EP0555676B1 - Exhaust hood and method for sucking off dust and mist - Google Patents

Description

The invention relates to an extractor hood according to the preamble of claim 1 and to a method according to the preamble of claim 9.

Basically, the problem with extractor hoods arises that the during operations, e.g. When cooking, the steam or vapor produced, which has only about half the air density, is greatly accelerated, so that the suction device installed above the work surface must suck in a vertically oriented turbulent free jet or a thermal upward flow. However, since within this upward flow after about half a meter of running distance from the haze source, speeds occur that significantly exceed the suction speed of the suction, a large part of the steam or haze breaks out into the environment.

The technical problem of such extractor hoods is that not only a turbulent but also an accelerated flow must be controlled to such an extent that it is extracted as completely as possible. This problem is currently solved by using very large detection hoods with screens protruding into the room, by increasing the blower output and / or by limiting the steam source laterally.

Furthermore, the use of additional blowing jets is proposed, which should either cover the rising steam from top to bottom as a fresh air curtain (e.g. DE-OSen 22 59 670, 19 63 456, 19 24 345, 16 04 293), or by the Blowing the front of the hood inwards either downwards or upwards to direct the steam to the rear suction surface (e.g. US Pat. Nos. 4,153,044, 4,127,106, 4,043,319, 3,513,766, DE-OS 25 31 862).

In the latter type, when using the blowing jets directed towards the suction surface, lateral partition walls are always used in order to spread the blowing jet and steam prevent. These partitions either reach down to the cooking surface or are concentrated on the area at the level of the suction surface, where they end with the protruding hood. The approach and the further course of the blow jet are always limited by these side walls.

The disadvantages of the prior art are that the cooking area is restricted by side wall boundaries, that a high noise level has to be accepted at high blower output, and / or that the hood is only of limited effectiveness if steam escapes in front of the hood, e.g. when handling or with strong steam generation. The blow jet itself is disturbed so far that it remains ineffective over a long period of time.

Furthermore, a generic extractor hood is known from DE-OS 37 18 686, which has an additional fan with a blow-out nozzle arranged on the underside of the hood for generating a horizontal air flow, which entrains the air rising from the stove, containing odors and cooking vapor into the filter. Means for generating a helical flow cannot be derived from this.

DE-A-3 918 870 describes a method and a device for extracting vapors and vapors.

From DE-GM 83 11 557 an exhaust and supply air device for a hotplate is known, in which, in addition to the exhaust air in the extractor conveying fans, roller-shaped cross-flow fans are provided along edge regions of the open housing underside, and in which the supply air is supplied by means of these cross-flow fans downward slit nozzles is supplied as an air curtain. The skilled person is hereby given no teaching about the type of flow, in particular the teaching of a helical flow is not imparted to him.

The object of the invention is to remedy these disadvantages and to concentrate the rising steam with the hoods open at the side, and the noise level of the blower by lowering it To reduce blower performance significantly and to hinder the wall blowing jet as little as possible by the rising steam.

According to the invention, this is achieved with the features of the characterizing part of claim 1 or of claim 9. Further embodiments of the invention are the subject of the dependent claims.

A helical or helical vortex structure within the blowing jets used is highly inherently stable. In the case of a convective boundary layer, e.g. on the underside of an extractor hood, this type of flow can not only integrate the individual convective elements, but also reinforce itself. In addition, the turbulent friction is lower in such a flow.

The individual counter-rotating vortex rollers can be connected via a respectively rotated by 90 ^o rolling eddy further, so that so that a U-shaped or horseshoe-shaped swirl is formed structure, which can correspond to the respective spatial conditions. This results in an additional stabilization of the connected vortex rollers.

A helical or helical flow is achieved in that the free blowing cross section of the nozzle has narrowing and widening across the cross section, for example in the form of a comb gap, through which the free blowing air is blown out from the front blowing nozzle to the rear suction device. The elevations and depressions or corresponding elements of the comb gap are narrowed at regular or almost regular intervals. In the case of the (two-dimensional) case, which is unlimited to the left and right, the optimal case is that the width of the depressions is equal to the width of the elevations and the vortex diameter corresponds to the width of the depressions.

