Heat exchanger module with two counter-current fluid circulation circuits, comprising a triply periodic minimum surface heat exchange structure (TPMS) with Schwartz D elementary patterns with preferred orientation in the module shell.

Abstract

A two-circuit, counter-current fluid circulation heat exchanger module comprising a triply periodic minimum surface area (TPMS) heat exchange structure with preferred orientation Schwartz-D elementary patterns in the module's shell. The invention relates to a two-circuit fluid heat exchanger module (1) extending along a longitudinal axis (Z) and comprising: a shell with a square or rectangular cross-section; a heat exchange structure arranged in the shell, the structure being a triply periodic minimum surface area (TPMS) structure with Schwartz-D elementary patterns delimiting the two fluid circuits; the TPMS structure being oriented such that the interfaces of the Schwartz-D elementary patterns at the periphery of the structure are aligned with the longitudinal edges of the shell. Figure for the abstract: Fig. 3A

Description

Title of the invention: Heat exchanger module with two counter-current fluid circulation circuits, comprising a triply periodic minimum surface heat exchange structure (TPMS) with Schwartz D elementary patterns with preferred orientation in the module shell. technical field

[0001] The present invention relates to two-fluid-circuit heat exchanger modules.

[0002] The invention aims more particularly at obtaining such exchanger modules with the greatest possible volumetric heat exchange power.

[0003] Known heat exchangers comprise either one or at least two internal fluid circulation channels. In exchangers with at least two fluid circuits, heat exchange occurs between the two fluid circuits.

[0004] A heat exchanger module according to the invention can also be implemented in any other application requiring an exchange between two fluids, such as a liquid and a gas, or two liquids or even two gases, in particular when rapid and / or large amplitude temperature variations are involved.

[0005] For the purposes of this invention, "primary fluid" means the usual meaning in thermal engineering, namely the hot fluid which transfers its heat to the secondary fluid which is the cold fluid.

[0006] Conversely, in the context of the invention, "secondary fluid" is understood in the usual sense in thermal engineering, namely the cold fluid to which heat is transferred from the primary fluid.

[0007] Although described with reference to a preferred application of a heat exchanger for a molten salt reactor (MSR), the invention can be implemented in all applications requiring heat exchangers, in particular with a minimal volume of fluid contained within them. Previous technique

[0008] The applicant, in partnership with other industrial entities, is developing a project for an MSR type nuclear reactor, known by the acronym ARAMIS "Advanced Reactor for Actinides Management in Said".

[0009] This project relates more specifically to a looped fast neutron reactor, with a power of 300MWth, fueled by liquid fuels, mixtures of salts NaCl, MgCl2, PuCl3, AmCl3, UC13 at 800°C, the Cl being enriched in 37C1 to 99% to avoid the creation of 36C1 (long-lived radioactive isotope) from 35C1.

[0010] In this context, the inventors must design an intermediate heat exchanger between a combustible salt of the primary circuit and a salt of the secondary circuit in a counter-current circulation configuration, which is optimized for operating conditions with the highest possible volumetric heat exchange power.

[0011] In fact, the volumetric thermal power of the core of a reactor according to the ARAMIS project is estimated to be on the order of 250MW / m3.

[0012] In this reactor design sketch, a portion of the fuel salt is drawn from the critical zone and circulated to the heat exchangers and associated pumps. To ensure better reactor controllability, it is necessary to avoid creating too large an imbalance between the volume of fuel salt in the critical zone and the volume of salt in the non-critical zone. It is therefore necessary to minimize the volume of fuel salt within the heat exchanger, that is, to maximize the volumetric heat output of the heat exchanger, which is the ratio of the total heat output exchanged to the volume of fuel salt in the heat exchanger. This requirement applies not only to the heat exchange zone itself but also to the manifolds connecting the heat exchange zone to the primary and secondary fluid circuits.

[0013] The inventors have taken stock of currently existing heat exchanger solutions.

[0014] Existing plate heat exchangers offer significant advantages over existing tube heat exchangers, particularly in terms of thermal performance and compactness, thanks to a favorablely high surface area to heat exchange volume ratio. However, plate heat exchangers generally have small channel diameters, which can pose problems during operation. Exposure to a corrosive environment and fission products can eventually clog or damage such small channel passages, which is prohibitively expensive.

