cen29305_ch00-fm

H E A T A N D M A S ST R A N S F E R

A PRACTICAL APPROACH

THIRD EDITION(SI Units)

YUNUS A. ÇENGELUniversity of Nevada, Reno

Singapore • Boston • Burr Ridge, IL • Dubuque, IA • Madison, WI • New York • San FranciscoSt. Louis • Bangkok • Kuala Lumpur • Lisbon • London • Madrid • Mexico City

Milan • Montreal • New Delhi • Seoul • Sydney • Taipei • Toronto

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page iii

Heat and Mass TransferA Practical ApproachThird Edition (SI Units)

Publication Year: 2006

Exclusive rights by McGraw-Hill Education (Asia), for manufacture and export. This book cannotbe re-exported from the country to which it is sold by McGraw-Hill.

Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenueof the Americas, New York, NY 10020. Copyright © 2006, 2002, 1998, 1994, 1989 by TheMcGraw-Hill Companies, Inc. All rights reserved. No part of this publication may be reproduced ordistributed in any form or by any means, or stored in a database or retrieval system, without the priorwritten consent of The McGraw-Hill Companies, Inc., including, but not limited to, in any networkor other electronic storage or transmission, or broadcast for distance learning.

Some ancillaries, including electronic and print components, may not be available to customersoutside the United States.

10 09 08 07 06 05 04 03 0220 09 08 07 06IT (CTF) BJE

When ordering this title, use ISBN 007-125739-X

Printed in Singapore

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page iv

Yunus A. Çengel is Professor Emeritus of Mechanical Engineering at theUniversity of Nevada, Reno. He received his B.S. in mechanical engineeringfrom Istanbul Technical University and his M.S. and Ph.D. in mechanicalengineering from North Carolina State University. He conducted research inradiation heat transfer, heat transfer enhancement, renewable energy, desali-nation, exergy analysis, and energy conservation. He served as the director ofthe Industrial Assessment Center (IAC) at the University of Nevada, Reno,from 1996 to 2000. He has led teams of engineering students to numerousmanufacturing facilities in Northern Nevada and California to do industrial as-sessments, and has prepared energy conservation, waste minimization, andproductivity enhancement reports for them.

Dr. Çengel is the coauthor of the widely adopted textbooks Thermodynamics:An Engineering Approach, 5th edition (©2006), Fundamentals of Thermal-Fluid Sciences, 2nd edition (©2005), and Fluid Mechanics: Fundamentals andApplications (©2006), all published by McGraw-Hill. He is the author of thetextbook Introduction to Thermodynamics and Heat Transfer (©1997), alsopublished by McGraw-Hill. Some of his textbooks have been translated intoChinese, Japanese, Korean, Thai, Spanish, Portuguese, Turkish, Italian, andGreek.

Dr. Çengel is the recipient of several outstanding teacher awards, and hehas received the ASEE Meriam/Wiley Distinguished Author Award in 1992and again in 2000 for excellence in authorship. Dr. Çengel is a registered pro-fessional engineer in the state of Nevada, and is a member of the AmericanSociety of Mechanical Engineers (ASME) and the American Society forEngineering Education (ASEE).

A B O U T T H E A U T H O R

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page v

vi

C H A P T E R O N EINTRODUCTION AND BASIC CONCEPTS 1

C H A P T E R T W OHEAT CONDUCTION EQUATION 61

C H A P T E R T H R E ESTEADY HEAT CONDUCTION 131

C H A P T E R F O U RTRANSIENT HEAT CONDUCTION 217

C H A P T E R F I V ENUMERICAL METHODS IN HEAT CONDUCTION 285

C H A P T E R S I XFUNDAMENTALS OF CONVECTION 355

C H A P T E R S E V E NEXTERNAL FORCED CONVECTION 395

C H A P T E R E I G H TINTERNAL FORCED CONVECTION 451

C H A P T E R N I N ENATURAL CONVECTION 503

C H A P T E R T E NBOILING AND CONDENSATION 561

C H A P T E R E L E V E NHEAT EXCHANGERS 609

C H A P T E R T W E L V EFUNDAMENTALS OF THERMAL RADIATION 663

C H A P T E R T H I R T E E NRADIATION HEAT TRANSFER 707

C H A P T E R F O U R T E E NMASS TRANSFER 773

A P P E N D I X 1PROPERTY TABLES AND CHARTS (SI UNITS) 841

B R I E F C O N T E N T S

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page vi

Preface xiii

C H A P T E R O N EINTRODUCTION AND BASIC CONCEPTS 1

1–1 Thermodynamics and Heat Transfer 2

Application Areas of Heat Transfer 3Historical Background 3

1–2 Engineering Heat Transfer 4

Modeling in Engineering 5

1–3 Heat and Other Forms of Energy 6

Specific Heats of Gases, Liquids, and Solids 7Energy Transfer 9

1–4 The First Law of Thermodynamics 11

Energy Balance for Closed Systems (Fixed Mass) 12Energy Balance for Steady-Flow Systems 12Surface Energy Balance 13

1–5 Heat Transfer Mechanisms 17

1–6 Conduction 17

Thermal Conductivity 19Thermal Diffusivity 23

1–7 Convection 25

1–8 Radiation 27

1–9 Simultaneous Heat Transfer Mechanisms 30

1–10 Problem-Solving Technique 35

Engineering Software Packages 37Engineering Equation Solver (EES) 38Heat Transfer Tools (HTT) 39A Remark on Significant Digits 39

