HEAT EXCHANGER BRAZING PROCESS

Abstract

The invention relates to a method for manufacturing a heat exchanger. In the first step (100), perforated flanges are made to house tubes. In the second step (200), the tubes are assembled onto the flanges. In the third step (300), copper washers are placed at each junction between a tube and a flange. In the fourth step (400), the assembly is placed in a vacuum furnace with a controlled-temperature atmosphere. In the fifth step (500), a vacuum is created. In the sixth step (600), the furnace is preheated to 750°C with a first temperature ramp. In the seventh step (700), it is heated to 1100°C with a second temperature ramp. In the eighth step (800), brazing is performed for 15 minutes. In the ninth step (900), the furnace is cooled to 900°C under vacuum. In the tenth step (1000), the furnace is cooled to ambient temperature under argon. Figure 10

Description

Title of the invention: HEAT EXCHANGER BRAZING METHOD

[0001] The invention relates to a method of producing a heat exchanger.

[0002] The invention relates to such a single-block exchanger.

[0003] The invention also relates to a motor vehicle comprising at least one turbo-generator comprising at least one such single-block exchanger.

[0004] Turbogenerator-type energy converters are a very promising technology for supplementing or replacing the internal combustion engine in highly electrified powertrains. The fluid circuits in such converters necessarily incorporate heat exchangers, particularly of the recuperator, intercooler, or other type.

[0005] Different types of exchangers are known: tube and fin exchangers, plate and fin exchangers, micro-channel exchangers produced by three-dimensional printing in metal, in particular in Inconel®, plate exchangers, or others.

[0006] These heat exchangers are made using several types of processes: brazing (a filler material is melted at high temperature to couple two components of the recuperator, for example the tubes and the plates), welding (the two components are welded by melting their own material to couple them), three-dimensional printing (metal printing of all the channels of the exchanger), assembly by temperature difference, called "tight entry" (a tube is made, for example, in a section smaller than the external diameter, by cooling the tube initially with a larger diameter and heating the plate with a smaller diameter).

[0007] These methods are expensive and time-consuming. The invention aims to save time in producing an exchanger and to reduce its cost.

[0008] The objective of the present invention is to overcome these drawbacks by proposing a heat exchanger which can be produced in a modular manner to take into account the constraints of the zones subject to more or less thermal and mechanical stress, and to adapt the structure of the exchanger by lightening it and reducing its cost wherever possible.

[0009] To achieve this objective, the invention proposes a method for producing a heat exchanger, according to which in a first step, flanges are supplied or produced having holes for housing exchanger tubes which are supplied or produced, in a second step, said tubes are assembled on said flanges, in a third step, copper washers are supplied or produced, and at least one said copper washer is placed at each junction between a said tube and a said flange, on at least one side of said flange, in a fourth step the assembly consisting of said flanges, said tubes, and said washers is placed in a vacuum furnace with a temperature-controlled atmosphere, in a fifth step the furnace is placed under vacuum, in a sixth step the furnace is preheated to a first temperature above 600°C with a first regular temperature rise ramp, in a seventh step the furnace is heated to a second temperature above 1000°C with a second regular temperature rise ramp, in an eighth step the brazing is carried out for at least 15 minutes, in a ninth step the furnace is cooled to a third temperature between said first temperature and said second temperature and above 800°C still under vacuum, and in a tenth step the furnace is cooled to room temperature with an argon atmosphere.

[0010] Thanks to the invention, the entire brazing operation can be carried out in a single operation, easily robotizable and automatable, suitable for large-scale production. This brazing is possible even if the exchanger comprises pairs of different materials, and the characteristic of brazing by fusion of a copper washer represents an inexpensive improvement of the brazing process, and the guarantee of the success of the brazing operation as well as the metallurgical quality obtained.

[0011] More particularly, during said sixth step, said first temperature is chosen to be between 700°C and 800°C, in said seventh step, said second temperature is chosen to be between 1050°C and 1150°C, in said eighth step, brazing is carried out for at least 15 minutes and less than 25 minutes, and in said ninth step, said third temperature is chosen to be between 850°C and 950°C.

[0012] These parameters allow the brazing process to run smoothly and ensure very good quality of the joint produced.

[0013] More particularly, during said first step the thickness of said flanges is chosen to be between 3 and 5 mm.

