xxiii PREFACE ACKNOWLEDGMENTS The authors would like to acknowledge with appreciation the numerous and valuable comments,suggestions,constructive criticisms,and praise from the following evaluators and reviewers: Edward Anderson Kevin Macfarlan Texas Tech University Johmn Brown University John Biddle Saeed Manafzadeh Cal Poly Pomona University University of Illinois-Chicago Gianfranco DiGiuseppe Alex Moutsoglou Kettering University South Dakota State University Shoeleh Di Julio Rishi Raj California State University-Northridge The City College of New York Afshin Ghajar Maria Sanchez Oklahoma State University California State University-Fresno Harry Hardee Kalyan Srinivasan New Mexico State University Mississippi State University Kevin Lyons Robert Stiger North Carolina State University Gonzaga University Their suggestions have greatly helped to improve the quality of this text.In particular we would like to express our gratitude to Mehmet Kanoglu of the University of Gaziantep,Turkey,for his valuable contributions,his critical review of the manuscript,and for his special attention to accuracy and detail. We also would like to thank our students,who provided plenty of feedback from students'perspectives.Finally,we would like to express our apprecia- tion to our wives,Zehra Cengel and Sylvia Boles,and to our children for their continued patience,understanding,and support throughout the preparation of this text. Yunus A.Cengel Michael A.Boles
xxiii PREFACE ACKNOWLEDGMENTS The authors would like to acknowledge with appreciation the numerous and valuable comments, suggestions, constructive criticisms, and praise from the following evaluators and reviewers: Edward Anderson Texas Tech University John Biddle Cal Poly Pomona University Gianfranco DiGiuseppe Kettering University Shoeleh Di Julio California State University-Northridge Afshin Ghajar Oklahoma State University Harry Hardee New Mexico State University Kevin Lyons North Carolina State University Kevin Macfarlan John Brown University Saeed Manafzadeh University of Illinois-Chicago Alex Moutsoglou South Dakota State University Rishi Raj The City College of New York Maria Sanchez California State University-Fresno Kalyan Srinivasan Mississippi State University Robert Stiger Gonzaga University Their suggestions have greatly helped to improve the quality of this text. In particular we would like to express our gratitude to Mehmet Kanoglu of the University of Gaziantep, Turkey, for his valuable contributions, his critical review of the manuscript, and for his special attention to accuracy and detail. We also would like to thank our students, who provided plenty of feedback from students’ perspectives. Finally, we would like to express our appreciation to our wives, Zehra Çengel and Sylvia Boles, and to our children for their continued patience, understanding, and support throughout the preparation of this text. Yunus A. Çengel Michael A. Boles cen98179_fm_i-xxvi.indd xxiii 11/29/13 6:39 PM
Online Resources for Students and Instructors MCGRAW-HILL CONNECT ENGINEERING McGraw-Hill Connect Engineering is a web-based assignment and assessment platform that gives students the means to better connect with their course- work,with their instructors,and with the important concepts that they will need to know for success now and in the future.With Connect Engineering, instructors can deliver assignments,quizzes,and tests easily online.Students can practice important skills at their own pace and on their own schedule. Connect Engineering for Thermodynamics:An Engineering Approach, Eighth Edition is available via the text website at www.mhhe.com/cengel COSMOS McGraw-Hill's COSMOS (Complete Online Solutions Manual Organization System)allows instructors to streamline the creation of assignments,quiz- zes,and tests by using problems and solutions from the textbook,as well as their own custom material.COSMOS is now available online at http://cosmos. mhhe.com/ WWW.MHHE.COM/CENGEL This site offers resources for students and instructors. The following resources are available for students: Glossary of Key Terms in Thermodynamics-Bolded terms in the text are defined in this accessible glossary.Organized at the chapter level or available as one large file Student Study Guide-This resource outlines the fundamental concepts of the text and is a helpful guide that allows students to focus on the most important concepts.The guide can also serve as a lecture outline for instructors. Learning Objectives-The chapter learning objectives are outlined here Organized by chapter and tied to ABET objectives. Self-Quizzing-Students can test their knowledge using multiple-choice quizzing.These self-tests provide immediate feedback and are an excellent learning tool. Flashcards-Interactive flashcards test student understanding of the text terms and their definitions.The program also allows students to flag terms that require further understanding. Crossword Puzzles-An interactive,timed puzzle that provides hints as well as a notes section. Errata-lf errors should be found in the text,they will be reported here
