Method for determining the proportion of a disperse gas phase in a fluid

Abstract

The invention proposes a method for determining the proportion of a disperse gas phase in a fluid flowing in a line in a direction of flow with the aid of ultrasound, comprising the following steps of: a) providing an ultrasonic measuring device (1) which is configured to determine a propagation time difference between two measurement signals which pass through the fluid in the line (100), b) emitting and receiving a first measurement signal (12) with the aid of the ultrasonic measuring device (1), wherein the first measurement signal (12) is emitted with the direction of flow (A), c) emitting and receiving a second measurement signal (21) with the aid of the ultrasonic measuring device (1), wherein the second measurement signal (21) is emitted counter to the direction of flow (A), d) transmitting the measurement signals (12, 21) to a storage and evaluation unit (20), e) determining an individual value (E) for the propagation time difference between the first measurement signal (12) and the second measurement signal (21), f) determining a plurality of individual values for the propagation time difference by repeating steps b) to e), g) determining a mean value (MW) for the propagation time difference from the individual values (E) for the propagation time difference, h) determining a dispersion parameter (SP) which is characteristic of the dispersion of the individual values (E) around the mean value (MW), i) providing a relationship between the mean value (MW) for the propagation time difference and the change in the dispersion parameter (SP) on the basis of the proportion of the disperse gas phase (DP), j) determining the proportion of the disperse gas phase (DP) from the dispersion parameter (SP) and said relationship, wherein the individual values (E) for the propagation time difference or a mean value of a plurality of individual values (E) is / are optionally transformed into individual values (E) for the flow rate of the fluid or into a mean value for the flow rate, and steps h) and i) are carried out with the individual values (E) for the flow rate or the mean value for the flow rate.

Description

[0001] Levitronix GmbH, CH-8005 Zurich (Switzerland)

[0002] Method for determining the proportion of a disperse gas phase in a fluid

[0003] The invention relates to a method for determining the proportion of a disperse gas phase in a fluid flowing in a line in a flow direction by means of ultrasound, wherein a transit time difference between two measuring signals passing through the fluid in the line is determined by means of an ultrasound measuring device.

[0004] In process engineering, non-invasive methods are used to examine fluids or to measure fluids flowing in pipes, such as flexible plastic hoses. This is particularly the case for highly pure or very sensitive fluids where contact between the fluid and the measuring device should be avoided as much as possible, for example, to prevent contamination of the fluid. Examples of this include the pharmaceutical and biotechnology industries. These industries frequently produce and convey solutions and suspensions that place very high demands on the purity and / or integrity of the fluid. Such fluids often even have to be treated under sterile conditions.

[0005] Ultrasonic measurement technology has proven particularly effective as a non-invasive method for measuring fluids flowing in pipes. Ultrasonic measuring devices for measuring a fluid flowing in a pipe are used, for example, to determine the flow rate of the fluid through a pipe. A common practice is to design the measuring device as a clamping device so that it can be clamped onto a flexible pipe, or so that the pipe is clamped by the measuring device. The pipe with the fluid flowing through it is then subjected to ultrasonic signals. After passing through the pipe and the fluid, the ultrasonic signals are received by an ultrasonic transducer, and the received signal is evaluated.

[0006] A known measure for determining flow is for the ultrasonic measuring device to comprise at least two ultrasonic transducers which, in operation, are arranged laterally on opposite sides of the line. The two ultrasonic transducers are offset from one another with respect to the flow direction of the fluid and are aligned such that the first ultrasonic transducer can receive a signal sent by the second ultrasonic transducer, and the second ultrasonic transducer can receive a signal sent by the first ultrasonic transducer. Due to the offset from one another, the two ultrasonic transducers are aligned such that they each emit their ultrasonic signals at an angle to the flow direction of the fluid, with one ultrasonic transducer emitting the signal at an angle with the flow direction, while the other ultrasonic transducer emits the signal at an angle against the flow direction.Now, the first ultrasonic transducer sends out a measurement signal which is received by the second ultrasonic transducer, and then the second ultrasonic transducer sends out a measurement signal which is sent out by the first ultrasonic transducer.

[0007] The measurement signal transmitted diagonally in the direction of flow is accelerated by the flow, while the measurement signal transmitted diagonally against the direction of flow is decelerated by the flow. The time difference between the two measurement signals is proportional to the flow velocity of the fluid, so the flow rate through the flexible pipe can be determined from this time difference.

[0008] In addition to ultrasound methods that are based on measuring transit times or transit time differences, methods are also known in which the amplitude, frequency, or attenuation of the ultrasound signals is determined. Using these parameters, and in particular combinations of these parameters, such as transit time and attenuation, other parameters of the fluid, such as its viscosity or optical density, can be determined in addition to the flow rate. Very often, however, the fluid is not a single-phase fluid, but a multi-phase system, such as a dispersion. A dispersion is characterized by the presence of undissolved components in another medium, the so-called dispersion medium. These undissolved components are referred to as the disperse phase. Typically, the undissolved components are randomly distributed in the dispersion medium.

[0009] An important example of such a multiphase system is a fluid, particularly a liquid, that contains undissolved gas bubbles as a dispersed phase. It is often necessary to analyze the fluid flowing through a line for the presence of gas bubbles. For example, if a patient's blood is pumped through lines during surgery, e.g., with a heart-lung machine, it is extremely important to analyze the blood flowing in the line for the presence of gas bubbles, such as air bubbles, because these could have life-threatening consequences.

[0010] To detect gas bubbles in ultrasonic flow measurements, EP 2 717 026 proposes determining not only the propagation time of the ultrasonic signal but also its amplitude after it has passed through the fluid. A sharp decrease or collapse in amplitude is used as an indicator that gas bubbles exist in the fluid. However, this amplitude-based measurement only allows a qualitative statement to be made that gas bubbles are present in the fluid; a quantitative statement about the proportion of gas bubbles in the fluid is practically impossible. This is due, for example, to the fact that many small gas bubbles can cause the same amplitude drop as one larger one, or that smaller gas bubbles flow in the acoustic shadow of a larger gas bubble and thus contribute nothing to the amplitude drop.The amplitude of the received ultrasonic signal also depends on many other factors, such as the temperature of the medium, the properties of the ultrasonic transducers, or the properties of the pipe or hose. Therefore, it is now common practice to use the amplitude of the received ultrasonic signal only to qualitatively determine whether or not air bubbles or gas bubbles are present in the fluid.

