Method for determining the fraction of dispersed gas phase in a fluid

Abstract

The method for determining the proportion of dispersed gas phase in a fluid flowing in a pipe in a flow direction using ultrasound comprises the steps of: a) providing an ultrasonic measuring device (1) designed to determine the transit time difference between two measurement signals passing through the fluid in the pipe (100); b) emitting and receiving by the ultrasonic measuring device (1) a first measurement signal (12) emitted along the flow direction (A); c) emitting and receiving by the ultrasonic measuring device (1) a second measurement signal (21) emitted against the flow direction (A); d) transmitting the measurement signals (12, 21) to a storage and evaluation unit (20); e) determining an individual value (E) of the transit time difference between the first measurement signal (12) and the second measurement signal (21); f) determining a plurality of individual values ​​of the transit time difference by repeating steps b) to e); g) determining a mean value (MW) of the transit time difference from the individual values ​​(E) of the transit time difference. h) determining a variability parameter (SP) characteristic of the variability of the individual values ​​(E) around a mean value (MW), i) providing a correlation between the mean value (MW) of the transit time difference and the change in the variability parameter (SP) as a function of the dispersed gas phase fraction (DP), and j) determining the dispersed gas phase fraction (DP) from the variability parameter (SP) and said correlation. Optionally, the individual values ​​(E) of the transit time difference or the mean value over several individual values ​​(E) are converted into individual values ​​(E) of the flow rate of the fluid or the mean value of the flow rate, and steps h) and i) are carried out using the individual values ​​(E) of the flow rate or the mean value of the flow rate.

Description

[Technical field]

[0001] The invention relates to a method for determining the proportion of dispersed gas phase in a fluid flowing in a pipe in a flow direction using ultrasound, in which the transit time difference between two measurement signals passing through the fluid in the pipe is measured by an ultrasonic measuring device. [Background technology]

[0002] In process engineering, non-invasive methods are used to inspect fluids or to measure fluids flowing in pipes (e.g. flexible plastic tubes). This is especially true for such highly pure or very sensitive fluids, where contact between the fluid and the measuring device should be avoided as far as possible, e.g. so that the fluid is not contaminated. Here we cite as examples the pharmaceutical and biotechnology industries, where solutions and suspensions are frequently produced and transported, making very high demands on the purity and / or integrity of the fluids. Often such fluids also need to be processed under sterile conditions.

[0003] In particular, ultrasonic measuring techniques have proven their worth as a method for non-invasively measuring fluids flowing in pipes. Ultrasonic measuring devices for measuring fluids flowing in pipes are used, for example, to determine the flow rate of the fluid through the pipe. Hereby, it is known to design the measuring device as a clamping device, so that it can be clamped onto a flexible pipe or the pipe is clamped by the measuring device. An ultrasonic signal is then applied to the pipe through which the fluid flows. After passing through the pipe and the fluid, the ultrasonic signal is received by an ultrasonic transducer and the received signal is evaluated.

[0004] It is a known means for determining the flow rate that an ultrasonic measuring device comprises at least two ultrasonic transducers arranged laterally on either side of a pipe in an operating state. The two ultrasonic transducers are arranged offset from each other with respect to the flow direction of the fluid, such that the first ultrasonic transducer can receive a signal emitted from the second ultrasonic transducer and the second ultrasonic transducer is aligned so that the first ultrasonic transducer can receive a signal emitted from the second ultrasonic transducer. Due to the offset from each other, the two ultrasonic transducers are aligned to emit ultrasonic signals obliquely with respect to the flow direction of the fluid, such that one ultrasonic transducer emits a signal obliquely with the flow direction and the other ultrasonic transducer emits a signal obliquely against the flow direction. Here, a measurement signal is emitted by the first ultrasonic transducer and received by the second ultrasonic transducer, and then a measurement signal is emitted by the second ultrasonic transducer and emitted by the first ultrasonic transducer.

[0005] A measurement signal emitted obliquely into the flow direction is accelerated in the flow, and a measurement signal emitted obliquely against the flow direction is decelerated by the flow. The transit time difference between the two measurement signals is proportional to the fluid velocity, so the flow rate through the flexible pipe can be determined from this transit time difference.

[0006] In addition to such ultrasonic methods based on measuring the transit time or transit time difference, methods are also known which determine the amplitude or frequency or attenuation of the ultrasonic signal. By means of these parameters, in particular from combinations of these parameters such as transit time and attenuation, it is possible to determine not only the flow rate but also other properties of the fluid, such as viscosity or optical density.

[0007] However, fluids are often not single-phase fluids but multiphase systems such as dispersions. Dispersions are characterized by the presence of undissolved components in another medium, the so-called dispersion medium. These undissolved components are designated as the dispersed phase. Usually, the undissolved components are statistically distributed in the dispersion medium.

[0008] An important example of such a multiphase system is a fluid, especially a liquid, that contains undissolved gas bubbles as the dispersed phase. It is often necessary to test for the presence of gas bubbles in a fluid flowing in a pipe. For example, during surgery, such as using a heart-lung machine, when a patient's blood is pumped through pipes, it is very important to test for the presence of gas bubbles (e.g. air bubbles) in the blood flowing in the pipes, as these could be life-threatening.

[0009] In order to detect air bubbles within the scope of ultrasonic flow measurements, it has been proposed in US Pat. No. 5,399,633 to determine the amplitude of the ultrasonic signal after passage through the fluid in addition to the transit time. A significant decrease or collapse of the amplitude is used as an indication of the presence of air bubbles in the fluid. However, this amplitude-based measurement only allows a qualitative statement that air bubbles are present in the fluid, and no quantitative statement is really possible about the proportion of air bubbles in the fluid. For example, this is due to the fact that a large number of small air bubbles can cause the same amplitude drop as one large air bubble, or that small air bubbles flow in the acoustic shadow of a large bubble and therefore do not contribute to the amplitude drop at all. The amplitude of the received ultrasonic signal also depends on many other factors, such as the temperature of the medium, the characteristics of the ultrasonic transducer, or the characteristics of the pipe or tube. For this reason, it is now common to use only the amplitude of the received ultrasonic signal for a qualitative statement of the presence or absence of air bubbles or gas bubbles in the fluid.

