WO2023088841A1

WO2023088841A1 - Thermoacoustic cell comprising a casing of composite material

Info

Publication number: WO2023088841A1
Application number: PCT/EP2022/081795
Authority: WO
Inventors: Thierry Le Polles; Philippe Bonnet
Original assignee: Equium Groupe
Priority date: 2021-11-18
Filing date: 2022-11-14
Publication date: 2023-05-25
Also published as: FR3129200B1; FR3129200A1

Abstract

The invention relates to a thermoacoustic cell (1) comprising a casing (14) forming a shell (15) made of a composite material, preferably obtained by filament winding.

Description

Title: Thermoacoustic cell comprising an envelope in composite material

Technical area

The invention relates to the field of thermoacoustic machines.

State of the prior art

In a manner known per se, a thermoacoustic machine is a thermal machine in which, according to the physical principle of thermoacoustics, thermodynamic cycles take place within a working fluid. In motor mode, these cycles generate mechanical energy in the form of an acoustic wave from a heat input. In heat pump mode, these cycles generate heat pumping using the mechanical energy of the acoustic wave.

Such a machine generally comprises a waveguide containing the working fluid capable of propagating an acoustic wave and one or more thermoacoustic cells each provided with a porous structure arranged between two heat exchangers so as to carry out a thermoacoustic energy conversion .

A conventional thermoacoustic cell comprises a metal casing intended to hold and position the exchangers and the porous structure relative to each other and to contain the pressurized working fluid under the conditions required for the production of the thermoacoustic phenomenon.

Among other drawbacks, such an envelope is bulky and massive, taking into account in particular its thickness, which is proportional to the pressure of the working fluid, and the use of fastening means such as flanges and screw-nut systems. This results in a high manufacturing cost and difficulties of implementation in an industrial context which present a brake on the industrial development of thermoacoustic technologies. Disclosure of Invention

The invention aims to reduce the manufacturing cost of a thermoacoustic cell and to simplify its implementation in an industrial context.

To this end, the subject of the invention is a thermoacoustic cell for a thermoacoustic machine, the cell defining an internal space intended to receive a working fluid, the cell comprising two heat exchangers, a porous structure interposed between the exchangers and an envelope, each of the exchangers being configured to carry out a heat exchange between the working fluid and a transport element, the porous structure and the exchangers being intended to be traversed by the working fluid, the exchangers and the porous structure being housed in the envelope. According to the invention, the envelope comprises a shell made of composite material.

A shell made of composite material makes it possible to reduce the mass and the volume of the envelope while ensuring adequate acoustic and thermal insulation as well as the mechanical strength of the various elements of the cell when the working fluid is pressurized.

The invention also makes it possible to simplify the manufacture and the envelope of the cell as well as its assembly.

In particular, the casing makes it possible to minimize the use of fastening means such as flanges and screw-nut systems.

The invention thus makes it possible to reduce the manufacturing cost of a thermoacoustic cell and to simplify its implementation in an industrial context.

Concerning more specifically the hull, the latter may comprise a matrix and reinforcement elements respectively chosen from among several types of materials.

In a non-limiting way, the matrix can be an organic matrix, for example plastic, or a ceramic matrix.

The reinforcing elements may for their part comprise fibers and/or beads of glass and/or carbon and/or aramid. Thus, the shell may for example comprise a thermoplastic resin matrix and fiberglass reinforcing elements.

In one embodiment, the casing comprises a membrane interposed between the shell and an assembly comprising the exchangers and the porous structure.

Such a membrane, commonly called a "liner", makes it possible to reduce the number of parts of the cell and to simplify its assembly.

Such a membrane also makes it possible to give an external shape to the cell.

Such a membrane also makes it possible to give an internal shape improving the thermoacoustic performance of the cell.

Optionally, such a membrane can be implemented to ensure or improve the tightness to the working fluid and/or the thermal and/or acoustic insulation of the cell.

It is preferred that this membrane be made of thermoplastic.

In one embodiment, the cell comprises two thermal insulation members housed in the casing and arranged on either side of an assembly comprising the exchangers and the porous structure.

Such organs are commonly called "thermal buffer tube" in English.

In addition to the thermal insulation function, such members can also make it possible to provide a mechanical and/or impedance and/or dimensional matching function between the exchangers and a waveguide of the thermoacoustic machine.

In particular, the exchangers can have a different diameter, for example greater, than the diameter of such a waveguide.

In such a case, the isolation members can define a section restriction, for example in the form of a conical section.

In one embodiment, the cell comprises a centering and/or holding and/or thermal insulation ring around the exchangers and the porous structure. This ring is preferably made of thermoplastic or ceramic.

