A Heat Transfer Handbook - 3ed - Jonh Lienhard

A Heat Transfer Handbook - 3ed - Jonh Lienhard

(Parte 1 de 4)

John H. Lienhard IV / John H. Lienhard V

A Heat

Transfer Textbook

Lienhard & Lienhard

Phlogiston PressISBN 0-9713835-0-2 PSB 01-04-0249

John H. Lienhard IV / John H. Lienhard V

A Heat

Transfer Textbook

Lienhard & Lienhard

A Heat Transfer Textbook A Heat Transfer Textbook

A Heat Transfer Textbook Third Edition

John H. Lienhard IV and John H. Lienhard V

Phlogiston

Press Cambridge Massachusetts

Professor John H. Lienhard IV Department of Mechanical Engineering University of Houston 4800 Calhoun Road Houston TX 77204-4792 U.S.A.

Professor John H. Lienhard V Department of Mechanical Engineering Massachusetts Institute of Technology 7 Massachusetts Avenue Cambridge MA 02139-4307 U.S.A.

Copyright ©2008 by John H. Lienhard IV and John H. Lienhard V All rights reserved

Please note that this material is copyrighted under U.S. Copyright Law. The authors grant you the right to download and print it for your personal use or for non-profit instructional use. Any other use, including copying, distributing or modifying the work for commercial purposes, is subject to the restrictions of U.S. Copyright Law. International copyright is subject to the Berne International Copyright Convention.

The authors have used their best efforts to ensure the accuracy of the methods, equations, and data described in this book, but they do not guarantee them for any particular purpose. The authors and publisher offer no warranties or representations, nor do they accept any liabilities with respect to the use of this information. Please report any errata to the authors.

Lienhard, John H., 1930–

A heat transfer textbook / John H. Lienhard IV and

John H. Lienhard V — 3rd ed. — Cambridge, MA : Phlogiston Press, c2008

Includes bibliographic references and index. 1. Heat—Transmission 2. Mass Transfer

I. Lienhard, John H., V, 1961– I. Title TJ260.L445 2008

Published by Phlogiston Press Cambridge, Massachusetts, U.S.A.

This book was typeset in Lucida Bright and Lucida New Math fonts (designed by Bigelow & Holmes) using LATEX under the Y&Y TEX System.

For updates and information, visit: http://web.mit.edu/lienhard/w/ahtt.html

This copy is: Version 1.31 dated January 16, 2008

Preface

This book is meant for students in their introductory heat transfer course —studentswhohavelearnedcalculus(throughordinarydifferentialequations) and basic thermodynamics. We include the needed background in fluid mechanics, although students will be better off if they have had an introductory course in fluids. An integrated introductory course in thermofluid engineering should also be a sufficient background for the material here.

Our major objectives in rewriting the 1987 edition have been to bring the material up to date and make it as clear as possible. We have substantially revised the coverage of thermal radiation, unsteady conduction, and mass transfer. We have replaced most of the old physical property data with the latest reference data. New correlations have been introduced for forced and natural convection and for convective boiling. The treatment of thermal resistance has been reorganized. Dozens of new problems have been added. And we have revised the treatment of turbulent heat transfer to include the use of the law of the wall. In a number of places we have rearranged material to make it flow better, and we have made many hundreds of small changes and corrections so that the text will be more comfortable and reliable. Lastly, we have eliminated Roger Eichhorn’s fine chapter on numerical analysis, since that topic is now most often covered in specialized courses on computation.

This book reflects certain viewpoints that instructors and students alike should understand. The first is that ideas once learned should not be forgotten. We have thus taken care to use material from the earlier parts of the book in the parts that follow them. Two exceptions to this are Chapter 10 on thermal radiation, which may safely be taught at any point following Chapter 2, and Chapter 1 on mass transfer, which draws only on material through Chapter 8.

We believe that students must develop confidence in their own ability to invent means for solving problems. The examples in the text therefore do not provide complete patterns for solving the end-of-chapter problems. Students who study and absorb the text should have no unusual trouble in working the problems. The problems vary in the demand that they lay on the student, and we hope that each instructor will select those that best challenge their own students.

