EP3562601B1 - Laboratory fume hood having guided wall and/or bottom jets - Google Patents

Description

The present invention relates to a laboratory hood, in particular to a flow-optimized and energy-efficient laboratory hood.

Saving energy is not only environmentally friendly, but also lowers the sometimes very high operating costs of a modern laboratory room, in which dozens of fume cupboards can be installed under certain circumstances, each of which is operated 24 hours a day and 7 days a week. However, the most important property of modern fume cupboards is that they enable the safe handling of toxic substances and prevent the escape of these substances from the working area of the fume cupboard. The degree of this safety is also referred to as the retention capacity. For this purpose, a detailed series of standards "EN14175 Part 1 to Part 7" has been published in which, among other things, the influence of dynamic air flows on the retention capacity is described. Many developments in the field of fume hoods therefore concern the question of how the energy consumption of such fume hoods can be reduced without adversely affecting the containment capacity.

As early as the 1950s, attempts were made to improve the escape security of laboratory fume cupboards by using an air curtain. This air curtain is generated with the help of air outlet nozzles provided on the side walls of the working area of the fume hood in the area of the front sash opening and is intended to prevent the escape of any toxic vapors from the working area ( U.S. 2,702,505 A ).

In EP 0 486 971 A1 it was proposed to provide so-called baffles ("air foil") on the front edge of the side posts and the front edge of the worktop, the contour of which is flow-optimized. Through these baffles it is said to be the teaching of EP 0 486 971 A1 As a result, when the front sash is open, there is less detachment of the inflowing room air on the inflow surface of the baffle plates and thus less turbulence. However, an area remains behind these baffles in which turbulence can occur, since the inflowing room air can separate at the downstream end of the baffles. This effect is amplified when room air enters the fume cupboard at an angle to the side walls.

In GB 2 336 667 A Containment has been further improved by providing airfoils at a distance from the front edge of the worktop and side jambs so that room air can enter the hood interior not only along the airfoils but also through the gap between the profiles and the front edge of the worktop on the one hand and the side post on the other hand, mostly funnel-shaped gap. The room air is accelerated in the funnel-shaped gap, so that the speed profile of the exhaust air is increased in the area of the side walls and the worktop.

Another milestone in increasing the security against escapes while at the same time reducing the energy requirement of a laboratory fume hood was achieved through the optimized supply of so-called supporting jets. Due to the fact that hollow profiles are provided both on the front edge of the worktop and on the front faces of the side posts, compressed air could be fed into the cavity of these profiles and blown into the work space in the form of compressed air jets through openings provided on the hollow profiles. The advantage of this is that the support jets, consisting of compressed air, enter the working space of the fume hood along the side walls and along the worktop, i.e. along areas that are critical in terms of risk of turbulence (backflow areas) and can therefore adversely affect the retention capacity . The effect of the compressed air jets in the area of the side walls and the floor of the work area is diverse. They not only prevent flow separation of the incoming room air at the downstream end of the hollow profiles, but also reduce any wall friction effects, so that there can be significantly less turbulence and thus backflow areas in these areas. The room air entering the work space glides, so to speak, on a dynamic, rearward-moving air cushion along the walls and the worktop into the rear area of the work space, where it is extracted. At first glance, this seems contradictory, because the provision of compressed air jets costs additional energy. However, this has a positive effect on the overall energy balance of the fume hood, since the air velocity in the other areas of the interior of the fume hood can be reduced without adversely affecting the retention capacity. These support jets made it possible to significantly reduce the minimum amount of exhaust air at which the escape safety of the fume hood still meets the standardized regulations when the sash is partially or fully open. An example of a fume hood equipped with support jet technology is in DE 101 46 000 A1 , EP 1 444 057 B1 and US 9,266,154 B2 described.

The document DE 101 46 000 A1 discloses a trigger according to the preamble of claim 1 or claim 2.

The inventors of the present invention were able to observe for the first time in fume cupboards equipped with conventional support jet technology that, contrary to previous investigations with fog, in which no significant flow separation of the wall jets could be detected, when investigating the flow field of the wall jets using PIV measurements ("Particle Image Velocimetry" measurements) a flow separation already occurs a relatively short distance behind the level of the sash and consequently dangerous backflow areas can develop on the side walls.

The main goal pursued with the present invention is therefore primarily to further improve the escape security of a fume hood equipped with support jet technology and at the same time to further reduce its energy consumption.

This object is solved by the features of patent claims 1 and 2. Optional or preferred features of the invention are specified in the dependent patent claims.

On the one hand, the invention provides, according to claim 1, a fume cupboard for a laboratory space which has a housing in which there is a work space which is delimited at the front by a sash, at the bottom by a base plate and at the sides by a side wall. The fume hood further comprises a first hollow profile arranged on a front end face of each side wall, each first hollow profile having a first pressure chamber which is fluidly connected to a plurality of first openings from which air jets in the form of wall jets consisting of compressed air along the respective side wall in the workspace can be issued. The trigger is characterized in that at least one of the first ports is fluidly connected to the first pressure chamber by a first elongate passage, and that the first passage has a flow direction length L that is at least 3 times the hydraulic diameter of a cross-sectional area, perpendicular seen to the direction of flow, of the first opening, in order to avoid a flow separation of the wall jet emerging from the first opening from the side wall in a region from the front side of the working space to at least 25% of the depth of the working space.

