Heat Pipes: Theory, Design and Applications

Heat Pipes: Theory, Design and Applications

by David Reay

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Heat Pipes 6th edition is an essential guide for practicing engineers and an ideal text for postgraduate students. This book takes a highly practical approach to the design and selection of heat pipes.

This new edition has been updated with new information on the underlying theory of heat pipes and heat transfer, fully updated applications, new data


Heat Pipes 6th edition is an essential guide for practicing engineers and an ideal text for postgraduate students. This book takes a highly practical approach to the design and selection of heat pipes.

This new edition has been updated with new information on the underlying theory of heat pipes and heat transfer, fully updated applications, new data sections, updated chapters on design and on electronics cooling applications. Reay’s book is a useful reference as well as an accessible introduction for those approaching the topic for the first time.

Editorial Reviews

The standard work on the subject, providing the background required by those wishing to use or to design heat pipes. The development of the heat pipe is discussed and a wide range of applications described. This revised and updated edition takes into account the introduction of new working fluids, and extended life test data; new types of heat pipes; and some of the latest uses. Annotation c. Book News, Inc., Portland, OR (booknews.com)
From the Publisher
"Overall…an excellent book that covers the subject in great depth for the benefit of heat pipe designers and users…Engineers will no doubt continue to stretch the boundaries of heat pipe technology, and this book would be a valuable addition to the technical library of any engineer working with heat pipes."—MachineBuilding.net, June 4, 2014 "…outlines the theory, design, and applications of heat pipes, including their historical development, heat transfer and fluid flow theory relevant to the operation of the classical wicked heat pipe, analytical techniques, components and materials and compatibility data, and testing…This edition has been revised to integrate new information on the underlying theory of heat pipes and heat transfer and has new data on thermosyphons, applications, and manufacturing methods."—ProtoView.com, February 2014

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Elsevier Science
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7.50(w) x 9.70(h) x 0.80(d)

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Heat Pipes

By D.A. Reay P.A. Kew


Copyright © 2006 David Reay and Peter Kew
All right reserved.

ISBN: 978-0-08-046477-0

Chapter One


The heat pipe differs from the thermosyphon by virtue of its ability to transport heat against gravity by an evaporation–condensation cycle. It is, however, important to realise that many heat pipe applications do not need to rely on this feature, and the Perkins tube, which predates the heat pipe by several decades and is basically a form of thermosyphon, is still used in heat transfer equipment. The Perkins tube must therefore be regarded as an essential part of the history of the heat pipe.


Angier March Perkins was born in Massachusetts, USA at the end of the eighteenth century, the son of Jacob Perkins, also an engineer. In 1827, A.M. Perkins came to England, where he subsequently carried out much of his development work on boilers and other heat distribution systems. The work on the Perkins tube, which is a two-phase flow device, is attributed in the form of a patent to Ludlow Patton Perkins, the son of A.M. Perkins in the mid-nineteenth century. A.M. Perkins, however, also worked on single-phase heat distribution systems, with some considerable success, and although the chronological development has been somewhat difficult to follow from the papers available, the single-phase systems preceded the Perkins tube, and some historical notes on both systems seem appropriate.

The catalogue describing the products of A.M. Perkins & Sons Ltd, published in 1898, states that in 1831 A.M. Perkins took out his first patent for what is known as 'Perkins' system of heating by small bore wrought iron pipes. This system is basically a hermetic tube boiler in which water is circulated in tubes (in single phase and at high pressure) between the furnace and the steam drum, providing an indirect heating system. The boiler using hermetic tubes, described in UK Patent No. 6146, was produced for over 100 years on a commercial scale. The specification describes this closed cycle hot water heater as adapted for sugar making and refining evaporators, steam boilers and also for various processes requiring molten metals for alloying or working of other metals at high temperatures, suggesting that the tubes in the Perkins system operate with high-pressure hot water at temperatures well in excess of 150 °C.

The principle of the 'ever full' water boiler, as devised in the United States by Jacob Perkins to prevent the formation of a film of bubbles on the inner wall of the heat input section of the tubes, is applied as described in the above patent.

'As water expands about one-twentieth of its bulk being converted into steam, I provide about double that extra space in the "expansion tube" which is fitted with a removable air plug to allow the escape of air when the boiler is being filled. With this space for the expansion of the heated water the boiler is completely filled, and will at all times be kept in constant contact with the metal, however high the degree of heat such apparatus may be submitted to; and at the same time there will be no danger of bursting the apparatus with the provision of the sufficient space as named for the expansion of the water'.