[0015] Known tube-shell heat exchangers include, for example, shell-and-tube heat exchangers, in which a bundle of straight or U-shaped or helical tubes is fixed to perforated plates and arranged inside a shell-and-tube enclosure. In these shell-and-tube heat exchangers, one fluid flows inside the tubes while the other fluid flows inside the shell. These shell-and-tube heat exchangers have a large volume and are therefore not very compact.

[0016] Shell and tube heat exchangers nevertheless have larger flow cross-sections than plate heat exchangers and could theoretically be considered within the framework of the ARAMIS project, with counter-current circulation between the salt of the primary circuit (fuel salt) in the calender and secondary circuit salt in the tubes.

[0017] But the volumetric powers associated with known shell and tube heat exchangers are generally insufficient to comply with the controllability requirements of a reactor according to the ARAMIS project.

[0018] Fig. 1 illustrates this deficiency.

[0019] The volumetric power of a square-pitch shell-and-tube heat exchanger is calculated using standard correlations. In this calculation, the tube thickness is 0.8 mm and the ratio between the tube pitch and their outside diameter is 1.4. The pressure variation is imposed at 5 bar in the tubes through which a salt from the secondary circuit would circulate. Regardless of the standard hydraulic diameter used, the volumetric thermal power of such a shell-and-tube heat exchanger is well below the target of 250 MW / m³.

[0020] This example of dimensioning of [Fig.1] was carried out under conditions representative of the hydraulic operation of the ARAMIS reactor, i.e. by considering the pressure losses envisaged and by considering geometric parameters of tubes and of the shell deemed manufacturable by usual techniques, in particular a ratio between the pitch and the outside diameter of the tubes greater than or equal to 1.4.

[0021] It should be noted, however, that the relationship between the inner diameter of the tubes and the hydraulic diameter of the calender is determined by the choice of the pitch and the thickness of the tubes, which is 0.8 mm for the example in [Fig. 1]. This relationship is illustrated in [Fig. 2] with the same numerical data as those in [Fig. 1].

[0022] Furthermore, the hydraulic diameter in the tubes is smaller than that in the shell. During the design phase, this constraint limits the choice of the two hydraulic diameters if the criterion of a ratio greater than or equal to 1.4 stated above is to be met, and a minimum tube thickness must be imposed. It is therefore impossible to size a heat exchanger while imposing pressure loss conditions in both the primary and secondary circuits.

[0023] Table 1 illustrates this problem by taking the example of the dimensioning of a shell and tube heat exchanger for a tube thickness of 0.8 mm and a hydraulic diameter Dh of 10 mm for the primary circuit.

[0024] The pressure loss AP can be imposed either in the primary circuit (configuration A), or in the secondary circuit (configuration B), or in both circuits at the same time (configuration C).

[0025] [Tables 1] Configuration A Configuration B Configuration C Ratio R, between pitch and outside diameter of tubes 1.40 1.40 1.28 Primary circuit pressure (mm) 10 10 10 Secondary circuit pressure (mm) 5.09 5.09 7.53 Primary circuit pressure (bar) 1 0.27 1 Secondary circuit pressure (bar) 18.5 5 5

[0026] Configuration C requires reducing the ratio R, which is equal to 1.28. However, with such a ratio, the heat exchanger is not considered manufacturable. In this example, the only feasible configuration is therefore configuration B, if the constraints on pressure drop and the ratio R are to be met. This choice is made at the expense of the pressure drop in the primary circuit, which reduces the overall performance of the heat exchanger.

[0027] Furthermore, the design of manifolds suitable for this type of heat exchanger is complex, as they must ensure a homogeneous flow distribution throughout all channels to allow for adequate thermal performance and thermomechanical resistance. This constraint results in the design of manifolds that may contain significant volumes of fluid (salts) relative to the total volume of the heat exchanger, which is contrary to the objective of minimizing the volume of salts sought within the framework of the ARAMIS project.

[0028] Recently, heat exchangers with a heat exchange zone based on triply periodic minimal surfaces (“TPMS”) have been considered. TPMS structures consist of two interpenetrating fluid volume domains separated by a thin wall. Examples of triply periodic unitary TPMS structures include structures based on known elementary patterns such as Schwarz-D, Schoen-G, Schwarz-P, and Schoen IWP.

[0029] TPMS structures offer improved heat and mass transfer due to the continuous rotation of the flow paths and large interface areas. Until recently, TPMS structures were largely theoretical, but with advances in additive manufacturing technology, the realization of heat exchangers with TPMS structures is being studied for industrial use.

