Capillary two-phase thermal diffuser comprising a mesh – additive manufacturing of this diffuser

Abstract

The invention relates to a two-phase thermal diffuser (10), said diffuser comprising a casing (11), an internal volume (20) for receiving a heat transfer fluid, and an internal structure for the condensation and capillary movement of said fluid. The internal structure comprises a three-dimensional lattice (9) extending through all or part of the internal volume (20) and supported by opposite portions of the casing (11), said lattice (9) being composed of body-centered hexahedral meshes (1). (Shorthand figure: 5)

Description

Title of the invention: Capillary two-phase thermal diffuser comprising a lattice - additive manufacturing of this diffuser. Technical field

[0001] The invention relates to linear or surface thermal diffusers and their manufacture. More particularly, the invention relates to thermal diffusers constructed around a cavity in which a two-phase heat transfer fluid circulates, the diffuser further comprising a capillary structure within the cavity. The invention is applicable to heat diffusion for cooling electronic devices, particularly in the space sector.

[0002] [BACKGROUND]

[0003] Two-phase heat diffusers are devices that allow the movement of heat from a localized source for the purpose of its spreading and eventual dissipation. This spreading is induced by the phase change of a heat transfer fluid, initially liquid, contained within a sealed casing in contact with the localized heat source. This casing transfers heat from the heat source to the fluid it contains. Under the influence of heat, the fluid evaporates locally while remaining within the internal volume (or cavity) of the sealed casing and moves to cooler areas, further from the localized source, where it condenses before being returned, or returning on its own, to the heat zone. The part of the diffuser where the fluid evaporates is the evaporation zone or evaporator. Similarly, the cooler part that allows condensation is the condensation zone or condenser.Returning the fluid to a liquid state at the hot spot is an important step and can be achieved through active methods using pumps, or through passive methods using capillary systems.

[0004] Two-phase loops, for example, can be passive with a capillary system or active with a pump that forces the movement of the fluid. Other systems, called oscillating systems, allow heat transfer through the presence of vapor bubbles in the liquid fluid that increase or decrease in volume depending on the temperature and thus oscillate.

[0005] Two-phase heat diffusers can be one-dimensional (linear), in which case they are called heat pipes, which often take the form of a tube shaped like a cylinder of revolution. Heat pipes can be implemented as networks of heat pipes independent of each other. Heat pipes may include a capillary system.

[0006] Two-phase thermal diffusers can also be two-dimensional (surface) structures such as vapor chambers or oscillating heat pipes, which are generally planar structures.

[0007] Vapor chambers (in two dimensions) comprise: a shell, a heat transfer fluid, and a capillary structure inside the shell. The capillary structure ensures the return of the condensed liquid to the evaporation zone and can be an applied metal mesh, also called a wick, grooves, or sintered metal powder.

[0008] Vapor chambers may also include a set of columns or pillars providing mechanical support. Such mechanical connecting elements are necessary to prevent the chamber from collapsing or bursting during pressure variations, which can sometimes be very significant. The materials used to manufacture the casing, as well as the heat transfer fluid, are chosen according to mechanical constraints and the minimum and maximum operating temperatures of the device, and therefore its application. For example, the copper-water combination is used for heat dissipation in common electronic circuits, while aluminum and ammonia are preferred for space applications.

[0009] During the manufacture of the vapor chamber, its various components are manufactured separately and assembled before the chamber is filled with the heat transfer fluid. The vapor chamber is then placed on the heat source and held in place by mounting brackets either directly integrated into the chamber structure or by added fasteners. These manufacturing steps are costly and complex. For example, the introduction of a wire mesh requires the wick to be manufactured before insertion, while a groove system requires an extrusion die with a complex geometry or machining. Depending on the capillary system, additional manufacturing steps must be considered. Furthermore, the various assembled parts and the fasteners are subjected to significant mechanical and thermal stresses.

