net cen58933_fm.qxd 9/11/2002 10:56 AM Page xviii PREFACE OBJECTIVES eat transfer is a basic science that deals with the rate of transfer of ther- H mal energy. This introductory text is intended for use in a first course in heat transfer for undergraduate engineering students, and as a reference book for practicing engineers. The objectives of this text are • To cover the basic principles of heat transfer. • To present a wealth of real-world engineering applications to give stu- dents a feel for engineering practice. • To develop an intuitive understanding of the subject matter by empha- sizing the physics and physical arguments. Students are assumed to have completed their basic physics and calculus se- quence. The completion of first courses in thermodynamics, fluid mechanics, and differential equations prior to taking heat transfer is desirable. The rele- vant concepts from these topics are introduced and reviewed as needed. In engineering practice, an understanding of the mechanisms of heat trans- fer is becoming increasingly important since heat transfer plays a crucial role in the design of vehicles, power plants, refrigerators, electronic devices, build- ings, 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” by adjusting the rate of heat transfer. We may not be aware of it, but we al- ready use the principles of heat transfer when seeking thermal comfort. We in- sulate our bodies by putting on heavy coats in winter, and we minimize heat gain by radiation by staying in shady places in summer. We speed up the cool- ing 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. GENERAL APPROACH This text is the outcome of an attempt to have a textbook for a practically ori- ented heat transfer course for engineering students. The text covers the stan- dard topics of heat transfer with an emphasis on physics and real-world applications, while de-emphasizing intimidating heavy mathematical aspects. This approach is more in line with students’ intuition and makes learning the subject matter much easier. The philosophy that contributed to the warm reception of the first edition of this book has remained unchanged. The goal throughout this project has been to offer an engineering textbook that xviii www.net cen58933_fm.qxd 9/11/2002 10:56 AM Page xix xix PREFACE • Talks directly to the minds of tomorrow’s engineers in a simple yet pre- cise manner. • Encourages creative thinking and development of a deeper understand- ing of the subject matter. • Is read by students with interest and enthusiasm rather than being used as just an aid to solve problems. Special effort has been made to appeal to readers’ natural curiosity and to help students explore the various facets of the exciting subject area of heat transfer. The enthusiastic response we received from the users of the first edition all over the world indicates that our objectives have largely been achieved. Yesterday’s engineers spent a major portion of their time substituting values into the formulas and obtaining numerical results. However, now formula ma- nipulations and number crunching are being left to 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 em- phasize these basic principles while also providing students with a look at how modern tools are used in engineering practice. NEW IN THIS EDITION All the popular features of the previous edition are retained while new ones are added. The main body of the text remains largely unchanged except that the coverage of forced convection is expanded to three chapters and the cov- erage of radiation to two chapters. Of the three applications chapters, only the Cooling of Electronic Equipment is retained, and the other two are deleted to keep the book at a reasonable size. The most significant changes in this edi- tion are highlighted next. EXPANDED COVERAGE OF CONVECTION Forced convection is now covered in three chapters instead of one. In Chapter 6, the basic concepts of convection and the theoretical aspects are introduced. Chapter 7 deals with the practical analysis of external convection while Chap- ter 8 deals with the practical aspects of internal convection. See the Content Changes and Reorganization section for more details. ADDITIONAL CHAPTER ON RADIATION Radiation is now covered in two chapters instead of one. The basic concepts associated with thermal radiation, including radiation intensity and spectral quantities, are covered in Chapter 11. View factors and radiation exchange be- tween surfaces through participating and nonparticipating media are covered in Chapter 12. See the Content Changes and Reorganization section for more details. TOPICS OF SPECIAL INTEREST Most chapters now contain a new end-of-chapter optional section called “Topic of Special Interest” where interesting applications of heat transfer are discussed. Some existing sections such as A Brief Review of Differential Equations in Chapter 2, Thermal Insulation in Chapter 7, and Controlling Nu- merical Error in Chapter 5 are moved to these sections as topics of special www.net cen58933_fm.qxd 9/11/2002 10:56 AM Page xx xx PREFACE interest. Some sections from the two deleted chapters such as the Refrigera- tion and Freezing of Foods, Solar Heat Gain through Windows, and Heat Transfer through the Walls and Roofs are moved to the relevant chapters as special topics. Most topics selected for these sections provide real-world applications of heat transfer, but they can be ignored if desired without a loss in continuity. COMPREHENSIVE PROBLEMS WITH PARAMETRIC STUDIES A distinctive feature of this edition is the incorporation of about 130 compre- hensive problems that require conducting extensive parametric studies, using the enclosed EES (or other suitable) software. Students are asked to study the effects of certain variables in the problems on some quantities of interest, to plot