HEAT-EXCHANGER MODULE WITH IMPROVED HEAT EXCHANGE AND COMPACTNESS, USE WITH LIQUID METAL AND GAS

Abstract

The invention relates to 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 a single 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 inside the first circuit.

Claims

1. A heat-exchanger module with a longitudinal axis comprising at least two fluid circuits, the first fluid circuit comprising, at least one pair of channels for fluid circulation, each extending parallel to the longitudinal axis, 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, each defining an area for mixing the fluid with itself in the first circuit.

2. The heat-exchanger module as claimed in claim 1, wherein each channel has at least in part a curved zigzag profile.

3. The heat-exchanger module as claimed in claim 2, wherein the curved zigzag profile is regular along its length.

4. The heat-exchanger module as claimed in claim 3, wherein the regular curved zigzag profile includes bends and straight segments, a straight segment connecting two consecutive bends.

5. The heat-exchanger module as claimed in claim 4, wherein the radius of curvature of the bends being is between 0.5 and 3 Dh inclusive, Dh being the hydraulic diameter of the channel.

6. The heat-exchanger module as claimed in claim 4, wherein the length of the straight segment is between 4 and 8 Dh inclusive, Dh being the hydraulic diameter of the channel.

7. The heat-exchanger module as claimed in claim 4, wherein the angle between the straight segment and the longitudinal axis is between 10 and 45 inclusive.

8. The heat-exchanger module as claimed in of claim 2, wherein the curved zigzag profiles is identical for the two channels and symmetrical to one another with respect to the longitudinal axis or a parallel axis.

9. The heat-exchanger module as claimed in claim 1, wherein the channels have an oval, circular, rectangular or square section.

10. The heat-exchanger module as claimed in claim 1, wherein the two channels of the same pair join at their longitudinal ends in the same rectilinear channel portion substantially parallel to the longitudinal axis.

11. The heat-exchanger module as claimed in claim 1 for two fluids, wherein each of the two fluid circuits includes at least one pair of fluid circulation channels each extending parallel to the longitudinal axis, the two channels of the same pair being stacked on one another and in communication with one another in a plurality of crossing areas each defining an area for mixing the fluid with itself in the first or second circuit.

12. The heat-exchanger module as claimed in claim 1 for two fluids, such as a liquid metal (Na) and an inert gas (N2), wherein the first fluid circuit includes at least one pair of fluid circulation channels each extending parallel to the longitudinal axis, the two channels of the same pair being stacked on one another and in communication with one another in a plurality of crossing areas 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.

13. A method of producing the heat exchange module as claimed in claim 1, comprising the following steps: machining at least one first groove in a first metal plate; machining at least one second groove in a second metal plate; positioning the machined second plate against the machined first plate so that the first and second grooves each delimit a fluid circulation channel each extending parallel to a longitudinal axis, the two channels being stacked on one another and in communication with one another in a plurality of crossing areas 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.

14. A heat exchanger comprising a plurality of heat-exchanger modules as claimed in claim 1 each extending parallel to the central axis of the enclosure and each arranged inside the enclosure.

15. The use of the heat exchanger as claimed in claim 14, 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.

16. The use of the heat exchanger as claimed in claim 15, the first fluid primarily comprising nitrogen and the second fluid being liquid sodium.

17. The use as claimed in claim 15, the first or second fluid coming from a nuclear reactor.

18. 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 claim 1.

Description

DETAILED DESCRIPTION

[0061] Other advantages and features of the invention will emerge more clearly on reading the detailed description of embodiments of the invention given by way of nonlimiting illustration with reference to the following figures, in which:

[0062] FIG. 1 is a perspective view of a prior art heat-exchanger module made from two plates;

[0063] FIG. 2 is a transparency detail view showing the zigzag profile of a channel of a heat-exchanger module according to FIG. 1;

[0064] FIG. 3A is a perspective view of two plates with machined grooves before assembling them to constitute a heat-exchanger module according to the invention;

[0065] FIG. 3B is a perspective view of a heat-exchanger module according to the invention produced from the two plates according to FIG. 3A;

[0066] FIG. 4 is a transparency detail view showing the crossing areas between channels of a heat-exchanger module according to the invention;

[0067] FIG. 5 is a perspective view of three pairs of channels in a heat-exchanger module according to the invention;

[0068] FIG. 6 is a summary of points comparing the thermal power exchanged as a function of the Reynolds number (Re) between examples of fluid circulation channels according to the invention and according to the prior art.

[0069] For clarity, elements that are the same according to the prior art and according to the invention are designated by the same reference numbers.

[0070] In FIG. 1 there has been represented a prior art heat-exchanger module with longitudinal axis X and including at least one fluid circuit.

[0071] The module including a pair of fluid circulation channels 1, 2 each of which extends parallel to the longitudinal axis X.

[0072] The two channels 1, 2 are stacked one on the other with no crossing over between them.

[0073] To be more precise, each channel 1, 2 has a regular curved zigzag profile. The curved zigzag profiles of the two channels 1, 2 are identical and symmetrical to one another with respect to the longitudinal axis X or a parallel axis.

[0074] As can be seen better in FIG. 2, the curved zigzag channel profile features bends 14, 16 and straight segments, a straight segment 15 connecting two consecutive bends.

[0075] In FIG. 3B there has been represented a heat-exchanger module according to the invention with longitudinal axis X and including at least one fluid circuit.

[0076] The module including a pair of fluid circulation channels 1, 2 each of which extends parallel to the longitudinal axis X.

