Chapter 1 Getting Started Using Thermodynamics Engineers use principles drawn from thermodynamics and other engineering sciences, including fluid mechanics and heat and mass transfer,to analyze and design devices intended to meet human needs.Throughout the twentieth century,engineering applica- tions of thermodynamics helped pave the way for significant improvements in our qual- ity of life with advances in major areas such as surface transportation,air travel,space flight,electricity generation and transmission,building heating and cooling,and improved medical practices.The wide realm of these applications is suggested by Table 1.1. In the twenty-first century,engineers will create the technology needed to achieve a sustainable future.Thermodynamics will continue to advance human well-being by addressing looming societal challenges owing to declining supplies of energy resources: oil,natural gas,coal,and fissionable material;effects of global climate change;and burgeoning population.Life in the United States is expected to change in several important respects by mid-century.In the area of power use,for example,electricity will play an even greater role than today.Table 1.2 provides predictions of other changes experts say will be observed. If this vision of mid-century life is correct,it will be necessary to evolve quickly from our present energy posture.As was the case in the twentieth century,thermodynamics will contribute significantly to meeting the challenges of the twenty-first century,includ- ing using fossil fuels more effectively,advancing renewable energy technologies,and developing more energy-efficient transportation systems,buildings,and industrial prac- tices.Thermodynamics also will play a role in mitigating global climate change,air pollution,and water pollution.Applications will be observed in bioengineering,bio- medical systems,and the deployment of nanotechnology.This book provides the tools needed by specialists working in all such fields.For nonspecialists,the book provides background for making decisions about technology related to thermodynamics-on the job,as informed citizens,and as government leaders and policy makers. Defining Systems The key initial step in any engineering analysis is to describe precisely what is being studied.In mechanics,if the motion of a body is to be determined,normally the first step is to define a free body and identify all the forces exerted on it by other bodies.Newton's second law of motion is then applied.In thermodynamics the term systemn is used to identify the subject of the analysis.Once the system is defined and the relevant interac- tions with other systems are identified,one or more physical laws or relations are applied. system The system is whatever we want to study.It may be as simple as a free body or as complex as an entire chemical refinery.We may want to study a quantity of matter contained within a closed,rigid-walled tank,or we may want to consider something such as a pipeline through which natural gas flows.The composition of the matter inside the system may be fixed or may be changing through chemical or nuclear reac- tions.The shape or volume of the system being analyzed is not necessarily constant, as when a gas in a cylinder is compressed by a piston or a balloon is inflated. surroundings Everything external to the system is considered to be part of the system's surroundings. boundary The system is distinguished from its surroundings by a specified boundary,which may be at rest or in motion.You will see that the interactions between a system and its surroundings,which take place across the boundary,play an important part in engi- neering thermodynamics. Two basic kinds of systems are distinguished in this book.These are referred to,respec- tively,as closed systems and control volumes.A closed system refers to a fixed quantity of matter,whereas a control volume is a region of space through which mass may flow. The term control mass is sometimes used in place of closed system,and the term open system is used interchangeably with control volume.When the terms control mass and control volume are used,the system boundary is often referred to as a control surface
4 Chapter 1 Getting Started 1.1 Using Thermodynamics Engineers use principles drawn from thermodynamics and other engineering sciences, including fluid mechanics and heat and mass transfer, to analyze and design devices intended to meet human needs. Throughout the twentieth century, engineering applications of thermodynamics helped pave the way for significant improvements in our quality of life with advances in major areas such as surface transportation, air travel, space flight, electricity generation and transmission, building heating and cooling, and improved medical practices. The wide realm of these applications is suggested by Table 1.1. In the twenty-first century, engineers will create the technology needed to achieve a sustainable future. Thermodynamics will continue to advance human well-being by addressing looming societal challenges owing to declining supplies of energy resources: oil, natural gas, coal, and fissionable material; effects of global climate change; and burgeoning population. Life in the United States is expected to change in several important respects by mid-century. In the area of power use, for example, electricity will play an even greater role than today. Table 1.2 provides predictions of other changes experts say will be observed. If this vision of mid-century life is correct, it will be necessary to evolve quickly from our present energy posture. As was the case in the twentieth century, thermodynamics will contribute significantly to meeting the challenges of the twenty-first century, including using fossil fuels more effectively, advancing renewable energy technologies, and developing more energy-efficient transportation systems, buildings, and industrial practices. Thermodynamics also will play a role in mitigating global climate change, air pollution, and water pollution. Applications will be observed in bioengineering, biomedical systems, and the deployment of nanotechnology. This book provides the tools needed by specialists working in all such fields. For nonspecialists, the book provides background for making decisions about technology related to thermodynamics—on the job, as informed citizens, and as government leaders and policy makers. 1.2 Defining Systems The key initial step in any engineering analysis is to describe precisely what is being studied. In mechanics, if the motion of a body is to be determined, normally the first step is to define a free body and identify all the forces exerted on it by other bodies. Newton’s second law of motion is then applied. In thermodynamics the term system is used to identify the subject of the analysis. Once the system is defined and the relevant interactions with other systems are identified, one or more physical laws or relations are applied. The system is whatever we want to study. It may be as simple as a free body or as complex as an entire chemical refinery. We may want to study a quantity of matter contained within a closed, rigid-walled tank, or we may want to consider something such as a pipeline through which natural gas flows. The composition of the matter inside the system may be fixed or may be changing through chemical or nuclear reactions. The shape or volume of the system being analyzed is not necessarily constant, as when a gas in a cylinder is compressed by a piston or a balloon is inflated. Everything external to the system is considered to be part of the system’s surroundings. The system is distinguished from its surroundings by a specified boundary, which may be at rest or in motion. You will see that the interactions between a system and its surroundings, which take place across the boundary, play an important part in engineering thermodynamics. Two basic kinds of systems are distinguished in this book. These are referred to, respectively, as closed systems and control volumes. A closed system refers to a fixed quantity of matter, whereas a control volume is a region of space through which mass may flow. The term control mass is sometimes used in place of closed system, and the term open system is used interchangeably with control volume. When the terms control mass and control volume are used, the system boundary is often referred to as a control surface. system surroundings boundary
1.2 Defining Systems 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 围 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 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 ung 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
Chapter 1 Getting Started TABLE 1.2 Predictions of Life in the United States in 2050 At home c 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. c Use of solar energy for space and water heating is common. 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 Efficient energy-use practices are utilized throughout society. Recycling is widely practiced,including recycling of water. c Distance learning is common at most educational levels. c Telecommuting and teleconferencing are the norm. 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. 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. 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 Fuel in Air in Driveshaft Air in Exhaust gas out Fuel in Driveshaft Exhaust gas out Boundary (control surface) > Boundary (control surface) (a) ( Fig. 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 radiation (food,drink) CO2,other gases 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.. Example of a control volume (open Fig..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
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. 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.bb bb 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