US20210088292A1

US20210088292A1 - Spacer element with surface texturing, and associated heat exchanger and production method

Info

Publication number: US20210088292A1
Application number: US16/954,488
Authority: US
Inventors: Frederic Crayssac; Raphael Faure; Nicolas Richet; Marc Wagner
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: 2021-03-25
Also published as: EP3728976A1; CN111465814A; JP2021508022A; WO2019122651A1; FR3075340A1; FR3075340B1

Abstract

Certain embodiments of the invention relate to a spacer element for a heat exchanger of the brazed plate and fin type, intended to be fitted between a first plate and a second plate of the exchanger, said spacer 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 toward the first plate and the other of the surfaces of the first pair being oriented toward the second plate when the spacer element is in the fitted state, several fins or corrugation legs extending from said first assembly portion so as to delimit, when the spacer element is in the fitted state, a plurality of channels for the flow of a first fluid, and at least one surface texturing in the form of a porous structure or of reliefs formed on the surface of the spacer element, at least one fin or corrugation leg exhibiting said surface texturing. According to the invention, the first assembly portion is free of surface texturing on the surface of the first pair which, in the fitted state, is oriented toward the first plate.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a § 371 of International PCT Application PCT/FR2018/053329, filed Dec. 17, 2018, which claims the benefit of FR1762414, filed Dec. 19, 2017, both of which are herein incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to a spacer element for a heat exchanger of the plate and fin type, said spacer element having a texturized surface, and to a method for producing such an element and to a heat exchanger comprising such an element.
The present invention notably finds application in the field of the cryogenic separation of gases, particularly the cryogenic separation of air, in what is known as an ASU (air separation unit) used to produce pressurized gaseous oxygen. In particular, the present invention may apply to a heat exchanger which vaporizes a flow of liquid, for example liquid oxygen, nitrogen and/or argon through exchange of heat with a calorigenic gas, for example air or nitrogen.
If the heat exchanger is in the bottom of a distillation column, it may constitute a vaporizer operating as a thermosiphon for which the exchanger is immersed in a bath of liquid running down the column or a vaporizer performing film vaporization fed directly with the liquid falling from the column and/or by a circulation pump.
The present invention may also apply to a heat exchanger which vaporizes at least one flow of liquid-gas mixture, particularly a flow of multi-constituent mixture, for example a mixture of hydrocarbons, through exchange of heat with at least one other fluid, for example natural gas.

BACKGROUND OF THE INVENTION

The technology commonly employed for an exchanger is that of aluminum brazed plate and fin or corrugated-fin exchangers, which make it possible to obtain devices that are highly compact and offer a large exchange surface area.
These exchangers comprise separation plates between which are inserted heat-exchange structures, generally corrugated structures or corrugated fins, formed of a succession of fins or corrugation legs, thus constituting a stack of passages for the various fluids to be put into a 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 heat-exchange coefficient of a structure is dependent notably on the nature of the material of which it is made, on the porosity of this material, on its roughness and on the regime of the flow of the fluids.
Documents US 2005/0121181 A, US 2016/0305720 A1 or U.S. Pat. No. 5,514,248 A for example disclose various heat-exchange configurations, notably corrugated structures having deformations in the form of bumps, perforations or openings of the louver type.
It is possible to modify the heat-exchange coefficient of an exchange structure by modifying the geometry or the physico-chemical properties of its surface. This makes it possible to increase the effective exchange surface area and/or to modify the interactions between the fluid and the surface by changing properties of the surface in question, such as its wettability or its ability to intensify the bubbling of a fluid. These are then said to be intensified surfaces. Such surfaces are described notably in the article “Heat transfer enhancement—A review of techniques and their possible impact on energy efficiency in the UK”, D. A. Reay, Heat recovery systems & CHP, Vol. 11, No. 1, pp. 1-40, 1991.
For example, surface deposits of porous coatings or coatings that form reliefs on the surface of the structures can be made, or else such surface states can be created using mechanical treatments or using chemical attack.
Document WO-A-2005/075920 discloses various techniques for depositing porous coatings or reliefs on the surface of a corrugation for a heat exchanger.
Document WO-A-2004/109211 describes a method for depositing a porous coating on the surface of a separation plate of a heat exchanger.
One problem which arises with the use of surfaces which have been intensified by texturizing in brazed-aluminum exchangers relates to the assembly of elements comprising such surfaces during manufacture of the exchanger.
Specifically, the connection between the elements that make up the exchanger is achieved by brazing, using a filler metal known as braze or braze material, assembly being achieved by the melting and diffusion of the braze material into the components that are to be brazed, without these components melting.
Now, the presence of a porous coating or of reliefs in the region of connection between the parts that are to be assembled, because added to the clearance that exists between the parts that are to be assembled, there is the open porosity of the coating or the cavities formed on the texturized surfaces. As it melts, the filler metal fills these porosities or cavities before filling the clearance between the parts, and this may give rise to defects in the brazed joint, such as porosities, a lack of braze, 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 associated with the quality of the brazed joint.
In order to attempt to overcome these disadvantages, one solution is to texturize the heat-exchange surfaces after these structures have been brazed in the exchanger.
However, it is then difficult to access the channels formed by the exchange structures in the passages of the exchanger and it is impossible to use mechanical texturizing or coating techniques that involve thermal spraying. Other surface treatment techniques are difficult to employ. For example, in the case of techniques involving preliminary steps of heat treatment or of application of an impregnation coat in order to ensure the adhesion of the coating, it is the entire exchanger that has to be treated. There are then risks of blocking the channels, of parts of the exchanger becoming unbrazed or of creating fragile metallurgical phases and of damaging the brazed matrix.
Furthermore, it has been proposed for surface texturing to be performed on the separation plates prior to brazing. However, in that case, there is no heat-exchange structure brazed to the plates and the plates have to be annealed. Now, the exchange structures also act as spacers and contribute to the rigidity of the assembly. In addition, plates that have been annealed lose their mechanical strength. It is then necessary to fit additional reinforcing bars in the passages and to double the thickness of the plates.

