Heat exchanger module with two counter-current fluid flow circuits, comprising a triply periodic minimal surface (TPMS) heat exchange structure with schwartz-d elementary patterns favourably oriented in the module shell

Abstract

The invention relates to a heat exchanger module (1) with two fluid circuits, extending along a longitudinal axis (Z) and comprising: - a shell having a square or rectangular cross section; - a heat exchange structure arranged in the shell, wherein the structure is a triply periodic minimal surface (TPMS) structure having Schwartz-D elementary patterns that define the two fluid circuits; wherein the TPMS structure is 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.

Description

[0001] Description

[0002] Title: 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.

[0003] Technical field

[0004] The present invention relates to heat exchanger modules with two fluid circuits.

[0005] The invention aims more particularly to obtain such exchanger modules with the greatest possible heat exchange volume power.

[0006] Known heat exchangers comprise either one or at least two circuits with internal fluid circulation channels. In exchangers with at least two fluid circuits, heat exchanges take place between the two fluid circuits.

[0007] 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.

[0008] By "primary fluid", we mean in the context of the invention, the usual meaning in thermal, namely the hot fluid which transfers its heat to the secondary fluid which is the cold fluid.

[0009] Conversely, in the context of the invention, by "secondary fluid" is meant the usual meaning in thermal science, namely the cold fluid to which the heat from the primary fluid is transferred.

[0010] Although described with reference to a preferred application of a heat exchanger in a molten salt nuclear reactor (MSR), the invention can be implemented in all applications requiring heat exchangers, in particular with a minimal volume of fluid contained within them. Prior art

[0011] The applicant, in partnership with other industrial entities, is developing a MSR-type nuclear reactor project, known by the acronym ARAMIS “Advanced Reactor for Actinides Management in Science”.

[0012] This project relates more specifically to a fast loop neutron reactor, with a power of 300MWth, fueled by liquid fuels, mixtures of NaCl, MgCh, PuCh, AmCh, UCh salts at 800°C, the Cl being enriched in 37 C1 at 99% to avoid the creation of 36 C1 (long-lived radioactive isotope) from 35C1.

[0013] In this context, the inventors must design an intermediate heat exchanger between a fuel salt of the primary circuit and a salt of the secondary circuit in a countercurrent circulation configuration, which is optimized for the operating conditions with the highest possible volumetric heat exchange power.

[0014] In fact, the thermal power per unit volume of a reactor core according to the ARAMIS project is estimated to be of the order of 250MW7m 3 .

[0015] In this reactor sketch according to this project, part of the fuel salt is taken from the critical zone to circulate towards the exchangers and the associated pumps. In order to ensure better controllability of the reactor, it is necessary not to create too great an imbalance between the volume of fuel salt in the critical zone and the volume of salt in the non-critical zone. It is thus necessary to minimize the volume of fuel salt within the exchanger, that is to say 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 in the exchanger. This necessity applies to the heat exchange zone but also to the collectors connecting the exchange zone to the primary and secondary fluid circuits.

[0016] The inventors have taken stock of the currently existing exchanger solutions.

[0017] Existing plate heat exchangers have significant advantages over existing tube heat exchangers, particularly in terms of their thermal performance and compactness thanks to a favourably high ratio of surface area to heat exchange volume. However, plate exchangers generally have small channel diameters, which may pose problems during their operation, exposed to a corrosive environment and fission products, which may eventually block or damage such small channel passage sections, which is prohibitive.

[0018] Known tube exchangers are, for example, shell and tube exchangers, in which a bundle of straight or curved tubes in a U-shape or helix shape is fixed on perforated plates and arranged inside an enclosure called a shell. In these shell and tube exchangers, one of the fluids circulates inside the tubes while the other fluid circulates inside the shell. These shell and tube exchangers have a large volume and are therefore not very compact.

[0019] Shell and tube exchangers nevertheless have larger flow sections than plate 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 shell and the salt of the secondary circuit in the tubes.

