WO2006072686A1

WO2006072686A1 - Device for heat exchange between two fluids comprising metal foam layers

Info

Publication number: WO2006072686A1
Application number: PCT/FR2005/003205
Authority: WO
Inventors: Patrice Jude
Original assignee: Areva Np
Priority date: 2004-12-29
Filing date: 2005-12-20
Publication date: 2006-07-13
Also published as: FR2880106B1; FR2880106A1

Abstract

The invention concerns a device comprising at least one heat exchanging module (2) consisting of a plurality of mutually parallel metal foam layers (10a, 10b) and a second plurality of mutually parallel solid flat metal foam layers (13), each metal foam layer (10a, 10b) being interposed between two successive solid metal foam layers and surrounded by a peripheral rim tightly fixed against at least one of the solid metal foam layers (13). The metal foam layers (10a, 10b) are each arranged in a closed space constituting a circulation element for the first or the second fluid. Means for dispensing and recovering (15a, 15b, 16) the first and the second fluids, at the successive foam layers in a longitudinal direction of the module are arranged so that, in one and in the other of the two fluid circulating elements with metal foam layers arranged adjacent in the longitudinal direction, the first and second fluids flow, respectively, in a transverse direction substantially perpendicular to the longitudinal direction, and so that the first and second fluids flow successively in one on two metal foam elements arranged successively in the longitudinal direction of the module.

Description

Device for exchanging heat between two fluids comprising layers of metallic foam

The invention relates to a device for exchanging heat between first and second fluids which can be at high temperature and / or high pressure.

In the field of energy production, and in particular electrical energy, it may be necessary to perform heat exchange between fluids that can be high or very high temperature and high pressure.

In particular, there are known nuclear power plants used for the production of energy and in particular of electrical energy, which comprise one or more high-temperature reactors whose heat transfer fluid cooling the fuel assemblies of the nuclear reactor core is constituted by a gas light and inert like helium. The core of the reactor at very high temperature produces a heating of the coolant to a temperature above 85O ⁰ C, this temperature can go up to 950 ⁰ C in the case of some high temperature reactors.

It may be advantageous to ensure heating of an intermediate gas with a higher density than helium, for example a mixture of helium and nitrogen, by taking heat transported by the heat transfer gas generally consisting of technically pure helium. Indeed, the use of a higher density gas, for example to drive gas turbines coupled to the alternator of the power plant provides significant benefits in terms of energy efficiency and efficiency. cost of realization of the power plant. However, a major difficulty of this type of operation of a high temperature nuclear reactor is related to the design of heat exchanger devices to ensure heat exchange with a very good performance between low density gas at high temperature. temperature and at high pressure, in an industrial plant for energy production in which it implements very high flow rates of exchange gas. Plate heat exchangers consisting of a stack of sheets having ribs of complex shapes to form between them The gas ducts could provide a solution by adapting the configuration of the heat exchanger to the characteristics of the gases on which a heat exchange is performed. However, the design and use of such heat exchangers with very high temperature gases present difficulties and above all, these heat exchangers are completely inadequate to ensure heat exchange between gases at different pressures, even if the pressure difference between the gases is low, for example a few bars.

It is also known, for example from the patent application WO-02/42707, a heat exchanger comprising tubes or ducts in which a first exchange fluid circulates in thermal contact with a metal foam body in which a second fluid circulates. whose heat is transmitted to the first fluid circulating in the tubes or conduits, via the metal foam and the wall of the tubes or conduits in thermal contact with the metal foam. However, such a device can have a good fluidic and thermal efficiency only by providing a volume density gradient of the metal foam, in directions perpendicular to the flow direction of the second fluid, the volume density of the metal foam to be increasing in direction of the wall of the tubes or circulation ducts of the first fluid. The design of such a device presents difficulties.

In addition, an exchange device comprising tubes or conduits for the circulation of a first fluid surrounded by a metal foam in which a second fluid circulates, allows efficient operation only in the case where the two exchange fluids have characteristics of density and heat exchange very different. Such a device can be used in fact only to achieve a heat exchange between a liquid flowing in the tubes or ducts and a gas flowing in the metal foam body. A problem inherent in carrying out a heat exchange between fluids, in particular gaseous fluids, flowing with a very large volume flow, which is the case for heat exchanges between a primary gas and a secondary gas in a nuclear power plant comprising a high reactor temperature, relates to the production of a compact heat exchanger for treating very large gas flows with a very good thermal efficiency, that is to say a heat exchange device having a very large exchange surface under a small volume and likely to receive and process very large quantities of gas.

The object of the invention is therefore to propose a device for exchanging heat between a first and a second fluid, capable of ensuring an efficient and very efficient heat exchange between low density fluids such as light gases which may be very high temperature and at different pressures, while having good compactness and very good resistance to thermal and mechanical stresses.

