1、CHAPTER 1 Introduction,KEY CONCEPTS Classical thermodynamics and the macroscopic perspective Fundamental concepts : open and closed systems(系统), boundary(边界), surroundings(外界), equilibrium(平衡), property(特性，物性参数), state(状态), process(过程), path(路径), work and heat(功和热), energy, entropy(熵)Laws of thermod
2、ynamics : first , second,Exergy（火用）(or availability可用能) and quality of energyApplications：steam, nozzle, compressors, heat engines(热机), refrigeration equipment(制冷设备) & heat pumps(热泵),moist air(湿空气) Problem-solving procedures, problem definition, solution outlines, reviews, and physical interpretatio
3、n of solutions.,1.1 Introduction Thermodynamics can be viewed as the science that deals with energy transformations and relationships between properties of systems. heat engines(热机)Thermal energy Mechanical energy heat pump（热泵）,A property（状态参数） is defined formally as any observable characteristic of
4、 a system. A system, or more precisely, a closed system, can be defined as any identifiable collection of matter. Thermodynamics has much in common with the experimental sciences. It relies entirely on observation and experimental measurements. Data obtained played a crucial role in the eventual for
5、mulation of the laws of thermodynamics. The laws of thermodynamics cannot be proved by demonstration.,Classical Thermodynamics and Statistical Thermodynamics Two approaches exist for determining properties of substances ( material or matter ) which make up systemsClassical thermodynamics involves th
6、e observation and measurement of properties on a large scale ( or macroscopic ) basis.,1.2 Basic Concepts and Thermodynamic Modeling Basic Concepts: Important thermodynamic properties include pressure(压力) , density(密度) , specific volume(比容，比体积), temperature , and several others that permit the preci
7、se definition of the condition , or state(状态) , in which the thermodynamic system exists .,Derived Concepts (Consequences of the laws of thermodynamics): Internal energy- derived from the first law of thermodynamics.Entropy(熵) and Exergy（火用）(or availability可用能) are derived from the second law .,The
8、first , and perhaps the most crucial step in thermodynamic-modeling entails what can be termed a process of abstraction(抽象化).,Modeling of a gasoline engine: 1. a mixture of air and fuel entering the engine 2. burning or combustion ofthe fuel in air inside the engine cylinder 3. work production resul
9、ting from fuel energy releasedin the combustion process 4. the original mixture entering the engine eventually leaves as an exhaust gas stream,A thermodynamic system(系统) is a region in space , or a fixed collection of matter , enclosed by a boundary(边界), and the system can be fixed or moving in spac
10、e.The boundary can be rigid or flexible, real or imaginary.,The boundary of a control volume(控制体) is called the control surface(控制面). Mass and energy can flow across the control surface.,4 types of systems : closed(闭口) , open(开口) , adiabatic(绝热) and isolated(孤立) .A closed system: Fig.1.5 (a) , has n
11、o mass crossing the system boundary . This type of system can have energy transfer (either as heat or work) across the boundary ,but no material substance crosses the system boundary.,An open system : Fig.1.5 (b) , across whose boundary transfers of energy and matter can occur . An open system is mo
12、re frequently referred to as a control volume(控制体).,An adiabatic system: the system has no heat exchange with surroundings(外界). An isolated system: Figure 1.5 ( c ) neither mass nor energy crosses the system boundary. Valuable for developing certain principles relating to the laws of thermodynamics
13、.,A closed system: An open system: Example of motor & fan,EXAMPLE1.1Appropriate modeling for the following operations,(a) pumping of water (using a centrifugal pump) from a ground-level tank to an elevated tank Solution: There is flow of mass (water) into and out of the pumping device. If the space
14、corresponding to the inside of the pump is of interest, an open system model would be the appropriate choice.The system boundary (or control surface) is shown with a dashed lineand is coincident with the inside surface of the pump casing.,(b) cooking of food (held in a covered container)Solution： Si
15、nce a fixed mass (the food) remains in a covered container throughout the cooking process, the closed system model is the appropriate choice. Figure 1.6(b) shows the inside of the container as the system boundary.,(c) generation of steam (by heating a steady stream of water entering a boiler) Soluti
16、on： Steam generation results from heating a stream of water as it passes through a boiler(锅炉). The open system model is appropriatehere since there is mass transfer acrossthe boundary of a fixed region in space. The inside surface of the boiler is the control surface, as shown in Figure 1.6(c).,(d)
17、inflating an automobile tire with air Solution：Both the open and closed system models are appropriate here and are depicted in Figure 1.6(d) for the tire inflation operation.,In part (ii) of the figure, the mass of air in the tire at any instant defines the system. Since the mass of air in the syste
