EP3387357B1 - Method of manufacture of a fluid device with a metal foam - Google Patents

Description

TECHNICAL AREA

The field of the invention is that of fluidic devices comprising a channel formed in a housing, in which there is a porous medium with open pores made of a metallic material called metallic foam. The invention applies for example as a heat exchanger ensuring the heat transfer between a component placed against a wall of the housing, for example a power electronic component or a component of the automotive or nuclear field, and a circulating heat transfer fluid. into the channel and through the metal foam. The invention can also be applied to the field of fluid filtration.

STATE OF THE PRIOR ART

There are known heat exchangers, also called heat sinks, in the form of a fluidic device comprising a channel, formed in a housing, which extends between inlet and outlet orifices. The housing can then include a main wall, called a heat exchange wall, the internal face of which helps to define the channel and the external face forms a support for receiving a component to be cooled, for example an electronic component. Finally, provision is made for a heat transfer fluid, liquid or gaseous, to flow in the channel to receive and then evacuate the heat produced by the electronic component.

In order to increase the heat exchange surface with the heat transfer fluid, a porous medium with open pores forming a three-dimensional fluidic network can be placed in the channel so as to be in contact with the exchange wall.

FROM 20 2011 110 243 describes a fluidic device, comprising: a housing comprising a channel delimited by walls, including a first main wall, the channel extending between two orifices, called inlet and outlet; and a porous medium with open pores in a metallic material, called metallic foam, located in the channel between said inlet and outlet orifices, the metallic foam and said first main wall being made in one piece and in the same material , and the metallic foam having a random spatial distribution of the pores.

The document WO2004 / 079792 describes an example of such a fluidic heat exchanger device. A channel is partially delimited by a housing and comprises a porous medium with open pores capable of being traversed by a heat transfer fluid. A main exchange wall thermal case has an outer face against which a component to be cooled is placed, and an inner face in contact with this porous medium. In this example, the porous medium is a regular network of balls assembled together, fixed to the internal faces of the channel by means of a brazing material.

It would however be desirable to be able to have a fluidic device having an improved heat transfer coefficient, this coefficient being relative to the heat transfer between the main heat exchange wall intended to receive a component to be cooled and the heat transfer fluid circulating in the channel. . This heat transfer coefficient is also called the global heat transfer coefficient.

It would also be desirable to be able to have, more generally, a fluidic device having, in operation, improved mechanical strength, thus preserving the flow properties of the fluid in the channel and, where appropriate, the heat transfer properties between. the main heat exchange wall and the heat transfer fluid.

There is also a need to be able to have a simplified method for producing a fluidic device exhibiting one and / or the other of these improvements.

DISCLOSURE OF THE INVENTION

The object of the invention is to remedy at least in part the drawbacks of the prior art, and more particularly to provide a method for producing a fluidic device comprising a channel in which is located a porous material with open pores, exhibiting a improved mechanical strength and, where appropriate, an improved overall exchange coefficient.

For this, the object of the invention is a method for producing a fluidic device according to claim 1.

According to the invention, the metal foam and said first main wall are made in one piece and in the same material, and the metal foam has a random spatial distribution of the pores.

Certain preferred but non-limiting aspects of this fluidic device are as follows:
Preferably, the metal foam has a specific surface area of between 200m2 / m3 and 1500m2 / m3, a porosity of between 65% and 85%, and an average pore size of between 2mm and 8mm.

The cross section of the inlet and outlet orifices may have a smaller surface than that of the cross section of the channel.

The housing may include a second main wall opposite the first main wall, partially delimiting the channel, the metal foam and said second main wall being further made in one piece and in the same material.

The housing may include a second main wall opposite the first main wall partly delimiting the channel, said second main wall being an attached wall, fixed in a sealed manner to a side wall of the housing.

The housing may include a side wall extending between the first main wall and a second main wall opposite the first wall, and delimiting the channel circumferentially, the metal foam and said side wall being further made in one piece. and in the same material.

The inlet and outlet orifices may open out into hollow chambers of the channel situated on either side of the metal foam along a longitudinal axis of the channel.

• une première mousse métallique réalisée d'un seul tenant avec ladite première paroi principale et en un même matériau, et
• une seconde mousse métallique réalisée d'un seul tenant avec une seconde paroi principale opposée à la première paroi, et en un même matériau,
• lesdites première et seconde mousses métalliques étant assemblées l'une à l'autre par l'intermédiaire d'un collecteur fluidique comportant au moins un conduit de collection s'étendant entre deux extrémités d'entrée débouchant au niveau desdites première et seconde mousses métalliques et une extrémité de sortie débouchant au niveau de l'orifice de sortie.

According to one embodiment, the fluidic device can comprise:

• a first metal foam made in one piece with said first main wall and in the same material, and
• a second metal foam made in one piece with a second main wall opposite the first wall, and in the same material,
• said first and second metal foams being assembled to each other by means of a fluidic manifold comprising at least one collection duct extending between two inlet ends opening at the level of said first and second metal foams and an outlet end opening at the level of the outlet orifice.

The first and second main walls, the first and second metal foams and the manifold may have a substantially circular profile, the main walls and the manifold being sealingly assembled to a circumferential side wall of the housing.

The inlet orifice may have a diameter suitable for allowing the introduction of a fluid on either side of the manifold so as to be able to flow into the first and second metal foams before reaching the inlet ends. of the collection duct.

The shape of the porous preform can be parallelepiped, circular or any other geometric shape. It can have side walls and upper and lower walls.

