FR3075340A1 - SURFACE TEXTURING INTERFACE ELEMENT, HEAT EXCHANGER, AND METHOD OF MANUFACTURING THE SAME - Google Patents

Abstract

 The invention relates to an intermediate element (22) for a heat exchanger of the brazed plate and fin type, intended to be mounted between a first plate (6) and a second plate (7) of the exchanger, said intermediate element (22 ) comprising at least a first assembly portion (121) configured to be assembled with the first plate (6) and comprising a first pair of opposite 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 (121b) 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 assembled state, a plurality of fins or wave legs (123) extending from said first assembly portion (121) so as to delimit, when the intermediate element (22) is in the assembled state, a plurality of channels (26) for the flow of a first fluid, and at least one text surface ration (23) in the form of a porous structure or reliefs formed on a surface of the intermediate element (22), at least one fin or wave leg (123) having said surface texturing (23) . According to the invention, the first assembly portion (121) is free of surface texturing (23) on the surface (121a) of the first oriented pair, in the assembled state, on the side of the first plate (6) .

Description

The present invention relates to an intermediate element for a plate and fin type heat exchanger, said intermediate element having a surface texturing, as well as to a process for manufacturing such an element and to a heat exchanger comprising such an element.

The present invention finds particular application in the field of gas separation by cryogenics, in particular air separation by cryogenics (known by the acronym "ASU" for air separation unit) used for the production of gaseous oxygen 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 circulating gas, by air or nitrogen, for example.

If the heat exchanger is in the tank of a distillation column, it can constitute a vaporizer operating as a thermosyphon for which the exchanger is immersed in a bath of liquid descending the column or a vaporizer operating as a vaporization with a supplied film 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 vaporizes at least one flow of liquid-gas mixture, in particular a flow of mixture with several constituents, for example a mixture of hydrocarbons, by heat exchange with at least another fluid, for example natural gas.

The technology commonly used for an exchanger is that of aluminum exchangers with plates and fins or brazed waves, which make it possible to obtain very compact devices offering a large exchange surface.

These exchangers include separating plates between which are inserted heat exchange structures, generally corrugated or wave structures, formed of a succession of fins or wave legs, thus constituting a stack of passages for the various fluids to be put in heat exchange relationship.

The performance of an exchanger is linked to the heat exchange coefficient of the heat exchange structures in contact with the fluids. The coefficient of heat exchange 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 fluids.

It is possible to modify the heat exchange coefficient of an exchange structure by modifying the geometry or the physicochemical properties of its surface. This makes it possible to increase the effective exchange surface and / or to modify the interactions between the fluid and the surface, by changing 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, it is possible to make surface deposits of porous coatings or forming reliefs on the surface of structures, or else to create such surface states by mechanical treatments or by chemical attack.

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

Document WO-A-2004/109211 describes a method of depositing a porous coating on the surface of a separating plate of a heat exchanger.

A problem which arises with the use of textured intensified surfaces in brazed aluminum exchangers relates to the assembly of elements comprising such surfaces during the manufacture of the exchanger.

Indeed, the connection of the constituent elements of the exchanger is carried out by brazing with the use of a filler metal, called brazing or brazing agent, the assembly being obtained by fusion and diffusion of the brazing agent within parts to be brazed, without fusion of these.

However, the presence of a porous coating or of reliefs at the level of the connection zone between the parts to be assembled, since to the clearance existing between the parts to be assembled, is added the open porosity of the coating or the cavities formed on the textured surfaces. During its fusion, the filler metal fills these porosities or cavities before the play between the parts, which can cause defects in the brazed joint, such as porosities, a lack of brazing, or even an absence of joint. This affects the mechanical and / or thermal properties of the joint, and therefore those of the exchanger which are directly linked to the quality of the brazed joint.

In an attempt to remedy these drawbacks, one solution is to texturize the heat exchange structures after the brazing of these structures in the exchanger has been carried out.

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

Furthermore, it has been proposed to produce surface textures on the separating plates before brazing. But in this case, there is no heat exchange structure brazed to the plates and it is necessary to anneal the plates. However, the exchange structures also have a role of spacers and contribute to the rigidity of the assembly. In addition, the annealed plates lose their mechanical strength. It is then necessary to arrange additional reinforcement bars in the passages and to double the thickness of the plates.

The object of the present invention is to solve all or part of the problems mentioned above, in particular to improve the manufacture of a heat exchanger of the brazed plate and fin type having exchange structures with improved thermal properties.

