WO2020109155A1

WO2020109155A1 - Method for manufacturing a heat exchanger or a heat pipe

Info

Publication number: WO2020109155A1
Application number: PCT/EP2019/082195
Authority: WO
Inventors: Pierre Billat
Original assignee: Stiral
Priority date: 2018-11-26
Filing date: 2019-11-22
Publication date: 2020-06-04
Also published as: FR3088999B1; EP3887743B1; EP3887743A1; FR3088999A1

Abstract

Method for manufacturing a heat exchanger or a heat pipe, comprising at least the following steps: - obtaining an assembly (5) comprising at least one part (53) which comprises at least 90% by weight of a metal or a metal alloy, the part having at least one surface defining a plurality of interstices (61), each of the interstices comprising at least two opposite edges (67, 69) separated on the surface by a maximum distance (D) less than or equal to 550 micrometres, the part defining a plurality of circulation channels (63, 65) for fluids, each of the circulation channels defining one of the interstices, and - immersing the assembly in an electrolytic bath and electroplating a metal layer on the surface, the layer being suitable for plugging the interstices. Corresponding heat exchanger or heat pipe.

Description

DESCRIPTION

TITLE: Process for manufacturing 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 circulation for one or more fluids.

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

It is well known to use soldering to assemble parts, in particular for the purpose of assembling a heat exchanger or a heat pipe.

In addition, a known type of heat exchanger implements a part consisting of a metal sheet folded back on itself in an accordion. Two plates fixed on either side of the metal sheet define parallel circulation channels between them and located on each side of the metal sheet. The longitudinal ends of the channels open onto faces of the accordion-shaped 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 sheet and exchanging heat with each other through the metal sheet.

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

To seal the assembly around its periphery, bars, called "closing bars" are generally fixed on the matrix. Fluid supply heads are then added to the matrix to form the exchanger.

Because of the expansion differentials between the parts, which prevent over-geometrically constraining the constituents of the future exchanger, it is generally practiced several brazing steps, between which machining operations are carried out so as to guarantee the play between parts. This practice requires great control of the nuances of filler alloys so as not to degrade during the next step the junctions made in the previous step.

A first method consists in making, initially, a closed or semi-open frame in which we will insert an accordion sheet to assemble it by brazing for the first time. In a second step, a set of these frames is assembled by brazing in order to constitute the exchanger matrix. Thirdly, the fluid connection tubes are brazed to the matrix.

A second method consists, firstly, in assembling by brazing all of the accordion sheets on all of the plates, to which are possibly joined the longitudinally oriented closing bars. In a second step, the sides of the accordion sheets are machined to align them perfectly, in order to assemble them by brazing with the closing bars oriented transversely. The matrix of the exchanger is thus obtained. Finally, in a third step, the fluid connection tubes are welded or brazed to the matrix.

Furthermore, there is a need, in different industrial sectors, such as the automobile or aeronautics, to reduce, on the one hand, the space created by the thermal circuits and their mass and, on the other hand, the 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, that is to say the brazing of the closure bars on the face of the accordion sheets having the interstices described above.

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

To this end, the invention relates to a process for 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 face defining a plurality of interstices, each of the interstices comprising at least two edges opposites 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

- immersion of the assembly in an electrolytic bath and electrodeposition of a metal layer on said face, said layer being adapted to plug the interstices.

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

- The part comprises a metal sheet folded in accordion, a corrugated edge of the sheet forming the edges of the interstices, the circulation channels extending parallel to, and on both sides of the sheet;

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

- The step of obtaining the assembly includes a sub-step for fixing the part on at least two plates, the part being located between the two plates in a direction;

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

- the method also comprises one or more of the following steps prior to the immersion and electroplating step:

- chemical degreasing of the whole,

- electrolytic degreasing of the assembly, and / or

- anodic acid activation of the whole;

- The electrolytic bath comprises nickel, the layer mainly comprising nickel;

- The electrolytic bath comprises nickel sulfamate; and

- The manufacturing process also includes a step of immersing the assembly in a Wood bath to pre-nickel the part before said step of immersing the assembly in an electrolytic and electroplating bath .

