Ultrasonic-based gas-liquid two-phase flow pattern identification method and volume fraction test method

Abstract

The invention discloses an ultrasound-based gas-liquid two-phase flow pattern recognition method and a holdup testing method.The flow pattern recognition method comprises the steps that a main probe is arranged at each of the top and the bottom of a pipeline, the two main probes are self-transmitting and self-receiving ultrasonic transducers, an auxiliary probe is arranged on each of the two sides of the bottom of the pipeline, and the two auxiliary probes are arranged on the two sides of the bottom of the pipeline; the two auxiliary probes are receiving type ultrasonic transducers and are symmetrically distributed; ultrasonic signals are transmitted and received in a three-time-period sampling mode; by setting a sound pressure threshold value, sound pressure signals received by the top main probe in the first time period and the second time period and sound pressure signals received by the bottom main probe in the third time period are subjected to binarization mapping, and feature vectors are obtained; inputting the feature vectors into a first classification model for identifying four types of flow patterns including layered flow, bubble flow, annular flow and plug flow; for the stratified flow, smooth stratified flow and wavy stratified flow identification is further carried out; and for the plug flow, identifying the slug flow and the plug-like flow. According to the method, the gas-liquid two-phase flow is subjected to flow pattern recognition, and then the phase volume fraction is tested.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluid measurement, and in particular relates to a gas-liquid two-phase flow pattern identification method and a content testing method based on ultrasound. Background Art

[0002] Gas-liquid two-phase flow patterns are widely present in the fields of petrochemicals, energy and power, and aerospace. Explaining the flow process mechanism of gas-liquid two-phase flow and accurately detecting the flow parameters of gas-liquid two-phase flow have always been hot issues in scientific research and engineering. The dynamic characteristics of single-phase fluids are relatively simple. Multiphase fluids are different from single-phase fluids. The flow characteristics of two-phase or three-phase flows are very complex. They have flow characteristics such as nonlinearity and interphase slippage. The problem of measuring their parameters is still relatively difficult.

[0003] The flow pattern information of gas-liquid two-phase flow is the basis for the study of process parameters such as gas-liquid two-phase flow velocity and gas phase content. According to the flow characteristics of different flow patterns, the corresponding measurement model can be established more specifically, thereby improving the measurement accuracy of process parameters such as phase content. Therefore, flow pattern information is crucial in the study of gas-liquid two-phase flow. In order to accurately obtain flow pattern information, the current method of combining sensor technology with signal processing is mostly used. Sensor technology is used to obtain the flow information of the fluid in the pipeline, and on this basis, the signal is extracted to obtain the features with greater correlation with the flow pattern in the sensor feedback information for identification and classification. It is worth mentioning that the higher the correlation between the extracted features and the gas-liquid flow pattern, the better the recognition effect. The features have clear physical meanings and are more helpful in explaining the flow characteristics of gas-liquid two-phase flow. According to the principle, the detection methods of gas-liquid two-phase flow process parameters can be divided into electrical method, ultrasonic method, optical method, ray method and microwave method.

[0004] The gas-liquid two-phase flow pattern identification method based on the ultrasonic reflection echo and transmission attenuation principle has the advantages of being non-invasive, no fluid radiation, not being affected by the salinity of the measured medium, and being suitable for non-transparent and non-conductive media. In particular, ultrasound has a relatively sensitive sensing ability to the oil-water interface. In addition, the ultrasonic transducer is easy to install, ready to use, and has a low cost. Summary of the invention

[0005] The object of the present invention is to provide a gas-liquid two-phase flow pattern identification method and a content measurement method based on ultrasound, so as to solve the problems of gas-liquid two-phase flow pattern identification and content measurement.

[0006] In the first aspect of the present invention, there is provided a method for identifying a gas-liquid two-phase flow pattern based on ultrasound, the method comprising:

[0007] A main probe is arranged at the top and bottom of the pipeline respectively. The two main probes are self-transmitting and self-receiving ultrasonic transducers. And a sub-probe is arranged on both sides of the bottom of the pipeline respectively. The two sub-probes are receiving ultrasonic transducers and are symmetrically distributed;

[0008] Adopt a three-period sampling mode to transmit and receive ultrasonic signals: in the first period and the second period, the bottom main probe transmits ultrasonic signals, and all four ultrasonic transducers receive sound pressure signals; in the third period, the top main probe transmits ultrasonic signals, and all four ultrasonic transducers receive sound pressure signals;

[0009] By setting a sound pressure threshold, perform binary mapping on the sound pressure signals received by the top main probe in the first period and the second period and the sound pressure signals received by the bottom main probe in the third period: if the average sound pressure value of the sound pressure signal is higher than the sound pressure threshold, it is mapped to 1, otherwise it is mapped to 0, and a feature vector with a dimension of 1*3 is obtained;

[0010] Input the feature vector into the first classification model for four-flow pattern recognition. The four flow patterns include stratified flow, bubbly flow, annular flow and slug flow;

[0011] For stratified flow, extract the transit time, the mean value of the sound pressure signal and the correlation coefficient of the sound pressure signals received by the two sub-probes, and input them into the second classification model for smooth stratified flow and wavy stratified flow recognition;

[0012] For slug flow, extract the transit time, the ultrasonic sound pressure stability coefficient and the kurtosis, and input them into the third classification model for slug flow and plug-like flow recognition.

