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Chapter One

Introduction and Basic Concepts

Sep. 11 - 13, 2012

1

Objectives

Identify the unique vocabulary associated with

thermodynamics through the precise definition of basic

concepts to form a sound foundation for the development

of the principles of thermodynamics.

Review the metric SI and the English unit systems.

Explain the basic concepts of thermodynamics such as

system, state, state postulate, equilibrium, process, and

cycle.

Review concepts of temperature, temperature scales,

pressure, and absolute and gage pressure.

Introduce an intuitive systematic problem-solving

technique.

2

1.1 Thermodynamics and Energy

Thermodynamics can be defined as the scienceof energy.

The name thermodynamicsstems from the Greek wordstherme (heat) and dynamis (power).

The conservation of energy (the first law)

-Energycannot be created or destroyed; it can only

change forms

-Energyis a thermodynamic property.

Energy has quality as well as quantity (the second law),

and actual processes occur in the direction of decreasing

quality of energy.3

1.1 Thermodynamics and Energy

Classical thermodynamics: The macroscopic approach to

study of thermodynamics that does not required a

knowledge of the behavior of individual particles.

Statistical thermodynamic: A more elaborate approach,

based on the average behavior of large groups of

individual particles.

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1-1() 1-2

1.1

5

1-3(the second law)

1.1

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1-4

1.1

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1-5

1.1

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1.2 Dimensions and Units()

Dimension: Any physical quantity

Primary or fundamental dimension:

- mass m, lengthL, time t, temperature T, etc

Second or derived dimension:

-velocity v, energyE, volume V, force F, etc.

Units: The arbitrary magnitudes assigned to thedimensions

9

SI units: (system international)

Length m; Electric current A (Ampere)

Mass kg; Amount of light cd (candela)

Time s; Amount of matter mole

Temperature K(Kelvin) or

C (Celsius)

EI units: (English units)

Length ft;Pound mass lbm;

Time s;

Temperature R (Rankine)or

F (Fahrenheit)

1.2 Dimensions and Units

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Force (F) = ma = (Mass) (Acceleration)

1N(Newton) = 1 kg m/s2

1 lbf = 32.174 lbmft/s2

Weight (W) = mg = (Mass) (Local gravitational acceleration)

g= 9.807 m/s2;

= 32.174 ft/s2;

Work = (Force) (Distance)

1 J (joule)= 1 Nm

Energy: Cal; Btu

1.2 Dimensions and Units

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Energy: Cal; Btu

Calorie (Cal):

The amount of energy needed to raise the temperatureof 1g of water at 15 C by 1 C.

British thermal unit (Btu):

The energy required to raise the temperature of 1 lbmof water at 68 F by 1 F.

Dimensional Homogeneity:All the terms in an equation must have the same unit

1.2 Dimensions and Units

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1N = 1 kg x 1 m/s 2

1kgf= 1 kg x 9.807 m/s2

1lbf = 1 slug x 1 ft/s2

= 32.174 lbmx 1 ft/s2

= 1 lbmx 32.174 ft/s2

1.2

13

1-9 150

25

() =x g (gravity)

1 kgf= 1 kg x 9.807 m/s2

1 lbf = 1 lbmx 32.174 ft/s2

1.2

14

1-10

1.2

15

Ex 1: pV = mRT P: N/m2; V: m3; m: kg; R=Ru/M; T: K

Ru=8.31434 kJ/kmolK; M=kg/kmol

1 J (joule) = 1 N x 1 m

)().()()()( KTkmol

kgM

Kkmol

kJRkgmmV

m

Np

31483

2

smKkg

kmol

Kkmol

mN

N

s

mkg

RTga c

/..

..

?../..

8348300728

103148141

03113007283148141

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Dimensional Homogeneity:

All the terms in an equation must have the same unit

Ex 2: sonic speed RTga c

16

1.3 Systems ()

System ():

A quantity of matter or a region in space chose n for

study

Surrounding or Environment ():

Everything external to the system

Boundary():

The real or imaginary surfaces that separate the systemfrom its surroundings.

