WO2021156233A1

WO2021156233A1 - Method for manufacturing a heat exchanger or a heat pipe

Info

Publication number: WO2021156233A1
Application number: PCT/EP2021/052389
Authority: WO
Inventors: Pierre Billat
Original assignee: Stiral
Priority date: 2020-02-05
Filing date: 2021-02-02
Publication date: 2021-08-12
Also published as: FR3106769B1; FR3106769A1

Abstract

Method for manufacturing a heat exchanger or a heat pipe, comprising at least the following steps: – obtaining an assembly comprising at least one part (53) comprising at least 90% by mass of a metal or an alloy of metals, the part having at least one face (59) defining a plurality of gaps (61) comprising at least two opposite edges separated on the face by a distance of less than or equal to 550 micrometers, the part defining a plurality of circulation channels, each one of the channels defining one of the gaps, and – spraying a powder (91) onto said face (59) using a vector gas, obtaining a material by coalescence of at least part of the powder, and forming of a layer comprising the material and suitable for blocking the gaps, the powder comprising at least one metal powder, or at least one metal powder and at least one ceramic powder.

Description

Manufacturing process of a heat exchanger or a heat pipe

The present invention relates to a method of manufacturing an exchanger or a heat pipe comprising an assembly comprising at least one part comprising at least 90% by mass of a metal or a metal alloy, the part defining a plurality of channels of circulation for one or more fluids.

The invention also relates to an exchanger or a corresponding heat pipe.

It is well known to use brazing to assemble parts, in particular in order to assemble a heat exchanger or a heat pipe.

In addition, a known type of heat exchanger uses a part made of a metal sheet folded back on itself like an accordion. Two plates attached to either side of the metal sheet define circulation channels parallel to each other and located on either side of the metal sheet. The longitudinal ends of the channels open onto faces of the accordion sheet in which the channels define interstices.

In the case of a heat exchanger, the channels located on one side of the metal sheet are traversed by a cold fluid, while those located on the other side are traversed by a hot fluid. Thus, between two plates circulate two fluids, separated from each other by the metal foil and exchanging heat with each other through the metal foil.

The accordion-like sheets and the plates covered on both sides with a solder film are stacked alternately on top of each other so as to constitute a block called a “matrix” or “assembly”. This stack is then assembled in a first step in a brazing furnace. The assembly includes, for example, a first and a last plates of greater thickness than the other plates.

To seal the assembly around its perimeter, bars, called "closure bars" are generally attached to the die. Fluid feed heads are then added to the die to form the exchanger.

Due to the expansion differentials between the parts, which prevent geometrically over-stressing the constituents of the future heat exchanger, several brazing steps are generally performed, between which machining operations are carried out so as to guarantee the clearances between the parts. This practice requires great mastery of the grades of filler alloys so as not to degrade the joints made in the previous step during the next step. A first method consists in making, first of all, a closed or semi-open frame in which an accordion sheet will be inserted in order to assemble it by brazing for the first time. Secondly, a set of these frames is assembled by brazing in order to constitute the matrix of the exchanger. Thirdly, the fluid connection tubes are soldered to the die.

A second method consists, in a first step, in assembling by brazing all of the accordion sheets on all of the plates, to which are optionally joined the closing bars oriented longitudinally. Secondly, the faces of the accordion sheets are machined to align them perfectly, in order to assemble them by brazing with the closing bars oriented transversely. We thus obtain the matrix of the exchanger. Finally, in a third step, the fluid connection tubes are welded or brazed to the die.

Furthermore, there is a need, in various industrial sectors, such as automotive or aeronautics, to reduce, on the one hand, the space created by the thermal circuits and their mass and, on the other hand, the bulk. quantity of fluids involved in the exchanges. Indeed, these fluids sometimes have an impact on the environment, which should be minimized.

The same remarks apply to heat pipes incorporating such accordion sheets or more generally metal parts comprising micro-interstices.

However, the smaller the exchangers, the more difficult the second step becomes, that is to say the brazing of the closure bars on the face of the accordion-like sheets having the interstices described above, and more generally, the blocking of interstices.

