Thermodynamics: An Engineering Approach [9th ed.] 1259822672, 9781259822674
Table of contents :
1) Introduction and Basic Concepts
2) Energy, Energy Transfer, and General Energy Analysis
3) Properties of Pure Substances
4) Energy Analysis of Closed Systems
5) Mass and Energy Analysis of Control Volumes
6) The Second Law of Thermodynamics
7) Entropy
8) Exergy
9) Gas Power Cycles
10) Vapor and Combined Power Cycles
11) Refrigeration Cycles
12) Thermodynamic Property Relations
13) Gas Mixtures
14) Gas-Vapor Mixtures and Air-Conditioning
15) Chemical Reactions
16) Chemical and Phase Equilibrium
17) Compressible Flow
18) Renewable Energy (Web Chapter)
Appendix 1 - Property Tables and Charts (SI Units)
Appendix 2 - Property Tables and Charts (English Units)
Citation preview
THERMODYNAMICS AN ENGINEERING APPROACH
NINTH EDITION
THERMODYNAMICS AN ENGINEERING APPROACH
NINTH EDITION
YUNUS A. ÇENGEL University of Nevada, Reno
MICHAEL A. BOLES North Carolina State University
MEHMET KANOĞLU University of Gaziantep
THERMODYNAMICS: AN ENGINEERING APPROACH, NINTH EDITION Published by McGraw-Hill Education, 2 Penn Plaza, New York, NY 10121. Copyright © 2019 by McGraw-Hill Education. All rights reserved. Printed in the United States of America. Previous editions © 2015, 2011, and 2008. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written consent of McGraw-Hill Education, including, but not limited to, in any network or other electronic storage or transmission, or broadcast for distance learning. Some ancillaries, including electronic and print components, may not be available to customers outside the United States. This book is printed on acid-free paper. 1 2 3 4 5 6 7 8 9 LWI 21 20 19 18 ISBN 978-1-259-82267-4 MHID 1-259-82267-2 Portfolio Manager: Thomas M. Scaife, Ph.D. Product Developer: Jolynn Kilburg Marketing Manager: Shannon O’Donnell Director of Digital Content: Chelsea Haupt, Ph.D. Content Project Managers: Jane Mohr, Tammy Juran, and Sandy Schnee Buyer: Susan K. Culbertson Design: Egzon Shaqiri Content Licensing Specialist: Beth Thole Cover Image Source: NASA/ Bill Ingalls Compositor: SPi Global All credits appearing on page or at the end of the book are considered to be an extension of the copyright page. Library of Congress Cataloging-in-Publication Data Names: Çengel, Yunus A., author. | Boles, Michael A., author. | Kanoğlu, Mehmet, author. Title: Thermodynamics : an engineering approach / Yunus A. Çengel, University of Nevada, Reno, Michael A. Boles, North Carolina State University, Mehmet Kanoğlu, University of Gaziantep. Description: Ninth edition. | New York, NY : McGraw-Hill Education, [2019] Identifiers: LCCN 2017048282| ISBN 9781259822674 (acid-free paper) | ISBN 1259822672 (acid-free paper) Subjects: LCSH: Thermodynamics. Classification: LCC TJ265 .C43 2019 | DDC 621.402/1—dc23 LC record available at https://lccn.loc.gov/2017048282 The Internet addresses listed in the text were accurate at the time of publication. The inclusion of a website does not indicate an endorsement by the authors or McGraw-Hill Education, and McGraw-Hill Education does not guarantee the accuracy of the information presented at these sites.
mheducation.com/highered
Quotes on Ethics Without ethics, everything happens as if we were all five billion passengers on a big machinery and nobody is driving the machinery. And it’s going faster and faster, but we don’t know where. —Jacques Cousteau Because you’re able to do it and because you have the right to do it doesn’t mean it’s right to do it. —Laura Schlessinger A man without ethics is a wild beast loosed upon this world. —Manly Hall The concern for man and his destiny must always be the chief interest of all technical effort. Never forget it among your diagrams and equations. —Albert Einstein To educate a man in mind and not in morals is to educate a menace to society. —Theodore Roosevelt Politics which revolves around benefit is savagery. —Said Nursi The true test of civilization is, not the census, nor the size of the cities, nor the crops, but the kind of man that the country turns out. —Ralph W. Emerson The measure of a man’s character is what he would do if he knew he never would be found out. —Thomas B. Macaulay
A BOUT
THE
A UTHORS
Yunus A. Çengel is Professor Emeritus of Mechanical Engineering at the University of Nevada, Reno. He received his B.S. in mechanical engineering from Istanbul Technical University and his M.S. and Ph.D. in mechanical engineering from North Carolina State University. His areas of interest are renewable energy, energy efficiency, energy policies, heat transfer enhancement, and engineering education. He served as the director of the Industrial Assessment Center (IAC) at the University of Nevada, Reno, from 1996 to 2000. He has led teams of engineering students to numerous manufacturing facilities in Northern Nevada and California to perform industrial assessments, and has prepared energy conservation, waste minimization, and productivity enhancement reports for them. He has also served as an advisor for various government organizations and corporations. Dr. Çengel is also the author or coauthor of the widely adopted textbooks Heat and Mass Transfer: Fundamentals and Applications (5th ed., 2015), Fluid Mechanics:Fundamentals and Applications (4th ed., 2018), Fundamentals of Thermal-Fluid Sciences (5th ed., 2017), and Differential Equations for Engineers and Scientists (1st ed., 2013), all published by McGraw-Hill. Some of his textbooks have been translated into Chinese (Long and Short Forms), Japanese, Korean, Spanish, French, Portuguese, Italian, Turkish, Greek, Tai, and Basq. Dr. Çengel is the recipient of several outstanding teacher awards, and he has received the ASEE Meriam/Wiley Distinguished Author Award for excellence in authorship in 1992 and again in 2000. Dr. Çengel is a registered Professional Engineer in the State of Nevada, and is a member of the American Society of Mechanical Engineers (ASME) and the American Society for Engineering Education (ASEE). Michael A. Boles
is Associate Professor of Mechanical and Aerospace Engineering at North Carolina State University, where he earned his Ph.D. in mechanical engineering and is an Alumni Distinguished Professor. Dr. Boles has received numerous awards and citations for excellence as an engineering educator. He is a past recipient of the SAE Ralph R. Teetor Education Award and has been twice elected to the NCSU Academy of Outstanding Teachers. The NCSU ASME student section has consistently recognized him as the outstanding teacher of the year and the faculty member having the most impact on mechanical engineering students. Dr. Boles specializes in heat transfer and has been involved in the analytical and numerical solution of phase change and drying of porous media. He is a member of the American Society of Mechanical Engineers (ASME), the American Society for Engineering Education (ASEE), and Sigma Xi. Dr. Boles received the ASEE Meriam/Wiley Distinguished Author Award in 1992 for excellence in authorship.
Mehmet Kanoğlu is Professor of Mechanical Engineering at University of Gaziantep. He received his B.S. in mechanical engineering from Istanbul Technical University and his M.S. and Ph.D. in mechanical engineering from University of Nevada, Reno. His research areas include energy efficiency, refrigeration systems, gas liquefaction, hydrogen production and liquefaction, renewable energy systems, geothermal energy, and cogeneration. He is the author or coauthor of over 60 journal papers and numerous conference papers.
vii ABOUT THE AUTHORS
Dr. Kanoğlu has taught courses at University of Nevada, Reno, University of Ontario Institute of Technology, American University of Sharjah, and University of Gaziantep. He is the coauthor of the books Refrigeration Systems and Applications (2nd ed., Wiley, 2010) and Efficiency Evaluation of Energy Systems (Springer, 2012). Dr. Kanoğlu has served as an instructor in certified energy manager training programs and as an expert for United Nations Development Programme (UNDP) for energy efficiency and renewable energy projects. He instructed numerous training courses and gave lectures and presentations on energy efficiency and renewable energy systems. He has also served as advisor for state research funding organizations and industrial companies.