Topic of Special Interest: Thermal Comfort 40

Summary 46References and Suggested Reading 47Problems 47

C H A P T E R T W OHEAT CONDUCTION EQUATION 61

2–1 Introduction 62

Steady versus Transient Heat Transfer 63Multidimensional Heat Transfer 64Heat Generation 66

2–2 One-Dimensional Heat Conduction Equation 68

Heat Conduction Equation in a Large Plane Wall 68Heat Conduction Equation in a Long Cylinder 69Heat Conduction Equation in a Sphere 71Combined One-Dimensional

Heat Conduction Equation 72

2–3 General Heat Conduction Equation 74

Rectangular Coordinates 74Cylindrical Coordinates 75Spherical Coordinates 76

2–4 Boundary and Initial Conditions 77

1 Specified Temperature Boundary Condition 782 Specified Heat Flux Boundary Condition 793 Convection Boundary Condition 814 Radiation Boundary Condition 825 Interface Boundary Conditions 836 Generalized Boundary Conditions 84

2–5 Solution of Steady One-DimensionalHeat Conduction Problems 86

2–6 Heat Generation in a Solid 97

2–7 Variable Thermal Conductivity, k(T) 104

Topic of Special Interest:A Brief Review of Differential Equations 107

Summary 111References and Suggested Readings 112Problems 113

C O N T E N T S

vii

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page vii

CONTENTSviii

C H A P T E R T H R E ESTEADY HEAT CONDUCTION 131

3–1 Steady Heat Conduction in Plane Walls 132

Thermal Resistance Concept 133Thermal Resistance Network 135Multilayer Plane Walls 137

3–2 Thermal Contact Resistance 142

3–3 Generalized Thermal Resistance Networks 147

3–4 Heat Conduction in Cylinders and Spheres 150

Multilayered Cylinders and Spheres 152

3–5 Critical Radius of Insulation 156

3–6 Heat Transfer from Finned Surfaces 159

Fin Equation 160Fin Efficiency 164Fin Effectiveness 166Proper Length of a Fin 169

3–7 Heat Transfer in Common Configurations 174

Topic of Special Interest:Heat Transfer through Walls and Roofs 179


C H A P T E R F O U RTRANSIENT HEAT CONDUCTION 217

4–1 Lumped System Analysis 218

Criteria for Lumped System Analysis 219Some Remarks on Heat Transfer in Lumped

Systems 221

4–2 Transient Heat Conduction in Large Plane Walls, Long Cylinders,and Spheres with Spatial Effects 224

Nondimensionalized One-Dimensional Transient Conduction Problem 225

4–3 Transient Heat Conduction in Semi-Infinite Solids 240

Contact of Two Semi-Infinite Solids 245

4–4 Transient Heat Conduction inMultidimensional Systems 248

Topic of Special Interest:Refrigeration and Freezing of Foods 256


C H A P T E R F I V ENUMERICAL METHODS IN HEAT CONDUCTION 285

5–1 Why Numerical Methods? 286

1 Limitations 2872 Better Modeling 2873 Flexibility 2884 Complications 2885 Human Nature 288

5–2 Finite Difference Formulation of Differential Equations 289

5–3 One-Dimensional Steady Heat Conduction 292

Boundary Conditions 294

5–4 Two-Dimensional Steady Heat Conduction 302

Boundary Nodes 303Irregular Boundaries 307

5–5 Transient Heat Conduction 311

Transient Heat Conduction in a Plane Wall 313Two-Dimensional Transient Heat Conduction 324

Topic of Special Interest:Controlling the Numerical Error 329


C H A P T E R S I XFUNDAMENTALS OF CONVECTION 355

6–1 Physical Mechanism of Convection 356

Nusselt Number 358

6–2 Classification of Fluid Flows 359

Viscous versus Inviscid Regions of Flow 359Internal versus External Flow 359Compressible versus Incompressible Flow 360Laminar versus Turbulent Flow 360Natural (or Unforced) versus Forced Flow 360Steady versus Unsteady Flow 361One-, Two-, and Three-Dimensional Flows 361

6–3 Velocity Boundary Layer 362

Surface Shear Stress 363

6–4 Thermal Boundary Layer 364

Prandtl Number 365

6–5 Laminar and Turbulent Flows 365

Reynolds Number 366

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page viii

6–6 Heat and Momentum Transfer in Turbulent Flow 367

6–7 Derivation of Differential Convection Equations 369

The Continuity Equation 369The Momentum Equations 370Conservation of Energy Equation 372

6–8 Solutions of Convection Equations for a Flat Plate 376

The Energy Equation 378

6–9 Nondimensionalized Convection Equations and Similarity 380

6–10 Functional Forms of Friction and ConvectionCoefficients 381

6–11 Analogies between Momentum and HeatTransfer 382

Topic of Special Interest:Microscale Heat Transfer 385


C H A P T E R S E V E NEXTERNAL FORCED CONVECTION 395

7–1 Drag and Heat Transfer in External Flow 396

Friction and Pressure Drag 396Heat Transfer 398

7–2 Parallel Flow over Flat Plates 399

Friction Coefficient 400Heat Transfer Coefficient 401Flat Plate with Unheated Starting Length 403Uniform Heat Flux 403

7–3 Flow across Cylinders and Spheres 408

Effect of Surface Roughness 410Heat Transfer Coefficient 412

7–4 Flow across Tube Banks 417

Pressure Drop 420

Topic of Special Interest:Reducing Heat Transfer through Surfaces: Thermal Insulation 423


