HEAT EXCHANGER - ACCUMULATOR

Abstract

The invention relates to a heat exchanger comprising a first free space (7) for a first fluid (3), a thermally conductive wall (11) which, at least locally, delimits said first free space (7), in such a way that an exchange of heat can occur between the first fluid and the thermally conductive wall (11) which is hollow and encloses a material (13) for storing thermal energy by accumulation of latent heat, by heat exchange with at least the first fluid. The first free space (7) is divided into at least two separated channels (7a, 7b) in which two streams of the first fluid (3) can circulate at the same time but separately, the thermally conductive wall (11) which encloses the thermal energy storage material (13) being interposed between the two channels (7a, 7b).

Description

The present invention relates to the field of thermal management.

This applies in particular to:

• • a heat exchanger for implementing an exchange of thermal energy with at least a first fluid or between a first fluid and a second fluid,
  • an element in the general shape of a polygonal plate for providing a hollow wall of this heat exchanger,
  • a first set comprising several such assembled elements,
  • a second set comprising the above-mentioned heat exchanger, with all or part of its characteristics, and a thermally insulating housing containing same,
  • and a thermal management installation provided with said exchanger.

The patent application publications EP165179 and WO1989000664 respectively provide for a plate exchanger and a tubular exchanger.

A heat exchanger is therefore known which comprises:

• • at least one first free space for a (first) fluid,
  • at least one (first) thermally conductive wall that:
    • at least locally limits said at least one first free space, so that a heat exchange can occur between said first fluid, and
    • is hollow and encloses a material for storing thermal energy by accumulation of latent heat (such as PCM), in thermal exchange with at least said first fluid, thereby providing a thermal energy storage function.

In this context, it may happen that a fluid, such as the first one here, has more to expect in the exchanger, in terms of temperature change, from the material for storing thermal energy than from an exchange with another fluid. In addition, the optimised thermal management of an installation, and trying to avoid unnecessary loss of thermal energy, are considerations to be taken into account.

In this case, it is proposed that said first free space should be divided into at least two (sub)-channels in the exchanger, where the two (a priori generally parallel) streams of the first fluid can circulate at the same time, with the thermally conductive wall containing the material for storing thermal energy being then interposed between said two (sub)-channels.

It may then also occur that at some point in time, this first fluid is in a position to release, or in need of having to release, a thermal energy that a second fluid may subsequently require, and/or that some fluids are at one time to be heated and at another time to be cooled.

It is within this framework that it is proposed here to implement a heat exchange between such first and second fluids, proposing that the exchanger should also comprise:

• • at least one second free space for the second fluid, in such a way that said first and second fluids circulate in the first and second free space(s), respectively,
  • and an additional thermally conductive wall separating said first and second free spaces, in such a way that heat exchange between the two fluids occurs through said additional thermally conductive wall.

A priori, this additional thermally conductive wall will be devoid of material for storing thermal energy.

And to also optimize heat exchange, manufacture and use, it is proposed that the additional thermally conductive wall should also be hollow, i.e. having a double wall in which said at least one second free space for the second fluid will be defined.

To manufacture the elements of the exchanger, it is also proposed to start from flat metal plates, press them to form recesses, fill the recesses of one of the plates with the material for storing thermal energy and cover them with the other plate, then fix them a priori by welding.

No need for containers for the storage material nor any other parts for closing the recesses or the volumes receiving this material.

When it is mentioned that the exchanger includes plates having inner faces with recesses, it may be only one plate folded back on itself.

To promote the rigidity of the plates while taking advantage of the bumpy and hollow areas then formed, it is also proposed that said plates should include corrugated plates defining elongated channels forming the recesses where said parts of the material for storing thermal energy are arranged.

This will also be an ergonomic, fairly simple realization, which can be obtained by stamping metal plates. A maximum of two plates, without a PCM container, will suffice.

Such a solution will guide the fluid into its circulation free space, at two different levels of the exchanger, typically in said first and second circulation free spaces.