[0020] But the volumetric powers associated with known shell and tube exchangers are generally insufficient to comply with the controllability requirements of a reactor according to the ARAMIS project.

[0021] Figure 1 illustrates this inadequacy.

[0022] The volumetric power of a square-pitch shell and tube heat exchanger is calculated using standard correlations. In this calculation, the thickness of the tubes is 0.8 mm and the ratio between the tube pitch and their external diameter is 1.4. The pressure variation is imposed at 5 bars in the tubes in which a salt from the secondary circuit would circulate. Whatever the standard hydraulic diameter used, the volumetric thermal power of such a shell and tube heat exchanger is much lower than that of 250 MW7 m 3 aim.

[0023] This dimensioning example in Figure 1 was carried out under conditions representative of the hydraulic operation of the ARAMIS reactor, i.e. considering the anticipated pressure losses and considering geometric parameters of tubes and the calender deemed to be manufacturable using standard techniques, in particular a ratio between the pitch and the external diameter of the tubes greater than or equal to 1.4.

[0024] It should be noted, however, that the relationship between the internal diameter of the tubes and the hydraulic diameter of the calender is fixed by the choice of the pitch and thickness of the tubes, equal to 0.8 mm for the example in Figure 1. This relationship is illustrated in Figure 2 with the same numerical data as those in Figure 1.

[0025] Furthermore, the hydraulic diameter in the tubes is smaller than that in the shell. In design, this constraint limits the choice of the two hydraulic diameters, if we wish to respect the criterion of the ratio greater than or equal to 1.4 stated above, and impose a minimum thickness on the tubes. It is then impossible to size an exchanger by imposing pressure loss conditions in both the primary circuit and the secondary circuit.

[0026] Table 1 illustrates this problem by taking the example of the sizing of a shell and tube exchanger for a tube thickness of 0.8 mm and a hydraulic diameter Dh of 10 mm for the primary circuit.

[0027] The AP pressure drop 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).

[0028] [Table 1]

[0029] Configuration C requires reducing the R ratio, which is equal to 1.28. However, with such a ratio, the exchanger is not considered manufacturable. In this example, the only possible configuration is therefore configuration B, if the pressure drop and R ratio constraints are to be respected. This choice is made to the detriment of the pressure drop in the primary circuit, which lowers the overall performance of the exchanger.

[0030] Furthermore, the design of collectors suitable for this type of exchanger is delicate, as they must ensure a homogeneous distribution of the flow in all the channels to allow suitable thermal performance and thermomechanical resistance. This constraint results in the design of collectors that can have significant volumes of fluid (salts) compared to the total volume of the exchanger, which is contrary to the objective of minimizing the volume of salts sought within the framework of the ARAMIS project.

[0031] Recently, heat exchangers with heat transfer area 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 TPMS triply periodic unit structures include structures based on known unit motifs such as Schwarz-D, Schoen-G, Schwarz-P, and Schoen IWP.

[0032] TPMS structures exhibit improved heat transfer and mass transfer due to the continuous rotation of flow paths and large interface areas. Until recently, TPMS structures were largely theoretical, but with the advancement of additive manufacturing technology, the realization of exchangers with TPMS structures is being studied for industrial use.

[0033] Patent US11181329 discloses a two-fluid heat exchanger, particularly in counter-current circulation, whose exchange zone is a TPMS structure. This exchanger has the following major drawbacks:

[0034] - 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 volume of fluid sought by the inventors;

[0035] - the geometries of the proposed TPMS structures are symmetrical and do not allow a free choice of design to optimize the pressure losses on either side of the structures;

[0036] - the described configurations of cross-flow fluid exchangers are incompatible with the performance criteria and the thermomechanical structural constraints linked to high temperatures, and with the temperature differences between molten salts of an MSR reactor like ARAMIS; - the configurations of counter-flow exchangers do not promote the circulation of fluids and leave significant dead zones, which is contrary to the objective of minimizing the fluid volume.

