EP3132222B1 - Heat-exchanger module, use with liquid metal and gas - Google Patents

Description

Technical area

The present invention relates to a heat exchanger module incorporating at least one fluid circuit. US 2010/0181055 describes a module according to the preamble of claim 1.

The invention relates more particularly to the realization of a new type of heat exchanger module to improve the compactness and heat exchange power, equivalent losses.

The known heat exchangers comprise either at least two internal fluid circulation channel circuits. In the single-circuit heat exchangers, the heat exchange takes place between the circuit and a surrounding fluid in which it is immersed. In the exchangers with at least two fluid circuits, the heat exchange takes place between the two fluid circuits.

It is known chemical reactors which implement a continuous process in which a small amount of co-reactants is simultaneously injected at the inlet of a first fluid circuit, preferably equipped with a mixer, and recovers the chemical product obtained at the outlet of said first circuit. Among these known chemical reactors, some include a second fluid circuit, usually called utility, whose function is to thermally control the chemical reaction, either by providing the heat necessary for the reaction, or on the contrary by removing the heat released by that -this. Such chemical reactors with two fluid circuits with utility are usually called reactor-exchangers.

The present invention also relates to the production of heat exchanger modules with only heat exchange function and integrating one or two fluid circuits that the realization of exchangers-reactors. Also, by "heat exchanger module with at least two fluid circuits", it is necessary to understand, in the context of the invention, both a heat exchanger module with a function solely of heat exchange and an exchanger. -reactor.

The main use of an exchanger module between two fluids according to the invention is its use with a gas as one of the two fluids. It may advantageously be liquid metal and gas, for example liquid sodium and nitrogen.

The main application targeted by an exchanger module according to the invention is the heat exchange between a liquid metal, such as liquid sodium, of the secondary loop and nitrogen as a gas of the tertiary loop of a fast neutron reactor cooled with the liquid metal, such as the liquid sodium called RNR-Na or SFR (acronym for " Sodium Fast Reactor ") and which is part of the so-called fourth-generation reactor family.

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, preferably when it is necessary to have a compact exchanger. and of great thermal power.

In the context of the invention, the term "primary fluid" means the usual thermal meaning, namely the hot fluid which transfers its heat to the secondary fluid which is the cold fluid.

In contrast, by "secondary fluid" is meant in the context of the invention, the usual thermal sense, namely the cold fluid to which is transferred the heat of the primary fluid.

In the main application, the primary fluid is the sodium that circulates in the so-called secondary loop of the thermal conversion cycle of a reactor RNR-Na, while the secondary fluid is the nitrogen that circulates in the tertiary loop of said cycle.

State of the art

The known tube exchangers are, for example, tube and shell exchangers, in which a bundle of upright or bent U-shaped or helical tubes is fixed on pierced plates and disposed inside a chamber waterproof called calender. In these tube and shell exchangers, one of the fluids circulates inside the tubes while the other fluid circulates inside the shell. These tube and shell exchangers have a large volume and are therefore of low compactness.

The heat exchangers, known as plate heat exchangers, have significant advantages over heat exchangers, known as tube heat exchangers, in particular their thermal performance and their compactness thanks to a ratio of the surface area to the heat exchange volume favorably. high. Compact plate heat exchangers are used in many industrial fields.

In this field of compact plate heat exchangers, numerous elementary forms defining thermal exchange patterns have been developed.

We can first of all mention plate heat exchangers incorporating fins, wherein a heat exchange pattern is defined by a structure delimited by fins, the structures being reported between two metal plates and can have very varied geometries. The exchange pattern may be different between one of the two fluid circuits of the exchanger and the other. The assembly between metal plates is usually by soldering or by diffusion welding.

Corrugated or corrugated plate heat exchangers are also known. The corrugations are created by stamping a plate separating the two fluid circuits. As a result, the exchange pattern is identical for each of the two fluid circuits. The flow of fluids generated by this type of exchange pattern is three-dimensional and, therefore, is very efficient. The joining between plates is done either by bolted connection or by their peripheral welding (conventional welding, or welding-diffusion).

It is finally known machined plate heat exchangers machining is mechanical or electrochemically. The channels defined by the machining are of millimeter section and are usually continuous and in a regular zigzag profile. The plates are assembled by welding-diffusion allowing welding on all points of contact between two adjacent plates. This type of milled plate heat exchanger is intrinsically very resistant to pressure.

