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King Fahd University ofPetroleum & Minerals
Mechanical EngineeringThermodynamics ME 203
BYDr. Esmail Mokheimer
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Outline Textbook
Catalog Description Grading system
Homework
Attendance Exams
What thermodynamics
Topics to be covered during the course
Application Areas of Thermal-Fluid Sciences
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Grading System
-0.5% Attendance(For unexcused absence, 0.5 mark will be deducted)
10% Homework Assignments
40% Exams and Quizzes
20% Mid Term Exam
30% Final Exam (Comprehensive)
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Homework
Homework problems are 5 problemsevery week.
All homework problems assigned duringa given week are due in class one weeklater unless stated otherwise.
Late Homework will not be accepted
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Attendance
1. Attendance will be checked during eachlecture.
2. Excuse should be authorized by the Deanship
of Student Affairs and submitted one week laterafter resumption of class attendance.
3. For any unexcused absence, 0.5 marks will be
deducted from the attendance grade.
4. Any student having more then 9 unexcused
absences will receive a grade of DN for the
course.
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Office Hours
Office Hours: 12:001:00 pm SUMTW
Location: Building 22 Room # 218 Phone 860-2959
email: [email protected]
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Basic Concepts
of
Thermodynamics
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Power plants
The human bodyAir-conditioning
systemsAirplanes
Car radiatorsRefrigeration systems
Application Areas of Thermal-FluidSciences
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Thermodynamics
Thermodynamics (from the
Greek words therme(heat)and dynamis(power)), isthe science that primarilydeals with energy.
The first law ofthermodynamicsis simplyan expression of theconservation of energyprinciple, and it assertsthat energy is a
thermodynamic property.
Energy cannot be createdor destroyed; it can onlychange forms (the first
law).
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Thermodynamics (continued)The second law ofthermodynamicsasserts thatenergy has quality as well asquantity, and actualprocesses occur in the
direction of decreasingquality of energy.
For example, a cup of hotcoffee left on a table
eventually cools to roomtemperature, but a cup ofcool coffee in the same roomnever gets hot by itself.
Heat flows in thedirection ofdecreasing
temperature.
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Heat Transfer
Temperature difference
is the driving force forheat transfer. The largerthe temperaturedifference, the higher is
the rate of heat transfer.
Thermodynamicsdeals with
equilibrium states and changesfrom one equilibrium state toanother.
Heat transfer, deals with
systems lacking thermalequilibrium, and thus it is a non-equilibrium phenomenon.
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Dimensions and Units
The sevenfundamentaldimensions and
their units in SI(International
System).
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Dimensions and Units
SI British System Conversion
Length Meter (m) Foot (ft) 1 ft = 0.3048 m
Time Second (s) Second (s)
Mass Kg
SlugPound mass (lbm)1 slug = 32.2 lbm
1 slug =14.59 kg1 lbm = 0.4536 kg
ForceNewton (N)
1 N = (1Kg).(1 m/s2)Pound force (lbf)
1 lbf = (1 slug)(1. ft/s2) 1 lbf = 4.448 N
Definitionof
Unit force
Newton (N): is the forcerequired to give a mass of1 kg an acceleration of 1
m/s2.
Pound force (lbf) is the forcerequired to give a mass of 1slug an acceleration of 1 ft/s2.
C = (5/9)*(F 32)
R = (9/5)*K
Tempe-rature
Degree Celsius.(C)Absolute Temp.: Kelvin (K).
K = C + 273.15
Degree Fahrenheit (F)
Absolute Temp.: Rankine (R)
R = F + 459.67
C = (5/9)*(F 32)
R = (9/5)*K
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Closed SystemsA closed system (orsimply a system), or a
control mass, isdefined as a quantity ofmatter or a region in
space chosen forstudy. The mass orregion outside thesystem is called the
surroundings.
The real or imaginary surface
that separates the systemfrom its surroundings iscalled the boundary.
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Closed Systems
No mass can cross itsboundary But energy can.
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Closed Systems with movingboundary
Consider the piston-
cylinder device shown inthe Figure. Let us say thatwe would like to find out
what happens to theenclosed gas when it isheated. Gas is oursystem. Since no mass is
crossing the boundary,therefore, it is still aclosed systembut with a
moving boundary
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Closed Systems vs open systems
Closed SystemOpen System
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Open SystemsAn open system, or acontrol volume, is aproperly selectedregion in space.
Both mass andenergy can cross theboundaries of acontrol volume.
It usually encloses a device that involves mass flowsuch as a compressor, turbine, or nozzle. Flowthrough these devices is best studied by selecting
the region within the device as the control volume.