The first three chapters form a minicourse in heat transfer, which is applied in all subsequent chapters. Students who have had a previous integrated course thermofluids may be familiar with this material, but to most students it will be new. This minicourse includes the study of heat exchangers, which can be understood with only the concept of the overall heat transfer coefficient and the first law of thermodynamics.

Wehaveconsistentlyfoundthatstudentsnewtothesubjectaregreatly encouraged when they encounter a solid application of the material, such as heat exchangers, early in the course. The details of heat exchanger design obviously require an understanding of more advanced concepts — fins, entry lengths, and so forth. Such issues are best introduced after the fundamental purposes of heat exchangers are understood, and we develop their application to heat exchangers in later chapters.

This book contains more material than most teachers can cover in three semester-hours or four quarter-hours of instruction. Typical onesemester coverage might include Chapters 1 through 8 (perhaps skipping some of the more specialized material in Chapters 5, 7, and 8), a bit of Chapter 9, and the first four sections of Chapter 10.

We are grateful to the Dell Computer Corporation’s STAR Program, the Keck Foundation, and the M.D. Anderson Foundation for their partial support of this project.

JHL IV, Houston, Texas

JHL V, Cambridge, Massachusetts August 2003

Contents

I The General Problem of Heat Exchange 1

1.1 Heat transfer3
1.2 Relation of heat transfer to thermodynamics6
1.3 Modes of heat transfer10
1.4 A look ahead35
1.5 Problems36
Problems37
References46

2 Heat conduction concepts, thermal resistance, and the overall heat transfer coefficient 49

2.1 The heat diffusion equation49
2.2 Solutions of the heat diffusion equation58
2.3 Thermal resistance and the electrical analogy62
2.4 Overall heat transfer coefficient, U78
2.5 Summary86
Problems86
References96
3.1 Function and configuration of heat exchangers9

3 Heat exchanger design 9

exchanger103
3.3 Heat exchanger effectiveness120
3.4 Heat exchanger design126
Problems129
References136

3.2 Evaluation of the mean temperature difference in a heat vii viii Contents

I Analysis of Heat Conduction 139

4 Analysis of heat conduction and some steady one-dimensional problems 141

4.1 The well-posed problem141
4.2 The general solution143
4.3 Dimensional analysis150
conduction problem159
4.5 Fin design163
Problems183
References190

4.4 Anillustrationofdimensionalanalysisinacomplexsteady

5.1 Introduction193
5.2 Lumped-capacity solutions194
5.3 Transient conduction in a one-dimensional slab203
5.4 Temperature-response charts208
5.5 One-term solutions218
5.6 Transient heat conduction to a semi-infinite region220
5.7 Steady multidimensional heat conduction235
5.8 Transient multidimensional heat conduction247
Problems252
References265

5 Transient and multidimensional heat conduction 193

I Convective Heat Transfer 267

6.1 Some introductory ideas269
6.3 The energy equation292

6 Laminar and turbulent boundary layers 269 6.2 Laminar incompressible boundary layer on a flat surface 276 6.4 The Prandtl number and the boundary layer thicknesses 296

over a flat surface300
6.6 The Reynolds analogy311
6.7 Turbulent boundary layers313
6.8 Heat transfer in turbulent boundary layers322
Problems330

6.5 Heattransfercoefficientforlaminar, incompressibleflow References ..................................... 338

Contents ix

7.1 Introduction341
7.2 Heat transfer to and from laminar flows in pipes342
7.3 Turbulent pipe flow355
7.4 Heat transfer surface viewed as a heat exchanger367
7.5 Heat transfer coefficients for noncircular ducts370
7.6 Heat transfer during cross flow over cylinders374
7.7 Other configurations384
Problems386
References393

