Thermodynamics (from the Greek
thermos meaning heat and dynamis
meaning power) is a branch of physics.
It relates heat and work
It deals with the effect of imposition of
energy on the physical properties of
The foundation of thermodynamics is
based on experimental observations.
The observations have been formalized
in to four thermodynamic laws.
Thermodynamics may be broadly
defined as a framework for viewing
and correlating the behaviour of the
developed out of the need to increase
the efficiency of early steam engines.
The first and second laws of
simultaneously in the 1850s, primarily
out of the works of William Rankine,
Rudolf Clausius, and William Thomson
Classical thermodynamics derives from
physicist Robert Boyle’s 1662
The first thermodynamic textbook was
written in 1859 by William Rankine, a
civil and mechanical engineering
professor at the University of Glasgow
Lord Kelvin coined the term
thermodynamics in his 1849 publication
‘An Account of Carnot's Theory of the
Motive Power of Heat’.
In thermodynamics, thermodynamic
efficiency, symbolized by (e), is defined
where W is the absolute value of work
done in one thermodynamic cycle. Q is the
absolute value of the change in heat.
A thermodynamic system is defined
as that part of the universe that is
under consideration. A real or
imaginary boundary separates the
system from the rest of the universe,
which is referred to as the environment
Isolated Systems – matter and energy do
not cross the boundary.
Adiabatic Systems – heat does not cross
Diathermic Systems - heat crosses
Closed Systems – matter does not cross
Open Systems – heat, work, and matter
may cross the boundary.
A control volume is a volume in
space of interest for a particular
study or analysis. The surface of
this control volume is called the
The size and shape of control
volume are arbitrarily chosen to
suit our analysis.
Mass as well as heat and work can
cross the control surface, and the
mass in the control volume (as well as
its properties) change with time.
The boundary may be fixed, or it
may move (expand or contract).
Control volume is an open system
Consider a tank with a
piston and one inlet,
and one outlet.
Through the inlet
mass comes in and
through the outlet it
No exchange of mass is allowed, it
resembles a closed system
As a control mass undergoes a change of
state, energy may cross the boundary as
either heat or work.
Microscopic point of view is based on
molecular level study to explain the
behaviour of a system.
A huge number of variables are required to
specify the condition of a system
Statistical thermodynamics is based on
Macroscopic point of view is based on
gross or time-averaged effects of many
In this approach the condition of system can
be specified by only measurable quantity
like P, V, T and the number of variables to
be dealt with are quite few.
These effects can be perceived by human
senses and measured by instruments.
Statistical thermodynamics is a branch
of thermodynamics concerned with the
study and analysis of actual phenomena
with full interpretation, explanation, and
evaluation of microscopic, i.e. statistical
energy-level atomic and molecular
It is a branch of thermodynamics
concerned with the study and analysis of
actual phenomena with avoidance of full
interpretation, explanation, and evaluation
of microscopic, i.e. statistical energy-level
atomic and molecular details. Generally,
phenomenological thermodynamics, being
synonymous with classical
These are the attributes that can
characterize the system by P, V, T,
density, specific heat etc.
Extensive property: It depend on the
system size or the amount of material in
the system. Mass, volume, entropy, energy
(Internal energy and enthalpy) are
examples of it.
Intensive Property: is the physical
property of the system that does not
depend on the system size or the amount
of material in the system. The examples
are temperature, pressure, and density.
The properties of the system can be
described by an equation of state which
specifies the relationship between these
extensive and intensive parameters or
Thermodynamic properties are defined for,
and significant to, only thermodynamic
The state of the thermodynamic system can
be thought of as an optimal ensemble of
thermodynamic parameters, namely
temperature, pressure, density, composition,
etc., which characterize the system. Neither
its surroundings nor its history characterize
For a system, each of the properties at a
particular state has unique set of intensive
properties regardless of the path, how the
system has arrived to that particular state.
State properties are path independent.
Phase: A quantity of matter homogeneous
throughout in chemical composition and
physical structure is called a phase. Vapour,
liquid and solid are the three phases.
A system is said to be in equilibrium,
where there is no change in
macroscopic property is registered,
when the system is kept isolated from
A system in equilibrium never changes
to any other state spontaneously.
At equilibrium the state properties do not
change until and unless there is an
energetic evolution from one to another
The word equilibrium implies a state of
balance. In an equilibrium state, there
are no unbalanced potentials (or driving
forces) within the system.
The system is in equilibrium in three
Thermodynamics studies mainly the
properties of physical systems that are
found in equilibrium state.
Mechanical equilibrium: In the absence
of any unbalanced force within the
system itself and between the system and
surrounding, the system is said to be in
Chemical equilibrium:If there is no
chemical reaction or transfer of matter
from one part of the system to another the
system is said to be in chemical
Thermal equilibrium: When the system
is separated from its surroundings by a
diathermic ( means allows the heat to
flow) wall and if there is no change in
temperature of the system, the system is
said to be in thermal equilibrium with the
Both classical and statistical
thermodynamics study mainly the
equilibrium states of a system.