MCGRAW-HILL CONNECT® ENGINEERING McGraw-Hill Connect Engineering is a web-based assignment and assessment platform that gives students the means to better connect with their coursework, with their instructors, and with the important concepts that they will need to know for success now and in the future. With Connect Engineering, instructors can deliver assignments, quizzes, and tests easily online. Students can practice important skills at their own pace and on their own schedule. Connect Engineering for Thermodynamics: An Engineering Approach, Eighth Edition is available via the text website at www.mhhe.com/cengel COSMOS McGraw-Hill’s COSMOS (Complete Online Solutions Manual Organization System) allows instructors to streamline the creation of assignments, quizzes, and tests by using problems and solutions from the textbook, as well as their own custom material. COSMOS is now available online at http://cosmos. mhhe.com/ WWW.MHHE.COM/CENGEL This site offers resources for students and instructors. The following resources are available for students: • Glossary of Key Terms in Thermodynamics—Bolded terms in the text are defined in this accessible glossary. Organized at the chapter level or available as one large file. • Student Study Guide—This resource outlines the fundamental concepts of the text and is a helpful guide that allows students to focus on the most important concepts. The guide can also serve as a lecture outline for instructors. • Learning Objectives—The chapter learning objectives are outlined here. Organized by chapter and tied to ABET objectives. • Self-Quizzing—Students can test their knowledge using multiple-choice quizzing. These self-tests provide immediate feedback and are an excellent learning tool. • Flashcards—Interactive flashcards test student understanding of the text terms and their definitions. The program also allows students to flag terms that require further understanding. • Crossword Puzzles—An interactive, timed puzzle that provides hints as well as a notes section. • Errata—If errors should be found in the text, they will be reported here. Online Resources for Students and Instructors cen98179_fm_i-xxvi.indd xxv 11/29/13 6:39 PM
XXVI THERMODYNAMICS The following resources are available for instructors under password protection: Instructor Testbank-Additional problems prepared for instructors to assign to students.Solutions are given,and use of EES is recommended to verify accuracy. Correlation Guide-New users of this text will appreciate this resource.The guide provides a smooth transition for instructors not currently using the Cengel/Boles text. Image Library-The electronic version of the figures are supplied for easy integration into course presentations,exams,and assignments. Instructor's Guide-Provides instructors with helpful tools such as sample syllabi and exams,an ABET conversion guide,a thermodynamics glossary, and chapter objectives. Errata-If errors should be found in the solutions manual,they will be reported here. Solutions Manual-The detailed solutions to all text homework problems are provided in PDF form. EES Solutions Manual-The entire solutions manual is also available in EES.Any problem in the text can be modified and the solution of the modified problem can readily be obtained by copying and pasting the given EES solution on a blank EES screen and hitting the solve button. PP slides-Powerpoint presentation slides for all chapters in the text are available for use in lectures Appendices-These are provided in PDF form for ease of use
xxvi THERMODYNAMICS The following resources are available for instructors under password protection: • Instructor Testbank—Additional problems prepared for instructors to assign to students. Solutions are given, and use of EES is recommended to verify accuracy. • Correlation Guide—New users of this text will appreciate this resource. The guide provides a smooth transition for instructors not currently using the Çengel/Boles text. • Image Library—The electronic version of the figures are supplied for easy integration into course presentations, exams, and assignments. • Instructor’s Guide—Provides instructors with helpful tools such as sample syllabi and exams, an ABET conversion guide, a thermodynamics glossary, and chapter objectives. • Errata—If errors should be found in the solutions manual, they will be reported here. • Solutions Manual—The detailed solutions to all text homework problems are provided in PDF form. • EES Solutions Manual—The entire solutions manual is also available in EES. Any problem in the text can be modified and the solution of the modified problem can readily be obtained by copying and pasting the given EES solution on a blank EES screen and hitting the solve button. • PP slides—Powerpoint presentation slides for all chapters in the text are available for use in lectures • Appendices—These are provided in PDF form for ease of use. cen98179_fm_i-xxvi.indd xxvi 11/29/13 6:39 PM
