EP2861922A1

EP2861922A1 - Refrigeration appliance

Info

Publication number: EP2861922A1
Application number: EP13730830.0A
Authority: EP
Inventors: Astrid Klingshirn; Immanuel RING; Markus Spielmannleitner
Original assignee: BSH Hausgeraete GmbH
Current assignee: BSH Hausgeraete GmbH
Priority date: 2012-06-13
Filing date: 2013-06-07
Publication date: 2015-04-22
Anticipated expiration: 2033-06-07
Also published as: US20150184918A1; US9546808B2; EP2861922B1; WO2013186128A1; CN104350343A; CN104350343B; DE102012209938A1

Abstract

In a refrigeration appliance, particularly a household refrigeration appliance, having a storage space (4) for cooled material, at least one passage (13) for the flow of air into and out of the storage space (4) is formed in a wall delimiting the storage space (4). A fan (17) drives an air flow. A moveable closure element (14; 49) between the fan (17) and the storage space (4) is arranged at the passage (13), which closure element in the open position allows a flow of air driven by said fan (17) to circulate in the storage space (4) and in the closed position guides the flow of air driven by the fan (17) through a duct (44) running along one outer side of a wall of the storage space (4).

Description

The refrigerator

The present invention relates to a refrigeration appliance, in particular a household refrigeration appliance, which is particularly suitable for the storage of desiccated refrigerated goods. The shelf life of non-sterile and airtight packaged foods in a refrigerator is limited by microbial spoilage, chemical and enzymatic spoilage processes, and drying out. Fresh foods such as fruits, vegetables, salads or fresh herbs - in addition to the moisture released by the natural respiration - release moisture into their environment until equilibrium is established between them and the surrounding air. The resulting dehydration of these foods is usually irreversible and causes these foods are judged to be no longer verzehrtauglich long before the consumption would be due to a possible colonization by microorganisms of health concern. To be able to store fresh food in a refrigerator for a long time while maintaining its quality, it is therefore desirable to minimize evaporation. On the other hand, a storage at too high humidity must be avoided, as this in turn would greatly promote the growth of microorganisms.

From DE 101 61 306 A1 a refrigeration device according to the preamble of claim 1 is known. In this no-frost refrigerator, a user has the ability to operate a fan that circulates air between a storage room and an evaporator chamber and a compressor that supplies the evaporator with liquid refrigerant at different times. If he observes condensate in the storage room, he can prevent the return of moisture from the evaporator to the storage room by keeping the evaporator at a low temperature even when the ventilator is at a standstill. Conversely, if he finds too much dehydration of refrigerated goods in the storage room, he can also run the fan, while the evaporator does not cool, so as to evaporate deposited moisture on the evaporator and back into the storage room. The effectiveness of this approach is limited by the fact that in practice the rate at which moisture is released in the storage room varies with the type and amount of refrigerated goods housed therein and it is therefore hardly possible for a user to find a setting that is durable good storage climate guaranteed. Rather, there is the problem that a desired high humidity increases the risk that condensate is reflected in a particularly cool place of the storage room. In addition, the constant change between the compressor on and off phases and the fan leads to fluctuations in the humidity in the storage room, with minima of humidity always occurring at the end of a common compressor and fan operating phase. The moisture that was previously in the air in the storage room is firmly bound to the evaporator until it heats up, generally only at the end of a standstill phase. Therefore, the moisture required to restore the balance between the air of the storage room and the food stored therein is primarily released from the food, resulting in premature spoilage.

The object of the invention is to provide a refrigeration device that can provide improved storage conditions for fresh, moisture-emitting refrigerated goods. The object is achieved by having at least one passage for the supply and / or outflow of air to or from the storage space in a refrigerator, in particular a household refrigeration appliance, with a storage room for perishable refrigerated goods, and in a wall bounding the storage room, and a fan for driving an air flow at the passage a movable closure element between the fan and the storage space is arranged, which circulates in the open position a fan-driven air flow in the storage room and in the closed position the fan-driven air flow over a along an outer side of a wall the storage room running channel leads. The closure element makes it possible to temper the storage chamber either by air exchange or by heat exchange with the circulating in the channel air, in the former case, moisture between the storage chamber and the environment can be replaced, while in the latter case, the exchange of moisture prevented is.

