Method for detecting the flow of a main gas in a flow space, use of a gas mixture for the method and gas mixture

Abstract

The invention relates to a method for detecting a main gas flow (18) in a flow space (10), wherein the main gas (18) flowing in the flow space (10) is locally injected with an injection substance and the movement of the injection substance representing the flow of the main gas (18) is detected by means of an image detector (28) with upstream imaging optics (30). The invention is characterized in that as injection substance a gas mixture (34) is used which moves with the main gas (18) without relative movement, which has a refractive index which can be distinguished from the main gas (18), and the detection by means of the Schlieren method is performed.

Description

Technical Field

[0001] The present invention relates to a method for detecting, in particular, slow main gas flow within a flow space, i.e., a main gas flow having a flow velocity of, in particular, 0.1 to 1 m / s, preferably 0.3 to 0.5 m / s, wherein the main gas flowing in the flow space is locally injected with an injection substance, and the movement of the injection substance, representing the flow of the main gas, is detected by means of an image detector having an upstream imaging optics. Background Technology

[0002] In the pharmaceutical industry, the filling process, such as filling liquid medication into dispensing bottles for sale, typically takes place in what is known as a flow box. A flow box is, in this context, a enclosure with mostly transparent walls that surround the filling equipment arranged on a workbench and through which sterile, filtered air flows to prevent any non-sterile material from entering. This airflow (also referred to herein as the main gas flow) must adhere to defined, pre-defined parameters. Specifically, this airflow is typically a slow flow at a velocity of 0.3 to 0.5 m / s, flowing from top to bottom through the flow space—in this case, the flow box—preferably in a laminar manner, and escaping only at pre-defined venting openings. However, the flow is subject to interference from surrounding structures and objects introduced into the flow box. Nevertheless, adherence to these defined flow parameters remains a fundamental quality standard for the filling process and is subject to strict official control. Therefore, in the United States, for example, the FDA requires regular inspection and recording of flow characteristics. The prescribed method involves injecting ethylene glycol aerosol as the injection material into the main gas flow via nozzles. Incident light is scattered across the aerosol, allowing optical detection of its movement through the transparent wall of the flow box, particularly using a camera for detection and imaging. Since aerosols are defined as suspended particles that move with the main gas flow, the captured aerosol movement can be considered representative of the main gas movement. A disadvantage is that the actual filling equipment is subject to considerable contamination due to ethylene glycol aerosol wetting. Therefore, a thorough cleaning of the filling equipment is necessary after each flow check before it can be put back into service.

[0003] Similar scenarios are known to technicians from other fields, such as food packaging under protective gas flow, or forced ventilation of spaces, such as in server farms or the interiors of homes or vehicles. In all cases, visualization of the respective main gas flow is typically achieved by injecting aerosols, which leads to the aforementioned drawbacks.

[0004] From the perspective of aerospace technology, for example, as described in DE 199 42 856B4, there is a known method called background schlieren measurement, commonly abbreviated as BOS (Background Oriented Schlieren). In high-speed flows, large pressure gradients occur, resulting in large local differences in mass density within the flow. These differences in mass density cause corresponding differences in the refractive index of the flowing gas. In the BOS method, a patterned background is positioned behind the flow to be visualized, and an image detector pointing towards this background is positioned in front of the flow. The imaging of the background on the image detector depends on the specific path of light from a given background point to the image detector, where this path is related to deflection characteristics, that is, particularly to the refractive index of the medium passing between the background and the image detector. As mentioned above, the refractive index of the flow extending between the background and the image detector can be locally different, thus the beam falling from different background points onto the image detector experiences different deflections along its path. The resulting changes in the detected pattern can be calculated using known correlation methods, and thus the refractive index gradient can be made apparent. Correlation algorithms known to those skilled in the art are used for calculation. For visualization, each pixel of the image detector is assigned a value for the refractive index change calculated at the corresponding location, encoded in color or via grayscale. It is also possible to overlay this BOS image with a conventional image of the scene. Image processing methods can also be considered within the scope of the BOS method for flow visualization. However, all of these are based on resolving the location of the refractive index changes associated with the flow, which are reflected in a time-varying image of the flow to be visualized against a patterned background. The BOS method is also suitable for visualizing heat flow, i.e., when the associated density differences are caused by temperature differences, such as when the flow is locally heated.

