basics definitions

8/3/2019 Basics Definitions

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ThermodynamicsThermodynamicsLesson ILesson I

Basic concepts and definitionsBasic concepts and definitions


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ObjectivesObjectives

Comprehend the terminologies used inComprehend the terminologies used inthermodynamics.thermodynamics.

To understand the definition of variousTo understand the definition of variousthermodynamic functions.thermodynamic functions.

To become familiar with various basicTo become familiar with various basicconcepts of thermodynamics.concepts of thermodynamics.


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ThermodynamicsThermodynamics--definitiondefinition

ThermoThermo -- ThermeTherme--HeatHeat

DynamicsDynamics--dynamisdynamis--WorkWork

A branch of science that deals with heatA branch of science that deals with heatwork and their mutual conversion.work and their mutual conversion.


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Application area ofApplication area ofthermodynamicsthermodynamics

Thermodynamic principles govern all theThermodynamic principles govern all thedevices involving energy transfer such asdevices involving energy transfer such as

Internal combustion enginesInternal combustion engines Rocket andjet enginesRocket andjet engines

Power plantsPower plants

Refrigerators and airRefrigerators and air--conditioners etc.,conditioners etc.,


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Classification of thermodynamicsClassification of thermodynamics

Statistical thermodynamics:Statistical thermodynamics:

It is a microscopic approach where theIt is a microscopic approach where the

behavior of individual molecules arebehavior of individual molecules arebeing investigatedbeing investigated

Classical thermodynamics:Classical thermodynamics:

It is a macroscopic approach where theIt is a macroscopic approach where thetotal effect is being investigated.total effect is being investigated.


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Thermodynamic System,Thermodynamic System,Boundary and surroundingsBoundary and surroundings

SystemSystem --A region in space or a quantity ofA region in space or a quantity ofmatter whose behavior is beingmatter whose behavior is beinginvestigated. Requires a workinginvestigated. Requires a working

substance to receive, store, transport, orsubstance to receive, store, transport, ordeliver energydeliver energy

SurroundingsSurroundings--Everything external to theEverything external to the

system is called surroundings.system is called surroundings. BoundaryBoundary--Surface that separates theSurface that separates the

system from the surroundings [Real orsystem from the surroundings [Real orImaginary, Fixed or moving]Imaginary, Fixed or moving]


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System, surroundings andSystem, surroundings andboundaryboundary

Water in

Water out

Water Water

Control

SurfaceBoundary


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Classification of thermodynamicsClassification of thermodynamicssystemssystems

Closed system:Closed system:

A fixed quantity of matter is takenA fixed quantity of matter is taken

for taken for analysisfor taken for analysis only energy is allowed to cross theonly energy is allowed to cross theboundary and matter is not allowed.boundary and matter is not allowed.

The same set of molecules areThe same set of molecules arepresent throughout the processpresent throughout the process


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Open systemOpen system

Open system: both mass and energy areOpen system: both mass and energy areallowed to cross the boundary.allowed to cross the boundary.

A region in space is analyzed. TheA region in space is analyzed. Theboundary is called control surface.boundary is called control surface.

Matter is entering and leavingMatter is entering and leavingsimultaneously hence different set ofsimultaneously hence different set ofmolecules are present at different instantmolecules are present at different instantof timeof time


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Isolated systemIsolated system

Isolated system: neither mass nor energyIsolated system: neither mass nor energyare allowed to cross the boundary.are allowed to cross the boundary.


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Examples of thermodynamicExamples of thermodynamic

systemssystems Water heated in a closed vesselWater heated in a closed vessel

Air being compressed in a leak proofAir being compressed in a leak proof

piston cylinder arrangement.piston cylinder arrangement. A liquid heated in a heat exchangerA liquid heated in a heat exchanger

(geyser)(geyser)

High pressure air throttled in a valve.High pressure air throttled in a valve. Hot fluid stored in an insulatedHot fluid stored in an insulated

container.container.


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Thermodynamic PropertiesThermodynamic Properties

Characteristics that are used to define theCharacteristics that are used to define thestate of the system are calledstate of the system are calledthermodynamics properties.thermodynamics properties.

