EP3217137A1 - Device for thermally cooling an object from a cold source such as a cryogenic fluid bath - Google Patents

Abstract

The cooling device comprises: A first heat exchange element (2) with the cold source (1); A set of first heat exchange fins (3) connected to the first heat exchange element (2) at one of their ends; A second heat exchange element (4) with the object to be cooled (200); A set of second heat exchange fins (5) connected to the second heat exchange element (4) at one of their ends; An enclosure (6) containing: the first fins (3) and the second fins (5) interposed and without direct mechanical contact with each other, each fin being inserted into an interstitial space, and a heat exchange gas (7) at a desired internal pressure;     According to the invention, the other end of each fin (3, 5), opposite the end connected to the heat exchange element (2, 4), carries a positioning wedge adapted to position, advantageously center, said fin in the interstitial space in which it is inserted.

Description

Technical field of the invention

The invention relates to a device for thermal cooling of an object constituting a hot source, from a cold source such as a bath of cryogenic fluid.

State of the art

• le refroidissement homogène d'une plaque supérieure d'une grande cellule cryogénique de Rayleigh-Bénard ;
• des tests de propriétés réalisés sur des matériaux à froid ;
• la recherche de températures critiques de matériaux supraconducteurs.

Many applications require temperature control at cryogenic temperatures (i.e., less than 120 K) of an object or element constituting a hot source. As illustrative examples, the following applications may be mentioned:

• homogeneous cooling of an upper plate of a large Rayleigh-Bénard cryogenic cell;
• property tests carried out on cold materials;
• the search for critical temperatures of superconducting materials.

In order to obtain a stable cryogenic temperature, a known solution relies on the use of a saturation bath containing a saturated cryogenic fluid (for example helium), in liquid form, acting as a cold source. The temperature of the saturation bath is set by the nature of the fluid and its pressure. For a given pressure, the temperature of the cryogenic bath is fixed. From this saturation bath, an object can be cooled to a temperature close to that of the bath. For example, one can immerse the object in the bath, entirely or partially. The heat received by the object is evacuated by evaporation of the bath fluid. This solution is, however, not very flexible because it is limited to cooling at a temperature close to that of the bath, which is fixed by the nature of the fluid and its pressure. On the figure 1 , we have shown the evolution of the saturation temperature (expressed in Kelvin) of several cryogenic fluids as a function of the pressure of the fluid in question. To obtain a desired cooling temperature, it is possible to choose the most suitable cryogenic fluid, that is to say that allowing easy access to the desired temperature, and to put the fluid at the pressure that is suitable for achieving this desired temperature. . However, as is apparent from the figure 1 there are temperature differences between the various cryogenic fluids such that even by varying the choice of fluid and the pressure variation, certain temperature values can not be reached. For example, it is particularly difficult to control the temperature of an object at a stable temperature in the temperature range between 5.2K and 15K with a saturated cryogenic fluid bath.

Different solutions exist to obtain a desired temperature outside the easily accessible temperatures by means of a cryogenic fluid bath. Take the example of an experiment requiring to cool an object at a temperature of 6 K from a saturation helium bath having a fixed temperature equal to 4.2 K.

A first solution consists in placing a thermal resistance between the fluid bath (cold source) and the object to be cooled (hot source). The thermal resistance makes it possible to evacuate the heat of the object and to obtain a controlled temperature difference between the bath and the object to be cooled. However, this solution has the disadvantage of significantly increasing the cryogenic fluid consumption when one seeks to obtain a temperature which is away from that of the bath.

A second solution is based on the use of a natural convection cell within which the gas density is varied to vary the thermal conductance. This solution is however not satisfactory because the variation in gas density is difficult to master, particularly in the vicinity of the critical and two-phase conditions of the exchange gas, and the behavior of the fluid is particularly unstable due to the natural convection phenomenon.

A third solution uses components called "thermal gas switches" to establish or remove (or almost eliminate), at will, a thermal connection between two parts. The document WO2007 / 147981 describes an example of a gas thermal switch. The performance of such a thermal switch depends in particular on its cutoff ratio. This parameter corresponds to the ratio of the maximum thermal conductance of the switch (corresponding to the ON or "closed" position of the switch) on the minimum thermal conductance of the switch (corresponding to the OFF or "open" position of the switch. 'light switch). This type of switch, comprising simple workpieces, is used for small refrigerating powers.

The present invention improves the situation.

Object of the invention

• un premier élément d'échange thermique avec la source froide ;
• un ensemble de premières ailettes d'échange thermique reliées au premier élément d'échange thermique, à l'une de leurs extrémités ;
• un deuxième élément d'échange thermique avec l'objet à refroidir ;
• un ensemble de deuxièmes ailettes d'échange thermique reliées au deuxième élément d'échange thermique, à l'une de leurs extrémités ;
• une enceinte contenant :
  • les premières ailettes et les deuxièmes ailettes intercalées et sans contact mécanique direct entre elles, chaque ailette étant insérée dans un espace interstitiel,
  • et un gaz d'échange thermique à une pression interne souhaitée ;

caractérisé en ce que l'autre extrémité de chaque ailette, opposée à l'extrémité reliée à l'élément d'échange thermique, porte une cale de positionnement adaptée pour positionner, avantageusement centrer, ladite ailette dans l'espace interstitiel dans lequel elle est insérée.For this purpose, the invention relates to a device for thermal cooling of an object, from a cold source, in particular a cryogenic fluid bath, comprising:

• a first heat exchange element with the cold source;
• a set of first heat exchange fins connected to the first heat exchange element, at one of their ends;
• a second heat exchange element with the object to be cooled;
• a set of second heat exchange fins connected to the second heat exchange element, at one of their ends;
• an enclosure containing:
  • the first fins and the second fins intercalated and without direct mechanical contact between them, each fin being inserted into an interstitial space,
  • and a heat exchange gas at a desired internal pressure;

characterized in that the other end of each fin, opposite the end connected to the heat exchange element, carries a positioning wedge adapted to position, advantageously center, said fin in the interstitial space in which it is inserted.

