HEAT TRANSFER A PRACTICAL APPROACH

Yunus A. Çengel

University of Nevada, Reno

Boston, Massachusetts Burr Ridge, Illinois Dubuque, Iowa

Madison, Wisconsin New York, New York San Francisco, California St. Louis, Missouri

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HEAT TRANSFER: A PRACTICAL APPROACH

Copyright © 1998 by The McGraw-Hill Companies, Inc. All rights reserved. Printed in the United States of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a data base or retrieval system, without the prior written permission of the publisher.

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1. Heat--Transmission. 2. Heat--Transmission--Industrial

Library of Congress Cataloging-in-Publication Data

Çengel, Yunus A.

Heat transfer: a practical approach / Yunus A. Çengel.

p.    cm.

Includes index.

ISBN 0-07-011505-2

1. Heat--Transmission. 2. Heat--Transmission--Industrial

applications. I. Title.

QC320.C46 1997

621.402¢2—dc2197-6640

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About the Author

Yunus A. Çengel received his Ph.D. in mechanical engineering from North Carolina State University and joined the faculty of mechanical engineering at the University of Nevada, Reno, where he has been teaching undergraduate and graduate courses in thermodynamics and heat transfer while conducting research. He has published primarily in the areas of thermodynamics, radiation heat transfer, natural convection, solar energy, geothermal energy, energy conservation, and engineering education. Dr. Çengel is the author of the textbook, Introduction to Thermodynamics and Heat Transfer, and the coauthor of Thermodynamics: An Engineering Approach, both published by McGraw-Hill. He has led teams of engineering students to numerous manufacturing facilities in northern Nevada and California to conduct energy audits and has prepared energy conservation reports for them. Dr. Çengel has been voted the outstanding teacher by the ASME student sections in both North Carolina State University and the University of Nevada, Reno. He is a member of the American Society of Mechanical Engineers (ASME) and the American Society for Engineering Education (ASEE). Dr. Çengel is also the recipient of the ASEE Meriam/Wiley Distinguished Author Award.

Contents

Preface

xxv

Nomenclature

xxxi

PART I

FUNDAMENTALS

1

1

BASIC CONCEPTS OF THERMODYNAMICS AND HEAT TRANSFER

3

1-1

Thermodynamics and Heat Transfer

4

1-2

Engineering Heat Transfer

6

1-3

Heat and Other Forms of Energy

9

1-4

The First Law of Thermodynamics

14

1-5

Heat Transfer Mechanisms

20

1-6

Simultaneous Heat Transfer Mechanisms

33

1-7

Summary

38

References and Suggested Reading

40

Problems

41

2

HEAT CONDUCTION EQUATION

57

2-1

Introduction

58

2-2

A Brief Review of Differential Equations

64

2-3

One-Dimensional Heat Conduction Equation

68

2-4

General Heat Conduction Equation

75

2-5

Boundary and Initial Conditions

78

2-6

Solution of Steady One-Dimensional Heat Conduction Problems

87

2-7

Heat Generation in a Solid

98

2-8

Variable Thermal Conductivity, k(T)

105

2-9

Summary

108

References and Suggested Reading

110

Problems

111

3

STEADY HEAT CONDUCTION

129

3-1

Steady Heat Conduction in Plane Walls

130

3-2

Thermal Contact Resistance

140

3-3

Generalized Thermal Resistance Networks

145

3-4

Heat Conduction in Cylinders and Spheres

148

3-5

Critical Radius of Insulation

155

3-6

Thermal Insulation

158

3-7

Heat Transfer from Finned Surfaces

177

3-8

Heat Transfer in Common Configurations

192

3-9

Summary

198

References and Suggested Reading

200

Problems

202

4

TRANSIENT HEAT CONDUCTION

225

4-1

Lumped System Analysis

226

4-2

Transient Heat Conduction in Large Plane Walls, Long Cylinders, and Spheres

232

4-3

Transient Heat Conduction in Semi-Infinite Solids

244

4-4

Transient Heat Conduction in Multidimensional Systems

248

4-5

Summary

255

References and Suggested Reading

257

Problems

258

5

NUMERICAL METHODS IN HEAT CONDUCTION

273

5-1

Why Numerical Methods?

