Heat And Mass Transfer

814 Pages·2009·56.586 MB·English

by  Nag

Heat and Mass Transfer
Third Edition
About the Author
P K Nag had been with the Indian Institute of Technology Kharagpur, for about four decades, almost since
his graduation. After retirement from IIT, he was an Emeritus Fellow of AICTE, New Delhi, stationed at
Jadavpur University, Kolkata, till June 2005. He was a Visiting Professor in the Technical University of
Nova Scotia (now Dalhousie University), Halifax, Canada, for two years during 1985–86 and 1993–94.
Dr Nag is the recipient of the President of India Medal (1995) from the Institution of Engineers
(India). He is a Fellow of the National Academy of Engineering (FNAE) and a Fellow of the Institution of
Engineers (India). In his early days, he was also an NCC Offi cer at IIT, Kharagpur. Besides these, Dr Nag
is a Life Member of the Indian Society for Technical Education, Indian Society for Heat and Mass Transfer,
and the Combustion Institute, USA (Indian section). He was formerly a member of the New York Academy
of Sciences, USA.
His areas of interest include circulating fl uidized bed boilers, combined cycle power generation, second
law analysis of thermal systems, and waste heat recovery. He has authored four books, including this one,
and more than 150 research papers in several national and international journals and proceedings. He has
also attended international conferences in the USA, Japan, Canada and Bangladesh where he has presented
several papers.
Other books by the author (all published by Tata McGraw-Hill Publishing Co. Ltd.)
∑ Engineering Thermodynamics, 4/e
∑ Power Plant Engineering, 3/e
∑ Basic and Applied Thermodynamics, 2/e
Heat and Mass Transfer
Third Edition
P K Nag

Emeritus Fellow (AICTE, Jadavpur University)
and
Formerly Professor
Department of Mechanical Engineering
Indian Institute of Technology, Kharagpur
Tata McGraw Hill Education Private Limited
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Heat and Mass Transfer, 3e
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Dedicated to all my students
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Preface
Heat transfer has long been a part of the curricula of disciplines such as mechanical, chemical, aerospace,
environmental and nuclear engineering. The signifi cance of heat transfer has heightened as a result of the
worldwide energy problem, and it is being widely recognized in other fi elds such as civil engineering and
architecture, electronics and electrical engineering, computer science, and metallurgical engineering.
The present book, an outcome of teaching of the subject for many years to the senior undergraduate
students of mechanical engineering at IIT Kharagpur was primarily developed for use as a text in
introductory undergraduate engineering heat transfer courses, taught at the junior or senior level, for which
some special topics may be skipped in certain chapters. The book should also serve as a useful reference for
graduate students, practising engineers, and persons interested in energy-related problems.
Since its last revision in 2007, it was felt necessary to again shift through the pages of the book
‘Heat and Mass Transfer’ to make it more relevant to the present times, eliminating some redundant or
unnecessary topics and incorporating some more pertinent materials. With this view in mind, this revision
process was carried out. Topics like ‘Heat conduction with moving heat sources’ (Art. 3.8) and ‘Cooling of
electronic equipment’ (Art. 9.5) have been removed, not because they are not important or irrelevant, but
to restrict the book to basic fundamentals. On the other hand, inclusions of applications of critical radius of
insulation with effect of radiation in Chapter 3, momentum and energy thicknesses in Chapter 4, and design
considerations and criteria for selection of heat exchangers as well as heat transfer equipment in Chapter 8
have been made to make the book more comprehensive. To summarize, the changes introduced in the latest
edition are the following:
∑ New topical inclusions
J Conduction Heat Transfer at Steady State
Application of the Principle of Critical Radius of Insulation
H
Effect of Radiation
H
J Convection Heat Transfer: Forced Convection
Momentum and Energy Thicknesses
H
Heat Transfer Enhancement
H
J Heat Exchangers
Design Considerations for selection of Heat Exchanger
H
∑ List of Important Equations and Formulas at the end of each chapter
Besides these, the signifi cant features of this book that distinguish it from other heat transfer texts are
(1) Thorough presentation of the fundamental concepts—complete coverage of the course on Heat and
Mass Transfer
(2) Large number of solved examples involving tutorial or step-by-step methodology of solving prob-
lems
(3) A practical understanding of the topics provided by emphasizing the physics and the underlying
physical phenomena involved
(4) Discussion on heat transfer in electronic components and heat pipes
(5) Wide coverage of radiation heat transfer
viii Preface
(6) Excellent pedagogy including
∑ 462 Figures
∑ 236 Solved Examples
∑ 53 Miscellaneous Solved Examples
∑ 363 Review Questions
∑ 223 Problems for Practice with Answers
∑ 62 Open Book Problems
∑ 100 Objective Type Questions
Chapter Organisation
Elementary aspects of calculus and differential equations are only needed as background material.
Throughout the text, the SI system of units has been used. The appendices contain a wide collection of data
on properties of various substances relevant to heat transfer.
Fundamental concepts pertaining to the mechanisms of heat transfer are introduced in Chapter 1. The
differences in approach and content of the subjects of ‘Thermodynamics’ and ‘Heat Transfer’ are pointed
out elaborately.
Chapter 2 is concerned with a fairly detailed study of steady state heat conduction for different
boundary conditions. Analytic and numerical expressions for the determination of temperature distributions
and heat fl ow in solids have been developed. In Chapter 2, the general heat conduction equation has been
derived in spherical coordinates. The application of the governing equation to solid and hollow spheres with
and without heat generation is demonstrated. The general conduction equation of fi ns has been derived and
its application to the cases of triangular fi ns and cylindrical fi ns has been considered. The limitation of an
extended surface is reviewed.
In Chapter 3, the concept of transient heat fl ow is fi rst introduced through the use of the lumped system
analysis, and the expressions of temperature transients with time and position are developed for simple
geometries. The use of temperature-time history and heat transfer charts have been illustrated with many
examples. The portion on periodic heat fl ow and moving heat sources may be omitted in the fi rst course on
the subject. The transient heat conduction in a semi-infi nite solid has been analysed with examples.
Chapters 4 and 5 are devoted to heat transfer in forced and natural convection. A detailed account of
dimensional analysis and similarity principle has been provided to determine the signifi cant dimensionless
parameters in convective heat transfer. Equations for continuity, momentum and energy for fl uid elements
were solved for simple forced convection problems to establish velocity and temperature distributions.
Both laminar and turbulent fl ows over fl at plates and through tubes are analyzed, and friction factor and
heat transfer coeffi cients are determined. The use of Reynolds analogy is adequately emphasized. Flow
over external bodies is then discussed to determine drag and heat transfer coeffi cients. The boundary layer
growth and velocity profi les are further clarifi ed. Simplifi ed heat transfer equations for natural convection
in air are tabulated for convenient use.
In Chapter 5, the principles of natural convection are elucidated. An approximate boundary layer
analysis is presented to illustrate the use of energy equation to predict the heat transfer coeffi cient for natural
convection from a vertical plate. Various correlations for other confi gurations are also presented. Chapter 6
provides the fundamentals of condensation and boiling. Various regimes of boiling and condensation are
discussed and the heat transfer correlations associated with them are presented. Radiation heat transfer is
covered in Chapter 7. Radiation exchange among surfaces separated by a non-participating medium is fi rst
Preface ix
discussed and then the network method is presented to provide a good insight into the physical nature of
problems. Radiation from gases and vapours is then presented.
Chapter 8 is devoted to the thermal analysis of heat exchangers. The uses of LMTD and NTU methods