So that the air circulation in the storeroom driven by the ventilator does not in turn promote the desiccation of the refrigerated goods, the speed of the air flow in the storeroom should never exceed 2 m / s with the closing element open. This can be achieved by a suitable arrangement and dimensioning of the fan; it may still be more appropriate if the passage on the air flow inside the storage room on throttles to a maximum of 2m / s, while with the passage closed in the duct, higher flow velocities may occur.

A control unit should be arranged to control the closure element on the basis of the prevailing humidity in the storage room to allow by opening the closure element, the delivery of moist air from the storage room, if this is necessary to prevent condensation in the storage room.

Conveniently, the control unit should therefore be set up to open the passage when the humidity exceeds a limit at at least one measuring point in the storage room.

The fan may conveniently also be controlled based on the humidity in the storage room or on the basis of the prevailing temperature there. In particular, the control unit can be set up to put the fan into operation if the difference between the humidity and / or the temperature between two measuring points in the storage space exceeds a limit value. The mixing of the air in the storage space resulting from fan operation when the closure element is open leads to a reduction in the difference, regardless of whether or not the circulating air outside the storage space is simultaneously cooled and / or dehumidified.

The path of the fan-driven airflow may pass through an evaporator to cool and / or dehumidify the circulating air at the evaporator if it is cooled during operation of the fan. Alternatively, a second fan may be provided to drive a second airflow in a path leading through an evaporator. By crossing the paths of the two air streams, cooled air at the evaporator can also enter the first air stream and cool the storage space.

According to a preferred embodiment, the storage space is a container which is arranged in a storage compartment of the refrigeration appliance. In order to handle refrigerated goods in the container convenient, it is advantageous if the container comprises at least a lower and an upper container part and the lower container part without the upper movable, in particular from the storage compartment removed.

Components which must be connected to their power supply or signal lines, such as the shutter, the fan or a sensor are preferably provided on the upper tank part. So they do not hinder the movement of the lower container part. The fan may also be located on a wall of the storage compartment surrounding the container. When an evaporator that cools the storage compartment is provided with a defrost heater, the control unit may be configured to keep the passage of the container closed while the defrost heater is in operation, and thus the entry of relatively warm, humid air into the interior of the container during defrosting. In order to minimize temperature fluctuations and associated variations in the relative humidity in the storage space, the wall of the storage space may be provided on at least part of its surface with an insulating heat storage medium. In order to store a large amount of heat in a small amount of the heat storage medium, the heat storage medium is suitably chosen so that a phase transition temperature of the heat storage medium coincides with the operating temperature of the cold reservoir. Preferably, the heat storage medium is disposed on that part of the wall of the storage room, which also limits the channel. Another measure that can minimize temperature gradients and fluctuations in the storage space is that the wall of the storage space comprises at least a portion of its surface an outer wall, an inner wall and an insulating gap therebetween. Further features and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying figures. From this description and the figures also show features of the embodiments, which are not mentioned in the claims. Such features can also be found in other than the combinations specifically disclosed herein. Therefore, the fact that several such features are mentioned in the same sentence or in a different type of textual context does not justify the conclusion that they can occur only in the specific combination disclosed; instead, it is generally to be assumed that it is also possible to omit or modify individual ones of several such features, provided this does not call into question the functionality of the invention. FIG. 1 shows a schematic section through a domestic refrigerator according to a first embodiment of the invention; FIG. a section through a household refrigerator according to a second embodiment with the door open and partially withdrawn lower container part; a section according to a third embodiment of the invention; a section according to a fourth embodiment of the invention; a section according to a fifth embodiment; a section according to a sixth embodiment; and a section according to a seventh embodiment of the invention. Fig. 1 shows a schematic section through a household refrigerator with a body 1 and a door 2, which surround a refrigerated storage compartment 3, in particular a zero-degree or fresh cooling compartment. Other, possibly with a door other than the door 2 shown locked storage compartments such as a normal refrigerator and a freezer compartment may be present.

A container 4 accommodated in the storage compartment 3, for example injection-molded plastic, comprises a lower container part 5 and an upper container part 6. The lower container part 5 is placed on the floor of the storage compartment 3 so as to be displaceable in the depth direction. To like in The Figure shown a channel 45 to keep open below a bottom 40 of the container part 5, 3 ribs oriented in the depth direction of the storage compartment from the bottom of the storage compartment 3 upwards or from the bottom 40 of the container part 5 downwardly projecting.

