System and method for producing bubbles and / or drops using a nozzle

Abstract

The invention relates to a system (1) for producing bubbles (2) and / or drops (32), wherein the system (1) comprises a production device (3) for the bubbles (2) and / or drops (32) which has a nozzle (4) and a monitoring device (5) for monitoring a production operation of the production device (3).In order to produce bubbles (2) and / or drops (32) with a desired defined buoyancy neutrality and consistency, and to be able to selectively adjust the properties of the bubbles (2) and / or drops (32) during production, it is proposed that the monitoring device (5) includes a sound transducer (6) which is configured to generate signals depending on sound waves (7) produced by the production of the bubbles (2) and / or drops (32), wherein the monitoring device (5) includes an evaluation device (8) which is configured to evaluate the signals generated by the sound transducer (6) to determine a characteristic property of the bubbles (2) and / or drops (32) produced by the production device (3) and / or to determine a characteristic parameter of the production.

Description

TECHNICAL AREA OF INVENTION

[0001] The invention relates to a system for producing bubbles and / or drops. The system comprises a bubble and / or droplet production device, which has a nozzle, and a monitoring device for monitoring the production operation of the production device.

[0002] Furthermore, the invention relates to a method for producing bubbles and / or drops using a bubble and / or drop production system. The method provides that a production unit of the system generates bubbles and / or drops by means of a nozzle and that the production operation of the production unit is monitored by means of a monitoring device. STATE OF THE ART

[0003] Systems and nozzles for producing bubbles and / or drops are known in the prior art in various designs.

[0004] Droplet production can be achieved, for example, through systems and processes for aerosol generation or for the additive manufacturing of components.

[0005] The production of bubbles can in turn be directed towards different types of bubbles, especially soap bubbles to visualize currents, but also underwater bubbles.

[0006] Soap bubbles are used in many technical fields, for example for the quantitative detection of flows using optical measurement methods such as Lagrange Particle Tracking (LPT) or Particle Image Velocimetry (PIV).

[0007] For use in the aforementioned measurement methods, it is essential to produce buoyancy-neutral bubbles of uniform size. Buoyancy neutrality of the bubble is achieved when the weight of the bubble equals the weight of the gas it displaces. Under ideal conditions, the buoyancy-neutral bubble will then neither sink nor rise in a stationary surrounding gas.

[0008] Systems and methods for producing such bubbles are known. These systems and methods utilize so-called orifice nozzles, which have two concentrically arranged tubes surrounded by an outer nozzle housing. The inner tube carries a gas, and the outer tube carries a liquid to a section within the nozzle housing through which an auxiliary gas flows. This creates a tubular, gas-filled film of bubbles, which breaks up into individual bubbles due to instabilities. For example, helium-filled soap bubbles with diameters in the sub-millimeter or millimeter range can be produced in this way. Ideally, the bubbles form within the nozzle housing and exit through an outlet opening. The diameter of the bubbles depends on several factors, particularly the volumetric flow rates of the fluids involved.Simply by varying the volume flows, it is possible to generate bubbles of different average sizes and to realize a variety of different operating modes, which are characterized primarily by different size distributions of the generated bubbles and the location of the detachment of the bubbles from the bubble film.

[0009] Of particular importance for the desired buoyancy neutrality and the consistency of the produced bubbles is therefore the precise adjustment of the volumetric flow rates. These must be adjusted to achieve a stable operating condition of the nozzle, characterized by the production of bubbles with a narrow size distribution (for example, with a standard deviation of up to 10% from the mean, preferably only 7% from the mean).

[0010] In the prior art, attempts are made to ensure the desired properties of the generated bubbles, in part, by determining the required volumetric flow rates through visualization of the produced bubbles using high-speed shadow imaging. The volumetric flow rates are then set to constant values ​​and are no longer checked and / or adjusted during subsequent bubble production (e.g., within the framework of a measurement method such as Lagrange Particle Tracking (LPT) or Particle Image Velocimetry (PIV)).

[0011] A disadvantage is that the volume flows cannot be variably adjusted to changing requirements, such as a desired change in bubble size, or changing influencing factors, such as the temperature / viscosity of the liquid. Furthermore, photographic imaging of the bubbles cannot capture all properties, for example, their buoyancy neutrality.

[0012] Furthermore, measurement techniques such as LPT or PIV typically use multiple nozzles simultaneously to generate bubbles. For this purpose, the nozzles are connected and operated in parallel in so-called "linear nozzle arrays" (LNAs).

[0013] Such a linear arrangement of nozzles for bubble production is disclosed, for example, in DE 10 2015 115 382 B3.

[0014] Manufacturing tolerances of the individual nozzles necessitate, in order to achieve homogeneous bubble generation across all nozzles of the LNA, the operating modes of all nozzles in the entire LNA, which can comprise several hundred nozzles, possibly in combination with individual adaptation of the supplied volume flows for each nozzle. However, such a procedure is not feasible with reasonable effort according to the current state of the art, but would offer significant advantages and simplifications in both the manufacturing of the LNAs and their operation in the field.

[0015] DE 10 2019 106 017 A1 discloses a test device for a gas bubble detector of a medical device that can detect gas bubbles within a human body using ultrasound. To calibrate the gas bubble detector before its initial use, gas bubbles of a specific size or volume are generated by a gas bubble generation device and used as reference bubbles for calibration. To ensure that the size or volume of the reference bubbles meets the requirements, a phase transition detector is associated with the gas bubble generation device, which detects a phase boundary between liquid and gas in a bubble generation capillary. The phase transition detector has a drive mechanism for moving the phase transition detector along the capillary and / or includes a photoelectric sensor. The size or volume of the reference bubbles is determined by the gas bubble generation device.The volume of the generated bubbles corresponds to the location of the detected phase boundary between gas and liquid in the capillary. A gas injection device of the gas bubble generation device can be controlled so that the phase transition occurs at a desired location, thus generating bubbles of a predetermined size.

[0016] US Patent 2004 / 0144175A1 discloses a method for determining the properties of a liquid. The method involves generating bubbles in the liquid using a nozzle located within the liquid, through which a gas is emitted. By detecting and evaluating the sound waves generated when the bubbles are pinched off and released, properties of the liquid, in particular its density, and the size of the bubbles can be determined. A hollow cylindrical piezoelectric transducer surrounding the nozzle is used to detect the sound waves. A Doppler probe positioned above the nozzle also detects a signal characteristic of the velocity of the bubbles rising in the liquid. The detection signals from the hollow cylindrical transducer and the Doppler probe are subjected to frequency analysis for evaluation.

[0017] US 2021 / 0346888A1 discloses a method for producing monodisperse droplets. In this process, a first liquid flows into a second liquid in a channel of a microfluidic device under stable conditions. The first and second liquids are immiscible. A plurality of particles are introduced into the stream of the first liquid, causing the stream to break up and the particles to be encapsulated in a plurality of monodisperse droplets of the first liquid within the second liquid.

[0018] US Patent 2017 / 0292199A1 discloses a method for producing gas bubbles in a liquid. The gas bubbles are generated at the tip of an electrode by applying an alternating voltage to the electrode, creating a voltage difference between the electrode and a counter electrode. Depending on the frequency of the alternating voltage, the gas bubbles are detached from the tip of the electrode at regular intervals. Additionally, an ultrasonic signal is emitted at comparable intervals in the direction of the gas bubbles to facilitate their detachment. The amplitude of the alternating voltage signal at the electrode and the duration of the ultrasonic signal determine the size of the generated gas bubbles. The size of the gas bubbles is determined optically, acoustically, capacitively, or resistively. TASK OF INVENTION

[0019] The invention is therefore based on the objective of creating a system and a method for producing bubbles and / or drops, by which bubbles and / or drops with defined uniform properties, for example a defined buoyancy neutrality, and / or a narrow size distribution, can be produced, wherein these are also monitored in particular during the production of the bubbles and / or drops and thus targeted adjustments can still be made during production. SOLUTION

[0020] The problem solved by the invention is addressed by the features of the independent claims. Further details are set out in the dependent claims. DESCRIPTION OF THE INVENTION

[0021] The invention relates to a system for producing bubbles and / or drops, wherein the system comprises a production device for the bubbles and / or drops, which has a nozzle, and a monitoring device for monitoring a production operation of the production device.