[0005] The patterned background required for the BOS method is typically provided by a correspondingly patterned surface. The pattern can be printed, pasted, projected, or otherwise applied to the surface in a manner detectable by an image detector. The aforementioned literature also discloses feasible schemes using natural backgrounds, whose natural patterns are sufficient to perform the BOS method, provided the image detector has adequate resolution and sufficient computational power.

[0006] By Meier, AH; Roesgen, Th.: Improved background-oriented schlieren imaging using laser speckle illumination, Exp. Fluids (2013) 54:1549 (DOI 10.1007 / s 00348-013-1549-8) 00348-013-1549-8)) It is known that a projection surface positioned behind a candle flame, as seen from an image detector, is used as the background for BOS-based visualization of heat flow. This projection surface is extensively illuminated by coherent light, that is, coherently lit. Under this coherent illumination, interference phenomena result in so-called laser speckle, which essentially appears as a dotted pattern. Depending on the spatial mass density and, consequently, the refractive index, this dotted pattern is imaged differently on the image detector. Furthermore, refer to the explanation of the classical BOS method above. Summary of the Invention

[0007] The objective of this invention is to improve the methods for detecting slow main gas flows, particularly in flowing spaces, so as to prevent adverse contamination of the flowing space.

[0008] This task is accomplished by using a gas mixture that moves with the host gas without relative motion, hereinafter referred to as the injection gas. As the injection material, the gas mixture has a refractive index that can be distinguished from the host gas, and imaging detection is performed using the background schlieren method (BOS method).

[0009] This invention is based on two approaches. According to the first approach, the aerosol, which is detrimental due to its polluting properties, is replaced by a gas mixture suitable for moving with the host gas without relative motion; that is, the injected gas must have a similar mass density to the host gas. In this context, "without relative motion" is understood to mean "no inherent motion due to mass difference," i.e., during the execution of the method, i.e., in terms of the respective flow velocities and distances traveled, there is no deviation (in direction and magnitude) between the flow velocities of the host gas and the injected gas, or no significant deviation for the desired measurement accuracy. As mentioned above, typical flow velocities are in the range of 0.1 to 1.0 m / s, preferably in the range of 0.3 to 0.5 m / s. Typical relevant distances are the length dimensions of their respective flow spaces. It will be understood by those skilled in the art that the greater the flow velocity of the host gas to be detected and the smaller the respective distances traveled, the greater the permissible deviation between the mass densities of the injected gas and the host gas can be, in order to still achieve the absence of relative motion between the injected gas and the host gas as per this invention. The injected gas, which is much heavier than the main gas, sinks independently of the main gas flow, while the much lighter injected gas rises. In each case, the movement of the injected gas will no longer represent the main gas flow to the desired extent.

[0010] This method avoids contamination problems within the flow space, such as those encountered when using aerosols as the injection material. However, the injection gas and the host gas are indistinguishable to conventional cameras and are typically transparent, or even invisible, within the optical spectrum. Therefore, as another fundamental idea, the present invention is to detect the injection gas using background schlieren measurement, a method generally known to those skilled in the art. However, for this to be effective, the injection gas must have a refractive index (within the scope of the BOS method) that distinguishes it from the host gas. Other types of optical distinguishability, such as color differences or scattering as in the case of aerosols, are not necessary and even undesirable within the scope of the present invention. It is understood by those skilled in the art that, under the same pressure and temperature conditions, the injection gas must possess the aforementioned characteristics relative to the host gas, i.e., similar mass density and different refractive indices. Therefore, pressure differences that naturally arise in the flow (based on typically slow flow rates) are insufficient to induce corresponding refractive index changes. Moreover, it is not stipulated within the scope of the present invention that a larger temperature difference is generated between the host gas and the injection gas, which will eventually disappear during the flow process.