C H A P T E R E I G H TINTERNAL FORCED CONVECTION 451


8–2 Average Velocity and Temperature 453Laminar and Turbulent Flow in Tubes 454

8–3 The Entrance Region 455Entry Lengths 457

8–4 General Thermal Analysis 458Constant Surface Heat Flux (q·s � constant) 459Constant Surface Temperature (Ts � constant) 460

8–5 Laminar Flow in Tubes 463Pressure Drop 465Temperature Profile and the Nusselt Number 467Constant Surface Heat Flux 467Constant Surface Temperature 468Laminar Flow in Noncircular Tubes 469Developing Laminar Flow in the Entrance Region 470

8–6 Turbulent Flow in Tubes 473Rough Surfaces 475Developing Turbulent Flow in the Entrance Region 476Turbulent Flow in Noncircular Tubes 476Flow through Tube Annulus 477Heat Transfer Enhancement 477

Topic of Special Interest:Transitional Flow in Tubes 482


C H A P T E R N I N ENATURAL CONVECTION 503

9–1 Physical Mechanism of Natural Convection 504

9–2 Equation of Motion and the Grashof Number 507The Grashof Number 509

9–3 Natural Convection over Surfaces 510Vertical Plates (Ts � constant) 512Vertical Plates (q·s � constant) 512Vertical Cylinders 512Inclined Plates 512Horizontal Plates 513Horizontal Cylinders and Spheres 513

9–4 Natural Convection from Finned Surfaces and PCBs 517Natural Convection Cooling of Finned Surfaces

(Ts � constant) 517

CONTENTSix

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page ix

CONTENTSx

Natural Convection Cooling of Vertical PCBs(qs � constant) 518

Mass Flow Rate through the Space between Plates 519

9–5 Natural Convection Inside Enclosures 521Effective Thermal Conductivity 522Horizontal Rectangular Enclosures 523Inclined Rectangular Enclosures 523Vertical Rectangular Enclosures 524Concentric Cylinders 524Concentric Spheres 525Combined Natural Convection and Radiation 525

9–6 Combined Natural and Forced Convection 530

Topic of Special Interest:Heat Transfer through Windows 533


C H A P T E R T E NBOILING AND CONDENSATION 561

10–1 Boiling Heat Transfer 562

10–2 Pool Boiling 564Boiling Regimes and the Boiling Curve 564Heat Transfer Correlations in Pool Boiling 568Enhancement of Heat Transfer in Pool Boiling 572

10–3 Flow Boiling 576

10–4 Condensation Heat Transfer 578

10–5 Film Condensation 578Flow Regimes 580Heat Transfer Correlations for Film Condensation 581

10–6 Film Condensation Inside Horizontal Tubes 591

10–7 Dropwise Condensation 591

Topic of Special Interest:Heat Pipes 592


C H A P T E R E L E V E NHEAT EXCHANGERS 609

11–1 Types of Heat Exchangera 610

11–2 The Overall Heat Transfer Coefficient 612Fouling Factor 615

11–3 Analysis of Heat Exchangers 620

11–4 The Log Mean Temperature Difference Method 622

Counter-Flow Heat Exchangers 624Multipass and Cross-Flow Heat Exchangers: Use of a

Correction Factor 625

11–5 The Effectiveness–NTU Method 631

11–6 Selection of Heat Exchangers 642

Heat Transfer Rate 642Cost 642Pumping Power 643Size and Weight 643Type 643Materials 643Other Considerations 644


C H A P T E R T W E L V EFUNDAMENTALS OF THERMAL RADIATION 663


12–2 Thermal Radiation 665

12–3 Blackbody Radiation 667

12–4 Radiation Intensity 673

Solid Angle 674Intensity of Emitted Radiation 675Incident Radiation 676Radiosity 677Spectral Quantities 677

12–5 Radiative Properties 679

Emissivity 680Absorptivity, Reflectivity, and Transmissivity 684Kirchhoff’s Law 686The Greenhouse Effect 687

12–6 Atmospheric and Solar Radiation 688

Topic of Special Interest:Solar Heat Gain through Windows 692


C H A P T E R T H I R T E E NRADIATION HEAT TRANSFER 709

13–1 The View Factor 710

13–2 View Factor Relations 713

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page x

1 The Reciprocity Relation 7142 The Summation Rule 7173 The Superposition Rule 7194 The Symmetry Rule 720View Factors between Infinitely Long Surfaces:

The Crossed-Strings Method 722

13–3 Radiation Heat Transfer: Black Surfaces 724

13–4 Radiation Heat Transfer: Diffuse,Gray Surfaces 727

Radiosity 727Net Radiation Heat Transfer to or from a Surface 727Net Radiation Heat Transfer between

Any Two Surfaces 729Methods of Solving Radiation Problems 730Radiation Heat Transfer in Two-Surface Enclosures 731Radiation Heat Transfer in Three-Surface

Enclosures 733

13–5 Radiation Shields and the Radiation Effect 739

Radiation Effect on Temperature Measurements 741

13–6 Radiation Exchange with Emitting andAbsorbing Gases 743

Radiation Properties of a Participating Medium 744Emissivity and Absorptivity of Gases and Gas Mixtures 746

