Household appliance for cooling and heating

Abstract

Household appliance with a storage chamber (5), an evaporator chamber (6) which communicates with the storage chamber (5), a microwave source (7) for feeding microwave energy into the storage chamber (5), and a shielding structure (4) which has a front side (17) facing the storage chamber (5) and a rear side (28) facing the evaporator chamber and a plurality of passages (20) extending from the front side (17) to the rear side (28), characterized in that a wall (21) between adjacent passages (20) of the shielding structure (4) has a thickness (d) which is smaller than the distance (I) between the front side (17) and the rear side (28), and the distance (I) between the front side (17) and the rear side (28) is at least as large as a cross-sectional dimension of the passages (20).

Description

The present invention relates to a household appliance with which food can be heated and cooled at high speed. A heating technique which is particularly suitable for this is microwave technology, since it releases heat directly in the item to be cooked without first having to heat a surrounding cooking chamber. In order to permit inspection into the cooking chamber of a microwave device, but at the same time to prevent the microwave energy from escaping, it is known to provide the door of a cooking chamber with a perforated plate, the holes of which are arranged in a large number and sufficiently close to permit inspection into the cooking chamber, but which on the other hand are small enough for the perforated plate to act for the microwaves as a continuous, reflecting wall.CN 1 02 927 767 A discloses a domestic appliance which combines the functions of a refrigerating appliance and a microwave appliance. A chamber of the apparatus can be supplied with microwave energy in order to heat food therein, and also, via feed and return ducts, with cold air from a cooling compartment. In order to prevent microwave energy from entering the channels, a perforated plate is also arranged here at the transition from the channel to the chamber. However, since this greatly narrows the free cross section of the channels, it also considerably impairs the cooling effect that can be achieved.JP 2004-248 586 A discloses a high-frequency thawing machine for thawing an object while cooling its surface without temperature fluctuations of the object, which are attributable to fluctuations in the electric field intensity.WO 2008 / 077 583 A1 discloses a sealing material comprising a planar layer composite composed of at least two layers of a graphite foil in alternation with at least one metal insert.KR 10 0 819 080 B1 discloses a heating cooker by preventing a magnetron or a waveguide from being damaged by a steam.The effect of the perforated plate is based on the fact that the holes are substantially smaller than the wavelength of the microwave radiation. A hole can be considered as a waveguide that is operated far below its cut-off frequency by model: in such a waveguide, a wave cannot propagate freely but decays exponentially. Only a small residue reaches the opposite side of the perforated sheet and can again spread freely from there. The size of this remainder depends on the number of holes and on the diameter thereof. The greater this is, the less attenuation of the radiation during passage through the hole. A required shielding effect can therefore be achieved only if the number and diameter of the holes does not become too large. However, the smaller and less the holes, the poorer the air permeability. As a result, the perforated plate prevents efficient cooling of the chamber.The object of the present invention is to provide a household appliance which enables both rapid heating and rapid freezing of food in a same storage chamber. For this purpose it is necessary to prevent the microwave energy from escaping from the chamber; at the same time, however, a shielding structure which does this should impair the air exchange between the storage chamber and the evaporator chamber as little as possible.To achieve this object, a household appliance is proposed having a storage chamber, an evaporator chamber communicating with the storage chamber, a microwave source for supplying microwave energy into the storage chamber, and a shielding structure having a main surface facing the storage chamber and a main surface facing the evaporator chamber, and a plurality of passages extending from one of the main surfaces to the other, in which a wall separating adjacent passages of the shielding structure from each other has a thickness smaller than the distance between the main surfaces.In order to achieve sufficient attenuation of the microwave propagation in the passage even if a cross-sectional dimension of the passages is greater than that of a conventional perforated plate, it is provided according to the invention that the distance between the main surfaces is at least as large as the cross-sectional dimension.In order to achieve a sufficient shielding effect despite the small thickness of the wall, the thickness of the shielding structure should be greater than that of a conventional perforated plate. The distance between the main surfaces should be not less than 1 mm, preferably it is greater than 3 or even 5 mm.A large cross-sectional dimension of the passages is important to prevent rapid freezing of the passages when freezing causes the air temperature in the storage chamber to decrease and excess moisture from the air in the storage chamber to subsequently precipitate on the passages of the shielding structure. In particular, the passages should be so large that they cannot be blocked by a single water drop. The cross-sectional dimension should therefore be at least 3 mm, preferably 5 mm or more.The relationship according to the invention between the thickness of the shielding structure and the thickness of the material between two adjacent passages cannot be realized by punching a metal sheet. One possibility of creating such a structure is to connect a plurality of identical components to form a grid.Such components can be, for example, sections of an extrusion profile, for example a simple round or angular tube or also a multi-chamber profile.Angular profiles with lateral planar surfaces are preferred because a planar contact between planar surfaces abutting each other improves an electrical contact between the components necessary for effective attenuation of the microwave radiation or facilitates the welding of the components to each other. With a hexagonal or octagonal profile, a particularly high ratio of opening cross section to the total cross-sectional area of the shielding structure can be achieved; with the hexagonal profile, moreover, relatively low flow losses (and therefore also a low operating noise) can be achieved.Alternatively, the components to be connected to one another can also be corrugated strips.It also applies to these that abutting planar surfaces facilitate the production of