DE102019123298A1 - Method and arrangement for the location-specific characterization of the phase composition and the flow conditions within a foam volume - Google Patents

Abstract

The invention relates to a method and an arrangement for the model-based determination of the location-specific properties of a foam volume. The invention enables the phase composition, in particular of particle-laden foams, to be recorded by measurement technology also in the interior of a flowing foam volume.

Description

The invention relates to a method and an arrangement for the spatially resolved characterization of the phase composition and the spatially resolved flow conditions within a foam volume.

In industrial production, in wastewater treatment, in paper recycling and in ore processing, the use of foams in foam flotation is known as a process for separating various solid particles. In doing so, chemical substances are often introduced into the solid-particle-liquid mixture present. These introduced substances often bind to the solid particles and give them the property "hydrophobic". By adding a foaming agent and using a bubble generator, which mostly blows air through the solid-liquid mixture, a foam is generated to which the now hydrophobic solid particles bind. The foam thus has a load of solid particles.

Optical methods for measuring the foam crown height are predominantly used to characterize a foam, which may also be loaded. Other widespread use includes Ultrasound-based systems or measurements of electrical conductivity to determine the fill level of a column of liquid located under a foam.

The DE 10 2004 036 645 A1 shows a level sensor device by means of which, for example, the fill level of liquids in containers can be determined using an ultrasonic measuring method. The invention provides for an ultrasonic transducer to be embedded in a dip tube, the transducer emitting signals being arranged as close as possible to the bottom of the container. The transducer then sends a signal to a) a reflector, which is also located in the liquid and attached at a defined distance, and b) to the liquid boundary layer. The liquid-specific speed of sound is determined from the signal propagation time of the echo from the reflector. The height of the liquid column is now determined on the basis of the signal transit time of the signal reflected from the interface between fluid and air, which has also been determined. However, the method is only suitable for liquids and does not allow foams to be characterized. Rather contrary to the existing technical problem, the invention claims that the method delivers error-free measured values despite foam formation on the surface of the liquid, since the sound signal does not even penetrate the foam due to the design.

The US 8,495,913 B2 discloses an acoustic method, which enables the determination of the positions, that is to say the phase boundaries, of different phases (e.g. liquid-phase-gas phase boundary) in containers. For this purpose, ultrasonic transducers are used, which are arranged in pairs on an axis parallel to the container wall (receiver-transmitter pair) both in the upper part and in the lower part of the container, the number of pairs between 2 and 500 being suggested for industrial applications. Each transmitter is assigned a corresponding opposite receiver, which generates an electrical signal from a sound signal from its transmitter. In the following, the electrical signals generated by the receivers are recorded. By comparing the acoustic properties of the electrical signals of the individual ultrasonic transducer pairs at different heights of the container, the acoustic properties of the different media within which the ultrasonic transducer pairs are attached in the container can be determined. This makes it possible to determine at which point (on the axis parallel to the container side wall) which phase prevails. However, the method and the arrangement are not suitable for the determination of phase contents or the vertical speed within a foam.

The DE 198 10 092 A1 shows an ultrasound-based method for real-time recording of foam parameters during the production process of polyurethane foam (PUR) from the liquid phase to the presence of a stable, solid foam. Here, the foam to be examined is fed into a separate measuring chamber and sounded through by an ultrasonic transducer using a transmission method . Material parameters such as viscosity, speed of sound, bubble size and bubble structure can be determined via a computer-aided evaluation (the invention does not mention a specific evaluation method here). However, the method does not include a spatially resolving measurement of the properties of the foam, for example flow fields within the developing foam. These cannot be recorded.

From the DE 10 2006 057 772 A1 a device for producing foam and an associated method for characterizing the foam produced are known. In this case, at least two pairs of electrodes are arranged in an electrode chamber, which is placed on a container containing a dispersion and connected to it, which measure the specific conductivity of the foam in a time-resolved manner while it rises in the electrode chamber during the manufacturing process. This enables a statement to be made about the aging process of the foam as well as the bubble size distribution or gas content. With an additionally arranged camera system, i.e. optical detection, the disintegration process of the Foam volume can be characterized and drainage (reduction in the proportion of liquid) can be observed. However, the method does not enable phase compositions to be determined, in particular particle content, and does not record spatially resolved flow velocities in the foam.

