covers the transfer port and stops the flow of air into cylinder. A little later, the piston covers the exhaust port as shown in Fig. (d), and actual compression of air starts. The upward motion of the piston lowers the pressure in the crank case below atmosphere and fresh air is induced in the crank case through the inlet port as it is uncovered. The compression of air is continued until the piston reaches TDC. The fuel supply starts just before the piston reaches TDC and the cycle is completed.
5. Compare and contrast four stroke cycle engines with two stroke cycle engines. Sl.No DETAILS FOUR
STROKE ENGINE
TWO STROKE ENGINE
1. No. of Strokes / Cycle Four strokes per cycle
Two strokes per cycle
2. No. of Revolutions / Cycle Two One 3 Power Stroke and Power
Output One power stroke for two revolutions. Hence, power
One power stroke per revolution. Hence, power output for the
output for the same size of the engine is less.
same size of the engine is more.
4. Torque Not uniform Uniform 5. Weight of the Engine Weight of the
engine is more for the same power output.
Weight of the engine is less for the same power output.
6. Operating temperature Less More 7. Lubrication and Cooling
Requirement Consumption of lubricating oil is less. Cooling requirement is less.
Lubricating oil consumption is more. Special piston cooling is necessary.
8. Fuel Consumption Less More 9. Thermal Efficiency High thermal
efficiency. Part load efficiency better than two-stroke engine,
Low thermal efficiency. Part load efficiency less than four-stroke engine.
10. Valves /Ports Contains valves Containns ports 11. InitialCost High, due to
heavy weight and complication of valve mechanism.
Low, due to lightweight and due to the absence of valve mechanism.
12. Wear and Tear Less More 13. Noise Less More 14 Uses Used for slow
speed high power applications, i.e., in cars, buses, tractors, aeroplanes, power generation, etc.
Used for high speed low power applications, i.e., scooters, motorcycles, lawn mowers, etc.
6. Discuss the merits and demerits of diesel engine over petrol engine. Sl.No. Details Petrol (S.I.) Engine Diesel (C.I.)
Engine 1. Fuel Petrol Diesel oil 2. Charge drawn in
suction stroke Air-fuel mixture is admitted.
Air alone is admitted.
3. Fuel admission Through carburettor. Through fuel pump and fuel injector.
4. Mixing of air and fuel Air and fuel mixed externally in the carburetor.
Mixing of air and fuel takes place inside the cylinder.
5. Fuel Ignition Requires an Ignition System with spark plug (Spark- Ignition)
Self-Ignition due to high temperature caused by high compression of air (Compression-Ignition).
6. Compression ratio Low (7 to 10) High (16 to 20) 7. Power Output Less due to low
compression ratio. More due to high compression ratio.
8. Cycle of operation Otto Cycle (Constant Volume Cycle)
Diesel Cycle (Constant Pressure Cycle)
9. Engine speed High speed (3000 rpm)
Low speed (400-1500 rpm)
10. Engine starting in cold weather
Easy Difficult due to high compression ratio.
11. Engine cost Less More 12. Fuel consumption More Less 13. Fuel cost More Less 14. Maintenance Cost Less Slightly higher 15. Thermal Efficiency Less(about 20%) due
to low compression ratio
More (about 30%) due to high compression ratio.
16. Weight Light Heavy 17. Uses Automobiles & aero-
planes. Buses, tractors, trucks, etc.
18. Vibration and Noise Almost nil More due to high operating pressure
BOILERS
1. Explain, with a neat sketch, the working of a Cochran boiler. Description [Fig. 11 Cochran Boiler is a vertical, multi-tubular, internally fired, fire tube boiler having a number of horizontal fire tubes. Maximum evaporative capacity is 4000 kg of steam per hour. Maximum pressure of steam is 10 bar. Cochran boiler consists of: 1. Cylindrical Shell 2. Grate and Ashpit 3. Fire Box (Furnace) 4. Flue Pipe 5. Fire Tubes or Flue Tubes 6. Combustion Chamber 7. Chimney 8. Manhole 9. Damper 1. Cylindrical Shell: The Cylindrical Shell is vertical. It is hemispherical on the top, which forms the steam space. 2. Grate and Ashpit: Grate is placed at the bottom of the furnace where coal is burnt. Ashpit is provided below the grate for the collection of ash. 3. Fire Box (Furnace): It is also dome-shaped like the shell so that the gases can be deflected back till they are passed out through the flue pipe to the combustion chamber. 4. Flue Pipe: It is a short passage connecting the fire box with the combustion chamber. 5. Fire Tubes or Flue Tubes (F): A number of horizontal fire tubes are provided, thereby the heating surface is increased. 6. Combustion Chamber: It is lined with fire bricks to prevent overheating of the boiler. Hot gases enter the fire tubes from the flue pipe through the combustion chamber. 7. Chimney: Chimney is provided for the exit of the flue gases to the atmosphere.
8. Manhole: It is provided for inspection and repair of the interior of the boiler shell. 9. Damper: Damper is provided in the chimney. Working The boiler is filled with water to the specified level. This level is maintained by supplying with make-up water using a feed pump as and when the water level drops below the specified level. The fuel (coal) is fed into the grate through the fire door and burnt. Ash formed is collected in the ashpit and then it is removed manually. The hot gases from the furnace along with the un-burnt volatile matter pass through the flue pipe to the combustion chamber. The un-burnt volatile matter leaving the furnace along with the hot gases are burnt in the combustion chamber. The fire tubes are completely submerged in water. The hot gases from the combustion chamber flow through the horizontal fire tubes and transfer the heat to the water by convection. Water is also heated by the furnace directly. The steam generated accumulates in the steam space. The flue gases from fire tubes pass through the smoke box and are exhausted to the atmosphere through the chimney. Smoke box door is for cleaning fire tubes and smoke box. Damper controls the waste flue gases leaving the chimney. When the damper is partly closed manually, the quantity of waste gases flowing out is reduced. Hence, the quantity of air entering the grate will also be reduced. This results in reduction of the fuel burnt and consequent reduction in the steam generation. Thus, the damper controls the rate of steam generation. Boiler Mountings: The following mountings are fitted to the boiler as per Indian Boiler Act: Pressure Gauge: This indicates the pressure of the steam inside the boiler. Water Gauge: This indicates the water level in the boiler. The water level should not fall below a particular level, otherwise the boiler tubes may burn out. Safety Valve: The function of the safety valve is to prevent an increase of steam pressure in the boiler above its normal working pressure. Steam Stop Valve: It regulates the flow of steam supply from the boiler to requirements. Blow—off Cock: It is located at the bottom of the boiler. When the blow-off cock is opened during the running of the boiler, the steam pressure acting on the water surface pushes (drains) out the impurities
like mud, etc., in the water collected at the bottom. Fusible Plug: It protects fire tubes from burning when water level falls abnormally low. Advantages 1. The dome shape of the furnace causes the hot gases to deflect back and pass through the flue. The unburnt fuel if any will also be deflected back. 2. Spherical shape of the top of the shell and the fire box gives higher area by volume ratio. 3. It occupies less floor area and is very compact. Construction cost is low. Disadvantages
