CN111465814A

CN111465814A - Spacer element with surface texture, and associated heat exchanger and production method

Info

Publication number: CN111465814A
Application number: CN201880080768.0A
Authority: CN
Inventors: 弗雷德里克·克雷萨克; 拉斐尔·福尔; 尼古拉斯·里歇; 马克·瓦格纳
Original assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2017-12-19
Filing date: 2018-12-17
Publication date: 2020-07-28
Also published as: FR3075340B1; EP3728976A1; JP2021508022A; WO2019122651A1; US20210088292A1; FR3075340A1

Abstract

The invention relates to a spacer element (22) for a brazed plate and fin heat exchanger intended to be fitted between a first plate (6) and a second plate (7) of the exchanger, the spacer 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), when the spacer element (22) is in the assembled state, one surface (121a) of the first pair of surfaces is oriented towards the first plate (6), and the other surface (121b) of the first pair is oriented towards the second plate (7), a number of fins or corrugated legs (123), the fins or corrugated legs extending from the first assembly part (121) to define channels (26) for flow of a first fluid when the spacer element (22) is in the assembled state, and at least one surface texture (23) in the form of a porous or relief structure formed on the surface of the spacer element (22), at least one fin or corrugated leg (123) exhibiting said surface texture (23). According to the invention, the first component part (121) is free of surface textures (23) on the surface (121a) of the first pair which is oriented towards the first plate (6) in the assembled state.

Description

Spacer element with surface texture, and associated heat exchanger and production method

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

The invention is particularly applicable in the field of cryogenic separation of gases, in particular of air, i.e. in so-called ASUs (air separation units) for the production of pressurized gaseous oxygen. In particular, the invention may be applied to heat exchangers that vaporize a liquid stream (e.g., liquid oxygen, nitrogen, and/or argon) by heat exchange with a heat-generating gas (e.g., air or nitrogen).

If the heat exchanger is at the bottom of the distillation column, it may constitute an evaporator operating as a thermosiphon (with the exchanger immersed in a bath of liquid flowing down the column), or an evaporator performing film evaporation directly with the liquid falling from the column and/or an evaporator operating by means of a circulating pump.

The invention can also be applied to heat exchangers in which at least one liquid-gas mixture stream, in particular a stream of a multi-component mixture (for example a stream of a hydrocarbon mixture), is vaporized by heat exchange with at least one other fluid (for example natural gas).

The technology commonly used for exchangers is that of aluminium brazed plate fin exchangers or corrugated fin exchangers, which makes it possible to obtain a device which is very compact and provides a large exchange surface area.

These exchangers comprise baffles between which are interposed heat exchange structures (usually corrugated structures or corrugated fins) formed by a series of fins or corrugated legs, thus constituting a stack of passages for bringing the various fluids into heat exchange relationship.

The performance of the exchanger is related to the heat exchange coefficient of the heat exchange structure in contact with the fluid. The heat exchange coefficient of a structure depends, among other things, on the nature of the material from which it is made, the porosity of the material, its roughness, and the flow scheme of the fluid.

For example, documents US 2005/0121181A, US 2016/0305720 a1 or US 5514248 a disclose various heat exchange arrangements, in particular corrugated structures, with deformations in the form of louvered protuberances, perforations or openings.

The heat exchange coefficient can be changed by changing the geometry or physicochemical properties of the surface of the heat exchange structure. This makes it possible to increase the effective exchange surface area and/or to change the interaction between the fluid and the surface by changing the properties of the surface in question, such as its wettability or its ability to enhance the foaming of the fluid. These are considered to be strengthened surfaces. Such surfaces are described in particular in the article "Heat transfer enhancement-a review of techniques and the possibility of Heat transfer on energy efficiency in the u.k. [ Heat transfer enhancement-technical review in the uk and its possible effect on energy efficiency ]", DA read, Heat recovery systems & CHP, vol.11, No.1, pp.1-40, 1991.

For example, a porous coating, or a surface deposit of a coating forming a relief structure on the surface of the structure, may be produced, or a mechanical treatment or chemical attack may be used to create such a surface state.

Document WO-A-2005/075920 discloses A number of different techniques for depositing A porous coating or relief structure on the surface of A corrugated member for A heat exchanger.

Document WO-A-2004/109211 describes A method for depositing A porous coating on the surface of A separator of A heat exchanger.

One problem that arises with the use of surfaces that have been strengthened by texturing in brazed aluminum exchangers relates to the assembly of elements that include such surfaces during the manufacture of the exchanger.

In particular, the connection between the elements constituting the exchanger is achieved by brazing using a filler metal, called solder or brazing material, the assembly being achieved by melting and diffusing the brazing material into the parts to be brazed, without melting these parts.

Now, there is a porous coating or relief structure in the connection area between the parts to be assembled, and therefore there is an open porosity of the coating or cavity formed on the textured surface, because the gap existing between the parts to be assembled is increased. Upon melting, the filler metal fills these voids or cavities before filling the gaps between the parts, and this may result in defects in the braze joint, such as voids, lack of solder, or even no joint. This affects the mechanical and/or thermal properties of the joint and therefore of the exchanger, which are directly related to the quality of the brazed joint.

