Under graduate Mechanical engineering, engineering thermodynamics, introduction chapter.

1. Chapter/ Unit No. Basic concepts
1
Topics: ( as per the lesson planning)
1. Introduction
2. Microscopic & macroscopic point of view
3. Thermodynamic system and control volume
4. Thermodynamic properties, processes and cycles
5. Thermodynamic equilibrium
6. Quasi-static process
7. Pure substance
8. Vapour-liquid-solid phase in a pure substance
9. P-v-t surface
10.Critical and triple point of pure substance
Cover page of Lecture Notes
Faculty Name: Asst. Prof. Ajaypalsinh G. Barad
Branch: Mechanical Semester: 3rd Name of Subject: ET
Sign: _______________________
Submission Date: _____________

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3.  Introduction
 Microscopic and macroscopic view
 Thermodynamic system and control volume
 Thermodynamic properties
 State, process and cycle
 Thermodynamic equilibrium
 Quasi – state process
 Pure substance
 Vapour-Liquid-Solid phase in a pure substance
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4.  Critical and tripal point of pure substance
 p-v-T surface
 Work and heat transfer
 Point function and path function
 Temperature and zeroth law of thermodynamics
 continuum
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5.  Thermodynamic can be defined as the science
of energy.
 It deals with the most basic processes
occurring in nature.
 One of the most fundamental laws of nature is
the conservation of energy principle.
 It simply states that during an interaction,
energy can change from one form to another
but the total amount of energy remains
constant.
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6.  The word thermodynamics is made up from
two Greek words:
(i) Thermo - hot or heat
(ii) Dynamic – power or powerful, the study of matter in
motion.
Thermodynamics means study of heat related
to matter in motion.
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7.  Thermodynamic may be defined as:
i. Science that deals with the interaction between
energy and material system.
ii. Law of science which deals with the relations
among heat, work and properties of system
which are in equilibrium.
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8. There are basically four laws,
i. Zeroth law : represents the concept of
temperature, and deals with thermal equilibrium.
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9. ii. First law : represents the concept of internal
energy.
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10. iii. Second law : indicates the limit of converting
heat into work and introduce principle of
increase of entropy.
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11. iv. Third law : concerned with the level of
availability of energy and defines the absolute
zero of entropy.
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12. Classical thermodynamics:
A macroscopic approach to the study of
thermodynamics that does not require a knowledge of
the behavior of individual particles.
It provides a direct and easy way to the solution of
engineering problems and it is used in this text.
Statistical thermodynamics:
A microscopic approach, based on the average
behavior of large groups of individual particles.
It is used in this text only in the supporting role.
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13.  System: A quantity of matter or a region in space
chosen for study.
 Surroundings: The mass or region outside the
system
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14.  Boundary: The real or imaginary surface that
separates the system from its surroundings.
The boundary of a system can be fixed or
movable.
Systems may be considered to be closed or
open.
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15.  Closed system (Control mass):
A fixed amount of mass, and no mass can cross
its boundary.
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16. Open system :
A properly selected region
in space.
It usually encloses a device
that involves mass flow
such as a compressor,
turbine, or nozzle. Both
mass and energy can cross
the boundary of a control
volume.
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17. Isolated System:
In this system, fixed mass
and fixed energy and there
is no mass or energy
transfer across the system
boundary as shown in fig.
The thermos flask is
example of an isolated
system.
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18.  Control volume:
In most of engineering problems of open system, (such as
in an engine, an air compressor, turbine etc) the mass of
the system is not fixed.
Therefore, in the analysis, attention is focused on a
certain volume in space surrounding the system
(equipment), known as the Control volume. The control
volume bounded by the surface is called Control
surface.
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19.  Control volume:
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20.  Property:
Any characteristic of a system.
Some familiar properties are pressure P, temperature T, volume
V, and mass m.
Properties are considered to be either intensive or extensive.
 Intensive properties:
Independent of the mass of a system, such as temperature,
pressure, and density.
 Extensive properties:
Whose values depend on the size—or extent—of the system.
 Specific properties:
Extensive properties per unit mass. And they became intensive
properties.
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21.  State:
It is the condition of the system at an instant of time as
described by its properties.
Consider a system that is not
undergoing any change.
At this point, all the properties
can be measured or calculated
throughout the entire system,
at a given state, all the properties
of a system have fixed values.
If the value of even one property
changes, the state will change to
a different one.
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22. Process:
Any change that a system undergoes from one state to another
state is called a process.
