Heat exchanger for refrigeration machine

Abstract

This presentation relates to a cooling device comprising a main body, a Stirling cooler disposed within the main body, and a pipe for conducting a heat transfer fluid from the Stirling cooler. The cooling device is characterized in that the pipe extends at least partially outside the main body. Figure for the abstract: Fig. 3

Description

Title of the invention: Heat exchanger for a refrigeration machine Technical field

[0001] The present invention relates to the field of refrigeration machines and more precisely to the heat exchangers of these refrigeration machines allowing the dissipation of heat. These refrigeration machines advantageously find an application in vision and / or infrared detection equipment. STATE OF THE ART

[0002] We know of infrared vision or detection equipment (binoculars or cameras for example), which make it possible to visualize or detect targets at night or through smoke.

[0003] [Fig.l] schematically represents an embodiment of infrared vision equipment J as described by international application WO 2019 / 002570. The infrared vision equipment J comprises a cooling device R, a housing 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 which 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.For this purpose, the user positions his eyes in front of the display screens 6. .

[0004] As schematically illustrated in [Fig.2], the cooling device R (also called a cold machine or micro-cooler) comprises a Stirling-type cooler 1 arranged in a main body M. A Stirling cooler is a machine which allows the production of cold by exploiting the Stirling thermodynamic cycle of a heat transfer fluid. Such a Stirling cooler 1 comprises, for example, a movable crank 8 rotating relative to a ball joint 7 and two pistons: a fluid compression piston 9, conventionally called a “hot” piston in translation in a compression cylinder 10, and a regenerative piston 12, conventionally called a “cold” piston in contrast to the following hot and movable piston 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, to compress or expand a fluid located in the compression chamber 11. The regeneration cylinder 13 and the regenerative piston 12 define a second chamber 14, hereinafter called the 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.

[0005] 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 movement 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.

[0006] 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:

[0007] • 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.

[0008] • 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 gives up part of its heat energy, or heat, to the regenerator 15, as it passes through it. The drop in temperature which is then caused results in a drop in pressure.

[0009] • An isothermal expansion phase, generated by a movement of the regulated piston generator 12 to the central cavity 17. The pressure drop causes the fluid contained in the expansion chamber 14 to cool.

[0010] • An isochoric heating phase, during which the fluid passes from the expansion chamber 14 to the compression chamber 11, via the pipe 16. By passing through the regenerator 15, the fluid recovers the heat that it gave up during the isochoric cooling phase.

[0011] However, the performance now expected for new infrared vision equipment requires operation with larger sensors, with higher cooling device powers than in the past and with a significantly increased fluid pressure in the cooler. The use of larger sensors, the increase in the number of acquisition pixels and the acceleration of refresh rates require greater cooling (colder cryogenic temperature), hence the need for higher cryogenic powers. However, the sealing provided by C-shaped gaskets between the main body M and other elements, such as for example a cylinder head 21 closing the expansion chamber 14, does not guarantee suitable sealing.

[0012] Furthermore, the new equipment must be able to operate at higher temperatures. However, increasing the power of the cooling device R leads to an increase in the temperature in the cooler 1, which can cause the equipment to overheat due to insufficient heat dissipation.

[0013] Furthermore, the increase in the power of the cooling device R induces differential expansions between the different parts, which reduces reliability, whereas new equipment is expected to have increased reliability and a significantly increased mean time to first failure. GENERAL STATEMENT

[0014] An aim of the invention is to propose a cooling device solving at least one of these problems, despite the increase in the operating power of the machine.

[0015] To this end, according to one aspect of the present invention, a cooling device is proposed comprising a main body, a Stirling cooler arranged inside the main body and a pipe suitable for conducting 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.

[0016] Such a cooling device makes it possible to improve the dissipation of the heat transported by the heat transfer fluid and therefore to promote the operation of the cooling device at high temperature.

