FR2907887A1 - Heat exchanger for motor vehicle, has fin portions respectively fixed in contact with fluid circulation tubes, where tubes are covered with filler metal plating at level of contact and fin portions are free from plating near rupture - Google Patents

Abstract

The exchanger has two fin portions (21B, 23B) respectively fixed in contact with fluid circulation tubes (3, 5) by brazing. The portions are separated with respect to each other by a material rupture (19B). The tubes are placed along an external fluid flow direction and are covered with a filler metal plating at the level of contact. The fin portions are free from the filler metal plating near the material rupture that is in the shape of a slit. An independent claim is also included for a method for fabricating a heat exchanger.

Description

Heat exchanger protected against thermal bridges and method of

  The invention relates to a heat exchanger and a method of manufacturing a heat exchanger. It is known that a heat exchanger has the function of ensuring a heat exchange between a first fluid and a second fluid. In particular, the first fluid can circulate inside tubes while the second fluid passes freely through the exchanger. To improve heat exchange, it is known to place heat exchange fins in contact with the tubes. These fins increase the heat exchange surface between the first and second fluids. Particular heat exchangers comprise a series of first tubes, or bundle, and a series of second tubes, facing each other. The first and second tubes 20 may be connected to each other, for example two by two, so that the first fluid entering the exchanger circulates first in a first tube and then in a second tube, before emerging from the exchanger. It is understood that the temperature of the fluid in the first tube is quite different from the temperature of the fluid in the second tube, because of the heat exchange existing at the first tube. In general, it is preferred to have the same heat exchange fin in contact with an assembly formed of a first and a second tube: this facilitates, among other things, the assembly of the exchanger. Sometimes, a different fin is available in contact with each of the first and second tubes. When the same fin is in contact with a first and a second tube, a first fin portion in contact with the first tube is in a temperature condition quite different from a second contact fin portion. the second tube. Thus, the fin tends to influence the temperature conditions of the fluid in the tubes by heat transfer occurring between the first and second fin portions. This effect is unfortunate in that it adversely affects the performance of the heat exchanger.

  It has therefore been proposed to provide a rupture of material in the fin, at least partially separating the first and second portions of fins. The thermal bridge formed between the first and second portions of fins is thus considerably reduced.

  In such exchangers, the fins and the tubes are quite often held together by brazing: the fins coated with a plating of filler metal are placed in contact with the fluid circulation tubes, then passed into a brazing furnace. The melting of the plating of filler metal ensures the attachment of the fin in contact with the tubes. The soldering fins having a material rupture, of the type mentioned above, often causes a deposition of filler metal covering said rupture of material: a thermal bridge is recreated between the first and second portions of fins, and found the aforementioned disadvantages.

  When a particular fin is disposed in contact with each of the first and second tubes, there is obviously an absence of material between the first fin portion in contact with the first tube and the second fin portion in contact with the second tube. . However, the brazing operation may result in deposition of filler metal joining the fins (or portions of fins) and thermal bridges are then created.

The object of the invention is to overcome the aforementioned drawbacks by proposing a heat exchanger, of the type comprising a first portion of heat exchange fin and a second portion of heat exchange fin respectively fixed, by brazing, in contact with a first fluid circulation tube and a second fluid circulation tube, said first and second portions being at least partially separated from each other by at least one material rupture, the first tube and the second tube being coated with a plating of filler metal, at least at said contact, while the first and second fin portions are free of plating of filler metal, at least in the vicinity of each rupture of matter.

Thus, the invention avoids thermal bridges being recreated after brazing. In an advantageous embodiment, the first tube and the second tube are substantially completely plated with filler metal. The first and second fin portions preferably have substantially no plating of the filler metal. In a particular embodiment, the first tube is intended to ensure a flow of fluid in a first pass while the second tube is intended to ensure a circulation of said fluid in a second pass. Preferably, the exchanger being intended to be traversed by an external fluid flow, the first tube and the second tube are arranged substantially aligned in the direction of an external fluid flow. Advantageously, each heat exchange fin has a generally undulating shape, composed of 4 bent portions interconnected by substantially flat portions. In this case, the first fin portion preferably comprises a bent portion and a substantially planar portion. In particular, the rupture of material may comprise a cut through a bent portion and a substantially planar portion. In both cases, the material break may comprise a partial cut of a substantially flat portion providing continuity of material between the first and second fin portions. Advantageously, the rupture of material is in the form of a slot cut in a heat exchange fin. In a particular embodiment, said first fin portion and said second fin portion are portions of a same heat exchange fin.