[0010] A solution recently proposed by OZGUC et al., 'Experimental Demonstration of an Additively Manufactured Vapor Chamber Heat Spreader', in: 18th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), Las Vegas, USA, 2019, pp. 416-422, consists of manufacturing the vapor chamber by additive synthesis, and more specifically by laser powder bed fusion. This manufacturing process involves fusing the powder composed of the desired material, in this case stainless steel. The laser forms the desired structure layer by layer, and varying the printing parameters, such as the laser power or its pitch, allows the creation of patterns or porous structures.

[0011] The vapor chamber thus fabricated comprises a shell, a porous capillary structure, and a series of columns serving as mechanical links to maintain the shell during pressure variations and thus prevent its bursting or collapse. The columns are porous and provide an additional capillary zone.

[0012] In order to avoid the presence of suspended horizontal structures such as bridges, the columns are inclined at 45° to the vertical.

[0013] The fabrication of two-phase capillary thermal diffusers involves constraints related to the diffuser's geometry (one or two dimensions) and the capillary system used, whether it be grooved, a metal mesh, or sintered metal powder. The use of additive manufacturing, which aims to overcome these problems, introduces new drawbacks mentioned previously, notably the requirement for powder removal.

[0014] During the manufacturing of a component by powder bed fusion, it is indeed necessary to remove excess powder through a process known as depowdering. This process can be carried out by projecting pressurized air onto the powder-coated components. However, in the context of manufacturing a thermal diffuser such as a vapor chamber, depowdering is a step that takes place within a cavity containing a capillary system, which could be, for example, sintered metal. It is therefore more complex.

[0015] Moreover, in addition to these manufacturing constraints, there is the need to obtain a system ensuring sufficient capillarity to diffuse the heat.

[0016] A solution is proposed by MENG et al., 'Experimental study on the heat transfer performance of a vapor chamber with porous wick structures printed via metallic additive manufacturing'. In: International Communications in Heat and Mass Transfer, Vol 40, 2023. The internal structure of the vapor chamber is produced by laser melting on a copper powder bed.

[0017] This structure comprises two trusses along the main walls of the chamber, separated by a set of columns. The trusses are composed of different mesh sizes.

[0018] The first lattice comprises cubic meshes that promote evaporation and vapor movement. According to the authors, these cubic meshes allow vapor to move easily.

[0019] The other lattice comprises meshes based on gyroid surfaces for fluid condensation. According to the authors, the gyroid surfaces provide a large surface area for the vapor to condense into liquid upon contact.

[0020] The columns located between the two lattices, which support the assembly, are composed of Schwarz surfaces, chosen according to the authors to allow capillary movement. These surfaces, in column form, allow The condensed fluid, in liquid form, returns to the heat zone. These columns are arranged, according to the authors, to provide mechanical support and capillary return while maintaining sufficient free space for vapor movement.

[0021] The vapor chamber thus created therefore has an imperative orientation of use so that the zones corresponding to evaporation or condensation are correctly oriented according to the heat source. Summary of the invention

[0022] In order to overcome all or part of the aforementioned drawbacks, the invention consists of a two-phase thermal diffuser, said diffuser comprising an envelope, an internal volume for receiving a heat transfer fluid and an internal structure for the evaporation, capillary movement and condensation of said fluid, said internal structure comprising a three-dimensional lattice running through all or part of the internal volume and supported by opposite portions of the envelope, said lattice being composed of parallelepiped, or more generally hexahedral, centered meshes.

[0023] These are characteristics which enable and facilitate evaporation, movement of the heat transfer fluid and condensation.

[0024] The lattice is composed of meshes that can be repeated in one or more directions of elongation of the casing. The meshes provide a large contact surface between the vapor and a solid material near any point within the diffuser's internal volume. The capillary effect is ensured by the meshes, due to their shape and surface condition, with respect to the fluid in question, which condenses upon contact with the lattice and then moves along the meshes. Furthermore, since the lattice extends throughout the internal volume, the return of the condensed fluid to the hot contact point is facilitated.

[0025] The capillary effect is then ensured by the lattice, which allows the fluid in liquid form to move from the condenser to the evaporator. Furthermore, the lattice bars, because they rest on opposite portions of the casing, provide mechanical support between the faces of the thermal diffuser casing, particularly when the diffuser is two-dimensional, such as a vapor chamber, and the opposite portions of the casing are parts of the larger faces of the chamber. This mechanical support provides compressive and shear resistance during operation. It is especially useful when the casing is not a cylinder of revolution. In this case, the casing has a small cross-sectional dimension (the thickness in the case of a flat vapor chamber), along which the lattice provides mechanical resistance.