[0017] Advantageously, but optionally, the cooling device comprises at least one of the following characteristics, taken alone or in any combination: - the Stirling cooler comprises a cylinder head attached to the main body, a sealing weld being interposed between said cylinder head and the main body;

[0018] - the cooling device comprises a heat exchanger in which extends at least partially the portion of the pipeline outside the main body;

[0019] - the main body and the heat exchanger are made of the same metal, in particular a metal whose coefficient of thermal expansion is lower than that of aluminum;

[0020] - the heat exchanger comprises at least one internal cooling fin extending into the portion of pipe provided in the heat exchanger, from an internal surface thereof this fin makes it possible to increase the exchange surface and to improve the cooling of the fluid by the heat exchanger;

[0021] - at least a portion of an internal cooling fin has a shape twisted;

[0022] - the heat exchanger comprises an external cooling fin arranged on an external surface of the heat exchanger and is suitable for improving heat exchange between the heat exchanger and the exterior;

[0023] - 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;

[0024] - the cooling device comprises a thermal mat in contact, with a part with the pipe and / or the heat exchanger and on the other hand with the heat sink, the thermal blanket being suitable for 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.

[0025] According to another aspect, there is provided an infrared vision and / or detection device comprising an infrared detector and a cooling device, of the type proposed, for cooling said infrared detector. DESCRIPTION OF FIGURES

[0026] Other characteristics, aims and advantages will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0027] - [Fig.l] illustrates a schematic view of infrared vision binoculars;

[0028] - [Fig.2] illustrates a schematic view of a cooling device;

[0029] - [Fig.3] illustrates a schematic view of a cooling device with a pipe extending outside the main body, according to an embodiment of the present invention;

[0030] - [Fig.4] illustrates a perspective view of a main body and an exchanger according to one embodiment of the present invention;

[0031] - Figure 5 illustrates a perspective view of a pipe of the cooling device development according to an embodiment of the present invention;

[0032] [Fig.6A]

[0033] [Fig.6B]

[0034] [Fig.6C]

[0035] - Figures 6A, 6B and 6C illustrate different schematic views in section and / or in perspective of a heat exchanger, according to an embodiment of the present invention;

[0036] - [Fig.7] illustrates a perspective view of the shape of a cooling fin construction of a thermal cooler, according to an embodiment of the present invention;

[0037] - [Fig.8] illustrates a sectional view of infrared vision equipment comprising an infrared detector and a cooling device according to one embodiment of the present invention;

[0038] - [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.

[0039] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION

[0040] [Fig. 3] illustrates a cooling device R for infrared vision and / or detection equipment J illustrated by [Fig. 1]. The cooling device R comprises, in addition to a main body M and a cooler 1, as described previously in relation to [Fig. 2], and a pipe 16 which extends outside the main body M.

[0041] The main body M is advantageously made from 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 external surface M1 defining an envelope thereof.

[0042] A portion of the pipe 16 is located outside the main body M and is suitable for being fixed to the external surface M1 thereof, as illustrated for example by [Fig.4]. Advantageously, this pipe 16 extends into a heat exchanger 18 which then defines a part 161 of the pipe 16 suitable for the fluid, called the heat transfer fluid, to pass through it. Subsequently, and for the sake of simplicity, the portion 161 of the pipe 16 extending outside the main body M will be called the 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 part 161 of the pipe 16 passing through the exchanger, as illustrated by way of example in [Fig.5].

[0043] The heat exchanger 18 advantageously has an internal surface, suitable for being in contact with the fluid circulating in the pipe 16, and an external surface suitable for being in contact with the outside. Advantageously, for each of the axial sections of the heat exchanger 18, the distance d between the internal surface and the external surface of the heat exchanger 18 is less than or equal to the wall thickness of the portion(s) of pipe 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.

[0044] The heat exchanger 18 therefore makes it possible to guarantee proper operation of the cooling device R, despite the increase in the operating temperature induced by the increase in power, by dissipating the heat of the heat transfer fluid passing through it towards 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 makes it possible to maintain the same temperature in the expansion chamber 14 or even a lower temperature, despite the increase in the temperature of the compression chamber 11.