In an attempt to overcome these drawbacks, one solution is to texture the heat exchange surface after the structures have been brazed in the exchanger.

However, access to the channels formed by the exchange structures in the passages of the exchanger is difficult and mechanical texturing or coating techniques involving thermal spraying cannot be used. It is difficult to adopt other surface treatment techniques. For example, in the case of techniques involving a heat treatment or a preliminary step of application of a dip coating to ensure the adhesion of the coating, the whole exchanger must be treated. Thus, there is a risk of plugging the channels, rendering a portion of the exchanger braze-free, or producing brittle metallurgical phases and damaging the brazed matrix.

Furthermore, it has been proposed to perform surface texturing on the separator plate prior to brazing. In that case, however, there is no heat exchange structure brazed to the plates and the plates must be annealed. The exchange structure now also acts as a spacer and contributes to the rigidity of the assembly. Furthermore, the sheet that has been annealed loses its mechanical strength. It is then necessary to fit additional reinforcing rods in the channels and double the thickness of the plate.

It is an object of the present invention to solve all or some of the above problems, in particular to improve the manufacture of brazed plate and fin heat exchangers presenting an exchange structure with improved thermal properties.

The solution according to the invention is therefore a spacer element for a brazed plate-fin heat exchanger intended to be fitted between a first plate and a second plate of the exchanger, said spacer element comprising:

-at least a first assembly part configured to be assembled with the first plate and comprising a first pair of opposite surfaces, one of which is oriented towards the first plate and the other of which is oriented towards the second plate when the spacer element is in the assembled state,

-a number of fins or corrugated legs extending from the first assembly part to define channels for the flow of the first fluid when the spacer element is in the assembled state, and

-at least one surface texture in the form of a porous or relief structure formed on the surface of the spacer element, at least one fin or corrugated leg exhibiting said surface texture,

characterized in that the surface of the first component part in the first pair which is oriented towards the first plate in the assembled state is free of surface texture.

Elements of the invention may include one or more of the following technical features, as appropriate:

the spacer element comprises a massive or solid substrate, the surface texture being formed or deposited on a surface of the substrate.

-at least one fin or corrugated leg comprises a third pair of opposite surfaces, one and/or the other of which exhibits said surface texture.

-one surface and/or the other surface of the third pair of surfaces exhibits said surface texture over the whole or almost the whole.

-the first assembly part exhibits said surface texture on the surface of said first pair oriented towards the second plate in the assembled state.

The first assembly portion is arranged between two consecutive fins or corrugated legs, the surface of the first pair, which in the assembled state is oriented towards the second plate, having two ends, each end being connected to a respective surface of each of said two fins or corrugated legs, the surface of the first pair and said respective surfaces of the fins exhibiting the surface texture.

-the element comprises at least a second assembly part configured to be assembled with the second plate and comprising a second pair of opposite surfaces, one surface of the second pair being oriented towards the second plate and the other surface of the second pair being oriented towards the second plate when the spacer element is in the assembled state, said second assembly part being free of surface texture on the surface of the second pair that is oriented towards the second plate in the assembled state.

-the second component part exhibits the surface texture on the surface of the second pair oriented towards the first plate in the assembled state.

The second assembly portion is arranged between two successive fins or corrugated legs, the surface of the second pair, oriented towards the first plate in the assembled condition, having two ends, each end being connected to a respective surface of each of said two fins or corrugated legs, said surfaces of the second pair and said respective surfaces of the fins exhibiting the surface texture.

The first assembly part and/or the second assembly part are arranged parallel to the first plate and the second plate in the assembled state, the fins or corrugated legs being arranged one after the other in a transverse direction and delimiting, in the assembled state, channels configured for guiding the first fluid in a longitudinal direction parallel to the first plate and the second plate and orthogonal to the transverse direction.

-said at least one fin or corrugated leg extends in a plane parallel to the longitudinal direction and forms an angle α with respect to the first assembly part and/or the second assembly part, the angle α being less than or equal to 90 °.

The surface texture is in the form of a porous structure with an open porosity of between 15% and 60%, preferably between 20% and 45% (volume percent), or in the form of a relief structure defining in cross section cavities open to the surface of the spacer element.

-the element is in the form of a corrugated product comprising a series of corrugated legs alternately connected by corrugation peaks and corrugation valleys, at least one corrugation peak comprising said first component part and/or at least one corrugation valley comprising said second component part.

-the corrugated legs are arranged one after the other in the transverse direction, the corrugated product having a density, defined as the number of corrugated legs per unit length measured in the transverse direction, which is less than 18 legs per 2.54 cm, preferably less than 10 legs per 2.54 cm, still more preferably less than or equal to 5 legs per 2.54 cm.

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

The invention also relates to a brazed plate and fin heat exchanger comprising: a plurality of plates arranged parallel to one another to define a series of passages for the flow of a first fluid to be in heat exchange relationship with at least one second fluid; and at least one spacer element fitted between two successive plates defining a passage to form channels for the flow of said first fluid in the passage, characterized in that the spacer element is a spacer element according to the invention.