From the WO 2005/003758 A1 a method for determining characteristic foam parameters is known. For this purpose, an image of the foam is recorded by means of a recording device (for example CCD camera) and an electronic image (binary image) of this is then generated. An image analysis using various mathematical methods is used to determine the parameters of the foam, especially the structure, composition or the state of aging. Flowing, disintegrating or stable, solid foams can be examined here. The disadvantage of the method is that the optical evaluation does not allow any conclusions to be drawn about structural parameters within the volume and thus any flow zones at various locations within the foam volume are not accessible from outside.

In the DE 10 2017 117 475 A1 A preferably acoustically designed analysis device and an analysis method are disclosed which are used for the automatic detection of filling level parameters, more precisely the pouring parameters, of a foaming beverage liquid. By analyzing the foam with regard to its liquid phase, the amount of drink bound in the foam is determined and the actual drink content of a glass is determined. Beyond that, no further phase distinction can be made.

Common to the cited publications is a general lack of location and flow information from the interior of the foam volume. Due to this circumstance, neither the information about the phase composition nor information about the actually prevailing flow conditions in or out of these spatial areas are accessible.

The object of the present invention is to overcome the disadvantages of the prior art and to propose a method and an arrangement for the location-specific characterization of the phase composition and the flow conditions within a foam volume.

The object is achieved by the features of the independent claims. For this purpose, a method for the location-specific characterization of the phase composition and the flow conditions within a foam volume is proposed.

In the context of the present invention, the nature of the foam-like medium to be examined is divided into several phases. A “gaseous phase” and a “liquid phase” are differentiated for the foam-like medium and the solid particles occurring in the foam are understood as the “solid phase”. The simultaneous presence of several of the phases described in a given or to be determined mixing ratio is understood as the phase composition.

The transitions from one phase to another phase (air-liquid, air-solid, liquid-solid) are understood as phase interfaces.

The portion that is accounted for by the solid phase of the phase composition is understood as particle loading in the context of this document.

The flow conditions affect both the behavior of the individual phases and the behavior of the entirety of all phases in the volume when they are subjected to speed.

1. a) Aussenden einer Ultraschallwelle mindestens einer Frequenz mittels eines Ultraschallsenders in ein Schaumvolumen,
2. b) Durchlaufen der Ultraschallwelle durch das Schaumvolumen,
3. c) Streuung der Ultraschallwelle an den verschiedenen Phasengrenzflächen,
4. d) Detektion des gestreuten Ultraschallechos mittels eines Ultraschallempfängers,
5. e) Rekonstruktion der Phasenzusammensetzung,
6. f) Vergleich der Rekonstruierten Phasenzusammensetzung mit akustischen Eigenschaften bekannter Phasengemische,
7. g) Zuordnung von Laufzeit des Schallsignals und Ort der Rückstreuung,
8. h) Rekonstruktion der ortsspezifischen Phasenzusammensetzung,
9. i) Messung der longitudinalen Geschwindigkeitskomponente im jeweiligen Zeitabschnitt durch Vergleich aufeinanderfolgender Echosignale,
10. j) Kombination der Informationen aus den Schritten e), f), g), h) und i), um die ortsspezifische Strömungsgeschwindigkeit der Phasengrenzflächen zu ermitteln,
11. k) Kombination der Phasenanteile mit der lokalen Geschwindigkeit um Stoffströme zu bestimmen.

The characterization is carried out using ultrasound and is carried out according to the steps

1. a) sending an ultrasonic wave of at least one frequency by means of an ultrasonic transmitter into a foam volume,
2. b) passage of the ultrasonic wave through the foam volume,
3. c) Scattering of the ultrasonic wave at the different phase interfaces,
4. d) Detection of the scattered ultrasound echo by means of an ultrasound receiver,
5. e) reconstruction of the phase composition,
6. f) Comparison of the reconstructed phase composition with acoustic properties of known phase mixtures,
7. g) Assignment of the time of flight of the sound signal and the location of the backscatter,
8. h) Reconstruction of the site-specific phase composition,
9. i) Measurement of the longitudinal speed component in the respective time segment by comparing successive echo signals,
10. j) Combination of the information from steps e), f), g), h) and i) to make the location-specific To determine the flow velocity of the phase interfaces,
11. k) Combination of the phase components with the local speed to determine material flows.