[0013] In some embodiments, the two sub-probes form an angle of ±22.5° with the bottom main probe, that is, the included angle between the connection line between the sub-probe and the top main probe and the connection line between the bottom main probe and the top main probe is 22.5°.

[0014] In some embodiments, the sampling duration of each period is 0.07 milliseconds, and the interval between adjacent periods is 0.03 milliseconds.

[0015] In some embodiments, the sound pressure threshold is 10% of the average sound pressure value of the transmitted ultrasonic signal.

[0016] In some embodiments, the first classification model, the second classification model and the third classification model are XGBoost classification models.

[0017] According to the second aspect of the present invention, a method for measuring the gas-liquid two-phase flow content is provided. The method includes:

[0018] Based on the ultrasonic-based gas-liquid two-phase flow pattern recognition method described in any item of the first aspect, obtain the gas-liquid two-phase flow pattern recognition result;

[0019] According to the flow pattern recognition result and the cross-sectional flow pattern of the gas-liquid two-phase flow at the ultrasonic transducer, the gas-liquid two-phase flow is divided into a gas-liquid stratified structure and a gas-liquid dispersed structure according to the phase structure type; among them, the stratified flow is a gas-liquid stratified structure, the bubbly flow is a gas-liquid dispersed structure, and the slug flow determines the phase structure type according to the cross-sectional flow pattern of the slug flow at the ultrasonic transducer.

[0020] For the gas-liquid stratified structure and the gas-liquid dispersed structure, a phase holdup model is constructed respectively, and the liquid phase holdup is determined based on the phase holdup model.

[0021] In some of these embodiments, for the gas-liquid stratified structure, the phase holdup model is as follows:

[0022]

[0023] In the formula, Φ Cl ' is the liquid phase holdup of the gas-liquid stratified structure, π is the pi, r is the pipe radius, and H is the equivalent liquid level height;

[0024] The calculation formula for the equivalent liquid level height H is as follows:

[0025]

[0026] In the formula, η 2 , η 3 and η 4 are the contribution coefficients of the liquid level heights measured by the bottom main probe and the two sub-probes respectively, is the liquid level height measured by the bottom main probe, and are the liquid level heights measured by the two sub-probes;

[0027] The calculation formula for the liquid level heights measured by the two sub-probes is as follows:

[0028]

[0029] In the formula, is the liquid level height measured by the two sub-probes, c is the ultrasonic signal liquid propagation speed, are the transit times of P 3 / P 4 of the two sub-probes respectively, Δt is the transit time of the bottom main probe, and x and y are the position coordinates of the sub-probes.

[0030] In some of these embodiments, for the smooth stratified flow, the equivalent liquid level height H is the liquid level height measured by the bottom main probe.

[0031] In some of these embodiments, the contribution coefficients of the liquid level heights measured by the bottom main probe and the two sub-probes are the ratios of the average sound pressure values of the sound pressure signals received by them respectively.

[0032] In some of these embodiments, for the gas-liquid dispersion structure, the phase holdup model is as follows:

[0033]

[0034] In the formula, Φ Dl is the liquid phase holdup of the gas-liquid dispersion structure, α is the total attenuation, K ext is the sound absorption efficiency, k c is the ultrasonic wave number of the continuous phase, R is the size of the dispersed phase, A 0 and A 1 are the scattering coefficients;

[0035] Among them, the total attenuation is obtained by linearly superimposing the absorption attenuation and the scattering attenuation, and the total attenuation model is as follows:

[0036]

[0037] In the formula, φ is the phase holdup of the dispersed phase.

[0038] Generally speaking, compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects:

[0039] The present invention designs a double-transmitter and four-receiver ultrasonic transducer arrangement scheme and working mode according to the propagation characteristics of ultrasonic signals in different phase structures, and uses the ultrasonic mechanism characteristics to identify the flow patterns of gas-liquid two-phase flows. The classification characteristics have obvious physical meanings and the classification accuracy is high. On this basis, the present invention uses the flow pattern recognition result as prior information to model the holdup measurement of typical flow patterns of gas-liquid two-phase flows, and realizes the measurement of the phase holdup.

[0040] This method is convenient to measure, fast, and low-cost. It can accurately measure the phase holdup of oil-water two-phase flows in pipelines, reduce the non-linearity, and is not affected by the salinity of the measured medium, does not interfere with the flow field, and there is no fluid corrosion or wear. It is applicable to non-transparent and non-conductive media, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 FIG. is a flow pattern diagram provided by an embodiment of the present application; wherein, Figure 1 (a) in is smooth stratified flow, Figure 1 (b) in is wavy stratified flow, Figure 1 (c) in is bubbly flow, Figure 1 (d) in is annular flow, Figure 1 (e) in is slug flow, Figure 1 (f) in is plug flow;

[0042] Figure 2 FIG. is a three-period test signal diagram of a gas-liquid two-phase flow provided by an embodiment of the present application;

[0043] Figure 3 An ultrasonic feature mapping threshold determination reference sound pressure attenuation signal diagram provided by an embodiment of the present application;

[0044] Figure 4 A schematic diagram of a probe installation method provided by an embodiment of the present application;

[0045] Figure 5 A schematic flow chart of a gas-liquid two-phase flow pattern recognition method provided by an embodiment of the present application;

[0046] Figure 6 A classification result diagram provided by an embodiment of the present application;

[0047] Figure 7 A smooth stratified flow and wavy stratified flow recognition rate diagram provided by an embodiment of the present application;

