thermo_lecturenote sep2013.pdf

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Universiti Kuala Lumpur

An Engineering Approach

!introduction to principles and applications of

macroscopic thermodynamics!

!"#$%&'()*%+,-

to accompany

Thermodynamics: An Engineering Approach, 6th editionby Yunus A. engel and Michael A. Boles


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General Overview

the ultimate goal is toDESIGNproductsthat meet society needs

Mechanical Engineering! Mechanics! Energy! Systems! Design

Thermodynamics!A part of the Energycomponentsof mechanical engineering.

! Governs ALL energyconsuming and transforming

devices and systems.


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Course OverviewBasic Concept

TerminologyPure Substance

Energy, Energy

Transfer and Analysis

Closed & Open System 2ndLaw

Thermodynamics

Thermodynamics ApplicationPower Generation Refrigeration

! Gas Power Cycle! Vapor Power Cycle! Combined Gas Power Cycle

! Refrigeration Cycle

!Thermodynamic& Energy

!Dimension!Unit!System &Control Volumes

!Process!Cycle!Temperature!Zeroth Law!Pressure

!Phase & PhaseChange

!Property Diagram!Property Table!Equation of State!Ideal Gas!Real Gas!CompressibilityFactor!ThermodynamicsProperties

!Forms of Energy!Energy Transfer

by Heat

!Energy Transferby work

!Mechanical Works!The 1stLaw!EnergyConversion!Energy &Environment

!Energy Balance!Specific Heats!Internal Energy!Enthalpy!Mass Balance!Flow Work andEnergy of Flowing

Fluid!Steady Flow!Unsteady Flow

!Energy Reservoir!Heat Engine!Refrigeration!Heat Pump!Reversible andIrreversible Process

!Carnot Cycle!Carnot Principle!Carnot Devices


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Course ObjectiveThe objective of this course are.

! to cover the basic principlesofthermodynamics

! to present a wealth of real-worldengineering applications forengineering practices

! to develop an intuitiveunderstanding of the subject matter


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Introduction and Basic Concepts

Chapter 1!"#$%&'()*%+,-

to accompany

Thermodynamics: An Engineering Approach, 6th editionby Yunus A. engel and Michael A. Boles


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Outline

! Thermodynamicsand Energy! Application AreasofThermodynamics

! Dimensionsand Units! Systemand Control Volume! Propertiesof a System! Density andSpecific Gravity! Stateand Equilibrium! Processesand Cycles! Temperature andZeroth Law!

Pressure


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THERMODYNAMICS and ENERGY

! thermodynamics is the science ofenergy it about understanding the

patterns of energy changeand how

these changes relate to the state of

matter

! thermodynamics is a branch ofphysics that is built upon the

fundamental laws that heatand workobey


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Conservation of Energy! During an interaction, energycan change from one form toanotherbut the total amount of

energy remains constant.

! Energy cannot be created ordestroyed.

Energy cannot be created ordestroyed; it can only change

forms (the first law).


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The 1stLaw of Thermodynamics

! An expression of theconservation of energy principle.! The first law asserts thatenergy is a thermodynamic

property.

Conservation of energyprinciple for the human

body.


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The 2ndLaw of Thermodynamics

! It asserts that energy hasqualityas well as quantity, andactual processes occur in the

direction of decreasing quality of

energy.

Heat flows in the directionof decreasing temperature.


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Classical vs Statistical

Classical thermodynamics!A macroscopic approachto the study ofthermodynamics that does not require a knowledge ofthe behavior of individual particles.

! It provides a direct and easy way to the solution ofengineering problems and it is used in this text.

Statistical thermodynamics!

A microscopic approach, based on the averagebehavior of large groups of individual particles.

! It is used in this text only in the supporting role.


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Application Areas


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DIMENSIONSrefer to physical nature of quantity

Primary/FundamentalMass m

Length LTime s

Temperature TPressure P

!"#$%'($)

Secondary/DerivedVelocity v

Energy EVolume V

Area A

+),-.)% 0,(1 2,-1#,3

! !

amF =


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UNITSdefining how measurements are made

English SystemUnited States Customary System (USCS)

12 in. in1 ft, 16 oz in1 lb

!no numerical base

! units are related arbitrarilyMetric System SIInternational System

meter (m), kilogram (kg)

! simple and logical based on a decimalrelationship between the various units

! mostly used for scientific andengineering work


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Dimensional HomogeneityAll equation MUSTbe dimensionally

homogeneous

( )

kJkJkJ

kgXkgkJkJkJ

+=

+!

( ) ( )

kgkJkJkJ

kg

kJkJkJE

+!

""#

$%%&

'+= 25

correction


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SYSTEM, SURROUNDINGS, BOUNDARY

Thermodynamics

System

System! a quantity of matter or a region

in space! may be considered as CLOSEDorOPEN

! system depending on whether a fixedMASS or fixed VOLUMEis chosen

Boundary!.control surface! real or imaginary surface thatseparates the system from its

surroundings! contact surface shared by the systemand its surroundings! zero thickness without mass andvolume

! can either be fixed or movable

Energy

Flow

Surroundings! mass or region outside thesystem


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SYSTEM

0=dtdm

ClosedSystem

OpenSystem

Mass Flow

Mass Flow

Energy

Flow

Energy

Flow

IsolatedSystem


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Closed SYSTEMAlso known as CONTROL MASS, when a

particular quantity of matter in a systemunder study contains the same matter with

fixed amount of mass.

no mass may enter or leave the system


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Open SYSTEMAlso known as CONTROL VOLUME,

has mass as well as energy crossingthe boundary or CONTROL

SURFACE.

mass FLOW across their control surface


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Open SYSTEM


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Isolated SYSTEM! Energy in the form of work or heat can cross theboundary. In the event that energy is not allowedto cross in a closed system, the system is known

as ISOLATED SYSTEM.

! Normally a collection of a a main system and itssurroundings that are exchanging mass andenergy among themselves and no other system.


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Properties of a SYSTEM! Every system has certain characteristics bywhich its physical condition is described. Such

characteristic of a system is called a PROPERTY,it is used to describe a system and predict its

behavior.

! Property is INDEPENDENT OF THE PATHused toarrive at the system condition! Some familiar properties are Pressure,Temperature, Volume and Mass. Other may include

viscosity, thermal conductivity, modulus of

elasticity, thermal expansion coefficient, electric

resistivity, and even velocity and elevation.


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Properties of a SYSTEM! Properties are considered to be either intensiveor extensive.

! Intensive properties are those that areindependent of the mass of the system. (not

additive to the

! Extensive properties are those whose valuesdepend on the size of the system.

EXTENSIVE

mass

volume

energy

velocity

additive over the

system

INTENSIVE

temperature

pressure

density

specific volume

not additive over the

system


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Properties of a SYSTEM

! Properties are considered to beeither intensive or extensive.! Intensive properties are thosethat are independent of the mass

of the system. (not additive over

the system)! Extensive properties are thosewhose values depend on the size

of the system. (additive over the

system)


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extensive properties per unit mass areintensive properties

SPECIFIC VOLUME DENSITY

Properties of a SYSTEM


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Density is defined as a mass per unit volume

Density

Specific volume is the reciprocal of density


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Continuum! Matter is made up of atoms that are widely spaced in

the gas phase. Yet it is very convenient to disregard theatomic nature of a substance and view it as acontinuous, homogeneous matter with no holes, that is,a continuum.! The continuum idealization allows us to

treat properties as point functions and toassume the properties vary continually inspace with no jump discontinuities.! This idealization is valid as long as the

size of the system we deal with is largerelative to the space between themolecules.! This is the case in practically all

problems.