B RIEF C ONTENTS CHAPTER ONE INTRODUCTION AND BASIC CONCEPTS
1
CHAPTER TWO ENERGY, ENERGY TRANSFER, AND GENERAL ENERGY ANALYSIS
CHAPTER THREE PROPERTIES OF PURE SUBSTANCES
109
CHAPTER FOUR ENERGY ANALYSIS OF CLOSED SYSTEMS
161
CHAPTER FIVE MASS AND ENERGY ANALYSIS OF CONTROL VOLUMES
CHAPTER SIX THE SECOND LAW OF THERMODYNAMICS
271
CHAPTER SEVEN ENTROPY
323
CHAPTER EIGHT EXERGY
413
CHAPTER NINE GAS POWER CYCLES
475
CHAPTER TEN VAPOR AND COMBINED POWER CYCLES
543
CHAPTER ELEVEN REFRIGERATION CYCLES
597
CHAPTER TWELVE THERMODYNAMIC PROPERTY RELATIONS
643
CHAPTER THIRTEEN GAS MIXTURES
675
CHAPTER FOURTEEN GAS–VAPOR MIXTURES AND AIR-CONDITIONING
711
CHAPTER FIFTEEN CHEMICAL REACTIONS
747
CHAPTER SIXTEEN CHEMICAL AND PHASE EQUILIBRIUM
791
CHAPTER SEVENTEEN COMPRESSIBLE FLOW
823
CHAPTER EIGHTEEN (WEB CHAPTER) RENEWABLE ENERGY
211
51
ix BRIEF CONTENTS
APPENDIX 1 PROPERTY TABLES AND CHARTS (SI UNITS)
881
APPENDIX 2 PROPERTY TABLES AND CHARTS (ENGLISH UNITS)
931
C ONTENTS Preface xvii
CHAPTER TWO
CHAPTER ONE
ENERGY, ENERGY TRANSFER, AND GENERAL ENERGY ANALYSIS 51
INTRODUCTION AND BASIC CONCEPTS 1 1–1
Thermodynamics and Energy
2
Application Areas of Thermodynamics
1–2
2–1 Introduction 52 2–2 Forms of Energy 53 Some Physical Insight to Internal Energy More on Nuclear Energy 56 Mechanical Energy 58
3
Importance of Dimensions and Units
3
Some SI and English Units 6 Dimensional Homogeneity 8 Unity Conversion Ratios 9
1–3 1–4
Continuum
1–5 1–6
2–4 Energy Transfer by Work 62
10
Electrical Work
12
Density and Specific Gravity
65
State and Equilibrium
Shaft Work 66 Spring Work 67 Work Done on Elastic Solid Bars 67 Work Associated with the Stretching of a Liquid Film Work Done to Raise or to Accelerate a Body 68 Nonmechanical Forms of Work 70
13
14
14
Processes and Cycles
15 16
Pressure 21 Variation of Pressure with Depth
68
2–6 The First Law of Thermodynamics 70
Temperature and the Zeroth Law of Thermodynamics 17 Temperature Scales 17 The International Temperature Scale of 1990 (ITS-90)
1–9
61
2–5 Mechanical Forms of Work 66
The Steady-Flow Process
1–8
Historical Background on Heat
12
The State Postulate
1–7
2–3 Energy Transfer by Heat 60
Systems and Control Volumes Properties of a System
55
Energy Balance 71 Energy Change of a System, ΔEsystem 72 Mechanisms of Energy Transfer, Ein and Eout 73 20
2–7 Energy Conversion Efficiencies 78 Efficiencies of Mechanical and Electrical Devices
23
2–8 Energy and Environment 85
1–10 Pressure Measurement Devices 26 The Barometer 26 The Manometer 29 Other Pressure Measurement Devices
82
Ozone and Smog 86 Acid Rain 87 The Greenhouse Effect: Global Warming and Climate Change 88 Topic of Special Interest: Mechanisms of Heat Transfer 91 Summary 96 References and Suggested Readings 97 Problems 97
32
1–11 Problem-Solving Technique 33 Step 1: Problem Statement 33 Step 2: Schematic 33 Step 3: Assumptions and Approximations 34 Step 4: Physical Laws 34 Step 5: Properties 34 Step 6: Calculations 34 Step 7: Reasoning, Verification, and Discussion Engineering Software Packages 35 Equation Solvers 36 A Remark on Significant Digits 37 Summary 38 References and Suggested Readings 39 Problems 39
34
CHAPTER THREE PROPERTIES OF PURE SUBSTANCES 3–1 Pure Substance 110 3–2 Phases of a Pure Substance 110
109
xi CONTENTS
3–3 Phase-Change Processes of Pure Substances 111
Internal Energy Changes 182 Enthalpy Changes 182 Topic of Special Interest: Thermodynamic Aspects of Biological Systems 185 Summary 192 References and Suggested Readings 193 Problems 194
Compressed Liquid and Saturated Liquid 112 Saturated Vapor and Superheated Vapor 112 Saturation Temperature and Saturation Pressure 113 Some Consequences of Tsat and Psat Dependence 114
3–4 Property Diagrams for Phase-Change Processes 116 1 The T-v Diagram 116 2 The P-v Diagram 118 Extending the Diagrams to Include the Solid Phase 3 The P-T Diagram 120 The P-v-T Surface 121
CHAPTER FIVE 118
3–5 Property Tables 122
5–1
Enthalpy—A Combination Property 122 1a Saturated Liquid and Saturated Vapor States 1b Saturated Liquid–Vapor Mixture 125 2 Superheated Vapor 128 3 Compressed Liquid 129 Reference State and Reference Values 130
123
3–6 The Ideal-Gas Equation of State 133 Is Water Vapor an Ideal Gas?
3–7
135
Compressibility Factor—A Measure of Deviation from Ideal-Gas Behavior 136
3–8 Other Equations of State 139 van der Waals Equation of State 140 Beattie-Bridgeman Equation of State 140 Benedict-Webb-Rubin Equation of State 141 Virial Equation of State 142 Topic of Special Interest: Vapor Pressure and Phase Equilibrium 144 Summary 148 References and Suggested Readings 149 Problems 149
CHAPTER FOUR ENERGY ANALYSIS OF CLOSED SYSTEMS 161 4–1
Moving Boundary Work Polytropic Process
MASS AND ENERGY ANALYSIS OF CONTROL VOLUMES 211 Conservation of Mass
212
Mass and Volume Flow Rates 212 Conservation of Mass Principle 214 Mass Balance for Steady-Flow Processes Special Case: Incompressible Flow 216
216
5–2 Flow Work and the Energy of a Flowing Fluid 219 Total Energy of a Flowing Fluid 220 Energy Transport by Mass 221
5–3 Energy Analysis of Steady-Flow Systems 222 5–4 Some Steady-Flow Engineering Devices 225 1 Nozzles and Diffusers 226 2 Turbines and Compressors 229 3 Throttling Valves 232 4a Mixing Chambers 233 4b Heat Exchangers 235 5 Pipe and Duct Flow 237
5–5 Energy Analysis of Unsteady-Flow Processes 239
Topic of Special Interest: General Energy Equation Summary 247 References And Suggested Readings 248 Problems 248
CHAPTER SIX THE SECOND LAW OF THERMODYNAMICS 271
162
166
4–2 Energy Balance for Closed Systems 167 4–3 Specific Heats 172 4–4 Internal Energy, Enthalpy, and Specific Heats of Ideal Gases 174 Specific Heat Relations of Ideal Gases
176
4–5 Internal Energy, Enthalpy, and Specific Heats of Solids and Liquids 181
6–1 Introduction to the Second Law 272 6–2 Thermal Energy Reservoirs 273 6–3 Heat Engines 274 Thermal Efficiency 275 Can We Save Qout? 277 The Second Law of Thermodynamics: Kelvin–Planck Statement 279
244
xii THERMODYNAMICS
6–4 Refrigerators and Heat Pumps 279
Relative Pressure and Relative Specific Volume
Coefficient of Performance 280 Heat Pumps 281 Performance of Refrigerators, Air Conditioners, and Heat Pumps 282 The Second Law of Thermodynamics: Clausius Statement 284 Equivalence of the Two Statements 285
6–5 Perpetual-Motion Machines 286 6–6 Reversible and Irreversible Processes 288 Irreversibilities 289 Internally and Externally Reversible Processes
The Reversed Carnot Cycle
7–10 Reversible Steady-Flow Work 354 Proof that Steady-Flow Devices Deliver the Most and Consume the Least Work When the Process Is Reversible 356
7–11 Minimizing the Compressor Work 357 Multistage Compression with Intercooling
Isentropic Efficiency of Turbines 361 Isentropic Efficiencies of Compressors and Pumps Isentropic Efficiency of Nozzles 365
363
7–13 Entropy Balance 367
293