[0022] According to the invention, the monitoring device includes a sound transducer. The sound transducer is configured to generate a signal based on the sound waves produced by the manufacture of the bubbles and / or drops. The generated signal can be, for example, an electrical signal or an optical signal. This signal is detected and further processed by the monitoring device.

[0023] The sound transducer can be a sound transducer for fluids, in particular a microphone or a hydrophone, or a structure-borne sound transducer, in particular a pickup based on an accelerometer.

[0024] The monitoring device also includes an evaluation device which is designed to evaluate the signals generated by the sound transducer in order to determine a characteristic property of the bubbles and / or drops produced by the manufacturing device and / or to determine a characteristic parameter of the manufacturing process.

[0025] The characteristic property of the bubbles and / or drops produced by the manufacturing device is - a size of the bubbles and / or drops and / or - a size distribution of the bubbles and / or drops and / or - a medium size of bubbles and / or drops and / or - a buoyancy neutrality of the bubbles.

[0026] The characteristic parameter of the manufacturing process is - an ejection frequency at which the bubbles and / or drops detach from the tubular bubble film and / or within the nozzle housing at regular intervals during the manufacturing process.

[0027] The monitoring device uses a sound transducer to monitor the properties of the produced bubbles and / or drops and / or the parameters of the production process. The evaluation unit then determines the properties of the bubbles and / or drops produced at the time the sound was generated and / or the parameters of the production process prevailing at that time.

[0028] The system is designed according to the invention to regulate the operation of the manufacturing equipment depending on the result of the evaluation by the evaluation device, by adjusting the volume flows of the supplied fluids.

[0029] In particular, with regard to soap bubble production, the signals can be used to determine whether the bubbles detach from the tubular bubble film and / or within the nozzle housing at regular intervals during the manufacturing process, thus indicating the desired mode of so-called "monodisperse bubbling." Regular bubble emergence from the nozzle housing results in a characteristic signal, which is characterized by a narrowband resonance in a frequency spectrum generated from the signal. This narrowband resonance, for example in the range between 5 kHz and 50 kHz (depending on bubble size), corresponds to the exit frequency of the bubbles from the nozzle housing. In addition to the fundamental frequency, the signal typically contains several harmonics whose resonant frequencies correspond to integer multiples of the fundamental frequency.These harmonics can also be detected by the evaluation unit from the generated signal. Based on this, the evaluation unit can then infer the properties of the currently generated bubbles and / or the characteristic parameters of the manufacturing process that produced these bubbles.

[0030] In the aforementioned "monodisperse bubbling" mode, the microbubbles detach at regular intervals from the tubular bubble film inside the nozzle housing. The precise location of detachment can be adjusted by selecting the operating parameters. This allows for a particularly fine distribution of bubble sizes.

[0031] The sound waves generated during bubble production are highly sensitive to changing production parameters. For example, as soon as the nozzle switches to a so-called "jetting mode," in which the bubbles detach from the bubble film outside the nozzle housing, the signal captured by the transducer transforms into a broadband noise similar to that of a turbulent free jet. However, even when bubbles are generated, if their detachment occurs within the nozzle housing far from the outlet, the characteristic resonances are dampened. Overall, therefore, non-invasive monitoring of bubble production and the bubbles themselves is possible by capturing and analyzing the nozzle signal.The advantages here are the comparatively low equipment costs compared to visualization using shadow techniques, and furthermore, the fact that sound transducers are inexpensive components and can also be integrated into the system or even the nozzle housing as microsystem components.

[0032] The transducers considered here include both airborne and structure-borne transducers, regardless of the signal generation method. Particularly suitable transducers for this system are MEMS transducers, i.e., components for creating microelectromechanical systems. The transducer can be, among other things, an airborne transducer such as a microphone or a structure-borne transducer such as a pickup or an accelerometer.

[0033] Preferably, the evaluation unit of the system is configured to generate a frequency spectrum based on the signals, in particular by means of a Fast Fourier transform, and to determine characteristic properties of the bubbles and / or drops produced by the manufacturing device and / or the operating mode of the manufacturing device from this frequency spectrum. The sound waves generated during the production of the bubbles and / or drops in the area of ​​the nozzle, in particular in the area of ​​the outlet opening of the nozzle housing, are characteristic of, on the one hand, the properties of the system or the parameters of the production process itself (for example, the supplied volume flows), and on the other hand, the bubbles and / or drops produced thereby. Therefore, conclusions can be drawn about the parameters of the production process or the properties of the produced bubbles and / or drops based on the sound waves or the generated signals.

[0034] The evaluation unit is designed to transform the signals from the time domain to the frequency domain. This is achieved, for example, through a Fast Fourier Transform. The frequency spectrum obtained by the transformation exhibits a characteristic sequence of frequency-dependent amplitudes, with the resonances characterized by amplitude maxima being particularly relevant for the evaluation. If the production of the bubbles and / or droplets proceeds optimally, e.g., if the nozzle operates in "monodisperse bubbling" mode during bubble production, the frequency spectrum contains a characteristic resonance with a fundamental frequency and, if applicable, one or more harmonics. The fundamental frequency generates an amplitude maximum at a characteristic fundamental frequency within the frequency spectrum.The harmonics form smaller amplitude maxima at harmonic frequencies that are multiples of the fundamental frequency. Depending on the size of the waveband, the fundamental frequency can, for example, range between 5 kHz and 50 kHz.

[0035] Both the fundamental frequency and the harmonic frequencies can be used for evaluation. The frequency spectrum is highly sensitive to changing properties of the bubbles and / or droplets and changing manufacturing parameters. As soon as the nozzle used to produce bubbles, for example, deviates from the preferred "monodisperse bubbling" mode, the resonances are dampened or may even cease to propagate altogether. Furthermore, a shift in the resonances towards other resonant frequencies is also possible.

[0036] Furthermore, the production rate of bubbles and / or drops, i.e., the number of bubbles and / or drops produced per time interval, can also be determined from the resonance frequency. In combination with the known volume flows of the fluids supplied to the nozzle, especially the gas and the liquid, the size of the bubbles and / or drops and, if applicable, their buoyancy neutrality can be determined. The evaluation of the spectral width of the resonances, or their quality factor, also provides information about the temporal regularity of bubble and / or droplet detachment and their size distribution. This allows all relevant characteristic properties of the bubbles and / or drops to be determined.All relevant characteristic parameters of the production process are determined using a measurement procedure, making it possible to achieve a particularly simple, fast and non-invasive quality control and determination of the properties of the process and the produced bubbles and / or drops.

[0037] In this context, it is specifically proposed that the evaluation unit be further configured to subtract an ambient frequency spectrum, derived from signals generated without the operation of the manufacturing equipment, from a signal frequency spectrum generated from the signals produced during operation of the manufacturing equipment. This makes it possible to disregard ambient noise not caused by the production of the bubbles and / or drops during the evaluation.

[0038] According to another interpretation, it is even possible to subtract all noises not directly attributable to bubble and / or droplet formation (in and / or at the nozzle), such as noises caused by pumps or other equipment during production. This leaves essentially only resonances in the frequency spectrum that are exclusively attributable to the formation of the bubbles and / or drops. This allows for a very precise determination of the characteristic properties of the bubbles and / or drops, or the characteristic parameters of the production process.

[0039] In particular, it is proposed that a characteristic property of the bubbles and / or drops produced by the manufacturing device and / or a characteristic parameter of the manufacturing process be determined from the frequency spectrum by - a resonance frequency of a resonance contained in the frequency spectrum is evaluated and / or - a resonance amplitude of a resonance contained in the frequency spectrum is evaluated and / or - an attenuation of a resonance contained in the frequency spectrum is evaluated and / or - a quality factor of a resonance contained in the frequency spectrum is evaluated - a ratio of different resonances contained in the frequency spectrum is evaluated and / or - a temporal change in the frequency spectrum is evaluated.

