elements of mechanical engineering for firs year

BASICS
OF
MECHANICAL ENGINEERING
Subject Code: 21ME15
Prof. Dushyanthkumar G L
Assistant Professor
Dept. of Mechanical Engg.
VVCE, Mysuru

Thermodynamics in engineering
is the study of energy and its
various interconversions from
one form to another.
Thermodynamics has several
types of applications in our daily
life.
All these work based on
the governing laws of
thermodynamics.
Fossil-fuelled
steam
power plants
IC engines Jet engines Cars Motorcycles Trucks
Ships Aeroplanes Refrigerators
Air
conditioners
Etc.

Thermodynamics also involves study of various types
of power plants.
Thermal
power plants
Nuclear
power plants
Hydroelectric
power plants
Solar power
plants
Wind power
plants
Geothermal
power plants
Biomass
power plants
Tidal power
plants
Ocean
Thermal
power plants

When you are cooking, you know the pan is going to
get hot because you are transferring energy (in form
of heat) to it. And you know you must eat it otherwise
your body will have no way of producing work to get
you through your daily job
By the end of the day, you are exhausted and
accidentally sleep on the wheel. You wreck
the car but, thankfully, you are out of it alive
because the hood and chassis of the car
were able to absorb the energy of the impact
in form of plastic deformation.
You get home and you notice your roommate is cleaning
the house. You know that before coming in because you
can smell. That only happened because the molecules of
the good smelling stuff is diffused in the air to achieve a
state of higher entropy.
Thermodynamics is not the study of heat and
work alone. Thermodynamics is the study of the
dynamics and behaviour of energy and its
manifestations.
Energy is the only
thing that keeps
things going.
You are Energy! You are Thermodynamics!!

INTRODUCTION TO THERMODYNAMICS
Thermodynamics:
“It is a branch of science that deals with energy in all its forms and the laws
governing the transformation of energy from one form to another.”
 It is the field of thermal engineering that studies the properties of systems that is
having temperature.
 It involves the laws that govern the conversion of energy from one form to another.
 The direction in which heat will flow, and the availability of energy to do work.
 The forms of energy are mechanical, thermal or heat, chemical, electrical etc.

INTRODUCTION TO THERMODYNAMICS
Thermodynamics:
 Thermodynamics deals with the behaviour of gases and vapours i.e., the
working substances when subjected to variation of temperature and
pressure
 Energy transformation takes place when a substance undergoes a
change from one condition to another in a process.
 The processes are heating or cooling, expansion or compression, with or
without production of mechanical work etc..

THERMODYNAMIC SYSTEM:
 In the analysis of energy interaction,
it becomes convenient to define
and restrict study to a region.
 Such a specified region where
transfer of energy and/or mass is to
be studied is known as system.

THERMODYNAMIC SYSTEM
 System is the fixed quantity of matter and/or the region that can
be separated from everything else by a well-defined
boundary/surface.
 Thermodynamic system is the system on which thermodynamic
investigation is done.
 The surface separating the system and the surroundings is known
as the control surface or the system boundary.
 Everything beyond the system is the surroundings.

CLASSIFICATION OF THERMODYNAMIC SYSTEMS
ISOLATED SYSTEM:
 These systems cannot have either energy or mass
transfer with the surroundings. This system is of
purely theoretical interest to study and analyze
thermodynamic principle and laws.
CLOSED SYSTEM (or CONTROL MASS):
 Across the boundary of a closed system the
transfer of energy (work and/or heat) takes place
but transfer of mass does not takes place.

Fig. Closed system with
moving boundary
Fig. Closed System

C) OPEN SYSTEM (or CONTROL VOLUME) :
 In this system mass and energy both may be transferred
between the system and the surroundings.
 E.g. Gas turbine, steam turbine, compressor, boiler etc.
Control Volume
”It is defined as a volume
in space through which
matter, momentum and
energy may flow”

Fig. An open system with one inlet
and one exit

THERMODYNAMIC PROPERTIES:
The variables which determine state or exact condition of a substance or
system is called as its properties. The various properties of thermodynamic
system are pressure, temperature, specific volume, internal energy, enthalpy,
entropy, etc.
DEFINITIONS AND UNITS:
Pressure: Pressure may be defined as normal force per unit area. In S.I system
the unit of pressure is pascal (pa).
1pa = 1N/m2;
1 Standard atmospheric pressure = 1.01325bar = 101.325Kpa
1bar = 105pa = 100kpa
1N/mm2 = 106N/m2 = 106pa = 1000kpa

