METHOD FOR CONSTRUCTING A PLATE HEAT EXCHANGER AND THE PLATE HEAT EXCHANGER THUS CONSTRUCTED

Abstract

This method of making a heat exchanger consisting of a stack of plates 1, 1'), defining between them two distinct circuits for the circulation of two fluids respectively primary and secondary, consists of: – producing identical metal plates by stamping, capable of defining a succession of alternating reliefs protruding on either side of the plane P in which each of the plates is inscribed, each of the stamped plates thus having a primary face and a secondary face; – stacking said plates one on top of the other, the primary face of one opposite the primary face of the following plate, and successively the secondary face of said following plate opposite the secondary face of a following plate so as to define channels for the circulation of the primary and secondary fluids; – inserting between two consecutive plates a spacer (10, 10') resting on the periphery of said plates;– to weld the opposite apexes together through the weld; – to repeat the welding operation for as many assemblies as necessary until a heat exchanger is formed. Figure for the abbreviation: Fig 4;

Description

Title of the invention: METHOD FOR IMPROVING OF A PLATE HEAT EXCHANGER AND PLATE HEAT EXCHANGER THUS CONSTRUCTED Scope of the invention

[0001] The present invention relates to a method suitable for enabling the production of a plate heat exchanger, more particularly intended to be implemented within small volumes and therefore for which compactness is particularly sought.

[0002] The invention also relates to plate heat exchangers resulting from this manufacturing process. Prior state of the art

[0003] Heat exchangers are mainly of two types: respectively those called shell and tube, and those of the plate type.

[0004] In the first type, one of the fluids circulates inside the tubes while the other fluid circulates inside the shell. This type of heat exchanger has a large volume and is therefore not compatible with applications where compactness is required.

[0005] In the second type, the two fluids, respectively primary and secondary, circulate in channels defined by the stacking of plates.

[0006] Plate heat exchangers, compared to tube heat exchangers, offer significant advantages stemming from their thermal performance and compactness, thanks to a favorablely high surface area to heat exchange zone ratio.

[0007] The invention relates to this category of plate heat exchangers.

[0008] Such plate heat exchangers are widely known to date. Among the known technologies for manufacturing such plate heat exchangers, the principle of creating channels by stamping plates, by machining said plates, by milling or by chemical or electrochemical means is known.

[0009] These plates are assembled together in order to ensure the sealing and / or mechanical strength of the exchangers, in particular the resistance to pressure of the fluids circulating inside the exchanger, or even the resistance to pressure of the fluids circulating outside the exchanger.

[0010] Thus, such plate heat exchangers are composed of primary and secondary plates stacked alternately one on top of the other, and have after implementation at a minimum of one primary fluid inlet, one secondary fluid inlet, as well as one primary fluid outlet and one secondary fluid outlet.

[0011] Among the known plate assembly techniques, one can mention the assembly achieved by mechanical means such as tie rods holding the stack sealed between two thick and rigid plates, arranged at the ends. The seal in this type of assembly is then achieved by the compression of added gaskets.

[0012] The assembly can also be obtained by welding, generally limited to the periphery of the plates, which sometimes requires inserting the exchanger after welding into a shell to allow it to withstand the pressure of the fluids.

[0013] Brazing assembly is also known, particularly for heat exchangers to which fins are added.

[0014] Regardless of the technology implemented, two essential problems must be solved: - First, the sealing between the primary and secondary circuits, a problem particularly exacerbated when, for example, the primary circuit is contaminated (in the nuclear field) and the secondary circuit must not be contaminated under any circumstances; and - then the mechanical strength, particularly at the junction zones between two consecutive plates defining the channels within which the respective fluids circulate.

[0015] Regarding the sealing problem, experience shows that the welds used between the plates are likely to crack, and therefore consequently the sealing between the two circuits is affected, resulting in contamination of the secondary circuit by the primary circuit if necessary.

