FR3139891A1 - Heat exchanger for a motor vehicle, with means of disturbing the fluid in the flow channels - Google Patents

Abstract

The invention proposes a heat exchanger (1), in particular for a motor vehicle, comprising a plurality of channels (6) in which a cooling fluid or a refrigerant circulates, each channel (6) being delimited by walls (12) having internal surfaces (7) directed towards the interior of the channel (6), said internal surfaces (7) comprising means for disturbing the fluid. Said disturbance means consist of segments (A, B) succeeding one another along a flow direction X of the fluid, said segments (A, B) presenting an alternation of hydrophobic surfaces (B) and normal or hydrophilic surfaces (A), the alternation taking place along the flow direction X of the fluid. Figure for abstract: Figure 3

Description

Heat exchanger for a motor vehicle, with means of disturbing the fluid in the flow channels Technical field of the invention

The field of the present invention is that of heat exchangers, in particular for motor vehicles.

It concerns more particularly heat exchangers comprising a bundle of tubes or plates, arranged in particular on the front of the motor vehicle.

The invention also relates to a method of manufacturing such a heat exchanger.

Such heat exchangers are in particular arranged on a loop of a cooling circuit, making it possible to dissipate calories coming from an internal combustion engine, or from a peripheral, such as an air conditioning module, of the motor vehicle. .

Technical background

In known manner, a heat exchanger for a motor vehicle comprises a plurality of tubes or plates extending parallel to each other and in which the cooling fluid present in the cooling circuit loop previously can circulate. mentioned, or the refrigerant (refrigerant) present in the air conditioning loop previously mentioned.

The heat exchanger is configured to allow an exchange of calories between an air flow passing through it and the fluid circulating inside the tubes or between the plates.

It is customary to provide heat dissipation devices in the air flow passage channels, defined between the tubes, or between two plates. These heat dissipation devices consist, for example, of a plurality of external fins, also called "spacers", extending into the air flow passage channels, increasing the exchange surface and thus promoting the dissipation of calories in the air. level of the heat exchanger. These external fins thus provide a secondary air exchange surface.

The heat exchanger is located in particular at the front of the motor vehicle. Thus, when the motor vehicle moves forward, the external fins of the heat exchanger are exposed to a flow of air coming from outside the motor vehicle, thus making it possible to improve the dissipation of calories at the level of the heat exchanger.

It is also customary to provide fluid disturbance devices in the fluid circulation channels, defined in the tubes or between two plates, to increase the exchange coefficients.

Indeed, the exchange coefficients between a fluid and a wall are much greater when the flows are turbulent.

There are several types of “disruptors” in the state of the art. The best known are the bosses which are deformations of the walls of the channels, and the internal fins which are parts added inside the channels.

Bosses, even if they are very effective, have two disadvantages. The first is to limit the passage section in the tube and therefore to create unnecessary pressure loss. The second is to reduce, in the case of air exchangers, the contact surface between the tubes/plates and the secondary air exchange surface (i.e. the external fins). In fact, the bosses are created by local depression of the wall of the circulation channel. The direct consequence is the formation of a bowl on the external surface of the channel, and the fins are therefore no longer in contact with the tube or the plate at the level of the bowls.

The internal fins also impact the pressure loss, by adding material to the channel. They also have the disadvantage of adding material in the tubes or between the plates, which has a negative impact in terms of weight and cost.

The objective of the present invention is to create turbulence in a fluid flow without generating unnecessary pressure loss, contact resistance, or even an increase in weight or cost.

The heat exchanger according to the invention comprises, in a conventional manner, a plurality of channels in which a cooling fluid or a refrigerant circulates, each channel being delimited by walls having internal surfaces directed towards the interior of the channel, said internal surfaces comprising means of disturbing the fluid.

This exchanger is mainly characterized in that said disturbance means consist of segments succeeding one another along a direction of flow of the fluid, said segments presenting an alternation of hydrophobic surfaces and normal or hydrophilic surfaces, the alternation operating along the direction of fluid flow.

The main idea of this invention consists of generating turbulence in the flows inside the tubes or between two plates of heat exchangers, thanks to surface changes. This makes it possible to increase thermal performance without generating unnecessary pressure losses.

The principle is as follows: by providing the internal surface of the channel with an alternation of hydrophobic surfaces and normal or hydrophilic surfaces, a shear stress is exerted on the fluid which flows in the channel, particularly in the vicinity of the internal surfaces. . This shear stress will cause a disturbance of the fluid and generate turbulence.