As a material or materials for storing thermal energy, using at least one PCM material should therefore be favourably considered. In an alternative solution, it is possible, although not considered as preferable here, to use a device operating on the basis of reversible thermochemical reactions provided for in the TCS technology.

In any case, it is confirmed that a phase change material (MCP in French; or PCM in English), refers to a material which can change physical state, for instance between liquid and solid state, with a temperature range of, for instance −50° C. to 180° C. Thermal transfer is made by using the Latent Heat thereof.

The thermally insulating material(s) mentioned hereunder may be a “simple” insulator such as glass wool, or a foam, for example of polyurethane, or a porous thermally insulating material laid out in a vacuum envelope, to define at least one insulating panel, VIP.

“VIP” means a “controlled atmosphere” structure, i.e. either filled with a gas having a thermal conductivity lower than that of the ambient air (26 mW/m·K) or “under vacuum”, i.e. under a pressure lower than the ambient pressure (therefore <10⁵ Pa).

The cavity wall containing the material for storing thermal energy, and preferably the exchanger itself, could be made of a preferably rubbery flexible material, so as to adapt to the shapes and locations of the applications for which the exchanger-accumulator unit will be used.

In particular in this case, said hollow wall, and preferably the exchanger itself again, could be tubular.

Applications to hoses and other pipes in vehicles in particular are planned, including in confined areas and where weight can be a major criterion.

Such a realization could be made from a shape like a flexible flat plate rolled on itself substantially in a cylinder and fixed at its rolled ends to obtain a laterally closed tube.

Connections, differentiated for each fluid, would make it possible for said first and second fluids to get in and out. In the centre could circulate a third fluid which could also be in thermal exchange with the first or second peripheral fluid which will circulate radially closest to it.

In general, for an industrial standard for the manufacture of the element intended for the construction of a hollow wall of the aforementioned heat exchanger, with all or part of its characteristics, a solution provides an element which comprises two identical parallel plates, two opposite edges of which are bent in the same direction and which each have recesses on the inner face and bumps on the outer face.

In one case said storage material will be housed in the face-to-face recesses of the plates, in another case the inter-plate volume will be left empty.

With the above-mentioned elements, it will also be possible to create a set wherein these stacked elements, will therefore be fixed together two by two along the folded edges, in order to define between two external faces of two elements arranged face to face, at least one free fluid space.

Thus, it will be possible to produce a modular exchanger, with elementary modules that are easy to manufacture, in series, typically by stamping thin light metal plates.

The invention also relates to another assembly comprising:

• • the heat exchanger involved, and
  • a thermally insulating housing containing this heat exchanger and provided with walls containing at least one thermal insulator, collecting volumes of said at least first fluid being interposed between end openings of each free space and at least some of the walls of the housing through which inlet or outlet connections of said at least first fluid pass.

The walls containing the thermal insulator will have a VIP structure if a good compromise between thermal performance/weight/impact is to be achieved.

Also concerned is a thermal management installation comprising:

• • the above-mentioned heat exchanger, with all or part of its characteristics, with this exchanger being arranged at a crossing between a first circuit for the first fluid and a second circuit for the second fluid, in such a way:
    • that outside the heat exchanger, the first and second fluids circulate independently in functional components (in an internal combustion engine, for example cylinders, an air/water radiator, a cylinder head, etc.) on which one and/or the other of the fluids act or with which they interact,
    • and that, in the heat exchanger, the first fluid can circulate in the first free space(s) and the second fluid can circulate in the second free space(s),
  • means (such as one or more pump(s)) for circulating the first and second fluids in the first and second circuits respectively, and at least one valve placed at least on the second circuit of the second fluid, for:
    • at a first time (T1) of operation of the installation, allowing the first fluid to circulate alone in the heat exchanger, without the second fluid, and
    • at a second time (T2) of operation of the installation, allowing the first and second fluids to circulate together in the heat exchanger.

In this installation, it may be preferred for the first and second fluids to be placed in direct thermal exchange through said additional thermally conductive wall, without interposing material for storing thermal energy between them.