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1-19 (system)(surrounding or environment)(boundary)

1.3

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The definition of systems

A fixed quantity of mass (control mass ()) or

- Closed system (())(a specified amount of mass, no flow of

matter)and

A control volume () or

- Open system()(a specified region in space, open to the flowof matter)

*Isolated system(one that is not influenced in anyway by surroundings)

*Adiabatic system (one that is without heat transfer by surroundings)

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1-20

1-21

1.3()

20

(control volume)

1.3()

21

1-22

1.3()

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1.4 Properties of a System

()

Property ():Any observable characteristic of a system

- properties (Characteristics)

P, T, V (measurable) viscosity, thermal conductivity,

U, S, H (un-measurable)

Extensive Properties ():depend on mass, size

(i.e. volume, m ass, energy, S, Availability)

Intensive Properties ():independent of the size of a system ( i.e.T, P, density, height)

Specific properties: extensive properties/total mass or moles

(i.e. specific volume, specific energy, specific entropy)

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1-24(intensive)(extensive)

(intensive property)

(extensive property)

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Continuum:

- Matter is made up of atoms, view it as a continuous,homogeneous matter with no holes.

- To treat properties as point function, and to assume

the properties to vary continually in space with no

jump discontinuities.

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1-25 (continuum)

26

Properties in macroscopic thermodynamics

m

lim0

Density,

Molecular and atomicMolecular and atomic

effects are importanteffects are important

Limit of the macroscopicLimit of the macroscopicmodel and assumptions.model and assumptions.

(m3)

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1.5 Density and Specific Gravity

Density : mass per unit volume, = m/V

Specific volume:volume per unit mass

Specific volume= V/M

Specific gravity:The ratio of the density of a s ubstance to

the density of some standard substance at a specified

temperature (usually water at 4 C, for which H2O= 1000

kg/m3

).SG =/H2O

Specific weight: The weight of a unit volume of a substance.

Specific weight s=g

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1.6 State and Equilibrium (

)

State ():

The state of a system is described by its properties, a description of

the system.

- For a simple compressible system:

The state postulaterequires - the state of a simple compressible

system is completely specified by two independent, intensive

properties.

or - two properties be specified independent to fix the state

Equilibrium ():

A state of balance in

- thermal equilibrium: T - mechanical equilibrium: P

- phase equilibrium: m - chemical equilibrium: t

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(a)1 (b)2

1-27

(a) (b)

1-28

1.6

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Phase Rule (no chemical reaction)

F=C-P+2

-F : # of intensive (internal) properties need to fix the

state of the system- C: # of components

-P: # of phases

Nitrogen gas F=2 (C=1,P=1)

Un-saturated water F=1 (C=1,P=2)

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(State Postulate):

1-29( Tand v)

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1.7 Processes and Cycles ()

Process: The sequence of states which a system passes in

going from one equilibrium stateto another

Path:A system passes during a pr ocess

Quasi-state process:

The system remains infinitesimally close to an

equilibrium state at all times

Cycle:Process in which the final state is identical to the

initial value

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1-3012(process)(path)

1.7

34

(b) ()

1-31(quasi-equilibrium)(non-quasi-equilibrium)

1.7

35

1-32P-V

1.7

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1.7 Processes and Cycles

Some Special Processes:

- Isothermal Process: T is constant

- Isobaric Process:P is constant

- Isochoric or isometric Process:

specific volume is constant

- Steady-flow Process (for open system only):

A process during which a fluid flows through a control

volume steadily (time independent).

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1-33(steady-flow)

1-34

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1.8 Temperature and the Zeroth Law

Temperature:

A measure of hotness or coldness

Thermodynamic Temperature Scale:- Celsius scale, C

- Fahrenheit scale, F

- Kelvin scale, K

- Rankine scale, R

- Ideal gas temperature scale, K

Constant-volume gas thermometer

At low pressure, the temperature of a gas is pro portionalto its pressure at constant volume.