[0026] Furthermore, the centered parallelepiped, or more generally hexahedral, mesh is very efficient both for the evaporation of the heat transfer fluid and for the condensation of the fluid and movement of the liquid. The openwork structure allows vapor to move efficiently between the mesh bars. The bars themselves provide a surface for condensation. Furthermore, the roughness of the bars and the grooves within them ensure efficient capillary return of the fluid to the heating zone.

[0027] Furthermore, the parallelepiped, or more generally hexahedral, mesh, centered since it comprises bars along the diagonals of the parallelepiped or hexahedron, offers improved mechanical support to the shell. This mechanical support encompasses all directions and makes it resistant to bursting or collapse.

[0028] The centered hexahedral mesh, and in some embodiments, centered parallelepiped mesh, is by definition based on bars and thus forms an openwork structure running through the internal volume of the heat diffuser, allowing vapor to circulate from the contact zone between the heating element and the diffuser's casing to cooler areas of the cavity (the internal volume of the casing, through which the mesh runs). The bars themselves allow the liquid to return to the heating zone by capillary action. The mesh is therefore a capillary mesh.

[0029] In one embodiment, the meshes constituting the capillary lattice are body-centered cubic.

[0030] The invention, and more particularly the internal body-centered cubic lattice, simplifies the consideration of manufacturing direction constraints associated with additive manufacturing. More specifically, the angles between the bars forming the body-centered cubic lattice allow the lattice to be manufactured in all possible directions without creating suspended elements. The lattice's mesh supports the closing wall during layer-by-layer manufacturing.

[0031] In one embodiment, the bars forming the mesh of the lattice have a star profile.

[0032] The angular grooves present between each branch of the star increase the capillary effect of said bar during the movement of the liquid. They then act as grooves along the bars.

[0033] In one embodiment, the junctions of the bars at the center of a mesh or at the common node of two neighboring meshes are drilled through.

[0034] The openings at the bar junctions provide additional passage for the liquid. Thus, the liquid reaches the hot zones of the heat diffuser more quickly and improves the diffuser's ability to transfer heat.

[0035] In one embodiment, the lattice comprises an integer number greater than or equal to two of half-meshes.

[0036] In one embodiment, the additive manufacturing method used is laser powder bed fusion.

[0037] In an original manner, the fabrication of the casing and internal structure includes the construction of a three-dimensional lattice extending through part, or even all, of the internal volume, originating on opposite portions of the casing and whose mesh ensures a capillary effect for the condensed fluid. This results in a single-piece 3D thermal diffuser comprising a large capillary lattice extending through the internal volume of the diffuser casing.

[0038] The mesh within the internal volume, by virtue of its openwork structure, facilitates the dust removal operation which is necessary before the introduction of the heat transfer fluid.

[0039] During the manufacture of the thermal diffuser, the mesh of the lattice originates on the inner faces of the diffuser's casing. In this way, the junction between the lattice and the casing is continuous and without any separation. This continuity enhances resistance to mechanical stresses, particularly pressure stresses, at very low or very high temperatures. Thus, the mesh of the lattice is continuous with the inner part of the diffuser's casing and provides a mechanical connection between the casing's faces. This prevents the casing from collapsing and bursting in the event of a significant pressure variation between the outside and inside of the chamber.

[0040] Thus, the manufacturing process is particularly advantageous.

[0041] Furthermore, the invention allows the thermal diffuser to be integrated into mechanical structures such as mechanical trusses. This type of structure is found, in particular, in radiant panels for satellites. The invention is directly integrated into the structure during its manufacturing process. Advantageously, the mechanical and thermal stresses at the interface between the thermal diffuser and the mechanical structure are reduced. In the example of integrating the diffuser into a satellite panel, manufacturing the panel and the diffuser as a single unit improves the panel's thermal rejection capacity.