1. Capacity is less because of the vertical design.
2. Sketch and describe the working principle of a locomotive boiler. Locomotive boiler is a horizontal, multi-tubular, internally fired, fire tube boiler. Steaming rate is 7000 kg per hour. It is used in railway engines, rod rollers, etc. In railways, the use of locomotive steam engine is being reduced gradually. It is replaced by diesel engines. Description [Fig. 2]: A locomotive boiler consists of the following parts: 1. Horizontal Cylindrical Shell or Barrel 2. Fire Box 3. Smoke Box 4. Fire Tubes and Water Tubes 5. Fire Hole
6. Grate 7. Steam Dome 8. Headers 9. Chimney 10. Damper 1. Horizontal Cylindrical Shell or Barrel: The Shell or Barrel is cylindrical in shape of 1.5 meters in diameter and 4 meters in length. It is fitted to a rectangular Fire Box. 2. Fire Box: The fire box is at the right end of the boiler shell. It forms the furnace. 3. Smoke Box: The smoke box is at the left end of the steam shell. 4. Fire Tubes (Flue Tubes) and Water Tubes: The steam barrel consists of fire tubes and water tubes. Flue gases flow through the fire tubes. 5. Fire Hole: The fuel, i.e., coal is fed into the barrel through the fire hole. It is burnt on the Grate which slopes towards the left side. 6. Grate: Grate is placed at the bottom of the fire box where coal is burnt. 7. Steam Dome: It is fitted at the top of the steam barrel, where the steam will be collected. 8. Headers: Headers are rectangular boxes. There are two headers, viz., Superheated Steam Header and Wet Steam Header. 9. Chimney: The hot gases from the smoke box are discharged to the atmosphere through a short chimney. The height of the chimney is kept low so that when the locomotive is passing under a bridge, it does not hit against the top. 10. Damper: Function of the damper is to control the quantity of air entering the fire box. Working See Fig. 2. Water is filled to three-fourth of the barrel so as to submerge the fire tubes and fire box. Fuel, i.e., coal is introduced into the boiler furnace through the fire hole. The grate is fitted in an inclined position for charging the coal into the furnace. A fire brick arch is fitted to the furnace above the grate. This arch deflects the flue gases causing them to come in contact more thoroughly with the whole heating surface of the furnace. The flue gases from the furnace pass through the flue tubes to the smoke box. Flue gases from the smoke box are led to the atmosphere
through the chimney. The path of the flue gases is shown by arrows in the Figure. Due to the continuous flow of hot gases from the fire box to fire .tubes, water surrounding the tubes becomes more and more heated and wet steam is produced. The wet steam enters the wet steam header. To remove the moisture in the wet steam and thereby, to increase the temperature of steam, it is superheated. From the wet steam header, steam flows through superheater tube, provided in the big fire tube. Note that the flue tube into which superheater tube is accommodated, is comparatively larger in diameter than the flue tubes which do not contain superheater tube. The superheated steam is accumulated in superheated steam header. It is then led to the engine cylinder. Inside the steam dome, there is a steam stop valve in the regulator. This valve is regulated by a regulating rod to allow the required quantity of steam to pass. Regulator is operated by the driver from the cabin by a hand wheel. A blast pipe is provided at the bottom of the smoke box. The exhaust waste steam from the engine cylinder enters the blast pipe and flows out, expanding with a high velocity. Due to the expansion of waste steam, a partial vacuum is created within the smoke box. This vacuum improves the movement of waste flue gases and rapidly removes the waste flue gases from within the smoke box through the chimney. This vacuum also draws in atmospheric air through the fuel in the furnace. The boiler is fitted with a pressure gauge, safety valve, water level indicator, whistle, fusible plug, blow-off cock and manhole.
3. Explain the working principle of Babcock and Wilcox boiler with neat sketch. Babcock and Wilcox boiler is a water tube boiler. In this, water is circulated inside the tubes and hot gases flow over the tubes. Description [Fig. 3] 1. Water and Steam Drum (Boiler Shell): One half of the drum is filled with water Steam remains in the top half of the drum. It is about 8 m in length and 2 m in diameter 2. Water Tubes: Water tubes are placed between the drum and the furnace in an incline position (at an angle of 12° to 15°) to promote water circulation. These tubes at connected at right angles to the uptake-header and the down-take header as shown. 3. Uptake Header and Down-take Header: Drum is connected at one end to uptake header by short tubes and at the other end to down-take header by long tubes. 4. Grate and Furnace: Grate and Furnace are provided below the uptake-header. Coal fed to the grate through the fire door. 5. Baffles: The fire-brick baffles, two in number, are provided to deflect the hot flue gases 6. Superheater: The boiler is fitted with a superheater tube of U-shape. It is placed just under the drum and above the water tubes. Its upper box is connected to a vertical tub the top of which is situated in the steam space. Its lower box is connected to stop valve. 7. Mud Box: Mud box is provided at the bottom end of the down-corner. 8. Two Inspection Doors: These are provided for cleaning and inspection of the boiler. Working A constant water level is maintained in the boiler drum. Coal is fed to the grate through the fire door and is burnt. There is a slow moving chain grate on which the coal is fed from the hopper. By using the moving grate, the rate of fuel burning is controlled by changing thickness of the coal bed and also by changing the speed of the moving grate. Flow of flue gases: The hot flue gases from the furnace rise upward and pass across the left-side portion of the water tubes. The baffles deflect the flue gases. Hence, the flow gases travel in a zig-zag manner (i.e., the hot gases are deflected by the baffles to move upward direction, then downward and again in the upward direction) over the water tubes and along the
superheater. The flue gases finally escape to the atmosphere through the chimney . A damper is fitted as shown to regulate the flue gas outlet. Water circulation: Water descends into the down-take header. It flows upward inclined water tubes, then in the uptake headers and finally to the drum. That portion of the water tubes which is just above the furnace is comparatively at a higher temperature than the rest of it. Water, its density being d rises into the drum through the uptake-header. Here, the steam and water are separated in the drum. Steam being lighter is collected in the upper part of the drum. The water from the drum comes down through the down-take header into the water tubes. A continuous circulation of water from the drum to the water tubes and water Tubes to the drum is thus maintained. The circulation of water is known as Natural Circulation. The mud or sediment in the water is collected in the mud box. It is blown-off time to time by means of a blow-off cock. Superheating: Steam is taken from the steam space of the drum through a tube to the superheater. Steam is superheated in the superheater, as it receives additional heat. From the superheater, the superheated steam goes to the stop valve and finally to the turbine. Boiler Mountings Pressure gauge and water level indicator are mounted on the boiler at its left end Steam safety valve and stop valve are mounted on the top of the drum. Salient Features 1. Its overall efficiency is higher than a fire tube boiler. 2. The defective tubes can be replaced easily. 3. All the components are accessible for inspection even during the operation. 4. The draught loss is minimum compared with other boilers. 5. Steam generation capacity and operating pressure are high compared with fire tube boilers. 6. Normally, the furnace is provided with a moving chain grate. By changing the speed of the moving Chain grate, the rate of fuel burning can easily be controlled. 7. The water tubes are kept inclined at an angle of 10deg to 15 deg to promote water circulation.