[0011] By injecting the main gas only locally, the corresponding refractive index disturbances are also confined to a local area, especially as the main gas flows through the flow space. Furthermore, as mentioned above, since the BOS method is based on detecting time-varying refractive index differences, disturbances that can be visualized using the BOS method can be considered representative of the main gas flow. Therefore, the method according to the present invention enables indirect visualization of the main gas flow.

[0012] Of particular importance to this invention is that the injected gas is a gas mixture, i.e., a composition of different types of pure gases. Only in this way is it possible to produce an injected gas having the properties of mass density and refractive index that are essential to this invention, as described above. Here, as the inventors have clarified, there is no need to worry that the different gas components of the injected gas will split within the scope of performing the method according to the invention, or that they will produce undesirable relative motions relative to the host gas, especially due to their different pure mass densities. Instead, the properties of the combined gas mixture are preserved.

[0013] A gas mixture consisting of 20% oxygen, 25% helium, and 55% argon has proven to be an exemplary injection gas for air as the main gas, particularly advantageous when the main gas is moving slowly, where deviations of + / -1% are considered insignificant. Such a gas mixture has a molar mass of 29.3 g / mol and a refractive index n' of 215 (expressed as (n-1) × 10⁻⁶). 6 (where n is the dimensionless refractive index). Therefore, a molar mass difference of 1.5 g / mol with air is small enough that there is no need to worry about relative motion with the main gas air, even at low flow rates within a few meters. On the other hand, the refractive index difference of -73 is so large that BOS-based detection methods lead to very good results in flow visualization.

[0014] The table below provides further exemplary gas mixtures suitable as injection gases according to the invention for a method using air as the primary gas, and their differences from air in terms of molar mass and refractive index. Based on these exemplary pre-given parameters, it will be readily apparent to those skilled in the art that the optimal gas mixture will be combined for their respective applications (primary gas, flow rate, flow path, resolution of the image detector, etc.), and economic considerations arising from the varying prices of different pure gases are also taken into account, if necessary.

[0015]

[0016] Table 1

[0017] In each case, a deviation of + / - 1% in terms of the amounts of the individual gas components is largely not critical.

[0018] A general formula for a gas mixture that is considered a favorable injection gas, having the properties of sufficient relative immobility and sufficient refractive index distinguishability, can be described as follows: Preferably < 1 g / mol, more preferably ≤ 0.5 g / mol.

[0019] And

[0020] Preferably > 100, more preferably ≥ 110.

[0021] Where m P is the molar mass of the main gas and n' P is its refractive index, m i is the molar mass of the i-th gas component in the injection gas and n' i is its refractive index, N is the number of gas components of the injection gas, and a i is their respective relative molar fractions in the injection gas. In other words, it is favorable that the absolute value of the difference between the molar mass of the main gas and the injection gas is less than 2 g / mol, preferably less than 1 g / mol, more preferably less than or equal to 0.5 g / mol, while the absolute value of the difference between the refractive index of the main gas and the injection gas is greater than 70, preferably greater than 100, more preferably greater than or equal to 110. The molar mass and refractive index of the injection gas are calculated here as the corresponding values averaged with their respective relative molar fractions of the gas components of the injection gas. Each gas component is preferably a pure gas, rather than already being a gas mixture itself, where preferably 1 < N < 6, that is, at least 2 and at most five, preferably three or four, particularly preferably exactly three pure gases are used to produce the gas mixture.

[0022] Of course, other pure gases not listed in the above table can also be used as components of the injection gas according to the present invention. However, especially in typical application cases where the flow space involved is not hermetically isolated from any personnel during normal operation, it is recommended that the gas mixture preferably contains only gas components that are non-toxic and non-asphyxiating to humans. On the contrary, on the other hand, in applications with an explosion hazard, the use of oxidizing gases should be eliminated. This limitation on the available gases will be particularly important in the context of labor protection regulations.