[0030] US patent 11181329 thus discloses a two-fluid heat exchanger, particularly in counter-current traffic, where the exchange area is a TPMS structure. This interchange presents the following major drawbacks: - The disclosed TPMS structures have a complex edge interface. As a result, the connection to the inlet / outlet pipes can only be made by successively blocking these inlets / outlets, generating significant pressure losses and dead volumes, which is contrary to the constraints of minimizing the fluid volume sought by the inventors; - the geometries of the proposed TPMS structures are symmetrical and do not allow for a free choice of design to optimize pressure losses on either side of the structures; - the described cross-flow fluid circulation exchanger configurations are incompatible with the performance criteria and thermomechanical structural constraints related to high temperatures, and with the temperature differences between molten salts in an MSR reactor like ARAMIS; - Counter-current circulation exchanger configurations do not promote fluid circulation and leave significant dead zones, which is contrary to the objective of minimizing fluid volume.

[0031] Patent application EP3835703A1 discloses a heat exchange TPMS structure with elementary motifs that feature hydraulic diameter adaptation. This TPMS structure has the following major drawbacks: - the disclosed TPMS structures have a complex edge interface. Consequently, the connection to the inlet / outlet pipes can only be made by successively blocking these inlets / outlets, generating significant pressure losses and dead volumes, which is contrary to the constraints of minimizing fluid volume; - no concrete solution is disclosed for designing a counter-current exchanger and connecting it to the various fluid circuits.

[0032] US patent 11389765B2 proposes a heat exchanger whose TPMS exchange structure has elementary patterns whose mesh size is progressively modified along the length so that the structure is non-uniform between the inlet and outlet. This exchanger has the following major drawbacks: - the disclosed TPMS structures have a complex edge interface. Consequently, the connection to the inlet / outlet pipes can only be made by successively plugging these inlets / outlets, generating significant pressure losses and dead volumes, which is contrary to the constraints of minimizing the fluid volume sought by the inventors; - The geometries of the proposed TPMS structures are symmetrical and do not do not allow a free choice of design to optimize pressure losses on both sides of the structures; - no concrete solution is provided for designing a counter-current exchanger and connecting it to the various fluid circuits.

[0033] Publication [1] describes a heat exchanger with a TPMS structure, with counter-current circulation of the two fluids and whose manifolds are integrated into the TPMS structure. These manifolds are complex.

[0034] There is therefore a need to further improve the two-fluid-circuit heat exchanger modules, in particular those with TPMS structure, in order to optimize their geometry and best meet the aforementioned specifications, in particular obtaining the highest possible volumetric thermal power with a minimum of pressure losses, and counter-current fluid circulation.

[0035] The object of the invention is to meet at least partially this need. Description of the invention

[0036] To this end, the invention relates to a heat exchanger module with two fluid circuits, extending along a longitudinal axis (Z) and comprising:

[0037] - a grille with a square or rectangular cross-section;

[0038] - a heat exchange structure arranged in the calender, the structure being triply periodic minimum surface (TPMS) with Schwartz-D elementary patterns delimiting the two fluid circuits; the TPMS structure being oriented so that the interfaces of the Schwartz-D elementary patterns at the periphery of the structure are aligned with the longitudinal edges of the shell.

[0039] The hydraulic diameters of the two circuits defined by the Schwartz-D elementary patterns can be equal or preferably different.

[0040] According to an advantageous feature, the hydraulic diameter of at least one of the two circuits is between 6 and 11 mm for a volumetric thermal power greater than or equal to 150 MW / m3.

[0041] Preferably, the inlet and outlet manifolds are arranged along the longitudinal axis (Z) and at the longitudinal ends of the module.

[0042] According to a first embodiment, the Schwartz-D elementary motifs have an identical mesh over the length of the calender, the collectors each comprising straight channels opening onto one of the two circuits of the TPMS structure, the straight channels of one of the two circuits being parallel and alternating with those of the other of the two circuits over the height of the calender.

[0043] According to this first mode, each manifold preferably comprises a trapezoidal-shaped casing, fixed or integrally formed at one longitudinal end of the grille, and the inlet or outlet opening of a manifold of one of the two circuits being along the longitudinal axis while the inlet or outlet opening of a collector of the other of the two circuits is orthogonal to the longitudinal axis.

[0044] According to a second embodiment, the Schwartz-D elementary motifs have the same mesh size over the length of the shell, the inlet and outlet manifolds comprising Schwartz-D elementary motifs of the same TPMS structure of the shell but with an increased mesh size compared to those of the shell, so as to obtain at each longitudinal end of the TPMS structure two inlet or outlet openings of the two fluid circuits, along the longitudinal axis, the manifolds each comprising a frustoconical envelope whose longitudinal edges are aligned with the interfaces of the Schwartz-D elementary motifs at the periphery of the structure.