5. With the aid of neat sketches, explain the constructional features and functioning of a Lancashire boiler. Lancashire boiler is a stationary, horizontal, internally fired, natural circulation, fire tube boiler. It can generate steam at the rate of about 9000 kg / hour at a pressure of 15 bar. Description (Fig. 4) Lancashire boiler consists of the following parts: 1. Horizontal Cylindrical Shell 2. Internal Flue Tubes (Furnace Tubes) 3. Side Flues and Bottom Flue 4. Grate 5. Furnace Door 6. Fire Bridge 7. Dampers 1. Horizontal Cylindrical Shell: It is placed in horizontal position over a brick work. It is partly filled up with water. The water level inside the shell
is well above the internal flue tubes. A Lancashire boiler may have cylindrical shell of diameter 2 — 3 meters and of length 8 — 10 meters. 2. Internal Flue Tubes (FT): Internal Flue Tubes are also known as Furnace Tubes. Two internal tubes extend from one end to the other end of the shell. These flue tubes are connected to the grate at their front end. An Enclosed Chamber (EC) is built for each of the flue tubes at the rear end of the boiler shell. 3. Side Flues (SF) and Bottom Flue (BF): There are two side flues and one bottom flue outside the shell. These flues are made of ordinary brick lines with fire bricks on their inner faces. Side Flues are connected at their rear end to a common rear passage, which is connected to the chimney flue. Internal flue tubes are connected to the Bottom Central Flue. Bottom flue, in turn, is connected to the side flues. 4. Grate (G): The grate is provided at the front end of the internal flue tubes. 5. Furnace Door (FD): Coal is fed on to the grate through the furnace door. 6. Fire Bridge (FB): It is made of brick work. It is built at the end of the grate. Its purpose is to prevent the flow of coal and ash particles into the interior of the flue tubes. Otherwise, the coal and ash particles carried with gases may settle down as deposits on the interior of the flue tubes. Thus, these deposits reduce the heat transfer from the flue tubes to the water surrounding the tubes. 7. Dampers (D1 and D2): Dampers are in the form of sliding doors. These are provided at the end of the side flues. Their function is to regulate the flow of gases from the side flues to the chimney flue. Thus, the dampers regulate the combustion rate and thereby the quantity of steam generated. NOTE : For examination purpose, only sectional front view and sectional side view need be drawn. Working Water Circulation: Boiler shell is filled with water to three-fourth of its volume so as to submerge both the internal flue tubes. The remaining space above water surface is the steam space. Path of hot flue gases See Fig. 4. The fuel (coal) is fed through the fire door on to the grate and is burnt. The hot flue gases leaving the grate move along the length of the internal flue tubes from the front end upto the rear end of the shell. As these hot gases pass through the flue tubes, heat transfer takes place from the hot gases to the water through the walls of the flue tubes. Note that the hot gases emerge from both the flue tubes into the respective rear enclosed chambers.
Then, from the rear enclosed chambers, the hot gases flow downwards to the bottom flue from its rear end to the front end. This results in the heat transfer from the hot gases to the water through the bottom portion of the boiler shell which is exposed to the bottom flue. Then, the flue gases divide into two streams at the front end of the shell and pass I the side flues. Thus, the two sides of the boiler shell exposed to the side flues are heated. Passing along the two side flues, the hot gases travel upto the rear end of the boiler 1 the chimney. Then, the flue gases are discharged into the atmosphere through the chimney. The above arrangement of the flow passages of the hot flue gases increases the heating surface of the boiler to a large extent. The path of the flow of the flue gases has been shown by arrows in the Figure. Dampers (D1 and D2): Dampers control the flow of hot flue gases and regulate the combustion rate of the fuel as well as the steam generation rate of the boiler. Dampers control the draught. The object of draught is to ensure complete combustion of coal by supplying sufficient quantity of air through the fuel. Boiler Mountings The boiler is fitted with necessary mountings. Water level indicator and pressure gauge fitted at the front. Steam stop valve, Safety valve, High steam and low water safety valve and Manhole are fitted on the top of the shell. High Steam and Low Water Safety Valve: It is mounted over the low water alai apparatus. It is a combination of two valves. One valve blows off steam when t working pressure of steam exceeds the design value. The other valve blows off ste when the level of water falls below the normal level. Blow-off Cock: It is placed below the front end of the shell for the removal of mud and sediments. It is also used to empty water in the boiler during inspection. Fusible Plug: It is placed at the top of the internal flues just above the grate. It prevents overheating of the boiler tubes by extinguishing the fire when the water le falls below the required level. Manhole: It is provided at the top of the shell for the purpose of periodical inspect and repair. Salient Features • The arrangement of flow of flue gases in Lancashire boiler increases the heat surface of the shell to a large extent. • It has a very good steaming capacity. • Coal of inferior quality can be used in this boiler without any operational defects.
• Superheater can be easily incorporated into the system at the end of the internal tubes. Thus, overall efficiency of the boiler can be increased. • Feed water used does not require strict treatment before use in the boiler shell. • Low initial cost. Its maintenance is easy. • Due to moderate working pressure and slow evaporation rate, it is excellent to supply steam to process industries like paper mills, sugar mills, chemical industries, etc.,
7. What are the advantages and disadvantages of water tube boilers over fire tube boilers? Advantages 1. Steam can be generated at very high pressures in water tube boilers. 2. In water tube boilers, water is contained in a large number of tubes. Hence, heating surface is more than that of fire tube boilers. Thus, evaporation rate increases.
3. Circulation of water is more positive in water tube boilers. Steam can be raised quickly than is possible with a fire tube boiler. Hence, it can be used for variations of load. 4. The hot gases flow almost at right angles to the direction of water flow. Hence, maximum amount of heat is transferred to water. 5. A good and rapid circulation of water can be made. 6. Bursting of one or two water tubes does not affect the boiler very much with regard to its working. Hence, water tube boilers are sometimes called as Safety Boilers. But, bursting of flue tubes in a fire tube boiler causes serious problems. 7. The different parts of a water tube boiler can be separated. Hence, it is easy to transport. 8. For a given power, water tube boiler occupies less space than that of fire tube boiler. 9. It is suitable for use in thermal power plants (because of various advantages listed above). Disadvantages 1.. Water tube boiler is not suitable for impure and sedimentary water, as a small deposit of scale may cause the overheating and bursting of tubes. Hence, water treatment is very essential for water tube boilers. 2. Failure in feed water supply even for a short period is liable to make the boiler overheated. Hence, the water level must be watched very carefully during operation of a water tube boiler. 3. Maintenance cost is high. 4. Initial cost of water tube boiler is more than that of fire tube boiler. 5. Water tube boilers are not suited for mobile purpose. 8. what are the advantages of high pressure boilers? 1. Method of Water Circulation: Water circulation through the boiler may be either natural circulation due to the density difference of water and steam or by forced circulation. In high pressure boilers, water circulation is made with the help of a centrifugal pump which forces water through the boiler tubes. This is called Forced Circulation of Water. Forced circulation increases the rate of heat transfer and hence increases the steam generating capacity of boilers. 2. Size of Drum: The high pressure boilers are characterized by the use of very small steam separating drum or by the complete absence of any drum. 3. Type and Arrangement of Tubes: The heat of combustion is utilized more efficiently by the use of small diameter and light weight tubes in large