18、m changes as the operation proceeds, the model to use is an open system. (the volume and shape of such a system changes during the operation),The closed system model is shown in part (i) of Figure 1.6(d) and defines the system as the final mass of air in the tire. Note that the system boundary initi
19、ally must include the air in the beginning and the additional atmospheric air ultimately into the tire as it is inflated.,Equilibrium(平衡) , Property(参数) and State(状态) A system is in equilibrium when no macroscopic changes (thermodynamic properties p, T, v), would occur within the system if it were t
20、o be isolated from its surroundings. Definition of equilibrium: no tendency exists for any property of the system to change. If a system is in a state of equilibrium , all the thermodynamic properties have uniform values throughout the system, and the only way to produce changes in these properties
21、is through some interaction across the boundary of the system.,Different types of equilibrium such as thermal(热) equilibrium, mechanical(力) equilibrium, and chemical equilibrium.Thermal equilibrium: the temperature is the same throughout the system. If a closed system is in thermal equilibrium with
22、its surroundings, this means that the temperature of the closed system is identical to the temperature of its surroundings. Example: water in a cup,Mechanical equilibrium: the pressure is uniform throughout the system and no tendency exists for the pressure to change with time. If a system is in mec
23、hanical equilibrium with its surroundings, no unbalanced forces are acting in the interior of the system or between the system and its surroundings.Example: water in a cup,The thermodynamic state of a system is identified by specifying the thermodynamic property values for the system. For most subst
24、ances encountered in engineering, however, it turns out that the values of only a few properties need to be specified to define the state. Such as the two property rule ( for the class of substances known as pure substances ).,Once the functional relationships are known precisely, the other properti
25、es can be determined at any given equilibrium state by using the values for just a few properties. The equations for the relationships among the thermodynamic properties of a substance are referred to as equation of state（状态方程）. e.g. pv=RT for ideal gas,Process（过程）, Path（路径）, and Interactions (Work
26、and Heat) A process can be defined simply as that which brings about a change of state of a system. When the thermodynamic state is changed, this is called a change of state for the system. The change of state for the system is specified in terms of the initial and final states. (始态，终态)Thus, the cha
27、nge of state can be defined by the changes that occur for different thermodynamic properties between the two end states.,A quasi-equilibrium(准平衡) or quasi-static（准静态）process is an ideal one in which the deviations from equilibrium are infinitesimal(无限小), so that all states that the system passes thr
28、ough during the process can be considered to be equilibrium states. If the system state deviates more than an infinitesimal amount from equilibrium during a process, it is termed a non-equilibrium process.,Examples of quasi-equilibrium(准平衡) or quasi-static（准静 态)processes of thermal & mechanical, mov
29、ing weight & heating, p-v plot,Most real processes are non-equilibrium processes, but in some instances, they can be approximated reasonably and accurately by ideal processes, which are those occurring in a quasi-static manner. In general, detailed and complete thermodynamic analyses can be made onl
30、y when the processes involved are ideal.,If the route cannot be identified, as is the case in non-equilibrium processes, it becomes meaningless to talk of the path for the process.,A thermodynamic path is defined as the series of states through which the system passes while undergoing a change from
31、one end state to the other. It should be evident that a path is identifiable only when a quasi-equilibrium process is taking place.,A solid line should be used to define the path for aquasi-equilibrium process, a dashed line should be used for a non-equilibrium process between any two equilibrium st
32、ates.,Reversible(可逆) & Irreversible processesReversible process: If at any time during the process both the system and the surroundings can be returned to their initial states along the reversed path.An ideal process without thermodynamic loss.,All real process are irreversible.The result of a real
33、process can be obtained by thecorrection of a reversible process.Quasi-equilibrium process aims at the state change inside a system & reversible process aims at the outside effect caused by a system.A reversible process must be a quasi-equilibrium process and quasi-equilibrium process is not necessa