In the case of a double slit nozzle with a slit opening in the horizontal direction for the wall jet and a separate slit for the outlet of the supply air approximately vertically downward, a roll vortex is created below the double nozzle, the direction of rotation of which in the sense of air deflection, e.g. runs clockwise. If the gap forming the horizontal jet is made wider than the gap forming the vertical jet within this double-gap nozzle, a horizontally extending jet, in particular a wall-blowing jet, is formed independently of the roll vortex below the nozzle.

A flat wall-blowing jet flows apart with the free jet angle O = 14 ^o . In order to prevent this, a deflection or guiding device is used, which is designed, for example, in the form of two triangular plate-like elevations formed at the opposite corner points of the front of the extractor hood. The thickness of the plates is several times the gap thickness. The acute angle of the right-angled triangle of the deflection devices is in the order of magnitude of the free jet angle. The deflecting device directs the jet inwards on both sides and imparts edge vortices to the jet acting as a wall jet.

The flow configuration due to the helical flow, the roll vortex and the edge vortex can be used individually or in combination. If a hotplate is between two walls, e.g. in a kitchen unit of a large kitchen, a blow jet is combined with the roll vortex as a leading edge vortex, which limits the vapor outlet at the front. This vortex acts as a border vortex.

In the case of a basin with evaporable liquid, a helical flow instead of a flat free jet enables a lower blower output, less turbulence and thus less mixing, ie better Extraction and, as a result, higher purity of the ambient air. These two applications are essentially two-dimensional suction problems.

When vacuuming over a stove isolated in a kitchen unit, the steam can escape both to the side and to the front. A corresponding comb-blowing nozzle with two lateral deflection devices generates a leading edge vortex and two lateral vertebrae, that is to say a circumferential border vortex, and inner vertebrae. The wall-blowing jet can be oriented horizontally or somewhat inclined. It is delimited at the top by the extractor hood and has a helical structure consisting of several vortex rollers, each rotating against each other. The flow is particularly stable due to this helicity and the double U-vortex structure. In the interior of the flow, the rising convective vapor elements are braked by the opposite direction of rotation of the inner vortex, while a backflow takes place on the outside. If haze nevertheless comes out, this haze is transported inwards by the boundary vortices composed of the side and front edge vortices and integrated into the helical flow. The extractor hood has two fans, one of which is intended for suction and the other for blowing, the ratio of suction volume flow to blowing volume flow being approximately 5: 1.

Fig. 1

eine Prinzipdarstellung einer helikalen Strömung,

Fig. 2

eine Prinzipdarstellung einer U-förmigen bzw. hufeisenförmigen Wirbelströmung,

Fig. 3

eine Schemadarstellung einer Helikalströmung mit Hilfe einer Ausblasung durch einen Kammspalt,

Fig. 4

eine Schemadarstellung einer Anordnung zur Erzeugung eines Rollwirbels und eines Wandstrahls mit Doppelstrahldüse,

Fig. 5

eine Prinzipdarstellung eines ebenen Freistrahls an einer Wand mit Randwirbeln,

Fig. 6

eine vergrößerte Darstellung eines Umlenkelementes in Aufsicht,

Fig. 7

eine vergrößerte Darstellung des Umlenkelementes nach Fig. 6 in Frontansicht,

Fig. 8

eine schematische Darstellung der Ausbildung des Vorderkantenwirbels,

Fig. 9

eine Prinzipdarstellung einer erfindungsgemäßen Dunstabzugshaube, wobei die Strömungsstruktur mit Umlenkelementen und Kammspalten gezeigt ist, und

Fig. 10

eine Schnittansicht einer speziellen Ausführungsform einer erfindungsgemäßen Dunstabzugshaube.

The invention is explained below in connection with the drawing using exemplary embodiments. It shows:

Fig. 1

a schematic diagram of a helical flow,

Fig. 2

a schematic representation of a U-shaped or horseshoe-shaped vortex flow,

Fig. 3

a schematic representation of a helical flow with the aid of a blow-out through a comb gap,

Fig. 4

2 shows a schematic representation of an arrangement for producing a roll vortex and a wall jet with a double jet nozzle,

Fig. 5

a schematic diagram of a flat free jet on a wall with vertebrae,

Fig. 6

an enlarged view of a deflecting element in supervision,

Fig. 7

6 shows an enlarged illustration of the deflection element according to FIG. 6 in a front view,

Fig. 8

1 shows a schematic representation of the formation of the leading edge vertebra,

Fig. 9

a schematic diagram of an extractor hood according to the invention, the flow structure is shown with deflection elements and comb gaps, and

Fig. 10

a sectional view of a special embodiment of an extractor hood according to the invention.