In any case, at least one of the first and second fluid circulation tubes may be made by extrusion. The invention also provides a method of manufacturing a heat exchanger of the type comprising a first heat exchanger fin portion and a second heat exchange fin portion in contact with a first heat exchange fin tube respectively. fluid circulation and a second fluid circulation tube, said first and second portions being at least partially separated from each other by at least one material break, the method comprising a step of brazing the first and second (23B) fin portions at the first and second tubes, respectively, a step of coating the first and second tubes with a plating of filler metal, at least at said contact, prior to at the fixing step, a step of providing the first and second fin portions without a filler metal plate, at least in the vicinity of each material break, ally at the fixing step. In particular, the method may further comprise a step of placing the first and second coated tubes in contact with the first and second veneer portions devoid of plating, prior to the fixing step. Other features and advantages of the invention will become apparent on reading the detailed description below and the drawings in which: FIG. 1 is a perspective view of a heat exchanger according to the invention; FIG. 2 is a perspective view of part of the exchanger of FIG. 1; FIG. 3 is a view from above of a portion of a heat exchange fin in a variant embodiment; FIG. 4 is a top view of a portion of a heat exchange fin for the exchanger of FIG. 1; FIG. 5 is a top view of a portion of a fin of FIG. heat exchange according to the state of the art.

The accompanying drawings may not only serve to complete the invention, but may also contribute to its definition, as appropriate. Reference is first made to FIG.

The heat exchanger 1 comprises a bundle of first fluid circulation tubes 3 aligned with each other and a bundle of second fluid circulation tubes 5 aligned with each other. Each time, a first tube 3 is vis-à-vis a second tube 5. The exchanger is intended to be traversed by an external fluid flow. Here, each first tube 3 is aligned with a second tube 5 substantially in the direction of this external fluid flow. The tubes 3 and 5 can be obtained for example by extrusion. The first tubes 3 open at one of their ends in an inlet manifold 7, while the second tubes 5 open at one of their ends in an outlet manifold 9. Each time, a first tube 3 and a second tube 5 are connected together in fluid communication at their ends not opening into the collectors 7 and 9. The first tubes 3 can thus ensure a flow of fluid in a first pass while the second 20 tubes 5 provide circulation said fluid according to a second pass. Here, each assembly formed of a first tube 3 and a second tube 5 is made integrally. In particular, the first tubes 3 and the second tubes 5 are made from tubes folded so as to have a general shape of U, the first tubes 3 and second tubes 5 forming the branches of said U. Of course, the first 3 and second 5 tubes may be in the form of two separate straight tubes interconnected by any suitable device, for example a junction box or bend. The tubes 3 and 5 can be obtained for example by extrusion.

In FIG. 1, each first tube 3 and second tube 5 has a plurality of fluid circulation channels 11. The invention applies in the same way to the case where only one circulation channel is provided in these tubes.

Each time, a heat exchange fin 13 is disposed in contact with a first 3 and a second tube 5. The fins 13 have a generally undulating shape defining a succession of substantially planar portions 15 connected to each other by bent portions 17. Reference is now made to FIG. 2, which shows a fin 13.

Some flat portions 15A of fin 13 exhibit a total material breakage 19A extending across the entire width of the planar surface. The rupture of material 19A can extend to the bent portion 17A extending the flat portion 15A. The rupture of material 19A can also extend to an adjacent flat portion 15A and extending the angled portion 17A. Thus, the total material break 19A can extend over a plurality of successive flat portions 15A of the fin 13. In FIG. 2, the material break 19A is made in the form of a cut of the flat surface 15A on its entire width and over a chosen length, for example 25 substantially close to the spacing between the tubes 3 and 5. As shown in Figure 3, the rupture of material 19A can also take the form of a slot made by cutting 30 of the flat surface 15A over its entire width. In this case, there is no drop of material. In any case, the rupture of material 19A thus separates first vane portions 21A in contact with a first tube 3 and second vane portions 23A in contact with a second tube 5. Other flat surfaces 15B present a partial material break 19B extending over only a portion of the width of the flat surface 15B. Such a planar surface 15B is shown in FIG. 4. Here, the material break 19B takes the form of one or more slots made by cutting the flat surface 15B. The breaking of material 19B does not produce a material drop. The rupture of material 19B may further extend over the bent portion 17B extending the flat surface 15B. As shown in FIG. 4, a planar surface 15B may have two material breaks 19B facing each other, each starting from an angled portion 17B opposite and providing a continuity of material 20 in the planar surface 15B. It will be understood that the two material breaks 15B of FIG. 4 may, where appropriate, be seen as the same rupture made in two parts. The material break (s) 19B of the planar surface thus partially separates a first fin portion 21B in contact with a first tube 3 from a second fin portion 23B in contact with a second tube 5. Thus, a link mechanics is maintained between the first 21B and second 23B portions of a surface 15B, giving it a certain mechanical strength, or rigidity, or stiffness. The surfaces 15B therefore contribute to the mechanical rigidity of the fin 13 as a whole. This allows in the assembly phase to handle a single fin 13 for the tubes 3 and 5.

