Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two...
Transcript of Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two...
![Page 1: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/1.jpg)
Thermodynamics
Lecture5Thermodynamics
![Page 2: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/2.jpg)
Objec6ves
• Energy,Work,andHeat• ThermodynamicSystems
• WorkingCycles
• FirstandSecondLawofThermodynamics
![Page 3: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/3.jpg)
ThermodynamicProper6es
• Inthermodynamics,aworkingsubstanceisanyfluid(includinggases)whichreceives,transports,andtransfersenergyinasystem.Thestateorcondi6onofaworkingsubstanceatanyloca6oninanysystemmaybedeterminedifthethermodynamicproper6esofthesubstanceattheloca6onofinterestareknown.Theseproper6esinclude:– Pressure– Temperature– Density(andSpecificVolume)– Internalenergy– Enthalpy– Entropy
![Page 4: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/4.jpg)
Phases
• Solid,liquid,andvapor–fluidmayexistinanyphaseorcombina6onofphases
![Page 5: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/5.jpg)
![Page 6: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/6.jpg)
Proper6es
• Anintensivepropertyisindependentofthemass;thevalueofanextensivepropertyvariesdirectlywiththemass.Thus,ifaquan6tyofmaTerinagivenstateisdividedintotwoequalparts,eachpartwillhavethesamevalueofintensiveproper6esastheoriginal,andhalfthevalueoftheextensiveproper6es.
• Pressure,temperature,anddensityareexamplesofintensiveproper6es.Massandtotalvolumeareexamplesofextensiveproper6es.Extensiveproper6esperunitmass,suchasspecificvolume,areintensiveproper6es.
![Page 7: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/7.jpg)
Proper6es
• Massandweight• Volume
• Velocity• Pressure• Temperature
![Page 8: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/8.jpg)
SpecificHeat• Heat(Q)isanenergyintransi6on.Ifthisheatissuppliedtoamass,m,itcausesthemasstoriseintemperaturefromT1toT2.ThismaybeexpressedbytheSpecificHeatEqua7on:
![Page 9: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/9.jpg)
PhaseChange• Thermalenergysuppliedtoasubstancecausesits
temperaturetorisewithanincreaseininternalenergyun6litreachesthetemperatureoffusionorevapora6on.– Whenthetemperatureoffusionisreached,theheatoffusion
causesthesubstancetochangefromasolidtoaliquidatthetemperatureoffusion.
– Whenthetemperatureofvaporiza6onorboiling(calledsatura6ontemperature)isreached,theheatofvaporiza6on(alsocalledlatentheatorenthalpyofvaporiza6on)causesthesubstancetochangefromaliquidtoavapor(gaseousform)atthevaporiza6ontemperature.
• Sensibleheataddi6onresultsinachangeoftemperaturebutnotachangeofphase
• Latentheataddi6onresultsinachangeofphasebutnochangeintemperature
![Page 10: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/10.jpg)
![Page 11: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/11.jpg)
LawsofThermodynamics
• TheFirstLawofThermodynamicssimplystated:Energycannotbecreatedordestroyed;thisisalsocalledtheLawofConserva6onofEnergy.
• TheSecondLawofThermodynamicssimplystated:Allenergyreceivedasheatbyaheat‐enginecyclecannotbeconvertedintomechanicalwork(someheatmustberejected).
![Page 12: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/12.jpg)
DerivedProper6es
• Internalenergyisamo6onenergystoredintheindividualmoleculesofasubstance.Internalenergydependsontemperatureandthephaseofthesubstancesuchassolid,liquidorgas.Usedfornon‐flowcalcula6ons
• Enthalpyisapropertythatconsistsoftwoparts:(1)internalenergy(U)storedintheindividualmoleculesasheatenergyand(2)flowenergypossessedbythefluidbecauseitisflowingwithapressure(P)andavolume(V).
• Entropyisamathema6calquan6tythatincreasesifheatisdegradedbyallowingittoflowfromahightemperaturetolowtemperaturewithoutproducingmechanicalwork.
![Page 13: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/13.jpg)
FormsofEnergy
• Poten6alEnergy• Kine6cEnergy• InternalEnergy• FlowEnergy
![Page 14: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/14.jpg)
FormsofEnergy
• Kine6cenergy,poten6alenergy,internalenergyandPVenergyareformsofenergythatareallproper6esofthesystem.