SUMMARY OF THE INVENTION

It is an object of certain embodiments of the present invention to solve all or some of the above-mentioned problems, notably to improve the manufacture of a heat exchanger of the brazed plate and fin type exhibiting exchange structures that have improved thermal properties.
The solution according to certain embodiments of the invention is therefore a spacer element for a heat exchanger of the brazed plate and fin type, intended to be fitted between a first plate and a second plate of the exchanger, said spacer 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 toward the first plate and the other of the surfaces of the first pair being oriented toward the second plate when the spacer element is in the fitted state,
- several fins or corrugation legs extending from said first assembly portion so as to delimit, when the spacer element is in the fitted state, a plurality of channels for the flow of a first fluid, and
- at least one surface texturing in the form of a porous structure or of reliefs formed on a surface of the spacer element, at least one fin or corrugation leg exhibiting said surface texturing,

wherein the first assembly portion is free of surface texturing on the surface of the first pair which, in the fitted state, is oriented toward the first plate.
As the case may be, the element of the invention may comprise one or more of the following technical features:

- the spacer element comprises a massive or solid substrate, the surface texturing being formed or deposited on a surface of the substrate;
- at least one fin or corrugation leg comprises a third pair of opposite surfaces, one and/or the other of the surfaces of the third pair exhibiting said surface texturing;
- all, or almost all, of one and the other of the surfaces of the third pair exhibits said surface texturing;
- the first assembly portion exhibits the surface texturing on the surface of the first pair which, in the fitted state, is oriented toward the second plate;
- the first assembly portion is arranged between two successive fins or corrugation legs, the surface of the first pair which, in the fitted state, is oriented toward the second plate having two ends each one connected to a respective surface of each of the two fins or corrugation legs, the surface of the first pair and said respective surfaces of the fins exhibiting 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 toward the second plate and the other of the surfaces of the second pair being oriented toward the second plate when the spacer element is in the fitted state, said second assembly portion being free of surface texturing on at least the surface of the second pair which, in the fitted state, is oriented toward the second plate;
- the second assembly portion exhibits the surface texturing on the surface of the second pair which, in the fitted state, is oriented toward the first plate;
- the second assembly portion is arranged between two successive fins or corrugation legs, the surface of the second pair which, in the fitted state, is oriented toward the first plate having two ends each one connected to a respective surface of each of the two fins or corrugation legs, said surface of the second pair and said respective surfaces of the fins exhibiting the surface texturing;
- the first assembly portion and/or the second assembly portion are arranged, in the fitted state, parallel to the first and second plates, the fins or corrugation legs succeeding one another in a lateral direction and, in the fitted state, delimiting a plurality of channels which are 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 corrugation leg extend in a plane parallel to the longitudinal direction and form an angle α with respect to the first assembly portion and/or the second assembly portion, the angle α 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% (percent by volume), or in the form of reliefs defining, in transverse cross section, cavities that are open to the surface of the spacer element;
- the element is in the form of a corrugated product comprising a succession of corrugation legs alternately connected by corrugation crests and corrugation troughs, at least one corrugation crest comprising said first assembly portion and/or at least one corrugation trough comprising said second assembly portion;
- the corrugation legs succeed one another in a lateral direction, the corrugated product having a density, defined as being the number of corrugation legs per unit length measured in the lateral direction, of less than 18 legs per 2.54 centimeters, preferably less than 10 legs per 2.54 centimeters, more preferably still less than or equal to 5 legs per 2.54 centimeters; and/or
- the corrugated product is formed from a flat product having a thickness of at least 0.15 mm, preferably of between 0.2 and 0.4 mm.