• les échangeurs à plaques intégrant des ailettes sont un mode d'élaboration difficilement compatible avec un composant nucléaire ;
• les échangeurs à plaques embouties, bien que présentant une compacité élevée et une puissance thermique unitaire élevée, ne sont pas compatibles avec une différence de pression entre gaz et métal liquide dans le cadre du réacteur nucléaire refroidi avec ce dernier et donc ne sont pas robustes ;
• les échangeurs à plaques à rainures usinées sont robustes, permettent à la fois de satisfaire les performances thermo-hydrauliques et thermomécaniques mais présentent une compacité inférieure aux échangeurs à plaques embouties pour une perte de charge équivalente.

The inventors of the present invention have evaluated these different plate heat exchanger technologies to design an exchanger between a gas and a liquid metal in the context of the realization of a nuclear reactor of the so-called fourth-generation reactor family. that is to say in a heat exchange configuration between an excellent coolant, the liquid metal, and a fluid with much lower thermal transport properties, the gas. They reached the main conclusions that can be enumerated as follows:

• the plate heat exchangers incorporating fins are a method of preparation difficult to compatible with a nuclear component;
• the stamped plate heat exchangers, although having a high compactness and a high unit thermal power, are not compatible with a pressure difference between gas and liquid metal in the context of the nuclear reactor cooled with the latter and therefore are not robust;
• Machined grooved plate heat exchangers are robust, both thermo-hydraulic and thermomechanical, but have lower compactness than stamped plate heat exchangers for equivalent pressure drop.

There is therefore a need to further improve the compact plate heat exchangers, in particular with a view to giving them both a high unit thermal power and a high compactness, while ensuring robustness.

The object of the invention is to at least partially meet this need.

Presentation of the invention

To do this, the subject of the invention is a heat exchanger module according to claim 1.

In other words, the invention essentially consists in proposing a fluid circuit whose flow is three-dimensional by the presence of the crossing zones and which can be produced according to the manufacturing technology of machined grooved plate heat exchangers, proven for its robustness.

Thus, for the same dimensions, an exchanger module according to the invention has both improved heat exchange performance compared to a machined plate heat exchanger according to the state of the art and an improved robustness compared to a stamped plate heat exchanger according to the state of the art.

In other words, for the same thermal performance, an exchanger module according to the invention has an increased compactness with respect to a heat exchanger according to the state of the art.

However, this represents a primary advantage in the main application of heat exchangers of fourth generation nuclear reactors because it is thus possible to limit the number of exchangers, the size of the buildings integrating them.

According to the invention, each channel has a curved zigzag profile at least in part, preferably regular along its length.

The regular curved zigzag profile has elbows and straight segments, a line segment connecting two consecutive elbows.

Such a curved regular zigzag profile for each of the intersecting channels according to the invention allows a great flexibility of design, by varying the geometrical parameters of each channel, in particular the geometry of the section of each channel, the angle of the segments right of the canal, the length between two elbows, the radius of curvature of the elbows, the distance between the channels.

• le coefficient d'échange thermique mais aussi le coefficient de frottement augmentent avec l'angle des segments de droite;
• lorsque la longueur entre deux coudes augmente, le coefficient d'échange thermique et le coefficient de frottement diminuent;
• lors que le rayon de courbure diminue, le coefficient d'échange thermique et le coefficient de frottement augmentent.

Preliminary studies by the inventors have shown that:

• the coefficient of heat exchange but also the coefficient of friction increase with the angle of the segments of right;
• when the length between two elbows increases, the heat exchange coefficient and the coefficient of friction decrease;
• as the radius of curvature decreases, the heat exchange coefficient and the coefficient of friction increase.

The constituent metallic material of the exchanger module according to the invention is chosen according to the conditions of its required use, namely the pressure of the fluids, the temperatures and natures of the fluids flowing through the module. It may be for example aluminum, copper, nickel, titanium or alloys of these elements as well as a steel, especially an alloy steel or a stainless steel or a refractory metal selected from alloys of niobium, molybdenum, tantalum or tungsten.

