Heat exchange – Non-communicating coaxial enclosures
Patent
1996-08-15
1999-09-14
Atkinson, Christopher
Heat exchange
Non-communicating coaxial enclosures
165 10, 165181, 165907, F28D 710
Patent
active
059507195
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fluid-circulation heat exchanger, in particular for an electron tube. Some electron tubes have high thermal stresses. These stresses are associated with two types of factors: either the intended average power performances are at the limit of known cooling systems, or the allowed size does not make it possible to develop appropriate heat exchangers.
2. Discussion of the Background
In gridded microwave tubes, it is the anode which requires efficient cooling; in linear-beam tubes it is, in particular, the collector which must be cooled, and also the drift tubes and the cavity ports in klystrons or travelling-wave tubes with coupled cavities. Crossed-field tubes must also be cooled at their anode. As regards fast-wave tubes such as gyrotrons, it is the cavity and/or the collector which requires effective cooling.
Those heat exchangers with the best performance which are currently used operate with a fluid.
In some heat exchangers, the part to be cooled is immersed in the fluid, which is often water. This type of exchanger is limited in terms of heat-flux density because a vapour film causes stagnation at the surface of the part to be cooled. This is the burn-out phenomenon. This vapour has low thermal conductivity. The part consequently heats up enormously and the heat exchanger no longer fulfils its function. This temperature rise may lead to destruction of the part to be cooled.
One known solution consists in using a forced fluid stream at high flow rate and high pressure around the part, but this requires voluminous and expensive equipment with a compressor whose energy consumption is far from negligible. These heat exchangers nevertheless have high performance.
Another solution consists in using heat exchangers of the VAPOTRON or derived type. The term VAPOTRON is a registered trademark belongs to the company Thomson SA. They use vaporization of the liquid in contact with a hot wall, this wall being provided with reliefs which promote pulsed expulsion of the vapour, which alternately provides access of the liquid against the wall to be cooled. Liquid circulation compatible with the mains distribution is sufficient.
These heat exchangers have only made it possible to achieve continuous heat-flux densities of 1 kW/cm.sup.2 and, exceptionally, 2 kW/cm.sup.2. These performances are poorer than those of forced-circulation exchangers, but they do not require an installation delivering a forced steam of fluid. However, these heat exchangers are relatively heavy and expensive because of the bulky relief wall.
Document JP-A-53 91 164 discloses a porous body formed by thin tubes grouped in a bunch in a pipe and assembled together with the aid of molten metal.
SUMMARY OF THE INVENTION
The object of the present invention is to overcome these drawbacks. It proposes a heat exchanger which is capable of extracting heat-flux densities which are much greater than those of exchangers of the VAPOTRON type and which do not require a forced-circulation installation with high flow rate and high pressure. Furthermore, because of its high performance, this heat exchanger makes it possible to reduce the surface area of the part to be cooled. This fluid-circulation heat exchanger includes a porous body in contact with at least one portion of the part to be cooled, this porous body, made of a thermally conductive material, has pores which generate directional changes of the fluid as it passes through the porous body and which are sufficiently large for the head loss of the fluid during its passage through the porous body to be as small as possible.
The porous body may be made of a honeycombed material with communicating cells or be formed by an interlaced wire. In another variant, the porous body may be formed by a succession of partitions pierced with openings.
It is also possible for the part to be cooled and the porous body to form an integral unit.
Advantageously, the porous body may be formed by a plurality of elements pierced through b
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Denis Philippe
Dubrovin Alexis
Lixon Jean-Claude
Pelletier Jean-Jacques
Atkinson Christopher
Thomson Tubes Electroniques
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