274

5-2

Finite Difference Formulation of Differential Equations

277

5-3

One-Dimensional Steady Heat Conduction

280

5-4

Solution Methods for Systems of Algebraic Equations

290

5-5

Two-Dimensional Steady Heat Conduction

294

5-6

Transient Heat Conduction

303

5-7

Controlling the Numerical Error

321

5-8

Summary

324

References and Suggested Reading

327

Problems

328

6

FORCED CONVECTION

349

6-1

Physical Mechanism of Forced Convection

350

6-2

Velocity Boundary Layer

352

6-3

Thermal Boundary Layer

356

6-4

Flow over Flat Plates

357

6-5

Flow across Cylinders and Spheres

363

6-6

Flow in Tubes

370

6-7

Summary

389

References and Suggested Reading

393

Problems

394

7

NATURAL CONVECTION

411

7-1

Physical Mechanism of Natural Convection

412

7-2

Natural Convection over Surfaces

416

7-3

Natural Convection inside Enclosures

421

7-4

Natural Convection from Finned Surfaces

428

7-5

Combined Natural and Forced Convection

431

7-6

Summary

433

References and Suggested Reading

435

Problems

436

8

BOILING AND CONDENSATION

451

8-1

Boiling Heat Transfer

452

8-2

Pool Boiling

454

8-3

Flow Boiling

467

8-4

Condensation Heat Transfer

468

8-5

Film Condensation

469

8-6

Film Condensation inside Horizontal Tubes

481

8-7

Dropwise Condensation

482

8-8

Summary

483

References and Suggested Reading

485

Problems

487

9

RADIATION HEAT TRANSFER

495

9-1

Introduction

496

9-2

Thermal Radiation

497

9-3

Blackbody Radiation

499

9-4

Radiation Properties

506

9-5

Atmospheric and Solar Radiation

514

9-6

The View Factor

519

9-7

Radiation Heat Transfer: Black Surfaces

532

9-8

Radiation Heat Transfer: Diffuse, Gray Surfaces

534

9-9

Radiation Shields and the Radiation Effect

547

9-10

Summary

551

References and Suggested Reading

554

Problems

555

10

HEAT EXCHANGERS

569

10-1

Types of Heat Exchangers

570

10-2

The Overall Heat Transfer Coefficient

574

10-3

Analysis of Heat Exchangers

581

10-4

The Log Mean Temperature Difference Method

583

10-5

The Effectiveness-NTU Method

592

10-6

The Selection of Heat Exchangers

603

10-7

Summary

607

References and Suggested Reading

609

Problems

610

11

MASS TRANSFER

623

11-1

Introduction

624

11-2

Analogy between Heat and Mass Transfer

625

11-3

Mass Diffusion

628

11-4

Boundary Conditions

634

11-5

Steady Mass Diffusion through a Wall

639

11-6

Water Vapor Migration in Buildings

643

11-7

Transient Mass Diffusion

647

11-8

Diffusion in a Moving Medium

650

11-9

Mass Convection

660

11-10

Simultaneous Heat and Mass Transfer

670

11-11

Summary

676

References and Suggested Reading

679

Problems

681

PART II

APPLICATIONS

697

12

HEATING AND COOLING OF BUILDINGS

699

12-1

A Brief History

700

12-2

Human Body and Thermal Comfort

701

12-3

Heat Transfer from the Human Body

706

12-4

Design Conditions for Heating and Cooling

711

12-5

Heat Gain from People, Lights, and Appliances

720

12-6

Heat Transfer through Walls and Roofs

726

12-7

Heat Loss from Basement Walls and Floors

736

12-8

Heat Transfer through Windows

742

12-9

Solar Heat Gain through Windows

752

12-10

Infiltration Heat Load and Weatherizing

759

12-11

Annual Energy Consumption

765

12-12

Summary

770

References and Suggested Reading

774

Problems

774

13

REFRIGERATION AND FREEZING OF FOODS

795

13-1

Control of Microorganisms in Foods

796

13-2

Refrigeration and Freezing of Foods

798

13-3

Thermal Properties of Foods

804

13-4

Refrigeration of Fruits, Vegetables, and Cut Flowers

808

13-5

Refrigeration of Meats, Poultry, and Fish

815

13-6

Refrigeration of Eggs, Milk, and Bakery Products

825

13-7

Refrigeration Load of Cold Storage Rooms

830

13-8

Transportation of Refrigerated Foods

837

13-9

Summary

842

References and Suggested Reading

845

Problems

846

14

COOLING OF ELECTRONIC EQUIPMENT

862

14-1

Introduction and History

864

14-2

Manufacturing of Electronic Equipment

865

14-3

Cooling Load of Electronic Equipment

870

14-4

Thermal Environment

873

14-5

Electronics Cooling in Different Applications

874

14-6

Conduction Cooling

876

14-7

Air Cooling: Natural Convection and Radiation

892

14-8

Air Cooling: Forced Convection

899

14-9

Liquid Cooling

913

14-10

Immersion Cooling

917

14-11

Heat Pipes

921

14-12

Summary

926

References and Suggested Reading

928

Problems

929

APPENDIX 1

Property Tables and Charts (SI Units)