CHAPTER INTRODUCTION AND BASIC CONCEPTS very science has a unique vocabulary associated with it,and thermo- ■夏■■■■■ dynamics is no exception.Precise definition of basic concepts forms OBJECTIVES a sound foundation for the development of a science and prevents The objectives of Chapter 1 are to: possible misunderstandings.We start this chapter with an overview of ther- ■ Identify the unique vocabulary modynamics and the unit systems,and continue with a discussion of some associated with thermodynamics basic concepts such as system,state,state postulate,equilibrium,and pro- through the precise definition of basic concepts to form a sound cess.We discuss intensive and extensive properties of a system and define foundation for the development density,specific gravity,and specific weight.We also discuss temperature of the principles of thermody- and temperature scales with particular emphasis on the International Tem- namics. perature Scale of 1990.We then present pressure,which is the normal force ◆ Review the metric Sl and the exerted by a fluid per unit area and discuss absolute and gage pressures,the English unit systems that will be variation of pressure with depth,and pressure measurement devices,such used throughout the text. as manometers and barometers.Careful study of these concepts is essential Explain the basic concepts for a good understanding of the topics in the following chapters.Finally,we of thermodynamics such as present an intuitive systematic problem-solving technique that can be used system,state,state postulate, equilibrium,process,and cycle. as a model in solving engineering problems. Discuss properties of a system and define density,specific gravity,and specific weight. Review concepts of temperature. temperature scales,pressure, and absolute and gage pressure. Introduce an intuitive systematic problem-solving technique. 1
1 I N T R O D U C T I O N A N D BASIC CONCEPTS E very science has a unique vocabulary associated with it, and thermodynamics is no exception. Precise definition of basic concepts forms a sound foundation for the development of a science and prevents possible misunderstandings. We start this chapter with an overview of thermodynamics and the unit systems, and continue with a discussion of some basic concepts such as system, state, state postulate, equilibrium, and process. We discuss intensive and extensive properties of a system and define density, specific gravity, and specific weight. We also discuss temperature and temperature scales with particular emphasis on the International Temperature Scale of 1990. We then present pressure, which is the normal force exerted by a fluid per unit area and discuss absolute and gage pressures, the variation of pressure with depth, and pressure measurement devices, such as manometers and barometers. Careful study of these concepts is essential for a good understanding of the topics in the following chapters. Finally, we present an intuitive systematic problem-solving technique that can be used as a model in solving engineering problems. 1 1 OBJECTIVES The objectives of Chapter 1 are to: ■ Identify the unique vocabulary associated with thermodynamics through the precise definition of basic concepts to form a sound foundation for the development of the principles of thermodynamics. ■ Review the metric SI and the English unit systems that will be used throughout the text. ■ Explain the basic concepts of thermodynamics such as system, state, state postulate, equilibrium, process, and cycle. ■ Discuss properties of a system and define density, specific gravity, and specific weight. ■ Review concepts of temperature, temperature scales, pressure, and absolute and gage pressure. ■ Introduce an intuitive systematic problem-solving technique. CHAPTER cen98179_ch01_001-050.indd 1 11/28/13 3:14 PM
2 INTRODUCTION AND BASIC CONCEPTS 1-1 THERMODYNAMICS AND ENERGY E=10 units Potential KE=0 energy Thermodynamics can be defined as the science of energy.Although every- body has a feeling of what energy is,it is difficult to give a precise defini- tion for it.Energy can be viewed as the ability to cause changes. The name thermodynamics stems from the Greek words therme (heat)and dynamis (power),which is most descriptive of the early efforts to convert heat into power.Today the same name is broadly interpreted to include all Kinetic aspects of energy and energy transformations including power generation, energy refrigeration,and relationships among the properties of matter. One of the most fundamental laws of nature is the conservation of energy principle.It simply states that during an interaction,energy can change from one form to another but the total amount of energy remains constant.That is, energy cannot be created or destroyed.A rock falling off a cliff,for example, picks up speed as a result of its potential energy being converted to kinetic energy (Fig.1-1).The conservation of energy principle also forms the back- bone of the diet industry:A person who has a greater energy input(food) FIGURE 1-1 than energy output(exercise)will gain weight (store energy in the form Energy cannot be created or of fat),and a person who has a smaller energy input than output will lose destroyed;it can only change weight (Fig.1-2).The change in the energy content of a body or any other forms (the first law). system is equal to the difference between the energy input and the energy output,and the energy balance is expressed as En-Eu=AE. Energy storage The first law of thermodynamics is simply an expression of the con- (1 unit) servation of energy principle,and it asserts that energy is a thermodynamic Energy in property.The second law of thermodynamics asserts that energy has gquality as well as guantity,and actual processes occur in the direction of (5 units) decreasing quality of energy.For example,a cup of hot coffee left on a table eventually cools,but a cup of cool coffee in the same room never gets hot by itself(Fig.1-3).The high-temperature energy of the coffee is degraded Energy out (transformed into a less useful form at a lower