The fluid circulation channels have a width and a height that depend in particular on the nature and characteristics of the fluids conveyed and the desired heat exchange. The widths and heights may vary in particular along the path of the channels.

The curved zigzag profile is regular over its length.

According to an advantageous embodiment, the regular curved zigzag profile comprises elbows and straight segments, a line segment connecting two consecutive elbows.

A channel may have an ovoid, circular, rectangular or square section.

A section with a plane of symmetry (rectangular, square or circular). facilitates the disturbances of the flows and a better mixing of the fluid with itself.

The square or rectangular sections also allow a better compactness.

The advantage of having a circular or ovoid section is to simplify the manufacture of the channels: one can indeed use a machining process by electrochemical erosion, easy to implement.

• le rayon de courbure des coudes est compris entre 0,5 et 3 Dh du canal ;
• la longueur du segment de droite est comprise entre 4 et 8 Dh de canal ;
• l'angle entre le segment de droite et l'axe longitudinal (X) est compris entre 10 et 45 °.

By defining the channel by its hydraulic diameter (Dh), the preferred dimensions are as follows:

• the radius of curvature of the elbows is between 0.5 and 3 Dh of the channel;
• the length of the line segment is between 4 and 8 Dh of channel;
• the angle between the line segment and the longitudinal axis (X) is between 10 and 45 °.

According to an advantageous embodiment, the curved zigzag profiles are identical for the two channels and symmetrical to one another with respect to the longitudinal axis (X) or a parallel axis.

According to an alternative embodiment, the two channels of the same pair meet at their longitudinal ends in the same rectilinear channel portion substantially parallel to the longitudinal axis (X).

According to a first embodiment, each of the two fluid circuits comprises at least one pair of fluid circulation channels each extending parallel to the longitudinal axis (X), the two channels of one and the same pair being superimposed on each other. one on the other and opening into each other in a plurality of crossing zones each defining a fluid mixing zone with itself within the first or second circuit.

According to a second embodiment, typically when one of the two fluids is a liquid metal (Na) and the other of the fluids an inert gas (N2), the first fluid circuit comprises at least one pair of fluid circulation channels. each extending parallel to the longitudinal axis (X), the two channels of the same pair being superimposed on one another and opening into one another in a plurality of crossing zones each defining a fluid mixing zone with itself within the first circuit, the second fluid circuit comprising at least one pair of straight-shaped channels.

• usinage d'au moins une première rainure dans une première plaque métallique ;
• usinage d'au moins une deuxième rainure dans une deuxième plaque métallique;
• positionnement de la deuxième plaque usinée contre la première plaque usinée de sorte à ce que les première et deuxième rainures délimitent chacune un canal de circulation de fluide s'étendant chacun parallèlement à un axe longitudinal (X), les deux canaux soient superposés l'un sur l'autre et débouchent l'un dans l'autre en une pluralité de zones de croisement définissant chacune une zone de mélange du fluide avec lui-même.
• assemblage des première et deuxième plaques métalliques entre elles, soit par compression isostatique à chaud (CIC), soit par un procédé appelé communément soudage-diffusion uniaxial à chaud, de sorte à obtenir un soudage par diffusion entre elles, soit par brasage.

The invention also relates to a method for producing a heat exchanger module described above:

• machining at least a first groove in a first metal plate;
• machining at least one second groove in a second metal plate;
• positioning the second machined plate against the first machined plate so that the first and second grooves each define a fluid circulation channel each extending parallel to a longitudinal axis (X), the two channels are superposed one on the other and open into each other in a plurality of crossing zones each defining a mixing zone of the fluid with itself.
• assembling the first and second metal plates together, either by hot isostatic pressing (CIC), or by a method commonly known as hot uniaxial diffusion welding, so as to obtain a diffusion bonding between them, or by soldering.

The invention also relates to a heat exchanger, comprising a plurality of heat exchanger modules such as that described above, each extending parallel to the central axis of the chamber and each arranged inside the pregnant.

The subject of the invention is also the use of the heat exchanger described above, the first fluid being a secondary fluid being a gas or a mixture of gases and the second fluid as the primary fluid being a liquid metal.

The first fluid may comprise mainly nitrogen and the second fluid being liquid sodium. The first or the second fluid can come from a nuclear reactor.