According to another aspect, the invention relates to a method for producing a spacer element for a brazed plate and fin heat exchanger, the method comprising the steps of:

a) the spacer element is shaped so as to exhibit: fins or corrugated legs which, when the spacer element is fitted between the first and second plates of the exchanger, delimit a plurality of channels for the flow of the first fluid; and at least one first assembly part configured to be assembled with a first plate and comprising a first pair of opposite surfaces, one of which is oriented towards the first plate and the other of which is oriented towards the second plate when the spacer element is in the assembled state,

c) a surface texture in the form of a porous structure or a relief structure is formed on the entire or almost the entire spacer element,

d) selectively removing at least a portion of said surface texture extending on the surface of the first pair of surfaces oriented toward the first plate in the assembled state.

The method according to the invention may comprise one or more of the following features:

-the method comprises, before step c), a step b): depositing a fusible coating on the one of the first pair of surfaces that is oriented toward the first plate in the assembled state, step d) comprising: the spacer element is heat treated in a manner to remove the fusible coating and the surface texture portions formed on said fusible coating.

The method comprises, before step c), applying a mask to the surface of the first pair of surfaces oriented towards the first plate in the assembled state, step d) being performed by removing the mask.

-performing step d) mechanically, preferably by brushing or polishing.

The invention will now be better understood by the following description, given purely by way of non-limiting example and with reference to the accompanying drawings, in which:

figure 1 illustrates an example of a heat exchanger comprising spacer elements according to the present invention;

figure 2 illustrates an example of an assembly of spacer elements brazed to an exchanger plate according to the invention;

figures 3 to 6 show a number of different views of a spacer element according to an embodiment of the invention;

figure 7 illustrates a number of different embodiments of spacer elements assembled between two exchanger plates;

fig. 8 illustrates steps in a method for producing a spacer element according to an embodiment of the invention.

In a manner known per se, the heat exchanger comprises a stack of plates arranged in parallel, one above the other, at a distance, thereby forming several series of passages for the flow of a first fluid and at least one second fluid, having a flat parallelepiped shape, via which the first fluid and the at least one second fluid are in indirect heat exchange relationship. Preferably, the first fluid comprises a liquid refrigerant that will at least partially evaporate.

Fig. 1 schematically shows an example of a passage 33 of an exchanger 1 of the evaporator-condenser type supplied with liquid oxygen, the evaporator-condenser evaporating liquid oxygen O L collected at the bottom of the column at low pressure (typically slightly above atmospheric pressure) by condensing nitrogen at medium pressure (typically from 5 bar to 6 bar absolute) circulating through a passage (not shown) adjacent to the passage 33 dedicated to the circulation of oxygen, medium-pressure nitrogen in the gaseous state is generally withdrawn from the top of a medium-pressure air distillation column to which the above-mentioned low-pressure column is connected, this nitrogen returning to the medium-pressure column after having passed through the evaporator-condenser and at least partially condensed.

More specifically, in the context of such an application of the invention described hereinafter, it is understood that its application in other contexts, in particular the use of different kinds of fluids, is conceivable. The heat exchanger 1 can therefore vaporize at least one liquid-gas mixture stream, in particular a stream of a multi-component mixture (for example a stream of a hydrocarbon mixture), by heat exchange with at least one other fluid (for example natural gas).

All or some of the evaporation passages 33 of the exchanger 1 are provided with spacer elements 22 which define channels 26 for the circulation of liquid oxygen within the passages 33 and which can take a number of different forms.

The spacer element 22 may have a corrugated shape (as shown in fig. 3) and comprises corrugated legs 123 alternately connected by corrugated peaks 121 and corrugated valleys 122. In this case, the corrugation legs connecting successive peaks and valleys of the corrugation are called "fins".

The spacer elements 22 may take other specific shapes defined according to the desired fluid flow characteristics. More generally, the term "fin" covers a blade or other secondary heat exchange surface extending between the primary heat exchange surfaces (that is to say the plates of the exchanger) in the passages of the exchanger.

The spacer elements 22 are connected to the plates of the exchanger by brazing. Advantageously, the joining is achieved by vacuum brazing using a filler metal 30, known as solder or brazing material, the assembly being achieved by melting and diffusing the brazing material 30 into the parts to be brazed (i.e. into the base metal) without melting these parts.

Fig. 2 is a partial view of a spacer element 22 assembled with a first plate 6 designed to define, together with another parallel second plate 7 (not shown), a passage 33 of the exchanger 1.

The spacer element 22 and the plate 6 comprise respectively

assembly portions

121, 60 intended to be brazed to each other. The

assembly parts

121, 60 are positioned against each other, preferably with a small gap between them, into which the brazing material 30 can be inserted. Typically, the

assembly portions

121, 60 may be the portions where the gap between the

components

22, 6 is minimal, typically the portions where the

components

22, 6 are in contact with each other or near contact with each other, meaning that there is very little gap between all or a portion of the portions relative to each other.

Preferably, the

plates

6, 7 of the exchanger are co-laminates comprising a central sheet 40, each face of which is covered with a layer 30. According to another embodiment, the brazing material 30 may take the form of tape or a surface coating 30. The coating 30 may be applied by spraying, or the braze material 30 may be brushed in a powder suspension containing powder, dispersant, binder, and additives for viscosity control.

