chapter one: Introduction to Thermodynamics

 Thermodynamics can be defined as the science of energy.
 Energy can be viewed as the ability to cause changes
 The name thermodynamics stems from the Greek words
therme (heat) and
dynamis (power),
which is most descriptive of the early efforts to convert heat into power.
 Today the same name is broadly interpreted to include all
aspects of energy and energy transformations, including power
generation, refrigeration, and relationships among the properties of matter.

 One of the most fundamental laws of nature is the
conservation of energy principle.
 It simply states that during an interaction, energy can change
from one form to another but the total amount of energy
remains constant.
That is, energy cannot be created or destroyed
𝑬𝒊𝒏 − 𝑬𝒐𝒖𝒕 = ∆𝑬

A rock falling off a cliff,
for example,
picks up speed as a result of
its potential energy being
converted to kinetic energy

A person who has a greater
energy input (food) than energy
output (exercise) will gain
weight (store energy in the form
of
fat), and a person who has a
smaller energy input than
output will lose
weight

 Thermodynamics emerge as a science after the construction
of the first successful atmospheric steam engines in
England by Thomas Savery in 1697 and Thomas
Newcomen in 1712. These engines were very slow and
inefficient, but they opened the way for the development of a
new science.

Was the first that uses the term
THERMODYNAMICS
In 1849
The Thermodynamics is a Science. As every
science, has it’s own studied subject:
THE TRANSFORMATION OF ENERGY FORMS
LIKE HEAT AND WORK; AND RELATIONSHIP
AMONG PHYSICAL PROPERTIES OF
SUBSTANCES
And it’s own Laws:
Four Laws

 The first and second laws of thermodynamics emerged simultaneously
in the 1850s, primarily out of the works of
 William Rankine,
 Rudolph Clausius, and
 Lord Kelvin (formerly William Thomson).
 The first thermodynamic textbook was written in 1859 by William
Rankine, a professor at the University of Glasgow.

 Any substance consists of a large number of particles called molecules.
 The properties of the substance naturally depend on the behaviour of these particles.
 There are two approaches to study the thermodynamic properties of substances;
1. Macroscopic Approach
2. Microscopic Approach
 The macroscopic approach to the study of thermodynamics does not require a knowledge of
the behaviour of individual particles and it is called classical thermodynamics.
 It provides a direct and easy way to the solution of engineering problems.
Example: Reading pressure using pressure gauge
 A more elaborate approach, based on the average behaviour of large groups of individual
particles, is called statistical(microscopic) thermodynamics.
Example: Analysis of pressure from momentum of individual molecules

 All activities in nature involve some interaction between energy and
matter; thus, it is hard to imagine an area that does not relate to thermodynamics
in some manner
 The application of the thermodynamic laws and principles are found in all fields of
energy technology, notably in
Steam And Nuclear Power
Plants,
Internal Combustion
(IC)Engines,
Gas Turbines,
Air Conditioning,
Refrigerators ,
Gas Dynamics,
Jet Propulsion,
Compressors,
Chemical Process Plants And
Direct Conversion Devices.

12
Applications of
Thermodynamics
Power plants
The human body Air-conditioning
systems
Airplanes
Car radiators Refrigeration systems

 A system is defined as a quantity of matter or a region in
space chosen for study.
 The mass or region outside the system is called the
surroundings.
 The real or imaginary surface that separates the system
from its surroundings is called the boundary.
 The boundary of a system can be fixed or movable.
Note that the boundary is the contact surface shared by both the system and the
surroundings. Mathematically speaking, the boundary has zero thickness, and
thus  it can neither contain any mass nor occupy any volume in space

C
A
B
 CLOSED
 OPEN
 ISOLATED

 The closed system is a system of fixed mass.
 There is no mass transfer across the system
boundary.
 There may be energy transfer into and out of
the system.
 also known as a control mass
 A certain quantity of fluid in a cylinder
bounded by piston constitutes a closed system.

 The open system is one in which matter crosses the
boundary of the system.
 There may be energy transfer also.
 Also known as a control volume
 Most of the engineering devices are open system.
E.g Air Compressor, Water Heater, turbine,
nozzle, …

 The boundaries of a control volume are called a control
surface, and they can be real or imaginary.
 In the case of a nozzle, the inner surface of the nozzle forms the real part of the boundary, and
the entrance and exit areas form the imaginary part, since there are no physical surfaces
there.
 A control volume can be fixed in size and shape, as in the case
of a nozzle, or it may involve a moving boundary as in the
piston.
 A control volume can also involve heat and work interactions
just as a closed system, in addition to mass interaction.