On the other hand, the invention provides, according to claim 2, a fume hood for a laboratory room, which has a housing in which there is a work space, the front of a Front sash, is bounded on the bottom by a base plate and on each side by a side wall. The fume hood also includes a second hollow profile arranged on a front end face of the base plate, the second hollow profile having a second pressure chamber which is fluidly connected to a plurality of second openings, from which air jets in the form of ground jets consisting of compressed air flow along the base plate into the Workspace can be issued. The trigger is characterized in that at least one of the second openings is fluidly connected to the second pressure chamber via a second elongate passage, and that the second passage has a flow direction length L that is at least 3 times the hydraulic diameter of a cross-sectional area, perpendicular seen to the direction of flow, of the second opening, in order to avoid a flow separation of the bottom jet emerging from the second opening from the bottom plate in a region from the front side of the working space to at least 25% of the depth of the working space

It is advantageous if the trigger has both a first hollow profile and a second hollow profile.

According to a preferred embodiment of the invention, the first and/or the second channel has a length L in the flow direction which is in a range of 4 times to 11 times the hydraulic diameter of the cross-sectional area of the first and/or the second opening.

Preferably, there is no flow separation of the wall jet exiting from the first opening from the side wall and/or the bottom jet exiting from the second opening from the bottom plate in an area from the front side of the working space to at least 50% of the depth of the working space.

More preferably, there is no flow separation of the wall jet exiting the first opening from the side wall and/or the bottom jet exiting the second opening from the bottom plate in an area from the front of the working space to at least 75% of the depth of the working space.

An advantageous embodiment of the invention is when a first and/or a second pressure transducer is/are provided, which is/are fluidly connected to the first and/or the second pressure chamber.

The first and/or the second pressure sensor also advantageously includes a first and/or a second pressure sensor line, which is/are arranged in such a way that an end of the first and/or second pressure sensor line on the pressure chamber side is flush with an inner surface of the first and/or the second pressure chamber ends.

A control device is preferably provided which sets the pressure in the first and/or the second pressure chamber in a range from 50 Pa to 500 Pa, preferably in a range from 150 Pa to 200 Pa, when the trigger is used as intended.

Even more preferably, the control device is electrically connected to the first and/or the second pressure sensor.

According to a further preferred embodiment of the invention, the control device is a pressure reducer or a mass flow controller, which is arranged upstream of the first and/or the second pressure chamber.

Furthermore, the pressure reducer or the mass flow controller is preferably arranged inside the housing.

It is advantageous if a cross-sectional area of at least one first and/or one second opening, viewed perpendicularly to the direction of flow, preferably all the first and/or second openings, is in a range from 1 mm ² to 4 mm ² .

It is even more advantageous if a cross-sectional area, viewed perpendicularly to the direction of flow, of at least one first and/or one second opening, preferably all the first and/or second openings, is in a range from 1.8 mm ² to 3 mm ² .

A further advantageous embodiment of the invention is when at least a first and/or a second opening, preferably all the first and/or second openings, is/are designed in such a way that the compressed air jet leaving the first and/or the second opening as a periodically oscillating wall jet and/or as a periodically oscillating floor jet into the working space.

The periodicity is preferably in a range from 1 Hz to 100 kHz, preferably in a range from 200 Hz to 300 Hz.

Even more preferably, the periodic oscillation of the wall jet and/or the periodic oscillation of the floor jet is generated only by non-moving components of the first and/or the second hollow profile, which are preferably designed in one piece.

Furthermore, it is advantageous if the periodic oscillation of the wall jet and/or the periodic oscillation of the ground jet are/is generated by self-excitation.

According to a further preferred embodiment of the invention, at least one first and/or one second fluidic oscillator is/are provided, which comprises/comprises the first and/or the second opening, preferably a plurality of first and second fluidic oscillators are provided, each of which comprise a first and/or a second opening and which/which/which generate the periodic oscillation of the wall jet(s) and/or the periodic oscillation of the ground jet(s).

The first and/or the second openings preferably have a circular, round, oval, rectangular or polygonal shape.

Fig. 1

eine perspektivische Ansicht eines herkömmlichen Laborabzuges;

Fig. 2

eine Querschnittsansicht des in Fig. 1 dargestellten Laborabzuges entlang der in Fig. 1 gezeigten Linie A-A;

Fig. 3

die Einspeisung von Druckluft in die Seitenpfostenprofile und das Bodenplattenprofil;

Fig.4

eine Querschnittsansicht eines erfindungsgemäßen Hohlprofils, das an der vorderseitigen Stirnseite der Seitenwand und/oder der vorderseitigen Stirnseite der Bodenplatte angeordnet ist;

Fig. 5

einen fluidischen Oszillator im Auslasskanal eines Hohlprofils;

Fig. 6

die Ergebnisse von PIV-Messungen des Strömungsfeldes der Wandstrahlen in einem herkömmlichen Laborabzug (Fig. 6A), in einem Laborabzug mit Jet-Düsen gemäß einer bevorzugten Ausführungsform der Erfindung (Fig. 6B) und in einem Laborabzug mit OsciJet-Düsen gemäß einer weiteren bevorzugten Ausführungsform der Erfindung (Fig. 6C);

