EP3552710B1 - Electrostatic filter unit and extraction hood device with electrostatic filter unit - Google Patents

Description

The present invention relates to an electrostatic filter unit for an extractor device and a ventilation device in the form of an extractor device with such a filter unit

It is known to filter out impurities from the air using ventilation devices. Mechanical filters can be used here, such as fleece mats, porous foam media, expanded metal filters or perforated sheet metal filters. In ventilation devices that represent extractor hoods that are operated in a kitchen, liquid and solid impurities are filtered out from the vapors and vapors created during cooking. The mechanical filters used here are in particular expanded metal filters, perforated sheet metal filters, baffle filters, which can also be referred to as eddy current filters, edge suction filters and porous foam media.

In addition, for example, from the DE 2146288 A an extractor hood is known in which an electrostatic filter is used. The electrostatic filter in this extractor hood consists of plate-shaped separation and counter electrodes as well as wire-shaped ionization electrodes. The plate-shaped deposition electrodes are connected to one another via electrically conductive webs and the counter electrodes are also connected to one another via electrically conductive webs. The deposition and counter electrodes are arranged in such a way that the air entering the filter first flows towards the deposition electrodes with wire-shaped ionization elements in between and then reaches the counter electrodes that are offset upwards. The deposition electrodes and counter electrodes are attached to the housing of the extractor hood via partitions that run perpendicular to the electrodes and parallel to each other. The deposition electrodes and counter electrodes interlock with each other alternately like a comb. In addition, a high-voltage device is provided in the housing of the extractor hood, which is connected to the electrodes of the filter.

A disadvantage of this electrostatic filter is, on the one hand, the large number of parts and the complex structure of the filter. On the other hand, with this structure, due to the use of wire as ionization electrodes, there is a high risk of damage, for example due to the wire breaking or the voltage flashing over.

In addition, filter units are, for example, in the US2015075379A1 , DE102005023521B3 , US2008034973A1 , DE3502148A1 , US2018093282A1 , WO2013065908A1 , JPH10235224A and US2017232823A1 described.

It is therefore the object of the present invention to create an electrostatic filter unit which, on the one hand, can be operated safely and reliably and, on the other hand, has a simple structure.

The object is achieved according to the invention by an electrostatic filter unit for a ventilation device in the form of an extractor device, which comprises an ionization unit with at least one ionization element and at least one counter electrode and a separation unit, the counter electrode having at least one opening and the ionization element an ionization electrode frame made of electrically conductive Material consists, and comprises at least one needle-shaped ionization electrode with a tip, the ionization electrode is attached to the ionization electrode frame, the ionization electrode is perpendicular to the opening of the counter electrode and the tip lies in the opening of the counter electrode, the ionization electrode frame and the ionization electrode having an insulating coating, the coating at the tip of the ionization electrode and at least one contact point of the ionization electrode frame of the ionization element is left out, the ionization unit has a housing in which the ionization element and the counter electrode are accommodated, the counter electrode is accommodated on the front of the housing, the counter electrode has a plate shape and forms the front of the ionization unit through which air enters the ionization unit.

A ventilation device is a device through which air can be extracted and cleaned from a room. According to the invention, the ventilation device is an extractor device, for example in a kitchen. However, the ventilation device in the form of an extractor device can also represent a ceiling ventilation, for example. The air flow can be caused by a fan of the ventilation device.

The electrostatic filter unit is used to filter out contaminants from the air that flows through it. According to the invention, the electrostatic filter unit has an ionization unit and a separation unit. The separation unit is connected downstream of the ionization unit in the flow direction. The separation unit preferably has at least two precipitation electrodes. In the ionization unit, particles in the air are charged. The electric field that builds up between the differently charged collecting electrodes causes the charged particles to be deposited on the collecting electrodes and thus filtered out of the air.

According to the invention, the ionization unit has at least one ionization element and at least one counter electrode. The counter electrode of the ionization unit, which in particular represents a negative electrode, has at least one opening. Preferably, a plurality of openings are provided in the counter electrode and the ionization element has a plurality of ionization electrodes. The counter electrode is therefore described below primarily with several openings and the ionization element with several ionization electrodes. The openings of the counter electrode are aligned so that their surface is perpendicular to the flow direction of the air that flows through the ionization unit to the separation unit.

