WO2019122663A1

WO2019122663A1 - Spacer element with surface texturing, heat exchanger comprising such an element

Info

Publication number: WO2019122663A1
Application number: PCT/FR2018/053341
Authority: WO
Inventors: Nicolas Richet; Frédéric Crayssac; Hakim Maazaoui
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 2017-12-19
Filing date: 2018-12-17
Publication date: 2019-06-27
Also published as: FR3075337B1; FR3075337A1; EP3728979A1

Abstract

The invention concerns a spacer element (22) for a brazed plate-fin heat exchanger, intended to be mounted between a first plate (6) and a second plate (7) of the exchanger, said spacer element (22) comprising at least one first assembly portion (121) configured to be assembled with the first plate (6) and comprising a first pair of opposing surfaces (121a, 121b), one (121a) of the surfaces of the first pair being oriented towards the first plate (6) and the other (121b) of the surfaces of the first pair being oriented towards the second plate (7) when the spacer element (22) is in the mounted state, a plurality of corrugated fins or legs (123) extending from said first assembly portion (121) so as to delimit a plurality of channels (26) for the flow of a first fluid, when the spacer element (22) is in the mounted state, and at least one surface texturing (23) in the form of a porous structure or reliefs formed on a surface of the spacer element (22), at least one corrugated fin or leg (123) having said surface texturing (23). According to the invention, the first assembly portion (121) has said surface texturing (23) on the surface (121a) of the first pair oriented towards the first plate (6), when in the mounted state.

Description

INTERCALAR ELEMENT WITH SURFACE TEXTURING, HEAT EXCHANGER COMPRISING SUCH A ELEMENT

The present invention relates to a surface-textured spacer element for a heat exchanger, and to a plate-and-fin type heat exchanger comprising such an element.

The present invention finds particular application in the field of gas separation by cryogenics, in particular the separation of air by cryogenics (known by the acronym "ASU" for air separation unit) exploited for the production of oxygen gas under pressure. In particular, the present invention can be applied to a heat exchanger which vaporizes a liquid flow, for example liquid oxygen, nitrogen and / or argon by heat exchange with a caloric gas, by example air or nitrogen.

If the heat exchanger is in the tank of a distillation column, it can constitute a vaporizer operating as a thermosiphon for which the exchanger is immersed in a bath of liquid descending the column or a vaporizer operating in vaporization with a film fed directly by the liquid falling from the column and / or by a recirculation pump.

The present invention can also be applied to a heat exchanger which vaporises at least one liquid-gas mixture flow rate, in particular a multi-component mixing flow rate, for example a mixture of hydrocarbons, by heat exchange with at least one another fluid, for example natural gas.

The technology commonly used for a heat exchanger is that of plate and finned aluminum exchangers or brazed waves, which allow to obtain very compact devices with a large exchange surface.

These exchangers comprise separating plates between which are inserted heat exchange structures, generally corrugated structures or waves, formed of a succession of fins or wave legs, thus constituting a stack of passages for the different fluids to be put in heat exchange relationship. The performance of an exchanger is related to the heat exchange coefficient of the heat exchange structures in contact with the fluids. The heat exchange coefficient of a structure depends in particular on the nature of the material constituting it, the porosity of this material, its roughness and the flow regime of the fluids.

For example, documents DE 10 2012 204 178 B3 or US 2012/002451 1 A1 disclose corrugated exchange structures with deformations in the form of bosses.

Furthermore, EP 0 764 488 A1 discloses a sintered metal heat exchange structure.

It is possible to modify the heat exchange coefficient of an exchange structure by modifying the geometry or physicochemical properties of its surface. This makes it possible to increase the effective surface of exchange and / or to modify the interactions between the fluid and the surface, by changing the properties of the surface considered as its wettability or its capacity to intensify the boiling of a fluid. We then speak of intensified surfaces.

For example, porous or textured surface coatings can be made, forming reliefs on the surface of the structures, or creating such surface conditions by mechanical treatments or by etching.

WO-A-2005/075920 discloses various techniques for deposition of porous coatings or texturing on the surface of a wave for a heat exchanger.

One problem concerns the assembly of elements comprising intensified surfaces.

During the manufacture of a brazed aluminum heat exchanger, the constituent elements of the exchanger are bonded together by brazing with the use of a filler metal, called solder or brazing agent, the assembly being obtained by melting and diffusion of the brazing agent into the parts to be brazed, without melting them.

In general, in order to optimally guarantee the mechanical and / or thermal properties of brazed joints, and thus maximize the resistance of the exchanger at high fluid pressures, it is avoided to perform surface texturing on the portions of the exchange structures at which a solder joint must be formed.

However, this involves locally modifying the surface condition of these parts, which complicates the manufacturing process. For example, it is possible to mask the areas where brazing is to take place or to remove the coating from these areas before brazing. But these additional steps entail additional costs and difficulties in implementation.

Another possibility is to effect the texturing of the heat exchange structures after brazing these structures in the exchanger.