For this purpose, the device according to the invention comprises at least one heat exchange module consisting of a first plurality of metal foam layers bounded by substantially plane faces and parallel to each other and a second plurality of metal layers. in that they are substantially plane and parallel to one another, each layer of metal foam being interposed between two successive solid metal layers and surrounded by a solid metal peripheral rim fixed in a sealing manner against at least one of the solid metal layers between which is interposed the layer of metal foam, so that the layers of metal foam are each placed in a tightly insulated closed space and constituting, with at least one adjacent solid layer, a circulation member of one of the first and second fluids and means for distributing and recovering the first and second fluids at the level of the successive foam layers in a longitudinal direction of the module substantially perpendicular to the foam layers such as in one and the other of two metal foam layer fluid circulation elements disposed adjacently in the longitudinal direction of the module, the first and second fluids circulate in a transverse direction substantially perpendicular to the longitudinal direction, respectively, and the first and second fluids flow successively in one of two of the metal foam, arranged successively in the longitudinal direction of the module.

According to more particular characteristics that can be taken separately or in combination: the heat exchange module consists of metal plates juxtaposed and assembled together, successively in the longitudinal direction of the module comprising foam support plates and plates solid metal separators for forming the metal foam layers and the solid metal layers, each of the support plates having a respective cavity for receiving a metal foam layer and a peripheral flange surrounding the cavity;

- The cavities of the support plates of the metal foam layers are flat bottom cuvettes machined in at least one of the faces of the metal plate, leaving the plane peripheral rim around the cavity;

the cavities of the foam support plates pass through the support plates over their entire thickness, the support plates constituting a frame surrounding the metal foam layer; the heat exchange module is constituted by metal plates juxtaposed and assembled together, successively in the longitudinal direction of the module, all the metal plates being foam support plates each having a cavity having the shape of a trough bounded by a rim and a flat bottom, the solid layers of separation of the foam layers being constituted by directly attached flat bottoms, each on a flange of an adjacent foam support plate;

the solid metal plates or the flat bottoms of the foam support plates comprise on at least one of their faces at least one projecting element such as a rib or a fixing and positioning pin, a fluid distribution rib or a heat exchange fin; two solid metal plates are attached against metal foam support plates at the longitudinal ends of the module and constitute end and closure plates of the module;

the module fluid distribution and recovery means totally integrated in the module are constituted by openings of the solid separation plates and metal foam layer support plates aligned in the longitudinal direction of the module with stop zones of the module; longitudinal circulation of the fluids in the cavities containing the metal foam layers and with passage zones of the first or second fluid through a corresponding layer of metal foam in the longitudinal direction of the module, so as to ensure a circulation of the first and second second fluids in transverse directions, each within one of two metal foam layers in the longitudinal direction of the module; the module comprises, at its longitudinal ends, means for introducing fluid into the module and means for extracting fluid from the module, so as to produce, inside the module, a general circulation of the first and second fluids; in one of the following modes:

. countercurrent circulation, the first fluid introduction means and the second fluid extraction means being located at a first longitudinal end of the module and the second fluid introduction means and the first fluid extraction means being arranged at the second longitudinal end of the module,

. co-current flow, the means for introducing first and second fluids being disposed at a first longitudinal end of the module and the extraction means of the first and second fluids of the module being located at the second longitudinal end of the module.

the device comprises a plurality of modules arranged in parallel, having means for supplying first and second fluids connected in parallel with a means for supplying, respectively, first and second fluids, and means for recovering first and second fluids, second fluids connected respectively to a first and second means for recovering first and second fluids. The invention relates in particular to a device for exchanging heat between a first gas at a temperature at least equal to 85O ⁰ C and a second gas which is heated to a temperature of at least 800 ⁰ C, characterized in that that the support plates of the foam layers and the solid metal separation plates are made of a refractory alloy such as a nickel alloy and the metal foam of a material such as nickel or an alloy of iron, chromium and aluminum .

In order to clearly understand the invention, reference will be made, by way of example, with reference to the appended figures, of several embodiments of a heat exchanger device according to the invention which can be used to ensure a heat exchange between two high temperature gases such as heat-carrier helium of a high temperature nuclear reactor and a mixture of helium and nitrogen.

Figure 1 is a cutaway perspective view of a device according to the invention.

FIG. 2 is a sectional view of a gas distribution manifold of the device, along 2-2 of FIG. 1.

Figure 3 is an exploded perspective view of a module of the heat exchange device according to a first embodiment. Figures 4A and 4B are schematic views showing the flow directions of the fluids within the module, according to a first and second variant.

Figure 5 is an exploded perspective view of a portion of a module according to a second embodiment. Figure 6 is a plan view of an alternative embodiment of a metal foam layer support plate.

FIG. 1 diagrammatically shows a heat exchanger device according to the invention which will generally be designated by the reference numeral 1. The heat exchanger 1, made in modular form, comprises elementary modules 2 which can be placed side by side and assembled as a compact unit with a number of Modules adapted to gas flows between which heat exchange is carried out.