Certain embodiments of the invention also relate to a heat exchanger of the brazed plate and fin type 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 placed in a heat-exchange relationship with at least one second fluid, and at least one spacer element fitted between two successive plates that define a passage so as to form, within the passage, several channels for the flow of said first fluid, wherein the spacer element is one according to embodiments discussed herein.
According to another aspect, certain embodiments of the invention relate to a method for producing a spacer element for a heat exchanger of the brazed plate and fin type, said method comprising the following steps:
a) shaping the spacer element so that it exhibits fins or corrugation legs which, when the spacer element is fitted between a first plate and a second plate of the exchanger, delimit a plurality of channels for the flow of a first fluid, and at least one first assembly portion configured to be assembled with a first plate and comprising a first pair of opposite surfaces of which one is oriented toward the first plate and the other is oriented toward the second plate when the spacer element is in the fitted state,
c) forming a surface texturing in the form of a porous structure or of reliefs over all, or almost all, of the spacer element, and
d) selectively removing at least a portion of said surface texturing extending over that one of the surfaces of the first pair which, in the fitted state, is oriented toward the first plate.
The method according to certain embodiments of the invention may comprise one or more of the following features:

- the method comprises, prior to step c), a step b) of depositing a meltable coating on that one of the surfaces of the first pair which, in the fitted state, is oriented toward the first plate, step d) comprising a heat treatment of the spacer element in such a way as to remove the meltable coating and the portion of surface texturing that is formed on said meltable coating;
- the method comprises, prior to step c), the application of a mask to that one of the surfaces of the first pair which, in the fitted state, is oriented toward the first plate, step d) being performed by removing the mask; and/or
- step d) is performed mechanically, preferably by brushing or rubbing down.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, advantages and possible applications of the invention are apparent from the following description of working and numerical examples and from the drawings. All described and/or depicted features on their own or in any desired combination form the subject matter of the invention, irrespective of the way in which they are combined in the claims the way in which said claims refer back to one another.

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

FIG. 2 illustrates an example of the assembly of a spacer element according to the invention brazed to an exchanger plate;

FIG. 3 shows a first view of a spacer element according to one embodiment of the invention;

FIG. 4 shows a second view of a spacer element according to one embodiment of the invention;

FIG. 5 shows a third view of a spacer element according to one embodiment of the invention;

FIG. 6 shows a fourth view of a spacer element according to one embodiment of the invention;

FIG. 7 illustrates various embodiments of a spacer element assembled between two exchanger plates;