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23. Cycle:
It is defined as a series of state changes such that the final state
is identical with the initial state.
The cycle as shown in fig. consists of two processes as 1-2, and
2-1.
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24.  Thermodynamic equilibrium:
The word equilibrium implies a state of balance.
This system is said to exist in a state of equilibrium when no
change in any macroscopic property.
“ A system is said to be in a state of thermodynamic
equilibrium if the value of properties is the same at all points
in the system.”
A system will be in a state of equilibrium, if the condition for
the following three types of equilibrium are satisfied :
i. Thermal equilibrium
ii. Mechanical equilibrium
iii. Chemical equilibrium
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25.  Thermal equilibrium:
If the temperature of the system does not change with time and
has same value at all points of the system, the system said in
thermal equilibrium.
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26.  Mechanical equilibrium:
A system is in mechanical equilibrium if there are no
unbalanced forces within the system or between surroundings.
The pressure in the system is same at all points and does not
change with respect to time.
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27.  Chemical equilibrium:
A system is in chemical equilibrium if its chemical
composition does not change with time and no chemical
reaction takes place in the system.
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28.  When a process proceeds in such a way that the
system remains close to an thermodynamic
equilibrium state at all times, it is called a Quasi-
static process.
 A quasi-static process is also called a reversible
process. The main characteristic of this process is
infinite slowness.
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29.  The quasi-static equilibrium process is an idealized
process and many actual processes can be modeled as
quasi-static equilibrium with negligible error.
 This process produces maximum work or consumes
less work, so this processes serve as standards to
which actual processes can be compared.
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31.  A substance that has a fixed chemical composition
throughout is called pure substance.
 For example water, helium, carbon dioxides etc.
 The pure substance must satisfied following conditions:
1. Homogeneous in composition – composition of each part
of the system is same as the composition of every other
part.
2. Homogeneous in chemical aggregation – chemical
elements must be combined chemically in same way in all
parts of the system.
3. Invariable in chemical aggregation – state of chemical
combination of the system does not change with time.
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32.  For example,
1) Air – has uniform chemical composition
2) Ice and liquid water – both phases have same chemical
composition and satisfies all three conditions
3) Steam and liquid water – same chemical composition
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33. 4) Mixture of oil and water – not pure substance, as oil is not
soluble in water, it will collect on top of the water
5) Mixture of gaseous air and liquid air – not pure substance,
compositions are different in both the cases.
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34.  Pure substance exist in different phases.
 There are three principle phases as solid, liquid and gas vapour.
 Solid:
The molecules in a solid are arranged in three-dimensional
pattern. The attractive forces of molecules on each other are
large due to small distances between molecules in a solid.
The molecules oscillate about their equilibrium position.
At sufficient high temperatures, the velocity of molecules may
reach a point where the intermolecular forces are overcome and
groups of molecules break away and beginning of melting
process.
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35.  Liquid:
The attractive forces of molecules on each other are less in
liquid compared to in solid.
So the molecules are no longer at fixed positions relative to
each other.
In liquid the groups of molecules float about each other,
however the molecules maintain an orderly structure within
each group and retain their original positions with respect to
one another.
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36.  Gas vapour:
The molecules are far apart from each other in gas.
So gas molecules move about at random, continually colliding
with each other and the walls of the container because in gas
there is no orderly structure of molecules.
 At low temperature the molecules exist as solids, when
temperature increases they may melt into the liquid phase
and then at higher temperatures they evaporates and
become vapour.
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37. For example, Water has three phases as ice, water and steam.
 When ice melts, there is a transformation of phase from solid
to liquid which is called the Melting of ice.
 When the water solidifies, there is a transformation of phase
from liquid to solid which is called Solidification or
Freezing.
 When water evaporates, there is a transformation of phase from
liquid to vapour phase is called Vaporization.
 When transformation take place from vapour to liquid, it is
called Condensation.
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38. Critical point:
We know that every substance exists in at least three
phases. However, at particular pressure and
temperature a mixture of saturated liquid and
saturated vapour states are identical. This situation is
known as Critical State of the substance.
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41.  We are familiar with two phases being in equilibrium,
but at particular pressure and temperature, all the
three phases of water as solid (ice), liquid (water) and
vapour (steam) can exists in equilibrium.
 This is known as triple point state.
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42.  We
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44.  The p-v-T surface is graphical representation of the
states of a pure substance which must have two
independent properties and any third as the dependent
property.