! In this text we will limit our considerationto substances that can be modeled as acontinuum.

Despite the large gapsbetween molecules, asubstance can be treatedas a continuum because ofthe very large number ofmolecules even in an

extremely small volume.


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When the density of a substance is given relative to the

density of a well-know substance, then it is called SpecificGravity or Relative Density.

Specific Gravity

OH

SG

2

!

!=

The specific gravity is defined asthe ratio of the density of a

substance to the density of somestandard substance at a specified

temperature.


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The weight of a unit volume of a

substance is called a specific weight.

Specific Weight

gs !" = )/( 3mN


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STATEThe word STATEin thermodynamics refers to the

condition of a system as described by its

properties. The properties can be measured orcalculated throughout the entire system which

described the condition or state of the system.

Changing one property, changes the state


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!Thermal equilibriumtemperature is the same throughout thesystem

!Mechanical equilibriumno change of pressure with time

!Phase equilibriummass of each phase reaches an

equilibrium level and stay there

!Chemical equilibriumchemical composition does not change

with time

EQUILIBRIUM Condition


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ST TE ND EQUILIBRIUMThe state of a system is described by its properties. Once a

sufficient number of properties are known, we would be able

to specify the state of any system and shall be able to

calculate all other properties of the system.

How many properties ?The number of properties required to specify a state of a simple,

homogeneous compressible system shall be given by the

The THERMODYNAMICS

STATE of a simple

homogeneouscompressible system is

completely specified bytwo independent,

intensive properties.

ST TE POSTUL TE


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PROCESSES and CYCLESAny change that a system undergoes from one equilibrium state to

another is called a PROCESS, and the series of states through

which a system passes during a processis called the PATHof theprocess. When the final state is identical with the initial state theprocess is defined as a CYCLE.

/0*0# 2 /0*0# 345678//9

/0*0# 2 /0*0# 3 /0*0# 27:7;8 9


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! Isothermal Processtemperature remains constant throughoutthe process

! Isobaric Processpressure remains constant throughoutthe process

! Isometric Processspecific volume remains constantthroughout the process

PROCESSES Condition


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EQUILIBRIUM PROCESSES

! Sufficiently slow process! Adjust itself internally! Represent idealized process! Easy to analyze! Deliver most work

as the piston-cylinder devices iscompressed suddenly, all the nearby

molecule will pile up in a small regionnear piston and creating a high-

pressure region thus the systemcan no longer be in an equilibrium

state..


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PROCESSES DI GR Mprovides mean to easily visualize processes.

Thermodynamic properties are used as

coordinates, such as temperature (T), pressure (P),and volume (V) or specific volume (v).


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STEADY-FLOW PROCESSESa process during which a working fluid flows through a

control volume (open-system) steadily at any time. Although

the properties of the working fluid may change from point topoint within the control volume system, but at any fixed point

they remain the same at any time.

%# ?


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ZEROTH LAW OF THERMODYNAMICSTwo bodies individually in THERMAL EQUILIBRIUMwith a third bodies are in thermal equilibrium with

each other.

T t S l


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Temperature Scales as a common basis for temperature

measurements, based on some reproducible

states such as freezing and boiling points of

water.Two-Points Scales! Celcius Scale C(0~100 C)and Fahrenheit Scale F(32~212 F)

Thermodynamics Temperature ScaleIndependent of the properties of any subtances

! Kelvin Scale Kand Rankine Scale RIdeal Gas Temperature ScaleBased on the principle that at low pressure, the temperature of a gas

is proportional with its pressure at constant volume, T=a + bP

Id l G T t S l


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Ideal Gas Temperature Scale

FIGURE 145

P versus T plotsof the experimental data obtained from a constant-volume gas thermometer using four different

gases at different (but low) pressures.

TEMPERATURE MEASUREMENTS


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TEMPERATURE MEASUREMENTSREFERENCE POINTS

Relationship between Kelvin and Celcius Scale

Relationship between Rankine and Farhrenheit Scale

Relationship between Two Unit System

PRESSURE


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PRESSUREdefined as the normal force exerted by a fluid per unit area

211

m

NPa =

Pa9.807x10m

N9.807x10

cm

N9.807

cm

kgf1

bars1.01325kPa101.325Pa101,325atm1

kPa100MPa0.1Pa101bar

4

2

4

22

5

===

===

===

A

FP =

PRESSURE


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PRESSURE

Absolute pressure

Is the actual pressure at a givenposition/location and measuredrelative to absolute zero pressure

Gage pressureIs the pressure difference between

the absolute pressure and local

atmospheric pressure

Vacuum pressureIs the pressure between the

atmospheric pressure and theabsolute pressure. It is the pressure

below the atmospheric pressure.

absatmvac

atmabsgage

PPP

PPP

!=

!=

PRESSURE


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PRESSUREVariation with depth

z

zg

PPP

!=

!=

"=!

#

$

12

PRESSURE


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PRESSURE


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Pascals Law


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Pascals Law

The ratio A2/A1is calledthe ideal mechanical

advantageof the hydrauliclift

PRESSURE measurement


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PRESSURE measurementmanometer

12

2

PP

ghPP atm

=

+= !

measuring pressure with fluid column



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1332211 PghghghPatm =+++ !!!



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( )( )ghPP

PgaghhagP

1221

21211

!!

!!!

"="

=""++

Barometric PRESSURE


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Barometric PRESSURE measuring atmospheric pressure



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Energy, Energy Transfer & General Energy Analysis

Chapter 2!"#$%&'()*%+,-

to accompanyThermodynamics: An Engineering Approach, 6th edition

by Yunus A. engel and Michael A. Boles

O tli


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Outline! Understanding energy and forms of Energy!

Concept of Energy Transfer! First Law of Thermodynamics! Energy Balance and Energy Transfer! Energy and the Environment

Understanding ENERGY


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Understanding ENERGY! If we take the entire roomincluding the air and the

refrigerator (or fan)as the system, which is an

adiabatic closed system since the room is well-sealedand well-insulated, the only energy interaction involved

is the electrical energy crossing the system boundary

and entering the room.

!As a result of the conversionof electric energy consumed by

the device to heat, the room

temperature will rise.

Form of ENERGY


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Form of ENERGY!energy exists in numerous forms such as thermal,

mechanical, kinetic, potential, electric, magnetic, chemical,

and nuclear, and their sum constitutes the total energy ofthe systemdenoted as E (kJ).On a unit mass basis it is

denoted ase=E/m (kJ/kg)

Macroscopic

With respect to outsidereference frame

MicroscopicRelated to the molecular

structure of the system

Macroscopic ENERGY


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!Kinetic energy, KEThe energy that a system

possesses as a result of its motion

relative to some reference frame.

!Potential energy, PEThe energy that a systempossesses as a result of its

elevation in a gravitational field.

