Engineering Thermodynamics

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April 11, 2015

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Contents

1 Preface 3

2 Introduction 52.1 Introduction to Classical Thermodynamics . . . . . . . . . . . . . . . . . . 5

3 Thermodynamic Systems 93.1 Properties of Pure Substances . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2 Thermodynamic Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.3 Zeroth Law of Thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . 123.4 Temperature Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.5 The Ideal Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4 Zeroth Law 17

5 First Law 195.1 Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195.2 Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195.3 Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225.4 First Law of Thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . . 245.5 Statement of the First Law for a Closed System . . . . . . . . . . . . . . . 255.6 Enthalpy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

6 Second Law 296.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296.3 Statement of the Second Law of Thermodynamics . . . . . . . . . . . . . . 296.4 Carnot Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316.5 Thermodynamic Temperature Scale . . . . . . . . . . . . . . . . . . . . . . 326.6 Statement of the Second Law of Thermodynamics . . . . . . . . . . . . . . 336.7 Carnot Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346.8 Thermodynamic Temperature Scale . . . . . . . . . . . . . . . . . . . . . . 366.9 NOTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376.10 Clausius Theorem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376.11 Entropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386.12 Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

7 Third Law 437.1 Third Law of Thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . . 43

8 Applications 458.1 One Component Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

III

Contents

8.2 Psychrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488.3 Common Thermodynamic Cycles . . . . . . . . . . . . . . . . . . . . . . . . 52

9 Further Reading 61

10 Contributors 63

List of Figures 65

11 Licenses 6911.1 GNU GENERAL PUBLIC LICENSE . . . . . . . . . . . . . . . . . . . . . 6911.2 GNU Free Documentation License . . . . . . . . . . . . . . . . . . . . . . . 7011.3 GNU Lesser General Public License . . . . . . . . . . . . . . . . . . . . . . 71

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1 Preface

The topic of thermodynamics is taught in Physics and Chemistry courses as part of theregular curriculum. This book deals with Engineering Thermodynamics, where concepts ofthermodynamics are used to solve engineering problems. Engineers use thermodynamics tocalculate the fuel efficiency of engines, and to find ways to make more efficient systems, bethey rockets, refineries, or nuclear reactors. One aspect of engineering in the title is thata lot of the data used is empirical (e.g. steam tables), since you wont find clean algebraicequations of state for many common working substances. Thermodynamics is the sciencethat deals with transfer of heat and work. Engineering thermodynamics develops the the-ory and techniques required to use empirical thermodynamic data effectively. However,with the advent of computers most of these techniques are transparent to the engineer, andinstead of looking data up in tables, computer applications can be queried to retrieve therequired values and use them in calculations. There are even applications which are tailoredto specific areas which will give answers for common design situations. But thorough un-derstanding will only come with knowledge of underlying principles, and the ability to judgethe limitations of empirical data is perhaps the most important gain from such knowledge.

This book is a work in progress. It is hoped that as it matures, it will be more up to datethan the dead tree editions.

Thermodynamics is the study of the relationships between HEAT (thermos) and WORK(dynamics). Thus, it deals with energy interactions in physical systems. Classical thermody-namics can be stated in four laws called the zeroth, first, second, and third laws respectively.The laws of thermodynamics are empirical, i.e. , they are deduced from experience, andsupported by a large body of experimental evidence.

The first chapter is an introduction to thermodynamics, and presents the motivation andscope of the topic. The second chapter, Thermodynamic Systems1, defines some basic termswhich are used throughout the book. In particular, the concepts of system and processes arediscussed. The zeroth law is stated and the concept of temperature is developed. The nextchapter, First Law2, develops ideas required for the statement of the first law of thermo-dynamics. Second Law3 deals with heat engines and the concept of entropy. Applications4of the tools developed in the previous chapters are illustrated, including the use of ther-modynamics in everyday engineering situations. Appendix5 gives a list of tables for somecommonly used properties.

1 Chapter 2.1.1 on page 72 Chapter 4 on page 173 Chapter 5.6.1 on page 284 Chapter 7.1 on page 435 http://en.wikibooks.org/wiki/Engineering%20Thermodynamics%2FAppendix

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Preface

This course forms the foundation for the Heat Transfer6 course, where the rate and mecha-nisms of transmission of energy in the form of heat is studied. The concepts will be used infurther courses in heat, Internal Combustion Engines7, Refrigeration and Air Conditioning8,and Turbomachines9 to name a few.

Category:Engineering_Thermodynamics10

6 http://en.wikibooks.org/wiki/Heat%20Transfer7 http://en.wikibooks.org/wiki/Internal%20Combustion%20Engines8 http://en.wikibooks.org/wiki/Refrigeration%20and%20Air%20Conditioning9 http://en.wikibooks.org/wiki/Turbomachines10 http://en.wikibooks.org/wiki/Category%3AEngineering_Thermodynamics

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2 Introduction

2.1 Introduction to Classical Thermodynamics

Thermodynamics is the study of energies. More specifically, introductory thermodynamicsis the study of energy transfer in systems. Classical thermodynamics consists of methodsand constructs that are used to account for macroscopic energy transfer. In fact, energyaccounting is an appropriate synonym for classical thermodynamics. In much the sameway that accountants balance money in and money out of a bank account, rocket scientistssimply balance the energy in and out of a rocket engine. Of course just as a bank accountsbalance is obfuscated by arcane devices such as interest rates and currency exchange, sotoo is thermodynamics clouded with seemingly difficult concepts such as irreversibility andenthalpy. But, also just like accounting, a careful review of the rules suggests a coherentstrategy for maintaining tabs on a particular account.

If a statement about the simplicity of thermodynamics failed to convert would-be students,they may be captured with a few words on the importance of understanding energy transferin our society. Up until about 150 years ago or so, the earths economy