EP0849558A1 - Improved metallic fin for heat exchanger, more particularly for automotive vehicles. - Google Patents

Abstract

The fin assembly consists of a central section (12) with at least one set (6) of fixed inclined fins (7), separated by gaps (8) to allow a passage for a fluid between them. The fins in the fixed set (6) are divided into at least two groups inclined in opposite directions, and with the fins in each of the groups being inclined at different angles, e.g. at 20 degrees , 24 degrees and 28 degrees . Sets of fins between and outside the inclined groups are made with both flat (11) and inclined (9,10) sections.

Description

The invention relates to the field of heat exchangers, especially for a motor vehicle.

It relates more precisely to the metal fins used in heat exchangers, brazed or assembled mechanically, to form exchange surfaces indirect intended to increase the areas of exchange between tubes in which a first fluid circulates hot or cold, and a second fluid, for example air, flowing between these tubes.

These fins are generally produced in the form of plates superimposed one above the other (exchanger mechanically assembled heat), and in this case they are crossed by the tubes, or bent substantially accordion (brazed heat exchanger) and in this case they are inserted between the tubes.

Some known fins include a central part provided with at least one series of fixed slats inclined with a constant angle, of selected shape, and spaced from each other others by openings of selected dimensions which allow the passage of fluid between the lamellae. Of such fins, called louvered fins, are by example described in publication US-5,289,874.

The production of louvers on exchange surfaces indirect certainly increases heat exchange, but at the same time it increases the losses of which decrease the efficiency of the heat exchanger heat. This effect is all the greater as the number of superimposed fins is important. He can be further strengthened if the installation has several exchangers heaters connected in series.

In addition, those skilled in the art know that the louvered shutters of constant inclination are all the more favorable to large pressure losses as their inclination is large, which is generally the case in heat exchangers known heat where the fins have an inclination about 35 °. Such angles cause detachment of the boundary layer in places where the fluid (e.g. air) begins its change of direction, and therefore, very weak areas are created near the walls so-called "air recirculation" and "dead water" speeds which, from a thermal point of view, are bad because convection can no longer occur normally.

Accordingly, an object of the invention is to provide a metal fin which does not have all or part of the disadvantages of the fins of the prior art.

To this end, the invention proposes a fin of the type described. in the introduction, in which the lamellae of the same series are divided into at least two groups of at least one unit, whose respective inclinations vary from group to the other.

The inclination of the slats of a group will be all the more great that the group order number will be high. So, the slats of a first group will present a first tilt whose value will be less than that of a second group, which will eventually be itself lower than that of a third group.

Insofar as the fins have lamellae of at least minus two different inclinations, we reduce significantly pressure losses.

Preferably, slats close to inclinations respective ones belong to two groups of slats whose serial numbers follow or precede each other. For example, a slide from the first group will be followed of a lamella of the second group whose inclination is more important. Fluid direction changes vary thus gradually, and therefore more gently, which allows limit the delamination of the boundary layer and therefore allow a larger indirect exchange area of to work.

Even more preferably, the slats placed respectively in the first row of a series of slats (i.e. at the start of the series) and / or the last row of this same series (i.e. at the end of the series) belong to the group of lamellae with serial number le below, says first group. In this way, we still soften plus changes in fluid direction.

In a preferred embodiment, the fin includes at least a series of at least two groups, called first and second groups, of lamellae which present first and second slopes respectively, and the series of lamellae has a median plane of symmetry.

It follows that such a series comprises at least one first lamella of the first group followed by at least one lamella of the second group, itself followed by at least a last strip of the first group.

Furthermore, some fins of the prior art include upstream of the first row lamella a lamella fixed upstream auxiliary spaced from the first row through an opening of selected shape. This auxiliary lamella is intended to channel the fluid at the start of the series. Gold, this upstream auxiliary lamella generally has a length substantially equal to half the length of slats of the series, so that it does not straighten enough fluid.