[0011] For many applications, however, it is desirable to be able to determine the proportion of gas bubbles or, more generally, the dispersed phase in a fluid, thus being able to make a reliable quantitative statement about the dispersed phase.

[0012] One example is automatic filling processes. In such filling processes, the weight is usually used as a reference, i.e. filling is stopped as soon as the container to be filled has reached a specified weight. If, for example, a liquid flowing into the container to be filled contains a large proportion of gas bubbles, such as air bubbles, particularly towards the end of the filling process, the volume corresponding to the specified weight increases. The air bubbles tend to collect at the upper end of the container. The average density of the liquid with the gas bubbles it contains decreases. This creates the risk that the container to be filled will overflow because there is no space in the container for the volume corresponding to the specified weight. The filling process is therefore stopped too late, which can cause damage to the container and, in the worst case, even destruction of the container.This poses a risk to operating personnel and machinery. Furthermore, it can result in economic losses. To prevent such consequences, very high safety margins are often provided, which in many cases would result in prematurely stopped or interrupted processes. If the proportion of the dispersed gas phase, in this case, the air bubbles, could be reliably determined, these safety margins could be reduced, thus making the process more efficient and economical.

[0013] The present invention addresses this problem.

[0014] Based on this prior art, it is therefore an object of the invention to propose a method with which the proportion of the dispersed gas phase in a fluid flowing through a line can be reliably determined. This method should be feasible using an ultrasonic measuring device. Thus, the method should enable a quantitative statement about the dispersed gas phase in a flowing fluid based on an ultrasonic measurement.

[0015] The subject matter of the invention that solves this problem is characterized by the features of the independent patent claim. According to the invention, a method is proposed for determining the proportion of a dispersed gas phase in a fluid flowing in a line in a flow direction using ultrasound, comprising the following steps: a) Providing an ultrasonic measuring device designed to determine a transit time difference between two measurement signals passing through the fluid in the line, b) Transmitting and receiving a first measurement signal using the ultrasonic measuring device, wherein the first measurement signal is transmitted in the flow direction, c) Transmitting and receiving a second measurement signal using the ultrasonic measuring device, wherein the second measurement signal is transmitted against the flow direction, d) Transmitting the measurement signals to a storage and evaluation unit,e) Determining an individual value for the transit time difference between the first measurement signal and the second measurement signal, f) Determining a plurality of individual values ​​for the transit time difference by repeating steps b) to e), g) Determining an average value for the transit time difference from the individual values ​​for the transit time difference, h) Determining a scattering parameter which is characteristic of the scatter of the individual values, i) Providing a relationship between the average value for the transit time difference and the change in the scattering parameter as a function of the proportion of the disperse gas phase, j) Determining the proportion of the disperse gas phase from the scattering parameter and the said relationship, wherein optionally the individual values ​​for the transit time difference or an average value over several individual values ​​are transformed into individual values ​​for the flow of the fluid or into an average value for the flow,and steps h) and i) are carried out with the individual flow values ​​or the mean flow value,

[0016] Essential to the invention is therefore the finding that the fluctuations in the transit time difference (or the flow rate values ​​determined from it) around the mean value of the transit time difference (or the flow rate values ​​determined from it) for a constant mean value of the transit time difference (or the flow rate) depend in a highly reproducible manner on the proportion of the dispersed phase in the fluid. Thus, the statistical fluctuations in the transit time difference (or the flow rate values ​​determined from it), i.e., the "noise" of the transit time difference (or the flow rate values ​​determined from it), around the mean value of the transit time difference (or the flow rate values ​​determined from it), can be used to reliably determine the proportion of the dispersed gas phase, for example, the proportion of gas bubbles, in the fluid.

[0017] This makes it possible to obtain a quantitative statement about the disperse gas phase in the fluid based on ultrasonic flow measurements.

[0018] A particular advantage of the method according to the invention is that it is based on time-of-flight measurements using ultrasound. Such time-of-flight measurements are, at least to a very good approximation, independent of the amplitude of the respective received ultrasonic measurement signal and are therefore influenced by considerably fewer factors than, for example, measurements of the amplitude of a received ultrasonic measurement signal.

[0019] It has also been shown that the determination of the proportion of the disperse gas phase based on the transit time difference of measurement signals leads to significantly more accurate and better reproducible results than, for example, determinations in which the proportion of the disperse gas phase is determined by evaluating the amplitude of ultrasonic signals, and then the proportion of the disperse gas phase is estimated from the statistical fluctuations of the amplitude values.

[0020] For a given mean value of the transit time difference of measurement signals, the proportion of the disperse gas phase can be reliably determined from the statistical fluctuations of the transit time difference around this mean value.

[0021] In principle, all ultrasonic measuring devices with which the transit time difference between two measuring signals passing through a fluid flowing in a line can be determined are suitable for the method according to the invention.

[0022] Preferably, at least one first ultrasonic transducer is provided for transmitting and receiving the measurement signals. This transducer is arranged laterally on a first side of the line in the operating state, and at least one second ultrasonic transducer is provided, which is arranged laterally on a second side of the line in the operating state, the second side being opposite the first side. The ultrasonic transducers are arranged and aligned such that the first ultrasonic transducer can transmit the first measurement signal to the second ultrasonic transducer at an angle to the flow direction of the fluid, and can receive the second measurement signal transmitted by the second ultrasonic transducer at an angle to the flow direction.

[0023] Furthermore, it is preferred that the flow of the fluid through the line is determined from the transit time differences between the first measurement signals and the second measurement signals.

[0024] Particularly preferably, the ultrasonic measuring device is designed as a clamping device, and the line is clamped in the ultrasonic measuring device. Such clamping devices are disclosed, for example, in EP 3 489 634 A1 or EP 3 816 590 A1. A particular advantage of the device disclosed in EP 3 816 590 A1 is that the ultrasonic signals are transmitted and received in several different measuring planes. This makes it possible, for example, to more reliably detect smaller gas bubbles in the edge region of the measuring volume, as well as those gas bubbles that move in the shadow of other gas bubbles.