945

Table A-1

Molar Mass, Gas Constant,

and Critical-Point Properties

946

Table A-2

Boiling- and Freezing-Point Properties

947

Table A-3

Properties of Solid Metals

948

Table A-4

Properties of Solid Nonmetals

951

Table A-5

Properties of Building Materials

952

Table A-6

Properties of Insulating Materials

954

Table A-7

Properties of Common Foods

955

Table A-8

Properties of Miscellaneous Materials

957

Table A-9

Properties of Saturated Water

958

Table A-10

Properties of Liquids

960

Table A-11

Properties of Gases at 1 atm Pressure

961

Table A-12

Properties of the Atmosphere at High Altitude

965

Figure A-13

Psychrometric Chart at 1 atm Total Pressure

966

Table A-14

Emissivity of Surfaces

967

Table A-15

Solar Radiative Properties of Materials

969

APPENDIX 2

Property Tables and Charts (English Units)

971

Table A-1E

Molar Mass, Gas Constant, and Critical-Point Properties

972

Table A-2E

Boiling- and Freezing-Point Properties

973

Table A-3E

Properties of Solid Metals

974

Table A-4E

Properties of Solid Nonmetals

977

Table A-5E

Properties of Building Materials

978

Table A-6E

Properties of Insulating Materials

980

Table A-7E

Properties of Common Foods

981

Table A-8E

Properties of Miscellaneous Materials

983

Table A-9E

Properties of Saturated Water

984

Table A-10E

Properties of Liquids

986

Table A-11E

Properties of Gases at 1 atm Pressure

987

Table A-12E

Properties of the Atmosphere at High Altitude

989

Figure A-13E

Psychrometric Chart at 1 atm Total Pressure

990

APPENDIX 3

Introduction to EES

991

Overview991

Background Information991

A Heat Transfer Example Problem995

Loading a Textbook File1003

INDEX1005

Table of Examples

Chapter 1

BASIC CONCEPTS OF THERMODYNAMICS AND HEAT TRANSFER

3

Example 1-1

Heating of a Copper Ball

13

Example 1-2

Heating of Water in an Electric Teapot

17

Example 1-3

Heat Loss from Heating Ducts in a Basement

18

Example 1-4

Electric Heating of a House at High Elevation

19

Example 1-5

The Cost of Heat Loss through the Roof

21

Example 1-6

Measuring the Thermal Conductivity of a Material

26

Example 1-7

Conversion between SI and English Units

28

Example 1-8

Measuring Convection Heat Transfer Coefficient

30

Example 1-9

Radiation Effect on Thermal Comfort

32

Example 1-10

Heat Loss from a Person

34

Example 1-11

Heat Transfer between Two Isothermal Plates

35

Example 1-12

Heat Transfer in Conventional and Microwave Ovens

36

Example 1-13

Heating of a Plate by Solar Energy

37

Chapter 2

HEAT CONDUCTION EQUATION

57

Example 2-1

Heat Transfer to a Refrigerator

63

Example 2-2

Heat Generation in a Hair Dryer

63

Example 2-3

Heat Conduction through the Bottom of a Pan

73

Example 2-4

Heat Conduction in a Resistance Heater

73

Example 2-5

Cooling of a Hot Metal Ball in Air

74

Example 2-6

Heat Conduction in a Short Cylinder

77

Example 2-7

Heat Flux Boundary Condition

81

Example 2-8

Convection and Insulation Boundary Conditions

83

Example 2-9

Combined Convection and Radiation Condition

85

Example 2-10

Combined Convection, Radiation, and Heat Flux

86

Example 2-11

Heat Conduction in a Plane Wall

87

Example 2-12

A Wall with Various Sets of Boundary Conditions

89

Example 2-13

Heat Conduction in the Base Plate of an Iron

92

Example 2-14

Heat Conduction in a Solar Heated Wall

93

Example 2-15

Heat Loss through a Steam Pipe

95

Example 2-16

Heat Conduction through a Spherical Shell

97

Example 2-17

Centerline Temperature of a Resistance Heater

101

Example 2-18

Variation of Temperature in a Resistance Heater

101

Example 2-19

Heat Conduction in a Two-Layer Medium

103

Example 2-20

Variation of Temperature in a Wall with k(T)

106

Example 2-21

Heat Conduction through a Wall with k(T)

