A method and system for measuring phase distribution of gas-liquid two-phase flow in small pipes based on light intensity distribution

Abstract

The application discloses a kind of small pipeline gas-liquid two-phase flow phase distribution measurement method and system based on light intensity distribution.The method utilizes laser to generate light intensity distribution information through small pipeline gas-liquid two-phase flow in CMOS sensor, establishes the correlation model between gas-liquid two-phase flow phase distribution parameter and light intensity distribution characteristic value, realizes the reconstruction of bubble flow and slug flow cross section phase distribution and the measurement of related parameters.The application also builds the measurement system of small pipeline gas-liquid two-phase flow phase distribution based on light intensity distribution, which utilizes light source and multiple spectrometers to realize transverse and longitudinal spectrometry, so that laser is injected into pipeline cross section to obtain the parameters of cross section phase distribution and flow rate according to the change of light intensity distribution.Experimental research shows that the liquid film thickness and phase content estimated by the model are consistent with the liquid film thickness empirical formula and the real phase content of pipeline, the application principle is simple, easy to operate, and can accurately realize the measurement of gas-liquid two-phase distribution and related parameters in pipeline.

Description

Technical Field

[0001] This invention relates to the field of two-phase flow detection technology, and specifically to an optical detection system and method for two-phase flow phase distribution in small pipelines. Background Technology

[0002] Small-pipe gas-liquid two-phase flow systems, such as microreactors, micromixers, and microfluidic chips, are important components of miniaturized instruments and devices. Due to the reduced pipe size, small-pipe gas-liquid two-phase flow exhibits flow states and bubble morphologies that differ from conventional gas-liquid two-phase flow. Furthermore, the reduced pipe size also affects the accuracy of two-phase flow parameter measurements. Therefore, research on small-pipe gas-liquid two-phase flow is essential.

[0003] Optical-based small-pipe gas-liquid two-phase flow phase distribution reconstruction technology acquires optical signals containing phase distribution information using optical sensors, and then combines signal processing, data mining, and pattern recognition technologies to reconstruct the phase distribution. Depending on the detection sensor, optical detection-based small-pipe gas-liquid two-phase flow phase distribution reconstruction technology can be broadly subdivided into three categories: high-speed imaging, optical imaging, and particle tracer methods. High-speed imaging requires expensive equipment, has stringent environmental requirements, and requires transparent pipes, which severely limits its application in actual industrial production. While optical imaging-based reconstruction technology has relatively low cost, its detection circuitry is complex, limiting its miniaturization and integration when applied to small-scale pipe systems. Particle tracer methods are invasive detection methods that inevitably disrupt the phase distribution within the pipe to some extent, and require expensive equipment such as laser transducers and high-speed cameras.

[0004] Furthermore, determining the phase holdup in gas-liquid two-phase flow is also crucial. Phase holdup in gas-liquid two-phase flow refers to the ratio of the gas phase to the total volume; it can also be called porosity or gas content. Phase holdup is an important indicator for studying the flow process state and is the foundation for establishing physical models that can predict mass, momentum, and energy transfer. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method and system for measuring the phase distribution of a gas-liquid two-phase flow in a small pipe based on light intensity distribution. This method and system are not only simple to operate and low in cost, but also can effectively measure the phase distribution within the small pipe and calculate the phase content within the small pipe.

[0006] First, this invention discloses a light intensity distribution acquisition device for the phase distribution of gas-liquid two-phase flow in a small pipeline. Based on this device, not only can the phase distribution of the cross section be measured, but the flow velocity of the gas-liquid two-phase flow in the pipeline can also be obtained. The system is used to obtain the phase distribution parameters of the cross-section and the flow velocity of the gas-liquid two-phase flow in the pipeline. It includes a laser, a beam expander, a slit, a first beam splitter, a first plane mirror, a second beam splitter, a second plane mirror, a third plane mirror, a first CMOS sensor, a second CMOS sensor, a third CMOS sensor, and a small pipeline. The laser generates light, which is expanded into a circular beam with a diameter of 10-30 mm by the beam expander. The light passes through the slit and, under the action of the first beam splitter, is converted into reflected light and transmitted light. The reflected light passes through the first plane mirror and is vertically incident on the pipeline and the fluid being measured. The transmitted light passes through the second beam splitter, the second plane mirror, and the third plane mirror, and is converted into two beams: one in the horizontal direction (same as the pipeline) and the other in the vertical direction (perpendicular to the pipeline). The three beams pass through the pipeline and the fluid being measured in both horizontal and vertical directions. Due to the different sizes, positions, and tilt angles of the bubbles in the pipeline cross-section, the three beams undergo different refraction, scattering, and absorption phenomena, resulting in different changes in light intensity signals, which then reach the three CMOS sensors parallel to the pipeline.