[0025] According to a preferred embodiment of the method according to the invention, the determination of the proportion of the disperse gas phase is updated at regular intervals or continuously.

[0026] The method according to the invention is particularly suitable for increasing the accuracy of measuring the fluid flow rate through the line. For this purpose, a corrected mean value for the flow rate can be determined, for example, using the proportion of the dispersed gas phase. This corrected mean value then takes into account the influence of the dispersed gas phase on the flow rate determination.

[0027] Preferably, the corrected mean value indicates the flow rate of the fluid without the dispersed gas phase. This means that based on the proportion of the dispersed gas phase, the influence of the dispersed gas phase on the individual flow values ​​or on the mean flow value can be determined. This allows, for example, the corrected mean value for the flow rate to be determined, which indicates the flow rate of the fluid without the dispersed gas phase. This allows the flow rate of the "pure" dispersion medium to be determined, which enables a significant increase in the accuracy of the flow measurement.

[0028] In principle, any parameter that measures the fluctuations or scatter of the individual values ​​of the transit time difference measurement (or the flow rate values) around the mean of the transit time difference (or flow rate) is suitable as a scatter parameter. Preferably, the scatter parameter is a statistical parameter that describes the statistical noise of the individual values ​​around the mean. Examples of scatter parameters include the variance of the individual values ​​with respect to the mean or the standard deviation of the individual values.

[0029] In a preferred embodiment of the method according to the invention, the change in the scattering parameter as a function of the proportion of the disperse gas phase is described by a linear determination function at a constant mean value for the transit time difference (or the flow rate).

[0030] It is particularly preferred that the linear determination function is defined by two linear coefficients, each linear coefficient being determined using a polynomial function whose variable is the mean value for the transit time difference (or for the flow).

[0031] To determine the proportion of the disperse phase from the transit time difference measurements, it is also possible to store the change in the scattering parameter as a function of the proportion of the disperse gas phase at a constant mean value for the transit time difference in a lookup table in the storage and evaluation unit.

[0032] Particularly for lower flow velocities of the fluid through the line, it may be advantageous to first determine the proportion of the dispersed gas phase, and then use a smoothing factor to determine a modified proportion of the dispersed gas phase. It is preferred that the smoothing factor be calculated using a polynomial function whose variable is the mean value of the transit time difference.

[0033] In a preferred application of the process according to the invention, the disperse gas phase consists of gas bubbles.

[0034] Preferably, the proportion of the dispersed gas phase is the volume fraction of gas bubbles in a liquid.

[0035] Since the transit time difference between the first measurement signal and the second measurement signal is proportional to the flow velocity of the fluid in the line, each transit time difference value can be very easily converted into a value for the flow rate. Therefore, it is also possible to convert each transit time difference into a value for the flow rate of the fluid through the line, and to determine the proportion of the dispersed gas phase using the flow rate values. However, this mere conversion does not change the fact that the determination of the proportion of the dispersed gas phase is based on the transit time differences.If the transit time differences are first converted into flow values, the corresponding values ​​or the corresponding relationship for the flow must of course also be used instead of the mean value for the transit time difference, the scattering parameter, and the relationship between the mean value for the transit time difference and the change in the scattering parameter as a function of the dispersed gas phase. This means that the individual values ​​and / or the mean value for the transit time difference are converted into individual values ​​and / or the mean value for the flow, the scattering parameter is determined accordingly for the flow values, and the relationship between the mean value for the transit time difference and the change in the scattering parameter as a function of the dispersed gas phase is transformed into a relationship between the mean value for the flow and the change in the scattering parameter as a function of the dispersed gas phase.

[0036] Furthermore, it is possible to first determine an averaged individual value from a predefined number of individual values, and then to perform the statistical evaluation, i.e., in particular, the determination of the scatter parameter based on the averaged individual values. This essentially corresponds to smoothing the individual values ​​prior to the statistical evaluation. Further advantageous measures and embodiments of the invention are set out in the dependent claims.

[0037] The invention is explained in more detail below using exemplary embodiments and the drawings. The drawings show:

[0038] Fig. 1 : a schematic representation of an ultrasonic measuring device for

[0039] Determination of a transit time difference between two measuring signals passing through a fluid in a pipe,

[0040] Fig. 2: a perspective view of an ultrasonic measuring device for

[0041] Determination of the transit time difference, designed as a clamping device,

[0042] Fig. 3: a schematic diagram illustrating a

[0043] Embodiment of a method according to the invention,

[0044] Fig. 4: a diagram showing the relationship between a

[0045] scattering parameters and the proportion of a dispersed gas phase in a fluid, and

[0046] Fig. 5: like Fig. 3, but for a variant of the embodiment.

[0047] The invention proposes a method for determining the proportion of a disperse gas phase in a fluid flowing in a line 100 (Fig. 1), in which an ultrasonic measuring device 1 is used to determine a transit time difference between two measuring signals which pass through the fluid in the line 100.

[0048] For example, the following description refers to the application case where the dispersed gas phase consists of gas bubbles. Furthermore, reference is made to the example where the fluid is a liquid. Furthermore, the volume fraction of gas bubbles is considered as an example of the proportion of the dispersed gas phase. As an example, the following will therefore consider the determination of the volume fraction of gas bubbles in a liquid, for example, water or an aqueous solution.

[0049] Of course, the invention is not limited to these examples, but also relates to other types of dispersions. In general, a dispersion refers to a multiphase system in which undissolved components, quantities, or objects are present in a medium. The undissolved components are usually referred to as the dispersed phase, and the medium as the dispersion medium. The undissolved components of the dispersed phase are usually distributed randomly in the dispersion medium.

[0050] In the process according to the invention, the dispersion medium is a fluid, for example, a liquid or a gas. The dispersed phase is a dispersed gas phase, i.e., the dispersed phase is gaseous. The process according to the invention is particularly suitable for applications in which the volume of the dispersed gas phase is at most 40% of the total volume, i.e., the volume of the dispersed gas phase and the volume of the dispersion medium.