the results, and to draw conclusions from the results obtained. These problems are designated by computer-EES and EES-CD icons for easy recog- nition, and can be ignored if desired. Solutions of these problems are given in the Instructor’s Solutions Manual. CONTENT CHANGES AND REORGANIZATION With the exception of the changes already mentioned, the main body of the text remains largely unchanged. This edition involves over 500 new or revised problems. The noteworthy changes in various chapters are summarized here for those who are familiar with the previous edition. • In Chapter 1, surface energy balance is added to Section 1-4. In a new section Problem-Solving Technique, the problem-solving technique is introduced, the engineering software packages are discussed, and overviews of EES (Engineering Equation Solver) and HTT (Heat Trans- fer Tools) are given. The optional Topic of Special Interest in this chap- ter is Thermal Comfort. • In Chapter 2, the section A Brief Review of Differential Equations is moved to the end of chapter as the Topic of Special Interest. • In Chapter 3, the section on Thermal Insulation is moved to Chapter 7, External Forced Convection, as a special topic. The optional Topic of Special Interest in this chapter is Heat Transfer through Walls and Roofs. • Chapter 4 remains mostly unchanged. The Topic of Special Interest in this chapter is Refrigeration and Freezing of Foods. • In Chapter 5, the section Solutions Methods for Systems of Algebraic Equations and the FORTRAN programs in the margin are deleted, and the section Controlling Numerical Error is designated as the Topic of Special Interest. • Chapter 6, Forced Convection, is now replaced by three chapters: Chap- ter 6 Fundamentals of Convection, where the basic concepts of convec- tion are introduced and the fundamental convection equations and relations (such as the differential momentum and energy equations and the Reynolds analogy) are developed; Chapter 7 External Forced Con- vection, where drag and heat transfer for flow over surfaces, including flow over tube banks, are discussed; and Chapter 8 Internal Forced Convection, where pressure drop and heat transfer for flow in tubes are www.net cen58933_fm.qxd 9/11/2002 10:56 AM Page xxi xxi PREFACE presented. Reducing Heat Transfer through Surfaces is added to Chap- ter 7 as the Topic of Special Interest. • Chapter 7 (now Chapter 9) Natural Convection is completely rewritten. The Grashof number is derived from a momentum balance on a differ- ential volume element, some Nusselt number relations (especially those for rectangular enclosures) are updated, and the section Natural Con- vection from Finned Surfaces is expanded to include heat transfer from PCBs. The optional Topic of Special Interest in this chapter is Heat Transfer through Windows. • Chapter 8 (now Chapter 10) Boiling and Condensation remained largely unchanged. The Topic of Special Interest in this chapter is Heat Pipes. • Chapter 9 is split in two chapters: Chapter 11 Fundamentals of Thermal Radiation, where the basic concepts associated with thermal radiation, including radiation intensity and spectral quantities, are introduced, and Chapter 12 Radiation Heat Transfer, where the view factors and radia- tion exchange between surfaces through participating and nonparticipat- ing media are discussed. The Topic of Special Interest are Solar Heat Gain through Windows in Chapter 11, and Heat Transfer from the Hu- man Body in Chapter 12. • There are no significant changes in the remaining three chapters of Heat Exchangers, Mass Transfer, and Cooling of Electronic Equipment. • In the appendices, the values of the physical constants are updated; new tables for the properties of saturated ammonia, refrigerant-134a, and propane are added; and the tables on the properties of air, gases, and liq- uids (including liquid metals) are replaced by those obtained using EES. Therefore, property values in tables for air, other ideal gases, ammonia, refrigerant-134a, propane, and liquids are identical to those obtained from EES. LEARNING TOOLS EMPHASIS ON PHYSICS A distinctive feature of this book is its emphasis on the physical aspects of subject matter rather than mathematical representations and manipulations. The author believes that the emphasis in undergraduate education should re- main 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. Developing an intuitive understanding should also make the course a more motivating and worthwhile experience for the students. EFFECTIVE USE OF ASSOCIATION An observant mind should have no difficulty understanding engineering sci- ences. After all, the principles of engineering sciences are based on our every- day 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 ex- ample, serves as an excellent vehicle to demonstrate the basic principles of heat transfer.net cen58933_fm.qxd 9/11/2002 10:56 AM Page xxii xxii PREFACE SELF-INSTRUCTING The material in the text is introduced at a level that an average student can follow comfortably. It speaks to students, not over students. In fact, it is self- instructive. Noting that the principles of sciences are based on experimental observations, the derivations in this text are based on physical arguments, and thus they are easy to follow and understand. EXTENSIVE USE OF ARTWORK Figures are important learning tools that help the students “get the picture.” The text makes effective use of graphics. It contains more figures and illus- trations than any other book in this category. 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; some serve as paragraph summaries. CHAPTER OPENERS AND SUMMARIES Each chapter begins with an overview of the material to be covered and its re- lation to other chapters. A summary is included at the end of each chapter for a quick review of basic concepts and important relations.