[0040] When parameters of bubble and / or droplet production change, or when the properties of the bubbles and / or drops change, the frequency spectrum can change in various ways. This allows one or more of the aforementioned properties of the frequency spectrum to be evaluated in order to deduce the properties of the bubbles and / or drops or the production parameters. Furthermore, the aforementioned properties can be determined not only for a single resonance contained in the frequency spectrum, but also for multiple resonances. In particular, the frequency of a fundamental frequency and / or harmonic(s) can shift to higher or lower frequencies, the amplitude of the resonance can be damped, and / or the spectral width and / or quality factor of the resonance can change.The frequency spectrum generated by the evaluation unit, or several frequency spectra recorded sequentially, can be compared in absolute terms with reference frequency spectra. In particular, several frequency spectra can be continuously evaluated and / or compared at defined intervals during the production of the bubbles and / or drops in order to determine time-dependent changes in the frequency spectrum and thus time-dependent changes in the produced bubbles and / or drops and / or the production process.

[0041] The evaluation device is designed according to the invention to determine, as a characteristic property of the bubbles and / or drops produced by the manufacturing device, a size of the bubbles and / or drops, a size distribution of the bubbles and / or drops, an average size of the bubbles and / or drops, and / or buoyancy neutrality of the bubbles. For this purpose, the evaluation device can, in particular, access numerous reference values ​​stored in a storage device. The resonance spectra or resonances are assigned to specific properties of the bubbles and / or drops, such as, in particular, their size, size distribution, average size, and / or buoyancy neutrality. The reference resonances or reference spectra are determined empirically or computationally beforehand for defined conditions of bubble and / or drop production, so that it is known which conditions give rise to which resonances / resonance spectra.

[0042] On the other hand, the evaluation device can also be configured to determine the aforementioned properties ad hoc by calculation, for example, by using the volume flow rates of the fluids supplied to the nozzle and the production frequency (in particular, the fundamental frequency of the resonances contained in the spectrum) of the bubbles and / or droplets in order to determine a bubble and / or droplet size and / or the degree of buoyancy neutrality of bubbles. Since the resonance frequency is characteristic of the production frequency of the bubbles and / or droplets, the droplet size and / or bubble size and the buoyancy neutrality of bubbles can be determined in combination with the known volume flow rates. The evaluation of the spectral width of one or more resonances, or...Their quality factor also provides information about the regularity of the detachment of the bubbles and / or drops and thus about a size distribution of the bubbles and / or drops produced successively over time.

[0043] Just as the bubble and / or droplet size and, if applicable, the buoyancy neutrality can be determined from the resonance frequency, it is possible to infer a distribution of the sizes of the produced bubbles and / or drops based on the damping of the resonance, i.e., based on the time-dependent change in the resonance amplitude.

[0044] Furthermore, the evaluation unit may be configured to take into account the volume flow rate of at least one fluid supplied to the production unit, namely a gas or a liquid, for determining the characteristic properties of the bubbles and / or drops produced by the production unit. In particular, a volume flow rate of helium and / or a soap solution may be considered when producing soap bubbles. As explained previously, the size of the bubbles, or their buoyancy neutrality, can then be determined by considering the bubble production rate, which can be read from the resonance frequency. The same applies to determining the size of the drops produced during droplet production.

[0045] As previously described, the evaluation unit can be configured to compare the determined frequency spectrum with one or more reference spectra. The characteristic reference spectra can be stored within the system's data memory or an external data storage device accessible to the evaluation unit. This comparison with references may be advantageous compared to an actual calculation of the bubble and / or droplet properties or manufacturing parameters.

[0046] The system is designed according to the invention to control the operation of the manufacturing device depending on the result of the evaluation by the evaluation unit. This advantageously allows for immediate intervention in the production of the bubbles and / or drops. In particular, a change can be made manually or automatically if the evaluation unit detects that the bubbles and / or drops exhibit undesirable properties, for example, that they are too large, too small, and / or form too early or too late in the manufacturing process. It is particularly advantageous that the production of the bubbles and / or drops can be influenced during the ongoing operation of the system in order to react to changing environmental conditions, such as ambient temperature and the resulting changes in the properties of the supplied fluids.It is also possible to react to changing requirements, for example, if a different size of bubbles and / or drops to be produced is desired.

[0047] If, for example, a resonance occurs in the frequency spectrum during bubble production, and its resonance frequency lies above a reference frequency characteristic of a desired bubble size, it can be concluded that the bubble film is breaking up into individual bubbles too quickly, resulting in bubbles that are smaller than desired. To eliminate this deviation, the flow rates of the supplied fluids can be adjusted, in particular the flow rate of the auxiliary air can be reduced.

[0048] Conversely, a resonance frequency that is too low compared to a reference frequency can indicate excessively large bubbles. This deviation can then be corrected by adjusting the volume flows of the fluids involved, in particular by increasing the volume flow of the auxiliary air.

[0049] The system's evaluation unit and / or a computer unit communicating with it can utilize artificial intelligence (AI) to generate and analyze resonance spectra and to control the operation of the manufacturing equipment based on the evaluation results. The aforementioned characteristics of the evaluation unit thus apply accordingly to the artificial intelligence (AI). Furthermore, the evaluation unit and / or the computer unit can be configured to apply machine learning (ML) methods, particularly to compare a generated frequency spectrum with reference frequency spectra. The AI ​​can then be trained using empirically recorded and analyzed frequency spectra of bubbles or drops with desired properties.

[0050] The nozzle for producing soap bubbles is preferably designed such that it has an inner tube, an outer tube concentrically surrounding the inner tube, and a nozzle housing concentrically surrounding both the inner and outer tubes. The nozzle housing has an outlet opening for bubbles produced by the nozzle to escape into the surrounding environment. The inner tube has an internal flow channel, an intermediate flow channel is formed between the inner tube and the outer tube, and an external flow channel is formed between the outer tube and the nozzle housing, with the internal flow channel and the intermediate flow channel opening into the external flow channel. In other words, the nozzle has two concentric tubes, namely the inner tube and the outer tube, and a nozzle housing surrounding them with an outlet opening for the bubbles to escape into the surrounding environment.A gas flows through the inner tube, which, without any further intervention, initially forms the liquid flowing between the two tubes into an elongated film of bubbles. This effect is enhanced by an auxiliary airflow flowing in the outer flow channel. Due to the so-called Rayleigh plateau instability, the tubular bubble film becomes unstable and breaks up into individual, significantly smaller bubbles, whose diameter, depending on the flow rates of the fluids involved, ranges from approximately 30% to 80% of the nozzle orifice diameter.

[0051] One embodiment of the system provides that the manufacturing device comprises several manufacturing device subunits, each configured for producing bubbles and / or droplets, with each manufacturing device subunit having its own dedicated transducer. Because each subunit has its own transducer, each nozzle, and thus the bubbles and / or droplets produced by it, can be monitored individually, and the operation of each nozzle can be adjusted separately. Preferably, each transducer receives only the sound waves from a single manufacturing device subunit and converts only these into signals. To achieve this, the transducer should be positioned as close as possible to the nozzle housing of the monitored nozzle, for example, on the outside or inside of the nozzle housing.

[0052] In principle, the system can have a single monitoring and / or evaluation unit for all manufacturing unit sub-units. However, a sound transducer should preferably be assigned to only one nozzle to prevent the received sound waves from being a mixture of sound waves from different nozzles, which could potentially lead to an incorrect evaluation result. This ensures that only the characteristic properties of the bubbles and / or droplets produced by this single manufacturing unit sub-unit, or the characteristic parameters of the production process of that single unit, can be evaluated.

[0053] The monitoring device can consist of multiple transducers that are not explicitly assigned to individual nozzles (e.g., in the form of a transducer array). The arrangement of the transducers can be adapted to the arrangement of the nozzles or, alternatively, be independent of it. The assignment of signals to individual nozzles can be achieved by analyzing the spatiotemporal waveforms based on time-of-flight and / or phase differences of the sound waves at various transducer positions. In particular, the position of the nozzle generating the signals can be determined using a technique called beamforming.

[0054] In addition to the system described above, the invention further proposes a method for producing bubbles and / or drops using a bubble and / or drop production system. The method can be implemented, in particular, using a system of the aforementioned type. The method provides that a production device generates bubbles and / or drops by means of a nozzle, and the production operation of the production device is monitored by means of a monitoring device.

