Basic concepts.pdf .

Department of Mechanical & Manufacturing Engineering, MIT, Manipal 1 of 3
OVERVIEW OF THERMODYNAMICS
THERMODYNAMICS - I

OVERVIEW OF THERMODYNAMICS
MME 2155: THERMODYNAMICS - I [2 1 0 3] No. of Lecture hours: 36
Basic concept and definitions: Macroscopic and Microscopic points of view,
system and surroundings, property and state, thermodynamic equilibrium, change
of state, process and cycle, Zeroth law of thermodynamics, concept of
temperature, temperature scales. Work and Heat-Thermodynamics definition of
work, displacement work for different thermodynamic processes, definition of heat,
comparison between heat and work. [06]

First law of thermodynamics: First law for a closed system undergoing a cyclic
process, non-cyclic process, Energy is a property of a system, First law for an
open system, steady flow energy equation and its applications. [05]
Second law of thermodynamics: Limitations of first law, definition of heat engine
and reversible heat engines and their performance, two statements of second
law, corollaries of second law, reversible and irreversible processes, Carnot cycle,
statement of third law, thermodynamic temperature scale. [07]

Entropy: Basic definition of entropy, Clausius inequality, entropy - property,
principle of increase of entropy, Temperature-entropy diagram, entropy relations to
other thermodynamic properties. [04]
Pure substance: Definition, two property rule, specific heats of pure substances,
phases, equilibrium between phases, PvT surface, P-T diagram, triple point and
critical point, dryness fraction and its measurement, Tabulated properties, State
change of a system involving pure substance, constant volume, constant pressure,
constant temperature and constant entropy processes. [07]

Ideal and real gases: Definition, universal gas constant, Thermodynamic
processes, Evaluation of properties of mixture of ideal gases, adiabatic mixing of
ideal gases, Vander Waal’s equation of state, law of corresponding states,
compressibility factor, generalized compressibility chart. [07]

References:
1. Nag P. K., Engineering Thermodynamics, McGraw - Hill Education India Pvt. Ltd,
2013.
2. Yunus A. Cengel and Michael A. Boles, Thermodynamics: An Engineering
Approach, Tata McGraw - Hill Education, 2011.
3. Gordon J. Van Wylen and Richard E. Sonntag, Fundamentals of Classical
Thermodynamics, Wiley, 1986.
4. Rogers G. F. C., and Yon Mayhew “Engineering Thermodynamics: Work and Heat
Transfer”, Prentice Hall, 1996.
5. Gupta S. C., Thermodynamics, Pearson Education, 2009.

Program Objectives (PO)
PO 1: Apply the knowledge of Mechanical engineering to design and
implement new systems, products, tools to address needs of the
society.
PO2 : Develop innovative technologies to solve engineering problems of
social relevance and contribute to sustainable development.
PO3 : Work effectively in a team to carry out multi-disciplinary projects
and exhibit leadership qualities and communication skills.
PO4 : Engage in lifelong learning for career advancement and adapt to
change in professional and social needs.

At the end of the course the students should be able to:
CO1: Understand the basic concepts of engineering thermodynamics and its
applications
CO2: Apply the principle of first law and second law of thermodynamics to different
systems and its applications
CO3: Explain the concept of entropy, availability as well as unavailability and to
understand the feasibility of a process in thermodynamic devices.
CO4: Explain the behavior of pure substances at different pressure and temperature
conditions their phase diagrams and change in properties for different
processes.
CO5: Evaluate the behavior of ideal and real gases under different thermodynamic
conditions.

THERMODYNAMICS - I
The design of many engineering systems, such as
solar hot water system, involves thermodynamics.

Performance Analysis of IC engines
THERMODYNAMICS - I

Performance Analysis of Jet engines
THERMODYNAMICS - I

Thermal Analysis of space systems
THERMODYNAMICS - I

CHAPTER 1
BASIC CONCEPTS AND DEFINITIONS
THERMODYNAMICS - I

THERMODYNAMICS - I
Introduction to Thermodynamics:
 It is the science that deals with heat and work
and these properties of substances that bear a
relation to heat and work
 It is the science of energy transfer and its effect
on the physical properties of substances.
 It deals with three E’s, namely Energy,
Equilibrium and Entropy.