107

Chapter 3

STEADY HEAT CONDUCTION

129

Example 3-1

Heat Loss through a Wall

137

Example 3-2

Heat Loss through a Single-Pane Window

138

Example 3-3

Heat Loss through Double-Pane Windows

139

Example 3-4

Equivalent Thickness of Contact Resistance

143

Example 3-5

Contact Resistance of Transistors

144

Example 3-6

Heat Loss through a Composite Wall

146

Example 3-7

Heat Transfer to a Spherical Container

152

Example 3-8

Heat Loss through an Insulated Steam Pipe

154

Example 3-9

Heat Loss from an Insulated Electric Wire

157

Example 3-10

Effect of Insulation on Surface Temperature

174

Example 3-11

Optimum Thickness of Insulation

175

Example 3-12

Maximum Power Dissipation of a Transistor

190

Example 3-13

Selecting a Heat Sink for a Transistor

190

Example 3-14

Effect of Fins on Heat Transfer from Steam Pipes

191

Example 3-15

Heat Loss from Buried Steam Pipes

193

Example 3-16

Heat Transfer between Hot and Cold Water Pipes

196

Example 3-17

Cost of Heat Loss through Walls in Winter

196

Chapter 4

TRANSIENT HEAT CONDUCTION

225

Example 4-1

Temperature Measurement by Thermocouples

230

Example 4-2

Predicting the Time of Death

231

Example 4-3

Boiling Eggs

240

Example 4-4

Heating of Large Brass Plates in an Oven

241

Example 4-5

Cooling of a Long Stainless Steel Cylindrical Shaft

242

Example 4-6

Minimum Burial Depth of Water Pipes to Avoid Freezing

247

Example 4-7

Cooling of a Short Brass Cylinder

249

Example 4-8

Heat Transfer from a Short Cylinder

252

Example 4-9

Cooling of a Long Cylinder by Water

253

Example 4-10

Refrigerating Steaks while Avoiding Frostbite

254

Chapter 5

NUMERICAL METHODS IN HEAT CONDUCTION

273

Example 5-1

Steady Heat Conduction in a Large Uranium Plate

286

Example 5-2

Heat Transfer from Triangular Fins

287

Example 5-3

Gauss-Siedel Iteration Method

292

Example 5-4

Steady Two-Dimensional Heat Conduction in L-Bars

296

Example 5-5

Heat Loss through Chimneys

300

Example 5-6

Transient Heat Conduction in a Large Uranium Plate

309

Example 5-7

Solar Energy Storage in Trombe Walls

312

Example 5-8

Transient Two-Dimensional Heat Conduction in L-Bars

318

Chapter 6

FORCED CONVECTION

349

Example 6-1

Flow of Hot Oil over a Flat Plate

361

Example 6-2

Cooling of a Hot Block by Forced Air at High Elevation

362

Example 6-3

Heat Loss from a Steam Pipe in Windy Air

368

Example 6-4

Cooling of a Steel Ball by Forced Air

369

Example 6-5

Heating of Water by Resistance Heaters in a Tube

382

Example 6-6

Heat Loss from the Ducts of a Heating System in the Attic

384

Example 6-7

Flow of Oil in a Pipeline through the Icy Waters of a Lake

386

Example 6-8

Cooling of Plastic Sheets by Forced Air

387

Chapter 7

NATURAL CONVECTION

411

Example 7-1

Heat Loss from Hot Water Pipes

417

Example 7-2

Cooling of a Plate in Different Orientations

419

Example 7-3

Heat Loss through a Double-Pane Window

424

Example 7-4

Heat Transfer through a Spherical Enclosure

425

Example 7-5

Heating of Water by Resistance Wires on the Tube Surface

426

Example 7-6

Heat Loss from the Ducts of a Heating System in the Attic

430

Chapter 8

BOILING AND CONDENSATION

451

Example 8-1

Nucleate Boiling of Water in a Pan

463

Example 8-2

Peak Heat Flux in Nucleate Boiling

464

Example 8-3

Film Boiling of Water on a Heating Element

465

Example 8-4

Condensation of Steam on a Vertical Plate

478

Example 8-5

Condensation of Steam on a Tilted Plate

479

Example 8-6

Condensation of Steam on Horizontal Tubes

480

Example 8-7

Condensation of Steam on Horizontal Tube Banks

481

Chapter 9

RADIATION HEAT TRANSFER

495

Example 9-1

Radiation Emission from a Black Ball

503

Example 9-2

Emission of Radiation from an Incandescent Light Bulb

504

Example 9-3

Average Emissivity of a Surface and Emissive Power

509

Example 9-4

Selective Absorber and Reflective Surfaces

518

Example 9-5

View Factors Associated with Two Concentric Spheres

526

Example 9-6

Fraction of Radiation Leaving through an Opening

527

Example 9-7

View Factors Associated with a Tetragon

529

Example 9-8

View Factors Associated with a Long Triangular Duct

529

Example 9-9

The Crossed-Strings Method for View Factors

531

Example 9-10

Radiation Heat Transfer in a Black Cubical Furnace

533

Example 9-11

Radiation Heat Transfer between Large Parallel Plates

539

Example 9-12

Radiation Heat Transfer in a Cylindrical Furnace

541

Example 9-13

Radiation Heat Transfer in a Triangular Furnace

543

Example 9-14

Heat Transfer through Tubular Solar Collector

544

Example 9-15

Radiation Shields

550

Example 9-16

Radiation Effect on Temperature Measurements

550

Chapter 10

HEAT EXCHANGERS

569

Example 10-1

Overall Heat Transfer Coefficient of a Heat Exchanger

578

Example 10-2

Effect of Fouling on the Overall Heat Transfer Coefficient

580

Example 10-3

The Condensation of Steam in a Condenser