numbers. To avoid large frictional resistance to the flow of water, the high pressure boilers have a parallel set of arrangement of tubes. 4. Compactness: High head required for natural circulation is eliminated by using forced circulation. The space required is less and the arrangement is compact. 5. Foundation Cost: Due to the light weight tubes and small size drum required and the arrangement being compact, the cost of foundation is reduced. 6. Efficiency: Overall efficiency of the power plant is increased upto 40%, by using high pressure superheated steam. Also, steam can be raised quickly after the boiler is fired. 7. Cost of Electricity: The cost of electricity production is less. 8. Overheating: All the parts are uniformly heated. Therefore, the danger of overheating is reduced. Also, thermal stress problem is avoided. 9. Scale Formation: The tendency of scale formation is eliminated due to the high velocity of flow of water through the boiler tubes. 10. Forced Draught using Blower: The flow of flue gases through the boiler furnace, economizer, pre-heater and chimney require a difference of pressure equal to that necessary to accelerate the hot gases. The purpose of draught is to supply required quantity of air for combustion. Also, it removes the burnt gases from the system. Draught can be obtained by the use of chimney or blower. The former is called Natural Draught and the later is Forced Draught. In the forced draught, a blower is located near the base of the chimney and accelerates the flow of hot gases through the economizer, pre-heater and chimney, thus improving the efficiency of the system. 9. Explain the working principle of La-Mont Boiler A Forced Circulation Boiler was first introduced by La-Mont in the year 1925 which is used in power plants. This is a modern high pressure water tube type steam boiler working on forced circulation system. Description [Fig. 9] Fig. 9 shows the flow-circuit of La-Mont boiler. 1. Furnace: In the furnace, water wall pipes are used to provide a large heating surface, thereby to increase the capacity of the boiler and also to
cool the furnace wall. Water Wall Pipes are vertical or inclined pipes in the interior walls of the furnace. These pipes are connected at the top and bottom to the other parts of the boiler so that there is continuous rapid circulation of water through the water wall. 2. Steam Separator Drum (Boiler): Steam Separator Drum is placed wholly outside the boiler setting. 3. Circulating Pump: It is a centrifugal pump used for forced circulation of water. Forced circulation of water prevents the tubes from being overheated. 4. Evaporator Tubes: These are provided above the furnace. 5. Convection Superheater: The wet steam should not b used in the steam turbine. The presence of moisture in it will cause corrosion of turbine blades. To raise the temperature of steam and thereby to increase the turbine efficiency, wet steam is passed into the Superheater. 6. Economiser: The feed pump supplies feed water to the economiser. 7. Air Preheater: A blower draws atmospheric air and supplies compressed high pressure air (forced draught) to the air preheater. Working Principle Water from the circulating pump is circulated through the evaporator tubes. Hot gases from the furnace heat the water and evaporate into steam. Wet steam from the evaporator enters the steam space in the steam separator drum. In the convection superheater, the moisture in the wet steam is removed and superheated steam is produced. The principle of convection superheater is similar to steam generating tubes of the boiler. The hot flue gases at high temperature sweep over convection superheater tubes and raise the steam temperature, producing superheated steam. The superheater, thus, receives heat from the flue gases flowing from the furnace, entirely by convective heat transfer. Such a superheater is conveniently located, since it is not necessary for it to “see” the furnace. Feed water is supplied by the feed pump to the economiser. Economiser is used to preheat the feed water using the waste hot gases before going to the chimney. Thus, some of the heat in the hot gases, which otherwise gets wasted, is used to preheat the feed water. This results in an increase in the boiler thermal efficiency. The heat of the exit gases cannot be fully extracted through the economizer. These exit gases preheat the air from the blower in the Air Preheater. The preheated air is supplied to the furnace for combustion.
Capacity Due to forced circulation of water, the rate of heat transfer and the steam capacity of the boiler are increased. The capacity of La-Mont boiler is about 50 Tonnes/hr of superheated steam at a pressure of 170 bar and at a temperature of 500°C. Boiler Mountings This boiler is fitted with mountings, viz., water gauge, pressure gauge and block-off cock. Also, three safety valves are fitted as per Indian Boiler Act. The design, manufacture and erection of these boilers are very difficult. It requires skilled personnel and huge investment.
10. Explain the working principle of BENSON BOILER Principle: The presence of steam bubbles in contact with the surface of water tubes seriously impairs heat transmission from the flue gases to water. By raising the boiler pressure to the critical pressure of steam (225 kgf/sq.cm.), this difficulty is overcome as suggested by Mark Benson in 1922. At the critical pressure, water and steam have the same density and no bubbles form.
The first modern high pressure drumless boiler developed by Benson was put into operation in 1927 in West Germany power station. Absence of Drum: Benson boiler is a water tube type, forced circulation, high pressure boiler. The unique characteristic of this boiler is that it does not use any drum at all. The entire process of heating, steam generation and superheating is done in a single continuous tube. Hence, it is also known as Once-Through Boiler. It withstands very high pressure, even higher than the critical pressure of steam. Description [Fig. 10] Fig. 10 shows the flow-circuit of Benson boiler. Feed pump is connected to the Economiser. Radiant Evaporator is placed just above the furnace. It is connected to the economiser at one end and to the convection evaporator at the other end. Convection Evaporator is connected to the radiant evaporator at one end and to the convection superheater at the other end. Convection Superheater is connected to the convection evaporator at one end and to the steam turbine at the other end. A Blower draws atmospheric air and supplies compressed high pressure air (forced draught) to the Air Preheater. Working The feed water from the feed pump is circulated through the Economiser Tubes. Hot flue gases pass over the economiser tubes and the feed water is preheated. Economiser is used to preheat the feed water using the waste hot gases before going to the chimney. Thus, some of the heat in the hot gases, which otherwise gets wasted, is used to preheat the feed water. This results in an increase in the boiler thermal efficiency. The preheated feed water from the economiser flows into the Radiant Evaporator with radiant parallel tube sections. The radiant evaporator receives heat from the burning fuel in the furnace through radiation process. Thereby, the major part of water is converted into steam in it. The remaining water is evaporated in the Convection Evaporator, absorbing the heat from the hot gases by convection. Thus, the saturated high pressure steam at a pressure of 230 bar is produced. The saturated steam available from the convection evaporator is passed through the Convection Superheater, where the saturated steam is superheated to 650°C. Note that the radiant evaporator, the convection evaporator and the convection superheater are all arranged in the path of the flue gases. The superheated steam is then supplied to the steam turbine.
The heat of the exit gases cannot be fully extracted through the economizer. These exit gases preheat the air from the blower in the Air Preheater. The preheated air is supplied to the furnace for combustion. Capacity: Capacity of Benson boiler is about 150 Tonnes/hr at a pressure of 230 bar and at a temperature of 650°C. (Efficiency may be improved by running the boiler at a pressure slightly lower than the critical pressure). Salient Features 1. High Thermal Efficiency: No higher limit for higher steam pressure. Therefore, highest steam pressure can be used to achieve high thermal efficiency. 2. Less Weight and Less Cost: As there are no drums, the total weight of Benson boiler is 20% less than other boilers. This also reduces the cost of the boiler. 3. Load Fluctuations: Sudden fall of demand creates circulation problems due to bubble formation. This never occurs in Benson boiler. 4. Easy Transportation: As no drums are required, the transfer of Benson parts is easy. Majority of the parts may be carried to the site without pre-assembly. 5. Once-through Boiler: Since no drum is used, this is an once-through boiler. The feed water entering at one end is discharged as superheated steam at the other end.
REVIEW QUESTIONS PART A 1. What is a heat engine? How do you classify heat engines? 2. Define the terms: Stroke, Top Dead Center, Bottom Dead Center, Compression Ratio, Air Fuel Ratio, Stroke Volume, Brake Horse Power and Thermal Efficiency. 3. What do you understand by scavenging? 4. Why are two stroke engines preferred for two wheelers? 5. Compare and contrast four stroke cycle engines with two stroke cycle engines. 6. Discuss the merits and demerits of diesel engine over petrol engine.