!Flowing Fluid

Macroscopic ENERGY

ke per unit mass

pe per unit mass

Mass flow rate

Energy flow rate

Microscopic ENERGY


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Microscopic ENERGYinternal energy = microscopic form of energy denoted as U

!related to the molecularstructure and the degree of

molecular activity

!viewed as the sum of kineticand potential energy of the

molecules

Total ENERGY


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Total energy of a system

Energy of a system per unit mass

Total energy per unit mass

Total ENERGY

Energy Transfer


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Energy Transfer

Mass

out

Massin

System Boundary

Control Volume

!energy may be transported across the system boundaryin several ways. In a closed system (fixed mass), energy is

transported in the form of heatand work. For controlvolume (open system), energy can cross the boundary in

the form of heat, workand energy transported by the

mass streamcrossing the control surface.

Heat

Work

Heat vs Work


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Heat vs WorkHeat,Qis defined as the form of energy that is transferredbetween two systems (or a system and its surroundings)

by virtue of temperature difference whereas Work, Wisthe energy transfer associated with a force acting through

a distance.

Sign Convention For Energy Transfer


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Sign Convention For Energy Transfer

by Heat and Work

Heat and work are directional quantities, thus theirmagnitude and direction are necessary to completely

describe them

Classical Sign Conventionheat transfer to a system and work done by a system are

positive

Energy Transfer by Heat


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Energy Transfer by Heat!form of energy that is transferred across a systemboundary by mean of temperature difference between

two systems!otherwise it is workno heat transfer if same temperature

Adiabatic Process


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Adiabatic Process!is defined as a process with perfectly insulated system

and the heat transfer is zero .0=Q

There are two methods toachieve adiabatic process:

! the system is well insulated! both the system and thesurrounding are at the sametemperature!no driving force

for heat transfer

Heat Transfer


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Heat Transfer

Heat transfer per unit mass Heat transfer per unit timeRate of Heat Transfer

t

QQ =!

!recall that heat is energy in transition across the

system boundary solely due to temperature difference

between the system and its surrounding. Therefore, thenet heat transferred to a system is defined as ...

QQQQ outinnet =

!= ( )kJ

mQq = !!

"

#$$%

&

kg

kJ!"

#$%

&

s

kJ

Heat Transfer


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!=2

1

t

tdtQQ !

tQQ != !

Heat Transferwhen the rate of heat transfer

varies with time, the amountof heat transfer during a

process is determined by

integrating the rate of heat

transfer over the time interval.

when the rate of heat transferremains constantduring a

process, the above reduces to

Is there any Heat Transfer?


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Is there any Heat Transfer?

Heat Transfer Mechanism


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is the transfer of energy from the more

energetic particles of a substance to theadjacent less energetic ones as a result of

interactions between the particles. In solid,

the interaction is due to the combination of

vibrations of molecules and the energy

transport by the free electrons. In liquid and

gases, the interaction take places during

collision of the molecules.

Conduction

Fouriers Law

the rate of heat conduction ina direction is proportional to

the temperature gradient in

that direction



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Conduction

xTAkQcond!

!=

1!0!"x

Where,

= heat flow/time(W)

k = thermal conductivity (W/m.K)

A = area normal to heat flow (m2)

= temperature gradient (K/m)

dx

dTAkQcond 1!=

!

condQ!

dx

dT


C


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!is the mode of heat transfer between a solid surface

and the adjacent liquid of gas that is in motion, and itinvolves the combined effects of conduction and fluid

motion.

Convection

E#*0 !$*)-F#$ G#,"*)+-%

+


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!the rate of heat transfer by convection is determined

from Newtons Law of Cooling

7&)H#,0+&)

fsconv TThAQ !=

!

Where,

= heat transfer rate (W)

A = heat transfer area(m2)

h = convection heat transfer coefficient (W/m2.K)

Ts = surface temperature (K)

Tf = temperature gradient (K)

convQ!



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!is the energy emitted by

matter in the form ofelectromagnetic waves as a

result of the changes in the

electronic configurations of

the atoms or molecules.

Unlike, other mechanisms,

radiation does not requires

medium for it to occur. It isfaster and suffers no

attenuation in a vacuum.

Just like sun light reaches

earth.

Radiation

/0#F*)IJ&=K%*) ;*L


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!gives the maximum rate of radiation that can be emitted by a

surface at an absolute Temperature Ts

. The idealized surface that

emits radiation at maximum rate is called blackbodyand the radiation

emitted by a blackbody is called blackbody radiation.

5*'+*0+&)

Where,Ais the surface area and

4

max, semit ATQ !=!

428./1067.5 KmWX

!

="

Stefan_Boltzman Constant

4

semit ATQ !"=!

Real surface

! is the emissivity of the surface

where 10 !! "

Blackbody surface

Kirchhoffs Law


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!states that the emissivity and absorptivity of a surface

are equal at the same temperature and wavelength.

Radiation

is the rate at which radiation is

incident on the surface

is the absorptivity of the surface

incQ!

!

incabs QQ !!

!=

Energy Transfer by Work


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Energy Transfer by Work!work is the energy transfer associated with a forceacting through a distance. If the energy crossing the

boundary of a closed system is not heat, it must be work.Thermodynamics workis defined as energy in transition

across the system boundary and is done by a system if

the sole effect external to the boundaries could have beenthe raising of the weight. Mathematical, the differential of

work can be expressed as

A rising piston, a

rotating shaft, and anelectric wire crossingthe system boundariesare all associated withwork interactions.



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!if the force Fis not constant, the work donebetween two states is obtained by adding (integrating)

the differential amounts of work,

!! ==2

1

2

112

FdsWW "


!total work done during aprocess 1-2 is determined by

following the process path andadding the differential amounts

of work done along the path



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m

Ww =

!

!

"

#

$

$

%

&

kg

kJ

Power is the work doneper unit time (kW)

Is there any Work Done?


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Is there any Work Done?

Heat & Work similarities


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Heat & Work similarities! both are recognized at the boundaries as they crossesthe boundary, they are boundary phenomena

!system possess energy, not heat or work

! both are path function,their magnitudes depend on

the path followed during a

process as well as end

states.

Properties are point functionshave exact differentials(d ).

! both are associated with aprocess, not a state. They

have no meaning at a state.

Path functions have inexactdifferentials( )

M&$N O&)#


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M&$N O&)#8=#,0$+,*= M&$N

Electrical work

Electrical power

When potential differenceand current change with

time

When potential difference

and current remain

constant

M&$N O&)#


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M&$N O&)#/"*F0 L&$N

( )

TnW

nTrnr

TFsW

sh

sh

!! !

!!

2

22

=

="#$%

&'==

M&$N O&)#


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M&$N O&)#/P$+)B L&$N

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( )2

1

2

2

2

1

xxkWspring !

=

The First Law of Thermodynamics


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yThe first Law of Thermodynamics states that energy can

neither be created nor destroyed; it can only change

forms. Implicitly, it is a statement of theConversation of Energy

Energy Balance


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gy

systemoutin EEE !="

the conservation of energy principle

the net change in the total energy of the system during aprocess is equal to the difference between the total

energy entering and the total energy leaving the system

during the process

Energy Change of a System, systemE!


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y

PEKEUE

EEEEE initialfinalsystem

!+!+!=!

"="=!12

!the determination of the energy change of the systemconcentrates the evaluation of the energy system at initial

and final state of the process, and taking the difference !

