US20200124359A1

US20200124359A1 - Recuperator

Info

Publication number: US20200124359A1
Application number: US16/477,996
Authority: US
Inventors: Marinus Henricus Johannes VAN KASTEREN
Original assignee: Recair Holding BV; Recair BV
Current assignee: Recair BV
Priority date: 2017-01-16
Filing date: 2018-01-16
Publication date: 2020-04-23
Also published as: LT3568655T; EP3568655B1; EP3568655A1; CN110418934A; WO2018132014A1; DK3568655T3; NL2018175B1; FI3568655T3; JP2020514659A; ES2942434T3; PL3568655T3; CA3049951A1

Abstract

A recuperator including a number of neighbouring hexagonal sheets which are connected to each other. Flow passages are formed between neighbouring sheets. Each of the sheets, at its periphery, is at least partially surrounded by and connected to an associated connecting body. Neighbouring connecting bodies are connected to each other at at least a part of the periphery of the associated sheets and together form the wall of a housing. Passage openings are provided in the wall which are connected to the flow passages for allowing air into the flow passages via the passage openings. Neighbouring connecting bodies are provided with protruding parts and with recesses respectively on sides facing each other, wherein the forms of the protruding parts and of the recesses adjoin each other in order to connect the connecting bodies to each other by a press fit. Methods for producing a connecting body and for producing a recuperator.

