Conjugate Heat and Mass Transfer in Heat Mass Exchanger Ducts

396 Pages·2014·23.105 MB·English

by  Li-Zhi Zhang (Auth.)

Conjugate Heat and Mass
Transfer in Heat Mass
Exchanger Ducts
Li-Zhi Zhang
AMSTERDAM • BOSTON • HEIDELBERG • LONDON
NEW YORK • OXFORD • PARIS • SAN DIEGO
SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO
Academic Press is an imprint of Elsevier
Academic Press is an imprint of Elsevier
225 Wyman Street, Waltham, MA 02451, USA
The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, UK
First edition 2014
© 2014 Elsevier Inc. All rights reserved.
No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any
means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the
publisher.
Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK:
phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email: [email protected]. Alternatively you
can submit your request online by visiting the Elsevier web site at http://elsevier.com/locate/permissions, and
selecting Obtaining permission to use Elsevier material.
Notice
No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of
products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or
ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular, indepen-
dent verification of diagnoses and drug dosages should be made.
Library of Congress Cataloging-in-Publication Data
A catalog record for this book is available from the Library of Congress
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
ISBN: 978-0-12-407782-9

For information on all Academic Press publications
visit our website at http://store.elsevier.com
Printed and bound in United States of America
13 14 15 16 17 9 8 7 6 5 4 3 2 1
Preface
In modern society, new materials and new processes are required to solve the emerging new energy and
environmental problems. Increasingly, novel heat and mass exchangers are being invented and used in
various industries, for instance, in energy recovery, gas separations, air purification, air cleaning, waste
water treatment, liquids separations, air dehumidification, and so on. Adsorbent beds, desiccant wheels,
membrane contactors, membrane total heat exchangers, and air cleaners all belong to this type of heat
and mass exchangers.
Ducts are the basic elements in these heat and mass exchangers. In this book, a systematic descrip-
tion of the conjugate heat and mass transfer in such ducts is presented. The basic physical phenomena
in these ducts are described. The methods to treat the conjugate boundaries, either steady-state or
transient, are introduced. The detailed transport data for ducts of various heat and mass exchangers are
presented: adsorbent beds, desiccant wheels, membrane total heat exchangers, membrane contactors,
either of parallel-plate type or of hollow fiber bundle type. The book also illustrates some examples of
the applications of novel heat and mass exchangers, with theoretical analysis combined with experi-
mental work: for instance, air dehumidification by honeycomb adsorbent beds, air dehumidification
and energy recovery by desiccant wheels, heat and moisture recovery by membrane total heat exchang-
ers, air humidification by hollow fiber membrane contactors, air dehumidification by salt solutions with
parallel-plate, or hollow fiber membrane contactors. Both the working theories and the heat and mass
transfer problems are addressed. The exchangers are constructed and their performances are optimized
with the obtained heat and mass transfer data. This book provides a reference book for the design of
these novel heat and mass exchangers.
The book combines theoretical analysis with engineering practices. It covers a wide range of knowl-
edge from fundamental heat mass transfer to novel system design and performance analysis. It also
gives deep insights and design guidelines for the heat and mass exchangers used in other industries
such as air conditioning, energy engineering, mechanical engineering, chemical engineering, environ-
mental engineering, food, and drug engineering, etc.
This is the first book systematically presenting conjugated heat and mass transfer in the ducts of
various heat and mass exchangers. Various duct cross-sectional shapes are included. The book may
also serve as a reference book for scientists, engineers, practitioners, and students in energy, chemical,
production, and environmental industries for component design.
xi
Acknowledgments
After 15 years accumulating knowledge and expertise, I began to write this book. After 8 months of
preparation and hard work, I am relieved that it is now completed. It is like a new born son to me. I am
full of joy, but more, a sense of responsibility. I hope readers can share with me the knowledge in this
book, as well as the heart of curiosity and the feeling of accomplishment in finishing this work.
This book is a cross-disciplinary endeavor which relies heavily on numerical heat mass transfer.