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

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be understood better by virtue of the following description, which is given solely by way of nonlimiting example and with reference to the appended drawings
In a way known per se, a heat exchanger comprises a stack of plates arranged parallel one above the other with spacing between them thus forming several series of passages of flat and parallelepipedal shape for the flow of a first fluid and of at least one second fluid that is to be placed in an indirect heat-exchange relationship via the plates. As a preference, the first fluid contains a liquid refrigerant that is to be at least partially vaporized.
FIG. 1 schematically illustrates one example of a passage 33 of an exchanger 1 of the vaporizer-condenser type supplied with liquid oxygen. This vaporizer-condenser vaporizes liquid oxygen OL at low pressure (typically slightly higher than atmospheric pressure) collected at the bottom of a column, by condensation of nitrogen at medium pressure (typically from 5 to 6 bar absolute) circulating through passages adjacent to the passages 33 (which are not illustrated) dedicated to the circulation of oxygen. The medium-pressure nitrogen is usually withdrawn in the gaseous state from the top of a medium-pressure air distillation column to which the above-mentioned low-pressure column is connected. After having passed through the vaporizer-condenser and been at least partially condensed, 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 hereinafter, it being appreciated that it is conceivable to apply it to other contexts, notably using fluids of a different kind. Thus, the exchanger 1 may vaporize at least a flow of a liquid-gas mixture, in particular a flow of a multi-constituent mixture, for example a mixture of hydrocarbons, through exchange of heat with at least one other fluid, for example natural gas.
All or some of the vaporization passages 33 of the exchanger 1 are provided with spacer elements 22 which, within the passages 33, define channels 26 for the circulation of the liquid oxygen and which may adopt various forms.
The spacer elements 22 may have corrugated shapes, as shown in FIG. 3, and comprise corrugation legs 123 connected alternately by corrugation crests 121 and corrugation troughs 122. In this case, the corrugation legs that connect the successive crests and troughs of the corrugation are referred to as “fins”.
The spacer elements 22 may adopt other particular shapes 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 passages of the exchanger.
The spacer elements 22 are connected by brazing to the separating plates of the exchanger. Advantageously, the connection is achieved by vacuum brazing with the use of a filler metal 30, known as a braze or braze material, assembly being achieved by the melting and diffusion of the braze material 30 into the components that are to be brazed, namely into the base metal, without these components melting.
FIG. 2 is a partial view of a spacer element 22 assembled with a first plate 6 designed to define, in combination with another, parallel, second, plate 7 (not illustrated) a passage 33 of the exchanger 1.
The spacer element 22 and the plate 6 respectively comprise assembly portions 121, 60 which are intended to be brazed to one another. The assembly portions 121, 60 are positioned against one another, preferably with a small clearance between them into which the braze material 30 can be inserted. Typically, the assembly portions 121, 60 may be those in which the clearance between the components 22, 6 is the smallest, typically the portions at which the components 22, 6 are in contact with one another or in near-contact with one another, which means to say with a very small clearance existing between all or part of said portions with respect to one another.
As a preference, the plates 6, 7 of the exchanger are colaminated plates comprising a central sheet 40, each face of which is covered with a layer 30. According to another embodiment, the braze material 30 may take the form of a tape or of a surface coating layer 30. The coating layer 30 may be applied by spraying, or the braze material 30 may be brushed on in the form of a powder suspension containing the powder, a dispersant, a binder, and additives for controlling the viscosity.
As a preference, the braze material 30 has a thickness e of between 50 and 300 μm, preferably of between 100 and 250 μm.
The braze material 30 is preferably formed of a metallic material having a melting point lower than that of the materials of which the components 6, 22 are made. The components 6, 22 and 30 are preferably formed of aluminum alloy. The plates 6 and the elements 22 of the exchanger are advantageously formed of a first aluminum alloy of the 3XXX family, preferably of the 3003 type (standard ASME SB-2019 SECTION 2-B). The braze material 30 is formed of a second aluminum alloy, preferably an alloy of the 4XXX type (standard ASME SB-2019 SECTION 2-B), particularly of the 4004 type.
As can be seen in transverse cross section in FIG. 4, the spacer element 22 comprises several fins or corrugation legs 123 which are configured to delimit, when the element 22 is fitted 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 121 a, 121 b, one 121 a of the surfaces of the first pair being oriented toward the first plate 6 and the other 121 b of the surfaces of the first pair being oriented toward the second plate 7 when the spacer element 22 is in the fitted state.
The spacer 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 spacer element 22.
In the context of the invention, at least one surface texturing is present on a surface of at least one fin or corrugation leg 123 of the spacer element 22. It should be noted that the spacer element may have one or more predetermined forms of surface texturing distributed over various zones of its surface, it being understood that a surface texturing may just as well be created in the surface of the material of which the spacer element is made as deposited thereon, namely as the result of an addition of additional material to the surface of the spacer element.
According to the invention, the first assembly portion 121 is free of surface texturing 23 on its surface 121 a which, in the fitted state, is oriented toward the first plate 6.
This therefore preserves the wettability and good brazeability of the surface of the spacer element that is intended to be positioned against an adjacent plate in order to be assembled thereto by brazing. During the course of the brazing, the distribution of the braze material in the joint may be controlled, and this leads to a joint that exhibits good mechanical and thermal properties. It is thus possible to use the traditional methods for the manufacture of brazed plate and fin exchangers.
In addition, there is no need to perform a surface texturing after the spacer element 22 has been fitted, because this element already has the texturing on the desired regions of the fins. It is thus possible to incorporate a heat-exchange structure with an intensified surface into the exchanger while at the same time preserving the structural integrity of the matrix of the exchanger and of its internal channels.
The absence of surface texturing on the surface situated facing the first plate also allows better control of the height of the spacer element. Now, the height of the spacer element is an important parameter which, being tailored with precision to suit the separation between the first and the second plates 6, 7 of the exchanger, governs the quality and therefore the properties of the brazed joint.
According to one advantageous embodiment, the spacer element 22 is a corrugated product comprising a succession of corrugation legs 123 alternately connected by corrugation crests 121 and corrugation troughs 122. At least one corrugation crest 121 comprises a first assembly portion 121 according to the invention.
The following explanations are given with reference to FIGS. 4 to 7, it being appreciated that the spacer element 22 may adopt any other suitable form and does not necessarily include all of the features detailed hereinafter.
FIG. 4 shows a view in transverse cross section of a corrugated heat-exchange structure 22. Several corrugation legs 123 of longilinear shape extend parallel to one another and overall in a direction referred to as longitudinal direction z. The corrugation legs succeed one another in a lateral direction x, which is perpendicular to the longitudinal direction z, and are connected alternately by corrugation crests 121 and corrugation troughs 122.
According to the example illustrated in FIG. 3, the corrugation crests 121 and corrugation troughs 122 are planar in shape and extend parallel to one another and perpendicular to the corrugation legs 123. The channels 26 for the first fluid, which are formed between two successive corrugation legs and a crest or a trough arranged between said successive corrugation legs, thus have a transverse cross section of rectangular overall shape.