Preferably, the thickness of the brazing material 30 is between 50 and 300 μm, preferably between 100 and 250 μm.

The brazing material 30 is preferably formed of a metallic material having a melting point lower than that of the material from which the

components

6, 22 are made. The

components

6, 22 and 30 are preferably formed of an aluminum alloy. The plates 6 and the elements 22 of the exchanger are advantageously formed of a first aluminium alloy of the 3XXX family (preferably of type 3003) (ASME SB-2019 standard, section 2-B). Brazing material 30 is formed from a second aluminum alloy, preferably a 4XXX type alloy (ASME SB-2019 standard, section 2-B), particularly a 4004 type alloy.

As can be seen in the cross section of fig. 4, the spacer element 22 comprises a number of fins or corrugated legs 123 configured to define a plurality of channels 26 for the flow of the first fluid when the element 22 is fitted between the first 6 and second 7 plates of the exchanger.

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 121a of which is oriented towards the first plate 6 and the other 121b of which is oriented towards the second plate 7 when the spacer element 22 is in the assembled condition.

The spacer element 22 further comprises at least one surface texture 23 in the form of a porous structure or a relief structure formed on the surface of the spacer element 22.

In the context of the present invention, there is at least one surface texture on the surface of at least one fin or corrugated leg 123 of the spacer element 22. It should be noted that the spacer element may have one or more predetermined surface texture forms distributed over different areas of its surface, it being understood that the surface texture may also be created, e.g. deposited, only on the surface of the material on which the spacer element is made, i.e. by adding additional material to the surface of the spacer element.

According to the invention, the first component part 121 is free of a surface texture 23 on a surface 121a thereof which, in the assembled state, is oriented towards the first plate 6.

This therefore maintains the wettability and good brazeability of this surface of the spacer element, which is intended to be positioned against an adjacent plate for assembly thereto by brazing. During the brazing process, the distribution of the brazing material in the joint can be controlled, which results in a joint exhibiting good mechanical and thermal properties. Thus, brazed plate fin exchangers can be manufactured using conventional methods.

Furthermore, no surface texturing is required after the spacer element 22 has been assembled, since this element is already textured on the desired regions of the fins. Thus, a heat exchange structure with an enhanced surface can be introduced into the exchanger while maintaining the structural integrity of the matrix of the exchanger and its internal channels.

The absence of surface texture on the surface facing the first plate allows for better control of the height of the spacer element. Now, the height of the spacer elements is an important parameter, precisely tailored to the spacing between the first plate 6 and the second plate 7 of the exchanger, determining the quality of the braze joint and therefore its characteristics.

According to an advantageous embodiment, the spacer element 22 is a corrugated product comprising a series of corrugated legs 123, which are alternately connected by corrugation crests 121 and corrugation troughs 122. At least one corrugation peak 121 comprises a first component part 121 according to the invention.

The following explanation is given with reference to fig. 4 to 7, wherein it is to be understood that the spacer element 22 may take any other suitable form and does not necessarily comprise all features detailed below.

Figure 4 shows a cross-sectional view of the corrugated heat exchange structure 22. Several corrugated legs 123 having a rectilinear shape extend parallel to each other and generally in a direction referred to as longitudinal direction z. These corrugated legs are arranged one after the other in a transverse direction x perpendicular to the longitudinal direction z and are alternately connected by corrugation hills 121 and corrugation valleys 122.

According to the example illustrated in fig. 3, the corrugation hills 121 and corrugation valleys 122 are flat in shape and extend parallel to each other and perpendicular to the corrugation legs 123. Thus, the channels 26 for the first fluid formed between two successive corrugation legs and the peaks or valleys arranged between said successive corrugation legs have a cross section of rectangular overall shape.

Fig. 4 shows a flat corrugation with corrugated legs 123 with flat surfaces. Of course, other configurations of the spacing elements 22 are conceivable, in particular of the perforated fin, serrated fin, corrugated fin or corrugated fin type of herringbone fin.

The element 22 according to fig. 4 is shown in fig. 7(a) in an assembled state, i.e. when assembled between directly adjacent first and

second plates

6, 7, thereby forming a passage 33. The passage 33 has the general shape of a parallelepiped and is configured for guiding the first fluid parallel to the longitudinal direction z.

In operation, the first fluid flows across the width of the passage 33 (measured in the transverse direction x) between an inlet and an outlet of the passage 33 at opposite ends along the length of the passage 33 (measured in the longitudinal direction z). The corrugated legs 123 define a plurality of channels 26 within the passage 33, which extend parallel to the longitudinal direction z.

As can be seen in fig. 7(a), the element 22 preferably extends across almost the entire or even the entire height of the passage (measured in a vertical direction y perpendicular to the plates 6, 7) to be in contact or near contact with the

plates

6, 7. The corrugation hills 121 and corrugation valleys 122 are arranged parallel to the

plates

6, 7.