The preform can be placed in a cavity of a mold and kept at a distance from an internal face of a yoke of the mold, the space separating said internal face and the preform being intended to form the first main wall.

The preform can be held in a hollow profile; preferably, at least one side wall of said preform is in contact with at least one inner face of the walls of said hollow section. Said hollow section in which the preform is placed can be inserted into a cavity of a mold. At least one lower or upper face of the preform is kept away from an internal face of a yoke of the mold. Preferably, during the molding step, the walls of the profile are partially or totally melted. Preferably, the fluidic device has at least one wall of the metal foam in contact with a wall of the profile. Preferably, at least part of the walls of the profile and part of the metal foam are in metallurgical continuity due to the mixing of the liquid metal injected to produce the foam with the molten metal of the profile.

The preform can be interposed longitudinally between two cores, said cores being intended to form hollow chambers of the channel.

Each core may include a second part intended to form an inlet or outlet orifice, said second portion extending from a first part intended to form one of said hollow chambers of the channel.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure la est une vue schématique en coupe longitudinale et en perspective d'un dispositif fluidique dans lequel la mousse métallique est réalisée d'un seul tenant et en un même matériau avec les parois du boîtier qui délimitent transversalement le canal ; la figure 1b est une vue schématique de dessous du dispositif fluidique représenté sur la figure la ; et la figure 1c illustre différentes valeurs de surface spécifique de la mousse métallique pour différentes valeurs de porosité et de taille moyenne de pores ;
• les figures 2a à 2e représentent des étapes d'un procédé de réalisation du dispositif fluidique selon le premier mode de réalisation ;
• la figure 3 est une vue schématique en perspective d'un dispositif fluidique selon un deuxième mode de réalisation, dans lequel l'une des parois principales délimitant le canal forme un capot rapporté ;
• les figures 4a à 4f représentent des étapes d'un procédé de réalisation du dispositif fluidique selon le deuxième mode de réalisation ;
• la figure 5 est une vue schématique en perspective d'un dispositif fluidique selon un troisième mode de réalisation, dans lequel deux mousses métalliques, réalisées chacune d'un seul tenant et en un même matériau avec des parois principales, sont assemblées l'une à l'autre par un collecteur fluidique.
• La figure 6a est une vue schématique de dessous selon un quatrième mode de réalisation, dans lequel les parois latérales du dispositif fluidique comprennent un profilé. La Figure 6b correspond à la vue en coupe selon l'axe A-A du dispositif selon le quatrième mode de réalisation.
• Les figures 7a et 7e représentent les étapes d'un procédé de réalisation du dispositif selon le quatrième mode de réalisation.

Other aspects, aims, advantages and characteristics of the invention will become more apparent on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings. on which ones :

• FIG. la is a schematic view in longitudinal section and in perspective of a fluidic device in which the metal foam is made in one piece and in the same material with the walls of the case which transversely define the channel; the figure 1b is a schematic bottom view of the fluidic device shown in FIG. 1a; and the figure 1c illustrates different values of specific surface area of the metallic foam for different values of porosity and average pore size;
• the figures 2a to 2e represent steps of a method for producing the fluidic device according to the first embodiment;
• the figure 3 is a schematic perspective view of a fluidic device according to a second embodiment, in which one of the main walls delimiting the channel forms an attached cover;
• the figures 4a to 4f represent steps of a method for producing the fluidic device according to the second embodiment;
• the figure 5 is a schematic perspective view of a fluidic device according to a third embodiment, in which two metal foams, each made in one piece and in the same material with main walls, are assembled to each other by a fluidic manifold.
• The figure 6a is a schematic bottom view according to a fourth embodiment, in which the side walls of the fluidic device comprise a profile. The Figure 6b corresponds to the sectional view along the axis AA of the device according to the fourth embodiment.
• The figures 7a and 7e represent the steps of a method for producing the device according to the fourth embodiment.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

In the figures and in the remainder of the description, the same references represent identical or similar elements. In addition, the various elements are not shown to scale so as to favor the clarity of the figures.

In the remainder of the description, the terms “substantially”, “approximately”, “approximately”, “of the order of” are understood to mean “within 10%”. In addition, the terms "between ... and ..." and "ranging from ... to ..." mean that the limits are included, unless otherwise specified. The limits are also understood to be “within 10%”.

The invention relates to a method of making a fluidics comprising a channel in which a fluid is intended to flow, the channel being delimited by the walls of a housing. Inside the channel is a porous medium with open pores capable of being traversed by the fluid. The porous medium is called hereafter metallic foam ( metallic foam, in English). According to the invention, the metal foam and at least a first main wall of the housing partially delimiting the channel are made of the same metal material and in a single piece.

The fluidic device can find various applications, for example in the field of heat exchangers or in that of filtration. In the remainder of the description, and purely by way of illustration, the fluidic device forms a heat exchanger suitable for dissipating the heat produced by a component, for example a power electronic component, the latter being placed against a wall of the fluidic device. . Other types of components can be cooled by such a heat exchanger, for example automotive or nuclear components. The heat transfer fluid intended to flow in channel 3 of the fluidic device may be liquid or gaseous.

The fluidic device comprises, located inside the channel, a metallic foam in the form of a solid porous medium with open pores. This porous medium therefore forms a three-dimensional network of interconnected pores. The metal foam is made of a solid metal material such as, for example, aluminum or an aluminum alloy, for example an alloy of the type AISi7MgO, 6, but any other type of casting alloy having good castability. can be used. Other materials can also be used such as, for example, zinc alloys, copper, cast irons, steels ...