[0037] Patent application EP3835703A1 discloses a heat exchange TPMS structure with elementary patterns that have an adaptation of the hydraulic diameter. This TPMS structure has the following major drawbacks:

[0038] - 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 plugging these inlets / outlets, generating significant pressure losses and dead volumes, which is contrary to the constraints of minimizing the fluid volume;

[0039] - no concrete solution is disclosed for designing a counter-current exchanger and connecting it to the different fluid circuits.

[0040] Patent US11389765B2 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 the outlet. This exchanger has the following major drawbacks:

[0041] - 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 volume of fluid sought by the inventors;

[0042] - the geometries of the proposed TPMS structures are symmetrical and do not allow a free choice of design to optimize the pressure losses on either side of the structures;

[0043] - no concrete solution is provided for designing a counter-current exchanger and connecting it to the different fluid circuits.

[0044] Publication [1] describes a heat exchanger with a TPMS structure, with a counter-current circulation of the two fluids and whose collectors are integrated into the TPMS structure. These collectors are complex.

[0045] There is therefore a need to further improve dual-fluid circuit heat exchanger modules, particularly those with a TPMS structure, in order to optimize their geometry and best meet the aforementioned specifications, in particular, obtaining the highest possible volumetric thermal power with minimal pressure losses, and counter-current fluid circulation.

[0046] The aim of the invention is to meet this need at least partially.

[0047] Statement of the invention

[0048] To do this, the invention relates to a heat exchanger module with two fluid circuits, extending along a longitudinal axis (Z) and comprising:

[0049] - a grille with a square or rectangular cross-section;

[0050] - a heat exchange structure arranged in the shell, the structure being of triply periodic minimal 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.

[0051] The hydraulic diameters of the two circuits defined by the Schwartz-D elementary patterns can be equal or preferably different.

[0052] According to an advantageous characteristic, 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 / m 3 .

[0053] Preferably, the inlet and outlet manifolds are arranged along the longitudinal axis (Z) and at the longitudinal ends of the module.

[0054] According to a first embodiment, the Schwartz-D elementary patterns have an identical mesh along the length of the grille, the collectors each comprising rectilinear channels each opening onto one of the two circuits of the TPMS structure, the rectilinear channels of one of the two circuits being parallel and alternating with those of the other of the two circuits along the height of the grille.

[0055] According to this first embodiment, each collector preferably comprises a trapezoidal-shaped envelope, fixed or made integrally at a longitudinal end of the calender, the inlet or outlet opening of a collector 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.

[0056] According to a second embodiment, the Schwartz-D elementary patterns have an equal mesh size along the length of the grille, the inlet and outlet manifolds comprising Schwartz-D elementary patterns of the same TPMS structure of the grille but with a mesh size increased compared to those of the grille, so as to obtain at each longitudinal end of the TPMS structure two inlet or outlet openings for the two fluid circuits, according to 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.

[0057] The invention also relates to a heat exchanger, comprising a plurality of heat exchanger modules as described above, connected by fluid connection to each other or not.

[0058] The invention also relates to the use of the heat exchanger as described above, 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.

[0059] 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.

[0060] The invention is essentially a heat exchanger module with two fluid circuits with a TPMS heat exchange structure with a judicious choice of Schwartz D elementary patterns which has the advantages of both allowing high volumetric thermal powers to be achieved, while presenting geometrically simple interfaces at the edges of the patterns.

[0061] A judicious orientation, in particular at 45°, of these patterns around the longitudinal axis of the module which corresponds to the flow axis of the fluids within it makes it possible to align the interfaces of the peripheral patterns with the longitudinal edges of the calender.

