ROHAN KAMATH
Internal combustion engine / Diesel engine cycles
Engine: An engine is a machine designed to convert one form of energy mainly heat energy into mechanical
energy. Heat engines, like the internal combustion engine, burn a fuel to create heat which is then used to
do work.
IC engine: The engines in which the combustion of fuel takes place inside the engine cylinder are called
internal combustion engines. The working pressure and temperature inside the cylinder of an IC engine is
very high. The efficiency of IC engine is about 35-40 percent.
Two stroke and Four stroke cycle engines:
In a two-stroke engine, the working cycle is completed in two strokes of the piston or one revolution of the
crankshaft. In a four-stroke engine, the working cycle is completed in four strokes of the piston or two
revolution of the crankshaft.
Sequence of operations in a cycle:
• Suction stroke: In this stroke the fuel vapour in a correct proportion is supplied to the engine cylinder.
• Compression stroke: In this stroke the fuel vapour is compressed in the engine cylinder.
• Expansion stroke: In this stroke the fuel vapour fired just before the compression is complete. It results
in the sudden rise of pressure, due to expansion of the combustion products in the engine cylinder. This
sudden rise of pressure pushes the piston with great force and rotates the crankshaft. The crankshaft, in
turn drives the machine connected to it.
• Exhaust stroke: In the stroke the burnt gases are exhausted from the engine cylinder so as to make space
available for the fresh fuel vapour.
Main Components diesel engine:
Cylinder, Piston, Piston rings, connecting rod, crank and crankshaft, crank case, flywheel, Inlet and exhaust
valve and spring, Fuel injector, cam shaft, rocker arm, combustion chamber, gudgeon or piston pin.
• Cylinder: It is a heart of engine where fuel is burnt and power is generated. The piston reciprocated inside
the cylinder (cast iron or aluminium alloy)
• Piston: The piston is a close fitted hollow body inside the cylinder which moves to-and-fro in the cylinder.
The power developed by the combustion of the fuel is transmitted by the piston to the crankshaft
through connecting rod. (aluminium alloy)
• Piston rings: The piston rings are metallic rings inserted into the circumferential grooves provided at the
top of the piston. These rings maintain a gas tight joint between the piston and the cylinder while the
piston is reciprocating in the cylinder. They also help in conducting the heat from piston to the cylinder.
(oil scrapper, compression ring) (alloying cast iron)
• Connecting rod: It is a link that connects the piston and the crankshaft by means of pin joints. It converts
the rectilinear motion of the piston into rotary motion of the crankshaft. (steel or Al alloy)
• Crank and crankshaft: The crank is a lever that is connected to the end of the connecting rod by a pin
joint with its other end rigidly connected to a shaft called crankshaft. It rotates about the axis of the
crankshaft and causes the connecting rod to oscillate. (forged steel or cast iron)
• Crank case: It is the lower part of the engine serving as an enclosure for the crankshaft and also sump for
lubricating oil. (light metal)
• Flywheel: It is a heavy wheel mounted on the crankshaft of the engine to maintain uniform speed and
rotation of the crankshaft. (steel)
• Intake and exhaust Valves and spring: The valves are the devices which controls the flow of the intake
and the exhaust gas to and from the cylinder. They are also called poppet valves. These are operated by
means of cams driven by crankshaft through a timing gear and chain. While spring will keep the valve
closed. (chrome, nickel, tungsten steel)
• Fuel injector: It is a valve that supplies fuel to the cylinder for combustion. (steel)
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•
•
•
•
Cam shaft: It is a component that have several cams, this cam has function to press the valves for inlet
or outlet valve to open. (cast iron)
Rocker arm: A rocker arm is an oscillating lever that conveys radial movement from the cam lobe into
linear movement at the inlet or outlet valve to open it. One end is raised and lowered by a rotating lobe
of the camshaft while the other end acts on the valve stem. (steel)
Combustion Chamber: The combustion chamber is a small space used for combustion in which a blast of
fire used to push the piston down.
Piston Pin: A pin located inside the piston to connect the piston with the connecting rod. (steel alloy)
Valve Timing Diagram:
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Port Timing Diagram:
Detonation: The loud pulsating noise heard within the engine cylinder of an IC engine is known as
detonation. It is caused due to propagation of a high speed pressure wave created by the auto ignition of
end portion of unburnt fuel.
It can be reduced by adding small amount of lead ethyl or ethyl fluid to the fuel called as doping.
Otto Cycle:
The processes are described by:
• Process 0–1 a mass of air is drawn into piston/cylinder arrangement at constant pressure.
• Process 1–2 is an adiabatic (isentropic) compression of the charge as the piston moves from bottom
dead centre (BDC) to top dead centre (TDC).
• Process 2–3 is a constant-volume heat transfer to the working gas from an external source while the
piston is at top dead centre. This process is intended to represent the ignition of the fuel-air mixture
and the subsequent rapid burning.
• Process 3–4 is an adiabatic (isentropic) expansion (power stroke).
• Process 4–1 completes the cycle by a constant-volume process in which heat is rejected from the air
while the piston is at bottom dead centre.
• Process 1–0 the mass of air is released to the atmosphere in a constant pressure process.
The Otto cycle consists of isentropic compression, heat addition at constant volume, isentropic
expansion, and rejection of heat at constant volume.
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Diesel Cycle:
Difference between otto and diesel cycle
Dual Cycle:
•
•
•
•
•
Process 1-2: Isentropic compression
Process 2-3: Addition of heat at constant volume.
Process 3-4: Addition of heat at constant pressure.
Process 4-5: Isentropic expansion.
Process 5-1: Rejection of heat at constant volume.
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Valve Overlap: Valve overlap has an advantage of improved scavenging of residual gases from the clearance
volume. This happens because when the piston retards towards the end of the exhaust stroke, the exhaust
gases which continue to move out with high velocity and kinetic energy cause temporary partial vacuum in
the cylinder due to which the fresh charge from the inlet valve can enter the cylinder in the overlap period
How is the actual cycle process measured in an operating engine?
• Morse test - Power developed in each cylinder of the engine.
• Retardation test - To find the frictional power of the engine
• Heat balance test - To find out the heat carried out by the exhaust gases and cooling water.
• Performance test - To measure the BHP of the engine by using dynamometers.
Four Stroke Cycle (diesel)
Suction Stroke:
• Inlet valve is open and exhaust is closed
• The piston moves from the TDC to BDC. Crankshaft revolves by half revolution
• The volume in the cylinder increases and the pressure decreases
• This sets up a pressure difference between the atmosphere and the inside of the cylinder
• Due to this pressure difference only, the atmospheric air is drawn into the cylinder
Compression Stroke:
• Both the inlet and exhaust valves are closed
• Piston moves from BDC to TDC
• Crankshaft revolves next half revolution
• The air in the cylinder is compressed
• The compression ratio of diesel engine varies from 16:1 to 22:1
• The process of compression is reversible adiabatic or isentropic
• At the end of stroke, a metered quantity of diesel is sprayed into the cylinder through the injector
• The high temperature of the air ignites the diesel as soon as it is sprayed
Power Stroke:
• Both inlet and exhaust valves are closed
• Piston moves from TDC to BDC
• Crank revolves by half revolution
• The auto ignition of diesel takes place almost at constant pressure till the injection is completed
• The high pressure of the burnt gases forces the piston downwards initially and later by expansion of
burnt gases performing power stroke.
• The linear motion of piston is converted to rotary motion of the crankshaft by connection rod.
• The theoretical expansion process of burnt gases is considered as isentropic.
Exhaust stroke:
• Exhaust is open and inlet is closed
• Piston moves from BDC to TDC
• Crank revolves by half revolution
• The burnt gases are expelled from cylinder at atmospheric pressure
• Crankshaft makes two revolutions to complete one full cycle
• The power is developed in every alternate revolution of the crankshaft
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Two stroke petrol engine
First stroke: exhaust
• Piston moves from TDC to BDC
• The spark plug ignites the compressed petrol and air mixture
• The hot gases are released during combustion increases the pressure in the cylinder which forces the
piston downwards
• The piston performs the power stroke till it uncovers the exhaust port.
• The combustion gases which are still at high pressure escape through the exhaust port and the process
is called scavenging
• This process is continued till the piston uncovers both exhaust and transfer port during the next stroke
• The crankshaft rotates by half revolution
Second stroke: compression
• Piston moves from BDC to TDC
• When it covers transfer port the supply of petrol and air mixture is cut off
• Further upward movement covers exhaust port and stops scavenging
• Further ascend of piston will compress the petrol and air mixture in the cylinder
• The compression ratio ranges from 7:1 to 11:1
• After piston reaches TDC, first stroke repeats again
• The crank rotates by half revolution
Comparison between 2S and 4S
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Comparison between Petrol and diesel engine
Advantages of 2S engine over 4S
• A 2-stroke engine has twice the number of power strokes than a 4-stroke engine at the same speed.
Hence theoretically a 2-stroke engine develops double the power output as that of 4-stroke
• The weight of a 2-stroke engine is less than the 4S engine because of the lighter flywheel due to more
uniform torque on crankshaft
• Construction is simple as there are no mechanical valves and gears
• It can be easily started than the 4-stroke
• 2 stroke engine occupies less space
• 2 stroke engine has less maintenance since less moving parts
Disadvantages of 2S engine over 4S
• Since the firing takes place in every revolution the time available for cooling will be less than a 4S engine
which results in overheating of the piston and other engine parts.
• A 2S engine needs better cooling arrangement because of high operating temperature
• A 2S engine consumes more lubricating oil.