588

Example 10-4

Heating Water in a Counter-Flow Heat Exchanger

589

Example 10-5

Heating of Glycerin in a Multipass Heat Exchanger

590

Example 10-6

Cooling of an Automotive Radiator

591

Example 10-7

Upper Limit for Heat Transfer in a Heat Exchanger

594

Example 10-8

Using the Effectiveness-NTU Method

600

Example 10-9

Cooling Hot Oil by Water in a Multipass Heat Exchanger

602

Example 10-10

Installing a Heat Exchanger to Save Energy and Money

605

Chapter 11

MASS TRANSFER

623

Example 11-1

Determining Mass Fractions from Mole Fractions

633

Example 11-2

Mole Fraction of Water Vapor at the Surface of a Lake

634

Example 11-3

Mole Fraction of Dissolved Air in Water

636

Example 11-4

Diffusion of Hydrogen Gas into a Nickel Plate

638

Example 11-5

Diffusion of Hydrogen through a Spherical Container

642

Example 11-6

Condensation and Freezing of Moisture in the Walls

645

Example 11-7

Hardening of Steel by the Diffusion of Carbon

649

Example 11-8

Venting of Helium into the Atmosphere by Diffusion

658

Example 11-9

Measuring the Diffusion Coefficient by the Stefan Tube

659

Example 11-10

Mass Convection inside a Circular Pipe

668

Example 11-11

Analogy between Heat and Mass Transfer

669

Example 11-12

Evaporative Cooling of a Canned Drink

672

Example 11-13

Heat Loss from Uncovered Hot Water Baths

673

Chapter 12

HEATING AND COOLING OF BUILDINGS

699

Example 12-1

Effect of Clothing on Thermal Comfort

710

Example 12-2

Summer and Winter Design Conditions for Atlanta

715

Example 12-3

Effect of Solar Heated Walls on Design Heat Load

719

Example 12-4

Energy Consumption of Electric and Gas Burners

724

Example 12-5

Heat Gain of an Exercise Room

725

Example 12-6

The R-Value of a Wood Frame Wall

730

Example 12-7

The R-Value of a Wall with Rigid Foam

731

Example 12-8

The R-Value of a Masonry Wall

732

Example 12-9

The R-Value of a Pitched Roof

733

Example 12-10

Heat Loss from a Below-Grade Basement

737

Example 12-11

Heat Loss to the Crawl Space through Floors

741

Example 12-12

U-Factor for Center-of-Glass Section of Windows

750

Example 12-13

Heat Loss through Aluminum-Framed Windows

750

Example 12-14

U-Factor of a Double-Door Window

752

Example 12-15

Installing Reflective Films on Windows

758

Example 12-16

Reducing Infiltration Losses by Winterizing

764

Example 12-17

Energy and Money Savings by Winterization

769

Example 12-18

Annual Heating Cost of a House

769

Example 12-19

Choosing the Most Economical Air Conditioner

770

Chapter 13

REFRIGERATION AND FREEZING OF FOODS

795

Example 13-1

Cooling of Apples while Avoiding Freezing

803

Example 13-2

Freezing of Beef

806

Example 13-3

Freezing of Sweet Cherries

807

Example 13-4

Cooling of Bananas by Refrigerated Air

814

Example 13-5

Chilling of Beef Carcasses in a Meat Plant

823

Example 13-6

Retrofitting a Dairy Plant with a Regenerator

829

Example 13-7

Freezing of Chicken

835

Example 13-8

Infiltration Load of Cold Storage Rooms

836

Example 13-9

Interstate Transport of Refrigerated Milk by Trucks

840

Example 13-10

Transport of Apples by Refrigerated Trucks

841

Chapter 14

COOLING OF ELECTRONIC EQUIPMENT

863

Example 14-1

Predicting the Junction Temperature of a Transistor

866

Example 14-2

Determining the Junction-to-Case Thermal Resistance

867

Example 14-3

Analysis of Heat Conduction in a Chip

878

Example 14-4

Predicting the Junction Temperature of a Device

880

Example 14-5

Heat Conduction along a PCB with Copper Cladding

883

Example 14-6

Thermal Resistance of an Epoxy–Glass Board

885

Example 14-7

Planting Cylindrical Copper Fillings in an Epoxy Board

885

Example 14-8

Conduction Cooling of PCBs by a Heat Frame

886

Example 14-9

Cooling of Chips by the Thermal Conduction Module

891

Example 14-10

Cooling of a Sealed Electronic Box

896

Example 14-11

Cooling of a Component by Natural Convection

897

Example 14-12

Cooling of a PCB in a Box by Natural Convection

898

Example 14-13

Forced-Air Cooling of a Hollow-Core PCB

906

Example 14-14

Forced-Air Cooling of a Transistor Mounted on a PCB

908

Example 14-15

Choosing a Fan to Cool a Computer

910

Example 14-16

Cooling of a Computer by a Fan

911

Example 14-17

Cooling of Power Transistors on a Cold Plate by Water

916

Example 14-18

Immersion Cooling of a Logic Chip

920

Example 14-19

Cooling of a Chip by Boiling

921

Example 14-20

Replacing a Heat Pipe by a Copper Rod

926

Preface

GENERAL APPROACH

This introductory text is intended for use in a first course in heat transfer for undergraduate engineering students in their junior or senior year, and as a reference book for practicing engineers. The text covers the basic principles of heat transfer with a broad range of engineering applications. It contains sufficient material to give instructors flexibility and to accommodate their preferences on the right blend of fundamentals and applications.