The architecture of the cooling device of the invention is close to that of a thermal switch with an exchange gas, as described in the document US 2005/0230097 , adapted for heat exchanges of low power typically between 0.01 W and 0.3 W. It differs in particular in that it comprises wedges positioning or centering fins. The presence of these wedges degrades the cutoff ratio of the device. Their use is therefore a priori not desirable within such a device. In the invention, the structure of a standard thermal switch is modified by adding wedges positioning or centering fins, which increases the size of the device and divert the use to ensure the thermal cooling of an object with a higher exchanged thermal power level, up to several watts.

In a particular embodiment, the cooling device comprises an element for adjusting the heat exchange gas pressure in the enclosure or a pump for introducing and extracting heat exchange gas into the enclosure, for varying the thermal conductance of said cooling device, by varying the internal pressure of the gas in the enclosure.

Thanks to this, the cooling device of the invention makes it possible to regulate in temperature the object to be cooled (that is to say to maintain the temperature of this object equal or substantially equal to a desired set temperature) from a cold source at a fixed temperature.

Advantageously, the wedges are made of a plastic material. The material is advantageously a thermal insulator. This limits the thermal bridge effect between fins adjacent wedges.

Preferably, the shims have a coefficient of linear thermal expansion greater than that of the fins. Thanks to this, the wedges contract more than the fins during thermal cooling, which avoids a mechanical degradation of the wedges under the action of compression of the fins during temperature changes.

In a particular embodiment, each fin comprises a free fixing end of reduced thickness intended to be introduced into a fixing groove in the wedge carried by said fin. Thanks to this, the wedges can be fixed to the fins by simple interlocking or sliding.

Advantageously, each wedge comprises three external bearing faces, including two lateral faces and a bottom face, in contact with walls delimiting the interstitial space in which said wedge is inserted and in that each lateral face of support of the wedge is connected to the bearing bottom face of the wedge by an oblique face which is not in contact with said walls. Thanks to this, it limits the heat exchange surface between the wedge carried by a fin and the or neighboring fins.

Advantageously, the distance between two adjacent fins, respectively connected to the first heat exchange element and the second heat exchange element, is less than or equal to 0.5 mm, advantageously less than or equal to 0.3 mm, advantageously still equal to 0.1 mm. The reduced distance between neighboring fins suppresses natural convection and allows the exchange between the fins 3 and 5 only by gas conduction. This is improved by reducing the distance (inversely proportional). Due to this small gap between the neighboring fins, it is necessary to avoid any deformation of the fins. Indeed, the deformation of a fin It could cause a direct mechanical contact of the latter with a neighboring fin, which would have the effect of considerably impairing the proper functioning of the cooling device. The wedges make it possible to avoid such deformations by mechanically holding the fins in position.

In a particular embodiment, the first heat exchange element is thermally connected to heat exchange fins intended to be immersed in the cold source. With these fins, the heat transfer between the cold source and the first heat exchange element is improved.

In a particular embodiment, the pump is an adsorption pump containing an adsorbent, a heating module and a thermal connection element to said cold source, intended to evacuate heat. The cold source is also used by the pump to adjust its internal temperature.

The cooling device may comprise a saturated cryogenic fluid bath, acting as a cold source, said fluid comprising one of the elements of the group comprising helium, hydrogen, neon, nitrogen, oxygen and argon.

Advantageously, the enclosure carries a welding lip to a sealing lip ring. The use of welding lips makes it possible to limit the rise in temperature of the shims during the assembly of the various elements of the cooling device.

Advantageously, the length of the wedge carried by a fin is less than the width of said fin.

Advantageously, each fin carries at least two shims.

Brief description of the drawings

• La figure 1 représente l'évolution de la température de saturation de plusieurs fluides cryogéniques en fonction de la pression du fluide ;
• La figure 2 représente de façon schématique le dispositif de refroidissement de l'invention, selon une première forme de réalisation particulière ;
• La figure 3A représente une vue de côté du dispositif de refroidissement de l'invention, selon la première forme de réalisation ;
• La figure 3B représente une vue en coupe selon AA du dispositif de refroidissement de la figure 3A ;
• La figure 3C représente une vue de dessus du dispositif de refroidissement de la figure 3A ;
• La figure 4A représente de façon schématique les flux de chaleur échangés entre les ailettes en « position ON » de transfert thermique ;
• La figure 4B représente de façon schématique les flux de chaleur échangés entre les ailettes en « position OFF » d'interruption thermique ;
• La figure 5 représente un schéma d'une cale, en section transversale.

The invention will be better understood with the aid of the following description of a particular embodiment of the cooling device of the invention, with reference to the appended drawings in which:

• The figure 1 represents the evolution of the saturation temperature of several cryogenic fluids as a function of the fluid pressure;
• The figure 2 schematically represents the cooling device of the invention, according to a first particular embodiment;
• The figure 3A represents a side view of the cooling device of the invention, according to the first embodiment;
• The figure 3B represents a sectional view along AA of the cooling device of the figure 3A ;
• The figure 3C represents a top view of the cooling device of the figure 3A ;
• The Figure 4A schematically represents the heat fluxes exchanged between the fins in "ON" position of heat transfer;
• The Figure 4B schematically represents the heat flows exchanged between the fins in "OFF" position of thermal interruption;
• The figure 5 represents a diagram of a wedge, in cross section.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS OF THE INVENTION

The thermal cooling device of the invention has the function of cooling an object, the latter constituting a hot source, from a cold source, for example a bath of cryogenic fluid.