[0045] The invention also relates to a heat exchanger, comprising a plurality of heat exchanger modules as described above, connected by fluidic linkage to each other or not.

[0046] The invention also relates to the use of the heat exchanger as described above, the fluid of the first circuit, as the primary fluid, being a combustible salt and the fluid of the second circuit, as the secondary fluid, being a heat transfer salt.

[0047] According to a preferred application, the fluid of the first or second circuit comes from a nuclear reactor, in particular a molten salt nuclear reactor, of the MSR type.

[0048] The invention is essentially a two-fluid-circuit heat exchanger module with a TPMS heat exchange structure and a judicious choice of Schwartz D elementary patterns which has the advantages of both enabling high volumetric thermal powers to be achieved, while presenting geometrically simple interfaces at pattern edges.

[0049] A judicious orientation, in particular at 45°, of these motifs around the longitudinal axis of the module which corresponds to the axis of fluid flow within it makes it possible to align the interfaces of the peripheral motifs with the longitudinal edges of the shell.

[0050] The choice of this orientation of the mesh of the Schwartz-D patterns with respect to the inlet and outlet of the fluids makes it possible to minimize pressure losses and to define very simple collectors, while minimizing the volume of fluids within the exchanger.

[0051] Thus, the exchanger module according to the invention is optimized for the operating conditions of a loop molten salt reactor, with the highest possible volumetric power.

[0052] Furthermore, the exchanger module can operate in counter-current circulation of in order to maximize thermal performance and limit thermomechanical stresses.

[0053] We finally want to be able to adapt the exchanger to the circulation conditions (pressure losses) of each circuit, which implies being able to choose independently and without constraint the hydraulic diameter on either side of the exchanger.

[0054] In the end, the invention has many advantages, among which we can mention: - an increase in the volumetric thermal power of the exchanger module by minimizing the volume of fluids within it compared to exchangers according to the state of the art, with fixed pressure losses, hydraulic diameters and wall thickness; - design freedom on the hydraulic diameters of the two circuits in the TPMS exchange structure, allowing finer optimization of pressure losses in each of the two circuits, typically with pressure losses of 1 bar maximum in the primary circuit and 5 bars maximum in the secondary circuit for an application to an exchange between a fuel salt and a heat transfer salt in a molten salt nuclear reactor; - a simplified design of the manifolds, made possible by the mixing properties of the 45° oriented Schwartz-D elementary pattern exchange TPMS structure, allowing to minimize the volume of fluids contained in the manifolds while allowing a counter-current circulation configuration; - a possible reduction in manufacturing costs.

[0055] Other advantages and features of the invention will become clearer from the detailed description of examples of implementation of the invention given by way of illustration and not limitation with reference to the following figures. Brief description of the drawings

[0056] [Fig-1] [Fig.1] illustrates the volumetric thermal power in the form of curves of a tube and shell heat exchanger with square pitch depending on the hydraulic diameter of the tubes, according to the state of the art.

[0057] [Fig.2] [Fig.2] illustrates in the form of curves the relationship between the hydraulic diameter of the tubes and the shell of a shell and tube heat exchanger according to the state of the art.

[0058] [Fig.3] [Fig.3] is an external perspective view of a heat exchanger module according to a first embodiment of the invention.

[0059] [Fig.3A] [Fig.3A] is a cutaway perspective view of the module according to [Fig.3].

[0060] [Fig.4] [Fig.4] reproduces [Fig.3] but without the grille of the exchange area thermal.

[0061] [Fig.5] [Fig.5] is a perspective view of a Schwartz-D elementary pattern TPMS structure constituting the heat exchange zone of the exchanger module according to figures 3 and 4.

[0062] [Fig. 6A], [Fig. 6B] Figures 6A and 6B are perspective views from the outside and from inside a manifold, both inlet of one of the two fluids, and outlet of the other of the two fluids of a heat exchanger module according to figures 3 and 4.

[0063] [Fig.7] [Fig.7] is an isometric perspective view of an elementary Schwartz-D motif.

[0064] [Fig.8] [Fig.8] is a perspective view of a representative volume element delimiting two identical hydraulic diameters and based on an elementary Schwarz-D pattern as in [Fig.7].

