工程热力学和制冷循环外文翻译本科学位论文Word文档格式.docx

工程热力学和制冷循环外文翻译本科学位论文Word文档格式.docx

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240112608

班级：

K暖通111

Class:

K-Nuantong111

所在学院：

康尼学院

College:

KangniCollege

专业：

建筑环境与设备工程

Profession:

BuildingEnvironmentandEquipmentEngineering

指导教师：

Tutor:

LiuMinghui

2015年3月7日

CHAPTER1

THERMODYNAMICSANDREFRIGERATIONCYCLES

THERMODYNAMICS...................................................................1.1

FirstLawofThermodynamics.........................................................1.2

SecondLawofThermodynamics.....................................................1.2

ThermodynamicAnalysisofRefrigerationCycles...........................1.3

EquationsofState..............................................................................1.3

CalculatingThermodynamicProperties.............................................1.4

COMPRESSIONREFRIGERATIONCYCLES................................1.6

CarnotCycle........................................................................................1.6

TheoreticalSingle-StageCycleUsingaPureRefrigerant

orAzeotropicMixture..................................................................1.8

LorenzRefrigerationCycle...................................................................1.9

TheoreticalSingle-StageCycleUsingZeotropic

RefrigerantMixture.....................................................................1.10

MultistageVaporCompressionRefrigerationCycles........................1.10

ActualRefrigerationSystems................................................................1.12

ABSORPTIONREFRIGERATIONCYCLES.....................................1.14

IdealThermalCycle..............................................................................1.14

WorkingFluidPhaseChangeConstraints...............................................1.14

WorkingFluids.......................................................................................1.15

AbsorptionCycleRepresentations..........................................................1.16

ConceptualizingtheCycle.......................................................................1.16

AbsorptionCycleModeling.....................................................................1.17

Ammonia-WaterAbsorptionCycles........................................................1.19

NomenclatureforExamples....................................................................1.20

THERMODYNAMICSisthestudyofenergy,itstransformations,anditsrelationtostatesofmatter.Thischaptercoverstheapplicationofthermodynamicstorefrigerationcycles.Thefirstpartreviewsthefirstandsecondlawsofthermodynamicsandpresentsmethodsforcalculatingthermodynamicproperties.Thesecondandthirdpartsaddresscompressionandabsorptionrefrigerationcycles,twocommonmethodsofthermalenergytransfer.

THERMODYNAMICS

Athermodynamicsystemisaregioninspaceoraquantityofmatterboundedbyaclosedsurface.Thesurroundingsincludeeverythingexternaltothesystem,andthesystemisseparatedfrom

thesurroundingsbythesystemboundaries.Theseboundariescanbemovableorfixed,realorimaginary.Entropyandenergyareimportantinanythermodynamicsystem.Entropymeasuresthemoleculardisorderofasystem.Themoremixedasystem,thegreateritsentropy;

anorderlyorunmixedconfigurationisoneoflowentropy.Energyhasthecapacityforproducinganeffectandcanbecategorizedintoeitherstoredortransientforms.

StoredEnergy

Thermal（internal）energyiscausedbythemotionofmoleculesand/orintermolecularforces.

Potentialenergy（PE）iscausedbyattractiveforcesexistingbetweenmolecules,ortheelevationofthesystem.

（1）

where

m=mass

g=localaccelerationofgravity

z=elevationabovehorizontalreferenceplane

Kineticenergy（KE）istheenergycausedbythevelocityofmoleculesandisexpressedas

（2）

where

Visthevelocityofafluidstreamcrossingthesystemboundary.

Chemicalenergyiscausedbythearrangementofatomscomposingthemolecules.

Nuclear（atomic）energyderivesfromthecohesiveforcesholdingprotonsandneutronstogetherastheatom’snucleus.

EnergyinTransition

HeatQisthemechanismthattransfersenergyacrosstheboundariesofsystemswithdifferingtemperatures,alwaystowardthelowertemperature.Heatispositivewhenenergyisaddedtothesystem（seeFigure1）.

Workisthemechanismthattransfersenergyacrosstheboundariesofsystemswithdifferingpressures（orforceofanykind）,alwaystowardthelowerpressure.Ifthetotaleffectproducedinthesystemcanbereducedtotheraisingofaweight,thennothingbutworkhascrossedtheboundary.Workispositivewhenenergyisremovedfromthesystem（seeFigure1）.

MechanicalorshaftworkWistheenergydeliveredorabsorbedbyamechanism,suchasaturbine,aircompressor,orinternalcombustionengine.

