Compact Heat Exchangers Kays And London PdfBy D'Arcy C. In and pdf 25.01.2021 at 22:24 9 min read
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Compact Heat Exchangers is a compilation of experimental data on the basic heat transfer and flow friction characteristics of "compact" heat exchanger surfaces, i. The data have a wide application, including space heating, spacecraft heat exchangers, aircraft heat exchangers, and cooling systems of all kinds.
- Compact Heat Exchangers by W. M. Kays A. L. London (z-lib.org).pdf
- Compact Heat Exchangers
- ISBN 13: 9781575240602
Compact Heat Exchangers by W. M. Kays A. L. London (z-lib.org).pdf
Compact Heat Exchangers. All rights reserved. No Part of this publication may be reproduced or transmitted in any form or by any means—electronic or mechanical, including photocopy, recording, or any information storage and retrieval system—without permission in writing from the publisher.
Disclaimer: Every effort has been made to avoid any error or omission in this publication. It may be noted that neither the author nor the publisher will be responsible for any damage or loss of action to any one of any kind, in any manner, therefrom. The authors, editors, contributors and the publisher have, as far as it is possible, taken care to ensure that the information given in this text is accurate and up-to-date.
However, readers are strongly advised to confirm that the information complies with current standards of practice. Every effort has been made where necessary to contact holders of copyright to obtain permission to reproduce copyright material.
If any have been inadvertently overlooked, the publisher will be pleased to make the necessary arrangements at the first opportunity. Most of the nomenclature is defined as it is introduced or else is obvious from the context of its use.
However, it is summarized here for convenience. Any consistent dimensioning system may be used. All the heat transfer and flow-friction parameters are presented in nondimensional form so that a shift to a preferred system of dimensions presents no complications.
Wcp maxl. Subscripts a Air side av Average C Cold-fluid side of heat exchanger h Hot-fluid side of heat exchanger i Refers to inner surface of an annular passage or inner radius of a circular fin L Coupling liquid in a liquid-coupled heat exchanger rn Mean conditions, defined as used o Refers to conditions at surface, or specifically to inner surface of an annular passage or inner radius of a circular fin p Refers to one pass of a multipass heat exchanger r Matrix rotor w Wall; water side x Local conditions 00 Conditions far downstream ii Conditions at inner surface of an annular passage when the inner surface alone is heated 00 Conditions at outer surface of an annular passage when the outer surface alone is heated 1,2 Indicate different sides of the heat exchanger; inlet and outlet conditions max Maximum min Minimum lrna Log mean average.
The following symbols and systems of units are used: English SI. In the SI, gc has the value of unity and is dimen- sionless. Note the dimensions consistently employed for the following properties, coefficients, and variables: English SI.
Table A-IS in App. A contains a set of conversion factors for shifting from one system of units to another, including some of the commonly used archaic units. Preface to the Reprint Edition Since the edition went out of print about three years ago the authors have received a continuous stream of letters and phone calls, primarily from people engaged in design of compact heat exchangers, or in design studies, all wanting to know how they could purchase or otherwise get their hands on a copy.
It soon became evident that there exists really no adequate substitute for this compilation of design data. This reprint is essentially the same as the previous edition with errors corrected and thus does not include any data obtained since that date, although the amount of such recent data appears to be small.
So it does still include the largest collection of compact heat exchanger data available in the world today and is still unique in that all of these data are presented in a consistent manner so that comparisons can be readily made. A large portion of these data was obtained in a single test system which simply adds to comparability as well as reliability.
The availability of a large collection of data for heat transfer surfaces with relatively small geometric differences also makes it feasible to infer with some confidence the behavior of other, non-tested, heat transfer surfaces by inter- polation. Until a more complete compilation of data becomes available it is our hope that this edition will satisfy the needs of heat exchanger designers in all those various fields involving heat transfer to and from gases where light weight and small size are of critical importance.
It is now 19 years since the second edition of Compact Heat Exchangers was published. In the intervening years manufacturing techniques have been devel- oped to fabricate some of the older compact surface configurations using high- temperature materials, new surface configurations with superior flow charac- teristics have been manufactured, and the area per unit volume has been increased substantially. The research program which generated the original data on which this book is based was slowed down and eventually terminated, but a number of the newer surfaces were tested using essentially the same techniques as were used for the earlier work.
In the meantime new research on some of the theoretical solutions for flow in the simple geometries has rendered obsolete some of the solutions presented in the second edition. The same thing can be said of the solutions for the transient behavior of heat exchangers. The availability of new data and more modern solutions suggested that the time was appropriate for a new edition.
This edition does not differ radically from its predecessor but it does contain the basic test data for 11 new surface configurations, including some of the very compact ceramic matrices. In addi- tion to modernization of the theoretical solutions and correlations for simple geometries, and the transient solutions, a number of other improvements will be found. Finally, the slow conversion at least in the United States to the Systeme Internationale SI system of units suggested that the time had come to make that conversion in Compact Heat Exchangers.