[0055] The monitoring device generates signals by means of a sound transducer depending on the sound waves produced by the manufacture of the bubbles and / or drops, wherein an evaluation device evaluates the signals generated by the sound transducer to determine a characteristic property of the bubbles and / or drops produced by the manufacturing device or to determine a characteristic parameter of the manufacturing process.

[0056] The characteristic property of the bubbles and / or drops produced by the manufacturing device is - a size of the bubbles and / or drops and / or - a size distribution of the bubbles and / or drops and / or - a medium size of bubbles and / or drops and / or - a buoyancy neutrality of the bubbles.

[0057] The characteristic parameter of the manufacturing process is - an ejection frequency at which the bubbles and / or drops detach from the tubular bubble film and / or within the nozzle housing at regular intervals during the manufacturing process.

[0058] According to the invention, the system regulates the operation of the manufacturing equipment depending on the result of the evaluation by the evaluation device by adjusting the volume flows of the supplied fluids.

[0059] The method according to the invention thus provides for monitoring the produced bubbles and / or drops, or the production process, by converting sound waves generated during production into signals using a sound transducer. These signals are then analyzed to evaluate characteristic properties of the bubbles and / or drops produced by the production device and / or characteristic parameters of the production process. The characteristic properties of the bubbles and / or drops can, in particular, be a quantity (and / or – with respect to bubbles – buoyancy neutrality). A characteristic parameter of the production process to be determined can, for example, be a volume flow rate of the supplied fluids, namely the gas and the liquid, or a production rate of bubbles and / or drops, or a production location of the bubbles and / or drops relative to the nozzle housing.relative to an outlet opening of the nozzle housing through which the bubbles and / or drops leave the nozzle housing.

[0060] The evaluation of the signals by the evaluation device is preferably carried out in such a way that a frequency spectrum is generated and the characteristic properties of the bubbles and / or drops produced by the manufacturing device and / or the characteristic parameters of the manufacturing process are determined from the frequency spectrum. The transformation from a time domain of the signals to the frequency domain can be carried out in particular by a Fast Fourier transform.

[0061] The frequency spectrum of the sound waves generated during the production of bubbles and / or drops is characteristic of one or more production parameters, as well as of the bubbles and / or drops themselves. Therefore, by analyzing the frequency spectrum, conclusions can be drawn about the properties of the bubbles and / or drops and whether the production process was carried out correctly. This can be achieved either computationally or by comparison with characteristic reference spectra for specific properties or parameters.

[0062] In particular, the evaluation unit for generating the frequency spectrum can subtract an ambient frequency spectrum, derived from signals generated during the operation of the manufacturing equipment, from a signal frequency spectrum generated during operation of the manufacturing equipment. This ambient frequency spectrum is derived from signals generated without the operation of the manufacturing equipment. This approach allows for the subtraction of "background noise," which includes sound waves not caused by the production of the bubbles and / or drops, from the generated frequency spectrum. If the monitoring device is designed as a transducer array, the background noise can be further suppressed by spatial filtering (e.g., based on time-of-arrival differences and / or phase differences).After this preprocessing, the frequency spectrum ideally contains only those frequencies that were generated during bubble and / or droplet production, or even only those frequencies attributable to the detachment of bubbles from the bubble film or the detachment of droplets from a liquid stream. This approach can positively influence the quality and reliability of the evaluation results.

[0063] Furthermore, it may be provided that the evaluation device determines a characteristic property of the bubbles and / or drops produced by the manufacturing device and / or a characteristic parameter of the manufacturing process from the frequency spectrum by means of the evaluation device - evaluates a resonance frequency of a resonance contained in the frequency spectrum and / or - evaluates a resonance amplitude of a resonance contained in the frequency spectrum and / or - evaluates the damping and / or quality factor of a resonance contained in the frequency spectrum and / or - evaluates the ratio of different resonances contained in the frequency spectrum and / or - evaluates a temporal change in the frequency spectrum.

[0064] As previously explained with regard to the system according to the invention, the bubbles and / or drops produced by the manufacturing device, or the manufacturing process itself, are characterized by different properties of the frequency spectrum or the resonances contained therein. In particular, one or more resonances can change with respect to their resonance frequency, amplitude, and / or spectral width. By examining successive frequency spectra, a damping of a resonance, that is, a change in the resonance amplitude over time, can be observed. Furthermore, it is possible to evaluate the relationships between different resonances, in particular between a fundamental frequency and one or more harmonics, based on the frequency spectrum, for example, by comparing their resonance amplitudes, spectral widths, quality factors, or resonance frequencies.

[0065] In particular, evaluating the characteristic property(ies) of the generated bubbles and / or drops allows for the determination of their size, size distribution, average size, and / or buoyancy. The size and / or buoyancy of the bubbles and / or drops can be determined if the volumetric flow rates of the fluid used in their production are known. Furthermore, the size and thus their buoyancy can be determined based on the resonance frequency of the fundamental frequency in the frequency spectrum, which also corresponds to the generation frequency of the bubbles and / or drops.By observing the size distribution of the bubbles and / or droplets and / or an average size of the bubbles and / or droplets over time and / or across multiple nozzles involved in the manufacturing process, this can be determined. This is also possible by examining the sizes of the bubbles and / or droplets for the same nozzle over a defined period.

[0066] To determine the properties of the bubbles and / or droplets, it is recommended that the evaluation device take into account the volume flow rate of at least one of the fluids supplied to the production device. With regard to the production of soap bubbles, the gaseous fluid can be helium, while the liquid fluid can be a soap solution. From this, helium-filled soap bubbles can be produced, which, depending on their size, can achieve neutral buoyancy.

[0067] As explained previously, the evaluation unit can compare the frequency spectrum with one or more reference spectra during the evaluation process.

[0068] According to the invention, the system controls the operation of the manufacturing device depending on the result of the evaluation by the evaluation unit. This allows for particularly advantageous intervention in the ongoing manufacturing process, as the evaluation unit monitors the manufacturing parameters or the properties of the currently produced bubbles and / or drops, for example, a production rate of bubbles and / or drops, and then adjusts the manufacturing parameters, for example, by changing the volume flow rates supplied to the nozzle, in order to produce bubbles and / or drops with the desired size and / or buoyancy neutrality and / or production rate and / or consistency.

[0069] For example, in the production of soap bubbles, the bubbles can be formed by means of the nozzle by the gas, in particular helium, flowing through an inner tube of the nozzle, wherein the liquid, namely soap solution, flows through an intermediate flow channel formed between the inner tube and an outer tube concentrically surrounding the inner tube, and wherein an auxiliary gas flows through a nozzle housing concentrically surrounding the inner tube and the outer tube, wherein the inner flow channel and the intermediate flow channel open into the outer flow channel, and wherein soap bubbles produced by the nozzles exit into an environment through an outlet opening of the nozzle housing.

[0070] In particular, the evaluation unit can use the signals, especially a frequency spectrum generated from them, to determine the origin of the bubbles and / or droplets inside or outside the nozzle housing and / or the production rate and / or exit frequency of the bubbles and / or droplets from the nozzle housing. Depending on the evaluation result, measures can then be taken to control the operation of the production unit in such a way that a desired bubble and / or droplet size, bubble and / or droplet consistency, and / or buoyancy neutrality of the bubbles is achieved.

[0071] Finally, it can be provided that the manufacturing device produces bubbles and / or drops using a plurality of manufacturing device subunits, each of which can be assigned a sound transducer that generates signals for that manufacturing device subunit depending on the sound waves produced by the manufacturing of the bubbles and / or drops using that manufacturing device subunit. According to this embodiment, several manufacturing device subunits are used simultaneously for bubble and / or drop production. The sound waves of a specific manufacturing device subunit or the sound waves of its nozzle are received by a sound transducer assigned only to that manufacturing device subunit / nozzle and converted into a signal. This signal can then be analyzed by the evaluation unit of the manufacturing device in order to determine the output for each manufacturing device subunit or nozzle.The system can separately determine the properties of each nozzle, the resulting bubbles and / or droplets, or the properties of the manufacturing process used, and then preferably take suitable measures that affect only that specific manufacturing unit. A particular advantage is that not the entire system or the entire manufacturing unit with all its subunits undergoes any changes, but only the subunit whose bubble and / or droplet properties or manufacturing parameters do not correspond to a desired reference target. Furthermore, the monitoring unit can be designed so that no explicit assignment of each transducer to a specific manufacturing unit is made. In this design, the signals from a sufficient number of transducers are initially analyzed together (e.g., using a transducer array).To monitor the individual manufacturing equipment sub-unit, a sound source localization (e.g. using "beamforming") is first carried out based on the phase differences of the recorded signals, and only then is the corresponding signal analysis of the manufacturing equipment sub-unit performed.