This is why, according to another characteristic of the invention, the fin may include an upstream auxiliary lamella fixed of dimensions substantially equal to or greater than those of the slats of the series. So the free end of the upstream auxiliary lamella is placed at a level lower than the respective levels of the slats of the series, which effectively straightens the fluid. This fluid is immediately oriented and, on the one hand, the leading edges of the series slats are better discussed, and on the other hand, the probability of detachment from the boundary layer of the wall is significantly reduced.

Certain fins of the prior art also include, downstream of the last row sipe, an auxiliary sipe fixed downstream spaced from the last row by an opening of selected shape. This auxiliary lamella downstream is intended, like the upstream auxiliary lamella to channel the fluid at the end of the series. Now, this lamella downstream auxiliary generally has a length substantially equal to half the length of the slats of the series, which means that it does not straighten the fluid.

This is why, according to yet another characteristic of the invention, the fin may include, downstream of the lamella of the last row in a series, an auxiliary lamella fixed downstream of substantially equal or greater dimensions to those of its slats.

When the fin has at least two sets of lamellae which follow each other (called respectively upstream series and series downstream), these can be linked together by through the auxiliary lamella downstream of one and the auxiliary lamella upstream of the other. This contributes to the pressure drop, and therefore improve efficiency of the heat exchanger.

Particularly advantageously, the auxiliary lamellae have an inclination less than or equal to that of the lamellae of the first group in the series. More preferentially, this inclination is less than that lamellae of the first group with a value between about 1 ° and about 20 °.

In a first embodiment, the series of lamellae neighbors have the same groups of lamellae.

In this case, it is preferable that groups of the same serial number of two series of neighboring lamellae present opposite directions. This subdivides the fluid in layers that will each penetrate between two slats of the upstream series and stand out in between corresponding lamellae of the downstream series placed symmetrically with respect to a median plane of symmetry.

In a second embodiment, the series of lamellae neighbors have different lamella groups.

Preferably, the inclinations of the lamellae are included in a range from about 15 ° to about 35 °. Strong inclinations (typically greater than 30 °) no longer present any disadvantages, since their harmful influence on the fluid is compensated at least by the fact that we use tilt slats different.

In addition, it is preferable that the inclination of the slats of the first group is less than that of slats of the group with the highest order number with a value between approximately 1 ° and approximately 15 °.

The invention applies more particularly to fins made of aluminum or an aluminum alloy, or still in copper.

• la figure 1 illustre une partie d'un échangeur de chaleur brasé équipé d'ailettes ondulées;
• la figure 2 illustre une partie d'un échangeur de chaleur assemblé mécaniquement, équipé d'ailettes planes; et
• la figure 3 illustre dans une vue en coupe transversale une partie d'une ailette selon l'invention, dans un mode de réalisation préférentiel.

In the description which follows, given by way of example, reference is made to the appended drawings, in which:

• Figure 1 illustrates part of a brazed heat exchanger fitted with corrugated fins;
• FIG. 2 illustrates a part of a mechanically assembled heat exchanger, equipped with plane fins; and
• Figure 3 illustrates in a cross-sectional view a part of a fin according to the invention, in a preferred embodiment.

The main purpose of a heat exchanger is to allow exchange of calories between a first fluid which circulates at the interior of some of these elements and a second fluid which circulates outside said elements. To do this, the heat exchanger generally comprises tubes 1 the ends of which open into manifolds and in which the first fluid circulates, for example a refrigerant, and which are licked by the second fluid, for example air.

In order to improve the exchange of calories (exchange thermal), the skilled person increases the exchange surface (here the walls of the tubes) by adding surfaces of indirect exchange which are called fins 2.

These fins are metallic, and preferably made of aluminum or aluminum alloy. They can be also made of copper.

As illustrated in Figures 1 and 2, according to the type of heat exchanger, the fins will take significantly different shapes.