(

( )

( )12

2

1

2

2

12

2

1

zzmgPE

VVmKE

uumU

!="

!="

!="where

Energy Change of a System, systemE!


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gy g yThe image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer,and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.!when the final and initial state is specified, the values of

the specific internal energy can be determined from the

property table or property relation.

When the system is stationary, thus, the kinetic andpotential energy is zero,

( )12

uumUE !="="

Therefore, the energy change reduces to

PEKEUE


!+!+!=!

"="=! 12=0 =0

Ein& Eout


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in out!energy can be transferred to or from a systemin the form of

heat, work and mass flow, and this energy interaction is only

recognized as it crosses the system boundary. It represent theenergy gained or lostby a system during a process.

Q"#*0 0$*)-F#$ 0& *-(-0#%A E8R! SRTUA+),$#*-#- 0"# #)#$B( &F0"# %&=#,>=#- *)' 0">-0"# +)0#$)*= #)#$B( &F 0"#-(-0#%A *)' "#*0 0$*)-F#$F$&% * -(-0#%A E8R!;6//A '#,$#*-#- +0 -+),#0"# #)#$B( 0$*)-F#$$#' &>0&F 0"# -(-0#% ,&%#- F$&%

0"# #)#$B( &F 0"#%&=#,>=#-V

Q#)#$B( +)0#$*,0+&)0"*0 +- )&0 ,*>-#' D( *0#%P#$*0>$# '+W#$#),#+- L&$NV M65X O6U86U* -(-0#% &$ L&$N0$*)-F#$ 0& * -(-0#%A+),$#*-#- 0"# #)#$B( &F0"# -(-0#%A *)' M65XO6U8 J:0"# -(-0#% &$L&$N 0$*)-F#$ F$&% 0"#-(-0#%A '#,$#*-#- 0"##)#$B( &F 0"# -(-0#%V

QL"#)GR// T/

8U!85TUS* -(-0#%A0"# #)#$B( &F 0"# -(-0#%+),$#*-#- D#,*>-# %*--,*$$+#- #)#$B(V ;+N#L+-#A

L"#) GR// T/;8R


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systemoutmassinmassoutinoutinoutin EEEWWQQEE !="+"+"=" ,,

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!realizing that energy is transferred in several forms, theenergy balance can be written as !

Energy Balance


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gy

!"!#$!"!#$

energypotentialandenergykineticenergy,internalinchange

flowmassandworkheat,bynsferenergy tranet

systemoutin EEE !="


the net change in the total energy of the system during a

process is equal to the difference between the totalenergy entering and the total energy leaving the system

during the process


Energy Balance


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gy

tWW != !

!"!#$%

!"!#$%%

energypotentialandenergykineticenergy,internalinchangeofrate

flowmassandworkheat,bynsferenergy tranetofrate

systemoutin EEE !="

tQQ != !


In the rate form, the energy balance is represented as

For constant rates, the total quantities during a timeinterval are related to the quantities per unit times as

follows:

tEE !!=! !

Energy Balance


93/351

9393

gy

systemoutin eee !="

other form of energy balance equation

Energy balance per unit mass

Energy balance in differential form

systemoutin

systemoutin

deee

dEEE

=!

=!

""

""

Energy Balance


94/351

9494

gy

outin

outin

EE

EE

=

=

! 0

012

=!="=! EEEEE systemoutin

For a closed system undergoing a CYCLEWhere the initial and final states are identical then

the energy balance for a cyclesimplifies to

In terms of heat and work

innetoutnet

innetoutnet

QW

QW

,,

,,

!! =

=

Ex 2-10: Cooling of a Hot Fluid in a Tank


95/351

9595


PEKEUEEWWQQ

EEEEE

outmassinmassoutinoutin

systemoutin

!+!+!="+"+"

"=!="

,,

12

Energy Balance

where )

( )( )

12

2

1

2

2

12

2

1

zzmgPE

VVmKE

uumU

!="

!="

!="

Ex 2-10: Cooling of a Hot Fluid in a Tank



96/351

9696


)00()0100()5000(

,,

!+!+!=

!+!+!=! outmassinmassoutinoutinoutin EEWWQQEE

For Einand Eout

00)800(

)()()(

2

121212

++!=

!+!+!=

"+"+"="

U

PEPEKEKEUU

PEKEUEsystem

For "Esystem

Energy Balance becomes

kJU

UUUUEWQEE systeminshtoutoutin

400

800100500

2

2

12,

=

!=+!

!="="=+!=!

ENERGY AND ENVIRONMENT! Th i f f f


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9797

! The conversion of energy from one formto another often affects the environmentand the air we breathe in many ways, and

thus the study of energy is not completewithout considering its impact on theenvironment.

! Pollutants emitted during the combustionof fossil fuels are responsible forsmog,acid rain, and global warming.

! The environmental pollution has reachedsuch high levels that it became a seriousthreat to vegetation, wild life, and humanhealth.

Ozone and Smog! Smog: Made up mostly of ground-level ozone (O3), but it also


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9898

! Smog:Made up mostly of ground level ozone (O3), but it alsocontains numerous other chemicals, including carbon monoxide(CO), particulate matter such as soot and dust, volatile organiccompounds (VOCs) such as benzene, butane, and other

hydrocarbons.! Hydrocarbonsand nitrogen oxidesreact in the presence of sunlight

on hot calm days to form ground-level ozone.! Ozoneirritates eyes and damages the air sacs in the lungs where

oxygen and carbon dioxide are exchanged, causing eventualhardening of this soft and spongy tissue.!

It also causes shortness of breath, wheezing, fatigue, headaches,and nausea, and aggravates respiratory problems such as asthma.! The other serious pollutant in smog is carbon

monoxide, which is a colorless, odorless,poisonous gas.! It is mostly emitted by motor vehicles.! It deprives the bodys organs from getting

enough oxygen by binding with the red bloodcells that would otherwise carry oxygen. It isfatal at high levels.! Suspended particulate mattersuch as dustand

sootare emitted by vehicles and industrialfacilities. Such particles irritate the eyes and the

lungs.

Acid Rain


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9999

! The sulfur in the fuel reacts with oxygen to form sulfur dioxide(SO2),which is an air pollutant.! The main source of SO2is the electric power plants that burn high-

sulfur coal.! Motor vehicles also contribute to SO2emissions since gasoline and

diesel fuel also contain small amounts of sulfur.

! The sulfur oxides and nitric oxidesreact with water vapor and otherchemicalshigh in the atmosphere inthe presence of sunlight to formsulfuric and nitric acids.! The acids formed usually dissolve

in the suspended water droplets inclouds or fog.! These acid-laden droplets, which

can be as acidic as lemon juice, arewashed from the air on to the soilby rain or snow. This is known asacid rain.

The Greenhouse Effect: Global Warming


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100100

! Greenhouse effect:Glass allows the solar radiation to enter freelybut blocks the infrared radiation emitted by the interior surfaces.This causes a rise in the interior temperature as a result of the

thermal energy buildup in a space (i.e., car).! The surface of the earth, which warms up

during the day as a result of theabsorption of solar energy, cools down atnight by radiating part of its energy intodeep space as infrared radiation.

! Carbon dioxide (CO2),water vapor, andtrace amounts of some other gases suchas methane and nitrogen oxides act like ablanket and keep the earth warm at nightby blocking the heat radiated from theearth. The result is global warming.!