Topic of Special Interest:Heat Transfer from the Human Body 753


C H A P T E R F O U R T E E NMASS TRANSFER 773


14–2 Analogy Between Heat and Mass Transfer 775

Temperature 776Conduction 776Heat Generation 776Convection 777

14–3 Mass Diffusion 777

1 Mass Basis 7782 Mole Basis 778Special Case: Ideal Gas Mixtures 779Fick’s Law of Diffusion: Stationary Medium Consisting

of Two Species 779

14–4 Boundary Conditions 783

14–5 Steady Mass Diffusion through a Wall 788

14–6 Water Vapor Migration in Buildings 792

14–7 Transient Mass Diffusion 796

14–8 Diffusion in a Moving Medium 799

Special Case: Gas Mixtures at Constant Pressure andTemperature 803

Diffusion of Vapor through a Stationary Gas: Stefan Flow 804

Equimolar Counterdiffusion 806

14–9 Mass Convection 810

Analogy between Friction, Heat Transfer, and Mass TransferCoefficients 814

Limitation on the Heat–Mass Convection Analogy 816Mass Convection Relations 816

14–10 Simultaneous Heat and Mass Transfer 819


A P P E N D I X 1PROPERTY TABLES AND CHARTS (SI UNITS) 841

Table A–1 Molar mass, gas constant, and ideal-gas specific heats of somesubstances 842

Table A–2 Boiling and freezing point properties 843

Table A–3 Properties of solid metals 844–846

Table A–4 Properties of solid nonmetals 847

Table A–5 Properties of building materials 848–849

Table A–6 Properties of insulating materials 850

Table A–7 Properties of common foods851–852

Table A–8 Properties of miscellaneous materials 853

Table A–9 Properties of saturated water 854

Table A–10 Properties of saturated refrigerant-134a 855

Table A–11 Properties of saturated ammonia 856

Table A–12 Properties of saturated propane 857

Table A–13 Properties of liquids 858

Table A–14 Properties of liquid metals 859

CONTENTSxi

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page xi

CONTENTSxii

Table A–15 Properties of air at 1 atm pressure 860

Table A–16 Properties of gases at 1 atm pressure 861–862

Table A–17 Properties of the atmosphere at highaltitude 863

Table A–18 Emissivities of surface 864–865

Table A–19 Solar radiative properties of materials 866

Figure A–20 The Moody chart for the frictionfactor for fully developed flow incircular pipes 867

INDEX 869

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page xii

B A C K G R O U N D

Heat and mass transfer is a basic science that deals with the rate oftransfer of thermal energy. It has a broad application area ranging frombiological systems to common household appliances, residential and

commercial buildings, industrial processes, electronic devices, and food pro-cessing. Students are assumed to have an adequate background in calculus andphysics. The completion of first courses in thermodynamics, fluid mechanics,and differential equations prior to taking heat transfer is desirable. However,relevant concepts from these topics are introduced and reviewed as needed.

O B J E C T I V E SThis book is intended for undergraduate engineering students in their sopho-more or junior year, and as a reference book by practicing engineers. The ob-jectives of this text are

• To cover the basic principles of heat transfer.

• To present a wealth of real-world engineering examples to give studentsa feel for how heat transfer is applied in engineering practice.

• To develop an intuitive understanding of heat transfer by emphasizingthe physics and physical arguments.

It is our hope that this book, through its careful explanations of concepts andits use of numerous practical examples and figures, helps the students developthe necessary skills to bridge the gap between knowledge and the confidencefor proper application of that knowledge.

In engineering practice, an understanding of the mechanisms of heat transfer isbecoming increasingly important since heat transfer plays a crucial role in the de-sign of vehicles, power plants, refrigerators, electronic devices, buildings, andbridges, among other things. Even a chef needs to have an intuitive understandingof the heat transfer mechanism in order to cook the food “right” by adjusting therate of heat transfer. We may not be aware of it, but we already use the principlesof heat transfer when seeking thermal comfort. We insulate our bodies by puttingon heavy coats in winter, and we minimize heat gain by radiation by staying inshady places in summer. We speed up the cooling of hot food by blowing on it andkeep warm in cold weather by cuddling up and thus minimizing the exposed sur-face area. That is, we already use heat transfer whether we realize it or not.

G E N E R A L A P P R O A C HThis text is the outcome of an attempt to have a textbook for a practicallyoriented heat transfer course for engineering students. The text covers the

P R E F A C E

xiii

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page xiii

standard topics of heat transfer with an emphasis on physics and real-worldapplications. This approach is more in line with students’ intuition, and makeslearning the subject matter enjoyable.

The philosophy that contributed to the overwhelming popularity of the prioreditions of this book has remained unchanged in this edition. Namely, ourgoal has been to offer an engineering textbook that

• Communicates directly to the minds of tomorrow’s engineers in a sim-ple yet precise manner.

• Leads students toward a clear understanding and firm grasp of the basicprinciples of heat transfer.

• Encourages creative thinking and development of a deeper understand-ing and intuitive feel for heat transfer.

• Is read by students with interest and enthusiasm rather than being usedas an aid to solve problems.

Special effort has been made to appeal to students’ natural curiosity and tohelp them explore the various facets of the exciting subject area of heat trans-fer. The enthusiastic response we received from the users of prior editions—from small colleges to large universities all over the world—indicates that ourobjectives have largely been achieved. It is our philosophy that the best way tolearn is by practice. Therefore, special effort is made throughout the book toreinforce material that was presented earlier.

Yesterday’s engineer spent a major portion of his or her time substituting val-ues into the formulas and obtaining numerical results. However, now formulamanipulations and number crunching are being left mainly to the computers.Tomorrow’s engineer will have to have a clear understanding and a firm graspof the basic principles so that he or she can understand even the most complexproblems, formulate them, and interpret the results. A conscious effort is madeto emphasize these basic principles while also providing students with a per-spective at how computational tools are used in engineering practice.

N E W I N T H I S E D I T I O NAll the popular features of the previous edition are retained while new onesare added. With the exception of the coverage of the theoretical foundations oftransient heat conduction and moving the chapter “Cooling of ElectronicEquipment” to the Online Learning Center, the main body of the text remainslargely unchanged. The most significant changes in this edition are high-lighted below.