FR 3,066,935 describes a brazing or resurfacing process suitable for closing the micro-interstices of such accordion sheets, in order to produce small-sized exchangers. Nevertheless, the implementation of this method remains expensive, because it generally requires several passes through the brazing furnace.

An object of the invention is therefore to provide a method of manufacturing a heat exchanger or a heat pipe incorporating a part such as the aforementioned accordion part, that is to say having micro-interstices, in particular. when the exchanger or the heat pipe is small.

To this end, the invention relates to a method of manufacturing a heat exchanger or a heat pipe, comprising at least the following steps:

- Obtaining an assembly comprising at least one part comprising at least 90% by mass of a metal or a metal alloy, the part having at least one side defining a plurality of interstices, each of the interstices having at least two opposite edges separated on the face by a maximum distance less than or equal to 550 micrometers, the part defining a plurality of circulation channels for fluids, each of the circulation channels defining one of the interstices, and

- projection of at least one powder on said face using a carrier gas, obtaining a material by coalescing at least part of the powder, and forming a layer comprising the material and suitable for plugging the interstices, the powder comprising at least one metallic powder, or at least one metallic powder and at least one ceramic powder.

According to particular embodiments, the method comprises one or more of the following characteristics, taken in isolation or in any technically possible combination:

- the part comprises an accordion-folded metal sheet, a corrugated edge of the sheet forming the edges of the interstices, the circulation channels extending parallel to and on either side of the sheet;

- said at least one metal powder comprises one of aluminum powder, steel powder, copper powder, and mixtures thereof;

- said at least one ceramic powder comprises an alumina powder;

- the part is made of stainless steel, the powder comprising a mixture of copper powder and alumina powder, or the part is made of aluminum, the powder comprising aluminum powder;

- In the projection step, the powder is projected along at least one main direction of projection intercepting the face at a point, the main direction of projection forming an angle between 20 ° and 70 ° with a direction normal to said face in this point;

the projection step comprises a plurality of successive passes of at least one device for projecting said powder, the successive passes respectively carrying out a sweeping of at least part of the face and forming a plurality of superimposed layers and included in layer ;

- each of the layers of said plurality has a thickness between 1 and 500 μm, preferably between 25 and 100 μm;

- the successive passes are carried out by projecting the powder cyclically in a plurality of main directions of projection distinct from each other, the main directions of projection respectively forming angles between 20 ° and 70 ° with a direction normal to said face and being distributed angularly around the direction;

- the part is made of stainless steel, copper, aluminum, or titanium;

- the step of obtaining the assembly comprises a sub-step of fixing the part on at least two plates, the part being located between the two plates in one direction; and

the fixing sub-step comprises brazing the part on said at least two plates.

The invention also relates to a heat exchanger or a heat pipe comprising:

- an assembly comprising at least one part comprising at least 90% by mass of a metal or a metal alloy, the part having at least one face defining a plurality of interstices, each of the interstices comprising at least two opposite edges separated on the face by a maximum distance less than or equal to 550 micrometers, the part defining a plurality of circulation channels for fluids, each of the circulation channels defining one of the interstices, and

- a layer comprising a material obtained by coalescing at least part of a powder sprayed cold onto said face, the layer being adapted to plug the interstices, the sprayed powder comprising at least one metal powder, or at least one powder metallic and at least one ceramic powder.

According to particular embodiments, the exchanger or the heat pipe can be obtained, or are obtained, by a manufacturing process as described above.

The invention will be better understood on reading the description which follows, given solely by way of example and made with reference to the accompanying drawings, in which:

- Figure 1 is a perspective view of a heat exchanger according to the invention,

- Figure 2 is a perspective view of an assembly (matrix) of the heat exchanger shown in Figure 1, the fluid collectors having been removed,

- Figure 3 is a partial front view of the assembly shown in the figures

1 and 2,

- Figure 4 is a perspective view of one of the floors of the assembly shown in Figures 2 and 3,

- Figure 5 is an exploded perspective view of the floor shown in Figure 4,

- Figure 6 is a schematic view illustrating the cold spraying of the powder on the face, and - Figure 7 is a schematic sectional view illustrating the formation of a layer suitable for filling the interstices, the layer comprising a material obtained by coalescing the sprayed powder.