In the case of the use of the heat exchanger device for heating an intermediate secondary gas from the cooling heat-transfer gas of a HTR reactor, the heat-transfer gas, which is generally helium, constitutes the primary fluid whose heat is transferred. a secondary fluid which is the intermediate fluid consisting of a gas such as a mixture of helium and argon.

Each of the modules 2 of the heat exchanger device 1 comprises, at one of its longitudinal ends, an inlet opening 3a of the first fluid and, at its opposite longitudinal end, an outlet opening 3b of the first fluid. Similarly, each of the modules comprises, at one of its longitudinal ends, an inlet opening 4a of the second fluid and, at its opposite longitudinal end, an outlet opening 4b of the second fluid.

In FIG. 1, the modules 2 are arranged in such a way that their longitudinal direction along which the general circulation of the fluids is carried out is the vertical direction. Of course, other arrangements could be provided in which the longitudinal direction of the modules would for example be horizontal.

Similarly, in Figure 1, there is shown the flow direction of the first and second fluids by arrows. In this embodiment, the fluids circulate in the longitudinal direction of the modules and in the opposite direction (countercurrent circulation), but it would also be possible to envisage a circulation of the first and second fluids in the longitudinal direction, in the same direction (co-current circulation).

As can be seen in FIGS. 1 and 2, the supply of the first and second fluids of all the modules 2 of the heat exchanger device 1 and the recovery of the first and second fluids after circulation in the modules can be ensured. by collectors 5a, 6a, 5b, 6b attached and fixed on the longitudinal ends of the modules 2.

A first collector 5a fixed on a first longitudinal end (upper end in FIG. 1) supplies the modules 2 with power. first fluid and a collector 5b attached to the second end (lower end of the modules), the recovery of the first fluid after circulation in the modules. Similarly, a first collector 6a feeds the second fluid modules at a first end of the modules and a second collector 6b ensures the recovery of the second fluid at a second end of the modules, after circulation in the modules.

As can be seen in FIG. 2, the collectors can be made in the form of elongate distribution ramps sealingly attached to the end portions of the modules and having a longitudinal center channel 7 and distribution channels 8 substantially perpendicular to the longitudinal channel 7 distributed along the length of the manifold so that each of the distribution channels 8 is vis-à-vis a feed opening such as 3a (or a recovery opening such as 4b), when the collector is fixed on the end part of the modules. The junction between the collectors and the ends of the modules must be fluid tight so as to avoid any fluid outlet, at the collector connection.

In this way, the power supply of the fluid modules and the recovery of the fluids are carried out in such a way that the modules 2, which are all identical, operate in parallel, so that the total flow rate of treatment of the heat exchanger is equal to the flow rate. processing of each of the modules multiplied by the number of modules. It is therefore easy to adapt the processing flow rate of the heat exchanger to the gas flow at the outlet of an industrial installation such as a nuclear reactor HTR. In addition, the heat exchanger as a whole that can have a parallelepiped shape is compact and has dimensions that are deduced from the size and number of the modules 2. The parallelepiped heat exchanger assembly 1 has a height equal to the longitudinal dimension L of the modules 2, a width equal to the transverse dimension 11 of the modules and a length equal to n times the transverse dimensions 12 of the modules, for an exchanger comprising n modules. To deal with large fluid flow rates, it is possible to use several exchanger devices such as the device 1 connected in parallel and arranged inside an enclosure.

Each of the modules comprises successive layers 9 and 10 brought against each other and juxtaposed, in the longitudinal direction of the module. As will be explained below, the successive layers 9 and 10 which are successively arranged, alternately, in the longitudinal direction of the module have different structures and functions, the layers 9 being separation layers and the layers 10, necks - Fluid circulation.

In general, the fluids circulate in each of the circulation layers 10 in a transverse direction, in one direction for a circulation layer and in the opposite direction for the next layer separated from the first layer by a separation layer. The separation layers 9 are made of a solid metallic material and the circulation layers comprise a metal foam having a network of porosities allowing a passage of fluid through the material whose contact surface with the circulating gases is very large, due to the presence of many porosities of small dimensions. Such materials are known and have been used in certain types of heat exchangers which are not, however, suitable for heat exchanges between gases, as mentioned above.

Preferably, (FIG. 3) the successive layers 9 for separating and circulating fluids 10 are made from rectangular metal plates having for length the transverse dimension 11 and for width 12 the dimension of the module, stacked and assembled together. in order to ensure a tight closure around the metal foam circulation layers 10, to avoid leakage of exchange fluid to the outside of the module and any mixing between the exchange fluids.