7. Defines the terms: External Combustion Engine and Internal Combustion Engine. 8. Define Compression Ratio of an I.C. engine. 9. What is the function of deflector in a two stroke engine? 10. What is the function of the choke in a carburettor? 11. What is meant by carburetion? 12. What is the function of the float, float chamber and needle valve assembly in a single jet carburettor? 13. State any two limitations of a single jet carburettor. 14. How do you provide an extra-rich mixture to the petrol engine during starting in cold weather? 15. What is the function of choke in the carburettor? 16. Name the three ports provided at the cylinder walls in a two stroke engine. 17. Why is diesel engine called as compression ignition engine? 18. How do the three ports in a two stroke engine function? 19. What is the function of a spark plug? 20. State any two advantages of LPG as SI engine fuel. 21. Enumerate the various types of steam generators. 22. What are the two different uses of steam produced in the boiler? 23. Where do you use process system? 24. State any two primary requirements of a boiler? 25. How do you classify boilers? 26. State any two salient features of Cochran boiler. 27. What is the function of baffles in Babcock and Wilcox boiler? 28. What do you understand by natural circulation? 29. State the functions of: i) Safety Valve iii) Fusible plug ii) Stop Valve iv) Blow-off Cock 30. State any two advantages of high pressure boilers. 31. What do you understand by forced circulation? PART B 1. Describe the principal parts and functions of a four stroke I.C. engine with a sketch. 2. Describe the principal parts and functions of a two stroke I.C. engine with a sketch.
3. Explain the working of a four stroke petrol engine with the help of PV diagram. 4. Explain the working of a four stroke diesel engine with the help of PV diagram. 5. Draw and explain the sequence of operations of a two stroke cycle petrol engine. 6. Draw and explain the sequence of operations of a two stroke cycle diesel engine. 7. Describe with a sketch the design of a single jet carburettor. 8. Sketch and explain the working of a diesel fuel pump. 9. Explain the working principle of the fuel injector with a neat diagram. 10. Draw a schematic circuit diagram of a coil (battery) ignition system and label all the components. State the functions of each component. 11. Discuss briefly the ignition system of SI engine. 12. Explain the working principle of spark plug with a neat diagram. 13. Explain, with a neat sketch, the working of a Cochran boiler. 14. Sketch and describe the working principle of a locomotive boiler. 15. With the aid of neat sketches, explain the constructional features and functioning of a Lancashire boiler. 16. Give an outline sketch showing the arrangement of water tubes and furnace of a Babcock and Wilcox boiler. Indicate on it the path of the flue gases and water circulation. Show the positions of superheater, fusible plug and blow-off cock. Mention the function of each. 17. Explain, with the help of a diagram, the construction and working of a fire tube boiler. 18. Distinguish between fire tube boilers and water tube boilers. 19. Name the important boiler mountings and briefly explain their functions. 20. Describe, with a neat sketch, a water level indicator. Explain how the flow of steam and water is automatically stopped when the glass tube breaks. 21. Explain how the Bourdon type pressure gauge works. 22. Explain why safety valves are needed in a boiler. Draw a neat sketch of a spring loaded safety valve and explain its working. 23. What is the purpose of a fusible plug? Explain. 24. Define a High Pressure Boiler. Mention the advantages of high pressure boilers. 25. Explain the working principle of La-Mont High Pressure Boiler with a neat sketch. 26. Discuss the working and the salient features of Benson Boiler with a neat sketch.
27. Discuss the concept of cogeneration. Explain topping cycle system. 28. Explain the bottoming cycle system of cogeneration with a suitable sketch.
UNIT V / REFRIGERATION AND AIRCONDITIONING
PART A
1. What are the types of refrigeration systems? a. Air Refrigeration System b. Vapour Compression Refrigeration System c. Vapour Absorption Refrigeration System d. Electro-Lux Refrigerator (Ammonia-Hydrogen Refrigerator) 2. What is human comfort? Human Comfort: The American Society of Heating, Refrigeration and Air conditioning Engineers (ASHRAE) defines the Human Comfort as: “Human Comfort is that condition of mind which expresses satisfaction with the thermal environment.” The heat produced in the body is dissipated from the body to the surrounding atmosphere by convection and by the evaporation of the sweat produced. The normal temperature of the human body is 98.4° Fahrenheit (or 37°C). This temperature is called sub-surface or deep tissue temperature rather than skin or surface temperature. 3. Define air-conditioning. Air Conditioning: Air Conditioning is defined as the simultaneous control of the temperature of air, humidity of air, purity of air and motion of air for the purposes of human comfort, food processing, and other industrial purposes. 4. Compare air-conditioning and refrigeration. Air Conditioning Vs Refrigeration: Air conditioning is the method of controlling the temperature of a closed space to bring it to a value less or greater than that of its surrounding atmosphere. However, refrigeration is the method of lowering down the temperature of a closed space to a value much less than that of its surrounding atmosphere. Temperature required in the refrigeration is less than that required by air conditioning. 5. What is air cooling? Air Cooling: Air Cooling is often confused with the term Air Conditioning. Air Cooling consists merely a blower with refrigerating unit. It provides only a flow of cool filtered air.
6. What is psychrometry? Psychrometry is that branch of physical science dealing with the study of the properties of air and water vapour mixture. A few psychrometric properties are defined below: 1. Atmospheric Air: Air in the atmosphere is referred to as Atmospheric Air. 2. Moisture: Atmospheric air normally contains water vapour, known as Moisture. 3. Moist Air: Moist Air is defined as a mixture of dry air and water vapour. The maximum quantity of water vapour present in the air depends upon the air temperature. 4. Humidity: Humidity is defined as the moisture content present in the atmospheric air. The atmosphere always contains some moisture in the form of water vapour. 5. Relative Humidity: It is the ratio of mass of water vapour present in a given volume of dry air to the mass of water vapour required to saturate the same volume of dry air at the same temperature. It is represented in percentage. It is 0% for dry air and 100% for saturated air. For example, 50% relative humidity means that the air contains one-half the amount of moisture that it is capable of holding. Relative humidity changes as the air temperature changes. 6. Absolute Humidity: It is defined as the mass of water vapour contained in a given volume of air, It is expressed in gram of water vapour per cubic meter of air. 7. Temperature-Humidity Index (T.H.I.): It is also termed as Discomfort Index. It expresses in numerical values the relationship between comfort or discomfort temperature and humidity. It is felt that T.H.I. at 20°C provides a comfortable atmosphere. 8. Dry Bulb Temperature: Dry Bulb Temperature is the atmospheric air temperature recorded by a thermometer whose bulb is exposed to the atmosphere. 9. Wet Bult Temperature: It is defined as the temperature of air measured by a thermometer when its bulb is covered with a wet cloth and is exposed to a current of air. 10. Air Purity: People do not feel comfortable while breathing contaminated air even if it is within the acceptable temperature and humidity ranges. So, proper filtration, cleaning and purification of air is necessary to keep it free from dust, dirt and other impurities.