However, it is difficult to access the channels formed by the exchange structures in the passages of the exchanger and it is impossible to use mechanical texturing techniques or thermal spray coating. Other surface treatment techniques are difficult to implement. For example, for the techniques involving prior stages of heat treatment or deposition of an impregnating layer to ensure the adhesion of the coating, it is the entire exchanger that must be treated. There is a risk of clogging the channels, debrushing parts of the exchanger or creating weak metallurgical phases and damaging the brazed matrix.

Moreover, it has been proposed to carry out surface texturations on the separating plates before brazing. WO-A-2004/10921 1 discloses a method of depositing a porous coating on the surface of a separator plate of a heat exchanger. In this case, there is no heat exchange structure brazed between the plates. However, the exchange structures also have a role of spacers. They contribute to the rigidity of the exchanger passages and to their compressive strength during vacuum brazing of the exchanger. It may then be necessary to arrange additional reinforcing bars in the passages and to double the thickness of the plates.

The present invention aims to solve all or part of the problems mentioned above, including facilitating the manufacture of a heat exchanger plate type and brazed fins having exchange structures with improved thermal properties. The solution according to the invention is then an intermediate element for a plate and fin type heat exchanger brazed, intended to be mounted between a first plate and a second plate of the exchanger, said intermediate element comprising:

at least a first assembly portion configured to be assembled with the first plate and comprising a first pair of opposed surfaces, one of the surfaces of the first pair being oriented on the side of the first plate and the other of the surfaces of the first pair. the first pair being oriented on the side of the second plate when the intermediate element is in the mounted state,

several fins or wavelengths extending from said first assembly portion so as to delimit, when the intermediate element is in the mounted state, a plurality of channels for the flow of a first fluid, and

at least one surface texturing in the form of a porous structure or of reliefs formed on a surface of the intermediate element, at least one fin or wave leg having said surface texturing,

characterized in that the first assembly portion has said surface texturing on the surface of the first oriented pair, in the mounted state, on the side of the first plate.

Depending on the case, the element of the invention may comprise one or more of the following technical characteristics:

the intermediate element comprises a solid or solid substrate, the surface texturing being formed or deposited on a surface of the substrate.

said fin or wave leg comprises a third pair of opposed surfaces, both of the surfaces of the third pair having said surface texturing.

all or substantially all of the surfaces of the third pair have said surface texturing.

the first assembly portion has the surface texturing on the surface of the first oriented pair, in the assembled state, on the side of the second plate. the first assembly portion has the surface texturing on all or almost all of the surface of the first oriented pair, in the mounted state, on the side of the first plate.

the first assembly portion has the surface texturing on all or almost all of the surface of the first oriented pair, in the mounted state, on the side of the second plate.

the intermediate element comprises at least a second assembly portion configured to be assembled with the second plate and comprising a second pair of opposed surfaces, one of the surfaces of the second pair being oriented towards the first plate and other surfaces of the second pair being oriented on the side of the second plate when the intermediate member is in the mounted state, said second joining portion having the surface texturing on the surface of the second pair oriented, mounted state, on the side of the second plate.

the second assembly portion has the surface texturing on the surface of the second oriented pair, in the mounted state, on the side of the first plate.

the second assembly portion has the surface texturing on all or almost all of the surface of the second pair oriented, in the assembled state, on the side of the second plate.

the second assembly portion has the surface texturing on all or almost all of the surface of the second pair oriented, in the mounted state, on the side of the first plate.

the surface texturing is formed on all or almost all of the intermediate element.

the first assembly portion and / or the second assembly portion are arranged, in the mounted state, parallel to the first and second plates, the fins or wave legs succeeding one another in a lateral direction and delimiting, mounted state, a plurality of channels configured to channel the first fluid in a longitudinal direction parallel to the first and second plates and orthogonal to the lateral direction.

the surface texturing is in the form of a porous structure having an open porosity of between 15 and 60%, preferably open porosity between 20 and 45%,% by volume, or in the form of reliefs defining, in cross-section, cavities open on the surface of the intermediate element.

the intermediate element is in the form of a corrugated product comprising a succession of wave legs alternately connected by wave tops and wave bases, at least one wave vertex comprising said first portion of assembly and / or at least one wave base comprising said second assembly portion.

the wave legs 123 follow each other in a lateral direction, the corrugated product having a density, defined as the number of wave legs per unit length measured along the lateral direction, less than 18 legs per 2.54 centimeters, preferably less than 10 wavelength legs per 2.54 centimeters, more preferably less than or equal to 5 wavelength legs per 2.54 centimeters.

- The corrugated product is formed from a flat product comprising two opposite faces, said opposite faces having all or almost all surface texturing.

In addition, the invention relates to a heat exchanger of the brazed plate and fin type comprising a plurality of plates arranged parallel to one another so as to define a series of passages for the flow of a first fluid to be connected to each other. heat exchange with at least one second fluid, and at least one intermediate element mounted between a first and a second plate forming a passage so as to delimit, within said passage, several channels for the flow of said first fluid, characterized in that the intermediate element is according to the invention.

