山东大学：《工程热力学》课程PPT教学课件（双语）第二章 Energy, Energy Transfer and General Energy Analysis

Chap. 1 SummaryEnergyTransferEnergyRelationshipstoTransformationsmatterpropertiesThermodynamicsApplicationareasZerothLawThe FirstLawCarnot PrinciplesTheSecondLawAScienceofEnergyTheIncreaseofetcEntropyPrincipleSystemClosed systemOpensystemThermodynamic SystemBoundary/SurroundingAdiabaticsystemIsolatedsystemAsetofpropertiesthatcompletelydescribestheconditionofthesystemStateEquilibrium:: Temperature(T), mechanical (P),phase, chemical State postulate: The state of a simple compressible system is completelyspecified bytwoindependentintensiveproperties.E.g.T(temperature)&v(specificvolume).orP&T (onephase)Isothermal,Isobaric,Path, CycleState 1 to State 2Isometric.IsoentropicQuasi-equilibrium:aprocessinwhichsystemremainsinfinitesimallyclosetoan equilibriumProcessstateaf alltimecReversible processSteadyflowprocessIreversibleprocessExtensivepropertiesV,E,H,SIntensive properties T.P,pPropertiesK273.15Triplepoint=0.01C=273.16K1Pascal=1N/m^2Pgage=Pabs - PatmPvac=Patm - Pabs

Chap. 1 Summary 1 Thermodynamics Energy Application areas A Science of Energy Thermodynamic System Zeroth Law The First Law The Second Law The Increase of Entropy Principle Carnot Principles etc Energy Transformations Relationships to matter properties Closed system Open system Isolated system Adiabatic system Intensive properties T, P, ρ Extensive properties V, E, H,S State State postulate: The state of a simple compressible system is completely specified by two independent, intensive properties. E.g. T(temperature)& ν (specific volume), or P&T (one phase) Equilibrium:: Temperature(T), mechanical (P), phase, chemical Path, Cycle Process State 1 to State 2 Steady flow process T K ℃ 273.15 Triple point=0.01℃=273.16K 1Pascal=1N/m^2 Pgage=Pabs - Patm Pvac=Patm - Pabs Transfer A set of properties that completely describes the condition of the system Properties Quasi-equilibrium: a process in which system remains infinitesimally close to an equilibrium state at all times. Isothermal, Isobaric, Isometric, Isoentropic Reversible process Irreversible process P System Boundary/Surrounding

Chap.2 SummaryTotal Energy, EIntermal Energy,UPotentialEnergy,PEKinetic Energy. KEEnergyForms of EnergyE=U+KE+PE=U+mV2/2+mgzMechanical energy,Nuclearenergy,Chemical Energy,SensibleenergyLatentenergy.Thermalenergy.Heat,Work,FlowworkConvectionTemperature diffBy Heat, QRadiationConductionEnergy Transfer, EForce*distanceBy Work, WForms ofwork:mechanical.shaft,spring,electrical,etcBy Mass, m=o,foraclosedsystemclosed systemQ=△U+ WEin-Eout=AEsystem1stLawofThermodynamicsEnergybalance:Ein-Eout=(Qin-Qout)+(Win-Wout)+(Emass,in-Emass,out)=EsystemEnergyChangeEffciency=desiredoutput/requiredinputEnergy Conversion EfficiencyCombustion efficiency.Overall efficiency,efficiency of generator, motor, pump, turbine, etc.福Energyand Environment

E=U+KE+PE=U+mV2 /2+mgz Chap.2 Summary 2 Forms of Energy Energy Transfer, E Total Energy, E Kinetic Energy, KE Potential Energy, PE Conduction Convection Radiation Effciency =desired output/ required input Ein-Eout= ∆Esystem Internal Energy,U 1st Law of Thermodynamics Energy balance: Ein-Eout=(Qin-Qout)+(Win-Wout)+(Emass,in-Emass,out)= ∆Esystem Energy Conversion Efficiency Energy and Environment Mechanical energy, Nuclear energy, Chemical Energy, Sensible energy, Latent energy, Thermal energy, Heat, Work, Flow work Energy By Heat , Q Temperature diff Forms of work: mechanical, shaft, spring,electrical, etc By Work, W Force*distance By Mass, m =0, for a closed system closed system Q=∆U+ W Energy Change: Combustion efficiency, Overall efficiency, efficiency of generator, motor, pump, turbine, etc