I hope peer engineers, scientists, and research students will benefit from the methodologies exhibited
in this analysis and extend them to analyses of other energy and environmental systems. Your feedback
of suggestions and comments, as well as criticisms is also valuable. Readers’ support is critical to the
success of my continuing writings.
I am deeply grateful to the Academician of the Chinese Academy of Sciences, Prof. Wenquan Tao at,
Xi’an Jiaotong University, for the precious time that he squeezed from his tense schedule to write a
Foreword for this book which has become an introduction to the content. I would also like to thank the
Natural Science Foundation of China (NSFC) for their continuing financial support. I am indebted to
my colleagues at South China University of Technology, and others all over China and throughout the
world who have provided suggestions and ideas which, in no small way, have contributed to the fabric
of this text. They all contributed a great deal to the results described in this book. I am also grateful to
my colleagues at South China University of Technology and elsewhere, who have provided positive
reinforcement for my efforts.
Li-Zhi Zhang
South China University of Technology
Guangzhou, China
Email: [email protected]
xiii
Foreword
Energy and environment are two critical issues today. Mankind is facing increasing energy and envi-
ronmental problems. New materials and new processes are required to solve these problems. More
frequently than before, novel heat and mass exchangers are being invented and applied in various
industries; for instance, in energy recovery, gas separations, air purifications, air cleaners, waste water
treatment, liquid separations, air dehumidification, toxic gas and liquid disposals, and so on. Depending
on the application fields, these exchangers can be adsorbent beds, desiccant wheels, membrane contac-
tors, membrane total heat exchangers, or cleaners. Regardless of the names, they all belong to these
types of exchangers.
For these new exchangers, the ducts are the basic elements where the processes take place. Heat
and mass transfer usually accompany each other. Simultaneous heat and mass transfer in the ducts are
the fundamental and basic phenomena in these novel heat and mass exchangers. Therefore, the data on
heat and mass transfer in these ducts are the fundamentals for component design, system optimization,
and performance evaluation.
Compared to traditional metal-type heat exchangers, there are special features in these new heat and
mass transfer ducts:
1. The solid walls have new functional materials. The heat and mass transfer in fluids are
closely related to those in the solid walls. So, they are conjugate heat and mass transfer
problems. The governing equations for the fluids and the solids should be solved together;
simultaneously.
2. The Biot numbers of these ducts are high. They are large Biot number ducts. So, material
properties have decisive impacts on the conjugate heat and mass transfer in ducts. The thermo-
chemical and interfacial characteristics of wall materials, which are new and always nonlinear,
should be considered, in addition to thermal and fluid-dynamics problems, in the fluids.
3. The duct geometries are always irregular. The simple analytical solutions of fluid flow for
common round or rectangular tubes are no longer applicable.
4. There are multi-variables that need to be solved. Velocity, temperature, concentrations are usually
coupled together. The complexities also include chemical reactions, sometimes in the solids.
These special features have led to many new phenomena:
1. The boundary conditions on duct walls have neither uniform values nor uniform fluxes. Rather,
they are formed by the coupling of the fluids and materials.
2. It is often difficult to find analytical solutions. Therefore numerical schemes are highly depended
on. Sometimes, new numerical schemes are required to solve a specific problem.
3. Transport data in the entry regions should be considered.
4. The final Nusselt and Sherwood numbers are highly dependent on materials, duct geometries,
and operating conditions. The traditional way of estimating mass transfer coefficients from heat
transfer coefficients with analogy correlations is not valid anymore.
Due to these new features and new difficulties, a comprehensive analysis and data collection of the
conjugate heat and mass transfer in ducts are highly desired, both for industries and for academics.
xv
xvi Foreword
Regretfully, such studies are still very limited now. It is ridiculous that nowadays, transport data in
old textbooks that are proposed for traditional heat transfer-only in simple cases, are usually adopted
in the design and optimization of emerging novel heat and mass exchangers. This is a dilemma
facing us.