[0014] This way the exchanger can be lightened.

[0015] More particularly, during said first step, the network of holes of each said flange is produced to delimit several sections nested within each other, with a first section, the outermost one, ensuring the heat exchange with the ambient environment, and which surrounds a second section where higher temperatures prevail, which itself surrounds a third section where the highest temperatures prevail in said exchanger.

[0016] Thus the structure of the exchanger is locally adapted to the local temperature and pressure conditions, and the overall mass and cost of the components are reduced by lightening where possible, thanks to these differentiated sections, which allow, again, to optimize exchanges with the external environment.

[0017] More particularly, during said second step, each said tube is mounted with a tight sliding fit or with a slight tightening on each said flange for its proper maintenance during the following step.

[0018] Thus the assembly can be transported without any particular precautions by a robotic manipulator.

[0019] More particularly, during said third step, at least one said copper washer is placed at each junction between a said tube and a said flange, on each side of said flange.

[0020] This reinforces the mechanical strength of the assembly.

[0021] More particularly, during said third step, each said washer is mounted with a tight sliding fit or with a slight tightening on its respective said tube for its proper maintenance during the following step.

[0022] Thus the assembly can be transported without any particular precautions by a robotic manipulator.

[0023] More particularly, during said third step, each said washer is chosen with a thickness between 0.7 and 0.9 mm.

[0024] This minimizes the cost of these filler components while ensuring the quantity of material necessary for quality brazing.

[0025] More particularly, chemical stripping of the pre-assembled assembly is carried out at the end of said first step and / or said second step and / or said third step.

[0026] Such stripping contributes to the success of the brazing operation by removing any polluting agent.

[0027] The invention also relates to a single-block exchanger produced by brazing said flanges, said tubes, and said washers, according to this method.

[0028] Thus the design of the exchanger can provide different sections, with different thermal and mechanical characteristics, with components made of different materials, while carrying out a single brazing operation.

[0029] The invention also relates to a motor vehicle comprising at least one turbo-generator comprising at least one single-block exchanger produced by brazing said flanges, said tubes, and said washers, according to the method described previously.

[0030] Thanks to the invention, the volume and mass of the exchanger are minimized as much as possible, as well as its cost.

[0031] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: - [Fig.l] illustrates schematically and in perspective, a heat exchanger according to the invention; - [Fig.2] illustrates schematically and in perspective, the exchanger of [Fig.l], with arrows illustrating the main gas flows; - [Fig.3] illustrates schematically and in front view, a heat exchanger according to the invention comprising three sections nested within each other, with a first, outermost section ensuring the heat exchange with the ambient environment, which surrounds a second section where higher temperatures prevail, which itself surrounds a third section where the highest temperatures prevail in the exchanger; - [Fig.4] illustrates schematically and in front view, a heat exchanger according to the invention with hot inlet / cold outlet positioned in the middle; - [Fig.5] illustrates schematically and in front view, a heat exchanger according to the invention with offset hot inlet / cold outlet; - [Fig.6] illustrates schematically and in section, before brazing, a constituent assembly of a heat exchanger according to the invention, with a flange into which tubes fitted with toric copper washers are threaded; - [Fig.7] illustrates schematically and in section, before brazing, an assembly constituting a heat exchanger according to the invention, with a flange into which tubes fitted with copper washers of rectangular section are threaded; - [Fig.8] illustrates schematically and in section, after brazing, a heat exchanger according to [Fig.6] or [Fig.7]; - [Fig.9] schematically illustrates a motor vehicle comprising a turbo- generator comprising such a single-block exchanger; - [Fig. 10] is a flowchart detailing the steps of the exchanger brazing process according to the invention.

[0032] Turbogenerator-type energy converters are a very promising technology for replacing the internal combustion engine in highly electrified powertrains, particularly for plug-in hybrid vehicles (PHEVs), whose traction battery is designed to be charged by connection to an external energy source, and in particular for PHEV (Plug-in Hybrid Electric Vehicle) type vehicles when the two engines act together to power the vehicle, with a series hybrid architecture (Series Hybrid Electric Vehicles). This technology promises many advantages: low emissions, low noise, no vibrations, very low maintenance (limited to changing the oil filter), and the ability to operate with several types of fuel.