[0065] [Fig.9] [Fig.9] is a perspective view of a representative volume element delimiting two different hydraulic diameters from an elementary Schwarz-D pattern as in [Fig.7] and an elementary pattern.

[0066] [Fig. 10] The [Fig. 10] illustrates, in the form of a curve obtained by CFD numerical simulation, the volumetric power of an exchanger module according to the invention as a function of the equal hydraulic diameter of the two fluid circuits.

[0067] [Fig. 11] [Fig. 11] reproduces the curve of [Fig. 10] and illustrates for comparison the curves obtained by CFD numerical simulation for an exchanger module according to the invention with different hydraulic diameters for the two fluid circuits and for a shell and tube exchanger module according to the state of the art.

[0068] [Fig. 12] The [Fig. 12] illustrates the velocity field obtained by CFD numerical simulation with an inhomogeneous inlet flow condition, at different planes along the longitudinal axis of the TPMS heat exchange structure according to the invention.

[0069] [Fig. 13A], [Fig. 13B] Figures 13A and 13B are perspective views of a Schwartz-D elementary pattern TPMS structure of a heat exchanger module according to a second embodiment of the invention.

[0070] [Fig.14A], [Fig.14B] Figures 14A and 14B are perspective views of the TPMS structure which integrates the fluid circuits within the collectors of the exchanger module, according to the second embodiment of the invention.

[0071] [Fig.15A], [Fig.15B] Figures 15A and 15B reproduce respectively 14A and 14B with the envelopes delimiting the collectors of the exchanger module, according to the second embodiment of the invention. Detailed description

[0072] It is specified that the different elements according to the invention are represented solely for the sake of clarity and that they are not necessarily to scale.

[0073] Figures 1 and 2 have already been discussed in the preamble. They will therefore not be detailed below.

[0074] The inventors sought to design intermediate heat exchangers of the sketch of the molten salt reactor, actinide converter, known by the acronym ARAMIS.

[0075] All the figures relate to operating conditions (flow rates, inlet / outlet temperatures and properties of the salts of the fuel circuit (primary) and of the secondary salt) of the ARAMIS reactor.

[0076] These exchangers must extract the thermal power from the combustible salt to a secondary salt circuit. Typically, the volumetric thermal power to be removed is on the order of 250MW / m3 as illustrated in [Fig.2].

[0077] On this reactor sketch, part of the fuel salt is taken from the critical zone (reactor core) to circulate through the exchangers and pumps.

[0078] To ensure better reactor controllability, it is necessary to avoid creating too large an imbalance between the volume of fuel salt in the critical zone and the volume of salt in the non-critical zone. It is therefore necessary to minimize the volume of fuel salt within each heat exchanger module, that is, to maximize the volumetric thermal power of the exchanger, which is the ratio of the total thermal power exchanged to the volume of fuel salt within the exchanger. This applies to the heat exchange zone as well as to the manifolds (connecting the heat exchange zone to the primary and secondary circuits).

[0079] The inventors thus propose a heat exchanger module 1 which extends along a longitudinal axis Z, as illustrated in figures 3 to 6B.

[0080] This module 1 includes first of all a square cross-sectional grille 10 delimiting the heat exchange area, and inlet manifolds 11 and outlet 12 of a heat transfer salt, as fluid 1, and inlet manifolds 21 and outlet 22 of the fuel fluid salt 2.

[0081] Within this exchanger module 1, the circulation of fluids 1 and 2 is counter-current, as illustrated in [Fig.5].

[0082] The heat exchange zone is constituted by a structure 3 called TPMS (Anglo-Saxon acronym "Triple Periodic Minimal Surface") obtained by replication over the length of the calender of elementary motifs of Schwartz-D type of equal mesh size and whose orientation is at 45° with respect to the longitudinal axis Z which constitutes the main axis of flow of fluids 1 and 2.

[0083] This structure 3 makes it possible to achieve high thermal volumetric powers, a balance of pressures throughout the heat exchange zone and the alignment of the interface of the edges of the peripheral elementary motifs with the longitudinal edges of the calender 10, as shown in [Fig.3A].

[0084] The choice of the orientation of the mesh of the Schwartz-D elementary motifs at 45° by The relationship to the inlet and outlet of the fluids allows us to minimize the volume of salts within the module and to create collectors 11, 12; 21, 22 whose architecture is simple.