Description

The invention relates to a recuperator comprising a number of neighbouring hexagonal sheets which extend parallel to each other and which are connected to each other at at least a part of their periphery and wherein flow passages are formed between neighbouring sheets.
Dutch publication NL 1030270 describes a method for producing a heat exchanger having hexagonal sheets which extend parallel to each other. In this case, sheets are stacked on top of each other and then neighbouring sheets are connected to each other at their periphery by means of chemical welding, wherein a solvent is used to partially dissolve the material of the sheets at their periphery. In practice, a housing is subsequently applied in order to the thus obtained stack of sheets welded to each other, which housing is connected to the stack by means of adhesive bonding. The housing ensures that the dimensions of the thus produced heat exchangers are relatively constant and that the heat exchangers are, for example, interchangeable as a result. Moreover, the housing provides mechanical protection to the stack and the possibility of attaching the heat exchanger to air supply and discharge lines which communicate with the flow passages between the sheets. Highly specialized assembly devices are needed to carry out the known method in an automated manner. It is an object of the invention to provide a recuperator according to the preamble, which recuperator can be made in a relatively simply automatable way. To this end, each of the sheets, at its periphery, is at least partially surrounded by and connected to an associated connecting body and neighbouring connecting bodies are connected to each other at at least a part of the periphery of the associated sheets and together the connecting bodies form the wall of a housing, wherein passage openings are provided in the wall which are connected to the flow passages for allowing air into the flow passages via the passage openings, wherein neighbouring connecting bodies are provided with protruding parts and with recesses respectively on sides facing each other, wherein the forms of the protruding parts and of the recesses adjoin each other in order to connect the connecting bodies to each other by a press fit. The use of a connecting body makes it superfluous to connect sheets to each other directly, for example by adhesive bonding or welding, such as in particular chemical welding or ultrasonic welding. Chemical welding and adhesive bonding have the significant drawback that they (may) require solvents which are dangerous and for this reason extra safety provisions are required. Neighbouring sheets of the recuperator according to the invention are connected to each other via the connecting bodies associated with the respective sheets during production of the recuperator. The connecting bodies which are connected to each other further function as a housing in the sense that they protect the sheets. The connecting bodies can further be formed in order to make attachment to supply and discharge lines possible in a simple manner. It is thus not necessary to use separate housings which are tailor made in advance. This also has the advantage that it is more likely to be cost-effective to produce recuperators in smaller numbers, for example specifically for a certain application or to customer specifications.
A correct positioning of the connecting bodies with respect to one another and thus of the sheets can readily be achieved by providing the neighbouring connecting bodies with protruding parts and with recesses respectively on sides facing each other, wherein the forms of the protruding parts and of the recesses adjoin each other in order to connect the connecting bodies to each other. The protruding parts and the recesses may also advantageously be used to produce an airtight or at least substantially airtight connection between the neighbouring connecting bodies. The connection between two neighbouring connecting bodies can be airtight with a high degree of reliability due to the press fit by means of which neighbouring connecting bodies are connected to each other. Such a connection by means of a press fit makes the application of welding or bonding neighbouring connecting bodies to each other superfluous, although it is also possible to combine the clamping connection with a welded or adhesive connection to increase the reliability of the connection. The additional welded or adhesive connection can then, for example, have an extra securing effect. The application, in the event of such a combination, of ultrasonic welding has the advantage that it is then not necessary to use any solvents in any case. For securing purposes, a band may also be arranged around the housing, which is optionally connected to each or at least a portion of the connecting bodies. The invention is particularly suitable for use in recuperators in which the sheets are made of plastic. In an embodiment, the passage openings are formed between neighbouring connecting bodies. In such a variant, the passage openings are formed by connecting the neighbouring connecting bodies to each other, which enables a relatively simple embodiment of the connecting bodies.
Alternatively, it is also possible for the passage openings to be formed in, instead of between, connecting bodies.
The assembly of the connecting bodies with associated sheets can be facilitated if the protruding parts and/or the recesses have a tapered form or at least partially a tapered form, as a result of which it is possible to realize a self-aligning positioning.
A practical embodiment, at least during assembly and optional disassembly, can be obtained if neighbouring connecting bodies are connected to each other by means of a click-fit connection.
In order to bring about an at least substantially airtight connection between neighbouring connecting bodies, it may be advantageous if the recuperator is provided with a sealing body between neighbouring connecting bodies at the location where they are connected to each other, wherein it may be further preferred, with a view in particular to achieving a simple assembly, for the sealing body to be connected to one of the two neighbouring connecting bodies.
The invention is suitable, inter alia, for recuperators of the membrane type. The sheets of such recuperators are suitable for exchanging moisture. The material of such sheets is not suited or is poorly suited to being welded. The use of adhesive for connecting membrane sheets to each other has the drawback that this is a step which is difficult to control and, partly as a result thereof, expensive, particularly if recuperators are produced in relatively large numbers, and that, depending on the type of adhesive that is used, it also involves the use of harmful solvents. Therefore, at least a portion of the sheets of a recuperator according to the invention may advantageously be permeable to moisture.
Advantageously, the recuperator may be configured to have sheets which are all provided with a profile. In this case, the connecting bodies can contribute to a correct positioning of the sheets, more specifically the profiles thereof, with respect to each other, since the sheets can behave in a relatively stiff way owing to the connection with the connecting bodies.
Alternatively, the invention is also suitable for a more traditional way in which sheets can be provided in a recuperator, namely wherein the neighbouring sheets are flat and are provided with a profile in an alternating fashion.
Especially as the invention makes it superfluous to directly connect neighbouring sheets to each other, the recuperator according to the invention may also advantageously be used if sheets are made of different materials, for example if neighbouring sheets are made of different materials in an alternating fashion.
An advantageous application of the invention may be in recuperators wherein a portion of the number of sheets is made of a moisture-permeable material and the other portion of the number of sheets is made of a material which is not permeable to moisture. In traditional recuperators, such materials are difficult to combine.
In order to produce a good connection between a connecting body and an associated sheet, it may be preferred, in the event that sheets made of different materials are used, for the connecting bodies to be made of different materials. In this case, a fixed combination is formed of the material of the connecting body and the material of the associated sheet.
In terms of construction, it may be advantageous if each of the sheets is at least substantially, including also completely, surrounded by an associated connecting body.
It may be preferred for the connecting bodies to be injection moulded, particularly in the case of relatively large production numbers.
According to a possible embodiment, the periphery of the housing is bar-shaped. The bar shape of the housing facilitates the attachment of other parts, such as in particular air ducts, to the recuperator. The invention provides the possibility of providing the housing with a bar-shaped periphery in a simple manner, namely by adapting the design of the connecting bodies hereto. Bar-shaped is understood to mean all forms in which six main surfaces are connected to each other at right angles. The definition of bar-shaped therefore also includes the form of a cube.
By positioning the peripheral edge of the sheet associated with the connecting body at least partially in the mould during the injection moulding, the connection between the sheet and the connecting body can be produced directly during the injection moulding. In the latter context, it may be advantageous if the sheets are over-moulded with the material of the connecting bodies along the first part of the periphery of the connecting bodies during the injection moulding of the connecting bodies at the periphery of the sheets. The invention therefore also relates to a method for producing a connecting body for use in a recuperator according to the invention, the method comprising the following steps