Mass in
Mass out
Boundaries
SYSTEM
Surroundings

 The Isolated system is one in which there is
no interaction between the system and
the surrounding.
 It is of fixed mass and energy, and there is
no mass and energy transfer across the
system boundary.
ISOLATED
E = Constant
System
Isolated
boundaries
Environment

 Any characteristic of a system is called a property.
Pressure, Temperature, Volume, Mass , Viscosity, Thermal
Conductivity…
 Properties are the coordinates to describe the state of a system.
 Properties are considered to be either
Intensive or Extensive
 Intensive properties are those that are independent of the mass of a system, such as temperature,
pressure, and density.
 Extensive properties are those whose values depend on the size—or extent—of the system. Total mass,
total volume, and total momentum are some examples of extensive properties

 To determine whether a property is intensive
or extensive is to divide the system into two
equal parts with an imaginary partition, as
shown in figure.
 Each part will have the same value of intensive
properties as the original system, but half the
value of the extensive properties.

 Generally, uppercase letters are used to denote extensive properties
(with mass m being a major exception), and lowercase letters are
used for intensive properties (with pressure P and temperature T
being the obvious exceptions).
 Extensive properties per unit mass are called specific properties. Some
examples of specific properties are specific volume (v = V/m) and specific
total energy (e = E/m).

Equilibrium Is State Of Balance
(Absence of potential to create a
change which makes the state to
remain as it is.)

 With a system not undergoing any change, all the properties can be measured or calculated
throughout the entire system, which gives us a set of properties that completely describes
the condition, or the state, of the system.
 At a given state, all the properties of a system have fixed values.
 If the value of even one property changes,  the state will change to a different
one

 Thermodynamics deals with equilibrium states. The
word equilibrium implies a state of balance. In an
equilibrium state there are no unbalanced potentials
(or driving forces) within the system. A system in
equilibrium experiences no changes when it is isolated
from its surroundings.
 There are many types of equilibrium, and a system is
not in thermodynamic equilibrium unless the
conditions of all the relevant types of equilibrium are
satisfied.

Types of Equilibrium
 Thermal Equilibrium 
 Mechanical Equilibrium
 Phase Equilibrium
 Chemical Equilibrium
No Unbalanced Force
No Temperature Variation
No Change in Chemical
Composition (No chemical
Reaction)
No Unbalanced mass across
multiple phase

 Even though the state of a system is described by its properties, It is not necessary
to specify all the properties in order to fix a state.
 Once a sufficient number of properties are specified, the rest of the properties
assume certain values automatically.
 The number of properties required to fix the state of a system is given by the
state postulate:
The state of a simple compressible system is completely specified by two
independent, intensive properties.

 State Principle: The particular state of any Thermodynamic
system will be determined knowing two independent
properties.
It means that the knowledge of two independent properties lead
to determine the others properties of the system that
characterize in that state.

 The state postulate requires that the two properties specified be
independent to fix the state.
 Two properties are independent if one property can be varied while the
other one is held constant.
 Temperature and Specific Volume, for example, are always independent
properties, and together they can fix the state of a simple compressible
system.
 Temperature and Pressure, however, are independent properties for
single-phase systems, but are dependent properties for multiphase systems.

 Any operation in which one or more of the
properties of a system changes is called a
change of state.
 The succession of states passed through
during a change of state is called the path of
the change of state.
 When the path is completely specified, the
change of state is called a process.

 A thermodynamic cycle is defined as series of
state of changes such that the final state is
identical with the initial state.
 A system consisting of a single phase is called
homogeneous system, while a system consisting
of more than one phase is known as a
heterogeneous system.

Homogeneity in physical structure means that the matter is all solid, liquid
or vapor. One system can contain more than one phase, and
Chemical homogeneity means that the chemical composition of the system
is invariable

Quasi-static or Quasi-EquilibriumProcess
 When a process proceeds in such a manner that
the system remains infinitesimally close to an
equilibrium state at all times.
 It can be viewed as a sufficiently slow process
that allows the system to adjust itself internally
so that properties in one part of the system do
not change any faster than those at other parts.

If the piston is moved slowly, the molecules will have sufficient time to
redistribute and there will not be a molecule pileup in front of the piston. As
a result, the pressure inside the cylinder will always be nearly uniform and
will rise at the same rate at all locations. Since equilibrium is maintained
at all times, this is a quasi-equilibrium process.

When a gas in a piston-cylinder device is compressed suddenly, the molecules
near the face of the piston will not have enough time to escape and they
will have to pile up in a small region in front of the piston, thus creating a
high-pressure region there.  Because of this pressure difference, the
system can no longer be said to be in equilibrium, and this makes the entire
process nonquasi equilibrium.

