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Chapter One
Introduction and Basic Concepts
Sep. 11 - 13, 2012
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Objectives
Identify the unique vocabulary associated with
thermodynamics through the precise definition of basic
concepts to form a sound foundation for the development
of the principles of thermodynamics.
Review the metric SI and the English unit systems.
Explain the basic concepts of thermodynamics such as
system, state, state postulate, equilibrium, process, and
cycle.
Review concepts of temperature, temperature scales,
pressure, and absolute and gage pressure.
Introduce an intuitive systematic problem-solving
technique.
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1.1 Thermodynamics and Energy
Thermodynamics can be defined as the scienceof energy.
The name thermodynamicsstems from the Greek wordstherme (heat) and dynamis (power).
The conservation of energy (the first law)
-Energycannot be created or destroyed; it can only
change forms
-Energyis a thermodynamic property.
Energy has quality as well as quantity (the second law),
and actual processes occur in the direction of decreasing
quality of energy.3
1.1 Thermodynamics and Energy
Classical thermodynamics: The macroscopic approach to
study of thermodynamics that does not required a
knowledge of the behavior of individual particles.
Statistical thermodynamic: A more elaborate approach,
based on the average behavior of large groups of
individual particles.
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1-1() 1-2
1.1
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1-3(the second law)
1.1
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1-4
1.1
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1-5
1.1
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1.2 Dimensions and Units()
Dimension: Any physical quantity
Primary or fundamental dimension:
- mass m, lengthL, time t, temperature T, etc
Second or derived dimension:
-velocity v, energyE, volume V, force F, etc.
Units: The arbitrary magnitudes assigned to thedimensions
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SI units: (system international)
Length m; Electric current A (Ampere)
Mass kg; Amount of light cd (candela)
Time s; Amount of matter mole
Temperature K(Kelvin) or
C (Celsius)
EI units: (English units)
Length ft;Pound mass lbm;
Time s;
Temperature R (Rankine)or
F (Fahrenheit)
1.2 Dimensions and Units
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Force (F) = ma = (Mass) (Acceleration)
1N(Newton) = 1 kg m/s2
1 lbf = 32.174 lbmft/s2
Weight (W) = mg = (Mass) (Local gravitational acceleration)
g= 9.807 m/s2;
= 32.174 ft/s2;
Work = (Force) (Distance)
1 J (joule)= 1 Nm
Energy: Cal; Btu
1.2 Dimensions and Units
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Energy: Cal; Btu
Calorie (Cal):
The amount of energy needed to raise the temperatureof 1g of water at 15 C by 1 C.
British thermal unit (Btu):
The energy required to raise the temperature of 1 lbmof water at 68 F by 1 F.
Dimensional Homogeneity:All the terms in an equation must have the same unit
1.2 Dimensions and Units
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1-7
1N = 1 kg x 1 m/s 2
1kgf= 1 kg x 9.807 m/s2
1lbf = 1 slug x 1 ft/s2
= 32.174 lbmx 1 ft/s2
= 1 lbmx 32.174 ft/s2
1.2
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1-9 150
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() =x g (gravity)
1 kgf= 1 kg x 9.807 m/s2
1 lbf = 1 lbmx 32.174 ft/s2
1.2
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1-10
1.2
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Ex 1: pV = mRT P: N/m2; V: m3; m: kg; R=Ru/M; T: K
Ru=8.31434 kJ/kmolK; M=kg/kmol
1 J (joule) = 1 N x 1 m
)().()()()( KTkmol
kgM
Kkmol
kJRkgmmV
m
Np
31483
2
smKkg
kmol
Kkmol
mN
N
s
mkg
RTga c
/..
..
?../..
8348300728
103148141
03113007283148141
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Dimensional Homogeneity:
All the terms in an equation must have the same unit
Ex 2: sonic speed RTga c
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1.3 Systems ()
System ():
A quantity of matter or a region in space chose n for
study
Surrounding or Environment ():
Everything external to the system
Boundary():
The real or imaginary surfaces that separate the systemfrom its surroundings.