A NEW TITLEThe title of the book is changed to Heat and Mass Transfer: A PracticalApproach to attract attention to the coverage of mass transfer. All topics relatedto mass transfer, including mass convection and vapor migration through build-ing materials, are introduced in one comprehensive chapter (Chapter 14).

EXPANDED COVERAGE OF TRANSIENT CONDUCTIONThe coverage of Chapter 4, Transient Heat Conduction, is now expanded to in-clude (1) the derivation of the dimensionless Biot and Fourier numbers bynondimensionalizing the heat conduction equation and the boundary and initial

PREFACExiv

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page xiv

conditions, (2) the derivation of the analytical solutions of a one-dimensionaltransient conduction equation using the method of separation of variables,(3) the derivation of the solution of a transient conduction equation in the semi-infinite medium using a similarity variable, and (4) the solutions of transientheat conduction in semi-infinite mediums for different boundary conditionssuch as specified heat flux and energy pulse at the surface.

FUNDAMENTALS OF ENGINEERING (FE) EXAM PROBLEMSTo prepare students for the Fundamentals of Engineering Exam (that is be-coming more important for the outcome-based ABET 2000 criteria) and to fa-cilitate multiple-choice tests, about 250 multiple-choice problems are includedin the end-of-chapter problem sets. They are placed under the title “Funda-mentals of Engineering (FE) Exam Problems” for easy recognition. Theseproblems are intended to check the understanding of fundamentals and to helpreaders avoid common pitfalls.

MICROSCALE HEAT TRANSFERRecent inventions in micro and nano-scale systems and the development ofmicro and nano-scale devices continues to pose new challenges, and the un-derstanding of the fluid flow and heat transfer at such scales is becoming moreand more important. In Chapter 6, microscale heat transfer is presented as aTopic of Special Interest.

THREE ONLINE APPLICATION CHAPTERSThe application chapter “Cooling of Electronic Equipment” (Chapter 15) isnow moved to the Online Learning Center together with two new chapters“Heating and Cooling of Buildings” (Chapter 16) and “Refrigeration andFreezing of Foods” (Chapter 17). Please visit www.mhhe.com/cengel.

CONTENT CHANGES AND REORGANIZATIONWith the exception of the changes already mentioned, minor changes are madein the main body of the text. Nearly 400 new problems are added, and many ofthe existing problems are revised. The noteworthy changes in various chaptersare summarized here for those who are familiar with the previous edition.

• The title of Chapter 1 is changed to “Introduction and Basic Concepts.”Some artwork is replaced by photos, and several review problems on thefirst law of thermodynamics are deleted.

• Chapter 4 “Transient Heat Conduction” is revised greatly, as explainedpreviously, by including the theoretical background and the mathemati-cal details of the analytical solutions.

• Chapter 6 now has the Topic of Special Interest “Microscale Heat Trans-fer” contributed by Dr. Subrata Roy of Kettering University.

• Chapter 8 now has the Topic of Special Interest “Transitional Flow inTubes” contributed by Dr. Afshin Ghajar of Oklahoma State University.

• Chapter 13 “Heat Exchangers” is moved up as Chapter 11 to succeed“Boiling and Condensation” and to precede “Radiation.”

• In the appendices, the values of some physical constants are updated,and Appendix 3 “Introduction to EES” is moved to the enclosed CD andthe Online Learning Center.

PREFACExv

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page xv

S U P P L E M E N T SThe following supplements are available to the adopters of the book.

ENGINEERING EQUATION SOLVER (EES) CD-ROM(Limited Academic Version packaged free with every new copy of the text)Developed by Sanford Klein and William Beckman from the University ofWisconsin–Madison, this software combines equation-solving capability andengineering property data. EES can do optimization, parametric analysis, andlinear and nonlinear regression, and provides publication-quality plotting ca-pabilities. Thermodynamic and transport properties for air, water, and manyother fluids are built in, and EES allows the user to enter property data or func-tional relationships. Some problems are solved using EES, and completesolutions together with parametric studies are included on the enclosedCD-ROM. To obtain the full version of EES, contact your McGraw-Hillrepresentative or visit www.mhhe.com/ees.

INSTRUCTOR’S RESOURCE CD-ROM(Available to instructors only)This CD, available to instructors only, includes the solutions manual bychapter.

A C K N O W L E D G M E N T SI would like to acknowledge with appreciation the numerous and valuablecomments, suggestions, constructive criticisms, and praise from the followingevaluators and reviewers:

PREFACExvi

Suresh Advani,University of Delaware

Mark Barker,Louisiana Tech University

John R. Biddle,California State Polytechnic University,Pomona

Sanjeev Chandra,University of Toronto

Shaochen Chen,University of Texas, Austin

Fan-Bill Cheung,Pennsylvania State University

Vic A. Cundy,Montana State University

Radu Danescu,North Dakota State University

Prashanta Dutta,Washington State University

Richard A. Gardner,Washington University

Afshin J. Ghajar,Oklahoma State University

S. M. Ghiaasiaan,Georgia Institute of Technology

Alain Kassab,University of Central Florida

Roy W. Knight,Auburn University

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page xvi

PREFACExvii

Milivoje Kostic,Northern Illinois University

Wayne Krause,South Dakota School of Mines andTechnology

Feng C. Lai,University of Oklahoma

Charles Y. Lee,University of North Carolina, Charlotte

Alistair Macpherson,Lehigh University

Saeed Manafzadeh,University of Illinois

A.K. Mehrotra,University of Calgary

Abhijit Mukherjee,Rochester Institute of Technology

Yoav Peles,Rensselaer Polytechnic Institute

Ahmad Pourmovahed,Kettering University

Paul Ricketts,New Mexico State University

Subrata Roy,Kettering University

Brian Sangeorzan,Oakland University

Michael Thompson,McMaster University

Their suggestions have greatly helped to improve the quality of this text.Special thanks are due to Afshin J. Ghajar of Oklahoma State University

and Subrata Roy of Kettering University for contributing new sections andproblems, and to the following for contributing problems for this edition:

Edward Anderson, Texas Tech UniversityRadu Danescu, General Electric (GE) EnergyIbrahim Dincer, University of Ontario Institute of Technology, CanadaMehmet Kanoglu, University of Gaziantep, TurkeyWayne Krause, South Dakota School of MinesAnil Mehrotra, University of Calgary, Canada

I also would like to thank my students and instructors from all over the globe,who provided plenty of feedback from students’ and users’ perspectives. Fi-nally, I would like to express my appreciation to my wife and children for theircontinued patience, understanding, and support throughout the preparation ofthis text.

Yunus A. Çengel

cen29305_ch00-fm.qxd 24/7/2006 9:21 AM Page xvii

E M P H A S I S O NP H Y S I C SThe author believes that the emphasisin undergraduate education shouldremain on developing a sense of underlying physical mechanisms anda mastery of solving practical prob-lems that an engineer is likely to facein the real world.

E F F E C T I V E U S E O FA S S O C I AT I O NAn observant mind should have no difficultyunderstanding engineering sciences. After all,the principles of engineering sciences are basedon our everyday experiences and experimentalobservations. The process of cooking, for ex-ample, serves as an excellent vehicle to demon-strate the basic principles of heat transfer.

T O O L S T O E N H A N C EL E A R N I N G

— T A K E A G U I D E D T O U R —

xviii

HOTEGG

Heattransfer

Warmair

Coolair

FIGURE 9–1The cooling of a boiled egg in a coolerenvironment by natural convection.

The temperature of the air adjacent to the egg is higherand thus its density is lower, since at constant pressure thedensity of a gas is inversely proportional to its temperature.Thus, we have a situation in which some low-density or“light” gas is surrounded by a high-density or “heavy” gas,and the natural laws dictate that the light gas rise. This is nodifferent than the oil in a vinegar-and-oil salad dressing ris-ing to the top (since roil � rvinegar). This phenomenon ischaracterized incorrectly by the phrase “heat rises,” whichis understood to mean heated air rises. The space vacatedby the warmer air in the vicinity of the egg is replaced bythe cooler air nearby, and the presence of cooler air in thevicinity of the egg speeds up the cooling process. The riseof warmer air and the flow of cooler air into its place con-tinues until the egg is cooled to the temperature of the sur-rounding air.

Ab

Ab

finε = ———

Tb

Tb

Qfin·

Qno fin·

Qfin·

Qno fin·

FIGURE 3–44The effectiveness of a fin.

Fin EffectivenessFins are used to enhance heat transfer, and the use offins on a surface cannot be recommended unless theenhancement in heat transfer justifies the added costand complexity associated with the fins. In fact,there is no assurance that adding fins on a surfacewill enhance heat transfer. The performance of thefins is judged on the basis of the enhancement inheat transfer relative to the no-fin case. The perfor-mance of fins is expressed in terms of the fin effec-tiveness efin defined as Fig. 3–44.

S E L F - I N S T R U C T I N GThe material in the text is introduced at alevel that an average student can followcomfortably. It speaks to students, not overstudents. In fact, it is self-instructive. The or-der of coverage is from simple to general.

EXAMPLE 4–3 Boiling Eggs

An ordinary egg can be approximated as a 5-cm-diameter sphere (Fig. 4–21). The eggis initially at a uniform temperature of 5�C and is dropped into boiling water at 95�C.Taking the convection heat transfer coefficient to be h � 1200 W/m2 · �C, determinehow long it will take for the center of the egg to reach 70�C.

SOLUTION An egg is cooked in boiling water. The cooking time of the egg is to bedetermined.Assumptions 1 The egg is spherical in shape with a radius of ro � 2.5 cm. 2 Heatconduction in the egg is one-dimensional because of thermal symmetry about themidpoint. 3 The thermal properties of the egg and the heat transfer coefficient areconstant. 4 The Fourier number is t � 0.2 so that the one-term approximate solu-tions are applicable.

cen29305_ch00-fm.qxd 24/7/2006 9:22 AM Page xviii

L E A R N I N GO B J E C T I V E SA N DS U M M A R I E SEach chapter begins withan Overview of the mate-rial to be covered andchapter-specific Learn-ing Objectives. A Sum-mary is included at theend of each chapter, pro-viding a quick review ofbasic concepts and im-portant relations, andpointing out the rele-vance of the material.

TOOLS TO ENHANCE LEARNINGxix

I N T R O D U C T I O N A N D B A S I C C O N C E P T S

The science of thermodynamics deals with the amount of heat transfer asa system undergoes a process from one equilibrium state to another, andmakes no reference to how long the process will take. But in engineer-

ing, we are often interested in the rate of heat transfer, which is the topic ofthe science of heat transfer.

