Gas-liquid two-phase flow pattern recognition method and flow pattern signal collection device

Abstract

This invention proposes a method and device for identifying flow patterns in gas-liquid two-phase flow. The method includes the following steps: S10: emitting a first ultrasonic wave into the fluid in a pipe, wherein the first ultrasonic wave is two pulsed ultrasonic waves emitted at intervals; S20: receiving the transmitted sound wave of the first ultrasonic wave at the other side of the pipe, and classifying the fluid into a first type of flow pattern, a second type of flow pattern, and bubbly flow based on the sound pressure value of the transmitted sound wave; S30: if the fluid is of the first type of flow pattern, emitting a second ultrasonic wave into the fluid, and classifying the flow pattern of the fluid into stratified flow or annular flow based on the sound pressure value of the reflected echo of the second ultrasonic wave; S40: if the fluid is of the second type of flow pattern, extracting the parameters of the transmitted sound wave of the first ultrasonic wave, and classifying the flow pattern of the fluid into slug flow or plug flow. The gas-liquid two-phase flow pattern identification method of this application has the advantages of being convenient, efficient, and widely applicable.

Description

Technical Field

[0001] This invention relates to the field of multiphase flow detection technology, and in particular to a method for identifying flow patterns in gas-liquid two-phase flow and a flow pattern signal acquisition device. Background Technology

[0002] Multiphase flow conditions are widely present in production equipment in fields such as oil and gas, chemical industry, energy, and metallurgy. The phase interface distribution of multiphase flow media, i.e., the flow pattern, greatly affects the flow characteristics and heat transfer characteristics of multiphase flow. Therefore, accurately revealing the parameter characteristics of multiphase flow has important academic value and industrial production guidance significance. Among them, flow pattern identification is one of the multiphase flow parameter detection methods, and it is also the foundation for the detection of other multiphase flow parameters.

[0003] Currently, the study of multiphase flow patterns and flow pattern transitions is fundamental to researching heat transfer and pressure drop characteristics under given flow conditions. Unlike the flow characteristics of single-phase fluids, multiphase flows exhibit nonlinearity and interphase slip, and are characterized by complex interphase structures, non-unique and variable flow states, and numerous process parameters to be measured. Traditional single-phase flow measurement methods cannot fully describe multiphase flow. Therefore, the detection and transition of multiphase flow patterns present significant challenges. Summary of the Invention

[0004] In view of the above, this application proposes a method for identifying gas-liquid two-phase flow patterns and a flow pattern signal acquisition device to solve the above problems.

[0005] This application provides a method for identifying the flow pattern of a gas-liquid two-phase flow, including the following steps;

[0006] S10: Emit a first ultrasonic wave into the fluid in the pipe, wherein the first ultrasonic wave is two pulsed ultrasonic waves emitted at intervals;

[0007] S20: Receive the transmitted sound wave of the first ultrasonic wave on the other side of the pipe, and classify the fluid into a first type of flow, a second type of flow, and a bubbly flow based on the sound pressure value of the transmitted sound wave;

[0008] S30: If the fluid is of the first type of flow pattern, then a second ultrasonic wave is emitted to the fluid, and based on the sound pressure value of the reflected echo of the second ultrasonic wave, the flow pattern of the fluid is classified as stratified flow or annular flow.

[0009] S40: If the fluid is of the second type of flow pattern, extract the parameters of the transmitted sound wave of the first ultrasonic wave and classify the flow pattern of the fluid as slug flow or plug flow.

[0010] In at least one embodiment, the gas-liquid interface of the fluid is a total reflection surface.

[0011] In at least one embodiment, the second ultrasonic wave is oriented opposite to the first ultrasonic wave.

[0012] In at least one embodiment, the emission interval Δt between the two pulsed ultrasound waves is:

[0013] Δt=nΔt U +Δt B (1)

[0014] Where n = 0, 1, 2, 3..., Δt U The transit time Δt refers to the transit time of the plug unit in the intermittent gas-liquid flow. B The transit time of long bubbles in the middle section of the gas-liquid intermittent flow block unit.