- closing a mould, wherein a mould cavity is formed and a sheet is positioned in the mould cavity at at least a part of the periphery of the sheet,
- injection moulding the connecting body in the mould, wherein the sheet is over-moulded with the material of the connecting body in the mould cavity at the location of at least a part of the peripheral edge of the sheet.

After or even during the solidification of the material that is injection moulded in order to form the connecting body, it is also possible to injection mould another material against the connecting body in order to form a sealing body. This is possible by temporarily enlarging the mould cavity locally after allowing the liquid injection moulding material into the mould cavity and before the mould is opened to remove the connecting body from the mould and injection moulding the other material in said enlarged part of the mould cavity.
The invention further provides a method for producing a recuperator according to the invention, the method comprising the following steps

- providing encircling connecting bodies, each having a sheet that is connected to the associated connecting body and extends on the inside of the encircling connecting body,
- connecting connecting bodies to each other by a press fit in such a way that flow passages are formed between neighbouring sheets associated with neighbouring connecting bodies.

The invention will be explained in more detail below on the basis of the description of a possible embodiment of a recuperator according to the invention with reference to the following figures which are not to scale:

FIG. 1 shows a partially exploded perspective view of a recuperator according to the invention;

FIGS. 2a and 2b show a perspective top view and a perspective bottom view of a layer of the recuperator according to FIG. 1;

FIGS. 3a to 3f diagrammatically show a vertical cross section of part of the layer as illustrated in FIGS. 2a and 2b during successive steps of the production process thereof;

FIGS. 4a to 4e show optional subsequent steps after the step according to FIG. 3 d;

FIG. 5 shows a perspective view of an alternative embodiment of a recuperator according to the invention;

FIGS. 6a and 6b show a perspective top view of two layers of the recuperator according to FIG. 5;

FIG. 7 shows a partially exploded perspective view of the recuperator according to FIG. 5 including attachment parts as may be used in practice.