The mechanical link dimension is variable and can be approximately 0.5 mm. The proportion of the planar 15A / bent surfaces 17A with a total material breakage 19A with respect to the planar 15B / bent surfaces 17B exhibiting a total material break 19B with a partial material break 19B is variable. This number results from a compromise between the necessary rigidity of the fin 13 and the desire to reduce as much as possible the number of thermal bridges in this fin 13. For example, a flat surface 15B with partial rupture can be provided. 19B every 20 or 40 planar surfaces 15A to total failure 19A. As mentioned above, the total material 19A or partial 19B breaks prevent, respectively reduce, the thermal bridges between the first 21A (respectively 21B) and the second 23A (respectively 23B) fin portions. The width of the partial material breaks 19B as well as that of the total material breaks 19A can be variable. In particular, they may be different from each other. According to the invention, the fin 13 is devoid of plating of filler metal in the vicinity of the partial ruptures 19B. Preferably, the fin 13 is also free of plating of filler metal in the vicinity of the total breaks 19A. In an advantageous embodiment, the entire surface of the fin 13 is devoid of plating of filler metal, which makes it possible to dispense with any coating of the fin 13. According to the invention, the tubes 3 and 15 are coated with a plating of filler metal.

The plating of the filler metal is formed essentially of an identical metal or alloy, here in aluminum, to that of the tubes 3 or 5. The plating of the filler metal comprises a proportion of silicon (Si) of between 6% and 12%, while the metal or alloy to which the plating is applied comprises between 0.1% and 0.9% silicon (Si). Thus, with the use of a heating furnace, the formation of a viscous paste on the surface of the plating of filler metal from about 577 Celsius (C) is obtained while the core of the metal veneer remains solid. This paste can also fill the spaces and vacuity between two components of an assembly: here between the angled surfaces 17A and one or other of the tubes 3 or 5 at the place where the soldering is to take place. welding and, after cooling, braze / solder all tightly and robustly.

It should also be noted that the plating of filler metal may have traces or low percentages of other metals, such as iron (Fe), copper (Cu), manganese (Mn), zinc (Zn) chromium (Cr), nickel (Ni), titanium (Ti), zirconium (Zr), vanadium (V) and magnesium (Mg). As examples, two particular compositions of plating of filler metal are indicated below, without indicating the share of aluminum. As will be seen below, when the exchanger is brazed, virtually no deposition of filler metal covers the partial 19B or 19A total material failures. This makes it possible to keep the material fractures 19A and 19B intact without recreating thermal bridges.

The invention also relates to a method of manufacturing an exchanger 1. A step consists in coating the first 3 and second 5 tubes with a plating of filler metal, at least at the level of the portions intended to come into contact with each other. with the fins 13. Preferably, the entire surface of the first 3 and second 5 tubes are coated, because industrially it is easier and cheaper to coat all of a tube than parts of it.

Subsequently or in parallel, a step is to pre-see fins 13 whose first 21B and 23B seconds portions are free of filler metal plating, at least in the vicinity of each material break 19B. Optionally, fins 13 are provided whose first 21A and second 23B portions are also free of filler metal plating, at least in the vicinity of each material break 19A. One step is to place the first 3 and second coated tubes 5 in contact with the first 21A, 21B and second 23A, 23B veneer portions without plating.

One step is to braze the first 21A, 21B and second 23A, 23B fin portions to the first 3 and second tubes 5, respectively. This step may include passing through a brazing furnace.

The Applicant has noted the absence of metal deposition at the material failures 19A and 19B material failures. Thus the thermal bridges avoided due to material failures are not recreated. This results in a significant improvement in the performance of the heat exchanger according to the invention compared to the exchangers of the state of the art. FIG. 5 illustrates a heat exchange fin according to the state of the art. It is noted that the material breaks 19B, made in the form of slots, are filled by the solder, recreating a thermal bridge between the portions 21B and 23B. After brazing, the fin 13 according to the invention is identical to the fin of FIG. 4. The breaks 19B, made in the form of slots, remain open. The dimension of the mechanical link 20 between the portions 21B and 23B is unchanged. The thermal bridge between the portions 21B and 23B can be controlled in that its dimensions remain unchanged after brazing. By overcoming these disadvantages relating to thermal bridges, the invention allows the use of heat exchange fins 13 in contact with both a first tube 2907887 12 and a second tube 5. It avoids the prediction of two fully separated half-fins, each being in contact with a first tube 3 or a second tube 5. This considerably simplifies the structure and assembly of the exchanger 5 1. The invention is particularly adapted to the case of heat exchangers in which circulates a fluid in the sub-critical state. Indeed, in this use, the temperature difference between the fluid flowing in the first tubes 3 and the fluid flowing in the second tubes 5 is greater than in conventional exchangers.