Entropy Change of a System, ΔSsystem 368 Mechanisms of Entropy Transfer, Sin and Sout 368 1 Heat Transfer 368 2 Mass Flow 369 Entropy Generation, Sgen 370 Closed Systems 371 Control Volumes 372 Entropy Generation Associated with a Heat Transfer Process 378 Topic of Special Interest: Reducing the Cost of Compressed Air 380 Summary 389 References and Suggested Readings 390 Problems 390
6–8 The Carnot Principles 293 6–9 The Thermodynamic Temperature Scale 295 6–10 The Carnot Heat Engine 297 The Quality of Energy 298 Quantity versus Quality in Daily Life
358
7–12 Isentropic Efficiencies of Steady-Flow Devices 361
290
6–7 The Carnot Cycle 291
350
299
6–11 The Carnot Refrigerator and Heat Pump 300 Topic of Special Interest: Household Refrigerators Summary 307 References and Suggested Readings 308 Problems 308
303
CHAPTER SEVEN ENTROPY
CHAPTER EIGHT
323
EXERGY 7–1
Entropy
A Special Case: Internally Reversible Isothermal Heat Transfer Processes 327
7–2 The Increase of Entropy Principle 328 Some Remarks About Entropy
7–3 7–4 7–5 7–6
413
324
330
Entropy Change of Pure Substances 331 Isentropic Processes
334
Property Diagrams Involving Entropy 336 What is Entropy? 337 Entropy and Entropy Generation in Daily Life
340
7–7 The T ds Relations 341 7–8 Entropy Change of Liquids and Solids 343 7–9 The Entropy Change of Ideal Gases 346 Constant Specific Heats (Approximate Analysis) Variable Specific Heats (Exact Analysis) 347 Isentropic Processes of Ideal Gases 349 Constant Specific Heats (Approximate Analysis) Variable Specific Heats (Exact Analysis) 350
347
8–1
Exergy: Work Potential of Energy
8–2 Reversible Work and Irreversibility 417 8–3 Second-Law Efficiency 422 8–4 Exergy Change of a System 425 Exergy of a Fixed Mass: Nonflow (or Closed System) Exergy 425 Exergy of a Flow Stream: Flow (or Stream) Exergy 428
8–5 Exergy Transfer by Heat, Work, and Mass 430 Exergy Transfer by Heat, Q 431 Exergy Transfer by Work, W 432 Exergy Transfer by Mass, m 432
8–6 The Decrease of Exergy Principle and Exergy Destruction 433 Exergy Destruction
349
414
Exergy (Work Potential) Associated with Kinetic and Potential Energy 415
434
8–7 Exergy Balance: Closed Systems 435
xiii CONTENTS
8–8 Exergy Balance: Control Volumes 446 Exergy Balance for Steady-Flow Systems 447 Reversible Work 447 Second-Law Efficiency of Steady-Flow Devices 448 Topic of Special Interest: Second-Law Aspects of Daily Life 454 Summary 458 References and Suggested Readings 459 Problems 460
9–1
475
Basic Considerations in the Analysis of Power Cycles 476
9–2 The Carnot Cycle and its Value in Engineering 478 9–3 Air-Standard Assumptions 480 9–4 An Overview of Reciprocating Engines 481 9–5 Otto Cycle: the Ideal Cycle for Spark-Ignition Engines 482 9–6 Diesel Cycle: the Ideal Cycle for Compression-Ignition Engines 489 9–7 Stirling and Ericsson Cycles 493 9–8 Brayton Cycle: the Ideal Cycle for Gas-Turbine Engines 497 Development of Gas Turbines 499 Deviation of Actual Gas-Turbine Cycles from Idealized Ones 502
9–9 The Brayton Cycle with Regeneration 504 9–10 The Brayton Cycle with Intercooling, Reheating, and Regeneration 506 9–11 Ideal Jet-Propulsion Cycles 510 Modifications to Turbojet Engines
Energy Analysis of the Ideal Rankine Cycle
545
10–3 Deviation of Actual Vapor Power Cycles From Idealized Ones 548 10–4 How Can we Increase the Efficiency of the Rankine Cycle? 551 Lowering the Condenser Pressure (Lowers Tlow,avg) 551 Superheating the Steam to High Temperatures (Increases Thigh,avg) 552 Increasing the Boiler Pressure (Increases Thigh,avg) 552
CHAPTER NINE GAS POWER CYCLES
10–2 Rankine Cycle: the Ideal Cycle for Vapor Power Cycles 545
514
9–12 Second-Law Analysis of Gas Power Cycles 516
Topic of Special Interest: Saving Fuel and Money by Driving Sensibly 519 Summary 526 References and Suggested Readings 527 Problems 528
CHAPTER TEN VAPOR AND COMBINED POWER CYCLES 543 10–1 The Carnot Vapor Cycle 544
10–5 The Ideal Reheat Rankine Cycle 555 10–6 The Ideal Regenerative Rankine Cycle 559 Open Feedwater Heaters 559 Closed Feedwater Heaters 561
10–7 Second-Law Analysis of Vapor Power Cycles 567 10–8 Cogeneration 569 10–9 Combined Gas–Vapor Power Cycles 574 Topic of Special Interest: Binary Vapor Cycles Summary 579 References and Suggested Readings 579 Problems 580
577
CHAPTER ELEVEN REFRIGERATION CYCLES
597
11–1 Refrigerators and Heat Pumps 598 11–2 The Reversed Carnot Cycle 599 11–3 The Ideal Vapor-Compression Refrigeration Cycle 600 11–4 Actual Vapor-Compression Refrigeration Cycle 603 11–5 Second-Law Analysis of Vapor-Compression Refrigeration Cycle 605 11–6 Selecting the Right Refrigerant 609 11–7 Heat Pump Systems 611 11–8 Innovative Vapor-Compression Refrigeration Systems 613 Cascade Refrigeration Systems 613 Multistage Compression Refrigeration Systems 615 Multipurpose Refrigeration Systems with a Single Compressor 617 Liquefaction of Gases 618
11–9 Gas Refrigeration Cycles 619 11–10 Absorption Refrigeration Systems 622
xiv THERMODYNAMICS Topic of Special Interest: Thermoelectric Power Generation and Refrigeration Systems 626 Summary 628 References and Suggested Readings 628 Problems 629
C H A P T E R T W E LV E THERMODYNAMIC PROPERTY RELATIONS 643 12–1 A Little Math—Partial Derivatives and Associated Relations 644 Partial Differentials 645 Partial Differential Relations
647
12–2 The Maxwell Relations 649 12–3 The Clapeyron Equation 650 12–4 General Relations for du, dh, ds, cv, and cp 653 Internal Energy Changes 654 Enthalpy Changes 654 Entropy Changes 655 Specific Heats cv and cp 656
12–5 The Joule-Thomson Coefficient 660 12–6 The Δh, Δu, and Δs of Real Gases 662 Enthalpy Changes of Real Gases 662 Internal Energy Changes of Real Gases 664 Entropy Changes of Real Gases 664 Summary 667 References and Suggested Readings 668 Problems 668
CHAPTER THIRTEEN GAS MIXTURES
675
13–1 Composition of a Gas Mixture: Mass and Mole Fractions 676 13–2 P-v-T Behavior of Gas Mixtures: Ideal and Real Gases 677 Ideal-Gas Mixtures 678 Real-Gas Mixtures 679
13–3 Properties of Gas Mixtures: Ideal and Real Gases 682 Ideal-Gas Mixtures 683 Real-Gas Mixtures 687 Topic of Special Interest: Chemical Potential and the Separation Work of Mixtures 690 Summary 700 References and Suggested Readings 701 Problems 702
CHAPTER FOURTEEN GAS–VAPOR MIXTURES AND AIR-CONDITIONING 711 14–1 14–2 14–3 14–4
Dry and Atmospheric Air
712
Specific and Relative Humidity of air
713
Dew-Point Temperature 715 Adiabatic Saturation and Wet-Bulb Temperatures 717
14–5 The Psychrometric Chart 720 14–6 Human Comfort and Air-Conditioning 721 14–7 Air-Conditioning Processes 723 Simple Heating and Cooling (ω = constant) 724 Heating with Humidification 725 Cooling with Dehumidification 727 Evaporative Cooling 728 Adiabatic Mixing of Airstreams 730 Wet Cooling Towers 732 Summary 734 References and Suggested Readings 736 Problems 736
CHAPTER FIFTEEN CHEMICAL REACTIONS
747
15–1 Fuels and Combustion 748 15–2 Theoretical and Actual Combustion Processes 752 15–3 Enthalpy of Formation and Enthalpy of Combustion 758 15–4 First-Law Analysis of Reacting Systems 762 Steady-Flow Systems 762 Closed Systems 763