BRIEF DESCRIPTION OF THE DRAWINGS

If necessary, the invention will be better understood and other characteristics, details and advantages thereof will become apparent upon reading the following description as a non-exhaustive example with reference to the appended drawings in which:

FIG. 1 is a diagram of an exchanger-accumulator according to the invention, in a pull-out view; FIG. 6 is an exploded view thereof,

FIGS. 3 and 5 are each a view of a generally polygonal-shaped plate element that can define in elevation half of a stage of the exchanger (respectively double walls 11 and 211 below),

FIGS. 2 and 4 are sections along lines II-II and IV-IV respectively, and

FIGS. 7, 8 show two applications where the above-mentioned exchangers can be used.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In particular, FIG. 1 shows an example of a heat exchanger 1 allowing an exchange of heat energy between a first fluid 3 and a second fluid 5, which can be liquid and/or gaseous respectively.

The exchanger 1 comprises:

• • at least a first free space 7 for the first fluid and at least a second free space 9 for the second fluid, in such a way that these first and second fluids circulate in the first and second free spaces, respectively,
  • and at least one thermally conductive wall 11 which separates two adjacent free spaces 7, 9, in such a way that the exchange of heat between the fluids 3,5 occurs through the (each) wall 11 concerned.

The expression “at least one . . . free space” indicates that this space can have one or more volume(s).

This is a situation where the exchanger 1, the outer housing of which is not shown here (with collecting volumes 163, side walls 165 gone through by supply channels 169 and covers 181 in FIG. 6) is adapted so that the first free space 7 (stage 270a) is, in the exchanger, divided into at least two sub-channels 7a, 7b wherein the (first) fluid 3 can circulate at the same time.

In the exchanger, one said thermally conductive wall 11 which contains the material for storing thermal energy 13 which is therefore interposed between the two sub-channels 7a,7b extends between same two sub-channels 7a, 7b.

Thus, the fluid 3 will divide, in the exchanger, into several streams, here two parallel (sub)-channels (see arrows in FIG. 10), with the intermediate material 13 (typically containing PCM) becoming loaded with or releasing thermal energy, depending on the temperature of the fluid 3.

All the stages of the exchanger 1 could be like the stage 270a mentioned above.

However, it may be beneficial if a second fluid 5 could also circulate in the exchanger 1, exchanging heat with the (first) fluid 3—stage 270b—with no mixing of such streams, as in the case illustrated in FIG. 1.

It is therefore proposed:

• • that the exchanger 1 should further comprise at least a second free space 9 for the second fluid 5, in such a way that said first and second fluids 3, 5 circulate into the first and second free spaces, respectively,
  • and that an additional thermally conductive 211 wall separates a first and a second adjacent free space 7, 9, in such a way that the heat exchange between the first and second fluids 270a, 270b at two adjacent, successive, stages 3, 5 occurs through this additional thermally conductive wall 211.

Between two sub-channels 7a, 7b, where the only first fluid 3 circulates, a material for storing thermal energy 13 will be interposed, whereas this will not be the case between the first and second channels 7, 9, where the first and second fluids 3, 5 respectively circulate, without mixing together, substantially transversely to each other. The double wall 211, which defines the second channel 9 between these two wall parts, is therefore devoid of material 13.

The walls 11, 211 can be metallic.

The material 13 exchanges heat with the first two divided streams 3a, 3b. Using one or more PCM materials will make it possible to combine efficiency, limited weight, adaptability in the choice of shapes or even flexibility.

As a choice of this type of material, a rubber composition as described in EP2690137 or EP2690141 can be used. As an alternative solution, the material can be a fatty acid- or paraffin-based material.

The, or each wall 11, has a succession of recesses 15 inside which parts of the material 13 are arranged. Preferably, this should be coupled with a succession of bumps 17 on the outside of this wall.

With reference to FIGS. 2-5, a way of manufacturing the walls 11, 211 of FIG. 1 will now be presented.