34、rily a reversible process. This is a powerful technique frequently employed in Classical Thermodynamics.,4. Mixing of gases,Factors that render processes irreversible,1.Friction,2.Unrestrained expansion,3. Heat transfer through a finite temperature difference,A thermodynamic cycle(循环)is any thermody
35、namic process, or set of processes, resulting in a final state for the system that is identical to its initial state. It should be noted that a thermodynamic cycle may comprise either quasi-equilibrium or non-equilibrium processes, only the final state for the system must be identical to the initial
36、 state. (A closed line on the plot),Certain processes are given particular designations with the prefix “iso-” added. A constant temperature process is one in which the temperature of the system stays constant during the process and is thus referred to as an isothermal process.A constant pressure pr
37、ocess is called an isobaric processA constant volume process is known as an isochoric process.,It is important to note that regardless of how a change of state is effected from an initial state to a final state, the change of any thermodynamic property is fixed and defined solely by the 2 end states
38、. This is true because properties are characteristics of a system at each equilibrium state, their values fixed at any given state regardless of how that state is reached.,For this reason, thermodynamic properties are often referred to as state properties(状态参数) or point functions(点函数). e.g. pressure
39、, temperature, Path integrationCyclic integrationOther quantities are computed in thermodynamics that are path functions and depend on the process. Work and Heat are typical of these other quantities, and they are not properties of a system.,They are referred to as interaction. Work and heat are bot
40、h energy interactions between systems and their surroundings. Work is in mechanics and heat in thermal physics as forms of energy flux (or flow of energy). These quantities are not point functions but rather path functions, meaning that they are process dependent. Plot for different work done for 2
41、points,EnergyEnergy is a central concept in thermodynamics.capacity to do work discussion on p.15Energy can exist in variety of forms. When a fuel burns in air, the chemical energy of the fuel is transformed to another form of energy commonly referred to as heat energy or thermal energyNeither of th
42、ese two terms is really appropriate in thermodynamics. Thus, in thermodynamics, the termInternal energy (内能)(thermodynamic energy) is used.,Kinetic energy(动能) is the energy that a system possesses by virtue of its motion and is a form of mechanical energyGravitational potential energy (势能)is the ene
43、rgy that a system has by virtue of its position in a gravita-tional field. This is a form of mechanical energy. Other forms of energy include nuclear energy，electrical energy, magnetic energy, surface tension energy, and so on.,Entropy Entropy is another concept of considerable importance in thermod
44、ynamics. It is a thermodynamic property whose existence is inferred as a corollary of the second thermodynamics law. Entropy is defined in terms of a change between equilibrium states, and is expressed mathematically as dS = Q / T where Q is the incremental heat addition to the system in a quasi-equ
45、ilibrium process during which the system temperature is T .,The change in entropy between an initial equilibrium state and a final equilibrium state is thus given by the integral ofQ/T in any quasi-equilibrium process between the two states. S = Q/T,Typical applications that require the use of this
46、property include: 1. establishing the direction in which physical or chemical processes can occur in nature.2. providing a quantitative measure of the extent of departure of real processes from thermodynamically ideal processes known as reversible processes.3. establishing performance limits and eva
47、luating performance efficiencies of actual devices.,Graphical Symbols for Devices and Typical Systems Many systems are in use today that essentially operate to transform energy from one form to another.The systems involved may be simple or quite complex, but to facilitate a diagrammatic representati
48、on of such a system, certain graphical symbols are commonly used for those device in engineering applications. Some typical devices used in thermodynamic systems include compressors(压气机) and pumps(泵), turbines(涡轮) and expanders(膨胀机), evaporators (蒸发器) and boilers(锅炉), condensers(冷凝器), nozzles(喷嘴), a
49、nd diffusers(扩压器).,Compressor(压气机), turbine(涡轮机), expander(膨胀器) boiler(锅炉), condenser(冷凝器), evaporator(蒸发器), nozzle(喷嘴), diffuser(扩压器 ),Figures 1.17,A compressor is a work-absorbing device that compresses a gas such as air or refrigerant vapor, resulting in a change from a low pressure to a high pressure state.,A pump similarly raises the pressure of a fluid; this term is used when the fluid is a liquid.,The common graphical symbols for a compressor and a pump are shown in Figures1.17(a) and (b), respectively.,