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1-19 (system)(surrounding or environment)(boundary)
1.3
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The definition of systems
A fixed quantity of mass (control mass ()) or
- Closed system (())(a specified amount of mass, no flow of
matter)and
A control volume () or
- Open system()(a specified region in space, open to the flowof matter)
*Isolated system(one that is not influenced in anyway by surroundings)
*Adiabatic system (one that is without heat transfer by surroundings)
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1-20
1-21
1.3()
20
(control volume)
1.3()
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1-22
1.3()
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1.4 Properties of a System
()
Property ():Any observable characteristic of a system
- properties (Characteristics)
P, T, V (measurable) viscosity, thermal conductivity,
U, S, H (un-measurable)
Extensive Properties ():depend on mass, size
(i.e. volume, m ass, energy, S, Availability)
Intensive Properties ():independent of the size of a system ( i.e.T, P, density, height)
Specific properties: extensive properties/total mass or moles
(i.e. specific volume, specific energy, specific entropy)
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1-24(intensive)(extensive)
(intensive property)
(extensive property)
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Continuum:
- Matter is made up of atoms, view it as a continuous,homogeneous matter with no holes.
- To treat properties as point function, and to assume
the properties to vary continually in space with no
jump discontinuities.
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1-25 (continuum)
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Properties in macroscopic thermodynamics
m
lim0
Density,
Molecular and atomicMolecular and atomic
effects are importanteffects are important
Limit of the macroscopicLimit of the macroscopicmodel and assumptions.model and assumptions.
(m3)
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1.5 Density and Specific Gravity
Density : mass per unit volume, = m/V
Specific volume:volume per unit mass
Specific volume= V/M
Specific gravity:The ratio of the density of a s ubstance to
the density of some standard substance at a specified
temperature (usually water at 4 C, for which H2O= 1000
kg/m3
).SG =/H2O
Specific weight: The weight of a unit volume of a substance.
Specific weight s=g
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1.6 State and Equilibrium (
)
State ():
The state of a system is described by its properties, a description of
the system.
- For a simple compressible system:
The state postulaterequires - the state of a simple compressible
system is completely specified by two independent, intensive
properties.
or - two properties be specified independent to fix the state
Equilibrium ():
A state of balance in
- thermal equilibrium: T - mechanical equilibrium: P
- phase equilibrium: m - chemical equilibrium: t
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(a)1 (b)2
1-27
(a) (b)
1-28
1.6
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Phase Rule (no chemical reaction)
F=C-P+2
-F : # of intensive (internal) properties need to fix the
state of the system- C: # of components
-P: # of phases
Nitrogen gas F=2 (C=1,P=1)
Un-saturated water F=1 (C=1,P=2)
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(State Postulate):
1-29( Tand v)
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1.7 Processes and Cycles ()
Process: The sequence of states which a system passes in
going from one equilibrium stateto another
Path:A system passes during a pr ocess
Quasi-state process:
The system remains infinitesimally close to an
equilibrium state at all times
Cycle:Process in which the final state is identical to the
initial value
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1-3012(process)(path)
1.7
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(b) ()
1-31(quasi-equilibrium)(non-quasi-equilibrium)
1.7
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1-32P-V
1.7
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1.7 Processes and Cycles
Some Special Processes:
- Isothermal Process: T is constant
- Isobaric Process:P is constant
- Isochoric or isometric Process:
specific volume is constant
- Steady-flow Process (for open system only):
A process during which a fluid flows through a control
volume steadily (time independent).
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1-33(steady-flow)
1-34
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1.8 Temperature and the Zeroth Law
Temperature:
A measure of hotness or coldness
Thermodynamic Temperature Scale:- Celsius scale, C
- Fahrenheit scale, F
- Kelvin scale, K
- Rankine scale, R
- Ideal gas temperature scale, K
Constant-volume gas thermometer
At low pressure, the temperature of a gas is pro portionalto its pressure at constant volume.
