HEAT EXCHANGER FOR A REFRIGERATION MACHINE

The present disclosure relates to a cooling device comprising a main part, a Stirling cooler arranged inside the main part, and a duct suitable for conducting a heat transfer fluid of the Stirling cooler, the cooling device being characterized in that the duct extends at least partly outside the main part.

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Description
TECHNICAL FIELD

The present disclosure concerns the field of refrigerating machines and more specifically the heat exchangers of the refrigerating machines allowing the dissipation of heat. These refrigerating machines find advantageous application in the infrared vision and/or detection equipment.

STATE OF THE ART

Infrared vision or detection equipment (for example binoculars or cameras) that allows viewing or detecting targets at night or through smoke is known.

FIG. 1 schematically represents one embodiment of infrared vision equipment J as described by the international Application WO 2019/002570. The infrared vision equipment J comprises a cooling device R, a casing 2, an optical system 3, an infrared detector 4, a processing module 5 and two display screens 6. The cooling device R has the function of maintaining the temperature of the infrared detector 4 at a very low temperature, of the order of 77 degrees Kelvin (i.e. approximately 200° C.). The optical system 3 has an optical axis Y and is arranged to transmit infrared radiation emitted by a target to the detection module 4. The detection module 4 converts the received infrared radiation into a detection signal that is transmitted to the processing module 5. The processing module 5 controls the display of an image on the display screens 6 to allow a user to view the target. To this end, the user positions their eyes in front of the display screens 6.

As schematically illustrated in FIG. 2, the cooling device R (also called refrigerating machine or micro-cooler) comprises a Stirling-type cooler 1 located in a main body M. A Stirling cooler is a machine that produces cold by exploiting the Stirling thermodynamic cycle of a heat transfer fluid. Such a Stirling cooler 1 comprises for example a movable crank 8 in rotation relative to a ball joint 7 and two pistons: a fluid compression piston 9, conventionally called “hot” piston in translation in a compression cylinder 10, and a regenerative piston 12, conventionally called “cold” piston in contrast to the hot piston and movable in translation in a regeneration cylinder 13. The compression cylinder 10 and the compression piston 9 define a first chamber 11 (compression chamber). The compression piston 9 has the function, when it is moved in translation, of compressing or expanding a fluid located in the compression chamber 11. The regeneration cylinder 13 and the regenerative piston 12 define a second chamber 14, hereinafter called expansion chamber 14. The regenerative piston 12 has the function, when it is moved in translation in the regeneration cylinder 13 of compressing or expanding the fluid located in the expansion chamber 14.

The cooler 1 further comprises a regenerator 15 arranged in the expansion chamber 14. The regenerator 15 is a hollow body adapted to store a portion of the heat energy of the fluid passing through it, when the compression piston 9 compresses the fluid located in the compression chamber 11 and then to restore this energy during an expansion of the fluid in the expansion chamber 14, caused by a displacement of the regenerator piston 12. The regenerator piston 12 is fixed to the regenerator 15, or forms a portion of the regenerator 15. The optical system 3, the infrared detector 4 and the cooler 1 are coaxial and arranged in this order in the infrared vision equipment J.

The cooler 1 further comprises a pipe 16 fluidly connecting the compression cylinder 10 and the regeneration cylinder 13. The heat transfer fluid (typically a gaseous heat transfer fluid) circulating in the pipe 16 transports heat from the compression cylinder 10 to the regeneration cylinder 13 according to a well-known method which is explained by the following steps:

    • An isothermal compression phase, during which the fluid in the compression chamber 11 is compressed by the compression piston 9 moving away from a central cavity 17.
    • An isochoric cooling phase, during which the compressed fluid is transferred from the compression chamber 11 to the expansion chamber 14 via the pipe 16. The fluid releases some of its heat energy or heat to the regenerator 15 when it passes through it. The temperature drop thus caused results in a pressure drop.
    • An isothermal expansion phase, generated by a displacement of the regenerator piston 12 towards the central cavity 17. The pressure drop causes the cooling of the fluid contained in the expansion chamber 14.
    • An isochoric heating phase, during which the fluid passes from the expansion chamber 14 to the compression chamber 11, via the pipe 16. While passing through the regenerator 15, the fluid recovers the heat it released during the isochoric cooling phase.
      However, the performance now expected for the new infrared vision equipment requires operation with larger sensors, higher cooling device powers than in the past, and significantly increased pressure of the fluid in the cooler. The use of sensors with larger dimensions, the increase of the number of acquisition pixels, and the acceleration of the refresh rates indeed require greater cooling (colder cryogenic temperature), hence the need for higher cryogenic powers. However, the sealing made by C-shaped seals between the main body M and other elements, such as a cylinder head 21 closing the expansion chamber 14, does not guarantee adequate sealing.