• Incomplete scavenging results in mixing of the exhaust gases with the fresh charge which will dilute it.
Purpose of camshaft in 2S diesel engine: The Camshaft carries the cams which operate the fuel pumps and
exhaust valves. Because these operate once every cycle of the engine, the camshaft on a two-stroke engine
rotates at the same speed as the crankshaft.
It is also very important that the fuel pump and exhaust valve operate at exactly the right time, so the
camshaft is driven by the crankshaft. Two methods are used, a geared drive and a chain drive
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Marine Exhaust gas turbo charger:
• Major parts of a turbocharger are turbine rotor with blades and the impeller/blower mounted on a
common shaft enclosed in a volute casing
• The exhaust gases enter the turbine casing through a grid which prevents any broken pieces of piston
rings from entering the turbine
• The exhaust gases pass through nozzles where the pressure energy is converted to kinetic energy
• The gas strikes upon the turbine blades, rotates the turbine wheel and comes out of the exhaust gas
outlet.
• The left gases pass through the economiser where it is used to convert the feedwater into steam.
• The turbine is connected to a centrifugal blower. The rotation of turbine rotates the blower
• At the blower end the impeller draws air from the engine room atmosphere, through the air filter
• The air inlet passage is called inducer. It guides the air smoothly to the impeller
• Impeller discharges the air radially through the diffuser and volute casing, to the air cooler
• According to gas law for a constant volume increasing the air pressure will increase the temperature so
there will be a difference in temperature after charging
• Forcing this air into the engine can reduce efficiency and cause knocking
• In order to cool this an intercooler is introduced which acts as an heat exchanger device and helps to
cool the air before entering the engine
• The diffuser and the volute casing have the divergence shape which reduce the speed of air passing
through them
• This reduction in speed converts kinetic energy into pressure energy
• In conclusion a turbocharger will provide more air to expand on combustion and produces more power
• An additional auxiliary blower is also run through electric motor
• The blower starts whenever the scavenge air pressure drops below pre-set limit
• It stops automatically when the pressure is sufficient
• If the turbo charger breaks down the auxiliary blower delivers sufficient air to run the engine at reduced
power to reach the next port.
• The turbine casing is water cooled and, in some design, it is air cooled
• The rotating parts are supported on spring mounted ball bearing at the ends
• There are two pumps, one on blower and other on turbine side
• The pumps direct the oil to the bearings
Why 2S engine in ships:
• Power/Weight ratio is much higher than 4-stroke engine. For same weight of engine, 2-stroke engine
produces huge power which is desired for propulsion of giant ship.
• Since less weight more cargo can also be loaded
• Maintenance is very less with respect to 4-stroke engine. As it has less moving parts and it’s another
great advantage for the ships. It’s more reliable for operation.
• Vibration & Noise are very less in 2 stroke engine with respect to 4-stroke engine and these factors enable
the good working environment in engine room. Also, it enhances the stability of the ship.
• No reduction attachments: As two stroke engines are low speed engine, there is no requirement of
reduction gear or speed reduction arrangement as required for high speed four stroke engine.
Scavenging of IC Engine:
The scavenging in an IC engine is the process of removing the burnt gases from the combustion chamber of
the engine cylinder.
Types of scavenging:
Crossflow scavenging: In this method the transfer port or inlet port and exhaust port are situated opposite
sides of the engine cylinder (2 stroke)
Back flow or loop scavenging: In this method the inlet and outlet ports are situated on the same side of the
engine cylinder.
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Uniflow scavenging: In this method the fresh charge while entering from one side of the engine cylinder
pushes out the gases through the exit valve situated on the top of the cylinder.
Supercharging of IC engine:
It is the process of increasing the mass or density of the air fuel mixture (SI) or air (CI) induces into the engine
cylinder. It is done with the help of compressor or blower known as supercharger
Carburettor: It is a device for atomising and vapouring the fuel and mixing it with the air in varying proportion
for required conditions of the engine.
The process of breaking up and mixing the fuel with air is called carburation.
Spark Plug: It is a device used for producing a spark for igniting the fuel.
It is designed to withstand pressure up to 35bar
Operating current 10000-30000volts
It is kept from 0.3mm to 0.7mm
Rating of SI Engine Octane number: The hydrocarbon fuel used in SI engine have a tendency to cause engine
knock when the engine operating conditions become severe. The knocking tendency of a fuel in SI engine is
generally expressed in octane number.
Percentage by volume of
Iso octane and Normal heptane
generally, octane number of petrol is 80 to 100
Rating of CI engine Cetane number
The knocking tendency is also found in CI engines similar like SI engines but here it is due to sudden ignition
and abnormal rapid combustion of accumulated fuel in combustion chamber. Such cases cause ignition lag
in the combustion of fuel between the time of ignition and actual burning.
• Property of ignition lag is generally measured in cetane number:
• Mixture of cetane and alpha methyl naphthalene
• Generally obtained cetane number of diesel is 40 to 55
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Definition:
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Thermodynamics
Law of perfect gases
A perfect gas or an ideal gas is defined as the state of a substance whose evaporation from liquid
state is complete. It may be noted that if its evaporation is partial, the substance is called vapour.
The physical properties of a gas are controlled by the following three variables:
Pressure exerted by gas, Volume occupied by the gas and temperature of the gas
Boyles’s Law: It states that the absolute pressure of a given mass of a perfect gas is inversely proportional
to its volume, when the temperature is constant.
Eg: Syringe, Bicycle pump
Charles Law: The volume of a given mass of a perfect gas is directly proportional to its temperature, when
the absolute pressure remains constant.
Eg: Hot air balloon
Gay-Lussac Law: This law states that the absolute pressure of a given mass of a perfect gas varies directly as
its absolute temperature, when the volume remains constant.
Eg: Pressure Cooker, water heater
Joule’s Law: It states “the change of internal energy of a perfect gas is directly proportional to the change of
temperature.”
Avogadro’s Law: It states that “Equal volume of all gases, at the same temperature and pressure, contain
equal number of molecules.”
Universal gas constant: The universal gas constant of a gas is the product of the gas constant and the
molecular mass of the gas. R=287 J/Kg K
There are 2 types specific heat at constant volume and specific heat at constant pressure.
Laws of Thermodynamics:
Zeroth law of Thermodynamics: This law states that when two bodies are in thermal equilibrium with a third
body, they are also in thermal equilibrium with each other.
First law of Thermodynamics: The law states that heat is a form of energy and energy can neither be created
nor be destroyed, it can be transformed from one form to another.
Q=W+E
Second law of Thermodynamics: It states that “It is impossible for a self-acting machine working in a cyclic
process to transfer heat from a body at a lower temperature to a body at a higher temperature without the
aid of an external agency” (Clausius)
“It is impossible to construct an engine working on a cyclic process, whose only purpose is to convert heat
energy in to work” (kelvin planck)
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Heat Engine and Heat Pump:
Heat Engine: It is a Thermodynamic process which converts heat energy into mechanical energy.
It is a device which operates continuously in a cyclic manner and it absorbs heat from heat reservoir or source
and performs some amount of mechanical work and rejects left heat to cold reservoir or sink.
Ex: IC engine, gas turbine
Heat Pump: A heat pump is a device that transfers or pumps heat energy from a source of heat or a thermal
reservoir by absorbing some amount of work from the surrounding.
Ex: Room heater
Carnot Cycle:
Carnot cycle engine is considered to be the most efficient heat engine, consisting of two isothermal
processes and two reversible adiabatic process
• Isothermal expansion: During this process heat supplied is fully absorbed by the air and is utilised in doing
external work
• Reversible Adiabatic expansion: During this no heat is absorbed or rejected by air. (expansion of gas)
• Isothermal compression: Heat is rejected and is equal to the work done on the air
• Reversible Adiabatic compression: No heat is absorbed or rejected by the air.
Thermodynamic Process:
Constant Volume or isochoric process: (governed by Gay-Lussac law): When the gas is heated at a constant
volume, its temperature and pressure will increase.
Constant pressure or iso-baric process: (governed by Charles law): When the gas is heated at a constant
pressure, its temperature and volume will increase.
Hyperbolic process: A process in which the gas is heated or expanded in such a way that the product of its
pressure and volume (p x v) remain constant.
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Constant temperature or isothermal process: A process in which the temperature of the working substance
remains constant during its expansion or compression is called isothermal process.
Adiabatic or isentropic process: A process in which the working substance neither receives nor gives out
heat to its surroundings, during its expansion or compression is called adiabatic process.
Reversible Cycle: A process in which some change in the reverse direction reverses the process completely
is known as reversible process.
Irreversible process: A process in which change in the reverse direction does not reverse the process is called
irreversible process.
Efficiency of a cycle: It may be defined as the ratio of work done to the heat supplied during a cycle.
Heat transfer theory:
Heat transfer is a process in which heat is transferred from body at higher temperature to another cooler
body. The rate of heat transfer depends upon the differences in temperature between the bodies, the
greater the difference in temperature, the greater the rate of heat transfer
Heat can be transferred in three ways: by conduction, by radiation and by convection.
In conduction, the molecular energy is directly exchanged, from the hotter to the cooler regions, the
molecules with greater energy communicating some of this energy to neighbouring molecules with less
energy. An example of conduction is the heat transfer through the solid walls of a refrigerated store.
Radiation is the transfer of heat energy by electromagnetic waves, which transfer heat from one body to
another, in the same way as electromagnetic light waves transfer light energy. An example of radiant heat
transfer is when a foodstuff is passed below a bank of electric resistance heaters that are red-hot.