[0016] Moreover, the production of plates by machining, whether conventional (milling) or chemical, proves to be particularly time-consuming and, among other things, extremely expensive.

[0017] In order to overcome these various disadvantages, the invention aims at a method for manufacturing plate heat exchangers, a method in which firstly the plates are made by stamping, allowing a significant gain in terms of time, and secondly in which the plates are assembled together by diffusion welding, that is to say a method tending to establish strong bonds between the two metal parts thus welded, resulting in the absence of discontinuity in the weld areas, of deformation and almost absence of residual stresses allowing a precision assembly, and finally offering a high level of mechanical resistance of the interface. Description of the invention

[0018] According to the invention, the method for making a heat exchanger consisting of a stack of plates, defining between them two distinct circuits for the circulation of two fluids respectively primary and secondary, consists of: - to produce identical metal plates by stamping, capable of defining: . on the one hand a central zone comprising a succession of alternating reliefs projecting on either side of the plane in which each of the plates is inscribed, and . on the other hand, two divergence and collection zones are provided on either side of the central zone; each of the stamped plates thus presenting a primary face and a secondary face; each of the plates has through-lights provided at the collection areas; - to stack said plates one on top of the other, the primary face of one opposite the primary face of the following plate, and successively the secondary face of said following plate opposite the secondary face of a following plate so as to define channels for the circulation of primary and secondary fluids; - to insert between two consecutive plates a spacer resting on the periphery of said plates, and whose thickness is adapted to the height of the reliefs resulting from the stamping, in such a way that the reliefs of the primary faces are vertically aligned with the reliefs of the opposing primary faces and that the reliefs of the secondary faces are vertically aligned with the reliefs of the opposing secondary faces, and for all or part of them, that the apices of the reliefs in question opposite are in contact, said spacers being provided with two types of through-holes at their two ends, respectively intended to form, after stacking with the plates, channels for collecting or conveying fluids oriented perpendicularly to the plane in which the plates and spacers are inscribed,and to form, between two consecutive plates, a channel for the introduction and evacuation of fluids respectively into and out of the channels resulting from the stacking of the plates; - to weld the opposite apexes in contact with each other by transparency; - to repeat the welding operation for as many assemblies as necessary until an exchanger is produced incorporating the number of plates according to the desired heat exchange capacity, with the spacers welded to the plates to ensure the seal between the primary and secondary circuits.

[0019] In other words, the invention consists primarily of producing these plates by stamping, a technique that is now widely mastered, this stamping making it possible to define different types of reliefs depending on the configurations of the exchanger and of the nature of the liquid / gas phase of the fluids undergoing heat exchange. Thus, it is conceivable: - to produce all the plates with a primary face and a secondary face presenting a succession of reliefs of the same height, so that after placement of the spacer and assembly, all the apices of said reliefs opposite each other come into contact with each other, in order to define channels respectively for the primary fluid and the secondary fluid; - to produce all the plates, again identical, but whose geometry, and in particular the height of the reliefs of the primary face is different from that of the reliefs of the secondary face, so as to define inter-channel passages for the circulation of the secondary fluid, optimizing the operation of the exchanger when in particular the secondary fluid changes phase following the heat exchange; - to produce all the plates, again identical, but whose geometry of the reliefs of the primary face is different, in particular in terms of amplitude than that of the reliefs of the secondary face, so as to define different passage sections between primary circuit and secondary circuit.

[0020] Depending on the pressure of the fluids passing through the primary and secondary circuits, the welding of the spacers to the plates can be carried out by transparency, and therefore as the plate / spacer / plate assemblies are made, or by diffusion welding, when the complete stack is made.

[0021] Diffusion welding can be implemented by hot isostatic compression welding, better known by the acronym CIC. This technology consists of placing the entire stack within a chamber (CIC furnace) after evacuating the interior of said chamber using a vacuum tube, and then subjecting said chamber to high pressure under inert gas, typically on the order of 1,000 bar at high temperature, although lower than the melting temperature of the metal constituting the plates and spacers. These temperature and pressure conditions allow intermolecular diffusion to occur at the interface between the parts to be welded.