Moreover, the new equipment must be able to operate at higher temperatures. However, the increase of the power of the cooling device R induces an increase of the temperature in the cooler 1, which can cause overheat of the equipment due to too low heat dissipation.

Furthermore, the increase of the power of the cooling device R induces differential expansions between the different parts, which reduces reliability, while new equipment is expected to have increased reliability and significantly increased mean time until first failure.

GENERAL DISCLOSURE

One aim of the disclosure is to propose a cooling device that solves at least one of these problems, despite the increase of the operating power of the machine.

To this end, according to one aspect of the present disclosure, a cooling device is proposed comprising a main body, a Stirling cooler located inside the main body and a pipe capable of conveying a heat transfer fluid from the Stirling cooler, the cooling device being characterized in that the pipe extends at least partly outside the main body.
Such a cooling device improves the dissipation of the heat transported by the heat transfer fluid and thus promotes the operation of the cooling device at high temperature.
Advantageously, but optionally, the cooling device comprises at least one of the following characteristics, taken alone or in any combination:

    • the Stirling cooler includes a cylinder head added onto the main body, a sealing weld being interposed between said cylinder head and the main body;
    • the cooling device includes a heat exchanger in which the portion of the pipe extends at least partly outside the main body;
    • the main body and the heat exchanger are made of the same metal, in particular a metal whose thermal expansion coefficient is lower than that of aluminum;
    • the heat exchanger comprises at least one inner cooling fin extending into the pipe portion arranged in the heat exchanger, from an inner surface thereof; this fin increases the exchange surface and improves the cooling of the fluid by the heat exchanger;
    • at least a portion of an inner cooling fin has a twisted shape;
    • the heat exchanger comprises an outer cooling fin located on an outer surface of the heat exchanger and is capable of improving heat exchange between the heat exchanger and the outside;
    • the cooling device comprises a heat sink in contact with the pipe and/or the heat exchanger; this heat sink is for example made of aluminum;
    • the cooling device comprises a thermal pad in contact on the one hand with the pipe and/or the heat exchanger and on the other hand with the heat sink, the thermal pad being capable of improving the contact between on the one hand the pipe and/or the heat exchanger and on the other hand the heat sink to promote heat dissipation.
      According to another aspect, an infrared vision and/or detection device comprising an infrared detector and a cooling device, of the type proposed, for cooling said infrared detector is proposed.

DESCRIPTION OF THE FIGURES

Other characteristics, aims and advantages will emerge from the following description, which is purely illustrative and non-limiting, and which should be read in relation to the appended drawings in which:

FIG. 1 illustrates a schematic view of infrared vision binoculars;

FIG. 2 illustrates a schematic view of a cooling device;

FIG. 3 illustrates a schematic view of a cooling device with a pipe extending outside the main body, according to one embodiment of the present invention;

FIG. 4 illustrates a perspective view of a main body and of an exchanger according to one embodiment of the present invention;

FIG. 5 illustrates a perspective view of a pipe of the cooling device according to one embodiment of the present invention;

FIGS. 6A, 6B and 6C illustrate various schematic sectional and/or perspective views of a heat exchanger, according to one embodiment of the present invention;

FIG. 7 illustrates a perspective view of the shape of a cooling fin of a thermal cooler, according to one embodiment of the present invention;

FIG. 8 illustrates a sectional view of an infrared vision equipment comprising an infrared detector and a cooling device according to one embodiment of the present invention;

FIG. 9 illustrates a schematic view of a cooling device with a heat exchanger and a heat sink, according to one embodiment of the present invention.

Throughout the figures, similar elements bear identical references.