[0010] However, in many applications it is desirable to be able to determine the proportion of gas bubbles in a fluid, or more generally the proportion of the dispersed phase, i.e. also to be able to make a reliable quantitative description of the dispersed phase.

[0011] An automatic filling process is described here as an example. In such filling processes, weight is usually used as a criterion, i.e. the filling is terminated as soon as the container to be filled reaches a predeterminable weight. For example, if the liquid flowing into the container to be filled contains a larger proportion of gas bubbles (e.g. air bubbles), especially towards the end of the filling process, the volume belonging to the given weight increases as a result. Air bubbles tend to accumulate at the top of the container. The average density of the liquid with air bubbles inside it decreases. As a result, there is a risk that the container to be filled will overflow, since the volume belonging to the given weight will not fit inside the container. This can therefore delay the end of the filling process, causing damage to the container and in the worst case leading to its destruction. This means danger for personnel and machines. Furthermore, economic losses can also occur. To prevent such consequences, very high safety margins are often provided so that the process is stopped or interrupted prematurely. If the proportion of dispersed gas phase (in this case air bubbles) could be reliably determined, these safety margins could be reduced and therefore the process could be carried out more efficiently and economically. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] European Patent Application Publication No. 2717026 Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention is directed to this problem.

[0014] Starting from this state of the art, it is therefore the object of the present invention to propose a method by which the proportion of dispersed gas phase in a fluid flowing through a pipe can be reliably determined, which method can be realised by means of an ultrasonic measuring device, and which thus allows a quantitative description of the dispersed gas phase in a flowing fluid on the basis of ultrasonic measurements. [Means for solving the problem]

[0015] The subject matter of the invention which meets this object is characterized by what is comprised in the independent patent claims.

[0016] Therefore, according to the invention there is provided a method for determining the fraction of dispersed gas phase in a fluid flowing in a pipe in a flow direction using ultrasound, comprising the steps of: a) providing an ultrasonic measurement device designed to determine the transit time difference between two measurement signals passing through a fluid in a pipe; b) emitting and receiving, by an ultrasonic measuring device, a first measurement signal emitted along a flow direction; c) emitting and receiving a second measurement signal emitted against the flow direction by an ultrasonic measuring device; d) transmitting the measurement signals to a storage and evaluation unit; e) determining respective values ​​of the transit time difference between the first and second measurement signals; f) determining a plurality of individual values ​​of the transit time difference by repeating steps b) through e); g) determining an average value of the transit time difference from the individual values ​​of the transit time difference; h) determining variability parameters characteristic of the variability of the individual values; i) providing a correlation between the average transit time difference and the change in the variability parameter as a function of the fraction of dispersed gas phase; j) determining the proportion of dispersed gas phase from the variability parameter and the aforementioned correlation; Including, Optionally, a method is proposed in which the individual values ​​(E) of the transit time difference or an average value over several individual values ​​(E) are converted into individual values ​​(E) of the flow rate of the fluid or the average value of the flow rate, and steps h) and i) are carried out using the individual values ​​(E) of the flow rate or the average value of the flow rate.

[0017] Therefore, the realization that the variation of the transit time difference (or the value of the flow rate determined therefrom) about the average value of the transit time difference (or the average value of the flow rate determined therefrom) when the average value of the transit time difference (or the flow rate) is constant is highly reproducibly dependent on the fraction of dispersed phase in the fluid is essential to the invention. Thus, the statistical variation of the transit time difference (or the value of the flow rate determined therefrom), i.e. the quasi-"noise" of the transit time difference (or the value of the flow rate determined therefrom) about the average value of the transit time difference (or the value of the flow rate determined therefrom), can be used to reliably determine the fraction of dispersed gas phase (e.g. the fraction of gas bubbles) in the fluid.

[0018] In doing so, a quantitative description of the dispersed gas phase in a fluid can be obtained based on ultrasonic flow measurements.

[0019] A particular advantage of the method according to the invention is that it is based on an ultrasonic transit time measurement, which, at least to a very good approximation, is independent of the amplitude of the respective received ultrasonic measurement signal and is therefore influenced by significantly fewer factors than, for example, a measurement of the amplitude of the received ultrasonic measurement signal.

[0020] It has also been shown that determining the percentage of dispersed gas phase based on the transit time difference of the measurement signal gives much more accurate and reproducible results than if the percentage of dispersed gas phase was determined, for example, by evaluating the amplitude of the ultrasonic signal and then estimating the percentage of dispersed gas phase from the statistical fluctuations of the amplitude values.

[0021] For a given mean value of the transit time differences of the measurement signal, the proportion of dispersed gas phase can be reliably determined from the statistical fluctuation of the transit time differences around this mean value.

[0022] In principle, all ultrasonic measuring devices are suitable for the method according to the invention, which can be used to determine the transit time difference between two measuring signals passing through a fluid flowing in a pipe.

[0023] Preferably, the system comprises at least one first ultrasonic transducer arranged laterally on a first side of the pipe in an operational state for emitting and receiving measurement signals, and at least one second ultrasonic transducer arranged laterally on a second side of the pipe in an operational state, the second side being opposite the first side. The ultrasonic transducers are arranged and aligned such that the first ultrasonic transducer can emit a first measurement signal obliquely to the fluid flow direction towards the second ultrasonic transducer and can receive a second measurement signal emitted by the second ultrasonic transducer obliquely to the flow direction.