The invention also relates to a thermoacoustic machine comprising such a cell.

According to another aspect, the subject of the invention is a method of manufacturing a cell as defined above.

In one mode of implementation, this method comprises a step of manufacturing the shell by filament winding.

Such a step makes it possible to produce in a single operation a hull of complex shape without it being necessary to resort to additional fixing and sealing components.

The invention makes it possible to produce a shell in a single piece that perfectly matches the shape of the internal components of the cell.

The method may comprise, before the step of manufacturing the shell, a step of assembling said centering and/or holding and/or thermal insulation ring around the exchangers and the porous structure.

This ring can be manufactured by molding or by injection or even by machining.

It is preferred that said filament winding be made so that the shell encapsulates the ring, the exchangers and the porous structure.

When the cell comprises insulation members as defined above, the filament winding is preferably carried out so that the shell also encapsulates these insulation members.

In one mode of implementation, the ring can be glued to the exchangers and/or the porous structure and/or, where appropriate, to the insulation members.

When the cell comprises a membrane as defined above, the method may include, before the step of manufacturing the shell, a step of manufacturing the membrane so that it extends around the exchangers and the porous structure. When the cell comprises insulation members as defined above, the membrane is preferably manufactured so that it also extends around the insulation members.

Preferably, said filament winding is made so that the shell encapsulates the membrane, the exchangers and the porous structure.

When the cell comprises insulation members as defined above, the filament winding can be carried out so that the shell also encapsulates the insulation members.

The manufacture of the membrane may include a blowing step carried out so as to press the membrane against a mould.

This blowing step gives the membrane its shape.

Other advantages and characteristics of the invention will appear on reading the detailed, non-limiting description which follows.

Brief description of the drawings

The following detailed description refers to the attached drawings in which:

Figure 1 is a schematic view of a thermoacoustic machine comprising four thermoacoustic cells, two being implemented to generate an acoustic wave, the other two being implemented to pump heat using the acoustic wave thus generated;

Figure 2 is a schematic view of a thermoacoustic cell according to a first embodiment of the invention, this cell comprising thermoacoustic components including a porous structure, two heat exchangers and two thermal insulation members, a centering ring and for holding the thermoacoustic components, two flanges intended to connect the cell to a waveguide and an envelope comprising a shell made of composite material which encapsulates the thermoacoustic components and said ring; Figure 3 is a schematic view showing two grooves of said ring of the cell of Figure 2, these grooves being crossed by a respective circuit of the exchangers of this cell;

Figure 4 is a schematic view of the thermoacoustic components and of the ring of the cell of Figure 2 arranged on a mandrel with a view to producing the shell by filament winding;

Figure 5 is a schematic view of a thermoacoustic cell according to a second embodiment of the invention, this cell comprising thermoacoustic components including a porous structure and two heat exchangers, a ring for centering and maintaining the thermoacoustic components, two flanges intended to connect the cell to a waveguide and an envelope comprising a membrane and a shell made of composite material which encapsulate the thermoacoustic components and said ring;

Figure 6 is a schematic view illustrating the cell of Figure 5 during manufacture, this figure showing on the one hand the thermoacoustic components and the ring assembled with each other as well as the membrane in two parts before forming and, on the other hand on the other hand, a tool comprising a holding and blowing rod as well as two half-molds in a first position in which they are distant from each other;

Figure 7 is a schematic view of the elements of Figure 6 after placement of the half-molds in a second position in which they are close to each other and conformation of the membrane by blowing.

Detailed Description of Embodiments

The thermoacoustic machine shown in Figure 1 comprises four thermoacoustic cells 1 mounted in series along a waveguide 2.

In this example, the waveguide 2 is a tube defining a closed-loop internal space, so as to form an acoustic resonator. The internal space of the waveguide 2 contains a pressurized working fluid making it possible to propagate an acoustic wave.

The working fluid can be a monatomic gas - typically favoring the propagation of the acoustic wave -, a polyatomic gas such as a mixture comprising helium and argon or other gas mixtures - typically improving the heat transfer -, or a mixture of liquid and gas.

One or more of the thermoacoustic cells 1 of FIG. 1 may conform to the cells described below.

Figure 2 shows a thermoacoustic cell 1 according to a first embodiment of the invention.

Referring to Figure 2, cell 1 comprises two heat exchangers 3 and 4, a porous structure 5, two thermal insulation members 6 and 7, a ring 8, two flanges 11 and 12 as well as an envelope 14.

In this example, these different elements each form a part extending circumferentially around an axis Al and are stacked along this axis Al.