Preferred embodiments are the subject of the dependent claims that refer back.

First, ultrasonic waves in the frequency range from 10 kHz to 1 MHz are introduced into the foam volume. A single frequency as well as a sequence or superposition of several frequencies can be used. The sound waves are coupled in such that the vector of the flow velocity of the foam volume prevailing in the target region with the bisector between the two direct connecting lines between the target region and the ultrasound transmitter or the target region and the ultrasound receiver assume a defined angle between 0 ° and 360 °, the angles being 90 ° and 270 ° are excluded, as these do not contain any information regarding a possible Doppler shift.

The sound wave is scattered in the target region. The scattering of the incoming whales towards the wave detector is understood as an ultrasonic echo.

The ultrasonic echo reaching the detector from the foam is recorded by the ultrasonic detector. The detected signal is divided into time segments with regard to the time of detection.

The time segments of the scattered echo obtained in this way are correlated with spatial coordinates along the sound axis within the foam volume at which the echo generation took place.

The amplitude spectrum of the scattered echo depends on the prevailing foam composition along the sound path and on the scattered object. For example, locations with a high particle load have different properties with regard to the scattering and transmittance that take place than the regions with low particle load. Here, transmittance is understood to mean the ability of a body to transmit waves. The attenuation properties along the sound path are calculated section-specifically from the measured sound echo using iterative mathematical methods. The specific attenuation characteristic for this segment is assigned to each temporal signal segment. A statement about the expected site-specific phase composition is made from the damping property. Based on models, the section-specific phase composition is used to determine the local speed of sound. From the totality of the speed of sound in each section, an association between the time section and the location of the echo generation is carried out.

The foam movements in each temporal signal segment are measured from the "phase position" of the echo signals using the Doppler effect. The longitudinal velocity component of the phase interfaces along the sound axis is reconstructed via the above relationship between the time segment and the location of the echo generation.

The invention thus advantageously enables a direct quantitative assessment of the proportionate composition of the foam with regard to its solid, liquid or gaseous phase constituents and the foam movement taking place in the collective.

The following applies to the concept of scattering: If an ultrasonic wave, also referred to as “wave” in the following, encounters a discontinuity in the acoustic impedance, in particular an interface between two different phases, the wave is diffracted, the wave is refracted and the wave is reflected Wave in different dimensions. What these processes have in common is that, depending on the medium and phase of the medium, they are able to change the wave propagation properties. Wave propagation properties are understood to be the speed of sound and the attenuation experienced in the medium. Processes that change these properties are understood as dispersion in this document.

Ultrasound, possibly abbreviated as US, is the term used to describe sound with frequencies above the human hearing frequency range. It covers frequencies from around 16 kHz up to frequencies of around 1 GHz. In this document, the range of ultrasound is understood as the frequency range from 10 kHz to 1 MHz, since in this range there is a compromise between sufficiently good high spatial resolution and the necessary penetration depth. The higher the sound frequency, the higher the attenuation and the lower the penetration depth.

Ultrasonic transducers are often used to generate the ultrasound. An ultrasonic transducer can be operated as an ultrasonic transmitter and / or as an ultrasonic receiver

An ultrasonic transducer array is the linear or flat arrangement of ultrasonic transducers.

By dividing the signal into time segments, it is possible to assign the spatial information. Location information is provided for each time window of the received wave assigned. In addition, it is now possible to combine the echo signals of several sound waves with different frequencies. As a result, the damping properties of a foam volume can be compared for different sound frequencies and a more reliable statement about the phase composition of the foam volume can be made than would be possible with just one frequency. With the claimed range limits of 0.01 MHz to 10 MHz, an average minimum spatial resolution of 3 cm and a maximum penetration depth of 30 cm are achieved. The foams used to collect the measurement data have an average diameter of the foam bubbles of 5 mm with an uncertainty of up to +/- 1 mm. The present foam thus has a liquid phase between 0.1% and 1%.