The basic illustration in FIG. 1 shows four flows arranged in parallel next to one another and directed helically from right to left, each of which two adjacent flows have different directions of rotation; this basic illustration is shown in connection with a coordinate cross xyz. The four parallel flows are designated 1, 2, 3 and 4.

2 shows two of these parallel flows 2, 3 with swirling rolls rotating in the opposite direction with a roll swirl 5 offset by 90 ° to both, so that in principle a U-shaped or horseshoe-shaped roll swirl 6 with a corresponding swirl flow 7 represented by arrows arises.

3, the blowing nozzle 8 is shown in cross section. The upper limit 9 of the blow nozzle is drawn in a meandering shape with depressions 10 and elevations 11 which merge into one another and alternate with one another. The opposite limitation of the gap of the blowing nozzle 8 is designated 12. The helical flow 2-4 is designed in the manner shown in FIG. 1. The axis 13 of the respective vortices running parallel to one another lies in the direction of the axis 13 of the blowing jet or in the blowing direction. The free blowing cross section of the nozzle is designated 14. The depressions 10 have a width d _s , the elevations 11 have a width d _b (applies to the two-dimensional case as the optimum), d _w = d _s applies to the vortex diameter.

4 shows an embodiment of the front section of the extractor hood with a double slit nozzle 15. 16 denotes the front boundary wall of the extractor hood, 17 the top of the hood, 18 the boundary wall (together with 17) of the air duct, 19, 20 the bottom wall and 21 a deflection wall for the supply air flow to the double-gap nozzle 15. The horizontal gap 22 of the nozzle 15 has between the bottom wall 20 and wall 23 running parallel thereto, a gap spacing s _x , while the vertical gap 24 with the gap spacing s _{z is formed} by the end face of the wall 23 and the inside of the front boundary wall 16. Arrow 25 indicates the direction of the supply air, arrow 26 the direction of the wall jet and arrow 27 the exit direction of the air flow which forms the roll vortex 28. The wall blowing jet 26 flows along the outer surface of the hood bottom wall 20 at an angle Θ backward to the suction surface, while the roll vortex 28 prevents the escape of haze and the air flow of the roll vortex introduces the rising haze in the direction of the wall jet into the latter.

The arrangement of the deflection device and the formation of the edge vortices when the air flow is detached from the deflection device is shown schematically in a top view in FIG. 5. The vertical front wall 29 of the hood has deflection elements 30, 31 arranged at the two corners in the blowing direction, which are wedge-shaped and whose hypotenuses are directed obliquely inwards. The wall-blowing jet 32 is deflected inward by the surfaces of the deflection elements 30 and 31 in the direction of the arrow 33, then detaches itself from the elements 30 and 31 and forms a left and a right edge vortex as the vortex jet 34. The deflection elements 30, 31 are shown in more detail in FIGS. 6 and 7, FIG. 6 showing the top view and FIG. 7 the front view of the element 31. 35 here denotes the outer boundary and 36 the obliquely inward deflection surface, the surfaces 35 and 36 forming a deflection angle O _u with one another. The thickness of the deflection elements 30, 31 is denoted by D in FIG. 7, the distance of the blow gap by d _x , where: $${\text{D = (3-4) d}}_{\text{x}}\text{.}$$

The formation of the leading edge vortex 37 and its influence on the flow rising from the steam source and removed by the suction device is shown in FIG. 8. The suction is carried out with the help of the wall-blowing jet and the front edge vortex between two lateral boundaries, which are formed by the side vortex.

In the representation according to FIG. 9, the extractor hood is indicated by 38 in a schematic, perspective representation. On the front of the hood, 39, 40 represent the comb splitting tines and 41, 42 the deflection devices. The helical flows 43, 44, 45, 46 run in the direction of the wall-blowing jet from the front of the hood 47 to the rear of the hood 48. The helical vortices are indicated by arrows, two adjacent vortices each having a different direction of rotation. Furthermore, the helical flows 43 to 46 are coupled to one another by crossflow vortices 49, so that the helical vortices 43 and 46 limit the lateral limitation of the vapor flow and the transverse vortices 49 limit the front side of the vapor flow.