For example, the fluid may be carbon dioxide (CO2). In this case, the fluid circulating in the first tube may be at a temperature in the region of 130 ° C., whereas when it passes into the second tube, its temperature can be reduced to approximately 40 ° C. In the description given above, above, the first 21A and the second 23A portions of fins are part of a same heat exchange fin 13. It is understood that the invention applies analogously to the case where these first 21A and 23A second portions of fins belong to separate heat exchange fins, that is to say in the case where a first heat exchange fin is disposed in contact with the tube 3 and a second heat exchange fin The invention therefore also applies in the case where the breaking of total material 19A extends over all the portions 35 of the fin 13. In the same manner, the invention applies to heat exchangers with more than one x rows of fluid circulation tubes. Material failures 19A and / or 19B may be partially and / or wholly between each row of tubes. The invention is not limited to the embodiment described above, but encompasses all the variants that can be envisaged by those skilled in the art.

Claims (14)

claims   1. Heat exchanger, of the type comprising a first portion of heat exchange fin (21B) and a second portion of heat exchange fin (23B) respectively fixed, by soldering, in contact with a first tube fluid circulation system (3) and a second fluid circulation tube (5), said first and second portions being at least partially separated from each other by at least one material rupture (19B), characterized in that that the first tube and the second tube are coated with a plating of filler metal, at least at said contact, while the first and second fin portions are free of filler metal plating, at least neighborhood of each material break (19B).   2. Heat exchanger according to claim 1, characterized in that the first tube (3) and the second tube (5) are substantially completely coated plating filler.   3. Heat exchanger according to one of claims 1 and 2, characterized in that the first (21B) and second (23B) fin portions are substantially completely free of plating of filler metal.   4. Exchanger according to one of the preceding claims, characterized in that the first tube (3) is intended to ensure a flow of fluid in a first pass while the second tube (5) is intended to ensure a circulation of said fluid according to a second pass.   5. Heat exchanger according to one of the preceding claims, characterized in that, the exchanger being intended to be traversed by an external fluid flow, the first tube (3) and the second tube (5) are arranged so substantially aligned in the direction of an external fluid flow. 14 2907887 15   6. Heat exchanger according to one of the preceding claims, characterized in that each heat exchange fin has a generally undulating shape, composed of angled portions (17A, 17B) interconnected by substantially flat portions (15A , 15B).   7. Exchanger according to claim 6, characterized in that the first fin portion (21B) comprises a bent portion (17B) and a substantially planar portion (15B).   8. Heat exchanger according to claim 7, characterized in that the rupture of material (19B) comprises a cut through a bent portion (17B) and a substantially flat portion (15B). 15   9. Heat exchanger according to one of claims 7 to 8, characterized in that the rupture of material comprises a partial cut of a substantially planar portion (15B) providing a continuity of material between the first 20 (21B) and second (23B) portions of fin.   10. Heat exchanger according to one of the preceding claims, characterized in that the rupture of material (19B) is in the form of a slot cut in a heat exchange fin.   11. Heat exchanger according to one of the preceding claims, characterized in that said first fin portion (21B) and said second fin portion (23B) 30 are portions of the same heat exchange fin (13).   12. Heat exchanger according to one of the preceding claims, characterized in that at least one of the first 35 and second (5) fluid circulation tubes is made by extrusion.   13. A method of manufacturing a heat exchanger of the type comprising a first heat exchange fin portion (21B) and a second heat exchange fin portion (23B) in contact with respectively a first fluid circulation tube (3) and a second fluid circulation tube (5), said first and second portions being at least partially separated from each other by at least one material rupture (19B) , the method comprising at. a step of brazing the first (21B) and second (23B) fin portions to the first (3) and second tubes (5), respectively, characterized in that the method further comprises: . a step of coating the first (3) and second (5) tubes with a plating of filler metal, at least at said contact, prior to step a. c. a step of providing the first (21B) and second (23B) fin portions without plating of filler metal, at least in the vicinity of each material break (19B), prior to step a. 25   14. The method of claim 13, characterized in that it further comprises: d. a step of placing the first (3) and second (5) coated tubes in contact with the first (21B) and second (23B) non-veneeable fin portions prior to step a.