CN111307809A - Small pipeline gas-liquid two-phase flow phase distribution optical detection system and method - Google Patents

Small pipeline gas-liquid two-phase flow phase distribution optical detection system and method Download PDF

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CN111307809A
CN111307809A CN202010113961.9A CN202010113961A CN111307809A CN 111307809 A CN111307809 A CN 111307809A CN 202010113961 A CN202010113961 A CN 202010113961A CN 111307809 A CN111307809 A CN 111307809A
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冀海峰
戴振韬
王保良
黄志尧
李海青
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Zhejiang University ZJU
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    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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    • G01—MEASURING; TESTING
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    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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Abstract

The invention discloses a system and a method for optical detection of gas-liquid two-phase flow phase distribution of a small pipeline. Firstly, irradiating the gas-liquid two-phase flow to be measured from two mutually perpendicular directions by adopting two flaky light beams, and synchronously measuring the light intensity distribution generated by the irradiation; then, the required light intensity distribution characteristic quantity is extracted from the measurement result by combining the light intensity distribution data when the pipeline is filled with the liquid phase; then, establishing a measurement model about the small pipeline section phase distribution parameters and the light intensity distribution characteristic quantity based on the geometrical optics principle, and realizing the gas-liquid phase distribution measurement of the pipeline section by using experimental data; and finally, further realizing gas-liquid phase distribution reconstruction and liquid film thickness estimation of the gas-liquid two-phase flow based on the multiple groups of phase distribution measurement results. The system has the advantages of non-contact/non-invasive measurement, high time/space resolution, simple device structure and the like; the method is based on the geometrical optics principle, and provides an effective and convenient new way for obtaining the section gas-liquid phase distribution information of the small-pipeline gas-liquid two-phase flow.

Description

Small pipeline gas-liquid two-phase flow phase distribution optical detection system and method
Technical Field
The invention belongs to the technical field of two-phase flow fluid detection, and relates to a small pipeline gas-liquid two-phase flow phase distribution optical detection system and method.
Background
The small-pipeline gas-liquid two-phase flow widely exists in the fields of energy, petroleum, chemical engineering and the like, and has extremely important value in the fields of scientific research and industrial application aiming at the phase distribution detection research of the flowing process. The technology can not only provide an effective data source for scientific research and theoretical modeling, but also provide support and guarantee for safe and efficient operation of industrial production.
In the existing gas-liquid two-phase flow distribution detection technology, a high-speed camera method and a particle tracing method are two types of methods which are successfully applied to small-channel gas-liquid two-phase flow detection, wherein the high-speed camera method is a method which is earlier applied to small-channel flow state detection and is also one of the methods which are more successful and have higher detection precision at present. Although this technique can obtain high precision two-phase flow images and has the advantages of non-invasive, non-contact detection, high speed cameras require the pipeline to be transparent to obtain the fluid images, which is difficult to achieve in many application scenarios. In addition, the high cost of the high speed camera itself is also a limiting factor in this technology. For the particle tracing method, although the method can obtain high-quality gas-liquid two-phase flow interface shape information and obtain more accurate flow field distribution information, the limitation of the technology is that: on one hand, corresponding equipment in the detection system, such as a high-energy pulse laser, a high-speed camera and the like, is very expensive in cost, and the structure of the device is complex; on the other hand, this type of technique requires the addition of tracer particles to the primary fluid, which may affect the physical properties of the working fluid.
Disclosure of Invention
In order to further improve the existing small pipeline gas-liquid two-phase flow phase distribution detection technology, the invention discloses a small pipeline gas-liquid two-phase flow phase distribution optical detection system, which comprises a laser, a beam expander, a slit, a spectroscope, a first plane mirror, a second plane mirror, a first high-speed CMOS sensor, a second high-speed CMOS sensor and a small pipeline gas-liquid two-phase flow; firstly, a light beam emitted by a laser sequentially passes through a beam expander and a slit to be changed into a parallel sheet-shaped light beam, and the parallel sheet-shaped light beam is divided into a horizontal sheet-shaped light beam and a vertical sheet-shaped light beam through a beam splitter, wherein the horizontal sheet-shaped light beam directly enters a small pipeline gas-liquid two-phase flow, and the vertical sheet-shaped light beam enters the small pipeline gas-liquid two-phase flow from the other vertical direction after being reflected by a first plane mirror and a second plane mirror; and finally, the first high-speed CMOS sensor and the second high-speed CMOS sensor respectively measure the light intensity distribution generated after the two horizontal and vertical sheet-shaped light beams pass through the gas-liquid two-phase flow.