[0042] In addition, additive manufacturing makes it possible to obtain rough bars which constitute the mesh of the lattice, the roughness thus improves the capillarity of the thermal diffuser.

[0043] In one embodiment, the additive synthesis manufacturing of the thermal diffuser of the envelope and the internal mesh is carried out in aluminium or aluminium alloy.

[0044] The thermal diffuser thus produced is then lightweight and can be used for space applications where weight constraints are important.

[0045] In one embodiment, the thermal diffuser is a vapor chamber whose envelope comprises two opposing surfaces, for example flat, and whose lattice originating on an internal surface of a face of the vapor chamber configured for contact with an element to be cooled.

[0046] The vapor chamber manufactured according to the aforementioned process can be placed against a heating element comprising one or more heat sources. The heating element is then in contact with the chamber's outer casing. More specifically, the element whose heat is to be spread and dissipated is in contact with one of the two large, opposite, flat surfaces of the vapor chamber's outer casing.

[0047] The mesh running through the steam chamber, the openings of which originate on the chamber's internal walls, allows the heat transfer fluid to circulate in liquid form throughout the chamber. The mesh thus advantageously diffuses heat from several localized sources and ensures mechanical connection within the steam chamber.

[0048] The vapor chamber then advantageously replaces a network of heat pipes, the placement of which requires a prior study of the heating element and its hot spots. Furthermore, the lattice, which occupies all or part of the internal volume and is composed of a repeating mesh in one or more directions of chamber elongation, allows the vapor chamber to be used on either side without distinction.

[0049] In one embodiment, the thermal diffuser is a heat pipe in the shape of a cylinder of revolution and whose lattice runs through the internal volume and originates on opposite portions of the envelope.

[0050] The cylindrical shape of the heat pipe allows it to withstand large pressure variations and prevents bursting or collapse of the casing. The lattice running through the internal volume, because it originates on opposite portions of the casing, reinforces this resistance to pressure variations. Thus, the heat pipe casing can be thinned without compromising the strength of the heat diffuser, and the mass of the heat pipe can therefore be reduced. This reduction in the device's mass is then an advantage when using the heat pipe in a space context.

[0051] According to another aspect of the invention, it relates to a two-phase thermal diffuser comprising an envelope, an internal volume for receiving a heat transfer fluid and an internal structure in the form of a lattice for the condensation and capillary movement of said fluid, the thermal diffuser being obtained by additive manufacturing according to the principles mentioned above.

[0052] In one embodiment, the vapor chamber thus made includes areas of solid material for the addition of fasteners passing through the envelope and the internal volume of the vapor chamber or not.

[0053] These fixing zones are solid elements that can be drilled or riveted. They allow the heat diffuser to be fixed to the heat source. Such zones, when directly integrated into the manufacture of the diffuser and extending through it, reduce the mechanical and thermal stresses on the system into which the heat diffuser is integrated. Brief description of the drawings

[0054] The invention will be better understood and other advantages, details and features will become apparent from the following explanatory description, given by way of example and with reference to the figures, among which: - [Fig.1] represents a body-centered cubic mesh that can be used to compose a lattice; - [Fig.2] is a section and illustrates the star shape of the bars of a capillary lattice according to one embodiment of the invention; - Figure 3 illustrates a mesh of the capillary lattice according to the same method of realization - [Fig.4] illustrates a view of an alignment of meshes forming a single-layer lattice; - Figure 5 illustrates a cross-sectional view of one embodiment of the invention constituting a steam chamber comprising a lattice; - Figure 6 illustrates two cross-sectional views of two embodiments of the invention each constituting a vapor chamber comprising a three-dimensional lattice; - [Fig.7] represents a three-quarter view of a steam chamber according to the invention; - Figure 8 illustrates, in three-quarter view, a single-piece assembly of mechanical structure and a steam chamber according to the invention integrated into the mechanical structure. Description of the implementation methods

[0055] [Fig. 1] [Fig. 1] schematically represents a body-centered cubic unit cell 1 that can form a lattice used in the invention. The black circles illustrate the nodes 2 and are arranged in a body-centered cubic lattice. The solid black lines represent the bars 3 of the unit cell and meet at nodes. The dashed lines represent the boundaries of a unit cell 1; two unit cells 1 can be adjacent. This unit cell 1, repeated in one, two, or three directions, forms the three-dimensional lattice.