for the sizing of heat exchangers are illustrated with examples. Various types of heat exchangers are
discussed. Some special heat transfer processes are deliberated in Chapter 9. It includes the heat transfer
in high velocity fl ows and rarefi ed gases, transpiration and ablative cooling, and heat pipes. Finally, in
Chapter 10, the analysis of mass transfer is presented with an analogy of heat transfer by diffusion and
forced convection. The concentration boundary layer and mass transfer coeffi cients in Chapter 10 are
further explained, and the analogy of momentum, heat and mass transfer is emphasized. Forced convection
mass transfer in laminar and turbulent fl ows is discussed on the basis of this analogy.
A Summary containing the gist of the topics covered is provided at the end of each chapter. To give
more thrust, Objective Type Questions with Answers have been provided at the end of each chapter with
an aim to aid the students in competitive examinations and to refurbish their knowledge. Miscellaneous
solved examples have been further added in Appendix D which also illustrates the step-by-step procedure
of solving numerical problems. It is followed by ‘Fill in the Blanks’ and ‘True or False statements’ in
Appendix E, which would help the students in better understanding the subject. Fundamental Formulae
and Equations have been tabulated chapterwise for ready reference. Open Book Problems have also been
provided at the of each chapter (except 9 and 10) which the students can easily solve with the hints given.
Web Supplements
The web supplements of this book can be accessed at https://www.mhhe.com/nag/hmt3e and contain
∑ 120 Objective Type Questions for students
Acknowledgements
I am grateful to my wife, Sikharini, for silently supporting the work during the years of its preparation. I
express my sincere thanks to Ms Vibha Mahajan and her publishing team, especially Ms Devshree Lohchab,
the erstwhile Development Editor of Tata McGraw-Hill, who had put in a lot of effort for getting the book
extensively reviewed. I am grateful to Ms Shalini Jha, Mr Suman Sen, Ms Sohini Mukherjee and Mr P L
Pandita of Tata McGraw-Hill for the deft supervision, organization and production of the book.
I am also thankful to the reviewers whose thoughtful comments were the backbone of the review
process. Their names are given below.
Akhilesh Gupta
Indian Institute of Technology Roorkee, Uttaranchal
B N Prasad
National Institute of Technology Jamshedpur, Jharkhand
Rajnish Kumar
Birla Institute of Technology Mesra, Patna Campus, Bihar
S B Thombre
Vivesvaraya National Institute of Technology, Nagpur, Maharashtra
M K Bhatt
Sardar Vallabbhai National Institute of Technology, Surat, Gujarat
x Preface
P Mohanan
National Institute of Technology Karnataka, Surathkal, Karnataka
Sunil Punjabi

Government Engineering College, Ujjain, Madhya Pradesh
Taslim Raza
Krishna Institute of Engineering and Technology, Ghaziabad, Uttar Pradesh
Kanchan Chatterjee
Dr B C Roy Engineering College, Durgapur, West Bengal
P R Thiyagarajan
Sri Krishna College of Engineering and Technology, Coimbatore, Tamil Nadu
S K Jagadeesh
Dr. Ambedkar Institute of Technology, Bangalore, Karnataka
P I Ugran
KLE College of Engineering and Technology, Belgaum, Karnataka
B Sudheer Kumar
JNTU College of Engineering, Kukatpally, Hyderabad
I would also take the opportunity to thank Prof. Syed Samsul Alam, Vice Chancellor of Aliah University,
with which I am now attached for giving me the scope and time to carry out the revision process.
I hope that the book would meet all the requirements of the curricula on the subject. Some materials not
considered important enough or not possible to cover in a one-semester course may be skipped. I would
appreciate any constructive criticism and suggestions from the readers for further improvement of the book.
P K Nag
Publisher’s Note
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