The invention also aims to provide a small pipeline gas-liquid two-phase flow phase distribution optical measurement method based on the geometrical optics principle, which comprises the following steps:
1) obtaining the light intensity distribution of the small pipeline gas-liquid two-phase flow: the detection system of claim 1 is adopted to synchronously acquire light intensity distribution data generated after parallel flaky incident light beams with mutually perpendicular angles pass through a small pipeline gas-liquid two-phase flow;
2) extracting light intensity distribution characteristic quantity: extracting the length of the relative missing part and the central offset of the relative missing part from the light intensity distribution acquired in the step 1) by combining the light intensity distribution data when the pipeline is filled with water, and normalizing the length and the central offset as final light intensity distribution characteristic quantity;
3) establishing a small pipeline gas-liquid two-phase flow phase distribution measurement model: describing the distribution condition of gas-liquid two-phase flow in the section of the small pipeline as an ellipse with variable central position and half-axis length, recording the central coordinates of the ellipse as (x, y), and the horizontal and vertical half-axis lengths of the ellipse as a and b respectively, and establishing a phase distribution measurement model related to gas-liquid phase distribution parameters (x, y, a and b) and light intensity distribution characteristic quantity of the section;
4) identifying model parameters of the phase distribution measurement model obtained in the step 3): under the experimental parameter condition in the step 1), obtaining theoretical light intensity distribution generated by section gas-liquid phase distribution parameters (x, y, a, b) under different value conditions according to a geometrical optics principle, and extracting theoretical light intensity distribution characteristic quantity; substituting the extracted theoretical light intensity distribution characteristic quantity into the phase distribution measurement model in the step 3) to obtain a measurement result of the gas-liquid phase distribution parameters of the section; finally, obtaining model parameters of the phase distribution measurement model by adopting a least square method;
5) measuring the gas-liquid two-phase flow phase distribution of the small pipeline: obtaining light intensity distribution in two mutually perpendicular directions within a period of sampling time according to the step 1) and the step 2), extracting light intensity distribution characteristic quantity, substituting the light intensity distribution characteristic quantity and the model parameters obtained by identification in the step 4) into a phase distribution measurement model, and obtaining a measurement result of the gas-liquid phase distribution parameters of the section.
Further, the step 2) is specifically:
1) measuring and recording the light intensity distribution in two mutually perpendicular directions when the pipeline is filled with water, and respectively recording the light intensity distribution lengths in the two directions as delta lh、Δlv；
2) When bubbles pass through the pipeline, the corresponding light intensity distribution generates a missing part, the light intensity distribution at the moment is differed from the light intensity distribution when the pipeline is filled with water, and the length delta l of the light intensity missing part is further obtained by an edge detection method1And the central offset Deltal of the light intensity missing part2；
3) The intensity distributions in two mutually perpendicular directions are characterized by (Δ l)1h,Δl2h) And (Δ l)1v,Δl2v) Normalizing to obtain final characteristic quantity of light intensity distribution
Figure BDA0002390917410000031
Wherein:
Figure BDA0002390917410000032
in the formula (I), the compound is shown in the specification,
Figure BDA0002390917410000033
and
Figure BDA0002390917410000034
the length of the light intensity missing portion in the horizontal direction and the central offset amount,
Figure BDA0002390917410000035
and
Figure BDA0002390917410000036
the length of the light intensity missing portion in the vertical direction and the central offset amount, respectively.
