1.2 Defining Systems 5 TABLE 1.1 Selected Areas of Application of Engineering Thermodynamics Aircraft and rocket propulsion Alternative energy systems Fuel cells Geothermal systems Magnetohydrodynamic (MHD)converters Ocean thermal,wave,and tidal power generation Solar-activated heating,cooling,and power generation Solar-cell arrays Thermoelectric and thermionic devices Wind turbines Automobile engines Bioengineering applications Biomedical applications Combustion systems 围 Compressors,pumps Cooling of electronic equipment Cryogenic systems,gas separation,and liquefaction Fossil and nuclear-fueled power stations Heating,ventilating,and air-conditioning systems Surfaces with thermal Absorption refrigeration and heat pumps control coatings Vapor-compression refrigeration and heat pumps International Space Station Steam and gas turbines Power production Propulsion Steam generator Electric Combustion power gas cleanup Turbine Coal Steam Cooling Generator tower Condenser Ash Condensate Cooling water Refrigerator Electrical power plant Vehicle engine Trachea Lung Fuel in Compressor Combustor Turbine Air in -Hot gases out He Turbojet engine Biomedical applications
1.2 Defining Systems 5 Selected Areas of Application of Engineering Thermodynamics Aircraft and rocket propulsion Alternative energy systems Fuel cells Geothermal systems Magnetohydrodynamic (MHD) converters Ocean thermal, wave, and tidal power generation Solar-activated heating, cooling, and power generation Thermoelectric and thermionic devices Wind turbines Automobile engines Bioengineering applications Biomedical applications Combustion systems Compressors, pumps Cooling of electronic equipment Cryogenic systems, gas separation, and liquefaction Fossil and nuclear-fueled power stations Heating, ventilating, and air-conditioning systems Absorption refrigeration and heat pumps Vapor-compression refrigeration and heat pumps Steam and gas turbines Power production Propulsion International Space Station Solar-cell arrays Surfaces with thermal control coatings Refrigerator Turbojet engine Compressor Turbine Air in Hot gases out Combustor Fuel in Coal Air Condensate Cooling water Ash Stack Steam generator Condenser Generator Cooling tower Electric power Electrical power plant Combustion gas cleanup Turbine Steam Vehicle engine Trachea Lung Heart Biomedical applications International Space Station control coatings TABLE 1.1
6 Chapter 1 Getting Started TABLE 1.2 Predictions of Life in the United States in 2050 At home Homes are constructed better to reduce heating and cooling needs Homes have systems for electronically monitoring and regulating energy use. Appliances and heating and air-conditioning systems are more energy-efficient. Use of solar energy for space and water heating is common. More food is produced locally. Transportation Plug-in hybrid vehicles and all-electric vehicles dominate. Hybrid vehicles mainly use biofuels. Use of public transportation within and between cities is common. An expanded passenger railway system is widely used. Lifestyle Efficient energy-use practices are utilized throughout society. Recycling is widely practiced,including recycling of water. Distance learning is common at most educational levels. Telecommuting and teleconferencing are the norm. The Internet is predominately used for consumer and business commerce. Power generation Electricity plays a greater role throughout society. Wind,solar,and other renewable technologies contribute a significant share of the nation's electricity needs. A mix of conventional fossil-fueled and nuclear power plants provides a smaller,but still significant,share of the nation's electricity needs. A smart and secure national power transmission grid is in place. 1.2.1 Closed Systems closed system A closed system is defined when a particular quantity of matter is under study.A closed system always contains the same matter.There can be no transfer of mass across its boundary.A special type of closed system that does not interact in any way isolated system with its surroundings is called an isolated system. Figure 1.1 shows a gas in a piston-cylinder assembly.When the valves are closed, we can consider the gas to be a closed system.The boundary lies just inside the pis- ton and cylinder walls,as shown by the dashed lines on the figure.Since the portion of the boundary between the gas and the piston moves with the piston,the system Gas Boundary volume varies.No mass would cross this or any other part of the boundary.If com- bustion occurs,the composition of the system changes as the initial combustible mix- ture becomes products of combustion. 1.2.2 Control Volumes In subsequent sections of this book,we perform thermodynamic analyses of devices such as turbines and pumps through which mass flows.These analyses can be con- ducted in principle by studying a particular quantity of matter,a closed system,as it passes through the device.In most cases it is simpler to think instead in terms of a given region of space through which mass flows.With this approach,a region within Fig.1.1 Closed system:A gas a prescribed boundary is studied.The region is called a control volume.Mass crosses in a piston-cylinder assembly. the boundary of a control volume. A diagram of an engine is shown in Fig.1.2a.The dashed line defines a control control volume volume that surrounds the engine.Observe that air,fuel,and exhaust gases cross the boundary.A schematic such as in Fig.1.2b often suffices for engineering analysis
