Dr. A. K. Bhat, Professor Mechanical GIT, Belgaum

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06 ME 33 Basic Thermodynamics
A WARM WELCOME TO ONE AND ALL
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
BASIC THERMODYNAMICS SUBJECT CODE 06ME33 LECTURE
HOURS 35
Presented by Dr. A. K. Bhat Professor, Dept. of
Mechanical Engg Gogte Institute of Technology,
Belgaum.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
OUTCOME OF SESSION - I

• P-T and P-V diagrams
• Triple Point and Critical Point
• Sub Cooled Liquid
• Saturated Liquid, Mixture of Saturated Liquid
  and Vapor
• Saturated vapor and superheated vapor states
  of a pure substance with water as example.

Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Introduction
A pure substance is one that has a homogeneous
and in variable chemical composition. It may
exist in more than one phase, but the chemical
composition is the same in all phases. Thus
liquid water, a mixture of liquid water and water
vapor, and a mixture of ice and liquid water are
all pure substance every phase has the same
chemical composition. On the other and mixture of
liquid air and gaseous air is not a pure
substance. Because of the composition of the
liquid phase is different from that of the vapor
phase
Some times a mixture of gases such as air is
considered a pure substance as long as there is
no change of phase. Strictly speaking this is not
true.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Vapor-Liquid-Solid phase equilibrium in a pure
substance
Constant pressure change from liquid to vapor
phase for a pure substance
Consider a system one kg of water contained in a
piston cylinder arrangement as shown in the
figure. Suppose that the piston and weight
maintain a pressure of 0.1 MPa in the cylinder
and that initial temperature be 200C.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
As the heat is transferred to the water the
temperature increases appreciably, the specific
volume increases slightly under constant
pressure. When the temperature 99.60C, additional
heat transfer results in a change of phase. I.e.
some of the liquid becomes vapor.
During this process both temperature and pressure
remain constant where as sp. volume increases
considerably. When the last drop of liquid has
vaporized further transfer of heat results in an
increase in both temperature and sp. volume of
the vapor.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Pressure
Vapor-pressure curve
Temperature Vapor Pressure curve of a pure
substance
The term saturation temperature designates the
temperature at which vaporization takes place at
a given pressure. Thus for water 99.60C the
saturation pressure is 0.1MPa, and for water at
0.1MPa the saturation temperature is 99.60C. Thus
there is a definite relation between saturation
pressure and saturation temperature.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics

• If the substance exists as liquid at the
  saturation temperature and pressure it is called
  saturated liquid. If the temperature of the
  liquid is lower than the saturation temperature
  for the existing pressure it is called either a
  sub cooled liquid or a compressed liquid.
• When the substance exists as a part liquid and
  part vapor at the saturation temperature a
  dryness fraction comes into picture. It is also
  called as quality and it is defined as the ratio
  of mass of vapor to the total mass. It is denoted
  by the symbol x. The quality x is an intensive
  property.
•  
• If a substance exists as vapor at the saturation
  temperature it is called saturated vapor or dry
  saturated vapor with x1. When the vapor is at a
  temperature greater than the saturation
  temperature at the saturation pressure, it is
  said to exist as superheated vapor.

Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Temperature Volume (T-V) diagram for water
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
It is clear from the figure that constant
pressure lines are ABCD, EFGH, IJKL etc. The peak
point of the fig. indicated by N is the critical
point of water. Thus the critical pressure 22.089
MPa and corresponding critical temperature is
374.14 0C.
 A constant pressure process at a pressure
greater than the critical pressure is represented
by curve PQ. Thus water at 40 MPa, 200C is
heated in a constant pressure process, there will
be never be two phases present at the state
shown. Instead there will be continuously in
density at all the times and there will be only
one phase present.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
The question arises is when do we have a liquid
and when do we have a vapor? The answer is that
this is not a valid question at super critical
pressures. We simply term the substance as
fluid. However rather arbitrarily at temperatures
below the critical temperatures we usually refer
to it as a compressed liquid and at temperatures
above the critical temperatures as superheated
vapor.
It should be noted that however at pressures
above the critical pressures we never have a
liquid and vapor phase of pure substance existing
in equilibrium.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Some Critical point data
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Sublimation If the initial pressure of the ice
at 200C is 0.26 kPa, heat transferred to the ice
results in an increase in the temperature to
100C. At this point however the ice passes
directly from the solid phase to the vapor phase.
This process is known as sublimation.
Triple Point Consider ice at 0.6113 kPa and
200C. Through heat transfer let the temperature
increase until it reaches 0.010C. At this point
however further heat transfer may cause some of
the ice to become vapor and some to become
liquid. At this point it is possible to have
three phases in equilibrium. This point is called
the triple point. Triple point is defined as the
state in which all three phases may be present in
equilibrium.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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Triple Point Data
06 ME 33 Basic Thermodynamics
Triple Point Data
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Allotropic Transformation It should be pointed
out that a pure substance can exist in a number
of different solid phases. A transition from one
solid phase to another is called an allotropic
transformation. This can be well understood by
the following figures. 
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
P-T Diagram for a pure substance such as water
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
P-T Diagram for iron
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum