lecture 1 eng. ther

8/8/2019 Lecture 1 Eng. Ther.

1/66

ENGINEERINGTHERMODYNAMICS

Dr. Tamer A. TabetCourse Code: KT20302Sems.-1-2010

Wed. 28/7/2010Lecture Room: DKP A1

Copyright Tamer A. Tabet


2/66

Chapter 1Getting Started: Introductory

Concepts and Definitions



3/66

3

N omenclature A area (m 2)C P specific heat at constant

pressure (kJ/(kg K))C V specific heat at constant volume

(kJ/(kg K))COP coefficient of performance

d exact differentialE stored energy (kJ)e stored energy per unit mass

(kJ/kg)F force ( N )g acceleration of gravity

( 9.807 m/s 2)

H enthalpy (H= U + PV) (kJ)h specific enthalpy (h= u + Pv)(kJ/kg)

h convective heat transfercoefficient (W/(m 2 K)

K Kelvin degreesk specific heat ratio, C P/CV k 10 3

k t thermal conductivity (W/(m- rC))M molecular weight or molar mass

(kg/kmol)M 10 6m mass (kg)N moles (kmol)n polytropic exponent (isentropic

process, ideal gas n = k)L isentropic efficiency for turbines,

compressors, nozzles

Lth thermal efficiency (net workdone/heat added)P pressure (kPa, MPa, psia, psig)Pa Pascal ( N /m 2)


4/66

4

X distance (m)X exergy (kJ)x q ualityZ elevation (m)W net net work done [( W out -

W in)other + W b] (kJ) where W b =for closed systems and 0 forcontrol volumes

w net W net / m, net work done per unitmass (kJ/kg)

W t weight ( N )inexact differential

I regenerator effectiveness

relative humidityV density (kg/m 3 )[ humidity ratio

Qnet net heat transfer ( Q in - Q out )(kJ)

qnet Q net /m, net heat transfer perunit mass (kJ/kg)particular gas constant(kJ/(kg K))

u universal gas constant(= 8.3 14 kJ/(kmol K) )S entropy (kJ/K)s specific entropy (kJ/(kg K))T temperature ( rC, K, rF, R)U internal energy (kJ)u specific internal energy

(kJ/(kg K))V volume (m 3 )

volume flow rate (m 3 /s)velocity (m/s)

v specific volume (m 3 /kg)molar specific volume (m 3 /kmol)

N omenclature con t

V TV

v


5/66

5

Subscripts, superscripts A actualB boundaryF saturated li q uid stateG saturated vapor statef g saturated vapor value

minus saturated li q uidvaluegen generationH high temperatureHP heat pumpL low temperaturenet net heat added to system

or net work done by systemother work done by shaft and

electrical means

P constant pressureREF refrigeratorrev reversibles isentropic or constant

entropy or reversible,

adiabaticsat saturation valuev constant volume1 initial state2 finial statei inlet statee exit state

per unit time


6/66

6

IN TRODUCTIONThe study of thermodynamics is concerned with the ways energy is stored within abody and how energy transformations, which involve heat and work, may take place.One of the most fundamental laws of nature is the conservation of energy principle. Itsimply states that during an energy interaction, energy can change from one form toanother but the total amount of energy remains constant. That is, energy cannot becreated or destroyed.

This review of thermodynamics is based on the macroscopic approach where a largenumber of particles, called molecules, make up the substance in question. Themacroscopic approach to thermodynamics does not require knowledge of thebehavior of individual particles and is called classical thermodynamics . It providesa direct and easy way to obtain the solution of engineering problems without being

overly cumbersome. A more elaborate approach, based on the average behavior of large groups of individual particles, is called statistical thermodynamics . Thismicroscopic approach is rather involved and is not reviewed here and leads to thedefinition of the second law of thermodynamics. We will approach the second law of thermodynamics from the classical point of view and will learn that the second law of thermodynamics asserts that energy has quality as well as quantity, and actual

processes occur in the direction of decreasing quality of energy.


7/66


Introduction: Chapter 1

Thermodynamics is thestudy of energyIt covers a wide rangeof applications wechoose the system of interestThe surroundings areexternal to our systemof interest


8/66

Important Terms and Types of thermodynamic Systems

H ere are some important terms which are found frequentlyin the subject area of thermodynamics and various typesof system.

Thermodynamics: Thermodynamics is the branch of science or physics that studies various forms of energiesand their conversion from one to the other like electrical

energy to mechanical energy, heat to electrical, chemicalto mechanical, wind to electrical etc.



9/66

System: A quantity of the matter or part of the spacewhich is under thermodynamic study is called as system.

There are three types of system: closed system, opensystem and isolated system.

Surroundings or environment : Everything external to thematter or space, which is under thermodynamic study iscalled surroundings or environment.

Boundary : The boundary that separates the system andsurrounding is called as system boundary. The systemboundary may be fixed or moving.



10/66

Cl osed system : The system of fixed mass across theboundary of which no mass transfer can take place is calledas closed system. H owever, across the closed system theenergy transfer may take place. An example is fluid beingcompressed by the piston in cylinder.

A special type of closed system that does not interact in any

way with its surroundings is called an isolated system .


Iso lated system : The system in which both the mass as wellas energy content remains constant is called an isolatedsystem. In this system no mass or energy transfer takes placeacross the boundary.


11/66

Closed System (Control Mass)

N o mass can crosssystem boundaryEnergy may crosssystem boundaryVolume is N OT fixed


Figure 1: Closed system: A gas in a piston-cylinder

assembly.


12/66

O pen system : The system across the boundary of whichtransfer of both mass as well as energy can take place across

the boundary is called as open system. An example is an air compressor.

Figure 2: Example of a control volume (open system): An automobile engine


13/66

Open System/Control Volume

Mass may cross systemboundary (controlsurface)

Volume may/may notbe fixedEnergy may crosssystem boundary

Contr ol Vol um es may op er a te a t ste a d y st a te, or chan ge wi th t ime ( em p t y/fi ll)



14/66

Closed, Open, and Isolated Systems

A thermodynamic system, or simply system , is defined as a quantity of matter or a region in space chosen for study. The region outside the systemis called the surroundings . The real or imaginary surface that separatesthe system from its surroundings is called the boundary . The boundary of asystem may be fixed or movable.

Surroundings are physical space outside the system boundary.

Systems may be considered to be c losed or open , depending on whether a fixed mass or a fixed volume in space is chosen for study.



15/66

A c losed system consists of a fixed amount of mass and no mass may cross thesystem boundary. The closed system boundary may move.

Examples of closed systems are sealed tanks and piston cylinder devices (note the

volume does not have to be fixed). H owever, energy in the form of heat and workmay cross the boundaries of a closed system.



16/66

An open system , or contro l vo lume , has mass as well as energy crossingthe boundary, called a control surface. Examples of open systems arepumps, compressors, turbines, valves, and heat exchangers .

An iso lated system is a general system of fixed mass where no heat or

work may cross the boundaries. An isolated system is a closed system withno energy crossing the boundaries and is normally a collection of a mainsystem and its surroundings that are exchanging mass and energy amongthemselves and no other system.

Isolated System Boundary

Mass

System Surr 3Mass

Work

Surr 1

H eat = 0Work = 0Mass = 0

AcrossIsolatedBoundary H eatSurr 2

Surr 4



17/66

Properties

System characteristic;carries both a numericalvalue and set of units

3 Types of thermodynamicsproperties: Extensive,Intensive, & Specific

Extensive: Depend onmass/size of system(Volume [V])

Intensive: Independentof system mass/size(Pressure [P],Temperature [T])

Specific:Extensive/mass(Specific Volume [v])



18/66

State of the system : The present status of the systemdescribed in terms of properties such as pressure,temperature, and volume is called the state of system.

Properties of the system : The characteristics by which thephysical condition of the system is described are called asproperties of system. Some examples of these characteristicsare: temperature, pressure, volume etc and are called asproperties of system. The system properties are of two types:

extensive and intensive properties.



19/66

Ex tensive properties of system : The properties of thesystem that depend on the mass or quantity of the system

are called extensive properties. Some examples of extensiveproperties are: mass, volume, enthalpy, internal energy,entropy etc.

Intensive properties of the system : These properties donot depend on the quantity of matter of the system. Some of the examples of intensive properties are: freezing pointtemperature, boiling point, temperature of the system,density, specific volume etc.



20/66

Since some of the thermodynamic relations that are applicable to closed andopen systems are different, it is extremely important that we recognize thetype of system we have before we start analyzing it.

Properties of a System

Any characteristic of a system in equilibrium is called a property . Theproperty is independent of the path used to arrive at the system condition.

Some thermodynamic properties are pressure P , temperature T , volume V ,and mass m.

Properties may be intensive or e x tensive .Extensive properties are those that vary directly with size--or extent--of thesystem.

Some Extensive Propertiesa. massb. volumec. total energyd. mass dependent property



21/66

Intensive properties are those that are independent of size.Some Intensive Propertiesa. temperatureb. pressurec. aged. color e. any mass independent property

Extensive properties per unit mass are intensive properties. For example,

the specific volume v , defined as

!!

kg m

m

V

mass

Volu mev

3



22/66

and density V, defined as

3mkg

V m

volu mema ss

V

are intensive properties.



23/66

Q uestion 1: Illustrate the difference between

extensive and intensive properties.



24/66

Definitions

State: Condition of asystem as defined by itsproperties

Process: Change asystem undergoes fromone e q uilibrium state toanother

Cycle: Series of processes that returnsystem to initial state

Special Types of Processes: Isothermal

Isobaric Isometric Isentropic Adiabatic



25/66

isometric process , or isovolumetric, is aThermodynamic process during which the volume of theclosed system undergoing such process remainsconstant.

Adiabatic and Isotherma l process:

Adiabatic means without any transfer of heat, andisotherma l means having only one constant temperature.

isobaric- constant pressure



26/66

Many chemical reactions release energy in the formof heat, light, or sound. These are exothermic

reactions. Exothermic reactions may occur spontaneously and result in higher randomness or entropy ( S > 0) of the system. They are denoted bya negative heat flow (heat is lost to the surroundings)and decrease in enthalpy ( H < 0). In the lab,exothermic reactions produce heat or may even beexplosive.



27/66

There are other chemical reactions that must absorb

energy in order to proceed. These are endothermicreactions. Endothermic reactions cannot occur spontaneously. Work must be done in order to getthese reactions to occur. When endothermic reactionsabsorb energy, a temperature drop is measured during

the reaction. Endothermic reactions are characterizedby positive heat flow (into the reaction) and an increasein enthalpy (+ H ).



28/66

Ex amp les of E ndothermic and Ex othermic Processes

Photosynthesis is an example of an endothermic chemicalreaction. In this process, plants use the energy from thesun to convert carbon dioxide and water into glucose andoxygen. This reaction requires 15MJ of energy (sunlight)for every kilogram of glucose that is produced

sunlight + 6CO 2(g) + H 2O(l) = C 6H 12 O 6(aq) + 6O 2(g)



29/66

An example of an exothermic reaction is the mixture of sodium and chlorine to yield table salt. This reactionproduces 411 kJ of energy for each mole of salt that isproduced:

Na(s) + 0.5Cl 2(s) = NaCl(s)



30/66

Isentropic Process: In thermodynamics, a processinvolving change without any increase or decrease of entropy. Since the entropy always increases in aspontaneous process, one must consider reversible or quasistatic processes. During a reversible process the

quantity of heat transferred is directly proportional tothe system's entropy change. Systems which arethermally insulated from their surroundings undergoprocesses without any heat transfer; such processesare called adiabatic. Thus during an isentropicprocess there are no dissipative effects and thesystem neither absorbs nor gives off heat. For thisreason the isentropic process is sometimes called thereversible adiabatic process.



31/66


32/66

Phase and Pure Substance

Phase: The term phase refers to a q uantity of matter that ishomogeneous throughout in both chemical composition andphysical structure.

Homogeneity in physical structure means that the matter is allsol i d or all l iqui d , or all va po r (or e q uivalently all gas).

A pure Substance: Is one that is uniform and invariable inchemical composition, a pure substance can exist in more

than one phase, but its chemical composition must be thesame in each phase.



33/66

Equilibrium

The concept Equilibrium is fundamental. In mechanics,eq uilibrium means a condition of balance maintained by aneq uality of opposing force.

In thermodynamics, the concept is more far-reaching,including not only balance of forces but also a balance of another influences refers to a particular aspects of thermodynamics, or complete e q uilibrium.

Eq uilibrium state:



34/66

Equilibrium state : We may think of testing to see if a systemis in thermodynamics e q uilibrium by the following procedure:Isolate the system from its surroundings and watch forchanges in its observable properties. If there are no changes,we conclude that the system was in e q uilibrium at themoment it was isolated.

Q uasiequilibrium Process: Is the process in which thedeparture from thermodynamics e q uilibrium is at mostinfinitesimal .



35/66

U nits

An important component to the solution of any engineering thermodynamicproblem requires the proper use of units. The unit check is the simplest of all engineering checks that can be made for a given solution. Since unitspresent a major hindrance to the correct solution of thermodynamicproblems, we must learn to use units carefully and properly. The system of units selected for this course is the SI System, also known as the

International System (sometimes called the metric system). In SI, the unitsof mass, length, and time are the kilogram (kg), meter (m), and second (s),respectively. We consider force to be a derived unit from Newton's secondlaw, i.e.,

F orc e mass a cc el er a tion F ma

!!( )( )



36/66

In SI, the force unit is the newton (N), and it is defined as the force required toaccelerate a mass of 1 kg at a rate of 1 m/s 2. That is,

1 1 12

N kg m

s! ( )( )

This definition of the newton is used as the basis of the conversion factor to convertmass-acceleration units to force units.

The term weight is often misused to express mass. Unlike mass, weight W t is aforce. Weight is the gravitational force applied to a body, and its magnitude isdetermined from Newton's second law,

=W m g t where m is the mass of the body and g is the local gravitational acceleration ( g is9.807 m/s 2 at sea level and 45 rlatitude). The weight of a unit volume of a substance

is called the specific weight w and is determined from w = Vg , where Vis density.Oftentimes, the engineer must work in other systems of units. Comparison of theUnited States Customary System (USCS), or English System, and the slug system of units with the SI system is shown below.



37/66


38/66

Measuring Mass, Length, Time and Force

SI Units:

SI base unitsThe SI is founded on seven SI b ase units for seven b asequantities assumed to be mutually independent, as given inTable 1



39/66

Tab le 1. SI base units

Base quantity Name Symbo llength meter m

mass kilogram kg

time second s

electric current ampere A

thermodynamictemperature

kelvin K

amount of substance mole mol

luminous intensity candela cd



40/66

SI derived units

Other quantities, called deri v ed quantities , are defined in

terms of the seven base quantities via a system of quantityequations. The SI deri v ed units for these derived quantitiesare obtained from these equations and the seven SI baseunits. Examples of such SI derived units are given in Table 2,where it should be noted that the symbol 1 for quantities of dimension 1 such as mass fraction is generally omitted.