15–5 Adiabatic Flame Temperature 767 15–6 Entropy Change of Reacting Systems 769 15–7 Second-Law Analysis of Reacting Systems 771 Topic of Special Interest: Fuel Cells 776 Summary 778 References and Suggested Readings 779 Problems 779
CHAPTER SIXTEEN CHEMICAL AND PHASE EQUILIBRIUM 791 16–1 Criterion for Chemical Equilibrium 792
xv CONTENTS Solar-Power-Tower Plant Solar Pond Photovoltaic Cell Passive Solar Applications Solar Heat Gain through Windows
16–2 The Equilibrium Constant for Ideal-Gas Mixtures 794 16–3 Some Remarks about the KP of Ideal-Gas Mixtures 798 16–4 Chemical Equilibrium for Simultaneous Reactions 802 16–5 Variation of KP with Temperature 804 16–6 Phase Equilibrium 806
18–3 Wind Energy
Phase Equilibrium for a Single-Component System 806 The Phase Rule 807 Phase Equilibrium for a Multicomponent System 808 Summary 813 References and Suggested Readings 814 Problems 815
Wind Turbine Types and Power Performance Curve Wind Power Potential Wind Power Density Wind Turbine Efficiency Betz Limit for Wind Turbine Efficiency
18–4 Hydropower Analysis of Hydroelectric Power Plant Turbine Types
18–5 Geothermal Energy Geothermal Power Production
CHAPTER SEVENTEEN COMPRESSIBLE FLOW
18–6 Biomass Energy
823
17–1 Stagnation Properties 824 17–2 Speed of Sound and Mach Number 827 17–3 One-Dimensional Isentropic Flow 829 Variation of Fluid Velocity with Flow Area 831 Property Relations for Isentropic Flow of Ideal Gases
833
Biomass Resources Conversion of Biomass to Biofuel Biomass Products Electricity and Heat Production by Biomass Solid Municipality Waste Summary References and Suggested Readings Problems
17–4 Isentropic Flow Through Nozzles 836 Converging Nozzles 836 Converging–Diverging Nozzles
APPENDIX ONE
840
17–5 Shock Waves and Expansion Waves 844 Normal Shocks 844 Oblique Shocks 850 Prandtl–Meyer Expansion Waves
PROPERTY TABLES AND CHARTS (SI UNITS) 881
854
17–6 Duct Flow with Heat Transfer and Negligible Friction (Rayleigh Flow) 858 Property Relations for Rayleigh Flow Choked Rayleigh Flow 865
864
17–7 Steam Nozzles 867 Summary 870 References and Suggested Readings Problems 872
Table A–1 Table A–2 Table A–3
872
CHAPTER EIGHTEEN (W E B C H A P T E R) RENEWABLE ENERGY 18–1 Introduction 18-2 Solar Energy Solar Radiation Flat-Plate Solar Collector Concentrating Solar Collector Linear Concentrating Solar Power Collector
Table A–4 Table A–5 Table A–6 Table A–7 Table A–8 Figure A–9 Figure A–10 Table A–11 Table A–12 Table A–13
Molar mass, gas constant, and criticalpoint properties 882 Ideal-gas specific heats of various common gases 883 Properties of common liquids, solids, and foods 886 Saturated water—Temperature table 888 Saturated water—Pressure table 890 Superheated water 892 Compressed liquid water 896 Saturated ice–water vapor 897 T-s diagram for water 898 Mollier diagram for water 899 Saturated refrigerant-134a— Temperature table 900 Saturated refrigerant-134a—Pressure table 902 Superheated refrigerant-134a 903
xvi THERMODYNAMICS
4 928 Table A–33 One-dimensional normal-shock functions for an ideal gas with k = 1.4 929 Table A–34 Rayleigh flow functions for an ideal gas with k = 1.4 930
Table A–2E
APPENDIX TWO
INDEX 973 NOMENCLATURE 981 CONVERSION FACTORS
Figure A–14 Figure A–15
PROPERTY TABLES AND CHARTS (ENGLISH UNITS) 931 Table A–1E
Molar mass, gas constant, and criticalpoint properties 932
Table A–3E Table A–4E Table A–5E Table A–6E Table A–7E Table A–8E Figure A–9E Figure A–10E Table A–11E Table A–12E Table A–13E Figure A–14E Table A–16E Table A–17E Table A–18E Table A–19E Table A–20E Table A–21E Table A–22E Table A–23E Table A–26E Table A–27E Figure A–31E
983
P REFACE BACKGROUND Thermodynamics is an exciting and fascinating subject that deals with energy, and thermodynamics has long been an essential part of engineering curricula all over the world. It has a broad application area ranging from microscopic organisms to common household appliances, transportation vehicles, power generation systems, and even philosophy. This introductory book contains sufficient material for two sequential courses in thermodynamics. Students are assumed to have an adequate background in calculus and physics.
OBJECTIVES This book is intended for use as a textbook by undergraduate engineering students in their sophomore or junior year, and as a reference book for practicing engineers. The objectives of this text are ⬤
⬤
⬤
To cover the basic principles of thermodynamics. To present a wealth of real-world engineering examples to give students a feel for how thermodynamics is applied in engineering practice. To develop an intuitive understanding of thermodynamics by emphasizing the physics and physical arguments that underpin the theory.
It is our hope that this book, through its careful explanations of concepts and its use of numerous practical examples and figures, helps students develop the necessary skills to bridge the gap between knowledge and the confidence to properly apply knowledge.
PHILOSOPHY AND GOAL The philosophy that contributed to the overwhelming popularity of the prior editions of this book has remained unchanged in this edition. Namely, our goal has been to offer an engineering textbook that ⬤
⬤
⬤
⬤
Communicates directly to the minds of tomorrow’s engineers in a simple yet precise manner. Leads students toward a clear understanding and firm grasp of the basic principles of thermodynamics. Encourages creative thinking and development of a deeper understanding and intuitive feel for thermodynamics. Is read by students with interest and enthusiasm rather than being used as an aid to solve problems.
Special effort has been made to appeal to students’ natural curiosity and to help them explore the various facets of the exciting subject area of thermodynamics. The enthusiastic responses we have received from users of prior editions—from small colleges to large universities all over the world— and the continued translations into new languages indicate that our objectives have largely been achieved. It is our philosophy that the best way to learn is
xviii THERMODYNAMICS
by practice. Therefore, special effort is made throughout the book to reinforce material that was presented earlier. Yesterday’s engineer spent a major portion of his or her time substituting values into the formulas and obtaining numerical results. However, formula manipulations and number crunching are now being left mainly to computers. Tomorrow’s engineer will need a clear understanding and a firm grasp of the basic principles so that he or she can understand even the most complex problems, formulate them, and interpret the results. A conscious effort is made to emphasize these basic principles while also providing students with a perspective of how computational tools are used in engineering practice. The traditional classical, or macroscopic, approach is used throughout the text, with microscopic arguments serving in a supporting role as appropriate. This approach is more in line with students’ intuition and makes learning the subject matter much easier.