WHY Quasi-equilibrium process ?
 First, they are easy to analyze;
 Second work-producing devices deliver the
most work when they operate on quasi-
equilibrium processes. Therefore, quasi-
equilibrium processes serve as standards to
which actual processes can be compared.
 A non quasi-equilibrium process is denoted by
a dashed line between the initial and final states
instead of a solid line.

 Steady implies no change
with time. The opposite of
steady is unsteady, or
transient.
 Uniform, however, implies no
change with location over a
specified region.

Processes involving such devices can be represented reasonably well
by a somewhat idealized process, called the steady-flow process,
 which can be defined as a process during which a fluid
flows through a control volume steadily.
That is, the fluid properties can change from point to point within
the control volume, but at any fixed point they remain the same
during the entire process. Therefore, the volume V, the mass m, and
the total energy content E of the control volume remain constant
during a steady flow process.

 Any physical property can be characterized by dimensions.
 The magnitudes assigned to the dimensions are called units.
 Some basic dimensions such as mass m, length L, time t, and temperature T
are selected as primary or fundamental dimensions,
 while others such as velocity V, energy E, and volume V are expressed in
terms of the primary dimensions and are called secondary dimensions, or
derived dimensions.

2
1
1
s
m
kg
N
a
m
F




FORCE UNIT: newton (N)
Pa
m
N
s
m
kg
m
s
m
kg
A
F
P 





 2
2
2
2
PRESSUREUNIT: PASCAL
J
m
N
s
m
kg
m
s
m
kg
x
a
m
x
F
W 













 2
2
2

Factor Prefix Symbol Factor Prefix Symbol
1012 Tera T 10-2 centi c
109 Giga G 10-3 mili m
106 Mega M 10-6 micro 
103 Kilo k 10-9 nano n
102 Hecto h 10-12 pico p
PREFIXES

 Mass : Pound mass (lbm)
 Length: Foot (ft)
 Time: Second (s)
 Temperature: Rankine (oR)
Metric
 Simple & Logical
 Various units are related based on
decimal r/nship
 Is being used for scientific and
engineering work in indurialized
nations including England
English Units System
 Has no apparent systematic
numerical base
 Various units are related to each other
rather arbitrarily
 Confusing & difficult to learn
 Used in US

Dimensions SI English Unit System
Mass Kilogram(kg) Pound mass (lbm)
Length Meter (m) Foot (ft)
Time Second (s) Second (s)
Temperature Kelvin (K) Rankine (oR)
1lbm = 0.45359 kg
1ft = 0.3048 m

lbf
s
ft
lbm
a
m
F 


 2
174
.
32
.
Is defined as the force required to accelerate a mass of one pound mass at
a rate of 32.174 feet per second squared
ft
lbf
W
x
F
W
a
m
F
.
and







N
lbf
kg
lbm
ft
m
448
.
4
1
453593
.
0
1
281
.
3
1



J
356
.
1
1 
 ft
lbf

BTU.- British Thermal Unit: It is the quantity of heat required to
increase the temperature of 1 pound mass of water in one Fahrenheit at
68 oF
Cal.-Calorie: It is the quantity of heat required to increase the
temperature of 1 gram of water in one degree Celsius at 14.5 oC
kcal.-Kilo calorie: It is the quantity of heat required to increase the
temperature of 1 kilogram of water in one degree Celsius at 14.5 oC

cal
BTU
J
ft
lbf
J
kcal
J
BTU
ft
lbf
BTU
252
1
356
.
1
1
4182
1
1055
1
16
.
778
1








 Density: (kg/m3), (lbm/ft3) Is the inverse of the specific
volume, is the mass per unit volume.
 Specific Volume: v(m3/kg), (ft3/lbm). Is defined as
volume per unit mass.
v
1



 The Specific Gravity - SG - is a dimensionless unit defined as the
ratio of density of the material to the density of water at a specified
temperature. Can be expressed as the density of a substance relative
to the known density of the other, usually the density of water at 4
oC.
It is widely used in the Oil Industry.
  C
O
H
S SG



4
2




 Pressure is the force exerted by the fluid per unit of area.
 The Thermodynamic Property is the Absolute Pressure measured
relative to absolute zero pressure.
 As the pressure is a primary property it can be measured.
 The instrument used to measure the pressure is a manometer. A
manometer measures a gage pressure, or vacuum not the absolute
pressure.
Pa
m
N
A
F
P 

 2

zero absolute pressure level
Atmospheric pressure level
Gage pressure
Absolute pressure 2
vacuum
Absolute pressure2
Patm
Pabs
Pm
Pv
Pabs
pressure)
(vacuum
pressure
c
atmospheri
the
below
is
P
pressure
the
if
-
pressure)
(gage
pressure
c
atmospheri
the
above
is
P
pressure
the
if