• refroidir de façon homogène une plaque supérieure d'une cellule de Rayleigh-Bénard de grande dimension, notamment dans le cadre de l'étude de la convection naturelle turbulente ;
• réaliser des tests d'étude de propriétés sur des matériaux froids à des températures cryogéniques ;
• rechercher des températures critiques de matériaux supraconducteurs ;
• réaliser des mesures de calorimétrie ;
• réaliser une désaimantation adiabatique pour la grande réfrigération ;
• réaliser un refroidissement homogène.

Such a device can be used in multiple applications, for example:

• homogeneously cool an upper plate of a large Rayleigh-Bénard cell, particularly in the study of turbulent natural convection;
• Conduct property tests on cold materials at cryogenic temperatures
• search for critical temperatures of superconducting materials;
• perform calorimetry measurements;
• perform adiabatic demagnetization for large refrigeration;
• perform a homogeneous cooling.

• une source froide 1 ;
• un premier élément 2 d'échange thermique avec la source froide 1 ;
• un ensemble de premières ailettes d'échange thermique 3 reliées au premier élément d'échange thermique 1, à l'une de leurs extrémités ;
• un deuxième élément 4 d'échange thermique avec l'objet à refroidir 200 ;
• un ensemble de deuxièmes ailettes d'échange thermique 5 reliées au deuxième élément d'échange thermique 4, à l'une de leurs extrémités ;
• une enceinte 6 contenant les deux ensembles 3, 5 de premières et deuxièmes ailettes et un gaz d'échange thermique 7 à une pression interne souhaitée.

On the figure 2 schematically an exemplary embodiment of the cooling device 100 of the invention is shown schematically. He understands

• a cold source 1;
• a first heat exchange element 2 with the cold source 1;
• a set of first heat exchange fins 3 connected to the first heat exchange element 1, at one of their ends;
• a second heat exchange element 4 with the object to be cooled 200;
• a set of second heat exchange fins 5 connected to the second heat exchange element 4, at one of their ends;
• an enclosure 6 containing the two sets 3, 5 of first and second fins and a heat exchange gas 7 at a desired internal pressure.

The cold source 1 is here a bath of cryogenic fluid. It has a fixed temperature. In the particular embodiment described here, the bath contains saturation liquid helium at a temperature equal to or close to 4.5 K (ie - 269 ° C). The cryogenic fluid could alternatively be hydrogen, neon, nitrogen, oxygen, argon or the like.

The heat exchange element 2 with the cold source 1 and the heat exchange element 4 with the object to be cooled 200 are thermal conducting elements. They are made of a material constituting a good thermal conductor, for example copper, and here have a disc shape.

The element 2 of heat exchange with the cold source 1 is thermally connected to the cold source 1 here constituted by the cryogenic fluid bath 1. For this purpose, it is in direct contact with the cryogenic fluid, here by immersion of the one of the faces of the thermal conductive disk, called the "submerged face" 20, in the cryogenic fluid bath 1. The submerged face 20 of the conductive element 2 can be extended longitudinally by third heat exchange fins 9 disposed at the bottom interior of the bath 1, as shown in figure 2 . These fins 9 heat exchange with the bath 1 can improve the heat transfer between the bath 1 and the heat exchange element 2.

The other side (or side) 21 of the heat exchange element 2, opposite to the immersed face 20, is extended longitudinally by the first heat exchange fins 3. These are confined in the internal chamber of the tube exchanger 6. Thereafter, the term "cold fins" will be called the first fins 3 because they are thermally connected to the cold source 1.

The assembly comprising the first heat exchange element 2, the first heat exchange fins 3 and the third heat exchange fins 9 form here a single piece. It is machined from a cylinder full of a good thermal conductor material, here copper. To obtain the fins 3 and 9, grooves are machined in planes parallel to each other and to the longitudinal axis of the cylinder. Each fin 3 or 9 thus extends in a plane parallel to the longitudinal axis and has the shape of a partial longitudinal slice of cylinder. In the exemplary embodiment shown on the figure 3B , the conductive disc 2 carries ten first fins 3 and five third fins 9. The conductive disc 2 and the cylindrical envelope of the third fins 9 have a diameter which is slightly smaller than the internal diameter of the exchanger tube 6. The first fins 3 have a cylindrical casing of diameter equal to or substantially equal to that of the internal diameter of the exchanger tube 6.

In a similar way, the heat exchange element 4 is extended longitudinally by the second fins 5. These are also confined in the internal chamber of the exchanger tube 6. Thereafter, the second fins will be called "hot fins". because they are thermally connected to the object to be cooled 200. The heat exchange element 4 and the hot fins 5 form here a single piece. This is made from a solid cylinder made of a good thermal conductor material, in this case copper. The hot fins 5 may be formed by machining grooves in the copper cylinder in planes parallel to each other and to the longitudinal axis of the cylinder. Each fin 5 thus extends in a plane parallel to the longitudinal axis and has the shape of a partial longitudinal portion of the cylinder. In the exemplary embodiment shown on the figure 3B , the conductive disc 4 carries eleven second fins 5. The diameter of the conductive disc 4 is greater than the internal diameter of the exchanger tube 6. The fins 5 have a cylinder-shaped envelope of diameter equal to or substantially equal to that of the internal diameter of the tube exchanger 6.