More precisely, the porous structure 5 is interposed between the exchangers 3 and 4 and the members 6 and 7 are arranged on either side of the assembly formed by the exchangers 3 and 4 and the porous structure 5. The flanges 11 and 12 each define a respective longitudinal end of the cell 1 being positioned on either side of the members 6 and 7, respectively.

The ring 8 extends radially outside these various elements so as to contribute to their holding in position, in particular during the manufacture of the casing 14 (see further below).

These various elements are housed within the casing 14 which ensures the mechanical strength of the assembly, in particular when the pressurized working fluid is received in the internal space formed by the cell 1.

In this example, the flanges 11 and 12 are configured to allow the assembly of the cell 1 to the waveguide 2 of a thermoacoustic machine as illustrated on the Figure 1, or more generally to a member for transmitting acoustic energy within a thermoacoustic machine, so that the porous structure 5 and the exchangers 3 and 4 are traversed by the working fluid.

The porous structure 5 is a structure provided with pores or cavities or openings making it possible to increase or maximize the surface of contact and therefore of exchange with the working fluid.

By way of example, the porous structure 5 can for this purpose comprise a stack of strips or grids, made of a material having a high heat capacity and a low thermal conductivity, for example a stainless steel or a ceramic material.

In this example, the porous structure 5 is a structure commonly referred to as a “regenerator”.

The heat exchangers 3 and 4 are arranged on either side of the porous structure 5 so as to be able to carry out, at the longitudinal ends of the porous structure 5, a heat exchange between the working fluid and a transport element of heat.

To this end, each of the exchangers 3 and 4 may comprise, in a manner known per se, conductive elements forming, for example, a stack of fins in contact with the working fluid. Such fins can be made of a conductive metal such as copper or aluminum or any other sufficiently heat-conductive material.

In this example, each of the exchangers 3 and 4 comprises a flow circuit 21, 22 respectively, in which a heat transfer fluid circulates in order to achieve a transfer of heat between this heat transfer fluid and said corresponding conductive elements.

Thus, in this example, the heat transfer fluid constitutes the aforementioned transport element. In this example, the exchangers 3 and 4 are connected by their flow circuit to external sources (not shown) configured so that the heat transfer fluid circulating in the flow circuit of the exchanger 3 has a different temperature from the fluid coolant circulating in the flow circuit of exchanger 4.

The ring 8 and the members 6 and 7 can in particular provide a sealing function to the working fluid.

In this example, exchangers 3 and 4 have a diameter greater than that of waveguide 2. The connection between these elements is possible here thanks to the conical section of members 6 and 7.

In operation, the cell 1 makes it possible to carry out a conversion of thermoacoustic energy according to principles well known in the field of thermoacoustics.

The cell 1 can in particular be implemented either to pump heat using the mechanical energy of an acoustic wave passing through the porous structure 5 and the heat exchangers 3 and 4, thus creating a temperature differential between the fluids heat carriers circulating in the exchangers 3 and 4, or on the contrary to generate an acoustic wave and propagate it in the working fluid by a supply of heat at the level of one of the exchangers which creates a temperature differential. Of course, the porous structure 5 is structured or dimensioned according to the mode of implementation of the cell 1.

In the simplified example of FIG. 1, two adjacent thermoacoustic cells 1 are implemented in motor mode in order to generate an acoustic wave in the waveguide 2 and the other two thermoacoustic cells 1 are implemented in pump mode. heat in order to achieve a heat transfer and a temperature rise between different external sources under the action of the acoustic wave generated by the other two cells 1.

Of course, the thermoacoustic cell 1 of the invention can be implemented within a different thermoacoustic machine. The invention relates more specifically to the structure of the casing 14 and to its manufacture.

According to the invention, the envelope 14 of the cell 1 comprises a shell 15 made of composite material preferably obtained by filament winding.

As part of a first type of manufacturing process, making it possible to manufacture the cell 1 of FIG. 2, a step of manufacturing the ring 8 is first carried out, for example by molding, by injection of thermoplastic, or else by machining a metallic or ceramic or thermoplastic material.

Passages 31 and 32 are machined on the ring 8 in order to be able to pass through them the flow circuits 21 and 22 of the exchangers 3 and 4, respectively (see FIG. 3). In a non-limiting way, these passages 31 and 32 can be grooves, notches or even holes or openings made in the ring 8.

The exchangers 3 and 4, the porous structure 5 and the ring 8 are then assembled, typically by placing the porous structure 5 in the center of the ring 8 then by inserting the exchangers 3 and 4 therein so as to make the flow circuits penetrate 21 and 22 in passages 31 and 32 of ring 8.