The solution according to the invention is then an intermediate element for a heat exchanger of the brazed plate and fin type, 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 opposite surfaces, one of the surfaces of the first pair being oriented towards the side of the first plate and the other of the surfaces of the first pair being oriented towards the side of the second plate when the intermediate element is in the assembled state,

- Several fins or wave legs extending from said first assembly portion so as to delimit, when the intermediate element is in the assembled 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 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 portion d The assembly is free of surface texturing on the surface of the first oriented pair, in the assembled state, on the side of the first plate.

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

- at least one fin or wave leg comprises a third pair of opposite surfaces, one and / or the other of the surfaces of the third pair having said surface texturing.

- all or almost 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 is arranged between two successive fins or wave legs, the surface of the first pair oriented, in the assembled state, on the side of the second plate having two ends each connected to a respective surface of each of the two fins or wave legs, the surface of the first pair and said respective surfaces of the fins having the surface texturing.

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

- The second assembly portion is arranged between two successive fins or wave legs, the surface of the second pair oriented, in the assembled state, on the side of the first plate having two ends each connected to a respective surface of each of the two fins or wave legs, said surface of the second pair and said respective surfaces of the fins having the surface texturing.

- The first assembly portion and / or the second assembly portion are arranged, in the assembled state, parallel to the first and second plates, the fins or wave legs succeeding each other in a lateral direction and delimiting, at the '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.

- Said at least one fin or wave leg extend in a plane parallel to the longitudinal direction and form an angle a with respect to the first assembly portion and / or the second assembly portion, the angle a being less than or equal to 90 °.

the surface texturing 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 45% (% by volume), or in the form of reliefs defining, in cross section, open cavities on the surface of the intermediate element.

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

- the wave legs follow one another in a lateral direction, the corrugated product having a density, defined as the number of wave legs per unit of length measured along the lateral direction, less than 18 legs per

2.54 centimeters, preferably less than 10 legs by 2.54 centimeters, more preferably less than or equal to 5 legs by 2.54 centimeters.

- the corrugated product is formed from a flat product having a thickness of at least 0.15 mm, preferably between 0.2 and 0.4 mm.

The invention further relates to a heat exchanger of the type with brazed plates and fins comprising a plurality of plates arranged parallel to each other so as to define a series of passages for the flow of a first fluid to be brought into exchange relationship. thermal with at least a second fluid, and at least one intermediate element mounted between two successive plates defining a passage so as to form, within the passage, several channels for the flow of said first fluid, characterized in that the intermediate element is in accordance with the invention.

According to another aspect, the invention relates to a method of manufacturing an intermediate element for a heat exchanger of the brazed plate and fin type heat exchanger, said method comprising the following steps:

a) shaping of the intermediate element so that it has fins or wave legs delimiting, when the intermediate element is mounted between a first plate and a second plate of the exchanger, a plurality of channels for the flow of a first fluid, and at least a first assembly portion configured to be assembled with a first plate and comprising a first pair of opposite surfaces, one of which is oriented towards the side of the first plate and the other is oriented on the side of the second plate when the intermediate element is in the assembled state,

c) formation of a surface texturing in the form of a porous structure or reliefs on all or almost all of the intermediate element,

d) selective removal of at least a portion of said surface texturing extending over that of the surfaces of the first oriented pair, in the mounted state, on the side of the first plate.

The method according to the invention may include one or more of the following characteristics:

the method comprises, prior to step c), a step b) of depositing a fusible coating on that of the surfaces of the first pair oriented in the assembled state, on the side of the first plate, step d ) comprising a heat treatment of the intermediate element so as to remove the fusible coating and the surface texturing portion formed on said fusible coating.

the method comprises, prior to step c), the application of a mask to that of the surfaces of the first oriented pair, in the assembled state, on the side of the first plate, step d) being carried out by removing the mask.

- step d) is carried out mechanically, preferably by brushing or sanding.

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

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

Figure 2 illustrates an example of assembly of an intermediate element according to the invention brazed to a heat exchanger plate;

Figures 3 to 6 show different views of an insert element according to an embodiment of the invention;

Figure 7 illustrates different embodiments of an intermediate element assembled between two exchanger plates;

Figure 8 illustrates steps of a method of manufacturing an insert element according to an embodiment of the invention.