[0033] The aim of the present invention is to optimize the production of a heat exchanger, of the recuperator type. The design of this exchanger takes into account several criteria: the improvement of the efficiency of the recuperator by proposing a counter-current exchanger, the reduction of thermal losses to the outside via the walls and external surfaces, the modularity of an exchanger adaptable according to the application and the energy levels present, the possibility of modifying the positions of the inlets / outlets of the exchanger, the possibility of modifying the number of passage sections (tubes) in each stage of the exchanger, the possibility of modifying the section of each passage in each stage of the exchanger, the possibility of modifying the materials in each passage section, the possibility of modifying the number of passengers (round trip) in the exchanger, the possibility of using different types of working fluids (air-air, air-water, air-ORC, water-water, water-ORC, other couples based on the use of other liquids and / or other gases),the possibility of using several working fluids (for example to use the recuperator in air-air mode and also preheat another ORC type fluid for a Rankine loop, or use the energy to preheat a heat transfer circuit to ensure the thermal needs of the vehicle especially in winter).

[0034] Advantageously, a heat exchanger well suited to a turbogenerator type application is modular, counter-current, high-efficiency, with variable flow section, with minimized thermal losses. This exchanger may be suitable for applications where the two fluids are gases, those where the two fluids are liquids or two-phase, a gas fluid and a liquid or two-phase fluid. This exchanger may operate with two fluids, or three, or more. This heat exchanger may be used as a recuperator or as an intercooler for a turbogenerator application, or for any other type of application.

[0035] The innovation is advantageously applicable to an energy converter of the turbogenerator type with a recuperative cycle ((RGT = Recuperative Gas Turbine), or with an IRReGT cycle with recovery and intermediate cooling and intermediate heating "intercooled recuperative reheat gas turbine") or any other thermodynamic cycle comprising a heat exchanger.

[0036] The innovation also targets any type of application where an exchanger is required.

[0037] The invention relates to a method for manufacturing the heat recuperator (heat exchanger), and in particular the brazing of the tubes onto the exchanger plates. This involves overcoming the problems encountered on exchangers, and identified during tests on several types of exchangers. The method for brazing the heat recuperator according to the invention must also make it possible to produce the exchanger at low cost.

[0038] Despite the apparent simplicity of the structure of an exchanger, the functionalities to be ensured must be taken into account.

[0039] The exchanger must have a high exchange efficiency between the hot source (the high temperature fluid) and the cold source (the low temperature fluid). This exchange efficiency is evaluated by an overall exchange coefficient (H [W / m2]).

[0040] To achieve high efficiency, high exchange coefficients and a counter-current heat exchange architecture are required. With a counter-current exchanger, the outlet temperature of the cold fluid can exceed the outlet temperature of the hot fluid, which is not possible in the case of an exchanger with a co-current architecture.

[0041] The exchanger must have a low pressure drop. This is a very important criterion in the case of a turbogenerator application. The flow passes through the exchanger twice (once at the compressor outlet and once at the turbine outlet). Reducing pressure drops as much as possible makes it possible to increase the expansion ratio of the turbine, and consequently, to increase the power generated by the turbine.

[0042] To minimize pressure losses, it is useful to adapt the exchange sections according to the position in the exchanger. Indeed, the more the fluid (in the case of a gas) cools down, the more the density decreases, and the more the sections can be reduced. Similarly, the more the fluid heats up, the more the volume flow increases, and the more the passage sections must be increased. This is not possible with plate exchangers; it is possible with exchangers produced by three-dimensional printing, but they are not very suitable for large-scale applications.

[0043] Thermal exchanges at the walls must be controlled: if the collectors are external, there will be significant thermal exchanges at the walls, which complicates the thermal insulation of the exchanger. Indeed, in the case of the turbogenerator, the hot inlet of the exchanger can be at temperatures above 750°C. If the collector is external, the surface temperature will be high and significant thermal losses will have to be managed.

[0044] To minimize heat losses at the walls, it is advantageous for the hot exchange surface in contact with the exterior to be minimized. Consequently, it is advantageous for the hot inlet to be inside the recuperator.