According to a particular embodiment, the height of the element 22 may be adapted to the height of the passage 33, so that there is a gap of predetermined value between the corrugation crests 121 and the first plate 6 and between the corrugation troughs 122 and the second plate 7, as indicated by reference "d" in fig. 8 (e). This may prevent capillary action drawing back the brazing material from the area of the braze joint during the vacuum brazing step, which may sometimes be detrimental to the performance of the exchanger, as the solder, by flowing, fills the pores or cavities present on the surface, possibly altering the microstructure of the surface texture.

Preferably, the gap d is between 0 and 0.1mm, still more preferably between 0 and 0.05 mm.

Preferably, the spacer element 22 is arranged in the passage 33 in a so-called "plain type" configuration, which means that the corrugated legs 123 extend generally in the flow direction in the first fluid passage 33. It should be noted that in operation the flow direction of the first fluid is preferably vertical, which may be upwards or downwards.

Advantageously, the spacer element 22 according to the invention can be arranged in the region 3 of the passages 33 of the exchanger, which is accessible to the oxygen flowing upwards, so that the spacer element has on its surface a porosity or relief structure, which doubles the number of sites where the gaseous oxygen OG can start to form bubbles.

Preferably, according to the present invention, each corrugation peak 121 comprises a first component part 121. Thus, the corrugated peak surface 121a, positioned against the first plate 6, is free of surface texture 23, which allows this surface to be brazed firmly to the mutually assembled parts on the first plate 6 during the manufacture of the exchanger.

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

As shown in fig. 4, the second component part comprises a second pair of

opposite surfaces

122a, 122b, one surface 122b of the second pair of surfaces, which is oriented towards the second plate 7, being free of the surface texture 23.

Thus, another part of the spacer element 22 can be firmly brazed to the mutually assembled part on the second plate 7 during manufacture of the exchanger, thereby further improving the robustness and rigidity of the passage 33.

Preferably, the first assembly part 121, the fins or corrugated legs 123, and the second assembly part 122 (if present) are integral, i.e. formed as a single piece.

Preferably, each corrugated 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 preferably having said surface texture 23 in its entirety, or almost in its entirety.

It should be noted that in the context of the present invention, almost the whole of a surface or an element refers to a portion that occupies at least 90%, preferably at least 95%, still more preferably at least 98% of the surface area of the surface or the total surface area of the element.

Fig. 5 illustrates an example where all of the corrugated legs 123 have at least one surface texture on both

surfaces

123a, 123b thereof. Thus, each channel 26 has two

side walls

123a, 123b, the inner surfaces of which are reinforced.

Preferably, the first component part 121 also exhibits a surface texture 23 on a surface 121b of the first pair, which is oriented towards the second plate 7 in the assembled state (preferably on the whole or almost the whole of said surface 121 b).

The second component part 122 may also exhibit a surface texture 23 on a surface 122a of the second pair, which is oriented in the assembled state towards the first plate 6 (preferably the entirety or almost the entirety of said surface 122 a). This makes it possible to maximise the surface area of the surface texture 23 present on the spacer elements 22 and hence to maximise the efficiency of heat transfer within the channels 26 defined by the spacer elements.

Such a configuration is illustrated in fig. 6 and 7 (a). In fact, each channel 26 has an inner surface which, in the assembled condition, is formed alternately by a surface 122a of the corrugation valley 122 oriented towards the first plate 6, a surface 6b of the first plate 6 oriented towards the corrugation valley 122, and

respective surfaces

123a, 123b of the two corrugation legs 123 connected to the two ends of said corrugation valley 122, and by a surface 121b of the corrugation peak 121 oriented towards the second plate 7, a surface 7a of the second plate 7 oriented towards the corrugation peak 121, and

respective surfaces

123a, 123b of the two corrugation legs 123 connected to the two ends of said corrugation peak 121.

By arranging at least one surface texture 23 on the bottom of the channels 26 formed alternately by the corrugation hills 121 or valleys 122, the heat exchange is enhanced over a larger proportion of the surfaces of the element 22, which surfaces form the inner surfaces of the channels 26 in the assembled state.

Preferably, the

surfaces

6a, 6b and 7a, 7b of the

plates

6, 7 are free of surface texture. This then preserves the quality of the braze joint formed with the sheet.

Fig. 7(a) illustrates the following configuration: the corrugation legs 123 extend parallel to the longitudinal direction z and perpendicular to the corrugation hills 121 and corrugation valleys 122 of the element 22.

According to an alternative form of embodiment shown in fig. 7(b) and 7(c), the corrugated legs 123 extend in a plane parallel to the longitudinal direction z and forming an angle α of less than 90 ° with the first component part 121 on the one hand and the second component part 122 on the other hand.

By forming an acute angle between the corrugated legs 123 and the corrugation peaks 121 or valleys 122, the portion of the inner surface of the channel 26 that can exhibit surface texture is maximized, and the portion of the inner surface of the channel 26 that cannot normally exhibit texture is minimized, this portion being formed by the surface 6b of the first plate 6 oriented towards the corrugation valleys 122, or the surface 7a of the second plate 7 oriented towards the corrugation peaks 121, depending on which channel is considered.