11. Air Movement and Circulation: Even if temperature, humidity and air purity are satisfactory, a certain amount of air motion (i.e., air velocity) and circulation is necessary for human comfort. 12. Degree of Saturation: Degree of Saturation is defined as the ratio of mass of water vapour in unit mass of dry air to mass of water vapour in unit mass of dry air when air is saturated at the same temperature. 7. What are the requirements of comfort air conditioning? Human Discomfort: Moisture from human body evaporates. Thus, body heat is disposed. Hence, humidity inside a room increases, causing difficulty in disposing of body heat. Also, the room temperature rises due to heat dissipated from the body, causing human discomfort. Human Comfort: Thermodynamically speaking, ideal human comfort exists when the rate of heat production becomes equal to the rate of heat loss. The following parameters are required to be maintained for the human comfort in air conditioning: 1. Temperature of Air: In air conditioning, the desired room temperature has to be maintained, though the temperature of the outside air is different. It has been found that for human comfort, we need a dry bulb temperature of 20°C. 2. Humidity of Air: The control of humidity of air means the increasing or decreasing of moisture contents of air during summer or winter respectively. 3. Purity of Air: You and I do not feel comfortable while breathing contaminated impure air, even if it is within the acceptable air temperature and humidity ranges. The conditioned air must be free from dust, bacteria, odour and toxic gases. 4. Air Circulation: A person inhales about 0.6 m3 of oxygen and exhales about 0.2 m3 of carbon-di-oxide per hour. If the carbon-di-oxide level in the room increases above 2%, it will cause human discomfort. Hence, air conditioner should supply enough quantity of fresh air. There should be continuous air circulation in the air-conditioned space. The feeling of comfort by individuals depends upon many factors such as age, types of cloth used, duration of stay, etc. This feeling also differs from individual to individual. 8. How do you classify the air conditioning systems 1. Classification as to Major Function (a) Comfort Air Conditioning: Window Air Conditioner or Split Type Air Conditioner used in rooms creates atmospheric conditions conducive to human comfort.
CentralAir Conditioning is used in offices, hospitals, theatres, hotels, industries, etc. (b) Industrial Air Conditioning: It is used in machine-part manufacturing plants, tool rooms, printing, photo-processing plants, including CAD / CAM / CIM centers, etc. 2. Classification as to Season of the Year (a) Summer Air Conditioning: This system controls all the four atmospheric conditions, (Temperature, Humidity, Air Purity and, Air Movement and Circulation) for summer comfort. The major problems are to cool the air and to remove excess moisture from it. (b) Winter Air Conditioning: Such a system maintains indoor atmospheric conditions for winter comfort. The major problems are to heat the air by electric heaters or furnaces and to bring moisture content up to an acceptable level. (c) Year-round Air Conditioning: This system has heating and cooling equipment with automatic controls to maintain the four parameters for human comfort round the year.
PART B
1. With neat sketch explain the working principle of vapour compression refrigeration system. Principle In the Vapour Compression Refrigeration System, Freon-12 or Freon-22 is used as the refrigerant. A compressor does work on the refrigerant vapour to increase its pressure and temperature. The refrigerant is circulated through the system. It alternately undergoes a change of phase from vapour to liquid and again liquid to vapour during the cycle. The latent heat of vaporization is utilized for absorbing the heat at low temperature from the refrigerated space. A constant temperature can be maintained in this space. Description See Fig. 1. Vapour Compression Refrigeration System consists of the following parts: 1. Evaporator 2. Compressor 3. Condenser 4. Expansion Valve 5. Thermostat Switch 1. Evaporator
An Evaporator consists of coiled tubes. The substance to be cooled is placed in the evaporator. It is the coldest region in the refrigerator and serves as the Freezing Compartment. 2. Compressor The evaporator tube is connected to the suction side of the Compressor. The compressor is driven by an electric motor. 3. Condenser The delivery side of the compressor is connected to a Condenser. The air or water is used as the cooling medium in the condenser. Air is used for refrigerators and window air conditioners. Water is used for large centralized air conditioning systems. 4. Expansion Valve (Throttling Valve) The condenser is connected to an Expansion Valve. The pressure of the liquid passing through the expansion valve drops for reuse in the evaporator. Low capacity systems like refrigerators, window air conditioners, etc., use a capillary tube as an expansion valve. Solenoid valve is used as expansion valve in large capacity systems.
Working
In Vapour Compression Refrigerator, the refrigerant alternately undergoes a change of phase from vapour to liquid and liquid to vapour during a cycle. The Low Pressure Low Temperature (LPLT) refrigerant Freon-12 or Freon-22 passing in the evaporator tubes absorbs the heat from the contents in the refrigerated space and evaporates. This absorption of heat will lower the temperature in the refrigerated space. The evaporated LPLT refrigerant vapour is now drawn by the compressor. The compressor compresses the vapour to a high pressure so that the corresponding saturation temperature is higher than that of the atmospheric air. The compressed High Pressure High Temperature (HPHT) vapour enters into the condenser.
In the condenser, the vapour refrigerant gives up its latent heat to the atmospheric air and is condensed into high pressure liquid. [ In domestic refrigerators, air cooling of refrigerant is arranged. This, heat is transferred from the refrigerated space to atmosphere, by the air passing over the condenser coils. The condensing medium may be water instead of air for large Capacity refrigerators]
The High Pressure (HP) condensed liquid refrigerant coming out from the condenser flows to an Expansion Valve (also known as Throttle Valve). In the expansion valve, the refrigerant is expanded to a LPLT liquid.
This LPLT liquid refrigerant passes to the Evaporator Coils. The refrigerant is recirculated. The cycle is thus repeated continuously. The required low temperature is maintained in the refrigerator by a Thermostat (not shown in Figure). It is used to switch ON or OFF the compressor motor. 2. Discuss in detail about the layout of typical domestic refrigerator Domestic Refrigerator works on Vapour Compression Refrigeration System. Description Fig. 2 shows the Layout of a Typical Domestic Refrigerator. 1. Evaporator or Cooling Coil 2. Compressor 3. Condenser 4. Expansion Valve or Throttling Valve 5. Thermally Insulated Cabinet 1. Evaporator or Cooling Coil: Evaporator is the heart of the refrigerator. As the name implies, the liquid refrigerant is evaporated in the evaporator by
absorbing heat from the contents (perishable vegetables, fruits, etc.) of the domestic refrigerator in the cabinet. The evaporator consists of copper metal tubing surrounding the freezing and cooling compartments. The purpose of metal tubing is to produce cooling effect required for lowering the temperature of perishables or for freezing ice in the cooling compartment. Since the evaporator coil produces the cooling effect, it is also known as Cooling Coil. 2. Compressor: It compresses the refrigerant vapour to a high pressure. Reciprocating Compressor is used for low capacity domestic refrigerator. It is in a hermetically sealed casing. [Centrifugal Compressor is used for high capacity refrigerators.] The compressor suction is connected to the evaporator. Its delivery is connected to the condenser. An electric motor runs the compressor. 3. Condenser: In the condenser, the heat from the refrigerant at a higher temperature is rejected to the atmospheric air. In domestic refrigerators, air cooling of refrigerant is arranged. Thus, the heat is rejected from the refrigerated space to the atmosphere, by the air passing over the condenser coil. 4. Expansion Valve or Throttling Valve: An Expansion Valve or Throttling Valve is use to reduce the temperature and pressure of the liquid refrigerant, before it passes to the evaporator. The high pressure refrigerant liquid is to be depressurized in the expansion device for reuse in the evaporator.The low capacity systems such as domestic refrigerator and window air conditioner use Capillary Tube. The capillary tube is a small diameter tube used as an expansion device Solenoid valve is used as an expansion device in large capacity refrigerators. 5. Thermally Insulated Cabinet: The refrigerator cabinet is thermally insulated to minimize heat flow from the atmosphere into the refrigerator. Without thermal insulation, the refrigerator would be heavily loaded resulting in large consumption of power and unsatisfactory cooling in the refrigerator.The refrigerator Cabinet is therefore double-walled. The space in between the walls is filled with insulation material such as poly-urethane foam.
