FR3060109A1 - HEAT EXCHANGER WITH A COLLECTOR PLATE OF ALUMINUM ALLOY AND METAL CARBIDE - Google Patents

Abstract

The invention relates to a heat exchanger 1 comprising: • metal tubes 5 parallel to each other and forming a bundle of tubes 7, in which a coolant is able to circulate, and • two collector plates 3, a collector plate 3 being arranged and brazed at each end of the bundle of tubes 7, characterized in that at least one of the collector plates 3 is made of a material comprising: • an aluminum or aluminum alloy matrix, and • inclusions of metal carbide in said matrix, said inclusions of metal carbide having a coefficient of expansion less than the expansion coefficient of the metal tubes 5, and a volume concentration greater than or equal to 5%.

Description

® FRENCH REPUBLIC

NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY © Publication number: 3,060,109 (to be used only for reproduction orders)

©) National registration number: 16 62209

COURBEVOIE © Int Cl ⁸ : F28 F 21/04 (2017.01), F28 F 9/02

A1 PATENT APPLICATION

©) Date of filing: 09.12.16. © Applicant (s): VALEO THERMAL SYSTEMS (30) Priority: Simplified joint stock company - FR. @ Inventor (s): CAPARROS MATHIEU, AZZOUZ KAMEL and DE VAULX CEDRIC. (43) Date of public availability of the request: 15.06.18 Bulletin 18/24. ©) List of documents cited in the report preliminary research: Refer to end of present booklet (© References to other national documents ® Holder (s): VALEO THERMAL SYSTEMS related: Joint stock company. ©) Extension request (s): © Agent (s): VALEO THERMAL SYSTEMS.

HEAT EXCHANGER WITH A COLLECTING PLATE OF ALLOY OF ALUMINUM AND METAL CARBIDE.

FR 3 060 109 - A1 (3 /) The invention relates to a heat exchanger 1 comprising:

metal tubes 5 parallel to each other and forming a bundle of tubes 7, in which a heat transfer fluid is able to circulate, and two collector plates 3, a collector plate 3 being arranged and brazed at each end of the bundle of tubes 7 , characterized in that at least one of the collector plates 3 is made of a material comprising:

an aluminum or aluminum alloy matrix, and metal carbide inclusions in said matrix, said metal carbide inclusions having a coefficient of expansion lower than the coefficient of expansion of metal tubes 5, and a volume concentration greater than or equal at 5 %.

Heat exchanger with a collector plate made of aluminum alloy and metal carbide

The invention relates to the field of heat exchangers and more specifically the field of brazed heat exchangers.

Brazed heat exchangers generally include tubes, parallel to each other, forming a bundle of tubes. The different tubes making up the tube bundle are generally separated by spacers. The ends of the tube bundle are connected to manifolds formed in particular by a collecting plate provided with holes into which the ends of the tubes open which are brazed to the collecting plate. The collecting plate is covered with a water box so as to form the collector. The collectors allow the distribution or recovery of a first heat transfer fluid which passes inside the tubes. A second heat transfer fluid passes between the tubes.

By brazed heat exchanger is meant that the different elements forming the exchanger are fixed together by brazing.

The connections of the tube ends, also called tube feet, with the collector plate are subjected to significant thermal shocks (exposure to significant temperature differences during operation]. These thermal shocks can cause ruptures, generally at the level of the solder joints, or cracking of the tube ends at the collector plate due to the expansion of the collector plate under the effect of thermal shock. This expansion of the collector plate will tend to be subjected to a tensile force at the ends of the brazed tubes. This tensile force can cause cracking in this area, which cracking can then lead to leakage. Furthermore, this traction of the collector plate can damage the brazing joints between the tubes and the collector plate The solder can break under the force of this force. ity of the connection of the tube with the collector plate is no longer ensured.

Document EP 2871437 discloses a heat exchanger composed of two superimposed collectors allowing a reinforcement of the tube / collector connection at the ends of the tubes.

However, the addition of a second manifold results in a significant increase in the distance between the manifold and the spacers, which decreases the performance of the heat exchanger. Furthermore, the addition of a second collector leads to an increase in the manufacturing costs of such a heat exchanger because the requirements for raw materials are considerably increased.

Also known from document KR 20150070772 is a heat exchanger having “clip” type inserts integrated into the tubes having the greatest stresses linked to expansion under the effect of thermal shocks. These inserts make it possible to reinforce the tube / collector connection by means of an increase in the thickness of material in the zone considered.