We start this chapter with a review of the fundamental concepts of thermo-dynamics that form the framework for heat transfer. We first present therelation of heat to other forms of energy and review the energy balance. Wethen present the three basic mechanisms of heat transfer, which are conduc-tion, convection, and radiation, and discuss thermal conductivity. Conductionis the transfer of energy from the more energetic particles of a substance to theadjacent, less energetic ones as a result of interactions between the particles.Convection is the mode of heat transfer between a solid surface and the adja-cent liquid or gas that is in motion, and it involves the combined effects ofconduction and fluid motion. Radiation is the energy emitted by matter in theform of electromagnetic waves (or photons) as a result of the changes in theelectronic configurations of the atoms or molecules. We close this chapterwith a discussion of simultaneous heat transfer.

OBJECTIVES

When you finish studying this chapter, you should be able to:

Understand how thermodynamics and heat transfer are related to each other,

Distinguish thermal energy from other forms of energy, and heat transfer from otherforms of energy transfer,

Perform general energy balances as well as surface energy balances,

Understand the basic mechanisms of heat transfer, which are conduction, convection,and radiation, and Fourier's law of heat conduction, Newton's law of cooling, and theStefan–Boltzmann law of radiation,

Identify the mechanisms of heat transfer that occur simultaneously in practice,

Develop an awareness of the cost associated with heat losses, and

Solve various heat transfer problems encountered in practice.

CHAPTER

1CONTENTS

1–1 Thermodynamics andHeat Transfer 2

1–2 Engineering Heat Transfer 4

1–3 Heat and Other Forms of Energy 6

1–4 The First Law ofThermodynamics 11

1–5 Heat Transfer Mechanisms 17

1–6 Conduction 17

1–7 Convection 25

1–8 Radiation 27

1–9 Simultaneous Heat TransferMechanism 30

1–10 Problem-Solving Technique 35

Topic of Special Interest:Thermal Comfort 40

Summary 46

References and SuggestedReading 47

Problems 47

70°C

70°C

70°C

70°C

70°C

(a) Copper ball

E X T E N S I V E U S E O FA R T W O R KArt is an important learning tool that helps stu-dents “get the picture.” The third edition of Heatand Mass Transfer: A Practical Approach con-tains more figures and illustrations than any otherbook in this category.(b) Roast beef

110°C

90°C

40°C

A small copper ball can be modeledas a lumped system, but a roastbeef cannot.

FIGURE 4–1

cen29305_ch00-fm.qxd 24/7/2006 9:22 AM Page xix

TOOLS TO ENHANCE LEARNINGxx

A W E A LT H O F R E A L - W O R L D E N D - O F - C H A P T E R P R O B L E M SThe end-of-chapter problems are grouped under specific topics to makeproblem selection easier for both instructors and students. Within eachgroup of problems are:

• Concept Questions, indicated by “C,” to check the students’ level ofunderstanding of basic concepts.

N U M E R O U SW O R K E D - O U TE X A M P L E S W I T HA S Y S T E M AT I CS O L U T I O N SP R O C E D U R EEach chapter contains severalworked-out examples that clarify thematerial and illustrate the use of thebasic principles. An intuitive and sys-tematic approach is used in the solu-tion of the example problems, whilemaintaining an informal conversa-tional style. The problem is firststated, and the objectives are iden-tified. The assumptions are thenstated, together with their justifica-tions. The properties needed to solvethe problem are listed separately, ifappropriate. This approach is alsoused consistently in the solutionspresented in the instructor’s solu-tions manual.

Room

30°C1.4 m2

Tsurr

Qrad·

FIGURE 1–38Schematic for Example 1–9.

EXAMPLE 1–9 Radiation Effect on ThermalComfort

It is a common experience to feel “chilly” in winter and“warm” in summer in our homes even when the thermostatsetting is kept the same. This is due to the so called “radi-ation effect” resulting from radiation heat exchange be-tween our bodies and the surrounding surfaces of the wallsand the ceiling.

Consider a person standing in a room maintained at22°C at all times. The inner surfaces of the walls, floors,and the ceiling of the house are observed to be at an aver-age temperature of 10°C in winter and 25°C in summer.Determine the rate of radiation heat transfer between thisperson and the surrounding surfaces if the exposed surfacearea and the average outer surface temperature of the per-son are 1.4 m2 and 30°C, respectively (Fig. 1–38).

SOLUTION The rates of radiation heat transfer between aperson and the surrounding surfaces at specified tempera-tures are to be determined in summer and winter.Assumptions 1 Steady operating conditions exist. 2 Heattransfer by convection is not considered. 3 The person iscompletely surrounded by the interior surfaces of the room.4 The surrounding surfaces are at a uniform temperature.Properties The emissivity of a person is e � 0.95 (Table1–6).Analysis The net rates of radiation heat transfer from thebody to the surrounding walls, ceiling, and floor in winterand summer are

Q·

rad, winter � esAs (T 4s � T 4

surr, winter)

1–91C We often turn the fan on in summer to helpus cool. Explain how a fan makes us feel cooler in thesummer. Also explain why some people use ceilingfans also in winter.

3–32 Reconsider Prob. 3–30. Using EES (or other)software, investigate the effect of thermal con-

ductivity on the required insulation thickness. Plot the thick-ness of insulation as a function of the thermal conductivity ofthe insulation in the range of 0.02 W/m · �C to 0.08 W/m · �C,and discuss the results.

1–148 A 30-cm-long, 0.5-cm-diameter electric resistancewire is used to determine the convection heat transfer coeffi-cient in air at 25°C experimentally. The surface temperature ofthe wire is measured to be 230°C when the electric power con-sumption is 180 W. If the radiation heat loss from the wire iscalculated to be 60 W, the convection heat transfer coefficient is

(a) 186 W/m2 · °C (b) 158 W/m2 · °C(c) 124 W/m2 · °C (d) 248 W/m2 · °C(e) 390 W/m2 · °C

• Review Problems are more comprehensive in nature and are not di-rectly tied to any specific section of a chapter—in some cases they re-quire review of material learned in previous chapters.