The students are assumed to have completed their basic physics and calculus sequence. The completion of first courses in thermodynamics, fluid mechanics, and differential equations prior to taking heat transfer is desirable. The relevant concepts from these topics are introduced and reviewed as needed. The emphasis throughout the text is kept on the physics and the physical arguments in order to develop an intuitive understanding of the subject matter.

There are several textbooks in heat transfer currently available, and one cannot help wondering if there is a need for another one. After all, heat transfer is a mature science, and the topics of heat transfer are well established. However, it is often stated that the current education system needs to be modernized, and major research programs have been undertaken in recent years to come up with a better match between engineering education and engineering practice. The author has long felt that current engineering education is academically oriented and geared toward bringing up academicians rather than practicing engineers. This text is the outcome of an attempt to have a suitable textbook for a practically oriented heat transfer course for engineering students. The text covers all the standard topics in heat transfer with an emphasis on physical mechanisms and practical applications, while de-emphasizing heavy mathematical aspects, which are being left to computers.

In engineering practice, an understanding of the mechanisms of heat transfer is becoming increasingly important since heat transfer plays a crucial role in the design of vehicles, power plants, refrigerators, electronic devices, buildings, and bridges, among other things. Even a chef needs to have an intuitive understanding of the heat transfer mechanism in order to cook the food "right" every time. We may not be aware of it, but we always use the principles of heat transfer when seeking thermal comfort. We insulate our bodies by putting on heavy coats in winter, and we minimize heat gain by radiation by staying in the shadow in summer. We speed up the cooling of hot food by blowing on it and keep warm in cold weather by cuddling up and thus minimizing the exposed surface area. That is, we already use heat transfer whether we realize it or not. So we might as well go ahead and learn what we already practice.

The philosophy that contributed to the popularity of the thermodynamics book I coauthored with Dr. Boles has remained unchanged in this text: talk directly to the minds of tomorrow’s engineers in a simple yet precise manner, and encourage creative thinking and development of a deeper understanding of the subject matter. The goal throughout this project has been to offer an engineering textbook that is read by the students with interest and enthusiasm instead of one that is used as a reference book to solve problems. Special effort is made to touch the curious minds and take them on a pleasant journey in the wonderful world of thermodynamics and heat transfer and explore the wonders of these exciting subjects.

Yesterday’s engineer spent a major portion of his or her time substituting values into the formulas and obtaining numerical results. But all the formula manipulations and number crunching are being left to the computers. Tomorrow’s engineer will have to have 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 lead students in this direction.

CONTENTS

In Chapter 1 we introduce the basic concepts of thermodynamics and heat transfer, and the first law of thermodynamics. We also review the ideal gas equation and the specific heat relations since they are commonly used in the heating and cooling of gases. In this chapter we also introduce the basic mechanisms of heat transfer. In Chapter 2 we derive the heat conduction equation, discuss the boundary conditions, and solve some steady one-dimensional heat conduction problems. We also discuss heat generation and variable conductivity.

Chapters 3 and 4 deal with steady and transient heat conduction, respectively, and Chapter 5 with numerical methods. A practical approach is used in these chapters and the thermal resistance concept is emphasized. Extensive discussions are given on thermal insulations and the optimum thickness of insulation because of the widespread use of insulations in industry and the key role they play in any energy conservation project. Chapters 6 and 7 deal with forced and natural convection, respectively. Again, a practical engineering approach is used with a wealth of physical explanations and empirical correlations. The velocity and thermal boundary layers are discussed without resorting to the boundary layer equations. Boiling and condensation heat transfer is presented in Chapter 8, followed by radiation heat transfer in Chapter 9, heat exchangers in Chapter 10, and mass transfer in Chapter 11.

