Th d a o

558 Pages·1995·16.321 MB·English

by  Adrian Bejan, George Tsatsaronis, Michael Moran

THERMAL DESIGN
AND
OPTIMIZATION
Adrian Bejan
Department of Mechanical Engineering and Material Science
Duke University
George Tsa t saro ni s
Institut fur Energietechnik
Technische Universitat Berlin
Michael Maran
Department of Mechanical Engineering
The Ohio State University
A WILEY-INTERSCIENCE PUBLICATION
JOHN WILEY & SONS, INC.
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Library of Congress Cataloging in Publication Data:
Bejan, Adrian, 1948-
Thermal design and optimization I Adrian Bejan, George
Tsatsaronis, Michael Moran.
p. cm.
Includes index.
ISBN 0-471-58467-3
1. Heat engineering. I. Tsatsaronis, G. (George) 11. Moran,
Michael J. 111. Title.
TJ260.B433 1996
621,402-dc20 95-1 207 1
Printed in the United States of America
IO 9 8 7 6 5 4 3
PREFACE
This book provides a comprehensive and rigorous introduction to thermal
system design and optimization from a contemporary perspective. The pre-
sentation is intended for engineering students at the senior or first-year grad-
uate level and for practicing engineers and technical managers working in the
energy field. The book is appropriate for use in a capstone design course, in
a technical elective course, and for self-study. Sufficient end-of-chapter prob-
lems are provided for these uses. In class testing, the material has been found
to work well with the intended audience.
We assume readers have had introductory courses in engineering thermo-
dynamics and heat transfer and are familiar with the basics of fluid mechanics.
Some background in engineering economics is also desirable but not required.
For readers with limited backgrounds in engineering thermodynamics, heat
transfer, and engineering economics, reviews are provided in Chapters 2, 4,
and 7, respectively. Our presentation does not provide a detailed discussion
of component design or extensive operating and cost data. Information on
these topics is available in various standard references, handbooks, imd man-
ufacturers’ catalogs. Readers should refer to such sources as needed; we have
provided extensive reference lists to facilitate this. The book has been written
to allow flexibility in the use of units. It can be studied using 1nte:mational
System (SI) units only or a mix of SI and English units.
In the area of thermal systems, engineering curricula are largely component
and design analysis oriented. Students initially learn to apply mass and energy
balances and, increasingly, entropy and exergy balances. Then, on the basis
of known engineering descriptions and specifications, students learn to cal-
culate the size, performance, and cost of heat exchangers, turbines, pumps,
and other components. These activities are important, but the scope of engi-
neering design is much wider. Design is primarily system oriented and the
objective is to effect a design solution: to devise a means for accomplishing
a stated purpose subject to real-world constraints. Design requires synthesis:
selecting and putting together components to form a smoothly working whole.
Design also often requires that principles from different disciplines be applied
V
Vi PREFACE
within a single problem, for example, principles from engineering thermo-
dynamics and heat transfer. Moreover, design usually requires explicit con-
sideration of engineering economics, for cost is almost invariably a key issue.
Finally, design requires optimization techniques that are not typically en-
countered elsewhere in the engineering curricula. Synthesis, engineering ec-
onomics, and optimization are among several design topics discussed in this
book.
The current presentation departs from those of previous books on the sub-
ject of thermal system design in three important respects: (1) A concerted
effort has been made to include material drawn from the best of contemporary
thinking about design and design methodology. Thus, Chapter 1 provides
discussions of concurrent design, quality function deployment, and other con-
temporary design ideas. (2) This book includes current developments in en-
gineering thermodynamics, heat transfer, and engineering economics relevant
to design. Many of these developments are based on the second law of ther-
modynamics. In particular, we feature the use of exergy analysis and entropy
generation minimization. We employ the term thermoeconomics to denote
exergy-aided cost minimization. (3) A case study is considered throughout
the book for continuity of the presentation. The case study involves the design
of a cogeneration system.
The presentation of design topics initiated in Chapter 1 continues in Chap-
ter 2 with the development of a thermodynamic model for the case study
cogeneration system and a discussion of piping system design. Chapter 3
provides a discussion of design guidelines evolving from reasoning using the
second law of thermodynamics and, in particular, the exergy concept.