Chapter2.Energy,EnergyTransferandGeneral EnergyAnalysis

Chapter 2. Energy, Energy Transfer and General Energy Analysis 3

2-1. IntroductionQuestion:ArefrigeratorinaroomRoom:closedandwell-insulated,no heat exchangewith outsideRoomRefrigerator:dooropen,electricityconnected.Tairintheroom:Increase?Decrease?Constant?A,:decrease:refrigeratorwill cooltheairdown国Az:increase:motor of refrigeratordissipateswasteheattowarm air upRight: increasetakethe ROOM+Refrigrator asa system, walls as boundaryMASS?NO!Aclosed system.Heat?NO!AnadiabaticsystemHave energy interactionby electricityNothing is storing the energySo: Electrical energy will transform to thermal energy. Tair will increaseaccordingtotheconversationofenergyprinciple

2-1. Introduction • Question: A refrigerator in a room. – Room: closed and well-insulated, no heat exchange with outside. – Refrigerator: door open, electricity connected. – Tair in the room: Increase? Decrease? Constant? • A1 : decrease: refrigerator will cool the air down • A2 : increase: motor of refrigerator dissipates waste heat to warm air up • Right: increase • take the ROOM+Refrigrator as a system, walls as boundary – MASS? NO! A closed system. – Heat? NO! An adiabatic system 4 – Have energy interaction by electricity. – Nothing is storing the energy – So: Electrical energy will transform to thermal energy. Tair will increase according to the conversation of energy principle

2-2, Forms of energyTotal energy/总能 (E, KJ):the sum of numerous forms of energy,e.g.:thermalmechanical,kinetic,potential,electric,magnetic,chemical,nuclear.e=E/m (kJ/kg)total energyperunitmassE Energy flow rate, kJ/s E= meThermodynamicsprovidesnoinformationabouttheabsolute valueofthetotalenergy. It deals only with the change of the total energy.Microscopicform: related tothe molecularstructureofa system,isdegreeofthe molecular activity,and independentof outsiderefInternal energy/热力学能 (U):the sumofallthemicroscopicformsofenergy- Sensible energy: internal energy associated with the kinetic energies of themoleculesLatent energy: internal energy associated with the phase of a systemMacroscopicform:systempossessesasawholewithoutsideref.kineticenergy/动能(KE):KE=(m*V2)/2V,asresultsofitsmotionrelativetosomereferenceframe.potential energy/势能 (PE):PE=(mgz)z,asa result of its elevation ina gravitationalfield.4

2-2, Forms of energy • Total energy/总能 (E, KJ): the sum of numerous forms of energy, e.g.: thermal, mechanical, kinetic, potential, electric, magnetic, chemical, nuclear. – e=E/m (kJ/kg) total energy per unit mass – Thermodynamics provides no information about the absolute value of the total energy. It deals only with the change of the total energy. – Microscopic form: related to the molecular structure of a system, is degree of the molecular activity, and independent of outside ref. • Internal energy/热力学能 (U): the sum of all the microscopic forms of energy. – Sensible energy: internal energy associated with the kinetic energies of the molecules – Latent energy: internal energy associated with the phase of a system – Macroscopic form: system possesses as a whole with outside ref. • kinetic energy/动能(KE): KE=(m*V2 )/2 V, as results of its motion relative to some reference frame. • potential energy/势能 (PE): PE=(mgz) z, as a result of its elevation in a gravitational field. 5 Energy flow rate, kJ/s