[0051] The term "fraction of the dispersed gas phase" means that a quantitative determination of the amount or volume or mass of the dispersed gas phase in the fluid is carried out, for example the determination of a volume percentage or a mass percentage.

[0052] In principle, all ultrasonic measuring devices 1 that can determine the transit time difference between two measurement signals in a fluid flowing through a line 100 are suitable for the method according to the invention. One measurement signal is emitted in the direction of flow of the fluid, and the other measurement signal is emitted against the flow direction. Ultrasonic measuring devices 1 that themselves form the line 100 or part of the line 100 are also suitable, for example, so-called inline measuring devices, in particular those marketed by the applicant under the brand name LEVI FLOW LFS.

[0053] Fig. 1 shows a schematic representation of an ultrasonic measuring device 1 for determining the transit time difference between two measurement signals passing through a fluid flowing through a line. The line is designated by the reference numeral 100. In the following, reference is made to the case, which is particularly important in practice, in which the line 100 is a flexible line 100, i.e. a line 100 whose wall 101 (Fig. 2) is deformable. The flexible line 100 is, for example, a plastic hose made of silicone rubber or PVC. Of course, the line 100 can also be made of other materials, in particular of a plastic or a rubber. Of course, the method according to the invention is also suitable for rigid, i.e. non-flexible lines.

[0054] The fluid flows through the line 100 in a flow direction A. For transmitting and receiving measurement signals 12, 21, which are ultrasonic signals, at least two ultrasonic transducers 11, 22 are provided, namely a first ultrasonic transducer 11 and a second ultrasonic transducer 22. In the operating state, the first ultrasonic transducer 11 is arranged laterally on a first side 51 of the line 100, and the second ultrasonic transducer 22 is arranged laterally on a second side 52 of the line 100, wherein the second side 52 is opposite the first side 51. The ultrasonic transducers 11, 22 are arranged and aligned such that the first ultrasonic transducer 11 can transmit a first measurement signal 12 obliquely to the flow direction A of the fluid to the second ultrasonic transducer 22, and can receive a second measurement signal 21 transmitted by the second ultrasonic transducer 22 obliquely to the flow direction A.

[0055] The measurement signals 12, 21 are each symbolically represented in Fig. 1 by dashed straight lines with an arrowhead. This is to be understood in such a way that the dashed line indicates the main propagation direction of the ultrasonic signal emitted by the corresponding ultrasonic transducer 11, 22, and the arrowhead indicates the direction, i.e. whether the respective ultrasonic signal is moving towards the respective ultrasonic transducer 11, 22 (i.e., is received), or moving away from it (i.e., is transmitted). The main propagation direction is usually perpendicular to the surface of the piezoelectric element of the corresponding ultrasonic transducer 11 or 22. The main propagation direction encloses an angle α with the flow direction A, which angle is different from 0° and from 90°.

[0056] In the case of ultrasonic measuring devices 1 which are designed as inline measuring devices, this angle α is often equal to 0° or 180°, i.e. the measuring signals are emitted such that their main direction of propagation is the same as the flow direction A or is directed exactly opposite to the flow direction A. This can be achieved, for example, with U-shaped or Z-shaped ultrasonic measuring devices. In the case of the ultrasonic measuring device 1 shown in Fig. 1, the procedure for determining the transit time difference is as follows, for example. The first ultrasonic transducer 11 emits a first measuring signal 12, wherein the first measuring signal 12 is emitted obliquely at the angle α to the flow direction A and with the flow direction A, which means that the main direction of propagation of the first measuring signal 12 also has a component in the flow direction A.The second ultrasonic transducer 22 emits a second measuring signal 21, wherein the second measuring signal 21 is emitted obliquely at the angle a to the flow direction A and against the flow direction A, which means that the main propagation direction of the second measuring signal 21 also has a component against the flow direction A.

[0057] The first measurement signal 12 is received by the second ultrasonic transducer 22 after passing through the fluid and transmitted via a signal line 22a to a storage and evaluation unit 20. The second measurement signal 21 is received by the first ultrasonic transducer 11 after passing through the fluid and transmitted via a signal line 11a to the storage and evaluation unit 20.

[0058] In the storage and evaluation unit 20, the transit time difference is determined between the first measurement signal 12, which was accelerated by the flowing fluid, and the second measurement signal 21, which was slowed by the flowing fluid. This transit time difference between the first measurement signal 12 and the second measurement signal 21 is directly dependent on the flow velocity of the fluid in the line 100. Thus, the transit time difference can also be used to determine, for example, the flow velocity and thus also the flow rate of the fluid through the line 100.

[0059] It is also frequently the case that at least four ultrasonic transducers 11, 22 are provided in the ultrasonic measuring device 1 for respectively transmitting and receiving ultrasonic signals, namely at least two of the first ultrasonic transducers 11, which are arranged laterally on the first side 51, and at least two of the second ultrasonic transducers 22, which are arranged laterally on the second side 52. The ultrasonic transducers 11, 22 are then arranged and aligned such that in each case one of the first ultrasonic transducers 11 can transmit a first measurement signal 12 obliquely to and with the flow direction A to one of the second ultrasonic transducers 22, and can receive a second measurement signal 21 transmitted by this second ultrasonic transducer 22 obliquely to and counter to the flow direction A. The four ultrasonic transducers 11, 12 are then arranged, for example, in the shape of an X.Such an arrangement of ultrasonic transducers 11, 22 is disclosed, for example, in EP 3489 634 A1. In this arrangement with four ultrasonic transducers, it is advantageous that two independent measurements are taken both in the flow direction A and against the flow direction A, which significantly increases the accuracy and reliability, for example, when determining the flow rate.

[0060] Particularly preferably, the ultrasonic measuring device 1 is designed as a clamping device, so that the line 100 can be clamped in the ultrasonic measuring device 1. Fig. 2 shows a perspective view of an embodiment of an ultrasonic measuring device 1 for determining the transit time difference between two measurement signals, which is designed as a clamping device.

