HEAT EXCHANGER WITH LIQUID CIRCULATION TUBE AND PROTECTION AGAINST MICROMETEORITES

Description

Technical field of the invention

[0001] The invention relates to a heat exchanger and a method for manufacturing said exchanger. In particular, the invention relates to a heat exchanger which may be of the stainless steel-aluminum type or other combinations of two materials for use in an aeronautical or space context. Technological background

[0002] Heat exchangers used in the aeronautical or space field may take the form of a casing, preferably made of aluminum, surrounding a tube, preferably made of stainless steel (commonly called stainless steel), in which a fluid circulates, in particular for heat transfer from the fluid to the outside of the casing via the tube and the casing. A heat exchanger according to the preamble of claim 1 is known from document US 9,897,383 B2.

[0003] The assembly of the exchanger is generally carried out by welding or soft soldering of the casing with the tube arranged in said casing.

[0004] The use of welding or soldering for the assembly of the exchanger has several disadvantages.

[0005] The main disadvantage of assembly by welding or soft soldering is the difficulty of industrialization for the production of several parts.

[0006] To address these issues, the inventors sought to use brazing that would facilitate the industrialization of the exchanger through the use of a furnace. However, the use of brazing leads to problems related to the higher temperature of brazing, which generally rises to more than 600°C compared to less than 450°C for soft brazing.

[0007] In particular, the assembly by brazing of elements of two materials of different nature generates differential expansions between the two materials due to their different coefficients of thermal expansion, which can lead to decohesions of the heat exchanger due to brazing. This can compromise the mechanical strength of the exchanger and specific solutions must be put in place to manage these thermal stresses during brazing.

[0008] Furthermore, the use of such an exchanger in a space domain requires the installation of protection for the fluid circulation tube against micrometeorites which could cause damage to said tube, even causing a fluid leak if the tube is pierced.

[0009] The inventors therefore sought a solution to guarantee the mechanical strength of the exchanger, the management of these thermal constraints during brazing, and the protection of the tube against micrometeorites. Objectives of the invention

[0010] The invention aims to provide a heat exchanger and a method of manufacturing said exchanger.

[0011] The invention aims in particular to provide, in at least one embodiment, an exchanger having a simple and industrializable assembly.

[0012] The invention also aims to provide, in at least one embodiment of the invention, a heat exchanger adapted to the thermal constraints of brazing.

[0013] The invention also aims to provide, in at least one embodiment of the invention, a heat exchanger comprising protection of the fluid circulation tube against the impacts of micrometeorites. Statement of the invention

[0014] To do this, the invention relates to a heat exchanger comprising a tube for circulating a fluid and configured to allow heat exchange between the fluid circulating in the tube and a casing surrounding the tube, characterized in that the envelope is formed of two profiled bars configured to surround the tube in at least part of its length, each comprising: a recess intended to receive the tube, the inner surface of the recess being a portion of a cylinder a joining surface distributed on either side of the recess and configured to form a junction with the other profiled bar following brazing of the bars, and in that the joining surfaces of the profiled bars are of complementary shapes so as to form a gap between them, at least one brazing element being arranged in at least part of said gap, and the joining surfaces of the profiled bars are arranged in different planes so that said gap forms at least one baffle on each side of the tube

[0015] An exchanger according to the invention is therefore suitable for brazing via the use of two bars arranged around the tube and separated by a gap which make it possible to reduce thermal stresses during brazing, in particular to avoid deformations of the exchanger. In particular, the presence of a bar on each side of the tube makes it possible to reduce the "bimetallic strip" effect when the tube and the bars are made of different materials, having different coefficients of thermal expansion.

[0016] Brazing is preferably vacuum brazing, particularly using a vacuum brazing furnace. The brazing element is advantageously created by brazing a brazing strip inserted into at least part of the gap during the manufacture of the heat exchanger. A brazing element is more generally understood to mean the result of brazing any filler element that allows a permanent connection between the profiled bars or between each profiled bar and the circulation tube.

[0017] The presence of the baffle makes assembly easier, reduces the risk of hyperstaticity when fixing the two profiled bars to the tube, and in the context of the use of the heat exchanger in a space domain, provides protection for the tube against micrometeorites by eliminating any direct path from the outside of the heat exchanger to the tube. Micrometeorites circulating in the gap are stopped or at least slowed down at the baffle, which greatly or totally reduces (depending on the dimensions of the baffle) the risk of piercing the tube.

[0018] According to a variant of the invention, at least part of the brazing can be implemented by prior application of a metallized layer on the tube before assembly with the bars, then brazing of the assembled exchanger. The metallized layer is for example nickel (added by nickel plating) and preferably applied by cold spraying or cold sprayin English, and the final brazing allows the brazing to be formed between the tube and the bar recesses. Brazing also improves the heat exchange between the tube and the profile.

[0019] The bars are, for example, made by extrusion, and preferably from aluminum. The tube is preferably made from stainless steel. The exchanger is therefore an "aluminum-stainless steel" heat exchanger. Other materials can be used.

