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 - 2

• Independent Property
• Tables of Thermodynamics Property
• P v T Surfaces
• T s Diagrams
• H s Diagrams

Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Independent properties of a pure substance One
important reason for introducing the concept of
pure substance is that the state of a simple
compressible pure substance is defined by two
independent properties. For ex if the specific
volume and temperature of a super heated steam
are specified the state of the steam is
determined.
 Consider the saturated liquid and vapor state of
a pure substance. These two states have the same
pressure and temperature but they are definitely
not the same state. In a saturation state
therefore pressure and temperature are not
independent properties. Two independent
properties such as pressure -specific volume,
pressure and quality, temperature-specific
volumes are required to specify a saturation
state of a pure substance.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Tables of Thermodynamic properties
Tables of thermodynamic properties of many
substances are available and in general these
tables have the same form. The steam table is
specially selected because they are a vehicle for
presenting thermodynamic tables and steam is used
extensively in power plants and industrial
purposes. The table consists of four separate
tables namely 1)     Saturated steam table
2)     Saturated water table 3)     Temperatur
e basis table and 4)     Pressure basis table.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
It contains values of enthalpy, internal energy,
specific volume and entropy. If the values of T
and P are given other all values can be directly
taken from the table.
The specific volume of a substance having given
quality can be found out by the definition of
quality. The volume is the sum of volume of
liquid and vapor. V Vliq V vap.
In terms of masses mv mliq vf mvap vg By
introducing the quality x we have v (1-x)
vf x vg We know that vfg vg - vf Specific
volume equation for wet steam as v vf x vfg
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Temperature Specific Volume Diagram
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Figure shows a T-v plot for water with an
indication of percent error in assuming ideal gas
behavior along the saturated vapor curve and also
in several area of superheated region.
Generally a slight decrease and only a small
error is made if one same that the volume of a
compressed liquid is equal to the specific volume
of the saturated liquid at the same temperature.
It is generally accepted procedure particularly
when compressed liquid data are not available. In
the modern scenario computerized table are
available. The main program operated with a
visual interface in the window environment on a
PC which is generally user friendly.
The program operates on DOS environment, which
covers not only the tables of water, but it
covers most of the pure substances used in
engineering industries. The generalized chart
with compressibility factor is also included so
it is possible to get the value of Z a more
little accurately than reading the graph. It is
useful in the case of two-phase mixture, like
saturated liquid and vapor values are needed.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Thermodynamic Surfaces  The matter discussed so
far can be well summarized by a consideration of
a pressure, specific volume, temperature surface
(PVT surface). Two such surfaces are shown for a
substance such as water in which the specific
volume increases during freezing and the other
substance in which specific volume decreases
during freezing.
PvT Surface -- Water
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
PvT Surface for a Substance which Contracts Upon
Freezing
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
PvT Surface for a Substance which Expands Upon
freezing
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
In these diagrams the pressure, specific volume
and temperature are plotted on a mutually
perpendicular coordinates and each possible
equilibrium state is thus represented by a point
on the surface. This follows directly from the
fact that a pure substance has only two
independent intensive properties. All points
along a quasi equilibrium surface lie on the PvT
surface since such a process always passes
through equilibrium states. 
The regions of the surfaces that represent a
single surface- the solid, liquid and vapor faces
are indicated. These surfaces are curved. The two
phase regions the solid-liquid, solid-vapor,
liquid-vapor regions are ruled by surfaces. It is
understood that they are made up of straight
lines parallel to the specific volume axis.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
This of course follows from the fact that in the
two-phase region lines of constant pressure are
also lines of constant temperature, although the
specific volume may change. The triple point
actually appears as the triple line on the PVT
surface, since the pressure and temperature of
the triple point are fixed but the specific
volume may vary depending upon the proportion of
each phase. 