FIG. 4 illustrates a plain corrugation having corrugation legs 123 with a planar surface. Other configurations of spacer element 22 are of course conceivable, notably corrugations of the perforated-fin, serrated-fin, wavy-fin or herringbone-fin corrugated fin type.
An element 22 according to FIG. 4 is visible in FIG. 7(a) in the fitted state, namely when fitted between a first and a second plate 6, 7 which are directly adjacent, forming a passage 33. The passage 33 is of parallelepipedal overall shape and configured to channel 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 lateral direction x, between an inlet and an outlet of the passage 33 which are situated at two opposite ends along the length of the passage 33, measured in the longitudinal direction z. The corrugation legs 123 delimit within the passage 33 a plurality of channels 26 which extend parallel to the longitudinal direction z.
As can be seen in FIG. 7(a), the element 22 preferably extends over almost all, or even all, of the height of the passages, measured in a vertical direction y perpendicular to the plates 6, 7, so as to be in contact or near-contact with the plates 6, 7. The corrugation crests 121 and the corrugation troughs 122 are arranged parallel to the plates 6, 7.
According to one 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 FIG. 8(e), between the corrugation crests 121 and the first plate 6, and between the corrugation troughs 122 and the second plate 7. This makes it possible to prevent braze material from being drawn back by capillary action away from the region of the brazed joint during the vacuum brazing step, something which could be detrimental to the performance of the exchanger because, by flowing, the braze may alter the micro-structure of the surface texturing by filling the porosities or cavities present on the surface.
As a preference, the clearance d is comprised between 0 and 0.1 mm, more preferably still comprised between 0 and 0.05 mm.
As a preference, the spacer element 22 is arranged in the so-called “easyway” configuration in the passage 33, which means to say that the corrugation legs 123 extend overall in the direction of flow of the first fluid in the passage 33. It should be noted that in operation, the direction of flow of the first fluid is preferably vertical, it being possible for the direction of flow to be upward or downward.
Advantageously, a spacer element 22 according to the invention may be arranged in a region 3 of a passage 33 of the exchanger that up-flowing oxygen enters, the spacer element thus having on its surface porosities or reliefs that multiply the number of sites at which bubbles of gaseous oxygen OG can begin to form.
As a preference, each corrugation crest 121 comprises a first assembly portion 121 according to the invention. The corrugation crest surface 121 a positioned against the first plate 6 is thus free of surface texturing 23, which allows it to be brazed securely to a mutual-assembly portion on the first plate 6 during the manufacture of the exchanger.
Advantageously, each corrugation trough 122 comprises a second assembly portion 122 configured to be assembled, in the fitted state, with the second plate 7.
As illustrated in FIG. 4, said second assembly portion comprises a second pair of opposite surfaces 122 a, 122 b, that one 122 b of the surfaces of the second pair that is oriented toward the second plate 7 being free of surface texturing 23.
Another portion of the spacer element 22 may thus be brazed firmly to a mutual-assembly portion on the second plate 7 during manufacture of the exchanger, thereby further improving the robustness and rigidity of the passage 33.
As a preference, said first assembly portions 121, the fins or corrugation legs 123, and said second assembly portions 122, if present, are monobloc, i.e. formed as a single piece.
As a preference, each corrugation leg 123 comprises a third pair of opposite surfaces 123 a, 123 b, one and/or the other of the surfaces 123 a, 123 b of the third pair having said surface texturing 23, preferably over all, or almost all, thereof.
It should be noted 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 still at least 98% of the surface area of this surface or of the total surface area of this element.
FIG. 5 illustrates an example in which all the corrugation legs 123 have at least one surface texturing on their two surfaces 123 a, 123 b. Each channel 26 thus has two lateral walls 123 a, 123 b the internal surfaces of which are intensified.
As a preference, the first assembly portion 121 also exhibits the surface texturing 23 on the surface 121 b of the first pair which, in the fitted state, is oriented toward the second plate 7, preferably over all or almost all of said surface 121 b.
The second assembly portion 122 may also exhibit the surface texturing 23 on the surface 122 a of the second pair which, in the fitted state, is oriented toward the first plate 6, preferably over all or almost all of said surface 122 a. This makes it possible to maximize the surface area of surface texturing 23 present on the spacer element 22 and therefore to maximize the heat-transfer efficiency within the channels 26 delimited by the spacer element.
Such a configuration is illustrated in FIGS. 6 and 7(a). In fact, each channel 26 has an internal surface which is formed, in the fitted state, alternately by the surface 122 a of a corrugation trough 122 oriented toward the first plate 6, the surface 6 b of the first plate 6 oriented toward the corrugation trough 122 and the respective surfaces 123 a, 123 b of the two corrugation legs 123 connected to the ends of said corrugation trough 122, and by the surface 121 b of a corrugation crest 121 oriented toward the second plate 7, the surface 7 a of the second plate 7 oriented toward the corrugation crest 121 and the respective surfaces 123 a, 123 b of the two corrugation legs 123 connected to the ends of said corrugation crest 121.
By arranging at least one surface texturing 23 on the bottom of the channels 26 formed alternately by a corrugation crest 121 or trough 122, the exchange of heat is intensified over a greater proportion of the surfaces of the element 22 which, in the fitted state, form the internal surface of the channels 26.
As a preference, the surfaces 6 a, 6 b, and 7 a, 7 b of the plates 6, 7 are free of surface texturing. This then preserves the quality of the brazed joints formed with the plates.
FIG. 7(a) illustrates a configuration in which the corrugation legs 123 extend parallel to the longitudinal direction z and perpendicular to the corrugation crests 121 and to the corrugation troughs 122 of the element 22.
According to an alternative form of embodiment illustrated in FIGS. 7(b) and 7(c), the corrugation legs 123 extend in a plane which is parallel to the longitudinal direction z and which forms an angle α 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 corrugation legs 123 and the corrugation crests or troughs 121, 122, the portion of internal surface of the channels 26 that can exhibit surface texturing is maximized and the portion of internal surface of the channels 26 that cannot generally exhibit texturing is minimized, this portion being formed, depending on which channel is being considered, by the surface 6 b of the first plate 6 oriented toward the corrugation trough 122 or by the surface 7 a of the second plate 7 oriented toward the corrugation crest 121.
As a preference, the angle α is comprised between 60 and 90°, more preferably still the angle α is comprised between 70 and 85°. Thus, the accessibility to the surfaces on which the surface texturing is to be formed is preserved, while at the same time increasing the intensified surface area of channel.
Within the scope of the invention, the corrugated product 22 is preferably formed from a flat product, such as a sheet or strip, having a thickness of at least 0.15 mm, preferably comprised between 0.2 and 0.4 mm. This thickness is indicated by the letter “t” in FIG. 3. The use of surface texturing 23 requires significant thermal flux, particularly when the purpose of the surface texturing 23 is to intensify the bubbling of the first fluid. It is therefore advantageous to use a spacer element that is relatively thick, in order to maintain the highest possible fin coefficient, namely the best ability of the fins to transmit the heat.
It is also advantageous to operate with a thicker spacer element when, because of the intensification of the exchanges of heat obtained by virtue of surface texturing, there is a desire to reduce the density of fins on the spacer element in order to reduce the pressure drops that it causes. The heat-exchange coefficient of the spacer element is thus maintained by increasing its thickness.
