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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 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 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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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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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.

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