[0045] In addition, the heat exchanger 18 preferably comprises one or more internal cooling fins 19. The internal cooling fin 19 is positioned on the internal 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 internal cooling fin 19 is present in the pipe 16 over the entire length of the heat exchanger 18. The internal cooling fin 19 improves the dissipation of heat from the fluid circulating in the pipe 16. Indeed, the internal cooling fin 19, with the same size of heat exchanger 18, increases the contact surface of the heat exchanger 18 with the fluid, which improves the cooling of the fluid circulating in the pipe 16.

[0046] According to an embodiment illustrated by Figures 6A, 6B and 6C, the internal cooling fin 19 has, on at least one portion, a twisted shape, for example helical. Such an internal cooling fin 19 is for example illustrated by [Fig.7]. The helical shape increases the contact surface between the internal fin 19 and the fluid circulating in the pipe 16. Thus, such an internal 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 other possible shapes of internal cooling fins 19.

[0047] According to one embodiment, the internal cooling fin 19 has a crenellated shape. Such an internal cooling fin 19 arranged 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 internal 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.

[0048] According to one embodiment, the heat exchanger 18 comprises one or more external cooling fins 26, referred to as external fin 26 for simplicity. The external fin 26 is arranged on the external surface of the heat exchanger 18 and in an arrangement suitable for increasing the contact surface between the heat exchanger 18 and the exterior. The external fin 26 therefore makes it possible to increase the dissipation of heat carried out by the heat exchanger 18, by conduction by increasing the external surface of the heat exchanger 18 and by convection by creating turbulence in the external environment.

[0049] The heat exchanger 18 is advantageously obtained by a manufacturing method, for example additive manufacturing, allowing the obtaining of heat exchanger shapes 18 and internal 19 and external 26 cooling fins of complex shapes. Additive manufacturing makes it possible to obtain parts of complex shape in a desired material.

[0050] The addition of a heat exchanger 18, produced separately from the main body M and fixed thereto, makes it possible to improve the thermal conductivity of the cooling device R without changing the general shape of the main body M, which is produced by machining. In addition, the heat exchanger 18, by being located outside the main body M, is capable of evacuating the heat from the fluid in all radial directions, which is not the case for the part 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 parts of the cooler 1, arranged in the main body M, which are not necessarily capable of promoting the dissipation of heat. In addition, the method of manufacturing the heat exchanger 18 makes it possible to produce the heat exchanger 18 with the internal 19 and / or external 26 cooling fin, which is not possible with the usual method of manufacturing the main body M.

[0051] Preferably, the sealing of the cooling device R is achieved by means of welds 20. The weld 20 makes it possible to withstand higher pressure levels than the joints usually used, such as C-joints. The cooling device R is made of metal and preferably of a metal whose properties allow the implementation of weld 20, such as for example steel or titanium. Aluminum is a material that has very high thermal conductivity, which allows good heat conduction, but it does not allow the implementation of efficient welding 20. Indeed, it is very sensitive to impurities and deforms easily if the heat is too high, which reduces its resistance and makes it difficult to weld correctly. The choice of titanium or steel is therefore preferable for implementing the sealing by welding 20. The welding process 20 is advantageously a laser welding process 20. Laser welding 20 has the advantage of allowing a fine and high-precision welding 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 laser welding 20 in order to seal the pipe 16.The same applies to the other seals of the cooling device R such as that 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 by [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 waterproof, 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 using the same materials.

[0052] According to one embodiment, the heat exchanger 18 comprises a base 25 suitable for allowing laser welding 20 between the heat exchanger 18 and the main body M. The base 25 makes it possible to improve the connection between these two elements and to make it watertight. 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.

[0053] Advantageously, the cooling device R is made of a metallic material whose coefficient of thermal expansion is lower than that of aluminum. This makes it possible to reduce 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 the elements constituting it, as well as the heat exchanger 18, are all made of a material whose coefficient of thermal expansion is lower than that of aluminum in order to limit the differential expansion in the cooling device R which induces, among other things, operating faults and limits its service life.