These gases are called greenhousegaseswith CO2being the primarycomponent.! CO2 is produced by the burning of fossil

fuels such as coal, oil, and natural gas.

!A 1995 report:The earth hasl d d b t 0 5C


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101101

already warmed about0.5Cduring the last century, and theyestimate that the earths

temperature will rise another2Cby the year 2100.!A rise of this magnitude can

cause severe changes inweather patternswith storms

and heavy rains and flooding atsome parts and drought inothers, major floods due to themelting of ice at the poles, lossof wetlands and coastal areasdue to rising sea levels, and

other negative results.! Improved energy efficiency,

energy conservation, and usingrenewable energy sourceshelpminimize global warming.

Systematic Solution Method


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102102

! Sketch the system and show energy interactionacrossthe boundary.

! Determine the property relation. Is the working substancean ideal gas or a real substance? Begin to set up and fill in

a property table.

! Determine the process and sketch the process diagram.Continue to fill in the property table.!Apply conservation of mass and conservation of energyprinciples.

! Bring in other information from the problem statement,called physical constraints, such as the volume doubles orthe pressure is halved during the process.

! Develop enough equationsfor the unknowns and solve.



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Chapter 3

Thermodynamics

Properties of Pure Substances



Outline


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104104

! Concept of Pure Substance!

Physics of Phase Change! Property Diagram! Property Tables! Ideal Gas and the Ideal Gas Equation! Real Gas and Compressibility Factor

PURE SUBSTANCESh homogeneous d fixed chemical composition


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105105

!has a homogeneousand fixed chemical compositionthroughout and may exist in more than one phase!but the chemical

composition is the same in all phases.

Phases of Pure Substance


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106106

! 3-D pattern and repeated! attractive forces are large! spacing very close!zero! molecules are in fixedpositions

! oscillate about equilibriumposition

! molecule velocity dependson T

! attractive force weaker thansolid

! spacing slightly greater thansolid

! molecules able to rotate andtranslate freely! molecules are no longer infixed position

! attractive forces are theweakest

! high energy level! far apart from each other! non-existent order! molecule moves at random andcollide within each other

! molecules are no longer infixed position

Phase-Change Processes


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107107

of a Pure Substance

Saturated

liquid

Saturated

vapor



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108108

State 1 T=20 C and P=1 atmAt state 1, water exists in the liquid phase, or socalled compressed liquidor subcooled liquid,meaning that it is not about to vaporize.

Process 1-2 T=20~100 C and P=1 atmAs heat being transfer and the temperature rises, the

liquid water expand thus increases the specific

volume. To accommodate this changes, the piston

will move up. The pressure is kept constant at P=1

atm since it depends on the outside atmospheric

pressure and the weight of the piston.

As more heat is being transferred, the

temperature will keep rising until it reaches

T=100 C, at this point, the water still exists in theliquid phaseand additional heat transfer will cause

some of the liquid water to vaporize.



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109109

Process 2 T=100 C and P=1 atmAt state 2, the liquid water has reached thetemperature, called saturation temperature, at

which it begins to boil and some of the liquid

water will start to vaporize (from liquid to vapor).

A liquid that is about to vaporize is called a

saturated liquid.

Process 2-3 T=100 C and P=1 atmOnce the boiling starts, additional heat transfer

does not increase the temperature of the liquid.

The temperature will remain at 100 C until all the

liquid is completely vaporized. This is where the

phase-change from liquid to vapor takes place if

the pressure remains constant at 1 atm. During

this process, the volume will increase and liquid

level will decrease as result of more liquid turning

to vapor. At this stage, the substance is called

saturated liquid-vapor mixture.



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110110

Process 3 T=100 C and P=1 atmAt state 3, midway about the vaporization line, thecylinder contains equal amount of liquid and

vapor at constant temperature and pressure.

Process 3-4 T=100 C and P=1 atmAs heat is continued being transferred, the

vaporization process will continue until all liquid

turns into vapor completely. More vapor will

occupy the cylinder as vapor will gradually

increase and liquid decreases. At this stage, the

substance is called saturated liquid-vapormixture.



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111111

Process 4 T=100 C and P=1 atmAt state 4, when the last drop of the liquid water is

completely vaporized, the entire cylinder now

contains with vapor that is on the border line of

the liquid phase. Any heat loss from this vapor

will cause some of this vapor to condense (from

vapor to liquid). A vapor that is about to condense

is called a saturated vapor.

Process 4-5 T=100~ C and P=1 atmAs heat is continued being transferred, both the

temperature and the volume will increase. At

temperature higher that the saturation

temperature, any heat loss will result intemperature drop but no condensation will take

place, as long as the temperature remains above

100 C. A vapor that is not about to condense is

called a superheated vapor.



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112112

Process 5 T= 300 C and P=1 atmAs heat is continued being transferred, both thetemperature and the volume will continue to

increase.



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113113

What happen if we reverse the process?If the entire process is

reversed by cooling offthe water and whilst

maintaining the pressure

at 1 atm, the liquid water

will return to state 1

retracing the same path .In doing so, the amount of

heat released will exactly

match the amount of heat

added during the heating

process.

Saturation Temperature and PressureAt a given pressure the temperature at which a pure substance changes


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114114

At a given pressure, the temperature at which a pure substance changes

phase is called Saturation Temperature.Likewise, at a giventemperature, the pressure at which a pure substance changes phase is called

Saturation Pressure.

Water boils at 100 C at 1 atm

Saturation Temperature and Pressure


115/351

115115


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Heat Transfer of Phase ChangeLatent Heat


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117117

The amount of energy absorbedand releasedduring phase changeLatent Heat ofFusionEnergy absorbed during melting

Latent Heat ofVaporizationEnergy absorbed during vaporization

L=Latent Heat of SubstancemLQ

=

Latent Heat ofSublimationEnergy absorbed during sublimation

! Latent heat: Th t f

Heat Transfer of Phase ChangeLatent Heat


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118118

! Latent heat:The amount of energyabsorbed or released during a phase-change process.

! Latent heat of fusion:The amountof energy absorbed during melting. It isequivalent to the amount of energyreleased during freezing.

! Latent heat of vaporization:Theamount of energy absorbed duringvaporization and it is equivalent to theenergy released during condensation.! The magnitudes of the latent heats

depend on the temperature or pressureat which the phase change occurs.!

At 1 atm pressure, the latent heat offusion of water is 333.7 kJ/kg and thelatent heat of vaporization is 2256.5 kJ/kg.! The atmospheric pressure, and thus

the boiling temperature of water,decreases with elevation.

Key Terms


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119119

Saturated

liquid

Saturated

vapor

The T-v Diagram


120/351

120120

The T-v Diagram


121/351

121121

The T-v Diagram


122/351

122122

The P-v Diagram


123/351

123123

The P-v Diagramsolid liquid vapor


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124124

solid-liquid-vapor

The P-T DiagramThe phase diagram


125/351

125125

The phase diagram

The P-v-T Surface Diagram


126/351

126126

Property Tablebecause the relationship among thermodynamics


127/351

127127

!because the relationship among thermodynamicsproperties are too complex to be expressed in term of a

simple equation, these data are normally tabulated in theform of table.

! Some thermodynamic properties can be measured easily, butothers cannot and are calculated by using the relations betweenthem and measurable properties.!