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1-35

1.8

40

1-36P-T

1.8

41

1-37-273.15

1.8

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1-38,39

1.8

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Zeroth Law

- The internal properties of a system are

functionally related

- If two bodies are in thermal equilibrium with a

third body, they are also in thermal equilibrium

with each other.

T1=T2, T2=T3, we have T1=T3

- in 1931, by R. H. Fowler

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1.9 Pressure (

)

is defined as the force exerted by a fluid per unitarea, F/A.

Units:

- 1 pascal (Pa) = 1 N/m2

-1 bar = 100 kPa

- 1 psi = 1 lbf/in2

- 1 atm = 76 cm-Hg (standard atmospheric pressure)

- 1 atm = 101,325 Pa = 1.01325 bar

- 1 kgf/cm2(kg/cm2)= 0.96788atm = 14.223psi

- 1 atm = 14.696 psi

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1-40()

1.9

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1.9 Pressure

Absolute Pressure:

The actual pressure at a given position and it is measuredrelative to absolute vacuum

Gage Pressure:

The difference between the absolute pressure and thelocal atmospheric pressure (measured)

Pgage= PabsPatm(P above Patm)

Vacuum Pressure:Pressure below atmospheric pre ssure

Pvac= PatmPabs(P below Patm)

471-41, 42

1.9

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1.9 Pressure

Variation of pressure with depth,

or P = Patm+gh; : liquid density

1-43()

49

1-44

zzgPPP

12

2

112 gdzPPP

For constant

1.9

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1-45

1.9

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1-47()

1.9

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1.9 Pressure

Pascals principle:

The pressure applied to a confined fluid increases the

pressure throughout by the same amount,

P1=P2; and F1/A1=F2/A2

P1= P2; a small height difference is negligible

at high pressure

1-48

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1.10 The Manometer (

)

Manometer:

A fluid column can be used to measure press ure

Pressure variations (as shown in previous)

- The pressure change across a fluid column of height is P =gh

- Pressure increases downward in a given fluid and

decreases upward. Pbottom > Ptop

- Two points at the same elevationin a continuous fluidat restare at the same pressure.

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1-501-61-49

P1= P2

1.10

Example 1-6

55

1-51hgh

1.10

56

1-52

PA= PB

1.10

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1-531-7

1.10

Example 1-7

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Other pressure measurement devices

Bourdon tube:

It consists of a hollow metal tubebent like a hook whose end is closed andconnected to a dial indicator needle.

Pressure tr ansducer:

It is made of semiconductor materials such as silicon and convert the pressure effectto an electrical effectsuch as a change in voltage, resistance, orcapacitance.

Gage pressure transducer:

The atmosphericpressure as a reference

Absolute pressure transducer:

It is calibrated to have azerosignal output at full vacuum.

Differential pressure transducer:

Measure the pressure difference between two locations directly instead of using twopressure transducers and taking their difference.

Piezoelectric effect:

The emergence of an electric potential in a crystalline substancewhen subjected tomechanical pressure.

Strain-gage pressure transducer:

The sensors of such transducers are made of thin metal wiresorfoilwhose electricalresistance changes when strained under the influence of fluid pressure .

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1-54

1.10

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1.11 Barometer and Atmospheric Pressure

(

)

Barometer:

A device is used to measure the atmosp heric pressure- Patm=gh; :density

- Torr: The unit mmHg

1 atm = 760 torr; and 1 torr = 133.3Pa

Atmospheric Pressure

The atmospheric pressure changes not only withelevation but also with weather conditions.

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1-551-56

1.11

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1-57

63

1-581-9

Example 1-9

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1.12 Problem-solving technique

Step 1:Problem statement

Step 2:Schematic

Step 3:Assumptions

Step 4:Physics laws

Step 5:Properties

Step 6:Calculation Step 7:Reasoning, verification, and discussion

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1.12

1-62

1.12

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1-63

1.12

671-67

1.12

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10, 15, 28, 40, 49, 54, 63, 74, 82, 92, 104, 110

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