Heat exchange – Tubular structure – Diverse materials
Patent
1988-02-12
1989-08-01
Kamen, Noah P.
Heat exchange
Tubular structure
Diverse materials
165185, 165905, 165 81, 138140, 122367R, 428408, 291574, F28F 2100
Patent
active
048526452
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns a thermal transfer layer with high transfer coefficient between two materials which can have different expansion coefficients, and its application to the cooling of a structure subjected to intense heat flux.
The materials of the invention are selected from among carbonaceous material, ceramics and metals or metal alloys. Carbonaceous materials in this sense include essentially industrial carbons graphites, and carbon-carbon composites.
STATE OF THE ART
It is generally known that, particularly if they have different expansion coefficients, such materials can be joined with a good thermal transfer only with some difficulty, and this lack of transfer can be detrimental in numerous applications.
Thus for example, in devices wherein an element of carbonaceous material must be cooled by water circulation, the fragility and porosity of the carbonaceous material generally prevent direct cooling and the element made of carbonaceous materials must be affixed to a metal element. Problems then arise concerning the mechanical fixation and the thermal contact.
Numerous cases are known wherein a structure subjected to intense heat flux is to be cooled, wherein this heat flux can be of external or internal origin in relation to the structure, which can be either a metal structure or a carbonaceous or ceramic material. The heat flux, according to circumstances, can be continuous, intermittent or pulsating.
Chemical reactors, combustion devices, continuous casting of molten metals, both fission and fusion nuclear reactors, targets which are subjected to high radiation fluxes (X-rays, lasers, etc.), or particles, which can be either continuous or pulsating, could be cited particularly. The traditional solution consists of placing assemblies of tubes in which a coolant fluid circulates inside the structure to be cooled.
The problem then is to obtain very good thermal transfer, in the course of the thermal cycles to which the structure is being subjected, between the passages in the structure and the external walls of the metal cooling tubes, despite the irregularities of the contacting surfaces which are often very rough (for instance in fusion thermonuclear reactors) and especially the different expansion coefficients of the tubes and the structure to be cooled.
In order to have an acceptable thermal transfer, clamping pressures higher than 100 kPa must be exerted between the components. Under the best circumstances, transfer coefficients on the order of 9.times.10.sup.3 W.m.sup.-2 .K.sup.-1 are obtained. Transfer coefficients are very sensitive to the surface conditions of the elements and can be reproduced only with the greatest difficulty, which is obviously quite awkward.
One method to resolve this problem is brazing. This solution, which is very effective with some materials, is costly and requires a temperature below the fusion temperature of the brazing process. Moreover, for the materials having very different expansion coefficients, it is possible in some cases to braze them by insertion of a metal sheet which accommodates the stresses. Then is it necessary to use costly and delicate metals such as molybdenum, zirconium, etc.... Finally, ceramics such as silicon carbide and nitride are extremely difficult to braze, especially if they are calcined to a density near theoretical.
The main purpose of the invention is to provide a thermal transfer which is simpler to utilize, more economical and which can be used at high temperature (above 2000 degrees C if the materials to be joined allow it).
SUMMARY OF THE INVENTION
A first object of the invention is a thermal transfer layer with high transfer coefficient between two materials which can have different expansion coefficients, characterized in that it is constituted of expanded and recompressed graphite, inserted between the materials to be joined.
The materials to be joined thermally are selected from among: carbon, polycrystalline graphites, etc. ..., carbon-carbon composites. carbide,
According to the
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Besson Daniel
Coulon Michel
Faron Robert
Kamen Noah P.
Le Carbone Lorraine
Navatome
Uranium Pechiney
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