Fig. 7

einen Versuchsaufbau zur Ermittlung des statischen Luftdruckes in den Druckkammern der beiden Seitenpfostenprofile und des Bodenprofils;

Fig. 8

einen Versuchsaufbau zur Ermittlung der Volumenströme der aus den Seitenpfostenprofilen austretenden Wandstrahlen;

Fig. 9

die Messergebnisse des statischen Druckes in den Druckkammern der Seitenpfostenprofile eines herkömmlichen Laborabzuges (durchgezogene Linie), eines Laborabzuges mit Jet-Düsen und OsciJet-Düsen bei unterschiedlichen Steuerspannungen des Ventilators (gepunktete Linie und gestrichelte Linie); und

Fig. 10

ein Diagramm, das die Reduktion der Volumenströme der Wandstrahlen bei unterschiedlichen Düsengeometrien der Seitenpfostenprofile zeigt.

The invention will now be described purely by way of example with reference to the attached figures. Show from the figures

1

a perspective view of a conventional laboratory hood;

2

a cross-sectional view of the in 1 illustrated fume hood along the in 1 shown line AA;

3

the feeding of compressed air into the side post profiles and the bottom plate profile;

Fig.4

a cross-sectional view of a hollow profile according to the invention, which is arranged on the front face of the side wall and/or the front face of the base plate;

figure 5

a fluidic oscillator in the outlet channel of a hollow profile;

6

the results of PIV measurements of the flow field of the wall jets in a conventional fume hood ( Figure 6A ), in a laboratory hood with jet nozzles according to a preferred embodiment of the invention ( Figure 6B ) and in a laboratory hood with OsciJet nozzles according to a further preferred embodiment of the invention ( Figure 6C );

7

a test setup for determining the static air pressure in the pressure chambers of the two side post profiles and the floor profile;

8

a test set-up to determine the volume flows of the wall jets emerging from the side post profiles;

9

the measurement results of the static pressure in the pressure chambers of the side pillar profiles of a conventional fume hood (solid line), a fume hood with jet nozzles and OsciJet nozzles at different control voltages of the fan (dotted line and dashed line); and

10

a diagram showing the reduction of the volume flows of the wall jets with different nozzle geometries of the side post profiles.

the inside 1 The fume hood 1 shown in perspective corresponds approximately to the fume hood that has been sold by the applicant almost worldwide since about 2002 under the name ^Secuflow® . Thanks to the support jet technology described above, this laboratory fume cupboard requires an exhaust air volume flow of only 270 m ³ /(h·lfm). This deduction (Designation: ^Secuflow® TA-1500) served as a reference for the measurements carried out within the scope of the present invention, which are described further below.

In terms of its basic structure, the trigger according to the invention corresponds to that in 1 illustrated fume cupboard 1. The fume cupboard according to the invention differs from the conventional Secuflow ^® fume cupboard, in particular with regard to the nozzle geometry of the hollow profiles 10, 20 and the way in which the compressed air jets 100, 200 emitted from the hollow profiles 10, 20 are generated.

the inside 1 The fume hood 1 shown has a fume hood interior which is preferably delimited at the rear by a baffle 40, at the sides by two side walls 36, at the bottom by a base plate 34 or worktop, at the front by a lockable sash 30 and at the top preferably by a ceiling panel 48.

The sash 30 is preferably designed in several parts in such a way that several vertically displaceable window elements extend telescopically one behind the other in the same direction when the sash 30 is opened and closed. The window element arranged furthest down when the sash 30 is in the closed position preferably has an aerodynamically optimized airfoil profile 32 ( 2 ) on. In addition, the sash 30 preferably has horizontally displaceable window elements, which allow the laboratory personnel access to the interior of the fume hood even when the sash 30 is in the closed position.

At this point it is pointed out that the sash 30 can also be designed as a two-part sliding window, the two parts of which can be moved in opposite directions in the vertical direction. In this case, the counter-rotating parts are coupled via cables or belts and pulleys with weights that balance the mass of the sash.

Preferably located between the baffle 40 and the rear wall 62 ( 2 ) of the hood housing 60 has a duct 63 which leads to an exhaust air collection duct 50 on the top of the fume hood 1. The exhaust air collecting duct 50 is connected to an exhaust air device installed in the building. A piece of furniture 38 is arranged below the worktop 34 of the fume cupboard interior, which serves as storage space for various laboratory utensils. This In the sense of the terminology used here, furniture is to be understood as part of the housing 60 of the laboratory hood 100 .

Hollow profiles 10 are provided on the front end faces of the side walls 36 of the fume hood 1, which are conventionally also referred to as side posts. A hollow profile 20 is also provided on the front face of the base plate 34 .

When "on the front face" is mentioned here, this term is not to be understood literally. Rather, this also means constructions that are only provided or attached in the area of the front side.

Similar to the aerodynamically optimized airfoil profile 32 on the underside of the lowest sash element 30, the airfoil-shaped inflow side 10a of the hollow profile 10 or the side post profile 10 ( 4 ) preferably formed aerodynamically optimized. The same preferably also applies to the hollow profile 20 on the front face of the base plate 34. The wing-like profile geometry enables a low-turbulence, in the best case even a turbulence-free, inflow of room air into the interior of the hood when the sash 30 is partially or fully open.