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• Thermodynamics pertains to the study of:
 Interaction of system and surroundings
 Energy and its transformation.
 Relationship between heat, work and physical
properties of substance employed to obtain
energy conversion.
 Feasibility of a process and the concept of
equilibrium

THERMODYNAMICS - I
• The study of thermodynamics is the basis for
 Steam power plants,
 IC Engines,
 Gas dynamics and aerodynamics,
 Refrigeration and Air conditioning
 Heat transfer
 Fluid mechanics,

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• Systematic observation of nature, study of the
properties of fluid and repeated experimentations
has resulted in four laws of thermodynamics
named as
 Zeroth law
 First law,
 Second law
 Third law
• There is no mathematical proof for any of these
laws of thermodynamics but they are deduced
from experimental observations.

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Macroscopic & Microscopic approaches:
 Macroscopic & Microscopic approaches are the
two approaches in the study of thermodynamics
 In macroscopic approach, certain quantity of
matter is considered, without a concern on the
events occurring at the molecular level.
 These effects can be perceived by human
senses or measured by instruments.
eg: Pressure, Temperature

THERMODYNAMICS - I
Characteristics of macroscopic point of view are:
 No attention is focused on the behavior of
individual particles constituting the matter.
 The system is regarded as continuum devoid of
any voids and cavities.
 Study is made of overall effect of several
molecules; the behavior and activities of the
molecules are averaged

THERMODYNAMICS - I
 In microscopic approach, the effect of molecular
motion is considered.
 At microscopic level the pressure of a gas is
not constant,
 The temperature of a gas is a function of the
velocity of molecules.
 Most microscopic properties cannot be
measured with common instruments nor can be
perceived by human senses

THERMODYNAMICS - I
Characteristics of microscopic point of view
are:
 Necessity of complete knowledge of the
structure of the matter
 Requirement of a large number of variables for
complete specification of the state of matter
 Easy and precise measurement of variables is
not possible
 It is complex, cumbersome and time consuming.

THERMODYNAMICS - I
System and surroundings
 In our study of thermodynamics, we will choose a
small part of the universe and apply the laws of
thermodynamics. We call this subset a System.
 It is analogous to the free body diagram to which
we apply the laws of mechanics.
 The system is a macroscopically identifiable
collection of matter on which we focus our
attention.

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 The rest of the universe outside the system close
enough to the system to have some perceptible
effect on the system is called the surroundings.

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Thermodynamic Systems
Closed system

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Open system

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Isolated System

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Property: -
 A property is any characteristic that can be used to
describe the state of the system.
 It is some characteristic of the system to which
some physically meaningful numbers can be
assigned without knowing the history behind it

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Types of Properties:
 Extensive property
 Intensive property

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Specific property:
 It is the value of an extensive property per unit mass
of system. (lower case letters as symbols)
eg: specific volume, density (v, , ρ)
 It is a special case of an intensive property.
 Specific properties are most widely used in
thermodynamics:
 Specific entropy, specific enthalpy; specific internal
energy are intensive properties.

THERMODYNAMICS - I
State:
 It is the condition of a system as defined by the
values of all its properties.
 It gives a complete description of the system. Any
operation in which one or more properties of a
system change is called a change of state.
 The state is described by some observable
macroscopic properties like pressure temperature
etc.

THERMODYNAMICS - I
Phase:
 It is a quantity of matter that is homogeneous
throughout in chemical composition and physical
structure.
 When the system is in more than one phase then
they are separated by phase boundaries.
 Phase consisting of more than one phase is
known as heterogenous system
eg: solid, liquid, vapour, gas.

THERMODYNAMICS - I
Equilibrium State (Thermodynamic equilibrium)
 A system is said to be in an state of equilibrium
when there is no change in any property is
observed if the system is isolated from its
surroundings.

 Between the system and surroundings, if there is no
difference in
 Pressure Mechanical equilibrium.
 Temperature Thermal equilibrium
 Concentration of species Chemical equilibrium
If the system satisfies all the above condition, then it is
said to be under thermodynamic equilibrium.
 The properties for a system are defined only under
equilibrium conditions.
THERMODYNAMICS - I

THERMODYNAMICS - I
 Nature has a preferred way of directing changes in
the system as:
 Water flows from a higher to a lower level.
 Electricity flows from a higher to lower potential.
 Heat flows from a higher temperature to the a
lower temperature body.
 Momentum transfer occurs from a point of
higher pressure to a lower one.
 Mass transfer occurs from higher concentration
to a lower one

THERMODYNAMICS - I
Quasi-static Processes
A quasi-static process is one in which
the deviation from thermodynamic
equilibrium is infinitesimal and all states
of the system passes during the change
of state are considered as equilibrium
states.