Finally, the subject of the invention is a nuclear installation comprising a fast neutron nuclear reactor cooled with liquid metal, in particular liquid sodium called RNR-Na or SFR and a heat exchanger comprising a plurality of exchanger modules described above. .

detailed description

• la figure 1 est une vue en perspective d'un module d'échangeur de chaleur selon l'état de l'art réalisé à partir des deux plaques ;
• la figure 2 est une vue de détail en transparence montrant le profil en zigzag d'un canal d'un module d'échangeur selon la figure 1 ;
• la figure 3A est une vue en perspective de deux plaques à rainures usinées avant leur assemblage pour constituer un module d'échangeur de chaleur selon l'invention;
• la figure 3B est une vue en perspective d'un module d'échangeur de chaleur selon l'invention réalisé à partir des deux plaques selon la figure 3A;
• la figure 4 est une vue de détail en transparence montrant les zones de croisement entre canaux d'un module d'échangeur de chaleur selon l'invention ;
• la figure 5 est une vue en perspective de trois paires de canaux dans un module d'échangeur de chaleur selon l'invention;
• la figure 6 est un relevé des points comparatifs de la puissance thermique échangée en fonction du nombre de reynolds (Re), respectivement entre des exemples de canaux de circulation de fluide selon l'invention et selon l'état de l'art.

Other advantages and characteristics of the invention will emerge more clearly on reading the detailed description of exemplary embodiments of the invention, given by way of nonlimiting illustration and with reference to the following figures among which:

• the figure 1 is a perspective view of a heat exchanger module according to the state of the art made from the two plates;
• the figure 2 is a detail view in transparency showing the zigzag profile of a channel of an exchanger module according to the figure 1 ;
• the figure 3A is a perspective view of two grooved plates machined before assembly to form a heat exchanger module according to the invention;
• the figure 3B is a perspective view of a heat exchanger module according to the invention made from the two plates according to the figure 3A ;
• the figure 4 is a detail view in transparency showing the crossing zones between channels of a heat exchanger module according to the invention;
• the figure 5 is a perspective view of three pairs of channels in a heat exchanger module according to the invention;
• the figure 6 is a statement of the comparative points of the thermal power exchanged as a function of the number of reynolds (Re), respectively between examples of fluid circulation channels according to the invention and according to the state of the art.

For the sake of clarity, the same elements are designated by the same reference numerals according to the state of the art and according to the invention.

In figure 1 , there is shown a heat exchanger module according to the state of the art of longitudinal axis X comprising at least one fluid circuit.

The module comprising a pair of fluid circulation channels 1, 2 each extending parallel to the longitudinal axis X.

The two channels 1, 2 are superimposed on one another without any crossing between them.

More precisely, each channel 1, 2 has a regular curved zigzag profile. The curved zigzag profiles are identical for the two channels 1,2 and symmetrical to each other with respect to the longitudinal axis X or a parallel axis.

As better visible in figure 2 the curved channel zigzag profile has bends 14, 16 and straight segments, a straight segment 15 connecting two consecutive bends.

In figure 3B , there is shown a heat exchanger module according to the invention of longitudinal axis X comprising at least one fluid circuit.

The module comprising a pair of fluid circulation channels 1, 2 each extending parallel to the longitudinal axis X.

According to the invention, the two channels 1, 2 are superimposed on one another and open into one another in a plurality of crossing zones 3 each defining a mixing zone of the fluid with itself.

More precisely, each channel 1, 2 has a regular curved zigzag profile. The curved zigzag profiles are identical for the two channels 1,2 and symmetrical to each other with respect to the longitudinal axis X or a parallel axis.

As better visible in figure 4 the curved channel zigzag profile has bends 14, 16; 24, 26 and line segments, a line segment 15; 25 connecting two consecutive elbows.

To produce an exchanger module according to the invention which has just been described, the procedure is as follows:

Each of two metal plates 10, 20 of rectangular shapes, identical to each other, is machined respectively with a groove opening according to the regular curved zigzag profile 11, 12, 13 and a through groove 20 according to the same regular curved zigzag profile 21. 22, 33.

As illustrated on the figure 3A , the machining profiles of the grooves of the two plates 10, 20 are made in two patterns in opposition to one another, that is to say that the top of a groove 11 and facing the top of the other groove 21 when the plates are facing one another.