The present invention will now be better understood from the description which follows, given solely by way of nonlimiting example and with reference to the attached drawings, among which:

Figure 1 illustrates an example of passage of a heat exchanger comprising a spacer element according to the invention;

Figure 2 illustrates an example of assembly of a spacer element according to the invention assembled to an exchanger plate; Figures 3 and 4 illustrate a three-dimensional view and a cross-sectional view of a spacer element according to one embodiment of the invention;

Figure 5 illustrates an embodiment of a spacer element assembled between two heat exchanger plates;

Figure 6 illustrates a flat product adapted to form a spacer element according to one embodiment of the invention.

In a manner known per se, a heat exchanger comprises a stack of plates arranged parallel to one above the other with spacing and thus forming several series of parallelepipedal and flat shaped passages for the flow of a first fluid. and at least one second fluid to be in indirect heat exchange relationship via the plates. Preferably, the first fluid comprises a refrigerant to be vaporized at least partially.

Figure 1 schematically illustrates an example of passage 33 of a exchanger 1 of the evaporator-condenser type fed with liquid oxygen. This vaporizer-condenser vaporizes the liquid oxygen OL under low pressure (typically slightly higher than the atmospheric pressure) collected at the bottom of a column, by medium pressure nitrogen condensation (typically from 5 to 6 bars absolute) circulating in passages adjacent passages 33 (not shown) dedicated to the circulation of oxygen. The medium pressure nitrogen is most often taken in the gaseous state at the head of a medium pressure air distillation column to which the low pressure column mentioned above is connected. After passing and at least partial condensation in the vaporizer-condenser, this nitrogen is returned to the medium pressure column.

It is more specifically in the context of this application that the invention will be described later, it being understood that its application can be envisaged in other contexts, in particular with fluids of another nature. Thus, the exchanger 1 can vaporize at least one liquid-gas mixture flow rate, in particular a multi-component mixing flow rate, for example a hydrocarbon mixture, by heat exchange with at least one other fluid, for example natural gas. In particular, the invention may relate to a method of heat exchange between a first fluid and at least a second fluid in a heat exchanger according to the invention, said first fluid flowing in the passage 33 at a lower pressure or equal to 5 bar, preferably a pressure of between 1 and 2 bar.

All or part of the passages 33 of the exchanger 1 are provided with spacers 22 defining, within the passages 33, channels 26 for the circulation of liquid oxygen and can take different forms.

The intermediate elements 22 may have corrugated shapes, as shown in FIGS. 3 and 4, and comprise wave legs 123 alternately connected by wave peaks 121 and wave bases 122. In this case, "Fins" the wave legs that connect the vertices and successive bases of the wave.

The spacer elements 22 may take on other particular shapes defined according to the desired fluid flow characteristics. More generally, the term "fins" covers blades or other heat exchange surfaces, which extend between the primary surfaces of heat exchange, that is to say the plates of the heat exchanger, in the passages of the exchanger.

In general, the spacer elements 22 are soldered to the separator plates of the exchanger. Advantageously, the bonding can be carried out by vacuum brazing using a filler metal 30, referred to as solder or brazing agent, the assembly being obtained by melting and diffusion of brazing agent 30 within the brazing parts. , that is to say in the base metal, without melting them.

Figure 2 is a partial view of an intermediate element 22 assembled to a first plate 6 adapted to define, in association with another second parallel plate 7 directly adjacent (not shown), a passage 33 of the exchanger 1.

The intermediate element 22 and the plate 6 respectively comprise assembly portions 121, 60 intended to be assembled with each other. The assembly portions 121, 60 are positioned against each other, preferably with a small clearance between them in order to interpose therein the soldering agent. 30. Typically the assembly portions 121, 60 may be those where the clearance between the parts 22, 6 is the smallest, typically the portions at which the parts 22, 6 are in contact with each other or in quasi-contact, that is to say with a very weak game existing between all or part of said portions, one with the other.

As seen in cross-section in FIG. 4, the intermediate element 22 comprises a plurality of fins or wave legs 123 configured to define, when the element 22 is mounted between the first plate 6 and the second plate 7, a plurality channels 26 of flow of the first fluid.

The element 22 comprises at least a first assembly portion 121 configured to be assembled with the first plate 6 and comprising a first pair of opposed surfaces 121a, 121b, one 121a having surfaces of the first pair being oriented on the side of the first plate 6 and the other 121 b of the surfaces of the first pair being oriented on the side of the second plate 7 when the intermediate element 22 is in the mounted state.

The intermediate element 22 further comprises at least one surface texturing 23 in the form of a porous structure or reliefs formed on a surface of the intermediate element 22.

In the context of the invention, at least one surface texturing 23 is present on a surface of at least one fin or wavelength 123 of the intermediate element 22. It should be noted that the intermediate element may have one or more predetermined forms of surface texturization distributed over different areas of its surface, it being understood that a surface texturing may be carried out as well in the surface of the material constituting the intermediate element as it is deposited therein; that is to say, result from an addition of additional material on the surface of the intermediate element.

According to the invention, said first assembly portion 121 has the surface texturing 23 on that 121 has surfaces of the first pair oriented on the side of the first plate 6.