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Open Systems (continued)
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Approaches
Macroscopic Approach (Classical Thermodynamics)
Microscopic Approach (Statistical Thermodynamics)
- is concerned with the overall behavior of a system- no model of the structure of matter at the molecular, atomic,
and subatomic level is directly use
- is concerned directly with the structure of matter
- characterize, by statistical means, the average behavior ofthe particles making up a system of interest and relate thisinformation to the observed macroscopic behavior of thesystem
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Properties of a System
Not all properties are
independent. Density is adependent property onpressure and
temperature.
Any characteristic of a
system is called a property.Some familiar properties arepressure P, temperature T,volume V, and mass m.
Properties describe the stateof a system only when thesystem is in an equilibrium
state.
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Density as a property
Density is mass per unit
volume;
= mass/volume (kg/m3)
Specific volume is volumeper unit mass.
= Volume/mass, (m3/kg)
= 1/
T
Liquids
Water
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Extensive and Intensive PropertiesIntensiveproperties are thosethat are independent of the size
of system, such as temperature,pressure, and density.
Extensiveproperties are
dependent on the size (or extent)of the system. Mass m, volume V,and total energy Eare someexamples of extensive
properties.
Criteria to differentiate extensiveand intensive properties are
illustrated in the Figure.
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State and Equilibrium
A state is defined as acondition of a substance that
can be described by certainobservable macroscopic
properties. (T, P, , etc.)
In above figure, the systemdoes not undergo anychange. All properties can bemeasured throughout the
system. Hence the conditionof the system is completelydescribed. This condition iscalled state 1.
Now remove some weights. Ifthe value of even one propertychanges, then the state willchange to different one (state
2).
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State and Equilibrium
Thermodynamics deals with equilibrium states.
The word equilibriumimplies a state of balance.
Equilibrium state means that there are no
unbalanced potentials (or driving forces) withinthe system.
A system is said to be in thermodynamicequilibriumif it maintains thermal, mechanical,phase, and chemical equilibrium.
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Thermal Equilibrium
Thermal equilibrium that there is no temperature
differential through the system.
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Mechanical Equilibrium
Mechanical equilibrium means that there is
no change in pressure in the system.
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Phase Equilibrium
Phase equilibrium means that the mass of each
phase reaches an equilibrium level and stays there.
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Chemical Equilibrium
Chemical equilibrium means that the chemical
composition of the system does not change withtime
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State Postulate: The state of asimple, compressible systemis completely specified by twoindependent, intensiveproperties.
The State Postulate
A system is called a simple,compressible system in the absence
of electrical, magnetic, gravitational,motion and surface tension effects
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Temperature and specific volume,for example, are always independent
properties, and together they can fixthe state of a simple compressiblesystem.
Temperature and pressure, however,are independent properties forsingle-phase systems, but are
dependent properties for multiphasesystems.
The State Postulate (continued)
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Processes and Cycles
Any change from one state toanother is called a process.
Process diagrams are very usefulin visualizing the processes.
The series of states through whicha system passes during a process iscalled a path
A process with identical end statesis called a cycle
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Processes and Cycles
Isothermal process means a process at constant T.
Isobaric process means a process at constant pressureIsochoric process means a process at constant volume
Any change from one state toanother is called a process.
Process diagrams plotted byemploying thermodynamic
properties as coordinates arevery useful in visualizing theprocesses.
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Quasi-Equilibrium process
Compression is very slow andthus equilibrium is attained at
any intermediate state.Therefore, the intermediatestates can be determined andprocess path can be drawn.
During a quasi-staticor quasi-equilibriumprocess, the
system remains practically inequilibrium at all times. Work-producing devices operating ina quasi-equilibriummanner
deliver the most work.
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Quasi-Equilibrium process (continued)
It is an idealized process
but many process canapproach it with negligibleerror.
Quasi-Equilibrium, Work-Producing Devices Deliver
the Most Work
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Non-Quasi-Equilibrium process
Compression
process is fast andthus equilibrium cannot be attained.
Intermediate statescan not bedetermined and theprocess path can not
be defined. Insteadwe represent it asdashed line.
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Forms of Energy
In absence of magnetic, electric, and surface tensioneffects, the total energy of a system consists of the kinetic,
potential, and internal energies and is expressed as
The change in the total energy Eof a stationary system(closed system) is identical to the change in its internal
energy U.
(kJ/kg)2
basismassunitaonor,
(kJ),
2
(kJ),
2
2
gzv
upekeue
mgzmv
mume
PEKEUE
++=++=
++=
++=
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Forms of Energy (continued)
The portion of the internal energyof a system associated with the kinetic energies of the moleculesis called the sensibleenergy. phase of a system is called the
latentenergy. atomic bonds in a molecule iscalled chemicalenergy. strong bonds within the nucleusof the atom itself is called nuclearenergy.
kgkJeU /1073.610
235=
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Temperature and the Zeroth Law of
Thermodynamics
The zeroth law ofthermodynamicsstatesthat: If two bodies are inthermal equilibrium withthe third body, they are
also in thermalequilibrium with eachother, as shown in the
Figure (right).The equality of
temperature is theonly requirement for
thermal equilibrium.
