DE3304262A1 - AIR-CONDUCTED HOOD AND METHOD FOR THEIR OPERATION - Google Patents

Abstract

1. Fume extraction hood with air circulation having longitudinal blow-out slots (7, 8 ; 24), which operates in connection with a working surface and which is provided above a kitchen stove (1) or a similar dust or fume source, with which by means of a hood fan (5) with filter (3) the fume is exhausted from the fume source (1) and is discharged within the hood through air passages (4, 6, 7, 8) for being discharged from the hood in order to be reabsorbed and further purified, and with which an air curtain (11) is generated by the lower peripheral rim, which restricts the fume flow, which extends downwardly and outwardly in an inclined manner, and which prevents the fume flow from escaping from the area above the fume source outwardly, characterized in that the air curtain on at least two opposite free lateral surfaces or on all free lateral surfaces is downwardly directed in the form of locally plane free jets (11) in an angle of about 10-15 degrees towards the edge of the working surface in such a manner that the air curtain when hitting the working surface forms a ram line (12) and the inwardly directed air flow is introduced into the suction area (10) as a dynamic updraft flow (13), whereby the speed of the updraft flow is a multiple of the speed of the suction flow at the introduction area.

Description

Dipl.-Ing. A. Wasmeier

Dipl.-Ing. H. Graf

Admitted to the European Patent Office · Professional Representatives before the European Patent Office Patent Attorneys P.O. Box 382 8400 Regensburg 1

To the

German Patent Office Zueibrückenstrasse 12

SDOO Munich 2 D-8400 REGENSBURG GREFLINGER STRASSE Telephone (09 41) 547 Telegram Begpatent Rgb. Telex 6 5709 repat d

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Day date

B. February 19Θ3 uj / ly

Applicant Hannelore Röhl-Hager
Schöneberger Strasse 18

BkOO Regensburg

Title:

Recirculating air extractor hoods also know how to operate them

Inventor applicant

Accounts: Bayerische Vereinsbank (bank code 750 20073) 5 839 place of jurisdiction Regensburg

Uml-uf t-extractor hood as well as the method for operating it

The invention relates to a method of operation a circulating air extractor hood according to the preamble of the claim 1 as well as a circulating air extractor hood according to the Preamble of claim 2. Such a circulating air extractor hood \ i / ird in connection with kitchen stoves, hobs, or other sources of vapor and dust.

For the removal of vapors, plastics, dust or other Pollutants are found in kitchens or other, e.g. commercial Workrooms, over the stoves or cooking areas or over the Dust and pollutant sources. Extractor hoods provided. These Extractor hoods are equipped with filters on suction fans and air ducts and blow when there is no air extraction duct. the filtered air through one or more exhaust openings back to the work area. This operation is referred to as recirculation mode.

With the well-known UmIu f extractor hoods, the filtered Air through a circulating air opening in the hood housing, which is usually pointing diagonally upwards, blown into the work area. The area of the suction filter, which is usually upstream of the fan is approx. 20 - 30 times the air circulation opening. A delivery volume of up to 500 cbm / h is required of the intake fan, which naturally produces a considerable flow noise caused. The tendency with such hoods is in the direction of even higher conveying volumes.

Since the degree of separation of filters is never 100 % , the unfiltered air pollutants are blown back into the working area with such air hoods. If it is insufficient

Filter separation efficiency can therefore be achieved by the ventilation hood as a result of the forced rapid circulation of the barely air an accelerated one Dun «exchange spreading result.

Dn is approximately the inflow velocity ν to the extractor hood depends on the square of the distance r from the suction surface (v ^ 1 / r ^), a very high air flow is necessary so that rapidly rising haze particles from the suction flow in the hoods are taken with you. Another increase in However, fan power is not acceptable due to noise, so that a significant part of the conventional hoods Haze can escape directly into the surrounding work area.