[0045] The inlets / outlets of the exchanger have an impact on the volume and physical architecture of the machine. If the inlets / outlets are difficult to move, the design of the turbogenerator is limited by the design of the exchanger. It is also interesting to have a modular design where the inlets / outlets can be placed at any location in the functional volume of the exchanger, which makes it possible to ensure better use of the total volume of the turbogenerator, and above all to reduce this volume.

[0046] The choice of materials for the exchanger components and sections is essential. The type of material has an impact on the heat exchange coefficient. However Some types of materials, such as copper or aluminum, have very high heat exchange coefficients, but on the other hand, poor high-temperature resistance characteristics. Similarly, some materials are lighter than others and allow the total mass of the exchanger to be reduced. Thus, having a heat exchanger design where the type of materials can be adapted allows the heat exchange performance to be increased and the mass of the exchanger to be minimized.

[0047] In certain applications and in particular in the case of the turbogenerator application, the gases leaving the recuperator remain hot. This is due to the fact that the air temperature at the compressor outlet is high, and therefore the outlet temperature of the gases towards the ambient on the hot side of the recuperator is necessarily higher than the inlet temperature, compressor outlet temperature (according to the second principle of thermodynamics: a heat exchange always passes from hot to cold). For example, the temperature of the gases leaving the recuperator of a turbogenerator application is of the order of 300°C. These gases still contain energy that can no longer be recovered in the thermodynamic cycle of the turbogenerator.

[0048] Having an exchange with a third (or even a fourth) working fluid, to recover the remaining energy, makes it possible to increase the overall efficiency of the system. Thus the possibility of exchanging with a third fluid is important in several types of applications. This makes it possible to reduce the complexity of the system (for example by using a single exchanger instead of two exchangers).

[0049] It is interesting to use such an exchanger to exchange with several fluids, we can therefore imagine having an architecture which combines both an ORC cycle with a fuel evaporator. Or even an architecture where tubes are added, where a refrigerant fluid circulates, to heat the passenger compartment of a vehicle carrying this turbogenerator, from the thermal / gas discharges at the outlet of the recuperator.

[0050] It is therefore a question of taking into account all these constraints to define a brazing process which allows the industrialization (large series) of a heat exchanger of the recuperator type, and also for other applications.

[0051] [Fig-1] and [Fig.2] illustrate a heat exchanger according to the invention, [Fig.2] illustrates flow inlets / outlets: arrow A compressed gas inlet from the compressor, arrow B gas inlet from the turbine or hot inlet 10, arrow C outlet to the combustion chamber or cold outlet 14.

[0052] The exchanger contains two paths: a path for a first fluid, and a path for a second fluid.

[0053] As regards the path for a first fluid, in the case of the turbogenerator application, this first fluid is generally, but not necessarily, pressurized air at the outlet of the compressor. This first pressurized fluid circulates in tubes.

[0054] As regards the path for a second fluid, in the case of the turbogenerator application, this second fluid corresponds to the hot gases leaving the turbine. This second fluid is channeled using channel-shaped sections which have the role of conveying the gases and maintaining a counter-current exchanger architecture. The gas in the tubes circulates in the opposite direction to the gases in the pipe sections.

[0055] The first fluid and the second fluid move back and forth. The first fluid passes through a settling volume on both sides of the exchanger. The second fluid changes direction by passing through slots that allow the second fluid to return in the opposite direction.

[0056] The second fluid can be collected to escape at the outlet of the exchanger at different locations. Thus the exhaust can be located at different locations on the external part of the exchanger.

[0057] The pressurized gas, in particular and not limited to air, circulating in the tubes is heated by the hot gases coming from the turbine circulating around the tubes in a counter-current manner. The number of passes (back and forth) is variable (one can have one pass, two passes, three passes, or other, depending on the heat exchange desired).

[0058] The total number of tubes in each section is variable. The cross-section of the tubes in each section is also variable. The number of tubes and the cross-section of the tubes can be adapted according to the characteristics of the fluid (temperature reached) at each section. This is an important parameter which allows the exchanger to be optimized and to have a behavior of the exchanger close to the variable cross-section exchangers resulting from three-dimensional printing.