Convection is the transfer of heat by the movement of groups of molecules in a fluid. The groups of molecules
may be moved by either density changes or by forced motion of the fluid. An example of convection heating
is cooking in a jacketed pan: without a stirrer, density changes cause heat transfer by natural convection;
with a stirrer, the convection is forced.
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Refrigeration and Air Conditioning
Refrigeration: It is defined as a method of reducing temperature of a system below that of the surrounding
and maintaining it at the lower temperature by continuously abstracting the heat from it.
UNIT of refrigeration: Tons of refrigeration
A ton of refrigeration is defined as the quantity of heat absorbed in order to form one ton of ice in
24 hours from water at 0 degree.
1 ton of refrigeration = 210 kJ/min = 3.5 KW
Coefficient of performance: It is defined as the ratio of heat extracted in the refrigerator to the work done
by refrigerant.
Basics of refrigeration cycle:
Parts of refrigeration: Circulating system/Compressor, Condenser, Expansion device, Evaporator
Circulating System: It consists of mechanical devices such as compressors and pumps necessary to circulate
the refrigerant to undergo refrigeration cycle. They increase pressure and temperature of the refrigerant.
They are driven by electrical motors.
Condenser: It is a device wherein the refrigerant vapour gives off its latent heat to the atmospheric air and
condenses into liquid so that it can be circulated in the refrigeration cycle.
Expansion Device: It is a device which reduces pressure and temperature of the liquid refrigerant before it
passes to the evaporator. An expansion valve or capillary tube serves the purpose
Evaporator: Here the liquid refrigerant evaporates by absorbing heat from the refrigerator cabinet in which
the substances have to be cooled are kept.
Vapour Compression Refrigerator:
Principle: In VCR system the refrigerant alternatively evaporates and condenses thus undergoing a change
of phase from vapor to liquid and again liquid to vapor. During evaporation it absorbs the latent heat from
the refrigerated space and gives of the heat while condensing.
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Working:
• The vapor refrigerant at low pressure from the evaporator is drawn by the compressor which compresses
it to high pressure, and hence relatively increases its temperature above atmospheric air. (isentropic
compression)
• The high-pressure high temperature vapor refrigerant from the compressor flows to the condenser
where it gives off its latent heat to the atmospheric air. As a result, loss of latent heat in the condenser,
the refrigerant condenses back to liquid. (At constant pressure and temperature)
• The high-pressure liquid refrigerant approximately at room temperature now flows to the throttle valve
in which it expands to a low pressure and low temperature and passes to the evaporator coils for
circulation.
• The liquid refrigerant at low pressure and low temperature passing in the evaporator coiled tubes
absorbs heat from the contents in the freezing compartment and it evaporates. And cycle continues.
Vapor Absorption Refrigerator:
Principle: The VAR system makes use of the heat energy to change the state of the refrigerant. This system
makes use of the ability of the substance called absorbent, to absorb large volumes of vapor of a refrigerant
and reduce it to liquid and subsequently give off its vapours when heated.
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Working:
• Ammonia is commonly used as the refrigerant and water as absorbent in this type of refrigerators
• In this the ammonia refrigerant vaporizes in the evaporator coils absorbing the latent heat from the
freezing compartment thus keeping it cool and rejects this heat in the condenser.
• Dry ammonia vapor is dissolved in the cold water contained in the absorber, which will produce a strong
ammonia solution. The strong ammonia solution from absorber is pumped to heat exchanger where it
is warmed by the warm weak ammonia solution flowing back from the generator.
• The warm high-pressure ammonia solution now passes to the generator where it is heated by heating
coils. The heating will drive out the ammonia vapor from it.
• Now the solution in generator becomes weak and flows back to the heat exchanger where it warms up
the strong ammonia solution passing through it.
• The high-pressure ammonia vapor from generator now passes to a condenser, where it is condensed.
The high-pressure ammonia liquid is now expanded to low pressure and low temperature in the throttle
valve and is passed onto the evaporator coils provided in the freezing compartment, where it absorbs
the heat and evaporates. And the cycle continues
Difference between VCR and VAR
Air Refrigerator working on Reverse Carnot cycle:
•
•
•
•
Isentropic Compression process: During this process no heat is absorbed or rejected by the air.
Isothermal compression process: During this process, heat is rejected by the air.
Isentropic expansion process: During this process no heat is absorbed or rejected by the air.
Isothermal expansion process: During this process, heat is absorbed by the air.
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Air Refrigerator working on Bell-Coleman cycle (Reverse Brayton or Joule):
• Isentropic Compression process: During this process no heat is absorbed or rejected by the air.
• Constant pressure cooling process: During this process heat is rejected by air.
• Isentropic expansion process: During this process no heat is absorbed or rejected by the air.
• Constant pressure expansion process: During this process, heat is absorbed by the air.
Properties of good refrigerant:
Refrigerants:
Parameter
Boiling Point
Latent heat
Pressure
Critical Temp
Others
Uses
GWP
R12 (CCl2F)
CFC
-29⁰
Low
159kJ/kg at -15⁰
0.82 bar at -15⁰
6.4 bar at 30⁰
R22(CHCLF2)
HCFC
-41⁰
216.5kj/kg at -15⁰
Nontoxic,
Noncorrosive,
Non-irritating,
Non-Flammable
Detected by soap
solution, Nontoxic,
Noncorrosive, Nonirritating, NonFlammable
Reciprocating,
Rotary, Centrifugal
compressor
High toxic,
Flammable,
irritating
Reciprocating
Industrial application
and aboard ships
1810
0
1
Reciprocating,
Rotary,
Centrifugal
compressor
10900
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1.92 bar at -15⁰
10.88 bar at 30⁰
Ammonia R717
Natural
-33.3⁰
High
1315kj/kg at -15⁰
10.78 bar at 30⁰
Carbon dioxide R744
Natural
-73.6⁰
20.7 bar at -15⁰
70 bar at 30⁰
Low 31⁰
Nontoxic,
Non-irritating, NonFlammable
Low efficiency
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Normally used in ships refrigerants both performance and value for money, are R22 and R12 low GHG and
other polar bear saving types.
Modern refrigerants are Hydro Fluro Carbons are a family of hydrocarbons containing one or several fluorine
atoms, but no chlorine atoms, thus no ozone depleting potential.
R134a - Long-term replacement for R-12. Best performance in medium and high temperature applications
(air conditioning). (GWP= 1430) HFC
R407C - Best performance in medium and high temperature applications. Suitable for new systems and R22 changeover (air conditioning). (GWP=1774) HFC
R437A (GWP = 1805) R442A (GWP=1888)
R404A - Best performance in low and medium temperature applications. Common in new marine systems.
Provision refrigeration. (GWP=3900) HFC
R507 - Best performance in low and medium temperature applications. Common in new systems. Provision
refrigeration. (GWP=3985)
Definitions:
Dry air: The pure dry air is a mixture of number of gases such as nitrogen, oxygen, co2, hydrogen, argon,
neon, helium etc nut the nitrogen and oxygen have major portion of the combination.
Moist air: It is a mixture of dry air and water vapour.
Saturated air: At a given temperature and pressure the air can only hold a certain maximum amount of
moisture, when the limit is reached, the air is said to be saturated.
Superheated air: If the temperature of steam is above saturated temperature then vapours is superheated
air.
Degree of Saturation: It is defined as the ratio of the actual specific humidity to the specific humidity of the
saturated mixture at the same temperature and pressure.
Dry bulb temperature: It is the temperature of the moist air measured by an ordinary thermometer.
Wet Bulb temperature: It is the temperature of the moist air measured by a thermometer whose bulb is
covered by a wetted wick and is exposed to current of moving air.
Humidity: It is the mass of water vapor present in 1Kg of dry air. (gm/kg of dry air)
Absolute Humidity: It is the mass of water vapour present in 1-meter cube of dry air (g/m3 of dry air)
Relative Humidity: It is the ratio of actual mass of water vapour in a given volume of moist air to the mass
of water vapour in the same volume of saturated air at the same temperature and pressure.
Specific Heat of a gas: The specific heat of a substance may be defined as the amount of heat required to
raise the temperature of its unit mass through 1 degree.
Sensible Heat: The amount of heat required to raise the temperature of 1 kg of water from 0 deg to 100 deg
at a given constant pressure is defined at sensible heat.
Sensible Heating: The heating of air, without any change in its specific humidity is known as sensible heating.
Sensible Cooling: The cooling of air, without any change in its specific humidity is known as sensible cooling.
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Latent heat of evaporation: The amount of heat requires to evaporate 1 kg of water at saturation
temperature to 1 kg of dry steam at the same saturation temperature at given constant pressure is called
latent heat of evaporation
Critical Temperature: The critical temperature of a refrigerant is the temperature above which a refrigerant
gas (vapour) cannot be liquefied, irrespective of pressure. This process normally takes place in the
condenser.
Enthalpy of superheat: The amount of heat required to increase the temperature of dry steam from its
saturation temperature to any desired higher temperature at the given constant pressure is called amount
of superheat of enthalpy of evaporation.
Degree of superheat: The difference between the superheated steam and the saturation temperature is
defined as degree of superheat.
Humidification: The addition of moisture to the air, without change in its dry bulb temperature is known as
humidification.
Dehumidification: The removal of moisture from the air, without change in its dry bulb temperature is
known as dehumidification.
Dew Point Temperature: It is the temperature to which moist air must be cooled at a constant pressure in
order to cause condensation of any of its water vapour.
Enthalpy: It is defined as the sum of the system's internal energy and the product of its pressure and volume.