[0015] In at least one embodiment, the transit time Δt of the gas-liquid intermittent flow slug unit U We obtain it from the following formula:

[0016] Δt U =Δt S +Δt B (2)

[0017] Where, Δt S The transit time of the liquid plug in the slug unit;

[0018]

[0019]

[0020] Among them, L S L is the length of the liquid plug. B V is the length of the long bubble. SL V is the apparent flow rate of the liquid. SG V is the apparent velocity of the gas. S V is the velocity of the hydraulic plug. B V0 is the velocity of the long bubble, and V0 is the drift velocity of the long bubble. g is the acceleration due to gravity, D is the pipe diameter; C0 is the slip coefficient of the liquid plug, and C1 is the slip coefficient of the long bubble.

[0021] In at least one embodiment, the fluid plug velocity V S We obtain it from the following formula:

[0022] V S =C0V m +V0 (5)

[0023] Among them, V m The velocity at the surface of the gas-liquid mixture;

[0024] Long bubble velocity V B We obtain it from the following formula:

[0025]

[0026] In at least one embodiment, step S20 includes:

[0027] S21: When there is no signal in the transmitted sound waves of the two pulsed ultrasounds, the fluid is classified as the first type of flow pattern;

[0028] S22: When one of the transmitted sound waves of the two pulsed ultrasounds is a signal-free signal, the fluid is classified as a second type of flow pattern;

[0029] S23: When the transmitted sound waves of the two pulsed ultrasounds are both non-zero signals, the fluid is classified as a bubbly flow.

[0030] In at least one embodiment, step S30 includes:

[0031] S31: The sound pressure value of the reflected echo of the second ultrasonic wave is not zero, classifying the fluid as an annular flow;

[0032] S32: The sound pressure value of the reflected echo of the second ultrasonic wave is zero, classifying the fluid as a stratified flow.

[0033] In at least one embodiment, step S40 includes:

[0034] Based on the dimensionless and dimensionless parameters of the projected sound wave of the first ultrasonic wave, a series of simulation models of slug flow and plug flow with different gas contents are established, and the fluids are classified.

[0035] Another embodiment of this application provides a gas-liquid two-phase flow pattern signal acquisition device for detecting fluid in a pipeline, used in the method described above, including:

[0036] A first ultrasonic transducer is located at the top of the pipe and is used to emit a first ultrasonic wave.

[0037] A second ultrasonic transducer is located at the bottom of the pipe and is positioned opposite the first ultrasonic transducer in the pipe. It is used to receive the first ultrasonic wave and transmit and receive the second ultrasonic wave.

[0038] Compared with the prior art, the gas-liquid two-phase flow pattern identification method proposed in this application can analyze and judge the flow pattern of the fluid without disturbing the fluid or pipeline, and is not affected by factors such as fluid erosion and pipeline material. It has the advantages of being convenient, efficient and widely applicable. Attached Figure Description

[0039] Figure 1 This is a flowchart of one embodiment of the gas-liquid two-phase flow pattern identification method in this application;

[0040] Figure 2 yes Figure 1 The flowchart of another embodiment of the method shown is a step diagram;

[0041] Figure 3 yes Figure 1 A schematic diagram of the acquisition of acoustic pressure reflection signals at the gas-liquid interface in the method shown;

[0042] Figure 4 is Figure 1 A schematic diagram comparing the parameters of the simulated sound pressure signal in the method shown;

[0043] Figure 5 This is a schematic diagram of an embodiment of the gas-liquid two-phase flow pattern signal acquisition device in this application.

[0044] Figure reference numerals: 100 - Gas-liquid two-phase flow pattern signal acquisition device; 10 - First ultrasonic transducer; 20 - Second ultrasonic transducer; 30 - Pipeline. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0046] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0047] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0048] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0049] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0050] This application identifies the flow pattern of a gas-liquid two-phase flow using a measurement method based on the principle of reflected echo. The principle of the reflected echo test method is based on the difference in acoustic impedance between the two phases. When ultrasound is incident from one medium to another, part of the ultrasound energy is transmitted into the other medium, while the other part is reflected back into the original medium due to the difference in acoustic impedance between the two media at the interface. The transmittance and reflectance of ultrasound at the interface between the two media are related to the incident angle of the ultrasound and the acoustic impedance of the medium; therefore, a perpendicular incident ultrasound method is used to avoid the influence of angle.