[0061] The ultrasonic measuring device 1 comprises a housing 4. The ultrasonic measuring device 1 is designed as a clamping device for a clamp connection with the line 100, ie the housing 4 of the ultrasonic measuring device 1 can be clamped onto the line 100 in such a way that the line 100 is fixed with respect to the housing 4. The basic design of the ultrasonic measuring device 1 with the housing 4 is known per se, for example from EP 3 489634 A1. EP 3 816 590 A1 also describes an ultrasonic

[0062] Measuring device 1 is disclosed, which is designed as a clamping device for releasable attachment to the line 100 and is suitable for the method according to the invention.

[0063] The housing 4 is designed as a closable housing 4 and comprises a first housing part 41 and a second housing part 42, which are connected to one another in an articulated manner via a joint 43. Fig. 2 shows the housing 4 in the open state. The housing 4 further has a continuous central recess 3, which extends through the entire housing 4 and serves to accommodate the line 100. The longitudinal extent of the central recess 3 determines the flow direction A in which the fluid flows through the line 100 or the housing 4.

[0064] The housing 4 further comprises a locking mechanism 44 to secure the housing

[0065] 4 and thus clamp the line 100 in the central recess 3. The locking mechanism 44 is arranged here on the first housing part 41 and comprises a bracket 46 and a foldable tab 45 for tensioning the bracket 46. The line 100 is inserted into the central recess 3, then the two housing parts 41, 42 are folded together, i.e. the first housing part 41 is folded over the line 100. The bracket 46 is brought into engagement with a projection 47 on the second housing part 42, and by actuating the tab 45, the two housing parts 41, 42 are clamped together. The housing 4 is then in its closed state, in which the line 100 is clamped in the central recess 3 and thus fixed with respect to the housing 4.

[0066] In the closed state of the housing 1, the line 100 is thus fixed between the first side 51 and the second side 52, which are opposite each other with respect to the central recess 3.

[0067] Furthermore, a marking element (not shown) can be provided on the housing 4, for example an arrow, which determines the flow direction in which the fluid is to flow through the ultrasonic measuring device 1.

[0068] The central recess 3 is preferably designed such that, when the housing 4 is closed, it has a substantially rectangular, in particular a square, cross-section perpendicular to the flow direction A. This has the advantage that ultrasonic measurement signals applied to the line 100 impinge on planar, i.e., non-curved, surfaces, which greatly simplifies the detection and evaluation of the measurement signals 12, 21 and increases the accuracy of the measurement.

[0069] Embodiments are also known in which the central recess is designed such that, when the housing is closed, it has a different polygonal cross-section, for example, a hexagonal cross-section perpendicular to the flow direction A. Embodiments are also known in which this cross-section is circular or oval. In such embodiments, acoustic lenses are often used to transmit and / or receive the measurement signals.

[0070] The ultrasonic transducers 11, 22, which are not shown in Fig. 2, are provided in the housing 4, namely on the first side 51 and the second side 52, respectively. The first ultrasonic transducer(s) 11 is / are arranged on the first side 51, and the second ultrasonic transducer(s) 22 is / are arranged on the second side 52.

[0071] Each of the ultrasonic transducers 11, 22 is signal-connected to the storage and evaluation unit 20 via one of the signal lines 11a, 22a (Fig. 1). The signal lines 11a, 22a and the storage and evaluation unit 20 are not shown in Fig. 2. The ultrasonic transducers 11, 22 are controlled to emit ultrasonic signals via the respective signal line 11a, 22a and transmit the respectively received measurement signals 12, 21 to the storage and evaluation unit 20. In the storage and evaluation unit 20, the received measurement signals 12 and 21 are analyzed, and the transit time difference between one of the first measurement signals 11 and one of the second measurement signals 21 is determined. Furthermore, it is possible to determine the flow of the fluid through the line 100 from the determined transit time differences.

[0072] The ultrasonic transducers 11, 22 can be designed in any known manner, in particular as piezoelectric transducers. The frequency of the ultrasonic signals is typically in the megahertz range, for example, in the range from 1 MHz to 30 MHz.

[0073] The preceding description of the ultrasonic measuring devices 1 is to be understood merely as an example. Any ultrasonic measuring device designed or suitable for determining the transit time difference between a measurement signal transmitted in the flow direction A and a measurement signal transmitted against the flow direction A is suitable for the method according to the invention.

[0074] Fig. 3 illustrates in a schematic representation an embodiment of a method according to the invention for determining the proportion of a disperse gas phase, which in this example consists of gas bubbles, in the fluid, which is a liquid here, wherein the fluid flows through the line 100.

[0075] Using the ultrasonic measuring device 1, a plurality of individual values ​​for the transit time difference between a first measurement signal 12 and a second measurement signal 21 are determined. These individual values ​​are represented in Fig. 3 by the arrow with the reference symbol E. Each individual value E is stored in a memory module 25 of the storage and evaluation unit 20. The memory module 25 is designed, for example, as a FIFO memory (FIFO: First in - First out). The stored individual values ​​E are collected in the memory module 25 and evaluated using an analysis method. The analysis method preferably uses statistical or stochastic methods to determine the proportion of the disperse phase, in this case the gas bubbles, in the fluid from the plurality of individual values ​​E, as will be described in more detail below.

[0076] Preferably, the determination of the dispersed phase fraction is updated at regular intervals or continuously. "Continuously updated" means that with each new individual value E for the transit time difference transmitted to the storage module, the evaluation is performed again, thus updating the determination of the dispersed phase fraction.

[0077] A mean value MW for the travel time difference is determined from the individual values ​​E for the travel time difference. The mean value MW is preferably the statistical mean MW or the arithmetic mean, i.e., the sum of n individual values ​​E divided by the number n of individual values, where n is a natural number.

[0078] A key finding for the invention is that the fluctuations of the individual values ​​E around the mean MW for a constant mean MW depend in a highly reproducible manner on the proportion of the dispersed gas phase in the fluid. The statistical fluctuations of the individual values ​​E around the mean MW, i.e., the "noise" of the transit time difference (or flow rate), around the mean MW can thus be used to reliably determine the proportion of the dispersed gas phase in the fluid.