The machined plate 20 is then positioned against the machined plate 10 so that the grooves 11, 21 each delimit a fluid circulation channel 1, 2 each extending parallel to a longitudinal axis X and that the two channels are superposed. one on the other and open into each other in a plurality of crossing zones 3 each defining a mixing zone of the fluid with itself.

The two metal plates 10, 20 are then assembled together, either by hot isostatic pressing (CIC), or by a hot uniaxial diffusion-diffusion process so as to obtain diffusion bonding between them.

Studies have been made by the inventors, in order to determine the thermal performance of channels 1, 2 with crossing zones 3 according to the invention, and to compare them with those of machined plate exchangers with a crossover channel according to the state of the invention. art.

It is specified here that a channel according to the state of the art as illustrated in Figures 1 and 2 has the same dimensions, ie width, length and height of a channel according to the invention.

It is specified that the thermal compactness is defined here as the thermal power exchanged Pth per unit volume, which proportional to the number of channels N times the overall overall length L of an exchanger.

All the comparative tests are summarized in the table below and shown as points in figure 6 .

Examples 1 and 3 are in accordance with the invention, i.e. correspond to two identically profiled channels 1, 2 which intersect at a plurality of crossing zones 3.

Examples 2 and 4 are in accordance with the state of the art, ie they correspond to a profile channel identical to that of the channels 1, 2 but without any crossing with another channel.

The geometrical data, namely the length L between bends 14, 16 or 24,26, the angle between a line segment 15, 25 and the axis X, the radius of curvature R mean of a bend are illustrated in FIG. figure 4 .

It is specified that the total length of a channel corresponds to that L according to the curved profile plus that of the rectilinear end portions, references 4, 5 in figure 3B . <B><u> TABLE </ u></b> Geometry (cross section in mm * mm) Angle α (degree) Elbow length L (mm) Radius of curvature R (mm) Total length (mm) Length L of Curved Zigzag Profile 1, 2 (mm) Pressure loss ΔP (Pa) Heat exchange coefficient (W / m ² K) Example 1 (2 x (2x1)) 45 9 4.3 124 149 29710 3769 Example 2 (2x2) 45 9 4.3 124 149 8931 2843 Example 3 (2 x (2x1)) 20 14 6 164 172 15590 3308 Example 4 (2x2) 20 14 6 164 172 5353 2493

From this table, it can be seen that, for the two reference geometries (examples 1 and 2 for one geometry, examples 3 and 4 for the other), the heat exchange coefficient is higher for the two channels 1, 2 with crossings 3 according to the invention for a channel without crossing according to the state of the art.

However, greater losses are observed for the two channels 1, 2 with crossovers 3 according to the invention. Nevertheless, these higher pressure drops are compensated by the gain in terms of thermal power exchanged: by comparing Examples 1 and 3 according to the invention to those 2 and 4 according to the state of the art in terms of thermal compactness, it is found that a two-channel pattern 1, 2 crosses according to the invention allows thermal performance better than a pattern single channel state of the art. It even appears from the plot of the points of the figure 6 that these best thermal performance can be encrypted at a heat exchanged power of at least 20% higher.

We have shown in figure 5 an exchanger module according to the invention with three pairs of channels 1.1, 2.1; 1.2, 2.2, 1.3, 3.3 according to the invention, arranged parallel to each other and regular curved profiles all identical to each other.

The figure 5 highlights the arrangement of the channels according to the invention at the plate scale: if the distance between channels is sufficiently small, other zones crossover and therefore other areas of fluid mixing with itself are created, especially at the elbows.

Other variants and improvements may be provided without departing from the scope of the invention.

Thus, in all the illustrated embodiments of the invention, only a fluid circuit with the profile of the zigzag channels and the crossing of the channels is shown and explained.

In a two fluid circuit exchanger module according to the invention, it is possible to envisage the other fluid circuit with channels identical to those of the invention, i.e. with crossover of the channels,

Alternatively, the other fluid circuit may be envisaged with rectilinear profile channels, i.e. straight and without crossing.

For example, in an exchanger module between a liquid metal, such as liquid sodium, and a gas, such as nitrogen, the gas circuit can advantageously be envisaged with the crossing channels according to the invention and a liquid metal circuit with straight channels, and preferably larger sections than those of the channels of the gas circuit to limit the risk of clogging.