In a manner known per se, a heat exchanger comprises a stack of plates arranged parallel one above the other with spacing and thus forming several series of passages of parallelepiped shape and flat for the flow of a first fluid and at least one second fluid to be put into 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 an exchanger 1 of the vaporizer-condenser type supplied with liquid oxygen. This vaporizer-condenser vaporizes the liquid oxygen OL under low pressure (typically slightly higher than atmospheric pressure) collected at the bottom of a column, by condensation of medium pressure nitrogen (typically from 5 to 6 bars absolute) circulating in passages adjacent passages 33 (not shown) dedicated to the circulation of oxygen. Medium pressure nitrogen is most often taken in the gaseous state at the top of a medium pressure air distillation column to which the low pressure column mentioned above is connected. After its passage 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 below, 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 flow of liquid-gas mixture, in particular a flow of mixture with several constituents, for example a mixture of hydrocarbons, by heat exchange with at least one other fluid, for example natural gas.

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

The intermediate elements 22 can have wavy shapes, as shown in FIG. 3, and include wave legs 123 connected alternately by wave vertices 121 and wave bases 122. In this case, we call "fins" »The wave legs which connect the summits and the successive bases of the wave.

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

The intermediate elements 22 are connected by brazing to the separating plates of the exchanger. Advantageously, the connection is made by vacuum brazing with the use of a filler metal 30, called brazing or brazing agent, the assembly being obtained by melting and diffusion of brazing agent 30 within the parts to be brazed, that is to say in the base metal, without fusion of these.

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 (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 brazed with each other. The assembly portions 121, 60 are positioned one against the other, preferably with a slight clearance between them in order to interpose therein the brazing agent 30. Typically the assembly portions 121, 60 may be those where the clearance between the pieces 22, 6 is the lowest, typically the portions at which the pieces 22, 6 are in contact with each other or in quasi-contact, that is to say with a very clear weak existing between all or part of said portions, with each other.

Preferably, the plates 6, 7 of the exchanger are laminated plates comprising a central sheet 40, each face of which is coated with a layer 30. According to another embodiment, the brazing agent 30 can take the form of a strip or a surface coating layer 30. The coating layer 30 can be deposited by spraying or by brush application of the brazing agent 30 in the form of a powder suspension containing the powder, a dispersant , a binder, additives to control viscosity.

Preferably, the soldering agent 30 has a thickness e of between 50 and 300 μm, preferably between 100 and 250 μm.

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

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

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

The intermediate element 22 further comprises 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.

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

According to the invention, the first assembly portion 121 is free of surface texturing 23 on its surface 121a which is oriented, in the assembled state, on the side of the first plate 6.

Thus, the wettability and good solderability of the surface of the intermediate element intended to be positioned against an adjacent plate is preserved to be assembled thereon by brazing. During brazing, the distribution of the brazing agent at the joint can be controlled, which leads to a joint with good mechanical and thermal properties. It is thus possible to use the traditional methods of manufacturing brazed plate and fin exchangers.

In addition, it is not necessary to perform a surface texturing after mounting of the intermediate element 22 since it already has the texturing on the desired areas of the fins. It is thus possible to incorporate an intensified surface heat exchange structure into the exchanger while preserving the structural integrity of the exchanger matrix and its internal channels.

The absence of surface texturing on the surface located on the side of the first plate also allows better control of the height of the intermediate element. However, the height of the intermediate element is an important parameter which conditions, by being precisely adapted to the difference between the first and second plates 6, 7 of the exchanger, the quality and therefore the properties of the brazed joint.

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

The explanations which follow are made with reference to FIGS. 4 to 7, it being understood that the intermediate element 22 can take any other suitable form and does not necessarily include all the characteristics detailed below.

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

According to the example illustrated in FIG. 3, the wave vertices 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 an apex or base arranged between said successive wave legs, thus have a generally rectangular cross section.

Figure 4 illustrates a straight wave with wave legs 123 with a flat surface. Other intermediate element configurations 22 are of course conceivable, in particular configurations of the perforated straight wave, partial offset wave, wave wave or herringbone type ("herringbone" in English).

An element 22 according to Figure 4 is visible in Figure 7 (a) 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 of generally parallelepiped shape 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 in the lateral direction x, between an inlet and an outlet of the passage 33 located at two opposite ends along the length of the passage 33, measured in the longitudinal direction z . The wave legs 123 delimit within the passage 33 a plurality of channels 26 which extend parallel to the longitudinal direction z.