Entropy: It is thermodynamic property of a working substance, which increases with the addition of heat,
and decreases with its removal.
Change of entropy: Over a small range of temperature, the increase or decrease of entropy, when multiplied
by the absolute temperature, gives the heat absorbed or rejected by the working substance.
dQ =T x dS
Calorific value of fuel (KJ/Kg): The calorific value or heat value of a solid or liquid fuel may be defined as
the amount of heat given out by the complete combustion of 1kg of fuel.
Superheated steam: when water is heated to the boiling point (sensible heating) and then vaporized with
additional heat (latent heating). If this steam is then further heated above the saturation point, it becomes
superheated steam (sensible heating).
Moller chart: The Moller diagram is a graphic representation of the relationship between air temperature,
moisture content and enthalpy.
Newtons law of cooling: The heat transfer from a hot body to cold body is directly proportional to the surface
area and difference of temperatures between the two bodies. This statement is called newtons law of
cooling.
If suction pressure is reduced what will be affect on compressor in VCRS?
Compression Ratio = Absolute discharge pressure/Absolute suction pressure
Therefore, if absolute suction pressure reduces, compression ratio increases hence more work should be
done by compressors resulting in reduced COP
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Boilers
Boiler: It is a closed vessel used to convert water into steam at required temperature and pressure by the
application of heat.
Classification of Boilers:
• Horizontal, vertical and inclined
• Fire tube boiler and water tube boiler
• Internally fired and Externally fired
• Forced circulation and natural circulation (La mont)
• High pressure boiler and low-pressure boiler
• Single tube and multi tube boiler
• Stationary and portable boiler (scotch marine, locomotive)
Types of boiler:
Lancashire Boiler:
Working:
• The Boiler is filled with substantial quantity of water
• The fuel is charged through the furnace door which burns in the grates
• The product of combustion first passes the flue tubes and return along the brick-built flue under the
boiler to the front end
• Here the hot gases divide and flow along the two side flues to the rear end and the pass through the
chimney.
• The steam is accumulated at the steam space above the surface of the water and can be tapped off
through the steam stop valve
Babock and Wilcox Boiler:
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Boiler Mounting:
• Two water level indicators
• Pressure gauge
• Two safety valves
• Steam stop valves
• Blow off cock
• Feed check valve
• Fusible plug
Water level indicator: It is an important fitting which indicates the water level inside the boiler to an
observer.
Its fixed Infront of steam boiler.
Pressure gauge: It is used to measure the pressure of the steam inside the steam boiler (Bourden type)
Its fixed Infront of steam boiler.
Safety Valve: The function of safety valve is to blow off the steam when the pressure of the steam inside the
boiler exceed the working pressure.
These are attached to steam chest for preventing explosions due to excessive internal pressure.
Types: Lever safety valve, Dead weight safety valve, High steam and low water safety valve, Spring loaded
safety valve.
Steam stop valve: Its function is to:
• To control the flow of steam from the boiler to the main steam pipe
• To shut off the steam completely when required
It is usually mounted on the highest part of the boiler
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Blow-off cock: The function of blow off cock is to
• To empty the boiler whenever required
• To discharge the mud, scale or sediments which are accumulated at the bottom of the boiler.
Feed check valve: Its function is to regulate the supply of water, which is pumped into the boiler, by the feed
pump. (non return valve)
It is fitted to a screwed spindle to regulate the lift
Fusible Plug: Its function is to put off the fire in the furnace of the boiler when the level of water in the boiler
falls to an unsafe limit.
It is fitted to crown plate of the furnace or the fire box
Boiler Accessories:
• Feed pump
• Super heater
• Economiser
• Air preheater
• Steam separator
• Steam trap
Feed Pump: It is used to deliver water to the boiler. A feed pump may be of centrifugal type or reciprocating.
Superheater: Its purpose is to increase the temperature of saturated steam without raising its pressure. The
heat obtained from flue gases is used in superheating the steam.
Economiser: It is a device used to heat feed water by utilising the heat in the exhaust flue gases before
leaving through the chimney.
Advantages:
• It Improves economy of steam boiler
• There are about 15 - 20 of coal saving
• It increases the steam raising capacity of a boiler because it shortens the time required to convert
water into steam.
Air Preheater: Air Pre-heaters are basically heat-exchangers installed in the exit flus gas duct of the boiler.
The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal
efficiency of the boiler by reducing the useful heat lost in the flue gas.
Steam Separator: A steam separator is a device for separating water droplets from steam.
Steam Trap: Steam traps are a type of automatic valve that filters out condensate (i.e. condensed steam)
and non-condensable gases such as air without letting steam escape.
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Types of Boiler:
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Fluid Mechanics
Work: Whenever a force acts on a body and the body undergoes a displacement in the direction of the force,
then the work is said to be done. (Joules or N-m)
Work done = F * x
Power: It is the rate of doing work or work done per unit time. (Watt)
Energy: It is the capacity of doing work.
The mechanical energy is equal to the work done on a body in altering either its position or its velocity.
Potential energy: It is the energy possessed by a body for doing work, by virtue of its position.
P.E= m x g x h
Strain Energy: It is the potential energy stored by an elastic body when deformed.
Kinetic Energy: It is the energy possessed by a body for doing work, by virtue of it mass and velocity of
motion.
Force: It may be defined as an agent which produces or destroys the motion of the body.
1 kgf = 9.81 N
Resultant Force: It is a single force which produces the same effect as produced by all the given forces
acting on a body.
System of Forces:
Coplanar forces: The forces whose line of action lie on the same plane are known as coplanar forces.
Concurrent forces: The forces which meet at one point are known as concurrent forces
Moment: It is the turning effect produced by a force, on the body on which it acts.
It is the product of the force and the perpendicular distance of the point about which the moment is
required and the line of action of the force.
Couple: The two equal and opposite forces, whose lines of action are different forms the couple.
Centre of Gravity: The point through which the whole mass of the body acts, irrespective of the position of
the body is known as centre of gravity.
Friction: A force acting in the opposite direction to the motion of the body is called force of friction.
Static Friction: The friction experienced by a body when at rest.
Dynamic Friction: The friction experienced by a body when at motion.
Sliding Friction: The friction experienced by a body when it slides over another body
Rolling Friction: The friction experienced by a body when balls or rollers are interposed between the two
surfaces
Limiting Friction: The maximum value of frictional force which comes into play when a body just begins to
slide over the surface of the other body is known as limiting friction.
Law of static Friction:
• The force of friction always acts in a direction opposite to that in which the body tends to move
• The magnitude of the force of friction is exactly equal to the force which tends the body to move.
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•
•
•
The magnitude of the limiting friction bears a constant ratio to the normal reaction between the two
surfaces.
The force of friction is independent of the area of contact between the two surfaces
The force of the friction depends upon the roughness of the surfaces
Law of Dynamic Friction:
• The force of friction always acts in a direction opposite to that in which the body tends to move
• The magnitude of the kinetic friction bears a constant ratio to the normal reaction between the two
surfaces.
• For moderate speed, the force of friction remains constant. But it decreases slightly with the increase of
speed
Coefficient of friction: It is defined as the ratio of limiting friction to the normal reaction between the two
bodies.
Limiting Angle of Friction: It is defined as the angle which the resultant reaction makes with the normal
reaction.
Angle of Repose: It is the angle of inclination of the plane to the horizontal at which the body just begins to
move down the plane.
Speed: It is the rate of change of displacement with respect to its surrounding. (Scalar)
Velocity: It is rate of change of displacement with respect to its surrounding in a particular direction. (Vector)
Acceleration: It is the rate of change of velocity of a body.
Newton’s Laws of motion:
First law: It states that everybody continues in the state of rest or of uniform motion in a straight line unless
it is acted upon by some external force.
Second law: It states that rate of change of momentum is directly proportional to the impressed force and
takes place in the same direction in which the force acts.
Third law: It states that to every action there is always an equal and opposite rection.
Mass: It is a matter contained in the body. (kg)
Weight: It is the force by which body is attracted towards the centre of gravity (N)
Momentum: It is defined as the total motion possessed by a body
Momentum= Mass x Velocity
Projectile: A particle moving under the combined effect of vertical and horizontal forces is called a projectile.
Trajectory: It is the path traced by a projectile in the space.
Velocity of projection: It is the velocity with which a projectile is projected.
Angle of projection: It is the angle with the horizontal at which the projectile is projected.
Time of flight: It is the total time taken by a projectile to reach maximum height and to return back to ground.
Range: It is the distance between the point of projection and the point where the projectile strikes the
ground.
Angular Displacement: It is the angle by a particle from one point to another with respect to time. (vector)
Angular Velocity: It is rate of change of angular displacement of a body. (rad/s) (vector)
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Angular Acceleration: It is a rate of change of angular velocity. (vector)
Simple Harmonic Motion: A body is said to be in simple harmonic motion if
• Its acceleration is always directed towards the centre known as point of reference
• Its acceleration is proportional to the distance from the point.
Amplitude: It is the maximum displacement of a body from its mean position.
Periodic time: It is time taken for one complete revolution of the particle.
Frequency: It is the number of cycles per second and it is the reciprocal of time period.
Archimedes’ Principle: When a body is immersed wholly or partially in a liquid it is lifted up by a force equal
to the weight of liquid displaced by the body. This statement is called as Archimedes principle
Buoyancy: The tendency of a liquid to uplift an immersed body because of the upward thrust of the liquid is
known as buoyancy.
If the force of buoyancy is more than the weight of the liquid displaced then the body will float or it will sink.