Note that the fin coefficient is a number typically comprised between 0 and 1, being equal to 1 at the point of contact with an adjacent plate and decreasing along the fin with distance away from the plate. The point situated at the middle of the fin is the point at which the fin coefficient is the lowest. Working with thicker fins makes it possible to reduce the heat conduction through the fin, from the plate toward the point at the middle of the fin, thereby increasing the fin coefficient.
As a preference, the corrugated product 22 has a density, defined as the number of corrugation legs per unit length measured in the lateral direction x, of less than 18 legs per 2.54 centimeters, preferably less than 10 corrugation legs per 2.54 centimeters, more preferably still less than or equal to 5 legs per 2.54 centimeters. Advantageously, the density may be comprised between 1 and 5 legs per 2.54 centimeters. It should be noted that these density values are applicable to a spacer element which is not necessarily a corrugated product, the fins succeeding one another in the lateral direction x and the density then being defined as the number of fins per unit length, measured in the lateral direction x.
The use of a relatively low density makes it possible to facilitate the phase of depositing the surface texturing on the fins or corrugation legs, because their surface is then more accessible. Furthermore, the use of a spacer element of a lower density facilitates the elimination of bubbles created at the surface texturing.
As a preference, the spacer element 22 comprises a massive substrate, or, put differently, a solid substrate, particularly a non-porous substrate, on which the texturing 23 is formed. The substrate can be seen in black in FIG. 7 for example. Depending on the structure of the spacer element, the substrate may comprise one or more first and/or second assembly portions, the fins or corrugation legs.
It should be noted that the spacer element is preferably monobloc, namely formed as a single piece.
In the context of the invention, the surface texturing 23 may be the result of a surface coating deposited on the element or else of a modification of the surface finish of said element, components obtained by chemical, mechanical or equivalent treatment, for example using sand-blasting, scoring, etc.
In particular, the surface coating may be deposited on the substrate applied via a liquid route, notably by dipping, spraying, or via an electrolytic route, or via a dry route, notably by chemical vapor deposition (CVD) or physical vapor deposition (CVD), or by thermal spraying, particularly using a flame or a plasma.
It being specified that the texturing 23 seeks to modify the surface finish of the spacer element and not to deform the spacer element in full or in part.
As a preference, the surface texturing is formed of aluminum or of an aluminum alloy containing, per 100 wt %, at least 80 wt % aluminum, preferably at least 90 wt %, more preferably still at least 99 wt % 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 may for example be formed of a deposit of slightly sintered aluminum particles, intermingled aluminum filaments, semi-molten aluminum particles stuck together, such as the aluminum particles that are obtained after spraying as obtained by thermal spraying using a flame.
As a preference, the surface texturing 23 exhibits, prior to brazing, an open porosity of between 15 and 60%, preferably between 20 and 45%, more preferably still an initial open porosity of between 25 and 35% (vol %). It should be noted that the open porosity is defined as the ratio between the volume of the open pores, namely the pores fluidically communicating with the external environment in which the component 22 is situated, and the total volume of the porous structure.
The pores of the porous structure 23 preferably have a diameter comprised between 1 and 200 μm, preferably comprised between 5 and 100 μm. Note that the pores are not necessarily circular in cross section but may exhibit irregular shapes. The term “diameter” therefore also covers an equivalent hydraulic diameter which can be calculated by measuring the pressure drop experienced by a gaseous flow through the porous structure and by assuming that the pores have a regular, notably a spherical, cylindrical, etc., shape.
The dimension of the pores can also be characterized by their volume. As a preference, the pores of the porous structure 23 have a volume comprised between 1000 and 1,000,000 μm³. The volume of the pores may for example be determined by tomography or by the analysis of images of polished cross sections of specimens taken in a multitude of directions in space.
Alternatively, the surface texturing 23 may be in the form of reliefs, or patterns, printed or created in or on the material of which the spacer element 22 is made. As a preference, these reliefs, in transverse cross section, define cavities open to the surface of the element 22. For example, micro-reliefs with diverse morphology or size, such as discrete or uninterrupted grooves, striations, protuberances, etc. may be formed or deposited at the surface of the element 22. In particular, the reliefs that form the surface texturing 23 may be produced by laser or mechanical and/or chemical machining.
What is meant by micro-reliefs is reliefs that have at least one characteristic dimension that is small in comparison with a dimension of the element, particularly reliefs which extend a height, measured in a direction perpendicular to the surface of the spacer element exhibiting the texturing, and/or a width, measured in a direction perpendicular to the surface of the spacer element exhibiting the texturing, from the order of a few microns to a few hundred microns.
FIG. 8 illustrates the main steps in a manufacturing method that can be used to produce a spacer element 22, in the event that the latter 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 hereinafter may apply to other forms of spacer element.
The spacer element 22 is first of all shaped, typically by pressing, then is cut in width and in length to form a corrugated mat 22 of the desired format and is degreased. As can be seen in transverse cross section in FIG. 8(a), the element 22 after shaping exhibits a succession of corrugation crests and troughs constituting first and second assembly portions intended to be vacuum brazed respectively to 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 spacer element 22. In other words, a surface texturing is applied to all of the surfaces of the spacer element, including the pairs of opposite surfaces situated at the crests and the troughs. For example, the texturing 23 may be formed by depositing a coating of the suspension type. In that case, the material constituting the texturing and additives such as thickeners, pore-generators, etc. are placed in suspension in a binder. This technique allows coatings to be achieved on corrugations of a higher density that are difficult to treat using thermal spraying because of the poor accessibility of the surfaces.
At least the portions of surface texturing 23 that extend over the surfaces of the first assembly portions which, in the fitted state, are oriented toward the first plate 6, are then selectively removed. If the spacer element comprises one or more second assembly portions intended to be assembled with the second plate 7, then the texturing 23 at the surfaces of the second assembly portions which, in the fitted state, are oriented toward the second plate 7, are also selectively removed.
There are various solutions that can be employed for selectively removing the surface texturing 23. A first solution, illustrated in FIG. 8(c), is to deposit, before forming the texturing 23, a meltable coating 25 on the surfaces of the element 22 that it is desired to see free of surface texturing 23 at the end of the manufacturing method. A heat treatment of the element 22 is then performed in such a way as to remove the meltable coating 25 and, with it, the surface portions 23.
Alternatively, a mask 25 may be affixed to these surfaces before the surface texturing is performed. Once the surface texturing has been formed on the entirety of the element 22, the mask is removed.
The mask may be made from sheet metal with openings. As a preference, the mask is pressed as closely as possible onto the surfaces of the element 22 that are to be masked so as to avoid any deposit there. The openings are positioned facing the surfaces of the element 22 on which the texturing 23 is to be formed.
The mask may be formed from an alloyed steel or of a nickel alloy, preferably a nickel-iron-chrome alloy, particularly an alloy of the 800H type, which offers good high-temperature heat resistance.
Another solution is to remove the surface texturing in the desired regions by means of a mechanical process, for example by brushing or rubbing down the surfaces of the element 22.
The spacer element 22 thus manufactured is then fitted between a first plate 6 and a second plate 7 of the exchanger, and then brazed to said plates, as illustrated in FIG. 8(e).