The lower container part 5 comprises a front wall 7 facing the door 2 on which a handle 8 is formed for ease of handling, a rear wall 9 which is less high than the front wall 7, and side walls 10 whose upper edges are from the front 7 fall continuously towards the rear wall 9. Along the upper edge of the walls 7, 9, 10 an obliquely sloping rearward sealing flange 1 1 is formed. On the sealing flange 1 1 is a complementary sealing flange 12 of the upper container part 6. The contact between the flanges 11, 12 does not have to be hermetically sealed, but a possible gap between them should be so narrow that the air circulation through such a gap is small compared to the passage 13 formed in the upper container part 6, if this is not closed by a closure element arranged thereon, here a plate 14 which is pivotable about an axis 42 oriented transversely to the sectional plane of the figure. Fig. 1 shows the plate 14 in its open position; in its closed position, it lies on the passage 13 of the upper container part 6.

The upper container part 6 is suspended on a ceiling 15 of the storage compartment 3 with vertical play, for example with the aid of engaging in slots hook 16, to allow close contact of the sealing flanges 1 1, 12, even if the container parts 5, 6 not are placed exactly above and below each other. There are a total of four hooks 16 provided at four corners of the substantially rectangular in plan view upper container part 6, two of which, a front and a rear, are shown in Fig. 1 in section. Between the two rear hooks 16, a gap is kept free, through which an air flow driven by a ventilator 17 can pass. In the open position of the plate 14, this directs the air flow of the fan 17 into the container 4. Through a second passage 43, which is provided here in the upper container 6 adjacent to its front edge, the air flow exits on the container 4 again. When in the closed position, the plate 14 rests flat on the upper container part 6, sweeps the air flow through a channel 44 which is bounded by the ceiling 15 of the storage compartment 3 and a cover 39 of the upper container part 6, flows between the front wall 7 and the Door 2 down and through the channel 45 back to a rear wall 29 of the body 1 and the fan 17 arranged there. At the upper container part 6 an attacking on the plate 14 actuator 18, a humidity sensor 19 and possibly also a temperature sensor 20 are mounted. A line bundle 21 connects the actuator 18 and the sensors 19, 20 with an electronic control unit of the refrigerator, not shown here, based on measurement data of the sensors 19, 20, the fan 17, the actuator 18 and, in a usual way, a compressor not shown here the refrigeration device and, if it is a Nofrost refrigeration device to control a second fan for circulating air between an evaporator 28 and the storage compartment 3. The control of the fan 17 and the actuator 18 by the control unit can be done in different ways. In the simplest case, the fan 17 is continuously in operation to keep in motion when the plate 14 is in the closed position, a circulating in the channels 44, 45 around the container 4 in air flow. When the air flow exchanges heat with the interior of the container 4 through its walls, it reduces any temperature and humidity gradients within the container 4, so that the air humidity value detected by the humidity sensor 19 locally at its installation location for the entire volume of the Container 4 is representative. If this value exceeds an upper limit of, for example, 85% + ε rH, where ε is a small positive value, for example 0.5%, then the control unit activates the actuator 18 in order to open the passage 13. Thus, the air flow in the container 4 is deflected in, and moist air in the container 4 is replaced by drier, flowing from the outside air. Thus, the humidity in the container 4 is lowered far enough to prevent the precipitation of condensation inside the container 4. When the measured value of the sensor 19 has decreased to 85% - ε, the actuator 18 is driven again to close the passage 13. Consequently, the humidity in the container 4 varies in a very narrow range of 2 ε, and the amount of moisture released from the refrigerated goods 23 stored in the container 4 to maintain an equilibrium value of the humidity is very small. Of course, the humidity limit may also be set to values other than the above 85% RH. The limit should be at least as high as the equilibrium humidity of the chilled goods 23, but should also be far enough below 100% rH to condensation in relatively cool, possibly by Refrigerated goods 23 to be able to exclude from the container 17 in the container 4 directed air flow of the fan 17 shielded areas of the container 4.

