Download Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ

“ BASIC CONCEPTS
OF
THERMODYNAMICS ”
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
 WHAT IS THERMODYNAMIC ?

Thermodynamic is the science that deals with the
energy interactions between material system.

In other words, It is the science which deals with the
transformation of energy of all kinds from one form
to another.

In short/in fact, thermodynamic means the science
of three “Es” namely Energy, Entropy and
Equilibrium.

Carnot, Joule, Kelvin and Clausius were the main
scientists who developed this science in the past
century.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
 THERMODYNAMIC SYSTEM
A thermodynamic system or simply a system is
defined as a quantity of matter or a region in space
chosen for study.
 Everything
external to the system is called
‘surrounding’ or the ‘environment’.
 The real or imaginary surface that separates the
system from its surrounding is called boundary.

Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
 TYPES OF SYSTEM



Open System.
Closed System.
Isolated System.
(1) Open System: Open system is the one in which
energy & mass transfer takes place at the system
boundary. E.g. Turbine, I.C. Engine etc.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
(2) Closed System: Closed system is the one in which
only energy transfers at its boundary. Such system have
no mass transfer across it’s boundary.
Example:- Air trapped in piston cylinder arrangement.
(3) Isolated System : An isolated system is the one in
which neither energy nor mass can cross the boundary.
Example:- Perfectly Insulated Thermos Flask
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
 CONTROL VOLUME
For thermodynamic analysis of an open system , like
air-compressor, attention is focused on a certain
volume in space which is known as ‘control volume’.
 Control volume is bounded by a surface called
‘control surface’.

THERMODYNAMIC PROPERTIES,
PROCESSES & CYCLES

Every system has certain characteristics by which its
physical condition may be described e.g. volume,
pressure, temperature etc. Such characteristics are
called properties of the system.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
CONTD…

Any operation in which one or more of the properties
of a system changes is called change of state.

The succession of states passed through during a
change of state is called the path of change of state.

When the path is completely specified , the change of
state is called a process, e.g. constant volume
process, constant pressure process , constant
temperature process etc.

A thermodynamic cycle is defined as a series of state
of changes such that final state is identical with the
initial state.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
CONTD…
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
MACROSCOPIC & MICROSCOPIC POINT
OF VIEW



Thermodynamic studies are undertaken by the following two
different approaches.
(1) Macroscopic approach – ( macro means big or total )
(2) Microscopic approach – ( micro means small )
Macroscopic approach
Microscopic approach
In this approach a certain
quantity
of
matter
is
considered without taking
into account the events
occurring at molecular level.
In
this
approach
every
quantity
of
matter
is
considered by taking into
account the events occurring
at molecular level. The
molecules
have different
This approach is concerned velocities & energies. The
with
gross
or
overall values of these energies are
behavior.
constantly changing with
time.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
CONTD…
Macroscopic approach
Microscopic approach
This is known as classical - This approach is known as
thermodynamics.
statistical thermodynamics.
The analysis of macroscopic In microscopic approach, the
system
requires
simple value of the quantity changes
mathematics formulae.
with
time
so
advanced
statistical & mathematical
methods
are needed to
explain the change in system.
Few properties are required Large number of variables
to describe a system.
are required describe a
system.
This
approach
simple.
is
quite This
approach
complicated.
is
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
 THERMODYNAMIC EQULIBRIUM
A system is said in thermodynamic equilibrium if the
temperature and pressure at all points are same ;
there should not be velocity gradient ; the chemical
equilibrium is also necessary.
 For attaining a state of thermodynamic equilibrium
following three types of equilibrium state must be
achieved:
(1) Thermal Equilibrium :- The temperature of the
system does not change with time & has the same
value at all points of system.
(2) Mechanical Equilibrium :- There are no
unbalanced forces within the system or between the
surrounding. The pressure in the system is same at all
the points and does not change with respect to time.

Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
CONTD…
(3) Chemical Equilibrium :- No chemical reaction
takes place in the system and the chemical
composition does not vary with time.
 QUASI-STATIC PROCESS
o
o
When process proceeds in such way that the system
remains close to a thermodynamic equilibrium state at
all times, it is called Quasi-Static process.
For example, consider system of gas contained in
cylinder. Now, let us consider the pressure of the gas
on the one face of a frictionless piston is p1 and a
pressure p2 on opposite face. If two pressures are
equal, the piston is in equilibrium. But if p1 is
infinitesimally larger than p2 the gas on both sides
still remains essentially in equilibrium . This is
known as Quasi-Static process.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
CONTD…
This Quasi-static process only can be represented on
a thermodynamic plane as shown in the below figure.
 Let AB represents a quasi-static process on a
thermodynamic plane, say p-V plane. Then at
successive state such as 1,2,3,4, etc.; the system is
very nearly in thermodynamic equilibrium.
 No real process is quasistatic,
but such processes can be
approximated by performing
them very slowly.

Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
 PURE SUBSTANCE



A pure substance is the one which has a fixed chemical
composition throughout. For example water, carbon
dioxide, nitrogen etc.
In other words, it is a system which is
(a) Homogeneous in composition (b) Homogeneous in
chemical aggregation.
The mixture of water & ice is a pure substance while the
mixture of oil & water isn’t a pure substance.
 CRITICAL POINT

The critical point may be defined as “the point at which
the saturated liquid & saturated vapor states are
identical.” The pressure & temperature at critical point
are known as critical pressure & critical temperature
respectively.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
 p-v-T
o
o
Surface
The p-v-T surface is a graphical representation of the state 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.
If any two of these state variables is specified, the third is
determined.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.
Thank you
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.