The layers 10 of metal foam are fixed inside recesses machined in plates 14a and 14b, the cavities of the plates 14a being intended to receive layers of metal foam 10a for the circulation. tion of the first fluid and the cavities of the plates 14b being intended to receive layers of foam 10b for the circulation of the second fluid.

The plates 14a and 14b are made from planar rectangular plates, one face of which is hollow-machined to form the cavity intended to receive a layer of metal foam having itself substantially in the form of a plate.

The metal foam layer may be attached and fixed in the cavity of the corresponding plate, for example by welding or brazing. The metal foam layer may also be formed in situ within the cavity of the plate. The cavities of the plates 14a and 14b are formed on one of the faces of a flat plate with parallel faces, by hollow machining, to a thickness less than the thickness of the plate with parallel faces.

As can be seen in FIG. 3, the cavity 14'a or 14'b has, in the plane of the plate, a substantially rectangular shape whose angles are rounded and protruding, either outwards or towards the inside the rectangular contour of the cavity. The cavity 14'a or 14'b which has the shape of a flat-bottomed bowl is surrounded and delimited by the non-machined portion of the plate having the shape of a planar frame 14 "a or 14" b. More generally, in the case of plates having different shapes of a rectangular shape and possibly having curved shapes, the cavities serving as a housing for the layers of metal foam are also surrounded by a flange extending in a closed contour having a flat surface. In the case of rectangular plates, as shown in Figure 3, two through openings 15a (or 15b) are provided in two corners of the frame arranged along a diagonal of the rectangular frame.

For each of the cavities 14'a and 14'b, the corresponding through openings 15a or 15b are located along a first diagonal and, following the second diagonal of the cavity at the corners of the contour of the cavity, that is to say say the inner contour of the frame 14 "a or 14" b, the cavity extends outwardly of the frame. As can be seen in FIG. 3, the module comprises, in addition to plates 14a and 14b intended to receive a layer of metal foam, solid metal plates 13 each having four through-openings 16 situated at the corners of the plate. According to an alternative embodiment, the successive layers 9 and 10 of the heat exchange module can be made from metal foam support plates (similar to the plates 14a and 14b), only. Each of the support plates 14a and 14b has a respective bowl 14'a and 14'b delimited by a peripheral rim (such as frames 14 "a and 14" b) and a flat bottom. The solid layers 9 of the module are constituted by the flat bottoms of the cavities of the foam support plates which are attached to one another, so that the peripheral rim of a plate is attached against the flat bottom of a plate adjacent support. The module also comprises, at its longitudinal ends, two rectangular metal plates forming closure plates 11 and 12 whose dimensions are identical to the dimensions of the plates 13 and plates 14a and 14b. The end plates 11 and 12 are traversed by apertures at two corners located at the ends of a transverse side of the plates of length 12. The openings of the upper end plate 11 correspond, for one, to the opening 3a inlet of the first fluid in the module and the other to the opening 4b output of the second fluid of the module. The second end plate (lower plate 12) is crossed at two angles at the ends of a transverse side of length 12, by two openings constituting, for one, the opening 3b of the first fluid outlet and, for the other, the inlet opening 4a of the second fluid in the module.

The arrangement of the inputs and outputs 3a, 4b and 3b, 4a of the module shown in FIG. 3 corresponds to a flow of the first and second countercurrent fluids, as shown diagrammatically in FIG. 4A.

FIG. 4B schematically shows a second embodiment of the circulation of the first and second fluids in the same direction or co-current circulation, the inlet openings 3a and 4a of the first and second fluids passing through a first end plate of the module (upper plate) and the outlet openings 3b and 4b of the second fluid passing through the second end plate (bottom end plate) of module 2.

The assembly of the module 2, as shown in Figure 3, is achieved by stacking on one another the plates that have just been described, in a certain order.

Above the first end plate (for example the bottom plate 12) is disposed a first plate providing support for a first layer of metal foam 10, for example a plate 14b of a layer 10b intended to be crossed. by the second fluid.

Above the first support plate of a metal foam layer 14b is disposed a first solid plate 13, then a second support plate of a metal foam layer for receiving the first exchange fluid 14a. which is itself covered by a solid plate 13. Stacking is continued by successively placing on one another a fluid circulation plate, a solid partition plate 13, and then a circulation plate of the fluid. Another fluid and a solid separator plate 13. Each of the assemblies comprising a foam support plate 14a or 14b, a foam layer 10a or 10b and a separation plate 13 resting on the foam layer constitutes an element of the module ensuring the circulation of one of the two fluids. Above the last circulation plate of a fluid (for example the plate 14a shown in FIG. 3, the second end plate (top end plate 11 in the case shown in FIG. ).

In the case of the embodiment where the layers 9 and 10 are made from the support plates only, these plates in which was fixed a metal foam are stacked directly on one another.

The various through openings of the plates are aligned axially in a longitudinal direction of the module perpendicular to the plates of the stack. In addition, the rounded corners of the outline of Cavities of the support plates of the foam layers located along the second diagonals delineate areas of the cavity vertically through the through openings of adjacent plates.