[0056] For heat pipes, it is planned to use such a lattice whose mesh repeats in a single direction, namely that of the heat pipe lumen. For steam chambers, it is planned to use such a lattice whose mesh repeats or the meshes... repeat in two directions, namely those of the internal cavity of the vapor chamber.

[0057] [Fig.2] The [Fig.2] is a section of a bar 3 usable for a truss whose The meshes comprise bars, for example, the centered cubic mesh 1 as shown in [Fig. 1]. The bar comprises a core 4, which is essentially a cylinder of revolution with a diameter, for example, 0.6 mm, and branches 5 (here four in number, but a different number can be considered), each of the same geometry, regularly distributed around the core 4 and gradually tapering towards it, up to a tip that can be pointed, approximately 1.3 mm above the axis of the cylinder of revolution forming the core 4 of the bar 3. At its base, each branch is adjacent to the neighboring branch 3, their junction forming a groove 6 with an angular bottom. This groove 6 promotes capillary action at the level of the bars 3, allowing a liquid fluid to move. The presence of four grooves is advantageous since it provides four favorable paths for the fluid.

[0058] [Fig. 3] [Fig. 3] illustrates an embodiment of a body-centered cubic lattice formed of bars 3 in the shape of a four-pointed star 5 conforming to [Fig. 2]. The unit cell 1 shown comprises four bars 3, each of which intersects the others at its midpoint, at the center of the cube: these are the diagonals of the cube. Each bar 3 has four salient edges corresponding to the points of the star shown in [Fig. 2], which are indicated in [Fig. 3] by thicker lines. The grooves 6 formed by the re-entrant angles between the points correspond, in [Fig. 3], to the thinner lines along the length of the bars.

[0059] The intersection at the center of the mesh 1 of the four bars 3 forms a node 2 in which three through-holes 8 have been provided. In the embodiment shown, the node 2 has three through-holes of diameter 0.4 mm, oriented at 90° to each other, parallel to edges of the cube. The diameter of the opening 8 is a variable parameter between 0 mm, characterizing the absence of an opening, and up to a value less than the diameter of the web of the bar 3 as defined in [Fig. 2].

[0060] The through-holes 8 in the center of the nodes 2 provide an additional passage for the liquid so that it reaches the evaporation zone more quickly. In addition, the fluid in liquid form moves along the bars 3 and the grooves 6 that compose them.

[0061] [Fig.4] [Fig.4] illustrates a view of an alignment of body-centered cubic lattices 1 along a direction, here horizontal, forming a lattice 9 with a single layer of centered cubic cells 1. The nodes 2 where the bars 3 meet, at the edge of a cell 1 or at its center, have three through openings 8 as mentioned above. The three openings 8 at the center of the nodes are perpendicular to each other. In the embodiment presented, the cells 1 of the The 8 lattices are adjacent and the cubes forming mesh 1 have a side of 2.85 mm. This value defines the spacing of the lattice 9 and can vary, in particular, between 1 mm and 5 mm, or even between 0.5 mm and 8 mm.

[0062] The joining of four bars 3 of adjacent meshes forms, in side view, a square. Two of the opposite vertices of this square constitute the junction of the bars 3 of the two adjacent meshes 1 on the outer faces of the layers. The other two vertices are located at the central nodes 2 of the two adjacent meshes 1.

[0063] [Fig. 5] Figure 5 illustrates a cross-sectional view of an embodiment of the invention constituting a two-phase thermal diffuser 10 comprising a lattice 9 as previously mentioned. The thermal diffuser 10 is formed of an envelope 11 in the shape of a rectangular prism with two extension dimensions (one of the two dimensions is not visible in the figure) and surrounding an internal volume 20 entirely occupied by a single layer of lattice 9 extending in both extension dimensions of the thermal diffuser 10. The thermal diffuser 10 can, for example, be a vapor chamber.