 It is relationships between pressure, specific volume
and temperature which is represented by a three
dimensional plot.
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46.  The heat and work are form of energy.
A closed system and surroundings can interact in two
ways:
(1) By work transfer and
(2) By heat transfer
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47.  Mechanical work:
Work done = Force * Distance
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48. Thermodynamics Work:
―It is the energy transferred, without transfer of mass
across the boundary of a system because of an
intensive property difference other than temperature
that exist between system and surroundings.‖
Work may be defined as ―a transient quantity which
only appears at the boundary while a change of state
is taking place within a system.‖
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49. Thermodynamics Work:
consider an electrical storage
battery as a system in which the
terminals are connected with a
resistance by means of a switch
as shown in fig.
When the switch is closed, the
current flows through the
resistance coil and the resistance
become warmer.
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50.  Thermodynamics Work:
According to definition of mechanical work, it is not work
because there is no force has moved through a distance.
But according to thermodynamics work definition, the battery
does work as the electrical energy crosses the system boundary.
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51.  Thermodynamics Work:
The resistance is replaced by an electrical motor with
frictionless pulley which can wind a string and lift the
suspended mass as shown in fig.
Therefore, only effect is the
work done by system, is the
rising of a mass.
So, interaction of battery
with resistance coil is a work,
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52.  Displacement work:
Consider a system, formed by a gas contained in a piston
cylinder arrangement as shown in Fig. Due to pressure of gas
acting on the face of the piston, the piston move outward
through a small distance dx, during a small time interval dt.
Assume that pressure p acting on piston is constant. The work
done by the system is,
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53.  Displacement work:
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54.  Displacement work:
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56.  Shaft work:
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57.  Paddle Wheel Work:
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58.  Heat is defined as form of energy that is transferred
between system and surroundings or between two
systems due to temperature difference.
 Two closed systems at different temperature,
 Due to temperature difference,
 Thermal equilibrium,
 “Heat is the form of energy which appears at the
boundary when a system changes its state due to
a difference in temperature between system and
its surroundings."
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59.  Sign convention :
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60.  Similarities:
• not properties of system
• boundary phenomenon
• associated with process, not a state.
• These energies interactions occurs only when a system
undergoes change of state.
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61.  Dissimilarities :
 Heat is energy interaction due to temperature difference.
Work is energy interaction by reasons other than
temperature difference.
 In stable system there can not be work transfer, however,
there is no restriction for the transfer of heat.
 Heat is low grade energy while work is high grade energy.
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62. • The temperature as a measure of hotness or
coldness.
• It may be defined as
1. Degree of hotness or coldness
2. Driving force causing the heat transfer
3. Determine the system is in thermal equilibrium
with another system or not
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64.  ― If two systems are each in thermal equilibrium with a third
system, they are also in thermal equilibrium with each other.‖
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65.  Application of Zeroth law:
• Zeroth law of thermodynamics is the concept of
temperature.
• The third system C is called
thermometer.
• It permits to test the
equality of temperature
without actually bringing
the system in thermal contact.
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66.  In macroscopic thermodynamic analysis, we consider
the matter as continuous rather than considering of
discrete particles.
 The spaces between and within the molecules are not
considered.
 Generally we consider pressure and temperatures of
large number of molecules in the system.
 Such continuous substance is known as ―Continuum‖.
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67.  The property of a system which does not depends on
path of process, but depends on state, this property is
called point function.
 Thermodynamic properties are point functions, for
given state, there is a definite value for each property.
 The differential of point functions are exact or perfect
differentials and the integration is simply,
 The change in volume depends only on the initial and
final state of the system, not depends on the path the
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68.  There are certain quantities which can not be located on a
graph by a point but are represented by the area on that
graph. Those quantities are dependent on the path of the
process and are called path function.
 Heat and work are inexact differentials. Their change can
not be written as difference between their initial and final
states.
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69.  Consider several reversible processes such as P, Q and R
from state 1 to state 2 as shown in fig.
 The work done for each process is represented by area under
each curve on p-V diagram.
 From the fig., it is clear that the work is different in each
process because process (path) depends on the nature of the
process.
 The amount of work involved in each case is not a function
of initial and final (end) states of the process, is not a
property of state function and its depends on the path of the
system follows in going from state 1 to state 2 Therefore,
work is a path function.
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70.  A system does not posses work, but work is a mode of
transfer of energy. This transfer occurs only at the
boundaries of the system during a change of state of the
system.
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