[0059] The materials in each section can also be adapted. For example, on a 3-pass round-trip exchanger, as seen in the example of [Fig.3], with three sections 11, 12, 13, nested within each other, aluminum can be used, which has good heat exchange characteristics and is not heavy, in the last hot gas section (or first section 11 preheats compressed air). Copper can be used in the second section 12, knowing that copper has good heat transfer coefficients (but begins to lose its mechanical strength characteristics at 700°C). Finally, inconels or steels can be used in the third section 13 (the hottest on the gas side) where there are high thermal constraints. This is an interesting characteristic allowing the optimization of heat exchanges and the weight of the exchanger.

[0060] The length of the tubes is variable and depends on the calculated thermal exchanges.

[0061] The gas, in particular air, compressed at the outlet of the compressor enters the tubes peripherals. This allows the peripheral area of ​​the exchanger to be insulated and heat losses to be reduced.

[0062] The hot gas leaving the turbine enters in the middle at the hot inlet 10. Any diffusion and thermal loss will be recovered by the surrounding flows. It is thus by choosing this nested architecture of the different sections that we manage to reduce the losses at the walls and to recover the thermal losses internally in the exchanger.

[0063] The gases leaving the turbine and entering the exchanger are channeled inside by sheets which will give the direction of the flow. The difference between the section of the sheets and the total surface area of ​​the tubes gives the passage section and consequently defines the passage speed.

[0064] The heat exchanger may be single-flow, double-flow, or cross-flow, or any other known type of fluid path. The number of passages in the recuperator is variable and the size thereof is variable.

[0065] The objective is to integrate the combustion chamber inside, and to be able to channel the gas so as to ensure its entry into the combustion chamber after preheating.

[0066] As regards the assembly process, a flange is advantageously produced, also called a flange, comprising the different holes, then the tubes can be assembled and positioned in the holes.

[0067] The position of the inputs and outputs can be changed. As shown in [Fig.4] and [Fig.5], a modular design allows the positions of the outputs to be changed.

[0068] For example, the outlet of the second fluid (hot gas in the case of the turbogenerator) can be placed on the left, right, top or bottom of the recuperator.

[0069] The position of the outlet of the first fluid is also variable. For example, on the exchanger in [Fig.4] it can exit coaxially with the inlet of the second fluid; [Fig.5] illustrates an offset hot inlet / cold outlet.

[0070] The tubes can be of rectangular section. This arrangement makes it possible to reduce the overall volume of the exchanger. However, it is necessary to develop a process facilitating their brazing on the flange.

[0071] The method for producing a heat exchanger 123 according to the invention comprises several steps.

[0072] In a first step 100, flanges 1 are supplied or produced, comprising holes for housing the exchanger tubes 2; the cross-section of the holes is adapted to the cross-section of the tubes 2, in particular circular or rectangular; the holes can be produced by drilling, stamping, rapid laser cutting, high-pressure water injection, or the like. For an automotive-type application, the thickness of the flanges can be quite small, for example between 2 and 10 mm, more particularly between 3 and 5 mm, this thickness of course depends on the material chosen for the flanges.

[0073] And we supply or produce exchanger tubes 2.

[0074] More particularly, the network of holes of each flange 1 is produced to delimit several sections, for example and not limited to three sections 11, 12, 13, nested one inside the other, that is to say with a first section 11, the outermost, ensuring the heat exchange with the ambient environment, and which surrounds a second section 12 where higher temperatures prevail, which itself surrounds a third section 13 where the highest temperatures prevail in the exchanger. Naturally, it is possible to have only two sections, or four sections or even more.

[0075] More particularly, chemical stripping is carried out at the end of the first step 100.

[0076] In a second step 200, the tubes 2 are assembled on the flanges 1, on both sides. More particularly, the nature of the tubes 2, in particular their constituent material, is differentiated according to the stage concerned. Advantageously, each tube 2 is mounted with a tight sliding fit or with slight tightening on each flange 1 for its proper maintenance during the following step.

[0077] More particularly, chemical stripping is carried out on the set of flanges and tubes thus pre-assembled at the end of the second step 200.

[0078] In a third step 300, copper washers 3 are supplied or produced, and at least one copper washer 3 is placed at each junction between a tube 2 and a flange 1, on at least one side of the flange 1. In a variant, at least one copper washer 3 is placed at each junction between a tube 2 and a flange 1, on each side of the flange 1. Advantageously, each washer 3 is mounted with a tight sliding fit or with slight tightening on its respective tube 2 for its proper retention during the following step. It is easy to produce a washer 3 whose internal profile corresponds to each shape of tube 2 and with corresponding dimensions, to ensure good brazing.