Bernoulli’s Equation: It states that “For a perfect incompressible liquid, flowing in a continuous stream, the
total energy of a particle remains the same, while the particle moves from one point to another.
Density: It is defined as the mass per unit volume of a liquid at a standard temperature and pressure. (kg/m3)
Weight Density or Specific Weight: It is defined as the weight per unit volume of a liquid at a standard
temperature and pressure. (N/m3)
Specific Volume: It is defined as the volume per unit mass of the liquid.
Specific gravity: It is defined as the ratio of specific weight of a liquid to the specific weight at a standard
temperature. (No unit).
Viscosity: It is a property of a liquid which offers resistance to movement of one layer over another adjacent
layer of liquid.
Newtons law of Viscosity: It states that shear stress on a layer of a fluid is directly proportional to the rate
of shear strain.
Newtonian Fluid: A fluid whose viscosity does not changes with rate of deformation of shear strain is known
as Newtonian Fluid.
Non-Newtonian Fluid: A fluid whose viscosity changes with rate of deformation of shear strain is known as
Non-Newtonian Fluid.
Laminar flow: A flow in which the viscosity of fluid is dominating over inertia forces, is called laminar flow.
(Re<2000)
Turbulent flow: A flow in which the inertia force is dominating over viscosity, is called turbulent flow.
(Re>4000)
Reynolds Number: The ratio of inertia force to the viscous force is called Reynold’s number.
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Venturi meter: It is an instrument used to measure the discharge of liquid flowing in a pipe.
I consist of 3 parts: converging cone, throat, diverging cone.
Orifice meter: It is a device used for measuring the discharge of the liquid flowing through the pipe.
Orifice: It is a small opening in the wall or base of the vessel through which the fluid flows. It is used to
increase the amount of discharge.
Pitot tube: It is a small open tube bent at right angle. It is used to measure the velocity of flow at the required
Point in a pipe. It is determined by measuring the rise of liquid in a tube.
Momentum Equation or law of momentum: It states that “The net force acting on a mass of fluid is equal
to the change in momentum of slow per unit time in that direction.”
Kinematic Viscosity: It is defined as the ratio of dynamic viscosity to the density of liquid.
Hydraulic Coefficients:
Coefficient of Contraction: It is defined as the ratio of area of jet at vena contract to area of orifice.
Coefficient of velocity: It is defined as the ratio of the actual velocity of the jet at vena contract to the
theoretical velocity.
Coefficient of discharge: It is defined as the ratio of actual discharge through the orifice to theoretical
discharge.
Coefficient of resistance: It is defined as the ratio of loss of head in the orifice to the head of water available
at the exit of the orifice.
Water Hammer: When a liquid flowing through a long pipe is suddenly brought to rest by closing the valve
at the end of a pipe, then a pressure wave of high intensity is produced behind the valve. This pressure wave
of high intensity has a effect of hammering action on the walls of the pipe. This is known as water hammer.
Compressibility: It is the property of liquid by virtue of which liquids undergo a change in volume with change
in pressure.
Surface Tension: It is that property of a liquid which enables it to resist tensile stress.
Capillarity: It is defined as a phenomenon of rise or fall of a liquid surface in a small vertical tube held in a
liquid relative to general level of the liquid.
Pascal’s Law: It states that the intensity of pressure at any point in a fluid at rest is same in all directions.
Atmospheric Pressure: The normal pressure acting upon all the surfaces with which it is in contact is known
as atmospheric pressure.
Fluid Kinematics: It’s a branch of fluid mechanics which deals with the study of velocity and acceleration of
the fluid particles without taking into consideration of any force or energy.
Rate of discharge: The quantity of liquid flowing per second through section of pipe. (m3/s)
Equation of Continuity: If an incompressible liquid flowing through a pipe or a channel, the quantity of liquid
passing per second is the same at all sections. This is known as equation of continuity.
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Pump: A pump, which is the heart of hydraulic system, converts mechanical energy into hydraulic energy.
Different Types or Classification of Pumps:
1) Dynamic Pump (Non-Positive Displacement Pump)
i) Centrifugal Pump
a) Axial flow
b) Radial flow
c) Mixed flow
2) Positive Displacement Pump
i) Rotary type positive displacement pump
a) Gear Pump
ai) External Gear
aii) Internal Gear
b) Rotary vane pump
ii) Reciprocating type positive displacement pump
a) Piston displacement pump
b) Diaphragm pump
1) Dynamic (non-positive displacement) pumps: This type is generally used for low pressure, high-volume
flow applications. Because they are not capable of withstanding high pressures, they are of little use in the
fluid power field. Normally their maximum pressure capacity is limited to 250-300psi. This type of pump is
primarily used for transporting fluids from one location to another.
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i) Centrifugal Pump: A centrifugal pump is a rotating machine in which flow and pressure are generated
dynamically. The energy changes occur by two main parts of the pump, the impeller and the volute casing.
The function of the casing is to collect the liquid discharged by the impeller and to convert some of the kinetic
(velocity) energy into pressure energy.
Centrifugal pumps use an impeller, which has curved blades that accelerate fluids towards their edge
when rotating. The impeller is normally driven by an electric motor, and its movement produces suction at
the pump inlet, drawing water inside.
An increase in the fluid pressure from the pump inlet to its outlet is created when the pump is in
operation. This pressure difference drives the fluid through the system or plant.
The centrifugal pump creates an increase in pressure by transferring mechanical energy from the
motor to the fluid through the rotating impeller. The fluid flows from the inlet to the impeller centre and out
along its blades. The centrifugal force increases the fluid velocity and consequently also the kinetic energy is
transformed to pressure.
a) Axial flow: The axial flow impeller discharges fluid along the shaft axis.
b) Radial flow: The radial flow impeller discharges the fluid radially at 90° to the shaft axis.
c) Mixed flow: The mixed flow impeller discharges fluid in a conical direction using a combined radial and
axial pumping action
Applications of Centrifugal Pumps:
This type is generally used for low pressure, high-volume flow applications.
Supplying water, pumping water for domestic requirements, regulating boiler
• Oil and Energy - pumping crude oil, slurry, mud; used by refineries, power generation plants
• Industrial - boiler feed applications, air conditioning, pressure boosting,
• Waste Management, Agriculture & Manufacturing - Wastewater processing plants, municipal
industry, drainage, irrigation.
• Pharmaceutical, Chemical & Food Industries - paints, hydrocarbons, petrochemical, cellulose, sugar
refining, food and beverage production
• Various industries (Manufacturing, Industrial, Chemicals, Pharmaceutical, Food Production,
Aerospace etc.) - for the purposes refrigerants.
Advantages of centrifugal pump:
• As there is no drive seal so there is no leakage in pump
• It can pump hazardous liquids
• There are very less frictional losses
• There in almost no noise
• Centrifugal pump has minimum wear with respect to others
• Centrifugal pump uses magnetic coupling which breakup on high load eliminating the risk of
damaging the motor
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Limitations of centrifugal pump:
• Because of the magnetic resistance there is some energy losses
• Unexpected heavy load may cause the coupling to slip
• ferrous particles in liquid are problematic when you are using magnetic drive. This is because
particle collect at impeller and cause corrosion of vanes.
2) Positive Displacement pump: Positive displacement pumps move a fixed amount of fluid at regular
intervals. They are built with internal cavities that fill up at the suction side, to be discharged with higher
pressure at the outlet. Based on how the fluid is displaced, positive displacement pumps can be reciprocating
or rotary.
i) Rotary type positive displacement pump: Positive displacement rotary pump can move the fluid by using
rotating mechanism that creates a vacuum that captures and draws in the liquid. It uses a rotor that traps
water in cavities, releasing it at the pump outlet. These cavities can be the spaces between gear teeth or
screw threads, among other configurations.
a) Gear Pump: Gear pumps are less expensive but limited to low pressures. It is noisy in operation than either
vane or piston pumps. Gear pumps are invariably of fixed displacement type, which means that the amount
of fluid displaced for each revolution of the drive shaft is theoretically constant.
Applications of gear pump: Gear pumps are commonly used for pumping high viscosity fluids such as oil, paints,
resins or foodstuffs. They are preferred in any application where accurate dosing or high-pressure output is required.
External: various fuel oils, lube oils, Industrial, agricultural
Internal: Food products, vegetable oil, molasses, chocolate, paint, tar, soap, glycol
Advantages of Gear pump
1. They are self-priming.
2. They give constant delivery for a given speed.
3. They are compact and light in weight.
4. Volumetric efficiency is high.
Disadvantages of gear pump
1. The liquid to be pumped must be clean, otherwise it will damage pump.
2. Large Noise, not easy to repair after wear
3. If they run dry, parts can be damaged because the fluid to be pumped is used as lubricant.
ai) EXTERNAL GEAR PUMPS:
External gear pumps are the most popular hydraulic pumps in low-pressure ranges due to their long
operating life, high efficiency and low cost. They are generally used in a simple machine. The external gear
pump consists of a pump housing in which a pair of precisely machined meshing gears runs with minimal
radial and axial clearance. One of the gears, called a driver, is driven by a prime mover. The driver drives
another gear called a follower. As the teeth of the two gears separate, the fluid from the pump inlet gets
trapped between the rotating gear cavities and pump housing. The trapped fluid is then carried around the
periphery of the pump casing and delivered to outlet port. The teeth of meshed gears provide almost a
perfect seal between the pump inlet and the pump outlet.