VOLUME:
The space occupied by the
substance is called volume. It
is measured in m3.
1 liter = 1000cc = 10-3 m3
SPECIFIC VOLUME:
Specific volume of a
substance is its volume per
unit mass. Its unit is m3/kg.
Density of a substance is its
mass per unit volume.
Unit : kg /m3
Specific volume

Temperature:
It is a thermodynamic property which determines
the degree of hotness or the level of heat intensity
of a body.
A body is said to be at a high temperature or hot if
it shows a high level of heat intensity in it. Similarly, a
body is said to be at low temperature or cold, if it
shows a low level of heat intensity in it.
Usually, temperature is measured by thermometer.
Very high temperature is measured by pyrometer.
Small and precise changes in temperature can be
measured by resistance thermometers or
thermocouple.

Energy:
Energy may be defined as the capacity a body
possesses for doing work. All forms of energy are
mainly classified as
1. Stored energy
2. Transient energy (or energy in transition)
Stored energy is the energy possessed by a
system within its boundaries. E.g., K.E, P.E, and I.E.
Transit energy is the energy possessed by a
system which is capable of crossing its
boundaries. E.g. Heat and Work.

Heat:
Heat is defined as the energy transferred
without transfer of mass across the boundary
of a system due temperature difference
between the system and the surroundings.
The energy in transition is called heat.
Unit for heat and any other form of energy is
joule (J).
Heat flow into a system is positive and heat
flow out of a system is negative.

Work:
In mechanics work is defined as,
“The product of force and the displacement in the direction of the force.”
Unit of work done is N-m or joule.
Work done by the system is positive and work done upon the system is negative.

State of a System, Process & Cycle
State of a system
 a thermodynamic state of a system is its condition at a specific time, that is
fully identified by values of a suitable set of parameters known
as state variables, state parameters or thermodynamic variables.

THERMODYNAMIC STATE
“The state of a system is described by its properties.”
 Change in State: Thermodynamic system undergoes changes due to flow of mass
and energy.
 The modes in which the changes in the state of a system takes place are,
 Isobaric (Constant Pressure) process,
 Isochoric (Constant Volume) process,
 Isothermal (Constant temperature) process,
 Adiabatic (Constant Entropy) process etc.
 Two states are identical if and only if, the properties of the two states are same.

Thermodynamic Process
 When a system changes its state from one equilibrium state to another
equilibrium state, then the path of successive states through which the
system has passed is known as thermodynamic process.
26

STATE AND PROCESS
 When any property of a system changes in
value there is change in state, and the system
is said to undergo a process.
 When a system from a given initial state
undergoes a sequence of processes and
finally returns to its initial state, it is said to
have undergone a cycle.
 Phase: Phase refers to a quantity of matter
that is homogeneous throughout in its
chemical composition and physical structure.
 A system can contain one or more phases.

Thermodynamic Cycle or Cyclic Process:
 When a process or processes are performed on a system in such a way that
the final state is identical with the initial state, it is then known
as thermodynamic cycle or cyclic process.
28

Thermodynamic Equilibrium
 A system is said to be in Thermodynamic Equilibrium if it is in thermal,
mechanical and chemical equilibrium at same time.
 If any one of the equilibrium condition disturb then the system cannot
comes under Thermodynamic Equilibrium. Let us understand these four
equilibrium
Thermal Mechanical
Chemical
29

 Equilibrium: If there are no changes in the observable properties
of an isolated system, then the system is said to be in equilibrium.
 At equilibrium, temperature and pressure are uniform throughout
the system.
Internal Energy: The internal energy of a system is the total
energy content of the system. It is the sum of Kinetic, potential,
chemical, electrical and all other forms of energy possessed by
the atoms and molecules of the system.

Internal energy:
“It is the energy possessed by a body or system due to its molecular
arrangement and motion of the molecules.”
It is the sum of internal K.E and internal P.E of the molecules. It is a function of
temperature and can be increased or decreased by adding or subtracting
heat to or from the substance.
It can be expressed in general way as;
du = u2 - u1

ENTHALPY:
Enthalpy is nothing but total heat and heat
content of a system.
Enthalpy = internal energy + product of absolute
pressure and volume.
H = U + PV expressed in kJ/kg
dh = h2 – h1 = (u2 - u1) + (pv2 – pv1)

ENTROPY:
Entropy is defined as a measure of randomness or
disorder of a system.
It is represented by the symbol ‘s’.
Small increase of entropy ‘ds’ of a substance is defined
as the ratio of small addition of heat dq to the absolute
temperature T of the working substance at which the
heat is supplied.
ds = dq/t or dq = t. ds
Unit of entropy is kJ/K.