[0051] Please see Figure 1 and Figure 2 This application proposes a method for identifying the flow pattern of a gas-liquid two-phase flow, comprising the following steps;

[0052] S10: Emit the first ultrasonic wave into the fluid in the pipe. The first ultrasonic wave is two pulsed ultrasonic waves emitted at intervals.

[0053] S20: Receive the transmitted sound wave of the first ultrasonic wave on the other side of the pipe, and classify the fluid into a first type of flow, a second type of flow, and a bubbly flow based on the sound pressure value of the transmitted sound wave.

[0054] S30: If the fluid is of type I flow, then emit a second ultrasonic wave into the fluid. Based on the sound pressure value of the reflected echo of the second ultrasonic wave, classify the flow type of the fluid as either stratified flow or annular flow.

[0055] S40: If the fluid is of the second type of flow pattern, extract the parameters of the reflected echo of the first ultrasonic wave and classify the flow pattern of the fluid as either slug flow or plug flow.

[0056] In this embodiment, the device for emitting the first and second ultrasonic waves is an ultrasonic transducer. The ultrasonic transducer can emit and receive ultrasonic waves. The ultrasonic transducer is located on the outside of the pipe, so that the flow pattern of the fluid can be identified without interfering with the inside of the pipe and the fluid.

[0057] In step S20, due to the total reflection characteristics of the interface and the fact that the first ultrasonic wave is a pulsed ultrasonic wave emitted twice at intervals, the fluid flow pattern can be preliminarily judged by the sound pressure of the transmitted sound waves of the two pulsed ultrasonic waves.

[0058] If the transmitted sound waves are almost zero in both cases, it means that the ultrasonic waves are basically completely reflected. At this point, the flow pattern is preliminarily judged to be the first type of flow pattern, including annular flow and stratified flow.

[0059] If one of the two transmitted sound waves is almost zero and the other is not zero, the flow pattern is preliminarily judged to be the second type of flow pattern, including slug flow and plug flow;

[0060] If both transmitted sound waves are not zero, the flow pattern is determined to be bubbly flow.

[0061] In step S30, for the first type of flow pattern, a second ultrasonic wave with a different direction from the first ultrasonic wave is emitted. The first type of flow pattern is further classified based on the sound pressure value of the reflected echo of the second ultrasonic wave. If the reflected echo of the second ultrasonic wave is basically zero, it means that the second ultrasonic wave is basically completely transmitted, and the fluid is judged to be a stratified flow; if the reflected echo of the second ultrasonic wave is not zero, that is, the second ultrasonic wave is basically completely reflected, it is judged to be a ring flow.

[0062] In step S40, for the second type of flow pattern, identification is performed by establishing a model. Based on multiphysics coupling, simulation models of slug flow and plug flow with gas contents of 3.5%, 6.8%, and 11% are established using simulation software. Dimensionless parameters of the transmitted acoustic signal of the first ultrasonic wave, such as kurtosis, skewness, peak factor, and impulse factor, as well as dimensional parameters, such as the peak value of the acoustic wave, are extracted. The second type of flow pattern is further determined by comparing these parameters.

[0063] Furthermore, the simulation model can be adjusted in detail according to the measured liquid to improve the accuracy of the judgment of the second type of flow pattern.

[0064] Thus, by emitting ultrasonic waves into the fluid in the pipeline, the flow pattern of the fluid can be identified and judged without intervening in the fluid or imposing requirements on the pipeline material. This method has the advantages of wide applicability and high efficiency.

[0065] In one embodiment, the gas-liquid interface of the fluid is a total reflection surface, or can be considered a total reflection surface, to facilitate the differentiation of ultrasonic wave reflection and transmission. Only in cases of high reflectivity can the reflection be easily determined by the sound pressure level of the transmitted sound wave. If it is not a total reflection surface, the sound pressure level of the transmitted sound wave needs to be analyzed by referring to the sound pressure level of the emitted ultrasonic wave and the attenuation in the fluid, complicating the situation and hindering rapid fluid identification.