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aii) INTERNAL GEAR PUMPS: Internal Gear Pumps consist of two gears: An external gear and an internal
gear. The crescent placed in between these acts as a seal between the suction and discharge. When a pump
operates, the internal gear drives the external gear and both gears rotate in the same direction. The fluid
fills the cavities formed by the rotating teeth and the stationary crescent. Both the gears transport the fluid
through the pump. The crescent seals the low-pressure pump inlet from the high-pressure pump outlet.
These pumps have a higher-pressure capability than external gear pumps.
b) Rotary vane pump: These pumps have a cylindrical rotor encased in a similar shaped housing. As the rotor
orbits, the vanes trap fluid between the rotor and the casing, drawing the fluid through the pump.
Applications: Automotive field, braking, power steering, transmission, supercharging, and in airplanes
Advantages of rotary vane pump
1. Vane pumps are self-priming, robust, and supply constant delivery at a given speed.
2. They provide uniform discharge
3. Their vanes are self-compensating for wear and vanes can be replaced easily.
4. These pumps do not require check valves.
5. They are light in weight and compact.
6. They can handle liquids containing vapours and gases.
7. Volumetric and overall efficiencies are high.
Disadvantages of rotary vane pump:
1. They are not suitable for abrasive liquids.
2. They require good seals.
3. They require good filtration systems and foreign particles can severely damage the pump.
ii) Reciprocating type positive displacement pump: Reciprocating pump move the fluid using one or more
oscillating pistons, plungers or diaphragms, while valves restrict fluid motion to the desired direction.
Pump in this category are simple with one cylinder or more. They can be either single-acting with
suction during one direction of the piston motion and discharge on the other or double-acting with suction
and discharge in both directions.
a) Piston displacement pump: In this design, the suction is created by a piston which plunges into and pulls
out of the material. Valves are used to ensure that the flow only moves in one direction. A reciprocating
design therefore pulses the liquid at identical intervals. The capacity of the pump can be adjusted by
changing the stroke, the rotating speed of the pump.
Applications: Plunger pumps / piston pumps are suitable for high pressure & high flow rates
Hydraulic systems for machining engine parts (Engine plant), coolant supply systems (Engine plant)
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Advantages of piston pump
• High efficiency
• No priming needed
• delivers water at high pressure
• work in wide pressure range
Disadvantages of piston pump
• More parts mean high initial cost
• High maintenance cost
• Pulsating flow
• Difficult to pump viscous fluid
b) Diaphragm pump: Diaphragm pumps also known as AOD pumps (Air operated diaphragms), pneumatic,
and AODD pumps. These pumps are responding pumps and include two diaphragms which are driven with
condensed air. The section of air by transfer valve applies air alternately toward the two diaphragms; where
every diaphragm contains a set of ball or check valves.
Applications: AOD pumps are particularly employed where power is not obtainable, otherwise in unstable
and combustible regions.
The applications of these pumps mainly include in continuous applications like in general plants,
industrial and mining. These pumps are also utilized for transferring chemical, food manufacturing, these
pumps are used to push liquids like corrosive chemical, volatile solvents, viscous, shear-sensitive foodstuffs,
pharma product, sticky fluids, dirty water, smaller solids, creams, abrasive slurry, oils, and gels.
Advantages of diaphragm pump
• Self-priming
• Explosion proof
• Portable
• Easy installation
• They can operate in the long term
• These are well suited for pumping chemicals otherwise other harming fluids
Disadvantages of diaphragm pump
• Most of the diaphragm pumps need approximately 20 typical cubic-feet for each minute & 100 PSI of
air intake for operating powerfully.
• These pumps are inclined not to push extremely accurate at their base end.
• This diaphragm pump pulsates, so a dampener has to be fixed on top of the pump to decrease pulsing.
Air Compressors: Compressor is a mechanical device which is used to increase the pressure of air from low
pressure to high pressure by using some external energy.
Classification of compressor:
1) Reciprocating Compressor
2) Rotary Compressor
3) Centrifugal Compressor
1) Reciprocating Compressor: These types of compressors adopt a volumetric compression system using
piston works much like an IC engine.
Working: It has a piston-cylinder arrangement, with inlet and outlet valves. The piston is driven by a crank
and connecting rod, which converts the rotary motion of the motor into reciprocating motion of the piston.
In operation, in the first cycle (the half revolution of the shaft) the inlet valve opens, the atmospheric air is
drawn-in by the piston as it moves down. In the next cycle (the second half revolution of the crank shaft),
the inlet valve gets closed, the outlet valve opens and the air is compressed as the piston moves up in the
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cylinder. The air compression process is accompanied with an increase in temperature. The air is cooled by
providing fins around the cylinder.
Main Parts: Piston, Cylinder, Connecting rod, Crankshaft and crankcase, Suction valve, Discharge valve, rings,
pulley.
Types of Reciprocating air compressor:
• Single Acting
• Double Acting
• Single Stage air compressor
• Double Stage air compressor
Single Acting: In this type of compressor only single side of the piston is used for the compression of the air
and other side is connected to the crankcase and not for the compression.
Double Acting: In this type of compressor both the sides of the piston is used for the compression of the air.
When suction takes place at one side than compression is taking place at other side. Both suction and
compression take place on each stroke of the piston.
Single Stage air compressor: In this the compression of the air takes place in a single cylinder. In the first
stroke, it sucks the air from the atmosphere and in the second stroke it compresses it and delivers it to the
storage tank. (Pressure around 120 PSI)
Double Stage air compressor: In this the compression of air takes place in two stages, the air is first
compressed to some extent in one cylinder and then it is transferred to the second cylinder for further
compression and finally then compressed air is stored in tank. (Pressure around 175 PSI)
Advantages of reciprocating compressor
• Used to produce high-pressure gas.
• High efficiency and flexibility.
• Cheap and rugged design.
Disadvantages of reciprocating compressor
• The size of compressor is very large for a given capacity.
• Part of the work input is lost due to frictional resistance between the piston and cylinder.
• Pulsating fluid flow.
• High vibration and noise.
• Piston rings and valves are extremely sensitive to the dirt present in the fluid.
Applications of Reciprocating Compressor: In spray painting shop, in workshop for cleaning machines, for
operation of pneumatic tool like rock drill, vibrator etc, in automobile service station to clean vehicle, to
drive air motors in coal mines, Food and beverage industry
2) Rotary Compressor: In a rotary air compressor the air is entrapped between two sets of engaging surfaces
and the pressure of air is increased by squeezing action or back flow of the air. It is driven either by an electric
motor or an engine. (The speed is high compared to reciprocating air compressor)
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Screw-type Compressor:
A screw compressor is a rotary type compressor. It has two intermeshing rotating screws with close working
tolerances. These screws are in a casing with inlet and outlet ports. In operation as the screw rotate, the
atmospheric air is drawn-in, trapped between the rotating screws, which is carried along the screws up to
the outlet port. Since, the screws mesh continuously, the air compression and delivery occur continuously
without any gap. For wear free and reduced noise operation some kind of lubrication forming a thin oil film
is used. The oil injected to the chamber lubricates the screw surfaces and forms a seal so that air is
compressed efficiently, as the screws mesh continuously.
Advantages of Rotary Compressor
• Compact size and complete package
• Economic first cost
• Vibration‐free operation does not require special foundation
Disadvantages of Rotary Compressor
• Less efficient compared to reciprocating air compressors
• Requires proper maintenance
Applications of rotary compressors: Industrial applications or to operate high-power air tools such as
jackhammers.
3) Centrifugal Compressor: A centrifugal blower compressor consists of a rotor or impeller to which a
number of curved vanes are fitted symmetrically. The rotor rotates in an air tight volute casing with inlet and
outlet points. The casing for the compressor is so designed that the kinetic energy of air is converted into
pressure energy before it leaves the casing
The curved vanes as well as the diffuser are so designed that air enters and leaves their tips tangentially,
without shock.
Basic Components: Impellers, Vanes, Discharge lines, Diffuser Plates, Shaft, Casing
Advantages of centrifugal compressor:
• Low weight, easy to design and manufacture.
• Suitable for continuous compressed air supply, such as cooling unit.
• They have fewer rubbing parts means less friction.
• Relatively energy efficient.
• Centrifugal compressors are reliable, low maintenance.
• It does not require special foundation.
Disadvantages of centrifugal compressor:
• Unsuitable for very high compression, limited pressure.
• They work at high speed, sophisticated vibration mounting needed.
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Applications of centrifugal compressor
• Food and beverage industry - centrifugal compressor provides oil frees compressed air for some
sensitive application such as food processing.
• Gas turbines, in automobile turbochargers and supercharger.
• Oil refineries, natural-gas processing.
• Refrigeration, air-conditioning and HVAC.
• Manufacturing process compressed air for pneumatic tools.
Major Factors affecting centrifugal pump:
•
•
•
•
•
•
•
•
•
Impeller design
Improper priming
Insufficient NPSH
Reduced capacity
Wrong direction of rotation
Clogging of suction pipeline and impeller
Improper shaft alignment
Packing troubles
Noisy operation
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Strength of Materials
Strength of materials: The strength of materials may be broadly be defined as that branch of engineering
science which deals with the ability of various types of materials to resist its failure and their behaviour under
the action of forces.
Stress: When some external system of forces or loads act on a body, the internal forces (equal and opposite)
are generated at various sections of the body, which resist the external forces. This internal force per unit
area at any section of the body is known as stress. (Pa)
Strain: When a system of forces acts on body, it undergoes some deformation. This deformation per unit
length is known as strain.
Young’s Modulus or Modulus of elasticity: According to Hooke’s law when a material is loaded within the
elastic limit the stress is directly proportional to strain.