[0022] Alternatively, this diffusion welding can be implemented by hot uniaxial compression welding, better known by the acronym CUC (or Uniaxial Diffusion Welding - SDU). This technology, similar to the previous one, consists of simultaneously applying a high temperature and a load perpendicular to the plates and spacers, limited to the areas where the plates and spacers are in contact, thus excluding the heat exchange zone. This operation is carried out under vacuum to prevent gas trapping at the interfaces.

[0023] Furthermore, the implementation of laser welding technology ensures a seal between the primary and secondary circuits. This welding can be easily automated, so that the time saved in the production of such exchangers is greatly optimized compared to prior art techniques.

[0024] According to the invention, the shape of the reliefs can be varied, and typically of a sinusoidal, triangular, or other nature.

[0025] Obviously, the respective thicknesses of the plates, the spacers and the amplitude (height of the raised areas) (waves) are determined to achieve the desired result, and in particular the definition of channels with or without interchannel circulation for the same fluid. Brief description of the figures

[0026] The manner in which the invention can be implemented and the resulting advantages will be more apparent from the following implementation examples, given by way of illustration and not limitation, in support of the attached figures.

[0027] Fig. 1 is a schematic perspective view of a stamped plate according to the invention.

[0028] Fig. 2 is a detailed view of Fig. 1, illustrating the transition between the central area of ​​said plate and the fluid collection area.

[0029] Fig. 3 is a schematic cross-sectional view taken within the heat exchange zone of the plate in Figures 1 and 2.

[0030] Fig. 4 is an exploded view illustrating the assembly of two plates and two spacers of the invention, in order to define a first series of channels for one of the two primary or secondary fluids of the exchanger to be made.

[0031] Fig. 5 is a schematic view illustrating a first step in the realization of a plate heat exchanger according to the invention.

[0032] Fig. 6 is a schematic view illustrating a second stage of realization of a plate heat exchanger according to the invention.

[0033] The [Fig.7] is a schematic partial sectional representation of the heat exchange zone of an assembly of a lower plate, a spacer and an upper plate.

[0034] Fig. 8 is a schematic plan view illustrating the placement of the welds.

[0035] Fig. 9 is a detail view of Fig. 8.

[0036] Fig. 10 is a schematic view illustrating a fourth step in the realization of a plate heat exchanger according to the invention.

[0037] Fig. 11 is a schematic view illustrating a fifth step in the realization of a plate heat exchanger according to the invention.

[0038] Figure 12 is a schematic partial sectional representation of the heat exchange zone of a lower plate assembly, of a spacer, an intermediate plate, another spacer and a top plate, obtained after the steps in figures 10 and 11.

[0039] Fig. 13 is a schematic plan view illustrating the placement of the welds made on the assembly shown in Fig. 12.

[0040] Fig. 14 is a schematic partial perspective view of the plate and spacer assembly according to the preceding figures, illustrating eight layers for the secondary circuit and nine layers for the primary circuit.

[0041] Fig. 15 is a schematic perspective representation illustrating the positioning of the inlet and outlet manifolds of the primary and secondary fluids within the plate heat exchanger of the invention.

[0042] Fig. 16 is a view analogous to Fig. 15 with a partial lateral section view.

[0043] Fig. 17 is a view analogous to Fig. 15 with a partial frontal section view.

[0044] Figure 18 is a schematic perspective view illustrating the transition zone of the exchanger conforming to the invention.

[0045] Fig. 19 is a view similar to Fig. 18 but made from a different location.

[0046] Fig. 20 is a schematic representation of a variant of the invention, implementing stiffeners at the level of the collection or introduction pipes of one of the fluids.

[0047] The [Fig.21] is a schematic perspective and partial section representation of the exchanger implementing the variant of the [Fig.20].