Zeroth Law of Thermodynamics
 The Zeroth law of thermodynamics states that
“If two thermodynamic systems are each in thermal equilibrium with
a third, then they are in thermal equilibrium with each other”

Significance of Zeroth law
SA= System whose temperature is to be measured
SB= A Quantity of melting ice at Std. Atmospheric pressure
SC= Thermometer (Eg. Mercury in Glass type)
Trial-1: SB= Fixed value at ice point (Marked as 0°C)
Trial-2: SB= Fixed value at Steam point (Marked as 100°C)
To measure temperature between ice point & steam
point, the distance between the 2 marks are divided into
100 equal parts and each graduation is marked as 1°C on
the Celsius scale.

First Law of Thermodynamics
 The First law of thermodynamics states that
“When a small amount of work (dw) is supplied to a closed
system undergoing a cycle, the work supplied will be equal to the
heat transfer or heat produced (dQ) in the system.”
Or the Law of conservation of energy, Gibbs in
1873 stated energy cannot be created or
destroyed, only transferred by any process

First Law of Thermodynamics
38

Second Law of Thermodynamics
 According to “Kelvin-Planck”
“It is impossible to construct an engine working
in a cyclic process, whose sole purpose is to
convert heat energy from a single thermal
reservoir into an equivalent amount of work.”
39

 According to “Clausius”
“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 external agency”.
Heat cannot flow naturally from a cold body to a hot
body without the help of work input.
40

“The entropy of a pure substance in thermodynamic equilibrium
approaches zero as the temperature approaches zero (Kelvin)”.
The entropy of a system approaches a constant value as its temperature
approaches absolute zero (Kelvin)
Third Law of Thermodynamics
41

Refrigeration and Air Conditioning
42
From earlier times the art of artificial cooling is employed in ice making,
preservation of perishables such as, milk, food, drinks , medicines, and
indoor air cooling to provide human comfort and cool environment .
The two methods employed for artificial cooling are
1) refrigerator – these are used in ice making , preservation of
perishables,
2) air- conditioning - these are used in indoor air conditioning .

➢ The process of reducing the temperature of a substance below that of
the surrounding atmosphere and maintaining this lower temperature
with in the boundary of a given space is called Refrigeration.
➢ The machine or device employed to produce refrigeration effect is
called Refrigerating machine or Refrigerator.
➢ AC involves simultaneous control of Temperature, Humidity,
Cleanliness and Air motion in confined space.
➢ Principle of refrigeration is that “the heat is to be removed
continuously from a system at a lower temperature and transfer it to
the surroundings at a higher temperature”
Introduction
43

Terms used in refrigeration
• REFRIGERATING EFFECT (RE)
o The rate at which the heat is absorbed in a cycle from the interior space to be
cooled. It is also known as capacity of refrigerator.
(or)
o The rate at which heat is removed from the system in one cycle of operation.
Expressed in kJ/sec or kW.
• TON OF REFRIGERATION (TOR)
o Ton of Refrigeration(TOR) is the unit of refrigeration capacity. Which
describes the heat extraction capacity of refrigeration and air conditioning
equipment.
o 1 TOR indicates the amount of heat that needs to be extracted from 1 ton of
water at zero degree centigrade to convert it to 1 ton of ice at zero degree
centigrade in 1 day/ 24hrs.
o 1 TOR = 3.5 kW = 210 kJ/min in SI Units.
44

 ICE MAKING CAPACITY
o Ice making machine is normally specified by its ice making capacity
o It is defined as the capacity of the refrigeration system to make ice beginning from
water (at room temp) to solid ice
o Specified by kg/hr
 COEFFICIENT OF PERFORMANCE (COP)
o The performance of a refrigeration system is expressed by a factor known as the
Coefficient of performance (COP)
o It is defined as the ratio of heat absorbed (Q) in a system to the work supplied (W).
o COP= Q/W
 RELATIVE COEFFICIENT OF PERFORMANCE (RELATIVE COP)
o The ratio of Actual COP to the Theoretical COP is known as Relative Co-efficient of
Performance
o Relative COP = Actual COP/ Theoretical COP
45