When the passages 31 and 32 are holes, the flow circuits 21 and 22 can pass through these holes 31/32 or can be screwed or held there by other means.

In this example, the exchangers 3 and 4, the porous structure 5 and the ring 8 thus assembled are glued or held by another means so as to form an assembly which is then placed on a mandrel 34 on which the organs 6 are then placed. and 7 as well as rings 35 and 36 as shown in Figure 4.

The members 6 and 7 and the rings 35 and 36 can also be glued or welded or held by any means to each other as well as to the aforementioned assembly.

The members 6 and 7 can be produced by stamping sheets of steel or aluminum or using another technique. The rings 35 and 36 are in this example rings, threaded externally or internally, which can be made of steel or of aluminum or of another material, for example a composite material. In another variant, the rings 35 and 36 are not threaded.

The casing 14 is then produced by filament winding, in this example by rotating the mandrel around the axis Al.

To produce the filament winding, a thermoplastic resin and glass fibers are used in this example.

To improve the adhesion of the resin and fibers, the parts can be subjected to a surface treatment beforehand. For example, the external surface of members 6 and 7 can be sandblasted.

Additional winding thicknesses can be made at the places where circuits 21 and 22 pass to locally increase the mechanical strength. The passages for circuits 21 and 22 can then be drilled.

Such a filament winding makes it possible to form the shell 15 of composite material so that the latter encapsulates the exchangers 3 and 4, the porous structure 5, the members 6 and 7 as well as the ring 8 (cf. FIG. 2).

In this example, the flanges 11 and 12 are then screwed onto the threaded rings 35 and 36, respectively, and the mandrel 34 is removed, which makes it possible to obtain a cell 1 conforming to that of FIG. 2. In particular when the rings 35 and 36 are not externally threaded, flanges 11 and 12 can be glued to rings 35 and 36.

Such a manufacturing process makes it possible to obtain, in a simple and rapid manner, a functional cell 1 which does not require finishing steps and which can therefore be directly assembled to a waveguide 2 or the like.

Compared to a conventional metal casing, such a shell 15 made of composite material also makes it possible to reduce the mass and the volume of the casing and to simplify its manufacture and its assembly. Figure 5 shows a thermoacoustic cell 1 according to a second embodiment of the invention, which differs from that of Figure 2 in that the casing 14 further comprises a membrane 41 and in that the cell 1 has no of said organs 6 and 7.

Cell 1 of FIG. 5 is described solely according to its differences with respect to that of FIG. 2. The preceding description applies by analogy to this second embodiment and to its variants.

Referring to Figure 5, the casing 14 comprises on the one hand said membrane 41, which provides in this example a sealing function, and on the other hand said shell 15 made of composite material.

The membrane 41 and the shell 15 respectively form a first layer and a second layer superimposed with respect to each other so that the membrane 41 is interposed between the shell 15 and an assembly comprising in this example the exchangers 3 and 4 , the porous structure 5 and the ring 8.

To obtain such a cell 1, a second type of manufacturing process according to the invention, described below, can be implemented.

This process firstly comprises a step of manufacturing the ring 8 and a step of assembling the exchangers 3 and 4, the porous structure 5 and the ring 8 which are similar to the corresponding steps described above.

The assembly formed by these elements thus assembled is positioned using a rod 51 between two half-molds 52A and 52B initially in a first position in which the half-molds 52A and 52B are spaced apart from each other. other (Figure 6).

With reference to FIG. 6, there are placed between this assembly and each of the half-molds 52A and 52B respectively two half-membranes 41A and 41B made of thermoplastic.

The half-molds 52A and 52B include notches 54 intended to receive one end of the flow circuits 21 and 22 of the exchangers 3 and 4, or more generally of the inputs and outputs of the components of the cell 1. The half-molds 52A and 52B are then brought closer to each other to reach a second position illustrated in FIG. 7, then an inflation fluid is introduced into the mold via the rod 51 so as to press the half-membranes 41A and 41B respectively against the half-molds 52A and 52B.

At the end of this step, the half-membranes 41A and 41B, which constitute said membrane 41, cover the inlets and outlets 21 and 22 of the exchangers 3 and 4 which are in this example released by machining the half-membranes 41A and 41B .

The half-membranes 41A and 41B can be fixed to each other, for example by welding or in another way.

In a variant not shown, the membrane 41 is made using not several parts 41A and 41B but a single hollow part comprising an opening provided for introducing the exchangers 3 and 4, the porous structure 5 and/or the ring 8.

The assembly thus obtained is then placed on a rotating mandrel to produce a filament winding similar to that described above, in order to form the shell 15 on the membrane 41.