[0048] Fig. 22 is a schematic cross-sectional representation of another embodiment of the invention illustrating the lateral diffusion of the secondary fluid.

[0049] Fig. 23 is a schematic perspective and sectional representation of yet another embodiment of the invention.

[0050] Fig. 24 is a schematic sectional view of another embodiment of the invention.

[0051] Fig. 25 is a schematic sectional view illustrating yet another embodiment of the invention. Detailed description of the invention

[0052] We have therefore schematically illustrated on [Fig.1] a plate (1) implemented in the context of the realization of the plate heat exchanger according to the invention.

[0053] This metal plate (1), for example made of titanium or nickel-based alloy, or stainless steel, has a typical thickness of between 0.5 and 2 millimeters.

[0054] It has a so-called primary face (2) and, on the opposite side, a so-called secondary face (3).

[0055] This plate is stamped in such a way as to define, at the level of a so-called heat exchange zone (4), a succession of reliefs (6), oriented parallel to the main dimension of the plate.

[0056] This heat exchange zone (4) has, in the example described, at its two ends, a divergence and collection zone (5), coplanar with said heat exchange zone (4), each of said divergence and collection zones (5) being pierced by two through lights (7) whose function will be specified later.

[0057] Furthermore, the heat exchange zone (4) has on either side of the succession of reliefs (6), a flat portion (8) whose function will also be described later.

[0058] A schematic cross-sectional view of the plate (1) at the heat exchange zone (4) is shown in [Fig. 3]. This figure helps to better illustrate the succession of reliefs (6), and in the example described, these reliefs consist of a succession of sinusoids of the same amplitude.

[0059] These reliefs are produced by stamping, a technique now widely mastered, so there is no need to describe it in more detail here. As can be seen in [Fig. 3], these reliefs protrude on either side of the general plane P, in which the plate (1) is inscribed.

[0060] These protruding reliefs (6) are intended to define, in cooperation with complementary reliefs provided within a consecutive plate (1), channels for the circulation of fluids, as will become clear from the following description.

[0061] In this regard, a schematic exploded view of an elementary assembly forming part of a plate heat exchanger according to the invention is shown in relation to [Fig.4], consisting of two plates (1) of the type in question associated with two spacers (10, 10').

[0062] These spacers (10, 10') have the same length and width as the plates (1) and are intended to be inserted between two consecutive plates (1). They are made of the same metal as the plates (1).

[0063] These spacers (10, 10') have, in line with the divergence and collection zones (5) of the plates (1), on the one hand, through-holes (11), identical in terms of dimensions to those (7) of the plates (1) and intended to be located in the alignment of said holes (7) when the assembly is assembled, and consequently to define channels (19) for collecting and conveying fluids, and on the other hand, a through-hole (12), extending over substantially the entire length of the spacer.

[0064] The width of the main dimension of this opening (12) corresponds substantially to the placement of the raised areas (6) of the stamped plates (1). This through-hole (12) extends at its two ends in a shape divergent (13), intended, when the exchanger is constructed, to define fluid inlet and outlet pipes respectively within and outside the channels resulting from the stacking of the plates. These fluid inlet and outlet pipes terminate at the level of the fluid collection and conveyance pipes (19, 19').

[0065] It is because of the divergence of these two ends (13) that it is possible to separate the primary circuit from the secondary circuit. Indeed, by alternating the orientation of said divergent ends (13) by reversing the spacers from one layer to the next ([Fig.4]), the ends of the fluid inlet and outlet pipes terminate within the respective collection and conveyance pipes (19, 19') of the primary and secondary fluids.

[0066] The realization of a first elementary assembly according to the invention will be described below.

[0067] Thus, after the plates (1) have been made by stamping, a spacer (10) is positioned on a plate (1) called the lower plate, the divergence zones (13) of which are both directed, in the [Fig.5], to the right.

