US 3438430 A
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p 1969 KESTEMONT 3, 3
DOUBLE WALL HEAT EXCHANGER UTILIZING FLEXIBLE CONDUCTOR PLATES BETWEEN THE WALLS Filed Aug. 25, 1966 Sheet 1 of 2 INVENTOR LUCIEN KESTEHONT ATTORNEYS April 15, 1969 L. KESTEMONT 3,438,430
DOUBLE WALL HEAT EXCHANGER UTILIZING FLEXIBLE CONDUCTOR PLATES BETWEEN THE WALLS Filed Aug. 25, 1966 Sheet 2 of 2 ATTORNEYS United States Patent 17,548 Int. Cl. G05d 23/08; F28f 27/02, 13/08 U.S. Cl. 16532 2 Claims ABSTRACT OF THE DISCLOSURE A heat exchanger having two spaced walls with gas therebetween and a bimetallic flexible conductor plate engaging the walls with a force which is variable in response to temperature changes.
This invention relates to a double-walled heat-exchanger. Such exchangers prevent the consequences of leaks or breaks in a wall. In the nuclear industry, for example for the production of irradiation capsules for the NaK-water exchangers of rapid reactors, or for some fuel elements of nuclear reactors, it is in practice in many cases essential, from the safety point of view, to place double walls between the media that have to exchange calories, without permitting the slightest contact or the slightest pollution of one medium by the other. This double sealing-tightness, which is necessary among other things for the provision of leak-detecting systems in the space between the walls so as to detect the beginning of a break in good time, inevitably results in pronounced temperature drops when this inter-wall space is full of gas.
The problem might be solved or reduced by filling this space with a liquid, for example a liquid metal that conducts heat well. But if this method is adopted, there is a risk of incompatibility or reaction between the liquid metal and other materials forming, for example,
' hot medium (the fuel element, the sample to be irradiated or the calorie-carrying fluid), or between the liquid metal and the cooling carlorie-carrying fluid. Another disadvantage of this solution is that with small leakages there may be solubility in this liquid, and this prevents detection.
Another possible solution would be to use extremely thick single walls, or even to separate the hot and cold media altogether while leaving a solid connection between them. The thermal efficiency of this system is low.
Alternatively, a gas-filled space might be provided between the walls, the hot and cold structures being made continuous at certain points or in certain portions. But owing to the heat gradients between the two zones in question, any rigid connection produces mechanical stresses, which may make the system impracticable.
The invention employs another solution with a gas space. Instead of a rigid connection, it proposes a flexible connection permitting a certain amount of play and differential expansion between the two zones.
In a double-walled heat-exchanger according to this invention, flexible plates made of a material that is a good conductor of heat are disposed in the space between the two walls and engage with these two walls, so as to produce by contact, good conduction of heat between the latter, the space between the two walls is filled with a gas, there is at least one detector for contamination of the gas by leakage through a wall of the container and means for circulating the gas so that it passes (preferably slowly) through the leak detectors.
Some specific embodiments of the invention will now be 3,438,430 Patented Apr. 15, 1969 described by way of example with reference to the accompanying drawings in which:
FIGURE 1 is a cross-section of part of a heat-exchanger according to the invention,
FIGURES 2, 3 and 4 are cross-sections of heat-exchangers according to the invention, and
FIGURES 5 and 6 are cross-sections of parts of heatexchangers according to the invention, wherein the flexible plates are made of bimetallic material.
These figures only show the elements necessary for an understanding of the invention; the corresponding elements of these figures have identical reference numbers.
FIGURE 1 shows part of a heat-exchanger between a hot medium 1 and a colder medium 2, comprising two walls, the hot wall 3 and the cold wall 4, with a gas-filled inter-wall space 5 between them. So that any leakages in either of the walls 3 or 4 may be detected as soon as possible, the gas travels through a circuit (not shown), which causes it to pass through leak-detectors (also not shown). These leak-detectors may be inside or outside the space 5. The same applies to the means for setting the gas in motion.
Heat transmission between the walls 3 and 4 is effected across the space 5 by means of resiliently fiexible plates, for example 6, made of a material that is a good conductor of heat and does not absorb neutrons to any great extent, if a neutron medium is present (for example irradiation capsules or fuel elements). These plates are simply engaged against both walls 3 and 4, the force with which they engage these walls and consequently their heat-conducting properties depending essentially on their outline, thickness and elasticity. In view of their elasticity and the fact that they are not welded or attached to the walls, any differential deformations of these walls can be effected freely without causing mechanical stresses, as the plates can be deformed and slide on the walls. All that is necessary is to provide sufiicient space between two adjacent plates. To prevent these plates from moving from one position to another position nearby, it is preferable, although not essential, to form in at least one of the two walls longitudinal grooves, for example 7, in which corners or projections of the outline of the flexible plates 6 can be wedged. To make drawing easier, the plates are shown in all the figures except the last one as having V-shaped cross-sections, but other forms and other cross-sections, for example triangular, circular, trapezoidal, X-shaped or M-shaped, are suitable.
FIGURES 5 and 6 show heat-exchangers according to the invention in which the flexible conductive plates 6 are bimetallic, so that these plates tend to straighten as a result of an increase in temperature. When the temperature of the hot wall, for example, increases, the plates 6 begin to straighten and bear harder on the walls 3 and 4, thereby improving the heat conduction at the plate-wall contact surfaces. As a result, the heat-transfer properties of the exchanger are automatically controlled according to the temperature. With bimetallic plates also, of course, many shapes or cross-sections are suitable, and can be so chosen that the plates react to a temperature increase by bearing harder on the walls.
1. A heat exchanger comprising an outer wall, an inner wall disposed within said outer wall and spaced therefrom, means for circulating a gas through the space between said walls, means to detect leakage of gas through said walls, and at least one bimetallic flexible conductor plate disposed in said space and engaging said walls with a predetermined force, said plate being adapted to vary said force in response to temperature changes.
2. The heat exchanger of claim 1, wherein at least one groove is formed in at least one of said walls and is adapted to receive a corresponding end of said plate to walls 3 4 prevent said plate from moving with respect to said 3,106,526 10/1963 Wolfe et a1 176-87 X 3,216,902 11/1965 Costes et a1 176-87 X References Cited FOREIGN PATENTS UNITED STATES PATENTS r 835,297 5/1960 Great Britain. Evans X o Glfiat Bl'ltall'l. 5/1955 Bonvillian et a1. 138148 X ROBERT A *LEARY P E 8/1960 Smith 165-32 0 Timmy f 1/1962 Lovingham 165 154 X ALBERT W. DAVIS, Asszstant Exammer. 1/1963 Young 176-52 10 7/1963 Schluderberg 165-11 X 9/1963 Speidel et a1 176-58 X 165-154, 81, 185; 220-9; 176-87, 52; 138-113