NEW IN THIS EDITION All the popular features of the previous editions have been retained. A large number of the end-of-chapter problems in the text have been modified and many problems were replaced by new ones. Also, several of the solved example problems have been replaced. Video Resources—Using the student response data from the eighth edition LearnSmart/SmartBook, 2D/3D animation videos have been added to the ebook to help clarify challenging concepts. In addition to these conceptual video resources, worked example problem videos are included in the ebook to help students apply their conceptual understanding to problem solving.
LEARNING TOOLS EARLY INTRODUCTION OF THE FIRST LAW OF THERMODYNAMICS The first law of thermodynamics is introduced early in Chapter 2, “Energy, Energy Transfer, and General Energy Analysis.” This introductory chapter sets the framework of establishing a general understanding of various forms of energy, mechanisms of energy transfer, the concept of energy balance, thermoeconomics, energy conversion, and conversion efficiency using familiar settings that involve mostly electrical and mechanical forms of energy. It also exposes students to some exciting real-world applications of thermodynamics early in the course, and helps them establish a sense of the monetary value of energy. There is special emphasis on the utilization of renewable energy such as wind power and hydraulic energy, and the efficient use of existing resources.
EMPHASIS ON PHYSICS A distinctive feature of this book is its emphasis on the physical aspects of the subject matter in addition to mathematical representations and manipulations. The authors believe that the emphasis in undergraduate education should remain on developing a sense of underlying physical mechanisms and a mastery of solving practical problems that an engineer is likely to face in the real world. Developing an intuitive understanding should also make the course a more motivating and worthwhile experience for students.
xix PREFACE
EFFECTIVE USE OF ASSOCIATION An observant mind should have no difficulty understanding engineering sciences. After all, the principles of engineering sciences are based on our everyday experiences and experimental observations. Therefore, a physical, intuitive approach is used throughout this text. Frequently, parallels are drawn between the subject matter and students’ everyday experiences so that they can relate the subject matter to what they already know. The process of cooking, for example, serves as an excellent vehicle to demonstrate the basic principles of thermodynamics.
SELF-INSTRUCTING The material in the text is introduced at a level that an average student can follow comfortably. It speaks to students, not over students. In fact, it is self-instructive. The order of coverage is from simple to general. That is, it starts with the simplest case and adds complexities gradually. In this way, the basic principles are repeatedly applied to different systems, and students master how to apply the principles instead of how to simplify a general formula. Noting that the principles of sciences are based on experimental observations, all the derivations in this text are based on physical arguments, and thus they are easy to follow and understand.
EXTENSIVE USE OF ARTWORK Figures are important learning tools that help students “get the picture,” and the text makes very effective use of graphics. This edition features an enhanced art program done in four colors to provide more realism and pedagogical understanding. Further, a large number of figures have been upgraded to become three-dimensional and thus more real-life. Figures attract attention and stimulate curiosity and interest. Most of the figures in this text are intended to serve as a means of emphasizing some key concepts that would otherwise go unnoticed; some serve as page summaries.
LEARNING OBJECTIVES AND SUMMARIES Each chapter begins with an overview of the material to be covered and chapter-specific learning objectives. A summary is included at the end of each chapter, providing a quick review of basic concepts and important relations, and pointing out the relevance of the material.
NUMEROUS WORKED-OUT EXAMPLES WITH A SYSTEMATIC SOLUTIONS PROCEDURE Each chapter contains several worked-out examples that clarify the material and illustrate the use of the basic principles. An intuitive and systematic approach is used in the solution of the example problems, while maintaining an informal conversational style. The problem is first stated, and the objectives are identified. The assumptions are then stated, together with their justifications. The properties needed to solve the problem are listed separately if appropriate. Numerical values are used together with their units to emphasize that numbers without units are meaningless, and that unit manipulations are as important as manipulating the numerical values with a calculator. The significance of the findings is discussed following the solutions. This approach is also used consistently in the solutions presented in the instructor’s solutions manual.
xx THERMODYNAMICS
A WEALTH OF REAL-WORLD END-OF-CHAPTER PROBLEMS The end-of-chapter problems are grouped under specific topics to make problem selection easier for both instructors and students. Within each group of problems are Concept Questions, indicated by “C,” to check the students’ level of understanding of basic concepts. The problems under Review Problems are more comprehensive in nature and are not directly tied to any specific section of a chapter—in some cases they require review of material learned in previous chapters. Problems designated as Design and Essay are intended to encourage students to make engineering judgments, to conduct independent exploration of topics of interest, and to communicate their findings in a professional manner. Problems designated by an “E” are in English units, and SI are comprehensive in nature users can ignore them. Problems with the and are intended to be solved with a computer, using appropriate software. Several economics- and safety-related problems are incorporated throughout to promote cost and safety awareness among engineering students. Answers to selected problems are listed immediately following the problem for convenience to students. In addition, to prepare students for the Fundamentals of Engineering Exam (that is becoming more important for the outcome-based ABET 2000 criteria) and to facilitate multiple-choice tests, over 200 multiplechoice problems are included in the end-of-chapter problem sets. They are placed under the title Fundamentals of Engineering (FE) Exam Problems for easy recognition. These problems are intended to check the understanding of fundamentals and to help readers avoid common pitfalls.
RELAXED SIGN CONVENTION The use of a formal sign convention for heat and work is abandoned as it often becomes counterproductive. A physically meaningful and engaging approach is adopted for interactions instead of a mechanical approach. Subscripts “in” and “out,” rather than the plus and minus signs, are used to indicate the directions of interactions.
PHYSICALLY MEANINGFUL FORMULAS The physically meaningful forms of the balance equations rather than formulas are used to foster deeper understanding and to avoid a cookbook approach. The mass, energy, entropy, and exergy balances for any system undergoing any process are expressed as Mass balance: Energy balance:
m in − m out = Δm system E −E
in out Net energy transfer by heat, work, and mass
Entropy balance:
ΔE system Change⏟ in internal, kinetic, potential, etc., energies
S in − S out + S gen = ΔS system ⏟ ⏟ ⏟ Net entropy transfer Entropy Change by heat and mass
Exergy balance:
=
X −X
in out Net exergy transfer by heat, work, and mass
generation
in entropy
− X destroyed = ΔX system ⏟ ⏟ Exergy Change destruction
in exergy
xxi PREFACE
These relations reinforce the fundamental principles that during an actual process mass and energy are conserved, entropy is generated, and exergy is destroyed. Students are encouraged to use these forms of balances in early chapters after they specify the system, and to simplify them for the particular problem. A more relaxed approach is used in later chapters as students gain mastery.
A CHOICE OF SI ALONE OR SI/ENGLISH UNITS In recognition of the fact that English units are still widely used in some industries, both SI and English units are used in this text, with an emphasis on SI. The material in this text can be covered using combined SI/English units or SI units alone, depending on the preference of the instructor. The property tables and charts in the appendices are presented in both units, except the ones that involve dimensionless quantities. Problems, tables, and charts in English units are designated by “E” after the number for easy recognition, and they can be ignored by SI users.
TOPICS OF SPECIAL INTEREST Most chapters contain a section called “Topic of Special Interest” where interesting aspects of thermodynamics are discussed. Examples include Thermodynamic Aspects of Biological Systems in Chapter 4, Household Refrigerators in Chapter 6, Second-Law Aspects of Daily Life in Chapter 8, and Saving Fuel and Money by Driving Sensibly in Chapter 9. The topics selected for these sections provide intriguing extensions to thermodynamics, but they can be ignored if desired without a loss in continuity.