In the particular embodiment, not limiting, described here, the first and second fins 3 and 5 have a height (in the longitudinal direction) of about 160 mm and a thickness (perpendicular to the plane of the fin) of 2 , 5 mm. The interstitial space, or gap, separating two adjacent fins 3 (or 5) integral with the same heat exchange element 2 (or 4) is here 2.7 mm. The width of a fin (in the direction perpendicular to the longitudinal direction in the plane of the fin) is less than or equal to the diameter of the disc 2 (or the internal diameter of the exchanger tube 6), here equal to 55.5 mm, and varies according to its position: the fins or fins disposed near or on the longitudinal axis of the cylinder are wider than those disposed at the outer periphery. The fins 3 could have other dimensions, including a thickness of between 1 and 10 mm, a height of between 10 and 500 mm and a maximum width of between 10 and 200 mm.

The machining of the fins 3, 5 and 9 can be performed by electroerosion.

The enclosure 6 is sealed. It comprises a wall here cylindrical which forms a tube of longitudinal axis AX, enclosing a receiving chamber of the first "cold" fins 3 and second "hot" fins 5. Thereafter, this tube will be called "heat exchanger tube" or "exchanger tube" because its internal chamber is the heat exchange seat between the first fins 3 "cold" and the second fins 5 "hot", interposed between them, as will be explained later. This exchanger tube 6 is for example stainless steel. Stainless steel has several advantages: it can be soldered easily, especially with copper, and has a low thermal conduction, which limits the thermal conduction in the OFF position. The stainless steel heat exchanger tube 6 thus advantageously has a low thermal conductivity. The exchanger tube 6 has a diameter less than or equal to 70 mm, advantageously less than or equal to 65 mm, advantageously still equal to 60 mm and advantageously still greater than or equal to 20 mm. The diameter of the tube depends on the power to be exchanged.

The first heat exchange element 2 is disposed at one end of the tube 6. It is here inserted inside the tube 6 and secured thereto by means of a sealing ring 13. welding lip.

The second heat exchange element 4 is disposed at the other end of the tube 6, opposite to that receiving the first heat exchange element 2. Its diameter is here greater than the external diameter of the tube 6 and it is abutted against this other end of the tube 6 by means of another sealing ring 16 to welding lip, as will be explained later.

The first fins 3, thermally connected to the first element 2 of heat exchange with the cold source 1, and the second fins 5, thermally connected to the second element 4 of heat exchange with the object to be cooled 200, are arranged at the inside the exchanger tube 6, or the enclosure. They are interposed between them and without direct mechanical contact between them. Each cold fin 3 is inserted into an interstitial space separating two adjacent hot fins 5 or a hot fin 5 and the inner face of the exchanger tube 6. Similarly, each hot fin 5 is inserted into an interstitial space separating two cold fins 3 adjacent or cold fin 3 and the inner face of the exchanger tube 6. In the embodiment described here, once the first fins 3 and the second fins 5 introduced into the exchanger tube 6 and nested, interposed between the other, the clearance or gap formed between two adjacent fins, respectively cold 3 and hot 5, is 0.1 mm. Similarly, the gap between each of the two peripheral fins (here hot fins 5), and the inner face of the exchanger tube 6 is of the order of 0.1 mm.

The free end of each fin 3 (or 5), opposite to that integral with the associated heat exchange element 2 (or 4), carries at least one positioning wedge 8 adapted to position, here center, this fin 3 (or 5) in the interstitial space in which it is inserted. The wedge 8 carried by the fin 3 (or 5) makes it possible to ensure the centering of this fin in the interstitial space in which it is received and to avoid any deformation of the fin, thanks to a forced holding in the center interstitial space.

The shims 8 are made of another thermally insulating material, having a low thermal conductivity, advantageously less than or equal to 0.2 Wm ^-1 .K ^-1 or less than 0.3 Wm ^-1 .K ^-1 . For example, they are about plastic, in particular polyimide plastic. They are preferably not metal or metal alloy.

The constituent material of the shims 8 advantageously has a coefficient of linear thermal expansion greater than that of the material constituting the fins 3, 5 (in this case copper). As a result, the thermal contraction of the wedges 8 is greater than that of the fins 3, 5, which makes it possible to prevent damage to the wedges by the fins when they contract under the effect of cooling.

On the figure 5 schematically shows a wedge 8, according to a particular embodiment, in cross section. The shim 8 intended to be carried by a fin 3 (or 5) comprises three outer bearing faces 80-82: two lateral faces 80, 81 and a bottom face 82. When the shim 8 carried by a fin 3 (or 5) is inserted in an interstitial space between two fins 3, 5 or between a fin 5 and the wall of the exchanger tube 6, the two lateral faces 80, 81 of the shim 8 are in contact with the lateral walls delimiting the interstitial space and the bottom surface 82 is in contact with the heat exchange element 4 (or 2) forming the bottom of the interstitial space. Each lateral bearing face 80, 81 of the wedge 8 is connected to the bearing base face 82 by an oblique face 83, 84 which is not in contact with the walls delimiting the interstitial space. Thanks to this, the heat exchange surface is reduced between the shim 8 and the neighboring elements (fin 3 or 5, heat exchange element 2 or 4 or exchanger tube 6), which contributes to limiting the effect of " thermal bridge "(that is to say thermal transfer) wedges 8. The thickness of the bottom of the shim is chosen so as to ensure a desired spacing of the fins 3 (or 5) relative to the element d heat exchange 4 (or 2) to limit the heat exchange between these fins 3 (or 5) and the heat exchange element 4 (or 2) and thus further reduce the effect of "thermal bridge" shims 8. This bottom thickness is advantageously between 1 and 10 mm.