The wall 11 of FIG. 2 is made as shown in FIG. 3, from two identical parallelepipedic plates 10b3, the two opposite edges 29b1, 29b2 of which are bent (at right angles) in the same direction.

The two plates are parallel. In the general plane of each plate, the frame 31 surrounds the central part with recesses 15 and bumps 17, again like a corrugated sheet.

Between the two plates 10b3 material 13 is interposed, here in the form of a succession of individualized blocks.

For assembly, one of the two plates is rotated by 180° relative to the other, about the X axis passing through the two opposite unfolded edges, with the edges 29b1, 29b2 being back to back. They are then sealingly assembled (typically by welding), by their frames 31 pressed against each other, after interposition of the material 13, so as to obtain the double wall 11 of FIG. 2.

The wall 211 of FIG. 4 is made as shown in FIG. 5, from the two plates 10b3 with identically folded opposite edges.

Nothing is interposed between the two parallel plates 10b3.

For assembly, one of the two plates is rotated again by 180° with respect to the other, about the X axis passing through the two opposite unfolded edges, with the edges 29b1 or 29b2 facing each other. They are then sealingly assembled (typically by welding), by the ends 290 of their folded edges so as to create the channel 9 between the two plates.

If the corrugated sheet shape is planned, the corrugations cross from one plate to another, which advantageously increases the heat exchange surfaces.

A stage 270b is then created. To create an adjacent stage 270a, it is sufficient to place a double plate 11 and a double plate 211 coaxially parallel, so that they overlap, and then sealingly attach the two end lengths 290 of the first one (typically by welding) to the two opposite edges of the frame 31 facing same.

Two superimposed, crossed channels, insulated from each other and separated by a “simple” wall (without any material 13) are thus obtained.

If above the double plate 11, another double plate 211 is placed, oriented as the previous one and always fixed at the ends 290, then the two superimposed sub-channels 7a, 7b separated by the double wall 11 with the material 13 are created.

To avoid mixing the fluids 3, 5 tabs 175 usefully form, in each corner, an edge parallel to the stacking direction A which makes it possible to obtain a multi-stage exchanger-accumulator (see FIG. 1), having an alternation of channels or free spaces 7, 9, crossed with respect to each other and closed on two sides.

This exchanger 1 can then be placed in the housing 183 as shown in FIG. 6, to collect the fluid(s) at the inlet/outlet of the exchange plates and for a peripheral thermal insulation.

An operational application of this exchanger-accumulator could be the following one, as shown in FIG. 7 or 8 on a thermal management installation comprising:

• • the heat exchanger 1, at a crossing between a first circuit 6 for the first fluid 3 and a second circuit 16 for the second fluid 5, in such a way that:
    • outside the heat exchanger, the first and second fluids circulate, independently from each other in functional components 14, 140, 213 on which they act or with which they interact,
    • and that, in said exchanger, the first fluid 3 can circulate in the first free space(s) 7 and the second fluid 5 can circulate in the second free space(s) 9,
  • means 12, 143, 217 for circulating the first and second fluids in the first and second channels (and in the exchanger) respectively,
  • and at least one valve 251 placed at least on the second circuit 16, for:
    • at a first time (T1) of operation of the installation, allowing the first fluid 3 to circulate alone in the heat exchanger, without the second fluid 5, and
    • at a second time (T2) of operation of the installation, allowing the first and second fluids to circulate together in the heat exchanger.

Typically, this thermal management system is intended to be mounted on a heat engine 8, in particular an internal combustion engine.

Let us consider, in a first case, as in FIG. 7, a first engine oil circuit 6 (e.g. an automatic gearbox oil 213) and a second water circuit 16. Then the exchanger-accumulator 1 (FIG. 10) will be mounted at the intersection of the circuits, as shown in the figure.

As soon as the engine 8 is started, for example after the vehicle has been parked outside for 5-7 hours at 5° C., and when the material for storing thermal energy 13 of each of the walls 11 of the stages 270a is assumed to be in liquid phase, for example around 80-100° C., the oil circulates in the circuit 6 via the oil pump 217.

