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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
The thermodynamics knowledge you need to succeed in class—and in your career
Thermodynamics For Dummies, 2nd Edition covers the topics found in a typical undergraduate introductory thermodynamic course (which is an essential course to nearly all engineering degree programs). It also brings the subject to life with exciting content on where (and how!) thermodynamics is being used today (spoiler alert: everywhere!). You'll grasp the basics of how heat and energy interact, thermodynamic properties of reactions and mixtures, and how thermodynamic cycles are used to make things go. This useful guide also covers renewable energy systems, new refrigerant technology, and a more diverse perspective on the history of the field.
Within, you'll:
- Get clear explanations of the laws of thermodynamics, thermodynamic cycles, and beyond
- Read about real-world examples to help you connect with the content
- Practice solving thermodynamic problems to internalize what you've learned
For students looking for resources to demystify thermodynamics, Thermodynamics For Dummies, 2nd Edition is the perfect choice. Become thermodynamically savvy with this accessible guide!
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Veröffentlichungsjahr: 2025
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Table of Contents
Cover
Title Page
Copyright
Introduction
About This Book
Conventions Used in This Book
What You’re Not to Read
Foolish Assumptions
How This Book Is Organized
Icons Used in This Book
Where to Go from Here
Beyond the Book
Part 1: Getting Started with Thermodynamics
Chapter 1: Thermodynamics in Everyday Life
Embracing Thermodynamics
Examining Energy’s Changing Forms
Watching Energy and Work in Action
Getting into Real Gases, Gas Mixtures, and Combustion Reactions
Discovering Old Names and New Ways of Saving Energy
Chapter 2: Laying the Foundation of Thermodynamics
Starting with the Atom
Defining Important Thermodynamic Properties
Understanding Thermodynamic Processes
Discovering Nature’s Law and Order
Chapter 3: Working with Phases and Properties of Substances
It’s Just a Phase: Describing Solids, Liquids, and Gases
Knowing How Phase Changes Occur
Finding Thermodynamic Properties from Tables
Admiring the Simplicity of Ideal Gases
Chapter 4: The Thermodynamic Duo: Work and Heat
Work: The Agent of Change
Warming Up and Cooling Down
Part 2: Employing the Laws of Thermodynamics
Chapter 5: Using the First Law in Closed Systems
Conserving Mass in a Closed System
Balancing Energy in a Closed System
Applying the First Law to Ideal Gas Processes
Applying the First Law to Processes with Liquids and Solids
Chapter 6: Using the First Law in Open Systems
Conserving Mass in an Open System
Balancing Mass and Energy in a System
Getting Ready for Steady-State Processes
Filling Up with Transient Processes
Using the First Law on Common Open-System Processes
Chapter 7: Governing Heat Engines and Refrigerators with the Second Law
Looking at the Impact of the Second Law
Defining Thermal Energy Reservoirs
Working with the Kelvin-Planck Statement on Heat Engines
Chilling with the Clausius Statement on Refrigeration
Chapter 8: The Second Law Predicts the Demise of the Universe
Unraveling the Mystery of Entropy
Coping with the Increase in Entropy Principle
Working with
T
-
s
Diagrams
Using
T
-
ds
Relationships
Calculating Entropy Change
Analyzing Isentropic Processes
Balancing Entropy in a System
Chapter 9: Analyzing Systems by Applying the Second Law
Understanding Energy Availability
Determining the Change in Availability
Balancing the Availability of a System
Understanding the Decrease in Availability Principle
Figuring Out Reversible Work and Irreversibility
Calculating the Second-Law Efficiency of a System
Part 3: Planes, Trains, and Automobiles: Making Heat Work for You
Chapter 10: Working with Carnot and Brayton Cycles
Analyzing the Ideal Heat Engine: The Carnot Cycle
Working with the Ideal Gas Turbine Engine: The Brayton Cycle
Improving the Brayton Cycle
Flying the Brayton Cycle in Jet Propulsion
Chapter 11: Working with Otto and Diesel Cycles