[0007] Another objective of this invention is to provide a method for measuring the phase distribution of a small-channel gas-liquid two-phase flow based on light intensity distribution, the steps of which are as follows:

[0008] S1: Fill the pipe with liquid phase and obtain CMOS light intensity distribution information in the horizontal and vertical directions when light passes through the pipe.

[0009] S2: When the bubble passes through the pipe, acquire CMOS light intensity distribution information in the horizontal and vertical directions as the light passes through the pipe, and extract the light intensity distribution feature information. Compare with the light intensity distribution when the pipe is full, and select the length of the missing segment of the straight light intensity distribution, the center offset of the missing segment of the straight light intensity distribution, and the distance between the curved light intensity distribution and the straight light intensity distribution as light intensity distribution feature quantities.

[0010] S3: Establish a phase distribution reconstruction model. The cross-sectional distribution of the bubble when light passes through the pipe cross-section is set as a circle with a variable center (coordinates (x, y)), radius (r), and bubble surface tilt angle (θ). The bubble cross-sectional model parameters are (x, y, r, θ). A mathematical regression algorithm is used to establish a relationship between the light intensity distribution characteristics obtained in S2 and the bubble cross-sectional model parameters, thus establishing the phase distribution reconstruction model.

[0011] S4: Reconstruct the phase distribution within the pipe. Based on S1-S2, obtain the full-pipe light intensity distribution and the light intensity distribution information in the horizontal and vertical directions over a period of time. After extracting the light intensity distribution feature values, use the phase distribution reconstruction model in S3 to obtain the bubble cross-section model parameters (x, y, r, θ).

[0012] Furthermore, S2 specifically refers to:

[0013] S2.1: The distance between the two side peaks in the horizontal and vertical light intensity distributions obtained in S1 when the tube is full is denoted as Δl, which represents the length of the light intensity distribution.

[0014] S2.2: When a bubble passes through a pipe, the average distance between the curved light intensity distribution and the straight light intensity distribution in both directions is set as h. The length of the missing segment in the straight light intensity distribution and the center offset of the missing segment are set as Δl1 and Δl2, respectively, and then normalized to the length of the light intensity distribution.

[0015]

[0016] Since there are CMOS sensors in both horizontal and vertical directions, i.e., selecting l 1h , l 1v , l 2h and l 2v The parameters, together with h, are used as characteristic quantities of light intensity distribution to establish the relationship between them and the parameters of the bubble cross-section model.

[0017] Furthermore, S3 specifically refers to:

[0018] By relating the changes in light intensity distribution characteristic quantities to the bubble cross-section model parameters in a small-pipe gas-liquid two-phase flow, it can be seen that the bubble cross-section model parameters x, y, and r are related to the linear light intensity distribution, while the bubble cross-section model parameter θ is related to the curved light intensity distribution. Furthermore, changes in the abscissa x of the circle center cause the center of the missing block in the vertical linear light intensity distribution to shift, changes in the ordinate y of the circle center cause the center of the missing block in the horizontal linear light intensity distribution to shift, changes in the radius r of the circle cause changes in the length of the missing blocks in the horizontal and vertical linear light intensity distribution, and changes in the tilt angle θ cause changes in the distance between the vertex of the curved light intensity distribution and the linear light intensity distribution. Through a mathematical regression algorithm, the light intensity distribution characteristic quantity (l) is obtained. 1h ,l 1v ,l 2h ,l 2v The relationship between (h) and the bubble cross-section model parameters (x,y,r,θ) is as follows:

[0019]

[0020]

[0021]

[0022]

[0023] The values ​​of each parameter obtained by the regression algorithm are shown in Table 1.