[0020] A surface treatment of the tube or bars is possible, in particular prior to assembly of the exchanger or after assembly, for example an OAS (Anodic Sulfur Oxidation), TCS PACS, physical vapor deposition treatment, otherwise called PVD (for Physical Vapor Deposition in English) and chemical vapor deposition treatment, otherwise called CVD (for Chemical Vapor Deposition in English).

[0021] Advantageously and according to the invention, at least one brazing element is further arranged between the circulation tube and each recess of the profiled bars.

[0022] According to this aspect of the invention, the presence of brazing between the tube and the profiled bars makes it possible to increase the thermal exchanges between these two elements of the heat exchanger, thus improving the overall performance of the heat exchanger.

[0023] Advantageously and according to the invention, at least one profiled bar comprises cooling fins.

[0024] According to this aspect of the invention, the cooling fins make it possible to increase the heat exchange with the exterior to improve the performance of the heat exchanger.

[0025] Advantageously and according to the invention, the two profiled bars are substantially rectilinear and identical, and are assembled so that one profiled bar has a rotation of 180° around a main axis of the circulation tube relative to the other profiled bar.

[0026] According to this aspect of the invention, the manufacture of the profiled bars is simplified because the bars are identical. The rotation of one bar relative to the other allows the assembly of the two parts and forms the baffle at the gap.

[0027] Advantageously and according to the invention, the profiled bars extend in a main longitudinal direction and comprise, at each of their ends, a transition zone in the form of lips.

[0028] According to this aspect of the invention, the transition zone makes it possible to limit the concentrations of residual thermomechanical stresses between the tube and the profiled bars at the ends of the heat exchanger, in particular at the ends of the profiled bars.

[0029] The invention also relates to a method of manufacturing a heat exchanger according to the invention, characterized in that it comprises: a step of placing at least one brazing strip on at least part of the joining surface of at least one profiled bar, a step of inserting the fluid circulation tube into at least one recess of one of the profiled bars, a step of joining the two profiled bars around the tube, a step of brazing the heat exchanger in a brazing furnace at a temperature above 450°C, preferably above 600°C, so that each brazing strip forms a permanent assembly between the bars and the tube.

[0030] A method according to the invention is easily industrializable thanks to the use of a brazing furnace, in particular a vacuum brazing furnace, which replaces the human operator for soft brazing. The method is also simpler, less expensive, more reliable, and repeatable. The use of the vacuum brazing furnace also allows for a wider choice of materials for the heat exchanger, in particular for the fluid circulation tube, reduces oxidation, produces fewer pollutants and allows better local temperature control because the heat is transmitted by radiation.

[0031] Advantageously and according to a variant of the invention, the manufacturing method comprises a preliminary step of applying a metallized layer to the tube, the metallized layer forming a brazing between the tube and the recesses of the profiled bars.

[0032] The invention also relates to a heat exchanger and a manufacturing method characterized in combination by all or part of the features mentioned above or below. List of figures

[0033] Other aims, characteristics and advantages of the invention will appear on reading the following description given solely for non-limiting purposes and which refers to the appended figures in which: [ Fig. 1 ] is a schematic perspective view of a heat exchanger according to a first embodiment of the invention; [ Fig. 2 ] is a schematic cross-sectional view of the heat exchanger according to a first embodiment of the invention. [ Fig. 3 ] is a schematic cross-sectional view of a heat exchanger according to a second embodiment of the invention. [ Fig. 4] is a schematic perspective view of a profile bar of a heat exchanger according to one embodiment of the invention. Detailed description of an embodiment of the invention

[0034] In the figures, scales and proportions are not strictly respected for the purposes of illustration and clarity. In particular, the interstices of the exchangers are represented so as to be visible but may be narrower than shown.

[0035] Furthermore, identical, similar or analogous elements are designated by the same references in all figures.

[0036] There figure 1 and the figure 2 schematically illustrate in perspective and in cross-section a heat exchanger 100 according to a first embodiment of the invention.

[0037] The exchanger 100 comprises a tube 14 for circulating a fluid, the exchanger 100 being configured to allow heat exchange between the fluid circulating in the tube and a casing surrounding the tube. The casing is formed of two profiled bars, called the upper bar 112a and the lower bar 112b, which are substantially identical and configured to surround the tube 14 in at least part of its length, each comprising a recess 16a, 16b intended to receive the tube 14, the inner surface of the recess being a portion of a cylinder.

[0038] Each bar also includes a junction surface 18a, 18b distributed on either side of the recess, on the figure 2 to the left and right of the tube 14, and configured to form a junction with the other profiled bar following brazing of the bars.

[0039] The joining surfaces of the profiled bars are of complementary shapes so as to form a gap 20 between them, at least one brazing element, here two brazing elements 22a, 22b being arranged in at least a part of said gap 20. Non-visible brazing elements are also present between the circulation tube 14 and the profiled bars, at the recesses 16a, 16b.