41/66

Tab le 2. Ex amp les of SI derived units

SI derived unitDerived quantity Name Symbo l

area square meter m 2

volume cubic meter m 3

speed, velocity meter per second m/s

acceleration meter per second squared m/s 2

wave number reciprocal meter m -1

mass density kilogram per cubic meter kg/m 3

specific volume cubic meter per kilogram m 3/kg

current density ampere per square meter A/m 2

magnetic field strength ampere per meter A/m

amount-of-substance concentration mole per cubic meter mol/m 3

luminance candela per square meter cd/m 2

mass fractionkilogram per kilogram, which may berepresented by the number 1

kg/kg = 1



42/66

Tab le 3. SI derived units with specia l names and symbo lsSI derived unit

Derivedquantity Name Symbo l

Ex pressionin terms of

other SI units

Ex pressionin terms of

SI base unitsp lane ang le radian (a) rad - mm -1 = 1 (b)

so lid ang le steradian (a) sr (c) - m 2m -2 = 1 (b)

frequency hertz Hz - s -1

force newton N - mkgs -2

pressure,stress

pasca l Pa N/m 2 m -1kgs -2

energy, work,

quantity of heat

jou le J Nm m 2kgs -2

power, radiantf lu x

watt W J/s m 2kgs -3



43/66

e lectriccharge,quantity of e lectricity

cou lomb C - sA

e lectricpotentia l difference,e lectromotiveforce

vo lt V W/A m 2kgs -3A -1

capacitance farad F C /V m -2 kg -1s 4A2e lectricresistance

ohm V/A m 2kgs -3A -2

e lectricconductance

siemens S A/V m -2 kg -1s 3A2

magnetic f lu x weber Wb Vs m2kgs

-2A

-1

magnetic f lu x density

tes la T Wb/m 2 kgs -2A-1

inductance henry H Wb/A m 2kgs -2A -2

C e lsius

temperature

degreeC

elsius

C - KCopyright Tamer A. Tabet


44/66

luminous f lu x lumen

lm cdsr (c)

m 2m -2cd =cd

ill uminance lu x lx lm/m 2 m 2m -4cd =m -2cd

activity (of aradionuc lide)

becquere l

Bq - s -1

absorbed dose,specific energy(imparted), kerma

gray Gy J/kg m2s

-2

dose equiva lent (d) siev

ert

Sv J/kg m 2s -2

cata lytic activity kata l kat s -1mo l



45/66

(a) The radian and steradian may be usedadvantageous ly in e x pressions for derived units todistinguish between quantities of a different nature butof the same dimension; some e x amp les are given inTab le 4.(b) In practice, the symbo ls rad and sr are used whereappropriate, but the derived unit "1" is genera ll yomitted.(c) In photometry, the unit name steradian and the unitsymbo l sr are usua ll y retained in e x pressions for derived units.(d) O ther quantities e x pressed in sieverts are ambientdose equiva lent, directiona l dose equiva lent, persona l dose equiva lent, and organ equiva lent dose.



46/66

W mg t !

Ex amp le 1-1

An object at sea level has a mass of 400 kg.a) Find the weight of this object on earth.

b) Find the weight of this object on the moon where the local gravitationalacceleration is one-sixth that of earth.

(a)

2

2

1807.9)400(

sm

kg

N sm

kg W t !

N 8.3922!Note the use of the conversion factor to convert mass-acceleration units into forceunits.



47/66

(b)

Ex amp le 1-2 E

An object has a mass of 180 lbm. Find the weight of this object at a location wherethe local gravitational acceleration is 30 ft/s 2.

( )(30

W m g

l bmft

s

l bf

l bmft

sl bf

t !

!

!

1801

32 2

167 7

2

2

)(.

)

.

N smkg

N sm

kg

mg W t

8.65 3

1

6

807.9

)400

(2

2

!

!

!



48/66

Quiz time !!!!


49/66

Both a gage and a manometer are attachedto a gas tank to measure its pressure. If thepressure gage reads 80 kPa, determine the

distance between the two f luid leve ls of themanometer if the f luid is mercury, whosedensity is 13,600 kg/m 3.


