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1、Chapter One Basic ConceptsEngineering ThermodynamicsJilin University Thermal energy engineering department2023/1/91System,surroundings,and boundary.1-1 Thermodynamic System Closed system(Control mass)Control volume 2023/1/92Jilin University Thermal energy engineering departmentJilin University Therm
2、al energy engineering departmentMass cannot cross the boundaries of a closed system,but energy can.1-1 Thermodynamic System2023/1/93Jilin University Thermal energy engineering departmentA control volume may involve fixed,moving,real,and imaginary boundaries.1-1 Thermodynamic System2023/1/94Jilin Uni
3、versity Thermal energy engineering department The thermodynamic state of a system is defined by specifying values of a set of measurable properties sufficient to determine all other properties.For fluid systems,typical properties are pressure,volume and temperature.1-2 The Concept of “State”2023/1/9
4、5Jilin University Thermal energy engineering departmentA process between states 1 and 2 and the process path.1-2 The Concept of “State”2023/1/96Jilin University Thermal energy engineering departmentAbsolute,gage,and vacuum pressures.1-2 The Concept of “State”2023/1/97Jilin University Thermal energy
5、engineering departmentComparison of temperature scales.Celsius scaleKelvin scaleFahrenheit scaleRankine scale 1-2 The Concept of “State”2023/1/98Jilin University Thermal energy engineering departmentCelsius Scale Triple point of water Triple point of water at P=1 at P=1 atmatmT=0 T=0 o oC C Steam po
6、int of water Steam point of water at P=1 at P=1 atmatmT=100 T=100 o oC C 1 1 o oC C=1 K=1 Kn nKelvin ScaleKelvin Scalen nTriple point of water at P Triple point of water at P=1=1 atmatmn nT=273.15 KT=273.15 Kn nSteam point of water at P Steam point of water at P=1=1 atmatmn nT=373.15 KT=373.15 K 1-2
7、 The Concept of “State”Temperature scalesTemperature scales2023/1/99Jilin University Thermal energy engineering department 1-3 Equilibrium StateA system in thermodynamic equilibrium satisfies:mechanical equilibrium(no unbalanced forces)thermal equilibrium(no temperature differences)chemical equilibr
8、ium2023/1/910Jilin University Thermal energy engineering departmentnState Postulate The thermodynamics state of a simple compressible system is completely specified by two independent,intensive properties.1-3 Equilibrium State2023/1/911Jilin University Thermal energy engineering departmentThe P-V di
9、agram of a compression process.1-3 Equilibrium State2023/1/912Jilin University Thermal energy engineering department 1-4 Gas Equation of State This implies:(1)very little molecular interaction(p 0),and(2)molecules are point masses,i.e.,zero volume.Gas equation of stateFor 1kgFor 1molThe ideal gas eq
10、uation of state2023/1/913Jilin University Thermal energy engineering departmentThe universal gas constantM=Molecular weight,M=Molecular weight,kg/kg/kmolkmol 1-4 Gas Equation of State 2023/1/914Jilin University Thermal energy engineering departmentA gas does a differential amount of work W as it for
11、ces the piston to move by a differential amount ds.1-5 Quasi-static Process and reversible process2023/1/915Jilin University Thermal energy engineering department Only“infinitesimal”unbalanced forces exist,so that the process can be viewed as taking place in a series of“quasi-equilibrium”states.(The
12、 term quasi can be taken to mean“as if”.)For this to be true the process must be slow in relation to the time needed for the system to come to equilibrium internally.1-5 Quasi-static Process and reversible process2023/1/916Jilin University Thermal energy engineering departmentA reversible process fo
13、r a system is defined as a process that,once having taken place,can be reversed,and in so doing leaves no change in either the system or surroundings.In other words the system and surroundings are returned to their original condition before the process took place.In reality,there are no truly revers
14、ible processes;however,for analysis purposes,one uses reversible to make the analysis simpler,and to determine maximum theoretical efficiencies.1-5 Quasi-static Process and reversible process2023/1/917Jilin University Thermal energy engineering department 1-6 The work of reversible processMaSystemf(
15、f(P P P Pk k,k=1.N)=0,k=1.N)=0 SurroundingsMass FlowMass FlowMass FlowMass FlowWorkWorkHeat Heat Interactions2023/1/918Jilin University Thermal energy engineering departmentNote:Pgas PambientDirection of MotionDirection of MotionPiston WallPiston WallSystem:A gasat p,V,and T.xDeformation of the syst
16、em boundary2023/1/919 1-6 The work of reversible processJilin University Thermal energy engineering departmentpV=AxV V1 1V V2 2p p1 1p p2 2Evaluating the work.Integral fora quasi-static process.2023/1/920 1-6 The work of reversible processJilin University Thermal energy engineering department 1-7 HeatA resistor heating water Evaluating the heat.Integral fora quasi-static process.2023/1/921Jilin University Thermal energy engineering department 1-8 Cyclic Processes IIIP P1 1P P2 22023/1/922Jilin University Thermal energy engineering department