EXAMPLE

Tests of depositing a porous structure were performed on a corrugated product having a density of 6 corrugation legs per 2.54 centimeters and a height of 5 mm. The corrugated product was formed from a strip 0.5 mm thick. A mask formed from a sheet of 800H-type alloy was affixed to the corrugated product. It had a series of laser-cut slots 4.2 mm wide. The solid parts of the mask were arranged at the corrugation crests of the corrugated product.
The deposit was applied by flame thermal spraying using an aluminum wire containing, per 100 wt %, 99.5 wt % aluminum. These tests allowed a surface texturing in the form of a porous layer 200 to 300 μm thick with an open porosity of the order of 30% to be deposited selectively on the corrugation legs of the corrugated product. The porous layer exhibited good properties of adhesion to the surface of the corrugated product.
While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.
Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.

Claims

1-20. (canceled)

21. A spacer element for a heat exchanger of the brazed plate and fin type, intended to be fitted between a first plate and a second plate of the exchanger, said spacer 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 toward the first plate and the other of the surfaces of the first pair being oriented toward the second plate when the spacer element is in the fitted state,

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

at least one surface texturing in the form of a porous structure or of reliefs formed on a surface of the spacer element, at least one fin or corrugation leg exhibiting said surface texturing,

wherein the first assembly portion is free of surface texturing on the surface of the first pair which, in the fitted state, is oriented toward the first plate.