The inventors of the present invention have demonstrated that for some applications, the brazing of surface texturizing insert elements could be achieved without particular preparation of the brazed portions and lead to satisfactory performance in terms of mechanical strength. This is the case especially when in operation, the channels 26 defined between the first and second parts 22, 6 channel a first fluid whose pressure is relatively low, typically less than or equal to 5 bar, preferably a pressure of between 1 and 2 bar, as is the case in the oxygen passages of the vaporizer-condenser previously described.

In addition, surface texturing has been found to be beneficial in forming a brazed joint. Indeed, since the solder is trapped in the pores or cavities of the coating by the capillary forces, it is less likely to diffuse through the intermediate element, which limits the risk of dissolution of the material constituting this element and allows reduce the thickness. The filling of the pores or cavities also leads to better thermal transfer performance between the brazed parts, as well as a better mechanical strength of the assembly.

Thanks to the invention, the manufacturing process is simplified since the surface texturing 23 can be formed or deposited on the surface of the intermediate element without requiring an additional step of masking or post-processing to eliminate the texturing of the surface. surface portions to assemble. The texturing is formed on the parts before assembly, which preserves the integrity of the matrix of the exchanger.

Preferably, the first assembly portion 121 has the surface texturing 23 on the surface 121b of the first pair oriented on the side of the second plate 7. Advantageously, both of the surfaces 121a, 121b of the first pair have the surface texturing 23 on all or almost all of them.

In addition, the fins or legs 123 comprise a third pair of opposed surfaces 123a, 123b. Preferably, the first assembly portion 121 of the intermediate element 22 is arranged between two successive fins or legs 123, the surface 121b oriented on the side of the second plate 7 having two ends each connected to a secondary surface. 123a of each of the two wings or legs 123.

Preferably, both surfaces 123a, 123b of the third pair have surface texturing 23, preferably all or substantially all of them. Thus, two successive fins or legs 123 define between them a channel 26 whose wall formed by the first assembly portion, and the side walls, formed by the two fins 123, has internal surfaces with an exchange coefficient. improved thermal.

According to a particular embodiment, the intermediate element 22 has at least a second assembly portion 122 configured to be assembled with the second plate 7, said second assembly portion 122 comprising a second pair of opposed surfaces 122a, 122b, one 122a of the surfaces of the second pair being oriented on the side of the first plate 6 and the other 122b of the surfaces of the second pair being oriented on the side of the second plate 7.

It is thus possible to assemble another portion of the intermediate element 22 with a reciprocal assembly portion on the first plate 7 during the manufacture of the exchanger, which further improves the strength and rigidity of the passage 33.

Preferably, the second assembly portion 122 has the surface texturing 23 on its two surfaces 122a, 122b, preferably all or substantially all.

In the example of FIG. 4, the second assembly portion 122 of the intermediate element 22 is arranged between two fins or legs 123, the surface 122a of the second pair oriented on the side of the first plate 6 having two ends each connected to a surface 123b of each of the two fins or legs 123, said surface 123b of the second pair and said surfaces 123b of the fins having the surface texturing 23.

Thus, the manufacturing process of the intermediate element is simplified since the surface texturing can be formed or deposited on all or almost all the surfaces of the intermediate element without the need for an additional step of masking or post-processing. treatment aimed at eliminating the surface texturing of the portions to be assembled.

According to a particular embodiment, the surface texturing 23 is formed on all or almost all of the intermediate element 22. Note that in the context of the present invention, almost all of a surface or element means a portion representing at least 90%, preferably at least 95%, more preferably at least 98%. % of the area of that area or the total area of that element.

Preferably, said first assembly portions 121, fins or wave legs 123, and said second assembly portions 122, if present, are monoblock, i. e. formed of a single piece.

According to a particular embodiment, the intermediate element 22 is a corrugated product comprising a succession of wave legs 123 alternately connected by wave-peaks 121 and wave-bases 122. At least one wave-peak 121 comprises a first assembly portion 121 according to the invention.

The following explanations are made with reference to Figures 4 to 6, it being understood that the spacer element 22 may take any other suitable form and does not necessarily include all the features detailed below.

FIG. 4 shows a cross-sectional view of a corrugated heat exchange structure 22. A plurality of wave legs 123 of elongate shape extend parallel to each other and generally in a so-called longitudinal direction z. The wave legs succeed one another in a lateral direction x, which is perpendicular to the longitudinal direction z, and are alternately connected by wave vertices 121 and wave bases 122.

According to the example illustrated in FIG. 4, the wave peaks 121 and wave bases 122 are of planar shape and extend parallel to each other and perpendicular to the wave legs 123. The channels 26 for the first fluid , which are formed between two successive wave legs and a vertex or a base arranged between said successive wave legs, and have a cross section of generally rectangular shape.

Figure 4 illustrates a straight wave having flat surface wave legs 123. Other configurations of intermediate element 22 are of course conceivable, including perforated straight wave, partial offset wave, wave wave or herringbone ("herringbone" in English) configurations. An element 22 according to Figure 4 is visible in Figure 5 in the assembled state, that is to say mounted between a first and a second plate 6, 7 directly adjacent forming a passage 33. The passage 33 is shaped generally parallelepipedic and configured to channel the first fluid parallel to the longitudinal direction z.