However, the manufacture of such a heat exchanger requires a modification of the manufacturing process in order to allow the integration of the inserts. Furthermore, the manufacture of such a heat exchanger is also more expensive since it involves an increase in the quantities of raw material necessary for the manufacture of such a heat exchanger. In addition, the inserts are not present in all the tubes, so it is not certain that all of the tubes making up the bundle of tubes are protected from thermal shock by the insertion of such inserts. Furthermore, it will be necessary to adapt the manufacturing methods to adapt the number of inserts according to the size of the heat exchanger, and also to arrange the inserts inside the tubes.

One of the objectives of the present invention is to at least partially overcome the problems of the prior art by proposing a brazed heat exchanger having brazings between the ends of the bundle tubes and the collector plate which are less sensitive to the expansion linked to thermal shocks than the heat exchangers of the prior art.

Another objective of the present invention is to propose a brazed heat exchanger presenting a limited risk of cracking of the ends of the tubes due to the expansion of the collector plate linked to thermal shocks.

Another object of the present invention is to provide a brazed heat exchanger less sensitive to the phenomena of expansion linked to thermal shocks which does not require adaptation of the manufacturing process of the heat exchanger.

Another object of the invention is to provide a heat exchanger which does not require the addition of material, and therefore an increase in manufacturing costs, in order to increase its resistance to expansion linked to thermal shocks.

To this end, the subject of the invention is a heat exchanger comprising:

• metal tubes parallel to each other and forming a bundle of tubes, in which a heat transfer fluid is able to circulate, and • two collector plates, a collector plate being arranged and brazed at each end of the bundle of tubes, with at at least one of the collector plates is made of a material comprising:

• an aluminum or aluminum alloy matrix, and • metal carbide inclusions in said matrix, said metal carbide inclusions having a coefficient of expansion lower than the coefficient of expansion of metal tubes, and a higher volume concentration or equal to 5%.

The presence of metallic carbide inclusions in the collector plate makes it possible to reduce the coefficient of expansion of the latter under the effect of thermal shocks. Thus, this plate is less prone to deformation, which makes it possible to reduce the tensile forces undergone by the solderings as well as by the ends of the tubes. The presence of metal carbide in the collector plate therefore makes it possible to increase the resistance to thermal shocks of such a heat exchanger.

Furthermore, the presence of metal carbide in the aluminum matrix of the collector plate makes it possible to preserve the architecture of the latter and therefore of the heat exchanger. The manufacturing process of such an exchanger therefore also remains unchanged and therefore does not lead to an increase in costs.

In addition, keeping the same architecture makes it possible to have a heat exchanger whose mass remains similar to existing heat exchangers.

The heat exchanger may also include one of the following characteristics, taken alone or in combination:

The metal carbide inclusions have an average size of between 5 µm and 50 µm, preferably between 15 µm and 35 µm.

The expansion coefficient of the collector plate made of a material comprising the metal carbide inclusions is at least 10% lower than the expansion coefficient of the metal tubes.

The heat exchanger comprises at least one box brazed on at least one header plate, said box being made of a material identical to the header plate on which said box is brazed.

Metal carbide is silicon carbide.

The matrix has a concentration for inclusions of silicon carbide of between 10% and 60% by volume.

The metal tubes are made of aluminum or an aluminum alloy.

Alternatively, only the header plate in contact with the heat transfer fluid before it flows through the tubes of the heat exchanger (header plate which is therefore in contact with the hottest heat transfer fluid, upstream of its flow in the tubes to be cooled) is made of a material comprising inclusions of metal carbide.

According to another variant, the two collector plates of the heat exchanger are made of a material comprising inclusions of metallic carbide.

Other characteristics and advantages of the invention will appear on reading the following description, given by way of illustrative and nonlimiting example, and the appended drawings in which:

FIG. 1 is a schematic view of the heat exchanger having a box brazed on each of the manifold plates,

FIG. 2 is a schematic representation of the aluminum matrix comprising inclusions of metallic carbide,

- Figure 3 is a graph showing the evolution of the coefficient of thermal expansion of the aluminum matrix comprising inclusions of silicon carbide as a function of the volume concentration of silicon carbide in this matrix.

In these figures, identical elements have the same reference numerals.