To minimize the likelihood of such shielded areas being created, as shown in FIG. 3, a tray 36 may be disposed in the container 4 spaced from its walls and bottom such that the plate 14 is in the open position into the container 4 deflected air circulate in a gap 37 between the lower container part 5 and shell 36, pass through openings 38 of the shell 36 and so can reach the refrigerated goods 23 from all sides. According to a further development, the fan 17 is not continuous, but needs-oriented in operation. Need for operation of the fan 17 is when there is a significant gradient of the temperature or humidity in the container 4. On the existence of a temperature gradient can, for. B. are closed when the measured value of the temperature sensor 20 differs significantly from that of a temperature sensor, not shown in the figure, which is mounted in a conventional manner to a wall of the storage compartment 3 and serves to control the compressor operation.

Of course, a gradient of temperature or humidity can also be measured directly in the container 4 if it has at least two sensors of the same type at different locations. Since, on the one hand, cold air tends to collect at the bottom of the container 4 and, on the other hand, the container is exposed to a heat inflow predominantly at its front, while it is from behind, either through a cold-wall evaporator or through a channel in the rear wall 29 Cooling air supplied from a Nofrost evaporator is most likely to form a temperature or humidity gradient between a relatively cold or wet area in the bottom or rear wall of the container 4 and a relatively warm or dry area in a front upper one Corner of the container 4. A second sensor should consequently be spaced vertically and / or in the depth direction from the sensors 19, 20 and preferably at the lower container part 5, in particular at the rear wall 9 thereof. If such a sensor is fixedly mounted on the lower container part 5 and this is to be removed for handling the Kühlguts 23 from the refrigerator, there is the problem to transmit the signals of such a sensor to the control unit. In the embodiment shown in Fig. 2, this problem is solved by 9 in the back wall - otherwise identical to that of FIG. 1 - lower container part 5, a large-area opening 24 is formed around which, when the container part 5 is not, as shown in the figure, partially withdrawn, but placed tightly closing under the upper container part 6, a elastic bellows 25 sealingly abuts against the rear wall 9. In this bellows 25 mounted temperature and / or humidity sensors 26, 27 are fixed with respect to the body 1 and fixed lines to the control unit connected, but are when the door 2 is closed and the container parts 5, 6 are placed close to each other exposed to the air of the container 4.

Alternatively to the representation of FIG. 2, the sensors 26, 27 can also be fixed in a storage compartment 3, e.g. be housed by its rear wall projecting housing 41 which engages in the opening 24 of the rear wall 9 when the container part 5 is inserted into the storage compartment 3. This housing 41 may, as shown in Fig. 4, be tapered forward so that it is easily and safely inserted into the opening 24 and a stop position, to which the container 4 in the storage compartment 3 is inserted and in the opening 24 is substantially sealed by the housing 41, is defined by contact of the housing 41 with the edges of the opening 24. The engaging in the stop position in the container 4 tip of the housing 41 is broken to allow an exchange of air between the interior of the container 4 and housed in the housing 41 sensors 26, 27.

According to another alternative shown in Fig. 5, the housing 41 may be provided with a peripheral flexible skirt 46, e.g. made of rubber, be provided, which conforms as shown in Fig. 2, the bellows 25 to the rear wall 9 in the inserted position and the opening 24 also closes tightly when the housing 41 itself does not touch the edges of the opening 24.

The presence of temperature and humidity sensors 19, 20, 26, 27 spaced apart in the direction of the temperature or humidity gradient allows, for example, control of the fan 17 and the actuator 18, in which the fan 17 is always switched on when the difference between the humidity values measured by the air humidity sensors 19, 27 exceeds a limit value of, for example, 4% rH or the difference between the measured values of the temperature sensors 20, 26 exceeds a limit value of 0.3 K, and the fan 17 is switched off again as soon as both Limit values are exceeded, and the actuator 18 opens the passage 13 when at least one of the humidity sensors 19, 27 reports an increase in humidity to over 85% rH + ε or the passage 13 is closed again, if both humidity sensors 19, 27 less than 85% rH - ε report. There are various possibilities to install an evaporator 28 in the refrigerator, which are shown in the figures in each case in conjunction with a specific embodiment of the container 4, but in principle can be combined with each of these embodiments. Thus, Fig. 1 shows a Nofrost evaporator 28, which is housed in a separate compartment 3 from the storage compartment 31, here within the rear wall 29 of the body 1. A passage 30, via which, if necessary driven by a second fan, not shown in the figure, cool air cooled in the storage compartment 3 at the evaporator 28, flows outside the cutting plane shown in the figure, laterally offset against the fan 17, approximately at its height in the storage compartment 3. Thus, the second fan drives a flow of air on a path that leads from the chamber 31 of the evaporator 28 via the passage 30 into the storage compartment 3 and from there via a passage, not shown, back into the chamber 31 ,