[0079] Therefore, a scatter parameter SP is determined from the individual values ​​E, which is characteristic of the scatter of the individual values ​​E around the mean MW. Suitable scatter parameters include, for example, the variance of the individual values ​​E, or the empirical variance or the standard deviation or the empirical standard deviation of the individual values ​​E from the mean MW. Usually, the standard deviation is the square root of the variance. The (empirical) variance is the sum of the squared deviation of the n individual values ​​E from the mean MW divided by the number n of individual values ​​E or divided by the number (n- 1) of degrees of freedom. Here, n is any natural number that specifies the number of individual values ​​E.It is also possible to determine an averaged individual value from a predefined number of individual values ​​E and then to use these averaged individual values ​​for further analysis, in particular for determining the mean value MW.

[0080] In a preferred embodiment, the variance SP defined as follows is used as the scatter parameter SP: where Ej denotes the i-th individual value E (or the i-th averaged individual value) and n denotes the number of individual values ​​E. Of course, the square root of the variance SP can also be used as a dispersion parameter. This is usually referred to as the (empirical) standard deviation.

[0081] For a constant mean value MW of the transit time difference (or also the flow rate), the change in the scattering parameter SP (here the variance SP) as a function of the proportion of the disperse gas phase is described by a linear determination function F, which is a linear relationship of the following form:

[0082] SP = m - DP + t where DP indicates the proportion of the dispersed gas phase in the fluid, in this case, for example, the volume fraction of gas bubbles in the liquid, and where m and t are two linear coefficients by which the linear determination function F is determined for a given and constant mean value MW. The determination of the linear coefficients m and t for a constant mean value MW will be discussed further below.

[0083] Using the linear determination function F, the proportion of the disperse gas phase DP can be calculated as follows:

[0084] (SP - 1) DP = - m As shown in Fig. 3, the mean value MW and the scattering parameter SP, in this case the variance SP, are determined from the individual values ​​E stored in the storage module 25. The two linear coefficients m and t are determined for the specific mean value MW. Thus, the linear determination function F is known for this specific mean value MW, and thus the change in the scattering parameter SP as a function of the proportion of the disperse gas phase DP. The proportion of the disperse phase DP can then be calculated as DP = (SP - t) / m.

[0085] Thus, the method according to the invention enables a quantitative statement about the disperse gas phase in the fluid.

[0086] The two linear coefficients m and t, which define the linear determination function F for a predeterminable and constant mean value MW, can, for example, be stored in a lookup table in the storage and evaluation unit 20 for different mean values ​​MW. It is also possible to describe the linear coefficients m, t by a functional relationship whose variable is the mean value MW. This functional relationship can be a polynomial function for each of the linear coefficients m, t, whose variable is the mean value MW.

[0087] Preferably, the linear coefficients m, t for the respective ultrasonic measuring device 1 are determined empirically or by measurement, for example, through calibration measurements. This can be done as follows.

[0088] By means of the ultrasonic measuring device 1, the mean value MW for the transit time difference and the scattering parameter SP, in this case the variance SP, are measured on a calibration fluid for different proportions of the disperse gas phase DP. The calibration fluid has a predeterminable proportion of the disperse phase DP. This can be achieved, for example, by adding a predeterminable volume fraction of a gas, e.g. air, to the liquid flowing in the line 100, e.g. water. For this fluid, e.g. water with the gas bubbles contained therein, the mean value MW of the transit time difference and the variance SP, i.e. the scatter of the individual values ​​E around the mean value MW, are then determined by means of the ultrasonic measuring device 1. While the volume fraction of the gas is kept constant, the flow rate is then increased in several steps, for example from zero to a value of 10 liters per minute. The mean value MW and the variance SP are determined in each case.This calibration measurement is repeated for different values ​​of the proportion of the disperse gas phase DP, i.e. in this case the gas bubbles, for example for volume fractions of the gas bubbles of 0%, 0.5%, 3% and 6%, to name just one example.

[0089] From these calibration measurements, a family of curves is obtained, as shown by way of example in the diagram in Fig. 4. The proportion of the disperse phase DP, in this case the volume fraction of gas bubbles in the liquid, is plotted on the horizontal axis, and the scattering parameter SP, in this case the variance, is plotted on the vertical axis. Fig. 4 shows three curves MW1, MW2, MW3. Each of the curves MW1, MW2 and MW3 corresponds to a constant mean value MW of the transit time difference. Curve MW1 corresponds to the smallest value of the constant mean value MW for the transit time difference, curve MW3 to the largest mean value MW for the transit time difference, and curve MW2 to an average value for the transit time difference.It is easy to see that for a constant mean value MW of the transit time difference, the relationship between the variance SP and the fraction of the disperse phase DP is, to a very good approximation, a linear relationship, which can consequently be described by the linear determination function F:.

[0090] SP = m - DP + t

[0091] In practice, it is often advantageous to determine significantly more than the three curves MW1, MW2, and MW3 shown as examples in Fig. 4. This means that the relationship between the scattering parameter SP (here, the variance SP) and the proportion of the dispersed phase DP, here, the volume fraction of gas bubbles, is determined for a larger number of constant flow rates—and thus constant transit time differences. For example, this relationship can be determined for twenty or more constant mean values ​​MW of the transit time difference or—which is essentially the same—of the flow rate.

[0092] From each of the curves MW1, MW2, MW3 and possibly further curves not shown in Fig. 4, a value for each of the two linear coefficients m and t can then be determined. Ideally, one would expect each of the curves MW1, MW2, MW3 to pass through the origin of the coordinate system, i.e., the value zero for the scattering parameter SP corresponds to the zero fraction of the disperse phase DP. In practice, however, it has been shown that the determination of the fraction of the disperse phase DP becomes more accurate if a value other than zero is allowed for the linear coefficient.

[0093] The set of linear coefficients m is then approximated by a polynomial function whose variable is the mean value MW for the time difference. Furthermore, the set of linear coefficients t is approximated by a polynomial function whose variable is the mean value MW for the time difference. Of course, other functions are also suitable for this approximation.