The plates 14a for supporting the metal layers in which the first fluid flows and the plates 14b for supporting the metal layers 10b in which the second fluid flows are arranged in such a way that the first diagonals of the plates 14a are parallel to the second diagonals of the plates 14b, the first diagonals of the plates 14b being parallel to the second diagonals of the plates 14a. The solid plates 13 comprise, on one of their faces intended to come into contact with a plane face of a support plate 14a or 14b, opposite the face on which is machined the corresponding cavity 14'a or 14 ' b, ribs 17 projecting to engage in corresponding grooves on the flat face of the support plate of a layer of metal foam. This provides a mechanical reinforcement of the solid plate 13 and a perfect positioning of the plate 13 relative to the metal foam support plate 14a or 14b. One of the end plates (lower end plate 12) also has, on its inner face facing the inside of the module, reinforcement and positioning ribs 18 intended to engage in grooves of the first metal foam support plate superimposed on the end plate 12.

The solid plates or the support plates may also comprise ribs intended to come into contact with a layer of metal foam. In this case, the ribs that are designed for this purpose can promote the distribution of gases over the entire surface of the plates and increase the gas exchange surface, avoiding for example a preferential flow in the center of the plates, in addition to a function of structural maintenance of the module. They can also act as fins promoting exchanges through the plates.

The plates which are stacked are assembled, so that each of the layers of metal foam 10a or 10b is inside a tightly closed space, the rim or frame rotating the cavity in which the metal foam is disposed being applied and sealed against an adjacent solid plate. For example, it is possible to seal the cavities 14'a and 14'b enclosing the metal foam layers, by welding the flange or frame surrounding the cavity enclosing the plastic foam on the flat face opposite the the solid plate 13 or an adjacent support plate (or the end plate 11 with respect to the upper metal foam support plate). It is also possible to seal tightly the solid plates 13 on the edges or frames of the metal foam support plates, with the interposition of a seal resistant to the temperature and pressure of the fluids.

Each layer of metal foam 10a and 10b is contained in a closed sealed space. However, all the spaces of the plates 14a and all the spaces of the plates 14b containing the metal foam communicate with each other to ensure the circulation of the first and second fluids. For this, an opening 15'a or 15'b crossing the bottom of the cavity of the support plates in one of the corners of the second diagonal of the cavity is in the axial extension of a through opening 16 of a plate adjacent solid 13 and a through opening 15a or 15b located in one of the corners of the first diagonal of a metal foam support plate located after the first metal foam support plate, in the general sense fluid flow in the longitudinal direction of the module.

For example, referring to Figure 3, starting from the plate 14a located below the upper plate 11, the first fluid introduced into the module through the opening 3a of the plate 11 reaches a first angle of the cavity of the first plate 14a, at the end of the second diagonal of the cavity, in a zone having no opening through the bottom of the cavity. In the angle at the second end of the second diagonal of the cavity of the plate 14a is provided an opening 15 'through the bottom of the cavity and located in the extension of the opening 16 of a first plate 13, the opening 15b of a metal foam support plate 14b and an opening 16 of a second plate full 13, located one after the other in the direction of flow of the first fluid, that is to say, in Figure 3, from top to bottom. The first fluid passing through the openings 15'a, 16, 15b and 16 of the second plate 13 arrives in the cavity of a second plate 14a located below the second plate 13, in an area having no opening at the end of the second diagonal of the second plate 14a. An opening 15 'passing through the bottom of the cavity is provided at a second end of the second diagonal of the second plate 14a, so that the first fluid flows in the general direction of the second diagonal of the plates 14a, in one direction then in the opposite direction, according to the length of the module in the longitudinal direction which is the general direction of circulation of the fluids.

As regards the second fluid, the support plates 14b of the metal foam layers for circulation of the second fluid comprise, at one of the ends of their second diagonal, an opening 15'b allowing the passage of the second fluid of a second fluid. plate 14b to the next.

In an alternative embodiment of the plates 14a and 14b, the cavity is made over the entire thickness of the plate which is fully perforated, the separation between the successive layers of metal foam being provided only by the intermediate solid plates 13 then that, in the case described above, the separation layers between two successive elements comprise both the bottom of the cavity and an intermediate separation plate, in contact with the face of the support plate 14a or 14b of the metal foam opposite the cavity or only the bottom of the cavity.

