Thermodynamics demystified

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Thermodynamics

Demystifi ed

Merle C. Potter, Ph.D.

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ABOUT THE AUTHOR

Merle C. Potter, Ph.D., has engineering degrees from Michigan Technological

University and the University of Michigan. He has coauthored Fluid Mechanics,

Mechanics of Fluids, Thermodynamics for Engineers, Thermal Sciences, Differential

Equations, Advanced Engineering Mathematics, and Jump Start the HP-48G in

addition to numerous exam review books. His research involved fluid flow stability

and energy-related topics. The American Society of Mechanical Engineers awarded

him the 2008 James Harry Potter Gold Medal. He is Professor Emeritus of Mechanical

Engineering at Michigan State University and continues to write and golf.

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CONTENTS

Preface xi

CHAPTER 1 Basic Principles 1

1.1 The System and Control Volume 2

1.2 Macroscopic Description 3

1.3 Properties and State of a System 4

1.4 Equilibrium, Processes, and Cycles 5

1.5 Units 7

1.6 Density, Specifi c Volume, and

Specifi c Weight 10

1.7 Pressure 11

1.8 Temperature 14

1.9 Energy 15

Quiz No. 1 17

Quiz No. 2 19

CHAPTER 2 Properties of Pure Substances 23

2.1 The P-v-T Surface 23

2.2 The Liquid-Vapor Region 26

2.3 The Steam Tables 27

2.4 Equations of State 30

2.5 Equations of State for a Nonideal Gas 33

Quiz No. 1 35

Quiz No. 2 37

CHAPTER 3 Work and Heat 41

3.1 Work 41

3.2 Work Due to a Moving Boundary 43

3.3 Nonequilibrium Work 48

3.4 Other Work Modes 49

3.5 Heat Transfer 52

Quiz No. 1 54

Quiz No. 2 57

CHAPTER 4 The First Law of Thermodynamics 61

4.1 The First Law Applied to a Cycle 61

4.2 The First Law Applied to a Process 63

4.3 Enthalpy 66

4.4 Latent Heat 67

4.5 Specifi c Heats 68

4.6 The First Law Applied to Various

Processes 72

4.7 The First Law Applied to Control

Volumes 78

4.8 Applications of the Energy Equation 81

Quiz No. 1 89

Quiz No. 2 94

CHAPTER 5 The Second Law of Thermodynamics 101

5.1 Heat Engines, Heat Pumps, and

Refrigerators 102

5.2 Statements of the Second Law 103

5.3 Reversibility 105

5.4 The Carnot Engine 107

5.5 Carnot Effi ciency 110

5.6 Entropy 113

5.7 The Inequality of Clausius 123

5.8 Entropy Change for an Irreversible Process 124

5.9 The Second Law Applied to a

Control Volume 128

viii Thermodynamics Demystifi ed

Quiz No. 1 133

Quiz No. 2 137

CHAPTER 6 Power and Refrigeration Vapor Cycles 143

6.1 The Rankine Cycle 144

6.2 Rankine Cycle Effi ciency 147

6.3 The Reheat Cycle 151

6.4 The Regenerative Cycle 153

6.5 Effect of Losses on Power Cycle Effi ciency 157

6.6 The Vapor Refrigeration Cycle 160

6.7 The Heat Pump 164

Quiz No. 1 167

Quiz No. 2 169

CHAPTER 7 Power and Refrigeration Gas Cycles 173

7.1 The Air-Standard Cycle 174

7.2 The Carnot Cycle 177

7.3 The Otto Cycle 177

7.4 The Diesel Cycle 180

7.5 The Brayton Cycle 184

7.6 The Regenerative Brayton Cycle 188

7.7 The Combined Cycle 191

7.8 The Gas Refrigeration Cycle 194

Quiz No. 1 198

Quiz No. 2 201

CHAPTER 8 Psychrometrics 205

8.1 Gas-Vapor Mixtures 205

8.2 Adiabatic Saturation and Wet-Bulb

Temperatures 210

8.3 The Psychrometric Chart 213

8.4 Air-Conditioning Processes 214

Quiz No. 1 220

Quiz No. 2 223

Contents ix

CHAPTER 9 Combustion 227

9.1 Combustion Equations 227

9.2 Enthalpy of Formation, Enthalpy of

Combustion, and the First Law 233

9.3 Adiabatic Flame Temperature 238

Quiz No. 1 241

Quiz No. 2 243

APPENDIX A Conversion of Units 245

APPENDIX B Material Properties 247

APPENDIX C Steam Tables 253

APPENDIX D R134a 263

APPENDIX E Ideal-Gas Tables 269

APPENDIX F Psychrometric Chart 277

APPENDIX G Compressibility Chart 279

Final Exams 281

Solutions to Quizzes and Final Exams 297

Index 335

x Thermodynamics Demystifi ed

PREFACE

This book is intended to accompany a text used in the first course in thermodynamics

that is required in all mechanical engineering departments, as well as several other

departments. It provides a succinct presentation of the material so that the students

more easily understand the more difficult concepts. Many thermodynamics texts

are over 900 pages long and it is often difficult to ferret out the essentials due to the

excessive verbiage. This book presents those essentials.

The basic principles upon which a study of thermodynamics is based are

illustrated with numerous examples and practice exams, with solutions, that allow

students to develop their problem-solving skills. All examples and problems are

presented using SI metric units. English-unit equivalents are given in App. A.

The mathematics required to solve the problems is that used in several other

engineering courses. The more-advanced mathematics is typically not used in an

introductory course in thermodynamics. Calculus is more than sufficient.

The quizzes at the end of each chapter contain four-part, multiple-choice

problems similar in format to those found in national exams, such as the Fundamentals

of Engineering exam (the first of two exams required in the engineering registration

process), the Graduate Record Exam (required when applying for most graduate

schools), and the LSAT and MCAT exams. Engineering courses do not, in general,

utilize multiple-choice exams but it is quite important that students gain experience

in taking such exams. This book allows that experience. If one correctly answers

50 percent or more of multiple-choice questions correctly, that is quite good.

If you have comments, suggestions, or corrections or simply want to opine,

please email me at [email protected]. It is impossible to write a book free of

errors, but if I’m made aware of them, I can have them corrected in future

printings.

Merle C. Potter, Ph.D.

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Thermodynamics

Demystifi ed

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