[0048] Figure 8 A slug flow and plug flow recognition rate diagram provided by an embodiment of the present application;

[0049] Figure 9 A test error curve diagram of a stratified flow phase holdup test model provided by an embodiment of the present application;

[0050] Figure 10 A simulation experiment curve result diagram of the effectiveness of a phase holdup model provided by an embodiment of the present application; wherein, Figure 10 in (a) is a variation trend diagram of simulation attenuation and model attenuation at different particle sizes of the discrete phase, Figure 10 in (b) is a variation trend diagram of simulation attenuation and model attenuation at different discrete phase holdups. Detailed implementation manners

[0051] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Based on the embodiments provided in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0052] Obviously, the accompanying drawings in the following description are only some examples or embodiments of the present application. For those of ordinary skill in the art, without creative efforts, the present application can also be applied to other similar scenarios based on these drawings. In addition, it can also be understood that although the efforts made in such a development process may be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present application, some design, manufacturing, or production changes based on the technical content disclosed in the present application are only conventional technical means and should not be understood as the content disclosed in the present application being insufficient.

[0053] In the present application, the mention of "embodiment" means that the specific features, structures, or characteristics described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those of ordinary skill in the art explicitly and implicitly understand that the embodiments described in the present application can be combined with other embodiments without conflict.

[0054] Unless otherwise defined, the technical terms or scientific terms involved in the present application should be of the ordinary meaning understood by those of ordinary skill in the technical field to which the present application belongs. The words such as "a", "an", "one", "the", etc. involved in the present application do not indicate a quantity limitation and can represent a singular or plural number. The terms "including", "comprising", "having" and any variations thereof involved in the present application are intended to cover non-exclusive inclusion; for example, a process, method, system, product or device including a series of steps or modules (units) is not limited to the listed steps or units, but may further include unlisted steps or units, or may further include other steps or units inherent to these processes, methods, products or devices. The terms "connected", "coupled", etc. involved in the present application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The term "plurality" involved in the present application means two or more. "And / or" describes the association relationship of associated objects and indicates that three relationships can exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally represents an "or" relationship between the associated objects before and after. The terms "first", "second", "third", etc. involved in the present application are only used to distinguish similar objects and do not represent a specific order for the objects.

[0055] The present application provides an ultrasonic-based gas-liquid two-phase flow pattern identification method and void fraction measurement method, specifically relating to a measurement method based on the transmission and reflection propagation mechanisms of ultrasonic waves in gas-liquid two-phase fluids, for non-contact measurement of gas-liquid two-phase flow pattern identification and void fraction measurement. Aiming at the basic test mechanism of ultrasonic technology for gas-liquid two-phase flow process parameters, the finite volume method is adopted to establish a three-dimensional dynamic simulation model of gas-liquid two-phase flow to obtain gas-liquid phase structure information under different flow patterns and working conditions. Then, the finite element method is used to construct a sectional dissection model of typical flow patterns of gas-liquid two-phase flow, simulate the sound field of different flow structures, obtain the distribution signal of ultrasonic pressure for analysis and feature extraction, and realize the classification and identification of gas-liquid two-phase flow patterns.

[0056] The present application proposes a method for constructing a gas-liquid two-phase flow phase distribution model and a test device for identifying gas-liquid two-phase flow patterns based on ultrasonic mechanisms. According to the propagation characteristics of ultrasonic signals in different phase structures, a transducer arrangement scheme and working mode of double-transmitter and multi-receiver with three-time sampling are designed. The flow patterns of gas-liquid two-phase flow are identified using the characteristics of ultrasonic mechanisms, and the classification features have obvious physical meanings and high classification accuracy. On this basis, the void fraction measurement model of typical gas-liquid two-phase flow patterns is established using the flow pattern identification results as prior information. The present application is a non-contact identification method for gas-liquid two-phase flow patterns with physical meaning support for characteristic parameters and high identification rate, and the void fraction is modeled and measured using this as prior information.

[0057] Figure 1 It is a schematic diagram of a flow pattern provided by an embodiment of the present application; wherein, Figure 1 (a) in it is smooth stratified flow, Figure 1 (b) in it is wavy stratified flow, Figure 1 (c) in it is bubbly flow, Figure 1 (d) in it is annular flow, Figure 1 (e) in it is slug flow, Figure 1 (f) in it is plug flow.

[0058] This application proposes a method for identifying gas-liquid two-phase flow patterns and measuring void fraction based on ultrasonic propagation characteristics. The device used includes four ultrasonic transducers. The ultrasonic transducer includes a transmitting sensor and a receiving sensor. The transmitting sensor has a crystal oscillator device and a voltage conversion circuit for generating signals, which is used to generate ultrasonic signals. In addition, the transmitting sensor also has the function of receiving signals (self-transmitting and self-receiving transducer). The sensor that only has the function of receiving signals is the secondary probe, and the self-transmitting and self-receiving sensor is the primary probe. There are two primary probes, which are installed directly opposite each other at the bottom and top of the pipeline; there are also two secondary probes, which are distributed on both sides of the pipeline at an angle of ±22.5° with the sensor at the bottom of the pipeline; the working mode of the crystal oscillator device and the voltage conversion circuit is that the voltage conversion circuit converts the 220V, 50Hz civil three-phase electricity into a weak voltage signal suitable for the crystal oscillator device, and generates ultrasonic waves with specific amplitude and frequency by controlling the amplitude and frequency of the electrical signal, so as to realize the ultrasonic test of the fluid. As Figure 5 shown, the specific steps are as follows:

[0059] Step 1: When the system is running, a periodic ultrasonic signal is generated according to the established settings. When the measured fluid flows through the pipeline, the sound pressure signal at the receiving end will show different characteristics due to the influence of the fluid. The overall sampling adopts a three-period sampling mode. In the first period and the second period, the ultrasonic signal is emitted by the bottom sensor, and in the third period, the ultrasonic signal is emitted by the top sensor. All three periods are received by all probes.