Preferably, as shown on the figures 2 , 4A and 4B each wedge is in permanent contact (without play) with the side walls of the interstitial space in which it is located. More preferably, each shim is also in permanent contact (without play) with the fin on which it is mounted or fixed. These different contacts can be more or less prestressed. Thus, the fin can not move laterally except to compress the material forming the wedge.

Preferably, as shown on the figures 2 , 4A and 4B each wedge is in permanent contact (without play) with the bottom of the interstitial space in which it is located. More preferably, each shim is also in permanent contact (without play) with the end face of the fin on which it is mounted or fixed. Thus, the fin can not move axially towards the bottom of the interstitial space except compressing the material forming the wedge.

Each wedge thus makes it possible to immobilize a fin at least laterally, that is to say perpendicularly to the main faces of the fin or horizontally in the planes of the fins. figures 2 , 4A and 4B . Each wedge can also make it possible to immobilize a fin at least axially, that is to say parallel to the main faces of the fin or vertically in the planes of the fins. figures 2 , 4A and 4B .

The mounting situation in contact or prestressed between the shims and the fins is found at room temperature, for example at 20 ° C. Indeed, during cooling, the differential contraction between the materials of the wedges and fins contributes to reducing the contacts between the wedges and the fins, or even ideally to remove them.

Each fin 3 (or 5) may carry at its free end, opposite to that integral with the associated heat exchange element 2 (or 4), one or more positioning wedges, or centering, 8. In the case where the fin 3 (or 5) carries a single shim 8, the length of the shim 8, that is to say its dimension according to the direction perpendicular to the axis AX in the plane of the fin, is equal to the width of the fin or less than it. In the case where the fin 3 (or 5) carries several shims 8, the different shims carried by a fin are spaced from each other and preferably distributed uniformly along the fin so as to ensure a good mechanical support of the fin. For example, each fin 3, 5 carries two shims.

Fixing wedges 8 to the fins 3 (or 5) can be made by interlocking a projecting part of one of the two elements (wedge or fin) in a recessed portion formed in the other element (fin or wedge) . For example, each fin 3 (or 5) comprises a fixing free end, of reduced thickness, intended to be introduced into an attachment groove 85 formed in the shim 8. The groove 85 has a shape complementary to that of the fixing end of the fin and here has a U-shaped cross section. The depth of the groove 85 is advantageously between 1 and 10 mm. The width of the groove 85 is advantageously between 1 and 10 mm.

The wedges 8 have a symmetry with respect to a median plane which extends here in the middle of the groove 85 perpendicular to the plane of the figure 5 . In addition, they have a width, orthogonal to this plane of symmetry, which is equal to the width of the interstitial space between two adjacent fins 3 and 5 (here 2.7 mm). This symmetry makes it possible to ensure the centering of the fin in the interstitial space in which it is inserted.

Preferably, a shim generally has a parallelepipedal shape of which two parallel edges are chamfered (between the faces 81 and 82 and between the faces 80 and 82). The chamfers form the oblique faces 83 and 84. The parallelepipedal shape also has the groove 85 or groove 85. This groove is intended to be fixed, for example by interlocking on one end of a fin, in particular to be fixed by example by interlocking on a tongue 86 formed at one end of a fin.

The shims are used to relatively position the fins and avoid their contacts which could be related to a release of the constraints in the fins and thus to the deformation of the fins (following their machining).

Note that the absence of direct mechanical contact between the cold fins 3 and hot 5 interposed between them, guaranteed by the wedges 8, is very important to ensure proper operation of the cooling device 100. Indeed, the thermal conductivity of the copper constituting the fins is much higher than that of the heat exchange gas 7 separating the fins 3 cold 3 and hot 5. The least direct mechanical contact between these fins would have the effect of considerably modify the heat flows between the cold fins 3 and the hot fins 5 in OFF position.

The exchanger tube 6 is closed by the first heat exchange element 2, at one of its ends, and by the second heat exchange element 4, at its other end. It contains a confined internal heat exchange chamber which contains the first fins 3 and the second fins 5. This heat exchange chamber is sealed, as will be explained later. It contains a heat exchange gas 7 at a desired internal pressure. This heat exchange gas is one of those previously mentioned for the bath 1 of cryogenic fluid (hydrogen, neon, nitrogen, oxygen, argon or other). Generally, the heat exchange gas used is the same as that of the bath 1 constituting the cold source.

The assembly comprising the tube (or enclosure) 6, the heat exchange elements 2 and 4, the first and second heat exchange fins 3, 5 and the heat exchange gas 7 allows a transfer of heat between the source 1 and the object to be cooled 200. This device has a certain thermal conductance which depends in particular on the internal pressure of the gas 7 in the chamber 6. By varying this pressure, the thermal conductance of the device can be varied. 'invention.

To vary the thermal conductance, the cooling device 100 comprises an element for adjusting the heat exchange gas pressure in the enclosure, for example here a pump 10 for introducing and extracting heat exchange gas 7 in the internal chamber of the chamber 6. The pressure variation of the heat exchange gas in the chamber makes it possible to obtain a variation of the thermal conductance and thus makes it possible to regulate the temperature of the second heat exchange element 4 that is to say to maintain this temperature equal to or substantially equal to a desired value, regardless of the temperature variations of the object to be cooled, from the cold source (here bath 1) at a fixed temperature .