7 Forced convection in a variety of configurations 341

8 Natural convection in single-phase fluids and during film condensation 397

8.1 Scope397
natural convection398

8.2 The nature of the problems of film condensation and of

surface401
8.4 Natural convection in other situations416
8.5 Film condensation428
Problems443
References452

8.3 Laminar natural convection on a vertical isothermal

9.1 Nukiyama’s experiment and the pool boiling curve457
9.2 Nucleate boiling464
9.3 Peak pool boiling heat flux472
9.4 Film boiling486
9.5 Minimum heat flux488
9.6 Transition boiling and system influences489
9.7 Forced convection boiling in tubes496
9.8 Forced convective condensation heat transfer505
9.9 Dropwise condensation506
9.10 The heat pipe509
Problems513

9 Heat transfer in boiling and other phase-change configurations 457 References ..................................... 517 x Contents

IV Thermal Radiation Heat Transfer 523

10.1 The problem of radiative exchange525
10.2 Kirchhoff’s law533
10.4 Heat transfer among gray bodies549
10.5 Gaseous radiation563
10.6 Solar energy574
Problems584
References592

10 Radiative heat transfer 525 10.3 Radiant heat exchange between two finite black bodies . 536

V Mass Transfer 595

1.1 Introduction597
1.2 Mixture compositions and species fluxes600
1.3 Diffusion fluxes and Fick’s law608
1.4 Transport properties of mixtures614
1.5 The equation of species conservation627
1.6 Mass transfer at low rates635
1.7 Steady mass transfer with counterdiffusion648
1.9 Simultaneous heat and mass transfer663
Problems673
References686

1 An introduction to mass transfer 597 1.8 Mass transfer coefficients at high rates of mass transfer . 654

VI Appendices 689

References694

A Some thermophysical properties of selected materials 691

References722

B Units and conversion factors 721

Citation Index 733 Subject Index 739

Part I

The General Problem of Heat Exchange

1. Introduction

The radiation of the sun in which the planet is incessantly plunged, penetrates the air, the earth, and the waters; its elements are divided, change direction in every way, and, penetrating the mass of the globe, would raise its temperature more and more, if the heat acquired were not exactly balanced by that which escapes in rays from all points of the surface and expands through the sky. The Analytical Theory of Heat, J. Fourier

1.1 Heat transfer

People have always understood that something flows from hot objects to cold ones. We call that flow heat. In the eighteenth and early nineteenth centuries, scientists imagined that all bodies contained an invisible fluid which they called caloric. Caloric was assigned a variety of properties, some of which proved to be inconsistent with nature (e.g., it had weight anditcouldnotbecreatednordestroyed). Butitsmostimportantfeature was that it flowed from hot bodies into cold ones. It was a very useful way to think about heat. Later we shall explain the flow of heat in terms more satisfactory to the modern ear; however, it will seldom be wrong to imagine caloric flowing from a hot body to a cold one.

The flow of heat is all-pervasive. It is active to some degree or another in everything. Heat flows constantly from your bloodstream to the air around you. The warmed air buoys off your body to warm the room you are in. If you leave the room, some small buoyancy-driven (or convective) motion of the air will continue because the walls can never be perfectly isothermal. Such processes go on in all plant and animal life and in the air around us. They occur throughout the earth, which is hot at its core and cooled around its surface. The only conceivable domain free from heat flow would have to be isothermal and totally isolated from any other region. It would be “dead” in the fullest sense of the word — devoid of any process of any kind. 3

The overall driving force for these heat flow processes is the cooling (or leveling) of the thermal gradients within our universe. The heat flows that result from the cooling of the sun are the primary processes that we experience naturally. The conductive cooling of Earth’s center and the radiative cooling of the other stars are processes of secondary importance in our lives.

The life forms on our planet have necessarily evolved to match the magnitude of these energy flows. But while “natural man” is in balance with these heat flows, “technological man”1 has used his mind, his back, and his will to harness and control energy flows that are far more intense than those we experience naturally. To emphasize this point we suggest that the reader make an experiment.