Referring to Figures 1 to 3, there is described a heat exchanger 1 according to the invention.

As visible in FIG. 1, the heat exchanger 1 comprises an assembly 5 (matrix), and four members 7, 9, 11, 13 for respectively supplying a cold fluid F1, recovering a heated fluid F1 ', supplying a hot fluid F2 , and recovering a cooled fluid F2 'in a cocurrent configuration.

The cold fluid F1 is for example water, a mixture of water and glycol or air, especially if the heat exchanger 1 is a heat pump condenser.

The hot fluid F2 is, for example, a refrigerant of the FIFE (hydrofluoroether) or FIFO (hydrofluoroolefin) type, as is the case in a heat pump. In the case of cooling the oil of a heat engine, the hot fluid is, for example, the oil to be cooled.

If the heat exchanger 1 is an evaporator, the nature of the cold fluid F1 and of the hot fluid F2 are for example reversed.

As visible in Figures 2 and 3, the assembly 5 comprises for example four stages 15, 17, 19, 21 superimposed in a direction Z, for example vertical, and two end plates 23, 25 respectively forming an upper face 27 and a face lower 29 of the set.

The assembly 5 is, for example, of generally parallelepipedal shape. The assembly 5 comprises two side faces 31, 33 (Figure 2) opposite in a Y direction substantially perpendicular to the Z direction, and two side faces 35, 37 opposite in an X direction substantially perpendicular to the Z direction and to the Y direction .

The side faces 31, 33, 35, 37 are for example rectangular, and two of them consecutive around the Z direction advantageously form a substantially right angle.

The lateral face 31 comprises for example three inputs E1, E2, E3 for three streams F11, F12 and F13 from the cold fluid F1, and two outputs S1 ', S2' for two streams F21 'and F22' intended to form the cooled fluid. F2 '.

The side face 33 has two inlets (not visible in Figure 2 because located at the rear) for two flows F21 and F22 from the hot fluid F2, and three outlets (also not visible in Figure 2) for three flows F11 ' , F12 'and F13' intended to form the heated fluid F1 '. As visible in Figures 2 and 3, the stages 15, 17, 19, 21 are substantially similar to each other.

The aforementioned inlets and outlets are, for example, as slots extending in the direction X on the side faces 31, 33.

The inputs E1, E2 and E3 are for example aligned in the Z direction and located opposite the component 7.

The same applies to the inlets located on the side face 33, except that they are located opposite the member 11.

The outputs S1 'and S2' are for example superimposed in the direction Z and located opposite the member 13. The same applies to the outputs located on the side face 33, except that 'they are located opposite the member 9.

Stages 15 to 21 are formed by plates 39, 41, 43, 45, 47 (Figure 3) substantially perpendicular to the Z direction and alternating with parts 49, 51, 53, 55. In the example shown, the parts 49, 51, 53, 55 are similar to each other, so only the part 53 belonging to the floor 19 will be described below with reference to Figures 3 to 5.

Part 53 comprises at least 90% by mass of a metal or metal alloy. Advantageously, part 53 is made of stainless steel, for example 316L.

According to variants, part 53 is made of copper, aluminum or titanium.

The part 53 is formed by a metal sheet 58 folded back on itself in an accordion, in the example parallel to the X direction. The part 53 defines a plurality of circulation channels 63 located above the metal sheet 58 and intended to receive the flow F12, and a plurality of circulation channels 65 located under the metal sheet and intended to receive the flow F22.

The part 53 is fixed to the plates 43, 45, advantageously by brazing.

According to a particular embodiment, the part 53 is glued to the rest of the assembly 5, in particular if the latter is not entirely metallic.

The part 53 has two faces 59, 60 opposite in the X direction, on which a corrugated edge 60A of the sheet 58 defines interstices 61.

The circulation channels 63, 65 are oriented substantially in the direction X.

The interstices 61 have two edges 67, 69 (FIG. 3) opposite in the Y direction and separated by a maximum distance D less than or equal to 1 mm, preferably less than or equal to 250 μm, and for example less than 150 μm.

The plates 39, 41, 43, 45, 47 are structurally similar to each other. The plates 39, 43, 47 have the same orientation in space, while the plates 41 and 45 have another orientation in space, deduced from the first, for example by a rotation of 180 ° around the X direction.