In operation, the first fluid flows over the width of the passage 33, measured along the lateral direction x, between an inlet and an outlet of the passage 33 situated at two opposite ends along the length of the passage 33, measured along the longitudinal direction z . The wave legs 123 define in the passage 33 a plurality of channels 26 which extend parallel to the longitudinal direction z.

As can be seen in FIG. 5, the element 22 preferably extends over almost all, or even all, of the height of the passages, measured in a vertical direction y perpendicular to the plates 6, 7, so as to in contact or near-contact with the plates 6, 7. The wave peaks 121 and the wave bases 122 are arranged parallel to the plates 6, 7.

Preferably, the intermediate element 22 is arranged in the so-called "easyway" configuration in the passage 33, that is to say that the wave legs 123 extend generally in the direction of flow of the first fluid in the passage 33. Note that in use, the direction of flow of the first fluid is preferably vertical, the direction of flow may be upward or downward.

Advantageously, it will be possible to arrange an intermediate element 22 according to the invention in a zone 3 of a passage 33 of the exchanger in which the ascending oxygen penetrates, the intermediate element thus having on the surface porosities or reliefs multiplying the priming for the formation of the oxygen gas bubble OG.

Preferably, each wave vertex 121 comprises a first assembly portion 121 according to the invention. The surface 121a of the wave vertex positioned against the first plate 6 thus has at least one surface texturing 23. Note that the terms "positioned against" means an assembly portion juxtaposed to a plate, with or without clearance existing between all or part of the portion and the plate.

Advantageously, each wave base 122 comprises a second assembly portion 122 configured to be assembled, in the assembled state, with the second plate 7.

As illustrated in FIG. 4, said second assembly portion comprises a second pair of opposed surfaces 122a, 122b, that 122b of the surfaces of the second pair oriented on the side of the second plate 7 having at least one surface texturing 23.

Preferably, each wave leg 123 comprises a third pair of opposed surfaces 123a, 123b, both of the surfaces 123a, 123b of the third pair having said surface texturing 23, preferably all or part thereof. almost all.

Figure 5 illustrates an example where all the wave legs 123 have at least one surface texturing on their two surfaces 123a, 123b. Each channel 26 thus has two side walls whose internal surfaces are intensified.

Preferably, the first assembly portion 121 also has the surface texturing 23 on the surface 121 b of the first pair positioned, in the mounted state, against the second plate 7. The second assembly portion 122 may also present the surface texturing 23 on the surface 122a of the second pair oriented, in the mounted state, on the side of the first plate 6. This makes it possible to maximize the area of surface texturing 23 present on the intermediate element 22 and therefore to maximize the heat transfer efficiency within the channels 26 delimited by the intermediate element.

Such a configuration is illustrated in Figure 5. In fact, each channel 26 has an inner surface formed, in the mounted state, alternately by the surface 122a of a wave base 122 facing the first plate 6, the surface of the first plate 6 oriented towards the wave base 122 and the respective surfaces 123a, 123b of the two wave legs 123 connected to the ends of said wave base 122, and by the surface 121b of a vertex of wave 121 facing the second plate 7, the surface of the second plate 7 facing the top 121 and the respective surfaces 123a, 123b of the two wave legs 123 connected to the ends of said wave peak 121. By arranging at least one surface texturing 23 on the surfaces of the intermediate element 22, the heat exchange is intensified within the channels 26.

Advantageously, the corrugated product 22 can be formed from a flat product, such as a sheet or strip, having two opposite surfaces 22a, 22b, as shown in FIG. 6. Either of these surfaces 22a, 22b has surface texturing 23. This product is then shaped mechanically, for example by a press tool, and then arranged in a passage of the exchanger.

Preferably, the corrugated product 22 has surface texturing 23 on all or substantially all of its surfaces.

Advantageously, at least one surface texturing 23 is formed on one and the other of said opposite faces 22a, 22b. Preferably, the opposite faces 22a, 22b on which the surface texturing 23 is formed have said texturing, in whole or almost all. The face 22a gives rise, after shaping, to the surfaces 121a, 123b, 122a of the corrugated product of FIG. 4. The face 22b gives rise, after shaping, to the surfaces 123a, 121b, 122b of the corrugated product of FIG. Figure 4.

Note that almost all of a face means a portion representing at least 90%, preferably at least 95%, preferably at least 98% of the surface of this face.

According to this embodiment, all the surfaces of the product 22 located, in the assembled state, on the side of the second plate 7 and all the surfaces of the product 22 located, in the mounted state, on the side of the first plate 6, therefore have surface texturing 23.

Thus, the manufacturing process is simplified since the surface texturing may be formed or deposited on the entire faces of the corrugated product without the need for an additional masking or post-processing step to eliminate the surface texturing of the portions to be joined.

It is not necessary to perform surface texturing after mounting of the intermediate element 22 in the exchanger since it already has texturing on the desired areas of the fins. We can incorporating an intensified surface heat exchange structure in the exchanger while preserving the structural integrity of the matrix of the exchanger and its internal channels.