[0024] Furthermore, the flow rate of the fluid through the pipe is preferably determined from the transit time difference between the first and second measurement signals.

[0025] Particularly preferably, the ultrasonic measuring device is designed as a clamping device, and the pipe is clamped in the ultrasonic measuring device. Such a clamping device is disclosed, for example, in EP 3 489 634 A or also in EP 3 816 590 A. A particular advantage of the device disclosed in EP 3 816 590 A is that the ultrasonic signals are emitted and received in several different measuring planes. This makes it possible, for example, to more reliably detect particularly small bubbles in the peripheral area of ​​the measuring volume and bubbles moving behind other bubbles.

[0026] According to a preferred embodiment of the method according to the invention, the determination of the proportion of dispersed gas phase is updated at regular intervals or continuously.

[0027] The method according to the invention is also particularly suitable for increasing the accuracy of the measurement of the flow rate of a fluid through a pipe. For this purpose, for example, the proportion of dispersed gas phase can be utilized to determine a corrected average value of the flow rate, which takes into account the influence of the dispersed gas phase on the determination of the flow rate.

[0028] Preferably, the corrected average value indicates the flow rate of the fluid without the dispersed gas phase. This means that, based on the percentage of dispersed gas phase, it is possible to determine how the dispersed gas phase affects the individual values ​​of the flow rate or the average value of the flow rate. Thus, for example, a corrected average value of the flow rate can be determined, which indicates how much higher the flow rate of the fluid would be in the absence of dispersed gas phase. Thus, the flow rate of the "pure" dispersion medium can be determined, which can significantly improve the accuracy of the flow rate measurement.

[0029] In principle, any parameter that is a measure of the fluctuation or scatter of the individual values ​​of the transit time difference measurement (or values ​​of the flow rate) around a mean value of the transit time difference (or flow rate) is suitable as the scatter parameter. Preferably, the scatter parameter is a statistical parameter that describes the statistical noise of the individual values ​​around the mean value. For example, the scatter parameter is the variance of the individual values ​​relative to the mean value or the standard deviation of the individual values.

[0030] In a preferred embodiment of the method according to the invention, the variation of the variability parameter as a function of the fraction of dispersed gas phase at a constant mean value of the transit time difference (or flow rate) is described by a linear decision function.

[0031] Here, it is particularly preferable that the linear decision function is defined by two linear coefficients, and each linear coefficient is determined based on a polynomial function that uses the average value of the transit time difference (or flow rate) as a variable.

[0032] To determine the fraction of dispersed phase from the transit time difference measurements, the variation of the variability parameter as a function of the fraction of dispersed gas phase at a constant mean value of the transit time difference can also be stored in a look-up table in the storage and evaluation unit.

[0033] In particular, when the fluid flow velocity through the pipe is low, it may be advantageous to first determine the fraction of dispersed gas phase and then determine a corrected fraction of dispersed gas phase from that by applying a smoothing factor.

[0034] The smoothing coefficient is preferably calculated using a polynomial function having the average value of the transit time difference as a variable.

[0035] In a preferred application of the method according to the invention, the dispersed gas phase consists of gas bubbles.

[0036] Therefore, the proportion of the dispersed gas phase is preferably the volume fraction of gas bubbles in the liquid.

[0037] Since the transit time difference between the first and the second measurement signal is proportional to the flow velocity of the fluid in the pipe, any value of the transit time difference can be converted in a very simple way into a value of the flow rate. Each transit time difference is therefore converted into a value of the flow rate of the fluid through the pipe, and it is also possible to determine the proportion of the dispersed gas phase using the value of the flow rate. 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 difference. If the transit time difference is first converted into a value of the flow rate, it goes without saying that instead of the average value of the transit time difference, the dispersion parameter and the relationship between the average value of the transit time difference and the change of the dispersion parameter as a function of the dispersed gas phase, the corresponding quantity or the corresponding relationship of the flow rate must also be used. This means that the individual and / or average values ​​of the transit time difference are converted into individual and / or average values ​​of the flow rate, the dispersion parameter is determined as a function of the flow rate value, and the relationship between the average value of the transit time difference and the change of the dispersion parameter as a function of the dispersed gas phase is converted into the relationship between the average value of the flow rate and the change of the dispersion parameter as a function of the dispersed gas phase.

[0038] Furthermore, it is possible that an averaged individual value is first determined from a predetermined number of individual values ​​and then the statistical evaluation, i.e. in particular the determination of the variability parameters, is carried out on the basis of the averaged individual values, which essentially corresponds to a smoothing of the individual values ​​before the statistical evaluation.

[0039] Further advantageous measures and embodiments of the invention are evident from the dependent claims.

[0040] The present invention will be described in more detail below based on embodiments and drawings. [Brief description of the drawings]

[0041] [Figure 1] FIG. 1 shows a schematic diagram of an ultrasonic measuring device for determining the transit time difference between two measuring signals passing through a fluid in a pipe. [Diagram 2] 1 shows a perspective view of an ultrasonic measuring device for determining transit time differences, designed as a clamping device; [Diagram 3] 1 is a schematic diagram illustrating an embodiment of the method according to the present invention. [Figure 4] FIG. 13 is a diagram showing the correlation between the variability parameter and the fraction of dispersed gas phase in a fluid. [Diagram 5] Similar to FIG. 3, but a variant of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] The present invention proposes a method for determining the proportion of dispersed gas phase in a fluid flowing in a pipe 100 (FIG. 1), in which an ultrasonic measuring device 1 is used to determine the transit time difference between two measurement signals passing through the fluid in the pipe 100.