Further, the step 3) is specifically:
approximately describing gas-liquid phase distribution conditions in the section of a small pipeline by adopting an ellipse with variable central position and half-axis length, recording central coordinates of the ellipse as (x, y), horizontal and vertical half-axis lengths of the ellipse as a and b respectively, establishing a plane rectangular coordinate system by taking the center of the section of the pipeline as an origin and taking the horizontal and vertical directions as horizontal and vertical coordinate axes, and recording the outer radius and the inner radius of the pipeline as R, R respectivelycThe refractive indexes of the channel, the gas phase and the liquid phase are respectively nc，ngAnd nlRecording the vertical distance between the optical detection boundary and the center of the pipeline as L; according to the geometrical optics theory, the parameters (x, y, a, b) of the gas-liquid phase distribution and the characteristic quantity of the light intensity distribution of the cross section are established
Figure BDA0002390917410000037
Phase distribution measurement model of (2):
Figure BDA0002390917410000038
Figure BDA0002390917410000039
Figure BDA00023909174100000310
in the formula, A1,A2,B1,B2,C1,C2,α1,α2,β1,β2,γ1,γ2For model parameters to be identifiedNumber R, Rc、nc、ng、nlAnd L is an experimental parameter,
Figure BDA00023909174100000311
is a dimensionless gas-liquid phase distribution parameter of the section.
Further, the step 4) is specifically:
converting the phase distribution measurement model established in the step 3) into:
P＝M-1N (5)
Figure BDA0002390917410000041
Figure BDA0002390917410000042
Figure BDA0002390917410000043
obtaining theoretical light intensity distribution of gas-liquid phase distribution parameters (x, y, a, b) of cross section under different values according to geometric optics principle, and calculating parameter R, Rc、nc、ng、nlL is the same as the experimental parameters in the step 1); extracting the characteristic quantity of the theoretical light intensity distribution
Figure BDA0002390917410000044
Recording the gas-liquid phase distribution parameters of corresponding preset cross sections
Figure BDA0002390917410000045
Figure BDA0002390917410000045
Figure BDA0002390917410000045
1,2, …, N; n represents the number of sets of sectional gas-liquid phase distribution parameters (x, y, a, b), i.e. the number of sections;
on this basis, the loss function L (θ) is defined as:
Figure BDA0002390917410000046
Figure BDA0002390917410000047
in the formula, θ represents a set of model parameters A to be identified1,A2,B1,B2,C1,C2,α1,α2,β1,β2,γ1,γ2；
Figure BDA0002390917410000048
Calculating the preset result of the gas-liquid phase distribution parameter of the corresponding section for the ith group of theories, PiThe method is a measurement result of section gas-liquid phase distribution parameters obtained by substituting the ith group of theoretical light intensity distribution characteristic quantities into phase distribution measurement model expressions (5) to (8);
the model parameter θ to be identified in the phase distribution measurement model can be determined according to the following formula*：
Figure BDA0002390917410000049
The invention also aims to provide a liquid film thickness estimation method of the small pipeline gas-liquid two-phase flow, which is based on the phase distribution measurement model, and firstly, a group of light intensity distribution characteristic quantities are obtained by utilizing the light intensity distribution measurement result in the horizontal direction within a period of sampling time according to the light intensity distribution characteristic quantity extraction method in the step 2)
Figure BDA0002390917410000051
Substituting the model parameters identified in the step 4) into a phase distribution measurement model to further obtain gas-liquid phase distribution parameters of the cross section
Figure BDA0002390917410000052
Characteristic quantity of light intensity distribution
Figure BDA0002390917410000053
The relationship between:
Figure BDA0002390917410000054
in the formula, A1,A2,C1,C2,α1,α2,γ1,γ2As the parameters of the model to be identified,
Figure BDA0002390917410000055
gas-liquid phase distribution parameters of a dimensionless section;
according to the definition of relative liquid film thickness:
Figure BDA0002390917410000056
wherein δ represents the absolute thickness of the liquid film, and D represents the inner diameter of the pipe;
then, the extracted light intensity distribution characteristic quantity is used according to the expressions (12) to (13)
Figure BDA0002390917410000057
Obtaining a set of relative liquid film thickness estimates (delta/D)iAnd taking the average value as the final liquid film thickness estimation result.