The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the characteristics apply only to a single embodiment. Simple features of different embodiments can also be combined or interchanged to provide other embodiments.

In the following description, reference is made to a first heat transfer fluid and to a second heat transfer fluid, or else to a first collecting plate and to a second collecting plate. This is simple indexing to differentiate and name similar but not identical elements. This indexing does not imply a priority of one element over another and one can easily interchange such names without departing from the scope of this description. This indexing does not imply an order in time either.

With reference to FIG. 1, the heat exchanger 1 comprises metal tubes 5, two collector plates 3 on either side of the metal tubes 5, spacers 10, and at least one box 9 allowing in particular the entry and the output of a first heat transfer fluid in the heat exchanger 1, such as for example coolant.

The metal tubes 5 are arranged in parallel with one another and form a bundle of tubes 7. The metal tubes 5 can be made of aluminum or an aluminum alloy. Furthermore, the metal tubes 5 are configured to allow the circulation within them of the first heat transfer fluid.

A second heat transfer fluid, for example air, is intended to circulate between the metal tubes 5. Dividers 10 can be arranged between the metal tubes 5 of the bundle of tubes 7. The purpose of these dividers is to disturb the flow of the second heat transfer fluid and also to increase the exchange surface between the first and second heat transfer fluids. The spacers 10 are preferably made of the same material as the metal tubes 5 and are brazed with these tubes.

With reference to FIGS. 1 and 2, a collecting plate 3 is arranged and brazed at each end of the bundle of tubes 7. At least one of the collecting plates 3 is made of a material comprising:

• a matrix 11 of aluminum or aluminum alloy, and • inclusions 13 of metal carbide in said matrix 11, said inclusions 13 of metal carbide having a coefficient of expansion lower than the coefficient of expansion of metal tubes 5, and a volume concentration greater than or equal to 5%.

The collector plate 3 comprising inclusions 13 of metal carbide has a lower coefficient of expansion than the collector plates 3 made of aluminum or an aluminum alloy without inclusions 13 of metal carbide. When a collector plate 3 comprising inclusions 13 undergoes thermal shocks, the deformation associated with the expansion thereof is less significant than that undergone by a collector plate 3 composed solely of aluminum or an aluminum alloy. Thus, the tensile stresses that the metal tubes 5 undergo, in particular at their ends are lower. The metal tubes 5 making up the bundle of tubes 7 therefore present a lower risk of cracking because they undergo a lower tensile force.

Furthermore, the use of metal carbide also makes it possible to obtain better resistance of the brazings connecting the collecting plate 3 to the metal tubes 5 since they also undergo lower tensile stresses than the brazing of the heat exchangers 1 having collecting plates 3 consist only of aluminum or an aluminum alloy without inclusions 13 of metal carbide. A volume concentration greater than or equal to 5% in metal carbide allows in particular a reduction in the coefficient of expansion sufficient for the tensile forces on the metal tubes 5 to be lower.

The expansion coefficient of the collector plate 3 made of a material comprising the inclusions 13 of metal carbide is at least 10% lower than the expansion coefficient of the metal tubes 5. Thus, the collector plate 3 will deform less than the metal tubes 5 during thermal shock. Thus, the improvement of the longevity of the metal tubes 5, for the tensile forces on the said metal tubes 5, of the solders, which are less stretched, and therefore of the heat exchanger 1 is possible.

According to the embodiment of Figure 1, the heat exchanger 1 comprises two boxes 9 brazed on each header plate 3 of the heat exchanger 1. These boxes 9 allow the circulation of the first heat transfer fluid in the heat exchanger 1. According to this particular embodiment, the box 9 is made of a material identical to that of the collector plate 3 on which the box 9 is brazed, that is to say a material comprising inclusions 13 of metal carbide in the matrix 11 of aluminum or aluminum alloy composing this box 9.

Referring to Figure 2 which is a schematic representation of the matrix 11 of aluminum or aluminum alloy comprising inclusions 13 of metal carbide, these inclusions 13 have an average size of between 5 μm and 50 μm. According to a preferred embodiment, the inclusions 13 have a size of between 15 μm and 35 μm. Advantageously, the use of inclusions 13 having a size of between 15 μm and 35 μm makes it possible to obtain a homogeneous distribution of these and contributes to obtaining good quality brazing without having to adapt the method of this last.

According to the particular embodiment of Figure 1 when the collector plate 3 has the matrix 11 of Figure 2, the inclusions 13 do not have a specific shape.