According to the invention, the metal foam has a network of pores distributed spatially in a random manner. The term “random spatial distribution” is understood to mean that the mutual arrangement of the pores is substantially aperiodic and has substantially no privileged direction: the orientation of the pores in the matrix is random. Such a network of pores is thus distinguished from regular networks of beads such as that described in the example of the prior art mentioned above.

In addition, according to the invention, the metal foam and at least a first main wall of the case delimiting at least in part the channel are made of the same metal material and in a single piece. By "produced in a single piece and in the same material" is meant that the metal foam and the first main wall are made monolithically, that is to say in a single piece, the mechanical connection being ensured. by the metallurgical continuity of the metallic material forming these two parts, cast together in one and the same operation. It is thus understood that by being made in one piece and in the same metallic material, the metallic foam is assembled to the first main wall without the presence of an intermediate fixing layer, such as a layer of a material. solder or solder, located at the interface between the metal foam and the first main wall.

The metal foam may have a porosity greater than or equal to 10%, for example between 60% and 90%, and preferably between 65% and 85%. Porosity is understood as the ratio between the cumulative volume of the pores over the total volume of the metal foam.

Furthermore, the pores may have an average millimeter size. The average pore size can be, for example, between 1mm and 10mm, or even between 2mm and 8mm. The mean size is understood to be the mean, for example arithmetic, of the mean maximum size and of the mean minimum size of the pores. The average maximum size is the average of the maximum pore sizes and the average minimum size is the average of the minimum pore sizes. Preferably, the pores are of a similar size. The term similar is understood to mean that the pores have a size of between +/- 10% of a value. Preferably, this value can be between 1 mm and 10 mm, and even more preferably between 2 mm and 8 mm.

In addition, the metal foam can have a specific surface area of between 200 m ² / m ³ and 1500 m ² / m ³ . By specific surface is meant the actual surface area of the pores, in other words, the developed surface of the foam, over the total volume of the metal foam. It can be estimated conventionally by X-ray tomography.

As described below, the metal foam can be made from aluminum, by a molding process comprising a casting step during which an infiltration of a destructible preform takes place. This preform can be made of a material based on salt dough, as described for example in document EP2118328 , or even in a silicone-based material as described for example in document FR2992660 .

In this heat exchanger application, the first main wall 10 is preferably a heat exchange wall, the outer face of which has a surface suitable for receiving a component to be cooled. By external face is meant a face of the wall opposite to the internal face oriented towards the channel 3.

Figure la is a schematic view in longitudinal section and in perspective of a fluidic device 1 and figure 1b is a bottom view, schematic in longitudinal section, of the fluidic device 1 shown in figure 1a .

In this example, as explained below, the fluidic device 1 comprises a channel 3 which extends along a substantially rectilinear longitudinal axis. Furthermore, the metal foam 30 is made in one piece and in the same material with the main walls 10, 20 transversely delimiting the channel 3.

We define here a three-dimensional orthonormal frame (X, Y, Z), where the plane (X, Y) is substantially parallel to the plane of the main walls 10, 20 of the fluidic device 1, the Z axis being oriented in a substantially orthogonal direction to the plane (X, Y). Thus, the terms “vertical” and “vertically” extend as relating to an orientation along the Z axis, and the terms “lower” and “upper” extend as relating to a positioning along the Z axis. .

The length of channel 3 is defined as the distance, here along the X axis, between two inlet 4A and outlet 4B ports; the width of the channel 3 as the distance, along the Y axis, between two internal faces opposite to each other of a side wall 40 of the channel 3; and the height of the channel 3 as the distance, along the Z axis, between the two internal faces 11, 21 of the main walls 10, 20.

The fluidic device 1 comprises a housing 2 formed of walls whose internal faces define a channel 3. The housing 2 is here formed of two main walls 10, 20 opposite to each other along the Z axis, and of a side wall 40 circumferentially connecting the main walls 10, 20 to one another, that is to say along the perimeter of the channel 3. The internal faces of the different walls, that is to say the faces facing channel 3 together delimit channel 3.

In this example, the first and second main walls 10, 20 are substantially planar and parallel to each other. They each have an internal face 11, 21 and an external face 12, 22, opposite to each other, substantially flat. They are connected to each other in a sealed manner by the side wall 40. In this example, the first main wall 10 forms a heat exchange wall with a component to be cooled, and has a surface of its external face. 12 substantially planar in order to receive the component to be cooled.

The housing 2 here has a profile, in the plane (X, Y), of rectangle shape, but other shapes are possible, for example circular or oval, or even square or polygonal. Channel 3 here has the general shape of a flattened parallelepiped. In other words, the channel has a height less than its width and its length, thus making it possible to optimize the exchange surface between the heat transfer fluid and the first main heat exchange wall 10.

The housing 2 has through orifices which open into the channel 3, and form inlet 4A and outlet 4B orifices. They are arranged along the longitudinal axis of channel 3 so as to allow the introduction and evacuation of the heat transfer fluid in channel 3. In this example, the inlet 4A and outlet 4B orifices are formed through the same second main wall 20, and are intended to receive the ends of fluid conduits (not shown) for the supply and discharge of the heat transfer fluid. As a variant, the orifices 4A, 4B can be arranged at the level of the first main wall 10, or even at the level of the side wall 40. Furthermore, the cross section of the orifices 4A, 4B has a surface smaller than that of a section. right of channel 3. By straight section, is meant a section along a plane orthogonal to the longitudinal axis of the element considered.