At this so-called T1 point: the oil enters (as the first fluid 3) through an inlet 169 (FIG. 6) in the stages 270a of the heat exchanger 1, for example around 6-8° C. It is heated there by PCM 13, when the access to the exchanger is then prohibited for water from circuit 16 (as the second fluid 5), with the inlet valve 251 being closed.

With the displacement engine 8 running, water then circulates in certain pipes and components of the vehicle (cylinders 14, cylinder head 141 for example) via the water pump 143 of circuit 16.

At this time, water 5 is still too cold to heat the oil. The motor thermostat 145 and the valve 251, then closed, force it to circulate only in the motor, without any circulation in the exchanger-accumulator 1.

Once the water reaches a temperature higher than that of the oil, the inlet valve 251 opens (and, when the time comes, the thermostat 145 passes the water through the radiator 18, if it is useful to cool it so that it does not exceed about 90° C., preferably). The second moment T2 has arrived, it being specified that another valve 252 can block a backflow of water to the exchanger 1 (FIG. 15).

While oil continues to circulate in the stages 270a, the circulating water 5 now reaches the stages 270b through an independent inlet 169.

Oil is then heated by water, and possibly by the material 13 which gives it energy through the walls 211, as long as the PCM has not fallen below its state (phase) change temperature (of the order of 60-70° C. in the example).

The engine continues to warm up. Water now reaches the exchanger 1 at 80° C. Oil continues to heat through the exchange with water 5, through the walls 211. Oil now reaches the heat exchanger-accumulator 1 at +70° C. Through this oil, the material 13 then becomes loaded with heat energy, which will then be available for the next engine operation, after another stop.

Warming on up in the engine, the temperature (t1) of oil 3 now exceeds 90 or even 100° C., thus the temperature (t2) of water 5.

To avoid overheating, oil then transfers thermal energy to water 5 (walls 11) and the material 13 (whenever possible) in the heat exchanger-accumulator 1.

In another case, as shown in FIG. 8, where, at the intersection of the circuits, said exchanger-accumulator 1′ (FIG. 1) will preferably be mounted, the second water circuit 16 in connection with the vehicle's air circuit will now be used in the engine 8 as the first circuit 6 on which a turbocharger 12 is mounted.

The vehicle is again assumed to have been parked, even in cold weather (negative temperature in winter), engine 8 stopped, for 5-6 hours. If, during its operation before this shutdown, the engine 8 ran for example 10-15 min with its turbo 12 running, the PCM 13 has exceeded its state change temperature and is therefore, in the example, above its liquefaction temperature.

Especially with the thermal insulation of the housing 183 and the multiple stages of the exchanger-accumulator 1, it is ready, for a certain time (5-6 hours in the example), to heat the fluid 3 (here air) when the engine starts next.

This engine start occurs then. The turbocharger 12 is still off. Outside air 3, still relatively cold from the first air circuit 6 to the combustion chamber(s) 14/140 of the engine 8, then circulates through the stages 270a.

The first moment T1 then comes: the valve 251 is closed and forces the water from the circuit 16 to circulate only in the motor, except for the exchanger-accumulator 1. Thus, since water is still cold, air is prevented from losing calories in a heat exchange between same, while it has heated up in the exchange with the material 13 that is hotter than air.

Having been heated from 5° C. to 40° C., for example, this air will be able to advantageously supply the combustion chamber(s) 14/140.

A few minutes (3 to 4 for example) after this first phase following the engine start, the turbocharger 12 starts. An immediate rise in pressure and temperature (above 150° C.) of air (oxidizer) in the first circuit 6 occurs.

However, supplying the combustion chambers 14 of the cylinders 140 at such temperatures is inappropriate: too high thermal constraints, drop in efficiency . . . . It is recommended to do this around 100-130° C. and preferably around 110° C.