[0079] More particularly, each washer 3 is made of MIE electrolytic copper.

[0080] More particularly, each washer 3 has a thickness of between 0.5 and 2.0 mm, more particularly between 0.6 and 1.0 mm, more particularly between 0.7 and 0.9 mm, more particularly still close to 0.8 mm.

[0081] More particularly, chemical stripping is carried out of the assembly of puddles, tubes and washers, thus pre-assembled at the end of the third step 300.

[0082] In a fourth step 400, the assembly consisting of the flanges, the tubes, and the washers is placed in a vacuum oven with a temperature-controlled atmosphere.

[0083] In a fifth step 500 the oven is placed under vacuum, in particular down to 0.1 mbar.

[0084] In a sixth step 600 the oven is preheated to a first temperature greater than 600°C with a first regular temperature increase ramp.

[0085] In a seventh step 700 the furnace is heated to a second temperature greater than 1000°C with a second regular temperature increase ramp.

[0086] In an eighth step, brazing is carried out for at least 15 minutes.

[0087] In a ninth step the furnace is cooled to a third temperature between the first temperature and the second temperature and above 800°C still under vacuum.

[0088] And in a tenth step the furnace is cooled to room temperature with an argon atmosphere.

[0089] The temperature and duration parameters of course depend on the pairs of materials present.

[0090] More particularly, during the sixth step 600 the first temperature is chosen between 700°C and 800°C, in the seventh step 700 the second temperature is chosen between 1050°C and 1150°C, in the eighth step 800 the brazing is carried out for at least 15 minutes and less than 25 minutes, and in the ninth step the third temperature is chosen between 850°C and 950°C.

[0091] More particularly still, in the sixth step 600 the oven is preheated to 750°C with a first regular temperature rise ramp, in particular 10°C per minute.

[0092] More particularly still, in the seventh step 700 the furnace is heated to 1100°C with a second regular temperature increase ramp, in particular 5°C per minute.

[0093] More particularly still, in the eighth step 800 the brazing is carried out for at least 15 minutes, in particular 15 minutes.

[0094] More particularly still, in the ninth step 900 the furnace is cooled to 900°C still under vacuum.

[0095] This gives a single-block exchanger 123.

[0096] In a non-limiting example of carrying out this method, the initial assembly of the heat exchanger comprises mounting a ring of 0.8 mm diameter MIE electrolytic copper wire on each connection between the tube and the plate, to be secured by brazing. The assembled construction is placed in a vacuum furnace with a controlled atmosphere. Before the brazing process, the furnace is pumped to a pressure of 0.1 mbar. The furnace charge is preheated to a temperature of 750 °C with a ramp of 10 °C per minute. Then, the temperature is increased to 1100 °C with a ramp of 5 °C per minute. The brazing process is carried out for 15 minutes. After the brazing process, the furnace charge is cooled to 900°C under vacuum, then to room temperature with a furnace under argon atmosphere.

[0097] The exchanger is compatible with a turbogenerator application or any other type of application.

[0098] The exchanger is also compatible with any other application where a heat exchange between two or more fluids is necessary.

[0099] The invention relates to such a single-block exchanger 123.

[0100] The invention also relates to a motor vehicle 50 comprising at least one such single-block exchanger 123.

[0101] More particularly, this motor vehicle 50 comprises at least one turbogenerator 60 comprising at least one such monobloc exchanger 123.

[0102] The brazing process described is compatible with different types of materials.

[0103] The invention provides various advantages: improving the efficiency of the recuperator by proposing a counter-current exchanger, reducing thermal losses to the outside via the walls and external surfaces which are strongly limited, the modular and adaptable design depending on the application, the possibility of modifying the positions of the inlets / outlets of the exchanger, the possibility of modifying the number of passage sections (tubes) in each stage of the exchanger, the possibility of modifying the section of each passage in each stage of the exchanger, the possibility of adapting the choice of materials to the thermal and dynamic constraints in each passage section, the possibility of modifying the number of passages (round trip) in the exchanger,the possibility of using different types of working fluids (for example and not limited to air-air / air-water / air-ORC / water-water / water-ORC) an ORC (from the English "Organic Rankine Cycle") being an organic compound as the working fluid used in an organic Rankine cycle, the possibility of using several working fluids (for example using the recuperator in air-air mode and also preheating another ORC type fluid for a Rankine loop, or using the energy to preheat a heat transfer circuit to ensure the thermal needs of a vehicle especially in winter.,

[0104] The invention has a technical and economic interest. Indeed, it makes it possible to propose a new design of high-performance heat exchanger. This exchanger can be used as a heat recovery unit for turbogenerator applications, and also in any other non-automotive application where a heat exchanger is necessary.