[0085] Thus, as shown in detail in Figures 6A and 6B, at one longitudinal end of the shell 10, the inlet manifold 21 of the fluid 1 comprises straight channels 211 each opening onto one of the two circuits of the TPMS structure 3. At this same longitudinal end, the outlet manifold 12 of the fluid 2 comprises straight channels 121 parallel and alternating with the channels 211 over the height of the shell 10, which open onto the other of the two circuits of the TPMS structure 3.

[0086] Preferably, each collector 21, 12 comprises a trapezoidal-shaped envelope, fixed or integrally formed at the longitudinal end of the shell with an inlet opening 210 of the collector 21 of the fluid 1 along the longitudinal axis Z while the outlet opening 120 of a collector 12 of the fluid 2 is orthogonal to the longitudinal axis.

[0087] An elementary motif 30 of Schwartz-D type is illustrated in [Fig.7].

[0088] The surface of the TPMS structure which is obtained by replication of the motifs Comments 30 can be approximated trigonometrically by the following equation 1:

[0089] [Equation 1]:

[0090] fl>(x,y,z) = sin(x)sin(y)sin(z) + sin(x)cos(y)cos(z) + cos(x)sin(y)cos(z) + cos(x)cos(y) sin(z) in which cp(x,y,z) is an iso-surface evaluated at the iso-value C.

[0091] It is then possible to define a volume such that cp(x,y,z)>C or cp(x,y,z) <C (réseau solide), ou créer une épaisseur solide définie par -C < fl>(x,y,z) < C (leaf lattice).

[0092] By generating a solid thickness, it is possible to obtain a cubic elementary exchange pattern of side L, as shown in [Fig.8].

[0093] This cubic motif 30 allows the initial volume to be split into two independent circuits of equal volumes 300, 301, enabling the counter-current flow of two fluids and creating a heat exchanger, as shown in [Fig. 8]. Replicating this elementary motif in a given volume then allows the creation of the TPMS heat exchange structure 3 with equal hydraulic diameters Dh of the two fluids.

[0094] As schematically illustrated in [Fig. 9], by combining an elementary motif based on a solid lattice with one based on a leaf lattice, a hybrid elementary motif can be obtained with non-equal fluid volumes 300, 301. Replicating this elementary motif in a given volume then makes it possible to create the TPMS heat exchange structure 3 with different hydraulic diameters Dh of the two fluids. This allows for the definition of a TPMS exchange structure that best adapts to the constraints of the two fluid circuits of the exchanger module.

[0095] The inventors judiciously selected a Schwartz-D elementary motif because it allows for high volumetric thermal capacities. Indeed, thanks to the complex structure of the flows circulating in the pattern, the convective exchange coefficients obtained by such a pattern are high.

[0096] Fig. 10 illustrates the result of a CFD (Computational Fluid Dynamics) numerical calculation which gives, as a function of the hydraulic diameter Dh, the volumetric power of a heat exchanger module with a TPMS heat exchange structure made up of Schwartz D elementary motifs.

[0097] The wall thickness was fixed at 0.8mm and the pressure variation AP was imposed at 1 bar for the fuel salt circuit (Fluid 1).

[0098] This [Fig. 10] clearly shows volumetric thermal powers with in particular values ​​above the target threshold of 250MW / m3 for the ARAMIS project, for hydraulic diameters between 6 and 7mm.

[0099] As explained above, it is possible to have different hydraulic diameters with Schwartz-D elementary patterns. The design freedom in choosing these hydraulic diameters allows for the optimization of heat transfers in the module, for maximum pressure losses on both the primary circuit (Fluid 1) and the secondary circuit (Fluid 2).

[0100] Fig. 11 illustrates the different volumetric thermal powers for a heat exchanger module according to the invention, with different hydraulic diameters compared to a module according to the invention with equal hydraulic diameters and a shell and tube heat exchanger module according to the state of the art.

[0101] This [Fig.1 1] clearly highlights a significant increase in volumetric thermal power, for the same constraints, obtained with an exchanger module according to the invention with different hydraulic diameters.

[0102] Table 2 summarizes the characteristics of the three exchanger modules for a hydraulic diameter imposed at 10 mm for the primary circuit (Fluid 1), corresponding to the fuel salt circuit for reactor according to the ARAMIS project.

[0103] It is specified that the values ​​in [Fig. 1 1] and Table 2 are obtained for each of these three modules. The wall thickness (Schwartz-D patterns and tubes) was set at 0.8 mm, with the same constraints on the maximum permissible pressure losses representative of reactor operation according to the ARAMIS project (1 bar for the primary circuit (Fluid 1), 5 bars for the secondary circuit (Fluid 2)).