Preferably, the angle α is between 60 and 90, and even more preferably, the angle α is between 70 and 85.

Within the scope of the present invention, the corrugated product 22 is preferably formed by a flat product (such as a sheet or strip) having a thickness of at least 0.15mm, preferably between 0.2 and 0.4 mm. This thickness is indicated by the letter "t" in fig. 3. The use of the surface texture 23 requires a significant heat flux, especially when the purpose of the surface texture 23 is to enhance foaming of the first fluid. It is therefore advantageous to use relatively thick spacer elements to maintain the maximum possible fin factor, i.e. the best ability of the fins to transfer heat.

It is also advantageous to operate with thicker spacer elements when it is desirable to reduce the density of fins on the spacer elements in order to reduce the pressure drop they cause due to the heat exchange enhancement obtained by the surface texturing. Thus, the heat exchange coefficient of the spacer element is maintained by increasing its thickness.

It should be noted that the fin coefficient is a number typically between 0 and 1, equal to 1 at the point of contact with the adjacent plate, and decreases with distance away from the plate along the fin. The point located in the middle of the fin is the point where the fin coefficient is lowest. Working with thicker fins can reduce heat conduction through the fins from the plates toward a point in the middle of the fins, thereby increasing the fin coefficient.

Preferably, the corrugated product 22 has a density (defined as the number of corrugated legs per unit length measured in the transverse direction x) of less than 18 legs per 2.54 cm, preferably less than 10 corrugated legs per 2.54 cm, still more preferably less than or equal to 5 legs per 2.54 cm. Advantageously, the density may be between 1 and 5 legs per 2.54 cm. It should be noted that these density values apply to spacer elements which are not necessarily corrugated products, in which the fins are arranged one after the other in the transverse direction x, and the density is then defined as the number of fins per unit length measured in the transverse direction x.

The use of a relatively low density may facilitate the stage of depositing surface texture on the fins or corrugated legs, as the surface is more accessible. Furthermore, the use of a lower density of spacer elements helps to eliminate air bubbles generated at the surface texture.

Preferably, the spacer element 22 comprises a massive substrate, or in other words a solid substrate, in particular a non-porous substrate, on which the texture 23 is formed. For example, the substrate can be seen in black in fig. 7. Depending on the structure of the spacer element, the substrate may comprise one or more first and/or second component parts, fins or corrugated legs.

It should be noted that the spacer element is preferably unitary, i.e. formed as one piece.

In the context of the present invention, the surface texture 23 may be the result of depositing a surface coating on the element, or of modifying the surface finish of said element, for example a part obtained using chemical, mechanical or equivalent treatments such as sandblasting, scoring or the like.

In particular, the surface coating can be deposited on the applied substrate via a liquid route, in particular by dipping, spraying, or via an electrolytic route, or via a dry route, in particular by Chemical Vapor Deposition (CVD) or physical vapor deposition (CVD), or by thermal spraying, in particular using a flame or plasma.

It should be noted that the texture 23 attempts to change the surface finish of the spacer element and does not deform the spacer element completely or partially.

Preferably, the surface texture is formed of aluminium or an aluminium alloy containing at least 80 wt% aluminium, preferably at least 90 wt%, still more preferably at least 99 wt% aluminium per 100 wt%.

According to a preferred embodiment, the surface texture 23 is in the form of a porous structure, preferably a porous layer. The porous structure may for example be formed by a deposit of slightly sintered aluminium particles, hybrid aluminium filaments, semi-molten aluminium particles that stick together (such as aluminium particles obtained after spraying, obtained by thermal spraying using a flame).

Preferably, the surface texture 23 exhibits an open porosity of between 15% and 60%, preferably between 20% and 45%, still more preferably between 25% and 35% (vol%) of the initial open porosity prior to brazing. It should be noted that open porosity is defined as the ratio between the volume of open porosity (i.e., the pores in fluid communication with the external environment in which the component 22 is located) and the total volume of the porous structure.

The diameter of the pores of the porous structure 23 is preferably between 1 and 200 μm, preferably between 5 and 100 μm. It should be noted that the cross-section of the pores need not be circular, but may exhibit an irregular shape. Thus, the term "diameter" also covers an equivalent hydraulic diameter which can be calculated by measuring the pressure drop experienced by the gas flow through the porous structure and assuming that the pores have a regular, in particular spherical, cylindrical, etc. shape.

The size of the pores can also be characterized by their volume. Preferably, the pores of the porous structure 23 have a size ranging from 1000 to 1,000,000 μm³The volume in between. The volume of the pores may be determined, for example, by tomography or by analysis of images of polished cross sections of the sample taken in multiple directions in space.

Alternatively, the surface texture 23 may be in the form of a relief structure, or in the form of a pattern printed or created in or on the material from which the spacing element 22 is made. Preferably, these relief structures define, in cross-section, cavities open to the surface of the element 22. For example, micro-relief structures having different morphologies or sizes, such as discrete or uninterrupted grooves, stripes, protrusions, and the like, may be formed or deposited on the surface of element 22. In particular, the relief structure forming the surface texture 23 may be produced by laser or mechanical and/or chemical machining.