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 opposite edges 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 metal layer electro-deposited on said face and covering the interstices.

According to particular embodiments, the exchanger or the heat pipe can be obtained, or are actually 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 appended drawings, in which:

[Fig 1] Figure 1 is a perspective view of a heat exchanger according to the invention,

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

[Fig 3] Figure 3 is a partial front view of the assembly shown in Figures 1 and 2,

[Fig 4] FIG. 4 is a perspective view of one of the stages of the assembly shown in FIGS. 2 and 3,

[Fig 5] FIG. 5 is an exploded perspective view of the stage shown in FIG. 4, and of electro-deposited layers,

[Fig 6] Figure 6 is a schematic view illustrating a step of immersing the assembly in an electrolytic bath of a process according to the invention, and

[Fig 7] Figure 7 is a schematic view, in section, illustrating a step of electrodeposition of a method according to the invention.

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

As shown in Figure 1, the heat exchanger 1 includes a set 5

(matrix), and four members 7, 9, 1 1, 13 for respectively supplying a cold fluid F1, recovering a heated fluid F1 ’, supplying a hot fluid F2, and recovering a cooled fluid F2’.

The cold fluid is for example water or a mixture of water and glycol.

The hot fluid is for example an HFE type refrigerant

(hydrofluoroether) or HFO (hydrofluoroolefin), as is the case in a heat pump. When cooling the engine oil, the hot fluid is the oil to be cooled.

As can be seen in FIGS. 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 lower face 29 of the assembly.

The assembly 5 is for example of general parallelepiped shape. The assembly 5 comprises two lateral faces 31, 33 (FIG. 2) opposite in a direction Y substantially perpendicular to the direction Z, and two lateral faces 35, 37 opposite in a direction X substantially perpendicular to the direction Z and to the direction Y .

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

The lateral face 31 comprises for example three inputs E1, E2, E3 for three flows F1 1, F12 and F13 coming from the cold fluid F1, and two outputs S1 ', S2' for two flows F21 'and F22' intended to form the fluid cooled F2 '.

The side face 33 has two inlets (not visible in FIG. 2 because they are located at the rear) for two streams F21 and F22 coming from the hot fluid F2, and three outlets (also not visible in FIG. 2) for three streams F1 1 ', F12' and F13 'intended to form the heated fluid F1'.

As shown in Figures 2 and 3, the stages 15, 17, 19, 21 are substantially similar to each other.

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

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

The same goes for the inputs located on the lateral face 33, except that they are located opposite the member 1 1.

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

The stages 15 to 21 are formed by plates 39, 41, 43, 45, 47 (FIG. 3) substantially perpendicular to the direction Z 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 stage 19 will be described below with reference to FIGS. 3 to 5.

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

According to variants, the 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 direction X. 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 direction X, on which a corrugated edge 60A of the sheet 58 defines interstices 61.

The faces 59, 60 are for example perpendicular to the direction X.

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 direction Y and separated by a maximum distance D less than or equal to 550 μm, 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 direction X .

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

Each of the cutouts 71, 73 extends in the example in the direction Y from one of the side faces 31 or 33 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 fixed respectively on the parts 49, 51, 53, 55, for example by conventional brazing.

Alternatively, 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 organs 7, 9, 1 1, 13 are advantageously similar to each other. Also, only the member 7 will be described in detail below.

The member 7 is made of metal or a metal alloy, for example stainless steel, advantageously 316L. Alternatively, the 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 a tubular upper part 79, and a lower part 81 situated in the extension of the first part in the direction Z 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 also comprises a bottom 83.

The heat exchanger 1 also includes electro-metallic layers 85 deposited in particular on the faces 59 and 60 of the parts 49, 51, 53, 55, and possibly on other faces.

The layers 85 are adapted to plug the interstices 61 on the faces 59, 60.