Mathematical equations for use in solving the problem of how the speed of the foam can be derived from the given measurement data are known from the general prior art. The advantage of this procedure is that the computing effort expended by the data processing system can be well predetermined. On the one hand, this advantageously enables the real-time capability of such a system to be guaranteed and, on the other hand, offers the possibility of using it on portable data processing systems, e.g. B. Smartphones and tablets to be used in transportable test and measuring equipment if necessary.

The use of a neural network offers the possibility of the advantageous use of self-learning algorithms. These are advantageously used in stationary systems, for example on an industrial scale. The possibility of using more powerful data processing systems ensures efficient processing of large amounts of data.

The use of a neural network advantageously enables the mapping of complex and ambiguous relationships between sound propagation properties and foam composition.

The arrangement for the location-specific characterization of the phase composition and the flow conditions within a foam volume by means of ultrasound has at least one ultrasound transducer.

In any case, the ultrasonic transducer is oriented in the relative vicinity of a foam volume in such a way that the ultrasound emitted by it follows a direct line from the transmitter to the target region, is scattered in the target region and, after scattering, propagates from the target region to the recipient. The propagation of the ultrasound will follow the following course in a direct line: entry into the foam volume, crossing the foam volume to the target region, scattering in the target region, among other things, in the direction of an ultrasound receiver, crossing the foam volume through the scattered wave, leaving the foam volume and subsequent detection through the ultrasonic transmitter.

The connecting lines from the transmitter to the target region and from the target region to the receiver preferably enclose an angle of 0 ° to +/- 180 °. The +/- 90 ° case is explicitly excluded here, since in this case no information about the foam speed can be obtained from the backscattered ultrasound.

Particularly preferably, angles of the connecting lines from the transmitter to the target region and from the target region to the receiver of -5 ° to 5 ° are assumed, since a lower uncertainty of the measurement can advantageously be achieved in this area.

Particularly preferably, ultrasonic transducers are used which work simultaneously as transmitter and receiver and thus the connection vectors starting from the transmitter to the target region and from the target region to the receiver are understood as antiparallel and thus include an angle of 0 °.

The arrangement for the location-specific characterization of the phase composition and the flow conditions within a foam volume by means of ultrasound additionally has at least one data processing system in one embodiment. The data processing system is preferably suitable for generating the ultrasonic signal, for supplying energy to the ultrasonic transducer (s) and for recording the signals of the ultrasonic receiver. The data processing system is designed in particular to measure the received signals with regard to their physical parameters “frequency”, “phase” and “amplitude spectrum”.

In order to enable and / or expand a flat coverage of the data recording in a further embodiment, the arrangement has an adjustment mechanism to which at least one ultrasound transmitter and / or at least one ultrasound receiver can be attached. The adjustment mechanism is suitable for varying the position of the ultrasonic elements in such a way that different, possibly neighboring locations can be irradiated with ultrasound. The combination of the position data of the adjustment mechanism and the measured physical parameters “frequency”, “phase” and “amplitude” of the backscattered wave can thus be used advantageously to expand the measuring range.

Any evaluation method is used after the detection of the ultrasonic wave properties of the respective scattered ultrasonic components. For this purpose, a computer program product for determining the phase composition of the flow conditions of a foam volume is executed on an advantageously used data processing system. For example, the measured wave properties “frequency”, “phase position” and “amplitude spectrum” over the duration of the echo signal are entered into the computer program product to cope with the calculation tasks.

The basis of the computer program are models that describe the relationship between phase components and acoustic properties.

The models used are preferably derived from model tests, since simulations often do not have the level of confidence required to adequately determine the site-specific characterization of the phase composition and the flow conditions within the foam volume.

Using the method for the location-specific characterization of the phase composition and the flow conditions within a foam volume by means of ultrasound advantageously enables the creation of image information, static or moving images. In particular in the case of moving images, the kinematics of the foam flow can thus advantageously be determined and quantified.

Characterization in real time is preferred, particularly when creating moving images. Real time here means that a given period of time is not exceeded between the recording of the measurement data and the output of the results after their evaluation by a data processing system. This also enables the required data processing system to be dimensioned advantageously in advance.

A stationary version of the measuring arrangement is preferred for use in large-scale systems for permanent process control. This enables the advantageous use of more powerful data processing systems for the acquisition and analysis of large amounts of data.