[0023] Preferably, the injection gas is injected into the main gas via one or more diffusers. Compared to injection via nozzles, injection gas introduced via diffusers is introduced into the main gas flow with almost no inherent motion, thus avoiding relative motion due to the initial inherent velocity of the injection gas. One or more diffusers, along with the associated injection gas supply lines, can be arranged in a movable, particularly mobile, manner within the flow space involved, thereby making the flow distribution throughout the flow space visible.

[0024] Advantageously, the patterned background required for background schlieren measurement is generated by coherently illuminating a projection surface arranged behind the main gas flow in the field of view of the image detector.

[0025] It can be configured such that at least some areas of the projection surface are formed by the boundary walls of the flow space. Alternatively or additionally, it can be configured such that at least some areas of the projection surface are formed by the outer walls of objects arranged in the flow space. A transparent wall between the image detector and the projection surface, such as the front window of the flow box, is in principle harmless in this regard.

[0026] A particular advantage of the laser speckle BOS method is that the laser speckle pattern is always clearly imaged on the image detector, regardless of the distance setting of the imaging optics. This property is derived from the interferometric physics that underlies the generation of the laser speckle pattern. On the other hand, it is known from conventional BOS variants with realistic background patterns that the greater the distance between the flow to be visualized and the patterned background on which the imaging optics must be focused for clear imaging, the higher the sensitivity of the method. This is because the interference of light deflection, which is the basis of visualization, is an angular phenomenon, and this angular phenomenon is more pronounced the longer the path traveled. In conventional BOS methods, large distances between the flow and the background, as in methods used in aerospace technology, are not a problem. Conversely, when measuring within a confined flow space, the dimensions are typically much smaller, and flows near walls (whether the boundary walls of the flow space itself or the outer walls of objects arranged within the flow space, such as structures or instruments) are particularly interesting. This is especially true in preferred applications, such as flow visualization in flow boxes. If a real patterned background is mounted on the rear wall of the flow tank opposite the image detector and the imaging optics are focused onto that background, the sensitivity of the method will be significantly limited. However, when using the laser speckle BOS method, as preferably configured within the scope of this invention, the laser speckle pattern can be projected directly onto the rear wall of the flow tank, onto the carrier inside the flow tank, and / or even onto the vessel itself to be filled into the flow tank. Conversely, the imaging optics of the image detector can be adjusted to a point behind the projection plane (possibly composed of multiple planes), thereby virtually shifting the pattern backward. This correspondingly improves the sensitivity of the measurement.

[0027] To achieve clear imaging of the flow space region where the required flow motion occurs, even with such fine-tuning of the imaging optics, it is preferable to reduce the aperture of the imaging optics to a distance that allows the main gas flow to be within the range of clear imaging. In other words, although the imaging optics are focused on a point behind the actual projection wall to improve sensitivity, a depth of field is still achieved using the imaging optics, which includes the structures located within the flow region.

[0028] Preferably, coherent illumination of the projection wall is achieved using a laser coaxially aligned with the optical axis of the image detector and through which the flow is transmitted. This has proven particularly advantageous in terms of imaging accuracy. Alternatively, a beam splitter can be used to deflect light from a laser that is not coaxially aligned with the optical axis of the image detector back to the optical axis of the image detector. Thus, the light detected by the image detector undergoes two refractive index interferences: first as projection light on its way to the projection wall, and second as probe light on its way from the projection wall to the image detector. This amplifies the beam deflection caused by refractive index interference. However, the non-coaxial alignment of the projection and probe light results in so-called ghosting on the detector, which interferes with image evaluation. Of course, it is also conceivable that the projection wall is illuminated without the projection light having passed through the flow beforehand, or is illuminated at an angle, so that the ghosting is redirected outside the sensitive detector area. Attached Figure Description

[0029] Further details and advantages of the invention will become apparent from the following detailed description and accompanying drawings. Wherein:

[0030] Figure 1 : A schematic diagram illustrating the implementation of a method for visualizing gas flow in a feed box according to the present invention; and

[0031] Figure 2 : A schematic diagram illustrating the preferred image detector adjustment when performing the method according to the invention.