DETAILED DESCRIPTION

FIG. 3 illustrates a cooling device R of an infrared vision and/or detection equipment J illustrated in FIG. 1. The cooling device R comprises, in addition to a main body M and a cooler 1, as previously described in relation to FIG. 2, and a pipe 16 which extends outside the main body M.

The main body M is advantageously made in the mass in a single block, in order to withstand significant mechanical stresses (such as for example pressures ranging from 10 bars to several tens of bars) and thermal stresses (such as for example temperature increases of more than a hundred degrees), and to limit the number of parts in the cooling device R. The main body M has an outer surface M1 defining a shell thereof.

A portion of the pipe 16 is located outside the main body M and is capable of being fixed to the outer surface M1 thereof, as illustrated for example in FIG. 4. Advantageously, this pipe 16 extends into a heat exchanger 18 which then defines a portion 161 of the pipe 16 through which the fluid, called heat transfer fluid, is capable of passing. Subsequently, and for simplicity, the portion 161 of the pipe 16 extending outside the main body M will be called heat exchanger 18. In other words, the pipe 16 goes from the compression chamber 11 to the expansion chamber 14 and passes through the heat exchanger 18. The fluid passing through the pipe 16 is a fluid having a high heat capacity, such as helium for example. The pipe 16 is advantageously partially defined by the main body M in order to connect the compression and expansion chambers 11, 14, to the portion 161 of the pipe 16 passing through the exchanger, as illustrated by way of example in FIG. 5.

The heat exchanger 18 advantageously has an inner surface, capable of being in contact with the fluid circulating in the pipe 16, and an outer surface capable of being in contact with the outside. Advantageously, for each of the axial sections of the heat exchanger 18, the distance d between the inner surface and the outer surface of the heat exchanger 18 is less than or equal to the wall thickness of the pipe portion(s) 16 which are located in the main body M. Thus, the heat exchanger 18 improves the dissipation by conduction of the heat transported by the fluid.

The heat exchanger 18 therefore allows guaranteeing proper operation of the cooling device R, despite the increase of the operating temperature induced by the increase of the power, by dissipating the heat of the heat transfer fluid passing through it to the outside of the cooling device R. Indeed, the efficiency of the cooling device R is increased by lowering the temperature of the fluid entering the expansion chamber 14. In other words, the heat exchanger 18 allows maintaining the same temperature in the expansion chamber 14 or even a lower temperature, despite the increase of the temperature of the compression chamber 11.

In addition, the heat exchanger 18 preferably comprises one or more inner cooling fins 19. The inner cooling fin 19 is positioned on the inner surface of the heat exchanger 18 and extends into the pipe 16 so as to maximize the exchange surface with the fluid circulating therein. Advantageously, the inner cooling fin 19 is present in the pipe 16 over the entire length of the heat exchanger 18. The inner cooling fin 19 improves the dissipation of heat derived from the fluid circulating in the pipe 16. Indeed, the inner cooling fin 19, at equal heat exchanger 18 size, increases the contact surface of the heat exchanger 18 with the fluid, which improves the cooling of the fluid circulating in the pipe 16.

According to one embodiment illustrated in FIGS. 6A, 6B and 6C, the inner cooling fin 19 has, over at least one portion, a twisted for example helical shape. Such an inner cooling fin 19 is for example illustrated in FIG. 7. The helical shape increases the contact surface between the inner fin 19 and the fluid circulating in the pipe 16. Thus, such an inner cooling fin 19 improves the heat transfer by conduction between the fluid and the heat exchanger 18 in order to dissipate the heat of this fluid to the outside of the cooling device R. The helical shape increases the exchange surface between the fluid and the heat exchanger 18 compared to the other possible shapes of inner cooling fins 19.

According to one embodiment, the inner cooling fin 19 has a crenellated shape. Such an inner cooling fin 19 located in the heat exchanger 18 is capable of creating a heat exchange by convection and by conduction with the fluid passing through the heat exchanger 18. In other words, the crenellated shape of the inner cooling fin 19 creates turbulence in the flow of the fluid in the heat exchanger 18 by the presence of barriers and thus in addition to the conduction between the fluid and the heat exchanger 18, develops exchanges by conduction in the fluid itself.