With the help of the hollow profiles 10, 20, so-called support jets, ie compressed air jets 100, 200 consisting of compressed air, are introduced along the side walls 36 and the base plate 34 into the interior of the fume hood. These compressed air jets are conventionally provided by a fan 70 ( 3 ) generated. Although in 2 the exact arrangement of the hollow sections 10, 20 is difficult to see, the hollow sections 10, 20 are preferably located in front of the level of the foremost sash element. The compressed air jets 100, 200 therefore preferably only reach the interior of the fume hood when the sash 30 is partially or fully open.

the inside 1 The laboratory hood 1 shown is to be seen purely as an example, because the invention can be applied to different types of laboratory hoods, for example bench hoods, low-room bench hoods, deep hoods, walk-in hoods or even mobile laboratory hoods. These fume cupboards also meet the European series of standards DIN EN 14175 valid on the filing date of the present patent application. The fume cupboards can also meet other standards, for example ASHRAE 110/1995, which is valid for the USA.

If reference is made to a standard in this description and the patent claims, the currently valid standard is always meant. This is because experience has shown that the regulations specified in the standards are becoming more and more stringent, and a deduction that meets the current standard also satisfies the regulations of an older standard.

2 shows in a highly simplified manner the course of the flow of the compressed air jets 100, 200 emerging from the hollow sections 10, 20 within the interior of the fume hood and the exhaust air in the duct 63 between the baffle wall 40 and the rear wall 62 to the exhaust air collection duct 50. The view in 2 corresponds to a cross-sectional view taken along the line AA in 1 .

As in 2 As can be seen, the baffle 40 is preferably spaced from the worktop 34 on the bottom side and preferably from the rear wall 62 of the housing, as a result of which the exhaust air duct 63 is formed. The baffle 40 preferably has a plurality of elongated openings 42 ( 1 ) through which the exhaust air or the toxic air in the fume cupboard flows through and can enter the duct 63. Further openings 47 are preferably provided on the ceiling 48 in the interior of the fume hood, through which, in particular, light gases and vapors can be guided to the exhaust air collecting duct 50 .

Although in 1 and 2 not shown, the baffle 40 may also preferably be spaced from the side walls 36 of the trigger housing 60. A gap formed in this way can also be used to introduce exhaust air through it into the exhaust air duct 63 .

A plurality of tripod holders 44 are preferably provided on the baffle wall 40, in which rods can be detachably clamped, which serve as holders for test setups in the interior of the fume hood.

As in 3 are shown at the in 1 and 2 illustrated conventional laboratory hood, the compressed air or support jets 100, 200 generated by a arranged below the base plate 34 and preferably within the housing 60 fan 70. The fan 70 used in the measurements carried out as part of the invention was a single inlet centrifugal fan from ebm Papst with the designation G1G097-AA05-01.

The compressed air generated by the fan 70 is first fed into the hollow profile 20 arranged in the area of the front face of the base plate 34 . The fan compressed air is preferably fed into the hollow profile 20 at a point which is approximately in the middle of the longitudinal extent of the hollow profile 20 extending in the width direction of the hood. In this way it is achieved that the pressure drop in the hollow profile 20 is approximately symmetrical relative to this point.

In 3 it can also be seen that the hollow sections 10, 20 are fluidly connected to one another. As a result, part of the compressed air reaches the two side post profiles 10 and emerges from the side post profiles 10 in the form of support jets 100 along the side walls 36 into the interior of the hood.

Although one would initially assume that the energy requirement of the fan 70 would worsen rather than improve the overall energy balance of the laboratory fume hood, the applicant's conventional Secuflow ^® laboratory fume hood, due to the positive effect of the support jets 100, 200, was able to achieve the minimum exhaust air volume flow required to maintain the standardized escape safety , ie that minimum volumetric flow which still meets the legal requirements for the escape safety of the deduction and which the exhaust air system installed in the building and connected to the exhaust air collecting duct 50 must be able to generate, can be lowered. As a result, the energy requirement of the fume hood could be reduced by an amount that exceeds the energy requirement of the fan, which in turn has a positive effect on the overall energy balance of the fume hood.

In 4 the structure or the geometry of a hollow profile 10, 20 designed according to an embodiment of the invention is shown in cross section, ie perpendicular to the longitudinal extension of the hollow profile 10, 20. The outer inflow side 10a, 20a is aerodynamically optimized as an airfoil profile. Inside the hollow profile 10, 20 there is a pressure chamber 10b, 20b. The compressed air generated by the fan 70 flows through the pressure chamber 10b, 20b along the longitudinal extent of the hollow profile 10, 20. Also along the longitudinal extent of the hollow profile 10, 20 are preferably a large number of outlet openings 10d, 20d, through which the compressed air escapes into the interior of the fume hood can.

The multiplicity of spatially separated outlet openings 10d, 20d are arranged in the hollow profile 10, 20 according to the respective purpose of use of the fume hood 1. They can be distributed irregularly over the length of the hollow profile 10, 20 or can be arranged according to a specific pattern or even equidistantly and regularly from one another.