Poisson’s ratio: The ratio of the proportional decrease in a lateral measurement to the proportional increase
in length in a sample of material that is elastically stretched.
It is the ratio of Lateral strain to longitudinal strain.
Stress Strain Curve:
Proportional Limit: This is limit up to which, the stress and the strain induced in the specimen are directly
proportional to each other, i.e. the specimen obeys Hooke’s law. Beyond this point, the stress is not
proportional to the strain.
Elastic Limit: This is limit up to which the material is said to be elastic. This means that the specimen regains
its original shape and dimensions after the removal of the external load. There are no residual deformations
seen in the specimen, on removal of the load. After this point, the material is said to become plastic.
Yield Point: It is limited by the upper yield point and the lower yield point. The stress – strain curve in this
part of the graph is almost horizontal, which implies that there is an appreciable increase in strain for a
negligible increase in stress. The material, due to strain hardening again starts taking load and the curve
rises. The material after yield point is said to be plastic and the deformation is of nearly permanent nature.
Ultimate Stress: It represents the maximum stress that a material can take before it fails. The specimen
however does not fail at this point. After this point, the curve starts dropping.
Breaking Point: This is the point at which the specimen fails. After the ultimate stress point, necking of the
specimen takes place, which causes a loss in the load carrying capacity of the specimen and ultimately causes
it to fail.
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Factor of Safety: The ratio of ultimate stress to working stress is known as factor of safety.
Shear Force and Bending Moment:
Shear Force: The shear force at the cross section of a beam may be defined as the algebraic sum of all the
forces on either side of the section
Bending Moment: The bending moment at the cross section of a beam may be defined as the algebraic sum
of all the moments of the forces on either side of the section.
Types of Beam:
Cantilever Beam: A beam fixed at one end and free at the other end is known as a cantilever beam.
Simply supported beam: A beam supported at its both ends is known as simply supported beam
Overhanging beam: A beam having its end portion extended beyond the support is known as overhanging
beam
Fixed Beam: A beam whose both ends are fixed is known as fixed beam
Continuous beam: A beam supported on more than two supports is known as continuous beam.
Types of Loading:
Concentrated or point load: A load acting at a point of a beam is known as concentrated or point load.
Uniformly distributed Load: A load which is spread over a beam in such a manner that each unit length is
loaded to the same extent is known uniformly distributed load.
Uniformly varying Load: These are the loads varying uniformly from zero to a particular value and spread
over a certain length of the beam. Such load is also called triangular load.
Combination of UVL and UDL
Types of Support:
Simple support
Roller support
Hinged Support
Fixed Support
Definitions:
Tensile Stress and Strain: When a body is subjected to two equal and opposite axial pulls, as a result of which
the body tends to extend its length, the stress and strain induced is known as tensile stress and tensile strain.
Compressive Stress and Strain: When a body is subjected to two equal and opposite axial pushes, as a result
of which the body tends to decrease its length, the stress and strain induced is known as compressive stress
and compressive strain.
Shear Stress and Strain: When a body is subjected to two equal and opposite forces, acting tangentially
across the resisting section, as a result of which the body tends to shear off the section, then the stress
induced is called shear stress. The corresponding strain is called shear strain.
Shear Modulus or Modulus of rigidity: Within elastic limit, the shear stress is directly proportional to shear
strain.
Principle Stress: It is defined as the normal stress when shear stress is considered as zero. The normal stress
can be obtained for maximum and minimum values. The maximum value of normal stress is known as major
principal stress and minimum value of normal stress is known as minor principal stress.
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Resilience: The strain energy stored in a body due to external loading within the elastic limit is known as
resilience.
Spring: It is a device whose function is to distort when loaded and to recover to its original shape when the
load is removed.
Stiffness of a spring: The load required to produce a unit deflection in a spring is called stiffness of a spring.
Material Testing / NDT:
• Tensile test (UTM)
• Compression test
• Impact test (Charpy or Izod test)
• Hardness test (Rockwell, Brinell, Vickers)
• Torsion test
• Shear test
• Bending test
• Pin on disc wear testing machine.
Non-Destructive Testing:
• Magnetic Crack Detector
• Ultrasonic testing
• Dye Penetration test
• Radiographic testing
• Infrared and thermal testing
• Spectroscopy or optical microscopy
Magnetic Crack Detector: This NDT process uses magnetic fields to find discontinuities at the surface of
ferromagnetic materials. The magnetic field can be created with a permanent magnet or an electromagnet,
which requires a current to be applied.
The magnetic field will highlight any discontinuities as the magnetic flux lines produce leakage, which can be
seen by using magnetic particles that are drawn into the discontinuity.
Ultrasonic Testing: Manual ultrasonic testing (UT) is one of the more common non-destructive
testing methods performed on materials. This testing utilises high frequency mechanical energy, i.e. high
frequency sound waves, to conduct examinations and measurements on a test area.
Typically, the UT inspection system consists of an ultrasonic transducer, receiver, and display unit. A
pulser/receiver is an electronic device that can produce high voltage electrical pulses to the transducer.
When driven by the pulser, the transducer generates high frequency ultrasonic sound energy into the
material in the form of sound waves.
When there are discontinuities such as inclusions, porosity, cracks, etc. in the sound path, part of the
mechanical energy will be reflected from the discontinuities (reflectors) surface.
The reflected sound waves signal received by the transducer is then transformed back into an electrical signal
and its intensity is shown on the display unit.
The sound waves travel time can be directly related to the distance that the signal has travelled. From the
signal, information about reflector location, size, orientation and other features can be determined.
Dye Penetration test:
Principle: It detects flaws that are open to the surface like cracks, seams laps, lack of bond, porosity, cold
shuts etc. It can be effectively used both is ferrous or nonferrous materials or non-metallic materials such as
ceramics, plastics and glass. The principle of dye penetrate test is that the liquid used enter small openings
such as cracks or porosities by capillary action.
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Procedure:
• Clean the surface of the component to remove dust and dirt, rust, paint etc.
• Spray the remover to remove oil, grease etc.
• Apply the dye penetrate adequately to cover the area to be tested. Allow for 3-5 minutes or more
for dye to penetrate into the cracks.
• Wipe off the excess penetrant on the surface
• Again, spray the surface with remover to remove the remaining of the dye.
• Spray the developer evenly on the surface to give thin layer. This layer absorbs the penetrant from
the cracks and red spots or lines appear on the surface to give a visible indication of the flaws.
• The crack if any will be indicated with the red dye absorbed by the white absorbent.
Radiographic testing: It uses radiation passed through a test piece to detect defects. X-rays are commonly
used for thin or less dense materials while gamma rays are used for thicker or denser items. The results can
be processed using film radiography or computed radiography Whichever method is used, the radiation will
show discontinuities in the material due to the strength of the radiation.
Engineering Materials
Some Important Mechanical Properties:
fd
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Production of PIG Iron:
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Steel:
Manufacturing of steel:
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Definition:
Isotropic: A physical property which has the same value when measured in different directions.
Cold Working: Cold working is a metal working process in which metal is shaped below its recrystallization
temperature, usually at the ambient temperature.
Hot Working: In this metal are plastically deformed above their recrystallization temperature.
Strain Hardening: When a metal is strained beyond the yield point it is called strain hardening.
An increasing stress is required to produce additional plastic deformation and the metal apparently becomes
stronger and more difficult to deform. Strain hardening is closely related to fatigue.
Forging: Forging is a manufacturing process involving the shaping of metal using localized compressive forces
like hammering, pressing, rolling.
Stress Concentration: A stress concentration is a location in an object where the stress is significantly greater
than the surrounding region.
Composition of materials:
Cast Iron:
Composition: Alloy of iron and 2-5% carbon, 1-3% Silicon, sulphur (< 0.1%), Manganese (<0.75%),
Phosphorus ( <1%)
Properties and characteristics: Hard Skin, Softer underneath, but brittle. It corrodes by rusting
Application: Parts with complex shapes which can be made by casting
Mild Steel:
Composition: Alloy of iron and 0.15-0.3% carbon
Properties and characteristics: Tough, ductile and malleable. Good tensile strength, poor resistance to
corrosion
Application: General purpose engineering material.
Stainless Steel:
Composition: Alloy of iron and carbon with 16-26% chromium, 8-22% nickel and 8% magnesium.
Properties and characteristics: Hard and tough, resists wear and corrosion
Application: Kitchen equipment
Heat Treatment:
Types of Heat treatment:
• Annealing, Normalising, Hardening, Austempering, Martempering, Tempering, Surface Hardening.
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Corrosion: It is defined as the destruction of metals or alloys by the surrounding environment through
chemical or electrochemical changes.
Ex: Rusting of iron, Green scales formed on copper vessels.
Erosion: It is a degradation of material surface due to mechanical action, often by impinging liquid, abrasion
by a slurry, particles suspended in fast flowing liquid or gas, bubbles or droplets, cavitation, etc.
Galvanic Series: In this series corrosion studies on various metals and alloy were performed in various
environments. An arrangement of metal and alloys in order of their corrosion resistance in the given
environment is known as galvanic series.
Here metal and alloys are dipped in sea water at 25 deg at 1 atm. In these series base metals (weaker) are
placed at higher that the noble metal lower in the series.