FIG. 1 shows a recuperator according to the invention which is configured as a heat exchanger 1. Twelve layers 2 of heat exchanger 1 are shown. Each of the layers 2 comprises an encircling hexagonal connecting body 3. The free passage on the inside of the encircling form of each connecting body 3 is sealed by a sheet 4, as illustrated in FIGS. 2a and 2b . The connecting bodies 3 are alternately provided in two different geometries 3 a, 3 b. Connecting body 3 b corresponds to a version of connecting body 3 a which is mirrored in vertical plane of symmetry 8. The connecting bodies 3 a, 3 b are alternately connected to each other in a manner which will be explained in more detail below. The connecting bodies 3 a, 3 b that are connected to each other together form the wall of a housing with six upright wall parts at the respective hexagonal sides 10 a to 10 f of heat exchanger 1. Where terms such as “upright” or “vertical” are used above, this refers to the situation in the position of use of the relevant heat exchanger.
In this example, the sheets 4 associated with the different connecting bodies 3, that is with the different layers 2, are made of the same material, namely of polystyrene (PS) that is not permeable to moisture. Alternatively, it is also possible, however, for all of the sheets 4 to be made of another material, typically of a plastic such as, for example, high-density polyethylene (HDPE), but also, for example, of a metal such as aluminium. The material used for the sheets 4 may further be permeable to moisture. It is also possible for the sheets 4 within a heat exchanger, in that case preferably in an alternating fashion, to be made from different materials, for example selected from the materials as mentioned above. The geometries of the sheets 4 differ from one another in an alternating fashion between profiled sheets 4 a and flat sheets 4 b. Insofar as the distinction is not important, this document uses reference numeral 4 for sheets 4 a and 4 b, thus irrespective of whether these are flat sheets or profiled sheets. Insofar as the distinction is important, reference numerals 2 a and 2 b are used for layers with a profiled sheet 4 a and a flat sheet 4 b respectively. In FIGS. 1 to 2 b, the profiling of sheets 4 a is not illustrated for the sake of clarity. Incidentally, it is also conceivable within the context of the invention for all of the sheets 4 to be profiled or for all of the sheets 4 to be flat. The thickness of the sheets 4 may typically vary between 0.05 mm and 2 mm. The width of the passage ducts may correspond to the period of a profile or half of it but also to a number of periods of a profile and even to the dimensions of the sheet seen at right angles to the flow direction.
Although twelve layers 2 are shown in FIG. 1, in reality the number of layers 2 of a heat exchanger 1 may be higher, for example 100 layers, but the number of layers 2 may also be lower, for example 8 layers. The heat exchanger has a sealing cover body 41 on the top side of the stack of layers 2 and a sealing base body 42 on the underside of the stack of layers 2. For the sake of clarity, the height of the layers 2 in the figures is shown to be higher than it actually is. It is mentioned by way of indication that the distance between two diametrically opposed points of the hexagonal form, which points are incidentally truncated, of the connecting bodies 3 is in reality typically between 5 cm and 100 cm, while the height of the layers 2 is typically between 2 mm and 20 mm.
Flow passages for air are formed between neighbouring sheets 4. During operation of the heat exchanger 1, energy is exchanged between air that flows in opposite directions through adjoining flow passages. To allow air into flow passages, inflow openings 11 a are formed between two neighbouring connecting bodies 3 a, 3 b, more specifically at the location of hexagonal side 10 a of heat exchanger 1. Outflow openings 12 a (not visible in FIG. 1 owing to the perspective) are formed on the opposite side at the location of hexagonal side 10 d. Each of the inflow openings 11 a is connected to an associated outflow opening 12 a via the flow passages between two neighbouring sheets 4. To allow air flowing in the opposite direction into flow passages, inflow openings 11 b (not visible in FIG. 1 owing to the perspective) are formed between two neighbouring connecting bodies 3 b, 3 a, more specifically at the location of hexagonal side 10 e. Outflow openings 12 b are formed on the hexagonal side 10 b between neighbouring connecting bodies 3 b, 3 a. Each of the inflow openings 11 b is connected to an associated outflow opening 12 b via flow passages between two neighbouring sheets 4. The flow passages are formed in the rectangular area between the two opposite hexagonal sides 10 c and 10 f. The triangular areas between said rectangular area and the hexagonal sides 10 a, 10 b, on one side, or the hexagonal sides 10 d, 10 e, on the other side, are collection areas in which either the air which flows into the heat exchanger 1 via an inflow opening 11 a, 11 b is distributed across the flow passages between two sheets 4 before the air flows into these flow passages, or the air which flows out of the flow passages between two sheets 4 is fed to an outflow opening 12 a, 12 b.