[0062] The choice of this orientation of the Schwartz-D pattern mesh relative to the fluid inlet and outlet makes it possible to minimize pressure losses and to define very simple collectors, while minimizing the volume of fluids within the exchanger. Thus, the exchanger module according to the invention is optimized for the operating conditions of a loop molten salt reactor, with the highest possible power density.

[0063] In addition, the exchanger module can operate in counter-current circulation so as to maximize thermal performance and limit thermomechanical constraints.

[0064] Finally, we want to be able to adapt the exchanger to the circulation conditions (pressure losses) of each circuit, which implies being able to choose the hydraulic diameter on either side of the exchanger independently and without constraints.

[0065] Ultimately, the invention has many advantages, including:

[0066] - 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;

[0067] - design freedom on the hydraulic diameters of the two circuits in the TPMS exchange structure, allowing finer optimization of the 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;

[0068] - a simplified design of the collectors, enabled by the mixing properties of the Schwartz-D elemental pattern exchange TPMS structure oriented at 45°, making it possible to minimize the volume of fluids contained in the collectors while allowing a counter-current circulation configuration;

[0069] - a possible reduction in manufacturing costs.

[0070] Other advantages and characteristics of the invention will become more apparent upon reading the detailed description of examples of implementation of the invention given by way of illustration and not limitation with reference to the following figures.

[0071] Brief description of the drawings

[0072] [Fig 1] Figure 1 illustrates in the form of curves the volumetric thermal power of a square pitch shell and tube exchanger as a function of the hydraulic diameter of the tubes, according to the state of the art. [Fig 2] Figure 2 illustrates in the form of curves the relationship between the hydraulic diameter of the tubes and the shell of a shell and tube exchanger according to the state of the art.

[0073] [Fig 3] Figure 3 is an exterior perspective view of a heat exchanger module according to a first embodiment of the invention.

[0074] [Fig 3 A] Figure 3 A is a cutaway perspective view of the module according to Figure 3.

[0075] [Fig 4] Figure 4 reproduces Figure 3 but without the heat exchange zone grille.

[0076] [Fig 5] Figure 5 is a perspective view of a Schwartz-D elementary patterned TPMS structure constituting the heat exchange zone of the exchanger module according to Figures 3 and 4.

[0077] [Fig 6A], [Fig 6B] Figures 6A and 6B are perspective views of the exterior and interior of a collector, both of the inlet of one of the two fluids, and of the outlet of the other of the two fluids of a heat exchanger module according to Figures 3 and 4.

[0078] [Fig 7] Figure 7 is an isometric perspective view of an elementary Schwartz-D pattern.

[0079] [Fig 8] Figure 8 is a perspective view of a representative volume element delimiting two identical hydraulic diameters and based on a Schwarz-D elementary pattern as according to Figure 7.

[0080] [Fig 9] Figure 9 is a perspective view of a representative volume element delimiting two different hydraulic diameters from a Schwarz-D elementary pattern as according to Figure 7 and an elementary pattern.

[0081] [Fig 10] Figure 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.

[0082] [Fig 11] Figure 11 reproduces the curve of Figure 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. [Fig 12] Figure 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.

[0083] [Fig 13 A], [Fig 13B] Figures 13 A and 13B are perspective views of a Schwartz-D elementary patterned TPMS structure of a heat exchanger module according to a second embodiment of the invention.

[0084] [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.

[0085] [Fig 15 A], [Fig 15B] Figures 15A and 15B respectively show 14A and 14B with the envelopes delimiting the collectors of the exchanger module, according to the second embodiment of the invention.

[0086] Detailed description

[0087] It is specified that the various elements according to the invention are represented solely for the sake of clarity and that they are not necessarily to scale.

[0088] Figures 1 and 2 have already been commented on in the preamble. They will therefore not be detailed below.

[0089] The inventors sought to design intermediate heat exchangers for the sketch of the molten salt reactor, actinide converter, known by the acronym ARAM IS.