In brazed heat exchangers (see Figure 1), the fins are made from a substantially folded plate accordion. They are then called dividers. A interlayer thus includes a multiplicity of fins placed substantially parallel to each other, in a position perpendicular to the longitudinal axis tubes 1, and between two neighboring tubes 1, or between a end plate 3 and a tube 1.

In mechanically assembled exchangers (see Figure 2), the fins are flat plates in which are formed holes 4 allowing the passage of tubes 1. On then speaks of fin plates. These are superimposed one above the other, substantially parallel, in a plane perpendicular to the longitudinal axis tubes 1.

Whatever the embodiment of the heat exchanger heat, the fin it contains is preferably made in the form of one or more blinds. Each louver is made in a central part 12 of the fin 1, and is made up of a series 6 of lamellae 7 which generally have identical chosen shapes and are separated from each other by openings 8, also of identical chosen shapes.

To make these louvers in a fin, we start from a metal plate in which we come to make parallel and spaced cuts of a length L. Then, in appropriately shaping metal areas between two cuts, of width L, the strips 7 while forming the openings 8.

The fins of the prior art are fixed, and have all the same inclination with respect to a contained X-X axis in the plane of the fin and substantially perpendicular to the alignment of the strips 7 of a series 6.

As explained in the introduction, the Applicant has noticed that the production of louvers with strips of constant inclination has a certain number of drawbacks, in particular with regard to pressure drops. This is why, according to the invention, the strips 7 of a series 6 have at least two different inclinations  ₁ and  ₂ .

A series 6 of blades therefore comprises at least two groups of identical fixed blades, each group having its own inclination. Thus, in the example illustrated in FIG. 3, the series 6-1 comprises a first group of four strips 7-1 of inclination  ₁ , and a second group of three strips 7-2 of inclination  ₂ .

Of course, there could be three groups of inclinations different, or more than three groups.

Preferably the first row in a series (first strip from the left), as well as the lamella of the last row (last lamella of the series in starting from the left or first strip starting from the right), belong to the first group.

Still according to the invention, it is preferable, as illustrated in FIG. 3, that the lamellae of the first group have an inclination  ₁ less than the inclination  ₂ of the lamellae of the second group.

More generally, it is preferable that lamellae belonging to groups whose order numbers are different, have inclinations whose amplitude depends on the order number of their group. More precisely, it is particularly advantageous for the amplitude of the inclination to increase with the value of the sequence number. Thus, the angle  ₁ of the lamellae of the first group will be smaller than the angle  ₂ of the lamellae of the second group, which will possibly be smaller than the angle  ₃ of the lamellae of the third group, etc.

Furthermore, in order to soften more gradually possible change of direction applied to the second fluid (for example air) which circulates between the lamellae of a series, it is preferable that the slats of the first group 7-1 of this series 6 are placed at the beginning and at the end of the series, thus framing lamellas belonging to groups of higher order numbers. In the example illustrated in figure 3, the series begins with two strips 7-1 of the first group, then it continues with three strips 7-2 of the second group, and finally it ends with two strips 7-1 from the first group. Of course, it is not not compulsory that the series of slats has a plane of symmetry, as is the case in the example illustrated on the Figure 3 where said plane of symmetry is placed substantially at center of the second strip 7-2 of the second group. Likewise, we could perfectly consider not having in a series 6 as slats 7-1 of a first group followed by slats 7-2 of a second group, and possibly lamellae (7-3) of a third group.

By making series 6-1 according to the invention, we subdivide the second fluid, which flows between the fins, in layers successive whose respective directions differ according to the angles of inclination of the slats between which they circulate. To the extent that the layers whose direction is slightly inclined precede the layers whose direction is more strongly inclined, the former will have tendency to press the seconds (following) against walls, thereby significantly increasing the exchange thermal fins (indirect exchange surfaces).