[0043] In the following description, reference is made to an application example having the exemplary feature that the dispersed gas phase consists of gas bubbles. Furthermore, reference is made to an example in which 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. In the following, the determination of the volume fraction of gas bubbles in a liquid (e.g. water or an aqueous solution) is considered as an example.

[0044] Of course, the invention is not limited to these examples and also relates to other types of dispersions. In general, a dispersion is defined as a multiphase system in which undissolved components, quantities or entities are present in a medium. The undissolved components are usually called the dispersed phase and the medium is called the dispersion medium. In this case, the undissolved components of the dispersed phase are usually statistically distributed in the dispersion medium.

[0045] In the method according to the invention, the dispersion medium is a fluid, i.e. for example a liquid or a gas. The dispersed phase is a dispersed gas phase, i.e. the dispersed phase is a gas. The method 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 plus the volume of the dispersion medium).

[0046] The term "fraction of dispersed gas phase" means that a quantitative determination is made of the amount, volume, or mass of dispersed gas phase in a fluid, i.e., a determination of, for example, volume percentage or mass percentage is made.

[0047] In principle, all ultrasonic measuring devices 1 that are capable of determining the transit time difference between two measuring signals in a fluid flowing through a pipe 100, where one measuring signal is emitted in the flow direction of the fluid and the other measuring signal is emitted against the flow direction, are suitable for the method according to the invention. Also suitable are ultrasonic measuring devices 1 that themselves form the pipe 100 or part of the pipe 100, i.e. for example so-called in-line measuring devices, such as, in particular, those marketed by the applicant under the trade name LEVIFLOW LFS.

[0048] Fig. 1 shows in a schematic diagram an ultrasonic measuring device 1 for determining the transit time difference between two measurement signals passing through a fluid flowing through a pipe. The pipe is designated by the reference number 100. In the following, reference is made to the case, which is of particular practical importance, that the pipe 100 is a flexible pipe 100, i.e. a pipe 100 whose wall 101 (Fig. 2) is deformable. A flexible pipe 100 is, for example, a plastic tube made from silicone rubber or PVC. Of course, the pipe 100 can also be made from other materials, in particular plastic or rubber. Of course, the method according to the invention is also suitable for rigid (i.e. non-flexible) pipes.

[0049] A fluid flows through the pipe 100 in a flow direction A. At least two ultrasonic transducers 11, 22 are provided for emitting and receiving ultrasonic measurement signals 12, 21, namely a first ultrasonic transducer 11 and a second ultrasonic transducer 22. In operation, the first ultrasonic transducer 11 is arranged laterally on a first side 51 of the pipe 100 and the second ultrasonic transducer 22 is arranged laterally on a second side 52 of the pipe 100, the second side 52 being opposite to the first side 51. The ultrasonic transducers 11, 22 are arranged and aligned such that the first ultrasonic transducer 11 can emit 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 emitted by the second ultrasonic transducer 22 obliquely to the flow direction A.

[0050] In Fig. 1, the measurement signals 12, 21 are each symbolically represented by a dashed straight line with an arrow. This should be understood in such a way that the dashed line indicates in each case the main propagation direction of the ultrasonic signal emitted by the corresponding ultrasonic transducer 11, 22, and the arrow indicates whether the respective ultrasonic signal is moving towards (i.e. received) or away from (i.e. emitted) the respective ultrasonic transducer 11, 22. 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 forms an angle α with the flow direction A, which angle is different from 0° and from 90°.

[0051] In ultrasonic measuring devices 1 designed as in-line measuring devices, this angle α is often equal to 0° or equal to 180°, i.e. the measuring signals are emitted such that their main direction of propagation is equal to or directly opposite to the flow direction A. For example, this can be realized with a U-shaped or Z-shaped ultrasonic measuring device.

[0052] For example, in the ultrasonic measuring device 1 shown in Fig. 1 the following procedure is used to determine the transit time difference: A first ultrasonic transducer 11 emits a first measurement signal 12, which is emitted obliquely at an angle α to the flow direction A and along the flow direction A, meaning that the main propagation direction of the first measurement signal 12 also has a component in the flow direction A. A second ultrasonic transducer 22 emits a second measurement signal 21, which is emitted obliquely at an angle α to the flow direction A and against the flow direction A, meaning that the main propagation direction of the second measurement signal 21 also has a component opposite to the flow direction A.

[0053] The first measurement signal 12 is received by the second ultrasonic transducer 22 after passing through the fluid and transmitted via signal line 22a to the 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 signal line 11a to the storage and evaluation unit 20.

[0054] In the storage and evaluation unit 20, the transit time difference between the first measurement signal 12 accelerated by the flowing fluid and the second measurement signal 21 decelerated by the flowing fluid is determined. This transit time difference between the first measurement signal 12 and the second measurement signal 21 depends directly on the flow velocity of the fluid in the pipe 100. The flow velocity of the fluid through the pipe 100, and thus also the flow rate, can thus be determined, for example, from the transit time difference.

[0055] It is also often the case that the ultrasonic measuring device 1 is provided with at least four ultrasonic transducers 11, 22 for the respective emission and reception of ultrasonic signals, i.e. at least two first ultrasonic transducers 11 arranged laterally on the first side 51 and at least two second ultrasonic transducers 22 arranged laterally on the second side 52. The ultrasonic transducers 11, 22 are then arranged and aligned in each case such that one of the first ultrasonic transducers 11 can emit a first measurement signal 12 obliquely to and along the flow direction A to one of the second ultrasonic transducers 22 and receive a second measurement signal 21 emitted by the second ultrasonic transducer 22 obliquely to and against the flow direction A. For example, the four ultrasonic transducers 11, 12 are arranged in an X-shape. Such an arrangement of ultrasonic transducers 11, 22 is disclosed, for example, in EP 3 489 634 A1. This arrangement with four ultrasonic transducers has the advantage that two mutually independent measurements are performed both in flow direction A and against flow direction A, which significantly increases the accuracy and reliability of the determination of e.g. the flow rate.