The fluidic device 1 further comprises a metal foam 30, located in the channel 3 between the inlet 4A and outlet 4B orifices. It is in the form of a porous block with open pores distributed spatially in a random manner, which here fills a part of the channel 3. More precisely, the metal foam 30 fills the surface of a cross section of the channel 3, in the plane (Y, Z), and extends longitudinally along the X axis over part of the channel 3. Thus, it is in contact with part of the internal faces of the main walls 10, 20 and side walls 40, so that the heat transfer fluid, flowing in the channel 3 between the inlet 4A and outlet 4B orifices, necessarily passes through the metal foam 30.

The metal foam 30 is made of the same material and integrally with the first main wall 10, and, in this example, with the second main wall 20 and the side wall 40. Thus, the metal foam 30 and the walls main 10, 20 and side 40 of the housing 2 form a single piece, monolithic, made of the same material. It is therefore understood that the metal foam 30 is not fixed to said walls by an intermediate fixing layer such as a layer of a brazing or welding material but that the mechanical connection is ensured by a metallurgical continuity formed by the material. metallic foams and said walls, cast together in one and the same operation.

In this example, the metal foam 30 is located between two hollow chambers, called inlet 5A and outlet 5B, and therefore does not extend over the entire length of channel 3. The inlet chamber 5A, into which opens the inlet orifice 4A, is delimited by the walls of the housing 2 and a free face called upstream 31A of the metal foam 30. The outlet chamber 5B, into which the outlet orifice 4B opens, is delimited by the walls of the housing 2 and a so-called downstream free face 31B of the metal foam 30.

Thus, by the fact that the first main wall 10 and the metal foam 30 are made in one piece and in the same material on the one hand, and that the metal foam 30 forms a network of open pores spatially distributed in a random manner, on the other hand, the thermal transfer properties of the fluidic device 1 are improved, and in particular the overall exchange coefficient. In addition, the mechanical strength of the fluidic device 1 is also improved, which makes it possible to preserve the fluidic and thermal properties of the device 1 in operation.

Indeed, the fixing of the metal foam 30 to the first main wall 10 is ensured by the metallurgical continuity between these two parts and is therefore not carried out by means of an intermediate layer of a welding or brazing material, such a material being capable of exhibiting a thermal conductivity lower than that of the metallic material of the first main wall 10 and of the metallic foam 30. The thermal transfer properties of the fluidic device 1 are therefore improved, and in particular the overall exchange coefficient h _g of the device. By global heat transfer coefficient h _g , or global heat transfer coefficient, is meant the coefficient quantifying the flow of energy which passes through the first main wall 10 and the metal foam 30, coming from the component to be cooled to the heat transfer fluid. This coefficient depends in particular on the heat exchange coefficient h _p of the first main wall 10 and on the coefficient h _m of the metal foam 30, and in general, on any possible intermediate layer located between the first main wall 10 and the foam metallic 30. The heat exchange coefficient is conventionally defined as the ratio ΔQ / S.ΔT where ΔQ is the thermal energy transferred, S the heat exchange surface, and ΔT the temperature difference on either side of the surface. exchange. The absence here of such an intermediate layer of brazing or solder therefore makes it possible not to degrade the value of the overall exchange coefficient of the fluidic device 1, which results in an optimization of the thermal transfer properties of the fluidic device 1. .

The thermal transfer properties of the fluidic device 1 are further improved by the fact that the open pores of the metallic foam are spatially distributed in a random manner. The heat transfer fluid then flows in the metallic foam 30 without presenting a preferred direction of flow, which tends to improve the heat transfer between the fluidic device 1 and the heat transfer fluid.

Furthermore, the mechanical strength of the fluidic device 1 is improved insofar as the absence of an intermediate layer of brazing or welding between the metal foam 30 and the first main wall 10, and here between the foam and the other walls of the housing , leads to better mechanical resistance vis-à-vis a possible concentration of mechanical stresses at the interface between the metal foam 30 and the walls of the case. In fact, the operating conditions of the fluidic device 1 in operation, in particular in terms of pressure and / or temperature, can generate mechanical stresses that come to be concentrated at the interface between the metal foam 30 and the wall or walls in contact with the latter. When an intermediate layer of solder or solder is present, the concentration of stresses can cause detachment of the wall vis-à-vis the metallic foam 30. This detachment can then lead to a degradation of the flow properties of the fluid in the wall. the metal foam 30, and, where appropriate, a degradation of the heat transfer properties.

In addition, such a fluidic device 1, of which the first main wall 10 and the metal foam 30 are made in one piece and in the same material, can be obtained by a simplified production process, an example of which is now described.

Furthermore, the metal foam 30 advantageously has a porosity ranging from approximately 65% to 85% and an average pore size of between approximately 2 mm and 8 mm. It is advantageous for the pores to have a similar dimension of between 2 mm and 8 mm. The inventors have in fact observed that such a metallic foam 30 with open pores and spatially distributed in a random manner then has a particularly large specific surface area, ranging from 200m ² / m ³ to 1500m ² / m ³ approximately, which greatly increases the thermal transfer properties of the fluidic device 1.