[0066] In one embodiment, the second ultrasonic wave is oriented opposite to the first ultrasonic wave. In this embodiment, the first ultrasonic wave is emitted downward from the top of the pipe, and the second ultrasonic wave is emitted upward from the bottom of the pipe. The first ultrasonic wave and the second ultrasonic wave are oriented opposite to each other.

[0067] In one embodiment, the emission interval Δt between the two pulsed ultrasonic waves is:

[0068] Δt=nΔt U +Δt B (1)

[0069] Where n = 0, 1, 2, 3..., Δt U The transit time Δt refers to the transit time of the plug unit in the intermittent gas-liquid flow. B This refers to the transit time of a long bubble within a slug unit in an intermittent gas-liquid flow. The length of a slug unit is the sum of the liquid plug length and the long bubble length. The emission interval is set based on the slug length to ensure that exactly one complete slug unit separates the first ultrasonic wave, facilitating the analysis of the intermittent flow pattern.

[0070] In one embodiment, the transit time Δt of the gas-liquid intermittent flow mid-slug unit U We obtain it from the following formula:

[0071] ΔtU =Δt S +Δt B (2)

[0072] Where, Δt S The transit time of the liquid plug in the slug unit;

[0073]

[0074]

[0075] Among them, L S L is the length of the liquid plug. B V is the length of the long bubble. SL V is the apparent flow rate of the liquid. SG V is the apparent velocity of the gas. S V is the velocity of the hydraulic plug. B V0 is the velocity of the long bubble, and V0 is the drift velocity of the long bubble. g is the acceleration due to gravity, D is the pipe diameter; C0 is the slip coefficient of the liquid plug, and C1 is the slip coefficient of the long bubble.

[0076] The value of C0 is based on the Reynolds number Re of the fluid, which determines whether the fluid is laminar or turbulent. If the fluid is laminar, C0 is 1.2; if it is turbulent, C0 is 2. C1 is 0.25.

[0077] Hydraulic plug velocity V S This refers to the translational velocity of the hydraulic plug in the slug unit. In one embodiment, the hydraulic plug velocity V is... S We obtain it from the following formula:

[0078] V S =C0V m +V0(5)

[0079] Among them, V m The velocity at the surface of the gas-liquid mixture;

[0080] Long bubble velocity V B This refers to the translational velocity of the long bubble in the liquid film region of the slug unit, based on the velocity relationship of a single bubble, the long bubble velocity V. B It can be obtained through the following formula:

[0081]

[0082] In one embodiment, step S20 includes:

[0083] S21: When there is no signal in the transmitted sound waves of two pulse ultrasounds, the fluid is classified as the first type of flow.

[0084] S22: When one of the transmitted sound waves from two pulsed ultrasounds is a signal-free signal, the fluid is classified as a second type of flow pattern.

[0085] S23: When the transmitted sound waves of two pulsed ultrasounds are both non-zero signals, the fluid is classified as a bubbly flow.

[0086] In this embodiment, the sound pressure values ​​of the transmitted sound waves of the two pulsed ultrasonic waves in the first ultrasonic wave are set as a and b, respectively. If the ultrasonic wave passes through the liquid film region to reach the ultrasonic transducer at the other end, the transmitted sound wave of the ultrasonic wave is not zero at this time, and a or b is defined as 1 at this time; if the sound pressure value of the transmitted sound wave of the ultrasonic wave is basically zero, a or b is defined as 0 at this time.

[0087] For step S21, when there is no signal in the transmitted sound waves of the two pulsed ultrasounds, that is, a&b=0 and a||b=0, that is, both a and b are 0, the fluid is determined to be of the first type of flow.

[0088] In step S22, when one of the transmitted sound waves of the two pulsed ultrasounds is a signal-free signal, i.e., a&b=0 and a||b=1, i.e., one of a and b is 0 and the other is 1, the fluid is determined to be of the second type of flow.

[0089] In step S23, when the transmitted sound waves of the two pulsed ultrasounds are both non-zero signals, i.e., a&b=1 and a||b=1, the fluid is determined to be a bubbly flow.

[0090] In one embodiment, step S30 includes:

[0091] S31: The sound pressure value of the reflected echo of the second ultrasound is not zero, classifying the fluid as an annular flow;

[0092] S32: The sound pressure value of the reflected echo of the second ultrasound is zero, classifying the fluid as a stratified flow.