According to one embodiment, the heat exchanger 18 comprises one or more outer cooling fins 26, called outer fin 26 for further simplicity. The outer fin 26 is located on the outer surface of the heat exchanger 18 and in an arrangement capable of increasing the contact surface between the heat exchanger 18 and the outside. The outer fin 26 therefore allows increasing the dissipation of heat made by the heat exchanger 18, by conduction by increasing the outer surface of the heat exchanger 18 and by convection by creating turbulence in the external environment.

The heat exchanger 18 is advantageously obtained by a manufacturing method, for example additive manufacturing, making it possible to obtain complex-shaped heat exchanger 18 and inner 19 and outer 26 cooling fins. The additive manufacturing allows obtaining parts with complex shapes from a desired material.

The addition of a heat exchanger 18, made separately from the main body M and fixed thereto, allows improving the thermal conductivity of the cooling device R without changing the general shape of the main body M, which is made by machining. In addition, the heat exchanger 18, by being located outside the main body M, is capable of discharging the heat from the fluid in all radial directions, which is not the case for the portion of the pipe 16 of which at least one of the walls is formed in the main body M and is in contact with other portions of the cooler 1, located in the main body M, which are not necessarily able to promote the dissipation of heat. Furthermore, the method for manufacturing the heat exchanger 18 allows making the heat exchanger 18 with the inner 19 and/or outer 26 cooling fin, which is not possible with the usual method for manufacturing the main body M.

Preferably, the sealing of the cooling device R is made by means of welds 20. The weld 20 allows withstanding higher pressure levels than the seals commonly used, such as C-shaped seals. The cooling device R is made of metal, preferably a metal whose properties allow the implementation of the weld 20, such as steel or titanium. Aluminum is a material with very high thermal conductivity, which allows good heat conduction, but it does not allow the implementation of efficient weld 20. Indeed, it is very sensitive to impurities and deforms easily if the heat is too high, which reduces its strength and makes it difficult to weld properly. The choice of titanium or steel is therefore preferable to implement the sealing by welding 20. The welding method 20 is advantageously a laser welding method 20. The laser welding 20 has the advantage of allowing a fine and high-precision weld 20, which can withstand high loads and on elements with complex shapes. Thus, the heat exchanger 18 is fixed to the main body M by a laser weld 20 in order to seal the pipe 16. The same applies to the other sealing of the cooling device R such as the one at the cylinder head 21 described in the introduction and closing the expansion chamber 14 and draining the heat from it to the outside, or the connection with the infrared detector 4 as illustrated in FIG. 8. The cylinder head 21 is made of the same material as the main body M and is joined to the main body M by a weld 20 made by laser welding. In order to guarantee a weld 20 of good quality, that is to say sealed, resistant and durable, it is advantageous to weld parts made of the same material, it is therefore preferable to make the main body M, the heat exchanger 18 and the cylinder head 21 by means of the same materials.

According to one embodiment, the heat exchanger 18 comprises a base 25 capable of allowing the laser weld 20 between the heat exchanger 18 and the main body M. The base 25 allows improving the connection between these two elements and sealing it. Advantageously, the heat exchanger 18 has the shape of a loop, joining on the base 25 in order to limit the size of the base 25, and therefore the length of the weld 20, as well as the space used by the heat exchanger 18.

Advantageously, the cooling device R is made of a metal material whose thermal expansion coefficient is lower than that of aluminum. This reduces the expansion of the elements constituting the cooling device R. The cooling device R is for example made of titanium, steel, etc. According to one embodiment, the main body M, the cooler 1 and all of its constituent elements, as well as the heat exchanger 18, are all made of a material whose thermal expansion coefficient is lower than that of aluminum in order to limit differential expansion in the cooling device R, which induces, among other things, operating defects and limits its service life.

FIG. 8 also represents several piston sleeves 27 made of hard steel. These piston sleeves 27 are positioned in a housing 28 arranged in the main body M, opposite the cylinder head 21 of the expansion chamber 14 and have tribological properties.