50/66

Specific Vo lume

Specific vo lume ( ) is the volume occupied by a unit of massof a material. The specific volume of a substance is equal tothe reciprocal of its mass density. Specific volume may beexpressed in:

, or

where, V is the volume, m is the mass and is the density of thematerial.



51/66

For an ideal gas ,

where, is the Specific gas constant , T is the temperatureand P is the pressure of the gas.

Specific volume may also refer to molar volume.



52/66

5 2

State, E qui librium, Process, and Properties State

Consider a system that is not undergoing any change. The properties can bemeasured or calculated throughout the entire system. This gives us a set of

properties that completely describe the condition or state of the system. At a givenstate all of the properties are known; changing one property changes the state.

E qui l ibrium

A system is said to be in thermodynamic equilibrium if it maintains thermal (uniform

temperature), mechanical (uniform pressure), phase (the mass of two phases, e.g.,ice and liquid water, in equilibrium) and chemical equilibrium.



53/66

Process

Any change from one state to another is called a process. During a quasi-equilibriumor quasi-static process the system remains practically in equilibrium at all times. We

study quasi-equilibrium processes because they are easy to analyze (equations of state apply) and work-producing devices deliver the most work when they operate onthe quasi-equilibrium process.

In most of the processes that we will study, one thermodynamic property is heldconstant. Some of these processes are

C onstant PressureProcess

Water F

SystemBoundary

Process Property held

constantiso bar ic pressu re

isoth ermal tem pera tu re

isocho r ic vo lu me

is en tr o p ic en tr o py (s ee Ch a p ter 7 )Copyright

Tamer A. Tabet


54/66

We can understand the concept of a constant pressure process by considering theabove figure. The force exerted by the water on the face of the piston has to equalthe force due to the combined weight of the piston and the bricks. If the combinedweight of the piston and bricks is constant, then F is constant and the pressure is

constant even when the water is heated.We often show the process on a P-V diagram as shown below.



55/66

Steady-F low Process

Consider a fluid flowing through an open system or control volume such as a water heater. The flow is often defined by the terms steady and uniform. The term steady

implies that there are no changes with time. The term uniform implies no change withlocation over a specified region. Engineering flow devices that operate for longperiods of time under the same conditions are classified as steady-flow devices. Theprocesses for these devices is called the steady-flow process. The fluid propertiescan change from point to point with in the control volume, but at any fixed point theproperties remain the same during the entire process.

State Postu late

As noted earlier, the state of a system is described by its properties. But byexperience not all properties must be known before the state is specified. Once asufficient number of properties are known, the state is specified and all other

properties are known. The number of properties required to fix the state of a simple,homogeneous system is given by the state postulate:

The thermodynamic state of a simp le compressib le system iscomp lete ly specified by two independent, intensive properties.



56/66

C yc le

A process (or a series of connected processes) with identical end states is called acycle. Below is a cycle composed of two processes, A and B. Along process A, the

pressure and volume change from state 1 to state 2. Then to complete the cycle, thepressure and volume change from state 2 back to the initial state 1 along process B.Keep in mind that all other thermodynamic properties must also change so that thepressure is a function of volume as described by these two processes.

ProcessB

Process A

1

2P

V

Pressure

Force per unit area is called pressure, and its unit is the pascal, N/m 2, in the SIsystem and psia, lbf/in 2 absolute, in the English system.



57/66


58/66

These pressures are related by

P P P g a ge ab s atm!

P P P va c atm ab s!

Or these last two results may be written as

P P P ab s at m gage! s

Where the + P gage is used when P abs > P atm and P gage is used for a vacuum gage.

The relation among atmospheric, gage, and vacuum pressures is shown below.



59/66

Some values of 1 atm of pressure are 101.325 kPa, 0.101325 MPa, 14.696 psia, 760mm H g, and 29.92 inches H 2O.