THERMODYNAMICS - I
 Eg -1. Consider a gas, piston cylinder arrangement
as shown:
 If we remove the weights slowly one by one the
pressure of the gas will displace the piston
gradually upwards, then the system is said to be
undergoing quasi-static process.
 On the other hand if we remove all the weights at
once the piston will be kicked
up by the gas pressure at once.

THERMODYNAMICS - I
 When the weights are removed at once it
leads to unrestrained expansion of gas
but we don’t consider that the work is
done because it is not in a sustained
manner.
 In both cases the systems have
undergone a change of state.

THERMODYNAMICS - I
Path and Process
 The succession of states passed through during a
change of state is called the path of the system.
 A system is said to undergone a process
whenever its properties changes from one
equilibrium state to another equilibrium state.
 The path of succession of states through which
system passes is called the process.

THERMODYNAMICS - I
 A system may undergo changes in some or all of
its properties.
 Processes in thermodynamics are like streets in a
city.
 Due to some specific reasons we allow one of the
properties (pressure, temperature, enthalpy,
entropy) to remain a constant during a particular
process
 If one property remains constant prefix ‘iso’ is
used for that process.
 We can consider as many processes as we can
with different property kept constant one by one.

THERMODYNAMICS - I
 Isothermal process - Temperature held constant
 Isobaric process - Pressure held constant
 Isochoric process - Volume held constant
 Isentropic process - Entropy held constant
 Isenthalpic process - Enthalpy held constant
 Isosteric process - Concentration held constant
 Reversible adiabatic process - No heat
addition/removal during the process

 Thermodynamic cycle
 When a system with a given initial state
undergoes number of different changes of state
or processes and finally returns to initial state
is said to undergone a cycle.
 For a cycle all the final properties should have
the same value as that of initial properties.
 Mechanical cycle
 Final and initial properties need not be same
but only processes repeat according to some
sequence.
THERMODYNAMICS - I

THERMODYNAMICS - I
Temperature
 It is a property of a system which
determines the degree of hotness or
coldness.
 It is a relative term.
eg: A hot cup of coffee is at a higher
temperature than a block of ice. On the
other hand, ice is hotter than liquid
hydrogen.

THERMODYNAMICS - I
 Two systems are said to be equal in
temperature, when there is no change in any
properties is observed during their thermal
communication.
 In other words, “when two systems are at the
same temperature they are said to be in thermal
equilibrium with each other.

THERMODYNAMICS - I
 Zeroth law of Thermodynamics:
 It states that when two bodies have equality of
temperature separately with the third body, they
in turn have equality of temperature with each
other.
 When a body A is in thermal equilibrium with
body B and also separately with body C then B
and C will be in thermal equilibrium with each
other.

THERMODYNAMICS - I
 Temperature scales
 In order to measure the relative hotness or
coldness quantitatively temperature scales are
constructed.
 Two scales commonly used for measurement of
temperature are Fahrenheit scale and Celsius
scale.
 The Celsius scale was formerly called the
centigrade scale but is now designated the
Celsius scale.

THERMODYNAMICS - I
 In order to construct the temperature scale- a
reference body is used, and a certain physical
characteristic of this body which changes with
temperature is selected.
 The changes in the selected characteristic may be
taken as an indication of change in temperature.
 The selected characteristic is called the
thermometric property and the reference body
which is used in the determination of temperature
is called the thermometer.