In this embodiment, it can be provided that the control unit always closes the passage 13 when the second fan is in operation so as to prevent very cold, dry air from entering the container 4 and drying out its contents. That is, when the second fan is in operation, the air flow driven by him in the storage compartment 3 via the channels 44, 45, but not through the container 4 itself. In the embodiment of FIG. 2, the evaporator 28 receiving chamber 31 with a merged into the rear wall 29 channel 47 merged, and arranged behind the fan 1 7 flap, here a butterfly flap 48 is between a solid line position in which it shuts off the chamber 31 and an air flow around the container 4 via the channel 47th allows, and a dashed lines shown position pivoted in which it locks the channel 47 and cold air from the chamber 31 can flow into the storage compartment 3. Depending on the position of the butterfly flap 48, the fan 17 thus drives the air circulation in the storage compartment 3 or the exchange of air between the storage compartment 3 and the chamber 31. The positions of the plate 14 and the Butterfly flap 48 may be coupled to each other here, so that whenever the butterfly flap 48 is in the position shown in dashed lines, the passage 13 is closed.

3 shows the evaporator 28 as a coldwall evaporator, in front of which the fan 17 is arranged. When the compressor is in operation and thereby the evaporator 28 is cooled, the fan 17 can intensify the cooling of the storage compartment 3 by driving an air flow over the surface of the evaporator 28 reaching into the storage compartment 3. During this time, the passage 13 should be closed. If this leads to a temporary exceeding of the humidity limit in the container 4 or even condensing out small amounts of moisture on the inner sides of the container 4, this can be tolerated relatively easily in this embodiment, since the shell 36 has a direct contact of the refrigerated goods 23 with prevents the condensate.

The evaporator 28 of a Nofrost refrigerator as shown in Fig. 1 or 2 is generally provided with a defrost heater to thaw the precipitate deposited on the evaporator 28 during operation and drain the condensate. When a defrosting operation has taken place, the compressor must first run for some time before the evaporator chamber 31 has cooled down to the point where all of the dew-water residues remaining there are frozen again. If the fan of the evaporator chamber 31 is running in such a time, the humidity of the air entering the storage compartment 3 from the evaporator chamber 31 may exceed the limit value for the air in the container 4, which would lead to the opening of the passage 13. Under these conditions, an open passage 13 would not lead to a reduction, but to an increase in the humidity in the container 4. Therefore, the monitoring of the humidity in the container 4 is preferably exposed in such a situation, and the passage 13 remains closed regardless of the humidity in the container 4 until the evaporator chamber 31 is cooled down again.

If, as in the evaporator arrangements of FIGS. 1 to 3, an air flow cooled off at the evaporator 28 is blown by a fan over a surface of the container 4, the high temperature difference between the air flow and the air inside the container 4 can occur lead to a strong local cooling in the container 4 and thus to condensation. If no humidity sensor 19 and / or 27 is arranged directly in the strongly cooled area, it may happen that nevertheless no exceeding of the humidity limit value in the container 4 is detected. In order to avoid this problem, the container 4 can, as shown in FIG. 6, be made locally double-walled. In Fig. 6, a doubled wall portion is formed on the ceiling 39 of the upper container part 6; in an analogous manner, however, any part of the container 4 which is exposed to a strong flow of cold air can be made double-walled. In the embodiment of Fig. 6, a gap 32 of the double wall portion is filled with air and thus forms an insulating layer which delays the heat exchange between the interior of the container 4 and the outside circulating air flow. Alternatively, the gap 32 could also be filled with a heat transfer fluid that cools in thermal contact with the outside circulating cold air, possibly even passes through a phase transition, and the heat released thereby time-delayed resuming from the container 4.