22. The element as claimed in claim 21, wherein the spacer element comprises a massive or solid substrate, the surface texturing being formed on a surface of the substrate.

23. The element as claimed in claim 21, wherein at least one fin or corrugation leg comprises a third pair of opposite surfaces, one and/or the other of the surfaces of the third pair exhibiting said surface texturing.

24. The element as claimed in claim 23, wherein all, or almost all, of one and the other of the surfaces of the third pair exhibits said surface texturing.

25. The element as claimed in claim 21, wherein the first assembly portion exhibits the surface texturing on the surface of the first pair which, in the fitted state, is oriented toward the second plate.

26. The element as claimed in claim 21, wherein the first assembly portion is arranged between two successive fins or corrugation legs, the surface of the first pair which, in the fitted state, is oriented toward the second plate having two ends each one connected to a respective surface of each of the two fins or corrugation legs, the surface of the first pair and said respective surfaces of the fins exhibiting the surface texturing.

27. The element as claimed in claim 21, further comprising 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 toward the first plate and the other of the surfaces of the second pair being oriented toward the second plate when the spacer element is in the fitted state, said second assembly portion being free of surface texturing on at least the surface of the second pair which, in the fitted state, is oriented toward the second plate.

28. The element as claimed in claim 27, wherein the second assembly portion exhibits the surface texturing on the surface of the second pair which, in the fitted state, is oriented toward the first plate.

29. The element as claimed in claim 27, wherein the second assembly portion is arranged between two successive fins or corrugation legs, the surface of the second pair which, in the fitted state, is oriented toward the first plate having two ends each one connected to a respective surface of each of the two fins or corrugation legs, said surface of the second pair and said respective surfaces of the fins exhibiting the surface texturing.

30. The element as claimed in claim 21, wherein the first assembly portion and/or the second assembly portion are arranged, in the fitted state, parallel to the first and second plates, the fins or corrugation legs succeeding one another in a lateral direction and, in the fitted state, delimiting a plurality of channels which are configured to channel the first fluid in a longitudinal direction parallel to the first and second plates and orthogonal to the lateral direction.

31. The element as claimed in claim 30, wherein that said at least one fin or corrugation leg extend in a plane parallel to the longitudinal direction and form an angle with respect to the first assembly portion and/or the second assembly portion, the angle being less than or equal to 90°.

32. The element as claimed in claim 21, wherein the surface texturing is in the form of a porous structure having an open porosity of between 15 and 60%, or in the form of reliefs defining, in transverse cross section, cavities that are open to the surface of the spacer element.

33. The element as claimed in claim 21, wherein the element is in the form of a corrugated product comprising a succession of corrugation legs alternately connected by corrugation crests and corrugation troughs, at least one corrugation crest comprising said first assembly portion and/or at least one corrugation trough comprising said second assembly portion.

34. The element as claimed in claim 33, wherein the corrugation legs succeed one another in a lateral direction, the corrugated product having a density, defined as being the number of corrugation legs per unit length measured in the lateral direction, of less than 18 legs per 2.54 centimeters.

35. The element as claimed in claim 33, wherein the corrugated product is formed from a flat product having a thickness of at least 0.15 mm.

36. A heat exchanger of the brazed plate and fin type 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 placed in a heat-exchange relationship with at least one second fluid, and at least one spacer element fitted between two successive plates that define a passage so as to form, within the passage, several channels for the flow of said first fluid, wherein the spacer element is as claimed in claim 21.

37. A method for producing a spacer element for a heat exchanger of the brazed plate and fin type, said method comprising the following steps:

a) shaping the spacer element so that it exhibits fins or corrugation legs which, when the spacer element is fitted between a first plate and a second plate of the exchanger, delimit a plurality of channels for the flow of a first fluid, and at least one first assembly portion configured to be assembled with a first plate and comprising a first pair of opposite surfaces of which one is oriented toward the first plate and the other is oriented toward the second plate when the spacer element is in the fitted state;

c) forming a surface texturing in the form of a porous structure or of reliefs over all, or almost all, of the spacer element; and

d) selectively removing at least a portion of said surface texturing extending over that one of the surfaces of the first pair which, in the fitted state, is oriented toward the first plate.

38. The method as claimed in claim 37, further comprising, prior to step c), a step b) of depositing a meltable coating on that one of the surfaces of the first pair which, in the fitted state, is oriented toward the first plate, step d) comprising a heat treatment of the spacer element in such a way as to remove the meltable coating and the portion of surface texturing that is formed on said meltable coating.

39. The method as claimed in claim 38, further comprising, prior to step c), the application of a mask to that one of the surfaces of the first pair which, in the fitted state, is oriented toward the first plate, step d) being performed by removing the mask.

40. The method as claimed in claim 39, wherein step d) is performed mechanically.