[0104] The volumetric thermal power is estimated using standard correlations for the prior art shell-and-tube module, and estimated from CFD numerical calculations for the modules according to the invention. These results do not take into account the volume of the collectors.

[0105] [Tables2] Heat exchanger module according to the state of the art, with shell and tube design. Heat exchanger module according to the invention, with identical hydraulic diameters. Heat exchanger module according to the invention, with different hydraulic diameters. Primary circuit diameter (mm) 10 10 10 Secondary circuit diameter (mm) 5.09 10 6.75 Primary circuit pressure (bar) 0.27 1 1 Secondary circuit pressure (bar) 5 1.54 5 Volumetric power (MW / m³) 120 168 196

[0106] According to [Fig. 1 1] and Table 2, it can be seen that:

[0107] - the increase in volumetric thermal power obtained with a module The efficiency of the heat exchanger according to the invention with different hydraulic diameters is estimated to be between 36 and 94% compared to a module according to the state of the art, with tubes and shell, depending on the hydraulic diameter considered, and about 17% compared to a heat exchanger module according to the invention with equal hydraulic diameters;

[0108] - the good performance of the heat exchanger modules according to the invention is obtained even for hydraulic diameters greater than 8mm;

[0109] - the heat exchanger modules according to the invention have an operating point with hydraulic diameters larger than a module according to the state of the art with tubes and shell, for better resulting volumetric powers.

[0110] Another advantage of a Schwartz-D pattern TPMS heat exchange structure is that it ensures efficient heat transfer between fluids and good flow distribution within it, as shown in [Fig. 12]. This [Fig. 12] shows the results of CFD calculations of the velocity fields in different planes of a cross-section of a heat exchanger module with a Schwarz-D pattern TPMS structure. The good flow distribution is due to the fact that, for a TPMS structure, all the fluid circulation channels communicate with each other, which makes it possible to balance the pressures and flow rates within the heat exchanger module. This greatly reduces the negative impact of poor flow distribution. at the inlet of the exchanger module, as is the case for state-of-the-art exchangers, where the fluid is divided into several independent channels.

[0111] Ultimately, the alignment of the peripheral elementary motifs of the TPMS structure with the shell, the efficient heat transfer between fluids, and the proper flow distribution within the structure allow for geometrically simplified manifolds, as shown in Figures 6A and 6B, to ensure the inlet and outlet of the fluids, the fuel and secondary salts in this example. This simple manifold design eliminates the constraints of fluid distribution within the heat exchanger module, and thus minimizes the volume of fluids (salts) contained in the manifolds, which was not possible with state-of-the-art heat exchanger modules.

[0112] Figures 13A to 15B show a second embodiment of a TPMS structure heat exchanger module with Schwartz-D elementary motifs, which is made possible by additive manufacturing.

[0113] In this mode, the TPMS structure includes not only the heat exchange area but also the interior of the fluid inlet and outlet manifolds.

[0114] Thus, as illustrated in figures 13A, 13B, in this TPMS 3 structure, an increase in the size of the elementary mesh of the Schwartz-D patterns is imposed progressively from the junction between the heat exchange zone 3Ze to the end of the collector zone 3coi to thus lead to end patterns compatible with the primary and secondary fluid circuits (Fluid 1, Fluid 2).

[0115] To obtain such an increase in the mesh size of the Schwartz-D motifs, the equation of the Minimal Periodic Triple Surface must be modified as developed in work [2].

[0116] Such a TPMS structure with Schwartz-D patterns of increased mesh size at its longitudinal ends can then be optimized to obtain, in the end, collectors of any shape adapted to the square or rectangular cross-section of the exchange area of ​​the exchanger module and to the inlets and outlets of the fluids.

[0117] An advantageous embodiment of frustoconical manifolds is shown in Figures 14A to 15B. A manifold 12, 21, serving as both the primary fluid inlet (Fluid 1) and secondary fluid outlet (Fluid 2), has a TPMS structure in which the manifold zone 3coi is frustoconical with Schwartz-D elemental patterns whose mesh size is increased compared to the exchange zone 3ZE. This manifold zone 3coi has only two openings 120, 210 at its longitudinal end, which respectively constitute a secondary fluid outlet and a primary fluid inlet. The peripheral Schwartz-D elemental patterns are aligned with the inner longitudinal edges of a frustoconical shell 13, 23. At the opposite longitudinal end, an identical manifold can be made for the outlet of the primary fluid and the inlet of the secondary fluid.

