METHOD FOR DETECTING PRIMARY GAS FLOWS IN FLOW CHAMBERS, USE OF A GAS MIXTURE THEREFOR AND GAS MIXTURE

Abstract

A method is provided for detecting primary gas flows (18) in flow chambers (10). The primary gas (18) flowing in a flow chamber (10) is locally seeded with a seed substance and the movement of the seed substance, representative of the flow of the primary gas (18), is detected by imaging by an image detector (28) and an imaging optics (30) arranged in front of said image detector (28). A gas mixture (34) that moves along with the primary gas (18) without relative motion and that has a refractive index distinguishable from that of the primary gas (18) is used as the seed substance, and imaging detection is carried out by a background schlieren measurement method.

Claims

1. A method for detecting primary gas flows (18) in a flow chamber (10), wherein a primary gas (18) flowing in the flow chamber (10) is locally seeded with a seed gas and wherein a movement of the seed gas, representative of the flow of the primary gas (18), is detected by imaging by means of an image detector (28) and an imaging optics (30) arranged in front of said image detector (28), wherein a gas mixture (34) that moves with the primary gas (18) and has a refractive index that can be distinguished from the primary gas (18) is used as the seed gas, and the imaging detection is carried out by a background schlieren measurement method, and wherein the gas mixture (34) is composed in such a way that:
|m.sub.P−Σ.sub.i=1.sup.Na.sub.im.sub.i|2 g/mol,
and
|n′.sub.P−Σ.sub.i=1.sup.Na.sub.in′.sub.i|>70, where m.sub.P is the molar mass and n′.sub.P is the refractive index of the primary gas, m.sub.i is the molar mass and n′i is the refractive index of the i-th gas component of the seed gas, N is the number of gas components of the seed gas, and a; is their respective relative mole fraction in the seed gas, so that a co-movement of the gas mixture (34) with the primary gas (18) flowing at a flow velocity of 0.1 to 1.0 m/s takes place without relative movement.

2. The method of claim 1, wherein the gas mixture contains 20+/−1% O.sub.2

3. The method of claim 1, wherein the gas mixture is prepared from two to five pure gases as its gas components.

4. The method of claim 1, wherein the gas mixture contains 25% He, 55% Ar and 20% O.sub.2 or 55% He, 25% Kr and 20% O.sub.2 or 65% He, 15% Xe and 20% O.sub.2, in each case with a tolerance of +/−1% of the amounts of the individual gas components adding up to 100%.

5. The method of claim 1, further comprising: generating a patterned background for the background schlieren measurement method by coherent illumination of a projection surface arranged in a field of view of the image detector behind the primary gas flow.

6. The method of claim 5, wherein at least portions of the projection surface are formed by a boundary wall of the flow chamber.

7. The method of claim 5, wherein at least regions of the projection surface are formed by an outer wall of an object arranged in the flow chamber.

8. The method of claim 5, further comprising: focusing the imaging optics (30) on a point (36) located behind the projection surface (14).

9. The method of claim 1, further comprising: stopping down the imaging optics (30) in such a way that the primary gas flow (18) lies in the sharply imaged distance range.

10. The method of claim 1, wherein the seeding of the primary gas (18) with the gas mixture (34) is carried out by one or more diffusers (32).

11. The method of claim 10, wherein the one or more diffusers (32) together with a supply line for the gas mixture (34) are movably arranged within the flow chamber (10).

12. The method of claim 1, wherein the gas mixture (34) exclusively contains gas components that are non-toxic and non-asphyxiating for humans.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is a schematic representation of the implementation of the method according to the invention for the visualization of air flows in a flow box.

[0027] FIG. 2 is a schematic diagram illustrating preferred image detector settings when carrying out the method according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0028] Identical reference signs in the figures indicate identical or analogous elements.

[0029] FIG. 1 illustrates in highly schematic sketch of a structure for carrying out a process according to the invention using the example of a so-called flow box 10. The flow box 10 has a transparent front wall 12 and a matted rear wall 14. The matting of the rear wall 14 can be carried out, for example, by applying a matting screen, for example a white paper, to the outside or inside of a transparent rear wall 14. In the case of a non-transparent rear wall 14, such measures are unnecessary. In its upper region, the flow box 10 has an air connection 16, symbolized as an arrow, via which sterile filtered air can be introduced into the interior of the flow box 10. In the embodiment described, this sterile filtered air serves as the primary gas. Of course, other primary gas types can also be used within the scope of the invention.