PressurePressure

TemperatureTemperature

VolumeVolume

DensityDensity Specific volumeSpecific volume

Enthalpy, entropy, internal energyEnthalpy, entropy, internal energy


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Intensive propertiesIntensive properties

Properties which are not depending onProperties which are not depending onthe quantity of matterthe quantity of matter


PressurePressure

Specific volumeSpecific volume specific enthalpyspecific enthalpy


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Extensive propertiesExtensive properties

Properties which are depending on theProperties which are depending on thequantity of matterquantity of matter

Example:Example:VolumeVolume

MassMass


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m

P

V

0.5 m

P

0.5 V

0.5 m

P

0.5 V

Intensive & ExtensiveIntensive & Extensivepropertiesproperties


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PressurePressure

PPabsabs == ppatmatm+p+pguageguage

Pabs

Patm

PGuage


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Units of common propertiesUnits of common properties

S.No Properties Units

1 Pressure Bar, Pa, kPa, atm.

2 Temperature rC, K

3 Volume lit, cm3, m3

4 Sp. Volume m3 / kg

5 Density kg /m3


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ContinuumContinuum

In systems made of gas and vapour, thereIn systems made of gas and vapour, thereare empty spaces between the moleculesare empty spaces between the moleculesor atoms. For all the practical purposesor atoms. For all the practical purposesthis space is ignored. Further it isthis space is ignored. Further it isassumed that the entire volume is filledassumed that the entire volume is filledwith gas. This is called concept ofwith gas. This is called concept of

continuum.continuum.


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Thermodynamic StateThermodynamic State

AA thermodynamicthermodynamic systemsystem isis saidsaidtoto existexist inin thermodynamicthermodynamic statestate

whenwhen itit isis notnot undergoingundergoing anyanychangechange andand allall thethe propertiesproperties arearehavinghaving aa fixedfixed valuevalue..


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Equilibrium stateEquilibrium state

An equilibrium state of aAn equilibrium state of athermodynamic system is a state thatthermodynamic system is a state thatcan not be changed without anycan not be changed without anyinteraction with its surroundingsinteraction with its surroundings

The factors that cause a change withoutThe factors that cause a change withoutany interactions with its surroundingsany interactions with its surroundings

are:are:1.1. Pressure differencePressure difference

2.2. Temperature differenceTemperature difference

3.3. Chemical reactionChemical reaction


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Thermal equilibriumThermal equilibrium

It related to temperature.It related to temperature.

If the temperature at every point withinIf the temperature at every point withinthe system remains the same there willthe system remains the same there willnot be any heat transfer within thenot be any heat transfer within thesystem. The system is said to be in a statesystem. The system is said to be in a stateof thermal equilibrium.of thermal equilibrium.

COLD COPPERBLOCK

HOT COPPERBLOCK


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It is related to pressure.It is related to pressure.

A system is said to be in a state of mechanicalA system is said to be in a state of mechanicalequilibrium if there is no pressure differenceequilibrium if there is no pressure differencebetween any two point within the system.between any two point within the system.

Pressure difference within the system results inPressure difference within the system results inchanges in state.changes in state.

Mechanical equilibriumMechanical equilibrium

HIGH PRESSURE AIR

LOW PRESSURE AIR


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Chemical EquilibriumChemical Equilibrium

If there is no chemical reaction takingIf there is no chemical reaction takingplace within the system, it is said to be inplace within the system, it is said to be ina state of chemical equilibrium.a state of chemical equilibrium.


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Thermodynamic equilibriumThermodynamic equilibrium

If there exists thermal, mechanical andIf there exists thermal, mechanical andchemical equilibrium, the system is saidchemical equilibrium, the system is saidto be in thermodynamic equilibrium.to be in thermodynamic equilibrium.


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State postulateState postulate

TheThe statestate ofof aa simplesimple compressiblecompressible systemsystemisis completelycompletely defineddefined byby twotwoindependent,independent, intensiveintensive propertiesproperties..


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Thermodynamic processesThermodynamic processes

Any change that a system undergoes fromAny change that a system undergoes fromone equilibrium state to another is calledone equilibrium state to another is calleda process.a process.

When a system is undergoing a process,When a system is undergoing a process,if all the intermediate states areif all the intermediate states areequilibrium states, the process is said toequilibrium states, the process is said to

be a quasibe a quasi--equilibrium or a quasiequilibrium or a quasi--staticstaticprocess.process.


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Example of quasi and nonExample of quasi and non--quasiquasiequilibrium processequilibrium process

GAS

Weight

Remove theweight

Remove the

weights one

by one

NonNon--quasiquasi

equilibrium processequilibrium process Quasi equilibrium processQuasi equilibrium process


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Property DiagramProperty Diagram

Quasi equilibrium processQuasi equilibrium processNonNon--quasi equilibriumquasi equilibrium

processprocess

P

v v

P1

2

1

2


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Thermodynamic cyclesThermodynamic cycles

If a thermodynamic system is takenIf a thermodynamic system is takenthrough a number of processes in such athrough a number of processes in such athat the final state of the last process isthat the final state of the last process isidentical to the initial state of the firstidentical to the initial state of the firstprocess, then the system is said to haveprocess, then the system is said to haveundergone a thermodynamic cycle.undergone a thermodynamic cycle.