Working Principle In the domestic refrigerator, the most commonly used refrigerant is Freon 12. The refrigerant at Low Pressure Low Temperature (LPLT) passing in the evaporator coil absorbs the heat from the contents in the freezing compartment and evaporates. This, inturn lowers the temperature in the freezing compartment. The evaporated refrigerant enters a compressor. The compressor compresses it to a higher pressure. This is necessary to condense the vapour to a liquid form. [ Note that the saturation temperature of the refrigerant corresponding to the increased pressure is higher than the temperature of the cooling medium (atmospheric air) surrounding the condenser. So, the High Pressure High Temperature (HPHT) refrigerant vapour can reject heat in the condenser.] The HPHT vapour from the compressor flows into the condenser. In the condenser, the vapour gives off its latent heat to the atmospheric air and
condenses into liquid. The high pressure condensed liquid refrigerant at room temperature flows into the expansion valve. The expansion of the refrigerant lowers its pressure and temperature. At the same time, the refrigerant partly evaporates. Therefore, the refrigerant coming out of the expansion valve will be a wet vapour at low temperature of the order of _100 C. This wet vapour passes to the evaporator coil where it absorbs its latent heat. It is then re-circulated and the cycle is repeated. Thus, heat is continuously extracted from the contents of the refrigerator by the evaporator. This heat is rejected in the condenser to the atmospheric air. This will keep the contents of the refrigerator at the required lower temperature. Thermostat Switch: The required low temperature is maintained in the refrigerator by a thermostat switch. It switches on and off the compressor motor by a relay as and when the temperature either falls below or rises above the required temperature. Freezer Compartment Freezer Compartment is used to make ice and store ice-cream and other frozen desserts. Also used to store meats, poultry, fish, fruit pulp and other frozen foods for extended periods of 8—12 weeks. The freezer is provided with two ice trays. Chiller In this chamber, food is stored at close to 0 C, which keeps items like milk packets, paneer. etc., soft. It eliminates the need for thawing the food before cooking. 3. Explain in detail about the concept of vapour absorption refrigeration system with neat sketch. Principle The difference between the Vapour Absorption System and Vapour Compression System is in the manner in which external heat is added to the vapourized refrigerant to increase its temperature above atmosphere. This is necessary to reject the heat in the condenser. In the vapour compression system, the motor-operated compressor adds energy in the form of heat to the refrigerant by compressing it to high pressure and high temperature. In the vapour absorption system, the compressor is replaced by the combined effects provided by an Absorber, Pump and Heater-cum-Separator. The compressor work is replaced by the
heat supplied in the heater-separator and pump work. The pump consumes comparatively lesser amount of electric power. Absorbent is a substance which absorbs large quantities of refrigerant vapour when cold and converts it into liquid. When heated subsequently, it produces vapour. Water has this property and is used as the absorbent. Ammonia (NH3) is used as the refrigerant, as it easily dissolves in water and vapourizes when heated subsequently. The homogenous mixture of Ammonia and water is called Aqua-Ammonia. So, the vapour absorption refrigeration system is also called Aqua-Ammonia Refrigeration System. Description See Fig. 3. The Vapour Absorption Refrigeration System consists of the following parts: 1. Evaporator * 2. Absorber 3. Circulation Pump 4. Heat Exchanger 5. Heater-cum-Separator 6. Condenser * 7. Expansion Valve * 8. Pressure Reducing Valve * Parts 1, 6 and 7 are described in the Vapour Compression System. 2. Absorber: Absorber contains an absorbent, i.e., water. It attracts the refrigerant vapour from the evaporator. Absorber carries absorbent to the heater-separator in a mixed liquid-vapour state. 3. Circulation Pump: Pump circulates the refrigerant to flow into the heater-separator. 4. Heat Exchanger: Heat Exchanger is placed between the pump and the heater-separator on the onward flow and between the heater-separator and the absorber in backward flow. 5. Heater-Separator: Heater-Separator is the heat energy source in the operating cycle. It is operated by the heat energy obtained from the heating coil, solar heater or gas flame. 8. Pressure Reducing Valve: It is placed between the heater-separator and heat exchanger. It reduces the pressure of the solution released from the heater-separator to the absorber pressure.
Working The LP aumonia vapour from the evaporator enters into the absorber. The absorber contains cold water. The ammonia vapour is dissolved in the cold water, producing a LP strong ammonia solution. The pump delivers this solution at HP to the heat exchanger. In the heat exchanger, the strong solution is pre-heated by the HT weak solution, flowing from the heater-separator returning back to the absorber. From the heat exchanger, the warm HP strong solution is passed to the heater-separator. The heating coils in the heater-separator heats the HP strong ammonia solution to separate ammonia from the solution. The resultant weak HPHT ammonia solution from the heater-separator is passed to a pressure reducing valve. The valve reduces the pressure of the solution to the absorber pressure. It flows through the heat exchanger, where it warms up the strong solution passing through it. The LPLT weak ammonia solution from the heat exchanger enters into the absorber. The FTP ammonia vapour from the heater-separator passes to the condenser, where it s condensed to liquid ammonia. The HP ammonia liquid is then expanded to LPLT in the expansion valve. The LPLT ammonia liquid is passed to the evaporator in the freezing compartment. In the evaporator, the LPLT liquid absorbs the heat and evaporates. The LP ammonia vapour from the evaporator flows again to the absorber. The cycle is repeated.
4. Discuss the layout of window air conditioner and its working methodology. Description [Fig. 1] As the name implies, all the components of the air conditioner, viz., compressor, condenser, evaporator, motor running the fan and the blower, etc., are assembled inside a casing installed in the window of a room at the window sill level. Window air conditioner is designed to condition the air in a single room. The window air conditioner consists of a Vapour Compression Refrigeration System (i.e., Evaporator, Compressor, Condenser, Expansion Valve in the form of a Capillary Tube, Thermostatic Switch), Air Filter, Motor, Blower and Fan. The evaporator part is facing the room. The condenser part projects outside the room. The evaporator part is insulated from the condenser part. That is, the evaporator and condenser coils are separated by an insulated partition to avoid the air movement between the room and atmosphere. A common motor drives a fan at one end and a blower at the other end. Working Principle The Low Pressure Low Temperature (LPLT) liquid refrigerant passes through the Evaporator Coils. Commonly used refrigerants are: Freon-12 and Freon-22. The blower sucks warm humid air from inside the room through the air filter and forces it to pass over the evaporator or cooling coil. [Air filter cleans the air by removing dust and dirt particles.] The LPLT refrigerant inside the evaporator coil absorbs the heat from the room air and evaporates. Therefore, the room air is cooled as well as dehumidified by continuous heat removal. The dehumidified-cooled air is blown back into the room. The desired temperature of 20°C to 25°C in the room for human body comfort is maintained using a thermostatic switch by means of an on-off control of the compressor. The LPLT evaporated refrigerant is drawn by the suction of the compressor. The compressor compresses it to High Pressure High Temperature (HPHT) vapour. This HPHT refrigerant vapour flows into the condenser coil. The fan draws the atmospheric air (called Coolant Air) as shown. This coolant air is circulated over the condenser coil. The HPHT refrigerant vapour inside the condenser condenses by giving-off the heat to the coolant air. The coolant air absorbs the heat. This hot air is discharged to the atmosphere.
The HPHT vapour is condensed to High Pressure Low Temperature (HPLT) liquid refrigerant in the condenser. Then the HPLT liquid expands to LPLT liquid in the capillary tube. This liquid refrigerant is re-circulated through the evaporator. The cycle is repeated. The evaporator outer surface is cold, as it contains low temperature liquid refrigerant. So, water vapour in the warm humid air condenses to form water droplets on the outer surface of the evaporator. { Have you observed the formation of water droplets on the outside of an ice-filled glass tumbler, due to the condensation of moisture in the surrounding air? ] These droplets are collected and drained. Window air conditioners operate on 230 V, singe phase AC supply.