Each of the plates 39, 41, 43, 45, 47 has for example a generally rectangular shape when viewed in the Z direction. Each of the plates comprises two cutouts 71, 73 (FIG. 5), for example symmetrical to each other by relative to a point S located at the center of the plate.

Each of the cutouts 71, 73 extends in the example in the Y direction from one of the side faces 31 or 33 of the assembly 5, above or below the circulation channels 63, 65.

The plates 39, 41, 43, 45, 47 are made of metal or a metal alloy, for example stainless steel, advantageously 316L. The plates are respectively fixed to the parts 49, 51, 53, 55, for example by conventional brazing.

As a variant, the plates are made of copper, aluminum, or titanium.

Advantageously, the plates are made of the same material as the parts 49, 51, 53, 55.

The members 7, 9, 11, 13 are advantageously similar to each other. Also, only component 7 will be described in detail below.

The member 7 is made of metal or a metal alloy, for example stainless steel, preferably 316L.

Alternatively, member 7 is made of copper, aluminum, or titanium.

Advantageously, the member 7 is made of the same material as the plates 39, 41, 43, 45, 47.

The member 7 comprises an upper tubular part 79, and a lower part 81 located in the extension of the first part in the Z direction and obtained by cutting along a plane corresponding to the upper face 27 and along a plane corresponding to the lateral face 31. The member 7 further comprises a bottom 83.

The heat exchanger 1 comprises, for example, layers 85 (two of which are shown in FIG. 5) formed by a material 89 obtained by coalescing at least part of a powder 91 sprayed cold onto the faces 59, 60 of the parts 49, 51, 53, 55, and possibly on other faces.

The layers 85 are suitable for filling the interstices 61 on the faces 59, 60.

The layers 85 are structurally similar to each other, so only one of them, located on the face 59 of one of the parts 53, will be described below with reference to FIG. 7. The total thickness of the layer 85 is advantageously between 0.5 mm and 5 mm, and is for example approximately 1 mm.

Layer 85 is advantageously formed of a plurality of layers 93 superimposed in a direction N normal to face 59.

In the example shown, the normal direction N is parallel to the direction X.

The layers 93 result from successive projections of powder 91, as will be explained below.

In the example, each of the layers 93 is formed by the material 89 resulting from the coalescence of the powder 91. Each of the layers 93 has a thickness between 1 and 500 μm, preferably between 25 and 100 μm, and for example approximately 50 pm.

Material 89 includes, for example, one of aluminum, steel, copper, and mixtures thereof.

According to a particular embodiment, the material 89 comprises alumina, for example in a volume proportion of between 10 and 20%, preferably approximately 30%.

Alternatively, part 53 is made of stainless steel, material 89 being a mixture of copper and alumina.

According to another variant, the part 53 is made of aluminum, the material 89 being aluminum.

Advantageously, the heat exchanger 1 comprises other layers (not shown) obtained by spraying a metal powder, or a mixture of a metal and ceramic powder. For example, the assembly 5 or the heat exchanger 1 are covered by one or more layers (not shown) obtained by spraying a metal powder, or a mixture of a metal powder and a ceramic powder.

Also described is a heat pipe according to the invention. This is not strictly represented in the figures, but is easily deduced from it. For example, in FIG. 5, the plates 43, 45 are replaced by plates without cutting. The circulation channels 63, 65 respectively define an upper space located above the room 53, and a lower space located below the room 53. These spaces are closed in the X direction by the metal layers 85, and according to the direction Y by the extreme folds of the part 53. Suitable fluids, distinct or not, are present in these spaces and free to circulate in the circulation channels 63, 65.

The heat pipe contains an enclosed fluid (via a hermetic filling device, for example a nozzle made on the part (43)). It is in a vertical position, that is say that the direction X is then vertical. For example, the face 60 is in the high position and the face 59 in the low position.

The lower face 59 is placed on an object (not shown) to be cooled, for example an electronic component, the temperature of which must be maintained between 20 and 30 ° C.