An embodiment of the extractor hood according to the invention is shown in section in FIG. 10 at 50. The hood part housing 51 receives a radial fan 52 that one Extraction filter 53 is assigned to the bottom of the hood 50. The second hood part housing 54 has a cross-flow fan 55, which supplies air flow in the direction of the arrow through the channel 56 to the blowing nozzle 57 at the front, lower hood end. The inflow gap of this blowing nozzle with the gap distance S1 is designated 58, the wall-blowing jet gap with the gap distance S3 with 59 and the roll vortex gap with the gap distance S2 with 60.

Claims (12)

1. Exhaust hood for use over a cooker, source of dust or fumes, having a suction fan, a filter means, air guides and an additional fan with a blast nozzle located on the underside of the hood for producing a horizontal wall blast jet directed from the front hood edge to the suction surface or towards the filter and which sucks the flow of fumes and entrains them to the suction surface, characterized in that blowing devices (8, 10, 11, 12, 16-23; 30, 31; 41, 42; 60) are located in the vicinity of the blast nozzle (15; 57), which produce in the wall blast jet spiral helical flow eddies blown towards the suction device in parallel and rotating in alternately opposite directions towards the wall blast jet.
2. Exhaust hood according to claim 1, characterized in that the additional fan (55) is a crossflow fan at the inlet to an air duct (57), at whose outlet is located the blast nozzle (57).
3. Exhaust hood according to claim 1 or 2, characterized in that the blast nozzle (57) is constructed on the front, lower hood edge (59), which produces the air blast as a wall jet, as a comb slot (8), which produces helical flow eddies in the direction of the wall jet.
4. Exhaust hood according to claim 3, characterized in that the comb slot (8) has a planar construction on one surface (10) and a meandering construction (11, 12) on the opposite, slot-forming surface (9), the meandering construction (11, 12) being provided on the underside of the exhaust hood base (20).
5. Exhaust hood according to one of the claims 1 to 4, characterized in that a device (15; 57, 58, 60) is constructed for forming a rolling eddy (28) on the leading edge of the exhaust hood in the form of a double slot nozzle (15, 57).
6. Exhaust hood according to claim 5, characterized in that the double slot nozzle has a larger slot (S3) parallel to the base side of the exhaust hood and a smaller slot (S2) at right angles thereto and in the vertical direction.
7. Exhaust hood according to one of the claims 1 to 6, characterized in that a device (41, 42) is provided for limiting the lateral edge of the wall blast jet and which comprises two facing guide elements (41, 42) on both lateral nozzles, which can be constructed on facing sides in inwardly and rearwardly inclined manner into the exhaust hood.
8. Exhaust hood according to claim 3 and 5 or one of the following claims, characterized in that the helical flow as a result of the comb slot (8) and the rolling eddy with wall jet as a result of the double slot nozzle (15, 57) are combined in the exhaust hood, the helical flow due to the comb slot (8), the rolling eddy and wall jet due to the double slot nozzle (15, 57) and the edge eddy due to the deflecting means (41, 42) being combined.
9. Method for sucking up dust or fumes by means of an exhaust hood positioned above a cooker, dust or fumes source, in which by means of the suction fan air is guided by means of an air guide within the hood to the front, lower hood edge and by means of a blast nozzle in the form of a wall blast jet on the hood base to the suction device, characterized in that in the vicinity of the blast jet are produced spiral, helical flow eddies blown in parallel to one another to the suction device in alternating oppositely rotating manner in the direction of the wall blast jet.
10. Method according to claim 9, characterized in that in each case two adjacent helical flow eddies are combined on the front, lower exhaust edge by a cross-eddy flow to give a U-shaped flow eddy, which is in particular horseshoeshaped.
11. Method according to claim 9 or 10, characterized in that on the front, lower exhaust edge the blast nozzle produces over the hood width downwardly and inwardly directed rolling eddies, particularly leading edge eddies.
12. Method according to claim 9, 10 or 11, characterized in that below the lateral face of the hood are produced lateral eddies, which bound the further inwardly located eddies, that the lateral eddies are produced in that the wall blast jet on the front lower hood end is directed over a short distance in inwardly inclined manner and that the lateral eddies are produced by the separation of the air flow from said guides.

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