[0064] In the embodiment shown, the meshes 1 of the lattice 9 are body-centered cubic and adjacent to each other. The meshes 1 composing the lattice 9 are aligned along the two directions mentioned, and the thickness of mesh 1 is equal to the height of the internal volume of the chamber. The lattice 9 consists of a single layer of meshes 1. The space between the bars 3 of the meshes 1 allows steam to pass through, while the lattice 9 nevertheless occupies the entire internal volume of the steam chamber.

[0065] In the embodiment shown, the lattice 9 covers the entire internal volume 20 of the thermal diffuser 10. Alternative embodiments will include a lattice 9 covering only a part of the internal volume 20, or covering discontinuously the internal volume 20 of the thermal diffuser 10.

[0066] The bars 3 themselves allow the liquid to move by capillary action. In addition, the lattice 9 originating on the internal walls of the casing 11 provides a mechanical connection to the thermal diffuser 10, preventing bursting or collapse during large temperature variations. The mesh 1 also has three through-openings 8 at their junctions and central nodes 2, increasing capillarity.

[0067] The casing 11 of the diffuser 10 has two large, solid, flat internal surfaces facing each other around the lattice, as well as four internal lateral sides also surrounding the lattice and joining the two large surfaces. The bars originate on these two large internal surfaces and on these four internal lateral sides.

[0068] The thickness of the walls composing the envelope 11 can, for example, be 1.5 mm and vary around this value. The thermal diffuser 10 supports, without alteration of the envelope 11, pressures up to more than 100 bars during its use.

[0069] A filling tube 12 for the heat transfer fluid is also present in the form of a hollow cylinder of revolution. This opening will subsequently be sealed to allow the operation of the heat diffuser 10.

[0070] The black arrow 13 indicates the manufacturing direction of the thermal diffuser 10 by additive synthesis and more specifically by laser melting on a powder bed of aluminum alloy, here starting from the face including the filling tube 12. The manufacturing direction, which is carried out vertically, follows one of the elongation directions of the thermal diffuser 10. The material used is aluminum, alloyed or unalloyed, and in any case, is chosen to conduct heat on the one hand and to be chemically compatible, including in the long term, with the fluid introduced into the cavity.

[0071] The fluid introduced through the filling tube 12 is, in the described embodiment, ammonia, introduced in liquid form (i.e., at low temperature and / or high pressure). Another fluid may be used.

[0072] Due to the requirements of additive manufacturing, the last meshes 1 produced have excess material extending from the center of the mesh 1 to the ends of the bars 3 constituting it, following the manufacturing direction. This excess is pyramidal in shape, with its base against the wall (one of the sides) of the thermal diffuser 10 and its apex formed by the central node 2 of the mesh 1. This excess has the same density as the envelope 11 and is integral with the last manufactured surface of the envelope 11, here the upper surface which constitutes the closing wall. In a particular embodiment, this excess can be replaced by a lattice (9) with a finer mesh size extending to the closing wall of the envelope.

[0073] The bars 3 constituting the mesh 1 of the lattice, here body-centered cubic, have a rough surface. This roughness results from additive manufacturing and increases the capillarity of the bars 3 of the lattice 9.

[0074] When using the thermal diffuser 10, a heating element is in contact with a limited area of ​​one of the large external faces of the casing 11. Upon heating, the heat transfer fluid contained in the vapor chamber changes to a gaseous state. In vapor form, the fluid moves through the lattice 9 away from the contact area with the heating element, between the bars 3 of the mesh 1. The vapor thus moves to cooler areas of the vapor chamber, considered as a condenser. Upon contact with cooler surfaces, such as the cold parts of the internal faces of the casing 11 or the bars 3, the vapor condenses. The heat transfer fluid, in liquid form, then moves along the bars 3, in the openings 8 present at the junctions of the meshes 1 and in the grooves 6 until they rejoin the heated area of ​​the thermal diffuser 10.