The heat thus collected at face 59 causes the fluid to boil, in the liquid phase in the lower part of the heat pipe. The vapor propagates to the upper part, in the direction of the face 60, which itself is cooled on its external part by a refrigerant / refrigerant device. Consequently, on this upper face 60, the vapor condenses and falls back by gravity towards the lower part. The changes of state by successive evaporations and condensations make it possible to extract a very large amount of heat from the object in contact with the face 59 in the lower part.

The heat pipe is particularly efficient, because both in the low zone (evaporation) and in the high zone (condensation), the exchange surface / volume ratio is very important.

The manufacture of the heat exchanger 1 will now be described. It illustrates a manufacturing process according to the invention.

First, parts 49, 51, 53, 55 are supplied, as well as spacer plates 39, 41, 43, 45, 47, end plates 23, 25, and components 7, 9, 11, 13.

These elements are stacked as shown in Figures 3 and 4 in the Z direction, by interposing between each of the brazing sheets 87 as shown in Figure 5.

The brazing sheets 87 are made of a brazing alloy, for example of BNi- 2 alloy, or of any other material suitable for the composition of the parts 49, 51, 53, 55 and of the plates 39, 41, 43, 45, for example in copper-silver eutectic alloy for brazing copper parts.

The assembly of the parts 49, 51, 53, 55, of the plates 39, 41, 43, 45, 47, of the end plates 23 and 25, and of the brazing sheets 87 is carried out by stacking, and maintained mechanically by means of a tool. adapted (not shown).

Then, the assembly is heated to a brazing temperature to obtain assembly 5.

As a variant, the assembly is not obtained by brazing, but for example by gluing.

Then, to obtain the layers 85 described above, the powder 91 is sprayed cold on the faces to be covered using a carrier gas, as shown schematically in FIG. 6. Only the production of the layer 85 covering the face 59 is described below. The other layers 85 or the possible similar layers mentioned above (not shown) are obtained in a similar manner.

The cold spraying, or dynamic spraying, of a powder is known per se to those skilled in the art under the English name of cold spraying, or gas dynamic cold spraying. The powder particles, typically 1 to 50 microns in diameter, are accelerated in a supersonic gas jet at speeds of up to about 1200 m / s.

Upon impact with face 59, the particles undergo plastic deformation and adhere to the surface. The kinetic energy of the particles, provided by the expansion of the gas, is converted into “cold” plastic deformation energy here means that the particles are thrown in the solid state against the surface, and that the plastic deformations are above all due to the kinetic energy that the gas has transferred to the particles.

Material 89 is obtained by coalescing at least part of powder 91 (except for losses), which forms layer 85.

The gas used for spraying, for example, air, helium, nitrogen and their mixtures, is advantageously expanded from a pressure of between 5 and 10 bars relative (i.e. - say in addition to atmospheric pressure), for example about 8 bars.

The powder 91 comprises at least one metallic powder, or at least one metallic powder and at least one ceramic powder.

The metal powder is, for example, one of aluminum powder, steel powder, copper powder, and mixtures thereof.

The ceramic powder is, for example, an alumina powder.

According to a variant mentioned above, if the part 53 is made of stainless steel, the powder 91 is a mixture of a copper powder and an alumina powder, for example at about 30% by volume.

According to a variant mentioned above, if the part 53 is made of aluminum, the powder 91 is a mixture of aluminum powder and alumina.

The projection step comprises, for example, a plurality of successive passes of at least one device 95 for projecting the powder 91.

The device 95 is for example the Russian model 423 DYMET, marketed in Europe by the Dutch company DYCOMET. Each of the successive passes respectively performs a scanning of all or part of the face 59 and forms one of the layers 93. The scanning is for example carried out in the Y direction, for example in a single movement.

In the projection step, the powder 91 is advantageously projected cyclically in four main directions of projection P1, P2, P3, P4 which are distinct from each other. On each pass, the powder 91 is projected in one of the main directions of projection P1, P2, P3, P4. Then, in the next pass, the powder is projected in the following direction among the main directions of projection P1, P2, P3, P4.

This is for example achieved by changing the orientation of the projection device 95 on each pass, or else by using a plurality of projection devices (not shown) respectively configured to project the powder 91 according to the main directions of projection P1, P2, P3, P4.