[0032] The same reference numerals in the figure indicate the same or similar elements. Detailed Implementation

[0033] Figure 1 The structure for performing the method according to the invention on an example of a so-called flow box 10 is illustrated in a highly illustrative form. The flow box 10 has a transparent front wall 12 and a matte rear wall 14. The matte finish on the rear wall 14 can be achieved, for example, by applying a matte screen, such as white paper, to the outside or inside of the transparent rear wall 14. This measure is unnecessary in the case of a non-transparent rear wall 14. The flow box 10 has an air inlet 16, symbolically indicated by an arrow, in its upper region, through which sterile filtered air can be introduced into the interior of the flow box 10. In the described embodiment, this sterile filtered air is used as the main gas. Of course, other types of main gases can also be used within the scope of the invention.

[0034] The introduced main gas is deflected into the main gas flow 18, also indicated by arrows, via a gas guiding element (not shown in detail). This main gas flow, in the illustrated embodiment, flows substantially in a laminar manner towards the lower parts 12 and 14 of the flow tank 10. Any equipment, particularly pharmaceutical filling facilities, can be installed on the worktable 20 within the flow tank 10. Of course, other types of facilities are also conceivable within the scope of this invention. Figure 1 In this diagram, the internal component or introduced object is schematically shown as an obstruction 21. A lateral air outlet 22 is arranged in the lower region of the flow box 10, which is configured as a dedicated outlet for the main gas flow 18.

[0035] The method according to the invention can be used to check whether the main gas flow 18 truly 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 (provided the obstacle obscures the rear wall 14), in which case they function as combined projection surfaces. For this purpose, a laser 24 is provided, whose laser radiation, preferably within the optical spectrum, is projected onto the projection surfaces by means of appropriate deflecting and amplifying optics 26. This generates a speckle pattern on the... Figure 1 The laser speckle pattern 27 is exemplarily shown on the left. This laser speckle pattern 27 is detected image-wise by means of an image detector 28 having an upstream imaging optics 30. In the illustrated embodiment, the deflection and magnification optics 26 of the laser 24 are designed to make the optical axis of the projection of the laser speckle pattern 27 coaxial with the optical axis of its imaging on the image detector 28.

[0036] The injected gas 34, a gas mixture having the characteristics discussed in detail in the general description, is mixed with the main gas flow 18 via a movable diffuser 32 within the feed box 10. The mobility of the diffuser 32 makes it possible to easily change the injection position to create a spatial flow pattern. The injected gas 34, introduced into the main gas flow 18 with almost no inherent velocity, has no relative motion with the main gas flow 18, but it does cause localized interference with the refractive index of the flow 18. This refractive index interference has a dual effect. On the one hand, it alters the imaging of the laser speckle pattern 27 on the projection plane; on the other hand, it affects the imaging of the pattern 27 on the image detector 28. Since the injected gas 34 and the resulting refractive index interference move with the main gas flow 18, the refractive index interference is time-varying. By continuously capturing images over time, especially at intervals significantly less than 1 second, preferably less than 1 / 10 of a second, and particularly preferably less than 1 / 100 of a second, and comparing the resulting images, particularly through a correlation algorithm, the spatially corresponding values ​​of the resulting disturbances can be calculated and displayed. This allows visualization of the main gas flow 18 disturbed in this way. Therefore, the correct direction of the main gas flow can be checked in near real-time using the method according to the invention. Here, the internal structure of the flow box 10, especially the obstacles 10, can be at least vaguely identified. To improve the recognizability of this detail, "normal" images can be repeatedly captured in between using incoherent illumination and superimposed with the calculated BOS image. In cases where narrow-band laser illumination occurs in addition to broadband ambient lighting, different cameras with corresponding filters can also be used to capture BOS images on one side and "normal" images on the other.