The disturbance of the fluid will first be apparent in the vicinity of the walls of the channel, then as the flow progresses the disturbance of the fluid will generalize to the center of the channel. Thus, after a few centimeters of flow, the disturbance of the fluid is general throughout the section of the channel.

• le canal présente une surface interne supérieure en vis-à-vis d’une surface interne inférieure, un décalage existant dans l’alternance des segments entre la surface interne supérieure et la surface interne inférieure, de sorte qu’un segment avec une surface hydrophobe appartenant à la surface interne supérieure soit disposé en vis-à-vis d’un segment avec une surface normale ou hydrophile appartenant à la surface interne inférieure, et inversement.
• les surfaces internes peuvent comprendre un alignement de plusieurs rangées de segments avec une alternance de surfaces s’opérant le long d’une direction perpendiculaire à la direction d’écoulement du fluide.
• il y a au moins deux alternances par surface interne dans chaque canal le long de la direction d’écoulement du fluide.
• il y a entre 10 et 70 alternances par surface interne dans chaque canal le long de la direction d’écoulement du fluide.
• la surface hydrophobe comporte des motifs en relief.
• lesdits motifs en relief se répètent uniformément sur la surface hydrophobe.
• lesdits motifs en relief consistent en des cuvettes.

According to the different embodiments of the invention, which can be taken together or separately:

• the channel has an upper internal surface facing a lower internal surface, an offset existing in the alternation of the segments between the upper internal surface and the lower internal surface, so that a segment with a hydrophobic surface belonging to the upper internal surface is arranged opposite a segment with a normal or hydrophilic surface belonging to the lower internal surface, and vice versa.
• the internal surfaces may include an alignment of several rows of segments with alternating surfaces occurring along a direction perpendicular to the direction of fluid flow.
• there are at least two alternations per internal surface in each channel along the fluid flow direction.
• there are between 10 and 70 alternations per internal surface in each channel along the direction of fluid flow.
• the hydrophobic surface has raised patterns.
• said relief patterns repeat uniformly on the hydrophobic surface.
• said relief patterns consist of bowls.

These bowls differ fundamentally from the bosses of the prior art by their dimensions and their orientation. In fact, the cups measure from a few tens to a few hundred microns, while the bosses measure a few millimeters. And the cups are concave, therefore form a bump directed towards the outside of the canal, while the bosses are convex, and form a bump directed towards the inside of the canal.

The invention also relates to a method of manufacturing a heat exchanger as described above, comprising at least one step of creating hydrophobic segments carried out on a metal strip forming said channel walls.

According to a first possible configuration, said step of creating the hydrophobic segments consists of surface texturing to form relief patterns.

For example, this texturing is carried out by stamping. Stamping is carried out in particular during the forming of a plate of a plate exchanger.

For example, this texturing is carried out by means of a textured wheel corresponding to a counter-imprint of the relief patterns of the hydrophobic segments, said wheel rolling on the metal strip by exerting pressure on it so as to deform and texture it in creating said relief patterns. This is carried out before a channel forming step, for the tubes of a tube exchanger.

According to a second possible configuration, said step of creating hydrophobic segments is carried out by means of a surface treatment, in particular by applying a layer to the surface of the segments intended to become hydrophobic segments, said layer comprising one or more substances suitable for conferring hydrophobic properties.

Brief description of the figures

Other characteristics and advantages of the invention will appear during reading of the detailed description which follows, for the understanding of which we will refer to the appended drawings in which:

There is a perspective view of part of a tube heat exchanger;

There is a perspective view of a plate heat exchanger;

There schematically represents the flow profile of a fluid in a channel according to the invention;

There illustrates the method of manufacturing tubes according to the invention for a heat exchanger;

There is a detailed view of a wheel for texturing the walls of the channels according to the invention.

Detailed description of the invention

In the remainder of the description, elements having an identical structure or similar functions will be designated by the same references.

There illustrates a perspective view of an example of tube heat exchanger 1.

The heat exchanger 1 comprises a plurality of tubes 2 each extending mainly along a first longitudinal axis X, and a second transverse axis Y perpendicular to the first axis X, thus defining a first plane. The tubes 2 are stacked in series one above the other along a third vertical axis Z perpendicular to the foreground.

The heat exchanger 1 is configured so that an air flow, generated by the movement of the motor vehicle in which the heat exchanger 1 is installed, or by a fan installed near the exchanger 1 of heat, circulates along the Y axis through the heat exchanger 1.

The heat exchanger 1 comprises spaces interposed between the tubes 2 along the third axis Z, these spaces allowing the passage of the air flow between the tubes 2 in order to promote the exchange of calories between a cooling fluid or a fluid refrigerant circulating inside the tubes 2 and the air flow coming against the exterior walls of these tubes 2.