THERMODYNAMICS - I
Standard reference points:
 Ice point- Equilibrium temperature of ice with air
saturated with water at a pressure of
101.325kPa which is assigned a value of 00C in
Celsius scale
 Steam Point: Equilibrium temperature of pure
water with its own vapor at a pressure of
101.325kPa which is assigned a value of 1000C
in Celsius scale.
Thermometric materials: Hg, ethyl alcohol for
normal range

THERMODYNAMICS - I
Temperature measurement using different
thermometric properties
 Mercury in Glass- Length – L
 Thermocouple - Thermal -emf – voltage
 Elect resistance thermometer resistance change
 Constant pressure thermometer- Volume change
 Constant volume thermometer – pressure change

Work and Heat
Work transfer
 The work is said to be done by a force when it acts
upon a body moving in a direction of force. This
action of force through a distance is called as work.
 Work is done when the point of application of a
force moves in the direction of the force.
 Work is identified only when a force moves its point
of application through an observable distance
THERMODYNAMICS - I

THERMODYNAMICS - I
 Thermodynamic definition of work:
 Work is said to be done by a system when the sole
effect on things external to the system could be
reduced to the rising of a weight.
Thermodynamic work requires
 Standard environment– system, surrounding, effect
 Fixed point or reference relative which rising or
lowering is considered.
Work is a transient phenomena, present during
interaction only does not exist before or after
Unit of work is Nm or Joules and power is Nm/s or Watts

THERMODYNAMICS - I
 Thermodynamic definition of heat:
 It is the energy in transition between the system
and the surroundings by virtue of the difference
in temperature.
 Like work heat is also a transient phenomena
 The unit of heat is Joules
 All our efforts are oriented towards how to
convert heat to work or vice versa:

THERMODYNAMICS - I
 Conversion of heat into work take place in
 Thermal power plant
 IC engines
 Conversion of work into heat take place in
 Refrigeration
 Electric heaters, furnaces
 We require a combination of processes to
convert heat into work or work into heat.
 Sustainability is ensured only when the
system undergoes a cycle

THERMODYNAMICS - I
Sign Conventions
• Work done BY the system is +ve
• Work done ON the system is –ve
• Heat given TO the system is +ve
• Heat rejected FROM the system is -ve

THERMODYNAMICS - I
 Heat Transfer (Q) [J or kJ]
 Heat is a form of energy that is transferred (without
transfer of mass) across the boundaries of a
system
 Heat transfer take place due of temperature
difference between the system and its
surroundings,
 It is always from a body at higher temperature to a
body at lower temperature.
 Conduction, convention and radiation are the
three modes of heat transfer.

THERMODYNAMICS - I
 All temperature changes need not be due to heat
alone. eg: Friction
 All heat interaction need not result in changes in
temperature
eg: condensation or evaporation.
 A process in which no heat crosses the boundary of
the system is called as adiabatic process.
 The unit of heat transfer is Joule and rate of heat
transfer is Watts.

THERMODYNAMICS - I
Various Types of Work
1. PdV or Dispalcement work
• Consider a piston cylinder arrangement as shown.
Displacement work (pdV work) or boundary work
can be obtained as follows:
Force exerted, F= p. A
Work done dW= F.dL= p. A dL= p.dV
• If the piston moves through a finite distance say 1-
2,Then work done has to be evaluated by
integrating
dV
p
dW .
2
1
2
1 



THERMODYNAMICS - I
 The conditions that must be satisfied for
 The system should be a closed one, the process
must be quasistatic and friction less.
 The boundary of the system should move in order
that work is done either by the system or on the
system.
 The pressure and all other properties are the same
on all the boundaries of the system.
 The system is not influenced by motion, gravity,
capillarity, electricity and magnetism
dV
p.


THERMODYNAMICS - I
 Point function
 During a process if the values of variables depend
on end states only then they are known as point
functions.
 All thermodynamic properties like pressure,
temperature, volume etc are point functions.
 For a given state, each property has a definite
value. The differentials of point functions are exact
or perfect differentials.

THERMODYNAMICS - I
 Path function
• Area under each curve on P V
diagram represents work for any
process.
• Since area under each curve is
different for different paths, the
amount of work obtained in each
case will be different and is not a
function of end states 1 and 2.
• Hence work is a path function and
dW is an inexact or imperfect
differential.

PdV work in various quasi-static processes
(a) Constant Pressure Process( P = Constant) – Isobaric Process
For a closed system which undergoes a
constant pressure process from state 1
(volume V1 and pressure p1) to a final state 2
(volume V2), the process is represented in the
p-V diagram as shown.

(b) Constant Volume Process ( V = Constant) – Isochoric Process
For a constant volume process i.e., V = constant,
hence dV = 0 as represented in the p-V diagram.

(c) Constant Temperature Process or Isothermal Process, PV = Constant
The hyperbolic expansion process from state 1 to state
2 is represented on a p-V diagram as shown.

Other types of Work Transfer

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