[0056] Particularly preferably, the ultrasonic measuring device 1 is designed as a clamping device, so that a pipe 100 can be clamped in the ultrasonic measuring device 1. Figure 2 shows an embodiment of an ultrasonic measuring device 1 for determining the transit time difference between two measuring signals in a perspective view, which is designed as a clamping device.

[0057] 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 a pipe 100, i.e. the housing 4 of the ultrasonic measuring device 1 can be clamped onto the pipe 100 such that the pipe 100 is fixed relative to the housing 4. The main design of the ultrasonic measuring device 1 with the housing 4 is known per se, for example from EP 3 489 634 A. EP 3 816 590 A also discloses an ultrasonic measuring device 1 designed as a clamping device for a removable attachment to the pipe 100 and suitable for the method according to the invention.

[0058] The housing 4 is designed as an openable housing 4 and comprises a first housing part 41 and a second housing part 42 which are articulated to each other via a joint 43. Figure 2 shows the housing 4 in the open state. The housing 4 further has a continuous central receptacle 3 which extends through the entire housing 4 and serves to receive a pipe 100. The longitudinal extension of the central receptacle 3 defines a flow direction A in which the fluid flows through the pipe 100 or the housing 4.

[0059] The housing 4 further comprises a closing mechanism 44 for closing the housing 4 and clamping the pipe 100 in the central receptacle 3. The closing mechanism 44 is here arranged on the first housing part 41 and comprises a bracket 46 and a folding strap 45 for tensioning the bracket 46. The pipe 100 is inserted into the central receptacle 3 and then the two housing parts 41, 42 are folded together, i.e. the first housing part 41 is folded over the pipe 100. The bracket 46 engages with a projection 47 on the second housing part 42 and the two housing parts 41, 42 are tensioned together by actuating the strap 45. The housing 4 is then in a closed state and the pipe 100 is clamped in the central receptacle 3 and thus fixed relative to the housing 4.

[0060] Thus, in the closed state of the housing 1 , the pipe 100 is fixed between the first and second faces 51 , 52 which face each other with respect to the central receptacle 3 .

[0061] Marking elements (not shown), for example arrows defining the flow direction in which fluid flows through the ultrasonic measuring device 1, may also be provided on the housing 4.

[0062] The central receptacle 3 is preferably designed to have a substantially rectangular, in particular a square, cross section perpendicular to the flow direction A, in the closed state of the housing 4. This has the advantage that the ultrasonic measurement signal applied to the pipe 100 strikes a plane (i.e. not a curved surface), which significantly simplifies the detection and evaluation of the measurement signals 12, 21 and increases the accuracy of the measurement.

[0063] Also known are embodiments in which the central receptacle is designed to have a different polygonal cross section perpendicular to the flow direction A in the closed state of the housing, for example a hexagonal cross section. Furthermore, also known are embodiments in which this cross section is circular or elliptical. In such embodiments, acoustic lenses are often used for measuring signal emission and / or reception.

[0064] 2, the ultrasonic transducers 11, 22 are provided within the housing 4, i.e., on a first surface 51 and a second surface 52, respectively. The first ultrasonic transducer(s) 11 are disposed on the first surface 51, and the second ultrasonic transducer(s) 22 are disposed on the second surface 52.

[0065] Each of the ultrasonic transducers 11, 22 is signal-connected to the storage and evaluation unit 20 via in each case 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. Via the respective signal lines 11a, 22a, the ultrasonic transducers 11, 22 are activated to emit ultrasonic signals and transmit respectively received measurement signals 12, 21 to the storage and evaluation unit 20. The received measurement signals 12 and 21 are analyzed in the storage and evaluation unit 20 and a transit time difference between one of the first measurement signals 11 and one of the second measurement signals 21 is determined in each case. Furthermore, it is possible to determine the flow rate of the fluid through the pipe 100 from the determined transit time difference.

[0066] The ultrasonic transducers 11, 22 can be designed in any manner known per se, in particular as piezoelectric transducers. Typically, the frequency of the ultrasonic signal is in the megahertz range, for example in the range from 1 MHz to 30 MHz.

[0067] The above description of the ultrasonic measuring device 1 should be understood only as an example: any ultrasonic measuring device designed or suitable for determining the transit time difference between a measurement signal emitted along the flow direction A and a measurement signal emitted against the flow direction A is suitable for the method according to the invention.

[0068] In a schematic diagram, FIG. 3 shows an embodiment of a method according to the invention for determining the proportion of a dispersed gas phase (consisting in this example of gas bubbles) in a fluid (here a liquid) flowing in a pipe 100 .

[0069] A number of individual values ​​for the transit time difference between the first measurement signal 12 and the second measurement signal 21 are determined in each case with the aid of the ultrasonic measuring device 1. These individual values ​​are represented in FIG. 3 by arrows with the symbol E. Each individual value E is stored in a storage module 25 of the storage and evaluation unit 20. For example, the storage module 25 is designed as a FIFO storage (FIFO: First In First Out). The stored individual values ​​E are collected in the storage module 25 and evaluated by an analysis procedure. The analysis procedure preferably uses statistical or probabilistic methods to determine the proportion of the dispersed phase (in this case air bubbles) in the fluid from the plurality of individual values ​​E, as will be explained in more detail below.

[0070] Preferably, the determination of the proportion of the dispersed phase is updated at regular intervals or continuously, where the term "continuously updated" means that for each new respective value E of the transit time difference transmitted to the storage module, an evaluation is performed again and the determination of the proportion of the dispersed phase is updated.