Understanding the Basics of Reciprocating Engines
Working with the Ideal Spark Ignition Engine: The Otto Cycle
Working with the Ideal Compression Ignition Engine: The Diesel Cycle
Chapter 12: Power up with Rankine Cycles
Understanding the Basics of the Rankine Cycle
Examining the Four Processes of the Rankine Cycle
Analyzing the Ideal Rankine Cycle
Improving the Rankine Cycle with Reheat
Improving the Rankine Cycle with Regeneration
Deviating from Ideal Behavior: Actual Rankine Cycle Performance
Chapter 13: Cooling Off with Refrigeration Cycles
Understanding the Basics of Refrigeration Cycles
Chilling with the Reverse Brayton Cycle
Cooling with the Vapor-Compression Refrigerator
Warming Up with Heat Pumps
Chapter 14: Thermodynamics of Renewable Energy Systems
Wind Powered Systems
Solar Powered Systems
Energy Storage Systems
Part 4: Handling Thermodynamic Relationships, Reactions, and Mixtures
Chapter 15: Understanding the Behavior of Real Gases
Deviating from Ideal Gas Behavior: Real Gas Behavior
Finding Pressure with van der Waals
Chapter 16: Mixing Non-Reacting Gases
Finding Thermodynamic Properties for a Mixture of Gases
Getting the Compressibility Factor for Real Gas Mixtures
Working with Psychrometrics: Air and Water Vapor Mixtures
Comfort with Air Conditioning
Chapter 17: Burning Up with Combustion
Forming Combustion Equations
Defining Combustion-Related Thermodynamic Properties
Using the First Law on Steady-Flow Combustion Systems
Analyzing Steady-Flow Systems
Using the First Law on Closed Combustion Systems
Analyzing Closed Systems
Ouch! That’s Hot: Determining the Adiabatic Flame Temperature
Part 5: The Part of Tens
Chapter 18: Ten Famous Names in Thermodynamics
George Brayton
Nicolas Léonard Sadi Carnot
Anders Celsius
Rudolf Diesel
Daniel Gabriel Fahrenheit
James Prescott Joule
Nikolaus August Otto
William John Macquorn Rankine
William Thomson or Lord Kelvin
James Watt
Chapter 19: Ten More Cycles of Note
Two-Stroke Engines
Wankel Engines
The Stirling Cycle
The Ericsson Cycle
The Atkinson Cycle
The Miller Cycle
The Absorption Cycle
The Einstein Cycle
Combined-Cycle Engines
Binary Vapor Cycles
Appendix A: Thermodynamic Property Tables
Index
About the Author
Connect with Dummies
End User License Agreement
List of Tables
Chapter 3
TABLE 3-1 Molecular Mass and Gas Constant of Selected Ideal Gases
Chapter 11
TABLE 11-1 Comparing Results of the Diesel Cycle Analyses
Chapter 12
TABLE 12-1 Rankine Cycle with Regeneration Performance Summary
TABLE 12-2 Rankine Cycle with Regeneration Performance Summary
TABLE 12-3 Actual Rankine Cycle Performance Summary
Chapter 14
TABLE 14-1 Results of Windmill Analysis
Chapter 15
TABLE 15-1 Critical Point Properties of Selected Fluids
Chapter 16
TABLE 16-1 Summary of Molar and Mass Fractions
TABLE 16-2 Summary of Gas Mixture Analysis
TABLE 16-3 Summary of Cooling Process Properties
Chapter 17
TABLE 17-1 Enthalpy of Formation of Some Compounds at 25°C and 100 KPa
TABLE 17-2 Enthalpy of Combustion at 25°C
TABLE 17-3 A Summary of Enthalpy Terms Used in the Open-Flow Combustion Process ...
Appendix A
TABLE A-1 Ideal Gas Properties of Air
TABLE A-2 Compressed Liquid Water Properties
TABLE A-3 Saturated Water Liquid-Vapor Properties – Temperature Table
TABLE A-4 Saturated Water Liquid-Vapor Properties – Pressure Table
TABLE A-5 Superheated Steam Properties
TABLE A-6 Saturated R-454B Liquid-Vapor Properties – Temperature Table
TABLE A-7 Saturated R-454B Liquid-Vapor Properties – Pressure Table
TABLE A-8 Superheated R-454B Properties
TABLE A-9 Ideal-Gas Properties of Combustion Gases
TABLE A-10 Thermodynamics Properties of Various Materials
TABLE A-11 Critical Point Properties of Various Materials
List of Illustrations
Chapter 2
FIGURE 2-1: A normal force (
F
) acts perpendicular to a surface.
FIGURE 2-2: Using two different paths to make a pitcher of tea.
FIGURE 2-3: A thermodynamic cycle connects several processes togethe...
Chapter 3
FIGURE 3-1: A
P-v-T
surface of a substance may contract or expand up...
FIGURE 3-2: A phase diagram tells you whether a material is a solid,...
FIGURE 3-3: A
T-v
diagram shows how temperature and specific volume ...
FIGURE 3-4: A
P-v
diagram shows how pressure and specific volume res...