[0024] Table 1

[0025]

[0026] Another objective of this invention is to provide a method for measuring the flow velocity of a gas-liquid two-phase flow in a small pipe based on light intensity distribution, the steps of which are as follows:

[0027] S1: Place the two CMOS sensors in the vertical direction at the same height, and select two pixels with the same height as P1 and P2, and record the distance between the two pixels as s.

[0028] S2: During the process of the bubble passing through the pipe, record the pixel grayscale changes of P1 and P2 over time.

[0029] S3: Let N be the sequence difference between the same peak values ​​of P1 and P2. The flow velocity of the gas-liquid two-phase flow in the pipe is...

[0030]

[0031] Where T is the CMOS sampling period and k is the calibration coefficient.

[0032] Another objective of this invention is to provide a liquid film estimation method for gas-liquid two-phase flow in a small pipe. This method utilizes the characteristic values ​​of light intensity distribution obtained over a period of time, which are then input into the phase distribution reconstruction model obtained in step S3. The estimated liquid film thickness is obtained using the bubble profile model parameters y and r.

[0033]

[0034] Where D is the diameter inside the pipe.

[0035] Another objective of this invention is to provide a method for estimating the phase content of a gas-liquid two-phase flow in a small pipe. This method utilizes the characteristic values ​​of light intensity distribution obtained over a period of time, which are then input into the phase distribution reconstruction model obtained in step S3. The obtained characteristic parameters can be used to construct the cross-sectional information of the gas phase distribution. Combined with the flow velocity and the frequency of CMOS sampling, the volume of the bubbles within the pipe can be obtained.

[0036]

[0037] Where v is the calculated flow velocity of the gas-liquid two-phase flow in the small pipe, and r i The radius of the bubble cross-section is obtained from the phase distribution reconstruction model. Using the characteristic values ​​of light intensity distribution obtained over a period of time, and substituting them into the phase distribution reconstruction model obtained in S3, the accumulated bubble volume over a continuous time period is summed up and compared with the total volume of the gas-liquid two-phase flow during that period to obtain the phase content of the gas-liquid two-phase flow in the small pipe, i.e.

[0038]

[0039] Where M represents the sequence difference of the same CMOS sample within the sampling time.

[0040] Along the flow direction of the gas-liquid two-phase flow, the distance traveled by the bubble in each sampling cycle is obtained using the bubble velocity. This allows for the reconstruction of the three-dimensional profile of the bubble cross-section, which is then stacked to form the overall three-dimensional shape of the bubble within the pipe. Figure 8 As shown, a three-dimensional reconstruction of the gas-liquid two-phase flow distribution is achieved. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the system for measuring the phase distribution of a small-pipe gas-liquid two-phase flow based on light intensity distribution according to the present invention.

[0042] Figure 2 This is a side view of the device used in the system to measure phase distribution parameters;

[0043] Figure 3 Characterization of bubble cross-section model parameters in gas-liquid two-phase flow in a small pipe;

[0044] Figure 4 This is a representation of the characteristic values ​​of the light intensity distribution in a full-tube light source;

[0045] Figure 5 This is used to characterize the light intensity distribution features of the reconstruction model;

[0046] Figure 6 Comparison between bubble profiles constructed based on phase distribution reconstruction models and real bubbles

[0047] Figure 7 This is a comparison between the phase content in the pipeline obtained from the phase distribution reconstruction model and the actual phase content.