6 Chapter 1 Getting Started 1.2.1 Closed Systems A closed system is defined when a particular quantity of matter is under study. A closed system always contains the same matter. There can be no transfer of mass across its boundary. A special type of closed system that does not interact in any way with its surroundings is called an isolated system. Figure 1.1 shows a gas in a piston–cylinder assembly. When the valves are closed, we can consider the gas to be a closed system. The boundary lies just inside the piston and cylinder walls, as shown by the dashed lines on the figure. Since the portion of the boundary between the gas and the piston moves with the piston, the system volume varies. No mass would cross this or any other part of the boundary. If combustion occurs, the composition of the system changes as the initial combustible mixture becomes products of combustion. 1.2.2 Control Volumes In subsequent sections of this book, we perform thermodynamic analyses of devices such as turbines and pumps through which mass flows. These analyses can be conducted in principle by studying a particular quantity of matter, a closed system, as it passes through the device. In most cases it is simpler to think instead in terms of a given region of space through which mass flows. With this approach, a region within a prescribed boundary is studied. The region is called a control volume. Mass crosses the boundary of a control volume. A diagram of an engine is shown in Fig. 1.2a. The dashed line defines a control volume that surrounds the engine. Observe that air, fuel, and exhaust gases cross the boundary. A schematic such as in Fig. 1.2b often suffices for engineering analysis. closed system isolated system control volume Predictions of Life in the United States in 2050 At home c Homes are constructed better to reduce heating and cooling needs. c Homes have systems for electronically monitoring and regulating energy use. c Appliances and heating and air-conditioning systems are more energy-efficient. c Use of solar energy for space and water heating is common. c More food is produced locally. Transportation c Plug-in hybrid vehicles and all-electric vehicles dominate. c Hybrid vehicles mainly use biofuels. c Use of public transportation within and between cities is common. c An expanded passenger railway system is widely used. Lifestyle c Efficient energy-use practices are utilized throughout society. c Recycling is widely practiced, including recycling of water. c Distance learning is common at most educational levels. c Telecommuting and teleconferencing are the norm. c The Internet is predominately used for consumer and business commerce. Power generation c Electricity plays a greater role throughout society. c Wind, solar, and other renewable technologies contribute a significant share of the nation's electricity needs. c A mix of conventional fossil-fueled and nuclear power plants provides a smaller, but still significant, share of the nation's electricity needs. c A smart and secure national power transmission grid is in place. Fig. 1.1 Closed system: A gas in a piston–cylinder assembly. Gas Boundary TABLE 1.2
1.2 Defining Systems 7 .Fuel in Air Driveshaft Air in Exhaust gas out Fuel in Driveshaft Exhaust gas out Boundary (control surface)- Boundary (control surface) (a) (b) Fig.1.2 Example of a control volume (open system).An automobile engine. BIOCONNECTIONS Living things and their organs can be studied as control volumes.For the pet shown in Fig.1.3a,air,food,and drink essential to sus- tain life and for activity enter across the boundary,and waste products exit.A schematic such as Fig.1.3b can suffice for biological analysis.Particular organs, such as the heart,also can be studied as control volumes.As shown in Fig.1.4 plants can be studied from a control volume viewpoint.Intercepted solar radiation is used in the production of essential chemical substances within plants by photosynthesis.During photosynthesis,plants take in carbon dioxide from the atmosphere and discharge oxygen to the atmosphere.Plants also draw in water and nutrients through their roots. 1.2.3 Selecting the System Boundary The system boundary should be delineated carefully before proceeding with any ther- modynamic analysis.However,the same physical phenomena often can be analyzed in terms of alternative choices of the system,boundary,and surroundings.The choice of a particular boundary defining a particular system depends heavily on the conve- nience it allows in the subsequent analysis. Solar Ingestion CO2,other gases radiation (food,drink) CO2,other gases Air Boundary Lungs (control surface) Ingestion (food,drink -Boundary Photosy nthesis (control Circulatory system Body (leaf) surtacel tissues Kidneys Excretion (waste products) Heart 7 Excretion Excretion H,O.minerals (undigested food) (urine) (a) (b) Fig.1.4 Example of a control volume (open Fig.1.3 Example of a control volume (open system)in biology. system)in botany