[0071] The average transit time difference MW is determined from the individual transit time difference values ​​E. Preferably, the average transit time difference MW is a statistical average value MW or an arithmetic mean (i.e. the sum of n individual values ​​E divided by the number of individual values ​​n, where n is a natural number).

[0072] It is a substantial recognition of the present invention that the variation of the individual values ​​E about the mean value MW for a constant mean value MW depends in a very reproducible way on the proportion of dispersed gas phase in the fluid. Therefore, the statistical variation of the individual values ​​E about the mean value MW, i.e. the "noise" of the transit time difference (or flow rate) about the mean value MW, can be used to reliably determine the proportion of dispersed gas phase in the fluid.

[0073] Thus, a variability parameter SP is further determined from the individual values ​​E of the flow rate, which is specific to the variability of the individual values ​​E around the mean value MW. For example, the variance of the individual values ​​E, or the empirical variance or standard deviation of the individual values ​​E from the mean value MW, is suitable as the variability parameter. Usually, the standard deviation is the square root of the variance. The (empirical) variance is the sum of the squares of the deviations of n individual values ​​E from the mean value MW divided by the number n of individual values ​​E, or by the number of degrees of freedom (n-1), where n is any natural number indicating the number of individual values ​​E.

[0074] It is also possible to determine averaged single values ​​from a predetermined number of single values ​​E and then use these averaged single values ​​for further analysis (i.e. also in particular for determining the mean value MW).

[0075] In a preferred embodiment, the variance SP is used as the dispersion parameter SP, defined as follows:

number

[0076] When the mean value MW of the transit time difference (or flow rate) is constant, the change in the variability parameter SP (i.e., the variance SP in this case) depending on the fraction of dispersed gas phase is described by a linear decision function F, which is a linear correlation of the following form:

number

[0077] Therefore, the dispersed gas phase fraction DP can be calculated using a linear decision function F as follows:

number

[0078] As represented in Fig. 3, the mean value MW and the dispersion parameter SP (in this case the dispersion SP) are determined from the individual values ​​E stored in the storage module 25. Two linear coefficients m and t are determined for a specific mean value MW. A linear determination function F is therefore known for the variation of the dispersion parameter SP depending on this specific mean value MW and therefore on the dispersed gas phase fraction DP. The dispersed phase fraction DP can be calculated as DP = (SP-t) / m.

[0079] The method according to the invention therefore allows a quantitative description of the dispersed gas phase in a fluid.

[0080] The two linear coefficients m and t which define the linear decision function F for a predeterminable constant mean value MW can, for example, be stored in a look-up 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 correlation, each with the mean value MW as a variable. For each of the linear coefficients m, t, this functional correlation can in each case be a polynomial function whose variable is the mean value MW.

[0081] Preferably, the linear coefficients m, t of the respective ultrasonic measuring device 1 are determined empirically or metrologically, for example by means of calibration measurements. For this purpose, this can be done as follows.

[0082] With the ultrasonic measuring device 1, the mean value MW of the transit time difference and the dispersion parameter SP (i.e. here the dispersion SP) are measured on a calibration fluid for different proportions of dispersed gas phase DP in each case. The calibration fluid has a predeterminable dispersed phase proportion DP. For example, this can be realized in such a way that a predeterminable volume fraction of gas (e.g. air) is mixed with a fluid (e.g. water) flowing in a pipe 100. The mean value MW of the transit time difference and the dispersion SP (i.e. the dispersion of the individual values ​​E around the mean value MW) are determined for this fluid (e.g. water with gas bubbles contained therein) by the ultrasonic measuring device 1. The volume fraction of gas is kept constant and the flow rate is increased in several steps, for example from zero to a value of 10 liters per minute. In each case the mean value MW and the dispersion SP are determined. This calibration measurement is repeated for various values ​​of the dispersed gas phase proportion DP (i.e., the proportion of bubbles here), e.g., volume fractions of bubbles of 0%, 0.5%, 3% and 6%, to name just a few examples.

[0083] From these calibration measurements, a series of curves is obtained, as represented by exemplary characteristics in the diagram of FIG. 4. The dispersed phase proportion DP (i.e. here the volume fraction of gas bubbles in the liquid) is plotted on the horizontal axis, and the scatter parameter SP (i.e. here the dispersion) is plotted on the vertical axis. Three curves MW1, MW2, MW3 are shown in FIG. 4. Each of the curves MW1, MW2 and MW3 belongs to the case where the average MW of the transit time differences has a constant value. The curve MW1 belongs to the case where the average MW of the transit time differences has a minimum constant value, the curve MW3 belongs to the case where the average MW of the transit time differences has a maximum, and the curve MW2 belongs to the case where the transit time differences have intermediate values. It is well recognized that when the average MW of the transit time differences is constant, the correlation between the dispersion SP and the dispersed phase proportion DP is to a very good approximation a linear correlation, which can therefore be described by a linear decision function F such as:

number

[0084] In practice, it is often advantageous to determine many more curves than the three curves MW1, MW2, MW3 shown by way of example in Fig. 4, i.e. to determine the correlation between the variability parameter SP (i.e. here the dispersion SP) and the proportion of the dispersed phase DP (i.e. here the volume fraction of bubbles) for many more respective constant flow rates and thus constant transit time differences. For example, this correlation can be determined for 20 or even more respective constant mean values ​​MW of transit time differences or flow rates (which is also the case).

[0085] The values ​​of each of the two linear coefficients m and t can then be determined in each case from each of the curves MW1, MW2, MW3 and, if necessary, from other curves not shown in Figure 4. In the ideal case, it is expected that each of the curves MW1, MW2, MW3 passes through the zero point of the coordinate system (i.e. the zero value of the scatter parameter SP belongs to the zero proportion of the dispersed phase DP). However, in practice it has been shown that the determination of the proportion of the dispersed phase DP becomes more accurate if non-zero values ​​of the linear coefficients are allowed.