FIG. 1e illustrates specific surface area values of the metal foam 30 as a function of the porosity and the average pore size, these specific surface values being obtained from measurements by X-ray tomography. It emerges that for a porosity ε between approximately 65% and 85%, the specific surface area Sp increases sharply, ranging from approximately 200 m ² / m ³ for an average pore size of approximately 8 mm, at around 1500m ² / m ³ for an average pore size of around 2mm. By way of illustration, the specific surface area of the metallic foam 30 is of the order of 630 m ² / m ³ for a porosity of approximately 73.9% and an average pore size of the order of 5 mm. The specific surface can increase to 1490 m ² / m ³ for a porosity of approximately 72.4% and an average pore size of the order of 2 mm. The presence in the channel 3 of a metallic foam 30 exhibiting these high specific surface values makes it possible to substantially increase the thermal transfer properties of the fluidic device 1.

The figures 2a to 2e illustrate different steps of an exemplary method of producing the fluidic device 1 according to the first embodiment as illustrated in FIG. The fluidic device 1 is produced here by a “low pressure” type molding technique comprising a step of infiltrating a preform simultaneously with the casting of the liquid metal.

Molding of the "low pressure" type is a technique in which a pressure force, here overpressure, is applied to the surface of a liquid metal located in a furnace supplying the mold, so as to cause the liquid metal to rise back into the mold. the mold as well as its infiltration into the preform. Alternatively, a vacuum can be applied in the mold so that the liquid metal undergoes a so-called suction vacuum force causing the mold to be filled as well as its infiltration into the preform. The pressure values used are suitable for the liquid metal to infiltrate the interstices of the preform so as to ultimately obtain the desired metal foam.

These molding techniques, applied to a preform made of salt dough or of a silicone-based material, are suitable for producing a metallic foam with open pores distributed spatially in a random manner and capable of reaching high specific surface values. The inventors have observed that other molding techniques, for example gravity molding, do not make it possible to produce metal foams having these characteristics.

During a first step ( figure 2a ), a part 50 is produced formed of a preform 51 assembled with two cores 53A, 53B arranged on either side of the preform 51. The two cores 53A, 53B are in contact with the two opposite transverse faces 52A, 52B. 'one to the other of the preform 51, called the upstream and downstream faces.

Each core 53A, 53B here comprises a first part 54A, 54B intended to form the inlet 5A or outlet 5B chamber, which extends along the longitudinal axis of the preform 51. It has here a thickness along the axis. Z substantially equal to that of the preform 51, and a profile in the plane (X, Y) which is substantially triangular with a rounded top. Each core 53A, 53B further comprises a second part 55A, 55B, intended to form the inlet 4A or outlet 4B, which extends from the first part 54A, 54B in a manner substantially orthogonal to the main plane. (X, Y) of the preform 51. Finally, each core 53A, 53B comprises a third part 56A, 56B, intended to ensure the maintenance of the part 50 in a so-called suspended position vis-à-vis the internal faces of a mold 60, which extends in the extension of the second part 55A, 55B. The cores 53A, 53B are destructible and can be made of sand typically agglomerated with resin.

The preform 51 is intended to form the metal foam 30. It can be made from salt dough in accordance with the process described in the document. EP2118328 or from a silicone-based material according to the process described in the document FR2992660 . By way of illustration, the preform 51 is made of silicone elastomer according to the method described in the document FR2992660 . First of all, separate elements of silicone elastomer, of millimeter size, for example by extrusion and then cutting are produced. These elements are then agglomerated using a binder then the assembly obtained is polymerized in a core box, the imprint of which defines the desired final dimensions of the preform 51. After stripping and then removing any solvents, one obtains a porous preform 51 with interconnected interstices of silicone elastomer.

In a second step ( figures 2b ), the part 50 is placed in a mold 60, for example a sand mold, and more precisely in the cavity 65 of the mold, the dimensions of which define the desired dimensions of the housing 2. The mold 60 is formed of two parts 61, 63, say yokes, which, when in contact, together delimit the cavity 65, namely the interior cavity of the mold 60 in which the part 50 is placed. The mold 60 further comprises a supply duct 66 for introducing the liquid metal into the cavity 65.

In this example, the upper yoke 63 has an internal face 64 which partially surrounds the part 50 without contacting it. The space separating the upper yoke 63 from the part 50 is intended to form the first main wall 10 and part of the side wall 40. Furthermore, the lower yoke 61 has an internal face 62 which partially surrounds the part 50, the space separating the yoke 61 from the part 50 is intended to form the second main wall 20 as well as a part of the side wall 40. This space is crossed by the second parts 55A, 55B of the cores intended to form the orifices d 'input 4A and output 4B.

Furthermore, the part 50, and more particularly the preform 51 and the first parts 54A, 54B of the cores, are kept at a distance from the internal faces of the mold 60 by the engagement of the third parts 56A, 56B of the cores in housings provided in the internal face 62 of the lower yoke 61.

Preferably, prior to its insertion into the cavity 65, the part 50 is preheated to a temperature which may be of the order of 80 ° C to 250 ° C, for example at approximately 150 ° C.

In a third step, the liquid metal is poured into the cavity 65 of the mold 60 according to the so-called “low pressure” process. The most commonly used alloy is of the AlSi7Mg0.6 type, but any other type of casting alloy having good flowability can be used. The temperature can be of the order of 800 ° C to 820 ° C. The liquid metal thus fills the supply duct 66 then fills the cavity 65 of the mold 60 placed under overpressure, typically from 700 mbar to 1.5 bar. The metal also infiltrates the interstices of the preform 51 made of silicone elastomer, and also surrounds the preform 51 and the cores 53A, 53B.

In a fourth step ( figures 2c and 2d ), after solidification and cooling, the mold 60 is released and the molded part 57 is removed. After deburring and machining of the part mold 57, and elimination of the remaining silica powder, the fluidic device 1 shown in FIG. figure 2e .