Flowworkisenergycarriedintoortransmittedacrossthesystemboundarybecauseapumpingprocessoccurssomewhereoutsidethesystem,causingfluidtoenterthesystem.Itcanbe

moreeasilyunderstoodastheworkdonebythefluidjustoutsidethesystemontheadjacentfluidenteringthesystemtoforceorpushitintothesystem.Flowworkalsooccursasfluidleavesthe

system.

Flowwork=pv（3）

wherepisthepressureandvisthespecificvolume,orthevolumedisplacedperunitmassevaluatedattheinletorexit.

Apropertyofasystemisanyobservablecharacteristicofthesystem.Thestateofasystemisdefinedbyspecifyingtheminimumsetofindependentproperties.ThemostcommonthermodynamicpropertiesaretemperatureT,pressurep,andspecificvolumevordensityρ.Additionalthermodynamicpropertiesincludeentropy,storedformsofenergy,andenthalpy.

Frequently,thermodynamicpropertiescombinetoformotherproperties.Enthalpyhisanimportantpropertythatincludesinternalenergyandflowworkandisdefinedas

（4）

whereuistheinternalenergyperunitmass.

Eachpropertyinagivenstatehasonlyonedefinitevalue,andanypropertyalwayshasthesamevalueforagivenstate,regardlessofhowthesubstancearrivedatthatstate.

Aprocessisachangeinstatethatcanbedefinedasanychangeinthepropertiesofasystem.Aprocessisdescribedbyspecifyingtheinitialandfinalequilibriumstates,thepath（ifidentifiable）,andtheinteractionsthattakeplaceacrosssystemboundariesduringthe

process.

Acycleisaprocessoraseriesofprocesseswhereintheinitialandfinalstatesofthesystemareidentical.Therefore,attheconclusionofacycle,allthepropertieshavethesamevaluetheyhadatthebeginning.Refrigerantcirculatinginaclosedsystemundergoesa

cycle.

Apuresubstancehasahomogeneousandinvariablechemicalcomposition.Itcanexistinmorethanonephase,butthechemicalcompositionisthesameinallphases.

Ifasubstanceisliquidatthesaturationtemperatureandpressure,itiscalledasaturatedliquid.Ifthetemperatureoftheliquidislowerthanthesaturationtemperaturefortheexistingpressure,itiscalledeitherasubcooledliquid（thetemperatureislowerthanthesaturationtemperatureforthegivenpressure）oracompressedliquid（thepressureisgreaterthanthesaturationpressureforthegiventemperature）.

Whenasubstanceexistsaspartliquidandpartvaporatthesaturationtemperature,itsqualityisdefinedastheratioofthemassofvaportothetotalmass.Qualityhasmeaningonlywhenthesubstanceissaturated（i.e.,atsaturationpressureandtemperature）.Pressureandtemperatureofsaturatedsubstancesarenotindependentproperties.

Ifasubstanceexistsasavaporatsaturationtemperatureandpressure,itiscalledasaturatedvapor.（Sometimesthetermdrysaturatedvaporisusedtoemphasizethatthequalityis100%.）

Whenthevaporisatatemperaturegreaterthanthesaturationtemperature,itisasuperheatedvapor.Pressureandtemperatureofasuperheatedvaporareindependentproperties,becausethetemperaturecanincreasewhilepressureremainsconstant.Gasessuchasairatroomtemperatureandpressurearehighlysuperheatedvapors.

FIRSTLAWOFTHERMODYNAMICS

Thefirstlawofthermodynamicsisoftencalledthelawofconservationofenergy.Thefollowingformofthefirst-lawequationisvalidonlyintheabsenceofanuclearorchemicalreaction.

Basedonthefirstlaworthelawofconservationofenergyforanysystem,openorclosed,thereisanenergybalanceas

NetamountofenergyNetincreaseofstored

=

addedtosystemenergyinsystem

or

[Energyin]–[Energyout]=[Increaseofstoredenergyinsystem]

Figure1illustratesenergyflowsintoandoutofathermodynamicsystem.Forthegeneralcaseofmultiplemassflowswithuniformpropertiesinandoutofthesystem,theenergybalancecanbewritten

（5）

wheresubscriptsiandfrefertotheinitialandfinalstates,respectively.

Nearlyallimportantengineeringprocessesarecommonlymodeledassteady-flowprocesses.Steadyflowsignifiesthatallquantitiesassociatedwiththesystemdonotvarywithtime.Consequently,

（6）

whereh=u+pvasdescribedinEquation（4）.

Asecondcommonapplicationistheclosedstationarysystemforwhichthefirstlawequationreducesto

（7）

SECONDLAWOFTHERMODYNAMICS

Thesecondlawofthermodynamicsdifferentiatesandquantifiesprocessesthatonlyproceedinacertaindirection（irreversible）fromthosethatarereversible.Thesecondlawmaybedescribedinseveralways.Onemethodusestheconceptofentropyflowinan