These disadvantages are partly due to the creation of an air curtain between the extractor hood and the earthen surface. For example, DE-QS 22 59 670 refers to an exhaust air hood Air curtain in which the air extracted from the stove is partially is discharged into the open via a flue duct and a pressure chamber kept under overpressure by the suction fan Veil radiator that feeds the part of the Supply air (or at least part of it) due to the overpressure directed downwards to the stove top surface. The air curtain is drawn inwards and upwards by the suction of the supply air taken away. The fan must be so strong that the air curtain reaches at least up to the top of the stove, around his Blocking function to meet ion, and that at the same time the pressure chamber is maintained under such a high pressure that the air curtain is formed. The fan sucks in the supply air flow (haze over the stove surface) and leads this supply air to a considerable extent through the exhaust opening into the open air. With this well-known There are a large number of exhaust hoods with air curtains on the edge of the hood of holes provided, which in their entirety have a shell-shaped Create air curtains on three sides of the cooker. The one created through these holes; Air curtain consists of a large number of parallel, round free jets. The flow energy of the air curtain

330A262

becomes approximately equal to 0 at the level of the hearth surface, so that the Suction through the fan a deflection to and a Upward movement results together with the influx. The speed the inflow with the curtain air is therefore determined exclusively by the suction power of the blower The fan output of this exhaust air hood is very high, i. H. that a large amount of air circulated and thereby inevitably a strong noise has to be accepted.

The object of the invention is to provide a recirculation hood with the lowest possible fan power or delivery rate and as large as possible To achieve effectiveness, the hood in particular with essential lower height than known, comparable hoods to be able to keep the flow noise in comparison to known hoods much lower, which is to be cleaned To circulate air faster than before, and to prevent primary vapor from escaping from the intake area into the work area impede.

According to the invention, this is in a method of the generic type Kind with the features of the characterizing part of claim 1 or in the case of a generic extractor hood achieved with the features of the characterizing part of claim 2. Further embodiments of the invention are the subject of Subclaims.

With the method according to the invention or with the method according to the invention Circulating air extractor hood, the suction effect of the fan is significantly supported, so that the fan power can be kept extremely ciering and the flow noise due to the lower air flow can be reduced so far that the operation of the hood occurring noise is no longer perceived as annoying. With the additional upflow and the support of the Suction of the fan is also achieved that the Exhaust air that forms upflow with its residual vapor does not enter the

Kitchen area, but I take over the stove and I do it additional vapor upwards into the suction surface of the hood roars. A major advantage of the invention is in particular also seen in the fact that the blower to be promoted Air volume only within the hood - source of vapor is circulated so that apart from the achievable thereby a much smaller amount of air, which is uin / uM / älzen extremely short amount of air to be circulated is reached, which means that a precisely defined and particularly effective recirculation is achieved takes place.

Essential for the flawless operation of the recirculating air extractor hood according to the invention, d ρ Β to generate the Air curtain the air through flat elongated slots instead through a series of small holes, as in the case of DE-OS 22 59 670 is blown out. A flat elongated slot creates a flat free jet, while a row of holes creates a series of round free rays. The free jet theory (reference H. Schlichting, Boundary Layer Theory, Verlag G. Braun, Karlsruhe) says that the plane free jet compared to. round free jets is slowed down less quickly because the flat free jet has a lower friction surface than the round free jet. The following applies to the speed curve:

For the plane free jet we have u (x) The following applies to the round free jet

Here, χ is the distance from the flow location, d is the height of the slot or the hole diameter, U _{0 is} the speed at the point χ = 0, and u (x) is the speed at a distance χ from the slot b? W. of the holes in each case along the beam axis.

'3-To understand the formation of the dynamic upflow and its speed in comparison with the inflow speed to a Sauqöf fnunqvi / i r d below briefly on the Theory received.

The dynamic upflow forms between two free jets which are blown vertically onto a flat surface (Reference H. Hertel "Wall currents and up currents from the redirection of free jet groups "progress reports VDI magazine, series 12, no.11, July 1966), see figure The outflow velocity u / \ is proportional to the free jet velocity u (x) at the storage area, i.e. u / \ = k u (x). The inflow to a suction surface takes place from the entire surrounding space. The inflow velocity uc; (x) increases with the Distance χ decreases rapidly (Figure 7).