1.2 Defining Systems 7 1.2.3 Selecting the System Boundary The system boundary should be delineated carefully before proceeding with any thermodynamic analysis. However, the same physical phenomena often can be analyzed in terms of alternative choices of the system, boundary, and surroundings. The choice of a particular boundary defining a particular system depends heavily on the convenience it allows in the subsequent analysis. Fig. 1.2 Example of a control volume (open system). An automobile engine. Living things and their organs can be studied as control volumes. For the pet shown in Fig. 1.3a, air, food, and drink essential to sustain life and for activity enter across the boundary, and waste products exit. A schematic such as Fig. 1.3b can suffice for biological analysis. Particular organs, such as the heart, also can be studied as control volumes. As shown in Fig. 1.4, plants can be studied from a control volume viewpoint. Intercepted solar radiation is used in the production of essential chemical substances within plants by photosynthesis. During photosynthesis, plants take in carbon dioxide from the atmosphere and discharge oxygen to the atmosphere. Plants also draw in water and nutrients through their roots. BIOCONNECTIONS Boundary (control surface) Driveshaft Driveshaft Exhaust gas out Fuel in Air in (a) (b) Exhaust gas out Fuel in Air in Boundary (control surface) Fig. 1.4 Example of a control volume (open Fig. 1.3 Example of a control volume (open system) in biology. system) in botany. Air Air Gut Excretion (undigested food) Excretion (waste products) Excretion (urine) Ingestion (food, drink) Ingestion (food, drink) CO2, other gases CO2 O2 CO2, other gases Heart Kidneys Boundary (control surface) Circulatory system Lungs Body tissues (a) (b) Boundary (control surface) Photosynthesis (leaf) H2O, minerals O2 CO2 Solar radiation
8 Chapter 1 Getting Started TAKE NOTE... Animations reinforce many of the text presentations. You can view these anima- tions by going to the student companion site for this book. Tank Air compressor Animations are keyed to specific content by an icon in the margin. The first of these icons Fig.1.5 Air compressor and storage appears directly below.In tank. this example,the label System_Types refers to the text content while In general,the choice of system boundary is governed by two considerations: A.1-Tabs a,b,&c refers to (1)what is known about a possible system,particularly at its boundaries,and(2)the the particular animation objective of the analysis. (A.1)and the tabs (Tabs a, b,c)of the animation recommended for viewing now to enhance your FOREXAMPLE Figure 1.5 shows a sketch of an air compressor connected to a storage tank.The system boundary shown on the figure encloses the compressor,tank, understanding. and all of the piping.This boundary might be selected if the electrical power input is known,and the objective of the analysis is to determine how long the compressor must operate for the pressure in the tank to rise to a specified value.Since mass crosses the boundary,the system would be a control volume.A control volume enclosing only the compressor might be chosen if the condition of the air entering System_Types and exiting the compressor is known,and the objective is to determine the electric A.1 Tabs a,b,c power input. Describing Systems and Their Behavior Engineers are interested in studying systems and how they interact with their sur- roundings.In this section,we introduce several terms and concepts used to describe systems and how they behave. 1.3.1 Macroscopic and Microscopic Views of Thermodynamics Systems can be studied from a macroscopic or a microscopic point of view.The mac- roscopic approach to thermodynamics is concerned with the gross or overall behavior. This is sometimes called classical thermodynamics.No model of the structure of mat- ter at the molecular,atomic,and subatomic levels is directly used in classical thermo- dynamics.Although the behavior of systems is affected by molecular structure,clas- sical thermodynamics allows important aspects of system behavior to be evaluated from observations of the overall system. The microscopic approach to thermodynamics,known as statistical thermodynam- ics,is concerned directly with the structure of matter.The objective of statistical thermodynamics is to characterize by statistical means the average behavior of the particles making up a system of interest and relate this information to the observed macroscopic behavior of the system.For applications involving lasers,plasmas,high- speed gas flows,chemical kinetics,very low temperatures(cryogenics),and others,the methods of statistical thermodynamics are essential.The microscopic approach is used in this text to interpret internal energy in Chap.2 and entropy in Chap 6.Moreover