Small to moderate pressure differences are measured by a manometer and a

differential fluid column of height h corresponds to a pressure difference between thesystem and the surroundings of the manometer.

This pressure difference is determined from the manometer fluid displaced height as

( P g h k P a! ( )The text gives an extensive review of the manometer pressure relations. For further study of the manometer pressure relations, see the text.

Other devices for measuring pressure differences are shown below .Copyright Tamer A. Tabet


60/66


61/66

Ex amp le 1-4

A pressure gage connected to a valve stem of a truck tire reads 240 kPa at a locationwhere the atmospheric pressure is 100 kPa. What is the absolute pressure in the

tire, in kPa and in psia? P P P

kP a kP a

kP a

ab s atm g a ge!

!

!

100 2 40

340

The pressure in psia is

P kP ap siakP a

p siaab s ! !3401 4 7101 3

49 3.

..

What is the gage pressure of the air in the tire, in psig?

P P P

p sia p sia

p si g

g a ge ab s atm!

!

!

49 3 1 4 7

34 6

. .

.Copyright Tamer A. Tabet

f


62/66

Check the side walls of the tires on your car or truck. What is the maximum allowedpressure? Is this pressure in gage or absolute values?

Ex amp le 1-5

Both a gage and a manometer are attached to a gas tank to measure its pressure. If the pressure gage reads 80 kPa, determine the distance between the two fluid levelsof the manometer if the fluid is mercury, whose density is 13,600 kg/m 3.

hP

g ! (

V

hk P a

kg

m

m

s

N mk P a

N

kg m sm

!

!

80

1 3600 9 807

10

1

0 6

3 2

3 2

2.

/

/.



63/66

Temperature

Although we are familiar with temperature as a measure of hotness or coldness, itis not easy to give an exact definition of it. H owever, temperature is considered as a

thermodynamic property that is the measure of the energy content of a mass. Whenheat energy is transferred to a body, the body's energy content increases and sodoes its temperature. In fact it is the difference in temperature that causes energy,called heat transfer, to flow from a hot body to a cold body. Two bodies are in thermalequilibrium when they have reached the same temperature. If two bodies are inthermal equilibrium with a third body, they are also in thermal equilibrium with eachother. This simple fact is known as the zeroth law of thermodynamics .

The temperature scales used in the SI and the English systems today are the Celsiusscale and Fahrenheit scale, respectively. These two scales are based on a specifiednumber of degrees between the freezing point of water ( 0 rC or 32 rF) and the boilingpoint of water (100 rC or 212 rF) and are related by

T F T C r r 95

32


E l 1 6


64/66

Ex amp le 1-6

Water boils at 212 rF at one atmosphere pressure. At what temperature does water boil in rC.

T = ( ) ( ) T F F C F

C r ! r rr ! r32 5

9212 32 5

9100

Like pressure, the temperature used in thermodynamic calculations must be inabsolute units. The absolute scale in the SI system is the Kelvin scale, which isrelated to the Celsius scale by

T K T + 27 3.15 r

In the English system, the absolute temperature scale is the Rankine scale, which isrelated to the Fahrenheit scale by

= F 459.67

T R T r

Also, note that

T R T K 1.8


B l i i f h l


65/66

Below is a comparison of the temperature scales.

This figure shows that that according to the International Temperature Scale of 1990(ITS-90) the reference state for the thermodynamic temperature scale is the triplepoint of water, 0.01 rC. The ice point is 0 rC, but the steam point is 99.975 rC at 1atm and not 100 rC as was previously established. The magnitude of the kelvin, K, is1/273.16 of the thermodynamic temperature of the triple point of water.

Trip lepoint of water

Boi lingpoint

of water at 1 atm

-273.15 0

0.01 273.16

99.975 373.125

rC K

0

32.02 491.69

211.955 671.625

rF R

-459.67

Abso lutezero



66/66

e N d oF Lecture o N e

THAN K YOU

lecture 1 eng. ther

Documents