Preferably, the flat product has a thickness of at least 0.15 mm, preferably between 0.2 and 0.4 mm. This thickness is indicated by the letter "t" on the element of FIG. 3. The implementation of surface texturing 23 requires large thermal fluxes, in particular when the function of the surface texturing 23 is to intensify the boiling of the first fluid. It is therefore advantageous to use a relatively thick spacer element, thus having thicker wavelengths or fins, in order to maintain the largest possible fin coefficient, that is to say a better fin ability. to transmit the heat.

It is also advantageous to work with a thicker interlayer when, due to the intensification of heat exchange obtained by surface texturing, it is desired to reduce the density of the intermediate element in order to reduce the pressure losses that it generates. The heat exchange coefficient of the intermediate element is then preserved by increasing its thickness.

Being noted that the fin coefficient is typically between 0 and 1, the latter being equal to 1 at the point of contact with an adjacent plate and decreasing on the fin when moving away from the plate. The point in the middle of the fin is the point where the fin coefficient is the lowest. Working with thicker fins reduces heat conduction through the fin of the separator plate to the center point of the fin, which increases the fin coefficient.

Preferably, the corrugated product 22 has a density, defined as the number of wave legs per unit length measured along the lateral direction x, less than or equal to 18 legs per 2.54 centimeters, preferably less than 10. wave legs by 2.54 centimeters, more preferably less than or equal to 5 wave legs per 2.54 centimeters. Advantageously, the density of the corrugated product 22 can be between 1 and 5 legs per 2.54 centimeters. Note that these density values are applicable to a spacer element which is not necessarily a corrugated product, the density then being defined as the number of fins per unit length, measured along the x direction.

The use of a relatively low density facilitates the deposition phase of the surface texturing 23 on the wavelengths of the intermediate element 22, the surface of the wave legs being then more accessible. In addition, the use of a corrugated product of lower density facilitates the removal of bubbles created in the surface texturing.

Preferably, the spacer element 22 comprises a solid substrate, or otherwise a solid substrate, in particular a non-porous substrate, on which the texturing 23 is formed. The substrate is visible in black in FIGS. 5 or 6, for example. Depending on the structure of the intermediate element, the substrate may comprise one or more first and / or second assembly portions, the fins or wave legs. Preferably, the surface texturing 23 covers all or almost all of the substrate.

Note that the intermediate element is preferably monobloc, that is to say formed of a single piece.

In the context of the invention, the surface texturing 23 present on the intermediate element 22 can result from a surface coating deposited on the substrates of the intermediate elements, in particular a coating deposited by a liquid route, in particular by dipping, spraying or electrolytically, by the dry route, in particular by chemical vapor deposition (Chemical Vapor Deposition or CVD) or physical vapor deposition (PVV), or by thermal spraying, in particular by flame or by plasma.

The surface texturing 23 may also result from a modification of the surface state of said parts that can be obtained by a chemical treatment or mechanical treatment, for example by sandblasting, grooving ....

It being specified that the texturing 23 is intended to modify the surface state of the intermediate element and not to deform all or part of the intermediate element.

According to a preferred embodiment, the surface texturing 23 is in the form of a porous structure, preferably a porous layer. The porous structure may for example be formed of a deposition of slightly sintered aluminum particles, entangled aluminum filaments, semi-fused aluminum particles bonded to each other, such as aluminum particles which are obtained after projection obtained by thermal flame projection.

Preferably, the surface texturing is formed of an aluminum alloy comprising for 100% of its mass, at least 80% by weight of aluminum, preferably at least 90%, more preferably at least 99% by weight. aluminum.

Preferably, the surface texturing 23 has, before assembly of the intermediate element, an open porosity of between 15 and 60%, preferably between 20 and 45%, more preferably an initial open porosity of between 25 and 35% ( % in volume). It should be noted that the open porosity is defined as the ratio between the volume of the open pores, that is to say the pores communicating fluidly with the external environment in which the intermediate element in question is located, and the total volume of the porous structure.

The pores of the porous structure 23 preferably have a diameter between 1 and 200 miti, preferably between 5 and 100 pm. Noting that the pores are not necessarily circular in section but may have irregular shapes. The term "diameter" therefore also covers an equivalent hydraulic diameter which can be calculated from the measurement of the pressure drop experienced by a gas flow through the porous structure and by assuming that the pores have a regular shape, in particular a spherical shape, cylindrical, ...

We can also characterize the size of the pores by their volume. Preferably, the pores of the porous structure 23 have a volume of between 1000 and 1000 000 pm ³ . The pore volume may for example be determined by tomography or image analysis of polished sections of samples taken in a multitude of directions in space.