As a variant (not shown), only one direction of projection is used, or else two, three, or more than four.

The main directions of projection P1, P2, P3, P4 respectively form angles a1, a2, a3, a4 of between 20 ° and 70 °, preferably between 40 ° and 50 °, and for example of about 45 °, with a direction N normal to the face 59. These ranges of angles make it possible to effectively plug the interstices 61 of the face 59.

The main directions of projection P1, P2, P3, P4 are angularly distributed around the direction N, advantageously regularly, that is to say at about 90 ° to each other.

In the example, the directions P1 and P3 are orthogonal to the Z direction, and the P2 and P4 directions are orthogonal to the Y direction.

The presence of at least one ceramic powder, mixed with at least one metal powder, smoothes the flow of the particles of the powder 91 in the device 95, and improves the adhesion of the particles on the face 59 by self-blasting.

Thus, the interstices 61 are closed in a simple and advantageous manner.

The members 7, 9, 11, 13 are then fixed to the assembly 5 by brazing, welding, gluing or any other process suitable for the heat exchanger 1.

According to a variant, the members 7, 9, 11, 13 are fixed to the assembly 5 during the assembly operation, before the step or steps of depositing the sealing layer 85 by spraying metal powders or mixing metal powders. and ceramics.

Optionally, other similar sealing steps by spraying one or more powders are carried out to complete the heat exchanger 1. The heat pipe described above is manufactured in a similar way. It is for example composed of five parts: a sheet folded in an accordion (53), two distribution plates 43 and 45 with openings 71 closed on their outer edge and two end plates 23 and 25. First, the parts 23, 25, 43, 45 and 53 are assembled by brazing, in a manner analogous to the case of the exchanger. Secondly, the faces (59) and (60) are closed by spraying metal powders or a mixture of metal and ceramic powders forming a sealed deposit. Thirdly, the end plates 23 and 25 are drilled to allow the fixing by welding or brazing of tubes used for filling the fluid. This last operation can also take place before the deposition or brazing step.

The operation of the heat exchanger 1 is deduced from its structure and will now be briefly described.

The cold fluid F1 (Figure 1) enters the organ 7. The cold fluid F1 flows along the side face 31 of the assembly 5 and divides into the flows F11, F12 and F13 (Figure 2).

Flows F11, F12 and F13 enter set 5 through inputs E1, E2, E3.

The flow F12 flows substantially in the Y direction in the cutout 73 of the plate 43 which acts as a distributor (Figure 5). The flow F12 then enters the circulation channels 63 (upper) of the part 53 and the circulation channels 65 (lower) of the part 51 (FIG. 3). As it flows in the X direction in the circulation channels 63, 65, the cold fluid exchanges heat with the hot fluid F2 located respectively on the other side of each of the parts 51, 53, and is cools and becomes the flow F12 '. The flow F12 ’exits the assembly 5 through the face 33 at the level of the cutout 71 of the plate 43.

Likewise, the streams F11 and F13 flow through the assembly 5 from the side face 31 to the side face 33 exchanging heat in co-current with the streams F21 and F22.

Once reheated, streams F11, F12, F13 become heated streams F11 ’, F12’ and F13 ’which emerge into organ 9 and combine to form heated fluid F1’.

Likewise, the hot fluid F2 enters the body 11 and is divided into the flows F21 and F22 which enter the assembly 5 through the side face 33.

For example, as visible in FIG. 4, the flow F22 enters through the cutout 73 of the plate 45 and enters the channels 65 (lower) defined by the part 53 and into the channels 63 of the part 55. The flows F21 and F22 are cooled by heat exchange through parts 49, 51 on the one hand and 53, 55 on the other hand and emerge in the form of flow cooled F21 'and F22'. The flows F21 'and F22' combine in the member 13 to form the cooled fluid F2 \

Thus, thanks to the characteristics described above, the method allows the manufacture of the heat exchanger 1 or the heat pipe described above, by treating the parts 49, 51, 53, 55 having the micro-interstices 61. This allows in particular to give small dimensions to the heat exchanger 1 or to the heat pipe described above.