FIGURE 3-5: A temperature-enthalpy diagram illustrating bilinear int...
Chapter 4
FIGURE 4-1: Work is proportional to the force (
F
) applied to an object and the ...
FIGURE 4-2: A spring can perform work if it is compressed or stretched.
FIGURE 4-3: Moving boundary work depends on the path taken and the end states.
FIGURE 4-4: A boiler makes steam out of water.
FIGURE 4-5: A condenser changes vapor into liquid.
FIGURE 4-6: An evaporator vaporizes a liquid using the environment as the heat ...
Chapter 5
FIGURE 5-1: Conservation of energy for a closed system.
FIGURE 5-2: A constant pressure process and its
P-v
diagram on the right.
FIGURE 5-3: A constant-temperature process and its
P-v
diagram on the right.
FIGURE 5-4: A reversible, adiabatic process and its
P-v
diagram on the right.
FIGURE 5-5: Heat transfer between ice and liquid in a closed system.
Chapter 6
FIGURE 6-1: A wind turbine is an example of an open system.
FIGURE 6-2: An open system with a transient process has a change in mass and en...
FIGURE 6-3: A nozzle or a diffuser is used to change the velocity (and kinetic ...
FIGURE 6-4: Compressors and turbines change the pressure of a fluid.
FIGURE 6-5: Heat exchangers add or remove heat from a fluid.
FIGURE 6-6: Throttling valves decrease the pressure in a fluid. The
T-s
diagram...
Chapter 7
FIGURE 7-1: A heat source reservoir supplies energy to a process, whereas a hea...
FIGURE 7-2: A heat engine absorbs heat from a source, uses it to do work, and r...
FIGURE 7-3: A refrigerator or heat pump uses work to absorb heat from a source ...
Chapter 8
FIGURE 8-1: A
T-s
diagram of water.
FIGURE 8-2: Find the entropy of a substance by using any two independent intens...
FIGURE 8-3: A
T-s
diagram of a refrigerant cooled in a constant-pressure proces...
FIGURE 8-4: A
T-s
diagram of air being compressed and heated from States 1 to 2...
FIGURE 8-5: An ideal turbine does work using an isentropic process.
Chapter 9
FIGURE 9-1: The expansion of air in a piston-cylinder process decreases availab...
FIGURE 9-2: The availability of energy changes in a heat exchanger.
FIGURE 9-3: A heat engine receives heat, produces a network output and rejects ...
FIGURE 9-4: A power plant has different second-law efficiencies if it operates ...
Chapter 10
FIGURE 10-1: A Carnot cycle engine uses the four steps shown to produce work.
FIGURE 10-2: The four Carnot engine processes mapped onto a
T-s
diagram.
FIGURE 10-3: A gas turbine engine is modeled with the Brayton Cycle.
FIGURE 10-4: The four Brayton cycle processes mapped onto
T-s
and
P-v
diagrams.
FIGURE 10-5: A Brayton cycle modified with regeneration, reheating, and interco...
FIGURE 10-6: The modified Brayton cycle mapped onto a
T-s
diagram.
FIGURE 10-7: The basic components of a turbojet engine.
FIGURE 10-8: The ideal turbojet engine cycle mapped onto a
T-s
diagram.
Chapter 11
FIGURE 11-1: Thermodynamic processes in reciprocating engines.
FIGURE 11-2: A
P-v
diagram of a real spark-ignition engine (Otto cycle).
FIGURE 11-3:
P-v
and
T-s
diagrams of an ideal Otto cycle.
FIGURE 11-4: Pressure-volume and temperature-entropy diagrams for the Diesel cy...
Chapter 12
FIGURE 12-1: The four basic components of an ideal Rankine cycle model of a pow...
FIGURE 12-2: The Rankine cycle processes mapped onto a
T-s
diagram of water.
FIGURE 12-3: The Rankine cycle modified with reheated steam between high-and lo...
FIGURE 12-4: The Rankine cycle with reheat processes mapped onto a water/steam
FIGURE 12-5: The Rankine cycle modified with regeneration using an open feedwat...
FIGURE 12-6: The Rankine cycle with open feedwater heater regeneration mapped o...
FIGURE 12-7: The Rankine cycle modified with regeneration using a closed feedwa...
FIGURE 12-8: The deviation of actual Rankine cycle processes from ideal process...
Chapter 13
FIGURE 13-1: The reverse Brayton cycle uses four processes for refrigeration.
FIGURE 13-2: The
T-s
diagram of the reverse Brayton refrigeration cycle.