According to the invention, the ionization element comprises at least one needle-shaped ionization electrode with a tip. The number of needle-shaped ionization electrodes preferably corresponds to the number of openings. A needle-shaped ionization electrode is an electrode that has a shape that tapers towards one end. The needle-shaped ionization electrode preferably has a shaft with a constant diameter and a tip. The tip, which can also be referred to as the electrode tip, can have a cone shape.

The ionization electrode is arranged so that it is perpendicular to the opening of the counter electrode. The ionization electrode thus extends in the flow direction of the air that flows through the ionization unit. In addition, the tip of the ionization electrode lies in the opening of the counter electrode. The ionization electrode with the electrode tip is preferably oriented coaxially in the opening of the negative counter electrode.

Directional indications such as top, bottom, front and rear refer to the filter unit and its parts in a mounted state in a ventilation device. The front side of the filter unit is understood to be the side through which air enters the filter unit. The ionization unit is located in the front area of the filter unit. The side of the filter unit through which air exits the separation unit is referred to as the back of the filter unit. The back of the ionization unit adjoins the front of the ionization unit. The depth of the filter unit, the separation unit and the ionization unit is the distance between the front and the back of the respective unit. The filter unit preferably has a box shape whose width is greater than the height. The width is therefore referred to as the larger dimension of the filter unit perpendicular to the depth direction. The height is perpendicular to the width. A side whose surface extends in the width and depth directions is referred to as the top of the filter unit. The other side opposite the side, the surface of which extends in the width and depth directions, is called the bottom side.

Because the ionization electrode extends perpendicular to the opening of the counter electrode and thus the longitudinal direction of the ionization electrode lies in the flow direction of the air, the obstruction created by the ionization electrode in the air flow is minimized. In particular, the obstruction is less than with a wire-shaped ionization electrode, which in the prior art is usually arranged perpendicular to the flow direction of the air. Since the tip of the ionization electrode is also located in the opening of the counter electrode, a corona discharge is formed between the tip and the counter electrode when the electric field is increased at the tip. The electric field increase is due to the pointed shape of the Needle-shaped ionization electrode is significantly higher than with an ionization wire. As a result, a significantly greater electric field strength in the corona range can be achieved with the same ionization voltage in the filter unit according to the invention and therefore the charging of the particles in the air can be promoted. In addition, fewer particles settle on a needle tip than on a wire. The risk of the voltage breaking through from the ionization electrode to the counter electrode can thus be reduced.

According to the invention, the ionization element has an insulating coating. The insulation coating can also be called insulation coating. The coating material has little or preferably no electrical conductivity. The coating is provided on the entire ionization element and is only left out at the tip of the at least one ionization electrode and at least one contact point for contacting the ionization element with a high-voltage unit. In the embodiment according to the invention, in which the ionization element consists of an ionization electrode frame with ionization electrodes provided thereon, the ionization electrode frame and the ionization electrodes are completely electrically insulated by means of an insulating surface coating except for the contact point and the electrode tips. By providing the ionization element with an electrically insulating coating except for the tip(s) and contact point(s), the formation of creepage distances can be further reduced. In the case of wire-shaped ionization electrodes, it is functionally necessary that they are bare, i.e. not insulated, over their entire length, as electrical creepage paths are formed. With the preferably provided insulation coating, which leaves out the tip(s) of the ionization electrode, such a formation is not to be feared. It has also been shown that the noise development is low when the electric field between the needle tip of the ionization electrode and the opening of the counter electrode for the corona discharge is used exclusively.

The insulation coating is particularly preferably a hydrophobic coating. On the one hand, this allows the electrical creepage distance to be formed further be prevented. In addition, resinification of the ionization electrodes due to the adhesion of particles, such as fat, can also be prevented.

The insulation coating, which can also be referred to as surface insulation of the ionization element, can be produced, for example, by a ceramic coating or a thermoplastic injection molding.