[0060] Step 2: A mapping method based on ultrasonic signal characteristics is proposed to achieve effective identification and processing of ultrasonic signals. This method performs binary mapping on the received ultrasonic signals by setting a specific threshold. Specifically, when the average sound pressure value at the receiving end is higher than this threshold, the signal is mapped to 1, indicating that the ultrasonic signal intensity is higher, which may represent the presence of the target or the response of some important characteristics; if the average sound pressure value at the receiving end is lower than this threshold, it is mapped to 0, indicating that the signal is weak or invalid. In this mapping process, the selection of the threshold is adjusted according to experimental conditions (such as ambient noise, sensor characteristics, etc.) to ensure the accurate identification of the signal and the sensitivity of the response.

[0061] Step 3: Extract the ultrasonic mechanism characteristics of specific flow patterns. Specific flow patterns refer to smooth stratified flow, wavy stratified flow, slug flow, and plug flow. Because these two types of flow patterns have similar phase structures, all ultrasonic feature mapping results are not sufficient to distinguish them, and it is necessary to further explore their ultrasonic features. Here, the ultrasonic transit time T = D / v is selected, where T is the transit time (unit: second, s), D is the distance traveled by the ultrasonic wave (unit: meter, m), and v is the propagation speed of the ultrasonic wave in the medium (unit: meter per second, m / s); the cross-correlation coefficient x i and y iare the data points of the i-th signal, etc.

[0062] Step 4: The XGBoost classification algorithm has the advantages of high efficiency, accuracy, strong robustness, and the ability to handle high-dimensional features. As an ensemble learning method, XGBoost constructs multiple weak classifiers (decision trees) and improves the classification performance through weighted voting. It can effectively avoid overfitting, has good generalization ability, and is particularly suitable for processing data with complex non-linear relationships and noise interference. In this application, the feature mapping of the ultrasonic signal (such as the thresholding result of the sound pressure value) is used as the dataset input, and the XGBoost classification algorithm is applied to classify the gas-liquid two-phase flow patterns. XGBoost can effectively capture the complex relationships between these features and perform flow pattern recognition quickly and accurately. At the same time, XGBoost has the ability to automatically handle missing data, noise, and high-dimensional features, and can help researchers identify the most critical factors for classification through feature importance evaluation, further optimizing the model performance.

[0063] Step 5: According to the flow pattern recognition results, the flow patterns of the gas-liquid two-phase flow can be further divided into different phase structures. Specifically, the common phase structures of the gas-liquid two-phase flow are mainly divided into the gas-liquid stratified structure and the gas-liquid dispersed structure. The gas-liquid stratified structure usually shows that the gas and liquid are distributed in different layers, and there is an obvious interface between the gas and the liquid, while the gas-liquid dispersed structure shows that the gas is evenly dispersed in the liquid in the form of bubbles, and the two-phase fluid presents a more complex distribution pattern. On this basis, for these two typical phase structures, the phase holdup models are constructed and optimized respectively. For the gas-liquid stratified structure, the model mainly considers the stability of the gas-liquid interface and the influence of the flow velocity, combines the ultrasonic signal and the fluid mechanics characteristics, and accurately measures the proportion of the gas phase and the liquid phase; for the gas-liquid dispersed structure, the model needs to consider factors such as the distribution density of the bubbles and the liquid viscosity to more accurately estimate the content of the gas phase and the liquid phase. During the model construction process, the model parameters are continuously adjusted through the optimization algorithm to enhance the adaptability of the model to different flow states, thereby improving the accuracy and stability of the phase holdup measurement. Through this method, the dynamic changes of the gas-liquid two-phase flow can be more effectively grasped, providing a scientific basis for flow pattern control and fluid monitoring in industrial applications.

[0064] First, for stratified flow, in smooth stratified flow, the liquid level height is determined by the main probe P 2 and the ultrasonic probe measures the height where c is the ultrasonic liquid propagation velocity and Δt is the transit time measured by the main probe. Ignoring the influence of the position of the sensor and the pipe wall embedding surface on the pipe cross-sectional area, the water area where h is the liquid level height measured by the ultrasonic sensor and r is the pipe radius.