The layers 2 are connected to each other via the connecting bodies 3 by means of a clamping connection. To this end, the connecting bodies 3 are each provided with a hexagonal part 14 with an encircling rib 15 on its upper side and in which hexagonal part 14 an encircling groove 16 is provided on the underside. For connecting bodies 3 a, the encircling rib 15 is interrupted at the location of the hexagonal sides 10 a and 10 d in order to form an inflow opening 11 a and an outflow opening 12 a, respectively. For connecting bodies 3 b, the encircling rib 15 is interrupted at the location of the hexagonal sides 10 b and 10 e in order to form an outflow opening 12 b and an inflow opening 11 b, respectively. Furthermore, at the location of hexagonal sides 10 b and 10 e the hexagonal part 14 of connecting bodies 3 a is provided on the underside with recesses 18 b, 18 a, respectively, as a result of which the groove 16 is interrupted in these areas and in order to form inflow opening 11 b and outflow opening 12 b. In a similar way, at the location of hexagonal sides 10 a and 10 d, the hexagonal part 14 of connecting bodies 3 b is provided on the underside with recesses 19 a, 19 b (not illustrated), as a result of which groove 16 is interrupted in these areas and in order to form inflow opening 11 a and outflow opening 12 a.
The encircling form and the cross sections of the ribs 15 and the grooves 16 are dimensioned with respect to each other in such a way that they can engage with each other by a press fit in a clamping, airtight or at least substantially airtight manner. The ribs 15 are provided with aligning edges 17 a, 17 b in order to facilitate engaging with each other during assembly. In order to produce the press-fit connection between neighbouring connecting bodies 3, the connecting bodies 3 are pressed onto each other, wherein the flanks of the ribs 15 of one connecting body 3 slide along the flanks of the grooves 16 with friction. This results in the situation wherein the ribs 15 and the grooves 16 fit into each other without play and the respective flanks of the ribs 15 and the grooves 16 adjoin one another in a clamping manner, which clamping force provides the connection between the connecting bodies 3. Alternatively or in combination, the ribs 15 and the grooves 16 may also have a slightly tapered form, without departing from the principle of a press fit as explained above. Alternatively, it is then further possible to use a soft seal between the ribs 15 and grooves 16, which could optionally be connected to the ribs 15 or the grooves 16 as will be explained below with reference to FIGS. 4a to 4e . It is also possible to make the connection airtight by, in addition to the press-fit connection, welding neighbouring connecting bodies 3, for example chemically or by ultrasound, or bonding them.
The above-mentioned cover body 41 of heat exchanger 1 has a hexagonal plate-shaped part 43, the periphery of which is the same as that of hexagonal part 14. The plate-shaped part is provided on the underside with an encircling (interrupted) groove similar to groove 16 for adjoining to the rib 15 of the top layer 2. The above-mentioned base body 42 of heat exchanger 1 has a hexagonal plate-shaped part 45, the periphery of which is also similar to that of hexagonal part 14. On the top side of the plate-shaped part 45, the base body 42 is provided with an encircling (interrupted) rib 46 similar to rib 15 for adjoining to groove 16 of the bottom layer 2. Incidentally, the cover body and the base body could alternatively also have a differently shaped periphery, for example for the purpose of attachments to air supply and air discharge facilities.
In the form used, two air supply ducts (not shown in more detail) are attached to hexagonal sides 10 a and 10 e of heat exchanger 1 in an airtight manner, via which two air flows are supplied to the flow passages on one side which adjoin the inflow openings 11 a and 11 b. Furthermore, two air discharge ducts (not shown in more detail) are attached to the hexagonal sides 10 b and 10 d of heat exchanger in an airtight manner so that the outflow openings 12 b, 12 a open into such an air discharge duct and the air flows leave the heat exchanger 1 again after they have passed through the flow passages. The various attachments and connections between the connecting bodies 3 with respect to each other and between the connecting bodies 3 on the one hand and the sheets 4 on the other hand are such that at least 97% of the air which flows into the heat exchanger 1 via inflow openings 11 a, 11 b flows out of the heat exchanger 1 again via outflow openings 12 a, 12 b. During operation, energy will be exchanged between, on the one hand, the air which flows through the flow passages that adjoin inflow openings 11 a and, on the other hand, the air which flows through the flow passages that adjoin inflow openings 11 b.
For the sake of completeness, it should be noted that the hexagonal sides of the recuperator could also differ from each other in terms of their length. More specifically, for example, the hexagonal sides 10 c and 10 f may be longer than the remaining hexagonal sides 10 a, 10 b, 10 d and 10 e. In that case, the hexagonal form of the recuperator is thus not rotationally symmetrical, as is illustrated in the figures. Although the inflow openings and outflow openings are now surrounded by two neighbouring connecting bodies 3, it is also possible to provide the inflow openings and/or the outflow openings in a single connecting body. Each of the inflow openings and/or the outflow openings are then fully surrounded by material of an associated connecting body. It is furthermore possible that the connecting bodies are not fully encircling or in fact consist of two or even more parts which are each provided on just a part of the periphery of a sheet, wherein use is possibly made of separate seals to prevent leakage of air.