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1-35
1.8
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1-36P-T
1.8
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1-37-273.15
1.8
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1-38,39
1.8
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Zeroth Law
- The internal properties of a system are
functionally related
- If two bodies are in thermal equilibrium with a
third body, they are also in thermal equilibrium
with each other.
T1=T2, T2=T3, we have T1=T3
- in 1931, by R. H. Fowler
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1.9 Pressure (
)
is defined as the force exerted by a fluid per unitarea, F/A.
Units:
- 1 pascal (Pa) = 1 N/m2
-1 bar = 100 kPa
- 1 psi = 1 lbf/in2
- 1 atm = 76 cm-Hg (standard atmospheric pressure)
- 1 atm = 101,325 Pa = 1.01325 bar
- 1 kgf/cm2(kg/cm2)= 0.96788atm = 14.223psi
- 1 atm = 14.696 psi
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1-40()
1.9
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1.9 Pressure
Absolute Pressure:
The actual pressure at a given position and it is measuredrelative to absolute vacuum
Gage Pressure:
The difference between the absolute pressure and thelocal atmospheric pressure (measured)
Pgage= PabsPatm(P above Patm)
Vacuum Pressure:Pressure below atmospheric pre ssure
Pvac= PatmPabs(P below Patm)
471-41, 42
1.9
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1.9 Pressure
Variation of pressure with depth,
or P = Patm+gh; : liquid density
1-43()
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1-44
zzgPPP
12
2
112 gdzPPP
For constant
1.9
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1-45
1.9
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1-47()
1.9
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1.9 Pressure
Pascals principle:
The pressure applied to a confined fluid increases the
pressure throughout by the same amount,
P1=P2; and F1/A1=F2/A2
P1= P2; a small height difference is negligible
at high pressure
1-48
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1.10 The Manometer (
)
Manometer:
A fluid column can be used to measure press ure
Pressure variations (as shown in previous)
- The pressure change across a fluid column of height is P =gh
- Pressure increases downward in a given fluid and
decreases upward. Pbottom > Ptop
- Two points at the same elevationin a continuous fluidat restare at the same pressure.
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1-501-61-49
P1= P2
1.10
Example 1-6
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1-51hgh
1.10
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1-52
PA= PB
1.10
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1-531-7
1.10
Example 1-7
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Other pressure measurement devices
Bourdon tube:
It consists of a hollow metal tubebent like a hook whose end is closed andconnected to a dial indicator needle.
Pressure tr ansducer:
It is made of semiconductor materials such as silicon and convert the pressure effectto an electrical effectsuch as a change in voltage, resistance, orcapacitance.
Gage pressure transducer:
The atmosphericpressure as a reference
Absolute pressure transducer:
It is calibrated to have azerosignal output at full vacuum.
Differential pressure transducer:
Measure the pressure difference between two locations directly instead of using twopressure transducers and taking their difference.
Piezoelectric effect:
The emergence of an electric potential in a crystalline substancewhen subjected tomechanical pressure.
Strain-gage pressure transducer:
The sensors of such transducers are made of thin metal wiresorfoilwhose electricalresistance changes when strained under the influence of fluid pressure .
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1-54
1.10
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1.11 Barometer and Atmospheric Pressure
(
)
Barometer:
A device is used to measure the atmosp heric pressure- Patm=gh; :density
- Torr: The unit mmHg
1 atm = 760 torr; and 1 torr = 133.3Pa
Atmospheric Pressure
The atmospheric pressure changes not only withelevation but also with weather conditions.
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1-551-56
1.11
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1-57
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1-581-9
Example 1-9
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1.12 Problem-solving technique
Step 1:Problem statement
Step 2:Schematic
Step 3:Assumptions
Step 4:Physics laws
Step 5:Properties
Step 6:Calculation Step 7:Reasoning, verification, and discussion
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1.12
1-62
1.12
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1.12
671-67
1.12
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10, 15, 28, 40, 49, 54, 63, 74, 82, 92, 104, 110
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