Chapters 12, 13, and 14 deal with common application areas of heat transfer in engineering practice. They are intended to show students how heat transfer is used in real-world situations and to give them a chance to practice what they have been mastering during much of the course. In Chapter 12 we discuss heat transfer in residential and commercial buildings, thermal comfort, heating and cooling loads, infiltration losses, and thermal design using the local weather data. In Chapter 13 we discuss heat transfer associated with the cooling and freezing of foods such as vegetables, fruits, fish, and meat products. Finally, in Chapter 14, we discuss the cooling techniques currently used in the thermal control of electronic equipment. These chapters are independent of each other and can be covered in any order. Or they can be skipped all together to allow more time on fundamentals in earlier chapters. Most students will find the material in these chapters very interesting and highly informative, and they will probably read them anyway even if they are not covered. The material in these chapters is based pri-marily on handbooks such as the authoritative series of handbooks by the American Society for Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), Inc.

LEARNING TOOLS

A distinctive feature of this book is the absence of heavy mathematical and theoretical aspects of subject matter such as the separation of variables and the Navier-Stokes equations. The author believes that such material has little practical value, and it is better suited for graduate-level courses. The emphasis in undergraduate education should remain on developing a sense of underlying physical mechanism and a mastery of solving practical problems an engineer is likely to face in the real world. The absence of such time-consuming and intimidating material should free the instructor to cover more material on the fundamentals and applications of heat transfer. This should also make heat transfer a more pleasant and worthwhile experience for the students.

An observant mind should have no difficulty understanding heat transfer. After all, the principles of heat transfer are based on our everyday experiences and experimental observations. A more 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 heat transfer.

The material in the text is introduced at a level that an average student can follow comfortably. It speaks to the students, not over the students. In fact, it is self-instructive. Noting that the principles of heat transfer 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.

Figures are important learning tools that help the students "get the picture." The text makes effective use of graphics. It probably contains more figures and illustrations than any other heat transfer book. Figures attract attention and stimulate curiosity and interest. Some of the figures in this text are intended to serve as a means of emphasizing some key concepts that would otherwise go unnoticed, or as paragraph summaries.

Each chapter contains numerous 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, with particular attention to the proper use of units. A summary is included at the end of each chapter for a quick overview of basic concepts and important relations.

The end-of-chapter problems are grouped under specific topics in the order they are covered to make problem selection easier for both instructors and students. The problems within each group start with 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. The problems under the Computer, Design, and Essay Problems title are intended to encourage students to make engineering judgments, to conduct independent searches on topics of interest, and to communicate their findings in a professional manner. Several economics- and safety-related problems are incorporated throughout to enhance cost and safety awareness among engineering students. Answers to selected problems are listed immediately following the problem for convenience to the students.

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 appendix 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. Frequently used conversion factors and the physical constants are listed on the inner cover pages of the text for easy reference.

SUPPLEMENTS

Solutions Manual

This manual features detailed typed solutions with illustrations suitable for posting.

EES Software

Developed by Sandy Klein and Bill Beckman from the University of Wisconsin—Madison, this software program allows students to solve problems, especially design problems, and to ask "what if" questions. EES (pronounced "ease") is an acronym for Engineering Equation Solver. EES is very easy to master, and equations can be entered in any form and in any order. The combination of equation-solving capability and engineering property data makes EES an extremely powerful tool for students.

EES can do optimization, parametric analysis, linear and nonlinear regression, and provide publication-quality plotting capability. Equations can be entered in any form and in any order. EES automatically rearranges the equations to solve them in the most efficient manner.

EES is particularly useful for heat transfer problems since most of the property data needed for solving heat transfer problems are provided in the program. For example, the steam tables are implemented such that any thermodynamic property can be obtained from a built-in function call in terms of any two properties. Similar capability is provided for many organic refrigerants, ammonia, methane, carbon dioxide, and many other fliuds. Air tables are built-in, as are psychometric functions and JANAF table data for many common gases. Transport properties are also provided for all substances. EES also allows the user to enter property data or functional relationships with lookup tables, with internal functions written with EES, or with externally compiled functions written in Pascal, C, C++, or Fortran.

The EES engine is available to those who adopt the text with the problems disk, or it will be available via a password protected system on the Web to departments who wish to use EES without a McGraw-Hill text. A license for EES is provided to departments of educational institutions that adopt Heat Transfer: A Practical Approach from WCB/McGraw-Hill. If you would like this option, be sure to order your book using ISBN 0-07-561176-7. If you need more information, contact your local WCB/McGraw-Hill representative, call 1-800-338-3987, or visit our Web site at www.mhhe.com.

EES Software Problems Disk contains the EES programs that have been developed to solve some of the problems in this text. Problems solved on the EES problems disk are denoted in the text with a disk symbol. Each program provides detailed comments and on-line help. These programs should help the student master the important concepts without the calculational burden that has been previously required. A Windows-based Software Demo is available for your review.