[0086] Here, the linear coefficients m are all approximated by a polynomial function with the average transit time difference MW as a variable. Furthermore, the linear coefficients t are all approximated by a polynomial function with the average transit time difference MW as a variable. Of course, other functions are also suitable for this approximation.

[0087] In the embodiment described here, a fourth-order polynomial is used in each case to determine each of the linear coefficients m, t. Thus, the linear coefficients m, t are approximated based on the following polynomial function:

number

number

[0088] Of course, the linear coefficients m and t can be described by polynomial functions of different orders. Furthermore, it is also possible to use two polynomials of different orders to determine the linear coefficient m and the linear coefficient t.

[0089] Next, the polynomial function y m and y t Using this, it is possible to determine the associated linear coefficients m, t for each value of the mean transit time difference MW, as also shown in FIG. 3, and these can then be used to calculate the linear decision function F in each case.

[0090] Thus, for each average value MW of the transit time difference between the first measurement signal 12 and the second measurement signal 21, the proportion DP of the dispersed phase in the fluid flowing in the pipe 100 can be determined from the variability parameter SP.

[0091] The reaction time of the overall system comprising the ultrasonic measuring device 1 and the pipe 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, for example designed as a FIFO storage device, as well as the measurement frequency at which the individual values ​​E are measured, influences the reaction time of the overall system, since usually a number of individual values ​​E are first collected in the storage module 25 in order to determine therefrom the mean value MW and the dispersion parameter SP.

[0092] If a short reaction time is desired in an application, it is advantageous to design the storage module 25 with a small capacity. However, if a greater stability of decisions is important in an application, it is advantageous to design the storage module 25 with a larger capacity.

[0093] FIG. 5 shows a variant of the above embodiment in a representation similar to FIG. 3. In the following, only the differences of the variant compared to the embodiment according to FIG. 3 will be described. The same components as those in the embodiment or configurations having equivalent functions are given the same reference numerals. It is understood that all the previous descriptions apply in the same or similar manner to the variant according to FIG. 5.

[0094] 5, the dispersed phase proportion DP is first determined, for example as described above. A corrected dispersed phase proportion DM is then determined from this dispersed phase proportion DP by applying a smoothing factor G.

[0095] In practice, it has been shown that for some applications, in particular for small values ​​of the mean value MW of the transit time differences and therefore for small values ​​of the flow rate through the pipe 100, the determination of the dispersed phase fraction DP can be improved by applying a smoothing factor G to the determined value of the dispersed phase fraction DP. Preferably, the corrected dispersed phase fraction DM is obtained by multiplying the dispersed phase fraction DP by the smoothing factor G. Thus:

number

[0096] For example, the smoothing factor G ensures that in the case of weak flows (i.e. when the transit time difference or the mean value MW of the flow rate is small) the statistical nature of the distribution of bubbles as dispersed phase is at least partially lost, for example due to buoyancy or flow conditions. In practice, the application of the smoothing factor G has been shown to be advantageous especially when the flow through the pipe 100 is less than 5 times the critical Reynolds number.

[0097] The smoothing coefficient G is also determined based on the curves MW1, MW2, MW3 as shown in FIG. 4, which therefore show the variation of the dispersion parameter SP (here the dispersion SP) depending on the proportion DP of the dispersed gas phase in each case with a constant mean value MW of the transit time differences. The smoothing coefficient G is calculated using, for example, a polynomial function (for example, the sixth-order polynomial function y G ) can be used.

number

[0098] After the expansion coefficients c1 to c7 are determined, the specific average value of the transit time difference MW S The smoothing coefficient G for this point MW S Function y in G This is obtained by calculating:

number

[0099] Depending on the particular application, other function types (eg, a hyperbola of the form: ) can also be used as the polynomial function for the calculation of the smoothing coefficients.

number

[0100] In the variant shown in FIG. 5, a smoothing factor G is thus additionally determined and the calculated dispersed gas phase proportion DP (in this case the proportion of gas bubbles) is multiplied by the smoothing factor G in this way to obtain a corrected proportion of dispersed phase DM, which is a quantitative measure of how much of the fluid is made up of dispersed phase, in this case what is the volume fraction of gas bubbles in the liquid.

[0101] Thus, using the method according to the invention, precise quantitative information can be determined about the proportion of dispersed phase DP, DM (i.e. the proportion of gas in a fluid, e.g. a liquid). This information can be used to extend or improve the process. As well as the increased precision, new possibilities for automation open up. An example is now given.

[0102] For example, during the decanting process of a fluid medium such as a liquid, a gas phase (i.e., gas bubbles, etc.) is inevitable, but where the amount of decanted medium plays a role, a quantitative gas fraction can be calculated from the decanted volume.

[0103] Flowmeters known per se as state of the art often also provide so-called volume counters. Here, the conveyed volume is calculated on the basis of time and flow rate. If an error occurs, for example if the presence of air bubbles is detected during the measurement, at best a message is displayed indicating that air bubbles were detected during the measurement. With these flowmeters, it remains unclear to what extent the volume determined by the volume counter deviates from the actual volume or how many air bubbles were detected.

[0104] Using the method according to the invention, it is possible to realize that the system, including the flow meter itself, performs the correction due to which a quantitative determination of the proportion of gas is now possible in order to determine the actual volume (i.e. the volume excluding the proportion of gas bubbles).

[0105] For this purpose, for example, the proportion of dispersed phase (i.e., in this case, air bubbles) can be used to determine a corrected average value of the flow rate of the fluid through the pipe 100, which takes into account the influence of the dispersed phase (i.e., in this case, air bubbles) on the determination of the flow rate. From this corrected average value of the flow rate, the volume of the pure liquid (i.e., the volume of the liquid excluding the volume of the air bubbles) can be determined.