The flow of fluid inside the tubes 2 takes place along the direction X.

The transverse ends of the tubes 2 are introduced into a collector 5 connected to a loop of a cooling circuit. In this way, the cooling flow can circulate in the plurality of tubes 2 of the heat exchanger 1.

External fins 4 in the shape of an accordion are arranged in the spaces between the tubes 2 and are supported against the external surfaces of the tubes 2. These external fins 4 make it possible to increase the exchange surface and thus promote the dissipation of calories at the level of heat exchanger 1.

Traditionally, each tube 2 is made up of a metal strip whose side edges are folded towards a central axis then welded or brazed together. We thus obtain a tube 2 with one or more channel(s) 6 for fluid flow inside the tube 2, depending on the way in which the plate is folded.

Each tube 2 has a lower wall and an upper wall connected together by side walls.

There is a perspective view of an example of plate heat exchanger 1.

The heat exchanger 1 comprises a plurality of plates 3 each extending mainly along a first longitudinal axis X, and a second transverse axis Y perpendicular to the first axis X, thus defining a first plane. The plates 3 are stacked in series one above the other along a third vertical axis Z perpendicular to the foreground.

The heat exchanger 1 is configured so that an air flow, generated by the movement of the motor vehicle in which the heat exchanger 1 is installed, or by a fan installed near the exchanger 1 of heat, circulates along the Y axis through the heat exchanger 1.

Two adjacent plates 3 form an internal space (between these two plates) inside which a cooling fluid or a refrigerant circulates. Side walls make it possible to close this internal space in order to create a channel 6 for fluid flow. The fluid flows in the X direction.

Above these two plates 3 and below these two plates 3, the heat exchanger 1 includes external spaces allowing the passage of the air flow in direction Y.

Each external space is also delimited by two adjacent plates 3.

The internal spaces and the external spaces thus alternate along the Z axis.

The air flow passing through the external spaces licks the external surfaces of the walls delimiting the internal spaces.

Thus, whatever the type of heat exchanger 1, tube or plate, there are fluid flow channels 6 extending in a flow direction lower wall and an upper wall.

There shows the flow of a fluid inside a channel 6, whether it is an exchanger 1 with plates 3 or an exchanger 1 with tubes 2.

The thin arrows correspond to the fluid velocity vector.

The thick arrows correspond to the friction level of the fluid.

The fluid flows in the X direction, from the left of the diagram to the right of the diagram.

This sectional view was taken along a transverse plane defined by the axes Z and X. We thus see the lower wall 12b and the upper wall 12a of the channel 6.

Each wall 12a, 12b has an internal surface 7a, 7b, directed towards the interior of the channel 6, and which is provided with means for disturbing the fluid.

These means of disturbing the fluid consist of a succession of segments A, B presenting an alternation of hydrophobic surface B and normal or hydrophilic surface A.

This alternation takes place along the direction of flow of the fluid, that is to say along the direction X.

In the example presented here, the first section at the start of channel 6 on the left has for example the same type of surface on the upper wall 12a and on the lower wall 12b, in this case a normal or hydrophilic surface A. This first end section is intended to be inserted inside a collector 5. Then the alternation of surfaces begins from the next section, and thus continues preferably until the end of channel 6, and the last end section intended to be inserted inside another collector 5 is identical to the first end section.

In the context of the present invention, it is possible that the first section and the last section do not have the same surface condition on the upper wall 12a and the lower wall 12b.

For the sake of clarity, we will call “hydrophobic segment B” a segment whose surface is hydrophobic, and “normal or hydrophilic segment A” a segment whose surface is normal or hydrophilic.

In the example presented here, there is a shift in the alternation of segments A, B, between the upper internal surface 7a and the lower internal surface 7b, so that a hydrophobic segment B belonging to the upper internal surface 7a is arranged opposite a normal or hydrophilic segment A belonging to the lower internal surface 7b, and vice versa.

Concretely, by providing the internal surface 7 of the channels 6 with this alternation of hydrophobic and normal or hydrophilic surfaces, a shear stress is exerted on the fluid which flows in the channel 6. This stress will cause a disturbance of the fluid and generate turbulence.

At the start of channel 6, that is to say on the left side of the , we see that the flow of the fluid follows a Gaussian profile, with a higher fluid speed at the center of the channel 6 compared to the fluid speed in the vicinity of the internal surfaces 7 of the channel 6. In fact, the friction is more high in the vicinity of the internal surfaces 7 of the channel 6, which slows down the flow of the fluid in the vicinity of the walls 12a, 12b.