[0048] Figure 8 The three-dimensional profile of the bubble obtained based on the phase distribution reconstruction model

[0049] In the figure, 1 is a He-Ne laser, 2 is a beam expander, 3 is a slit, 4 and 6 are beam splitters, 5, 7 and 8 are plane mirrors, 9, 10 and 11 are CMOS array sensors, and 12 is a small pipe. Detailed Implementation

[0050] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The purpose and effects of the present invention will become clearer. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0051] like Figure 1-2As shown, the light intensity distribution acquisition device includes a He-Ne laser 1, a beam expander 2, a slit 3, a first beam splitter 4, a first plane mirror 5, a second beam splitter 6, a second plane mirror 7, a third plane mirror 8, a first CMOS sensor 9, a second CMOS sensor 10, a third CMOS sensor 11, and a small pipe 12. The He-Ne laser generates light, which is then expanded into a circular beam with a diameter of approximately 25 mm by the beam expander. The light passes through the slit and, under the action of the first beam splitter, is divided into reflected and transmitted light. The reflected light passes through the first plane mirror and enters the pipe and the fluid being measured; the transmitted light, after passing through the second beam splitter and the second and third plane mirrors, becomes two beams, one horizontal and one vertical, passing through the pipe and the fluid being measured in both directions. Due to the different sizes, positions, and tilt angles of the bubbles within the pipe cross-section, the three beams undergo different refraction, scattering, and absorption phenomena, resulting in different changes in light intensity signals before reaching the CMOS sensor parallel to the pipe.

[0052] For gas-liquid two-phase flows in small pipes where the flow patterns are bubbly flow and slug flow, such as Figure 3 As shown, when light passes through the bubble cross-section, it is assumed to be a circle with a variable center position, radius, and surface tilt angle. That is, the bubble cross-section model parameters are (x, y, r, θ).

[0053] First, obtain the light intensity distribution when the tube is full. For example... Figure 4 As shown, only a straight line s1s2 can be observed in the light intensity distribution, which is called a linear light intensity distribution. The linear light intensity distribution changes with a maximum value in the middle, then decreases and then increases as it expands outwards, reaching a maximum at the two side peaks, and then drops to zero as it expands further outwards. Let the distance between the two side peaks be Δl. When the pipe contains air bubbles, as... Figure 5 As shown, two light intensity distributions will first be generated on the sensor: one is a straight line s1s2, which is the light intensity distribution with missing blocks, and the other is a curve resembling a parabola. This is called the curved light intensity distribution. Analysis shows that the parameters x, y, and r of the bubble cross-section model are related to the changes in the straight light intensity distribution, while θ is related to the changes in the curved light intensity distribution. Based on the observed patterns, changes in the circle's center x cause the center of the missing block in the vertical straight light intensity distribution to shift; changes in the circle's center y cause the center of the missing block in the horizontal straight light intensity distribution to shift; changes in the circle's radius r cause changes in the length of the missing blocks in the horizontal and vertical straight light intensity distributions; and changes in the tilt angle θ cause changes in the distance between the vertex of the curved light intensity distribution and the straight light intensity distribution. Therefore, the distance between the straight and curved light intensity distributions is set as h, and the length of the missing segment in the straight light intensity distribution and the center shift of the missing segment are set as Δl1 and Δl2, respectively, and normalized to the length of the light intensity distribution.

[0054]

[0055] Then there are a total of l CMOS in the horizontal and vertical directions. 1h , l 1v , l 2h and l 2v Four parameters, along with h, are used as characteristic quantities of light intensity distribution to establish the relationship between the parameters of the bubble cross-section model, i.e., constructing (x, y, r, θ) and (l) 1h ,l 1v ,l 2h ,l 2v The relationship between ,h).

[0056] The bubble cross-section model parameter h is related to the bubble surface tilt angle θ; changes in the bubble position do not affect h. When the bubble surface tilt angle θ is constant, the change in the light path is also constant, so the minimum distance between the curved light intensity distribution and the straight light intensity distribution remains almost constant. Taking the straight line containing the straight light intensity distribution as the x-axis, h > 0 when the curved light intensity distribution appears below, and h < 0 when the curved light intensity distribution appears below. As the angle between the bubble cross-section tilt angle and the horizontal light ray changes, the distance between the highest point of the curved light intensity distribution and the straight light intensity distribution exhibits a quadratic function relationship. Through quadratic fitting, the relationship between the bubble cross-section tilt angle θ and the distance h between the two light intensity distributions is obtained as follows:

[0057]

[0058] Furthermore, the relationship between the parameters x, y, and r of the bubble cross-section model is obtained using the horizontal light intensity distribution information. Since the density of bubbles is lower than that of water, the bubbles float in the upper part of the pipe, so y > 0 always holds. Additionally, the relationship between l and r is obtained using the horizontal light intensity distribution information. 1h and l 1v The radius values ​​obtained in both the horizontal and vertical directions are averaged and recorded as the radius of the bubble.