FIG. 9 illustrates the cooling device R comprising a heat sink 23. The heat sink 23 is fixed to the main body M, for example between the infrared detector 4 and the main body M of the cooling device R. The heat sink 23 optionally has a shape of revolution about the axis Y so as to dissipate the heat from the cooler 1 to which it is fixed. A portion of the heat sink 23 is advantageously in contact with the heat exchanger 18. The contact between the heat sink 23 and the heat exchanger 18 is formed along at least one contact plane W and allows promoting the dissipation of heat from the heat exchanger 18 to the outside and therefore improving the cooling of the fluid passing through the heat exchanger 18.

According to one embodiment, the heat sink 23 is in contact with the outer surface of the heat exchanger 18 over only a portion of the total length of the heat exchanger 18.

According to another embodiment, the heat sink 23 is in contact with the outer surface of the heat exchanger 18 over the entire length of the heat exchanger 18. In this embodiment, each of the axial sections of the heat exchanger 18 has at least one point of its outer surface in a tangent plane X. The tangent plane X, comprising at least one point of the outer surface of the heat exchanger 18 over the entire length thereof, is parallel to the contact plane W between the heat exchanger 18 and the heat sink 23.

Advantageously, the heat sink 23 is made of aluminum in order to increase the heat discharge performance. The shape of the heat sink 23 can be of different types but is capable of promoting heat conduction while optimizing the space occupied. Advantageously, the thermal cooler 1 is fixed to the outer wall of the main body M and is formed so that a point on the outer surface of each axial section belongs to a common plane A. In other words, the plane A comprises a point on the outer surface of each axial section of the thermal cooler 1. In this way, and as illustrated in FIG. 8, the exchange surface between the heat sink 23 and the heat exchanger 18 is increased.

The cooling device R advantageously comprises a thermal pad 24 positioned between the heat exchanger 18 and the heat sink 23. The thermal pad 24 is for example a GTG-type thermally conductive pad formed from a thermal paste providing flexibility that takes into account all the surface asperities and thus ensures optimal contact at both low and high temperatures. In other words, the thermal pad 24 is capable of improving the contact between the two elements by compensating for surface defects. By improving the contact between the heat exchanger 18 and the heat sink 23, the thermal pad 24 increases the dissipation of heat from the heat exchanger 18 to the heat sink 23.

Claims

1. A cooling device comprising a main body, a Stirling cooler disposed inside the main body, and a pipe capable of conveying a heat transfer fluid from the Stirling cooler, wherein the pipe extends at least partly outside the main body.

2. The cooling device according to claim 1, wherein the Stirling cooler includes a cylinder head added onto the main body, a sealing weld being interposed between said cylinder head and the main body.

3. The cooling device according to claim 1, wherein it includes a heat exchanger wherein a portion of the pipe extends at least partly outside the main body.

4. The cooling device according to claim 3, wherein the main body and the heat exchanger are made of the same metal.

5. The cooling device according to claim 3, wherein the heat exchanger comprises at least one inner cooling fin extending into the pipe portion arranged in the heat exchanger, from an inner surface thereof.

6. The cooling device according to claim 5, wherein at least a portion of the inner cooling fin has a twisted shape.

7. The cooling device according to claim 3, wherein the heat exchanger comprises an outer cooling fin disposed on an outer surface of the heat exchanger.

8. The cooling device according to claim 3, comprising a heat sink in contact with the pipe and/or the heat exchanger.

9. The cooling device according to claim 8, comprising a thermal pad in contact, on the one hand with the pipe and/or the heat exchanger and on the other hand with the heat sink.

10. An infrared vision and/or detection device comprising an infrared detector and a cooling device, according to claim 1, for cooling said infrared detector.

11. The cooling device according to claim 3, wherein the main body and the heat exchanger are made of the same metal having thermal expansion coefficient is lower than that of aluminum.

Patent History
Publication number: 20260218945
Type: Application
Filed: Jan 12, 2024
Publication Date: Jul 30, 2026
Applicant: Safran Electronics & Defense (PARIS)
Inventors: Bertrand COTTEREAU (MOISSY-CRAMAYEL), Jean-Yves LONCLE (MOISSY-CRAMAYEL), Nicolas DUVAL (MOISSY-CRAMAYEL), Laurent GRISON (MOISSY-CRAMAYEL)
Application Number: 19/146,850
Classifications
International Classification: F25B 9/14 (20060101); F25D 19/00 (20060101);