8 Chapter 1 Getting Started Air Air compressor Tank + – System_Types A.1 – Tabs a, b, & c 1.3 Describing Systems and Their Behavior Engineers are interested in studying systems and how they interact with their surroundings. In this section, we introduce several terms and concepts used to describe systems and how they behave. 1.3.1 Macroscopic and Microscopic Views of Thermodynamics Systems can be studied from a macroscopic or a microscopic point of view. The macroscopic approach to thermodynamics is concerned with the gross or overall behavior. This is sometimes called classical thermodynamics. No model of the structure of matter at the molecular, atomic, and subatomic levels is directly used in classical thermodynamics. Although the behavior of systems is affected by molecular structure, classical thermodynamics allows important aspects of system behavior to be evaluated from observations of the overall system. The microscopic approach to thermodynamics, known as statistical thermodynamics, is concerned directly with the structure of matter. The objective of statistical thermodynamics is to characterize by statistical means the average behavior of the particles making up a system of interest and relate this information to the observed macroscopic behavior of the system. For applications involving lasers, plasmas, highspeed gas flows, chemical kinetics, very low temperatures (cryogenics), and others, the methods of statistical thermodynamics are essential. The microscopic approach is used in this text to interpret internal energy in Chap. 2 and entropy in Chap 6. Moreover, In general, the choice of system boundary is governed by two considerations: (1) what is known about a possible system, particularly at its boundaries, and (2) the objective of the analysis. Figure 1.5 shows a sketch of an air compressor connected to a storage tank. The system boundary shown on the figure encloses the compressor, tank, and all of the piping. This boundary might be selected if the electrical power input is known, and the objective of the analysis is to determine how long the compressor must operate for the pressure in the tank to rise to a specified value. Since mass crosses the boundary, the system would be a control volume. A control volume enclosing only the compressor might be chosen if the condition of the air entering and exiting the compressor is known, and the objective is to determine the electric power input. b b b b b Fig. 1.5 Air compressor and storage tank. TAKE NOTE... Animations reinforce many of the text presentations. You can view these animations by going to the student companion site for this book. Animations are keyed to specific content by an icon in the margin. The first of these icons appears directly below. In this example, the label System_Types refers to the text content while A.1–Tabs a, b, & c refers to the particular animation (A.1) and the tabs (Tabs a, b, & c) of the animation recommended for viewing now to enhance your understanding
1.3 Describing Systems and Their Behavior 9 as noted in Chap.3,the microscopic approach is instrumental in developing certain data,for example ideal gas specific heats. For a wide range of engineering applications,classical thermodynamics not only provides a considerably more direct approach for analysis and design but also requires far fewer mathematical complications.For these reasons the macroscopic viewpoint is the one adopted in this book.Finally,relativity effects are not significant for the systems under consideration in this book. 1.3.2 Property,State,and Process To describe a system and predict its behavior requires knowledge of its properties and how those properties are related.A property is a macroscopic characteristic of a property system such as mass,volume,energy,pressure,and temperature to which a numerical value can be assigned at a given time without knowledge of the previous behavior (history)of the system. The word state refers to the condition of a system as described by its properties. state Since there are normally relations among the properties of a system,the state often can be specified by providing the values of a subset of the properties.All other prop- erties can be determined in terms of these few. When any of the properties of a system changes,the state changes and the system is said to undergo a process.A process is a transformation from one state to another. process If a system exhibits the same values of its properties at two different times,it is in the same state at these times.A system is said to be at steady state if none of its steady state properties changes with time. Many properties are considered during the course of our study of engineering thermodynamics.Thermodynamics also deals with quantities that are not properties, such as mass flow rates and energy transfers by work and heat.Additional examples of quantities that are not properties are provided in subsequent chapters.For a way Prop_State_Process to distinguish properties from nonproperties,see the box on p.10. A.2-Tab a 1.3.3 Extensive and Intensive Properties Thermodynamic properties can be placed in two general classes:extensive and inten- sive.A property is called extensive if its value for an overall system is the sum of its extensive property values for the parts into which the system is divided.Mass,volume,energy,and sev- eral other properties