In this case, the intermediate plates 13 must have openings 16, only in positions intended to ensure the passage of the first or second fluid of a metal foam layer element to the next element in the longitudinal direction of the module, intended to receive the same fluid. Each of the two fluids is transmitted from a first metal foam layer member, through an opening 16 of the adjacent solid plate, to an opening 15a or 15b of the plate of the next metal foam member to receive the other fluid and an opening 16 of the next full plate. The fluid arrives in the metal foam layer of a next fluid receiving member in a closed area by a solid portion of the separating plate closing the second face of the next metal foam member receiving the fluid. The presence or absence of openings in the successive solid plates makes it possible to channel the fluid, so that it passes successively in one of the two metal foam layer elements, in the longitudinal direction of general circulation of the fluid through the module. The means of distribution and gas recovery constituted by openings, as described above, are therefore integrated into the heat exchange module and not reported, which has advantages in the manufacture of modules, their size and to their manufacture.

As can be seen in FIGS. 4A and 4B, the general circulation of the first and second fluids through the module can be ensured so that the fluids flow countercurrently or co-currently.

FIG. 4B schematically shows a module in which the flow of fluids in the longitudinal general direction of the module is made in the same direction. In this case, the inlet opening 3a of the first fluid in the module 2 and the inlet opening 4a of the second fluid are arranged at one and the same longitudinal end of the module and pass through, for example, the end plate 11. .

The outlet opening 3b of the first fluid and the outlet opening 4b of the second fluid are provided at a second end of the module and pass through the plate 12.

FIG. 5 shows a part of a module 2 in exploded perspective, the module 2 being fed with first and second fluids so that the general circulation of the first and second fluids in the longitudinal direction of the module is performed in the same direction. The module comprises successive elements of circulation of the first and second fluids which each comprise a plate such as 14a or 14b recessed over a portion of its thickness, so as to form a bowl of substantially rectangular or square shape with rounded corners wherein a metal foam layer 10a or 10b is fixed, respectively. Each of the square-shaped plates 14a has, at two angles, through-openings 15a along a first diagonal, at one end of the second diagonal, a blind opening 15 "a and, at the second end of the second diagonal, an opening 15a Also, the plates 14b comprise, in a first diagonal, through openings 15b in corner portions and the cavity machined in the plate 14b, a blind opening 15 "b and a through opening 15'b following a second diagonal of the plate. The module is assembled by stacking plates 14a and plates

14b separated by solid plates 13 having openings 16 in their corner portions, so that the openings 16 are substantially aligned with the openings 15a, 15'a, 15 "a, 15b, 15'b and 15" b, during the constitution of the module. The module consists of elements in successive layers of metal foam comprising a plate 14a or 14b whose cavity is closed by a solid plate 13.

In order to ensure the positioning and the maintenance of a plate 13 with respect to a plate 14a or 14b of an adjacent element, the plate 13 comprises, on one of its faces, a pin 20 projecting engaging in a opening in the bottom of the cavity receiving a metal foam layer of an adjacent element.

The assembly of the stacked plates is achieved by welding the parts in contact with the plates by uni-axial compression under conditions adapted to the materials of the plates. During the compression of the plates, the foam layers whose thickness is sufficient to fill the cavities of the support plates 14a and 14b come into contact with the solid planes ensuring the closure of the cavity on one side, so as to ensure a intimate contact and very good heat exchange between the metal foam and the solid separation plates through which heat is transmitted from one circulating fluid to the other circulating fluid.

In Figure 6, there is shown a plate designated as 14ab, 14ab this plate having substantially a double thickness plates 14a and 14b and being machined on both sides, in the form of cavities such as 14'ab separated by a median wall of the plate 14ab, so as to be able to place, on either side of the median wall of the plate 14ab, a first layer of metal foam 10a and a second metal layer 10b, respectively.

Openings 15a, 15'a and 15b, 15'b are made in corners of the plate, so as to be superimposed on through openings of solid plates reported on the faces of the plate 14ab to form two adjacent elements with layers of metal foam intended to receive, for the first, on a first face of the plate 14ab, the first fluid and, for the second, on the second face of the plate 14ab, the second fluid. The openings 15'a, 15 "a and 15'b, 15" b are made so that the fluids circulate in the foam layer, in a transverse direction substantially perpendicular to the longitudinal direction of the module, between an opening 15a or 15b supplying the foam layer first or second fluid, respectively, and an opening 15'a or 15'b discharging the first or second fluid, respectively to a foam layer element disposed subsequently in the flow direction of the fluid and intended to receive the same fluid. We will now describe, in more detail, the method of producing a module and a heat exchange device according to the invention, in the case where the heat exchanger is used to perform heat exchange between very high temperature gases and in particular between the cooling helium of a nuclear reactor HTR and a mixture of helium and nitrogen, the heat-carrying helium, at the outlet of the reactor core, being at a temperature greater than 850 ⁰ C and up to even 95O ⁰ C.

The second gas consisting of a mixture of helium and nitrogen which must be heated by the heat-carrying helium reaches the module at a temperature which may be, for example, 300 ^° C., the temperature of the second exchange gas. taking the heat of the heat transfer gas being of the order of 800 ⁰ C at the outlet of the heat exchanger device and the temperature of the helium coolant of the order of 35O ⁰ C at the outlet of the heat exchanger device.