[0118] The exchanger modules 1 according to the invention which have just been described can be made with metallic or ceramic materials, in particular silicon carbide (SiC).

[0119] The TPMS structure can be produced by additive manufacturing, and the calender and collectors can be attached and welded directly to the longitudinal ends of the heat exchange zone.

[0120] In the second mode, the TPMS structure is manufactured by additive manufacturing in a single block comprising the heat exchange zone and, on either side, the collector zones with elementary patterns whose mesh size is increased compared to that of the patterns of the heat exchange zone.

[0121] Other variations and improvements may be made without departing from the scope of the invention.

[0122] The heat exchanger modules 1 according to the invention have been described in a preferred manner for counter-current fluid circulation within them. Such circulation is particularly preferred for high-temperature fluid applications. A heat exchanger module 1 can also operate with cross-flow circulation.

[0123] In the first embodiment, the fluid inlet and outlet manifolds have a generally trapezoidal external shape. A cubic or other shape may be considered. List of cited references

[0124] [1]: “Additively Manufactured Heat Exchangers – Development and Testing. »Mark. Wadsô, Isak LU and Holmqvist, Simon (2020) MMKM10 20201. Innovation.

[0125] https: / / lup.lub.lu.se / luur / download?func=downloadFile&recordOId=9019472&fileOI d=9019479

[0126] [2]: “Functionally graded porous scaffolds in multiple patterns: New design method, physical and mechanical properties », Liu et al, Materials & Design Volume 160, 15 December 2018, Pages 849-860.

Claims

Demands

1. Module (1) of a two-fluid-circuit heat exchanger, extending along a longitudinal axis (Z) and comprising: - a shell of square or rectangular cross-section; - a heat exchange structure arranged in the shell, the structure being of triply periodic minimum surface area (TPMS) with Schwartz-D elementary patterns delimiting the two fluid circuits; the TPMS structure being oriented so that the interfaces of the Schwartz-D elementary patterns at the periphery of the structure are aligned with the longitudinal edges of the shell.

2. Module (1) of a two-fluid-circuit heat exchanger according to claim 1, the hydraulic diameters of the two circuits defined by the Schwartz-D elementary patterns being equal or different.

3. Module (1) of a two-fluid-circuit heat exchanger according to claim 2, the hydraulic diameter of at least one of the two circuits being between 6 and 11 mm for a volumetric thermal power greater than or equal to 150 MW / m3.

4. Two-fluid-circuit heat exchanger module (1) according to any one of the preceding claims, the inlet (11, 21) and outlet (12, 22) manifolds being arranged along the longitudinal axis (Z) and at the longitudinal ends of the module.

5. Module (1) of a two-fluid-circuit heat exchanger according to claim 4, the Schwartz-D elementary motifs having the same mesh over the length of the shell, the manifolds each comprising straight channels opening onto one of the two circuits of the TPMS structure, the straight channels of one of the two circuits being parallel and alternating with those of the other of the two circuits over the height of the shell.

6. Module (1) of a two-fluid-circuit heat exchanger according to claim 5, each manifold comprising a trapezoidal-shaped shell, fixed or integrally formed at one longitudinal end of the shell, the inlet or outlet opening of a manifold of one of the two circuits being along the longitudinal axis while the inlet or outlet opening of a manifold of the other of the two The circuits are orthogonal to the longitudinal axis.

7. Module (1) of a two-fluid-circuit heat exchanger according to claim 4, the Schwartz-D elementary patterns having an equal mesh size along the length of the shell, the inlet (11, 21) and outlet (12, 22) manifolds comprising Schwartz-D elementary patterns of the same TPMS structure as the shell but with an increased mesh size compared to those of the shell, so as to obtain at each longitudinal end of the TPMS structure two inlet or outlet openings of the two fluid circuits, along the longitudinal axis, the manifolds each comprising a frustoconical-shaped envelope whose longitudinal edges are aligned with the interfaces of the Schwartz-D elementary patterns at the periphery of the structure.

8. Heat exchanger, comprising a plurality of heat exchanger modules (1) according to any one of the preceding claims, connected by a fluidic link between them or not.

9. Use of the heat exchanger according to claim 8, the fluid of the first circuit, as primary fluid, being a combustible salt and the fluid of the second circuit, as secondary fluid, being a heat transfer salt.

10. Use according to claim 9, the fluid from the first or second circuit originating from a nuclear reactor, in particular a molten salt nuclear reactor, of type MSR.

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