• un adsorbant logé dans une chambre interne ;
• un module de chauffage comportant par exemple une résistance électrique (reliée à une source d'alimentation électrique),
• un élément de liaison thermique à une source froide destiné à évacuer de la chaleur, et
• un module de pilotage.

In the particular embodiment described herein, the pump 10 is an adsorption pump containing the following elements:

• an adsorbent housed in an internal chamber;
• a heating module comprising for example an electrical resistance (connected to a power supply),
• a thermal connection element to a cold source for discharging heat, and
• a steering module.

The pump 10 here uses the cryogenic fluid bath 1 as a cold source. It is connected to the bath 1 by a calibrated braid acting as thermal resistance. The control module controls the operation of the thermal resistance to adjust the internal temperature of the pump 10 and therefore the temperature of the adsorbent. The adsorbent here comprises grains of activated carbon, for example carbonized coconut (activated carbon), housed in an internal chamber of the pump 10. In operation, gas atoms 7 stick to the surface of the grains of carbon. coal forming layers. The number of layers of exchange gas atoms bonded to the grains of coal depends on the temperature of the grains, in other words on the internal temperature of the pump 10. By varying this internal temperature, using the heating module, the control module can modulate the amount of gas trapped by the pump 10 and thus vary the internal pressure of the gas 7 in the chamber 6.

The inner chamber of the tube 6 is connected to a filling tube or capillary 12A, via a barrel 12B. Initially, heat exchange gas 7 is introduced into the chamber from an external gas supply (not shown) by the filling capillary. The internal chamber of the tube 6 is also connected to a capillary or tube 11 for connection to the pump 10. The pump 10 is thus mounted on the exchanger tube 6, advantageously close to the adjacent end of the cryogenic bath 1. Two openings of receiving the capillary 11 and the barrel 12B are formed in the wall of the tube 6.

The heat exchange gas pressure adjusting element in the chamber enables the thermal conductance of the thermal cooling device to be adjusted and controlled actively and at will. Thus, the thermal conductance of the thermal cooling device can be set to a given value independently of other physical parameters, in particular regardless of the temperature of the cold source and / or the temperature of the object to be cooled.

The first heat exchange element 2 is assembled to the exchanger tube 6 via the ring 13. In this case, it is a flap or lip ring. The end of the ring 13 carrying the flap (or the lip) is introduced into the end portion of the tube 6 and mounted around the heat exchange disk 2. The ring 13 is here fixed to the exchange element 2 by soldering and the tube 6 by TIG welding at the lip (or flap). The ring 13 protrudes out of the tube 6. It is secured, at its other end (opposite to that carrying the flap or the lip), to another ring 14 for adaptation to a reservoir containing the bath 1 of cryogenic fluid (no represented on the Figures 3A and 3B ), here by TIG welding. The adaptation ring 14 is secured here by TIG welding, to a flange 15 for connection to the tank of the bath 1. This connecting flange 15 is intended to be fixed, by means of a seal, to the tank, to the right to an adapted opening formed therein. The lip ring 13, the adapter ring 14 and the connecting flange 15 are here made of stainless steel.

The tube 6 is connected to the second heat exchange element 4 by means of the other other lip seal ring 16. The ring 16 is mounted around a solid cylinder portion connecting the second fins 5 and the element 4 of heat exchange. It has, at one of its ends, a lip in the form of a flange which is secured to another lip-shaped flange provided at the end of the exchanger tube 6, here by TIG welding. The other end of the ring 16 is joined by brazing to the heat exchange element 4.

The heat exchange element 4 is here secured, for example by screwing, to the object to be cooled, as shown in FIG. figure 3B . The assembly can also be made by direct contact, by welding or, for the sake of ease of assembly, with the aid of an intermediate piece (for example copper).

• fabrication d'une première pièce monobloc comportant les premières ailettes 3, les troisièmes ailettes 9 et l'élément d'échange thermique 2 à partir d'un premier cylindre en cuivre, ici par électroérosion ;
• fabrication d'une deuxième pièce monobloc comportant les deuxièmes ailettes 5 et l'élément d'échange thermique 4 à partir d'un deuxième cylindre en cuivre, ici par électroérosion ;
• brasure des bagues 13 et 16 respectivement aux éléments 2 et 4 d'échange thermique ;
• mise en place d'une partie des cales 8, soit au fond des espaces interstitiels entre ailettes, soit directement sur les extrémités libres des ailettes ;
• emboîtement des deux pièces précédemment fabriquées, avec intercalation des premières ailettes 3 et des deuxièmes ailettes 5 ;
• mise en place des cales restantes 8 ;
• assemblage du tube 6, du capillaire de connexion 6, de la pompe 10, du canon 12B et du capillaire remplissage 12A ;
• mise en place du tube 6 autour des ailettes 3, 5, par le haut (c'est-à-dire par la partie comportant les ailettes 9 d'échange thermique avec le bain 1) ;
• soudure TIG « au torchon mouillé » (afin limiter la montée en température au voisinage des cales) de la lèvre de la bague 13 au tube 6 et de la lèvre de la bague 16 à la lèvre du tube 6 ;
• soudure de la bague 14 d'adaptation au réservoir à la bague 13 et à la bride de raccordement 15 ;
• raccordement de la bride 15 au réservoir de bain de fluide cryogénique ;
• fixation de l'élément d'échange thermique 3 à la bride de raccordement 17 et raccordement de celle-ci à l'objet à refroidir ;
• vidage du tube échangeur 6, remplissage de celui-ci avec du gaz d'échange thermique 7 par le capillaire 12A puis scellage du capillaire 12A ;
• remplissage du réservoir en fluide cryogénique afin d'obtenir le bain 1 ;
• mise en fonctionnement de la pompe 10 afin de régler la pression interne du gaz dans le tube 6.