FIGURE 13-3: The vapor-compression refrigeration cycle processes.
FIGURE 13-4: A vapor-compression refrigeration cycle on a refrigerant
T-s
diagr...
FIGURE 13-5: A heat-pump system for heating a house in the winter and cooling i...
Chapter 14
FIGURE 14-1: Functional relationship between power coefficient and tip speed ra...
FIGURE 14-2: The Prairie Windmill.
FIGURE 14-3: A concentrated solar power system.
FIGURE 14-4: A compressed air energy storage system with thermal energy storage...
Chapter 15
FIGURE 15-1: The ideal gas law is valid in the shaded region of the
T-s
diagram...
FIGURE 15-2: The generalized compressibility chart is used to determine the com...
Chapter 16
FIGURE 16-1: The psychrometric chart is used for heating and air conditioning a...
FIGURE 16-2: Reading a psychrometric chart.
FIGURE 16-3: A heating with humidification process on a psychrometric chart.
FIGURE 16-4: A schematic of the cooling with dehumidification process and the p...
Chapter 17
FIGURE 17-1: Combustion starts with reactants and ends with products.
FIGURE 17-2: Exothermic and endothermic enthalpy of formation reactions.
FIGURE 17-3: An open-system, steady-flow combustion process.
FIGURE 17-4: A closed-system combustion process.
Chapter 19
FIGURE 19-1: A schematic of the two-stroke engine.
FIGURE 19-2: A schematic of the Wankel engine.
FIGURE 19-3: A
P-v
diagram of the Stirling cycle.
FIGURE 19-4: A
P-v
diagram of the Ericsson cycle.
FIGURE 19-5: A
P-v
diagram of the Atkinson cycle.
FIGURE 19-6: A
P-v
diagram of the Miller cycle.
FIGURE 19-7: A schematic of the Absorption cycle.
FIGURE 19-8: A schematic of the Einstein cycle.
FIGURE 19-9: A schematic of the combined Brayton/Rankine cycle.
FIGURE 19-10: A schematic of the binary-vapor cycle.
Guide
Cover
Table of Contents
Title Page
Copyright
Begin Reading
Appendix A: Thermodynamic Property Tables
Index
About the Author
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Thermodynamics For Dummies®, 2nd Edition
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Introduction
Thermodynamics often stands as a “gateway” course in engineering schools. It can make or break an aspiring engineer’s journey. For some, passing through the gate means continuing with engineering, while for others, it may lead to a change in direction (which isn’t necessarily a bad thing).
The difference between struggling and succeeding often lies in having a great teacher and an engaging book. However, learning styles vary; some students may not connect with “Professor A,” while others may find them to be the best educator they’ve ever had. Similarly, some students grasp concepts from the chosen textbook easily, while others don’t.
It's unfortunate when people give up on something they find difficult. Many subjects aren’t as hard as they initially seem; they just require a moment of clarity for understanding. You can understand thermodynamics. This book can help you through that gate into engineering.
About This Book
Thermodynamics For Dummies, 2nd Edition can help you understand how energy is used in systems we use frequently such as automobiles, refrigerators, water heaters, and power plants. This book is written with you in mind, using relatable examples to help explain concepts. Some of the examples in this book are interconnected providing a cohesive learning experience. For example, when exploring the thermodynamics of a diesel engine in Chapter 11, you read that its energy source is derived from combustion. Later, as you study combustion reactions in Chapter 17, you see exactly how much energy these reactions provide to power a diesel engine.
In engineering schools, thermodynamics is often taught in both mechanical engineering and chemical engineering curriculums. This book comes at thermodynamics from a mechanical engineering perspective. I focus on how energy is used in vehicles, refrigeration, and power plants. Although I cover nonreacting gas mixtures and combustion reactions, I don’t go into chemical equilibrium.
In this second edition of Thermodynamics For Dummies, I updated numerous example problems in each chapter and added new problems for you to solve on your own (complete with answers to check your work). As I set out to update this book, I reflected on the changes that have occurred over the past decade since the first edition was published. While the fundamental laws of thermodynamics remain unchanged, many of their applications have evolved significantly.
For instance, the production of energy from renewable sources has grown tremendously since the early 2000s. Today, wind turbines, electric vehicles, and solar panels are commonplace across the globe. To address this shift, I include a new Chapter 14 that focuses on the thermodynamics of renewable energy systems. Your classroom textbook may not delve deeply into topics such as wind and solar power systems, but this chapter provides a more detailed exploration of these technologies.