The metal foam support plates such as 14a, 14b and 14ab and the solid intermediate plates 13 are made of a refractory alloy, for example a nickel-based alloy such as alloy 617 or other nickel refractory alloys generally containing nickel and chromium.

The metal foam of the foam layers is obtained by depositing a metal material on polyurethane foam which is burnt out after deposition to obtain a foam layer whose pore size or fiber cross-section is generally between 100 and a few hundred micrometers and preferably close to 200 microns. The texture of the metal foam obtained from the polyurethane foam is optimized according to the nature of the gases between which the heat exchange is performed and the physical parameters of these gases.

The support plates are machined, for example by water jets, to make a flat bottom cavity on at least one of the faces of the support plate or, optionally, an opening through the support plate. Preferably, the layers of metal foam are brazed or electrically welded by Joule effect on the support plates after being placed in the cavity. In some cases, the metal foam is not fixed by welding or brazing on the support plate, in particular in the case where the cavity passes through the support plate. In this case, the layer of foam is only held by clamping between two solid plates 13.

The support plates filled with metal foam and the solid separation plates are stacked in a determined order, so that successive elements with foam layers separated by the intermediate plates are formed, the foam layer elements intended to receive the first layer. fluid and the foam layer elements for receiving the second fluid being alternately placed in adjacent positions and separated by the solid separation plates. Each of the modules of the heat exchange device manufactured as indicated above is placed in a compression tool for exerting a uni-axial compression on the stack of plates, so as to make a connection between the plates by diffusion. of metal. The size of the elementary modules (especially in the longitudinal direction) is dependent on the capacity of the uniaxial compression tools available.

In some cases, to obtain the desired characteristics of the exchange device, it may be necessary to place several modules in series after each other in the exchange device.

The heat exchange device comprising elementary modules in a sufficient number to obtain the heat exchange conditions and the desired gas treatment capacity may comprise an outer shell constituted in the form of a tank in which the modules are placed. elementary dules, for example in a radial arrangement, possibly on several levels, the modules then being connected to each other and to means for supplying and discharging fluids, such as collectors and pipes.

The heat exchange device according to the invention has a very good compactness and can easily be adapted to the nature of the gases between which the exchange is carried out and to the physical parameters of these gases. For this purpose, it is possible to adapt characteristics of the foam layers (for example the size of the fibers constituting the foam and / or the texture of the foam). The module can also be adapted to the nature and physical parameters of the fluids between which a heat exchange is carried out, by adapting the thickness of the foam layers and therefore the thickness of the support plates, to each of the exchange gases. The foam layer support plates of the elements intended to receive the first fluid may have a thickness (e1) different from the thickness (e2) of the support plates of the foam layer elements intended to receive the second fluid. The intermediate separation plates generally have the same thickness (e3). In the case of modules of parallelepipedal shape with a rectangular cross-section, the sides of these rectangular sections have dimensions which are chosen so as to obtain satisfactory exchange conditions in each of the layers of the module and a good mechanical resistance of the module. .

The invention is not limited strictly to the embodiments that have been described.

Thus, the plates and modules may have any geometrical shape in cross-section, these shapes being adapted to the arrangement of the modules in the envelope of the heat exchanger.

The support plates of the foam layers may be excavated to present a bowl on one of their faces or on both faces or a through opening, the plate then being a simple frame enclosing the layer of foam intended to be inserted between two plates full.

The means for reinforcing and positioning the solid intermediate plates with respect to the support plates of the foam layers may be made in a different form of ribs or pawns protruding on one face of the solid plate. For example, sidebands can be used to secure the plates.

It is also possible to perform the stacking of the plates constituting each of the modules, inside an envelope providing certain functions of holding the constituent plates of the module. The materials constituting the metal foam and the plates are adapted to the nature and the physical conditions in which the heat exchange is carried out (in particular the temperature of the gases). In the case of very high temperature gases as described above, the foam may advantageously be nickel or iron-chromium-aluminum alloy. The invention applies not only in the case of heat exchange between gases at very high temperature but also in other types of heat exchange between fluids of any kind (liquid or gas), whatever the temperature of these gases. The heat exchanger according to the invention also makes it possible to exchange gas between gases having different pressures.