The hollow profiles 10, 20 can preferably be designed in one piece with the respective side wall 36 and/or the base plate 34, e.g. as an extruded aluminum profile. It is also conceivable to attach and fix the hollow profiles 10, 20 to the end face of the respective side wall 36 and/or the base plate 34, or to attach them in some other way.

Likewise, the multiplicity of outlet openings 10d, 20d—with or without outlet channel 10c, 20c—can be introduced into the respective hollow profile 10, 20 in the form of a profile strip or formed in one piece therewith.

In the 4 The geometry shown can be used both on the side post hollow profiles 10 and on the hollow profile 20 arranged on the front face of the worktop or base plate 34 . For better differentiation, the side post profile is sometimes referred to as the first hollow profile 10 and the base plate profile as the second hollow profile 20 in this description and the patent claims.

In order to be able to compare various channels through which a fluid flows with different cross-sectional shapes, the so-called hydraulic diameter is used. The term "hydraulic diameter" is well known to those skilled in the art and represents an operand that specifies the diameter of a flow channel with any cross-section which, with the same length and the same mean flow rate, has the same pressure loss as a flow pipe with a circular cross-section and same diameter.

In the applicant's conventional laboratory fume hood ^Secuflow® , the longitudinal dimension of the outlet openings 10d, 20d, ie the extent of the outlet openings 10d, 20d in the longitudinal direction of the hollow profiles 10, 20, is 30 mm and the transverse dimension is perpendicular thereto equal to 2mm. For a rectangular outlet opening, the hydraulic diameter is calculated using the formula dh=2ab/(a+b). If a=30mm and b=2mm, the hydraulic diameter of each outlet opening 10d, 20d in the conventional Secuflow ^® laboratory fume hood is 3.75 mm and the surface area is 60 mm ² .

At the in 4 However, in the hollow profiles 10, 20 shown according to a preferred embodiment of the invention, the surface area of the outlet openings 10d, 20d is preferably only 1 mm ² to 4 mm ² and more preferably 1.8 mm ² to 3 mm ² . The outlet openings 10d, 20d can preferably have a circular, round, oval, rectangular or polygonal shape.

The longitudinal extent of the almost rectangular outlet openings 10d, 20d is preferably 3 mm and the transverse dimension perpendicular thereto is preferably 1 mm. This gives a hydraulic diameter of 1.5 mm. A hollow profile 10, 20 with outlet openings 10d, 20d designed in this way was also used in the series of measurements carried out within the scope of the invention. In the following, this hollow profile 10, 20 is also referred to as "jet nozzles".

According to another aspect of the invention, at least one outlet opening 10d, 20d, preferably all outlet openings 10d, 20d provided in the hollow profile 10, 20, are fluidically connected to the pressure chamber 10b, 20b via a channel 10c, 20c having a length L ( 4 ).

At the in 4 shown hollow profile 10a, 20a, the length L of the channel is preferably 9 mm. The ratio of the length L to the hydraulic diameter (1.5 mm) is therefore equal to 6.

The series of measurements carried out within the scope of the invention suggest that the channel 10c, 20c, which is fluidly connected to preferably one outlet opening 10d, 20d, should have a length L that is at least 3 times, preferably 4 times to 11 times of the hydraulic diameter of the outlet opening 10d, 20d. Only with a duct length L that fulfills this condition are jets of compressed air released into the interior of the fume cupboard, which are "given" a direction that is significantly more pronounced than with air jets that only have to pass through a shorter duct. This reduces the Opening angle of the compressed air jets 100, 200 spreading in the interior of the fume hood. In other words, the compressed air jets 100, 200 are already directed so strongly at the time they leave the outlet openings 10d, 20d that they are as close as possible to the side walls 36 and the base plate 34.

In contrast to this, the hollow profile 10, 20 used in the conventional ^Secuflow® laboratory fume hood and extruded from aluminum had a thickness of 2 mm, ie the channel in front of the outlet opening had a length L of only 2 mm. The ratio of the length L to the hydraulic diameter (3.75 mm) was thus significantly less than 1.

The angle α ( 4 ), which the channel 10c, 20c, which preferably extends in a straight line, encloses relative to the side wall 36 and/or to the base plate 34, is preferably in a range from 0° to 10°. At this point it should be mentioned that an air jet that runs through a duct that includes an angle of 0° to the associated side wall or base plate will not propagate absolutely parallel to the side wall or base plate in the interior of the fume hood. This is due to the fact that the mean velocity vector will always assume an angle greater than 0° to the side wall 36 or to the base plate 34, even with parallel blow-out.

According to a further preferred embodiment of the invention, instead of a channel 10c, 20c ( 4 ) one in figure 5 provided outlet geometry shown, which allows the blowout of a preferably periodically oscillating jet of compressed air. This nozzle geometry is also referred to below as OsciJet.

In this context, it is pointed out that the figure 5 The section shown is roughly the same as in 4 dashed-marked portion corresponds, so that the other features of the hollow profiles 10, 20, in connection with the 4 were explained, also to the hollow profiles 10 ', 20' of figure 5 are transferrable.

The periodic oscillation is preferably generated by self-excitation and preferably with the help of non-moving components, which are preferably formed in one piece with the hollow profile 10', 20'. For this purpose, within the scope of the invention, measurements were carried out with the aid of so-called fluidic oscillators.