REFRIGERANTS
• A Refrigerant is a chemical substance, that is used in a refrigeration cycle
to cool a space.
• Refrigerants extracts heat and then release it to another space by using the
thermodynamic phenomena of phase changes, in which a fluid changes to a
gas or vice versa in the refrigeration cycle.
46

Required Properties of Ideal Refrigerant:
• The refrigerant should have low boiling point, low freezing point and high
latent heat of evaporation.
• It must have low specific heat, low specific volume, low viscosity and high
thermal conductivity.
• It should be non-flammable, non-toxic and non-corrosive.
• It must have good chemical stability.
• It should not have any bad effects on the stored material or food, when
any leak develops in the system.
• It should give high COP in the working temperature range. This is
necessary to reduce the running cost of the system.
• It must be readily available and it must be cheap also.

• Ammonia(NH3)
o Oldest and widely used
o Boiling temperature -33.3oC
o Soluble in water, produce high refrigeration
effect, cost less, doesn’t harm ozone layer
o Highly toxic, explosive, moderately
flammable, irritating and corrosive
o Large scale applications like ice manufacturing
plants, packing plants, cold storage etc
• Sulphur dioxide(SO2)
o Boiling point -10oC
o Non flammable, non corrosive, absorbs a lot of
heat in evaporation
o Low refrigeration effect, suffocating, irritating
odour, corrosive
o Used in olden days, but now obsolete
Types of Refrigerants
 Carbon dioxide (CO2)
o Boiling point -77.6oC
o Non flammable, non toxic, inexpensive and
odourless gas
o 1.53 times heavier than air, and hence
requires high operating pressure thereby
lowering the efficiency of refrigeration
o Due to low specific volume, plant size can
be made compact
o large ships, theater air conditioning system
 Freon
o Highly efficient, and overcomes the
disadvantages of all the above types of
refrigerants
o However, these refrigerants were discovered
to deplete the ozone layer
49

 Freon – 12 (R 12) (di chloro difluoromethane)
o Non flammable, non-explosive, non-corrosive and odourless
o Small capacity equipments – Domestic refrigerator, water coolers, air conditioners, automobile etc.
 Freon – 22 (R 22) (chloro difluoromethane)
o High pressure refrigerant
o High capacity plants like packaged air conditioning units, low and medium temperature
refrigeration
 Modern Refrigerants – HFC (Hydro Fluoro Carbon)
o No chlorine atoms; thus, have no ozone depleting potential.
o Possess favourable thermodynamic, health and safety properties
o R134A (tetra fluoromethane) is non-corrosive, non toxic and non flammable
o Boiling point -15oC
o HFC compounds include R407C, R410A etc. 50

Parts of a Refrigerator
There are FOUR basic components in a mechanical refrigeration.
➢ Evaporator.
➢ Compressor.
➢ Condenser.
➢ Expansion valve or Throttle valve.
51

Parts of a Refrigerator
EVAPORATO
R
EXPANSION
DEVICE
CONDENSER
COMPRESSO
R OR PUMP
52

Types of Refrigerators
The TWO major types of refrigerators include
➢ Vapour Compression Refrigerator (VCR)
➢ Vapour Absorption Refrigerator (VAR)
53

Vapour Compression Refrigerator (VCR)
54

Working
• Evaporator is kept inside the cabinet which has to
be cooled.
• The low pressure and low temperature liquid
refrigerant entering the evaporator, absorbs heat
from the cabinet and undergoes a change of phase
from liquid to vapour.
• This vapour refrigerant at low pressure is drawn
into the compressor, where it is compressed to high
temperature and pressure. Thus, increasing the
saturation temperature of the refrigerant.
• The compressor then circulates the high pressure
refrigerant to the condenser, where the vapour gets
condensed to liquid state by rejecting heat to the
surroundings.

• The high pressure liquid refrigerant
then passes through the expansion
valve, where it expands to low
pressure, decreasing the saturation
temperature of the refrigerant and thus
forming low temperature liquid.
• This low pressure liquid enters the
evaporator and the cycle repeats.
• Commonly used refrigerant in VCR is
Freon 12.