[0094] In the embodiment described here, a fourth-degree polynomial is used to determine each of the linear coefficients m and t. The linear coefficients m and t are thus approximated using the following polynomial functions: y m = a,MW 4 + a2MW 3 + a3MW 2 + a4MW + a5y t = b r MW 4 + Ö2MV / 3 + b3MW 2+ b MW + ö5with the expansion coefficients ai , a2, as, a4, as and bi , b2, bs, b4, bs, which usually depend on the specific ultrasonic measuring device 1 or the geometry of the line 100, for example its outer and / or inner diameter.

[0095] Of course, the linear coefficients m and t can also be described by polynomial functions of a different degree. Furthermore, it is possible to use two polynomials of different degrees to determine the linear coefficient m and the linear coefficient t.

[0096] Using the polynomial functions y m and y t As shown in Fig. 3, the corresponding linear coefficients m, t can then be determined for each value of the mean value MW of the transit time difference, with which the linear determination function F can then be calculated.

[0097] Thus, for each mean value MW of the transit time difference between the first measurement signal 12 and the second measurement signal 21, the proportion of the disperse phase DP in the fluid flowing in the line 100 can be determined from the scattering parameter SP. The response time of the entire system comprising the ultrasonic measuring device 1 and the line 100 through which the fluid flows can be influenced in particular by the design of the storage module 25. The size or storage capacity of the storage module 25, which is designed, for example, as a FIFO memory, together with the measuring frequency with which the individual values ​​E are measured, influences the response time of the entire system because typically a plurality of individual values ​​E are first collected in the storage module 25 in order to determine the mean value MW and the scattering parameter SP therefrom.

[0098] If a short response time is desired in an application, it is advantageous to design the memory module 25 with a small capacity. However, if greater stability of the determination is important in an application, it is advantageous to design the memory module 25 with a larger capacity.

[0099] Fig. 5 shows a variant of the previously described embodiment in a representation analogous to Fig. 3. The following only discusses the differences between the variant and the embodiment shown in Fig. 3. Identical components or functionally equivalent features are designated by the same reference numerals as in the embodiment shown in Fig. 5. It is understood that all the preceding explanations apply in the same way or in the same sense to the variant shown in Fig. 5.

[0100] In the variant shown in Fig. 5, the fraction of the dispersed phase DP is first determined—for example, as described above. From this fraction of the dispersed phase DP, a modified fraction of the dispersed phase DM is then determined by applying a smoothing factor G.

[0101] In practice, it has been shown that in some applications, and particularly with small values ​​for the mean value MW of the transit time difference and thus with small values ​​of the flow through the line 100, the determination of the proportion of the dispersed phase DP can be improved by applying the smoothing factor G to the determined value for the proportion of the dispersed phase DP. The modified proportion of the dispersed phase DM is preferably obtained by multiplying the proportion of the dispersed phase DP by the smoothing factor G. It is therefore: DM = G ■ DP

[0102] The smoothing factor G, for example, allows for the fact that in weak flows, i.e., with small mean values ​​MW for the transit time difference or the flow rate, the statistical character of the distribution of gas bubbles as a dispersed phase is at least partially lost, for example, due to buoyancy or flow conditions. In practice, it has been shown that the application of the smoothing factor G can be particularly advantageous when the flow through line 100 is less than five times the critical Reynolds number.

[0103] The smoothing factor G is also determined using curves MW1, MW2, MW3, as shown in Fig. 4, which thus represent the change in the scattering parameter SP, here as the variance SP, as a function of the proportion of the disperse gas phase DP for a constant mean value MW of the transit time difference. For the calculation of the smoothing factor G, a polynomial function can be used, for example, a polynomial function yc of the sixth degree with y G = C1 MW 6 + C2MW 5 + c3MW 4 + c4MW 3 + C5MW 2 + c6MW + c7with the development coefficients Ci, C2, C3, C4, C5, Ce, C7, which generally depend on the specific ultrasonic measuring device 1 or the geometry of the line 100, for example its outer and / or inner diameter.

[0104] After the expansion coefficients Ci to c? have been determined, the smoothing factor G for a specific mean value MWs of the runtime difference is obtained by calculating the function yc at this point MWs. It is therefore

[0105] GCMWs) = y c MW s )

[0106] Depending on the specific application, other function types than a polynomial function can be used to calculate the smoothing factor, for example a hyperbola of the form:

[0107] 1 year G — 1 H -

[0108] 76 di ■ MW With the coefficient di , which is then determined using curves as shown in Fig. 4.

[0109] In the variant shown in Fig. 5, the smoothing factor G is also determined, and the calculated proportion of the disperse gas phase DP (here the proportion of gas bubbles) is multiplied by the smoothing factor G in order to obtain the modified proportion of the disperse phase DM, which is a quantitative measure of how much of the fluid consists of the disperse phase, in this case how large the volume fraction of the gas bubbles in the liquid is.

[0110] The method according to the invention can therefore be used to determine precise quantitative information on the proportion of the dispersed phase (DP, DM), for example, the gas content in a fluid, e.g., a liquid. This information can be used to expand or improve processes. As well as increasing accuracy, it opens up new possibilities for automation.

[0111] Examples of this are:

[0112] If, for example, during a transfer process of a fluid medium, e.g. a liquid, a gas phase, such as gas bubbles, cannot be avoided, but the quantity of the transferred medium plays a role, the quantitative gas content can be deducted from the transferred volume.

[0113] State-of-the-art flow meters often also offer a so-called volume counter. This calculates the pumped volume based on time and flow rate. In the event of an error, for example, if the presence of gas bubbles is detected during the measurement, at best a message appears indicating that bubbles were detected during the measurement. How much the volume determined by the volume counter deviates from the actual volume, or how many gas bubbles were detected, remains unknown with these flow meters.

[0114] With the method according to the invention, it is possible for the system comprising the flow meter to carry out a correction itself based on the now possible quantitative determination of the gas content in order to determine the actual volume, i.e. the volume without the proportion of gas bubbles. For this purpose, a corrected mean value for the flow of the fluid through line 100 can be determined, for example, using the proportion of the disperse phase, i.e. in this case the gas bubbles. This corrected mean value then takes into account the influence of the disperse phase, i.e. in this case the gas bubbles, on the determination of the flow. From this corrected mean value for the flow, the volume of the pure liquid, i.e. without the volume of the gas bubbles, can then be determined.