The results of these measurements and calculations are presentedin tables in a convenient format.

No Phase Table for H20

1 Saturated liquid and vapor A-4 and A5

2 Superheated vapor A-6

3 Compressed liquid A-7

Property Tableforsaturated liquid and saturated vapor Table A-4Ex1


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128128

q px1chap3.ppt

Key Thermodynamics Properties

Enthalpy


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129129

py!the combination of properties derived for the sake of

simplicity and convenience.

Pvuh

PVUH

+=

+=

Property Tableforsaturated liquid and saturated vapor


130/351

130130

q p

Key Thermodynamics Properties

Enthalpy


131/351

131131

py!the combination of properties derived for the sake of

simplicity and convenience. The quantity hfgis called theenthalpy of vaporization (or latent heat of vaporization. It

represent the amount of energy needed to vaporize a unit

mass of saturated liquid at a given temperature or

pressure.

Pvuh

PVUH

+=

+=



132/351

132132



133/351

133133

Property Tableforsaturated liquid-vapor mixture


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134134

q p

!for constant pressure heat addition process, there is a

mixture of saturated liquid and saturated vapor during thevaporization process.


Q lit th ti f f t th t t l f


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135135

Quality x the ratio of mass of vapor to the total mass ofthe mixture



136/351

136136

Property TableForsuperheated vapor Table A-6


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137137

Property TableForsuperheated vapor Table A-6


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138138

Property TableForsuperheated vapor


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139139

Property Tableforcompressed liquid Table A-7


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140140



141/351

141141

In the absence of compressed liquid

data, approximatecompressedliquid as saturated liquid at the

temperature



142/351

142142

How to choose the right Table?!the correct table to use to find the thermodynamics


143/351

143143

yproperties of a real substances can always be determined

by comparing the known state properties to the propertiesin the saturation region.

vf vg v=superheatedtable

v=vf+ x(vg-vf)

Using Steam Tables Ex 4-9 pg 135


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144144

Sat. mixture


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145

vf vg

T= Tsat@P=200 kPa

u=uf+ x(ug-uf)

X=0.6

P=200 kPa

Step 1Step 3

intensive properties


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146

uf ug

T= Tsat@P=1000 kPa

P=1000 kPa

u=2950

4 30 Ten kg of R134A fill a 1 348 m3 rigid container at an initial

extensive properties System, rigid=v constant

m=mass (kg) V=volume (m3) V1=V2


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147

4-30 Ten kg of R134A fill a 1.348 m3rigid container at an initialtemperature of -40C. The container is then heated until the pressure is

200 kPa. Determine the final temperature and initial pressure.

State T P v Phase

1 -40

C

0.1348

m3/kg

2 200kPa

Working fluid

Step 1Find intensive

properties

kg

m

kg

m

m

Vv

mvV

33

1348.010

348.1===

=

State T P v Phase

1 -40C 51.25kPa

0.1348 m3/kg Since vf


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148

2 200kPa

v2=v10.1348 m3/kg

Since vg


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149

Vf=0.0007054 Vg=0.36081

v=vf+ x(vg-vf)=0.1348 m3/kg

T

T= C

P= 51.25kPa

P= 200kPa

T= Tsat@P=200kPa

-10.09C

Vf=0.0007533 Vg=0.099867

2

1

Step 2

T2


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150

P= 1000 kPa T= C

vf= m3/kg vg= m

3/kg

uf= kJ/kg ug= kJ/kg

State T P v Phase

1 -40C 51.25kPa

0.1348 m3/kg Since vf


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151

2 66.30C

200

kPa

v2=v1

0.1348 m3

/kg

Since vg


152/351

State T P v Phase

1 200kPa

0.12322 m3/kg

Since vf


153/351

v=vf+ x(vg-vf)=0.0616 m3/kg

T= Tsat@P=200kPa

-10.09C

Vf=0.0007533 Vg=0.099867

2 1

Step 2

T1

2 -10.09C

200kPa

v2=0.5v10.0616 m3/kg

Since vf


154/351

Then,

( )

kg

kJ

uuxuu fgfmix

6.152

28.3848.2246140.028.38

2,

=

!+=

!+=

2 -10.09C

200kPa

v2=0.5v10.0616 m3/kg

152.6 Since vf


155/351

155155

A liquid will take theshape of its container

but exhibits a free

surface.

A gas will fill its containercompletely and does not

exhibit a free surface.

gasgas

containergas

PTVV

,

=

Ideal-GasEquation of State


156/351

156156

!an equation that relates pressure, volume and

temperature of a sample of matter. Its provides a morepractical and desirable approach in establishing

relationships between the properties of the gases and it

predicts the P-v-T behavior of a gas quite accurately

within some properly selected region.

RTPvv

T

RP =!"

#$%

&= ,

gas constant R

!is different for each gas and Ruis the universal gast t


157/351

157157

M

RR

u=

!

!#

$

Kkmolmbar

KkmolmkPa

KkmolkJ

Ru

./.08314.0

./.314.8

./314.8

3

3

The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and theninsert it again.

mol

gram

kmolN

kgmM ==

)(

)(

constant

Ideal-GasSeveral different forms of Equation of State


158/351

158158

( )

vNV

NRRMNmR

mvV

u

=

==

=

Ideal-GasFor a fixed mass, the properties of an ideal gas at twodiff t t t l t d t h th b


159/351

159159

different states are related to each other by

2

22

1

11

RT

VP

RT

VPm ==

How to defineIdeal-Gas


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160160

!determination based on

errors yield !

Compressibility Factora measure of deviation from ideal-gas behavior

real gases deviate from ideal-gases behavior


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161161

!real gases deviate from ideal-gases behaviorsignificantly especially near the saturation region and

critical point. This deviation can be accurately accounted

for by a correction factor called the

compressibility factor Z

ZRTPvRT

PvZ == ,

ideal

actual

v

vZ = wherePRTv

actual =

Compressibility Factor


162/351

162162

Principle of Corresponding States!gases behave differently at a given temperature andpressure real gases, but they behave very much the


163/351

163

pressure real gases, but they behave very much the

same at temperature and pressure normalized with

respect to their critical temperatures and pressures

cr

R

P

PP =

cr

R

T

TT =

!

!

!!#

$

...=Z

Generalized Compressibility Chart


164/351

164164

Observation from Generalized Compressibility Chart

! at very low pressures, PR


165/351

165165

! at high temperatures, TR > 2, ideal gasbehavior can be assumed with good accuracy

regardless of pressure (except when PR >> 1)

! the deviation of a gas from ideal-gas behavior isgreatest in the vicinity of the critical point

pseudo-reduced specific volume!when Pand v, or Tand vare given instead of Pand

T, the pseudo-reduced specific volume can be


166/351

166166

, p p

calculated to used the generalized compressibility

chart

crcr

actual

R

PRT

vv

/=

cr

R

P

PP =

!!

"

!!

#

$

...

=Z

Van der WaalsEquation of State


167/351

167167

( ) RTbvv

aP =!"

#

$%

&

'+

2

cr

cr

cr

cr

P

RTb

P

TRa

8,

64

27 22

==

Beattie-BridgemanEquation of State


168/351

168168

!"#$

%& '=!