• Workandheatalsoareformsofenergy,buttheyareenergyintransit.Theyarenotproper6esofthesystem.– Workisdonebyoronasystem,butasystemcontainsnowork.
– Heatistransferredtoorfromasystem,butasystemcontainsnoheat.
![Page 15: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/15.jpg)
ThermodynamicSystem
• Asystemisapar6cularpor6onoftheuniverse,normallyapar6cularquan6tyofmaTerorapar6cularspace,whichweintendtostudydirectly
• Thestateofaworkingfluidinasystemisdefinedintermsofitsthermodynamicproper6es:pressure,temperature,specificvolume,enthalpy,internalenergy,andentropy.Onlytwoindependentthermodynamicproper6esarerequiredtocompletelydefinethestateoftheworkingfluid.
• Workingfluid• Systemboundary
– Closedvs.Open• Equilibrium,process,andcycle
![Page 16: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/16.jpg)
ThermodynamicSystem
• Areversibleprocessforasystemisdefinedasaprocessthat,oncehavingtakenplace,canbereversed,andinsodoingleavesnochangeineitherthesystemorsurroundings.
• Anirreversibleprocessisaprocessthatcannotreturnboththesystemandthesurroundingstotheiroriginalcondi6ons.
• Anadiaba6cprocessisoneinwhichthereisnoheattransferintooroutofthesystem.Thesystemcanbeconsideredtobeperfectlyinsulated.
• Anisentropicprocessisoneinwhichtheentropyofthefluidremainsconstant.
• AthroTlingprocessisdefinedasaprocessinwhichthereisnochangeinenthalpy
![Page 17: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/17.jpg)
CarnotCycle
• 1‐2:adiaba6ccompressionfromTCtoTHduetoworkperformedonfluid.
• 2‐3:isothermalexpansionasfluidexpandswhenheatisaddedtothefluidattemperatureTH.
• 3‐4:adiaba6cexpansionasthefluidperformsworkduringtheexpansionprocessandtemperaturedropsfromTHtoTC.
• 4‐1:isothermalcompressionasthefluidcontractswhenheatisremovedfromthefluidattemperatureTC.
![Page 18: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/18.jpg)
CarnotCycle
• ThemostefficientheatenginecycleistheCarnotcycle,consis6ngoftwoisothermalprocessesandtwoadiaba6cprocesses.TheCarnotcyclecanbethoughtofasthemostefficientheatenginecycleallowedbyphysicallaws.Whenthesecondlawofthermodynamicsstatesthatnotallthesuppliedheatinaheatenginecanbeusedtodowork,theCarnotefficiencysetsthelimi6ngvalueonthefrac6onoftheheatwhichcanbesoused.
![Page 19: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/19.jpg)
![Page 20: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/20.jpg)
![Page 21: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/21.jpg)
RankineCycle• TherearefourprocessesintheRankinecycle,thesestatesareiden6fied
bynumberinthediagramtotheright.• Process1‐2:Theworkingfluidispumpedfromlowtohighpressure,asthe
fluidisaliquidatthisstagethepumprequiresliTleinputenergy.• Process2‐3:Thehighpressureliquidentersaboilerwhereitisheatedat
constantpressurebyanexternalheatsourcetobecomeadrysaturatedvapor.
• Process3‐4:Thedrysaturatedvaporexpandsthroughaturbine,genera6ngpower.Thisdecreasesthetemperatureandpressureofthevapor,andsomecondensa6onmayoccur.
• Process4‐1:Thewetvaporthenentersacondenserwhereitiscondensedataconstantpressureandtemperaturetobecomeasaturatedliquid.Thepressureandtemperatureofthecondenserisfixedbythetemperatureofthecoolingcoilsasthefluidisundergoingaphase‐change.
![Page 22: Thermodynamics · for non‐ flow calculaons • Enthalpy is a property that consists of two parts: (1) internal energy (U) stored in the individual molecules as heat energy and](https://reader033.fdocuments.us/reader033/viewer/2022041816/5e5b16d7c9500134c178e5bc/html5/thumbnails/22.jpg)