[0090] All figures relate to operating conditions (flow rates, inlet / outlet temperatures and properties of the fuel circuit salts (primary) and the secondary salt) of the ARAMIS reactor.

[0091] These exchangers must extract the thermal power from the combustible salt to a secondary salt circuit. Typically, the volumetric thermal power to be evacuated is of the order of 250MW / m 3 as shown in Figure 2.

[0092] In this reactor sketch, part of the fuel salt is taken from the critical zone (reactor core) to circulate through the exchangers and pumps.

[0093] To ensure better controllability of the reactor, it is necessary not to create too great 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 exchanger module, i.e. 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 but also to the collectors (connecting the exchange zone to the primary and secondary circuits).

[0094] The inventors thus propose a heat exchanger module 1 which extends along a longitudinal axis Z, as illustrated in Figures 3 to 6B.

[0095] This module 1 firstly comprises a calender 10 of square cross-section delimiting the heat exchange zone, and inlet 11 and outlet 12 collectors for a heat transfer salt, as fluid 1, and inlet 21 and outlet 22 collectors for the fluid fuel salt 2.

[0096] Within this exchanger module 1, the circulation of fluids 1 and 2 is counter-current, as illustrated in figure 5.

[0097] The heat exchange zone is made up of a structure 3 called TPMS (English acronym "Triple Periodic Minimal Surface") obtained by replication along the length of the calender of elementary Schwartz-D type patterns of equal mesh size and whose orientation is at 45° relative to the longitudinal axis Z which constitutes the main flow axis of fluids 1 and 2.

[0098] This structure 3 makes it possible to achieve high thermal power volumes, a balance of pressures throughout the heat exchange zone and the alignment of the interface of the edges of the peripheral elementary patterns with the longitudinal edges of the calender 10, as shown in Figure 3 A.

[0099] The choice of the orientation of the mesh of the Schwartz-D elementary patterns at 45° in relation to the fluid inlet and outlet makes it possible to minimize the volume of salts within the module and to produce collectors 11, 12; 21, 22 whose architecture is simple.

[0100] Thus, as shown in detail in Figures 6A and 6B, at one longitudinal end of the grille 10, the inlet manifold 21 of the fluid 1 comprises rectilinear 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 rectilinear channels 121 parallel and alternating with the channels 211 over the height of the grille 10, which open onto the other of the two circuits of the TPMS structure 3.

[0101] Preferably, each collector 21, 12 comprises a trapezoidal-shaped casing, fixed or made integrally 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.

[0102] An elementary Schwartz-D type motif 30 is illustrated in Figure 7.

[0103] The surface of the TPMS structure which is obtained by replication of the elementary patterns 30 can be trigonometrically approximated by the following equation 1:

[0104] [Equation 1]: (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 (x,y,z) is an iso-surface evaluated at Tiso-value C.

[0105] It is then possible to define a volume such that (x,y,z)>C or (x,y,z) <C (réseau solide), ou créer une épaisseur solide définie par -C < (x,y,z) < C (réseau feuille).

[0106] By generating a solid thickness, it is possible to obtain a cubic elementary exchange pattern of side L, as shown in Figure 8.

[0107] This cubic pattern 30 makes it possible to split the initial volume into two independent circuits of equal volumes 300, 301, making it possible to circulate two fluids in counter-current and to create an exchanger, as highlighted in figure 8. A replication of this elementary pattern in a given volume then makes it possible to create the TPMS heat exchange structure 3 with equal hydraulic diameters Dh of the two fluids.

[0108] As shown schematically in Figure 9, by combining an elementary pattern according to a solid network with one according to a sheet network, it is possible to obtain a hybrid elementary pattern with non-equal fluid volumes 300, 301. A replication of this elementary pattern in a given volume then makes it possible to create the TPMS heat exchange structure 3 with hydraulic diameters Dh of the two different fluids. This makes it possible to define a TPMS exchange structure which best adapts to the constraints of the circuits of the two fluids of the exchanger module. The inventors have judiciously selected a Schwartz-D elementary pattern because it makes it possible to achieve high volumetric thermal powers. Indeed, thanks to the complex structure of the flows circulating in the pattern, the convection exchange coefficients obtained by such a pattern are high.