ACKNOWLEDGMENTS

I would like to acknowledge with appreciation the numerous and valuable comments, suggestions, criticisms, and praise of the following academic reviewers:

Edward Anderson, Texas Tech University

Bahman Litkouhi, Manhattan College

Hameed Metghalchi, Northeastern University

William Moses, Mercer University

Sidney Roberts, Old Dominion University

Ramendra P. Roy, Arizona State University

Brian Vick, Virginia Polytechnic Institute & State University

Their suggestions have greatly helped to improve the quality of this text. I also would like to thank my students at the University of Nevada, Reno, who provided plenty of feedback from students’ perspectives while class-testing the material. Finally, I would like to express my appreciation to my wife Zehra and my children for their continued patience, understanding, and support throughout the preparation of this text.

Yunus A. Çengel

Nomenclature

A

Area, m2

Ac

Cross-sectional area

ACH

Air changes per hour

Bi

Biot number

C

Specific heat, kJ/kg · K; capacity ratio

C

Molar concentration, kmol/m3

Ch, Cc

Heat capacity rate, W/°C

CD

Drag coefficient

Cf

Friction coefficient

Cp

Constant pressure specific heat, kJ/kg · K

Cv

Constant volume specific heat, kJ/kg · K

COP

Coefficient of performance

d, D

Diameter, m

DAB

Diffusion coefficient

Dh

Hydraulic diameter, m

e

Specific total energy, kJ/kg

erfc

Complimentary error function

E

Total energy, kJ

Eb

Blackbody emissive flux

f

Friction factor

fl

Blackbody radiation function

F

Force, N

FD

Drag coefficient

Fij

View factor

g

Gravitational acceleration, m/s2

g

Heat generation rate, W/m3

G

Incident radiation, W/m2

Gr

Grashof number

h

Enthalpy, u + Pv, kJ/kg

h

Convection heat transfer coefficient, W/m2 · °C

hc

Thermal contact conductance, W/m2 · °C

hfg

Latent heat of vaporization, kJ/kg

hif

Latent heat of fusion, kJ/kg

j

Diffusive mass flux, kg/s · m2

J

Radiosity, W/m2; Bessel function

k

Thermal conductivity

keff

Effective thermal conductivity, W/m · °C

L

Length; half thickness of a plane wall

Lc

Characteristic or corrected length

Lh

Hydrodynamic entry length

Lt

Thermal entry length

Le

Lewis number

m

Mass, kg

m

Mass flow rate, kg/s

M

Molar mass, kg/kmol

N

Number of moles, kmol

NTU

Number of transfer units

Nu

Nusselt number

p

Perimeter, m

P

Pressure, kPa

Pv

Vapor pressure

Pr

Prandtl number

Q

Total amount heat transfer, kJ

q

Heat flux, W/m2

Q

Heat transfer rate, kW

r

Radius, m

rcr

Critical radius of insulation

R

Gas constant, kJ/kg · K

R

Thermal resistance, °C/W

Ra

Rayleigh number

Rc

Thermal contact resistance, m2 · °C/W

Rf

Fouling factor

Ru

Universal gas constant, kJ/kmol · K

R-value

R-value of insulation

Re

Reynolds number

S

Conduction shape factor

Sc

Schmidt number

Sh

Sherwood number

St

Stanton number

SC

Shading coefficient

SHGC

Solar heat gain coefficient

t

Thickness, m

t

Time, s

T

Temperature, °C or K

Ti

Initial temperature, °C or K

Tf

Film temperature, °C

Tsat

Saturation temperature, °C

Tsky

Sky temperature, K

u

Internal energy, kJ/kg

U

Overall heat transfer coefficient, W/m2 · °C

v

Specific volume, m3/kg

V

Total volume, m3

V

Volume flow rate, m3/s

V

Velocity, m/s

V¥

Free stream velocity

w

Mass fraction

W

Power, kW

y

Mole fraction

Greek Letters

a

Absorptivity; thermal diffusivity, m2/s

as

Solar absorptivity

b

Volume expansion coefficient, 1/K

d

Characteristic length

DTlm

Log mean temperature difference

e

Emissivity; heat exchanger or fin effectiveness

hfin

Fin efficiency

m

Dynamic viscosity, kg/m · s

n

Kinematic viscosity, m2/s; frequency, 1/s

r

Density, kg/m3

s

Stefan–Boltzmann constant

t

Transmissivity; Fourier number

f

Relative humidity

q

Dimensionless temperature

Subscripts

atm

Atmospheric

av

Average

b

Bulk fluid

cyl

Cylinder

e

Electrical

e

Exit conditions

f

Saturated liquid; fluid

gen

Generation

i

Inlet, initial, or indoor conditions

i

ith component

l

Liquid

m

Mixture

o

Outdoor conditions

rad

Radiation

s

Surface

sat

Saturated

semi-inf

Semi-infinite medium

sph

Sphere

surr

Surrounding surfaces

sys

System

v

Vapor

¥

Ambient conditions

Superscripts

. (over dot)

Quantity per unit time

_ (over bar)

Quantity per unit mole

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