GLOSSARY OF THERMODYNAMIC TERMS Throughout the chapters, when an important key term or concept is introduced and defined, it appears in boldface type. Fundamental thermodynamic terms and concepts also appear in a glossary located on our accompanying website. This unique glossary helps to reinforce key terminology and is an excellent learning and review tool for students as they move forward in their study of thermodynamics.
CONVERSION FACTORS Frequently used conversion factors and physical constants are listed at the end of the text.
SUPPLEMENTS The following supplements are available to users of the book.
PROPERTIES TABLE BOOKLET (ISBN 1-260-04899-3) This booklet provides students with an easy reference to the most important property tables and charts, many of which are found at the back of the textbook in both the SI and English units.
xxii THERMODYNAMICS
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
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. We thank Mohsen Hassan Vand for his valuable suggestions and contributions. 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, and to our children for their continued patience, understanding, and support throughout the preparation of this text. Yunus A. Çengel Michael A. Boles Mehmet Kanoğlu
Online Resources for Students and Instructors McGraw-Hill Connect® Connect® is a highly reliable, easy-to-use homework and learning management solution that utilizes learning science and award-winning adaptive tools to improve student results.
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Connect InSight generates easy-to-read reports on individual students, the class as a whole, and on specific assignments. The Connect Insight dashboard delivers data on performance, study behavior, and effort. Instructors can quickly identify students who struggle and focus on material that the class has yet to master. Connect automatically grades assignments and quizzes, providing easy-to-read reports on individual and class performance.
Find the following instructor resources available through Connect: ■
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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. Correlation Guide—New users of this text will appreciate this resource. The guide provides a smooth transition for instructors not currently using this 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. PowerPoint 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.
xxiv THERMODYNAMICS
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/
Adaptive SmartBook® SmartBook helps students study more efficiently by delivering an interactive reading experience through adaptive highlighting and review.
CHAPTER
INTRODUCTION AND BASIC CONCEPTS 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, process, and cycle. 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 we 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.
E
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.
1
2 INTRODUCTION AND BASIC CONCEPTS
PE = 10 units KE = 0
PE = 7 units KE = 3 units
Potential energy
Kinetic energy
FIGURE 1–1 Energy cannot be created or destroyed; it can only change forms (the first law). Energy storage (1 unit) Energy in (5 units)
Energy out (4 units)
FIGURE 1–2 Conservation of energy principle for the human body.
Cool environment 20°C Hot coffee 70°C
Heat
FIGURE 1–3 Heat flows in the direction of decreasing temperature.
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 − Eout = ΔE. 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
3 CHAPTER 1
study of thermodynamics that does not require a knowledge of the behavior of individual particles is called classical thermodynamics. It provides a direct and easy way to solve engineering problems. A more elaborate approach, based on the average behavior of large groups of individual particles, is called statistical thermodynamics. This microscopic approach is rather involved and is used in this text only in a supporting role.
Application Areas of Thermodynamics All activities in nature involve some interaction between energy and matter; thus, it is hard to imagine an area that does not relate to thermodynamics in some manner. Therefore, developing a good understanding of basic principles of thermodynamics has long been an essential part of engineering education. Thermodynamics is commonly encountered in many engineering systems and other aspects of life, and one does not need to go very far to see some application areas of it. In fact, one does not need to go anywhere. The heart is constantly pumping blood to all parts of the human body, various energy conversions occur in trillions of body cells, and the body heat generated is constantly rejected to the environment. Human comfort is closely tied to the rate of this metabolic heat rejection. We try to control this heat transfer rate by adjusting our clothing to the environmental conditions. Other applications of thermodynamics are right where one lives. An ordinary house is, in some respects, an exhibition hall filled with wonders of thermodynamics (Fig. 1–4). Many ordinary household utensils and appliances are designed, in whole or in part, by using the principles of thermodynamics. Some examples include the electric or gas range, the heating and air-conditioning systems, the refrigerator, the humidifier, the pressure cooker, the water heater, the shower, the iron, and even the computer and the TV. On a larger scale, thermodynamics plays a major part in the design and analysis of automotive engines, rockets, jet engines, and conventional or nuclear power plants, solar collectors, and the design of vehicles from ordinary cars to airplanes (Fig. 1–5). The energy-efficient home that you may be living in, for example, is designed on the basis of minimizing heat loss in winter and heat gain in summer. The size, location, and the power input of the fan of your computer is also selected after an analysis that involves thermodynamics.
1–2
■
IMPORTANCE OF DIMENSIONS AND UNITS
Any physical quantity can be characterized by dimensions. The magnitudes assigned to the dimensions are called units. Some basic dimensions such as mass m, length L, time t, and temperature T are selected as primary or fundamental dimensions, while others such as velocity V, energy E, and volume V are expressed in terms of the primary dimensions and are called secondary dimensions, or derived dimensions. A number of unit systems have been developed over the years. Despite strong efforts in the scientific and engineering community to unify the world with a single unit system, two sets of units are still in common use today: the English system, which is also known as the United States Customary System (USCS), and the metric SI (from Le Système International d’ Unités), which
Solar collectors
Shower Hot water Hot water tank
Cold water Heat exchanger
Pump
FIGURE 1–4 The design of many engineering systems, such as this solar hot water system, involves thermodynamics.
4 INTRODUCTION AND BASIC CONCEPTS
(a) Refrigerator
(b) Boats
(c) Aircraft and spacecraft
(d) Power plants
(e) Human body
(f) Cars
(g) Wind turbines
(h) Food processing
(i) A piping network in an industrial facility.
FIGURE 1–5 Some application areas of thermodynamics. (a) ©McGraw-Hill Education/Jill Braaten; (b) ©Doug Menuez/Getty Images RF; (c) ©Ilene MacDonald/Alamy RF; (d) ©Malcolm Fife/Getty Images RF; (e) ©Ryan McVay/Getty Images RF; (f) ©Mark Evans/Getty Images RF; (g) ©Getty Images/iStockphoto RF; (h) ©Glow Images RF; (i) Courtesy of UMDE Engineering Contracting and Trading. Used by permission.
is also known as the International System. The SI is a simple and logical system based on a decimal relationship between the various units, and it is being used for scientific and engineering work in most of the industrialized nations, including England. The English system, however, has no apparent systematic numerical base, and various units in this system are related to each other rather arbitrarily (12 in = 1 ft, 1 mile = 5280 ft, 4 qt = 1 gal, etc.), which makes it confusing and difficult to learn. The United States is the only industrialized country that has not yet fully converted to the metric system.
5 CHAPTER 1
The systematic efforts to develop a universally acceptable system of units dates back to 1790 when the French National Assembly charged the French Academy of Sciences to come up with such a unit system. An early version of the metric system was soon developed in France, but it did not find universal acceptance until 1875 when The Metric Convention Treaty was prepared and signed by 17 nations, including the United States. In this international treaty, meter and gram were established as the metric units for length and mass, respectively, and a General Conference of Weights and Measures (CGPM) was established that was to meet every six years. In 1960, the CGPM produced the SI, which was based on six fundamental quantities, and their units were adopted in 1954 at the Tenth General Conference of Weights and Measures: meter (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for electric current, degree Kelvin (°K) for temperature, and candela (cd) for luminous intensity (amount of light). In 1971, the CGPM added a seventh fundamental quantity and unit: mole (mol) for the amount of matter. Based on the notational scheme introduced in 1967, the degree symbol was officially dropped from the absolute temperature unit, and all unit names were to be written without capitalization even if they were derived from proper names (Table 1–1). However, the abbreviation of a unit was to be capitalized if the unit was derived from a proper name. For example, the SI unit of force, which is named after Sir Isaac Newton (1647–1723), is newton (not Newton), and it is abbreviated as N. Also, the full name of a unit may be pluralized, but its abbreviation cannot. For example, the length of an object can be 5 m or 5 meters, not 5 ms or 5 meter. Finally, no period is to be used in unit abbreviations unless they appear at the end of a sentence. For example, the proper abbreviation of meter is m (not m.). The recent move toward the metric system in the United States seems to have started in 1968 when Congress, in response to what was happening in the rest of the world, passed a Metric Study Act. Congress continued to promote a voluntary switch to the metric system by passing the Metric Conversion Act in 1975. A trade bill passed by Congress in 1988 set a September 1992 deadline for all federal agencies to convert to the metric system. However, the deadlines were relaxed later with no clear plans for the future. The industries that are heavily involved in international trade (such as the automotive, soft drink, and liquor industries) have been quick to convert to the metric system for economic reasons (having a single worldwide design, fewer sizes, smaller inventories, etc.). Today, nearly all the cars manufactured in the United States are metric. Most car owners probably do not realize this until they try an English socket wrench on a metric bolt. Most industries, however, resisted the change, thus slowing down the conversion process. At present the United States is a dual-system society, and it will stay that way until the transition to the metric system is completed. This puts an extra burden on today’s engineering students, since they are expected to retain their understanding of the English system while learning, thinking, and working in terms of the SI. Given the position of the engineers in the transition period, both unit systems are used in this text, with particular emphasis on SI units. As pointed out, the SI is based on a decimal relationship between units. The prefixes used to express the multiples of the various units are listed in Table 1–2. They are standard for all units, and the student is encouraged to memorize them because of their widespread use (Fig. 1–6).