[0077] According to the invention, the two channels 1, 2 are stacked one on the other and in communication with one another in a plurality of crossing areas 3 each defining an area of mixing of the fluid with itself.

[0078] To be more precise, each channel 1, 2 has a regular curved zigzag profile. The curved zigzag profiles of the two channels 1, 2 are identical and symmetrical with each other with respect to the longitudinal axis X or a parallel axis.

[0079] As can be seen better in FIG. 4, the curved zigzag channel profile features bends 14, 16; 24, 26 and straight segments, a straight segment 15; 25 connecting two consecutive bends.

[0080] The following procedure is employed to produce a heat-exchanger module according to the invention as just described.

[0081] There are machined in each of two identical rectangular metal plates 10, 20 a respective open-ended groove along the regular curved zigzag profile 11, 12, 13 and an open-ended groove 20 along the same regular curved zigzag profile 21, 22, 23.

[0082] As shown in FIG. 3A, the machining profiles of the grooves of the two plates 10, 20 are produced according to two opposite patterns, i.e. the summit of one groove 11 faces the summit of the other groove 21 when the plates face one another.

[0083] The machined plate 20 is then positioned against the machined plate 10 so that each of the grooves 11, 21 delimits a fluid circulation channel 1, 2 each extending parallel to a longitudinal axis X and so that the two channels are 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.

[0084] The two metal plates 10, 20 are then assembled with one another, either by hot isostatic pressing (HIP) or by a hot uniaxial diffusion welding process, so as to produce diffusion welding between them.

[0085] Studies have been carried out by the inventors in order to determine the thermal performance of the channels 1, 2 with crossing areas 3 according to the invention and to compare the latter with that of prior art machined plate heat exchangers with channels that do not cross.

[0086] It is specified here that a prior art channel as shown in FIGS. 1 and 2 has the same dimensions, i.e. width, length and height, as a channel according to the invention.

[0087] It is specified here that the thermal compactness is defined as the thermal power Pth exchanged per unit volume, which is proportional to the number N of channels multiplied by the overall length L of a heat exchanger.

[0088] All of the comparative tests are summarized in the table below and shown in the form of points in FIG. 6.

[0089] Examples 1 and 3 represent the invention, i.e. correspond to two channels 1, 2 with identical profiles that cross in a plurality of crossing areas 3.

[0090] Examples 2 and 4 represent the prior art, i.e. correspond to a channel of identical profile to the channels 1, 2 but not crossing another channel.

[0091] The geometrical data, namely the length L between bends 14, 16 or 24, 26, the angle between a straight segment 15, 25 and the axis X, the mean radius of curvature R of a bend, are shown in FIG. 4.

[0092] It is specified that the total length of a channel corresponds to that L of the curved profile plus that of the rectilinear end parts, referenced 4, 5 in FIG. 3B.

TABLE-US-00001 TABLE Length L Length L of curved Head Coefficient Geometry between Radius R Total zigzag loss of thermal (cross section Angle bends of curvature length profile 1, 2 P exchange in mm*mm) (degrees) (mm) (mm) (mm) (mm) (Pa) (W/m.sup.2K) Example 1 45 9 4.3 124 149 29710 3769 (2 x (2x1)) Example 2 45 9 4.3 124 149 8931 2843 (2x2) Example 3 20 14 6 164 172 15590 3308 (2 x (2x1)) Example 4 20 14 6 164 172 5353 2493 (2x2)

[0093] From this table it is clear that, for the two reference geometries (examples 1 and 2 for one geometry, examples 3 and 4 for the other), the coefficient of thermal exchange is higher for the two channels 1, 2 with crossings 3 according to the invention than for a channel according to the prior art with no crossing.

[0094] However, higher head losses are seen for the two channels 1, 2 with crossings 3 according to the invention. However, these higher head losses are compensated by the improvement in terms of the thermal power exchanged: comparing examples 1 and 3 according to the invention and those 2 and 4 according to the prior art in terms of thermal compactness, it is seen that a pattern with two channels 1, 2 with crossings according to the invention enables better thermal performance than a prior art single channel pattern. It is even clear from the points plotted in FIG. 6 that this improved thermal performance can be quantified as a 20% increase in the thermal power exchanged.

[0095] There has been represented in FIG. 5 a heat-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 one another and all with identical regular curved profiles.

[0096] FIG. 5 shows the arrangement of the channels according to the invention at the scale of one plate: if the distance between channels is sufficiently small, other crossing areas and therefore other areas for mixing the fluid with itself are created, notably at the level of the bends.

[0097] Other variants and improvements may be provided without this departing from the scope of the invention.

[0098] Thus in all of the embodiments of the invention shown only one fluid circuit with the zigzag channel profile and the crossing of the channels is shown and explained.

[0099] In a heat-exchanger module according to the invention with two fluid circuits the other fluid circuit may be envisaged with channels identical to those of the invention, i.e. with the channels crossing.

[0100] Alternatively, the other fluid circuit may equally well be envisaged with rectilinear profile, i.e. straight and not crossing, channels.

[0101] For example, in a heat-exchanger module between a liquid metal, such as liquid sodium, and a gas, such as nitrogen, the gas circuit may therefore and advantageously be envisaged with the channels crossing according to the invention and a liquid metal circuit with straight channels, preferably of larger section than the channels of the gas circuit in order to limit the risks of blocking them.

[0102] It goes without saying that a liquid metal/gas heat exchanger is one example of application and having the pattern with crossing profile according to the invention may very well be envisaged for both fluid circuits in the same heat exchanger.