 P
P
P atm
abs

C
0
at
Hg
mm
760
bar
01325
.
1
cm
kgf
1.0332
Pa
10
01325
.
1
F
32
at
Hg
92
,
29
1
in
lbf
696
,
14
:
to
equal
is
(1atm)
atmosphere
standard
1
2
5
2




in
psi

 It is a very important Thermodynamic
property that is the measure the average
kinetic energy of the particles of a
substance or body, is a measure of the
thermal equilibrium.
 The temperature difference between two
point of the system causes the heat transfer
until the equilibrium state is achieved
 The temperature difference between the
system and the environment causes the heat
transfer exchange
The temperature of an ideal monatomic gas is a
measure related to the average kinetic energy of its
atoms as they move. In this animation, the size of
helium atoms relative to their spacing is shown to
scale under 1950 atmospheres of pressure. These
room-temperature atoms have a certain, average
speed (slowed down here two trillion fold).

 If one body is in thermal equilibrium, with a second and is in
thermal equilibrium with a third then the second and the third
are in thermal equilibrium too.
T1 T1
A B
T1
A C
T1
If and then
T1
B C
T1

 Temperature scale like Celsius and Fahrenheit use
the ice point and boiling point of water.
 Celsius proposed temperatures of 0 oC and100 oC .
 Fahrenheit scale the ice point and the boiling point of
water read about 32 and 212 respectively at standard
normal pressure.

Where measurements are made in SI units, thermodynamic temperature is measured in
kelvins (symbol: K).
By international agreement, the unit “kelvin” and its scale are defined by two points:
absolute zero, and the triple point of Vienna Standard Mean Ocean Water (water with a
specified blend of hydrogen and oxygen isotopes).
 Absolute zero—the coldest possible temperature—is defined as being precisely 0 K
and −273.15 °C.
 The triple point of water is defined as being precisely 273.16 K and 0.01 °C. This
definition does three things:

This definition does three things:
 It fixes the magnitude of the kelvin unit as being precisely 1 part in 273.16
parts the difference between absolute zero and the triple point of water.
 It establishes that one kelvin has precisely the same magnitude as a one-
degree increment on the Celsius scale; &
 It establishes the difference between the two scales’ null points as being
precisely 273.15 kelvins (0 K = −273.15 °C and 273.16 K = 0.01 °C).

William John Macquorn Rankine FRS (5 July 1820 – 24 December 1872) was
a Scottish engineer and physicist. He was a founding contributor, with Rudolf
Clausius and William Thomson (1st Baron Kelvin), to the science of
thermodynamics. Rankine developed a complete theory of the steam engine
and indeed of all heat engines. His manuals of engineering science and
practice were used for many decades after their publication in the 1850s and
1860s. He published several hundred papers and notes on science and
engineering topics, from 1840 onwards, and his interests were extremely
varied, including, in his youth, botany, music theory and number theory, and,
in his mature years, most major branches of science, mathematics and
engineering. He was an enthusiastic amateur singer, pianist and cellist who
composed his own humorous songs. He was born in Edinburgh and died in
Glasgow

 Rankine is a thermodynamic (absolute) temperature scale named after the British
engineer and physicist William John Macquorn Rankine, who proposed it in 1859.
 The symbol is R .Occasionally this is written °R, but as with the Kelvin scale the
usage of the degree symbol is incorrect.
 Zero on both the Kelvin and Rankine scales is absolute zero, but the Rankine
degree is defined as equal to one degree Fahrenheit, rather than the one degree
Celsius used by the Kelvin scale.
 A temperature of -459.67 °F is exactly equal to 0 R.

From Rankine To Rankine
Celsius [°C] = ([R] − 491.67) × 5⁄9 [R] = ([°C] + 273.15) × 9⁄5
Fahrenheit [°F] = [R] − 459.67 [R] = [°F] + 459.67
Kelvin [K] = [R] × 5⁄9 [R] = [K] × 9⁄5
For temperature intervals rather than specific temperatures,
1 R = 1 °F = 5⁄9 °C = 5⁄9 K

From Kelvin To Kelvin
Celsius [°C] = [K] − 273.15 [K] = [°C] + 273.15
Fahrenheit [°F] = [K] × 9⁄5 − 459.67 [K] = ([°F] + 459.67) × 5⁄9
For temperature intervals rather than specific temperatures,
T=1 K = 1 °C = 1.8 °F = 1.8 °R

 The temperature is usually determined by indirect
measurement using its effects on substances.

chapter one: Introduction to Thermodynamics

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chapter one: Introduction to Thermodynamics