According to the invention, the ionization element has an ionization electrode frame. The ionization electrode frame is made of electrically conductive material. An electrically conductive or electrically conductive material is in particular a solid material that has an electrical conductivity that is preferably >10 ⁶ S/m at 25°C. In particular, metals or conductive plastic can be used as electrically conductive material. The term conductive plastic refers to plastic that is an intrinsically conductive polymer or is a polymer provided with conductive fillers. Aluminum, for example, can be used as the metal for the ionization electrode frame.

The ionization electrode can be molded onto the ionization electrode frame or attached to it. An ionization electrode frame is a component that serves to hold the ionization electrode(s). The ionization electrode frame preferably represents an elongated component, along the length of which ionization electrodes are arranged perpendicular to the length of the ionization electrode frame. The ionization electrode frame thus preferably extends parallel to the surface of the openings of the counter electrode. Since the ionization electrode frame is perpendicular to the air flow through the ionization unit in this orientation, its extension in the height direction is preferably small in order to keep the obstruction to a minimum. The ionization electrode frame therefore preferably has a web shape, with the webs being equal to or slightly larger than the diameter of the ionization electrode.

The embodiment in which the at least one ionization electrode is attached to the ionization electrode frame has the advantage that a different material can be used for the ionization electrode frame than for the actual ionization electrode. In particular, the ionization electrode can be made of tungsten, for example, while the ionization electrode frame can be made of another metal or electrically conductive plastic.

By providing an ionization electrode frame, the overall structure of the filter unit is simplified. In particular, separate contacting of the ionization electrodes integrated into the ionization electrode frame or attached to it is not necessary. Rather, the ionization electrode frame, which consists of conductive material, can be connected to the high-voltage unit, that is, connected to it.

According to the invention, the counter electrode of the ionization unit represents a plate shape. The openings in which the ionization electrodes, in particular the tips of the needle-shaped ionization electrodes, are arranged can be introduced or formed in the plate. A tubular projection can be formed at the opening(s). This increases the area of the counter electrode surrounding the tip of the ionization electrode without the wall thickness of the counter electrode having to be increased. The tubular projection or the tubular projections are preferably formed in one piece with the plate of the counter electrode.

The at least one opening in the counter electrode can have different geometries, in particular the opening can have a round or hexagonal cross section. Alternatively, it is also possible for the openings to have a square cross section. By appropriate mutual alignment of the openings to one another, the weight of the counter electrode can be minimized and the blockage of air can be kept to a minimum. For this purpose, only thin material webs can be present between the openings in the counter electrode. The openings with the centrally arranged ionization electrodes can thus be offset from one another.

The filter unit is also known as a filter module. The filter unit preferably represents a portable filter unit that can be removed from the ventilation device and is preferably pre-assembled. A filter unit is referred to as pre-assembled, which is inserted as a structural unit into the ventilation device and can be removed from it in one unit.

According to the invention, the ionization unit has a housing in which the ionization element is accommodated. The housing preferably has a box shape that is open at the front and back. The housing can therefore also be referred to as a frame. The ionization element includes an ionization electrode frame and the ionization electrode. The ionization electrode and the ionization electrode frame are accommodated in the housing. In addition, the counter electrode is also accommodated in the housing. According to the invention, the counter electrode is accommodated on the front of the housing and forms the front of the ionization unit. In addition, the housing can have a protective grid which is arranged in front of the counter electrode in the direction of flow.

The front of the housing is the side through which air enters the ionization unit and which faces away from the separation unit. The back side is the side where the air exits the ionization unit and which faces the separation unit.

The separation unit and the ionization unit can be accommodated in a common housing. The housing of the ionization unit can also be designed separately to form a separation housing of the separation unit and can be connected to the separation housing. The separation housing is the housing of the separation unit in which the precipitation electrodes are housed. In the embodiment in which the ionization housing is connected to the separation housing, this can in particular be removed from the separation housing.