• Design and Essay are intended to encourage students to make engi-neering judgments, to conduct independent exploration of topics ofinterest, and to communicate their findings in a professional manner.

cen29305_ch00-fm.qxd 24/7/2006 9:22 AM Page xx

TOOLS TO ENHANCE LEARNINGxxi

• Fundamentals of Engineering Exam problems are clearly markedand intended to check the understanding of fundamentals, to help stu-dents avoid common pitfalls, and to prepare students for the FE Examthat is becoming more important for the outcome based ABET 2000criteria.

These problems are solved using EES, and complete solutionstogether with parametric studies are included on the enclosedCD-ROM.

These problems are comprehensive in nature and are intended to besolved with a computer, preferably using the EES software that ac-companies this text.

Several economics- and safety-related problems are incorporated throughoutto enhance cost and safety awareness among engineering students. Answers toselected problems are listed immediately following the problem for conve-nience to students.

3–75 Consider a cold aluminum canned drink that is initiallyat a uniform temperature of 4�C. The can is 12.5 cm high andhas a diameter of 6 cm. If the combined convection/radiationheat transfer coefficient between the can and the surroundingair at 25�C is 10 W/m2 · �C, determine how long it will take forthe average temperature of the drink to rise to 15�C.

In an effort to slow down the warming of the cold drink, aperson puts the can in a perfectly fitting 1-cm-thick cylindricalrubber insulator (k � 0.13 W/m · �C). Now how long will ittake for the average temperature of the drink to rise to 15�C?Assume the top of the can is not covered.

12.5 cm

6 cm

4°C

Tair = 25°C

cen29305_ch00-fm.qxd 24/7/2006 9:22 AM Page xxi

TOOLS TO ENHANCE LEARNINGxxii

Heat Transfer through Windows

Windows are glazed apertures in the building envelope that typically con-sist of single or multiple glazing (glass or plastic), framing, and shading. Ina building envelope, windows offer the least resistance to heat transfer. In atypical house, about one-third of the total heat loss in winter occurs throughthe windows. Also, most air infiltration occurs at the edges of the windows.The solar heat gain through the windows is responsible for much of thecooling load in summer. The net effect of a window on the heat balance ofa building depends on the characteristics and orientation of the window aswell as the solar and weather data. Workmanship is very important in theconstruction and installation of windows to provide effective sealingaround the edges while allowing them to be opened and closed easily.

Despite being so undesirable from an energy conservation point of view,windows are an essential part of any building envelope since they enhancethe appearance of the building, allow daylight and solar heat to come in,and allow people to view and observe outside without leaving their home.For low-rise buildings, windows also provide easy exit areas during emer-gencies such as fire. Important considerations in the selection of windowsare thermal comfort and energy conservation. A window should have agood light transmittance while providing effective resistance to heat trans-fer. The lighting requirements of a building can be minimized by maximiz-ing the use of natural daylight. Heat loss in winter through the windows canbe minimized by using airtight double- or triple-pane windows with spec-trally selective films or coatings, and letting in as much solar radiation aspossible. Heat gain and thus cooling load in summer can be minimized byusing effective internal or external shading on the windows.

TOPIC OF SPECIAL INTEREST*

T O P I C S O FS P E C I A LI N T E R E S TMost chapters contain a real worldapplication, end-of-chapter optionalsection called “Topic of Special Interest” where interesting applica-tions of heat transfer are discussedsuch as Thermal Comfort in Chap-ter 1, A Brief Review of DifferentialEquations in Chapter 2, Heat Trans-fer through the Walls and Roofs inChapter 3, and Heat Transfer throughWindows in Chapter 9.

C O N V E R S I O NFA C T O R SFrequently used conversionfactors and physical constantsare listed on the inner coverpages of the text for easyreference.

Conversion Factors

DIMENSION METRIC METRIC/ENGLISH

Acceleration 1 m/s2 � 100 cm/s2 1 m/s2 � 3.2808 ft/s2

1 ft/s2 � 0.3048* m/s2

Area 1 m2 � 104 cm2 � 106 mm2 1 m2 � 1550 in2 � 10.764 ft2

� 10�6 km2 1 ft2 � 144 in2 � 0.09290304* m2

Density 1 g/cm3 � 1 kg/L � 1000 kg/m3 1 g/cm3 � 62.428 lbm/ft3 � 0.036127 lbm/in3

1 lbm/in3 � 1728 lbm/ft3

1 kg/m3 � 0.062428 lbm/ft3

Energy, heat, work, 1 kJ � 1000 J � 1000 Nm � 1 kPa · m3 1 kJ � 0.94782 Btuinternal energy, 1 kJ/kg � 1000 m2/s2 1 Btu � 1.055056 kJenthalpy 1 kWh � 3600 kJ � 5.40395 psia · ft3 � 778.169 lbf · ft

1 cal† � 4.184 J 1 Btu/lbm � 25,037 ft2/s2 � 2.326* kJ/kg1 IT cal† � 4.1868 J 1 kJ/kg � 0.430 Btu/lbm1 Cal† � 4.1868 kJ 1 kWh � 3412.14 Btu

1 therm � 105 Btu � 1.055 � 105 kJ (natural gas)

cen29305_ch00-fm.qxd 24/7/2006 9:22 AM Page xxii

cen29305_ch00-fm

Documents