[0030] Via air guide elements not shown in detail, the introduced primary gas is deflected into a primary gas flow 18 also shown as arrows, which in the embodiment shown flows essentially laminarly downward 12, 14 of the flow box 10. Any type of apparatus, in particular a filling apparatus for pharmaceutical liquids, may be installed on a work table 20 within the flow box 10. Other types of equipment are of course also conceivable within the scope of the invention. In FIG. 1, such installations or inserted objects are shown schematically as an obstacle 21. In the lower area of the flow box 10, lateral air outlets 22 are arranged, which are provided as exclusive outlets for the primary gas flow 18.

[0031] The method according to the invention can be used to check whether the primary gas flow 18 actually follows the desired flow path. For this purpose, a laser speckle pattern is projected onto the rear wall 14 and the outer wall of the obstacle 21 (insofar as it covers the rear wall 14), which to this extent act as a composite projection surface. For this purpose, a laser 24 is provided whose laser radiation, preferably lying in the optical spectral range, and is projected onto the projection surface by means of suitable deflection and expansion optics 26. A laser speckle pattern 27 is created, which is indicated as an example on the left in FIG. 1. This laser speckle pattern 27 is detected by means of an image detector 28 with an imaging optics 30 arranged in front of the image detector. In the embodiment shown, the deflection and expansion optics 26 of the laser 24 are designed so that the optical axis of the projection of the laser speckle pattern 27 is coaxial with the optical axis of its imaging on the image detector 28.

[0032] A seed gas 34, i. e. a gas mixture having the properties discussed in detail within the general description, is added to the primary gas flow 18 via a movable diffuser 32 within the flow box 10. The movability of the diffuser 32 allows for easy variation of the seeding location to create a spatial flow pattern. The seed gas 34 introduced into the primary gas flow 18 via the diffuser 32 with virtually no inherent velocity follows the primary gas flow 18 without relative motion, but it creates a local perturbation of the refractive index of the flow 18. This refractive index perturbation acts in two ways. First, it changes the projection of the laser speckle pattern 27 onto the projection surface; second, it affects the imaging of the pattern 27 onto the image detector 28. Since the seed gas 34, and therefore the refractive index perturbation it produces, moves with the primary gas flow 18, the refractive index perturbation is subject to temporal changes. Temporally successive images, in particular with time intervals of significantly less than 1 second, preferably less than 1/10 second, particularly preferably less than 1/100 second and comparison of the resulting images, in particular by correlation algorithms, then allows a calculation and display of the respective spatially assigned value of the caused perturbation. Thus a visualization of the primary gas flow 18 disturbed in such a way is possible. Its correct course can therefore be checked in quasi-real time by means of the method according to the invention. At the same time, the internal structure of the flow box 10, in particular the obstruction 10, remains at least schematically recognizable. To improve the recognizability of such details, “normal” images with non-coherent illumination can be taken in between and superimposed on the calculated BOS images. In the usual case where the spectrally narrowband laser illumination is in addition to a broadband ambient illumination, different cameras with appropriate filters can also be used for recording the BOS images on the one hand and the “normal” images on the other.

[0033] As already explained in the context of the general description, it is preferably provided that the imaging optics 30, as schematically illustrated in FIG. 2, are focused on a point 36 behind the projection surface (of which only the rear wall 14 is shown in FIG. 2 for reasons of clarity), i. e. behind the laser speckle pattern 27. The laser speckles of all areas of the projection surface, including possible existing obstacle outer sides, are nevertheless sharply imaged on the image detector 28. The quantity essential for the sensitivity of the method, namely the distance between the refractive index perturbation and the patterned background, is thereby virtually enlarged. In this context, it is favorable if the imaging optics 30 are stopped down in such a way that the depth of field 38 still (sufficiently) sharply images the structures within the flow box 10 despite focusing on the distant point 36.

[0034] Of course, the embodiments discussed in the specific description and shown in the figures are only illustrative examples of embodiments of the present invention. The person skilled in the art is provided with a wide range of possible variations in light of the present disclosure. In particular, the method according to the invention is also suitable for visualizing flows in other types of spaces, for example, in forced-ventilated spaces. In any case, the application of the laser speckle variant has the advantage that a highly sensitive visualization is possible under spatially confined conditions.

LIST OF REFERENCE SIGNS

[0035] 10 Flow box [0036] 12 Front wall of 10 [0037] 14 Back wall of 10 [0038] 16 Air connection [0039] 18 Primary gas flow [0040] 20 Working table [0041] 21 Obstacle [0042] 22 Air outlet [0043] 24 Laser [0044] 26 Deflection and expansion optics [0045] 27 Laser speckle pattern [0046] 28 Image detector [0047] 30 Imaging optics [0048] 32 Diffuser [0049] 34 seed gas/gas mixture [0050] 36 Sharp point [0051] 38 Depth of focus