[0065] Therefore, the liquid level height of stratified flow and the liquid-phase holdup can be calculated

[0066] For the gas-liquid distribution in the cross-section of the wavy stratified structure, the ultrasonic echo direction is affected by the fluctuating gas-liquid interface and deviates from the vertical reflection direction, resulting in inaccurate calculation of the transit time of the bottom ultrasonic transducer. Therefore, two auxiliary receiving probes on the left and right are introduced to correct the transit time in order to obtain a more accurate equivalent height value of the gas-liquid interface and improve the accuracy of the phase holdup measurement. The liquid level height of the auxiliary probe where h (P3 / P4) represents the liquid level height calculated by the auxiliary probes on the left and right at the bottom of the pipeline. c is the ultrasonic liquid propagation velocity, and Δt is the transit time measured by the main probe. x and y are sensor position constants, which are taken as 9.4227 and 2.1845 respectively in this embodiment. The optimized total liquid level height where η 2 、η 3 and η 4 are the contribution coefficients of the test heights of the bottom sensor and the auxiliary probes on both sides of the bottom respectively. The contribution coefficient is the ratio of the average sound pressure signals received by the three ultrasonic transducers. To sum up, the liquid-phase holdup of stratified flow after optimization is:

[0067] Step 6: For the dispersed flow pattern, the absorption attenuation is the absorption of ultrasonic energy by the liquid and bubbles at the molecular level, and its mechanism involves the heat conduction ability, viscosity and various relaxation processes of the ultrasonic propagation medium. McClements DJ believes that the heat conduction and viscosity mechanisms are very important for many practical situations. At the same time, in the sequence of the coefficients A n in the classical ECAH model, analyzing the first two terms A 0 and A 1 plays a dominant role. The expression of the McClements attenuation model is:

[0068] In the formula, k = w / c is the ultrasonic propagation constant. k is a common parameter in ultrasonic research, which is equal to the angular frequency w divided by the sound velocity c. The subscript c represents the continuous phase. Φ Da is the volume concentration of the dispersed-phase gas in the dispersed flow considering absorption attenuation, that is, the gas holdup, and R is the size of the dispersed phase.

[0069] The scattering coefficients A 0 , A 1 can be obtained by solving a sixth-order linear equation proposed by Epstein and Carhart:

[0070]

[0071] where

[0072]

[0073] In the formula, α c , α s and α T are respectively the product of the discrete droplet radius and the wave numbers (Wavenumber, WN) of the compression wave, thermal wave, and shear wave. κ is the thermal conductivity of the discrete phase. j n is the spherical Bessel function, h n is the spherical Hankel function, where t is the ambient temperature. “’” represents the parameters related to the discrete phase.

[0074] During the propagation of ultrasonic waves in gas-liquid bubbly flow, the scattering of ultrasonic waves by the discrete phase and the absorption effect of the gas-liquid medium on the acoustic wave energy cannot be ignored. In the construction of the attenuation model of this application, the scattering attenuation and absorption attenuation of ultrasonic waves are mainly considered. Among them, the absorption attenuation is characterized by the McClements model, and the scattering attenuation is characterized by the BLBL model. The two attenuation mechanisms are independent of each other and linearly superimposed to obtain the total attenuation model That is, the dispersed flow pattern liquid phase holdup

[0075] Specifically, in this embodiment, based on the finite element method, the multi-physics coupling software COMSOL is used to establish a two-dimensional geometric dissection model of the pipeline. The radius of the transducer is set to 4.5 mm, the diameter of the pipeline is 50 mm, and the ultrasonic transducers are distributed at the top and bottom of the pipeline and on both sides of the pipeline at an angle of 22.5° with the bottom. The distribution of the ultrasonic transducers is as Figure 4 shown, where P 1 and P 2 are self-emit and self-receive transducers with a transmission frequency of 1 MHz, and P 3 and P 4 are receiving ultrasonic transducers. The experiment adopts a three-period, non-equidistant sampling mode. In the first and second periods (Δt 1 , Δt 2 ) of the three periods, the instantaneous sound pressure difference-time data of P2 transmission and four-terminal reception are extracted. In the third period (Δt 3 ), the instantaneous sound pressure difference-time data of P 1 transmission and four-terminal reception are extracted. In addition, to extract sufficient ultrasonic information and avoid ultrasonic interference between different transmission and reception methods, each period of sampling lasts for 0.07 milliseconds. The sampling interval for each period is 0.03 milliseconds.

[0076] Figure 6 , Figure 7 and Figure 8 are the identification results of the gas-liquid two-phase flow pattern in the multi-sensor structure mode of the embodiment of this application, where Figure 6It is a confusion matrix diagram for the identification of four major types of gas-liquid flows (stratified flow, bubbly flow, annular flow, and slug flow) by XGBoost, with an accuracy rate of over 98%. Figure 7 and Figure 8 are the subdivisions of stratified flow and slug flow. Stratified flow is subdivided into smooth stratified flow and wavy stratified flow, with the highest recognition rate of over 96.8%; slug flow is subdivided into slug flow and plug-like flow, with the highest recognition rate of over 98.1%.

[0077] Figure 9 It is the test error curve of the stratified flow phase holdup test model. The calculation results of the optimized holdup test model are basically within the error band of ±5%. This indicates that introducing the measurement signal of the auxiliary probe to correct the height can effectively reduce the holdup test error of wavy flow. The root mean square error of the liquid phase holdup in stratified flow after model optimization is 9.699%. However, the errors in experimental group 1 and experimental group 2 are relatively large, and the maximum error appears in the working condition of low liquid holdup in wavy flow. The reason is that when the liquid level is too low, the ultrasonic echo time is shorter than the ultrasonic emission duration, and the ultrasonic waves reflected by the interface interfere with the ultrasonic waves that have not been fully emitted, resulting in inaccurate calculation of the transit time and thus affecting the calculation of the liquid level height. As the liquid holdup increases, the holdup test error gradually decreases.