A portable system for use in measuring and testing tasks for monitoring purposes is preferred as a further embodiment. This advantageously enables the use of portable data processing systems, such as. B. Smartphones or tablet computers.

For the implementation of the invention, it is also expedient to combine the above-described configurations, embodiments and features of the claims with one another.

• 1 zeigt schematisch die Anordnung eines Wandlerarrays aus Ultraschallwandlern (101) vor einer Schaumablaufkante. Ein partikelbeladener Schaum mit Feststoffpartikeln (401) strömt in Richtung des Wandlerarrays zeigend über diese Kante. Schematisch wird das Einstrahlen mehrerer Wellenfronten (201) des Ultraschalls in das Schaumvolumen (301) dargestellt. Die gestreuten Anteile und die Fließrichtung des strömenden Schaums nehmen somit einen Winkel im beanspruchten Bereich zwischen 0° und 90° ein.
• 2 zeigt schematisch den Ablauf des Verfahrens zur Bestimmung der ortsspezifischen Zusammensetzung eines Schaumvolumens. Bei dieser Darstellung liegt die Echowelle bzw. das Echosignal (102) bereits vor und wird zunächst in verschiedene Zeitabschnitte (202) eingeteilt. Die jeweiligen Intensitäten des Echosignals zum gegebenen Zeitabschnitt wird in einer Analyseeinrichtung in Form einer Datenverarbeitungsanlage mit Rekonstruktionsalgorithmus (302) zugeführt. In der Analyseeinrichtung wird das Echosignal hinsichtlich der Amplituden bei verschiedenen Frequenzen ausgewertet. Daraus werden wiederum Reflexion und Transmission an dieser Position bestimmt. Mittels eines Modells, beispielsweise einer Modellrechnung, kann daraus die Phasenzusammensetzung ermittelt werden. Aus der Phasenzusammensetzung kann wiederum auf die lokale Schallgeschwindigkeit geschlossen werden und somit jeder Zeitabschnitt einem Ort zugewiesen werden. Weiterhin wird damit die Auswertung der Strömungsgeschwindigkeit in diesem Zeitabschnitt ermöglicht

The invention is described below in several exemplary embodiments and illustrated in the associated figures.

• 1 shows schematically the arrangement of a transducer array made up of ultrasonic transducers ( 101 ) in front of a foam runoff edge. A particle-laden foam with solid particles ( 401 ) flows over this edge, pointing in the direction of the transducer array. The radiation of several wave fronts ( 201 ) of the ultrasound into the foam volume ( 301 ) shown. The scattered parts and the direction of flow of the flowing foam thus assume an angle in the claimed range between 0 ° and 90 °.
• 2 shows schematically the sequence of the method for determining the site-specific composition of a foam volume. In this representation, the echo wave or the echo signal ( 102 ) already and is initially divided into different time periods ( 202 ) assigned. The respective intensities of the echo signal at the given time segment are recorded in an analysis device in the form of a data processing system with a reconstruction algorithm ( 302 ) supplied. In the analysis device, the echo signal is evaluated with regard to the amplitudes at different frequencies. From this, in turn, reflection and transmission at this position are determined. The phase composition can be determined therefrom by means of a model, for example a model calculation. The phase composition can in turn be used to deduce the local speed of sound and thus each time segment can be assigned to a location. This also enables the flow velocity to be evaluated in this time segment

Thus, the reconstruction of the site-specific phase composition, the local speed of sound and the flow speed ( 402 ) respectively.

For example, to build the device, a round piezoelectric ultrasonic transducer is attached by means of a holder in the vicinity of a foam flow zone. In this case, the foam flow zone is the run-off edge of a foam flotation cell, over which the movement of the foam occurs. The direction of sound propagation of the ultrasonic transducer is to this trailing edge arranged in such a way that the active, sound-generating surface points in the direction of the run-off edge. The ultrasonic transducer used has a diameter of the sound-generating surface, the so-called oscillator, of 19 mm and a nominal center frequency of 175 kHz.

The ultrasonic transducer is controlled by suitable electronics. An ultrasonic wave is generated from the electrical signal. The electrical signal coupled into the converter corresponds to a square-wave signal and has a center frequency of 175 kHz. The signal amplitude is set to 160 V (peak to peak). As expected, the resulting ultrasonic wave thus has a center frequency of 175 kHz. This corresponds to a wavelength in air of approx. 2 mm. The ultrasonic signal is sustained for 5 periods.