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Temperature scales( ) ( )
( ) ( )( ) ( )( ) ( )
( ) ( )( ) ( )FTRT
CTKT
CTFT
KTRTFTRT
CTKT
o
o
oo
o
o
=
=
+=
=+=
+=
328.1
8.1
67.
459
15.273
Note: it makes no difference to use K orC in formulas involving temperaturedifference. However, you should useAbsolute temperature in formulasinvolving temperature only like the ideal
gas low.
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Pressure
Pressure is defined as the force exerted by a fluidper unit area.
Units in SI are Pa=N/m2. The pressure unit Pascal istoo small for pressure encountered in practice.
Therefore, kPa and MPa are commonly used.
Units in British are : psf = lbf/ft2, psi = lbf/in2
You have to convert from psi to psf ( 144 in2 = 1 ft2)
psibarskPaPaatm
kPaMPaPabar
696.1401325.1325.101325,1011
1001.0101 5
====
===
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Pressure(continued)
Absolute pressure, ismeasured relative to
absolute vacuum (i.e.,absolute zero pressure.)
Gauge pressure, ismeasured relative toatmospheric pressure
( )
( )atmabsatmvac
atmatmabsgage
PPPP
PPPP
belowpressurefor
abovepressurefor
=
=
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Pressure (continued)
Variation of Pressure with Depth
The pressure variation in a constant density fluid is
given asP +Z = constant
Or P1+ Z1 = P2 + Z2
Z is the vertical coordinate ( positive upward).
is the specific weight of fluids, (N/m3)
For small to moderate distances, the variation ofpressure with height is negligible for gases becauseof their low density.
g=
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Pressure (continued)
Pressure Variation in horizontal planes
Pressure is constant inhorizontal planesprovided the fluid doesnot change. ( this leads
toPascals principle.)
.1
2
1
2
2
2
1
1
21
A
A
F
F
A
F
A
FPP ===
Noting that P1
= P2, the area ratio A
2/A
1is called the ideal mechanical
advantage. Using a hydraulic car jack with A2/A
1= 10, a person can
lift a 1000-kg car by applying a force just 100 kgf (= 908 N).
P
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Pressure (continued)
Pressure at a Point
The pressure at a pointin a fluid has the samemagnitude in all direction.
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The Manometer
A device based on P +Z= constant is called amanometer(Left), and it iscommonly used tomeasure small and
moderate pressuredifferences.
w
f
w
f
w
f
sg
g
====S
Specific gravity
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Barometer and the Atmospheric
Pressure
The atmospheric pressure
is measured by a devicecalled a barometer; thus theatmospheric pressure isoften referred to as the
barometric pressure.
gh
ZZPP
PP
ZPZP
Hg
atm
vapor
=
==
=
+=+
)1(
0
21
2
2211
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Barometer and the Atmospheric
Pressure (continued)
The standard atmosphericpressure is 760 mm HG (29.92
in HG) at 0oC. The unit of mmHG is also called the torrinhonor of Evangelista Torricelli
(16081647).
The length or the
cross-sectional area ofthe tube has no effecton the height of thefluid column of abarometer.
( )
kPaPkPaP
kPaPkPaP
Patorr
kPatorrmmHgP
mm
Denvermm
atm
5.26;05.54
4.83;88.89
3.1331
325.101760
000,105000
:16101000
==
==
=
==
B d h A h i
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Barometer and the Atmospheric
Pressure (continued)
Example 2-7:Effect of Piston Weight on Pressure in a Cylinder
The piston of a vertical piston-cylinder devicecontaining a gashas a mass of 60 kg and across-sectional area of 0.04 m2. The local
atmospheric pressure is 0.97 bar, and thegravitational acceleration is 9.81 m/s2. (a)Determine the pressure inside the cylinder, (b) ifsome heat is transferred to the gasand itsvolume is doubled, do you expect the pressureinside the cylinder to change?
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Problem Solving TechniqueThe assumptions made while solving
an engineering problem must be
reasonable and justifiable.
Step-by-step approach:
1. Problem Statement
2. Schematic3. Assumptions
4. Physical Laws
5. Properties
6. Calculations
7. Reasoning, Verification, andDiscussion
Problem Solving Technique
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Problem Solving Technique
(continued)
A result with moresignificant digits than that ofgiven data falsely implies
more accuracy.
When solvingproblems, we will
assume the giveninformation to beaccurate to at least 3
significant digits.Therefore, if the lengthof a pipe is given to be40 m, we will assume it
to be 40.0 m in order tojustify using 3
significant digits in thefinal results.