The invention has the following beneficial effects:
(1) compared with the traditional gas-liquid two-phase flow optical measurement system, the system adopts two high-speed CMOS sensors to synchronously measure light intensity distribution signals generated by sheet incident light after passing through gas-liquid two-phase flow in two mutually perpendicular directions, can fully utilize gas-liquid phase interface shape information contained in the light intensity distribution signals, has the advantages of non-invasive and non-contact measurement, high time, spatial resolution and the like, and is suitable for application scenes of small-pipeline gas-liquid two-phase flow parameter measurement, state monitoring and the like.
(2) In the light intensity distribution extraction process in the method for measuring the gas-liquid two-phase flow phase distribution of the small pipeline, the light intensity distribution missing part is extracted in a poor mode by combining the light intensity distribution data when the pipeline is filled with water, so that the influence of light intensity noise caused by stray light on the extraction of the light intensity distribution characteristic quantity can be effectively avoided. In addition, the light intensity distribution characteristics are subjected to normalization processing, so that the influence of measurement errors of experimental conditions (such as gas-liquid phase medium refractive index, glass pipeline refractive index, pipeline size and the like) on the light intensity distribution characteristic quantity can be effectively reduced.
(3) Compared with the traditional optical tomography method, the method for measuring the gas-liquid two-phase flow phase distribution of the small pipeline adopts the parameter-adjustable ellipse to approximately describe the gas-liquid phase distribution condition in the pipeline section according to the flow characteristics of the gas-liquid two-phase flow in the small pipeline, realizes the measurement of the section phase distribution condition only by adopting light intensity distribution signals in two directions, and has higher precision in the measurement result.
(4) The method for measuring the thickness of the liquid film in the two-phase gas-liquid flow of the small pipeline only needs a light intensity distribution signal in the horizontal direction, and a spectroscope 4, a first plane mirror 5, a second plane mirror 6 and a second high-speed CMOS sensor 8 can be further omitted on the basis of FIG. 1 in actual use. Compared with the traditional liquid film thickness measuring method, the method has the advantages of simple and convenient device structure, simple measuring process and the like. The experimental measurement result shows that the liquid film thickness measurement result has better consistency with the existing liquid film thickness empirical formula.
Drawings
FIG. 1 is a schematic structural diagram of a proposed small-pipeline gas-liquid two-phase flow optical detection system;
FIG. 2 is a diagram showing characteristic quantities of light intensity distribution;
FIG. 3 is a coordinate and parameter definition used in the theoretical calculation of light intensity distribution;
FIG. 4 shows the result of the reconstruction of the two-phase gas-liquid flow continuous bubbles in the example;
in the figure: the device comprises a laser 1, a beam expander 2, a slit 3, a spectroscope 4, a first plane mirror 5, a second plane mirror 6, a first high-speed CMOS sensor 7, a second high-speed CMOS sensor 8 and a small pipeline gas-liquid two-phase flow 9.
Detailed Description
The system and the invention will be further explained with reference to the drawings.
As shown in fig. 1, a small-pipeline gas-liquid two-phase flow phase distribution optical detection system is composed of a laser 1, a beam expander 2, a slit 3, a spectroscope 4, a first plane mirror 5, a second plane mirror 6, a first high-speed CMOS sensor 7, a second high-speed CMOS sensor 8, and a small-pipeline gas-liquid two-phase flow 9. Firstly, a light beam emitted by a laser 1 passes through a beam expander 2 and a slit 3 and then is changed into a parallel sheet-shaped light beam with proper width, and the width is equal to the outer diameter of a measured pipeline; then, the original parallel sheet-shaped light beam is divided into two horizontal and vertical sheet-shaped light beams by the spectroscope 4, the horizontal light beam directly enters the small pipeline gas-liquid two-phase flow 9, and the vertical sheet-shaped light beam enters the small pipeline gas-liquid two-phase flow 9 from the other vertical direction after being reflected by the first plane mirror 5 and the second plane mirror 6; finally, the first high-speed CMOS sensor 7 and the second high-speed CMOS sensor 8 measure light intensity distribution data generated after passing through the gas-liquid two-phase flow, respectively.