As seen in Figure 7 (a), the element 22 preferably extends over almost all, if not all, of the height of the passages, measured in a vertical direction y perpendicular to the plates 6, 7, so as to be in contact or almost in contact with the plates 6, 7. The wave vertices 121 and the wave bases 122 are arranged parallel to the plates 6, 7.

According to a particular embodiment, the height of the element 22 can be adapted to the height of the passage 33 so that there is a clearance of a predetermined value, as indicated by the reference “d” in the Figure 8 (e), between the wave vertices 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 the brazing agent outside the zone of the joint brazed during the vacuum brazing step, which can be detrimental to the performance of the exchanger since by flowing, the brazing can modify the microstructure of the surface texturing by filling in the porosities 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, the intermediate element 22 is arranged in a 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 service, the direction of flow of the first fluid is preferably vertical, the direction of flow can be ascending or descending.

Advantageously, an intermediate element 22 according to the invention may be arranged in a zone 3 of a passage 33 of the exchanger into which the rising oxygen penetrates, the intermediate element thus having porosities or reliefs multiplying the sites on the surface. priming for the formation of oxygen gas bubbles OG.

Preferably, each wave summit 121 comprises a first assembly portion 121 according to the invention. The surface 121a of the wave summit positioned against the first plate 6 is thus free of surface texturing 23, which allows it to be brazed securely to a portion of reciprocal assembly on the first plate 6 during the manufacture of the exchanger. .

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 opposite surfaces 122a, 122b, that 122b of the surfaces of the second pair oriented towards the side of the second plate 7 being free of surface texturing 23.

Another portion of the intermediate element 22 can thus be brazed solidly to a portion of reciprocal assembly on the first plate 7 during the manufacture of the exchanger, which further improves the solidity and the rigidity of the passage 33.

Preferably, said first assembly portions 121, the fins or wave legs 123, and said second assembly portions 122 if present, are in one piece, i. e. made in one piece.

Preferably, each wave leg 123 comprises a third pair of opposite surfaces 123a, 123b, one and / or the other of the surfaces 123a, 123b of the third having said surface texturing 23, preferably on its entirety or almost all of it.

Note that in the context of the present invention, almost all of a surface or of an element means a portion representing at least 90%, preferably at least 95%, more preferably at least 98 % of the area of this area or the total area of this element.

FIG. 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 123a, 123b whose internal surfaces are intensified.

Preferably, the first assembly portion 121 also has the surface texturing 23 on the surface 121b of the first oriented pair, in the assembled state, on the side of the second plate 7, preferably on all or almost all of the entire surface 121b.

The second assembly portion 122 may also have the surface texturing 23 on the surface 122a of the second oriented pair, in the assembled state, on the side of the first plate 6, preferably on all or almost all of said surface 122a. This makes it possible to maximize the surface texturing area 23 present on the intermediate element 22 and therefore to maximize the efficiency of heat transfer within the channels 26 delimited by the intermediate element.

Such a configuration is illustrated in Figures 6 and 7 (a). In fact, each channel 26 has an internal surface formed, in the assembled state, alternately by the surface 122a of a wave base 122 oriented towards the first plate 6, the surface 6b of the first plate 6 oriented towards the base wave 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 wave top 121 oriented towards the second plate 7, the surface 7a of the second plate 7 oriented towards the wave summit 121 and the respective surfaces 123a, 123b of the two wave legs 123 connected to the ends of said wave summit 121.

By arranging at least one surface texturing 23 on the bottom of the channels 26, formed alternately by a vertex 121 or a wave base 122, heat exchange is intensified on a greater part of the surfaces of the element 22 which form , in the assembled state, the internal surface of the channels 26.

Preferably, the surfaces 6a, 6b, and 7a, 7b of the plates 6, 7 are free from surface texturing. This preserves the quality of the solder joints formed with the plates.

Figure 7 (a) illustrates a configuration in which the wave legs 123 extend parallel to the longitudinal direction z and perpendicular to the wave vertices 121 and the wave bases 122 of the element 22.

According to an alternative embodiment, illustrated in Figures 7 (b) and 7 (c), the wave legs 123 extend in a plane which is parallel to the longitudinal direction z and which forms an angle a less than 90 ° with the first assembly portion 121 on the one hand and with the second assembly portion 122 on the other hand.