[0093] Similar to the first ultrasound, let the sound pressure value of the reflected echo of the second ultrasound be c. If the sound pressure value of the reflected echo of the second ultrasound is basically zero, then c is defined as 0; otherwise, c is defined as 1.

[0094] In step S31, when the sound pressure value of the reflected echo of the second ultrasonic wave is not zero, i.e., when c = 1, the fluid is determined to be an annular flow.

[0095] In step S32, when the sound pressure value of the reflected echo of the second ultrasonic wave is basically zero, that is, when c=0, the fluid is determined to be a stratified flow.

[0096] By defining the values ​​of a, b, and c, and using logical operations for discrimination, the method of this embodiment can be easily applied to computer software, improving computational efficiency and facilitating the rapid acquisition of discrimination conclusions.

[0097] In one embodiment, step S40 includes:

[0098] Based on dimensionless and dimensional parameters, a series of simulation models of slug flow and plug flow with different gas contents were established, and the fluids were classified.

[0099] Based on multi-physics coupling, simulation models of slug flow and plug flow with gas contents of 3.5%, 6.8%, and 11% were established using simulation software. Dimensionless parameters of the transmitted sound wave signal of the first ultrasonic wave, such as kurtosis, skewness, peak factor, and impulse factor, as well as the peak value of the sound pressure with dimensional parameters, were extracted. The second type of flow pattern was judged by comparing the parameters.

[0100] Please see Figure 5 Another embodiment of this application provides a gas-liquid two-phase flow pattern signal acquisition device 100 for detecting fluid in a pipe 30, used in the method described above, including:

[0101] The first ultrasonic transducer 10 is located at the top of the pipe 30 and is used to emit the first ultrasonic wave.

[0102] The second ultrasonic transducer 20 is located at the bottom of the pipe 30 and is positioned opposite the first ultrasonic transducer 10 in the pipe 30. It is used to receive the first ultrasonic wave and transmit and receive the second ultrasonic wave.

[0103] In this embodiment, the first ultrasonic transducer 10 is disposed at the bottom of the pipe 30 and facing the center of the cross-section of the pipe 30, and the second ultrasonic transducer 20 is disposed at the top of the pipe 30 and facing the center of the cross-section of the pipe 30. The first ultrasonic transducer 10 and the second ultrasonic transducer 20 are arranged opposite each other. Due to the influence of gravity, the gas-liquid interface in the pipe 30 is basically horizontal. In order to ensure that each ultrasonic wave and the reflected echo can be perpendicularly incident on the gas-liquid interface, the first ultrasonic transducer 10 and the second ultrasonic transducer 20 are arranged perpendicularly opposite each other.

[0104] The following examples verify this application.

[0105] In this embodiment, the ambient temperature is 25°C, the fluid is water, the inner diameter of pipe 30 is 50mm, and the ultrasonic wave is reflected when it propagates from the liquid phase to the gas phase interface, with a reflectivity E. r(g / w) We obtain it from the following formula:

[0106]

[0107] Among them, Z g and Z w The acoustic impedances of air and water at 25℃ are ρ, respectively. g and ρ w c represents the density of air and water at 25°C, respectively. g and cw What are the speeds of sound in air and water at 25°C? Under these conditions, the gas-liquid interface in the fluid can be considered as total internal reflection.

[0108] Please see Figure 3 The figures represent the sound pressure levels of the reflected echo and transmitted sound wave generated by ultrasound at the gas-liquid interface. The test fluid is a slug flow, with a gas content of 3.5% in the slug region, primarily consisting of long bubbles entrained at their tails. The gas content in the liquid film region is 73%. The figures show that when the liquid film flows through the test area, the peak sound pressure level of the transmitted sound wave is zero, while the sound pressure level of the transmitted sound wave is significantly non-zero when the liquid slug passes through.

[0109] Please refer to Figure 4, which shows the characteristic parameters of the transmitted sound wave of the first ultrasonic wave received by the second ultrasonic transducer 20, namely the simulated sound pressure signal of the slug flow and plug-like flow liquid plug region, including the characteristic parameters of the flow pattern data of 23 groups of plug-like flow and 46 groups of slug flow. Figures 4(a) to 4(e) The following are the parameter distribution diagrams for the kurtosis, skewness, peak factor, impulse factor, and signal peak value of the first ultrasound wave, respectively. Based on the comparison of these characteristic parameters, the accuracy of manifold identification is 100%.