The housing of the ionization unit, which can also be referred to as an ionization housing, consists of an electrically insulating material. For example, this can Ionization housing made of PBT (polybutylene terephthalate). The ionization housing can be designed in one piece or in several parts. For example, the ionization housing can consist of an upper part and a lower part. The ionization housing is open at the front and back and, if necessary, closed at the front by a protective grille. The protective grille is designed in such a way that it hinders the air flow into the ionization housing as little as possible.

According to a preferred embodiment, the ionization element is attached to the housing by means of at least one insulator. The ionization electrode frame is particularly preferably attached to the housing. The ionization electrode frame can be attached to the inside of the top of the housing, for example. The insulator or insulators consist of electrically insulating material. In particular, the insulators can be made of ceramic or electrically insulating plastic, for example. In particular in the embodiment in which the ionization housing consists of electrically insulating plastic, the insulator or insulators can be made in one piece with the housing. For example, the housing with insulator(s) can be manufactured by injection molding. The ionization element can be held in a predetermined position relative to the counter electrode in the interior of the ionization housing via the insulator(s).

Particularly preferably, the at least one insulator has a ribbed surface, which can also be referred to as a surface structure. This increases the electrical ionization creepage distance between the ionization element under electrical voltage and the negative counter electrode.

According to one embodiment, a partition wall is introduced into the housing of the ionization unit, which delimits a contact space to the part of the housing in which the at least one ionization electrode is arranged. The part of the housing in which the at least one ionization electrode is arranged is also referred to as the flow-guiding ionization region, since the air flow from which the particles are to be filtered out is guided through this region. This can happen in the contact room Ionization element and in particular the ionization electrode frame are connected to the high-voltage unit. In the embodiment in which a partition is provided, the electrical contact of the ionization electrode frame is separated from the flow-carrying ionization area by the partition. There is preferably no mechanical contact between the partition and the ionization electrode frame. For this purpose, the partition can have a passage through which the ionization electrode frame projects without contact. The electrical creepage distance in this area between the ionization electrode frame and the negative counter electrode is also extended by constructive insulation elements such as ribs on the partition. The electrical contact between the high-voltage supply and the ionization electrode frame can take place both on the housing surface of the filter module and in the contact space that is formed by the partition.

According to one embodiment, the ionization electrode frame has a connecting web and at least two fastening webs branching off from it. At least one ionization electrode can be formed or attached to the fastening webs. The ionization electrode preferably extends perpendicular to the fastening web. The connecting web can, for example, extend in the width direction of the ionization unit. The fastening webs can protrude from the connecting web, for example upwards and downwards, in particular vertically upwards and downwards. With such a shape of the ionization electrode frame, which represents a double comb shape, a large number of ionization electrodes can be brought into corresponding openings in the counter electrode and still be securely held via the ionization electrode frame. The ionization electrode frame is preferably formed in one piece in order to ensure sufficient stability. In the embodiment of the ionization electrode frame with connecting web and fastening webs, the ionization electrode frame can be attached, for example, by snapping the connecting web onto one end of insulators that are attached to the top of the inside of the ionization housing. When inserted into the housing, the ionization electrodes extend towards the front of the housing. This can block the tip of the ionization electrode can be prevented by the fastening web to which the ionization electrode is attached.

According to a further aspect, the invention relates to a ventilation device in the form of an extractor device, which comprises at least one electrostatic filter unit according to the invention.

Advantages and features that are described with regard to the electrostatic filter unit also apply - where applicable - to the ventilation device and vice versa.

The electrostatic filter unit can preferably be arranged in the suction opening on the ventilation device. Alternatively, the electrostatic filter unit can also be installed in the ventilation device in the direction of flow downstream of the suction opening. The electrostatic filter unit is installed in the ventilation device in such a way that incoming air first flows through the ionization unit before it reaches the separation unit.