Applications of VCR
•Household refrigerators and
freezers
•Home, industrial and commercial
air conditioners
•Automobile air conditioners
•Large buildings
•Theatres, restaurants etc.

Vapour Absorption Refrigerator (VAR)

VAPOUR ABSORPTION REFRIGERATOR
• Same as VCR, here the compressor is replaced by an
absorber, generator and pump.
• Refrigerant is ammonia, which is highly soluble in
water.

Working
ammonia (NH3) entering the evaporator, absorbs
heat from the cabinet and undergoes a change of
phase from liquid to vapour.
• The vapour ammonia is passed to the absorber,
which contains water.
• Vapour ammonia dissolves in water resulting in a
strong ammonia solution.
• This strong solution is pumped to the generator,
passing through the heat exchanger. Pump raises
the pressure of the solution.
• In generator the strong solution is heated by
heating coil.

• Due to heating, ammonia vapour forms at the top
and weak ammonia solution settles in the
bottom.
• The weak ammonia solution is sent to the
absorber passing through the heat exchanger.
• The high pressure ammonia vapour is sent to the
condenser, where it gets condensed to liquid
state.
• Then the high pressure ammonia liquid enters
the expansion valve where it is expanded to low
pressure.
• This low pressure and low temperature liquid
ammonia is passed onto the evaporator and the
cycle repeats.

Domestic Refrigeration
➢Compressor used is a reciprocating type and is hermetically sealed which means
the compressor and electric motor are a single unit enclosed in a container
➢ The Condenser of small refrigeration is of natural air convection type, while large
refrigerators may have a fan for forced air circulation over a condenser coil.
➢ The Expansion device is a small capillary tube made from copper.

Air Conditioning (AC)
➢ It is defined as the process of simultaneous control of temperature, humidity (moisture
content in air), cleanliness and air motion of the confined space.
or
Air conditioning is the process of conditioning the air by heating, cooling, de-
humidification, cleaning, ventilation or movement of air.
➢ Air conditioning was coined by Stuart Cramer in 1905, Willis Carrier is known as the
‘father of Air conditioning system’.
➢ Principle of Air conditioning is similar to that of refrigeration. (VCR)

WINDOW TYPE AIR CONDITIONING
SYSTEMS
69

Principle of Air Conditioner
73

Basic components
1. Evaporator – kept inside the room
2. Compressor – kept outside the room
3. Condenser – kept outside the room
4. Expansion valve – kept outside the
room
5. The refrigerant used is usually
Freon 22, R134A, R410A.

Working
• Evaporator is kept inside the room to be cooled.
• The blower draws the warm air from the room over
the evaporator.
refrigerant in the evaporator, absorbs heat from the
air and undergoes a change of phase from liquid to
vapour.
• The blower then delivers the cool air into the room.
• The low temperature and low pressure vapour
refrigerant is drawn into the compressor, where it is
compressed to high temperature and pressure.
Thus, increasing the saturation temperature of the
refrigerant.

• The compressor then circulates the refrigerant to
the condenser.
• The fan located at the outside draws atmospheric
air over the condenser coils.
• The heat contained in the refrigerant gets
condensed to liquid state by rejecting heat to this
atmospheric air.
• The high pressure and high temperature liquid
refrigerant passes through the expansion valve,
where it expands to low pressure and low
temperature liquid. Thus, decreasing the
saturation temperature of the refrigerant.
• The low pressure, low temperature liquid enters
the evaporator and the cycle repeats.

Application of Air Conditioning
Provides comfort for human beings and also a controlled environment for
various industrial activates
 Comfort applications : Residential buildings, Institutional buildings,
Commercial buildings, Transportation.
 Process applications : Hospitals, Industrial environment, Nuclear power
plant, Chemical Labs, Biological Labs, Textile factories, printing, mines,
food processing, etc.
79

Application of Air conditioning
1. Comfort applications
i. in residential buildings
ii. Institutional buildings
iii. Commercial buildings
iv. Transportation like cars, buses, aircrafts, ships.
2. Process Applications.
i. Hospitals, especially for operation theaters
ii. For breeding laboratory animals
iii. Textiles factories
iv. Printing factories
v. Food processing centers. Etc.,

List of formula
• COPactual =
QL
W
• COPactual =
QL
QH − QL
where, W= QH − QL
• COPideal =
TL
TH − TL
81

elements of mechanical engineering for firs year

elements of mechanical engineering for firs year

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