工程热力学：02 第一章 基本概念（2）.ppt

1、Jilin University Thermal Engineering department,1,Chapter One Basic Concepts（2）,主讲教师：金英爱 教授 汽车工程学院热能工程系 吉林大学,Engineering Thermodynamics,Jilin University Thermal Engineering department,2,System, surroundings, and boundary. Equilibrium state Typical properties Specific volume v Absolute pressure、Gage

2、pressure、Vacuum pressure Temperature T,Chapter One Basic Concepts,T（K）= 273.15 + t ( ),Properties may be extensive or intensive The ideal gas equation of state,Chapter One Basic Concepts,Jilin University Thermal Engineering department,4,A gas does a differential amount of work W as it forces the pis

3、ton to move by a differential amount dx ., 1-5 Quasi-static Process and reversible process,Process Any change that a system undergoes from one equilibrium state to another is called process.,Jilin University Thermal Engineering department,5,Only “infinitesimal” unbalanced forces exist, so that the p

4、rocess can be viewed as taking place in a series of “quasi-equilibrium” states. (The 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 proc

5、ess,Jilin University Thermal Engineering department,6,Quasi-static process 1-2 Nonquasi-static process 1-2, 1-5 Quasi-static Process and reversible process,Jilin University Thermal Engineering department,7,A reversible process for a system is defined as a process that, once having taken place, can b

6、e 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., 1-5 Quasi-static Process and reversible process,Reversible process,Jilin University Thermal Engineeri

7、ng department,8,In reality, there are no truly reversible 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 process,Reversible process,Irreversible process,An irreve

8、rsible process is a process that is not reversible.,Jilin University Thermal Engineering department,9, 1-5 Quasi-static Process and reversible process,Irreversibilities include: friction unrestrained expansion mixing of two fluids heat transfer across a finite temperature difference electric resista

9、nce inelastic deformation of solids chemical reactions,Jilin University Thermal Engineering department,10, 1-6 The work of quasi-static process,Interactions,Jilin University Thermal Engineering department,11,Work is energy expanded by a force acting through a distance. Thermodynamic work is defined

10、as energy in transition across the system boundary and is done by a system if the sole effect external to the boundaries could have been raising weight., 1-6 The work of quasi-static process,Work,W J,Jilin University Thermal Engineering department,12,Deformation of the system boundary, 1-6 The work

11、of quasi-static process,Jilin University Thermal Engineering department,13,Integral for a reversible process., 1-6 The work of quasi-static process,Evaluating the work :,For 1kg:,J,J/kg,Jilin University Thermal Engineering department,14, 1-6 The work of quasi-static process,Work:,Sign convention: Wo

12、rk done by a system is positive Work done on a system is negative,Work is path function, depend on the path.,Jilin University Thermal Engineering department,15, 1-7 Heat,Heat is defined as the form of energy that is transferred between two system by virtue of a temperature difference.,A resistor hea

13、ting water,Difference between: Heat Thermal Energy,Difference between: Heat Work,Q J,Jilin University Thermal Engineering department,16, 1-7 Heat,Heat of reversible process :,Heat is defined as the form of energy that is transferred between two system by virtue of a temperature difference.,J/kg,J,En

14、tropy: S J/K Clausius , 1865 Entropy per unit mass: s J/(kg.K),Jilin University Thermal Engineering department,17, 1-7 Heat,Sign convention: Heat transfer to a system is positive Heat transfer from a system is negative,Heat is path function, depend on the path.,Jilin University Thermal Engineering d

15、epartment,18,Heat and the specific heat,The specific heat c J/(kgK),The specific heat at constant volume: cV The specific heat at constant pressure: cp,Cp,m=22.410-3Cp=Mcp,Reversible process,Jilin University Thermal Engineering department,19, 1-8 Cyclic Processes,The net work,The net heat,Jilin Univ

16、ersity Thermal Engineering department,20,Summary,In this chapter, the basic concepts of thermodynamics are introduced. Property 1. For a given state, all have their own state parameters. 2. The property is independent of the path used to arrive at the system. Equilibrium state State Postulate The id

17、eal gas equation of state,Jilin University Thermal Engineering department,21,Summary,Quasi-static Process and reversible process The work of quasi-static process,Heat of quasi-static process :,Cyclic Processes,Jilin University Thermal Engineering department,22,Questions,Describe the energy exchange

18、processes necessary for natural gas to be used to provide electricity for the lights in the room you are in. What is the difference between extensive and intensive properties? Is the amount of heat needed to go from one state to another path independent? If an irreversible process have taken place, can system return to original state?,