• Figur 1: eine schematische Perspektivansicht einer Ausführungsform der erfindungsgemäßen Lüftungsvorrichtung;
• Figur 2: eine schematische Perspektivansicht einer ersten Ausführungsform der erfindungsgemäßen elektrostatischen Filtereinheit;
• Figur 3: eine schematische Schnittansicht der ersten Ausführungsform der Filtereinheit;
• Figur 4: eine schematische Perspektivansicht der Ionisationseinheit der ersten Ausführungsform der Filtereinheit;
• Figur 5: eine schematische Rückansicht der Ionisationseinheit der ersten Ausführungsform der Filtereinheit;
• Figur 6: eine schematische Detailansicht eines Teils der Ionisationseinheit aus Figur 5;
• Figur 7: eine schematische perspektivische Rückansicht der Ionisationseinheit aus Figur 5 ohne Gehäuse;
• Figur 8: eine schematische Perspektivansicht eines Teils eines lonisationselementes der ersten Ausführungsform der Filtereinheit; und
• Figur 9: eine schematische Prinzipskizze der Ionisationseinheit.

The invention is explained again below with reference to the accompanying drawings. Show it:

• Figure 1 : a schematic perspective view of an embodiment of the ventilation device according to the invention;
• Figure 2 : a schematic perspective view of a first embodiment of the electrostatic filter unit according to the invention;
• Figure 3 : a schematic sectional view of the first embodiment of the filter unit;
• Figure 4 : a schematic perspective view of the ionization unit of the first embodiment of the filter unit;
• Figure 5 : a schematic rear view of the ionization unit of the first embodiment of the filter unit;
• Figure 6 : a schematic detailed view of part of the ionization unit Figure 5 ;
• Figure 7 : a schematic perspective rear view of the ionization unit Figure 5 without housing;
• Figure 8 : a schematic perspective view of part of an ionization element of the first embodiment of the filter unit; and
• Figure 9 : a schematic principle sketch of the ionization unit.

In Figure 1 an embodiment of a ventilation device 5 according to the invention is shown, which represents an extractor hood in the form of a ceiling ventilation. In the embodiment shown, the ventilation device 5 has a ventilation housing 50 and a baffle plate 51 located underneath, that is to say in front of the underside of the ventilation housing 50 in the flow direction. A suction opening 52 is formed between the underside of the ventilation housing 50 and the baffle plate 51, which can also be referred to as a suction gap. Several filter units 1 are introduced into the suction opening 52. In the view shown, two filter units 1 are installed over the width of the ventilation device 5 and one over the depth of the ventilation device 5. The ventilation device 5 is mounted above a hob 6 and can, for example, be accommodated in the ceiling (not shown), with at least the suction opening 52 being at least temporarily below the ceiling. Of the filter units 1 are in the Figure 1 only the protective grilles 10, which are attached to the front sides of the filter units 1, can be seen.

In Figure 2 a schematic perspective view of a first embodiment of the filter unit 1 according to the invention is shown. The filter unit 1 consists of an ionization unit 2 and a separation unit 3. The ionization unit 2 is in operation air flows in from the front. The direction of flow is in the Figure 2 indicated by the arrow S. The separation unit 3 follows the ionization unit 2 in the direction of flow. In the embodiment shown, the separation unit 3 has a housing 33. The ionization unit 2 also has a housing 23 in the embodiment shown. The housings 33, 23 each represent rectangular frames that are open to the front and rear. In the separation unit 3, precipitation electrodes 30, 31 are arranged alternately. In the embodiment shown, the precipitation electrodes 30, 31 are plate-shaped and arranged parallel to one another. The precipitation electrodes 30, 31 extend between the front of the separation unit 3 and the back of the separation unit 3. The precipitation electrodes 30, 31 extend over the entire width of the separation unit 3. However, it is also within the scope of the invention for the separation unit 3 to be designed differently is, for example, that the precipitation electrodes 30, 31 run perpendicular to the top and bottom of the housing 33 and are arranged parallel to one another in the width direction of the separation unit.

In the embodiment shown, the ionization unit 2 comprises an ionization element 28 and a counterelectrode 22. The counterelectrode 22 has a plate shape. The counter electrode 22 covers the front of the housing 23 of the ionization unit 2. Openings 220 are provided in the counter electrode 22 and have a round shape in the illustrated embodiment. The openings 220 are introduced into the counter electrode 22 in two rows one above the other. At each opening 220, an annular projection 221 is provided, which extends from the plate of the counter electrode 22 into the interior of the housing 23 perpendicular to the opening 220.