P

v

1

2

3


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Point and path functionsPoint and path functions

Point functions are those for which thePoint functions are those for which thechange depends on only the end stateschange depends on only the end statesand not on the path followedand not on the path followed

Path functions are those for which thePath functions are those for which thechange depends not only on the endchange depends not only on the endstates but also on the path followedstates but also on the path followed


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Example of path and pointExample of path and pointfunctionfunction

A

B

PATH - 1

PATH - 2

Difference in heightDifference in height same in path1 and path2same in path1 and path2--point functionpoint function

Distance traveledDistance traveled different in path1 and path2different in path1 and path2--path functionpath function


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Temperature of a system is defined as itsTemperature of a system is defined as itsthermal state with reference to its abilitythermal state with reference to its abilityto communicate heat to other bodies.to communicate heat to other bodies.

HOT BODY COLD BODYHEAT


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ZEROTH LAW OFZEROTH LAW OFTHERMODYNAMICSTHERMODYNAMICS

Two systems , each in mutual equilibriumwith aTwo systems , each in mutual equilibriumwith athird system, are also in mutual equilibriumwiththird system, are also in mutual equilibriumwitheach other in the same manner.each other in the same manner.

Zeroth law forms the basis for temperatureZeroth law forms the basis for temperaturemeasurementmeasurement

A

C

B


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Temperature scaleTemperature scale Contd.,Contd.,

Boiling point ofwater at 1 atm.

Melting point/Freezing point

Absolute zero

CelsiusCelsius KelvinKelvin FahreheitFahreheit RankineRankine

100100 373373 212212 672672

00 273273 3232 492492

273273 00 --460460 00


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Conversion of Temperature scalesConversion of Temperature scales

95)32(

273

!

!

FC

CK


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Homogeneous and heterogeneousHomogeneous and heterogeneous

systemssystems

Matter can exist in any one of the threeMatter can exist in any one of the three

phases namely solid, liquid, gas.phases namely solid, liquid, gas. A system consisting of a single phase isA system consisting of a single phase is

known as homogeneous systemknown as homogeneous system

A system consisting matter existing inA system consisting matter existing inmore than one phase is known asmore than one phase is known asheterogeneous systemheterogeneous system


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Pure substancesPure substances

Substances of fixed chemicalSubstances of fixed chemicalcomposition throughout are known ascomposition throughout are known aspure substances.pure substances.

Pure substances have homogeneous andPure substances have homogeneous andinvariable chemical compositioninvariable chemical compositionirrespective of the phase or phases inirrespective of the phase or phases in

which they exist.which they exist.


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GasGas vsvs VapourVapour

Closure to saturationClosure to saturation vapourvapour

Far away from saturationFar away from saturation GasGas


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Boyles LawBoyles Law

WhenWhen thethe temperaturetemperature remainsremains constant,constant,pressurepressure andand volumevolume areare varied,varied, thetheproductproduct pvpv remainsremains constantconstant


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Charles lawCharles law

Charles law states that, at constantCharles law states that, at constantpressure, the volume of a given mass of apressure, the volume of a given mass of agas is proportional to its absolutegas is proportional to its absolutetemperature.temperature.


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GayGay--Lussacs lawLussacs law

GayGay--Lussacs law states that, at constantLussacs law states that, at constantpressure, the volumetric coefficient ofpressure, the volumetric coefficient ofexpansion is constant for all gases. Theexpansion is constant for all gases. Thevariation of the volume of a gas withvariation of the volume of a gas withtemperature at constant pressure is given bytemperature at constant pressure is given by

kelvininetemperaturT

xpansionvolumetricofcd

etemperaturreferenceaatvolumeVTatvolumeV

TVV

T

CpT

e

1

0

0

F

F!

!


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To increase the pressureTo increase the pressure

Increase

the massIncrease the

temperature

Decrease the

volume


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mRTpV

VmTp

Vp

Tp

mp

!

w

w

w

w

/

/1


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IdealGasIdealGas

Substances that obey the followingSubstances that obey the followingrelation known as equation of state arerelation known as equation of state arecalled as ideal gasescalled as ideal gases

mRTpV!

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