[0075] [Fig. 6] [Fig. 6] illustrates cross-sectional views of two embodiments of the invention, each constituting a thermal diffuser 10 comprising a three-dimensional lattice 9 that runs through an internal volume 20. In both embodiments, the mesh 1 composing the lattice 9 is body-centered cubic and formed of star-shaped bars 3, as described in relation to Figures 3 and 4. The mesh thickness of the lattice 9 running through the internal volume 20 varies from one layer composed of a single mesh 1 (in [Fig. 5]) to one and a half meshes for the embodiment of part A of [Fig. 6] and two meshes 1 for the embodiment of part B of [Fig. 6]. The mesh thickness 1 of the lattice 9 can indeed be expressed in half-meshes, due to the body-centered cubic structure.

[0076] The embodiment of part A of [Fig.6], whose mesh thickness 9 is 1.5 mesh, comprises a complete mesh 1 originating on the inner wall and a half-mesh 1 which terminates with the central node 2 against the inner wall of the diffuser 10.

[0077] The embodiment of part B of [Fig. 6] comprises two cubic meshes 1 of thickness. The meshes 1 originate and terminate on the inner wall of the diffuser by the bars 3 constituting said meshes.

[0078] For both embodiments with one and a half mesh and two 1 meshes, the tube 12 of the diffuser 10 is centered both according to the lattice 9 and according to the face on which it is located.

[0079] On parts A and B of Figure 6, the black arrow 13 indicates the manufacturing direction of the thermal diffusers 10, and an excess of material is present between the last upper meshes and the closing wall for both embodiments.

[0080] In these different embodiments, the geometry and roughness of the lattice lead to high capillarity.

[0081] [Fig. 7] Figure 7 represents a steam chamber 15 according to the invention. The chamber steam 15 is in the form of a flat and planar rectangular block whose faces form the envelope 11. The interior of the envelope 11 which includes the internal volume of the chamber can accommodate a lattice 9 of one or more mesh thicknesses 1. The upper and lower faces have the largest dimensions, constituting two facing planes.

[0082] The vapor chamber includes at least two orifices 16 used for dust removal, which in this embodiment take the form of a hollow cylinder of revolution. Openings are present on two lateral sides orthogonal to each other, namely the filling tube 12 and a dust removal orifice 16. A second dust removal orifice 16 is present on a side not visible in the figure. These Depowder removal ports are used to remove excess powder from additive manufacturing by laser powder bed fusion.

[0083] The openings are located on elongated lateral sides and their outside diameter is less than or equal to the smallest dimension of the side through which it passes.

[0084] In one embodiment of the invention, the vapor chamber 15 comprises solid material attachment zones 17, which are solid cylinders of dense material extending through the chamber and flush with the upper flat surface. Each of these volumes can be drilled to screw or rivet an external element into the chamber material, or to pass a link through this dense material, without creating a discontinuity in the functional internal volume of the vapor chamber. These solid material attachment zones 17 are then used to attach the vapor chamber 15 to a heating element.

[0085] The distribution of the solid cylinders 17 on the surface is one example of a possible arrangement; other distributions are conceivable depending on the constraints related to the use of the chamber.

[0086] [Fig-8] [Fig.8] illustrates, in three-quarter view, a monobloc assembly 18 of a mechanical structure 19 and a steam chamber 15 according to the invention integrated into the mechanical structure 19. The mechanical structure 19 is represented in the form of a regular cubic tiling of a single thickness.

[0087] The mechanical structure 19 can be either a mechanical lattice or honeycomb-shaped, in which case it is referred to as a Nida (honeycomb) structure. Such a structure can be manufactured by additive manufacturing and, more particularly, according to the invention disclosed by document EP 3 208 200, the structure thus manufactured can constitute panel elements for a satellite. The structure presented in the aforementioned invention is manufactured by additive manufacturing and is formed of a mechanical lattice whose cores are made up of meshes, for example, body-centered cubic or other meshes that can be manufactured without support structures by additive manufacturing. The integration of the diffuser, here a vapor chamber 15, is carried out directly during the manufacturing process of the structure it incorporates. This integration reduces the mechanical and thermal stresses at the interfaces of the structure and the diffuser, and more particularly on external fastening elements.