By forming an acute angle between the wave legs 123 and the vertices or wave bases 121, 122, the internal surface portion of the channels 26 which may have surface texturing is maximized and the internal surface portion of the channels is minimized. channels 26 which generally cannot have any texturing, this portion being formed, depending on the channel considered, by the surface 6b of the first plate 6 oriented towards the wave base 122 or by the surface 7a of the second plate 7 oriented towards the wave summit 121.

Preferably, the angle a is between 60 and 90 °, more preferably the angle a is between 70 and 85 °. This preserves accessibility to the surfaces on which the surface texturing is to be formed while increasing the intensified channel surface.

In the context of the invention, the corrugated product 22 is preferably formed from a flat product, such as a sheet or sheet, having a thickness of at least 0.15 mm, preferably between 0.2 and 0.4 mm. This thickness is indicated by the letter "t" in Figure 3. The implementation of a surface texturing 23 requires significant heat 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 intermediate element, in order to maintain the highest possible coefficient of fins, that is to say a better ability of the fins to transmit heat.

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

It being noted that the fin coefficient is a number typically between 0 and 1, this 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 with the lowest fin coefficient. Working with thicker fins reduces heat conduction through the fin from the plate to the mid point of the fin, which increases the coefficient of the fin.

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

The use of a relatively low density makes it possible to facilitate the deposition phase of the surface texturing on the fins or struts, their surface being more accessible. In addition, the use of a lower density interlayer facilitates the removal of bubbles created at the surface texturing.

Preferably, the intermediate element 22 comprises a solid substrate, in particular a non-porous substrate, on which the texturing 23 is formed. Depending on the structure of the intermediate element, the substrate may include one or more first and / or second assembly portions, the fins or wave legs.

Note that the intermediate element is preferably monobloc, that is to say formed in one piece.

In the context of the invention, the surface texturing 23 may result from a surface coating deposited on the element or else from a modification of the surface state of said part element obtained by chemical, mechanical or equivalent treatment , for example by sandblasting, grooving ....

In particular, the surface coating can be deposited on the substrate deposited by the liquid route, in particular by soaking, spraying or by electrolytic route, by the dry route, in particular by chemical vapor deposition (in English Chemical Vapor Deposition or CVD) or physical deposition. in the vapor phase (in English Physical Vapor Deposition or CVD), or by thermal spraying, in particular by flame or plasma.

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

According to a preferred embodiment, the surface texturing 23 is in the form of a porous structure, preferably a porous layer. The porous structure can for example be formed of a deposit of lightly sintered aluminum particles, of tangled aluminum filaments, of semi-molten aluminum particles stuck together, such as the aluminum particles which are obtained after projection which is obtained in flame thermal projection.

Preferably, the surface texturing 23 has, before brazing, an open porosity of between 15 and 60%, preferably between 20 and 45%, more preferably an initial open porosity of between 25 and 35% (% by volume). Note 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 part 22 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 μm, preferably between 5 and 100 μm. Being noted that the pores are not necessarily of circular section but can present irregular shapes. The term “diameter” therefore also covers an equivalent hydraulic diameter which can be calculated from measurement of the pressure drop undergone by a gas flow through the porous structure and assuming that the pores have a regular shape, in particular spherical, 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 1,000,000 μm ³ . The pore volume can for example be determined by tomography or by analysis of images of polished sections of samples taken in a multitude of directions in space.

Alternatively, the surface texturing 23 can be in the form of reliefs, or patterns, printed or produced in or on the material constituting the intermediate element 22. Preferably, these reliefs define, in cross section, open cavities on the surface of the element 22. For example, micro-reliefs or various size or morphology, such as grooves, discrete or uninterrupted, streaks, protuberances, ... may be formed or deposited on the surface of the element 22. In particular, the reliefs forming the surface texturing 23 can be produced by laser or mechanical and / or chemical machining.

Figure 8 illustrates the main steps of a manufacturing process which can be used to manufacture an intermediate element 22, in the case where this is in the form of a corrugated product intended to be arranged between a first plate 6 and a second plate 7. Of course, the manufacturing method described below can be applied to other forms of intermediate elements.

The intermediate element 22 is first shaped, typically by stamping, then cut in width and in length to form a corrugated mat 22 of the desired format and degreased. As seen in cross section in Figure 8 (a), the element 22 has, after shaping, a succession of vertices and wave bases constituting first and second assembly portions intended to be brazed under vacuum respectively with adjacent plates 6, 7 of the exchanger.