Purely by way of illustration, the metal foam 30 has a length of 105mm, a width of 50mm for a thickness of 10mm to 35mm. It has a porosity of the order of 70% to 75% with open pores and distributed spatially in a random manner. The first main wall 10 has a thickness of about 2mm and the second main wall 20 has a thickness of about 5mm. The inlet 4A and outlet 4B orifices may have a diameter of the order of 5 to 15 mm. The specific surface of the metal foam can be adjusted as a function of the average size of the pores and of the porosity, these parameters being adapted during the manufacture of the preform, in particular via the dimensions of the agglomerated elements of silicone elastomer.

As a variant, as mentioned above, the production of the fluidic device 1 can be carried out by a molding technique of the “low pressure” type comprising the infiltration of a preform based on salt dough previously obtained according to the process described in the document. EP2118328 .

The method comprises steps identical or similar to those described with reference to figures 2a to 2e .

It differs from it in that, during a first step, the preform 51 is produced by mixing ground salt particles, a thermodegradable organic binder, and a wetting agent. A preform 51 of porous salt dough with interconnected interstices is thus obtained. A step of removing the wetting agent, decomposing the binder and hardening the preform 51 can be carried out, in particular by a step of baking the preform 51 at a temperature of the order of 100 ° C., followed by a pyrolysis step at a temperature of the order of 500 ° C.

During a second step, the part 50 formed of the preform 51 and of the cores 53A, 53B is placed in the cavity 65 of the mold 60, this part 50 preferably being preheated to a temperature for example of 600 ° C.

In a third step, the liquid metal is poured at a temperature of the order of 750 ° C. with an overpressure typically of 700 mbar to 1.5 bar. The most commonly used alloy is of the AlSi7Mg0.6 type, but any other type of casting alloy having good flowability can be used.

During this casting step, concomitantly with the formation of the walls 10, 20, 40 of the housing, the liquid metal infiltrates into the interconnected interstices of the preform 51 so as to form the metal foam 30.

In a fourth step, after solidification and cooling, the molded part 57 is removed from the cavity 65 of the mold 60 and the salt of the preform 51 is removed with a solvent. After deburring and machining of the molded part, the fluidic device 1 illustrated in figure 2e . The metallic foam forms a network of open pores distributed in a random manner. As mentioned above, the specific surface of the metal foam can be adjusted as a function of the average size of the pores and of the porosity, these parameters being adapted during the manufacture of the preform, in particular via the dimensions of the agglomerated particles of salt dough.

Thus, the method of producing the fluidic device 1 is simplified in that the production of the metal foam 30 and of the first main wall 10 in one piece and in the same material is carried out during a single and same step of casting of the liquid metal, this step allowing the molding of the housing 2 and the infiltration of the preform 51. This avoids any step of machining the housing to form the channel 3, as well as any step of fixing the metal foam 30 to the first main wall 10 by means of a fixing layer, for example a layer of solder.

This example of a method is particularly advantageous here insofar as the metal foam 30 is also made in one piece and in the same material with the second main wall 20 and with the side wall 40, and that the metal foam obtained forms a network of open pores with random spatial distribution. The mechanical strength of the fluidic device 1 and the overall exchange coefficient are thereby improved.

The figure 3 is a schematic perspective view of a fluidic device 1 with metallic foam 30 according to a second embodiment.

The fluidic device 1 differs from the fluidic device 1 described above with reference to figures 1a and 1b in that the metal foam 30 is made in one piece and in the same material with the first main wall 10 and the side wall 40, the second main wall 20 being an attached wall forming a cover for the channel 3.

Thus, the housing 2 comprises a channel 3 delimited transversely by the first main wall 10 and by the side wall 40. The walls are here made in one piece and in the same material. The metal foam 30 is located in the channel 3 between the two inlet 5A and outlet 5B chambers.

The housing 2 comprises a second main wall 20 which is in the form of an attached wall, the attachment of which to the side wall 40 of the housing 2 enables the channel 3 to be closed transversely in a sealed manner. It has two through orifices, called inlet 4A and outlet 4B, which respectively open into inlet chamber 5A and into outlet chamber 5B. Alternatively, the inlet 4A and outlet 4B orifices can be made, not at the level of the attached cover, but at the level of the side wall 40 or even at the level of the first main wall 10.

The attached cover 20 can be fixed to the side wall 40 of the housing 2 at the level of its upper contact face 43, as well as, preferably, to the metal foam 30. The fixing can be carried out in a sealed manner by an intermediate layer of a solder material (not shown). Thus, fixing and sealing is obtained between the attached cover 20 on the one hand, and the side wall 40 of the housing 2 and, where appropriate, the metal foam 30 on the other hand.

The channel 3 and the metal foam 30 have here a general shape and dimensions identical or similar to those described previously with reference to FIGS. 1a and 1b, and are not described again here.

The figures 4a to 4f illustrate steps of an exemplary method for producing the fluidic device 1 according to the second embodiment.

In a first step, a porous preform 51 with interconnected interstices made of a material of salt dough or of silicone elastomer is produced in a manner identical or similar to the methods described above. Furthermore, no provision is made here to assemble the cores to the preform 51 as in part 50 described with reference to figure 2a .

In a second step, as shown in figure 4a , a mold 60 is prepared with two screeds 61, 63, the lower screed 61 of which is similar or identical to the lower screed of figures 2b and 2c . Furthermore, the upper yoke 63 comprises cores 53A, 53B in the form of portions projecting vis-à-vis an internal face 64, these cores being intended to form the inlet 5A and outlet 5B chambers. These cores are mounted to move in translation with respect to the upper yoke 63 so as to form the jaws of a vice making it possible to maintain the preform 51 in a so-called suspended position during molding.