It is also of interest to note that the pressure
temperature and pressure volume projections of
these surfaces. We have already considered the
P-T diagram for water. It is on this diagram we
observe the triple point. Various lines of
constant temperature are shown on the P-v diagram
and corresponding constant temperature sections
are identically seen on the P-v-T surfaces. The
critical isotherm as a point of intersection at
the critical point.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
One notices that for a substance such as water
which expands on freezing, the freezing
temperature decreases with an increase in
pressure. For a substance that contracts on
freezing, the freezing temperature increases as
the pressure increases. Thus as the pressure of
the vapor is increased along the constant
temperature line a substance that expands on
freezing first becomes solid and then liquid. For
substance that contract on freezing, the
corresponding constant temperature line indicates
that as the pressure of the vapor increases, it
first becomes liquid and then solid.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
T-s Diagram for a pure substance   Consider
the heating of 1 kg of ice at 50C to steam at
2500C. The pressure being maintained at 1 atm.
It is observed that the entropy of steam
increases in different regimes of heating
namely 1)      Entropy increase of ice to
saturated freezing temperature 2)      Entropy
increase of ice as it melts into water. 3)     
Entropy increase of water as it is heated from
0Oc to 100OC. 4)      Entropy increase of
water as it is vaporized at 100OC absorbing
latent heat of vaporization. 5)      Entropy
increase of vapor as it is heated from
100OC to 250OC.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Isobars on T-S Plot
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
These entropy changes are shown in T-S graph. It
is a constant pressure process. If during heating
process the pressure had been maintained constant
at 2 atm, a similar curve would be obtained. If
these states for different pressures are joined
the phase equilibrium diagram of a pure substance
on the T-s coordinate would be obtained as shown
below.
Phase Equilibrium diagram on T-s coordinates
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Most often liquid vapor transformation only are
of interest, the following figure the liquid,
the vapor and the transition zones only at a
particular pressure, sf specific entropy of
saturated water and sg - specific entropy of
saturated vapor. The entropy change of the system
during the phase change from a liquid to vapor at
that constant pressure is sfg. ( sg sf). The
value of sfg decreases as pressure increases. And
becomes zero at the critical point.
Saturation dome for water
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
H-S diagram (Mollier diagram) for a pure
substance   From the first and second law of
thermodynamics following property relations are
obtained. Tds dh v dp ( ?h / ?s )p T These
equations form the basis of h-s diagram of a pure
substance
The slope of an isobar on the h-s coordinates is
equal to the absolute temperature. If the
temperature remains constant the slope will
remain constant. If the temperature increases the
slope of the isobar will increase.  
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
Consider once again the heating of ice at 5OC to
steam at 250OC the pressure being maintained
constant at 1 atm. The slope of the isobar of 1
bar on the h-s coordinates first increases as the
temperature of the ice increases from 5OC to
0OC. the slope then remains constant as ice melts
to water at 0OC. Te slope of isobar again
increases as the temperature of water rises from
0OC to 100OC. the slope again remains constant as
water vaporizes at constant temperature. Finally
the slope of the isobar continues to increase as
the temperature of steam increases to 250OC and
beyond.
Isobars on h-s plot
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
 Similarly the isobars of different pressures can
be drawn on h-s diagrams as shown in the figure
below 
Phase equilibrium diagram on h-s coordinates
This figure shows the phase equilibrium diagram
of a pure substance on the h-s coordinate
indicating the saturated solid line, saturated
liquid line saturated vapor line, the various
phases and the transition zones.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
h-s diagram for water
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum
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06 ME 33 Basic Thermodynamics
 This figure is the Mollier diagram indicating
only the liquid and vapor phases. As the pressure
increases the saturation temperature increases,
slope of the isobar increases. Hence the constant
pressure lines diverge from one another and the
critical isobar is at a tangent to the critical
point. In the vapor region the states of equal
slopes at various pressures are joined by lines
as shown, which are the constant temperature
lines. Here at a particular pressure hf is the
specific enthalpy of saturated water and hg is
specific enthalpy of saturated vapor and hfg (
hg - hf) is the latent heat of vaporization at
that pressure. As the pressure increases hfg
decreases and at the critical pressure hfg
becomes zero.
Dr. A. K. Bhat, Professor (Mechanical) GIT,
Belgaum