Chapters 4, 5, and 6 all contain design-related material, including heat
exchanger design. These presentations are intended to illuminate the design
process by gradually introducing first-level design notions such as degrees of
freedom, design constraints, and thermodynamic optimization. In these chap-
ters the role of second-law reasoning in design is further emphasized. Ex-
amples familiar from previous courses in thermodynamics and heat transfer
are used to illustrate principles. Chapters 5 and 6 also illustrate the effective-
ness of elementary modeling in design. Such modeling is often an important
element of the concept development stage. Elementary models can highlight
key design variables, the relations among them, and fundamental trade-offs.
In some instances, such models can lead directly to design solutions, as for
example in the case of electronic package cooling considered in Chapter 5.
With Chapter 7 detailed engineering economic evaluations enter the pre-
sentation explicitly and are featured in the remainder of the book. Chapter 8
presents a powerful and systematic design approach that combines the exergy
concept of engineering thermodynamics with principles of engineering eco-
nomics. Exergy costing methods are introduced and applied in this chapter.
These methods identify the real cost sources at the component level:
the capital investment costs, the operating and maintenance costs, and the
PREFACE vii
costs associated with the destruction and loss of exergy. The optimization of
thermal systems is based on a careful consideration of these cost sources.
Chapter 9 provides discussions of the pinch method for the design of heat
exchanger networks and the iterative optimization of complex systems. Re-
sults of the thermoeconomic optimization of the cogeneration system case
study are also presented.
This book has been developed to be flexible in use: to satisfy various
instructor preferences, curricular objectives, course durations, and self-study
needs. Some instructors will elect to present material in depth from all nine
chapters. Shorter presentations are also possible. For example, courses might
be built around Chapters 1-6 plus topics from Chapter 7, or formed from
Chapters 1-3 plus Chapters 7-9. Some instructors may want to provide a
highly-focused presentation by simply tracking the cogeneration system case
study or another case study drawn from the references provided or the indi-
vidual instructor’s professional experience. Other course arrangements are
also possible, and instructors are encouraged to contact the authors directly
concerning alternatives.
The use of the second law of thermodynamics in thermal system design
and optimization is still a novelty in U.S. industry, but not in Europe and
elsewhere. This approach is featured here because an increasing number of
engineers and engineering managers worldwide agree that it has considerable
merit and are advocating its use. We offer it in an evolutionary spirit as a
worthy alternative. Our aim is to contribute to the education of the next gen-
eration of thermal system designers and to the background of currently active
designers who feel the need for more effective design methods. We welcome
constructive comments and criticism from readers. Such feedback is essential
for the further development of the design approaches presented in this book.
Several individuals have contributed to this book. A. Ozer Arnas and Gor-
don M. Reistad reviewed the manuscript and provided several helpful sug-
gestions. We appreciate their input. Additionally, we owe special thanks to
faculty colleagues, staff and students at our respective institutions for their
support and assistance: at Duke University, Kathy Vickers, Linda Hayes, Jose
V. C. Vargas, Oana Craciunescu, and Gustavo Ledezma; at Tennessee Tech-
nological University, Kenneth Purdy, David Price, Helen Haggard, Agnes
Tsatsaronis, and the 126 student members of the thermal design class in the
academic year 1993-19 94; at Technische Universitat Berlin, Yanzi Chen,
Frank Cziesla, Andreas Krause, and Christine Gharz; and at The Ohio State
University, Kenneth Waldron, Margaret Drake, and Carol Bird.