[0072] Advantageous further developments of the invention result from the patent claims, the description and the drawings.

[0073] The advantages of features and combinations of features mentioned in the description are merely exemplary and can have an effect alternatively or cumulatively, without the advantages necessarily having to be achieved by embodiments according to the invention.

[0074] Regarding the disclosure content—not the scope of protection—of the original application documents and the patent, the following applies: Further features can be derived from the drawings—in particular, the geometries depicted and the relative dimensions of several components to one another, as well as their relative arrangement and functional connection. The combination of features from different embodiments of the invention or from features of different claims is also possible, deviating from the chosen cross-references of the claims, and is hereby encouraged. This also applies to features that are illustrated in separate drawings or mentioned in their description. These features can also be combined with features from different claims.Likewise, features listed in the patent claims may be omitted for further embodiments of the invention, but this does not apply to the independent patent claims of the granted patent.

[0075] The features mentioned in the claims and the description are to be understood, with regard to their number, as meaning that exactly that number or a greater number than the stated number is present, without the need for the explicit use of the adverb "at least". Thus, for example, if a nozzle is mentioned, this is to be understood as meaning that exactly one nozzle, two nozzles, or more nozzles are present. The features listed in the claims may be supplemented by further features or may be the only features that the subject matter of the respective claim possesses.

[0076] The reference numerals contained in the patent claims do not constitute a limitation of the scope of the subject matter protected by the patent claims. They merely serve the purpose of making the patent claims easier to understand. BRIEF DESCRIPTION OF THE FIGURES

[0077] The invention will now be further explained and described with reference to exemplary embodiments shown in the figures. Fig. Figure 1 shows a system for the production of bubbles with a manufacturing device for the bubbles and a monitoring device for monitoring a manufacturing operation of the manufacturing device. Fig. Figure 2 shows an illustration of a frequency spectrum generated by an evaluation unit of the monitoring device. Fig. Figure 3a shows a side view of a plurality of nozzles of a manufacturing apparatus and part of a monitoring apparatus with an array of transducers arranged in rows and columns. Fig. Figure 3b shows a frontal view of the nozzles and array of transducers according to Fig. 3a. Fig. Figure 4a shows a side view of another embodiment of a plurality of nozzles of a manufacturing apparatus and part of a monitoring apparatus with an associated array of several transducers. Fig. 4b shows a frontal view of the nozzles and array of transducers according to Fig. 4a. Fig. Figure 5 shows another embodiment of a system for producing bubbles, comprising a bubble manufacturing device and a monitoring device for monitoring the manufacturing operation of the manufacturing device. Fig. Figure 6 shows another embodiment of a system for producing bubbles, comprising a bubble manufacturing device and a monitoring device for monitoring the manufacturing operation of the manufacturing device. Fig. Figure 7 shows an embodiment of a nozzle of a manufacturing device for producing drops and part of a monitoring device for monitoring a manufacturing operation of the manufacturing device. FIGURE DESCRIPTION

[0078] Fig. Figure 1 shows an exemplary embodiment of a system 1 for producing bubbles 2, here soap bubbles.

[0079] The bubbles 2 can be used for various technical purposes, such as visualizing flows or measuring flow velocities (for example, in Particle Image Velocimetry (PIV)). For such applications, it is often essential that the bubbles 2 exhibit uniform characteristic properties or characteristic properties with a predefined distribution, as well as properties that remain constant over time (at least throughout the application). These properties of the bubbles 2 include, for example, their buoyancy neutrality and their size.

[0080] System 1 for producing bubbles 2 includes a bubble-producing device 3. This device 3 has a single nozzle 4. The nozzle 4 is designed for producing soap bubbles (so-called orifice nozzle).

[0081] The operation of the nozzle 4 and the bubbles 2 produced by it are significantly influenced by the volume flows of the fluids 13, 14, 15 supplied to the nozzle 4.

[0082] The nozzle 4 has a nozzle housing 18 in which an inner tube 16 and an outer tube 17 are arranged concentrically within each other. An inner flow channel 20 is formed within the inner tube 16. An intermediate flow channel 21 is formed between the outer surface of the inner tube 16 and the inner surface of the outer tube 17, and an external flow channel 22 exists between an outer surface of the outer tube 17 and an inner surface of the nozzle housing 18. Each of the channels 20, 21, 22 serves to supply a fluid 13, 14, 15, which contributes to the formation of the bubbles 2. Preferably, the inner flow channel 20 has a circular cross-section, while the intermediate flow channel 21 has an annular cross-section.

[0083] Here, the inner flow channel 20 is supplied with a first fluid 14, namely gas (here, for example, helium), from a source not shown, while the intermediate flow channel 21 is supplied with a second fluid 13, namely a liquid, here, for example, bubble fluid, from another source not shown. The outer flow channel 22 serves to supply a third fluid 15, here air as an auxiliary gas, into the nozzle housing 18 to promote the formation of the bubbles 2.

[0084] The nozzle housing 18 has an outlet opening 19 at one end region of the inner flow channel 20 and the intermediate flow channel 21, as well as at the end region of the outer flow channel 22. The outlet opening 19 is located near the end faces of the inner flow channel 20 and the intermediate flow channel 21, where all fluids 13, 14, 15, i.e., the soap bubble fluid, the helium, and the air, meet.

[0085] When fluids 13, 14, and 15 come into contact, a tube-like bubble film 30 is initially formed. This bubble film 30 is a helium-filled tube of bubble fluid. Depending on the flow rates of the fluids 13 and 14 (helium and bubble fluid) supplied, the bubble film 30 divides into individual bubbles 2. Ideally, the bubble film 30 breaks down into the bubbles 2 within the nozzle housing 18, so that the formed bubbles 2 flow through the outlet opening 19 of the nozzle housing 18.

[0086] System 1 also includes a monitoring device 5, which monitors the manufacturing operation of the manufacturing device 3 as well as the characteristic properties of the bubbles 2 produced by the manufacturing device 3.

[0087] The monitoring device 5 comprises a sound transducer 6 in the form of a microphone and an evaluation unit 8. The sound transducer 6 is arranged in the vicinity of the outlet opening 19 of the nozzle housing 18, preferably at a distance of 10 cm, less than 10 cm, less than 8 cm, or less than 5 cm. The evaluation unit 8 includes, by way of example, a signal amplifier 25 and a signal processing unit 24; however, alternatively or additionally, other electronic components can be used. The sound transducer 6 converts sound waves 7 generated by the production of the bubbles 2 into signals. These signals are then amplified by the signal amplifier 25 and analyzed and evaluated by the signal processing unit 24 in order to determine characteristic properties of the produced bubbles 2 and / or characteristic parameters of the production process.

[0088] The signal processing unit 24 is designed to analyze the generated signals. For this purpose, it transforms the signals from the time domain to the frequency domain, for example by applying a Fast Fourier Transform (FFT).

[0089] Fig. Figure 2 shows a frequency spectrum 9 (schematic) generated by the evaluation unit 8. This frequency spectrum 9 exhibits a plurality of resonances 10, 11, 12 (not all resonances are labeled with a reference numeral). The frequency spectrum 9 is represented as a diagram where the x-axis indicates a frequency f in Hz and the y-axis an amplitude, in this case the sound pressure level "SPL-Ref" in decibels. This amplitude is calculated by subtracting a reference amplitude (Ref) from the total signal amplitude (SPL). The reference amplitude is taken from an ambient frequency spectrum generated from acoustic ambient signals that occur without the operation of the manufacturing unit 3. The resulting frequency spectrum 9, or the signal amplitudes (SPL - Ref), are therefore already corrected for ambient noise.