Non-equilibrium thermodynamics is a
branch of thermodynamics concerned
with studying irreversible
The path of the succession of states through
which the system passes is called the
A thermodynamic process may be defined
as the energetic evolution of a
thermodynamic system proceeding from an
initial state to a final state.
Quasi equilibrium process: Such a
process is the locus of all the equilibrium
points through which the system passes.
Infinite slowness is the attribute of the
In quasi--static process the departure of
the state of the system from the
thermodynamic equilibrium state is
An isothermal process occurs at a constant
temperature. An example would be to have
a system immersed in a large constant-
temperature bath. Any work performed by
the system will loose equivalent amount of
energy to the bath, but its temperature will
An isobaric process occurs at constant
pressure. An example would be to have a
movable piston in a cylinder, so that the
pressure inside the cylinder is always at
atmospheric pressure, although it is
isolated from the atmosphere.
An isochoric process is one in which the volume
is held constant, meaning that the work done by
the system will be zero. An isochoric process is
also known as an isometric process.
An example would be to place a closed tin can
containing only air into a fire. To a first
approximation, the can will not expand, and the
only change will be that the gas gains internal
energy, as evidenced by its increase in
temperature and pressure.
cycle is a series of
returns a system to its
Thermodynamic cycles often use quasi-
static process to model the workings of
actual devices to obtain maximum
Two primary classes of thermodynamic
Power cycles are cycles which convert
a heat input into a work output.
e.g.,Internal combustion engine.
Refrigeration cycles transfer heat from
low to high temperatures using work
input. e.g., refrigerator.
A dimension is a physical variable used to
specify the behavior or nature of the
particular system. The length of a rod is a
dimension of the rod.The gas temperature is
a thermodynamic dimension of a gas.
Units and Dimensions
Units are needed to measure the dimension.
M. K. S
S.I (System International)
Basic units (S. I)
Mass (M), kg
Length (L), m
Time (t), s
Amount of substance, mole
Electrical current, A
Luminous Intensity, candela, cd
Plane angle, rad
Derived units (S.I)
Force (F), N
Energy (E), Joules, J, Nm
Power, watt, W, J/s
Pressure, pascal, Pa
English Engineering unit system
Amount of substance, lb mole
Force (F), lbf
The value of gc in SI and Engineering unit
The unit of force is derived from Newton.s
F m X a or F X C = m X a
where ‘m’ is the mass and ‘a’ is the
In SI unit, m = 1 kg and a = 9.80665 m/s2
Then F = 9.80665 N
9.80665 N X C = 1 kg X 9.80665 m/s2
C=1 kg m/s2/N
If we replace C by gc, the gravitational
F= m a/ gc
In SI unit, gc, = 1 kg m/s2/N = 1
In Engineering unit, F= 1 lbf , m= 1 lbm
a=32.174 ft/ s2
Hence, 1 lbf X C = 1 lbm X 32.174 ft/ s2
C = 32.174 lbm ft/ s2/ lbf
gc, = 32.174 lbm ft/ s2
Macroscopic mode of energy
Microscopic mode of energy
The two types of macroscopic mode of
Molecular Kinetic energy: It is
associated with the translational
velocity of individual molecules.
Microscopic mode of energy are of three
Intermolecular potential energy: It is
associated with the forces between the
molecules and their position with
respect to each other.
Intramolecular energy: It is associated
with molecular and atomic structure and
Total Energy= Macroscopic energy +
=Kinetic energy + Potential
energy + Internal Energy
From macroscopic point of view we
deal with volumes which are very large
compared to its molecular dimension.
Within this volume span we can
assume the substance to be continuous
and can be divided infinite times
disregarding the action of individual
The continuum concept looses its
validity when molecular mean free path
of the molecules approaches the
dimension of the vessel. e.g., In vacuum
technology, in microchannel flow.
Specific Volume and Density
The Specific Volume of a system in a
gravitational field may vary from point
Specific Volume: volume per unit mass
Specific Density: mass per unit volume
Both are intensive properties
where is the smallest volume for
which the mass can be considered a
The specific volume and density are
defined at a point in system. It may vary
But change in specific volume with
elevation is not significant. So we can
take one value of and
The specific volume and density
may be given either on mass or on
Molal specific volume =
Molal density =
With liquids and gases: pressure, with
It is defined as the normal component of
force per unit area.
where is the smallest area for
which the fluid can be considered a
Units of Pressure
Unit for Pressure in International
System: force of one newton acting on
a square meter area.
1bar = 10 Pa = 0.1MPa
1atm = 101325Pa = 14.696lbf/in
Measurement of pressure difference
Patm. = Po
Force acting at B
0 0P A mg P A AgH
Force acting at A
Pressure Difference: ghPPP 0
Because of difficulties in defining
temperature, we define equality of
The two bodies have equality of
temperature, if there is no change in any
observable property occurs when they
are in thermal communication.
The Zeroth Law of Thermodynamics
When two bodies have equality of
temperature with a third body, they
must have equality of temperature with