A micro-relief structure refers to a relief structure having at least one characteristic dimension that is small compared to the dimensions of the elements, in particular a relief structure extending for a height (measured in a direction perpendicular to the surface of the spacer element exhibiting the texture) and/or a width (measured in a direction perpendicular to the surface of the spacer element exhibiting the texture) of from a few micrometers to a few hundred micrometers.

Fig. 8 illustrates the main steps in a manufacturing method that can be used to produce the spacer element 22, in the form of a corrugated product, intended to be arranged between the first plate 6 and the second plate 7. Of course, the manufacturing method described below may be applied to other forms of spacer elements.

The spacer elements 22 are first formed, typically by pressing, and then cut to width and length to form the desired pattern of corrugated mat 22 and degreased. As can be seen in the cross-section of fig. 8(a), the element 22 exhibits, after forming, a series of corrugated peaks and valleys constituting first and second assembly portions intended to be vacuum brazed to

adjacent plates

6, 7, respectively, of the exchanger.

According to the invention, the method comprises a step c) during which at least one surface texture 23 is formed on the whole or almost the whole of the spacing element 22. In other words, the surface texture is applied to all surfaces of the spacing element, including pairs of opposing surfaces located at the peaks and valleys. For example, the texture 23 may be formed by depositing a suspension type coating. In this case, the material constituting the texture and additives such as a thickener and a pore former are suspended in the binder. This technique allows to achieve coatings on corrugations of higher density, which are difficult to treat using thermal spraying due to the poor accessibility of the surface.

These portions of the surface texture 23, which extend at least over the surface of the first component part oriented in the assembled state towards the first plate 6, are then selectively removed. If the spacer element comprises one or more second assembly parts intended to be assembled with the second plate 7, the texture 23 at the surface of the second assembly part oriented towards the second plate 7 in the assembled state is also selectively removed.

There are a number of different solutions that can be used to selectively remove the surface texture 23. A first solution, shown in figure 8(c), is to deposit a fusible coating 25 on the surface of the element 22 where it is desired to see at the end of the manufacturing process that there is no surface texture 23, before the texture 23 is formed. The heat treatment of the element 22 is then carried out in a manner to remove the fusible coating 25 and therewith the surface portion 23.

Alternatively, the mask 25 may be attached to the surfaces before performing surface texturing. Once the surface texture has been formed over the entire element 22, the mask is removed.

The mask may be made of a metal sheet having an opening. Preferably, the mask is pressed as tightly as possible onto the surface of the element 22 to be masked to avoid any deposits. These openings are positioned to face the surface of element 22 on which texture 23 is to be formed.

The mask may be formed of alloy steel or of a nickel alloy, preferably of a nickel-iron-chromium alloy, in particular of type 800H alloy, which provides good high temperature heat resistance.

Another solution is to remove the surface texture in the desired areas by a mechanical process, for example by brushing or polishing the surface of the element 22.

The spacer element 22 thus produced is then fitted between the first plate 6 and the second plate 7 of the exchanger and then brazed to said plates, as shown in figure 8 (e).

Examples of the invention

The tests for depositing the porous structure were carried out on a corrugated product having a density of 6 corrugated legs per 2.54 cm and a height of 5 mm. The corrugated product is formed from strips of 0.5mm thickness. A mask formed from an 800H alloy sheet was attached to the corrugated product. It has a series of laser cut slots 4.2mm wide. The solid portions of the mask are arranged at the corrugation peaks of the corrugated product.

The deposit was applied by flame thermal spraying using an aluminium wire containing 99.5 wt% aluminium per 100 wt%. These tests allow to selectively deposit on the corrugation peaks of the corrugated product a surface texture in the form of a porous layer 200 to 300 μm thick with an open porosity of the order of 30%. The porous layer exhibits good adhesion properties to the surface of the corrugated product.

Claims

1. Spacer element (22) for a brazed plate-fin heat exchanger intended to be fitted between a first plate (6) and a second plate (7) of the exchanger, said spacer 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 surface (121a) of which is oriented towards the first plate (6) and the other surface (121b) of which is oriented towards the second plate (7) when the spacer element (22) is in the assembled state,

-a number of fins or corrugated legs (123) extending from said first assembly part (121) to delimit channels (26) for the flow of a first fluid when the spacer element (22) is in the assembled state, and

-at least one surface texture (23) in the form of a porous or relief structure formed on the surface of the spacing element (22), at least one fin or corrugated leg (123) exhibiting said surface texture (23),

characterized in that the first component part (121) is free of surface texture (23) on the surface (121a) of the first pair which is oriented towards the first plate (6) in the assembled state.

2. The element of claim 1, wherein the spacer element (22) comprises a massive or solid substrate, the surface texture (23) being formed on a surface of the substrate.

3. Element as in one of claims 1 and 2, characterized in that at least one fin or corrugated 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 exhibiting said surface texture (23).

4. An element as claimed in claim 3, characterized in that the entirety or almost the entirety of one and/or of the other surface of the third pair of surfaces (123a, 123b) exhibits said surface texture (23).