Over the past 15 years, the author of this book, Professor Li-Zhi Zhang, has conducted a sys-
tematic study of the conjugate heat and mass transfer in the ducts of heat and mass exchangers. The
basic transport phenomena in the ducts were investigated and new data on Nusselt and Sherwood
numbers for these ducts were disclosed. He published many papers in this area. However, the data on
this topic is quite sporadic and a systematic introduction is still not available. From this background
Professor Zhang wrote this book: Conjugate Heat and Mass Transfer in Heat Mass Exchanger
Ducts.
This is the first book that systematically presents the conjugated heat and mass transfer in ducts of
various heat and mass exchangers. The basic physical phenomena in these ducts are introduced. The
governing equations for mass, momentum, and energy are presented and solved. Detailed numerical
schemes to solve these conjugate problems are given. The detailed finite difference forms to solve the
equations are specifically presented. The techniques of coordinate transformations from the physical
domain to computational domain on various duct cross-sections are elucidated. The final algebraic
forms of the partial differential equations are presented. The iterative procedures to solve these multi-
elements and non-linear equations are also introduced. The methods to treat the conjugate boundaries,
either steady state or transient, are introduced. Most of them are from the experiences of the author in
solving them, besides the knowledge from classical textbooks. Experimental procedures and results are
presented to validate the calculation results with various practical heat and mass exchangers. To some
extent, this is also a reference book for numerical heat and mass transfer. Finally the detailed transport
data for duct of various heat and mass exchangers is presented: adsorbent beds, desiccant wheels, mem-
brane total heat exchangers, membrane contactors, either in parallel-plates type, plate-fin type, plate-fin
and tube type, or in hollow fiber bundles type.
Based on the fundamental heat mass transfer data, this book illustrates some examples of the
applications of novel heat and mass exchangers. For instance, air dehumidification by honeycomb
adsorbent beds, air dehumidification and energy recovery by desiccant wheels, heat and moisture
recovery by membrane total heat exchangers, air humidification by hollow fiber membrane contac-
tors, air dehumidification by solutions with parallel-plates or hollow fiber membrane contactors.
Both the working theories and the heat and mass transfer problems are discussed. The exchangers
are constructed and their performances are optimized with the obtained heat and mass transfer
data.
This book combines theoretical analysis with engineering practices. It covers a wide range of
knowledge from fundamental heat mass transfer, to novel systems design and performance analysis,
from materials introduction, characterization, to heat and mass exchanger thermodynamics and fluid
dynamics. It can also provide insights and design guidelines for the other heat and mass exchangers,
in various industries like air conditioning, energy engineering, mechanical engineering, chemical engi-
neering, environmental engineering, food and drug engineering, etc.
This book is a cross-disciplinary endeavor which relies heavily on numerical heat mass transfer.
I hope peer researchers, engineers, and research students could benefit from the methodologies exhib-
ited in this analysis and extend them to the analyses of other energy and environmental systems.
Foreword xvii
At last, let me extend my congratulations to Professor Zhang on his new book. I hope he can con-
tinue his researches on this topic, which in no doubt, will benefit both industrial progress and academic
developments.
Professor Wenquan Tao
Academician of the Chinese Academy of Science
Xi’an Jiaotong University
Xi’an, China
Email: [email protected]
CHAPTER
1
An Introduction to Conjugate
Heat and Mass Transfer in Ducts
1.1 Heat and mass transfer ducts
Energy and the environment are of increasing concern today, because mankind is facing greater energy
and environmental problems than ever before. According to a report released recently [1], world energy
consumption is projected to increase by 47% from 2010 through 2035. Most of the growth is projected
for emerging economies outside the OECD (Organization for Economic Cooperation and Development),
where robust economic growth is accompanied by increased demand for energy. Total non-OECD
energy use grows by 72%, compared with an 18% increase in OECD energy use. Energy consumption
in non-OECD Asia shows the most robust growth among the non-OECD regions, rising by 91% from
2010 to 2035. However, strong growth also occurs in many of the rest of the non-OECD regions: 69%
in Central and South America, 65% in Africa, and 62% in the Middle East. Accompanying energy use,
global carbon emissions from fossil fuels have significantly increased since 1900. Emissions increased
by over 16 times between 1900 and 2008 and by about 1.5 times between 1990 and 2008. It is projected
that the trend will continue for the next decades. These two factors have led to many energy and envi-
ronmental problems such as fossil fuel depletion, global warming, ozone depletion, air pollution, new
diseases, etc. The increased concerns with regard to energy and environmental problems have placed
demands on new technologies.