Alternatively, the surface texturing 23 may be in the form of reliefs, or patterns, printed or made in or on the surface of the substrate material material of a spacer element. Preferably, these reliefs define, in cross section, cavities open on the surface of the element. For example, micro-reliefs of different size or morphology, such as gorges, discrete or uninterrupted, streaks, protuberances, ... may be formed or deposited on the surface of the element. By micro-reliefs we mean reliefs which have at least one small characteristic dimension with respect to a dimension of the element, in particular reliefs which extend a height, measured in a direction perpendicular to the surface of the element insert having the texturing, and / or a width, measured in a direction perpendicular to the surface of the interlayer having the texturing, of the order of a few micrometers and several hundred micrometers. In particular, the reliefs forming the surface texturing 23 may be made by laser or mechanical and / or chemical machining.

According to one embodiment, the intermediate element 22 is intended to be assembled at least to the first plate 6, preferably to the first and second plates 6, 7 by brazing.

Preferably, brazing between the first and second assembly portions 121, 122 of the intermediate element and the plates 6, 7 is made in the context of the overall brazing of the matrix of the exchanger. The stack of plates, the intermediate elements and the other constituent elements of the heat exchanger are pressed against each other by means of a compression device. The matrix thus formed is placed in a vacuum oven and heated to temperatures between 550 and 650 ° C, preferably of the order of 580 to 600 ° C. The compression force applied to the matrix is generally in the range of 20,000 to 40,000 N / m ² .

Preferably, the plates 6, 7 of the exchanger are rolled plates comprising a central sheet 40, each face of which is coated with a layer of brazing agent 30. An example of such a plate 6 is illustrated in FIG. According to another embodiment, the brazing agent 30 may take the form of a strip or a surface coating layer 30. The coating layer 30 may be deposited by spraying or by brushing brazing agent 30 in the form of a powder suspension containing the powder, a dispersant, a binder, additives for controlling the viscosity. Preferably, the first and second plates 6, 7 are free of surface texturing.

The brazing agent 30 is preferably formed of a metallic material having a lower melting temperature than the materials constituting the parts 6, 22. The parts 6, 22 and 30 are preferably formed of aluminum alloy. The plates 6 and the elements 22 of the exchanger are advantageously formed of a first aluminum alloy of the 3XXX family, preferably of the 3003 type (ASME SB-2019 SECTION 2-B). The brazing agent 30 is formed of a second aluminum alloy, preferably an alloy of the 4XXX type (ASME SB-2019 SECTION 2-B), in particular of the 4004 type.

Advantageously, the brazing agent 30 has a thickness of less than 300 miti, preferably between 50 and 200 μm. Thus, it avoids an excess of solder which would be detrimental to the performance of the exchanger since flowing out of the brazed joint area, the solder could change the microstructure of the coating or surface texturing and therefore its performance filling the porosities or cavities or promoting closure of the open porosity of the intensified surface element.

According to a particular embodiment, it is possible to adapt the height of the element 22 to the height of the passage 33 so that there is a set of a predetermined value, as indicated by the letter "d" in FIG. 5, between the wave peaks 121 and the first plate 6 and between the wave bases 122 and the second plate 7. This makes it possible to prevent capillary rise of brazing agent outside the area of the brazed joint during the vacuum brazing step, which can be detrimental to the performance of the exchanger since flowing, the solder can modify the microstructure of the surface texturing by filling the pores or cavities present on the surface. Preferably, the clearance d is between 0 and 0.1 mm, more preferably between 0 and 0.05 mm.

Preferably, after brazing connection of the first assembly portion of the intermediate element 22 with the first plate 6 and / or the second assembly portion with the second plate 7, the surface texturing 23 is modified at the said first and second portions assembly 121. In particular, at least part of the surface texturing 23 is infiltrated by the brazing agent 30 at the assembly portions 220, 60. This effect is related to the compressive force applied to the brazed pieces and to the voiding brazing agent 30 in the texturing.

Depending on the case, the open porosity or the cavities of the surface texturing 23 may be completely or partially filled by the brazing agent 30 at the level of the first assembly portion 121 and / or the second assembly portion .

Preferably, after formation of the bond by soldering, the surface texturing 23 has at the level of the first assembly portion 121 and / or the second assembly portion, a residual open porosity of between 0% and 90%, preferably between 10% and 50%, of the initial open porosity, that is to say before formation of the bond (0% indicating that the initial open porosity is completely filled following the soldering or the direct bond).

More generally, the surface texturing 23 may have, before bonding, at the level of the assembly portions 220, 60, an initial volume of open pores or cavities. After bonding, the surface texturing 23, at the first assembly portion 121 and the respective portion 60 of the plate 6, a residual volume of pores or open cavities representing from 0% to 90%, preferably from 10% to 50%, of the initial volume of pores or open cavities.

Advantageously, after bonding, the surface texturing 23 is retained in front of the first assembly portion 121 and the respective portion 60 of the plate 6. In particular, the surface texturing 23 has, apart from the portions of FIG. assembly 121, 60, an open porosity which is identical or substantially identical to the initial open porosity and / or a volume of open pores or cavities identical or nearly identical to the initial volume of pores or cavities.