TABLE 1–1 The seven fundamental (or primary) dimensions and their units in SI Dimension
Unit
Length Mass Time Temperature Electric current Amount of light Amount of matter
meter (m) kilogram (kg) second (s) kelvin (K) ampere (A) candela (cd) mole (mol)
TABLE 1–2 Standard prefixes in SI units Multiple
Prefix
1024 1021 1018 1015 1012 109 106 103 102 101 10−1 10−2 10−3 10−6 10−9 10−12 10−15 10−18 10−21 10−24
yotta, Y zetta, Z exa, E peta, P tera, T giga, G mega, M kilo, k hecto, h deka, da deci, d centi, c milli, m micro, μ nano, n pico, p femto, f atto, a zepto, z yocto, y
200 mL (0.2 L)
1 kg (103 g)
1 MΩ (10 6 Ω)
FIGURE 1–6 The SI unit prefixes are used in all branches of engineering.
6 INTRODUCTION AND BASIC CONCEPTS
Some SI and English Units In SI, the units of mass, length, and time are the kilogram (kg), meter (m), and second (s), respectively. The respective units in the English system are the pound-mass (lbm), foot (ft), and second (s). The pound symbol lb is actually the abbreviation of libra, which was the ancient Roman unit of weight. The English retained this symbol even after the end of the Roman occupation of Britain in 410. The mass and length units in the two systems are related to each other by 1 lbm = 0.45356 kg 1 ft = 0.3048 m
a = 1 m/s2 m = 1 kg
F=1N
In the English system, force is usually considered to be one of the primary dimensions and is assigned a nonderived unit. This is a source of confusion and error that necessitates the use of a dimensional constant (gc) in many formulas. To avoid this nuisance, we consider force to be a secondary dimension whose unit is derived from Newton’s second law, that is, Force = (Mass)(Acceleration)
a = 1 ft/s2 m = 32.174 lbm
F = 1 lbf
FIGURE 1–7 The definition of the force units.
1 kgf
or F = ma
(1–1)
In SI, the force unit is the newton (N), and it is defined as the force required to accelerate a mass of 1 kg at a rate of 1 m/s2. In the English system, the force unit is the pound-force (lbf) and is defined as the force required to accelerate a mass of 1 slug (32.174 lbm) at a rate of 1 ft/s2 (Fig. 1–7). That is, 1 N = 1 kg⋅m / s2 1 lbf = 32.174 lbm⋅ft / s2
10 apples m ≈ 1 kg 1 apple m ≈ 102 g
1N
4 apples m ≈1 lbm
1 lbf
A force of 1 N is roughly equivalent to the weight of a small apple (m = 102 g), whereas a force of 1 lbf is roughly equivalent to the weight of four medium apples (mtotal = 454 g), as shown in Fig. 1–8. Another force unit in common use in many European countries is the kilogram-force (kgf), which is the weight of 1 kg mass at sea level (1 kgf = 9.807 N). The term weight is often incorrectly used to express mass, particularly by the “weight watchers.” Unlike mass, weight W is a force. It is the gravitational force applied to a body, and its magnitude is determined from Newton’s second law, W = mg (N)
FIGURE 1–8 The relative magnitudes of the force units newton (N), kilogram-force (kgf), and pound-force (lbf).
(1–2)
where m is the mass of the body, and g is the local gravitational acceleration (g is 9.807 m/s2 or 32.174 ft/s2 at sea level and 45° latitude). An ordinary bathroom scale measures the gravitational force acting on a body. The mass of a body remains the same regardless of its location in the universe. Its weight, however, changes with a change in gravitational acceleration. A body weighs less on top of a mountain since g decreases with altitude.
7 CHAPTER 1
On the surface of the moon, an astronaut weighs about one-sixth of what she or he normally weighs on earth (Fig. 1–9). At sea level a mass of 1 kg weighs 9.807 N, as illustrated in Fig. 1–10. A mass of 1 lbm, however, weighs 1 lbf, which misleads people into believing that pound-mass and pound-force can be used interchangeably as pound (lb), which is a major source of error in the English system. It should be noted that the gravity force acting on a mass is due to the attraction between the masses, and thus it is proportional to the magnitudes of the masses and inversely proportional to the square of the distance between them. Therefore, the gravitational acceleration g at a location depends on latitude, the distance to the center of the earth, and to a lesser extent, the positions of the moon and the sun. The value of g varies with location from 9.832 m/s2 at the poles (9.789 at the equator) to 7.322 m/s2 at 1000 km above sea level. However, at altitudes up to 30 km, the variation of g from the sea-level value of 9.807 m/s2 is less than 1 percent. Therefore, for most practical purposes, the gravitational acceleration can be assumed to be constant at 9.807 m/s2, often rounded to 9.81 m/s2. It is interesting to note that at locations below sea level, the value of g increases with distance from the sea level, reaches a maximum at about 4500 m, and then starts decreasing. (What do you think the value of g is at the center of the earth?) The primary cause of confusion between mass and weight is that mass is usually measured indirectly by measuring the gravity force it exerts. This approach also assumes that the forces exerted by other effects such as air buoyancy and fluid motion are negligible. This is like measuring the distance to a star by measuring its redshift, or measuring the altitude of an airplane by measuring barometric pressure. Both of these are also indirect measurements. The correct direct way of measuring mass is to compare it to a known mass. This is cumbersome, however, and it is mostly used for calibration and measuring precious metals. Work, which is a form of energy, can simply be defined as force times distance; therefore, it has the unit “newton-meter (N·m),” which is called a joule (J). That is, 1 J = 1 N·m
FIGURE 1–9 A body weighing 150 lbf on earth will weigh only 25 lbf on the moon.
kg g = 9.807 m/s2 W = 9.807 kg·m/s2 = 9.807 N = 1 kgf
lbm
g = 32.174 ft/s2 W = 32.174 lbm·ft/s2 = 1 lbf
FIGURE 1–10 The weight of a unit mass at sea level.
(1–3)
A more common unit for energy in SI is the kilojoule (1 kJ = 103 J). In the English system, the energy unit is the Btu (British thermal unit), which is defined as the energy required to raise the temperature of 1 lbm of water at 68°F by 1°F. In the metric system, the amount of energy needed to raise the temperature of 1 g of water at 14.5°C by 1°C is defined as 1 calorie (cal), and 1 cal = 4.1868 J. The magnitudes of the kilojoule and Btu are almost identical (1 Btu = 1.0551 kJ). Here is a good way to get a feel for these units: If you light a typical match and let it burn itself out, it yields approximately one Btu (or one kJ) of energy (Fig. 1–11). The unit for time rate of energy is joule per second (J/s), which is called a watt (W). In the case of work, the time rate of energy is called power. A commonly used unit of power is horsepower (hp), which is equivalent to 746 W. Electrical energy typically is expressed in the unit kilowatt-hour (kWh), which is equivalent to 3600 kJ. An electric appliance with a rated power of 1 kW consumes 1 kWh of electricity when running continuously for one hour.