Another new feature in this edition is a series of sidebars titled Inspirational Spotlights, which highlight individuals who have made remarkable contributions to the field of thermodynamics. If any of these individuals spark your interest, I encourage you to explore and research their stories further. For example, Chapter 14 features William Kamkwamba, who, inspired by a library book titled Using Energy, constructed a windmill from salvaged parts to generate electricity for his family’s home in Malawi.
Conventions Used in This Book
Every subject has its own language, and thermodynamics is no different. I use the following conventions in this book:
Whenever I introduce a technical term, I use
italics
so you can quickly see it and look for an explanation.
I also use
italics
to indicate variables in mathematical equations.
I work all the examples in the metric system, because it’s less confusing than the system of feet, inches, pounds, and so on that is common in the U.S.
I use
boldface
for velocity (
V
) and
italics
for total volume (
V
) to distinguish between these two variables.
I also use
boldface
to denote the action parts of numbered steps and to highlight key words or phrases in bulleted lists.
What You’re Not to Read
If you want to read this book cover-to-cover, that’s up to you. But if you just want to get an explanation of something you’re stuck on, you can skip the sidebars (they appear in gray-shaded boxes).
Sidebars are tidbits of information that have interesting information related to a topic. You can grasp the fundamentals without reading them, but they do enhance your overall enjoyment because many feature modern day heroes in thermodynamics.
Foolish Assumptions
I assume that you’ve taken an introductory physics class. If so, you may have seen a little bit of thermo already. But if you haven’t had physics, don’t worry; you can probably grasp the concepts in this book anyway.
I also assume you’ve had some calculus. In some parts of thermodynamics, you have to understand how to use an integral (Chapters 8 and 9). You don’t have to be an expert in calculus to follow along because these parts of thermodynamics involve the simplest kinds of equations. Even if you don’t know a thing about calculus, you can still solve almost all the problems in this book using basic algebra.
How This Book Is Organized
I organized this book along the lines of most undergraduate thermodynamic textbooks, which start with the basics and progress to more difficult subjects. Four parts of the book deal directly with thermodynamics, while the fifth part gives you a quick peek at well-known names and processes in thermodynamics. You can follow this book from beginning to end along with your own thermodynamics textbook, or you can just dip into any section and chapter to get help with something you may be stuck on.
Part 1: Getting Started with Thermodynamics
In Part 1, I begin by presenting examples of both natural and engineered thermodynamic systems to help you recognize and relate to the concepts of thermodynamics. After you’re comfortable with these examples, I explain how energy can be used to perform work and how work can be used to transfer energy.
I demonstrate that a thermodynamic system consists of several processes, each with a distinct starting point and endpoint, defined by the properties of the materials involved. Some of the basic properties discussed include temperature, pressure, internal energy, enthalpy, entropy, and specific heat. And yes, I know you’re eager to read about the laws of thermodynamics, so I introduce them here as well.
Part 2: Employing the Laws of Thermodynamics
In this part, I cover the fundamental concepts of the conservation of mass and the conservation of energy. Simply put, these principles state that neither mass nor energy can be created or destroyed, but both can change form. In essence, the total amount of mass and energy at the start of any process equals the total amount at the end. While this idea may seem straightforward, it can get tricky when mass transitions from one state — such as a liquid to a gas — or when energy transforms, such as heat converting to work. I simplify these complexities by demonstrating how to apply the first law of thermodynamics to various systems and processes.
The second law of thermodynamics, often considered the most challenging aspect of thermodynamics, is more approachable than it may seem. At its core, the second law is about the direction of energy flow, which, like a river, moves in one direction: downhill. The idea is that energy begins in a high-energy reservoir, performs some useful work — such as spinning a motor — and then flows into a lower-energy reservoir. Sometimes the energy in this lower reservoir can still be harnessed; other times, it cannot. The abstract concept of entropy captures this behavior, helping you determine whether a process is feasible or not.
Part 3: Planes, Trains, and Automobiles: Making Heat Work for You
Part 3 dives into some of the most fascinating aspects of thermodynamics. If you find yourself feeling stuck as you begin studying the subject, I suggest spending a few minutes exploring this section to discover the exciting applications that await after you mastered the basics. Think of it as window shopping — it may just motivate you to push through and reach the “fun” part of thermodynamics.
In this part, I explain how to apply the first and second laws of thermodynamics to systems such as gasoline and diesel engines, jet engines, electric power plants, refrigerators, and air conditioners. You discover how to calculate the efficiency of these machines and explore ways to make them even better. Intriguing, isn’t it?