More precisely, the jaws are spaced from one another by a distance substantially equal to the length of the preform 51, and are arranged on either side of a surface 64c of the internal face 64 of the yoke upper 63, the latter being intended to be in contact with the preform 51.

As shown in the figure 4b , the preform 51 is placed in contact with the contact surface 64c, so that the upstream and downstream faces of the preform 51 are in respective contact with the jaws. These exert a holding force on the preform 51 making it possible to keep the latter in position, without causing compression of the preform 51 capable of modifying its porosity.

In a third step ( figure 4c ), the mold 60 is closed by placing the upper 63 and lower 61 yokes in mutual contact. The preform 51 is held in a suspended position vis-à-vis the internal face 62 of the lower yoke 61, this space being intended for in particular, forming the first main wall 10. A lateral space between the jaws and the internal face 62 of the lower yoke 61 is intended for forming the lateral wall 40 of the housing 2.

The liquid metal is then poured through the supply duct 66, so that the metal fills the cavity 65 of the mold 60 and therefore the space separating the internal face 62 from the preform 51 on the one hand. , and bits on the other hand. At the same time, the metal infiltrates into the interstices of the preform 51. This step is similar or identical to that described above with reference to figure 2b .

Insofar as the preform 51 is in contact with the contact surface 64c of the upper yoke 63, the second main wall 20 of the housing 2 is not produced during this step.

In a fourth step ( figures 4d and 4e ), after solidification and cooling, the mold 60 is released and the molded part 57 is removed. The housing 2 thus comprises the metal foam 30 made in one piece and in the same material with the first main wall 10 and with the wall lateral 40 delimiting the channel 3.

The remaining silica or salt paste is then removed. This step is simplified insofar as the channel 3 does not have a closed cross section delimited by the different walls of the housing 2. We have in fact access to the channel 3 and to the metal foam 30 through an opening formed by the absence of the second main wall 20.

In a last step ( figure 4f ), after deburring and machining of the molded part 57, a layer of a brazing material is deposited in the contact zone between the insert cover 20 and the side wall 40, as well as in the contact zone between the insert cover 20 and the free face of the metal foam 30. The channel 3 is closed using the attached cover and the fluidic device 1 thus obtained is placed in a brazing furnace.

The figure 5 is an exploded perspective view of a fluidic device 1 according to the third embodiment. In this example, the fluidic device 1 is formed by a housing 2 of substantially circular transverse profile. It comprises a side wall 40 delimiting the channel 3 in the plane (X, Y) and two opposite main walls 10, 20 delimiting the channel 3 along the Z axis.

In this example, the two main walls 10, 20 are fixed to the side wall 40 in a sealed manner by a layer of solder (not shown). Alternatively, at least one of the main walls 10, 20 can be made in one piece and in the same material with the side wall 40.

Each main wall 10, 20 is made in one piece and in the same material with a metal foam 30-1, 30-2. The metal foams 30-1, 30-2 can have a diameter equal to or less than that of the main walls 10, 20.

The two main walls 10, 20 provided with the respective metal foams 30-1, 30-2 are assembled to one another along the Z axis by means of a fluidic manifold 6 interposed between the two metal foams 30 -1, 30-2. The collector 6 has a solid volume of cylindrical shape, with a diameter substantially equal to that of the main walls 10, 20, and is assembled in a sealed manner to the side wall 40. The collector 6 comprises a collection duct which extends between two input ends 7A and an output end 7B. The inlet ends 7A both open out onto the upper and lower faces, opposite one another, of the manifold 6, and therefore face the metal foams 30-1, 30-2, and are preferably positioned in the center of the manifold 6. The outlet end 7B opens onto the circumferential face of the manifold 6.

Thus, the channel 3 is formed of a lower part delimited between the first main wall 10 and the lower face of the manifold 6 and containing the metal foam 30-1, and an upper part delimited between the second main wall 20 and the upper face of the collector 6 and containing the metal foam 30-2. Channel 3 continues through the collection duct which connects the two parts of channel 3 to the outlet end 7B.

The housing 2 further comprises an inlet 4A and an outlet 4B of the channel 3 positioned at the side wall 40 of the housing 2, intended to allow the supply of the fluid in the two lower and upper parts of the channel. 3, and the discharge of the fluid from the outlet end 7B of the collection duct. The inlet 4A has a transverse dimension adapted to allow the introduction of the fluid at the same time in the two parts of the channel 3, so that the fluid flows through the two metal foams 30-1, 30 -2 and receives heat from of one or the other, or of the two main walls 10, 20. The fluid then flows in the collection duct from the inlet ends 7A to the outlet end 7B. The outlet orifice 4B is positioned opposite the outlet end 7B of the collection duct, so that the fluid can be directly discharged without circulating again in the lower and upper parts of the channel 3.

The method of making this fluidic device 1 can be carried out in a manner similar to the manufacturing methods described above. Thus, each main wall 10, 20 can be made in one piece and in the same material with the corresponding metal foam 30-1, 30-2, by a low-pressure molding process with an infiltration step of a preform 51 made of salt dough or silicone-based, this infiltration step being concomitant with the casting. The assembly of the walls 10, 20, 40 and the collector 6 can be carried out by brazing.