According to the invention, the method comprises a step c) during which at least one surface texturing 23 is formed on all or almost all of the intermediate element 22. In other words, a surface texturing is applied at all the surfaces of the insert, including the pairs of opposite surfaces located at the vertices and bases. For example, the texturing 23 can be formed by depositing a coating of the suspension type. In this case, the constituent material of the texturing and additives such as thickening, pore-forming elements, etc. are suspended in a binder. This technique makes it possible to produce coatings on waves of greater density than it is difficult to treat by thermal spraying due to poor accessibility to surfaces.

Next, at least the surface texturing portions 23 which extend over the surfaces of the first assembly portions oriented, in the assembled state, on the side of the first plate 6 are selectively removed. intermediate element comprises one or more second assembly portions intended to be assembled with the second plate 7, there is also a selective removal of the texturing 23 at the surfaces of the second oriented assembly portions oriented, in the assembled state, on the side of the second plate 7.

Different solutions can be used to selectively remove the surface texturing 23. A first solution, illustrated in FIG. 8 (c), is to deposit, before forming the texturing 23, a fusible coating 25 on the surfaces of the element 22 that we wish to see, at the end of the manufacturing process, free of surface texturing 23. A heat treatment of the element 22 is then carried out so as to remove the fusible coating 25, and with it the surface portions 23.

Alternatively, a mask 25 can be affixed to these surfaces before performing surface texturing. Once the surface texturing has formed on the entire element 22, the mask is removed.

The mask can be made from a sheet with openings. Preferably, the mask is pressed as close as possible to the surfaces to be masked of the element 22 in order to avoid any deposit there. The openings are positioned opposite the surfaces of the element 22 on which the texturing 23 is to be formed.

The mask can be formed from an alloy steel or a nickel alloy, preferably a nickel-iron-chromium alloy, in particular an alloy of the 800H type, which offers good resistance at high temperature.

Another solution is to remove the surface texturing in the desired areas by means of a mechanical process, for example by brushing or sanding the surfaces of the element 22.

The intermediate element 22 thus produced is then mounted between a first plate 6 and a second plate 7 of the exchanger, then brazed to said plates, as illustrated in Figure 8 (e).

Example

Tests for depositing a porous structure were carried out on a corrugated product having a density of 6 wave legs per 2.54 cm and a height of 5 mm. The corrugated product was formed from a strip 0.5 mm thick. A mask made of an 800H alloy sheet was affixed to the corrugated product. It featured a series of 4.2mm laser-cut slits. The solid parts of the mask were arranged at the peaks of the corrugated product.

The deposition was carried out by thermal flame projection from an aluminum wire comprising, for 100% of its mass, 99.5% of aluminum. These tests made it possible to selectively deposit on the wave legs of the corrugated product a surface texturing in the form of a porous layer with a thickness of 200 to 300 μm and an open porosity of the order of 30%. . The porous layer had good adhesion characteristics on the surface of the corrugated product.

Claims (19)