Part 4: Handling Thermodynamic Relationships, Reactions, and Mixtures
In Part 4, I cover how gases behave and relate to one another in different situations. Many gases obey a special relationship law called the ideal gas law; others don’t behave that way and are called real gases. Some gas mixtures react with each other, such as the combustion of gasoline vapor in air, and form carbon dioxide and water vapor. Combustion reactions are especially important because they’re the energy source for many kinds of thermodynamic engines. Other gas mixtures don’t react with each other at all, such as air and water vapor. The presence of moisture in the air is very important in understanding applications related to heating, ventilating, and air conditioning. I help you sort out these thorny relationship issues.
Part 5: The Part of Tens
In this book, I cover a lot of ground and throw in a bunch of names along the way, such as Celsius, Watt, Fahrenheit, and Diesel. Who were these people, and how did they get into a thermodynamics book? In Part 5, I give you a thumbnail sketch of ten early pioneers in thermodynamics. I also talk about ten new or less common ways of producing work from energy — in things such as automobiles, jets, and power plants — that you may be interested in discovering more about.
Finally, because solving problems in thermodynamics relies on material property data for substances, I provide an Appendix that includes abridged versions of thermodynamic property tables. You can use these tables to follow along with examples presented throughout the book. Although these tables aren’t as extensive as ones you find in textbooks, they provide all the information you need to grasp the fundamental concepts.
Icons Used in This Book
You find some icons in the margins of this book. These icons are flags that point out different elements. Here’s what the icons stand for.
This icon tells you that you should either remember a certain fact for future reference or recall this fact from an explanation that appears earlier in the book.
I use this icon when I give you a bit of extra information to help you understand a topic or a suggestion for a shortcut to working a problem.
When you see this icon, it means pay attention! I’m giving you important information to keep you from making a common mistake.
Where to Go from Here
Each chapter in this book is written with the idea that you may want to jump around and read about individual topics. For example, if you’re stuck on entropy, you can turn to Chapter 8 to get a grasp on the fundamentals. You don’t need to read the first seven chapters. If you need to understand certain basic concepts before you start reading a particular chapter, I act as your traffic cop and direct you to where those concepts are explained more fully.
Beyond the Book
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To access the Cheat Sheet created specifically for this book, go to: www.dummies.com/cheatsheet/thermodynamics.
Part 1
Getting Started with Thermodynamics
IN THIS PART …
Thermodynamics is part of natural law — it governs the use of energy in everything from the weather to your diet. I walk you through the basic concepts of energy, describing how it changes form in both natural and engineered systems. Armed with just four simple laws, a table of material properties, and a trusty calculator, you’ll soon be crunching the numbers behind how much energy it takes to boil an egg or operate a power plant. Before you know it, you’ll be calculating all kinds of interesting facts related to energy.
Chapter 1
Thermodynamics in Everyday Life
IN THIS CHAPTER
Seeing thermodynamics in the world around you
Changing energy from one form to another
Getting energy to do work and move heat for you
Figuring out relationships, reactions, and mixtures (nothing personal)
Inspiring you to save the world from an energy shortage
Thermodynamics is as old as the universe, which itself is the largest known thermodynamic system. When the universe ends in a whimper and the total energy of the universe dissipates to total uniformity, then thermodynamics will end.
Broadly speaking, thermodynamics is all about energy: how it gets used and how it changes from one form to another. In many cases, thermodynamics involves using heat to provide work, as in the case of your automobile engine, or doing work to move heat, as in your refrigerator. With thermodynamics, you can find out how efficient things are at using energy for useful purposes, such as moving an airplane, generating electricity, or even riding a bicycle.
The word thermodynamics has a Greek heritage. The first part, thermo, conveys the idea that heat is involved, and the second part, dynamics, makes you think of things that move. Keep these two ideas in mind as you look at your world in terms of the basic laws of thermodynamics. This book is written to help you understand that thermodynamics is about turning heat into power, a concept that really isn’t so complicated after all.
Embracing Thermodynamics
Many thermodynamic systems are at work in the natural world. Our sun in the sky is the ultimate energy source for the earth, warming the air, the ground, and the oceans. Huge masses of air move over the earth’s surface. Giant currents of water swirl in the oceans. This movement and swirling happen because of the transformation of heat into work.
Energy takes many different forms — it can’t be created or destroyed, but it can change form. This statement is one of the fundamental laws of thermodynamics. Consider how energy changes form in storm clouds:
Storm clouds have motion within them.
Motion between moisture droplets in clouds rubbing against each other creates friction.
Friction causes a buildup of static charge.
When the charge becomes high enough, the clouds produce lightning.