Claims

1.- Device for heat exchange between a first fluid and a second fluid, characterized in that it comprises at least one heat exchange module (2) consisting of a first plurality of layers of metal foam ( 10a, 10b) bounded by substantially plane faces and parallel to each other and a second plurality of solid metal layers (13) substantially flat and parallel to each other, each layer of metal foam (10a, 10b) being interposed between two successive solid metal layers (13) and surrounded by a solid metal peripheral rim sealingly attached to at least one of the solid metal layers (13) between which is interposed the metal foam layer (10a, 10b) so that the layers of metal foam (10a, 10b) are each placed in a tightly insulated closed space and constituting, with at least one adjacent solid layer, an element of circula one of the first and second fluids and means for dispensing and recovering the first and second exchange fluids at the successive foam layers in a longitudinal direction of the module substantially perpendicular to the foam layers (10a, 10b) such that in both of two metal foam layer fluid circulation elements disposed adjacently in the longitudinal direction of the module, circulate, in a transverse direction substantially perpendicular to the longitudinal direction, respectively, the first and second fluids and that the first and second fluids flow successively in one of two metal foamed layer elements, arranged successively in the longitudinal direction of the module (2).

2. Heat exchanger according to claim 1, characterized in that the heat exchange module (2) consists of metal plates (11, 12, 13, 14a, 14b) juxtaposed and assembled together, successively in the longitudinal direction of the module (2) having foam support plates (14a, 14b) and solid metal separating plates (13) for forming the metal foam layers (10a, 10b) and the solid metal layers (13). ), each of the plates support (14a, 14b) having a respective cavity (14'a, 14'b) for receiving a metal foam layer (10a, 10b) and a peripheral rim surrounding the cavity (14'a, 14'b).

3.- Device according to claim 2, characterized in that the cavities (14'a, 14'b) of the plates (14a, 14b) for supporting the layers (10a, 10b) of metal foam are flat-bottomed cuvettes machined in at least one of the faces of the metal plate, leaving the plane peripheral rim around the cavity (14'a, 14'b).

4.- Device according to claim 2, characterized in that the cavities (14'a, 14'b) of the foam support plates (14a, 14b) through the support plates (14a, 14b) over their entire thickness, the support plates (14a, 14b) constituting a frame surrounding the metal foam layer (10a, 10b).

5.- Device according to claim 1, characterized in that the heat exchange module is constituted by metal plates juxtaposed and assembled together, successively in the longitudinal direction of the module, all the metal plates being support plates of foam (14a, 14b) each having a cavity (14'a, 14'b) in the form of a bowl defined by a rim and a flat bottom, the solid layers of separation of the foam layers being constituted by the funds directly attached plates, each on a rim of an adjacent foam support plate.

6.- Device according to any one of claims 2 to 5, characterized in that the solid metal plates (13) or the flat bottoms of the foam support plates (14a, 14b) comprise on at least one of their faces to the least one projecting element such as a rib (17) or a fixing and positioning pin (20), a fluid distribution rib or a heat exchange fin.

7. Device according to any one of claims 2 to 6, characterized in that two solid metal plates (11, 12) are attached against metal foam support plates (14a, 14b) at the longitudinal ends of the module and constitute end and closure plates of the module.

8.- Device according to any one of claims 2 to 7, characterized in that the fluid distribution and recovery means of the module (2) totally integrated in the module are constituted by openings (15a, 15b, 16). solid separation plates (13) and metal foam layer support plates (14a) aligned in the longitudinal direction of the module with stop zones of the longitudinal circulation of the fluids in the cavities (14'a, 14). b) containing the metal foam layers (10a, 10b) and with passage areas (15'a, 15'b) of the first or second fluid through a corresponding metal foam layer (10a, 10b) in the longitudinal direction of the module (2), so as to ensure a circulation of the first and second fluids in transverse directions, each inside a layer of metal foam (10a, 10b) out of two in the longitudinal direction of the module .

9. A device according to any one of claims 1 to 8, characterized in that the module comprises at its longitudinal ends means for introducing fluid into the module (3a, 4a) and extraction means of fluid of the module (3b, 4b), so as to realize, inside the module, a general circulation of the first and second fluids according to one of the following modes: - countercurrent circulation, the means of introducing first fluid (3a) and the second fluid extraction means (4b) being located at a first longitudinal end of the module (2) and the second fluid introducing means (4a) and the second fluid extraction means first fluid (3b) being arranged at the second longitudinal end of the module (2), - cocurrent circulation, the means for introducing first and second fluids (3a, 4a) being arranged at a first longitudinal end of the module (2) and the extraction means (3b, 4b) of the first and the second fluids of the module (2) being located at the second longitudinal end of the module (2).

10.- heat exchange device according to any one of claims 1 to 9, characterized in that it comprises a plurality of modules (2) arranged in parallel, having means for feeding first and second fluids connected in parallel with supply means (5a, 6a), respectively, first and second fluids, and means for recovering first and second fluids respectively connected to first and second means for recovering first and second fluids (5b, 6b).

11.- Device for heat exchange between a first gas at a temperature of at least 850 ⁰ C and a second gas which is heated to a temperature of at least 800 ⁰ C, according to any one of claims 2 at 10, characterized in that the support plates of the foam layers and the solid metal separation plates (13) are made of a refractory alloy such as a nickel alloy and the metal foam of a material such as nickel or iron, chromium and aluminum alloy.