5. The element of one of the preceding claims, characterized in that the first assembly portion (121) exhibits the surface texture (23) on the surface (121b) of the first pair oriented towards the second plate (7) in the assembled state.

6. The element as claimed in one of the preceding claims, characterized in that the first assembly portion (121) is arranged between two successive fins or corrugated legs (123), the surface (121b) of the first pair, which is oriented towards the second plate (7) in the assembled state, having two ends, each end being connected to a respective surface (123a, 123b) of each of said two fins or corrugated legs (123), the surface (121b) of the first pair and said respective surfaces of the fins exhibiting the surface texture (23).

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 opposite surfaces (122a, 122b), one surface (122a) of which is oriented towards the first plate (6) and the other surface (122b) of which is oriented towards the second plate (7) when the spacer element (22) is in the assembled condition, said second assembly portion (122) being free of surface texture (23) on the surface (122b) of the second pair that is oriented towards the second plate (7) in the assembled condition.

8. The element as claimed in claim 7, characterized in that the second component part (122) exhibits the surface texture (23) on the surface (122a) of the second pair which is oriented towards the first plate (6) in the assembled state.

9. The element as claimed in one of claims 7 and 8, characterized in that the second assembly portion (122) is arranged between two successive fins or corrugated legs (123), the surface (122a) of the second pair, which in the assembled state is oriented towards the first plate (6), having two ends, each end being connected to a respective surface (123a, 123b) of each of said two fins or corrugated legs (123), said surfaces (122a) of the second pair and said respective surfaces of the fins exhibiting the surface texture (23).

10. The element of one of the preceding claims, characterized in that the first assembly portion (121) and/or the second assembly portion (122) are arranged parallel to the first and second plates (6, 7) in the assembled state, the fins or corrugated legs (123) being arranged one after the other in a transverse direction (x) and delimiting, in the assembled state, a plurality of channels (26) configured for guiding the first fluid along a longitudinal direction (z) parallel to the first and second plates (6, 7) and orthogonal to the transverse direction (x).

11. The element as claimed in claim 10, characterized in that said at least one fin or corrugated leg (123) extends in a plane parallel to the longitudinal direction (z) and forms an angle (α) with respect to the first assembly portion (121) and/or the second assembly portion (122), the angle (α) being less than or equal to 90 °.

12. Element according to one of the preceding claims, characterized in that the surface texture (23) is in the form of a porous structure with an open porosity of between 15% and 60%, preferably an open porosity of between 20% and 45% (volume%) or in the form of a relief structure defining in cross section cavities open to the surface of the spacer 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 series of corrugated legs (123) connected alternately by corrugation crests (121) and corrugation troughs (122), at least one corrugation crest (121) comprising said first assembly portion (121) and/or at least one corrugation trough (122) comprising said second assembly portion (122).

14. Element as claimed in claim 13, characterized in that the corrugated legs (123) are arranged one after the other in the transverse direction (x), the corrugated product (22) having a density defined as the number of corrugated legs per unit length measured in the transverse direction (x), which is less than 18 legs per 2.54 cm, preferably less than 10 legs per 2.54 cm, still more preferably less than or equal to 5 legs per 2.54 cm.

15. Element according to one of claims 13 and 14, characterized in that the corrugated product (22) is formed by a flat product having a thickness of at least 0.15mm, preferably between 0.2 and 0.4 mm.

16. A brazed plate fin heat exchanger, the heat exchanger comprising: a plurality of plates (6, 7) arranged parallel to each other to define a series of passages (33) for the flow of a first fluid to be in heat exchange relationship with at least one second fluid; and at least one spacer element (22) fitted between two successive plates (6, 7) defining a passage (33) to form a plurality of channels (26) for the flow of said first fluid in the passage (33), characterized in that the spacer element (22) is a spacer element according to one of claims 1 to 15.

17. A method of producing a spacer element for a brazed plate fin heat exchanger, the method comprising the steps of:

a) the spacer element (22) is shaped so as to exhibit: -fins or corrugated legs (123) which delimit a plurality of channels (26) for the flow of the first fluid when the spacer element (22) is fitted between the first plate (6) and the second plate (7) of the exchanger; and at least one 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 towards the first plate (6) and the other of which (121b) is oriented towards the second plate (7) when the spacer element (22) is in the assembled state,

c) a surface texture (23) in the form of a porous structure or a relief structure is formed over the entire or almost the entire spacer element (22),

d) -selectively removing at least a portion of said surface texture (23) extending on the surface (121a) of the first pair of surfaces oriented towards the first plate (6) in the assembled state.

18. The method of claim 17, wherein the method comprises step b) prior to step c): depositing a fusible coating (25) on the surface (121a) of the first pair of surfaces oriented towards the first plate (6) in the assembled state, step d) comprising: the spacer element (22) is heat treated in a manner to remove the fusible coating (25) and the portion of the surface texture (23) formed on said fusible coating (25).

19. Method according to claim 18, characterized in that it comprises, before step c), the application of a mask to the surface (121a) of the first pair of surfaces oriented, in the assembled state, towards the first plate (6), step d) being carried out by removing the mask.

20. The method according to claim 19, wherein step d) is performed mechanically, preferably by brushing or polishing.