As shown in fig. 2, the light intensity distribution when the tube is filled with water is a "bell-shaped" curve (a light gray curve with a triangular mark in fig. 2), and when the bubble passes through the plane irradiated by the sheet-shaped incident light, the corresponding light intensity distribution curve generates a part of "missing" part (a black curve with a square mark in fig. 2), and theoretical calculation shows that the relatively missing part of the light intensity distribution is caused by scattering of the bubble to the original incident light beam, so that the length Δ l of the light intensity distribution relative to the missing part can be extracted from the measurement result1Central offset Deltal from the missing part2And then the ratio of the two to the light intensity distribution length delta l when the pipeline is filled with water is taken as the final light intensity distribution characteristic quantity. Since the measurement involves light intensity distribution data in two mutually perpendicular directions, the characteristic quantity of the light intensity distribution in the horizontal direction is (Δ l)1h,Δl2h) The characteristic quantity of the light intensity distribution in the vertical direction is expressed as (Deltal)1v,Δl2v) And the light intensity distribution lengths when the tubes in two directions are filled with water are respectively recorded as delta lhAnd Δ lvThen the final light intensity distribution characteristic quantity can be obtained
Figure BDA0002390917410000071
Comprises the following steps:
Figure BDA0002390917410000072
in the formula (I), the compound is shown in the specification,
Figure BDA0002390917410000073
and
Figure BDA0002390917410000074
the length of the light intensity missing portion in the horizontal direction and the central offset amount,
Figure BDA0002390917410000075
and
Figure BDA0002390917410000076
the length of the light intensity missing portion in the vertical direction and the central offset amount, respectively.
As shown in FIG. 3, a rectangular plane coordinate system is established with the center of the cross section of the pipe as the origin and the horizontal and vertical directions as the abscissa and ordinate axes, and the outer radius and the inner radius of the pipe are respectively R and RcThe refractive indices of the channel, gas phase and liquid phase are respectively denoted as nc，ngAnd nlRecording the vertical distance between the light detection boundary and the center of the pipeline as L, approximately describing the gas-liquid phase distribution condition in the section of the small pipeline by adopting an ellipse with variable central position and half-axis length, recording the central coordinates of the ellipse as (x, y), and the horizontal and vertical half-axis lengths of the ellipse as a and b respectively, and establishing the gas-liquid phase distribution parameters (x, y, a, b) and the light intensity distribution characteristic quantity of the section according to the geometric optics theory
Figure BDA0002390917410000077
Phase distribution measurement model of (2):
Figure BDA0002390917410000078
the coefficients a, B, C, α, γ in the above formula (2) satisfy the following relationship:
Figure BDA0002390917410000079
the final expressions (4) to (6) of the phase distribution measurement model can be obtained by integrating the formulas (2) to (3):
Figure BDA0002390917410000081
Figure BDA0002390917410000082
Figure BDA0002390917410000083
in the formula, A1,A2,B1,B2,C1,C2,α1,α2,β1,β2,γ1,γ2To identify the model parameters, R, Rc、nc、ng、nlAnd L is an experimental parameter,
Figure BDA0002390917410000084
is a dimensionless gas-liquid phase distribution parameter of the section.
After the gas-liquid two-phase flow phase distribution measurement model is established, the established model needs to be further identified, namely, appropriate model parameters are obtained according to experimental measurement conditions. Firstly, the light intensity distribution of the phase distribution parameters (x, y, a, b) under different value conditions is obtained through theoretical calculation, and the parameters (R, R) required by the theoretical calculation are obtainedc、nc、ng、nlAnd L) were set according to experimental conditions. Then, the theoretical calculation result is preprocessed according to the parameter form required by the phase distribution measurement model, and the required light intensity distribution characteristic quantity and the corresponding phase distribution parameter are extracted. And finally, identifying the phase distribution measurement model by adopting a least square method.