According to another embodiment not shown here, the inclusions 13 can have a particulate shape such as a spherical or cylindrical shape for example. Particulate inclusions are simple to implement, they do not require complicating the process of obtaining with particular treatments.

According to a particular embodiment, the metal carbide used for the inclusions 13 in the matrix 11 can be silicon carbide (SiC). This alloy comprising aluminum and silicon carbide has a low coefficient of expansion, compared to the aluminum alloys conventionally used for the production of collector plates 3, which makes it a good candidate for the resistance to thermal shocks of header plates 3 of the heat exchanger 1.

On the other hand, the thermal conductivity of silicon carbide is quite close to that of aluminum, which makes it possible to obtain a heat exchanger 1 having performances close to those of an exchanger solely composed of aluminum or d '' an aluminum alloy.

Silicon carbide also has mechanical properties close to those of aluminum. This allows the same brazing process to be used as that used for the manufacture of a heat exchanger 1 not having inclusions 13 of silicon carbide in its matrix 11 of aluminum or aluminum alloy. Thus, it is not necessary to adapt the manufacturing process using this alloy comprising inclusions 13 of metal carbide, and in particular silicon carbide, which allows maintenance of the production costs of such heat exchangers 1.

According to a particular embodiment not shown here, only the collector plate in contact with the heat transfer fluid before it flows through the tubes of the heat exchanger (collector plate in contact with the hottest heat transfer fluid, upstream of its flow in the tubes to be cooled) is made of a material comprising inclusions 13 of metal carbide. According to this particular embodiment, the second collector plate 3 of the heat exchanger 1 is made of aluminum or an aluminum alloy, generally identical to that of the metal tubes 5. In fact, the collector plate 3 located at the inlet of the heat exchanger vis-à-vis the direction of flow of the heat transfer fluid within the exchanger, undergoes the most significant thermal shocks. Thus, it is necessary to limit the expansion of this collector plate 3 linked to these thermal shocks so as to prevent the appearance of cracks at the ends of the metal tubes 5 or even the breakage of the solders between the collector plate 3 and the tubes metallic 5 due to the tensile forces that these elements will intrinsically undergo during the operation of the heat exchanger 1.

According to the embodiment of Figure 1, the two header plates 3 of the heat exchanger 1 are made of a material comprising inclusions 13 of metal carbide. Advantageously, this embodiment makes it possible to produce only one type of collector plates 3 and therefore to maintain good production rates for the heat exchanger 1 without having to identify the collector plates 3 comprising the inclusions 13 of metal carbide manifold plates 3 not having one.

With reference to FIG. 3 which corresponds to a graph representing a curve 20 corresponding to the change in the coefficient of thermal expansion of the alloy as a function of the volume concentration of silicon carbide. According to FIG. 3, the curve 20 is a straight line where the coefficient of thermal expansion decreases with the increase in the volume concentration of silicon carbide in the aluminum alloy.

According to FIG. 3, the coefficient of thermal expansion of the aluminum alloy conventionally used in the composition of the tubes 5 and of the collector plate 3 is approximately 21 ppm / ° C. According to FIG. 3, the addition of silicon carbide makes it possible to reduce the coefficient of expansion of the alloy comprising inclusions 13 in a linear fashion according to the volume concentration of silicon carbide present in the alloy. For example, a volume concentration of 10% of silicon carbide makes it possible to obtain an alloy having a coefficient of thermal expansion of approximately 18.75 ppm / ° C, which corresponds to a reduction of approximately 10% of the coefficient of thermal expansion of the alloy comprising inclusions 13 of silicon carbide relative to the coefficient of thermal expansion of a standard aluminum alloy.

Advantageously, the inventors have shown that when the matrix 11 has a concentration for the inclusions 13 of silicon carbide, of between 10% and 60% by volume, the coefficient of expansion of the collector plate 3 is sufficiently low to limit the appearance cracks at the ends of the metal tubes 5 or the rupture of the solders between the metal tubes 5 and the collector plate 3. The inventors have also noticed that when the concentration of silicon carbide is within 10% by volume, the coefficient of expansion of the collector plate 3 remains too high to prevent the appearance of cracks at the ends of the metal tubes 5 or the rupture of the solders between the collector plate 3 and the metal tubes 5. Furthermore, the inventors have also noticed that when the volume concentration of silicon carbide is greater than 60% by volume, the brazing between the metal tubes 5 of the lai tube seal 7 and the collector plate 3 is more difficult to achieve.