The manufacture of the cooling device 100 advantageously comprises the following steps:

• manufacturing a first piece comprising the first fins 3, the third fins 9 and the heat exchange element 2 from a first copper cylinder, here by electroerosion;
• manufacturing a second one-piece part comprising the second fins 5 and the heat exchange element 4 from a second copper cylinder, here by electroerosion;
• brazing of the rings 13 and 16 respectively to the elements 2 and 4 of heat exchange;
• placing part of the wedges 8, either at the bottom of the interstitial spaces between the fins, or directly on the free ends of the fins;
• nesting of the two previously manufactured parts, with intercalation of the first fins 3 and second fins 5;
• setting up the remaining holds 8;
• assembly of the tube 6, the connecting capillary 6, the pump 10, the barrel 12B and the filling capillary 12A;
• placing the tube 6 around the fins 3, 5, from above (that is to say, by the part comprising the fins 9 of heat exchange with the bath 1);
• Wet TIG "wet towel" (to limit the rise in temperature in the vicinity of shims) of the lip of the ring 13 to the tube 6 and the lip of the ring 16 to the lip of the tube 6;
• welding of the ring 14 for adaptation to the reservoir to the ring 13 and to the connection flange 15;
• connecting the flange 15 to the cryogenic fluid bath tank;
• fixing the heat exchange element 3 to the connection flange 17 and connecting it to the object to be cooled;
• emptying the exchanger tube 6, filling it with heat exchange gas 7 by the capillary 12A and then sealing the capillary 12A;
• filling the reservoir with cryogenic fluid in order to obtain the bath 1;
• operating the pump 10 to adjust the internal pressure of the gas in the tube 6.

• soudage TIG du canon de connexion 12B au tube 6 ;
• brasure à l'étain du capillaire de remplissage 12A au canon 12B ;
• collage de grains de charbon (environ vingt grains ici) dans le fond d'une chambre interne de la pompe 10 ;
• fixation d'un couvercle de fermeture de la chambre interne de la pompe 10 au capillaire de connexion 11 ici par soudage TIG au torchon mouillé ;
• fermeture de la chambre interne de la pompe à l'aide du couvercle solidarisé au tube de connexion 11 ;
• fixation de l'ensemble (capillaire de connexion 11 et pompe 10) au tube étanche 6 ici par soudage TIG.

The assembly of the pump 10, the filling elements 12A, 12B and the exchanger tube 6 comprises the following sub-steps:

• TIG welding of the connection barrel 12B to the tube 6;
• tin solder of filling capillary 12A at barrel 12B;
• bonding of coal grains (about twenty grains here) in the bottom of an internal chamber of the pump 10;
• fixing a closing cap of the inner chamber of the pump 10 to the connection capillary 11 here by Wet TIG welding;
• closing the internal chamber of the pump with the lid secured to the connecting tube 11;
• fixing the assembly (capillary connection 11 and pump 10) to the sealed tube 6 here by TIG welding.

The use of welding lips makes it possible to greatly limit the rise in temperature of the device and thus to protect the plastic wedges against damage due to high temperatures. They also facilitate the subsequent disassembly of the cooling device, in particular to perform a re-centering of the fins in case of problems.

The operation of the cooling device 100 will now be described, according to a particular implementation.

It is assumed that initially the various elements of the cooling device 100 are assembled as indicated in the previously described manufacturing method. The bath 1 contains, for example, saturation liquid helium at a fixed temperature equal to approximately 4.5 K. The heat exchange fins 9 are immersed in the bath 1 and the face of the heat exchange disk 2 carrying these fins 9 is in direct contact with the cryogenic fluid. Furthermore, the internal chamber of the exchanger tube 6 is filled with heat exchange gas 7 at an internal pressure controlled by the pump 10.

• elle est fonction de la pression interne du gaz 7 dans le tube 6. Sur les figures 4A et 4B, à titre d'exemple illustratif, on a représenté schématiquement les flux de chaleur entre une ailette 3 portant une cale 8 et deux ailettes voisines 5 lorsque la pression interne du gaz d'échange 7 est maximale (figure 4A) et lorsque la pression interne du gaz d'échange 7 est nulle ou quasi-nulle (figure 4B). Dans le premier cas, le flux de chaleur passe de l'ailette 3 aux ailettes voisines 5 principalement par le biais du gaz d'échange 7. Dans le deuxième cas, un flux de chaleur résiduel passe de l'ailette aux ailettes voisines 8 par le biais de la cale 8.

With the aid of the pump 10, the internal pressure of the gas 7 is regulated inside the tube 6 in order to adjust the thermal conductance of the cooling device 100 to the energy requirements for cooling the object 200 and keeping it at a minimum. desired setpoint temperature. This thermal conductance is variable:

• it is a function of the internal pressure of the gas 7 in the tube 6. On the Figures 4A and 4B by way of illustrative example, there is shown diagrammatically the heat flows between a fin 3 carrying a wedge 8 and two neighboring fins 5 when the internal pressure of the exchange gas 7 is maximum ( Figure 4A ) and when the internal pressure of the exchange gas 7 is zero or almost zero ( Figure 4B ). In the first case, the heat flow passes from the fin 3 to the neighboring fins 5 mainly through the exchange gas 7. In the second case, a residual heat flow passes from the fin to the neighboring fins 8 through through the hold 8.