In addition, the process enables the manufacture of heat exchanger 1 or the heat pipe by minimizing the number of brazing steps. This makes it possible to obtain exchangers of small dimensions, at reduced cost, and possibly in a single brazing step. The optional feature according to which the powder 91 is projected along at least one main projection direction P1 at an angle of between 20 ° and 70 ° with the direction N normal to the face 59 makes it possible to reduce the duration of the powder projection.

The optional feature according to which the successive passes are carried out by projecting the powder 91 cyclically in a plurality of main directions of projection distinct from each other forming respectively angles between 20 ° and 70 ° with the direction N and distributed angularly around the normal direction N makes it possible to improve the homogeneity of the deposit 85 and to adapt to some minor roughness of the face 59 to be sealed.

Claims

1. A method of manufacturing a heat exchanger (1) or a heat pipe, comprising at least the following steps:

- Obtaining an assembly (5) comprising at least one part (53) comprising at least 90% by mass of a metal or a metal alloy, the part (53) having at least one face (59) defining a plurality of interstices (61), each of the interstices (61) comprising at least two opposite edges (67, 69) separated on the face (59) by a maximum distance (D) less than or equal to 550 micrometers, the part (53) defining a plurality of circulation channels (63, 65) for fluids (F1, F2), each of the circulation channels (63, 65) defining one of the interstices (61), and

- projection of at least one powder (91) on said face (59) using a carrier gas, obtaining a material (89) by coalescing at least part of the powder (91), and forming a layer (85) comprising the material (89) and adapted to plug the interstices (61), the powder (91) comprising at least one metallic powder, or at least one metallic powder and at least one ceramic powder.

2. The method of claim 1, wherein the part (53) comprises a sheet (58) of metal accordion folded, a corrugated edge (60A) of the sheet (58) forming the edges (67, 69) of the interstices (61). ), the circulation channels (63, 65) extending parallel to and on either side of the sheet (58).

3. The method of claim 1 or 2, wherein said at least one metal powder comprises one of aluminum powder, steel powder, copper powder, and mixtures thereof.

4. A method according to any one of claims 1 to 3, wherein said at least one ceramic powder comprises alumina powder.

5. A method according to any one of claims 1 or 2, wherein:

- the part (53) is made of stainless steel, the powder (91) comprising a mixture of a copper powder and an alumina powder, or

- The part (53) is made of aluminum, the powder (91) comprising an aluminum powder.

6. The manufacturing method according to any one of claims 1 to 5, wherein, in the projection step, the powder (91) is projected in at least one main direction of projection (P1) intercepting the face (59). at a point (O), the main direction of projection (P1) forming an angle (a1) between 20 ° and 70 ° with a direction (N) normal to said face (59) at this point (O).

7. Method according to any one of claims 1 to 6, wherein the projection step comprises a plurality of successive passes of at least one device (95) for projecting said powder (91), the successive passes respectively carrying out scanning at least part of the face (59) and forming a plurality of layers (93) superimposed and included in the layer (85).

8. The method of claim 7, wherein each of the layers (93) of said plurality has a thickness between 1 and 500 µm, preferably between 25 and 100 µm.

9. The method of claim 7 or 8, wherein the successive passes are carried out by projecting the powder (91) cyclically in a plurality of main directions of projection (P1, P2, P3, P4) distinct from each other, the directions principal projections (P1, P2, P3, P4) respectively forming angles (a1, a2, a3, a4) between 20 ° and 70 ° with a direction (N) normal to said face (59) and being distributed angularly around direction (N).

10. Heat exchanger (1) or heat pipe comprising:

- an assembly (5) comprising at least one part (53) comprising at least 90% by mass of a metal or a metal alloy, the part (53) having at least one face (59) defining a plurality of interstices (61), each of the interstices (61) comprising at least two opposite edges (67, 69) separated on the face (59) by a maximum distance (D) less than or equal to 550 micrometers, the part (53) defining a plurality circulation channels (63, 65) for fluids (F1, F2), each of the circulation channels (63, 65) defining one of the interstices (61), and

- a layer (85) comprising a material (89) obtained by coalescing at least part of a powder (91) sprayed cold onto said face (59), the layer (85) being adapted to plug the interstices ( 61), the sprayed powder (91) comprising at least one metallic powder, or at least one metallic powder and at least one ceramic powder.