temperature)once it is trans- (4 units) ferred to the surrounding air. Although the principles of thermodynamics have been in existence since FIGURE 1-2 the creation of the universe,thermodynamics did not emerge as a science Conservation of energy principle for until the construction of the first successful atmospheric steam engines in the human body. England by Thomas Savery in 1697 and Thomas Newcomen in 1712.These engines were very slow and inefficient,but they opened the way for the development of a new science. The first and second laws of thermodynamics emerged simultaneously in Cool the 1850s,primarily out of the works of William Rankine,Rudolph Clausius, environment and Lord Kelvin (formerly William Thomson).The term thermodynamics 20℃ was first used in a publication by Lord Kelvin in 1849.The first thermody- Hot namics textbook was written in 1859 by William Rankine,a professor at the coffee Heat University of Glasgow. 70°C It is well-known that a substance consists of a large number of particles called molecules.The properties of the substance naturally depend on the behavior of these particles.For example,the pressure of a gas in a container is the result of momentum transfer between the molecules and the walls of FIGURE 1-3 the container.However,one does not need to know the behavior of the gas Heat flows in the direction of particles to determine the pressure in the container.It would be sufficient to decreasing temperature. attach a pressure gage to the container.This macroscopic approach to the
2 INTRODUCTION AND BASIC CONCEPTS 1–1 ■ THERMODYNAMICS AND ENERGY Thermodynamics can be defined as the science of energy. Although everybody has a feeling of what energy is, it is difficult to give a precise definition for it. Energy can be viewed as the ability to cause changes. The name thermodynamics stems from the Greek words therme (heat) and dynamis (power), which is most descriptive of the early efforts to convert heat into power. Today the same name is broadly interpreted to include all aspects of energy and energy transformations including power generation, refrigeration, and relationships among the properties of matter. One of the most fundamental laws of nature is the conservation of energy principle. It simply states that during an interaction, energy can change from one form to another but the total amount of energy remains constant. That is, energy cannot be created or destroyed. A rock falling off a cliff, for example, picks up speed as a result of its potential energy being converted to kinetic energy (Fig. 1–1). The conservation of energy principle also forms the backbone of the diet industry: A person who has a greater energy input (food) than energy output (exercise) will gain weight (store energy in the form of fat), and a person who has a smaller energy input than output will lose weight (Fig. 1–2). The change in the energy content of a body or any other system is equal to the difference between the energy input and the energy output, and the energy balance is expressed as Ein 2 Eout 5 DE. The first law of thermodynamics is simply an expression of the conservation of energy principle, and it asserts that energy is a thermodynamic property. The second law of thermodynamics asserts that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy. For example, a cup of hot coffee left on a table eventually cools, but a cup of cool coffee in the same room never gets hot by itself (Fig. 1–3). The high-temperature energy of the coffee is degraded (transformed into a less useful form at a lower temperature) once it is transferred to the surrounding air. Although the principles of thermodynamics have been in existence since the creation of the universe, thermodynamics did not emerge as a science until the construction of the first successful atmospheric steam engines in England by Thomas Savery in 1697 and Thomas Newcomen in 1712. These engines were very slow and inefficient, but they opened the way for the development of a new science. The first and second laws of thermodynamics emerged simultaneously in the 1850s, primarily out of the works of William Rankine, Rudolph Clausius, and Lord Kelvin (formerly William Thomson). The term thermodynamics was first used in a publication by Lord Kelvin in 1849. The first thermodynamics textbook was written in 1859 by William Rankine, a professor at the University of Glasgow. It is well-known that a substance consists of a large number of particles called molecules. The properties of the substance naturally depend on the behavior of these particles. For example, the pressure of a gas in a container is the result of momentum transfer between the molecules and the walls of the container. However, one does not need to know the behavior of the gas particles to determine the pressure in the container. It would be sufficient to attach a pressure gage to the container. This macroscopic approach to the FIGURE 1–1 Energy cannot be created or destroyed; it can only change forms (the first law). Potential energy Kinetic energy PE = 7 units KE = 3 units PE = 10 units KE = 0 FIGURE 1–2 Conservation of energy principle for the human body. Energy out (4 units) Energy in (5 units) Energy storage (1 unit) FIGURE 1–3 Heat flows in the direction of decreasing temperature. Heat Cool environment 20°C Hot coffee 70°C cen98179_ch01_001-050.indd 2 11/28/13 3:14 PM