[0078] Figure 10 It is the effective verification curve of the dispersed flow phase holdup test model. The attenuation coefficient calculated by the attenuation model established in this application has the same trend as the attenuation coefficient measured in the simulation experiment. Figure 10 In (a) of [], when the particle size of the measured discrete phase (bubbles) is less than 500 μm, the fitting degree between the model attenuation and the simulation attenuation is poor. This is because in the simulation experiment, the bubbles are evenly distributed in the pipeline, and the attenuation caused by the bubbles on the left and right sides of the pipeline cannot be fully captured by the ultrasonic transducer, resulting in the simulation attenuation being significantly lower than the model attenuation. Under the same conditions, the smaller the bubble particle size, the greater the ultrasonic attenuation. When the bubble particle size increases, the influence of the attenuation caused by the bubbles on both sides on the total attenuation weakens, resulting in the situation where the trends of the model attenuation and the simulation attenuation are getting closer and closer, as shown in Figure 10 (a) and (b) of

[0079] Taking the specific experimental data of gas-liquid two-phase flow as an example below, the two-phase flow pattern identification and holdup test methods of the embodiments of this application will be described.

[0080] The measurement method using the above measurement device is as follows:

[0081] Step 1: Control the boundary conditions to allow the gas-liquid two-phase flow fluid to pass through the test section. Start the ultrasonic testing system. First, the voltage conversion circuit loads a voltage on the crystal oscillator of the ultrasonic transducer to modulate the amplitude and frequency. Subsequently, the crystal oscillator vibrates under the applied voltage signal, generating ultrasonic waves with specific amplitude and frequency. To avoid affecting sampling, the duration is set to 0.001 milliseconds. The sampling mode is a three-period cycle. In the first and second periods (Δt 1 , Δt 2 ), the bottom sensor emits ultrasonic waves, and four sensors including the bottom sensor receive the sound pressure signals. The sampling duration is 0.07 milliseconds. In the third period (Δt 3 ), the top sensor emits ultrasonic waves, and four sensors including the top sensor receive the sound pressure signals. Sampling is cycled in a three-period cycle. In addition, to avoid the influence of afterwaves on the next sampling, after testing, the minimum interval between two samplings is 0.03 milliseconds. Sample the sound pressure signals of the full flow pattern of the gas-liquid two-phase flow according to this sampling mode.

[0082] Step 2: Arrange the sound pressure signals obtained in Step 1 in chronological order to obtain partial signals of the gas-liquid two-phase flow as shown in Figure 2 . From the first and second diagrams of Figure 2 , it can be seen that for each group of unit signals of gas-liquid stratified flow (smooth stratified flow, wavy stratified flow), they are all close to 0. This is because ultrasonic waves are almost totally reflected at the gas-liquid interface due to the significant difference in acoustic impedance between the gas and liquid phases. When ultrasonic waves enter the air, they will rapidly decay due to the properties of air such as density, viscosity, and molecular structure, and can be approximately regarded as having no effective sound and pressure signals compared to the propagation of ultrasonic waves in liquids. From the third diagram of Figure 2 , it can be seen that for each group of three unit signals of bubbly flow, they are similar, and the sound pressure fluctuates and the peak values vary due to factors such as the number, position, and diameter of the bubbles. Figure 2 The fourth diagram of Figure 2 is the sampling signal of annular flow. The three unit signals of annular flow are almost the same. Since the propagation distance of ultrasonic waves through the liquid film is limited, the signals in the Δt 1 and Δt 2 periods are almost 0, and in the Δt 3 period, the sound pressure signal of ultrasonic waves remains at a relatively high level due to multiple reflections in the short liquid film zone. Figure 2 The fifth and sixth diagrams of Figure 2 are the sound pressure signals of slug flow (slug flow and plug-like flow). Affected by the periodically alternating liquid slug zone and liquid film zone of slug flow, when sampling across the liquid slug-liquid film transition zone, there are significant differences in the sound pressure conditions of the three periods of each group of unit signals.

[0083] Step 3: Since the acoustic impedances of the gas-liquid two-phase media are different, when ultrasonic waves are incident from the liquid phase to the gas phase, a part of the ultrasonic waves are transmitted from the liquid phase to the gas phase, which is called the transmitted wave. The incident ultrasonic waves are reflected back to the original medium at the gas-liquid interface due to the acoustic impedance difference, which is called the reflected wave. When the temperature is 293K, the acoustic pressure reflection coefficients when ultrasonic waves are vertically incident on the water-gas and oil-gas interfaces are expressed as and Therefore, the up and down received signals in stratified flow are close to 0. Taking the highest gas holdup (16.5%) of the slug flow pattern set as the evaluation condition of the effective acoustic pressure threshold, the ultrasonic test results are as Figure 3 shown. The ultrasonic signal is emitted from P 1 and propagates to the bottom of the pipeline and is received by P 2 . After testing, the average acoustic pressure value under this condition is approximately attenuated to 12% of the initial value. From the reflectivity of ultrasonic waves at the gas-liquid interface, it can be known that if there is a stratified structure of gas and liquid phases in the pipeline, Δt 1 , Δt 2 and Δt 3 The acoustic pressure signal at the receiving end is almost 0 Pa. Thus, it can be defined that if the average acoustic pressure value of a single sampling is higher than 10% of the initial value, that is, 6000 Pa, then the acoustic pressure signal of this section is an effective acoustic pressure signal, and the feature mapping is "1", otherwise it is defined as an invalid acoustic pressure signal, and the feature mapping is "0". The threshold can be adjusted in combination with the actual working conditions and on-site noise conditions. The partial mapping results of gas-liquid flow patterns are shown in Table 1

[0084] Table 1 Feature mapping results of four types of flow patterns

[0085]

[0086]

[0087] The sampling signals of the main probe in three time periods are mapped into a 1*3 feature vector. The 571 obtained feature vectors are randomly divided into a test set and a training set in a ratio of 3:7, and the XGBoost classification algorithm is used for flow pattern classification. The confusion matrix is as Figure 6 shown, and the accuracy rate is 98.5%.