[0068] Next, a new plate (F) is positioned ([Fig. 6]), having taken care to turn it over so that its primary face (2') is located opposite the primary face (2) of the lower plate (1). This results in a stacking arrangement illustrated in [Fig. 7] which, due to the turning over of the upper plate (1'), allows, in the example described, the apices (16) of all the respective reliefs (6) of the lower plate (1) to be brought into contact with those of the upper plate (1').

[0069] It can also be observed on this [Fig.7], that the thickness of the spacer (10) is chosen precisely to allow this precise contact of the respective apices (16).

[0070] Once this positioning has been achieved, a transparent weld is then carried out, and in this case by laser welding at the level (14) of the area of ​​the apexes (16) of the reliefs (6) in contact with each other, and therefore only concern the plates (1,1')-

[0071] Corollarily, or even simultaneously, if the pressure of the fluids passing through the primary and secondary circuits is not too high, and typically less than 10 bar, such a laser welding (15) is also carried out on the one hand at the level of the periphery of the assembly, that is to say respectively all along the area (8) of the plates (1, 1') and of the corresponding area of ​​the spacer (10), and on the other hand at the level of the divergence areas (13) and the lights (7, 11) respectively of the plates (1, 1') and of the spacer (10), as can be seen in figures 8 and 9.

[0072] Laser welding can easily be automated, allowing considerable time savings in the production of such an assembly, and ultimately, of the heat exchanger itself.

[0073] The laser welds were illustrated by arrows (14) and (15) on [Fig.7], and by lines bearing the same numerical references on Figures 8 and 9, these lines being intended to illustrate the continuity of the welds for the main purpose of sealing between the circuits, respectively primary and secondary.

[0074] Once these welds have been made, a new spacer (10') ([Fig. 10]) is positioned on the elementary assembly thus formed, but reversed so as to orient the divergence zones (13) in a direction opposite to that of the spacer (10).

[0075] Then, as a corollary, a third stamped plate (1) is placed on top of this spacer (10') ([Fig. 11]), thus resulting in the stacking illustrated in [Fig. 12], said third plate (1) being again inverted and therefore strictly parallel to plate (1), so that once again the apices of the reliefs of plate (1) are in contact with the corresponding apices of the reliefs of plate (1'). Here again, the thickness of the spacer (10') is selected to allow this contact of the respective apices.

[0076] Further laser welding is then carried out, illustrated by the arrows (14'), (15') on [Fig.12] and the lines bearing the same references on [Fig.13].

[0077] It is therefore defined, as illustrated in [Fig. 14], after repeating the preceding operations a certain number of times, channels (17) for the primary fluid and channels (18) for the secondary fluid, distributed alternately in strata in order to promote heat exchange between the primary fluid and the secondary fluid.

[0078] On the other hand, if the pressure of one or both of the fluids is too high, and in particular greater than 10 bar, laser welding between the plates and the spacers may prove insufficient to guarantee the mechanical strength of the exchanger.

[0079] Diffusion welding is then used. However, due to the pressure exerted, particularly perpendicular to the plane of the plates, in this diffusion welding technique, the difficulty arises from the free spaces generated by the fluid circulation channels. Therefore, in such a configuration, laser welding of the apices (16) is carried out, an operation performed as often as necessary depending on the number of plates used, and then diffusion welding of the entire stack is performed, limited to the areas where there is contact between the plates and the spacers.

[0080] However, even when using diffusion welding, it may be envisaged to also carry out laser welding (15) at the interface between the plates (1, 1') and the spacers (10, 10'), capable of guaranteeing a prior seal, allowing the primary and secondary circuits to be evacuated during the diffusion welding cycle.