The layers 85 are for example made of nickel.

According to variants, the layers 85 are made of copper, copper-nickel alloy, or aluminum.

The thickness of the layer 85 is advantageously between 0.5 mm and 5 mm, and is for example around 1 mm.

Advantageously, the heat exchanger 1 comprises other electro-deposited layers (not shown). For example, the assembly 5 or the heat exchanger 1 are covered by one or more electro-deposited layers.

A heat pipe according to the invention is also described. This is not strictly represented in the figures, but is easily deduced therefrom. For example, in Figure 5, we replace the plates 43, 45 by plates without cutting. The circulation channels 63, 65 respectively define an upper space situated above the part 53, and a lower space situated below the part 53. These spaces are closed in the direction X by the electro-deposited layers 85, and in 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 a fluid injected by an airtight filling device (not shown), for example a tapping made on the plate 43.

The heat pipe is used in vertical position, that is to 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 whose temperature must be maintained between 20 and 30 ° C.

The heat thus collected at the 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, towards the face 58, which itself is cooled on its external part by a refrigeration / refrigeration device. Consequently, on this upper face 60, the vapor condenses and falls 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 effective, 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 we supply the parts 49, 51, 53, 55, as well as the plates 39, 41, 43, 45, 47 inserts, the end plates 23, 25, and the members 7, 9, 1 1, 13.

These elements are stacked as shown in FIGS. 3 and 4 in the direction Z, by interposing between each of the brazing sheets 87 as shown in FIG. 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 parts 49, 51, 53, 55 and plates 39, 41, 43, 45, for example made of 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 produced by stacking, and mechanically maintained by means of a tool. adapted (not shown).

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

Alternatively, the assembly is not obtained by brazing, but for example by gluing.

Advantageously, the assembly 5 then undergoes chemical degreasing and electrolytic degreasing. These operations are known in themselves to those skilled in the art in order to clean surfaces with a view to depositing them by electrolysis.

Electrolytic degreasing is for example carried out in a conventional bath for stainless steel and nickel in cathodic polarization, with a current density of 4A / dm ² for 10 minutes at 35 ° C.

Advantageously, the assembly 5 then undergoes anodic activation in an acid medium, for example for two minutes.

Optionally, the assembly 5 thus cleaned and activated undergoes an electrolytic pre-nickel plating by immersion in a Wood bath, for example at 25 ° C., with a cathodic current density of 6 A / dm ² for 8 minutes. Wood's bath includes, for example, nickel chloride NiCI ₂ .6H ₂ 0 at 100-250 g / liter, and hydrochloric acid HCl at 85-125 cm ³ / liter.

Then, as shown diagrammatically in FIG. 6, the assembly 5 thus prepared is immersed in an electrolytic bath 89, and the layer 85 is electro-deposited on the faces 59, 60 of the parts 49, 51, 53, 55.

The electrolytic bath 89 advantageously comprises nickel sulfamate.

Alternatively, if the parts 49, 51, 53, 55 are made of copper, the electrolytic bath 89 is for example a mixture of copper sulphate and sulfuric acid.

Alternatively, if the parts 49, 51, 53, 55 are made of aluminum, the electrolytic bath 89 comprises for example an organic solvent, such as a mixture of tetrahydrofuran and benzene, in which aluminum chloride AICI is advantageously dissolved. ₃ and lithium aluminum hydride UAIH ₄ .

During the plating of layer 85, the assembly 5 is electrically connected to the cathode of a generator 91. The assembly 5 therefore plays the role of cathode in electrolysis.

A consumable anode 93 is immersed in the electrolytic bath 89 and connected to the anode of the generator 91. Anode 93 is for example made of nickel beads depolarized with sulfur.

Surprisingly, as visible in FIG. 7, metallic seeds 95 appear almost only at the level of the gap 61 on the wavy edge 60A of the parts 49, 51, 53, 55. The seeds 95 grow by forming a swelling of the wavy edge. Then, the seeds 95 join in the direction Y and grow further to form the layer 85, which completely blocks the interstices 61 of the faces 59, 60.