Fig. 7 shows an embodiment of the refrigerator, wherein the fan 17 is not formed as in the previously considered embodiments as axial but as a radial rotor. This fan 17 has, in a manner known per se, an elongated cylindrical shape and is surrounded by a housing 49, which has an intake opening 50 on at least one end face and an exhaust opening 51 on a peripheral surface. The housing 49 is rotatable about the axis of rotation of the fan 17 between a position shown in Fig. 7 in which it overlaps with a passage 13 of the upper container part 6, and a position in which there is air in between the ceiling 15 of the Storage compartment 3 and the upper container part 6 extending channel 44 blows.

In the rear wall 29 of the body 1 as in Fig. 1, 2, a chamber 31 is formed, which receives the evaporator 28, and a second fan, which drives the exchange of air between the evaporator chamber 31 and the storage compartment 3, is designated 22. The housing 49 prevents the air flow driven by the fan 22 from passing between the ceiling 15 and the upper container part 6 and forces it onto a path leading around the lower container part 5. LIST OF REFERENCE NUMBERS

1 corpus

2 door

3 storage compartment

4 containers

5 lower container part

6 upper container part

7 front wall

8 handle

9 rear wall

10 sidewall

1 1 flange

12 flange

13th passage

14 plate

15 ceiling

16 hooks

17 fans

18 actuator

19 Humidity sensor

20 temperature sensor

21 trunk groups

22 fans

23 refrigerated goods

24 opening

25 bellows

26 temperature sensor

27 Humidity sensor

28 evaporator

29 rear wall

30 passage 31 chamber

32 space

36 shell

37 gap

38 opening

39 ceiling

40 floor

41 housing

42 axis

43 passage

44 channel

45 channel

46 apron

47 channel

48 butterfly flap

49 housing

50 intake opening

51 outflow opening

Claims

839 3/186128 PCT/EP2013/061770 15 PATENT CLAIMS

Refrigeration appliance, in particular household refrigeration appliance, with a storage space (4) for refrigerated goods, at least one passage (13) for the inflow and/or outflow of air to or from the storage space (4) being formed in a wall delimiting the storage space (4). is, and a fan (17) for driving an air flow, characterized in that a movable closure element (14; 49) is arranged on the passage (13) between the fan (17) and the storage space (4), which in the open position allows the air flow driven by the fan to circulate in the storage room and, in the closed position, guides the air flow driven by the fan (17) over a channel (44) running along an outside of a wall of the storage room (4).

Refrigeration device according to claim 1, characterized in that the speed of the air flow in the storage room (4) is not more than 2 m/s.

Refrigeration appliance according to claim 1 or 2, characterized in that a control unit is set up to control the closure element (14) based on the humidity prevailing in the storage room (4).

Refrigeration appliance according to claim 3, characterized in that the control unit is set up to open the passage (13) when the air humidity at at least one measuring point (19) in the storage room (4) exceeds a limit value.

Refrigeration appliance according to one of the preceding claims, characterized in that a control unit is set up to control the fan (17) based on the humidity and/or temperature prevailing in the storage room (4).

Refrigeration appliance according to claim 5, characterized in that the control unit is set up to put the fan (17) into operation when the difference in air humidity and/or temperature between two measuring points (19, 20; 26, 27) in the storage room ( 4) exceeds a limit value. 201200839

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Refrigeration device according to one of the preceding claims, characterized in that the air flow driven by the fan (17) is guided via an evaporator (28).

Refrigeration device according to one of claims 1 to 6, characterized in that a second fan (22) drives a second air flow on a path (31, 30, 3) leading via an evaporator (28) and that the paths of the two air flows cross each other.

Refrigeration appliance according to one of the preceding claims, characterized in that the storage space is a container (4) which is arranged in a storage compartment (3) of the refrigeration appliance.

Refrigeration appliance according to claim 9, characterized in that the container (4) comprises at least one upper and one lower container part (5, 6) and that the lower container part (5) can be removed from the storage compartment (3) without the upper container part (6). .

Refrigeration appliance according to claim 10, characterized in that the passage

(13) and the closure element (14; 49) are arranged on the upper container part (6).

Refrigeration appliance according to claim 10 or 1 1, characterized in that an air humidity or condensation sensor (19) is arranged on the upper container part (6).

Refrigeration appliance according to one of the preceding claims, characterized in that the wall has a heat storage medium on at least part of its surface.

14. Refrigeration device according to one of the preceding claims, characterized in that the wall has an outer wall, an inner wall, on at least part of its surface. 839

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inner wall and a gap (32) between the outer and inner walls.