Fluidic oscillators are characterized in that they generate a self-excited oscillation in the fluid passing through them. This oscillation results from the splitting of the fluid flow into a main flow and a partial flow. While the main stream flows through a main channel 10c', 20c', the partial stream flows alternately through one of the two secondary channels 10f', 20f' ( figure 5 ). In the area of the outlet opening 10d', 20d', the partial flow meets the main flow again and deflects it alternately downwards or upwards, depending on which secondary channel 10f', 20f the partial flow had previously passed through. Because of the alternately changing pressure conditions in the side channels 10f', 20f', the partial flow flows through the respective other side channel 10f', 20f in the next cycle. This results in a deflection of the main and partial flow, which combine in the area of the outlet opening 10d', 20d', in the respective other direction. Then the processes repeat themselves.

Even with the nozzle geometry of the figure 5 the outlet opening 10d', 20d' is fluidly connected to a pressure chamber 10b', 20b' via a channel 10c', 20c' (here the main channel) having a length L. Here, too, the channel length L is at least 3 times, preferably 4 times to 11 times the hydraulic diameter of the outlet opening 10d', 20d'. In a preferred embodiment of the invention, the longitudinal extension of the substantially rectangular outlet opening 10d', 20d' is 1.8 mm and the extension perpendicular thereto is 1 mm. This gives a hydraulic diameter of 1.3 mm. The channel length L is preferably 14 mm and thus approximately 11 times the hydraulic diameter.

As an alternative to the OsciJet nozzle geometry, nozzle geometries that generate a non-periodic jet of compressed air are also conceivable. In other words, such nozzle geometries produce a roaming, stochastically moving jet of compressed air. In contrast to fluidic oscillators, feedback-free fluidic components can be used to generate such non-periodic compressed air jets.

6 shows the result of PIV measurements of the flow field of the wall jets emitted from the side mullion profile 10 using the conventional nozzle geometry of the Secuflow ^® hood ( Figure 6A ), the jet nozzle geometry ( Figure 6B ) and the OsciJet nozzle geometry ( Figure 6C ). The fan voltage was at the in 6 measurements shown is 9.85V.

In Figure 6a It can be clearly seen how the room air flowing in through the open sash, despite blowing out support jets 100 from the hollow profile 10, detaches itself from the side wall after about 150 mm behind the sash plane, which corresponds to the 0 position. This detachment was not observed in previous fog studies. Such a detachment is in the Figures 6b and 6c not recognizable. In the Figure 6B and the Figure 6C the room air flows along the side wall without turbulence and the formation of backflow areas. The field line density, which indicates higher air speeds, is also in the area of the side wall in the Figure 6B and the Figure 6C significantly higher than in the Figure 6A . From this it can be concluded that the room air in the case of the jet nozzle geometry ( Figure 6B ) and the OsciJet nozzle geometry ( Figure 6C ) flows significantly faster in the direction of the impact wall of the fume hood interior than in the case of the conventional nozzle geometry of the Secuflow ^® fume hood ( Figure 6A ). Likewise in the Figure 6B and the Figure 6C to see how the air in the room runs even at a distance from the side post profile 10, 10 '(y-axis) to the side wall, while in the Figure 6A the room air tends to flow away from the side wall.

The PIV measurements of the flow field thus show very clearly that with both the jet nozzle ( 4 ) and the OsciJet nozzle ( figure 5 ) Flow separations can be effectively prevented. In addition, the inflowing room air fits better in the front, wing-shaped area of the side post, which further reduces the risk of backflow.

A series of PIV measurements were made at different drive voltages of the fan 70 ( 3 ) carried out. A higher control voltage corresponds to a higher blow-out speed of the supporting jets. The PIV measurements made it clear that the goal of avoiding flow separation is achieved even better at higher jet velocities. In order to realize this aspect of the invention, it is sufficient if flow separation is avoided in an area from the front of the working space to at least 25% of the depth of the working space. This corresponds to that area of the workroom that is to be assessed particularly critically with regard to dangerous backflow areas. Preferably this value is at least 50% and more preferably 75%.

After the control voltage of the fan 70 was experimentally determined at which an almost turbulence-free course of the flow could be determined without significant backflow areas, the inventors addressed the question of what minimum volume flow is necessary in order to be able to reproduce a turbulence-free flow field.

Due to the small dimensions of the jet and OsciJet nozzle outlet openings 10d, 20d and 10d', 20d', a measurement of the air outlet speed using a hot-wire aneometer does not provide reproducible results. In the case of the OsciJet nozzles, the hot-wire aneometer even oscillates with the periodically oscillating supporting jets.

According to a further aspect of the invention, a method for determining the minimum volume flows was then developed. The corresponding experimental setup is in the Figs. 7 and 8th shown.