An estimate of the upstream velocity ratio U ^ to suction speed ut; results in:

On flow velocity u / \ = k χ u (x)

k r- 0.5 means u ^ - half speed in the free jet, where k = empirical factor

For u (x) fm plane free jet applies (reference H. Schlichting "Boundary Layer Theory"):

whereby

U ₀ = blowing speed, h = slot width, l = slot length For Uß the following results:

because U ₀ = - ~ -, where V = air flow rate

* AF _A = exhaust air slot area =

Roman speed

The following applies to the inflow velocity to a suction surface (Literature reference W. Pfeiffer, exhaust air volumes from detection Open-plan facilities, dust-clean. Luft (1982) No. 8, Pages 303 - 308):

ι. _Ä * / t ~ S where F ₃ = suction area

+ - IO - * Vf ^, y _ Air flow rate

χ = distance speed ratio u ^ / ug:

_ η-μ

This equation shows that the liability to pay with the The ratio of suction to exhaust area increases. Decisive int, however, that the objectivity ratio increases with increasing Distance between the storage area χ increases significantly. This results from the fact that the suction speed U5 decreases with 1 / χ2, u / while the current velocity u ^ only decreases with / | f! \. This is shown using a numerical example that is typical for use with extractor hoods:

Area ratio FS / r A = ¹ 0 Entrance area ^F £ = 0.1 m ² distance X = 0.6 m Slot width H 0.01 m Empirical factor k = 0.5 Upstream velocities it u _A

Suction speed ucj \ & O

From this numerical example it follows that the dynamic upflow unites above the hearth? Speed towards the Extractor hood supplies that is 4 6 times larger than the pure one Suction flow. Even if the upstream speed is just that Should be 10 times the suction speed the up-current effect, the suction effect very decisive, so that the effect that can be achieved with the invention is extraordinarily large is.

The invention is described below in conjunction with the drawing explained on the basis of exemplary embodiments. It shows:

Fig. 1 is a cross-sectional view along the line I - I of the figure 2 an extractor hood according to the invention with an indicated stove, in a schematic representation

Fig. 2 is a longitudinal sectional view along the line II - II of Figure 1 through the hood according to Figure 1 in a schematic representation,

3 is a cross-sectional view in a representation similar to according to Figure 1 of a further embodiment of a Extractor hood with pull-out screen, in schematic Depiction ,

A shows a detail from the illustration according to FIG. 3 in enlarged scale,

Fig. 5 is a schematic representation of the speed profile in a flat free jet,

6 shows a schematic representation of the formation of the dynamic upflow between two free jets,

7 shows a schematic representation of the intake flow.

r

Above a need; Cooker L b / w. ei nor hotplate or one The source of haze is the extractor hood 2 at the normal working distance arranged. Via a filter 3, the suction flow 10 is the Suction chamber 4 of the hood 2 and the fan 5 are supplied. The fan conveys the filtered air into the pressure chamber 6. Off the pressure chamber 6 of the hood 2 is the air at the lower outer peripheral edge of the hood through a front exhaust slot 7 as well as by two lateral blow-out slots 8 downwards against the stove 1 blown.

The area of the blow-out slots 8 is a special one Embodiment of the invention about 1/10 of the suction area of the Filters 3. The inclination of the blow-out slots 8 is chosen so that that the blow-out jet 11, which spreads according to the free jet theory, when it hits the work surface of the kitchen range a stowage line 12 forms which the hob area encloses. Within this stagnation line that is shown in the sectional drawings According to Figures 1-3 is visible as a stagnation point, the upstream 13 is formed, which the suction effect of the Fan significantly supported. The divides at the congestion line Blow-out mass flow into a portion I,. the one in the upstream again is fed to the hood, and in the portion II, which gets into the work space, but which is due to the suction effect of the The area of the cooker or the source of haze leaves and continuously in the recirculation mode again Upstream is added.

Fig. 3 shows an embodiment of the invention in which on the Hood 14, a screen 15 which can be pulled out to the front is arranged. At the lower, front edge of the hood; 14 is a blow-out slot 16 is provided, the front blowout flow 17 in the area of Screen 15 aimed at the underside of the screen. Due to the Coanda effect, a wall jet 18 is formed, in the exhaust air from the underside of the umbrella up to the front edge de: s of the umbrella and adjoining the underside, and the umbrella at its front edge as a free jet downwards

-Away ·

leaves to the stove. This is preferably done in the example shown in FIG. 4 illustrated way. The flowing out of the fan 19 Air flow 20 passes through the air duct 21 downwards onto a deflection and baffle surface 22 which forms the air flow 20 deflects and as a wall jet 23 through the blow-out slot 16 against the underside of the screen 15 and along its surface up to the separation edge 24 and then downwards as a free jet 17 directed against the stove 1.