Capacity: The room air conditioners have capacities ranging from I TR to 3 TR in sizes of 1, 1.5,2 and 3 TR. Advantages • Window air conditioner is a self-contained single-package unit. • For more than one room in a residential building, several window units can be used. A separate temperature control is provided in each room in which the unit is installed.
• Ducts are not required for air distribution. This advantage is especially noticeable in residences in mild climates where central heating systems are not required. • Installation is simple and plumbing is not required. Disadvantages • Not suitable for large halls and applications where heat and moisture loads are high. • The unit has circulation of a fixed air quantity. • The installation must be made only on an outside wall of the room. 5. Explain the working principle of split type room air conditioner The present trend in the Indian market is to go for the Split Type of the air conditioning system. It is built in two parts: Cooling Unit and Condensing Unit and hence the name Split System. Split Type Room Air Conditioner is also known as Split Package Unit. A split package unit is designed with the fan and cooling or heating coil in one equipment section and the condenser as well as the compressor in another section. See Fig. 2. The cooling unit section is located in the room. The condenser and compressor are placed in a remote location either indoors or outdoors. COOLING UNIT (INDOOR UNIT) It comprises the following: 1. Evaporator Coil and Capillary Tubes: The High Pressure Low Temperature (HPLT) liquid refrigerant from the condenser is passed to the capillary tube. In the capillary tube the refrigerant expands. The Low Pressure Low Temperature (LPLT) liquid refrigerant then passes to the evaporator. 2. Evaporator Fans: The evaporator fan draws air continuously from the inside space of the room through an air filter. The air is forced to pass over the evaporator coil by the fan and is cooled by the refrigerant. Consequently, the refrigerant evaporates by absorbing the heat from the air. 3. Mounting of Cooling Units: Cooling unit may be floor mounted, wall mounted or ceiling mounted, depending on the requirement. 4. Controls: When a controlled atmosphere is required in air conditioning, the humidity of the air is varied. When dry air is required, it is dehumidified by cooling or by dehydration. In the latter process, the air is passed through absorptive chemicals such as silica jel. Air is humidified by circulation through water sprays. CONDENSING UNIT (OUTDOOR UNIT) The Condensing Unit houses the following:
1. Compressors: The high temperature evaporated refrigerant from the evaporator is drawn by the suction of the compressor. The compressor compresses it and delivers it to the condenser. 2. Condenser Coils: The condenser can be air cooled in the case of room air conditioner or water cooled in the case of centralized air conditioner. If a water cooled condenser is to be used, the condenser is provided with connections for either city water or well water. For an air cooled condenser, these connections are not required. 3. Condenser Fans: The condenser fan draws the atmospheric air from the exposed side. The High Pressure High Temperature (HPHT) refrigerant passing inside the condenser condenses by giving-off the heat to the atmospheric air. To avoid any flashing of the liquid refrigerant, a small receiver in the liquid line recommended, where the distance between the condensing unit and cooling unit exceeds eight meters.
INSTALLATION There can be a number of combinations for the installation of cooling and condensing units, depending on the location and site. However, the following three combinations are very common in practice:
• Cooling unit and condensing unit at same level • Cooling unit being at higher elevation than condensing unit and vice versa. Combination-1: This is similar to a unitary air conditioning system with extended suction and liquid line. Combination-2: Normally, the maximum recommended height of the cooling unit when compared to the condensing unit is 8 meters. Moreover, it is advisable to provide a suction line riser at the outlet of the evaporator to prevent liquid refrigerant from draining to the compressor during off-cycles. This would be an additional protection apart from the suction line. Combination-3: Here, in addition to the proper selection of liquid line and suction line, an oil trap on the suction line, near the evaporator outlet should be provided, if the elevation between cooling unit and condensing unit exceeds 3 meters However, the recommended elevation is 8 meters maximum. Advantages 1. No constraints on the installation of the split type air conditioner, as the condensing unit can be located in any remote plate. 2. Noise free operation, because of remote location of the condensing unit. 3. No breakage or opening in the wall necessary. 4. Feasibility of using multiple evaporators with single condensing unit making its use more flexible. Disadvantages 1. Split type is a split package unit and not a single package self-contained unit. 2. While it is true that the Split System offers outstanding user conveniences, it is necessary to be aware of the disadvantages also. Of course, these can be counterbalanced by taking the following actions: • Usually a drop of 5-10% in capacity is observed in the split system due to the extended system tubing, when compared to that of the Window unit. This loss in efficiency would be compensated partially by selecting suitable sizes of the system tubes. The other part of the loss can be taken care by increasing the air flow using four pole motor for the condenser fan resulting in lower discharge pressure. • Split system has lot of joints in the form of flare connections or quick couplers. It is prone to refrigerant leakage. To avoid this problem, it is becoming a common practice to eliminate these joints by brazing the system
tubes at the site. The unit is then evacuated and charged in the installed condition itself. 6. Explain the working principle of central air conditioning system It is used for large commercial buildings, theatres, auditoriums, hospitals, hotels, libraries. etc. In this system, the cooling and heating devices and the control unit are installed in one particular location. It is economical over multiple window systems for larger space. It spreads cooled air more uniformly inside the hail. The ducts carry the conditioned air to several parts of the building. Cooling capacity is 25 tonnes or more. Advantages • It is totally isolated from the hall. Therefore, noise level is reduced very much. • Comfort conditions are perfectly maintained in each and every room. • A central automatic control point is provided. Hence, maintenance is easier. • Since the cooling and heating equipment is installed in one location rather than several locations, the maintenance of the system is easier. Disadvantage • The equipment and installation cost of the central system is very high.
PART A 1. Name any two commonly used refrigerants. 2. What do you understand by refrigerating effect? 3. State the basic concept of refrigeration. 4. When we rub petrol or alcohol on our skin, we feel cooler. Why? 5. What is the function of the absorbent in a vapour absorption refrigerator? 6. What is phychrometry? 7. What is the definition of human comfort as suggested by ASHRAE? 8. “The feeling of comfort by individuals depends upon many factors.” State any two factors. 9. Why window air conditioner is called in that name? 10. Have you observed that water droplets are formed on the outside of an ice-filled glass tumbler? State the reason. 11. Mention any two disadvantages of a window air conditioner. 12. State any two advantages of a window air conditioner. 13. How do you express the capacity of a room air conditioner?
PART B
1. Define the terms: Refrigeration, Refrigerator and Refrigerant. 2. What are the desired properties of an ideal refrigerant? 3. With the help of a neat sketch, explain the working of a vapour compression refrigerator. 4. Draw a neat layout of a typical domestic refrigerator. Describe its components and the working principle. 5. What is the principle of vapour absorption refrigeration system? Explain the working of a vapour absorption refrigerator with a suitable sketch. 6. Compare the vapour absorption refrigeration system with vapour compression refrigeration system. 7. Define the following terms: Humidity, Relative humidity, Dry bulb temperature, Degree of saturation and Human comfort. 8. State the principle of air conditioning. What are the parameters required for the human comfort in air conditioning. 9. How do you classify the air conditioning systems? 10. Discuss the working principle of a window room air conditioner with a neat sketch. 11. Explain the working principle of a split type room air conditioner with a neat diagram. 12. Discuss the advantages and disadvantages of split type room air conditioner. ------------------------------------------------------------------------------------------------------------