[0109] Figure 10 illustrates the result of a CFD (Computational Fluid Dynamics) numerical calculation which gives, as a function of the hydraulic diameter Dh, the power density of an exchanger module with a TPMS heat exchange structure made up of Schwartz D elementary patterns.

[0110] The wall thickness was set at 0.8mm and the pressure variation AP was imposed at 1 bar for the fuel salt circuit (Fluid 1).

[0111] This figure 10 clearly shows volumetric thermal powers, notably with values ​​above the target threshold of 250MW7m 3 for the ARAMIS project, for hydraulic diameters between 6 and 7mm.

[0112] As explained above, it is possible to have different hydraulic diameters with Schwartz-D elementary patterns. The design freedom on the choice of these hydraulic diameters makes it possible to optimize heat transfers in the module, for maximum pressure losses on both the primary circuit (Fluid 1) and secondary circuit (Fluid 2) sides.

[0113] Figure 11 illustrates the different volumetric thermal powers for an 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 exchanger module according to the state of the art.

[0114] This figure 11 clearly highlights a significant increase in the volumetric thermal power, for the same constraints, obtained with an exchanger module according to the invention with different hydraulic diameters.

[0115] 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 the reactor according to the ARAMIS project.

[0116] It is specified that the values ​​in Figure 11 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 drops 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)).

[0117] The estimation of the volumetric thermal power is calculated using standard correlations for the state-of-the-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.

[0118] [Table 2]

[0119] From Figure 11 and Table 2, it can be seen that: - the increase in the volumetric thermal power obtained with an exchanger module according to the invention with different hydraulic diameters is estimated 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 approximately 17% compared to an exchanger module according to the invention with equal hydraulic diameters;

[0120] - the good performance of the exchanger modules according to the invention is obtained even for hydraulic diameters greater than 8mm;

[0121] - the exchanger modules according to the invention have an operating point with larger hydraulic diameters than a module according to the state of the art with tubes and shell, for better resulting volumetric powers.

[0122] Another advantage of a TPMS heat exchange structure with Schwarz-D elementary patterns is to ensure efficient heat transfer between fluids and good flow distribution within it, as highlighted in Figure 12. This Figure 12 shows the results of CFD calculations of the velocity fields in different planes of a cross-section of an exchanger module with a TPMS structure with Schwarz-D patterns. The good flow distribution is due to the fact that, for a TPMS structure, all the fluid circulation channels communicate with each other, which allows balancing the pressures and flow rates within the exchanger module. This greatly reduces the negative impact of poor flow distribution at the inlet of the exchanger module, as is the case for exchangers according to the state of the art, where the fluid is divided into several independent channels.

[0123] Ultimately, the alignment of the peripheral elementary patterns of the TPMS structure with the shell, the efficient heat transfer between fluids and the good distribution of the flow within the structure allow for geometrically simplified collectors, as shown in Figures 6A and 6B, to ensure the entry and exit of the fluids, the combustible and secondary salts in the example. This design of simple collectors makes it possible to overcome the constraints of fluid distribution in the exchanger module, and thus makes it possible to minimize the volume of fluids (salts) contained in the collectors, which was not possible for exchanger modules according to the state of the art.

[0124] Figures 13A to 15B show a second embodiment of a Schwartz-D patterned TPMS structure exchanger module, which is made possible by additive manufacturing.

[0125] In this mode, the TPMS structure includes not only the heat exchange zone but also the interior of the fluid inlet and outlet manifolds. Thus, as illustrated in Figures 13A, 13B, in this TPMS structure 3, 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 3 coi to thus lead to end patterns compatible with the primary and secondary fluid circuits (Fluid 1, Fluid 2).