The schematic graphic representations according to FIGS. 5, 6 and 7 are in connection with the theoretical explanations to read further above and do not require a detailed explanation at this point.

Claims (9)

■■■■ * - ■■ Claims Procedure for operating a recirculating air extractor hood for use over a hotplate or a corresponding source of dust or haze, with the help of a hood fan With a filter, the haze is extracted from the source of the haze and in.the hood via air ducts for renewed suction and further cleaning is released again from the hood, and the one from the lower peripheral edge of the hood An air curtain that limits the vapor flow is generated Escape of the vapor stream from the area above the Prevents source of vapor to the outside, characterized in that the air curtain has elongated slots in the form of locally flat free jets or in the form of a flat free jet downwards onto the edge of the work surface is directed that the air curtain is inclined at a small angle to the vertical from the slots obliquely downwards and blown outside that the air curtain from the Point of impact on the work surface distracted at the Work surface pent up, and the ngch internally diverted part as a dynamic upflow (fountain effect) into the intake flow is introduced, the flow velocity of the upstream being a multiple of the flow velocity of the suction flow is at the insertion point. 2. Attachable or suspendable to the wall or ceiling Circulating air extractor hood for use over a hob or a corresponding source of dust or haze an intake fan, a filter assembly, a hood fan with air ducts and a device for generating an air curtain directed downwards from the hood, which prevents the outflow or escape of the through the fan of completely or at least partially prevents the haze drawn in from the source of the haze, characterized in that the lower edge of the hood on the Sides of the hood (2; 14) which are not closed at the bottom by the surrounding walls, elongated blow-out slots (7; 24), through which the fan (5; 19) a local, flat free jet (11; 17) downwards directs that the dimensions of the extractor hood (2) in their projection in their on the work surface of the source of vapor (1) are smaller than that of the work surface so that the plane of the blow-out slots (7; 24) is slightly inclined towards the outside is employed in such a way that the exiting flat jets hit the edge of the work surface of the source of vapor (1) are directed and thus form a congestion line (12) on the work surface, and that the speed of the dynamic upflow (13) (deflected blowout jet in Towards the hood) a multiple of the speed of the Suction flow (10) is on the work surface. 3. Circulating air extractor hood according to claim 2, characterized in that the plane of the blow-out slots (7, 8; 24) is inclined at an angle of approximately 10-15 ° with respect to the plane of the work surface (1). 4. circulating air extractor hood according to claim 2 or 3, characterized characterized in that the congestion line (12) in the immediate vicinity the edge of the work surface along the side edges and the The front edge of the working surface of the vapor source (1) is formed j s t. 5. Circulating air extractor hood according to one of claims 2 to 4, characterized in that the area ratio of Blow-out slots (7; 24) to the total suction area about 1:10 is, or that the area ratio of the entrance area to the outlet area of the extractor hood is 1:10. 6. circulating air extractor hood according to one of claims 2 to 5, characterized in that the speed of the blow-out jet (11) at least ten times the speed the intake flow is (10). 7. Circulating air extractor hood according to one of claims 2 to 6, characterized in that the flow velocity of the upstream (13) is at least ten times the velocity the intake flow (10). 8. Circulating air extractor hood according to one of claims 2 to 8, characterized in that the extractor hood (14) has a known pull-out screen (15) that in Channel (21) of the fan (19) a deflection and impact device (22) is arranged, which the fan (19) generated flow (20) directed against the lower surface of the screen (15), and that the flow (23) due to the Coanda effect along the underside of the screen (15) the separation edge (24) and as a free jet (17) downwards is directed towards the work surface. 9. circulating air extractor hood according to claim 8, characterized in that that the deflection and impact device (22) is slightly inclined relative to the horizontal and against the Underside of the screen (15) is directional plate.