This electrical surge of energy can then start a fire on the ground, and before you know it, you have a combustion problem on your hands.
Not only does energy change form, but matter (that is, a material or substance) also changes form in many thermodynamic systems. Storm clouds are formed by water evaporating into the air. As the water vapor reaches the colder parts of the atmosphere, it condenses to form cloud particles. Eventually, the particles collect into droplets and form liquid water again, so it rains.
One detail people have observed about energy is that it flows in a preferred direction. This observation is the fundamental law of thermodynamics. Heat flows from a hot object to a cold object. Wind blows from a region of high pressure to a region of low pressure. Some forms of energy are developed by forces of nature. Air bubbles move upward in water against gravity because buoyancy forces them to rise. Water droplets fall in the atmosphere because the force of gravity pulls them toward the ground.
Another brilliant observation about energy is that if you have absolutely no energy at all, you have no temperature. The concept of absolute zero temperature is a fundamental law of thermodynamics.
I cover the changing forms of energy and matter and the fundamental laws that govern how these changes work in Part 1.
Examining Energy’s Changing Forms
Many ingenious individuals have applied the fundamental laws of thermodynamics observed in natural systems to create remarkable methods of harnessing energy to perform work. Heat is used to generate steam or to heat air, which then moves a piston in a cylinder or spins a turbine. This movement can turn a shaft, which can operate a lawn mower, move a car, a truck, or a ship, turn an electric generator, or propel an airplane.
Other innovative minds have used thermodynamic principles to move heat from one place to another using work. Refrigerators and heat pumps remove heat from one location to produce a desired cooling or heating effect. The work required for this cooling shows up on your electric bill every month.
In Part 2, I show you how the fundamental laws of thermodynamics can quantify the amount of heat required to produce work that can move a car, fly an airplane, or turn an electric generator. You can also use the laws of thermodynamics to find out how efficient something is at using energy.
Energy is the foundation of every thermodynamic process. As you use energy to perform tasks, it changes form along the way. For example, when you start your car, the battery initiates the process. This heavy box of chemical energy converts its stored energy into electrical energy. The electric motor then takes this electrical energy to rotate the engine, which is a form of kinetic energy. Meanwhile, the spark plugs fire, igniting the fuel. Through the combustion process, the chemical energy in gasoline is transformed into thermal energy, known as internal energy. In the few seconds it takes to start your car, energy transitions from chemical to electrical to kinetic and finally to thermal energy.
Kinetic energy
A car battery provides electricity to operate your starter. As the motor turns, the electrical energy is converted into a form of mechanical energy called kinetic energy. Kinetic energy involves moving a mass so that it has velocity. The mass doesn’t have to be very large to have kinetic energy — even electrons have kinetic energy — but the mass must be moving. Before you start the car, nothing in the engine is moving so it has no kinetic energy. After the engine is started, it has kinetic energy because of its moving pistons and rotating shafts. If the car is parked while the engine is running, the car as a “system” has no kinetic energy until the car moves.
Potential energy
If you drive your car up a hill and park it there, you change the kinetic energy into another form of energy called potential energy. Potential energy is only available with gravity. You must have a mass located at an elevation above some ground state. Potential energy gets its name from its potential to be converted into kinetic energy. You see this conversion process when you park on a hill and forget to apply the parking brake. Potential energy changes back into kinetic energy as your car rolls down the hill.
Internal energy
When you apply the brakes to stop your car, energy changes form again. You know the car has kinetic energy because it’s moving. Stopping the car changes all this kinetic energy into heat. Brake pads squeeze onto steel disks or steel drums, creating friction. Friction generates heat — sometimes a lot of heat. When materials heat up, another form of energy called internal energy increases.
Watching Energy and Work in Action
Until the invention of the steam engine, people had to slug it out against nature with nature. Horses pulled coaches, mules pulled plows, sails moved ships, windmills ground grain, and water wheels pressed apples into cider that fermented and made people feel happy for all their labors. The steam engine was able to replace these natural work sources and move coaches, plows, and ships, among many other things. For the first time, fire was harnessed to provide something more than just heat — it was used to do work. This use of heat to accomplish work is what Part 3 is all about. Over time, many kinds of work machines were developed, theories were made, and experiments were done until a rational system of analyzing heat and work was developed into the field of thermodynamics.
Engines: Letting energy do work
A heat engine is a machine that can take a source of heat — burning gasoline, coal, natural gas, or even the sun — and make it do work, usually in the form of turning a shaft. With a rotating shaft, you can make things move — think of elevators or race cars. Every heat engine uses four basic processes that interact with the surroundings to accomplish the engine’s job. These processes are heat input, heat rejection, work input, and work output.