• Magnesium (Base metal)
• Zinc
• Aluminium
• Cast iron
• Lead
• Tin
• Copper
• Nickel
• Silver (Noble metals)
• Titanium
• Gold
• Platinum
Types of corrosion:
• Galvanic Corrosion (Differential metal corrosion)
• Differential aeration corrosion
a) Waterline Corrosion
b) Pitting Corrosion
• Stress Corrosion
a) Caustic Embrittlement of boilers
1) Galvanic Corrosion: This occurs when two dissimilar metals are in contact with each other in a corrosive
conductive medium, a potential difference is set up resulting in a galvanic current. The two metals differ in
their tendencies to undergo oxidation. The metal with lower electrode potential or more active metal acts
as anode and the metal with higher electrode potential acts as cathode. The potential difference is the main
factor for corrosion to take place. The anodic metal undergoes corrosion whereas cathodic metal gets un
attacked.
Eg: When iron contact with copper, iron has lower electrode potential acts as anode and undergoes oxidation
and copper acts as cathode remains un attacked.
2) Differential aeration corrosion
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Eg: Part of the nail inside the wall which is exposed to lower oxygen concentration that the exposed part
undergoes corrosion
a) Water line corrosion:
b) Pitting Corrosion:
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3) Stress Concentration:
a) Caustic embrittlement of boilers
Corrosion Control:
• Protective Coating
Metal coating and Inorganic coating
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Workshop Technology
Workshop tools:
• Wrenches: Adjustable wrenches, open end wrenches, Box wrenches
• Screwdrivers: Phillips head and flat-head (slotted), hex head, torx head.
• Drills: Drill bits, Drilling machine.
• Measuring Tools: Tri square, Spirit level, Vernier Caliper
• Allen keys
• Tap and die
• Holding clamp
• Pliers
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Types of Hot Rolling:
Hot forging, Hot Rolling, Hot extrusion, Hot drawing, Hot peircing
Types of Cold Rolling:
Cold Rolling, Cold Forging, Cold Spinning, Cold Extrusion, Cold Drawing
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Types of Arc Welding: Shielded and Unshielded arc welding
Arc Welding process:
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ELECTRICAL MACHINES AND BASIC ELECTRONICS/INSTRUMENTATION
Basic Electrical Theory: Electric Charge: Every piece of matter is made up of molecules and all molecules are
made up of atoms, which are made of protons, electrons, and neutrons.
The negative charge is carried by electrons, while the positive charge is carried by the protons, and
neutrons are naturally neutral. The number of protons in an atom does not change because they are locked
in the nucleus.
Basic Electrical Theory: Electric Current: An electric current is the rate of flow of electric charge past a point
or region. An electric current is said to exist when there is a net flow of electric charge through a region.
Basic Electrical Theory: Electrical Resistance: Resistance is an electrical quantity that measures how the
device or material reduces the electric current flow through it.
Laws of Electricity:
Ohm’s law:
The current through a conductor between two points is directly proportional to the voltage across the two
points and inversely proportional to resistance.
𝑣
I=𝑅
Coulomb’s Law of electrostatics:
First Law: Like charges repel each other while unlike charges attract each other.
Second Law: It states that the force between two charged bodies is directly proportional to the product of
the charges and is inversely proportional to the square of the distance between their centres.
Kirchhoff’s Laws:
First Law (Point or Current Law): The sum of the currents entering a junction is equal to the sum of the
currents leaving the junction.
Second law (Mesh or Voltage Law): It states that the algebraic sum of the potential drops in a closed
network (mesh) is zero.
Faraday’s law: (Electromagnetism)
It states that the voltage induced in a circuit by a changing magnetic field is equal to the rate at which the
flux linking the circuit is changing.
Faraday’s Law of electrolysis:
Faraday’s First Law of Electrolysis: It states that the chemical deposition due to the flow of current through
an electrolyte is directly proportional to the quantity of electricity passed through it.
Faraday’s second law of electrolysis: It states that, when the same quantity of electricity is passed through
several electrolytes, the mass of the substances deposited are proportional to their respective chemical
equivalent or equivalent weight.
Lenz’s law: It states that the direction of the electric current which is induced in a conductor by a changing
magnetic field is such that the magnetic field created by the induced current opposes the initial changing
magnetic field.
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AC Circuit: The circuit that is excited using alternating source is called an AC Circuit. The alternating current
(AC) is used for domestic and industrial purposes. In an AC circuit, the value of the magnitude and the
direction of current and voltages is not constant, it changes at a regular interval of time.
DC Circuit: The closed path in which the direct current flows is called the DC circuit. The current flows in only
one direction and it is mostly used in low voltage applications.
AC Current Generation: An alternating current is produced by an electric generator. An electric generator
consists of a magnet and a loop of wire which rotates in the magnetic field of the magnet. As the wire rotates
in the magnetic field, the changing strength of the magnetic field through the wire produces a force which
drives the electric charges around the wire. The force initially generates an electric current in one direction
along the wire. Then as the loop rotates through 180 degrees the force reverses to give an electric current
in the opposite direction along the wire. Every time the loop rotates through 180 degrees the direction of
the force and therefore the current changes. The changing direction of the force after every 180 degrees of
rotation gives the alternating current. As well as having the magnet and wire an electric generator also has
slip rings which make sure that the ends of the wire are always connected to the same side of the electric
circuit. This makes sure that the direction of the current changes every half revolution of the wire.
DC Current Generation:
A direct current is caused by an imbalance between these electric charges.
In a battery chemical energy is converted into electrical energy. Every battery is filled with a certain chemical
called an electrolyte fluid and two different types of metal. The two different types of metal have different
electrical properties, and one is connected to the negative end of the battery and the other to the positive
end. Both of these metals react differently to the electrolyte fluid and the metal connected to the negative
terminal gains electrons and becomes negatively charged while the piece of metal connected to the positive
terminal loses electrons and becomes positively charged. While the battery remains unconnected the
electrons on the negative terminal cannot reach the positive terminal.
If the two terminals of the battery are connected together electrons are then able to pass along the wire
from the negative terminal to the positive terminal to attempt to balance the electrical charge. As the
electrons move through the wire, they lose energy and this energy turns into heat. Since the energy that the
electrons have comes from chemical energy in the electrolyte eventually the chemical energy runs out and
the battery becomes flat. This is a direct current.
Semiconductor: It is any of a class of solids (such as germanium or silicon) whose electrical conductivity is
between that of a conductor and that of an insulator in being nearly as great as that of a metal at high
temperatures and nearly absent at low temperatures.
Transducer: A transducer is a device that converts energy from one form to another. Usually a transducer
converts a signal in one form of energy to a signal in another.
A device that converts variations in a physical quantity, such as pressure or brightness, into an electrical
signal, or vice versa.
Electrical Measuring Instrument:
• Ammeter: Measures Current
• Capacitance meter: Measures the capacitance of a component
• Electricity meter: Measures the amount of energy dissipated
• Multimeter: General purpose instrument measures voltage, current and resistance (and sometimes
other quantities as well)
• Ohmmeter: Measures the resistance of a component
• Tachometer: Measures speed of motors
• Wattmeter: Measures the power
• Voltmeter: Measures the potential difference between two points in a circuit.
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AC Motor: The motor that converts the alternating current into mechanical power by using an
electromagnetic induction phenomenon is called as AC motor.
DC Motor: It converts direct current electrical energy into mechanical energy.
Theory of operation of Induction motors:
Induction motor: An induction motor or asynchronous motor is an AC electric motor in which the electric
current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic
field of the stator winding.
Synchronous Speed:
Synchronous speed is the speed of rotation of the magnetic field in a rotary machine, and it depends upon
the frequency and number poles of the machine. The induction motor always runs at speed less than its
synchronous speed. The rotating magnetic field produced in the stator will create flux in the rotor, hence
causing the rotor to rotate. Due to the lag between the flux current in the rotor and the flux current in the
stator, the rotor will never reach its rotating magnetic field speed (i.e. the synchronous speed).
Types of Induction Motor:
Single phase Induction motor
Three phase Induction motor
Working Principle of Induction Motor: The main parts in an AC induction motor are rotor and stator. The
rotor is made of copper or aluminium bars and it fits into slots in end rings to form complete electrical
circuits.
Single Phase: A single phase motor has only one stator winding. This winding generates a field which merely
pulsates instead of rotating. When the rotor is stationary, the expanding and collapsing stator field induces
current into the rotors. These currents generate a rotor field opposite in polarity to that of the stator. The
opposition of the field exerts a turning force on the upper and lower parts of the rotor trying to turn it 180
deg from its position. Since these forces are exerted through the centre of the rotor, the turning force is
equal in each direction.
The motor is nor self-starting. Hence number of methods are used to make the motor self-starting.
One method is to use auxiliary starting winding to give an initial push to rotor.
Applications: Ceiling fan, mixer, grinder, portable power tools.
Three Phase: Three Phase induction motors are similar to single phase induction motor but the stator has
three windings located 120 deg apart and they are connected to three lines of supply. The three-phase
current produces a rotating magnetic field in the stator. This rotating magnetic field causes a magnetic field
to be set up in the rotor also. The attraction and repulsion between these two magnetic fields causes the
rotor to turn. As a result, it completes one full rotation in one full cycle of the current. The direction of
rotation can be changed by interchanging any two of line connections.
Applications: Compressors, hydraulic pumps, irrigation pumps, Air conditioning compressors.
Why Rotor never runs at Synchronous Speed?
If the speed of the rotor is equal to the synchronous speed, no relative motion occurs between the rotating
magnetic field of the stator and the conductors of the rotor. Thus, the EMF is not induced on the conductor,
and zero current develops on it. Without current, the torque is also not produced.
Because of the above mention reasons the rotor never rotates at the synchronous speed. The speed of the
rotor is always less than the speed of the rotating magnetic field.
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