Preferably, provision is made upstream and downstream of a series 6 of lamellae 7 respectively an auxiliary lamella upstream 9 and an auxiliary downstream lamella 10 of the same width L than the 7-i slats in the series. These auxiliary slats are also produced by cutting the central part 12 of the fin and are spaced from the lamella which precede or follow them by an opening 13 of dimensions chosen, which are in fact substantially equal to the dimensions an auxiliary lamella. The free end 14 of auxiliary slats is placed at a lower level than the respective levels of the series 7-i slats that they frame, which makes it possible to straighten out effectively the second fluid at the entry and at the exit of the series, and therefore to better guide the flow of this second fluid. The leading edges of each lamella, and in particular of the first strip in the 7-1 series are better addressed, thereby reducing the likelihood of delamination boundary layers which form on the constituent wall a fin.

Still preferably, the upstream auxiliary 9 and downstream 10 lamellae have an inclination  ₀ less than or equal to the inclination  ₁ of the lamellae 7-1 of the first group. Even more preferably, the inclination  ₀ of the auxiliary lamellae is about 1 ° to about 20 ° lower than the inclination  ₁ .

A complete shutter then comprises a series 6 of strips 7 framed between two auxiliary strips 9 and 10. The angle of inclination  _i is preferably increasing from the upstream auxiliary strip 9, at least to the center of the series lamellae, then always preferably decreases substantially symmetrically to the downstream auxiliary lamella 10. This allows to further soften the changes of direction imposed on the fluid, further improving the efficiency of the heat exchanger.

The Applicant thus realized that one could obtain, thanks to the fins according to the invention, an improvement performance of the heat exchanger.

Furthermore, and as illustrated in FIG. 3, a fin may have two series 6-1 and 6-2 of strips 7 or more, such as three, or four.

In order to promote the flow between two superposed fins 1-1 and 1-2, provision is preferably made on each fin for two series 6-1 and 6-2 of identical lamellae, but oriented in opposite directions. Thus, a layer of second fluid which penetrates between, for example, two fins 7-1 of the first group of the first series 6-1 will naturally tend to come out between the two lamellae 7-1 of the second series 6-2, d 'tilt incl ₁ opposite, and placed symmetrically with respect to the YY axis. Similarly, a layer of second fluid which penetrates between two strips 7-2 of the second group of the first series 6-1 will naturally tend to come out between two strips 7-2 of the second series 6-2, of inclination  ₂ opposite, and placed symmetrically with respect to the YY axis.

This circulation is partially materialized on the Figure 3 by the arrows F1 and F2.

The distance from the end of the first 6-1 series to the end of second series 6-2 is usually chosen from so as to allow direct circulation (arrow F3) of the second fluid between the couples made up, on the one hand, of the first strip 7-1 of the first series 6-1 and the downstream auxiliary lamella 10 of this same series 6-1, and on the other hand, the upstream auxiliary lamella 9 of the second series 6-2 and the first strip 7-1 of this second series 6-2. To do this, the two downstream auxiliary blades 10 of the first series 6-1 and upstream 9 of the second series 6-2 are connected either directly to each other or by through a flat 11, as illustrated in the figure 3. Of course, this flat is not essential. he depends in particular on the amplitude of the inclination of the auxiliary lamellae.

According to the Applicant, it is preferable that the difference tilt between two neighboring slats belonging to two groups of successive serial numbers (for example between a first group and a second group) is included between about 1 ° and 15 °, so that the changes in direction of the neighboring layers of second fluid be progressive.

In addition, it is preferable that the maximum angle of inclination of the slats of a series (slats belonging to the group of highest order numbers) is less than 35 °. In the example illustrated in FIG. 3, the three angles of inclination chosen are thus, respectively, equal to 20 ° for  ₀ , 24 ° for  ₁ , and 28 ° for  ₂ . But of course, other values of angle of inclination can be envisaged depending on the configurations chosen.