Take your automobile engine as an example of a heat engine. Here are the four basic processes that go on under the hood:
Work input
Air is compressed in the cylinders. This compression requires work from the engine itself. Initially, this work comes from the starter. As you can imagine, this process takes a lot of work, which is why they don’t have those crank handles on the front of cars anymore.
Heat input
Heat is added to the engine by burning fuel in the cylinder. The heated air in the cylinder naturally wants to increase pressure and expand. The pressure and expansion move the piston in the cylinder.
Work output
As the expanding gas in the cylinder pushes the piston, work is output by the engine. Some of this work compresses the air in adjacent cylinders.
Heat rejection
The last process removes heat with the exhaust from the engine.
Refrigeration: Letting work move heat
When Willis Carrier made air conditioners a popular home appliance, he did more than make people comfortable and give electric utilities a reason for growth and expansion. He brought thermodynamics into the home. Thermodynamics has been there all along, and you never realized it. Refrigerators, freezers, air conditioners, and heat pumps are all the same in thermodynamics. Only three basic processes involve energy interacting with the surroundings in what is known as the refrigeration cycle:
Heat input
Heat is absorbed from the cold space to keep it cold.
Work input
Work is added to the system to pump the heat absorbed from the cold space out to the hot space.
Heat rejection
Heat is rejected to the hot space.
In most refrigeration cycles, there is a fourth process that does not involve a change in energy. Unlike heat engines, which include a work-output process, refrigerators use a pressure-reducing device within the system. In this device, energy does not change form; instead, it simply facilitates the reduction of pressure to help maintain the cycle.
In this edition of Thermodynamics For Dummies, 2nd Edition, a new Chapter 14 has been added in Part 3 that focuses on renewable energy systems. These systems often feature unique energy conversion processes that transform one form of kinetic energy into another, more useful form. For example, wind turbines harness the kinetic energy of wind to drive electric generators, while solar panels convert the kinetic energy of photons into the kinetic energy of electrons.
Getting into Real Gases, Gas Mixtures, and Combustion Reactions
Using energy to generate electric power, cool your house, or racing cars around the Indianapolis Motor Speedway is the glamorous side of thermodynamics. But behind the movie stars are a supporting cast and crew of thermodynamic relationships (this is jargon for “mathematical equations”) for real gases, gas mixtures, and combustion reactions that make it all happen.
In Part 4, you discover the difference between a real gas and an ideal gas. There you see that real gases behave a bit differently than ideal gases. You also figure out the thermodynamic properties of a mixture of gases, such as water vapor and air for heating, air conditioning, and ventilating purposes. Lastly, you calculate how much energy you can get out of fuel in a combustion reaction to power your jet, your race car, or your lawn mower.
If you want to sell jet engines to an aircraft manufacturer, you must show that your engine burns fuel efficiently. To build a jet engine, you need to know how much energy a combustion reaction adds to an engine and how much the air in the engine heats up because of the combustion. To figure out the latter, you use thermodynamic relationships of real gases to calculate properties such as temperature, pressure, and energy.
Discovering Old Names and New Ways of Saving Energy
As you read about thermodynamics, you’ll run across several names. Some of the names may be familiar; others may be new to you. For example, when you get your electric bill, it tells you how many watt-hours of electricity you used last month. If you reheat yesterday’s leftover pizza, you set your oven to 350 degrees Fahrenheit. (Or, if you live outside the U.S., you set your oven to 175 degrees Celsius.) That big rig that’s riding your bumper on the highway burns diesel fuel.
How did these terms — Watt, Fahrenheit, Celsius, and Diesel — become part of our language? In Part 5, you discover that these words (and six more) are the last names of characters bent on figuring out what energy is and how to harness it for the benefit of humanity.
Pioneers in thermodynamics didn’t just work in the good old days; there are modern-day pioneers as well. Throughout this edition, I added sidebars with mini biographies of inspirational people who have made some interesting contributions related to thermodynamics. I hope you enjoy reading about these people who deserve to be recognized.
The world’s demand for energy steadily increases while energy resources dwindle. Part 5 shows you ten ways innovative thinkers have improved energy consumption for automobiles, air conditioners, refrigerators, and electric power plants. Making a better future for all has motivated many people to think of better ways to use energy. Even Albert Einstein got a patent for making a better air-conditioning system (see Chapter 19). Maybe you’ll be inspired to create your own innovation and make a name for yourself in thermodynamics.