[0088] Step 4: On the basis of Step 3, extract ultrasonic-related characteristic parameters, such as attenuation coefficient, transit time, peak sound pressure, average total sound pressure, correlation coefficient of the signal of the auxiliary probe, etc., to further subdivide the gas-liquid stratified flow and slug flow. For smooth stratified flow and wavy stratified flow, the optimal feature combination is transit time, mean value of the sound pressure signal, and correlation coefficient of the ultrasonic signal of the auxiliary probe. The highest recognition rate of smooth stratified flow and wavy stratified flow is 96.15%. For slug flow and plug-like flow, the optimal recognition feature combination is: transit time, ultrasonic sound pressure stability coefficient, and kurtosis. The optimal recognition rate of slug flow and plug-like flow is 96.85%. In addition, to highlight the advantages of the feature extraction method proposed in the present invention, a comparison is also made with the time-domain signal feature extraction method. In contrast, compared with the classification effect of ordinary time-domain features, it has a higher recognition rate for identifying the flow patterns of gas-liquid two-phase flows. Based on ultrasonic mechanism features, it is more suitable for identifying similar gas-liquid flow patterns (stratified flow and slug flow) than ordinary time-domain features.

[0089] It should be noted that except for the correlation coefficient of the ultrasonic signal of the auxiliary probe, the remaining characteristic parameters are all related parameters of the two main probes.

[0090] Step 5: On the basis of the flow pattern as a prior condition, the void fraction test models for gas-liquid stratified structures and dispersed structures are constructed and optimized respectively. Among them, due to the uncertainty of the incident angle between the ultrasonic wave and the fluctuating interface of the wavy stratified flow, there is a deviation between the echo direction and the vertical direction, resulting in a deviation in the calculation of the transit time by the bottom transducer, which in turn affects the measurement of the liquid level height and the void fraction. Therefore, auxiliary probes on both sides of the bottom are introduced for height correction. The final void fraction calculation method is as follows: As Figure 9 shown, the root mean square error of the liquid-phase void fraction of the stratified flow after model optimization is 9.699%. The errors of Experimental Group 1 and Experimental Group 2 are relatively large, and the maximum error occurs in the condition of low liquid holdup in wavy flow. The reason is that when the liquid level is too low, the ultrasonic echo time is shorter than the ultrasonic emission duration, and the ultrasonic wave reflected by the interface interacts with the ultrasonic wave that has not been fully emitted, resulting in inaccurate calculation of the transit time, which in turn affects the calculation of the liquid level height. As the liquid holdup increases, the void fraction measurement error gradually decreases.

[0091] Step 5: In gas-liquid two-phase flows, dispersed flows are divided into bubbly flows with gas as the discrete phase and liquid as the continuous phase, and misty flows with liquid as the discrete phase and gas as the continuous phase. However, in horizontal pipelines, it is difficult to form misty flows. Mostly, on the basis of the annular flow pattern, the gas velocity is further increased, and small liquid droplets are carried into the gas column in the center of the pipeline, thus forming annular misty flows. In this study, the void fraction of bubbly flows with simple formation conditions is mainly measured.

[0092] During the propagation of ultrasonic waves in gas-liquid bubbly flow, the scattering of the dispersed phase on ultrasonic waves and the absorption effect of the gas-liquid medium on the acoustic wave energy cannot be ignored. In the construction of the attenuation model in this study, the scattering attenuation and absorption attenuation of ultrasonic waves are mainly considered. Among them, the absorption attenuation is characterized by the McClements model, and the scattering attenuation is characterized by the BLBL model. The two attenuation mechanisms are independent of each other and linearly superimposed to obtain the total attenuation model Dispersed flow pattern liquid holdup The results of the dual-frequency inversion are shown in Table 2

[0093] Table 2 Inversion results of particle size (bubbles) and test error of holdup

[0094]

[0095] In summary, in this application, the acoustic pressure information in different directions is obtained through the sensor arrangement of the double-transmitter and four-receiver method to obtain the flow pattern information of the gas-liquid two-phase flow. And taking this as a prior condition, the holdup is tested with the ultrasonic homologous signal. The holdup of the two-phase flow is obtained in a non-invasive manner, avoiding the non-linear response of ultrasonic detection, and there is no need to pre-separate or mix the measured fluid. This method is not affected by the salinity of the measured medium, does not interfere with the flow field, does not have fluid corrosion and wear, is applicable to non-transparent and non-conductive media, etc., and is convenient to measure, fast in speed, low in cost, can accurately measure the holdup of the oil-water two-phase flow in the pipeline, and reduces the non-linearity

[0096] It should be noted that the technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification. In addition, according to the needs of implementation, each step / component described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of this application

[0097] Those skilled in the art can easily understand that the above-described embodiments only represent several implementation manners of this application, and their descriptions are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of this application, several modifications and improvements can still be made, and these all belong to the protection scope of this application. Therefore, the protection scope of this application patent shall be subject to the appended claims