[0088] A steam chamber 15 according to the invention is integrated into the center of the mechanical structure 19. In this embodiment, the steam chamber 15 is a flat, rectangular prism having the filling tube 12 on one of its faces. The filling tube 12 is located on the upper face of the steam chamber 15. The filling tube 12 must be accessible for introducing the heat transfer fluid; thus, the filling tube 12 may, if necessary, be located on one of the faces or one of the sides of the steam chamber 15.

[0089] The lateral faces of the chamber are included in the mechanical structure 19. The thickness of the vapor chamber 15 is less than that of the mechanical structure 19 of which it is an integral part. In an alternative embodiment, the thickness of the vapor chamber 15 may vary so as to be greater than or equal to the thickness of the mechanical structure 19.

[0090] The steam chamber 15 is oriented parallel to the mechanical structure 19 along its two elongation directions. However, the chamber can be positioned perpendicular to the mechanical structure 19, so that it protrudes in one of the directions. In an alternative embodiment, the steam chamber 15 is located on the mechanical structure 19.

[0091] In one embodiment of the invention, the heat diffuser may be linear and in the form of a cylinder of revolution containing the three-dimensional lattice. The diffuser thus formed is then a heat pipe whose internal volume is traversed by the lattice and whose meshes originate inside the cylinder of revolution on the internal walls of the cylinder. The lattice may be composed of one or more layers of mesh constituting the thickness of the lattice. The lattice then acts as the capillary structure allowing the return of the liquid heat transfer fluid to the point of contact with the heat source.

[0092] Other variations of the invention can be deduced by those skilled in the art. For example, the invention can be implemented in two-phase capillary loops, the mesh then replacing the capillary system such as cloth or sintered metal. Furthermore, the invention can be implemented in vapor chambers that are angled or curved to adapt to the contact area with the heating element.

[0093] Furthermore, the lattice can be made up of alternative meshes which allow the evaporation as well as the condensation of the heat transfer fluid.

[0094] Laser powder bed fusion is an advantageous example of a possible additive manufacturing technique. However, other techniques also fall within the scope of the invention.

Claims

Demands

1. Capillary two-phase thermal diffuser (10), said diffuser (10) comprising a shell (11), an internal volume (20) for receiving a heat transfer fluid and an internal structure for evaporation and gas displacement, and condensation and liquid displacement, said two-phase thermal diffuser (10) being characterized in that the internal structure comprises a three-dimensional lattice (9) running through the internal volume (20) and supported by opposite portions of the shell, said lattice (9) being composed of centered hexahedral meshes (1).

2. Capillary two-phase thermal diffuser (10) according to claim 1, characterized in that junctions (2) of the lattice (9) are drilled through.

3. Capillary two-phase thermal diffuser (10) according to claims 1 or 2, characterized in that the mesh (1) of the lattice (9) is body-centered cubic.

4. Capillary two-phase thermal diffuser (10) according to any one of claims 1 to 3, characterized in that the bars which constitute the mesh (1) have a star profile.

5. Capillary two-phase thermal diffuser (10) according to any one of claims 1 to 4, characterized in that the capillary thermal diffuser (10) is a vapor chamber (15), the mesh (9) is included between two flat plates of the vapor chamber on which said mesh (9) is rigidly fixed.

6. Capillary two-phase thermal diffuser (10) according to any one of claims 1 to 4, characterized in that the thermal diffuser (10) is a heat pipe in the form of a cylinder of revolution.

7. Capillary two-phase thermal diffuser (10) according to any one of claims 1 to 6, characterized in that the lattice (9) comprises an integer number greater than or equal to two of half-meshes (1).

8. Capillary two-phase thermal diffuser (10) according to any one of claims 1 to 7, characterized in that the capillary thermal diffuser (10) is a single-piece assembly comprising the envelope (11) and the mesh (9) running through all or part of the internal volume (20), said mesh (9) originating on opposite portions of the envelope (11).

9. Method of manufacturing a capillary thermal diffuser (10) according to claim 8 characterized in that it comprises a step of constructing the three-dimensional lattice by additive manufacturing whereby the envelope and the lattice are manufactured together.

10. Method of manufacturing a capillary thermal diffuser (10) according to claim 9 characterized in that the additive manufacturing is done by adding aluminium or aluminium alloy.

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