A device obtained according to the invention, and preferably by the third embodiment described above, makes it possible to obtain a thermal performance similar to the known products, with a lower pressure loss, by a factor at least greater than 2 , preferably 5 and even more preferably 7. Such a device thus makes it possible, for example, to use less powerful fluid circulation pumps.

The figure 6a is a schematic bottom view of a metal foam fluidic device according to a fourth embodiment. In this fourth embodiment, the fluidic device 1 differs from the fluidic devices 1 described above in Figures la, 1b and 3 in that the metallic foam 30 is made in one piece and in the same material with the first main wall 10 ( Fig 6b ). The side wall 40 comprises the walls of a hollow section 70. Optionally, the metal foam 30 is made in one piece and in the same material with the second main wall 20 ( Fig 6b ), opposite the main wall 10.

This fourth embodiment differs from the embodiments previously described by the fact that the preform 51 intended to form the metal foam 30 is held in a hollow profile 70. The use of a profile 70 facilitates the handling of the preform and its positioning in the mold 60. It may be advantageous for the dimensions of the profile 70 to be adapted such that the external faces of the walls of the profile are in contact with the side walls of the cavity 65 of the mold and constitute the side faces of the housing 2. Preferably, the thickness of the walls of the profile is between 1 mm and 5 mm, or even more preferably between 2 mm and 3 mm.

The figures 7a to 7e illustrate steps of an exemplary method for producing the fluidic device 1 according to the fourth embodiment.

During a first step ( Fig 7b ), a part 80 is produced formed of a hollow section 70 'and a part 50'. The part 50 'consists of a preform 51' assembled with two cores 53A ', 53B' arranged on either side of the preform 51 'as in the first embodiment ( Fig 7a ). The preform 51 ′ is intended to form the metal foam 30. It can be obtained from salt dough or from silicone. The part 50 'fits into a chamber of the hollow section 70'. In the example as described, the hollow section 70 'has a single chamber. The side faces of the preform 51 'are in contact with the interior walls of the chamber of the profile 70'.

The following steps are then similar to those previously described for the first or second embodiments, depending on the type of box desired. In a second step, the part 80 is then placed in the cavity 65 'of the mold 60'. The mold 60 'consists of two parts 61' and 66 '. This part 80 is preferably preheated ( Fig 7c ). In a third step, the liquid metal is poured into the cavity 65 'of the mold 60'. In a fourth step, after solidification and cooling ( Fig 7d ), the mold 60 'is unhooked and the molded part 57' is removed. After deburring and machining of the molded part 57 ', and removal of the residues from the preform 51', the fluidic device 1 shown in FIG. figure 7e .

It is advantageous to avoid the wetting of the outer walls of the hollow section 70 by the liquid metal. This can be achieved through the design of the mold or by some other means such as the use of a liquid metal resistant gasket.

This fourth embodiment allows the production of a case 2, the two main walls of which and the metal foam 30 are obtained in one piece if the cores 55A, 55B, 56A and 56B are used as described in the first embodiment. realization or the realization of a box 2 of which a single main wall and the metal foam 30 are obtained in one piece as described in the second embodiment

The use of a profile whose walls are partially melted during the casting step is particularly advantageous. Indeed, this local fusion can allow a metallurgical bond between the foam and the profile and thus induce a metallurgical continuity between the foam and the profile and allow an optimal thermal performance. It may thus be advantageous to use an aluminum profile.

Particular embodiments have just been described. Different variants and modifications will appear to those skilled in the art.

Thus, the fluidic device may not include inlet chambers located on either side of the metal foam. The inlet and outlet openings pass through a wall of the housing and then open directly at the level of the metal foam.

The fluidic device may include structures located at the level of the external faces of the walls of the case, these structures being able to improve the dissipation of heat emitted by the component to be cooled. These structures can, by way of illustration, be in the form of cooling fins.

The fluidic device can be subjected to a heat treatment in order to improve its mechanical strength and / or its thermal conductivity. This heat treatment step can be carried out after demolding, before or after machining of the molded part. It may for example consist of a solution and quenching treatment, optionally followed by tempering.

The fluidic device can be subjected to a surface treatment in order to improve its resistance to corrosion or its resistance to abrasion or any other property necessary for the use of the device.

Claims (3)

1. A method for producing a fluidic device (1), including:

   - a case (2) comprising a channel (3) delimited by walls, including a first main wall (10), the channel (3) extending between two orifices, called inlet (4A) and outlet (4B) orifices;

   - a porous medium with open pores made of a metallic material, called metal foam (30), located in the channel (3) between said inlet (4A) and outlet (4B) orifices;

   - a metal foam (30)

   - wherein the metal foam (30) and the first main wall (10) are produced by moulding such that said metal foam (30) and said first main wall (10) are made in one piece and from the same material, during the same step of casting a metallic material into a mould (60), during which an infiltration, by said metallic material, of a destructible porous preform (51) located in a mould cavity (65) takes place, said casting step being carried out by the application of a pressure force on the surface of said metallic material so as to cause it to rise into the mould (60) and to be infiltrated into the preform (51), said preform (51) being produced in salt paste or based on silicone such that the metal foam (30) has a random spatial distribution of the pores.
2. The method according to claim 1, wherein the preform (51) is disposed in the cavity (65) of a mould (60) and kept at a distance from an inner face (62, 64) of a yoke of the mould (60), the space separating said inner face (62, 64) and the preform (51) being intended to form the first main wall (10).
3. The method according to any one of claims 1 or 2 wherein a side wall of said preform (51) is in contact with at least one inner face of the walls of a hollow profile (70).

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