The ionization element 28 will now be described with reference to Figures 4 to 7 described in more detail. In the embodiment shown, the ionization element 28 consists of an ionization electrode frame 20, to which several ionization electrodes 21 are attached. The ionization electrode frame 20 has a connecting web 200 which extends in the width direction of the ionization unit 2. In the height direction lies the Connecting web 200 in the middle of the height of the ionization housing 23. From the connecting web 200, several fastening webs 201 extend upwards and downwards. The fastening webs 201 extend vertically from the connecting web 200 and each have a length that is less than half the height of the ionization housing 23. In particular, each of the connecting webs 200 has a length that corresponds to a quarter of the height of the ionization housing 23. An ionization electrode 21 is attached to the free end of each of the fastening webs 201. The ionization electrode 21 extends perpendicular to the fastening web 201 and perpendicular to the connecting web 200. In particular, each ionization electrode 21 is directed towards the front of the ionization unit 2 and runs parallel to the top and bottom of the housing 23. The ionization element 28 is on the inside of the top of the housing 23 attached. In particular, the connecting web 200 is attached to the top via insulators 24 which extend downwards from the top of the housing 23. The connecting web 200 can, for example, be clamped or locked into the free end of the insulator 24. In the embodiment shown, three insulators 24 are arranged distributed over the width of the housing 23. In addition, the insulators 24 shown have a ribbed surface, that is, a surface structure.

The shape of the ionization electrodes 21 is in Figure 8 shown in more detail. In particular, the ionization electrode 21 has a shaft 210, at one end of which the ionization electrode 21 is attached to the fastening web 201. In the embodiment shown, the ionization electrode 21 is guided through an opening at the free end of the fastening web 201. The tip 211 of the ionization electrode 21 lies at the opposite end of the shaft 210. The tip 211 has a conical shape that tapers from the shaft 210.

The ionization electrodes 21, which are attached to the fastening webs 201, extend in the direction of the counter electrode 22. In particular, the ionization electrodes 21 are arranged such that the tip 211 of the ionization electrode 21 extends into the opening 220 of the counter electrode 22. The top 211 each In the embodiment shown, ionization electrode 21 lies in the middle of circular opening 220 and is surrounded by tubular projection 221.

In Figure 9 the principle of the ionization unit 2 is shown schematically. In particular, it is shown here that the tip 211 of the ionization electrode 21 lies in the middle of the length of the tubular projection 221. An electric field F is formed between the tip 211 and the projection 211. In particular, the ionization takes place via a positive corona discharge by means of the needle-shaped ionization electrode 21. At the tip 211 of the ionization electrode 21, which can also be referred to as the needle tip, a corona discharge is formed between the ionization element and the negative counter electrode 22 when the electric field is increased . The particles in the air flowing through are charged in this ionization area and deposited on the precipitation electrodes 30, 31 in the downstream separation unit 3.

In order to apply the required voltage to the ionization element 28, the ionization element 28 must be connected to a high-voltage unit (not shown), that is, brought into contact with it. In the embodiment shown, the ionization element 28 has a contact point 202 for this purpose, which is provided at a longitudinal end of the connecting web 200. An insulating coating, which is provided on the ionization element, is left out at the contact point 202. In the illustrated embodiment, the contact point 202 is provided on a part of the connecting web 200 that is bent upwards and backwards at a longitudinal end. This bend brings the free end of the connecting web 200 close to the top of the housing 23 and the contacting can be made there. How out Figure 5 As a result, a passage for a contact 26, which extends upwards beyond the top of the housing 23, is provided in the top of the housing 23. The contact 26 can thus be connected on its underside to the contact point 202 of the ionization element 28 and the ionization element 28 can thus be connected to a high-voltage unit (not shown) via the contact 26.