Claims

1. An intermediate member (22) for a plate and fin type heat exchanger brazed to be mounted between a first plate (6) and a second heat exchanger plate (7), said intermediate member (22) comprising:

at least a first assembly portion (121) configured to be assembled with the first plate (6) and comprising a first pair of opposing surfaces (121a, 121b), one (121a) of the surfaces of the first pair being oriented on the side of the first plate (6) and the other pair (121b) of the surfaces of the first pair being oriented on the side of the second plate (7) when the intermediate element (22) is at the mounted state,

several fins or wavelength legs (123) extending from said first assembly portion (121) so as to delimit, when the intermediate element (22) is in the mounted state, a plurality of channels (26); ) for the flow of a first fluid, and

at least one surface texturing (23) in the form of a porous structure or of reliefs formed on a surface of the intermediate element (22), at least one fin or wave leg (123) having said texturing of surface (23),

characterized in that the first assembly portion (121) has said surface texturing (23) on the surface (121a) of the first oriented pair, in the mounted state, on the side of the first plate (6).

2. Element according to claim 1, characterized in that the intermediate element (22) comprises a solid or solid substrate, the surface texturing (23) being formed on a surface of the substrate.

3. Element according to one of claims 1 or 2, characterized in that said fin or wave leg (123) comprises a third pair of surfaces (123a, 123b) opposite, one and the other of the surfaces ( 123a, 123b) of the third pair having said surface texturing (23).

4. Element according to claim 3, characterized in that all or almost all of the one and the other of the surfaces (123a, 123b) of the third pair has said surface texturing (23).

5. Element according to one of the preceding claims, characterized in that the first assembly portion (121) has the surface texturing (23) on the surface (121 b) of the first oriented pair, in the mounted state on the side of the second plate (7).

6. Element according to one of the preceding claims, characterized in that the first assembly portion (121) has the surface texturing (23) on all or almost all of the surface (121 a) of the first pair oriented, in the mounted state, on the side of the first plate (6) and / or on all or substantially all of the surface (121b) of the first oriented pair, in the mounted state, on the side of the second plate (7).

7. Element according to one of the preceding claims, characterized in that it comprises at least a second assembly portion (122) configured to be assembled with the second plate (7) and comprising a second pair of surfaces (122a, 122b), one (122a) of the surfaces of the second pair being oriented on the side of the first plate (6) and the other (122b) of the surfaces of the second pair being oriented on the side of the second plate (7). ) when the intermediate member (22) is in the mounted state, said second joining portion (122) having the surface texturing (23) on the surface (122b) of the second oriented pair, in the mounted state on the side of the second plate (7).

8. Element according to claim 7, characterized in that the second assembly portion (122) has the surface texturing (23) on the surface (122a) of the second pair oriented, in the mounted state, on the the first plate (6).

9. Element according to one of claims 7 or 8, characterized in that the second assembly portion (122) has the surface texturing (23) on all or almost all of the surface (122b) of the second pair oriented, in the mounted state, on the side of the second plate (7) and / or on all or substantially all of the surface (122a) of the second pair oriented, in the assembled state, on the side of the first plate (6).

10. Element according to one of the preceding claims, characterized in that the surface texturing (23) is formed on all or almost all of the intermediate element (22).

1 1. Element according to one of the preceding claims, characterized in that the first assembly portion (121) and / or the second assembly portion (122) are arranged, in the mounted state, parallel to the first and second plates ( 6, 7), the fins or legs of wave (123) succeeding one another in a lateral direction (x) and delimiting, in the assembled state, a plurality of channels (26) configured to channel the first fluid in a longitudinal direction (z) parallel to the first and second plates (6, 7) and orthogonal to the lateral direction (x).

12. Element according to one of the preceding claims, characterized in that the surface texturing (23) is in the form of a porous structure having an open porosity of between 15 and 60%, preferably an open porosity of between 20 and 60%. and 45% (% by volume), or in the form of reliefs defining, in cross-section, cavities open on the surface of the intermediate element (22).

13. Element according to one of the preceding claims, characterized in that it is in the form of a corrugated product (22) comprising a succession of wave legs (123) alternately connected by wave vertices (121). ) and wave bases (122), at least one wave vertex (121) comprising said first assembly portion (121) and / or at least one wave base (122) comprising said second portion of assembly (122).

14. Element according to claim 13, characterized in that the wave legs (123) succeed one another in a lateral direction (x), the corrugated product (22) having a density, defined as the number of wave legs by unit of length measured along the lateral direction (x), less than 18 legs by 2.54 centimeters, preferably less than 10 legs by 2.54 centimeters, more preferably less than or equal to 5 legs of wave by 2.54 centimeters.

15. Element according to one of claims 13 or 14, characterized in that the corrugated product (22) is formed from a flat product comprising two opposite faces (22a, 22b), said opposite faces (22a, 22b). presenting all or almost all surface texturing (23).

16. Brazed plate and fin type heat exchanger comprising a plurality of plates (6, 7) arranged parallel to each other so as to define a series of passages for the flow of a first fluid to be in exchange relation. with at least one second fluid, and at least one intermediate element (22) mounted between a first and a second plate (6, 7) forming a passage (33) so as to delimit, within said passage (33), several channels (26) for the flow of said first fluid, characterized in that the intermediate element (22) is according to one of claims 1 to 15.