[0110] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be incorporated into the present invention.

[0111] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for identifying the flow pattern of a gas-liquid two-phase flow, characterized in that, Includes the following steps; S10: Emit a first ultrasonic wave into the fluid inside the pipe. The first ultrasonic wave is a series of two pulsed ultrasonic waves emitted at intervals; the interval between the two pulsed ultrasonic waves... for: （1） in, , The transit time of the plug unit in the intermittent gas-liquid flow refers to the time of transit. The transit time of long bubbles in the middle section of the gas-liquid intermittent flow plug unit; transit time of the gas-liquid intermittent flow mid-slug unit We obtain it from the following formula: （2） in, The transit time of the liquid plug in the slug unit; （3） （4） Among them, L S L is the length of the liquid plug. B V is the length of the long bubble. SL V is the apparent flow rate of the liquid. SG V is the apparent velocity of the gas. S V is the velocity of the hydraulic plug. B V0 is the velocity of the long bubble, and V0 is the drift velocity of the long bubble. g is the acceleration due to gravity, D is the pipe diameter; C0 is the slip coefficient of the liquid plug, and C1 is the slip coefficient of the long bubble; The velocity of the liquid plug V S We obtain it from the following formula: （5） Among them, V m The velocity at the surface of the gas-liquid mixture; Long bubble velocity V B We obtain it from the following formula: （6） S20: Receive the transmitted sound wave of the first ultrasonic wave on the other side of the pipe, and classify the fluid into a first type of flow, a second type of flow, and a bubbly flow based on the sound pressure value of the transmitted sound wave; S30: If the fluid is of the first type of flow pattern, then a second ultrasonic wave is emitted to the fluid, and based on the sound pressure value of the reflected echo of the second ultrasonic wave, the flow pattern of the fluid is classified as stratified flow or annular flow. S40: If the fluid is of the second type of flow pattern, extract the parameters of the transmitted sound wave of the first ultrasonic wave and classify the flow pattern of the fluid as slug flow or plug flow.

2. The gas-liquid two-phase flow pattern identification method as described in claim 1, characterized in that, The gas-liquid interface of the fluid is a total reflection surface.

3. The gas-liquid two-phase flow pattern identification method as described in claim 2, characterized in that, The second ultrasonic wave is oriented in a direction opposite to that of the first ultrasonic wave.

4. The gas-liquid two-phase flow pattern identification method as described in claim 3, characterized in that, Step S20 includes: S21: When there is no signal in the transmitted sound waves of the two pulsed ultrasounds, the fluid is classified as the first type of flow pattern; S22: When one of the transmitted sound waves of the two pulsed ultrasounds is a signal-free signal, the fluid is classified as a second type of flow pattern; S23: When the transmitted sound waves of the two pulsed ultrasounds are both non-zero signals, the fluid is classified as a bubbly flow.

5. The gas-liquid two-phase flow pattern identification method as described in claim 4, characterized in that, Step S30 includes: S31: The sound pressure value of the reflected echo of the second ultrasonic wave is not zero, classifying the fluid as an annular flow; S32: The sound pressure value of the reflected echo of the second ultrasonic wave is zero, classifying the fluid as a stratified flow.

6. The gas-liquid two-phase flow pattern identification method as described in claim 4, characterized in that, Step S40 includes: Based on the dimensionless and dimensionless parameters of the transmitted sound wave of the first ultrasonic wave, a series of simulation models of slug flow and plug flow with different gas contents are established, and the fluids are classified.

7. A gas-liquid two-phase flow pattern signal acquisition device for detecting fluid in a pipeline, characterized in that, The method as described in any one of claims 1 to 6 includes: A first ultrasonic transducer is located at the top of the pipe and is used to emit a first ultrasonic wave. A second ultrasonic transducer is located at the bottom of the pipe and is positioned opposite the first ultrasonic transducer in the pipe. It is used to receive the first ultrasonic wave and transmit and receive the second ultrasonic wave.

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