electrically conductive connections between the components, in particular by welding.Furthermore, the shielding structure may comprise at least two interconnected components, each of which forms one of the main surfaces.At least one of these components can be a perforated plate with punched holes as described at the beginning, wherein according to the invention the punched holes of this plate form only a section of the passages. In order to achieve the necessary length of the passages, a plurality of congruent perforated plates can be combined to form a stack, or one or more perforated plates can be combined with the components connected to form a grid.If only one perforated plate is provided, this is preferably arranged on the side of the shielding structure facing the storage chamber, since, owing to its one-part construction, it can reflect the microwave radiation more effectively than a composite structure, at the joints of which a not negligible electrical resistance can occur.In order to enable rapid cooling, the storage chamber and the evaporator chamber are preferably arranged directly next to one another, so that one of the main surfaces of the shielding structure delimits the evaporator chamber and the other delimits the storage chamber.Both chambers and the shielding structure can be accommodated in a common housing.The housing may have one-piece metallic walls, one part of which delimits the storage chamber and another part of which delimits the evaporator chamber.Further features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the appended figures. The following are shown: FIG. 1 shows a schematic section through a household appliance according to the invention; FIG. 2 shows a shielding structure according to a first embodiment of the invention; FIGS. 3, 4 and FIG. 5 shows further developments of the first embodiment FIG. 6 shows a second embodiment; FIG. 7 shows a third embodiment; and FIG. 8 shows a combination of the first and third embodiments.FIG. 1 shows a schematic horizontal section through a household appliance according to the invention. The apparatus comprises a cabinet-like cabinet 1 similar to a refrigerator or oven having at least one interior 2 which is lockable by a door or flap 3. Further interior spaces can be provided above or below the interior space 2.The interior 2 is divided by a shielding structure 4 into a storage chamber 5 facing the door or flap 3 and an evaporator chamber 6 facing away from the door 3. The evaporator chamber 6 contains an evaporator 9 and at least one fan 10, which are each arranged to allow an air exchange between the storage chamber 5 and the evaporator chamber 6 through the shielding structure 4. In the case shown, this is achieved by the evaporator 9 being designed as a lamellar evaporator enclosed between bypass blockers 11 and two fans 10 being arranged in a space which is bounded by the shielding structure 4, the evaporator 9 and the bypass blockers 11 and blowing lateral regions 4'' of the shielding structure 4 into the storage chamber via a central region 4' of the shielding structure 4 from the front sucked in to the rear through the evaporator 9, a space 12 between an outlet side of the evaporator 9 and a rear wall 13 of the interior 2, channels 14 adjoining the latter between the bypass blockers 11 and adjacent side walls 15 of the interior 2.In order to prevent cold air ejected via the lateral regions 4'' of the shielding structure from being sucked back immediately into the evaporator chamber 6, channels 16 can be formed in the storage chamber 5 as an extension of the channels 14, which channels extend from a front side 17 of the shielding structure 4 into the storage chamber 5. These channels 16 can be formed, for example, by guide walls 18 arranged as extensions of the bypass blockers 11 or by pipe sections projecting from the shielding structure 4 into the storage chamber 5.In order to enable shock freezing of cooled goods in the storage chamber 5, the shielding structure 4 must on the one hand have the highest possible air permeability, on the other hand must keep microwaves from the storage chamber 5 away from the evaporator chamber 6, in order to prevent damage to the components mounted therein by the microwave energy and uncontrolled back reflection into the storage chamber 5, possibly resulting in local overheating due to focusing, by the components such as 9 or 10, of the evaporator chamber 6.The above-described direction of circulation of the air between storage chamber 5 and evaporator chamber 6 is chosen in view of the fact that the shock freezing of goods to be cooled releases large amounts of moisture which condenses out on the first solid surface on which it impinges, i.e. the screening structure 4. Because the moisture-laden air distributes itself over the relatively extended central region of the shielding structure 4, a greater amount of moisture can precipitate there without critically impairing the air circulation than if it first applied--in the case of the opposite direction of rotation--to the edge regions of the shielding structure 4.A first embodiment of a suitable shielding structure 4 is shown in detail in FIG. 2. It comprises a plurality of round metallic pipe sections 19 arranged in a regular grid. Each pipe section 19 of the grid shown here is in contact with up to six adjacent pipe sections 19; alternatively, a grid is also possible in which each pipe section contacts up to four adjacent pipe sections. The contacting pipe sections 19 are also electrically conductively connected, for example by means of spot welding. The pipe sections 19 connected to one another thus form a wall 21 between each two passages 20 adjacent to one another, the thickness of which wall corresponds to twice the wall thickness of the pipe sections 19. The diameter of the tube sections 19 is considerably smaller than the wavelength of the microwave radiation emitted by the magnetron 7. While its wavelength is conventionally over 10 cm, the diameter of each internal passage 20 of the pipe sections 19 is a few millimeters. The microwave radiation is therefore neither capable of propagating in the passages 20 nor in the coils 22 bounded jointly by three tube sections 19 in each case. The length of the pipe sections can be 6 mm.The attenuation experienced by the microwave radiation in the passageways is the greater the smaller its diameter. In order to achieve a desired damping, it is therefore sufficient to define a sufficiently small diameter or a sufficiently large length. The wall thickness of the pipe sections can then be reduced to the extent necessary for a desired mechanical strength, so that a high ratio of open cross-sectional area to the total cross-sectional area of the shielding structure 4 and a correspondingly good air permeability can be achieved.The round cross-sectional shape entails that the pipe sections 19 can only contact one another over a small area and welding or otherwise electrically conductive connection without simultaneous