In the example illustrated in Figure 3, there is shown a fin fitted with two sets of identical louvers, but opposite orientation relative to the Y-Y axis. Moreover, the different fins are superimposed one above the other others, substantially parallel to each other, and identical. We can however consider making fins asymmetrical, i.e. presenting series of non-identical slats. Likewise, the overlapping fins one above the other may be different between them, that is to say present one or more series with groups of fins with respective numbers of slats and the slopes are not identical from one fin to another.

The invention applies equally well to the intermediate fins of the type of those illustrated in Figure 1, that fin plates of the type illustrated in Figure 2.

The invention is not limited to the embodiment described previously, only as an example, but it extends to other variants that those skilled in the art may develop in the context of the claims below.

Claims (16)

Metal fin (1) for a heat exchanger, of the type comprising a central part (12) provided with at least one series (6) of fixed inclined lamellae (7), of selected shape, and spaced from one another by openings (8) of selected dimensions suitable for allowing the passage of a fluid between said lamellae,
characterized in that the lamellae (7) of the same series (6) are divided into at least two groups of at least one unit, the respective inclinations of which vary from group to group, the groups having a number ascending with the inclination of their respective lamellae. Fin according to claim 1, characterized in that that two neighboring lamellae (7-1,7-2) of different inclinations belong to two groups of lamellae whose order numbers follow or precede each other. Fin according to one of claims 1 and 2, characterized in that the slats placed respectively at first row and last row in a series (6) of slats belong to the group of lamellae (7-1) with serial number the lowest, says first group. Fin according to one of claims 1 to 3, characterized in that it comprises at least one series (6) of at least minus two groups of lamellae, called first and second groups, presenting first and second respectively inclinations, said series (6) of lamellae having a median plane of symmetry. Fin according to one of claims 3 and 4, characterized in that it comprises upstream of the lamella (7-1) of the first row a fixed upstream auxiliary lamella (9) of dimensions substantially equal to or greater than those of lamellae (7-i) of the series (6), and spaced from the lamella (7-1) of the first row by an opening (13) of selected shape. Fin according to claim 3 to 5, characterized in what it includes downstream from the last row lamella (7-1) of a series (6) a downstream auxiliary lamella (10) fixed of dimensions substantially equal to or greater than those lamellae (7) of said series, and spaced from said lamellae of the last row by a shape opening (13) chosen. Fin according to one of claims 1 to 6, characterized in that it comprises at least two series (6-1,6-2) of strips (7) which follow each other, one being called series upstream (6-1) and the other downstream series (6-2), and in that two series of neighboring lamellae are interconnected by through the downstream auxiliary lamella (10) of one and the upstream auxiliary lamella (9) on the other. Fin according to one of claims 5 to 7, characterized in that the auxiliary lamellae (9,10) have an inclination less than or equal to that of the slats (7-1) from the first group in the series (6). Fin according to claim 8, characterized in that that the inclination of the auxiliary lamellae (9,10) is lower than that of the slats (7-1) of the first group with a value between approximately 1 ° and approximately 20 °. Fin according to one of claims 7 to 9, characterized in that the series of neighboring lamellae have the same groups of lamellae (7-i). Fin according to claim 10, characterized in that than groups of the same serial number from two series (6-1,6-2) of neighboring slats have orientations opposite. Fin according to one of claims 7 to 9, characterized in that the series of neighboring lamellae have different slat groups. Fin according to one of claims 1 to 12, characterized in that the inclinations of the lamellae (7-i) are included in a range from about 15 ° to about 35 °. Fin according to one of claims 3 to 13, characterized in that the inclination of the lamellae (7-1) of the first group is less than that of the slats of the group whose serial number is the highest of a value between about 1 ° and about 20 °. Fin according to one of claims 1 to 14, characterized in that it is made of aluminum or in a aluminum alloy. Fin according to one of claims 1 to 14, characterized in that it is made of copper.

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