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Archives of Heat Transfer
1988, Dubrovnik, Yugoslavia

DOI: 10.1615/ICHMT.1988.20thAHT


ISBN Print: 978-0-89116-877-5

ISSN: 0899-5311

HEAT TRANSFER IN LOW-TEMPERATURE INSULATION

pages 431-441
DOI: 10.1615/ICHMT.1988.20thAHT.380
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RÉSUMÉ

Thermal insulation has long been a subject of great importance to engineers and was indeed one of the major concerns in the early development of the heat transfer technology. During the period between the 1930's and 1960's, however, a multitude of new heat transfer research and developments moved the subject of insulation heat transfer from its earlier prominence to a level of stagnant obscurity. Thermal insulation had become a classical subject that was considered by many as already well developed and of concern only to the manufacturing and design engineers. In the meantime, developments in aerospace, nuclear, computing, cryogenic and other modern technologies have extended a great number of formidable engineering problems at the extreme temperature limits. Consequently, the past twenty years have registered an intensive surge of interest in thermal insulation for both high and low temperature applications.
Insulation for low temperature conditions differs in several ways from insulations for other temperature ranges. The different temperature ranges dictate the use of different insulation materials and methods that in turn result in fundamentally different thermophysical characteristics as well as transport phenomena. For example, cryogenic insulation is normally operated under vacuum conditions while high-temperature insulation often encounters oxidizing or reducing atmospheres, where material sublimation and reactivity are a major problem. Insulation technology for energy conservation at room temperatures is usually inadequate for the stringent control of heat flow necessary in cryogenics.
The importance of insulation in very low temperature applications is easily realized by noting that the latent heat of vaporization of cryogenic liquids as well as the specific heat of solids at cryogenic temperatures are much smaller than the corresponding properties at room temperatures. Therefore, it takes very little inflow of heat to boil off cryogenic liquids or to raise the system temperature. The development of better insulations for low temperatures has created tremendous growth in the field of cryogenic science, and has supported the largescale use of liquefied gases in industry and many new low-temperature devices for special applications such as cryogenic infrared sensors and Josephson junctions.
The purpose of this paper is to give some in sight into the physical processes occurring in low temperature insulations and to discuss several insulation types which represent state-of-the-art in this field. The relatively young field of cryogenics provides ample opportunity for further fundamental research to bridge the gap between the wide acceptance of newly developed cryogenic insulations and the lack of understanding about the basic underlying physical mechanisms involved. In view of the increasing interest in low temperature insulation, several monographs and review articles have been written over the past two decades [1-5]. Many important topics which could affect the thermal performance of cryogenic insulation will not be treated here: manufacturing processes, mechanical support and penetration, evaluation and test standards, systems design, etc. Discussion on these topics can be found in the literature [6, 7].

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