[0090] The process for producing bubbles 2 using system 1 is carried out, for example, by supplying defined volume flows of fluids 13, 14, 15 to the production device 3 of system 1. As previously explained, a bubble film 30 is initially generated, which, due to Rayleigh plateau instability, becomes unstable along its longitudinal axis after approximately five times its diameter and breaks up into individual bubbles 2 (soap bubbles) several millimeters in size (for example, about 5 mm to 10 mm). The diameter of the bubbles 2 depends on the supplied volume flows of fluids 14 (helium) and 13 (soap bubble fluid) and is approximately in the range of 30% to 80% of the diameter of the outlet opening 19 of the nozzle housing 18.

[0091] The size of the produced bubbles 2 depends on the flow rates of the fluids 13 and 14 remaining within a defined range. By precisely adjusting the flow rates of helium and bubble fluid, up to eight different stable operating modes of the production device 3, as reported in the literature, can be achieved. The desired range for bubble production 2 is referred to as "monodisperse bubbling." This "monodisperse bubbling" is characterized by high operational stability of the production process and very low size variation in the produced bubbles 2. The standard deviation, for example, is approximately 7% of the mean. This low size variation is a prerequisite for producing a large number of bubbles 2 with highly similar properties such as size, consistency, and / or buoyancy.

[0092] In the preferred manufacturing mode of "monodisperse bubbling," the bubbles 2 detach themselves from the tubular bubble film 30 at regular intervals within the outer flow channel 22 of the nozzle housing 18. The point of detachment before reaching the outlet opening 19 can be adjusted by selecting the operating parameters of the manufacturing device 3, in particular the supplied volumetric flow rates of the fluids 13, 14, 15. This results in a very small size variation between the produced bubbles 2.

[0093] The formation of the bubbles 2 generates characteristic sound waves 7, which are received by the sound transducer 6 of the monitoring device 5 and converted into electrical signals. The acoustic signal has a resonant frequency characteristic of the bubbles 2 produced and the bubble production process (usually a fundamental frequency), which corresponds to the production frequency of the bubbles 2, i.e., the number of bubbles 2 produced per time interval. In addition to this fundamental frequency, numerous integer harmonics are typically excited, whose resonant frequency is a multiple of the fundamental frequency. Depending on the size of the bubbles 2 produced, the fundamental frequency, when the desired "monodisperse bubbling" is achieved, preferably lies between 5 kHz and 50 kHz.

[0094] The acoustic signal, or the generated sound waves 7, react sensitively to changes in the characteristic properties of the bubbles 2 or the parameters of the manufacturing process. As soon as the nozzle 4, for example, switches to an undesired so-called "jetting" mode, the resonances 10, 11, 12 are replaced by a broadband noise signal, the so-called "jet noise." However, much earlier, if the detachment of the bubbles 2 occurs too far in or too far out in the nozzle housing 18, the resonances 10, 11, 12 in the frequency spectrum 9 are already damped. This creates an "acoustic footprint" of the nozzle 4, based on which the desired operating mode of the nozzle 4 can be recognized and / or set.

[0095] As explained, the fundamental resonant frequency of the frequency spectrum 9 corresponds to the formation rate of the bubbles 2. This allows the signal processing unit 24 of the evaluation unit 8, in combination with the known volume flows of the supplied fluids 13, 14, to determine the size of the bubbles 2 and thus their buoyancy neutrality. The spectral width of a resonance 10, 11, 12 within the frequency spectrum 9 also provides information about the regularity of the bubble detachment and thus about their size distribution. The same applies not only to the width of the resonance 10, 11, 12, but also to its quality factor (= resonance frequency / resonance width). Therefore, all characteristic properties of the bubbles 2 can be determined by a single measurement of the monitoring unit 5.

[0096] The acoustic signals generated and evaluated by the sound transducer 6 and the evaluation unit 8 are spectrally analyzed during the ongoing operation of the manufacturing unit 3, e.g. by a sliding Fast Fourier analysis.

[0097] If, for example, it is determined based on the production frequency (and / or the size determined therefrom) of the bubbles 2 that the detachment of the bubbles 2 from the bubble film 30 takes place at a location defined as optimal within the external flow channel 22 of the nozzle housing 18, the production process can be continued unchanged.

[0098] In contrast, with a 15% increase in the helium volume flow, the bubbles 2 detach only outside the nozzle housing 18. As a result, the sound waves 7, or the acoustic signal generated by the transducer 6, undergo such a significant change that the resonances 10, 11, 12 are excessively damped or considerably weaker. The "maxima" formed in the frequency spectrum 9 from several individual and spectrally closely spaced resonances exhibit a large spectral width or a low quality factor and are also shifted to lower frequencies. Individual resonances 10, 11, 12 are superimposed by a multitude of further resonances 10, 11, 12, so that they are hardly discernible anymore.

[0099] However, once a resonance frequency of a resonance 10, 11, 12 in the frequency spectrum 9 has been identified – assuming an optimal operating mode of the manufacturing device 3 (for example, by comparison with reference frequencies) – the mean diameter of the produced bubbles can be determined from the volume flows of the fluids 13, 14. For example, assuming that leakage of the helium volume flow during bubble production is negligible, the mean diameter of the bubbles 2 can be calculated directly from the helium volume flow and the separation frequency. The calculation is given by the formula d=qV,Hef⋅6π3 where q v, He specifies the volume flow rate of the helium, f the detachment frequency and d the mean (inner) diameter of the bubbles 2.

[0100] Furthermore, by analyzing error propagation, changes in the resonance frequency or the quality factor of the resonance 10, 11, 12 can be used to determine the size distribution of the bubbles 2. The ratio of the volume flow rates of helium and soap bubble fluid, in turn, provides information about the degree of buoyancy neutrality of the bubbles 2. This also applies under the assumption that leakage of the volume flow rates is negligible.

[0101] Fig. 3a and Fig. Figure 3b shows a section of a manufacturing device 3 with a plurality of nozzles 4 arranged one above the other, and a section of a monitoring device 5 with a circuit board 27 on which an array of a plurality of transducers 6 arranged one above the other and next to each other is arranged. The transducers 6 are microphones located on the back side of the circuit board 27, which are connected to a front side of the circuit board 27 via connecting channels 26 and can thus be influenced by the sound waves 7 generated in the area of ​​the nozzles 4.

[0102] According to this embodiment, the circuit board 27 is oriented relative to the nozzles 4 such that the large surface plane of the circuit board 27 is essentially orthogonal to the exit plane of the outlet openings 19 of the nozzles 4. Fig. Figure 3a shows a side view of nozzle 4. Fig. Figure 3b shows the corresponding frontal view of the nozzles 4. As in particular in Fig. As can be seen in 3b, the circuit board 27 is located laterally offset next to the nozzles 4 arranged one above the other, so that the bubbles 2 emerging from the nozzles 4 flow mainly along the front of the circuit board 27.

[0103] A total of six nozzles 4 are arranged one above the other in a linear arrangement, each nozzle 4 belonging to one of several manufacturing unit sub-units 23, 23', 23" of the manufacturing unit 3. Each nozzle 4 can be targeted by means of "beamforming" by a plurality of the transducers 6 arranged on the circuit board 27.

[0104] The circuit board 27 has a plurality of windows 28, between which grid struts extend in the vertical and horizontal directions. Several sound transducers 6 are arranged around the circumference of each window 28, with each section of a grid strut that defines one side of the respective window 28 carrying a sound transducer 6. The sound transducers 6 are located centrally on the respective grid strut, both with respect to the distance between adjacent windows 28 and with respect to the side length of the respective window 28.

[0105] Between adjacent or superimposed windows 28 there is a sound transducer 6, which is equally assigned to both windows 28.

[0106] The array of sound transducers 6 is oriented relative to the nozzles 4, as shown in the figures, such that the centers of two windows 28 arranged one behind the other lie on a straight extension of a surface normal of the outlet opening 19 of a nozzle 4. This allows the sound waves 7 from a nozzle 4 to pass through the windows 28 arranged one behind the other in succession. In the illustrated embodiment, there is no explicit assignment of the sound transducers 6 to the individual nozzles 4; the source of the acoustic signals is determined here from the time-of-flight differences of the acoustic signals from the nozzles 4 to the sound transducers 6 (beamforming).