2-2, Forms of energyTotal energyl 总能 (E, KJ): the sum of numerous forms of energy, e.g.:thermal,mechanical,kinetic,potential,electric,magnetic,chemical,nuclearMagnetic,electric,andsurfacetensioneffects are significantinsomespecializedcasesonlyandareusuallyignored.Intheabsenceof sucheffects,thetotal energyofa systemconsistsof:E=U+mV2/2+mgz(KJ)(KJ/Kg)- Per unit mass: e=u+v2/2+gzForastationarysystem:△E=△U

2-2, Forms of energy • Total energy/总能 (E, KJ): the sum of numerous forms of energy, e.g.: thermal, mechanical, kinetic, potential, electric, magnetic, chemical, nuclear. • Magnetic, electric, and surface tension effects are significant in some specialized cases only and are usually ignored. • In the absence of such effects, the total energy of a system consists of: – E=U+mV2 /2+mgz (KJ) – Per unit mass: e=u+v2 /2+gz (KJ/Kg) – For a stationary system: ∆E=∆U 6

2-2, Forms of energyMass flowrate/质量流率 m:the amount of mass flowing throughacross section perunittime. (kg/s)Volume flow rate/体积流率 V : the volume of a fluid flowing through across section per unit time. (m3/s)m=pV=pA,Vavg一Energyflowrate/能量流率（功率）E：kJ/skWE=meE=me

2-2, Forms of energy – Mass flow rate/质量流率 : the amount of mass flowing through a cross section per unit time. (kg/s) – Volume flow rate/体积流率 : the volume of a fluid flowing through a cross section per unit time. (m3 /s) – Energy flow rate/能量流率（功率） ： kJ/s kW 7

2-2, Forms of energyNuclear energy: changes in the core or nucleus.一fusion（聚变)：twosmallnucleicombineintoalargeroneDifficulttouse.E6neutron5.1x10-13j(b)Fusionof hydrogen-Fission(裂变):split one atom into other elements. E.g.U-235commonlyusedtogenerateelectricityinnuclearpowerplantsnuclearpowersubmarinesandaircraftcarriers,nuclearbombsUranium3.2 × 1011 JU-23514eutronsnneutronRb-93(a)Fissionofuranium

2-2, Forms of energy • Nuclear energy: changes in the core or nucleus. – fusion (聚变)：two small nuclei combine into a larger one. Difficult to use. – Fission(裂变): split one atom into other elements. E.g. U-235. commonly used to generate electricity in nuclear power plants, nuclear power submarines and aircraft carriers, nuclear bombs. 8

2-2, Forms of energyChemical energy(化学能): changes in the structure of theelectrons of the atoms; Mechanical energy(机械能): the form of energy that can beconverted to mechanical work completely and directly by an idealmechanicaldevicesuchasanidealturbine-Kinetic energy: kJ-Potential energy: kJ- Flow energy for flowing fluids: The mechanical energy of a flowing fluid :(量纲一致性)emech=P/p+V2/2+gzkJ/kg Flow energy, P/p: a pressure force acting on a fluid throughadistanceproducesworkV2PTotal energy in rate form:Emech=imnemechm2p

2-2, Forms of energy • Chemical energy(化学能): changes in the structure of the electrons of the atoms; • Mechanical energy(机械能): the form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device such as an ideal turbine. – Kinetic energy: kJ – Potential energy: kJ – Flow energy for flowing fluids • The mechanical energy of a flowing fluid : – emech=P/ρ+ν2 /2+gz kJ/kg (量纲一致性) • Flow energy, P/ρ: a pressure force acting on a fluid through a distance produces work • Total energy in rate form: 9

2-2, Forms of energyThe only two forms of energy interactionsassociatedwith a closed system are:HEAT（传热):drivingforceisatemperaturedifference.一 WORK （作功）： otherwise,itis work10

2-2, Forms of energy • The only two forms of energy interactions associated with a closed system are: – HEAT (传热): driving force is a temperature difference. – WORK （作功）：otherwise, it is work. 10