[0037] As explained in the general description, it is preferred that the imaging optics 30, such as Figure 2 As illustrated in the diagram, focus on the projection plane (for clarity, in...). Figure 2 Only point 36 behind the rear wall 14) is shown, i.e., behind the laser speckle pattern 27. The laser speckle over all areas of the projected surface, including the outer edges of any potential obstacles, is still clearly imaged on the image detector 28. This virtually increases the spacing between the refractive index interference and the patterned background, a parameter crucial to the sensitivity of the method. Advantageously, the aperture of the imaging optics 30 is reduced such that the depth of field 38 remains (sufficiently) clear, even when focused on the distant point 36.

[0038] Of course, the embodiments discussed in the specific description and shown in the figures are merely illustrative examples of the invention. Based on this disclosure, those skilled in the art will find a wide range of possible variations. In particular, the method according to the invention is also applicable to visualizing flows in other types of spaces, such as those in forced-ventilation spaces. In any case, the application of the laser speckle variant has the advantage of enabling highly sensitive visualization under spatially enclosed conditions.

[0039] List of reference numerals

[0040] 10 Flow Box

[0041] 12 10 Anterior wall

[0042] 14 10 posterior wall

[0043] 16 Air Interfaces

[0044] 18. Main gas flow

[0045] 20 workbenches

[0046] 21 Obstacles

[0047] 22 Air outlet

[0048] 24 lasers

[0049] 26 Deflecting and Enlarging Optical Elements

[0050] 27 Laser speckle pattern

[0051] 28 Image Detectors

[0052] 30 Imaging Optics

[0053] 32 Diffuser

[0054] 34. Injected gas / gas mixture

[0055] 36 Focus Points

[0056] 38 Depth of field range

Claims

1. Method for detecting a main gas flow (18) in a flow space (10), wherein The main gas flowing in the flow space (10) is locally injected with an injection gas and the motion of the injection gas representing the flow of the main gas is visualized by means of an image detector (28) with upstream imaging optics (30), wherein a gas mixture (34) moving with the main gas is used as injection gas, the gas mixture having a refractive index which is distinguishable from the main gas, and the visualization is performed by means of a background schlieren measurement, characterized in that the gas mixture (34) is composed in such a way that it is applicable that and wherein m P is the molar mass of the main gas and n' P is the refractive index of the main gas, m i is the molar mass of the i-th gas component of the injection gas and n' i is the refractive index of the i-th gas component of the injection gas, N is the number of gas components of the injection gas, and a i is the respective relative molar fraction of the gas components in the injection gas, so that the movement of the gas mixture (34) with the main gas flowing at a flow rate of 0.1 to 1.0 m / s takes place without relative motion.

2. The method according to claim 1, characterized in that the gas mixture contains 20 + / - 1 % of O2.

3. The method according to claim 1, characterized in that the gas mixture is prepared from two to five pure gases as its gas components.

4. The method according to claim 1, characterized in that the gas mixture contains 25 % of He, 55 % of Ar and 20 % of O2, or 55 % of He, 25 % of Kr and 20 % of O2, or 65 % of He, 15 % of Xe and 20 % of O2, the tolerance of the amount of each gas component, which amounts to 100 %, is + / - 1 % respectively.

5. The method according to claim 1, characterized in that the patterned background required for the background schlieren measurement is generated by coherently illuminating a projection surface arranged behind the main gas flow in the field of view of the image detector.

6. The method according to claim 5, characterized in that at least several regions of the projection surface are formed by boundary walls of the flow space.

7. The method according to any one of claims 5 to 6, characterized in that at least several regions of the projection surface are formed by outer walls of an object arranged in the flow space.

8. The method according to any one of claims 5 to 6, characterized in that the imaging optics (30) are focused onto a point (36) located behind the projection surface (14).

9. The method according to claim 1, characterized in that the stop of the imaging optics (30) is reduced in such a way that the main gas flow (18) is located within the range of distances for sharp imaging.

10. The method according to claim 1, characterized in that the injection of the gas mixture (34) into the main gas is performed by means of one or more diffusers (32).

11. The method according to claim 10, characterized in that the one or more diffusers (32) are arranged movably within the flow space (10) together with the supply line of the gas mixture (34).

12. The method according to claim 1, characterized in that the gas mixture (34) only contains gas components which are non-toxic and non-asphyxiating for humans.

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