[0081] As already mentioned, the diverging ends (13) of the slots (12) of the spacers (10, 10') are intended to define, in cooperation with the lower plates and upper sections to which they are welded, conduits respectively for the introduction and evacuation of primary and secondary fluids into and out of the primary and secondary channels (17, 18). As can be seen, for example, in Figures 4, 5, and 6, these diverging ends (13) alternate from one spacer to the next. Indeed, it is necessary to completely isolate the path of the primary fluid from that of the secondary fluid.In fact, the conduits defined by the lower plate / spacer / upper plate assembly terminate laterally relative to the main dimension of the heat exchanger, respectively on one side and the other of said exchanger (see Figures 15 to 17), thus allowing primary (20) and secondary (21) fluid inlet manifolds to introduce the primary and secondary fluids into the exchanger, and primary (22) and secondary (23) fluid outlet manifolds to collect said fluids after heat exchange, while allowing the primary fluid to be isolated from the secondary fluid. Therefore, the primary fluid inlet (20) and outlet (22) manifolds are positioned on the same side of the exchanger, while the secondary fluid inlet (21) and outlet (23) manifolds are positioned on the other side of said exchanger.

[0082] The alternating collectors are shown schematically in Figures 18 and 19, drawn from two separate sections of the heat exchanger of the invention. The barrier function of the spacers, which prevent any communication between the primary and secondary circuits, can thus be observed.

[0083] Where appropriate, when significant pressures of the fluids or of one of the two fluids (primary or secondary) are to be managed, and in order to avoid any collapse of one of these two circuits, stiffeners (24), illustrated in figures 20 and 21, may be installed, fixed in particular by laser corner welding, and / or by laser transparency through the immediately superior plate or by a combination of the two, on the plates (1) or (1') concerned, and of a thickness corresponding to the thickness of the spacer.

[0084] In this hypothesis, the quantity and geometry of these stiffeners are selected according to the mechanical strength under pressure sought, in addition to the thermo-hydraulic optimization of the exchanger.

[0085] According to a second embodiment of the invention illustrated in [Fig. 22], the opposite apices of the reliefs of two consecutive plates intended to define the secondary circuit (18) may not be in contact with each other, thus allowing lateral diffusion of the fluid flowing through the circuit thus formed due to free space (25) provided between the opposite apices of the reliefs in question. In fact, this particular embodiment is especially suitable when the secondary fluid undergoes a liquid / gaseous phase change. To achieve this embodiment, the amplitude of the reliefs of the plates, at the level of one of the faces (2, 3) that they define, is less important than the amplitude of said reliefs protruding on the other face.

[0086] According to another embodiment of the invention, illustrated in [Fig. 23], when the heat exchanger is likely to be subjected to significant pressures, substantial pressure differentials may occur. Therefore, in order to maintain the cohesion of the heat exchanger, lower (26) and upper (27) end plates, respectively, with a thickness considerably greater than that of the stamped plates (1, 1'), are attached to either side of the heat exchanger. In this configuration, the upper plate is welded to the stack, for example, using TIG torches. These plates (26, 27), due to their thickness, cannot be stamped. They are therefore machined to define the protruding reliefs on their functional face, which, together with an opposing stamped plate, defines the fluid circulation circuits.

[0087] Furthermore, while the preceding examples have illustrated sinusoidal reliefs, other types of reliefs can be considered, such as the triangular one shown in [Fig. 24]. The important factor is the placement of these reliefs, which must be perfectly aligned and directly above each other during stacking.

[0088] Finally, it is also possible to seek a volume for one of the two circuits that differs from the other. To this end, channels of the primary and secondary circuits, respectively, are defined with distinct cross-sectional areas, as can be seen in [Fig. 25]. In order to achieve this result, the protrusions projecting from one face (2, 3) of the plates (1, 1') have a different amplitude than the protrusions projecting from the other face. It can thus be observed that the cross-sectional area of ​​the channels of the primary circuit (17) is significantly larger than that of the channels of the secondary circuit (18).

[0089] It should also be emphasized that it is possible to play with the thicknesses of the spacers to maintain a ratio between the passage sections in the divergence zones, i.e. leading to the level of the collectors.