FIGS. 3a to 3d show successive steps during the production of a layer 2 a with a profiled sheet 4 a. The profiling of sheet 4 a is such that the profiling does not extend up to the outer periphery of sheet 4 a. There is thus a flat area 21 there. The flat area 21 is accommodated in a clamping manner between two mould parts 22, 23. Mould parts 22, 23 define between them a mould cavity 24, the form of which corresponds to that of the connecting part 3 a. The flat area 21 of sheet 4 a extends into the mould cavity 24. Liquid thermoplastic, such as polystyrene or polyethylene, is supplied to the mould cavity 24 via injection-moulding channels 25, which each open into the mould cavity 24 and a number of which are distributed over the periphery of the mould cavity 24, by means of injection moulding so that it completely fills said mould cavity 24 (FIGS. 3c and 3d ). Subsequently, the liquid plastic solidifies, during which solidification the plastic adheres to (the flat area 21 of) sheet 4 a insofar as sheet 4 a extends into the mould cavity 24. The selection of the material of the connecting parts 3 may be adapted to that of sheet 4 in order to promote sufficient adhesion. For an even stronger connection between a sheet 4 and the solidified plastic material, it is also conceivable to arrange holes in sheet 4 so that the plastic material can extend through these holes and can also ensure mechanical anchoring. After solidification, the mould parts 22, 23 are opened by moving them apart from each other. The thus created product is a layer 2 a (FIG. 3e ).
It will be clear to those skilled in the art that a layer 2 b with a completely flat sheet 4 b can also be produced in a similar way. The layers 2 a and 2 b can be alternately clamped on top of one another (FIG. 3f ), with the peaks 9 of the profiling of sheet 4 a adjoining an adjacent flat sheet 4 b, as a result of which flow passages are formed between neighbouring sheets 4 a and 4 b. Clamping layers 2 a and 2 b on top of one another may be done manually but optionally also in an automated manner, for which purpose a relatively simple assembly machine may be sufficient. This machine may be suitable for heat exchangers of different dimensions, with no or only limited re-setting being required.
FIGS. 4a to 4c show successive steps of an alternative method for producing a layer 2, wherein, after solidification of the plastic material as explained with reference to FIGS. 3a to 3e , an extra mould cavity 26 is formed at the underside of the connecting body 3 by moving injection duct body 27, which extends over the entire length of groove 16, downwards with respect to the bottom mould body 23′. Subsequently, liquid plastic material is supplied to the extra mould cavity 26 via injection duct 28 in injection duct body 27. The material of this plastic differs from the plastic material in mould cavity 24 in the sense that it behaves resiliently in solidified form, like a rubber. After solidification of the plastic material in the extra mould cavity 26, it is adhered to the plastic material in mould cavity 24 and forms a seal 29. The product thus produced is denoted as layer 2 a′. It is of course also possible to provide layer 2 b with a seal in a similar way as seal 29. This layer is denoted by reference numeral 2 b′. The seal 29 serves to promote an airtight attachment of neighbouring layers 2 a′, 2 b′ (FIG. 4e ).
FIGS. 5 to 7 relate to a heat exchanger 51 which can be considered as a variant to heat exchanger 1. The wall parts 61 c and 61 f on the opposite hexagonal sides 60 c and 60 f of heat exchanger 51 are (viewed from above) extended at both ends with respect to the corresponding wall parts of heat exchanger 1. As a result, heat exchanger 51, or at least the outside thereof, has the form of a bar with a rectangular, more specifically square, top view. The sheets in the heat exchanger 51 are hexagonal, analogously to sheets 4 in heat exchanger 1. The ends 64 a, 64 b of the parts of the connecting bodies 62 a, 62 b of layers 52 a, 52 b which form the wall parts 61 c and 61 f, which wall parts 64 a, 64 b in FIG. 5 are situated at the front of heat exchanger 51, are aligned with each other and are situated with the truncated points 64 c between the parts of the connecting bodies 62 a, 62 b of layers 52 a, 52 b which are situated on the hexagonal sides 60 a and 60 b. These ends 64 a, 64 b, points 64 c together with cover body 71 and base body 72 thus form a contact surface which has the form of a lying, block-shaped figure eight.
FIG. 7 shows how funnel-shaped flow bodies 81, 82 adjoin the two opposite contact surfaces of heat exchanger 51 in a clamping manner. Gaskets 83, 84 are provided between the flow bodies 81, 82 and the two associated contact surfaces. At the location of the two openings in the figure eight shape of the contact surfaces, both the gaskets 83, 84 and the flow bodies 81, 82 are also provided with identical openings. In order to separate the air flows, the flow bodies 81, 82 comprise a partition 85 between the openings. The flow bodies 81, 82 clamp heat exchanger 51 between them with the aid of draw bars 86 which, for example, may be threaded and which extend through holes in the flow bodies 81, 82.