1. Intermediate element (22) for a heat exchanger of the brazed plate and fin type, intended to be mounted between a first plate (6) and a second plate (7) of the exchanger, said intermediate element (22) comprising: - at least a first assembly portion (121) configured to be assembled with the first plate (6) and comprising a first pair of opposite surfaces (121a, 121b), one (121a) of the surfaces of the first pair being oriented towards the side of the first plate (6) and the other (121b) of the surfaces of the first pair being oriented towards the side of the second plate (7) when the intermediate element (22) is in the assembled state, - Several fins or wave legs (123) extending from said first assembly portion (121) so as to delimit, when the intermediate element (22) is in the assembled 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 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) is free of surface texturing (23) on the surface (121a) of the first pair oriented, in the assembled state, on the side of the first plate (6). 2. Element according to claim 1, characterized in that at least one fin or wave leg (123) comprises a third pair of opposite surfaces (123a, 123b), one and / or the other of the surfaces ( 123a, 123b) of the third pair having said surface texturing (23). 3. Element according to one of claims 1 or 2, characterized in that all or almost all of one and the other of the surfaces (123a, 123b) of the third pair has said surface texturing (23 ). 4. Element according to one of the preceding claims, characterized in that the first assembly portion (121) has the surface texturing (23) on the surface (121b) of the first oriented pair, in the assembled state, on the side of the second plate (7). 5. Element according to one of the preceding claims, characterized in that the first assembly portion (121) is arranged between two successive fins or wave legs (123), the surface (121b) of the first pair oriented, in the assembled state, on the side of the second plate (7) having two ends each connected to a respective surface (123a, 123b) of each of the two fins or wave legs (123), the surface (121b) of the first pair and said respective surfaces of the fins having the surface texturing (23). 6. 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) opposite, one (122a) of the surfaces of the second pair being oriented towards the side of the first plate (6) and the other (122b) of the surfaces of the second pair being oriented towards the side of the second plate (7 ) when the intermediate element (22) is in the assembled state, said second assembly portion (122) being free of surface texturing (23) on at least the surface (122b) of the second oriented pair, at the 'assembled state, on the side of the second plate (7). 7. Element according to claim 6, characterized in that the second assembly portion (122) has the surface texturing (23) on the surface (122a) of the second pair oriented, in the assembled state, on the side of the first plate (6). 8. Element according to one of claims 6 or 7, characterized in that the second assembly portion (122) is arranged between two successive fins or wave legs (123), the surface (122a) of the second pair oriented, in the assembled state, on the side of the first plate (6) having two ends each connected to a respective surface (123a, 123b) of each of the two fins or wave legs (123), said surface (122a) of the second pair and said respective surfaces of the fins having the surface texturing (23). 9. 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 assembled state, parallel to the first and second plates (6, 7), the fins or wave legs (123) succeeding each other in a lateral direction (x) and delimiting, in the assembled state, a plurality of channels (26) configured to channel the first fluid according to a longitudinal direction (z) parallel to the first and second plates (6, 7) and orthogonal to the lateral direction (x). 10. Element according to claim 9, characterized in that said at least one fin or wave leg (123) extend in a plane parallel to the longitudinal direction (z) and form an angle (a) relative to the first assembly portion (121) and / or the second assembly portion (122), the angle (a) being less than or equal to 90 °. 11. 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 between 15 and 60%, preferably an open porosity between 20 and 45% (% by volume), or in the form of reliefs defining, in cross section, open cavities on the surface of the intermediate element (22). 12. 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) connected alternately by wave vertices (121 ) and wave bases (122), at least one wave top (121) comprising said first assembly portion (121) and / or at least one wave base (122) comprising said second portion assembly (122). 13. Element according to claim 12, characterized in that the wave legs (123) follow one another in a lateral direction (x), the corrugated product (22) having a density, defined as the number of wave legs per 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 by 2.54 centimeters . 14. Element according to one of claims 12 or 13, characterized in that the corrugated product (22) is formed from a flat product having a thickness of at least 0.15 mm, preferably between 0, 2 and 0.4 mm. 15. Plate-type heat exchanger and brazed fins comprising a plurality of plates (6, 7) arranged parallel to each other so as to define a series of passages (33) for the flow of a first fluid to be connected heat exchange with at least a second fluid, and at least one intermediate element (22) mounted between two successive plates (6, 7) defining a passage (33) so as to form, within the 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 14. 16. Method for manufacturing an intermediate element for a heat exchanger of the brazed plate and fin type, said method comprising the following steps: a) shaping the intermediate element (22) so that it has fins or wave legs (123) delimiting, when the intermediate element (22) is mounted between a first plate (6) and a second plate (7) of the exchanger, a plurality of channels (26) for the flow of a first fluid, and at least a first assembly portion (121) configured to be assembled with a first plate (6) and comprising a first pair of opposite surfaces (121a, 121b) one of which (121a) is oriented on the side of the first plate (6) and the other (121b) is oriented on the side of the second plate (7) when the intermediate element (22) is in the assembled state, c) formation of a surface texturing (23) in the form of a porous structure or of reliefs on all or almost all of the intermediate element (22), d) selective removal of at least a portion of said surface texturing (23) extending over that (121a) of the surfaces of the first oriented pair, in the mounted state, on the side of the first plate (6). 17. The method of claim 16, characterized in that it comprises, prior to step c), a step b) of depositing a fusible coating (25) on that (121a) of the surfaces of the first oriented pair in the assembled state, on the side of the first plate (6), step d) comprising a heat treatment of the intermediate element (22) so as to remove the fusible coating (25) and the surface texturing portion (23) formed on said fusible coating (25). 18. The method as claimed in claim 16, characterized in that, prior to step c), the application of a mask to that (121a) of the surfaces of the first oriented pair, in the assembled state, on the side of the first plate (6), step d) being carried out by removing the mask. 19. The method of claim 16, characterized in that step d) is carried out mechanically, preferably by brushing or sanding.