[0059]

[0060] x = sgn(l 2v )k x |l 2v |β x (4)

[0061]

[0062]

[0063]

[0064] Taking the logarithm of both sides of the expression yields

[0065] logy = logk y +β y logl 2h (8)

[0066] logx = logk x +β x logl 2v (9)

[0067] logr1 = logk r1 +β r1 logl 1h (10)

[0068] logr2 = logk r2 +β r2 logl 1v (11)

[0069] Additionally l 1h l 2j It has coupling relationships with y and r respectively, and l 1v l 2v It has coupling relationships with x and r respectively. Therefore, the least squares regression algorithm is used to obtain...

[0070] k y =C y1 r+C y2 (12)

[0071] k x =C x1 r+C x2 (13)

[0072] k r1 =C r1 y+C r2 (14)

[0073] k r3 =C r3 x+C r4 (15)

[0074] β y β x β r1 and β r2 After regression, all values ​​are constants. Therefore, we obtain...

[0075]

[0076]

[0077]

[0078] Integrate the various methods:

[0079]

[0080]

[0081]

[0082]

[0083] The parameters are shown in Table 1.

[0084] Table 1

[0085]

[0086] Based on the established phase distribution reconstruction model, the phase distribution of gas-liquid two-phase flow within a small pipe can be reconstructed. A gas-liquid two-phase flow is introduced into the pipe, and when light enters the pipe cross-section, the light intensity distribution information in both the horizontal and vertical directions is obtained (l... 1h ,l 1v ,l 2h ,l 2v Substitute these values ​​into the phase distribution reconstruction model to obtain the distribution of the gas phase in the current cross section.

[0087] In addition, the flow velocity of the gas-liquid two-phase flow in the pipe is obtained by receiving two CMOS (10,11) images of different pipe cross-sections in the vertical direction. The two CMOS images in the vertical direction are placed at the same height, and two pixels with the same height are selected as P1 and P2, and the distance between the two pixels is denoted as s.

[0088] As the bubbles pass through the pipe, the grayscale changes of P1 and P2 over time are recorded. Let N be the sequence difference between the same peak values ​​of P1 and P2, then the flow velocity of the gas-liquid two-phase flow inside the pipe is...

[0089]

[0090] Where T is the CMOS sampling period and k is the calibration coefficient.

[0091] The bubble profile can be obtained using the acquired bubble cross-sectional profile parameters and flow velocity. A small-pipe gas-liquid two-phase flow phase distribution measurement method based on light intensity distribution can also represent the bubble profile, where the upper boundary p... u lower boundary p d Left boundary p l right boundary p r The distance u between each sampling point can be expressed as

[0092] p u =y+r (24)

[0093] p d =yr (25)

[0094] p l =xr (26)

[0095] p r =x+r (27)

[0096] u=v·T (28)

[0097] Figure 7 This represents a comparison between the continuous phase distribution changes obtained from the model in two dimensions and the actual bubble side and top views. The pipe used in the experiment had an outer diameter of 2.78 mm and an inner diameter of 1.71 mm. The comparison between bubble profiles also demonstrates the accuracy and reliability of the gas-liquid two-phase flow phase distribution measurement model proposed in this invention. The estimated liquid film thickness is obtained using the bubble profile model parameters y and r:

[0098]

[0099] Where D is the diameter inside the pipe.

[0100] The estimated liquid film thickness obtained by the model was compared with the empirical formula for liquid film thickness. The relative errors obtained by the comparison are shown in Table 2. It was found that the two have a good consistency.