Claims

1. A recuperator comprising a number of neighbouring hexagonal sheets which extend parallel to each other and which are connected to each other at at least a part of their periphery and wherein flow passages are formed between neighbouring sheets, wherein each of the sheets, at its periphery, is at least partially surrounded by and is connected to an associated connecting body and neighbouring connecting bodies are connected to each other at at least a part of the periphery of the associated sheets and together form the wall of a housing, wherein passage openings are provided in the wall which are connected to the flow passages for allowing air into the flow passages via the passage openings, wherein neighbouring connecting bodies are provided with protruding parts and with recesses respectively on sides facing each other, wherein the forms of the protruding parts and of the recesses adjoin each other in order to connect the connecting bodies to each other by a press fit.

2. The recuperator according to claim 1, wherein the sheets are made of plastic.

3. The recuperator according to claim 1, wherein the passage openings are formed between neighbouring connecting bodies.

4. The recuperator according to claim 1, wherein the passage openings are formed in connecting bodies.

5. The recuperator according to claim 1, wherein the passage openings are situated on opposite sides of the hexagonal form.

6. The recuperator according to claim 1, wherein the protruding parts and/or the recesses have a tapered form or at least partially a tapered form.

7. The recuperator according to claim 1, wherein the recuperator is provided with a sealing body between neighbouring connecting bodies at the location where they are connected to each other.

8. The recuperator according to claim 7, wherein the sealing body is connected to one of the two neighbouring connecting bodies.

9. The recuperator according to claim 1, wherein at least a portion of the sheets is permeable to moisture.

10. The recuperator according to claim 1, wherein all of the sheets are provided with a profile.

11. The recuperator according to claim 1, wherein the neighbouring sheets are flat and are provided with a profile in an alternating fashion.

12. The recuperator according to claim 1, wherein the sheets are made of different materials in an alternating fashion.

13. The recuperator according to claim 12, wherein a portion of the number of sheets is made of a moisture-permeable material and the other portion of the number of sheets is made of a material which is not permeable to moisture.

14. The recuperator according to claim 13, wherein the connecting bodies are made of different materials in an alternating fashion.

15. The recuperator according to claim 1, wherein the periphery of the housing is bar-shaped.

16. The recuperator according to claim 1, wherein each of the sheets is at least substantially surrounded by an associated connecting body.

17. The recuperator according to claim 16, wherein each of the sheets is completely surrounded by an associated connecting body.

18. The recuperator according to claim 1, wherein the connecting bodies are injection-moulded.

19. The recuperator according to claim 18, wherein the sheets are over-moulded with the material of the connecting bodies along the first part of the periphery of the connecting bodies during the injection moulding of the connecting bodies at the periphery of the sheets.

20. A method for producing a connecting body for use in a recuperator according to claim 1, comprising the steps of:

closing a mould wherein a closed mould cavity is formed and a sheet is positioned in the mould cavity at at least a part of the periphery of the sheet, and

injection moulding the connecting body in the mould, wherein the sheet is over-moulded with the material of the connecting body in the mould cavity at the location of at least a part of the peripheral edge of the sheet.

21. The method according to claim 20, further comprising the steps of injection moulding a sealing body against the connecting body.

22. The method for producing a recuperator according to claim 1, comprising the steps of:

providing encircling connecting bodies, each having a sheet that is connected to the associated connecting body and extends on the inside of the encircling connecting body, and

connecting neighbouring connecting bodies to each other by a press fit in such a way that flow passages are formed between neighbouring sheets associated with neighbouring connecting bodies.