"#$

%& '=

v

bBBv

aAAoo

1,1

( )232

1v

ABvTv

c

v

TRP u !+"

#$%

&' !=

Equation of State

Benedict-Webb-Rubin


169/351

169169

2

33

/

22622 1

1 vuoouo

u

evTv

c

v

a

v

aTbR

vT

C

ATRBv

TR

P !!" #

$%

&'(

)+++

#+$%

&'(

)##+=

VirialEquation of State


170/351

170170

( ) ( ) ( ) ( ) .....5432 +++++= vTd

v

Tc

v

Tb

v

Ta

v

RTP

ComparisonEquation of State


171/351

171171

Enthalpy Changes

forLiquids


172/351

172172

Tconstant, pump 0=!T

Pconstant, heater 0=!P TCuh av!"!=!

( )1212 PPvhhPvh

!=!

"="

( )satTfTfTP

TfTP

PPvhh

hh

!+"

"

###

##

,

,

By taking state 2 to be compressed liquid at given P and T andstate 1 to be saturated liquid at the same T



173/351

Energy Analysis of Closed System

Chapter 4

!"#$%&'()*%+,-



Outline

! Examine the PdV Works


174/351

174174

!Identify Energy Balance for Closed System

! Define Specific Heat, Internal Energy andEnthalpyfor Ideal Gas

! Describe incompressible substances! Analyze Energy Balance for Heat and WorkInteraction of a Closed System

Energy Transfer by Work!work is the energy transfer associated with a forceacting through a distance. If the energy crossing the


175/351

175175

g g gy g

boundary of a closed system is not heat, it must be work.

Thermodynamics workis defined as energy in transition

across the system boundary and is done by a system if

the sole effect external to the boundaries could have beenthe raising of the weight. Mathematical, the differential of

work can be expressed as

A rising piston, arotating shaft, and an

electric wire crossingthe system boundariesare all associated withwork interactions.

!if the force Fis not constant, the work donebetween two states is obtained by adding (integrating)



176/351

176176

between two states is obtained by adding (integrating)

the differential amounts of work,

!! ==2

1

2

112

FdsWW "

!total work done during aprocess 1-2 is determined by

following the process path and

adding the differential amountsof work done along the path

Energy Transfer by WorkW

w = !!#

$$& kJ


177/351

177177

m

w = !!

"

$$

%kg

Power is the work doneper unit time (kW)

Work Done

the net work done by a closed system may be in two

By a closed system


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178178

!the net work done by a closed system may be in two

forms:-1. Rotating shaft, electrical , that is otherworks not

associated with moving boundary works.

2. Moving Boundary Work

Thus, the net work done by a closed systemis defined as

( )

( ) bothernet

botherinoutnet

WW

WWWW

+=

+! !"=

Moving Boundary WorkPdVwork Consider, Fig 4-2, initial pressure P, volume

of piston V and total area A If the piston is


179/351

179179

!one form of mechanical

works. It is the expansion andcompression work of a

moving boundary in piston-

cylinder devices.

of piston Vand total areaA. If the piston is

allowed to move a distance ds, in a quasi-equilibrium manner, the work done during

a process is given by

PdVPAdsFdsWb

===!

work is done bythe gas on the

piston

Total work Done

Moving Boundary Work


180/351

180

The total area A under the process

curve 1-2 is obtained by adding all the

differential areas.

!=

2

1

PdVWb

!by adding all the differentialworks from the initial stage 1

to the final stage 2.

!! ===

2

1

2

1

PdVdAAArea

therefore, the area under the



181/351

181181

process curve on a P-V diagram

is equal, in magnitude, to the

work done during a quasi-equilibrium expansion or

compression process of a

closed system

Quasi-equilibrium processA process during which the

system remains nearly in

equilibrium at all times.

Wbis positive for expansionWbis negative for compression



182/351

182182

Energy is conserved


183/351

183183

( )dxFAPF

WWWW

crankatmfriction

crankatmfrictionb

! ++=

++=

2

1

Work DoneMoving boundary for Constant Volume

Total Work Done


184/351

184184

02

1

== ! PdVWb

!if the volume is held constant, dV=0, the boundary work equationbecomes

Work DoneMoving boundary for Constant Pressure

Total work Done


185/351

185185

!if the pressure is held constant, the boundary work equation

becomes

( )122

1

2

1 VVPdVPPdVWb !="="=

Work DoneMoving boundary for Constant Temperature Ideal Gas

Total work Done!if the temperature of an ideal gas system is held constant, then the


186/351

186186

!if the temperature of an ideal gas system is held constant, then the

equation of state provides the pressure volume relation, then

boundary work equation becomes

!!"

#$$%

&=== ''

1

22

1

2

1

lnV

VmRTdV

V

mRTPdVW

b

For an ideal gas in a closed system (mass, m=constant),

1

2

2

1

2

22

1

1121

thus

,,

V

V

P

P

RT

VP

RT

VPmm

=

==

!!"

#$$%

&=

2

1ln

P

PmRTW

b

Work DoneMoving boundary for Constant Temperature Ideal Gas

Total work DoneC


187/351

187187

1

2

11

1

2

2

1

2

1

2

1

ln

ln

V

VVP

V

VC

V

dVC

dVV

C

PdVWb

=

=

=

==

!

!!

V

C

P

or

CmRTPV

=

==

mRTVPVP ==2211

where

Work Done!for actual expansion and compression processes of

gases pressure and volume are often related by

Polytropic Process


188/351

188188

gases, pressure and volume are often related by

PVn=C, where n and C are constants.

Work DonePolytropic Process

The pressure for a polytropic process can be expressedas


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1

1

1

1

2

2

2

2

1

+!!=

==

+!+!

!""

n

VVC

dVCVPdVW

nn

nb

nCVP !=

as

Thus,

Work DonePolytropic Process

nn


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190190

nn

VPVPC 2211 ==

1

1

1122

!

"

"

=

n

n

VPVPWb

since

Work DonePolytropic Process for Ideal Gas

Ideal Gas mRTPV =


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191191

1

112

!

"

"

=

n

n

TTmR

Wb

Ideal Gas mRTPV

Work DonePolytropic Process for n=1


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192192

!!#

$$&

=

== '' (

1

2

2

1

12

1

ln

V

VPV

dVCVPdVWb

Energy Balancethe conservation of energy principle



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193193

systemoutin EEE !="

process is equal to the difference between the total

energy entering and the total energy leaving the systemduring the process

Energy Change of a System,The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer,and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.

systemE!

!the determination of the energy change of the systemconcentrates the evaluation of the energy system at initial

and final state of the process and taking the difference


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194194

PEKEUE


!+!+!=!

"="=!12

and final state of the process, and taking the difference !

(

( )

( )12

2

1

2

2

12

2

1

zzmgPE

VVmKE

uumU

!="

!="

!="where

Energy Change of a System,The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer,and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.

systemE!

!when the final and initial state is specified, the values ofthe specific internal energy can be determined from the

property table or property relation


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property table or property relation.

When the system is stationary, thus, the kinetic andpotential energy is zero,

( )12

uumUE !="="

Therefore, the energy change reduces to

PEKEUEEEEEE initialfinalsystem

!+!+!=!

"="=! 12=0 =0

Ein& EoutThe image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer,and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.!realizing that energy is transferred in several forms, the

energy balance can be written as !