The thermal conductance of the cooling device 100 can be modulated in time as a function of the heat transfer requirements between the bath 1 and the object to be cooled 200. A temperature sensor measures the temperature of the object to be cooled 200. Measured temperature values of the object 200 are regularly transmitted to the control module of the pump 10, which consequently adjusts the internal pressure of the gas 7 (if necessary changing it over time) to obtain a stable target temperature or The cooling device 100 thus makes it possible to cool the object 200 to a desired setpoint temperature and to regulate this temperature over time, otherwise to keep the object 200 at a stable temperature. equal to or substantially equal to this set temperature, by varying the internal pressure of the exchange gas 7.

The cooling device of the invention makes it possible to control the heat transfer at cryogenic temperatures between a cold source (here a bath of cryogenic fluid) and an object to be cooled and to regulate in temperature this object, in an easy, flexible and economic. It allows a thermal regulation over a wide range of temperatures, from the same cold source and by means of internal gas pressure adjustments, simple to perform. The device of the invention has a structure similar to that of the device described in the document US 2005/0230097 but is adapted to allow heat transfer at much higher power levels. This adaptation is made possible thanks to the use of wedges 8 of positioning, or centering. These make it possible to construct a heat exchange system comprising cold fins and hot fins of large dimensions and small thicknesses, interposed between them but separated from each other by a small difference (less than or equal to 0). , 5 mm, advantageously less than or equal to 0.3 mm, advantageously still equal to 0.1 mm). This small gap between fins leads to suppress natural convection and allows the exchange between the fins 3 and 5 only by gas conduction which is improved by the reduction of the distance between fins. The shims 8 allow to intercalate the cold fins 3 and 5 hot with a reduced distance between them, without risk of deformation of the fins and direct thermal contact between them.

Note that these wedges degrade the cutoff ratio of the cooling device 100. The use of a suitable material for the realization of wedges nevertheless allows to maintain a cutoff ratio sufficient for the desired use of cooling and thermal regulation. The cutoff ratio of the cooling device 100 is for example between 40 and 100, while it is generally greater than 1000 for conventional thermal switches. By way of illustrative example, a cooling device according to the invention having a cut-off ratio of 40 would make it possible to regulate in temperature between 5.4 K and 40 K an experiment consuming 2 W of power from a bath of saturation helium having a temperature of 4.4 K, without varying the helium consumption which would be substantially 0.1 g / s. In order to obtain thermal regulation at 40 K by means of a fixed thermal resistance interposed between the saturation helium bath and the object to be regulated in temperature, it would be necessary to consume a power of approximately 800W and to consume 4 g / s helium. The deterioration of the cut ratio induced by the positioning wedges 8 of the fins in the device of the invention still allows, surprisingly, to save a large amount of cryogenic fluid.

Claims (13)

Device for the thermal cooling of an object (200), from a cold source (1), in particular a cryogenic fluid bath, comprising: A first heat exchange element (2) with the cold source (1); A set of first heat exchange fins (3) connected to the first heat exchange element (2) at one of their ends; A second element (4) for heat exchange with the object to be cooled (200); • a set of second heat exchange fins (5) connected to the second heat exchange element (4) at one of their ends; An enclosure (6) containing: the first fins (3) and the second fins (5) interposed and without direct mechanical contact with each other, each fin being inserted into an interstitial space, and a heat exchange gas (7) at a desired internal pressure; characterized in that the other end of each fin (3, 5), opposite the end connected to the heat exchange element (2, 4), carries a positioning wedge adapted to position, advantageously center, said fin in the interstitial space in which it is inserted. Device according to Claim 1, characterized in that it comprises an element (10) for adjusting the heat exchange gas pressure (7) in the chamber (6) or in that it comprises a pump (10). ) for introducing and extracting heat exchange gases (7) into the enclosure (6) for varying the thermal conductance of said cooling device by varying the internal pressure of the gas (7) in the enclosure (6). Device according to one of the preceding claims, characterized in that the wedges (8) are made of a plastic material. Device according to one of the preceding claims, characterized in that the shims (8) have a coefficient of linear thermal expansion greater than that of the fins. Device according to one of the preceding claims, characterized in that each fin (3, 5) comprises a free fixing end of reduced thickness to be introduced into a fixing groove in the wedge carried by said fin. Device according to one of the preceding claims, characterized in that each shim (8) comprises three outer bearing faces, including two side faces (80, 81) and a bottom face (82), in contact with walls defining the interstitial space in which said wedge (8) is inserted and in that each lateral bearing face (80, 81) of the wedge (8) is connected to the bearing base face (82) of the hold (8) by an oblique face which is not in contact with said walls. Device according to one of the preceding claims, characterized in that the distance between two adjacent fins (3, 5), respectively connected to the first heat exchange element (2) and the second heat exchange element (4), is less than or equal to 0.5 mm, advantageously less than or equal to 0.3 mm, advantageously still equal to 0.1 mm. Device according to one of the preceding claims, characterized in that the first heat exchange element (2) is thermally connected to heat exchange fins (9) intended to be immersed in the cold source (1). Device according to one of claims 2 to 8, characterized in that the pump (10) is an adsorption pump containing an adsorbent, a heating module and a thermal connection element to said cold source (1), intended to evacuate heat. Device according to one of the preceding claims, characterized in that it comprises a saturation cryogenic fluid bath (1) acting as a cold source, said fluid comprising one of the elements of the group comprising helium, hydrogen, neon, nitrogen, oxygen and argon. Device according to one of the preceding claims, characterized in that the chamber carries a sealing lip (60) to a sealing lip ring (16). Device according to one of the preceding claims, characterized in that the length of the shim carried by a fin is less than the width of said fin. Device according to one of the preceding claims, characterized in that each fin carries at least two shims.

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