The following measurement steps are repeated at a rate of 250 Hz. The recording of the measurement data begins with the transmission of the ultrasonic signal. After it is emitted, it first spreads in the air and then penetrates the foam volume. In the foam volume, the sound is scattered on the foam structure and on the particles in the foam and thus experiences changes in its “frequency” and / or “amplitude” properties.

Part of the scattered ultrasound is directed in the direction of the ultrasonic transducer and received by it and converted into an electrical analog signal. The electrical analog signal is converted into an electrical digital signal by means of an analog-digital converter, AD converter, amplified and stored on a hard disk. The AD converter used for this has a sampling frequency of 625 kHz.

The received and stored signals are divided into time-based sections for computer-aided post-processing. In this example, a time segment comprises a time span of 3.2 µs. The reflection, attenuation and transmission of the signal are determined for each of these sections and the phase components of the solid, liquid and gaseous phase are determined for each section from the reflection, attenuation and transmission of the signal.

A computer program is used for the model-based determination of the flow velocity of the foam, which calculates these signal sequences recorded one after the other from the measurement data of the time segments using a Doppler-based evaluation method.

100 consecutive signal transmissions are understood here as successively recorded signal sequences. In this way, the speed component of the foam in the direction of sound propagation is recorded as a line and can be determined for the given combination of parameters up to a maximum value of the flow speed of up to 123 mm / s.

The combination of the phase proportions and the flow rate thus provides the volume flow of the individual phases.

List of reference symbols

101

Ultrasonic transducer

102

Echo signal

201

Ultrasonic wavefront

202

Time segments of the echo signal

301

Foam volume

302

Data processing system with reconstruction algorithm

401

Solid particles

402

Reconstruction of the phase composition F, the speed of sound c and the assignment of the location x at time t

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102004036645 A1 [0004]
• US 8495913 B2 [0005]
• DE 19810092 A1 [0006]
• DE 102006057772 A1 [0007]
• WO 2005/003758 A1 [0008]
• DE 102017117475 A1 [0009]

Claims (9)

Method for the location-specific characterization of the phase composition and the flow conditions within a foam volume by means of ultrasound, comprising the steps a) sending an ultrasonic wave of at least one frequency by means of an ultrasonic transmitter into a foam volume, b) passage of the ultrasonic wave through the foam volume, c) Scattering of the ultrasonic wave at the different phase interfaces, d) Detection of the scattered ultrasound echo by means of an ultrasound receiver, e) reconstruction of the phase composition, f) Comparison of the reconstructed phase composition with acoustic properties of known phase mixtures, g) Assignment of the time of flight of the sound signal and the location of the backscatter, h) Reconstruction of the site-specific phase composition, i) Measurement of the longitudinal speed component in the respective time segment by comparing successive echo signals, j) Combination of the information from steps e), f), g), h) and i) in order to determine the site-specific flow velocity of the phase interfaces, k) Combination of the phase components with the local speed to determine material flows. Procedure according to Claim 1 , whereby in step e) the phase composition is reconstructed based on frequency and time. Procedure according to Claim 1 or 2 , the phase composition being reconstructed in step e) by means of an analytical model. Procedure according to Claim 1 or 2 , the reconstruction of the phase composition carried out in step e) being carried out by a trained neural network. Method according to one of the preceding claims, wherein the ultrasonic wave front emitted for measurement is shaped. Arrangement for the location-specific characterization of the phase composition and the flow conditions within a foam volume by means of ultrasound, having at least one ultrasonic transducer and at least one data processing system, the data processing system executing a computer program product for modeling the phase composition of the flow conditions of a foam volume and this being fed with measurement data from the ultrasonic transducer. Arrangement according to Claim 6 , this having at least one linear and / or angular adjustment mechanism of at least one US converter and / or array of US converters. Use of the method according to one of the Claims 1 to 6th , for the location-specific characterization of the phase composition and the flow conditions within a foam volume by means of ultrasound Use an arrangement according to Claim 6 or 7th to carry out one of the methods according to one of the Claims 1 to 5 .

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