Advantageously, for a volume concentration of between 10% and 60% of the inclusions 13 of silicon carbide, in the matrix 11 of the collector plate 3, the collector plate 3 has an optimal coefficient of expansion for its use, in particular for the realization of 'a heat exchanger having for example bent tubes with double circulation channels, called "B". More specifically, when the volume concentration of silicon carbide is 10%, the coefficient of expansion of the collector plate 3 is within 10% relative to the coefficient of expansion of the metal tubes 5, as shown in Figure 3. This decrease the coefficient of expansion makes it possible to obtain a coefficient of expansion sufficiently reduced to limit the risks of cracking of the metal tubes 5 or else the risks of rupture of the solder at the ends of the metal tubes 5 and of the collector plate 3.

According to another embodiment not shown here, the metal carbide can be nickel carbide (NiC). Nickel carbide has characteristics close to those of silicon carbide and therefore similar advantages.

These exemplary embodiments are turned by way of illustration and not limitation. Indeed, it is entirely possible for those skilled in the art, without departing from the scope of the invention, to replace the silicon carbide with any other metallic carbide making it possible to reduce the coefficient of thermal expansion of the collector plate 3.

Thus, the reduction in the appearance of cracks at the ends of the 10 metal tubes 5 and the reduction in ruptures at the level of the solders between the collector plates 3 and the metal tubes 5 of a brazed heat exchanger 1, linked to shocks thermal, is possible thanks to the presence of inclusion 13 of metal carbide, and in particular of silicon carbide, in the matrix 11 of aluminum or aluminum alloy composing the collecting plates 3 arranged on each side of the sheet 7 of metal tubes 5. These inclusions 13 make it possible to reduce the coefficient of expansion of the collector plates 3 and thus the tensile forces which the ends of the metal tubes 5 or the brazings undergo. Advantageously, the presence of inclusion 13 of metal carbide in the matrix 11 of the collector plates 3 makes it possible to keep the same processes of labrication and brazing. In addition, the modification of the alloy makes it possible to keep the same structure of heat exchanger 1 as those known in the state of the art, the addition of material is therefore not necessary to increase the resistance of such a heat exchanger 1 to thermal shock.

Claims (9)

1. Heat exchanger (1) comprising: • metal tubes (5) parallel to each other and forming a bundle of tubes (7), in which a heat transfer fluid is able to circulate, and • two collecting plates (3), a collecting plate (3) being arranged and brazed at each end of the bundle of tubes (7), characterized in that at least one of the collector plates (3) is made of a material comprising: • a matrix (11) of aluminum or of aluminum alloy, and • inclusions (13) of metallic carbide in said matrix (11), said inclusions (13) of metallic carbide having a coefficient of expansion lower than the coefficient metal tubes (5), and a volume concentration greater than or equal to 5%. 2. Heat exchanger (1) according to claim 1, wherein the inclusions (13) of metal carbide have an average size between 5 pm and 50 pm, preferably between 15 pm and 35 pm. 3. Heat exchanger (1) according to any one of the preceding claims, in which the coefficient of expansion of the collecting plate (3) made of a material comprising the inclusions (13) of metal carbide is less than at least 10 % to the coefficient of expansion of the metal tubes (5). 4. Heat exchanger (1) according to any one of the preceding claims, comprising at least one box (9) brazed on at least one header plate (3), said box (9) being made of a material identical to the plate manifold (3) on which said box (9) is brazed. 5. Heat exchanger (1) according to any one of the preceding claims, in which the metal carbide is silicon carbide. 5 6. Heat exchanger (1) according to claim 5, wherein the matrix (11) has a concentration for the inclusions (13) of silicon carbide between 10% and 60% by volume. 7. Heat exchanger (1) according to any one of the preceding claims, in which said metal tubes (5) are composed of aluminum or an aluminum alloy. 8. Heat exchanger (1) according to any one of the preceding claims, in which only the collector plate (3) which is in contact with the 15 hottest heat transfer fluid of the heat exchanger (1) is made of a material comprising inclusions (13) of metal carbide. 9. Heat exchanger (1) according to any one of claims 1 to 7, in which the two header plates (3) of the heat exchanger (1) are 20 made of a material comprising inclusions (13) of metal carbide.