[0101] Table 2

[0102]

[0103] Among them: [1] is Bretherton F P. The motion of long bubbles in tubes. [J]. Journal of Fluid Mechanics, 1961, 10 (2): 166-188; [2] is Aussillous P, Quéré D. Quick deposition of a fluid on the wall of a tube [J]. Physics of fluids, 2000, 12 (10): 2367-2371; [3] Han Y, Shikazono N. Measurement of the liquid filmthickness in micro tube slug flow [J]. International Journal of Heat and FluidFlow, 2009, 30 (5): 842-853.

[0104] Finally, by combining the obtained bubble cross-sectional phase distribution parameters with the flow velocity of the gas-liquid two-phase flow, the bubble volume in each sampling period is obtained, i.e.

[0105]

[0106] Where v is the calculated flow velocity of the gas-liquid two-phase flow in the small pipe, and r i The radius of the bubble cross section is obtained in the phase distribution reconstruction model.

[0107] The phase content of the gas-liquid two-phase flow in a small pipe is obtained by comparing the volume of air bubbles in the pipe with the total volume flowing through the pipe during the same period.

[0108]

[0109] Where M represents the sequence difference of the same CMOS sample within the sampling time.

[0110] By comparing the phase inclusion rate obtained from the model with the actual phase inclusion rate, such as... Figure 6 The results showed that the phase holdup calculated by the phase distribution model and the actual results exhibited good consistency, with the relative error controlled within -5% to +6%. The experimental results demonstrate the accuracy and feasibility of the phase holdup estimation method for gas-liquid two-phase flow in small pipes based on light intensity distribution.

[0111] Along the flow direction of the gas-liquid two-phase flow, the distance traveled by the bubble in each sampling cycle is obtained using the bubble velocity. This allows for the reconstruction of the three-dimensional profile of the bubble cross-section, which is then stacked to form the overall three-dimensional shape of the bubble within the pipe. Figure 8 As shown, a three-dimensional reconstruction of the gas-liquid two-phase flow distribution is achieved.

Claims

1. A small-pipe gas-liquid two-phase flow phase distribution measurement system based on light intensity distribution, characterized in that: The system is used to obtain the phase distribution parameters of the cross section and the flow velocity of the gas-liquid two-phase flow in the pipe. It includes a laser (1), a beam expander (2), a slit (3), a first beam splitter (4), a first plane mirror (5), a second beam splitter (6), a second plane mirror (7), a third plane mirror (8), a first CMOS sensor (9), a second CMOS sensor (10), a third CMOS sensor (11), and a small pipe (12). The laser generates light, which is then expanded by the beam expander to a diameter of 10-30 mm. A circular light ray, denoted by mm, passes through a slit and, under the action of a first beam splitter, is divided into reflected and transmitted light. The reflected light, after passing through a first plane mirror, is vertically incident on the pipe and the fluid being measured. The transmitted light, after passing through a second beam splitter, a second plane mirror, and a third plane mirror, becomes two beams: one horizontal and one vertical, both perpendicular to the pipe. These beams pass through the pipe and the fluid in both horizontal and vertical directions. Due to the different sizes, positions, and tilt angles of the bubbles within the pipe cross-section, the three beams undergo different refraction, scattering, and absorption phenomena, resulting in different changes in light intensity signals before reaching three CMOS sensors parallel to the pipe.