The volume flow of the wall jets is determined in two steps. As in 7 is shown, the control voltage of the fan 70 is adjusted with the aid of a voltage regulator 72 to a value at which the flow field of the wall jets, verified with the aid of PIV measurements, shows almost no significant flow separations. The static pressure within the hollow profiles 10, 10' and 20, 20' is then determined at the measuring points 1, 2, 3, 4, 5 and 6. A pressure sensor 80 is used for this purpose, which preferably measures the static pressure in the pressure chambers 10a, 10a' and 20a, 20a' of the hollow profiles 10, 10' and 20, 20' via respective pressure sensor lines 82. The pressure sensor lines 82 are preferably arranged in such a way that their pressure-chamber-side end ends flush with an inner surface of the respective pressure chamber 10a, 10a' and 20a, 20a'. In this first measurement step, as an example, a hollow profile 10 with jet nozzles is used on the left side post and a hollow profile 10' with OsciJet nozzles is used on the right side post.

In a second measurement step, as in 8 can be seen, the fan 70 is replaced by a compressed air connection 74 . A calibrated pressure reducer or mass flow controller 76 is arranged downstream of the compressed air connection 74 . The mass flow controller used here was from Teledyne Hastings Instruments, series 201. After setting the static reference air pressure determined in the first measuring step in the The mass flow associated with the hollow profiles 10, 10' and 20, 20' can thus be determined with the aid of the mass flow controller. The volume flow can be calculated from the respective mass flow, taking into account the ambient pressure and the ambient temperature.

In 9 the measured static air pressures in the pressure chambers 10a, 10a' of the hollow sections 10, 10' are shown. The bottom solid line is only for comparison purposes and shows the static air pressure in the hollow profile of the standard Secuflow ^® fume cupboard at a fan voltage of 4.41 V. The average static air pressure here is 12.5 Pa. The dotted line indicates an average value of 65 Pa and was determined for the Jet and OsciJet nozzles at a fan voltage of 4.41V. The top dashed line corresponds to an average air pressure of 197 Pa. This was determined at a fan voltage of 9.85 V using the Jet and OsciJet nozzles. At this point it is pointed out that in 9 the average static air pressures measured within the series profile of the Secuflow ^® hood at a fan voltage of 9.85 V are not shown.

The resulting volume flows are in 10 listed. With the optimized Jet and OsciJet wall jet nozzles, the required minimum volume flow is reduced by 68% in the Jet version and by 76% in the OsciJet version compared to the Secuflow ^® series fume hood.

According to a further aspect of the invention, the inventors have concluded that due to the greatly reduced volume flows, it is now possible to use a fully-fledged fume hood, i. H. to operate a fume hood that meets the DIN EN 14175 series of standards in accordance with the regulations with a compressed air system that is usually available in the building. At this point, the person skilled in the art is aware that such compressed air systems installed on the building side can usually provide an air pressure in a range from 0 to 7 bar. A power-driven fan is therefore unnecessary.

Not all outlet openings 10d, 10d' of the side post profile 10, 10' and not all outlet openings 20d, 20d' of the base plate profile 20, 20', which are intended for the output of wall rays 100 or ground rays 200 in the respective hollow profile 10, 20, according to the invention, the in 4 or figure 5 have nozzle geometry shown in order to realize the object specified in the claims. It is therefore sufficient that at least one outlet opening 10d, 10d' of the side post profile 10, 10' and/or at least one outlet opening 20d, 20d' of the base plate profile 20, 20' is/are designed in this way. The same applies to the length L of the channel 10c, 10c' and 20c, 20c', which is provided directly upstream of the respective outlet opening 10d, 10d' and 20d, 20d'.

Claims (20)