It goes without saying that a liquid / gas metal exchanger is an example of an application, and it is very possible to envisage having the cross-profile pattern according to the invention, for the two fluid circuits within the same exchanger. .

Claims (14)

1. A heat-exchanger module with a longitudinal axis (X) comprising at least two fluid circuits, the first of which comprises at least one pair of channels (1, 2) for fluid circulation, each extending parallel to the longitudinal axis (X), wherein the two channels of the same pair are stacked on top of one another and are in communication with one another in a plurality of crossing areas (3) each defining an area for mixing the fluid with itself in the first circuit, each channel having at least in part a curved zigzag profile, the curved zigzag profile being regular along its length, characterized in that the regular curved zigzag profile includes bends (14, 16; 24, 26) and straight segments, a straight segment (15; 25) connecting two consecutive bends.
2. The heat-exchanger module as claimed in claim 1, the radius of curvature of the bends being between 0.5 and 3 Dh inclusive, Dh being the hydraulic diameter of the channel.
3. The heat-exchanger module as claimed in claim 1, the length of the straight segment being between 4 and 8 Dh inclusive, Dh being the hydraulic diameter of the channel.
4. The heat-exchanger module as claimed in any one of claims 1 to 3, the angle between the straight segment and the longitudinal axis (X) being between 10 and 45° inclusive.
5. The heat-exchanger module as claimed in any one of claims 1 to 4, the curved zigzag profiles being identical for the two channels and symmetrical to one another with respect to the longitudinal axis (X) or a parallel axis.
6. The heat-exchanger module as claimed in any one of the preceding claims, the channels having an oval, circular, rectangular or square section.
7. The heat-exchanger module as claimed in any one of the preceding claims, the two channels of the same pair joining at their longitudinal ends in the same rectilinear channel portion (4, 5) substantially parallel to the longitudinal axis (X).
8. The heat-exchanger module as claimed in any one of the preceding claims for two fluids, each of the two fluid circuits including at least one pair of fluid circulation channels (1, 2) each extending parallel to the longitudinal axis (X), the two channels of the same pair being stacked on one another and in communication with one another in a plurality of crossing areas (3) each defining an area for mixing the fluid with itself in the first or second circuit.
9. The heat-exchanger module as claimed in any one of claims 1 to 7 for two fluids, such as a liquid metal (Na) and an inert gas (N2), the first fluid circuit including at least one pair of fluid circulation channels (1, 2) each extending parallel to the longitudinal axis (X), the two channels of the same pair being stacked on one another and in communication with one another in a plurality of crossing areas (3) each defining an area for mixing the fluid with itself in the first circuit, the second fluid circuit including at least one pair of channels of straight shape.
10. A method of producing the heat exchange module as claimed in any one of claims 1 to 9,

    - machining at least one first groove (11) in a first metal plate (10);

    - machining at least one second groove (21) in a second metal plate (20);

    - positioning the machined second plate (10) against the machined first plate so that the first and second grooves each delimit a fluid circulation channel (1, 2) each extending parallel to a longitudinal axis (X), the two channels being stacked on one another and in communication with one another in a plurality of crossing areas (3) each defining an area for mixing the fluid with itself;

    - assembling the first and second metal plates with one another, either by hot isostatic pressing (HIP) or by a process commonly called hot uniaxial diffusion welding, so as to produce diffusion welding between them, or by brazing.
11. A heat exchanger comprising a plurality of heat-exchanger modules as claimed in claims 1 to 9 each extending parallel to the central axis of the enclosure and each arranged inside the enclosure.
12. The use of the heat exchanger as claimed in claim 11, the first fluid, as the secondary fluid, being a gas or a mixture of gases and the second fluid, by way of primary fluid, being a liquid metal.
13. The use as claimed in claim 12 of the heat exchanger, the first fluid primarily comprising nitrogen and the second fluid being liquid sodium, preferably, the first or second fluid coming from a nuclear reactor.
14. A nuclear installation comprising a fast neutron reactor cooled with liquid metal, notably liquid sodium (FNR-Na or SFR), and a heat exchanger comprising a plurality of heat-exchanger modules as claimed in any one of claims 1 to 7.

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