Experiment 1.1

Generate as much power as you can, in some way that permits you to measure your own work output. You might lift a weight, or run your own weight up a stairwell, against a stopwatch. Express the result in watts (W). Perhaps you might collect the results in your class. They should generally be less than 1 kW or even 1 horsepower (746 W). How much less might be surprising.

Thus, when we do so small a thing as turning on a 150 W light bulb, we are manipulating a quantity of energy substantially greater than a human being could produce in sustained effort. The power consumed by an oven, toaster, or hot water heater is an order of magnitude beyond our capacity. The power consumed by an automobile can easily be three orders of magnitude greater. If all the people in the United States worked continuously like galley slaves, they could barely equal the output of even a single city power plant.

Our voracious appetite for energy has steadily driven the intensity of actual heat transfer processes upward until they are far greater than those normally involved with life forms on earth. Until the middle of the thirteenth century, the energy we use was drawn indirectly from the sun

1Some anthropologists think that the term Homo technologicus (technological man) serves to define human beings, as apart from animals, better than the older term Homo sapiens (man, the wise). We may not be as much wiser than the animals as we think we are, but only we do serious sustained tool making.

§1.1 Heat transfer 5 using comparatively gentle processes — animal power, wind and water power, and the combustion of wood. Then population growth and deforestation drove the English to using coal. By the end of the seventeenth century, England had almost completely converted to coal in place of wood. At the turn of the eighteenth century, the first commercial steam engines were developed, and that set the stage for enormously increased consumption of coal. Europe and America followed England in these developments.

The development of fossil energy sources has been a bit like Jules

Verne’s description in Around the World in Eighty Days in which, to win a race, a crew burns the inside of a ship to power the steam engine. The combustion of nonrenewable fossil energy sources (and, more recently, the fission of uranium) has led to remarkably intense energy releases in power-generating equipment. The energy transferred as heat in a nuclear reactor is on the order of one million watts per square meter.

A complex system of heat and work transfer processes is invariably needed to bring these concentrations of energy back down to human proportions. We must understand and control the processes that divide and diffuse intense heat flows down to the level on which we can interact with them. To see how this works, consider a specific situation. Suppose we live in a town where coal is processed into fuel-gas and coke. Such power supplies used to be common, and they may return if natural gas supplies ever dwindle. Let us list a few of the process heat transfer problems that must be solved before we can drink a glass of iced tea.

• A variety of high-intensity heat transfer processes are involved with combustion and chemical reaction in the gasifier unit itself.

• The gas goes through various cleanup and pipe-delivery processes to get to our stoves. The heat transfer processes involved in these stages are generally less intense.

• The gas is burned in the stove. Heat is transferred from the flame to the bottom of the teakettle. While this process is small, it is intense because boiling is a very efficient way to remove heat.

• The coke is burned in a steam power plant. The heat transfer rates from the combustion chamber to the boiler, and from the wall of the boiler to the water inside, are very intense.

• The steam passes through a turbine where it is involved with many heat transfer processes, including some condensation in the last stages. The spent steam is then condensed in any of a variety of heat transfer devices.

• Cooling must be provided in each stage of the electrical supply system: the winding and bearings of the generator, the transformers, the switches, the power lines, and the wiring in our houses.

• The ice cubes for our tea are made in an electrical refrigerator. It involves three major heat exchange processes and several lesser ones. The major ones are the condensation of refrigerant at room temperature to reject heat, the absorption of heat from within the refrigerator by evaporating the refrigerant, and the balancing heat leakage from the room to the inside.

• Let’s drink our iced tea quickly because heat transfer from the room to the water and from the water to the ice will first dilute, and then warm, our tea if we linger.

A society based on power technology teems with heat transfer problems. Our aim is to learn the principles of heat transfer so we can solve these problems and design the equipment needed to transfer thermal energy from one substance to another. In a broad sense, all these problems resolve themselves into collecting and focusing large quantities of energy for the use of people, and then distributing and interfacing this energy with people in such a way that they can use it on their own puny level.

(Parte 1 de 4)

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