[0115] For example, if a process requires that a specified target volume of a medium be reached, the method according to the invention can be used to quantitatively determine the proportion of the dispersed phase, e.g., gas bubbles, which should not contribute to the specified target volume. By making appropriate corrections, such as feedback to a pump, valve, or control unit, the process can then continue until the specified target volume is actually reached.

[0116] As already mentioned, the method according to the invention can be carried out with all ultrasonic measuring devices 1 which are suitable for determining the flow of a fluid.

[0117] Since the method according to the invention makes it possible to determine quantitative information about a disperse phase in a fluid, it can also be used, for example, for threshold switches, limit switches or detectors, and in particular also in combination with existing measurement or analysis technology.

[0118] In a non-exhaustive list, some applications are mentioned for which the method according to the invention is particularly suitable:

[0119] - for monitoring the purity of liquid or gaseous end products or medicines in the pharmaceutical industry,

[0120] - for monitoring the air supply of clean rooms, for example in the semiconductor industry,

[0121] - for monitoring filling processes for end products, for example in the food industry or in the biotechnology industry, - for monitoring in medical technology when returning blood to the patient in order to avoid embolisms, for example when using a heart-lung machine,

[0122] - in the automotive industry, for example for fuel monitors or for monitoring brake fluids,

[0123] - for monitoring or measuring the degree of cavitation in pump technology.

Claims

A method for determining the proportion of a dispersed gas phase in a fluid flowing in a conduit in a flow direction using ultrasound, comprising the following steps: a) providing an ultrasonic measuring device (1) configured to determine a transit-time difference between two measurement signals passing through the fluid in the conduit (100), b) transmitting and receiving a first measurement signal (12) using the ultrasonic measuring device (1), wherein the first measurement signal (12) is transmitted in the direction of flow (A), c) transmitting and receiving a second measurement signal (21) using the ultrasonic measuring device (1), wherein the second measurement signal (21) is transmitted against the direction of flow (A), d) transmitting the measurement signals (12, 21) to a storage and evaluation unit (20), e) determining a single value (E) for the transit-time difference between the first measurement signal (12) and the second measurement signal (21).f) Determine a plurality of individual values ​​for the transit-time difference by repeating steps b) to e), g) Determine a mean (MW) for the transit-time difference from the individual values ​​(E) for the transit-time difference, h) Determine a scattering parameter (SP) that is characteristic of the scatter of the individual values ​​(E), i) Provide a relationship between the mean (MW) for the transit-time difference and the change in the scattering parameter (SP) as a function of the fraction of the dispersed gas phase (DP), j) Determine the fraction of the dispersed gas phase (DP) from the scattering parameter (SP) and the aforementioned relationship, optionally transforming the individual values ​​(E) for the transit-time difference or a mean over several individual values ​​(E) into individual values ​​(E) for the fluid flow rate or into a mean value for the flow rate, and performing steps h) and i) with the individual values ​​(E) for the flow rate or the mean value for the flow rate.The method according to claim 1, wherein at least one first ultrasonic transducer (11) is provided for transmitting and receiving the measurement signals (12, 21), which in the operating state is arranged laterally on a first side (51) of the line (100), and at least one second ultrasonic transducer (22), which in the operating state is arranged laterally on a second side (52) of the line (100), wherein the second side (52) is opposite the first side (51), wherein the ultrasonic transducers (11, 22) are arranged and aligned such that the first ultrasonic transducer (11) can transmit the first measurement signal (12) obliquely to the flow direction (A) of the fluid to the second ultrasonic transducer (22), and can receive the second measurement signal (21) transmitted by the second ultrasonic transducer (22) obliquely to the flow direction (A).A method according to any one of the preceding claims, wherein the flow rate of the fluid through the line (100) is determined from the transit-time differences between the first measurement signals (12) and the second measurement signals (21). A method according to any one of the preceding claims, wherein the ultrasonic measuring device (1) is configured as a clamping device, and the line (100) is clamped in the ultrasonic measuring device (1). A method according to any one of the preceding claims, wherein the determination of the proportion of the dispersed gas phase (DP) is updated at regular intervals or continuously. A method according to any one of claims 3-5, wherein a corrected mean value for the flow rate is determined using the proportion of the dispersed phase (DP). A method according to claim 6, wherein the corrected mean value indicates the flow rate of the fluid without the dispersed gas phase.Method according to one of the preceding claims, wherein the dispersion parameter (SP) is the variance of the individual values ​​(E) with respect to the mean (MW).

9. Method according to one of the preceding claims, wherein the change in the scattering parameter (SP) as a function of the proportion of the dispersed gas phase (DP) at a constant mean value (MW) for the transit time difference is described by a linear determination function (F).

10. Method according to claim 9, wherein the linear determining function (F) is determined by two linear coefficients (m, t), each linear coefficient (m, t) being determined by a polynomial function whose variable is the mean (MW) for the runtime difference.

11. Method according to one of the preceding claims, wherein the change in the scattering parameter (SP) as a function of the proportion of the dispersed gas phase (DP) at a constant mean value (MW) for the transit time difference is stored in a lookup table in the storage and evaluation unit (20).

12. Method according to one of the preceding claims, in which the proportion of the dispersed gas phase (DP) is first determined, and a modified proportion of the dispersed gas phase (DM) is determined from this by applying a smoothing factor (G).

13. Method according to claim 12, wherein the smoothing factor (G) is calculated using a polynomial function whose variable is the mean (MW) for the runtime difference.

14. Method according to any of the preceding claims, wherein the dispersed gas phase consists of gas bubbles, and wherein the fraction of the dispersed gas phase (DP) is the volume fraction of the gas bubbles in a liquid.

15. Method according to any of the preceding claims, wherein each transit time difference is converted into a value for the flow rate of the fluid through the line (100) and the proportion of the dispersed gas phase (DP) is determined using the flow rate values.

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