[0090] The advantages of the invention's process, which allows for: - firstly, to drastically simplify the production of the plates used in a plate heat exchanger, by simple stamping, the technology of which is widely mastered; consequently, this production makes it possible to significantly reduce the corresponding costs; - to ensure optimum sealing between the primary and secondary circuits due to laser welding by transparency, this welding can be carried out automatically, supplemented or not by diffusion welding.

[0091] By doing so, a plate heat exchanger is obtained by this process, the heat exchange capacities of which are adaptable according to, on the one hand, the number of stamped plates conforming to the invention, and on the other hand, the cross-section of the channels which said plates define between them.

Claims

1. Demands Method for making a heat exchanger consisting of a stack of plates 1, 1'), defining between them two distinct circuits for the circulation of two fluids respectively primary (17) and secondary (18), consisting of: - to produce identical metal plates by stamping, suitable for defining: . on the one hand a central zone (4) comprising a succession of alternative reliefs (6) projecting on either side of the plane P in which each of the plates is inscribed, and . on the other hand two divergence and collection zones (5) provided on either side of the central zone (4); each of the stamped plates thus presenting a primary face and a secondary face; each of the plates having through lights (7) provided at the collection areas; - to stack said plates one on top of the other, the primary face of one opposite the primary face of the following plate, and successively the secondary face of said following plate opposite the secondary face of a following plate so as to define continuous channels (17, 18) for the circulation of primary and secondary fluids; - to insert between two consecutive plates a spacer (10, 10') resting on the periphery of said plates, and whose thickness is adapted to the height of the reliefs (6) resulting from the stamping, such that the reliefs of the primary faces are vertically aligned with the reliefs of the opposing primary faces and that the reliefs of the secondary faces are vertically aligned with the reliefs of the opposing secondary faces, and for all or part of them, that the apices (16) of the reliefs in question opposite are in contact, said spacers being provided with two types of through-holes at their two ends, respectively (11) intended to form, after stacking with the plates, channels (19, 19') for collecting or conveying fluids oriented perpendicularly to the plane in which the plates and spacers are inscribed, and to form between two consecutive plates an introduction channel and - to evacuate fluids respectively within and out of the channels resulting from the stacking of the plates; - to weld the apexes (16) opposite each other and in contact with each other by transparency; - to repeat the welding operation for as many assemblies as necessary until an exchanger is produced incorporating the number of plates according to the desired heat exchange capacity, the spacers being welded to the plates to guarantee the seal between the primary and secondary circuits.

2. Method of making a heat exchanger according to claim 1, wherein the welding of the spacers to the plates is carried out by transparency, and therefore as the plate / spacer / plate assemblies are made.

3. Method of making a heat exchanger according to claim 1, wherein the welding of the spacers to the plates is carried out by diffusion welding, when the complete stack is achieved.

4. Method of making a heat exchanger according to claim 3, wherein the welding of the spacers to the plates is first carried out by transparency during the making of the plate / spacer / plate assemblies, then by diffusion welding, when the complete stack is made.

5. Method of making a heat exchanger according to any one of claims 1 to 4, wherein the protruding reliefs (6) made by stamping on the primary and secondary faces are of the same amplitude.

6. Method of making a heat exchanger according to any one of claims 1 to 4, wherein the geometry of the protruding reliefs (6) of the primary face is different from that of the protruding reliefs of the secondary face, so as to generate secondary circuit channels with a cross-section distinct from the primary circuit channels.

7. Method of making a heat exchanger according to any one of claims 1 to 4, in which diffusion spaces (25) are provided within the secondary circuit, and resulting from a different height of the protruding reliefs of one of the two primary or secondary faces of the plates.

8. Method of making a heat exchanger according to any one of claims 1 to 7, wherein the shape of the protruding reliefs is chosen from the group comprising sinusoids, triangles.

9. Plate heat exchanger made according to the process of any one of claims 1 to 8.

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