In addition, since the engine 8 is already operating, and thus the channel 16 is active, for a few minutes, water (as a cooling liquid for the relevant parts of the engine) is already relatively hot in the channel 16 even if the temperature around is cold. As a matter of fact, for example, an engine thermostat, then closed, could have forced the water to circulate only in the engine, without therefore temporarily circulating in the engine exchanger (which can be a radiator) 18. This water will have quickly warmed up as it circulated around the cylinders 140 and in the cylinder head 141 of the engine 8 before returning to the water pump 143.

Thus, it is reasonable to consider a rise in water temperature up to 40-60° C. at that time.

The cycle of said moment T2 in the exchanger-accumulator 1 can occur, especially since this second fluid 5 is at the moment T2 at a favourable temperature (50° C. for example) to reduce that of air from the turbo 12 which, when passing through the stages 270a, was able to supply thermal energy to the material 13.

With these two, here simultaneous, thermal exchanges, it can be considered that at the same time T2, while at the exit of turbo 12 the compressed air (for example towards 2×10⁵ Pa in absolute pressure) is at a temperature of 170-190° C., it can go down to 110-120° C. after the exchange, in the exchanger-accumulator 1, with the material 13 and water 5.

Referring again to FIGS. 1, 6, it should be noted that with a stacking in a direction A of elements corresponding to a staged and alternating succession of hollow walls 11, with cells containing material 13, and hollow walls 211 with no such material, it will be possible to create a succession of free spaces 7 then 9, stage after stage.

The fluids 3, 5 will therefore circulate in the free spaces 7, 9 on one stage out of two, here in two transverse directions, each perpendicular to the axis A.

One collecting volume 163 per side face stands around this stack, as illustrated specifically in FIG. 6.

Each series of free space stages 7 (respectively 9) communicates upstream (with respect to the direction of circulation of the fluid under consideration) with a first collecting volume 163 and, downstream, with a second collecting volume 163 located on the opposite side face.

Externally, each collecting volume 163 is limited by a side wall 165.

Each side wall 165 will preferably be traversed at 167 by a passage, thus communicating with a collecting volume 163 to be connected to a fluid supply or discharge 3 or 5 pipe 169.

Moreover, each side wall 165 will preferably contain a thermally insulating material 171.

Between two adjacent side faces, such as 165a, 165b, the collecting volumes 163 are fluidically isolated from each other.

To obtain a complete block, i.e. a multi-stage exchanger-accumulator, it will therefore be sufficient, as shown in FIGS. 1, 6, to superimpose elements with alternating walls 11, 211 and plates welded together along the folded edges and vertical tabs 175. An alternation of free channels or spaces 7, 9, crossing one with another and closed on two opposite sides, is thus obtained.

The final step of realisation embodiment of the block will then pass through an interface with the side walls 165, for the peripheral sealing, and thus the insulation between the collecting volumes 163.

Rather than a direct engagement with these walls, what is proposed here is that the axial (thus vertical in this case) lines of the tabs 175 fastened to each other engage between two, for example bevelled, vertical corners 179 of intermediate frames 177.

The intermediate frames 177 will then be laterally interposed between the stack of plates 100 and the opposite side wall 165.

In the lateral corners, pillars 179 stand axially between two adjacent side walls 165, or, as in the example shown, between two adjacent lateral intermediate frames 177, the whole assembly then being covered by the side walls 165.

Fixing means, such as screws 173, may unite the whole assembly, in this case engaged in the side walls 165 and the corner pillars 179.

Transversally to the axis A, in this case above and below same, solid cover plates 181 are involved in the closing, thus preferably sealed and thermally insulated, of the collecting volumes 163. Like the walls 165, the plates 181 each preferably contain a thermally insulating material 171.

As a matter of fact, it is advised that (preferably all) such walls 165 and plates 181 should have a VIP structure. The passages for the channels 169 and screws 173 will then be sealed.

The pillars 179 may not consist of VIP structure.