Claims

1. A gas-liquid two-phase flow pattern identification method based on ultrasound, characterized in that: The method includes: A main probe is set at the top and bottom of the pipeline, and the two main probes are self-transmitting and self-receiving ultrasonic transducers. A sub-probe is set at both sides of the bottom of the pipeline, and the two sub-probes are receiving ultrasonic transducers and are symmetrically distributed. The ultrasonic signal is transmitted and received in a three-period sampling mode: in the first and second periods, the bottom main probe transmits the ultrasonic signal, and all four ultrasonic transducers receive the sound pressure signal; in the third period, the top main probe transmits the ultrasonic signal, and all four ultrasonic transducers receive the sound pressure signal; By setting the sound pressure threshold, the sound pressure signals received by the top main probe in the first and second periods and the sound pressure signals received by the bottom main probe in the third period are binary mapped: if the average sound pressure value of the sound pressure signal is higher than the sound pressure threshold, it is mapped to 1, otherwise it is mapped to 0, and a feature vector with a dimension of 1*3 is obtained; The feature vector is input into the first classification model to identify four types of flow patterns, including stratified flow, bubbly flow, annular flow and plug flow; For stratified flow, the transit time, the mean value of the sound pressure signal, and the correlation coefficient of the sound pressure signals received by the two auxiliary probes are extracted and input into the second classification model for the identification of smooth stratified flow and wavy stratified flow; For plug flow, the transit time, ultrasonic sound pressure stability coefficient and kurtosis are extracted and input into the third classification model for slug flow and plug flow identification.

2. The method for identifying gas-liquid two-phase flow pattern based on ultrasound according to claim 1, characterized in that: The two auxiliary probes form an angle of ±22.5° with the bottom main probe, that is, the angle between the connecting line between the auxiliary probe and the top main probe and the connecting line between the bottom main probe and the top main probe is 22.5°.

3. The ultrasonic-based gas-liquid two-phase flow pattern identification method according to claim 1, characterized in that: The sampling duration of each period is 0.07 milliseconds, and the interval between adjacent periods is 0.03 milliseconds.

4. The method for identifying gas-liquid two-phase flow pattern based on ultrasound according to claim 1, characterized in that: The sound pressure threshold is 10% of the average sound pressure value of the emitted ultrasonic signal.

5. The method for identifying gas-liquid two-phase flow pattern based on ultrasound according to claim 1, characterized in that: The first classification model, the second classification model and the third classification model are XGBoost classification models.

6. A method for testing the holdup of a gas-liquid two-phase flow, characterized in that: The method includes: Based on the gas-liquid two-phase flow pattern identification method based on ultrasound as described in any one of claims 1 to 5, obtaining a gas-liquid two-phase flow pattern identification result; According to the flow pattern identification results and the cross-sectional flow pattern of the gas-liquid two-phase flow at the ultrasonic transducer, the gas-liquid two-phase flow is divided into a gas-liquid stratified structure and a gas-liquid dispersed structure according to the phase structure type; among them, the stratified flow is a gas-liquid stratified structure, the bubbly flow is a gas-liquid dispersed structure, and the plug flow determines the phase structure type according to the cross-sectional flow pattern of the plug flow at the ultrasonic transducer; For the gas-liquid stratified structure and the gas-liquid dispersed structure, phase holdup models are constructed respectively, and the liquid phase holdup is determined based on the phase holdup models.

7. The gas-liquid two-phase flow holdup test method according to claim 1, characterized in that: For the gas-liquid stratified structure, the phase holdup model is as follows: In the formula, Φ Cl ' is the liquid phase content of the gas-liquid stratified structure, π is the pi, r is the pipe radius, and H is the equivalent liquid level height; The calculation formula of equivalent liquid level H is as follows: Where η2, η3 and η4 are the contribution coefficients of the liquid level measured by the bottom main probe and the two auxiliary probes, respectively. P2 is the liquid level measured by the bottom main probe, and It is the liquid level measured by two auxiliary probes; The calculation formula for the liquid level measured by the two auxiliary probes is as follows: In the formula, is the liquid level measured by the two auxiliary probes, c is the liquid propagation speed of the ultrasonic signal, are the transit time of the two auxiliary probes P3 / P4, Δt is the transit time of the bottom main probe, and x and y are the position coordinates of the auxiliary probes.

8. The gas-liquid two-phase flow holdup test method according to claim 7, characterized in that: For smooth stratified flow, the equivalent liquid level height H is the liquid level measured by the bottom main probe.

9. The gas-liquid two-phase flow holdup test method according to claim 7, characterized in that: The contribution coefficient of the liquid level measured by the bottom main probe and the two auxiliary probes is the ratio of the average sound pressure values ​​of the sound pressure signals received by each.

10. The gas-liquid two-phase flow holdup test method according to claim 6, characterized in that: For the gas-liquid dispersion structure, the phase holdup model is as follows: In the formula, Φ Dl is the liquid phase fraction of the gas-liquid dispersed structure, α is the total attenuation, K ext is the noise reduction efficiency, k c is the continuous phase ultrasonic wave number, R is the dispersed phase size, A0 and A1 are scattering coefficients; Among them, the total attenuation is obtained by linear superposition of absorption attenuation and scattering attenuation. The total attenuation model is as follows: Where φ is the dispersed phase content.

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