introduced later are extensive.Extensive properties depend on the size or extent of a system.The extensive properties of a system can change with time,and many thermodynamic analyses consist mainly of carefully accounting for changes in extensive properties such as mass and energy as a system interacts with its surroundings. Intensive properties are not additive in the sense previously considered.Their val- intensive property ues are independent of the size or extent of a system and may vary from place to place within the system at any moment.Intensive properties may be functions of both position and time,whereas extensive properties can vary only with time.Specific volume(Sec.1.5),pressure,and temperature are important intensive properties;sev- eral other intensive properties are introduced in subsequent chapters. FREXAMPLE to illustrate the difference between extensive and intensive prop- erties,consider an amount of matter that is uniform in temperature,and imagine that it is composed of several parts,as illustrated in Fig.1.6.The mass of the whole is the sum of the masses of the parts,and the overall volume is the sum of the volumes of the parts.However,the temperature of the whole is not the sum of the temperatures of the parts;it is the same for each part.Mass and volume are extensive,but tem- Ext Int Properties perature is intensive. A.3-Tab a
1.3 Describing Systems and Their Behavior 9 as noted in Chap. 3, the microscopic approach is instrumental in developing certain data, for example ideal gas specific heats. For a wide range of engineering applications, classical thermodynamics not only provides a considerably more direct approach for analysis and design but also requires far fewer mathematical complications. For these reasons the macroscopic viewpoint is the one adopted in this book. Finally, relativity effects are not significant for the systems under consideration in this book. 1.3.2 Property, State, and Process To describe a system and predict its behavior requires knowledge of its properties and how those properties are related. A property is a macroscopic characteristic of a system such as mass, volume, energy, pressure, and temperature to which a numerical value can be assigned at a given time without knowledge of the previous behavior (history) of the system. The word state refers to the condition of a system as described by its properties. Since there are normally relations among the properties of a system, the state often can be specified by providing the values of a subset of the properties. All other properties can be determined in terms of these few. When any of the properties of a system changes, the state changes and the system is said to undergo a process. A process is a transformation from one state to another. If a system exhibits the same values of its properties at two different times, it is in the same state at these times. A system is said to be at steady state if none of its properties changes with time. Many properties are considered during the course of our study of engineering thermodynamics. Thermodynamics also deals with quantities that are not properties, such as mass flow rates and energy transfers by work and heat. Additional examples of quantities that are not properties are provided in subsequent chapters. For a way to distinguish properties from nonproperties, see the box on p. 10. 1.3.3 Extensive and Intensive Properties Thermodynamic properties can be placed in two general classes: extensive and intensive. A property is called extensive if its value for an overall system is the sum of its values for the parts into which the system is divided. Mass, volume, energy, and several other properties introduced later are extensive. Extensive properties depend on the size or extent of a system. The extensive properties of a system can change with time, and many thermodynamic analyses consist mainly of carefully accounting for changes in extensive properties such as mass and energy as a system interacts with its surroundings. Intensive properties are not additive in the sense previously considered. Their values are independent of the size or extent of a system and may vary from place to place within the system at any moment. Intensive properties may be functions of both position and time, whereas extensive properties can vary only with time. Specific volume (Sec. 1.5), pressure, and temperature are important intensive properties; several other intensive properties are introduced in subsequent chapters. property state process steady state extensive property intensive property Prop_State_Process A.2 – Tab a Ext_Int_Properties A.3 – Tab a to illustrate the difference between extensive and intensive properties, consider an amount of matter that is uniform in temperature, and imagine that it is composed of several parts, as illustrated in Fig. 1.6. The mass of the whole is the sum of the masses of the parts, and the overall volume is the sum of the volumes of the parts. However, the temperature of the whole is not the sum of the temperatures of the parts; it is the same for each part. Mass and volume are extensive, but temperature is intensive. b b b b b