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!"!#$!"!#$

energypotentialandenergykineticenergy,internalinchange

flowmassandworkheat,bynsferenergy tranet

systemoutin EEE !="

process is equal to the difference between the total

energy entering and the total energy leaving the systemduring the process



In the rate form, the energy balance is represented as


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198198

tWW != !

!"!#$%

!"!#$%%

energypotentialandenergykineticenergy,internalinchangeofrate

flowmassandworkheat,bynsferenergy tranetofrate

systemoutin EEE !="

tQQ != !

For constant rates, the total quantities during a timeinterval are related to the quantities per unit times as

follows:

tEE !!=! !

Energy Balanceother form of energy balance equation

Energy balance per unit mass


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systemoutin eee !="Energy balance in differential form

systemoutin

systemoutin

deee

dEEE

=!

=!

""

""

Energy BalanceFor a closed system undergoing a CYCLE

Where the initial and final states are identical then


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200200

outin

outin

EE

EE

=

=

! 0

012 =!="=! EEEEE systemoutinthe energy balance for a cyclesimplifies to

In terms of heat and work

innetoutnet

innetoutnet

QW

QW

,,

,,

!! =

=

Energy Balance for Closed System!the energy balance for a closed system, based on the classical

thermodynamics sign convention, is represented as


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201201

PEKEUWQ

EWQ

outnetinnet

systemoutnetinnet

!+!+!="

!="

,,

,,

If the system is does not move with a velocity and hasno change in the elevation

12

,,

)( UUWWQQ

UWQ

inoutoutin

outnetinnet

!=!!!

"=!

Energy Balance for a Cycle!a thermodynamics cycle is composed of processes that cause

the working fluid to undergoes a series of processes such that the

final and initial states are identical therefore the change in the

Closed system


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202202

inoutoutin

outnetinnet

outnetinnet

WWQQ

WQ

UWQ

!=

!

=

"=!

,,

,,

final and initial states are identical, therefore, the change in the

internal energy of the working fluid is zero for whole number of cycle,thus the energy balance becomes

0

Systematic Solution Method! Sketch the system and show energy interactionacrossthe boundary.


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203203

y

! Determine the property relation. Is the working substancean ideal gas or a real substance? Begin to set up and fill ina property table.

! Determine the process and sketch the process diagram.Continue to fill in the property table.

!Apply conservation of mass and conservation of energyprinciples.

! Bring in other information from the problem statement,called physical constraints, such as the volume doubles or

the pressure is halved during the process.! Develop enough equationsfor the unknowns and solve.

Key Thermodynamics PropertiesEnthalpy

!the combination of properties derived for the sake of


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simplicity and convenience. The quantity hfgis called theenthalpy of vaporization (or latent heat of vaporization. Itrepresent the amount of energy needed to vaporize a unit

mass of saturated liquid at a given temperature or

pressure.

Pvuh

PVUH

+=

+=

EnthalpyKey Thermodynamics Properties


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dPP

hdT

T

hdh

TP

!

"

#$

%

&

'

'+!

"

#$

%

&

'

'=

),( PThh =

Key Thermodynamics PropertiesInternal Energy


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206206

dvv

udTT

udu

Tv

!

"

#$

%

&

'

'+!

"

#$

%

&

'

'=

),( vTuu =

Key Thermodynamics PropertiesSpecific Heat

! it take different amounts of energyto raise the temperature of identical


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! is defined as the energy requiredto raise the temperatureof a unit

mass of a substance by one degreeat maintained volume cVor

pressure cP

p

masses of different substances byone degree due to energy storage

capabilities of various substances!

! is specified by two independentintensive properties, thus it is

different at different temperature and

pressure

Specific HeatAt constant volume cv

= 0


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dvvudT

Tudu

Tv

!"#$

%&''+!

"#$

%&''=

v

v

T

uc !

"

#$%

&

'

'=

!is the change in internal energy

with temperature at constant volume

Specific HeatAt constant pressure cp

hh

= 0


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209209

dPP

hdT

T

hdh

TP

!"#$

%& ''

+!"#$

%& ''

=

P

P

T

hc !

"

#$

%

&

'

'=

!is the change in enthalpy with

temperature at constant pressure

Specific Heat-Summary


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210

Internal EnergyForIdeal Gases


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211211

)(Tuu =(Shown in experiments performed by

Joule in 1843.)

EnthalpyForIdeal Gases


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212212

( ) ( )( )Thh

RTTuTh

Pvuh

=

+=

+=

Specific HeatForIdeal Gasesfor constant volume cv

Tu =


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213213

( )dTTcdudT

du

T

uc

Tu

v

v

v

=

=!"#$

%& ''

=

=

Specific HeatForIdeal Gasesfor constant pressure cp

=


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214214

( )dTTcdhdT

dh

T

hc

Th

P

v

P

=

=!"#$

%&''=

=

Internal Energy and EnthalpyFor Ideal Gases

==

2T


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215215

( ) ( )

( ) ( ) !

!="=#

=

"=

#2

1

1

12

12

T

T P

T v

dTcThThh

dTcTuTuu

Specific Heat forIdeal Gas


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216216


( )12,12TTcuu avev !=!


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( )

( )12,12

12,12

TTchh avep

avev

!=!


THREEmethods to determine the internal energy andenthalpy changesof ideal gases


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218

py g g

( )( )

12,12

12,12

TTchhh

TTcuuu

avep

avev

!=!="

!=!="

( ) ( )( ) ( ) !

!="=#

=

"=

#2

1

2

1

12

12

T

T p

T

T v

dTcThThh

dTcTuTuu

12

12

hhh

uuu

!="

!=

"! using property table

!using the temperaturefunction and performing

integration (Table A-2c)

! using average specificheat (Table A-2b)

Specific Heat RelationsofIdeal Gases

RTuh +=


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219219

Rcc

RdTdTcdTc

RdTdudh

vP

vP

+=

+=

+=

v

P

c

ck =Specific Heat

Ratio

Specific Heats

forSolids and Liquids


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220220

cccvp

==

Internal Energy ChangesforSolids and Liquids

=


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221221

( ) ( )

( )

( )12

2

1

12

TTcu

dTTcuuu

dTTcdTcduTuu

ave

v

!"#

=!=#

==

=

$

Enthalpy Changes

forSolids

Pvuh +=


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222222

Tcuh

vdPTcvdPuh

vdPduPdvvdPdudh

ave

ave

!"!=!

+!"+!=!

+=++=

= 0 for incompressible

= 0 for solid

Enthalpy Changes

forLiquids constant pressure processPvuh +=


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223223

vdPTcvdPuh

vdPduPdvvdPdudh

ave +!"+!=!

+=++=

Pconstant, heater

0=!P Tcuhave!"!=!

= 0

Enthalpy Changes

forLiquids constant temperature process

vdPTcvdPuh +!"+!=!

= 0


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224

avTconstant, pump

0=!T

( )1212 PPvhh

Pvh

!=!

"="

( )satTfTfTP

TfTP

PPvhh

hh

!+"

"

###

##

,

,

By taking state 2 to be compressed liquid at given P and T andstate 1 to be saturated liquid at the same T



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Mass and Energy Analysis of Control VolumesChapter 5

!"#$%&'()*%+,-



Outline! Develop the conservation of mass principle! Apply the conservation of mass principle to

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