FIGURE 1–11 A typical match yields about one Btu (or one kJ) of energy if completely burned. ©John M. Cimbala
8 INTRODUCTION AND BASIC CONCEPTS
When dealing with electric power generation, the units kW and kWh are often confused. Note that kW or kJ/s is a unit of power, whereas kWh is a unit of energy. Therefore, statements like “the new wind turbine will generate 50 kW of electricity per year” are meaningless and incorrect. A correct statement should be something like “the new wind turbine with a rated power of 50 kW will generate 120,000 kWh of electricity per year.”
Dimensional Homogeneity We all know that apples and oranges do not add. But we somehow manage to do it (by mistake, of course). In engineering, all equations must be dimensionally homogeneous. That is, every term in an equation must have the same unit. If, at some stage of an analysis, we find ourselves in a position to add two quantities that have different units, it is a clear indication that we have made an error at an earlier stage. So checking dimensions can serve as a valuable tool to spot errors.
EXAMPLE 1–1
Electric Power Generation by a Wind Turbine
A school is paying $0.12/kWh for electric power. To reduce its power bill, the school installs a wind turbine (Fig. 1–12) with a rated power of 30 kW. If the turbine operates 2200 hours per year at the rated power, determine the amount of electric power generated by the wind turbine and the money saved by the school per year.
SOLUTION A wind turbine is installed to generate electricity. The amount of electric energy generated and the money saved per year are to be determined. Analysis The wind turbine generates electric energy at a rate of 30 kW or 30 kJ/s. Then the total amount of electric energy generated per year becomes
Total energy = (Energy per unit time)(Time interval) = (30 kW)(2200 h) = 66,000 kWh The money saved per year is the monetary value of this energy determined as
Money saved = (Total energy)(Unit cost of energy) = (66,000 kWh)($0.12 / kWh) = $7920 Discussion The annual electric energy production also could be determined in kJ by unit manipulations as
FIGURE 1–12 A wind turbine, as discussed in Example 1–1.
3600 s 1 kJ / s Total energy = (30 kW)(2200 h)(_)(_) = 2.38 × 108 kJ 1 h 1 kW which is equivalent to 66,000 kWh (1 kWh = 3600 kJ).
©Bear Dancer Studios/Mark Dierker RF
We all know from experience that units can give terrible headaches if they are not used carefully in solving a problem. However, with some attention and skill, units can be used to our advantage. They can be used to check formulas; sometimes they can even be used to derive formulas, as explained in the following example.
9 CHAPTER 1
EXAMPLE 1–2
Obtaining Formulas from Unit Considerations
A tank is filled with oil whose density is ρ = 850 kg/m3. If the volume of the tank is V = 2 m3, determine the amount of mass m in the tank.
Oil
V = 2 m3 ρ = 850 kg/m3 m=?
SOLUTION The volume of an oil tank is given. The mass of oil is to be determined. Assumptions Oil is a nearly incompressible substance and thus its density is constant. Analysis A sketch of the system just described is given in Fig. 1–13. Suppose we forgot the formula that relates mass to density and volume. However, we know that mass has the unit of kilograms. That is, whatever calculations we do, we should end up with the unit of kilograms. Putting the given information into perspective, we have
FIGURE 1–13 Schematic for Example 1–2.
ρ = 850 kg / m3 and V = 2 m3 It is obvious that we can eliminate m3 and end up with kg by multiplying these two quantities. Therefore, the formula we are looking for should be
m = ρV Thus,
m = (850 kg / m3)(2 m3) = 1700 kg Discussion Note that this approach may not work for more complicated formulas. Nondimensional constants also may be present in the formulas, and these cannot be derived from unit considerations alone.
You should keep in mind that a formula that is not dimensionally homogeneous is definitely wrong (Fig. 1–14), but a dimensionally homogeneous formula is not necessarily right.
Unity Conversion Ratios
FIGURE 1–14 Always check the units in your calculations.
Just as all nonprimary dimensions can be formed by suitable combinations of primary dimensions, all nonprimary units (secondary units) can be formed by combinations of primary units. Force units, for example, can be expressed as m 1 N = 1 kg __2 s
and
ft 1 lbf = 32.174 lbm __2 s
They can also be expressed more conveniently as unity conversion ratios as 1 N ________ = 1 1 kg·m / s2
and
1 lbf ______________ = 1 32.174 lbm·ft / s2
Unity conversion ratios are identically equal to 1 and are unitless, and thus such ratios (or their inverses) can be inserted conveniently into any calculation to properly convert units (Fig. 1–15). You are encouraged to always use unity conversion ratios such as those given here when converting units. Some textbooks insert the archaic gravitational constant gc defined as gc = 32.174 lbm·ft/ lbf·s2 = 1 kg·m/N·s2 = 1 into equations in order to force units to match. This practice leads to unnecessary confusion and is strongly discouraged by the present authors. We recommend that you instead use unity conversion ratios.
32.174 lbm.ft/s2 1 lbf 1W 1 J/s
1 kg.m/s2 1N
1 kJ 1000 N.m
0.3048 m 1 ft
1 min 60 s
1 kPa 1000 N/m2 1 lbm 0.45359 kg
FIGURE 1–15 Every unity conversion ratio (as well as its inverse) is exactly equal to 1. Shown here are a few commonly used unity conversion ratios, each within its own set of parentheses.
10 INTRODUCTION AND BASIC CONCEPTS
EXAMPLE 1–3
The Weight of One Pound-Mass
Using unity conversion ratios, show that 1.00 lbm weighs 1.00 lbf on earth (Fig. 1–16).
SOLUTION A mass of 1.00 lbm is subjected to standard earth gravity. Its weight
lbm
in lbf is to be determined. Assumptions Standard sea-level conditions are assumed. Properties The gravitational constant is g = 32.174 ft/s2. Analysis We apply Newton’s second law to calculate the weight (force) that corresponds to the known mass and acceleration. The weight of any object is equal to its mass times the local value of gravitational acceleration. Thus,
FIGURE 1–16 A mass of 1 lbm weighs 1 lbf on earth.
1 lbf W = mg = (1.00 lbm)(32.174 ft / s2 )( ______________2) = 1.00 lbf 32.174 lbm·ft/s Discussion The quantity in large parentheses in this equation is a unity conversion ratio. Mass is the same regardless of its location. However, on some other planet with a different value of gravitational acceleration, the weight of 1 lbm would differ from that calculated here.
Net weight: One pound (454 grams)
When you buy a box of breakfast cereal, the printing may say “Net weight: One pound (454 grams).” (See Fig. 1–17.) Technically, this means that the cereal inside the box weighs 1.00 lbf on earth and has a mass of 453.6 g (0.4536 kg). Using Newton’s second law, the actual weight of the cereal on earth is 1N 1 kg _ W = mg = (453.6 g)(9.81 m / s2) ________2 = 4.49 N (1 kg·m/s )(1000 g)
1–3
FIGURE 1–17 A quirk in the metric system of units. Surroundings
System
Boundary
FIGURE 1–18 System, surroundings, and boundary.
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SYSTEMS AND CONTROL VOLUMES
A system is defined as a quantity of matter or a region in space chosen for study. The mass or region outside the system is called the surroundings. The real or imaginary surface that separates the system from its surroundings is called the boundary (Fig. 1–18). The boundary of a system can be fixed or movable. Note that the boundary is the contact surface shared by both the system and the surroundings. Mathematically speaking, the boundary has zero thickness, and thus it can neither contain any mass nor occupy any volume in space. Systems may be considered to be closed or open, depending on whether a fixed mass or a fixed volume in space is chosen for study. A closed system (also known as a control mass or just system when the context makes it clear) consists of a fixed amount of mass, and no mass can cross its boundary. That is, no mass can enter or leave a closed system, as shown in Fig. 1–19. But energy, in the form of heat or work, can cross the boundary; and the volume of a closed system does not have to be fixed. If, as a special case, even energy is not allowed to cross the boundary, that system is called an isolated system.
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