[0040] The junction surfaces 18a, 18b of the profiled bars are arranged in different planes so that said gap 20 forms at least one baffle 24a, 24b on each side of the tube configured so as to protect the tube 14 from any micrometeorites entering the gap 20 from the outside. The baffles prevent any direct trajectory from the outside of the exchanger to the circulation tube via the gap.

[0041] The thickness e of the gap is for example of the order of 0.25 mm. At the level of the brazing element, a clearance j for example between 0.25 mm and 1 mm and a spacing i for example at least equal to 1 mm allows the insertion, during manufacturing, of the brazing strip to form the brazing element. In these figures and the following ones, these thicknesses may not be to scale so that the gap and the clearance are visible.

[0042] There figure 3schematically represents in cross-section a heat exchanger 200 according to a second embodiment of the invention. In this embodiment, the upper bar 212a and the lower bar 212b have geometric shapes that are identical to each other but different from the profiled bars of the first embodiment. The gap 20, the baffles 24a and 24b as well as the brazing elements 22a, 22b are present with identical functions but are of different shapes. These shapes can for example make it possible to increase the brazing surface between the two bars or between each bar and the tube so as to maximize the heat exchange, and / or make it possible to guarantee that no micrometeorite can reach the tube.

[0043] There figure 4schematically represents in perspective a profiled bar 312 of a heat exchanger according to an embodiment of the invention. The bar 312 comprises, at at least one of its ends, at the level of the recess 316 intended to accommodate the fluid circulation tube, a transition zone 326 in the form of a lip making it possible to extend the accommodation of the fluid circulation tube at the end while limiting the residual thermomechanical stresses.

[0044] The invention is not limited to the embodiments described. In particular, the profiled bars may have different shapes. In particular, the baffle may have different shapes depending on the constraints of the heat exchanger, for example manufacturing, assembly and / or protection against micrometeorites.

Claims

1. Heat exchanger comprising a fluid flow tube (14) and configured to allow an exchange of heat between the fluid flowing in the tube and an enclosure surrounding the tube, the enclosure being formed of two profiled bars (112a, 112b; 212a, 212b; 312) configured to surround the tube (14) over at least one part of its length, each comprising: - a recess (16a, 16b, 316) intended to receive the tube, the inner surface of the recess being a portion of a cylinder, characterized in that each of the bars comprises: - a joint surface (18a, 18b) distributed on either side of the recess and configured to form a joint with the other profiled bar following soldering of the bars, and in that the joint surfaces (18a, 18b) of the profiled bars are complementary in shape so as to form a gap (20) therebetween, at least one soldering element (22a, 22b) being arranged in at least one part of said gap (20), and the joint surfaces (18a, 18b) of the profiled bars are arranged in different planes such that said gap forms at least one baffle (24a, 24b) on each side of the tube (14).

2. Heat exchanger as claimed in claim 1, characterized in that at least one soldering element (22a, 22b) is obtained by hard soldering in a vacuum soldering furnace of a soldering strip inserted in at least one part of said gap (20).

3. Heat exchanger as claimed in any one of claims 1 or 2, characterized in that at least one soldering element is further arranged between the flow tube (14) and each recess (16a, 16b) of the profiled bars.

4. Heat exchanger as claimed in any one of claims 1 to 3, characterized in that the enclosure is made from aluminum and the tube (14) is made from stainless steel.

5. Heat exchanger as claimed in any one of claims 1 to 4, characterized in that the profiled bars (112a, 112b; 212a, 212b; 312) are made by extrusion.

6. Heat exchanger as claimed in any one of claims 1 to 5, characterized in that at least one profiled bar (112a, 112b; 212a, 212b; 312) comprises cooling fins.

7. Heat exchanger as claimed in any one of claims 1 to 6, characterized in that the two profiled bars (112a, 112b; 212a, 212b; 312) are substantially straight and identical and are assembled such that one profiled bar is rotated by 180° about a main axis of the flow tube with respect to the other profiled bar.

8. Heat exchanger as claimed in any one of claims 1 to 7, characterized in that the profiled bars (112a, 112b; 212a, 212b; 312) extend in a main longitudinal direction and comprise, at each of their ends, a transition zone (326) in the form of lips.

9. Method of manufacturing a heat exchanger (100, 200) as claimed in any one of claims 1 to 8, characterized in that it comprises: - a step of placing at least one soldering strip on at least one part of the joint surface (18a, 18b) of at least one profiled bar, - a step of inserting the fluid flow tube (14) in at least one recess (16a, 16b) of one of the profiled bars, - a step of joining the two profiled bars (112a, 112b; 212a, 212b; 312) around the tube (14), - a step of hard soldering the heat exchanger in a soldering furnace at a temperature greater than 450°C, preferably greater than 600°C, such that each soldering strip forms a permanent assembly between the bars and the tube.

10. Method of manufacture as claimed in claim 9, characterized in that it comprises a preliminary step of applying a metallized layer to the tube (14), the metallized layer forming a solder joint between the tube (14) and the recesses (16a, 16b) of the profiled bars.