Once the whole is assembled and fastened, the operational housing 183 forming a thermally-efficient exchanger-accumulator is thus obtained. One advantage of the VIP solution is that it limits the thickness of the insulating material 171, and thus the internal volume of the housing available for the exchanger, or the overall volume of the housing can thus be increased. Better insulation and/or limited weight can also be expected.

Claims

1. A heat exchanger for implementing an exchange of heat between a first fluid and a liquid, with said exchanger comprising therefor, in a staged manner: first free spaces for the first fluid,thermally conductive walls which, each, at least locally delimit at least one of said first free spaces, in such a way that an exchange of heat can occur between said first fluid and said thermally conductive walls, which are hollow and contain a material for storing thermal energy by accumulation of latent heat, disposed in heat exchange with at least said first fluid, with said first free spaces being, in the heat exchanger, individually divided into at least two separated channels in which two streams of the first fluid can circulate at the same time but separately, with one of said thermally conductive walls, which contains the thermal energy storage material, being interposed between the two channels,second free spaces for the liquid, in such a way that the first fluid and the liquid can flow into the first and second free spaces, respectively,additional thermally conductive walls which each separate said successive first and second free spaces from each other, in such a way that the exchange of heat between said first fluid and the liquid occurs through said additional thermally conductive walls,wherein:in the first free spaces, only one of said hollow thermally conductive walls containing the thermal energy storage material separates two channels, in such a way that two streams of the first fluid can individually exchange heat with the thermal energy storage material directly through only one of said thermally conductive walls,whereas the thermal energy storage material of each said hollow thermally conductive wall is separated from each second free space by at least: one of said additional thermally conductive walls, one of said two channels of one said first free spaces and one of said thermally conductive walls.

2. A heat exchanger according to claim 1, wherein the following elements are provided in a staged manner: one first of said at least two channels for the circulation of said first fluid,at least one of said thermally conductive walls, containing one said thermal energy storage material,one second of said at least two channels for the circulation of said first fluid,one of said second free spaces for the circulation of said second fluid, which second free space is positioned between at least two of said additional thermally conductive walls.

3. An element in the general shape of a polygonal plate for providing a hollow wall of the heat exchanger according to claim 1, which comprises two identical, parallel plates two opposite edges of which are bent in a same direction, and two other opposite plane edges are not bent, and which each have, between said bent and not bent edges thereof, recesses on the inner face and bumps on the outer face.

4. An assembly of individual elements according to claim 3, which comprises several of said elements: some of which are fixed together in pairs, along the bent edges positioned face to face, to define, between two outer faces of two elements positioned face to face, at least one free space for the circulation of a fluid,some other ones of which are fixed together in pairs along the not bent plane edges, with the edges positioned back to back and with a thermal energy material for storing by accumulation of latent heat being interposed between same.

5. An assembly comprising: the heat exchanger according to claim 1; anda thermally insulating housing containing the heat exchanger and provided with walls containing at least one thermal insulator, with volumes for collecting said at least first fluid being interposed between end openings of each free space and at least some of the walls of the housing through which inlet or outlet connections of said first fluid, for some of them, and of said liquid for the other ones, pass.

6. A thermal management installation comprising: the heat exchanger according to claim 1, with the heat exchanger being arranged at a crossing between a first circuit for the first fluid and a second circuit for the second fluid, so that: outside the heat exchanger, the first fluid and the liquid circulate independently in functional components on which they act or with which they interact,in the heat exchanger, the first fluid can circulate in the first free spaces and the liquid can circulate in the second free spaces,means for the circulation of the first fluid and the liquid, in the first and second circuits, respectively,at least one valve placed at least on the second circuit of the liquid, for: at a first time of operation of the installation, allowing the first fluid to circulate alone in said first free spaces of the heat exchanger, without the liquid, andat a second time of operation of the installation, allowing the first fluid and the liquid to circulate together in the first free spaces and second free spaces of the heat exchanger respectively.

7. An installation according to claim 6, wherein, through said additional thermally conductive wall, the first fluid and the liquid are placed in direct heat exchange, without interposition of material for storing thermal energy.

8. (canceled)