[0054] In [Fig. 8], several piston sleeves 27 made of hard steel are also shown. These piston sleeves 27 are positioned in a housing 28 provided in the main body M, opposite the cylinder head 21 of the expansion chamber 14 and have tribological properties.

[0055] [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 around the Y axis so as to dissipate the heat from the cooler 1 to which it is fixed. A part 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 makes it possible to promote the dissipation of heat from the heat exchanger 18 to the outside and therefore to improve the cooling of the fluid passing through the heat exchanger 18.

[0056] According to one embodiment, the heat sink 23 is in contact with the external surface of the heat exchanger 18 over only a portion of the total length of the heat exchanger 18.

[0057] According to another embodiment, the heat sink 23 is in contact with the external 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 external surface in a tangent plane X. The tangent plane X, comprising at least one point of the external 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.

[0058] Advantageously, the heat sink 23 is made of aluminum in order to increase the heat evacuation performance. The shape of the heat sink 23 can be of different types but is suitable for promoting heat conduction while optimizing the space occupied. Advantageously, the thermal cooler 1 is fixed on the external wall of the main body M and is formed so that a point on the external surface of each axial section belongs to a common plane A. In other words, the plane A comprises a point on the external surface of each axial section of the thermal cooler 1. In this way, and as illustrated by [Fig.8] the exchange surface between the heat sink 23 and the heat exchanger 18 is increased.

[0059] The cooling device R advantageously comprises a thermal blanket 24 positioned between the heat exchanger 18 and the heat sink 23. The thermal blanket 24 is, for example, a GTG-type thermally conductive blanket formed from a thermal paste providing flexibility that takes into account all surface roughness and thus ensures optimal contact at both low and high temperatures. In other words, the thermal blanket 24 is capable of improving the contact between the two elements by compensating surface defects. By improving the contact between the heat exchanger 18 and the heat sink 23, the thermal blanket 24 increases the heat dissipation from the heat exchanger 18 to the heat sink 23.

Claims

Claims

1. Cooling device (R) comprising a main body (M), a Stirling cooler (1) arranged inside the main body (M) and a pipe (16) suitable for conducting a heat transfer fluid from the Stirling cooler (1), the cooling device (R) being characterized in that the pipe (16) extends at least partly outside the main body (M).

2. Cooling device (R) according to claim 1, wherein the Stirling cooler (1) comprises a cylinder head (21) attached to the main body (M), a sealing weld being interposed between said cylinder head (21) and the main body (M).

3. Cooling device (R) according to any one of claims 1 or 2, comprising a heat exchanger (18) in which extends at least partly a portion (161) of the pipe (16) outside the main body (M).

4. Cooling device (R) according to claim 3, in which the main body (M) and the heat exchanger (18) are made of the same metal, in particular a metal whose coefficient of thermal expansion is lower than that of aluminum.

5. A cooling device (R) according to any one of claims 3 or 4, wherein the heat exchanger (18) comprises at least one internal cooling fin (19) extending into the pipe portion provided in the heat exchanger (18), from an internal surface thereof.

6. A cooling device (R) according to claim 5, wherein at least a portion of the internal cooling fin (19) has a twisted shape.

7. A cooling device (R) according to any one of claims 3 to 6, wherein the heat exchanger (18) comprises an external cooling fin (26) disposed on an external surface of the heat exchanger (18).

8. Cooling device (R) according to any one of claims 3 to 7, comprising a heat sink (23) in contact with the pipe (16) and / or the heat exchanger (18).

9. Cooling device (R) according to claim 8, comprising a thermal mattress (24) in contact, on the one hand with the pipe (16) and / or the heat exchanger (18) and on the other hand with the heat sink of heat (23).

10. An infrared vision and / or detection device (J) comprising an infrared detector (4) and a cooling device (R), according to any one of claims 1 to 9, for cooling said infrared detector (4).

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