In this example, the flanges 11 and 12 are then screwed onto the longitudinal ends of the membrane 41, which are provided with a thread formed during the blow molding thanks to helical grooves (not shown) machined in the half-molds 52A and 52B . As a variant, rings similar to rings 35 and 36 of the embodiment of FIG. 4 can be screwed or fixed by other means on said longitudinal ends of the membrane 41, before filament winding, and the flanges 11 and 12 can be screwed and /or glued to these rings after formation of the shell 15.

This second type of process makes it possible to reduce the number of parts of the cell 1, the cell of figure 5 being in this case devoid of the members 6 and 7 of the cell of figure 2.

In the second embodiment (Figure 5), the functions of sealing and section adaptation are provided by the membrane 41 and not by additional parts such as the members 6 and 7 of the cell of Figure 2. As part of a third embodiment, not shown, the cell 1 is similar to that of Figure 5 but has no ring 8.

To manufacture such a cell, a process similar to the process according to the second type which has just been described can be implemented, which is distinguished by the absence of manufacture of the ring 8 and of corresponding assembly.

In particular in such a case, the exchangers 3 and 4 and the porous structure 5 can be assembled by gluing and/or embedding, and this assembly can be arranged with the half-membranes 41A and 41B in the mold formed by the half-molds 52A and 52B by being subjected to the steps described above with reference to Figures 6 and 7.

This makes it possible to further reduce the number of parts of the cell 1 while consequently simplifying the manufacture and the cost of the cell.

Of course, the above description is not limiting and many variants can be envisaged without departing from the scope of the invention. For example, the envelope 14 of the cell 1 of FIG. 2 or of FIG. 5 can comprise an additional layer, for example of metal. Such a metal layer can make it possible to improve sealing and/or mechanical strength.

More generally, the envelope 14 can comprise a superposition of layers of different material, for example.

In an embodiment not shown, a cell can be manufactured which differs from cell 1 in FIG. 2 by the absence of ring 8. In this case, the holding in position of the internal elements of the cell, in the occurrence of the exchangers 3 and 4, of the porous structure 5 and if necessary of the members 6 and 7, can be ensured only by gluing and/or embedding these elements to each other and/or by the envelope 14. Concerning the tightness to the working fluid, this can be ensured radially around the porous structure 5 by the casing 14.

Claims

1. Thermoacoustic cell (1) for a thermoacoustic machine, the cell (1) defining an internal space intended to receive a working fluid, the cell (1) comprising two heat exchangers (3, 4), a porous structure (5) interposed between the exchangers (3, 4) and a casing (14), each of the exchangers (3, 4) being configured to carry out a heat exchange between the working fluid and a transport element, the porous structure (5) and the exchangers (3, 4) being intended to be traversed by the working fluid, the exchangers (3, 4) and the porous structure (5) being housed in the casing (14), characterized in that the casing ( 14) comprises a shell (15) made of composite material.

2. Cell (1) according to claim 1, wherein the shell (15) comprises a thermoplastic resin matrix and glass fiber reinforcing elements.

3. Cell (1) according to claim 1 or 2, wherein the casing (14) comprises a membrane (41) interposed between the shell (15) and an assembly comprising the exchangers (3, 4) and the porous structure ( 5).

4. Cell (1) according to any one of claims 1 to 3, comprising two thermal insulation members (6, 7) housed in the casing (14) and arranged on either side of an assembly comprising the exchangers (3, 4) and the porous structure (5).

5. Thermoacoustic machine comprising a cell (1) according to any one of claims 1 to 4.

6. A method of manufacturing a cell (1) according to any one of claims 1 to 4.

7. Method according to claim 6, comprising a step of manufacturing the shell (15) by filament winding.

8. Method according to claim 7, comprising, before the step of manufacturing the shell (15), a step of assembling a centering and/or holding and/or thermal insulation ring (8) around exchangers (3, 4) and the porous structure (5), said filament winding being made so that the shell (15) encapsulates the ring (8), the exchangers (3, 4) and the porous structure (5).

9. Method according to claim 7 or 8 for the manufacture of a cell (1) according to claim 3, comprising, before the step of manufacturing the shell (15), a step of manufacturing the membrane (41) of so that the latter extends around the exchangers (3, 4) and the porous structure (5), said filament winding being produced so that the shell (15) encapsulates the membrane (41), the exchangers (3, 4) and the porous structure (5).

10. Method according to claim 9, in which the manufacture of the membrane (41) comprises a blowing step carried out so as to press the membrane (41) against a mold (52A, 52B).