deformation of the pipe sections 19 is difficult. In addition, because of their small cross-sectional area, the coils 22 have a clearly higher flow resistance for the air flowing through than the passages 20, and according to a preferred development shown in FIG. 3, the round pipe sections 19 are therefore replaced by pipe sections 19' with a hexagonal cross-section. The walls of each pipe section 19' each comprise six planar surfaces 23, and since planar surfaces 23 of different pipe sections 19' each touch in pairs in the honeycomb arrangement shown, the gussets 22 are omitted, and the large-area contact also facilitates the production of a well-electrically conductive connection in the walls 21 between the pipe sections 19', which is important for low-loss reflection of the microwave radiation at the front side 17 of the shielding structure 4.It would also be conceivable to form a grid of pipe sections of rectangular, in particular square, cross section; however, the hexagonal pipe sections 19' are preferred since a shielding structure 4 formed therefrom has lower flow losses with the same microwave attenuation than a shielding structure made of square pipe sections.In the modification of Fig. 4, the pipe sections 19' are replaced by sections 19'' of a multi-chamber profile, each having a plurality of hexagonal passages 20. By thus realizing a plurality of passages in a same component, the effort in assembling the shielding structure 4 can be reduced. In the case considered here, the multi-chamber profile has three passages 20 in a V-arrangement with an angle of 120°. As outlined in FIG. 4, these can fill an area uniformly, with a further passage 20' being provided on each of three internal passages 20 of each section 19'', said passage being bounded by a plurality of mutually contacting sections 19''. By virtue of this passage 20' being produced to a certain extent without the use of material, both the manufacturing outlay can be reduced further and the ratio of open cross section to overall cross section of the shielding structure 4 can be improved.FIG. 5 shows a detail of a shielding structure 4, in which octagonal tube sections 19"' form a grid. As in the case of Fig. 2, there are passages 20 in the interior of each pipe section 19"' as well as gusset 22, which are bounded by several pipe sections 19"' and have a smaller cross section than the passages 20. A low-loss flow can nevertheless be realized here by keeping those planar surfaces 23 of the pipe sections 19"', which contact one another in pairs, narrower than those planar surfaces 24 which adjoin the gusset 22. By limiting the width of the planar surfaces 23 to the value necessary for reliable welding, the material outlay can also be kept low and a favorable ratio of open cross section to total cross section can be achieved.As shown in Figure 6, a grid structure having a plurality of passages 20 may also be realized by forming bands 25 of metal each into a wave profile, stacking them offset by one-half wavelength from each other, and then welding or otherwise electrically conductively connecting them together at their contact surfaces 26 to form the walls 21.While according to the above examples a shielding structure is obtained by joining a plurality of identical members to each other in longitudinal and transverse directions of the shielding structure to be realized, a suitable shielding structure may be made of members consecutive in the thickness direction of the shielding structure. A one-piece production of the shielding structure by punching from a sheet metal fails because walls 21 between two passages 20, the extent of which in the punching direction is greater than their thickness, would collapse during punching. However, in sufficiently thin sheets, passages in the required dense arrangement can be realized by punching, and a shielding structure in which the length I of the passages 20 is greater than the thickness d of the walls 21 between them can be obtained by joining n punched sheets 27 having a thickness I / n less than d into a stack.The stamped sheet metal 27 has the advantage, in particular when it forms the front side 17 of the shielding structure facing the storage chamber 5, of being free of joints at which a non-attenuating electrical contact resistance between joined components could impair the reflection of the microwave radiation and lead to local heating. On the other hand, a passage 20 formed by stacking a large number n of sheets 27 together tends to have uneven inner surfaces that impede the air flow. According to a particularly preferred embodiment of the invention, a shielding structure 4 with a sandwich structure as shown in FIG. 8 is therefore provided: at least the front side 17, preferably also a rear side 28, of the shielding structure 4 is formed by a stamped sheet metal 27; an intermediate layer is formed by a grid 29, which can be constructed as shown in one of FIGS. 2 to 6. In order to allow the structure of both sheets 27 to be seen, Fig. 8 does not show a complete grid, but only single pipe sections 19' of hexagonal cross-section of the type shown in Fig. 3, the passages of which are respectively aligned with the holes punched in the sheets 27.Referring again to Fig. 1, it can be seen that a small thickness of the screening structure 4 is required, above all in its central region, opposite the evaporator 9, while it could be extended in the lateral regions 4", in particular into the channels 14, without losing usable space as a result. Instead of providing passages 20 of equal cross-section and equal length over the entire extent of the screening structure, the lateral areas 4'' of the screening structure may be formed by pipe sections whose cross-section is larger than that of the pipe sections in the central area. The lower damping of these further pipe sections can be compensated for by an increased length, which is in turn advantageous for free air circulation and rapid freezing of cooled goods in the storage chamber 5. The large cross-section of these wide pipe sections also has the result that a large amount of frost can precipitate on their inner surfaces before the air circulation is critically impaired as a result. It may therefore be appropriate in this case--although the cross section of the channels 14 is substantially smaller than that of the evaporator 9--to reverse the direction of circulation of the air compared with the above-described case and to suck air out of the storage chamber 5 via the lateral regions 4'' of the shielding structure 4 and to blow it in again via the central region 4'.REFERENCE NUMERALS1 Housing 2 Interior 3 Door 4 Shielding structure 5 Storage chamber 6 Evaporator chamber 7 Magnetron 8 Rotary plate 9 Evaporator 10 Fan 11 Bypass blocker 12 Intermediate space 13 Rear wall 14 Channel 15 Side wall 16 Channel 17 Front side 18 Guide wall 19 Pipe section 20 Passage 21 Wall 22 Gusset 23 Planar surface 24 Planar surface 25 Strip 26 Contact surface 27 Stamped sheet metal 28 Rear side 29 Grid