[0126] To achieve such an increase in the mesh size of Schwartz-D patterns, the equation of the Minimal Triple Periodic Surface must be modified as developed in the work [2],

[0127] Such a Schwartz-D patterned TPMS structure with increased mesh size at its longitudinal ends can then be optimized to ultimately obtain collectors of any shape suitable for the square or rectangular cross-section of the exchanger module's exchange area and the fluid inlets and outlets.

[0128] An advantageous variant embodiment of truncated cone-shaped collectors is shown in Figures 14A to 15B. A collector 12, 21 for both the primary fluid inlet (Fluid 1) and the secondary fluid outlet (Fluid 2) has a TPMS structure whose collector zone 3 coi is of truncated cone shape with Schwartz-D elementary patterns whose mesh size is increased compared to the 3ZE exchange zone. This collector zone 3 coihas only two openings 120, 210 at its longitudinal end, which respectively constitute an outlet for the secondary fluid and an inlet for the primary fluid. The peripheral Schwartz-D elementary patterns are aligned with the inner longitudinal edges of a frustoconical envelope 13, 23. At the opposite longitudinal end, an identical collector can be produced for the outlet of the primary fluid and the inlet of the secondary fluid.

[0129] 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).

[0130] It is possible to consider producing the TPMS structure by additive manufacturing, and to add and weld the grille and the collectors directly to the longitudinal ends of the heat exchange zone.

[0131] In the second embodiment, 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. Other variants and improvements can be made without departing from the scope of the invention.

[0132] The exchanger modules 1 according to the invention have been described in a preferred manner for a counter-current circulation of fluids within them. Such circulation is preferred in particular for high-temperature fluid applications. An exchanger module 1 can also operate with cross-current circulation.

[0133] In the first embodiment, the fluid inlet and outlet manifolds have a generally trapezoidal external shape. A cubic or other shape can be considered.

[0134] Liste des références citées [1] : « Additively Manufactured Heat Exchangers- Development and Testing. » Mark.

[0135] Wadsô, Isak LU and Holmqvist, Simon (2020) MMKM10 20201. Innovation. https: / / lup.lub. lu. se / luur / download?func=downloadFile&recordOId=9019472&fileOId=90 19479

[0136] [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

Claims 1. Module (1) of a heat exchanger with two fluid circuits, extending along a longitudinal axis (Z) and comprising: - a grille with a square or rectangular cross-section; - a heat exchange structure arranged in the shell, the structure being of triply periodic minimal 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.

2. Module (1) of a heat exchanger with two fluid circuits, 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 heat exchanger with two fluid circuits, 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 / m 3 .

4. Module (1) of a heat exchanger with two fluid circuits, according to 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 heat exchanger with two fluid circuits, according to claim 4, the Schwartz-D elementary patterns having an identical mesh along the length of the shell, the collectors each comprising rectilinear channels each opening onto one of the two circuits of the TPMS structure, the rectilinear channels of one of the two circuits being parallel and alternating with those of the other of the two circuits along the height of the shell.

6. Module (1) of heat exchanger with two fluid circuits, according to claim 5, each collector comprising a trapezoidal shaped casing, fixed or made integrally at a longitudinal end of the shell, the inlet or outlet opening of a collector of one of the two circuits being according to 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.

7. Heat exchanger module (1) with two fluid circuits, according to claim 4, the Schwartz-D elementary patterns having a mesh of equal 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 of the shell but with a mesh of increased size compared to those of the shell, so as to obtain at each longitudinal end of the TPMS structure two inlet or outlet openings for the two fluid circuits, according to the longitudinal axis, the manifolds each comprising a frustoconical-shaped casing 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 one of the preceding claims, connected by a fluid connection 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 of the first or second circuit coming from a nuclear reactor, in particular a molten salt nuclear reactor, of the MSR type.

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