In 1839 most of the well-known forms of A.M. Perkins hot water hermetic heating tubes were patented in UK Patent No. 8311, and in that year a new invention, a concentric tube boiler, was revealed. The hot water closed circuit heating tubes in the concentric tube system were fork-ended and dipped into two or more steam generation tubes. These resembled superheater elements as applied on steam locomotives and a large boiler operating on this principle would consist of many large firetubes, all sealed off at one end and traversed by the inner hot water tubes, connected up externally by U bends. This proved to be the most rapid producer of superheated steam manufactured by the Perkins Company and was even used as the basis for a steam actuated rapid firing machine gun, offered to the US Federal Government at the time of the Civil War. Although not used, they were 'guaranteed to equal the efficiency of the best Minie rifles of that day, but at a much lower cost for coal than for gun powder'. The system was, however, used in marine engines, '... it gives a surprising economy of fuel and a rapid generation, with lightness and compactness of form; and a uniform pressure of from 200 lbs to 800 lbs per sq. in., may be obtained by its use'.

Returning to the Perkins hermetic tube single-phase water circulating boiler, as illustrated in Fig. 1.1, some catalogues describe these units as operating at pressures up to 4000 psi and being pressure-tested in excess of 11 000 psi. Operators were quick to praise the cleanliness, both inside and outside, of the hermetic tubes after prolonged use.

The first use of the Perkins tube, i.e. one containing only a small quantity of water and operating on a two-phase cycle, is described in a patent by Jacob Perkins (UK Patent No. 7059, April 1936). The general description is as follows:

'One end of each tube projects downwards into the fire or flue and the other part extends up into the water of the boiler; each tube is hermetically closed to prevent escape of steam. There will be no incrustation of the interior of the tubes and the heat from the furnace will be quickly transmitted upwards. The interior surfaces of the tubes will not be liable to scaleage or oxidation, which will, of course, tend much to preserve the boiler so constructed.' The specification says 'These tubes are each one to have a small quantity of water depending upon the degree of pressure required by the engine; and I recommend that the density of the steam in the tubes should be somewhat more than that intended to be produced in the boiler, and, for steam and other boilers under the atmospheric pressure, that the quantity of water to be applied in each tube is to be about 1:1800 part of the capacity of the tube; for a pressure of 2 atm to be two 1:1800 parts; for 3 atm, three 1:1800 parts, and so on, for greater or less degrees of pressure, and by which means the tubes of the boiler when at work will be pervaded with steam, and any additional heat applied thereto will quickly rise to the upper parts of the tubes and be given off to the surrounding water contained in the boiler – for steam already saturated with heat requires no more (longer) to keep the atoms of water in their expanded state, consequently becomes a most useful means of transmitting heat from the furnace to the water of the boiler'.

The earliest applications for this type of tube were in locomotive boilers and in locomotive fire box superheaters (in France in 1863). Again, as with the single-phase sealed system, the cleanliness of the tubes was given prominent treatment in many papers on the subject. At the Institution of Civil Engineers in February 1837, Perkins stated that following a 7-month life test on such a boiler tube under representative operating conditions, there was no leakage or incrustation, no deposit of any kind occurring within the tube.


Reference has already been made to several patents taken by A.M. Perkins and J. Perkins on hermetic single-phase and two-phase heating tubes, normally for boiler applications. The most interesting patent, however, which relates to improvements in the basic Perkins tube, is UK Patent No. 22272, dated 1892, and granted to L.P. Perkins and W.E. Buck: 'Improvements in Devices for the Diffusion or Transference of Heat'.

The basic claim, with a considerable number of modifications and details referring to fluid inventory and application, is for a closed tube or tubes of suitable form or material, partially filled with a liquid. While water is given as one specific working fluid, the patent covers the use of antifreeze type fluids as well as those having a higher boiling point than water.

It is obvious that previous work on the Perkins tube had revealed that purging of the tubes of air, possibly by boiling off a quantity of the working fluid prior to sealing, was desirable, as Perkins and Buck indicate that this should be done for optimum operation at low temperatures (hence low internal pressures) and when it is necessary to transmit heat as rapidly as possible at high temperatures.

Safety and optimum performance were also considered in the patent, where reference is made to the use of 'suitable stops and guides' to ensure that tubes refitted after external cleaning were inserted at the correct angle and with the specified amount of evaporator section exposed to the heat source (normally an oil, coal or gas burner). Some form of entrainment had also probably occurred in the original straight Perkins tube, particularly when transferring heat over considerable distances. As a means of overcoming this limitation, the patent provides U bends so that the condensate return occurs in the lower portion of the tube, vapour flow to the heat sink taking place in the upper part.