1. Fume cupboard (1) for a laboratory space, having a housing (60) with a work space located therein, which is delimited on the front side by a front sash (30), on the bottom by a base plate (34) and on each side by a side wall (36), and a first hollow profile (10, 10') arranged on a front end face side of each side wall (36), wherein each first hollow profile (10, 10') defines a first pressure chamber (10b, 10b'), which is fluidically connected to a plurality of first openings (10d, 10d'), from which air jet streams in the form of wall jet streams (100) consisting of pressurised air can be emitted along the respective side wall (36) into the work space, characterized in that at least one of the first openings (10d, 10d') is fluidically connected to the first pressure chamber (10b, 10b') via a first longitudinal duct (10c, 10c'), and that the first duct (10c, 10c') has a length L in the direction of flow that is at least three times as long as the hydraulic diameter of a cross-sectional area of the first opening (10d, 10d') viewed perpendicularly to the direction of flow, in order to prevent a flow separation of the wall jet stream (100) exiting the first opening (10d, 10d') of the side wall (36) in an area from the front side of the work space up to at least 25% of the depth of the work space.
2. Fume cupboard (1) for a laboratory space, having a housing (60) with a work space located therein, which is delimited on the front side by a front sash (30), on the bottom by a base plate (34) and on each side by a side wall (36), and a second hollow profile (20, 20') arranged on a front end face side of the base plate (34), wherein the second hollow profile (20, 20') defines a second pressure chamber (20b, 20b'), which is fluidically connected to a plurality of second openings (20d, 20d'), from which air jet streams in the form of bottom jet streams (200) consisting of pressurised air can be emitted along the base plate (34) into the work space, characterized in that at least one of the second openings (20d, 20d') is fluidically connected to the second pressure chamber (20b, 20b') via a second longitudinal duct (20c, 20c'), and that the second duct (20c, 20c') has a length L in the direction of flow that is at least three times as long as the hydraulic diameter of a cross-sectional area of the second opening (20d, 20d') viewed perpendicularly to the direction of flow, in order to prevent a flow separation of the base jet stream (200) exiting the second opening (20d, 20d') of the base plate (34) in an area from the front side of the work space up to at least 25% of the depth of the work space.
3. Fume cupboard (1) having the features of Claims 1 and 2.
4. Fume cupboard (1) according to any one of the preceding claims, characterized in that the first (10c, 10c') and/or the second (20c, 20c') duct has a length L in the direction of flow, which is in a range from four to eleven times as long as the hydraulic diameter of the cross-sectional area of the first (10d, 10d') and/or the second (20d, 20d') opening.
5. Fume cupboard (1) according to any one of the preceding claims, characterized in that no flow separation takes place of the wall jet stream (100) exiting the first opening (10d, 10d') from the side wall (36) and/or of the base jet stream (200) exiting the second opening (20d, 20d') from the base plate (34) in an area from the front side of the work space up to at least 50% of the depth of the work space.
6. Fume cupboard (1) according to any one of the preceding claims, characterized in that no flow separation takes place of the wall jet stream (100) exiting the first opening (10d, 10d') from the side wall (36) and/or of the base jet stream (200) exiting the second opening (20d, 20d') and/or of the base jet stream (200) exiting the second opening (20d, 20d') from the base plate (34) in an area from the front side of the work space up to at least 75% of the depth of the work space.
7. Fume cupboard (1) according to any one of the preceding claims, characterized in that a first and/or a second pressure transducer (80) is provided, which is/are fluidically connected to the first (10b, 10b') and/or the second (20b, 20b') pressure chamber.
8. Fume cupboard (1) according to Claim 7, characterized in that the first and/or the second pressure transducer (80) comprises a first and/or a second pressure transducer line (82), which is arranged in such a way that an end of the first and/or second pressure transducer line (82) on the pressure chamber side ends flush with an inner surface of the first (10b, 10b') and/or the second (20b, 20b') pressure chamber.
9. Fume cupboard (1) according to any one of the preceding claims, characterized in that a control device (76) is provided which is designed such that, when the fume cupboard is operated according to its intended use, said control device adjusts the pressure in the first (10b, 10b') and/or the second (20b, 20b') pressure chamber in a range from 50 Pa 500 Pa, preferably in a range from 150 Pa 200 Pa.
10. Fume cupboard (1) according to Claim 9, to the extent that it depends on either of Claims 7 or 8, characterized in that the control device (76) is electrically connected to the first and/or second pressure transducer (80).
11. Fume cupboard (1) according to Claim 9 or 10, characterized in that the control device is a pressure reducer or a mass flow regulator (76) that is arranged upstream to the first (10b, 10b') and/or the second (20b, 20b') pressure chamber.
12. Fume cupboard (1) according to Claim 11, characterized in that the pressure reducer or mass flow regulator (76) is arranged inside the housing (60).
13. Fume cupboard (1) according to any one of the preceding claims, characterized in that a cross-sectional area of at least one first (10d, 10d') and/or at least one second (20d, 20d') opening, viewed perpendicularly to the direction of flow, preferably of all first and/or second openings, is in a range from 1 mm² to 4 mm².
14. Fume cupboard (1) according to any one of the preceding claims, characterized in that a cross-sectional area, viewed perpendicularly to the direction of flow, of at least one first (10d, 10d') and/or at least one second (20d, 20d') opening, preferably of all first and/or second openings, is in a range from 1.8 mm² to 3 mm².
15. Fume cupboard (1) according to any one of the preceding claims, characterized in that at least one first (10d, 10d') and/or at least one second (20d, 20d') opening, preferably all first and/or second openings, is/are designed that the compressed air stream exiting the first (10d, 10d') and/or the second (20d, 20d') opening is emitted into the work space as a periodically oscillating wall jet stream (100) and/or as a periodically oscillating base jet stream (200).
16. Fume cupboard (1) according to Claim 15, characterized in that the periodicity is in a range from 1 Hz to 100 kHz, preferably in a range from 200 Hz to 300 Hz.
17. Fume cupboard (1) according to Claim 15 or 16, characterized in that the periodic oscillation of the wall jet stream (100) and/or the periodic oscillation of the base jet stream (200) can be generated by merely non-moving components of the first (10, 10') and/or the second (20, 20') hollow profile, which are preferably constructed as a single part.
18. Fume cupboard (1) according to any one of Claims 15 to 17, characterized in that the periodic oscillation of the wall jet stream (100) and/or the periodic oscillation of the base jet stream (200) can be generated by auto-excitation.
19. Fume cupboard (1) according to any one of Claims 15 to 18, characterized in that at least one first and/or at least one second fluidic oscillator (11) is/are provided, which comprise/comprises the first (10d') and/or the second (20d') opening, preferably that a multiplicity of first and second fluidic oscillators are provided, each comprising a first (10d') and/or a second (20d') opening, and are designed in such manner that it/they generate(s) the periodic oscillation of the wall jet stream/wall jet streams (100) and/or the periodic oscillation of the base jet stream/base jet streams (200).
20. Fume cupboard (1) according to any one of the preceding claims, characterized in that the first (10d, 10d') and/or the second (20d, 20d') openings have a circular, round, oval, rectangular or polygonal shape.

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