Since the contact point 202 should preferably be protected from a direct flow of air and thus also particles, a partition 25 is provided in the housing 23 in the illustrated embodiment. The partition wall 25 is provided parallel to a side wall of the housing 23 near the side wall. A contact space 27 is thus formed between the side wall and the partition 25. A passage 250 is introduced into the partition 25, through which the ionization element 28 and in particular the ionization electrode frame 20 protrudes from the area of the housing 23 through which flow passes into the contact space 27. The contact 26 extends through the top of the housing 23 into the contact space 27. In addition, the bend of the connecting web 200 of the ionization electrode frame 20 lies in the contact space 27. At the passage 250 there is no mechanical contact between the partition 25 and the ionization electrode frame 20. This means that the size of the passage 250 is larger than the cross section of the ionization electrode frame 20, in particular of the connecting web 200 of the ionization electrode frame 20. In addition, a ribbed surface is provided on the passage 250, which is also referred to as a surface structure and over which the electrical creepage distance between the ionization element 28 and the counter electrode 22 is further extended. In the embodiment shown, the surface structure is formed by two concentrically arranged pipe sections on the passage 250.

In order to contact the counter electrode 22 with a high-voltage unit, in the illustrated embodiment a contact point 222 is provided on the upper edge of the plate-shaped counter electrode 22 near a side edge of the counter electrode 22. The side edge, near which the contact point 222 is located, faces away from the side edge of the counter electrode 22, on which the contact point 202 of the ionization element 28 lies behind the counter electrode 22. The contact point 222 on the counter electrode 22 can be connected to a contact 26 which extends through the top of the housing 23 and is accessible from the outside. The contact 26, which is to be connected to the contact point 222 of the counter electrode 22, lies opposite the contact 26, which is connected to the contact point 202 of the ionization element 28, on the other side edge of the housing 23. Although not shown, it can also be close the side wall of the housing 23, which is close to the contact point 222 of the counter electrode 22, a partition wall may be provided parallel to the side wall and thus a contact space for contacting the counter electrode 22 can be created in the housing.

In the embodiment shown, the housing 33 of the separation unit 3 and the housing 23 of the ionization unit 2 are separate housings, each consisting of a top and bottom, as well as two side walls. To connect the housings, in particular for releasably attaching the ionization housing 23 to the separation housing 33, 23 locking arms 230 are provided on the ionization housing 23, which extend backwards over the back of the ionization housing 23. These are particularly in the Figures 2 and 4 to recognize.

The invention is not limited to the embodiment shown in the figures. In particular, other forms of the ionization element, in particular the ionization electrode frame, and the counter electrode are also possible. However, it is essential that the ionization electrodes are needle-shaped and the tip of the ionization electrodes each lies in an opening in the counter electrode.

The present invention has a number of advantages over the prior art. In many known electrostatic filter devices, particle ionization occurs using thin tungsten ionization wires with a diameter of 0.1 < d < 0.25 mm. However, thin wires are susceptible to breakage under strong mechanical stress and can tear. Furthermore, it has been found that electrical insulation can only be implemented with increased effort because, for functional reasons, the ionization wire has to be kept bare, i.e. uninsulated, over an entire lateral surface. Especially when cooking, very large amounts of water can condense inside the extractor hood and inside the filter modules and electrical creepage distances can therefore form. Here, special requirements are placed on the electrical insulation properties to ensure the filter function. Another disadvantage of ionization wires is the fact that if the air has a high particle charge, the wire surface becomes contaminated (oil particles stick to the wire surface) and the wire can gum up over time if the wire is subjected to heavy cooking. In addition to thin wire ionization elements, there are known electrostatic ones Filter devices also sawtooth ionizers application. However, a disadvantage of these sawtooth ionizers is the high level of noise in the ionization area.

An advantage achieved by the present invention is that very good electrical tracking and short-circuit resistance can be achieved when exposed to water, dirt and moisture. This property is particularly pronounced in the embodiment in which the ionization element, which preferably consists of ionization electrode frames and ionization electrodes, is completely electrically insulated with the exception of the electrode tips and the contact point. A hydrophobic coating, for example a ceramic coating of the ionization element, also causes solid and liquid particles to roll off and drip from the surface of the ionization element.

The electrical creepage distance is additionally extended by a ribbed surface structure of the insulators to which the ionization element can be attached. Additional insulation elements such as ribs on the inner surfaces of the ionization housing, in particular on a partition wall to a contact space, also contribute to electrical tracking resistance.