Also surprisingly, the germs 85 grow little in the X direction towards the inside of the circulation channels 63, 65.

Thus, the interstices 61 of the faces 59, 60 are closed in a simple and advantageous manner.

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

Alternatively, the members 7, 9, 1 1, 13 are fixed on the assembly 5 during the assembly operation, before the step or steps of electroplating.

Optionally, other plating steps are carried out to complete the heat exchanger 1.

The heat pipe described above is produced in a similar manner. It is for example composed of five parts: the sheet 58, the two distribution plates 43 and 45 provided with opening 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 similar manner to the case of the exchanger. Secondly, the faces 59 and 60 are closed by electrodeposition. 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 deposit step.

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

The cold fluid F1 (FIG. 1) enters the member 7. The cold fluid F1 flows along the lateral face 31 of the assembly 5 and is divided into the flows F1 1, F12 and F13 (FIG. 2) .

The flows F11, F12 and F13 enter the set 5 through the inputs E1, E2, E3.

The flow F12 flows substantially in the direction Y in the cutout 73 of the plate 43 which plays the role of distributor (FIG. 5). The flow F12 flows then penetrates into the circulation channels 63 (upper) of the part 53 and into the circulation channels 65 (lower) of the part 51 (FIG. 3). As it flows in the direction X in the circulation channels 63, 65, the cold fluid exchanges heat with the hot fluid F2 situated respectively on the other side of each of the parts 51, 53, and becomes cools and becomes flow F12 '. The flow F12 ′ leaves the assembly 5 via the face 33 at the cutout 71 of the plate 43.

Likewise, the flows F1 1 and F13 flow through the assembly 5 from the side face 31 to the side face 33 by exchanging heat against the current with the flows F21 and F22.

Once heated, the flows F1 1, F12, F13 become heated flows F1 1 ’, F12’ and F13 ’which open into the member 9 and combine to form the heated fluid F1’.

Likewise, the hot fluid F2 penetrates into the member 11 and divides into the flows F21 and F22 which enter the assembly 5 through the lateral face 33.

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

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

In addition, the method allows the manufacture of the heat exchanger 1 or the heat pipe while 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.

Claims

1. Method for 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, and

- immersion of the assembly (5) in an electrolytic bath (89) and electrodeposition of a layer (85) of metal on said face (59), said layer (85) being adapted to plug the interstices (61).

2. The manufacturing method according to claim 1, in which the part (53) comprises a metal sheet (58) folded in accordion, 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 manufacturing method according to any one of claims 1 or 2, wherein the part (53) is stainless steel, copper, aluminum, or titanium.

4. Manufacturing method according to any one of claims 1 to 3, wherein the step of obtaining the assembly (5) comprises a sub-step of fixing the part (53) on at least two plates ( 43, 45), the part (53) being located between the two plates (43, 45) in a direction (Z).

5. The manufacturing method according to claim 4, wherein the fixing sub-step comprises brazing the part (53) on said at least two plates (43, 45).

6. The manufacturing method according to any one of claims 1 to 5, in which the method further comprises one or more of the following steps prior to the immersion and electroplating step:

- chemical degreasing of the assembly (5), - electrolytic degreasing of the assembly (5), and / or

- acid anodic activation of the assembly (5).

7. The manufacturing method according to any one of claims 1 to 6, wherein the electrolytic bath (89) comprises nickel, the layer (85) mainly comprising nickel.

8. The manufacturing method according to claim 7, wherein the electrolytic bath (89) comprises nickel sulfamate.

9. Manufacturing method according to any one of claims 1 to 8, further comprising a step of immersing the assembly (5) in a Wood bath to perform a pre-nickel plating of the part (53) before said step of immersing the assembly (5) in an electrolytic bath (89) and of electrodeposition.

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 metal layer (85) electro-deposited on said face (59) and covering the interstices (61).