When the fluid flows near a hydrophobic segment B, it can slide quickly, the friction being less. The fluid therefore tends to accelerate in the vicinity of hydrophobic segments B, compared to the speed it would have with a normal or hydrophilic segment A.

When this same fluid passes from a hydrophobic segment B to a normal or hydrophilic segment A, it is suddenly slowed down and completely disrupted.

The fluid continues to flow along the X axis, but taking bumpy paths. We thus obtain a turbulent flow, that is to say with disordered agitation of the fluid.

The fluid disturbances propagate to the center of channel 6.

Each time a hydrophobic segment B passes towards a normal or hydrophilic segment A, disturbances are created.

Each time a normal or hydrophilic segment A passes towards a hydrophobic segment B, the disturbances previously created propagate.

According to a possible configuration of the invention, it is also possible to provide, within each channel 6, an alternation between hydrophilic segments A and normal or hydrophobic segments B along the direction Y. This alternation along the direction Y is then added to the alternation in the direction X. We obtain a sort of checkerboard.

Thus, the internal surfaces 7 of the channel 6 may comprise an alignment of rows of several segments A, B with an alternation of surface along a direction perpendicular Y to the flow direction X of the fluid.

Preferably, there are at least two alternations per internal surface in each channel 6 along the flow direction X of the fluid.

On the , which represents only a section of channel 6, there are 3 alternations represented along the direction X on the lower internal surface 7b, and two alternations represented along the direction X on the upper internal surface 7a.

Preferably, there are between 10 and 70 alternations per internal surface 7 in each channel 6 along the flow direction X of the fluid. This is valid for a total length of a channel 6. This therefore corresponds to between 20 and 140 alternations for the two faces of the same channel 6, that is to say when we accumulate the alternations of the upper internal surface 7a and the lower internal surface 7b.

The number of alternations depends on the different technologies of tubes 2 and plates 3, and depends on the length ranges of the segments A, B.

For example, the length of a hydrophobic segment B may be less than the length of a normal or hydrophilic segment A.

Conversely, the length of a normal or hydrophilic segment A may be less than the length of a hydrophobic segment B.

For example, the hydrophobic segments B and the normal or hydrophilic segments A have identical lengths.

According to an example of possible configuration, the hydrophobic segment B includes relief patterns.

These raised patterns repeat uniformly on the hydrophobic surface.

Preferably, the relief patterns consist of cups.

The invention also relates to a method of manufacturing a heat exchanger 1 comprising at least one step of creating the hydrophobic segments B produced on metal strips forming the walls of the channel 6, before a step of forming the channels 6.

There shows the different steps for creating tubes 2 comprising hydrophobic segments B. These tubes 2 are used for a tube exchanger.

On this , there is on the left side a roller 8 of a metal strip which gradually unwinds until it forms tubes 2 at the end of the process.

In step E1, roll 8 unfolds horizontally.

In step E2, the unrolled section of strip is flat, and a textured metal wheel 9 presses on this section of strip, so as to deform it.

In step E3, rollers 10 fold the side edges of the strip towards the center so as to form a cylindrical or flat tube.

In step E4, the side edges are welded or brazed to each other so as to hermetically close the tube. It is also possible to weld/braze the tube later.

In step E5, the tube is calibrated using casters 11.

In step E6, the tube is cut so as to create a plurality of tubular sections, which correspond to the tubes 2 of the heat exchanger 1.

Step E2 is the one that interests us more particularly, because it concerns surface texturing to create the hydrophobic segments B.

The metal wheel 9 which carries out this texturing is more particularly illustrated in according to a possible example of the invention.

This wheel 9 has an external periphery composed of a tangential alternation of segments like the segments A, B which are printed on the internal surface 7 of the strip. When rotating the wheel 9, a succession of segments are printed with alternating surfaces. In this case, there is an alternation of hydrophobic segment B and normal or hydrophilic segment A.

The hydrophobic segments B of the wheel 9 are textured, either by laser or mechanically, so as to present grains. These grains are preferably spherical, and distributed uniformly over the segment. The grain diameter is between 5 and 50 micrometers.

Thus, during step E2, the wheel 9 rolls on the metal strip by exerting pressure on it so as to deform and texture it by creating relief patterns, the imprint of which is the opposite of the grains, and corresponds to bowls.

Thus the hydrophobic surfaces B are made up of a homogeneous distribution of cups with a diameter of between 5 and 50 micrometers. In fact, the grains of the wheel 9 correspond to the counter-print of the cups of the final tube 2.

These cups have the effect of generating a low surface tension. The cohesive forces of the liquid prevail, and the liquid will tend not to wet the surface. In fact, the fluid has difficulty spreading on this surface with cups.