ADRIAN BEJAN
GEORGE TSATSARONIS
MICHAEL MORAN
June. 1995

CONTENTS
1 Introduction to Thermal System Design 1
1.1 Preliminaries I 2
1.2 Workable, Optimal, and Nearly Optimal Designs I 3
1.3 Life-Cycle Design I 6
1.3.1 Overview of the Design Process I 6
1.3.2 Understanding the Problem: “What?” not “How?” I 9
1.3.3 Project Management I 11
1.3.4 Project Documentation I 12
1.4 Thermal System Design Aspects / 15
1.4.1 Environmental Aspects I 16
1.4.2 Safety and Reliability I 17
1.4.3 Background Information and Data Sources I 19
1.4.4 Performance and Cost Data I 20
1.5 Concept Creation and Assessment I 21
1.5.1 Concept Generation: “How?” not “What?” I 21
1.5.2 Concept Screening I 22
1.5.3 Concept Development I 25
1.5.4 Sample Problem Base-Case Design I 29
1.6 Computer-Aided Thermal System Design I 3 1
1.6.1 Preliminaries I 31
1.6.2 Process Synthesis Software I 32
1.6.3 Analysis and Optimization: Flowsheeting Software / 32
1.7 Closure I 33
References I 34
Problems I 36
ix
X CONTENTS
2 Thermodynamics, Modeling, and Design Analysis 39
2.1 Basic Concepts and Definitions / 39
2.1.1 Preliminaries / 40
2.1.2 The First Law of Thermodynamics, Energy / 42
2.1.3 The Second Law of Thermodynamics / 46
2.1.4 Entropy and Entropy Generation / 50
2.2 Control Volume Concepts / 55
2.2.1 Mass, Energy, and Entropy Balances / 55
2.2.2 Control Volumes at Steady State / 59
2.2.3 Ancillary Concepts / 60
2.3 Property Relations / 64
2.3.1 Basic Relations for Pure Substances / 64
2.3.2 Multicomponent Systems / 76
2.4 Reacting Mixtures and Combustion / 78
2.4.1 Combustion / 78
2.4.2 Enthalpy of Formation / 78
2.4.3 Absolute Entropy / 80
2.4.4 Ancillary Concepts / 81
2.5 Thermodynamic Model-Cogeneration System / 84
2.6 Modeling and Design of Piping Systems / 97
2.6.1 Design Considerations / 97
2.6.2 Estimation of Head Loss / 99
2.6.3 Piping System Design and Design Analysis / 102
2.6.4 Pump Selection / 105
2.7 Closure / 107
References / 108
Problems / 108
3 Exergy Analysis 113
3.1 Exergy / 113
3.1.1 Preliminaries / 113
3.1.2 Defining Exergy / 114
3.1.3 Environment and Dead States / 115
3.1.4 Exergy Components / 116
3.2 Physical Exergy / 117
3.2.1 Derivation / 117
3.2.2 Discussion / 120
CONTENTS Xi
3.3 Exergy Balance / 121
3.3.1 Closed System Exergy Balance I 121
3.3.2 Control Volume Exergy Balance I 123
3.4 Chemical Exergy I 131
3.4.1 Standard Chemical Exergy I 131
3.4.2 Standard Chemical Exergy of Gases and Gas
Mixtures I 132
3.4.3 Standard Chemical Exergy of Fuels / 134
3.5 Applications I 138
3.5.1 Cogeneration System Exergy Analysis / 139
3.5.2 Exergy Destruction and Exergy Loss I 143
3.5.3 Exergetic Efficiency I 150
3.5.4 Chemical Exergy of Coal, Char, and Fuel Oil / 156
3.6 Guidelines for Evaluating and Improving
Thermodynamic Effectiveness / 159
3.7 Closure / 162
References I 162
Problems I 163
4 Heat Transfer, Modeling, and Design Analysis 167
4.1 The Objective of Heat Transfer / 167
4.2 Conduction / 170
4.2.1 Steady Conduction / 170
4.2.2 Unsteady Conduction I 176
4.3 Convection I 184
4.3.1 External Forced Convection I 184
4.3.2 Internal Forced Convection I 190
4.3.3 Natural Convection / 195
4.3.4 Condensation / 199
4.3.5 Boiling / 202
4.4 Radiation I 207
4.4.1 Blackbody Radiation I 208
4.4.2 Geometric View Factors / 209
4.4.3 Diffuse-Gray Surface Model / 213
4.4.4 Two-Surface Enclosures I 214
4.4.5 Enclosures with More Than Two Surfaces I 220
4.4.6 Gray Medium Surrounded by Two Diffuse-Gray
Surfaces / 221