[0106] For example, if a process requires reaching a predeterminable target volume of a medium, the proportion of dispersed phase (e.g., air bubbles), which of course should not contribute to the given target volume, can be quantitatively determined using the method according to the invention. By appropriate corrections (e.g., pumps or valves or control units and feedback to an open-loop control unit), the process can continue to run until the predeterminable target volume is actually reached.

[0107] As already mentioned, the method according to the invention can be carried out with any ultrasonic measuring device 1 suitable for determining the flow rate of a fluid.

[0108] The method according to the invention allows quantitative information about the dispersed phase in a fluid to be determined and therefore can also be used, for example, in threshold switches, limit switches or detectors, particularly in combination with existing measurement or analytical techniques.

[0109] In a non-exhaustive list, we mention some applications for which the method according to the invention is particularly suitable. For monitoring the purity of liquid or gaseous final products or medicines in the pharmaceutical industry. - Monitoring the air supply to clean rooms, e.g. in the semiconductor industry. For control during the filling process of the final product, e.g. in the food or biotechnology industry. For monitoring in medical technology, e.g. when returning blood to a patient to prevent embolism, e.g. when using a heart-lung machine. In the automotive industry, e.g. for fuel monitoring or brake fluid monitoring. In pump technology for monitoring or measuring the degree of cavitation.

Claims

1. 1. A method for determining the fraction of dispersed gas phase in a fluid flowing in a pipe using ultrasound, the method comprising: a) providing an ultrasonic measuring device (1) designed to determine the transit time difference between two measuring signals passing through the fluid in the pipe (100); b) emitting and receiving, by said ultrasonic measuring device (1), a first measurement signal (12) emitted along said flow direction (A); c) emitting and receiving a second measurement signal (21) emitted by the ultrasonic measuring device (1) against the flow direction (A); d) transmitting said measurement signals (12, 21) to a storage and evaluation unit (20); e) determining individual values ​​(E) of the transit time difference between the first measurement signal (12) and the second measurement signal (21); f) determining a plurality of individual values ​​of said transit time difference by repeating steps b) to e); g) determining a mean value of the transit time difference (MW) from the individual values ​​of the transit time difference (E); h) determining a variability parameter (SP) characteristic of the variability of said individual values ​​(E); i) providing a correlation between the mean value (MW) of the transit time difference and the variation of the variability parameter (SP) as a function of the dispersed phase fraction (DP); j) determining the dispersed gas phase fraction (DP) from the dispersion parameter (SP) and the correlation; Including, Optionally, the method further comprises converting the individual value (E) or an average value over several individual values ​​(E) of the transit time difference into an individual value (E) of the flow rate of the fluid or an average value of the flow rate, and performing steps h) and i) using the individual value (E) of the flow rate or the average value of the flow rate.

2. 2. The method according to claim 1, further comprising providing at least one first ultrasonic transducer (11) arranged transversely on a first side (51) of the pipe (100) in an operational state for emitting and receiving the measurement signal (12, 21), the second side (52) being opposite to the first side (51), the ultrasonic transducers (11, 22) being arranged and aligned such that the first ultrasonic transducer (11) can radiate the first measurement signal (12) obliquely to the flow direction (A) of the fluid towards the second ultrasonic transducer (22) and can receive the second measurement signal (21) emitted by the second ultrasonic transducer (22) obliquely to the flow direction (A).

3. 3. The method according to claim 1 or 2, wherein the flow rate of the fluid through the pipe (100) is determined from the transit time difference between the first measurement signal (12) and the second measurement signal (21).

4. The method according to any one of claims 1 to 3, wherein the ultrasonic measuring device (1) is designed as a clamping device and the pipe (100) is clamped in the ultrasonic measuring device (1).

5. The method according to any one of claims 1 to 4, wherein the determination of the dispersed gas phase fraction (DP) is updated at regular intervals or continuously.

6. 6. The method according to claim 3, wherein the dispersed phase fraction (DP) determines the corrected average value of the flow rate.

7. The method of claim 6 , wherein the corrected average value is indicative of the flow rate of the fluid without the dispersed gas phase.

8. The method according to any one of claims 1 to 7, wherein said variability parameter (SP) is the variance of said individual values ​​(E) relative to said mean value (MW).

9. 9. The method according to any one of claims 1 to 8, wherein the variation of the variability parameter (SP) as a function of the dispersed gas phase fraction (DP) at a constant mean value of the transit time difference (MW) is described by a linear decision function (F).

10. 10. The method of claim 9, wherein the linear decision function (F) is defined by two linear coefficients (m, t), each of which is determined from a polynomial function that has the mean value (MW) of the transit time difference as a variable.

11. 11. The method according to claim 1, wherein the variation of the variability parameter (SP) as a function of the dispersed gas phase fraction (DP) at a constant mean value (MW) of the transit time difference is stored in a look-up table (20) in the storage and evaluation unit.

12. 12. The method according to any one of claims 1 to 11, wherein first the dispersed gas phase proportion (DP) is determined, from which the modified dispersed gas phase proportion (DM) is determined by applying a smoothing factor (G).

13. 13. The method of claim 12, wherein the smoothing factor (G) is calculated using a polynomial function that has the mean value (MW) of the transit time difference as a variable.

14. 14. The method according to any one of claims 1 to 13, wherein the dispersed gas phase consists of gas bubbles and the dispersed gas phase fraction (DP) is the volume fraction of gas bubbles in a liquid.

15. The method according to any one of claims 1 to 14, wherein each transit time difference is converted into a value of the flow rate of the fluid through the pipe (100), and the dispersed phase fraction (DP) is determined by the value of the flow rate.

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