1BasicConceptsofThermodynamics

1-1ThermodynamicsandEnergyThermodynamicsisdefinedasthescienceofenergy.Engineeringthermodynamic

dealswiththeprinciplesofenergyandenergyconversioninengineeringandthethermalpropertiesofsubstancesaswell.1-1-1DefinitionofThermodynamics

TheBasicLawsofThermodynamics:

(1)TheFirstLawofThermodynamics:anexpressionofthequantityrelationshipduringenergychange

(2)TheSecondLawofThermodynamics:anexpressionofthequalityrelationshipduringenergychange1-1-2ContentsofThermodynamics

Itcanbedividedinto:

ClassicalThermodynamics--------macroscopicapproachStatisticalThermodynamics--------microscopicapproach

ThePropertiesofMaterial(1)IdealGas(2)Vapor:WaterSteam,Freon,Ammonia(3)Mixtures:Gasmixture,Gas-vapormixturePracticalApplicationGasPowerCycleVaporandCombinePowerCycleRefrigerationAnyphysicalquantitycanbecharacterizedbydimensionThearbitrarymagnitudesassignedtothedimensionsarecalledUnitsPrimary(foundamental)dimensionsandunits:Massm,LengthL,timet,temperature,T,molSecondarydimensions:velocityV,energyE,volumeV

Englishsystem:AlsoknownastheUnitedStatesCustomarySystem(USCS)SI:InternationalSystem1-1-3DimensionsandUnits

FromLeSystemeInternationald’UnitesHistory:1.1790FrenchNationalAssemblychargedtheFrenchAcademyofScience2.1875TheMetricConvectionTreatywassignedby17nations.GeneralConferenceofWeightsandMeasures(CGPM)wasestablished3.1960theCGPMproducedtheSISomeSIandEnglishunits

RefertoourTextbookDimensionalHomogeneityEveryterminanequationmusthavethethesameunits.*thestudentmustkeepinmindthataformulawhichisnotdimensionallyhomogeneousisdefinitelywrong,butadimensionallyhomogeneousformulaisnotnecessarilyright1-2-1ThedefinitionofThermodynamicsSystemSystem:AquantityofmatteroraregioninspaceforstudyTherealorimaginarysurfacethatseparatesthesystemfromitssurroundingsiscalledboundary

AnythingoutsidetheboundaryiscalledsurroundingTheboundarycanberealorimaginary;fixedorchangeable,hasnothicknessandvolume,anddoesnotcontainanysubstance.1-2ThermodynamicsSystemClosedsystem:

1-1-3-2TheClassificationofThermodynamicssystemAsystemthatonlyenergycancrosstheboundarybutnomasscanenterorleave

(alsoknownascontrolmass)Openedsystem:

Asystemthatnotonlyenergybutalsomasscancrosstheboundary(alsoknownascontrolvolume)isolatedsystem:

Asystemthatneitherenergynormasscancrosstheboundary(aspecialclosedsystem)TheUniverse1-3StateandEquilibrium1-3-1

Definition:

Allmacroscopiccharacteristicsofasystematonetimepoint1-3-2Classification:

1-3-3.ConditionsofEquilibriumEquilibriumstate:

anypartofthesystemhavethesamecharacteristicsanycharacteristicsdon’tchangewithtimeNonequilibriumstate:ThermalequilibriumMechanicalequilibriumChemicalequilibriumPhaseequilibrium1-4PropertiesofSystem1-4-1DefinitionAnycharacteristicofasystemiscalledaproperty1-4-2CharacteristicofpropertyRelatedwithStatesbuthavenothingtodowiththepathfromonestatetoanotherAccordingtomathematics：∮dx=01-4-3ClassificationofpropertyIntensiveproperty：Propertiesindependentofthesizeofsystem,suchas：temperature,pressure,specificvolumeExtensiveproperty：Propertieswhosevaluesdependonthesizeorextentofsystem,suchas：volume,entropy,enthalpy1-5ThestatepostulateThestateofsystemisdescribedbyitsproperties,Butobviouslywedon’tneedtospecifyallthepropertiestofixastate,Thenhowmanypropertiesareenoughtofixastate?Statepostulate

Thestateofa

simplecompressiblesystem

iscompletelyspecifiedbytwoindependent,intensivepropertiesAsystemiscalledsimplecompressiblesystem

intheabsenceofelectrical,gravitational,motion,andsurfacetensioneffects.1-6ThermodynamicsPropertyCoordinatesSincetwopropertiescanfixastate,it’sveryconvenienttodrawastatepointonatwo-dimensioncoordinates.

pvequilibriumstatenonequilibriumstateTheusuallyusedcoordinatesare:p-vcoordinates,T-scoordinates,h-scoordinates1-7ProcessandCycleProcess:

anychangethatasystemundergoesfromoneequilibriumstatetoanotheraprocessproceedsinsuchmannerthatthesystemremainsinfinitesimallyclosetoanequilibriumstateatalltimeHowtochangeunderequilibriumstate?Quasi-staticprocess:pvQuasi-staticprocessnonequilibriumprocessInitialstatefinalstateCycle:Apath-closedprocesspv1-8Formsofenergy1-8-1TotalenergyThetotalenergy

Eofasystemisthesumofthermal,mechanical,kinetic,potential,electric,chemicalandnuclearenergy.Onaunitmassbasis,1-8-2Classificationofenergy1.Macroscopicform:kineticenergyKEandpotentialenergyPE

Onaunitmassbasisandand2.Microscopicform:relatetothemolecularstructureofasystemandthedegreeofthemolecularactivity.Thesumofallthemicroscopicformsofenergyiscalledtheinternalenergy,denotedbyUor

u

onaunitmassbasis.1-8-3ExpressionoftotalenergyOnaunitmassbasis1-9Pressure1-9-1

definitionTheforceexertedbyafluidperunitareaCalculation:Unit:SI:Pa--------N/m2English:psi------lbf/in21bar=105Pa=0.1Mpa

=100kPa1atm=101,325Pa=101.325kPa

=1.01325bar=14.696psi1-9-2

GagepressureandvacuumPressureAbsolutepressure:theactualpressureatagivenpositioniscalledtheabsolutepressureThepressurecalculatedbyformulaP=F/AmanometerGagepressure:Thepressureoveratmosphericpressurewhilegaspressureislargerthanthatofatmosphere，expressedbyPgVacuumpressure:Thepressurebelowatmosphericpressurewhilegaspressureissmallerthanthatofatmosphere，expressedbyPvInSItheunitalsoisPa,butinEnglishpsigusuallyemployedAbsolutepressure?gagepressure?vacuumpressure?woooooooo!Whichoneisthestateproperty?1-10-1Thezerothlawofthermodynamics

Iftwobodiesareinthermalequilibrium

withathirdbody,theyarealsointhermalequilibriu