In addition, the structure according to the invention has a robust construction in contrast to wire ionization elements. Even under heavy mechanical stress, there is no risk of the ionization element breaking or tearing.

Furthermore, the electrode tip causes a significantly higher field increase in contrast to an ionization wire with a radius r > 0, which leads to significantly larger electric field strengths in the corona area with the same ionization voltage Vi and consequently promotes field charging for particles with a diameter of > 1 µm.

Finally, the risk of contamination and resinification of the tip of the ionization electrode, which can also be referred to as the ionization tip, is reduced compared to wire ionization elements.

Reference symbols

1

Filter unit

10

Protective grille

2

Ionization unit

20

ionization electrode frame

200

connecting bridge

201

Fastening bridge

202

Contact point

21

ionization electrode

210

shaft

211

Great

22

counter electrode

220

opening

221

Got over

222

Contact point

23

Housing

230

Detent arm

24

insulator

25

partition wall

250

passage

26

Contact

27

Contact room

28

ionization element

3

Separation unit

30

deposition electrode

31

counter electrode

32

Contact

33

Housing

4

Contact room

5

Ventilation device

50

Ventilation housing

51

Baffle plate

52

Intake opening

6

hob

S

Direction of flow

F

electric field

Claims (10)

1. Electrostatic filter unit for a vapour extraction apparatus (5), which comprises an ionisation unit (2) with at least one ionisation element (28) and at least one counter-electrode (22) and a separation unit (3), wherein the counter-electrode (22) has at least one opening (220) and the ionisation element (28) comprises an ionisation electrode frame (20), which consists of electrically conductive material, and at least one needle-shaped ionisation electrode (21) with a tip (211), to which ionisation electrode frame (20) the ionisation electrode (21) is fastened, the ionisation electrode (21) is perpendicular to the opening (220) of the counter-electrode (22) and the tip (211) lies in the opening (220) of the counter-electrode (22), wherein
   the ionisation electrode frame (20) and the ionisation electrode (21) have an insulation coating, the coating is omitted on the tip (211) of the ionisation electrode (21) and at least one contact point (202) of the ionisation electrode frame (20) of the ionisation element (28), the ionisation unit (2) has a housing (23), in which the ionisation element (28) and the counter-electrode (22) are accommodated, the counter-electrode (22) is accommodated on the front side of the housing, the counter-electrode (22) has a platform and forms the front side of the ionisation unit (2), via which air enters into the ionisation unit (2).
2. Electrostatic filter unit according to claim 1, characterised in that the insulation coating represents a hydrophobic coating.
3. Electrostatic filter unit according to claim 1 or 2, characterised in that the ionisation element (28) is fastened to the housing (23) by means of at least one insulator (24) on the housing (23) and the insulator (24) has a ribbed surface.
4. Electrostatic filter unit according to one of claims 1 to 3, characterised in that the inner area of the housing (23) has a ribbed surface, at least in regions.
5. Electrostatic filter unit according to one of claims 1 to 4, characterised in that a tube-shaped protrusion (331) is formed on the opening (220).
6. Electrostatic filter unit according to one of claims 1 to 5, characterised in that the opening (220) in the counter-electrode (22) has a round or hexagonal cross-section.
7. Electrostatic filter unit according to one of claims 1 to 6, characterised in that the housing (23) of the ionisation unit (2) is embodied as separate from a separation housing (33) of the separation unit (3) and can be connected to the separation housing (33).
8. Electrostatic filter unit according to one of claims 1 to 7, characterised in that introduced in the housing (23) of the ionisation unit (2) is a dividing wall (25), which delimits a contact space (27) from the part of the housing (23) in which the ionisation electrode (21) is arranged.
9. Electrostatic filter unit according to one of claims 1 to 8, characterised in that the ionisation electrode frame (20) has a connecting web (200) and at least two fastening webs (201) branching off therefrom.
10. Vapour extraction apparatus, characterised in that it has at least one electrostatic filter element (1) according to one of claims 1 to 9.

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