Applications cited included heating of greenhouses, rooms, vehicles, dryers, and as a means of preventing condensation on shop windows, the tubes providing a warm convection current up the inner face of the window. Indirect heating of bulk tanks of liquid is also suggested. The use of the device as a heat removal system for cooling dairy products, chemicals and heat exchanging with the cooling water of gas engines is also proposed, as its use in waste heat recovery, the heat being recovered from the exhaust gases from blast furnaces and other similar apparatus, and used to preheat incoming air.

On this and other air/gas heating applications of the Perkins tube, the inventors have neglected to include the use of external finning on the tubes to improve the tube-to-gas heat transfer. Although not referring to the device as a Perkins tube, such modifications were proposed by F.W. Gay in US Patent No. 1725906, dated 27 August, 1929, in which a number of finned Perkins tubes or thermosyphons are arranged as in the conventional gas/gas heat pipe heat exchanger, with the evaporator sections located vertically below the condensers, a plate sealing the passage between the exhaust and inlet air ducts, as shown in Fig. 1.2. Working fluids proposed include methanol, water and mercury, depending upon the likely exhaust gas temperatures.


The main use of the Perkins tube was in baking ovens. One of the earliest forms of baking ovens to which the Perkins tube principle was applied was a portable bread oven supplied to the British army in the nineteenth century. In common with static ovens employing the Perkins tube, the firing was carried out remote from the baking chamber, the heat being transferred from the flames to the chamber by the vapour contained within the tubes. The oven operated at about 210 °C, and it was claimed that the fuel savings using this type of heating were such that only 25 per cent of the fuel typically consumed by conventional baking ovens was required.

A more detailed account of the baking oven is given in Ref. This paper, published in 1960 by the Institution of Mechanical Engineers, is particularly concerned with failures of the tubes used in these ovens, and the lack of safety controls which led to a considerable number of explosions in the tube bundles.

Gas or oil firing had replaced coal and coke in many of the installations, resulting in the form of an oven shown in Fig. 1.3, in which 80 tubes are heated at the evaporator end by individual gas flames. This illustration shows the simplest form of Perkins tube oven in which straight tubes are used. Other systems employ U tubes or a completely closed loop, as put forward by Perkins and Buck as a method for overcoming entrainment. In the particular oven under consideration, maximum oven temperatures were of the order of 230 °C.

One feature of interest is the very small evaporator length, typically less than 5 cm, of many ovens. This compares with a typical overall tube length of 3 m and a condenser section of about 2.5 m depending upon the thickness of the insulating wall between the furnace and the oven. The diameter of the tubes is typically 3 cm and the wall thickness can be considerable, of the order of 5–6 mm. Solid drawn tubes were used on the last Perkins ovens constructed, with one end closed by swaging or forging prior to charging with the working fluid. Originally seam-welded tubes or wrought iron tubes were used. The fluid inventory in the tubes is typically about 32 per cent by volume, a very large proportion when compared with normal practice for heat pipes and thermosyphon, which generally have much longer evaporator sections, in addition. However, Perkins and Buck, in proposing a larger fluid inventory than that originally used in the Perkins tube, indicated that dryout had been a problem in earlier tubes, leading to overheating, caused by complete evaporation of the relatively small fluid inventory.


Excerpted from Heat Pipes by D.A. Reay P.A. Kew Copyright © 2006 by David Reay and Peter Kew. Excerpted by permission of Butterworth-Heinemann. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Meet the Author

David Reay manages David Reay & Associates, UK, is a Visiting Professor at Northumbria University, Researcher at Newcastle University, and Honorary Professor at Nottingham University, UK. His main research interests are compact heat exchangers, process intensification, and heat pumps. He is also Editor-in-Chief of Applied Thermal Engineering and Author/Co-author of eight other books, including the second edition of Process Intensification published in 2013.

Ryan McGlen is Senior Advanced Technologies Engineer at Thermacore Europe Ltd. where he leads research and development of future heat pipe technologies. Current research interests include novel heat pipe materials and working fluids combinations and additive layer manufacture of aluminium heat pipes with complex 3D Sintered Style wicks (SSHP).

Peter Kew first became involved in heat pipes in the late 1970s as a research officer with International Research and Development working on a range of heat transfer and energy conservation projects, including heat pipe development which was then led by David Reay. He has maintained this interest for over 20 years as a Lecturer and Senior Lecturer at Heriot-Watt University researching evaporative heat transfer. Currently Dr Kew is Associate Head of the School of Engineering and Physical Sciences, Heriot-Watt University responsible for the School’s activities on the Dubai Campus of the University.

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