Since the English system is apparently destined to disappear only slowly in the United States, it was decided to intro- duce a dual system of units in the new edition.
So all dimensions are given in both systems, and the fluid properties in the Appendix are likewise presented in both systems. A unique feature of Compact Heat Exchangers has always been that virtually all of the basic test data originate from a single research program under the supervision of the authors. There is thus no question about the comparability of the test results of one surface to another. In recent years additional data have been obtained by others, but the authors have chosen to maintain the original tradition so that there is almost complete internal consistency.
Kays A. For many years the only generally available basic heat transfer and flow-friction data of sufficient accuracy for heat-exchanger design was for flow through and over banks of circular tubes.
The need for small-size and lightweight heat exchangers in all varieties of powered vehicles from automobiles to spacecraft, as well as in a multitude of other applications, has resulted in the development of many heat transfer surfaces that are much more compact than can be practically realized with circular tubes. In addition, many of these surfaces possess other characteristics that are superior to circular tubes.
However, lack of basic heat transfer and flow-friction design data, and a lack of understanding of the basic mechanisms involved, for a long period of time restricted their use to heat exchangers that could be developed by cut-and-try methods. It ultimately became apparent that rationally optimized heat-exchanger design, the develop- ment of new surfaces of superior characteristics, and the development of methods of fabrication of compact surfaces for high-temperature service could only take place after the basic characteristics of the already existing surfaces were known and understood.
Recognizing the need for such data the U. In , the Office of Naval Research, in cooperation with the Bureaus of Ships and Aeronautics, extended this work by establishing a similar program at Stanford University. Later the Atomic Energy Commission joined in support.
Most of the test cores were of low-temperature construction employing soldering or brazing techniques. However, the primary objective of this pro- gram was to investigate the effects of geometry on convective heat transfer and flow-friction performance, with the hope that the geometrical advantages would provide incentive for the development of high-temperature fabrication tech- niques and of new superior surfaces.
Since the first publications of the results of the program, both kinds of developments have indeed occurred. Kays, A. London, and D. In , Compact Heat Exchangers, by W.
Kays and A. London, was published; it contained a considerable additional body of basic data from the test program, as well as data from other investigators. Following the publication of Compact Heat Exchangers, the test program was continued, and new test cores were obtained, some of which were developed directly as a result of the earlier work.
This second edition of Compact Heat Exchangers contains all the new basic data that have been obtained, as well as extensive revisions and additions to the chapters on analytic solutions for flow in tubes, an extension of the chapter on heat exchanger design theory, and a new chapter on the transient behavior of heat exchangers; various other sections have been brought up to date in the light of more recent research.
The basic data section has been expanded to include the characteristics of 25 new surfaces, and this section, reporting the characteristics of more than 90 surfaces, remains the real core of the book.
Although too numerous to name specifically, the authors take this opportu- nity to acknowledge the assistance over the past 15 years of the approximately 60 Stanford University mechanical engineering students who participated in various phases of the test program. Without their assistance this book could never have been written.
The design of a heat exchanger involves a consideration of both the heat transfer rates between the fluids and the mechanical pumping power expended to overcome fluid friction and move the fluids through the heat exchanger. For a heat exchanger operating with high-density fluids, the friction-power expendi- ture is generally small relative to the heat transfer rate, with the result that the friction-power expenditure is seldom of controlling influence.
However, for low-density fluids, such as gases, it is very easy to expend as much mechanical energy in overcoming friction power as is transferred as heat. And it should be remembered that in most thermal power systems mechanical energy is worth 4 to 10 times as much as its equivalent in heat.
It can be readily shown that for most flow passages that might be used for the heat transfer surfaces of an exchanger, the heat transfer rate per unit of surface area can be increased by increasing fluid-flow velocity, and this rate varies as something less than the first power of the velocity.
The friction-power expendi- ture is also increased with flow velocity, but in this case the power varies by as much as the cube of the velocity and never less than the square. It is this behavior that allows the designer to match both heat transfer rate and friction pressure-drop specifications, and it is this behavior that dictates many of the characteristics of different classes of heat exchangers. If the friction-power expenditure in a particular application tends to be high, the designer can reduce flow velocities by increasing the number of flow passages in the heat exchanger.
This will also decrease the heat transfer rate per unit of surface area, but according to the above relations the reduction in heat transfer rate will be considerably less than the friction-power reduction.
The loss of heat transfer rate is then made up by increasing the surface area length- ening the tubes , which in turn also increases the friction-power expenditure, but only in the same proportion as the heat transfer surface area is increased. In gas-flow heat exchangers the friction-power limitations generally force the designer to arrange for moderately low mass velocities.