[0107] Fig. 4a and Fig. Figure 4b shows another possible embodiment of a system 1 with a manufacturing device 3 for the bubbles 2 and a monitoring device 5. The manufacturing device 3 again has a linear arrangement with several nozzles 4 arranged one above the other. The monitoring device 5 comprises a circuit board 27 with a plurality of sound transducers 6, which in turn can detect sound waves 7 on the front of the circuit board 27 opposite the sound transducers 6 via connecting channels 26, which connect the back of the circuit board 27 with the front of the circuit board 27.

[0108] According to this embodiment, the circuit board 27 is oriented relative to the nozzles 4 such that the large surface plane of the circuit board 27 is essentially parallel to the outlet plane of the outlet openings 19 of the nozzles 4. In order not to obstruct the exit of the bubbles 2 from the nozzles 4, the circuit board 27 has a plurality of windows 28 through which the bubbles 2 can pass unhindered.

[0109] Each nozzle 4 is assigned its own window 28, the center point of which lies on a straight extension of a surface normal of the associated outlet opening 19. The transducers or the connecting passages 26 extending through the circuit board 27 are arranged regularly around the windows 28. Here, the windows 28 are arranged in a square pattern, with each window 28 assigned four transducers 6. Alternatively, the windows 28 can have a different number, geometric shape, or arrangement of transducers 6.

[0110] Fig. Figure 5 shows a further embodiment of a system 1 for producing bubbles 2. The system 1 again comprises a production device 3 and a monitoring device 5. The production device 3 has a nozzle 4 with a sound transducer 6 that is in contact with or attached to a nozzle housing 18 of the nozzle 4.

[0111] Although not shown here, the manufacturing device 3 can have additional nozzles 4 besides the single nozzle 4 shown, so that an array arrangement as in the Fig. 3a, Fig. 3b, Fig. 4a, Fig. 4b results.

[0112] The nozzle housing 18 carries a circuit board 27 on its outer surface in the area of ​​the outlet opening 19, containing the transducer 6 (among other electronic components not shown). The transducer 6 is a microphone, in this case a digital MEMS microphone. A connecting channel 26 extends from the transducer 6 through the nozzle housing 18 to the outlet opening 19, with the connecting channel 26 and the outlet opening 19 being separated by a diaphragm 31. The connecting channel 26 is preferably oriented orthogonally to the surface normal of the exit plane of the outlet opening 19 and the longitudinal axis of the bubble film 30.

[0113] The sound transducer 6 is connected via the circuit board 27 to a circuit 29 (FPGA) and a power supply, wherein a signal processing unit 24 processes the acoustic signals generated by the sound transducer 6 and transforms them into a frequency range in order to produce a frequency spectrum 9 (as already described above). Fig. 1 and Fig. 2 explained) to analyze. This allows characteristic properties of the produced bubbles 2 and / or characteristic parameters of the production plant to be determined.

[0114] Fig. Figure 6 shows another possible embodiment of a system 1 for producing bubbles 2.

[0115] The monitoring device 5 includes a sound transducer 6 in the form of an accelerometer, specifically a digital MEMS accelerometer. The sound transducer 6 is located on the outside of the nozzle housing 18 of the nozzle 4, near the outlet opening 19, and can detect structure-borne sound transmitted via the nozzle housing 18. The sound transducer 6 is part of a circuit board 27, which also includes associated logic and / or circuits for signal processing and analysis (shown here only).

[0116] Fig. Figure 7 shows an exemplary embodiment of a (not fully illustrated) system 1 for producing drops 32.

[0117] The system comprises a nozzle 4, which is designed here as a so-called two-fluid nozzle with an inner flow channel 20 for liquid and an outer flow channel 22 for gas and / or air concentrically surrounding the inner flow channel 20. The inner flow channel 20 and the outer flow channel 22 open into a common outlet opening 19 of a nozzle housing 18 of the nozzle 4, namely the inner flow channel 20 with a liquid outlet 35 that has a reduced diameter compared to a first subsection of the inner flow channel 20, and the outer flow channel 22 with an annular gap 34 surrounding the liquid outlet 35.

[0118] An outer surface of the nozzle housing 18 carries a circuit board 27 near the outlet opening 19, which includes a sound transducer 6 as part of a monitoring device 5. The circuit board 27 may also include other electronic components in addition to the sound transducer 6, which are not shown here.

[0119] In the production of droplets 32, the gas escaping through the annular gap 34, for example air, serves to break up the liquid exiting from the liquid outlet 35 into droplets 32, which then usually spread out into the surroundings in a droplet cone 33 emanating from the outlet opening 19 of the nozzle 4.

[0120] The formation of the droplets 32 generates characteristic sound waves 7 in the nozzle housing 18. The sound waves 7 propagate as structure-borne sound through the nozzle housing 18 and are received by the sound transducer 6 of the monitoring device 5 and converted into electrical signals.

[0121] The electrical signals are then evaluated by an evaluation unit (not shown) of the monitoring device 5 using frequency analysis, for example, Fourier analysis. The signal processing and analysis can be performed analogously to the preceding embodiments of the bubble production process. To avoid repetition, reference is made to the description accompanying the preceding figures. REFERENCE MARK LIST 1 system 2 bladders 3 Manufacturing equipment 4 nozzles 5 Monitoring device 6 sound transducers 7 sound wave 8 Evaluation unit 9 Frequency spectrum 10 Resonance 11 Resonance 12 Resonance 13 Fluid 14 Fluid 15 Fluid 16 inner tube 17 Outer pipe 18 nozzle housings 19 Outlet opening 20 internal flow channel 21 Intermediate flow channel 22 External flow channel 23 Manufacturing equipment sub-unit 24 Signal processing unit 25 signal amplifiers 26 Connecting corridor 27 circuit boards 28 windows 29 circuit 30 bubble film 31 Membran 32 drops 33 droplet cones 34 Annular gap 35 Liquid outlet