Claims

Household appliance having a storage chamber (5), an evaporator chamber (6) which communicates with the storage chamber (5), a microwave source (7) for feeding microwave energy into the storage chamber (5), and a shielding structure (4) which has a front side (17) facing the storage chamber (5) and a rear side (28) facing the evaporator chamber and a plurality of passages (20) extending from the front side (17) to the rear side (28), characterized in that a wall (21) between adjacent passages (20) of the shielding structure (4) has a thickness (d) which is smaller than the distance (I) between the front side (17) and the rear side (28), and the distance (I) between the front side (17) and the rear side (28) is at least as large as a cross-sectional dimension of the passages (20).Domestic appliance according to claim 1, characterised in that the distance (I) between the front side (17) and the rear side (28) is over 1 mm, preferably more than 3 mm.Household appliance according to one of the preceding claims, characterised in that the passages (20) have a cross-sectional dimension of at least 3 mm, preferably at least 5 mm.Domestic appliance according to one of the preceding claims, characterised in that the screening structure (4) has a plurality of identical components (19, 19', 19", 19"', 25, 27) connected to form a grid.Domestic appliance according to claim 4, characterised in that the components (19, 19', 19", 19"', 27) each surround at least one passage (20).Domestic appliance according to claim 4 or 5, characterised in that the components (19, 19', 19"') are pipe sections.Household appliance according to one of claims 4 to 6, characterised in that the components (19', 19"') have a rectangular, in particular square, hexagonal or octagonal cross-section.Household appliance according to claim 4, characterised in that the components are corrugated strips (25).Domestic appliance according to one of claims 4 to 8, characterised in that one component (19', 19", 19"', 25) has a plurality of planar surfaces (23, 24) extending along the passages (20), which are fastened in each case in a manner lying against a planar surface (23, 24) of an adjacent component (19', 19", 19"', 25).Household appliance according to one of claims 1 to 5, characterised in that the shielding structure (4) comprises at least two interconnected components (27, 29), each of which forms one of the front and rear sides (17, 28) of the shielding structure (4).Household appliance according to one of claims 1 to 5 or according to claim 10, characterised in that at least one of the components (27) is a sheet with punched holes, which each form a section of the passages (20).Household appliance according to one of the preceding claims, characterised in that the shielding structure (4) forms a partition wall between the storage chamber (5) and the evaporator chamber (6).

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