2. A method for measuring the phase distribution of a gas-liquid two-phase flow in a small pipe based on light intensity distribution, characterized in that, The method includes the following steps: S1: Fill the pipe with liquid phase and obtain the CMOS sensor light intensity distribution information in the horizontal and vertical directions of the pipe when the light passes through the pipe; S2: When the bubble passes through the pipe, the light intensity distribution information of the light passing through the pipe and the CMOS sensor in the horizontal and vertical directions of the pipe is obtained, and the light intensity distribution feature information is extracted; compared with the light intensity distribution when the pipe is full, the length of the missing segment of the straight light intensity distribution, the center offset of the missing segment of the straight light intensity distribution, and the distance between the curved light intensity distribution and the straight light intensity distribution are selected as light intensity distribution feature quantities for both directions. S3: Establish a phase distribution reconstruction model; set the gas phase distribution when light passes through the bubble cross section as a circle with variable center, radius and bubble surface tilt angle, and bubble cross section model parameters (x, y, r, θ). Use mathematical regression algorithm to construct a relationship between the light intensity distribution characteristics obtained in S2 and the bubble cross section model parameters to establish a phase distribution reconstruction model. S4: Reconstructs the phase distribution within the pipeline; Specifically, S2 is: S2.1: The distance between the full pipe time obtained in S1 and the two side peaks in the horizontal and vertical light intensity distributions of the pipe is denoted as... It represents the length of the light intensity distribution; S2.2: When the bubble passes through the pipe, the average distance between the curved light intensity distribution and the straight light intensity distribution in both directions is set as h, and the length of the missing segment in the straight light intensity distribution and the center offset of the missing segment in the straight light intensity distribution are respectively set as h. and And it is normalized to the length of the light intensity distribution, that is （1） Because there is information about the light intensity distribution in both the horizontal and vertical directions of the pipe, i.e., selecting , , and The parameters are defined as follows: the subscript h represents the horizontal direction, v represents the vertical direction, subscript 1 represents the length of the missing segment in the linear light intensity distribution, and subscript 2 represents the center offset of the missing segment in the linear light intensity distribution. Together with h, these parameters are used as light intensity distribution feature quantities to establish the relationship between the parameters and the bubble cross-section model. Based on the light intensity distribution information obtained from S1-S2, including the light intensity distribution in both horizontal and vertical directions over a period of time, and after extracting the light intensity distribution feature values, the bubble cross-section model parameters (x, y, r, θ) are obtained using the phase distribution reconstruction model in S3. Finally, the light intensity distribution feature quantities are obtained through a mathematical regression algorithm. , , , The relationship between (h) and the bubble cross-section model parameters (x, y, r, θ) is as follows: （2） （3） （4） （5） The values ​​of each parameter obtained by the regression algorithm are shown in Table 1: Table 1 。 3. The method for measuring the phase distribution of a gas-liquid two-phase flow in a small pipe based on light intensity distribution according to claim 2, characterized in that, The method for measuring the velocity of gas-liquid two-phase flow in a small pipeline includes the following steps: S1: Place two CMOS sensors in the vertical direction at the same height, and select two pixels with the same height as P1 and P2, and record the distance between the two pixels as s; S2: When the bubble passes through the pipe, record the pixel grayscale changes of P1 and P2 over time; S3: Let N be the sequence difference between the same peak values ​​of P1 and P2, and let the flow velocity of the gas-liquid two-phase flow in the pipe be... （6） Where T is the sampling period of the CMOS sensor, and k is the calibration coefficient.

4. The method for measuring the phase distribution of a gas-liquid two-phase flow in a small pipe based on light intensity distribution according to claim 2, characterized in that, The liquid film estimation method for gas-liquid two-phase flow in a small pipeline includes: using the characteristic values ​​of light intensity distribution obtained over a period of time, substituting them into the phase distribution reconstruction model obtained in S3, and using the bubble profile model parameters y and r to obtain the liquid film thickness. The estimated value is: （7） Where D is the diameter inside the pipe.

5. The method for measuring the phase distribution of a gas-liquid two-phase flow in a small pipe based on light intensity distribution according to claim 2, characterized in that, The method for estimating the phase holdup of gas-liquid two-phase flow in a small pipe includes: using the characteristic values ​​of light intensity distribution obtained over a period of time, substituting them into the phase distribution reconstruction model obtained in S3, summing up the accumulated bubble volume obtained over a continuous time period, and comparing it with the total volume of the gas-liquid two-phase flow during this period to obtain the phase holdup of the gas-liquid two-phase flow in the small pipe, i.e. （8） Where n is the number of bubbles, r i Let be the radius of the i-th bubble, D be the inner diameter of the pipe, and M be the sequence difference between samples taken by the same CMOS sensor within the sampling time.

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