[0105] The security of brazing provided by this process is important for a small exchanger whose components are difficult to access and not interchangeable, and an exchanger made using this process is particularly well suited to automotive applications. Of course, this process can be implemented, and use such an exchanger in applications other than automobiles.

[0106] A turbogenerator equipped with such an exchanger is a low-cost solution for hybridizing the battery of an electric or hybrid motor vehicle, offering a long range with a bio-fuel with low environmental impact. This solution allows the advantages of electric vehicles to be retained: driving pleasure, reduced maintenance, low noise level, while increasing the range and reducing the cost.

Claims

Claims

1. Method for producing a heat exchanger (123), according to which in a first step (100) flanges (1) are supplied or produced having holes for housing exchanger tubes (2) which are supplied or produced, in a second step (200) said tubes (2) are assembled on said flanges (1), in a third step (300) copper washers (3) are supplied or produced, and at least one said copper washer (3) is placed at each junction between a said tube (2) and a said flange (1), on at least one side of said flange (1), in a fourth step (400) the assembly consisting of said flanges (1), said tubes (2), and said washers (3) is placed in a vacuum furnace with a temperature-controlled atmosphere, in a fifth step (500) the furnace is placed under vacuum,in a sixth step (600) the furnace is preheated to a first temperature above 600°C with a first regular temperature rise ramp, in a seventh step (700) the furnace is heated to a second temperature above 1000°C with a second regular temperature rise ramp, in an eighth step (800) the brazing is carried out for at least 15 minutes, in a ninth step (900) the furnace is cooled to a third temperature between said first temperature and said second temperature and above 800°C still under vacuum, and in a tenth step (1000) the furnace is cooled to room temperature with an argon atmosphere.,

2. Method according to claim 1, according to which in said sixth step (600) said first temperature is chosen between 700°C and 800°C, in said seventh step (700) said second temperature is chosen between 1050°C and 1150°C, in said eighth step (800) brazing is carried out for at least 15 minutes and less than 25 minutes, in said ninth step (900) said third temperature is chosen between 850°C and 950°C.

3. Method according to claim 1 or 2, according to which during said first step (100) the thickness of said flanges (1) is chosen to be between 3 and 5 mm.

4. Method according to one of claims 1 to 3, according to which during said first step (100) the network of holes of each said flange (1) is produced to delimit therein several sections (11; 12; 13) nested together in the others, with a first section (11), the outermost ensuring the heat exchange with the ambient environment, and which surrounds a second section (12) where higher temperatures prevail, which itself surrounds a third section (13) where the highest temperatures prevail in said exchanger (123).

5. Method according to one of claims 1 to 4, according to which during said second step (200) each said tube (2) is mounted with a tight sliding fit or with a slight tightening on each said flange (1) for its proper maintenance during the following step.

6. Method according to one of claims 1 to 5, according to which during said third step (300) at least one said copper washer (3) is placed at each junction between a said tube (2) and a said flange (1), on each side of said flange (1).

7. Method according to one of claims 1 to 6, according to which during said third step (300), each said washer (3) is mounted with a tight sliding fit or with a slight tightening on its respective said tube (2) for its good maintenance during the following step.

8. Method according to one of claims 1 to 7, according to which during said third step (300), each said washer (3) is chosen with a thickness of between 0.7 and 0.9 mm.

9. Method according to one of claims 1 to 8, according to which chemical stripping of the pre-assembled assembly is carried out at the end of said first step (100) and / or said second step (200) and / or said third step 300.

10. Motor vehicle (50) comprising at least one turbogenerator (60) comprising at least one single-piece exchanger (123) produced by brazing said flanges (1), said tubes (2), and said washers, according to the method according to any one of claims 1 to 9.

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