Unlike a normal or hydrophilic surface (without a bowl) where the fluid spreads better because the surface tension of the normal or hydrophilic surface is greater, compared to that of the hydrophobic surface.

Note that the wheel 9 as illustrated in comprises a periphery divided axially into two parts 9a, 9b, so as to present two rows of successive segments A, B. There is a shift in the alternation of segments between these two rows.

It is possible to have a wheel 9 divided into more than two parts, depending on the number of rows of segments desired on the strip before forming.

This wheel 9 makes it possible to produce several rows of segments with an alternation of hydrophobic segment B and normal or hydrophilic segment A, offset between the upper internal surface 7a and the lower internal surface 7b of the tubes 8.

An identical wheel 9 can be used to texture the plates 3 of the plate exchanger 1. In this case, manufacturing is simpler, because there is no forming of the strip, in this case steps E3, E4 and E5 do not exist.

According to another possibility, steps E2 and E3 of the can be replaced by stamping, with a textured stamping die in place of wheel 9.

The creation of the hydrophobic segments B produced on metal strips forming the walls of channel 6 can be carried out in another way, in this case by means of a surface treatment.

This may involve the application of a layer to the surface of the segments intended to become hydrophobic segments B.

The layer comprises one or more substances capable of conferring hydrophobic properties.

Most often, hydrophobic coatings are composed of an assembly of polymers. As they have a very low surface tension, the cohesive forces of the water oppose the formation of a coating/liquid interface.

The configurations shown in the figures cited are only possible examples, in no way limiting, of the invention which on the contrary encompasses variants of shapes and designs within the reach of those skilled in the art.

Claims (13)

Heat exchanger (1), in particular for a motor vehicle, comprising a plurality of channels (6) in which a cooling fluid or a refrigerant circulates, each channel (6) being delimited by walls (12) having internal surfaces (7 ) directed towards the interior of the channel (6), said internal surfaces (7) comprising means for disturbing the fluid,
characterized in that said disturbance means consist of segments (A, B) succeeding one another along a flow direction X of the fluid, said segments (A, B) presenting an alternation of hydrophobic surfaces (B) and normal or hydrophilic surfaces (A), the alternation taking place along the flow direction X of the fluid. Heat exchanger (1) according to the preceding claim, characterized in that the channel (6) has an upper internal surface (7a) facing a lower internal surface (7b), an offset existing in the alternation segments (A, B) between the upper internal surface (7a) and the lower internal surface (7b), so that a segment with a hydrophobic surface (B) belonging to the upper internal surface (7a) is arranged opposite -to a segment with a normal or hydrophilic surface (A) belonging to the lower internal surface (7b), and vice versa. Heat exchanger (1) according to one of the preceding claims, characterized in that the internal surfaces (7) can comprise an alignment of several rows of segments (A, B) with an alternation of surfaces operating along a direction Y perpendicular to the flow direction X of the fluid. Heat exchanger (1) according to one of the preceding claims, characterized in that there are at least two alternations per internal surface (7) in each channel (6) along the flow direction X of the fluid. Heat exchanger (1) according to the preceding claim, characterized in that there are between 10 and 70 alternations per internal surface (7) in each channel (6) along the flow direction X of the fluid. Heat exchanger (1) according to one of the preceding claims, characterized in that the hydrophobic surface (B) has relief patterns. Heat exchanger (1) according to the preceding claim, characterized in that said relief patterns are repeated uniformly on the hydrophobic surface (B). Heat exchanger (1) according to one of claims 6 to 7, characterized in that said relief patterns consist of bowls. Method of manufacturing a heat exchanger (1) according to one of the preceding claims, comprising at least one step of creating hydrophobic segments (B) carried out on a metal strip forming said walls (12) of the channels (6). Manufacturing method according to the preceding claim, characterized in that said step of creating the hydrophobic segments (B) consists of surface texturing to form relief patterns. Manufacturing process according to the preceding claim, characterized in that the texturing is carried out by stamping. Manufacturing method according to claim 10, characterized in that the texturing is carried out by means of a textured wheel (9) corresponding to a counter-imprint of the relief patterns of the hydrophobic segments (B), said wheel (9) rolling on the metal strip by exerting pressure on it so as to deform and texture it by creating said relief patterns, before a step of forming the channels (6). Manufacturing method according to claim 9, characterized in that said step of creating the hydrophobic segments (B) is carried out by means of a surface treatment, in particular by application of a layer on the surface of the segments intended to become segments hydrophobic (B), said layer comprising one or more substances capable of conferring hydrophobic properties.