Claims

[1] System (1) for producing bubbles (2) and / or drops (32), wherein the system (1) comprises a production device (3) for the bubbles (2) and / or drops (32) having a nozzle (4), and a monitoring device (5) for monitoring a production operation of the production device (3), wherein the monitoring device (5) comprises a sound transducer (6) which is configured to generate signals depending on sound waves (7) generated by the production of the bubbles (2) and / or drops (32), wherein the monitoring device (5) comprises an evaluation device (8) which is configured to evaluate the signals generated by the sound transducer (6) to determine a characteristic property of the bubbles (2) and / or drops (32) produced by the production device (3) and / or to determine a characteristic parameter of the production, wherein the system (1) is configured,in order to control the operation of the manufacturing device (3) depending on the result of the evaluation of the evaluation device (8) by adjusting the volume flows of the supplied fluids (13, 14, 15), whereby the characteristic property of the bubbles (2) and / or drops (32) produced by the manufacturing device (3), - a size of the bubbles (2) and / or drops (32) and / or - a size distribution of the bubbles (2) and / or drops (32) and / or - a medium size of bubbles (2) and / or drops (32) and / or - a buoyancy neutrality of the bubbles (2) and wherein the characteristic parameter of the production is an exit frequency with which the bubbles (2) and / or droplets (32) detach from the tubular bubble film and / or within the nozzle housing (18) at regular intervals during the production process. [2] System (1) according to claim 1, wherein the evaluation device (8) is configured to generate a frequency spectrum (9) based on the generated signals, in particular by Fast Fourier transformation, and to determine from the frequency spectrum (9) the characteristic property of the bubbles (2) and / or drops (32) produced by the manufacturing device (3) and / or the characteristic parameter of the manufacturing process. [3] System (1) according to claim 2, wherein the evaluation device (8) is configured to subtract an ambient frequency spectrum, which is derived from signals generated without the operation of the manufacturing device (3), for the generation of the frequency spectrum (9) from a signal frequency spectrum generated from the signals generated during the operation of the manufacturing device (3). [4] System (1) according to claim 2 or 3, wherein a characteristic property of the bubbles (2) and / or drops (32) produced by the manufacturing device (3) and / or a characteristic parameter of the manufacturing process is determined from the frequency spectrum (9) by - a resonance frequency of a resonance (10, 11, 12) contained in the frequency spectrum (9) is evaluated and / or - a resonance amplitude of a resonance (10, 11, 12) contained in the frequency spectrum (9) is evaluated and / or - a damping and / or a quality factor of a resonance (10, 11, 12) contained in the frequency spectrum (9) is evaluated and / or - a ratio of different resonances (10, 11, 12) contained in the frequency spectrum (9) is evaluated and / or - a temporal change of the frequency spectrum (9) is evaluated. [5] System (1) according to one of the preceding claims, wherein the evaluation device (8) is configured to take into account a volume flow of at least one of the fluids (13, 14, 15) supplied to the manufacturing device (3) for the determination of the characteristic property of the bubbles (2) and / or drops (32) produced by the manufacturing device (3). [6] System (1) according to any one of claims 2 to 5, wherein the evaluation device (8) is configured to compare the frequency spectrum (9) with one or more reference spectra. [7] System (1) according to one of the preceding claims, wherein the nozzle (4) has an inner tube (16), an outer tube (17) concentrically surrounding the inner tube (16) and a nozzle housing (18) concentrically surrounding the inner tube (16) and the outer tube (17), wherein the nozzle housing (18) has an outlet opening (19) for the release of bubbles (2) produced by the nozzle (4) into an environment, wherein the inner tube (16) has an inner flow channel (20), wherein an intermediate flow channel (21) is formed between the inner tube (16) and the outer tube (17) and wherein an outer flow channel (22) is formed between the outer tube (17) and the nozzle housing (18), wherein the inner flow channel (20) and the intermediate flow channel (21) open into the outer flow channel (22). [8] System (1) according to one of the preceding claims, wherein the manufacturing device (3) comprises several manufacturing device sub-units (23', 23'', 23''') each configured to produce bubbles (2) and / or drops (32), wherein each manufacturing device sub-unit (23', 23'', 23''') is associated with a sound transducer (6, 6', 6''). [9] System (1) according to one of the preceding claims, wherein the manufacturing device (3) comprises several manufacturing device sub-units (23', 23'', 23''') each configured to produce bubbles (2) and / or drops (32), wherein at least one sound transducer (6) is jointly assigned to two or more manufacturing device sub-units (23', 23'', 23'''). [10] System (1) according to one of the preceding claims, wherein the monitoring device (5) comprises a plurality of sound transducers (6, 6', 6'') which are jointly assigned to at least one nozzle (4) of the manufacturing device (3) so that the latter receives sound waves (7) generated by the manufacturing operation of this nozzle (4). [11] Method for producing bubbles (2) and / or drops (32) using a system (1) for producing bubbles (2) and / or drops (32), in particular a method using a system (1) designed according to one of the preceding claims, wherein a production device (3) produces bubbles (2) and / or drops (32) using a nozzle (4) and wherein the production operation of the production device (3) is monitored by means of a monitoring device (5), wherein the monitoring device (5) generates signals using a sound transducer (6) depending on sound waves (7) generated by the production of the bubbles (2) and / or drops (32), wherein an evaluation device (8) evaluates the signals generated by the sound transducer (6) to determine a characteristic property of the bubbles (2) and / or drops (32) produced by the production device (3) and / or to determine a characteristic parameter of the production,wherein the system (1) regulates the operation of the manufacturing device (3) depending on the result of the evaluation of the evaluation device (8) by adjusting the volume flows of the supplied fluids (13, 14, 15), wherein the evaluation device (8) is a characteristic property of the bubbles (2) and / or drops (32) produced by the manufacturing device (3), - a size of the bubbles (2) and / or drops (32) and / or - a size distribution of the bubbles (2) and / or drops (32) and / or - a medium size of bubbles (2) and / or drops (32) and / or - a buoyancy neutrality of the bubbles (2) is determined and the evaluation device (8) determines an exit frequency as a characteristic parameter of the production, with which the bubbles (2) and / or drops (32) detach from the tubular bubble film and / or within the nozzle housing (18) at regular intervals during the production process. [12] Method according to claim 11, wherein the evaluation device (8) generates a frequency spectrum (9) based on the signals, in particular by Fast Fourier transform, and determines from the frequency spectrum (9) the characteristic property of the bubbles (2) and / or drops (32) produced by the manufacturing device (3) and / or the characteristic parameter of the manufacturing process. [13] Method according to claim 12, wherein the evaluation device (8) for generating the frequency spectrum (9) subtracts from a signal frequency spectrum, which is generated from the signals generated during the operation of the manufacturing device (3), an ambient frequency spectrum, which is generated from signals generated without the operation of the manufacturing device (3). [14] Method according to claim 12 or 13, wherein the evaluation device (8) determines from the frequency spectrum (9) a characteristic property of the bubbles (2) and / or drops (32) produced by the manufacturing device (3) and / or a characteristic parameter of the manufacturing process by the evaluation device (8) - evaluates a resonance frequency of a resonance (10, 11, 12) contained in the frequency spectrum (9) and / or - evaluates a resonance amplitude of a resonance (10, 11, 12) contained in the frequency spectrum (9) and / or - evaluates a damping and / or a quality factor of a resonance (10, 11, 12) contained in the frequency spectrum (9) and / or - evaluates a ratio of different resonances (10, 11, 12) contained in the frequency spectrum (9) and / or - evaluates a temporal change in the frequency spectrum (9). [15] Method according to one of claims 11 to 14, wherein the evaluation device (8) for determining the characteristic property of the bubbles (2) and / or drops (32) produced by the manufacturing device (3) takes into account a volume flow of at least one of the fluids (13, 14, 15) supplied to the manufacturing device (3). [16] Method according to any one of claims 11 to 15, wherein the evaluation device (8) compares the frequency spectrum (9) with one or more reference spectra. [17] Method according to any one of claims 11 to 16, wherein for the production of bubbles (2) a gas, in particular helium, flows through an inner flow channel (20) of an inner tube (16) of the nozzle (4), a liquid, in particular a soap solution, flows through an intermediate flow channel (21) formed between the inner tube (16) and an outer tube (17) concentrically surrounding the inner tube (16), and an auxiliary gas flows through a nozzle housing (18) concentrically surrounding the inner tube (16) and the outer tube (17), wherein the inner flow channel (20) and the intermediate flow channel (21) open into the outer flow channel (22), and wherein bubbles (2) produced by the nozzle (4) exit into an environment through an outlet opening (19) of the nozzle housing (18). [18] Method according to one of claims 11 to 17, wherein the evaluation device (8) infers, on the basis of the signals, in particular on the basis of a frequency spectrum (9) generated therefrom, the origin of the bubbles (2) and / or drops (32) inside or outside a nozzle housing (18) of the nozzle (4) and / or a production rate and / or exit frequency of the bubbles (2) and / or drops (32) from the nozzle housing (18). [19] Method according to one of claims 17 or 18, wherein the evaluation device (8) is aware of a volume flow rate of at least one of the fluids (13, 14, 15) supplied to the production device (3) and of a production rate of the bubbles (2) and / or drops (32). - a size of the bubbles (2) and / or drops (32) and / or - a size distribution of the bubbles (2) and / or drops (32) and / or - a medium size of bubbles (2) and / or drops (32) and / or - concludes that the bubbles are buoyantly neutral (2). [20] Method according to any one of claims 11 to 19, wherein the manufacturing device (3) produces bubbles (2) and / or drops (32) by means of a plurality of manufacturing device subunits (23, 23', 23"), wherein each manufacturing device subunit (23, 23', 23") is assigned its own sound transducer (6, 6', 6'') which generates signals for the manufacturing device subunit (23, 23', 23") depending on the sound waves (7) generated by the production of the bubbles (2) and / or drops (32) by means of this manufacturing device subunit (23, 23', 23"). [21] Method according to one of claims 11 to 20, wherein the monitoring device (5) generates signals by means of a plurality of signals arranged in an array, wherein the evaluation device (8) analyzes spatiotemporal waveforms of the signals by evaluating time-of-flight differences and / or phase differences of electromagnetic waves at different transducer positions, in particular by means of beamforming, in order to determine a position of the nozzle (4) causing a particular signal.

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