Thus large amounts of surface area become a typical characteristic of gas-flow heat ex- changers. Gas-to-gas heat exchangers may require up to 10 times the surface area of condensers or evaporators or Iiquid-to-liquid heat exchangers in which the total heat transfer rates and pumping-power requirements are comparable. For example, a regenerator for a gas-turbine plant, if it is to be effective, requires several times as much heat transfer surface as the combined boiler and con- denser in a steam power plant of comparable power capacity.
These considerations have led to the development of many ways to construct heat transfer surfaces for gas-flow applications in which the surface area density is large. Such surfaces will be referred to here as compact heat transfer surfaces. Several typical compact heat transfer surface arrangements are illustrated in Fig. Perhaps the simplest and most common surface arrangement for a two-fluid heat exchanger is the circular tube bundle shown in Fig.
This arrangement, of course, has long been used for both high- and low-density fluids, but the only way in which surface area density can be substantially increased is to decrease the diameter of the tubes. Fabrication difficulties and cost place a rather severe limitation on what can be accomplished in this direction, and large heat ex- changers with tube diameters of less than tin.
An effective way to increase surface area density is to make use of secondary surfaces, or fins, on one or both fluid sides of the surface. Figure I-lb illustrates a finned circular tube surface in which circular fins have been attached to the outside of circular tubes.
Such an arrangement is frequently used in gas-to-liquid heat exchangers where optimum design demands a maximum of surface area on the gas side.
Fins could be used in a liquid-to-liquid heat exchanger, or on the liquid side of a gas-to-liquid heat exchanger, but here another difficulty arises.
The low friction-power requirement characteristic of high-density fluids, to- gether with the relatively high thermal conductivity of liquids, results in high convection heat transfer rates in any optimum design high heat transfer coeffi- cients.
If fins are employed, the high heat transfer rates must be conducted along the fins, and the conduction resistance may destroy all or most of the advantage of the extra surface area gained see the discussion of fin effectiveness in Chap.
Another popular variation of the flnned-tube arrangement is shown in Fig. Here the tubes are illustrated as flat, but they can also be circular.
In compact gas-to-gas heat exchangers, large area density is desirable on both fluid sides, and a method for accomplishing this objective with fins is illustrated by the plate-fin arrangement of Figs.
I-ld and e. The heat exchanger is built up as a sandwich of flat plates bonded to interconnecting fins. The two fluids are carried between alternate pairs of plates and can be arranged in either counter- flow or crossflow, which provides an added degree of flexibility in this arrange- ment. Figure I-Ie also illustrates another variation; the nns can be interrupted rather than continuous, an arrangement which alters the basic convection heat transfer and flow-friction characteristics in a manner that will be discussed presently.
Introduction 3. In the periodic-flow-type heat exchanger, energy is transferred by convec- tion and stored in a matrix, from which it is later given up to the other fluid. Figure I-If illustrates one such compact matrix, which could be built up of stacks of solid rods or stacks of wire screens.
Compact Heat Exchangers
Compact Heat Exchangers A. London, W. Kays Publisher: Krieger Publishing Company. Latest Developments in Heat exchanger Technology. Compact heat exchangers are the types having large surface area per unit.
Compact Heat Exchangers. All rights reserved. No Part of this publication may be reproduced or transmitted in any form or by any means—electronic or mechanical, including photocopy, recording, or any information storage and retrieval system—without permission in writing from the publisher. Disclaimer: Every effort has been made to avoid any error or omission in this publication. It may be noted that neither the author nor the publisher will be responsible for any damage or loss of action to any one of any kind, in any manner, therefrom. The authors, editors, contributors and the publisher have, as far as it is possible, taken care to ensure that the information given in this text is accurate and up-to-date.
Embed Size px x x x x Compact Heat Exchanger Design, Kays and London, Compact Heat Exchangers, Shah, Editor, Begell House Kays and London Kays, and London, The heat transfer between the twostreams is represented using the heat flux,
ISBN 13: 9781575240602
The purpose of this paper is to present a novel and applied method for optimum designing of plate-finned heat exchanger network. Considering the total annual cost as the objective function, a network of plate-finned heat exchanger is designed and optimized. Accurate evaluation of plate-finned heat exchanger networks depends on different fin types with 10 different geometrical parameters of heat exchangers. In this study, fin numbers are considered as the main decision variables and geometrical parameters of fins are considered as the secondary decision variables. The algorithm applies heat transfer and pressure drop coefficients correction method and differential evolution DE algorithm to obtain the optimum results.
London Professor of. Views 13 Downloads 3 File size 13MB. Chapter Seven Heat Exchangers 7. DOI: No Part of this publication may be reproduced or transmitted in any form or by any means—electronic or mechanical, including photocopy, recording, or any information storage and retrieval system—without permission in writing from the publisher.
Compact Heat Exchangers A. London, W.
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