To date, many new technologies are emerging to help to solve these energy and environmental
problems. New types of equipment are invented to reclaim waste heat and to increase energy utiliza-
tion efficiency; for example, total heat exchangers, desiccant wheels, etc. Other new equipment is
constructed to get rid of air pollution from our environment, from either air or water, for example air
cleaners and water cleaners. The basic processes in these types of equipment are heat and mass transfer.
The nature of these processes is that substances and energy are transported from one place to another,
and from one medium to another. Energy and pollutants are treated, transferred and processed in terms
of heat and mass transfer. Without heat and mass transfer, energy and environmental problems cannot
be controlled. All these novel forms of equipment can be called heat and mass exchangers.
Ducts are the basic units in these heat and mass exchangers. There is no site to accomplish heat
and mass transfer without these ducts. They provide the interfaces for gases, solids and liquids to make
Conjugate Heat and Mass Transfer in Heat Mass Exchanger Ducts. http://dx.doi.org/10.1016/B978-0-12-407782-9.00001-0 1
© 2014 Elsevier Inc. All rights reserved.
2 CHAPTER 1 An Introduction to Conjugate Heat and Mass Transfer in Ducts
contact and be transported. These ducts are usually very fine and are numerous, to provide sufficient
area for gas-solid or gas-liquid contact. So the basic transport phenomenon in these small ducts, or
channels, is the key for system design and performance optimization. Here are some examples.
Figure 1.1 shows a total heat exchanger unit for the reclamation of waste heat from buildings.
The whole machine includes two fans, the ducting work for the two flows and the sealing walls sepa-
rating the two flows, and the shell. The heart of the machine is the core. Figure 1.2 shows the core
inserted in the total heat exchanger [2]. It is in either a parallel-plate ducts or a plate-fin ducts struc-
ture. Figure 1.3 shows a schematic of the heat and moisture exchange between the outside air and
the indoor air through these numerous ducts. It is a cross-flow membrane based total heat exchanger.
Because the heat and mass transfer between a solid surface and an air stream is usually very low, to
achieve the required magnitude of treatment capability, large contact areas between the two flows are
required. Therefore the cores are made of numerous fine channels.
With total heat exchangers, the efficiency of the existing HVAC systems can be improved sub-
stantially. With them, 20–40% of the energy use for air conditioning can be saved. The reason is that
normally the fresh air is dehumidified by through condensation in a cooling coil followed by a re-
heating process, which is very energy intensive. This energy can be saved if total heat exchangers are
installed to reduce the dehumidification load. Besides energy conservation, total heat exchangers have
the additional benefits of ensuring a sufficient supply of fresh air, which is crucial for the prevention of
epidemic respiratory diseases such as SARS and bird flu. As can be seen from Figure 1.2, the exchanger
is composed of numerous ducts. Fresh air and exhaust air exchange heat and moisture simultaneously
in these ducts. In this way, fresh air is dehumidified and cooled by the exhaust air in summer and heated
and humidified by the exhaust air in winter. The hot and humid incoming fresh air becomes cool and
dry in summer, thus decreasing the cooling load in summer. The cold and dry incoming fresh air is
heated and humidified in winter, thus decreasing the heating load in winter. The ducts are the basic
units for heat and moisture exchange between fresh air and exhaust air in a total heat exchanger. Two
FIGURE 1.1
A total heat exchanger for heat and moisture recovery.
1.1 Heat and Mass Transfer Ducts 3
FIGURE 1.2
The core inserted in the total heat exchanger.
FIGURE 1.3
Schematic of heat and mass transfer through ducts of a total heat exchanger.