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Overview of Course
• Conservation of mass
• Conservation of momentum
• Conservation of energy
• Laws of Thermodynamics (includes Conservation of Energy)
• Equation of state
• Property tables and charts
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Problems in this course are solved using the above
Conservation of Mass
• Empedocles (c. 490 - 430 BC)
For it is impossible for anything to come to be from what is not, and it
cannot be brought about or heard of that what is should be utterly
destroyed.
• A similar concept was expressed by the Persian Muslim scholar Nasr
al-Dn Tus (5 Esfand 579 11 Tir 653)1
A body of matter cannot disappear completely. It only changes its
form, condition, composition, color and other properties and turns
into a di erent complex or elementary matter.
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February 1201 to 2 July 1274 (Gregorian calendar)
Conservation of Momentum
• Pur Sna (1 Shahrivar 359 31 Khordad 416) 2
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The Persian polymath3 proposed that the motion of a projectile was
the consequence of an impulse imparted to the projectile by the
thrower, and that such motion would not cease in a vacuum, but
would be dissipated by external forces such as air resistance
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August 980 to 21 June 1037
known as Ibn Sna. The Latinized version of the name is Avicenna. He was the author
of 450 works, including 150 on philosophy and 40 on medicine. He is a central character in the
historical novel The Physician, by Noah Gordon, published in 1986 and later adapted for a
screenplay premiered in 2013. The r le of Pur Sna was portrayed by Sir Ben Kingsley.
3Also
Conservation of Momentum
• Isaac Newton (1642 - 1727)
Proposed three fundamental laws of mechanics in Philosophi
Naturalis Principia Mathematica (Mathematical Principles of Natural
Philosophy)
First Law (the Law of Inertia): In the absence of a net external force,
an object at rest remains at rest and an object in uniform motion
remains in uniform motion as observed in an inertial frame of
reference
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Second Law (the Conservation of Momentum): The time rate of
change of momentum of an object (de ned as the product of its mass
and velocity as viewed in an inertial frame of reference) is equal to
the net external force on the object
Third Law (the Law of Reactions: The force of object A on object B is
equal and opposite to the force of object B on object A
Conservation of Energy (First Law of
Thermodynamics)
• Gottfried Wilhelm von Leibniz (1646-1716)
Proposed the concept of conservation of mechanical energy. Given a
system of n individual masses mi each with speed ci, a quantity denoted
V vis viva (living force) was conserved V = Pii==n1mici2. This is now
recognized as twice the mechanical energy of the system.
• James Prescott Joule (1818-1889)
Proposed the mechanical equivalent of heat in a series of experiments
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• Hermann von Helmholtz (1821-1894)
Pstulated a uni ed concept of conservation of energy in the
framework of mechanics, heat, light, electricity, and magnetism
(First Law of Thermodynamics)
Second Law of Thermodynamics
• Nicolas LØonard Sadi Carnot (1796-1832)
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Presented the theory of the maximum e ciency of heat engines later
known as the Carnot cycle1
• Rudolf Clausius (1822-1888)
First postulated the basic concept of the Second Law of
Thermodynamics in 1850. In 1854 he summarized the concept by
stating Heat can never pass from a colder to a warmer body without
some other change, connected therewith, occurring at the same time
1 In modern terms, it states that the maximum rate of conversion of heat Q to work W
H
due to an engine operating reversibly (quasi-statically) between two in nite heat reservoirs
with temperatures TH and Tc (TH > TC) is W/QH = (TH − TC)/TH.
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Second Law of Thermodynamics
• Lord Kelvin (William Thompson, 1824-1907)
Postulated an equivalent statement: It is impossible, by means of
inanimate material agency, to derive mechanical e ect from any
portion of matter by cooling it below the temperature of the coldest
of the surrounding objects
• Max Planck (1858-1947)
O ered an equivalent statement of the Second Law as It is impossible
to construct an engine which will work in a complete cycle, and
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produce no e ect except the raising of a weight and cooling of a heat
reservoir
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Fundamental Units
• All physical processes involve units
• The fundamental units in the SI system are
Dimension
Unit
Length
meter (m)
Mass
kilogram (kg)
Time
second (s)
Temperature
kelvin (K)
Electric current
ampere (A)
Amount of light
candela (cd)
Amount of matter mole (mol)
• The fundamental units in the English system are
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Fundamental Units
Dimension
Unit
Length
Mass
Time
Temperature
Electric current
foot (ft)
slug (slug)
second (s)
rankine (R)
ampere (A)
• The fundamental units can be converted between English and SI
1 foot
1 slug
1 deg R
=
=
=
0.3048 meters
14.5939029 kilograms
0.55556 deg K
• Derived units
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Fundamental Units
Unit
English
SI
Force
Energy
Power
pound force (lbf)
British Thermal Unit (BTU)
Horsepower (HP)
Newton (Nt)
Joule (J)
Watt (W)
• Derived units can be converted between English and SI
1 lbf = 4.44822162 Nt
1 BTU = 1055.05585 J
1 HP = 745.699872 W
• What is pound mass (lbm) ?
One lbm is the amount of mass that weighs one lbf on earth
• Since weight is the force of gravity on an object
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Fundamental Units
weight =
1 lbf =
1 · slug·ft/s2 =
1 lbm · gravity
1 lbm · 32.17 ft/s2
1 lbm · 32.17 ft/s2
and therefore
.
• The di erences between lbm and lbf and slug are important
• Failure to understand the di erences can lead to an error of nearly
two orders of magnitude and thus ...
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Fundamental Units
• The di erences between lbm and lbf and slug are important
• Failure to understand the di erences can lead to an error of nearly
two orders of magnitude and thus ...
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Fundamental Units
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Systems and Control Volumes
• A system is a quantity of matter or region of space
• A closed system comprises a
xed amount of mass
• An open system is a properly selected region of space
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Closed system
Closed system
Open system
moving boundary
State and Equilibrium
• Thermodynamics deals with equilibrium states
• An equilibrium state represents a condition wherein there are no
unbalanced forces or potentials in the system
• Thermal equilibrium implies that the temperature is the same
throughout the system
• Mechanical equilibrium implies that the net forces and moments on
the system are zero
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• Phase equilibrium implies that the mass of each phase (e.g., solid,
liquid and gas) remains constant
• Chemical equilibrium implies that the chemical composition of the
system remains constant
State Postulate
• Once a su
cient number of properties of a system are speci ed,
the remaining properties can be determined • As an example,
consider the ideal gas equation
pV = nRT
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For a given volume V, knowing the pressure p, and temperature T is
su cient to determine2 the number of moles n
• The State Postulate
The state of a simple compressible system
is completely speci ed by two
independent, intensive properties
Processes and Cycles
• The change of a system from one state to another is a process
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R = 8.31447 kJ/kmole·K is the Universal Gas Constant
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• The series of states through which a system passes from its initial to
nal state is the path
• The path may be quasi-equilibrium or non-equilibrium
Processes
p−V diagram
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Steady Flow Processes
• During a steady ow process, the ow variables at a xed location do not
change in time; however, they may change with position
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Zeroth Law of Thermodynamics
• Two bodies in thermal equilibrium with a third body are in thermal
equilibrium with each other (i.e., all have the same temperature)
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