According to the final expressions (4) to (6) of the established phase distribution measurement model, the following can be obtained:
P＝M-1N (7)
Figure BDA0002390917410000085
Figure BDA0002390917410000086
Figure BDA0002390917410000087
obtaining theoretical light intensity distribution of gas-liquid phase distribution parameters (x, y, a, b) of cross section under different values according to geometric optics principle, and calculating parameter R, Rc、nc、ng、nlL is the same as the experimental parameters for obtaining the light intensity distribution of the gas-liquid two-phase flow of the small pipeline; extracting the characteristic quantity of the theoretical light intensity distribution
Figure BDA0002390917410000091
Recording the gas-liquid phase distribution parameters of corresponding preset cross sections
Figure BDA0002390917410000092
Figure BDA0002390917410000092
Figure BDA0002390917410000092
1,2, …, N; n represents the number of sets of sectional gas-liquid phase distribution parameters (x, y, a, b), i.e. the number of sections;
on this basis, the loss function L (θ) is defined as:
Figure BDA0002390917410000093
Figure BDA0002390917410000094
in the formula, θ represents a set of model parameters A to be identified1,A2,B1,B2,C1,C2,α1,α2,β1,β2,γ1,γ2；
Figure BDA0002390917410000095
Calculating the preset result of the gas-liquid phase distribution parameter of the corresponding section for the ith group of theories, PiTo substitute the ith group of theoretical light intensity distribution characteristic quantitiesMeasuring results of section gas-liquid phase distribution parameters obtained after phase distribution measurement model expressions (7) to (10);
the model parameter θ to be identified in the phase distribution measurement model can be determined according to the following formula*：
Figure BDA0002390917410000096
After the parameter identification of the phase distribution measurement model is completed, the phase distribution measurement of the small pipeline gas-liquid two-phase flow at different sampling moments can be realized according to the experimental measurement result of the light intensity distribution.
Based on the established phase distribution measurement model, the gas-liquid phase distribution reconstruction of the small-pipeline gas-liquid two-phase flow can be further realized. Firstly, a group of light intensity distribution characteristic quantities can be extracted by using the light intensity distribution measurement results in two mutually perpendicular directions within a period of sampling time
Figure BDA0002390917410000097
Combining the phase distribution parameter measurement model to obtain a set of measurement results of the medium distribution parameters { (x, y, a, b)iAnd on the basis, the gas-liquid phase distribution condition in a period of sampling time can be reconstructed by combining the sampling frequency of the sampling light intensity distribution and the bubble velocity. Specifically, the reconstruction of the bubble profile is equivalent to that under the condition of known discrete points, the continuous gas-liquid phase distribution is obtained by adopting an interpolation method, namely, the interpolation is carried out under the condition of three dimensions. Firstly, a series of known ellipses are arranged in sequence, the space interval is calculated by sampling frequency (namely sampling time interval) and bubble speed, and then a curved surface is adopted to sequentially connect adjacent ellipses to obtain a three-dimensional bubble shape. Under the two-dimensional condition (observed from the side of the pipeline, only the upper edge and the lower edge of the bubble need to be considered at the moment), the simplest one-time interpolation is adopted to obtain the contour reconstruction result of the continuous bubble, and a group of gas-liquid two-phase flow continuous bubble reconstruction results completed by adopting the method are shown in the figure 4.
Based on the established phase distribution measurement model, the liquid film thickness of the gas-liquid two-phase flow of the small pipeline can be further realizedAnd (5) measuring the degree. Specifically, first, a set of light intensity distribution characteristic quantities is obtained by using the measurement result of the light intensity distribution in the horizontal direction within a period of sampling time and extracting the light intensity distribution characteristic quantities
Figure BDA0002390917410000101
Substituting the identified model parameters into the phase distribution measurement model to further obtain the gas-liquid phase distribution parameters of the cross section
Figure BDA0002390917410000102
Characteristic quantity of light intensity distribution
Figure BDA0002390917410000103
The relationship between:
Figure BDA0002390917410000104
in the formula, A1,A2,C1,C2,α1,α2,γ1,γ2As the parameters of the model to be identified,
Figure BDA0002390917410000105
gas-liquid phase distribution parameters of a dimensionless section;
solving the above formula (14) to obtain:
Figure BDA0002390917410000106
Figure BDA0002390917410000107
according to the definition of relative liquid film thickness:
Figure BDA0002390917410000108
wherein δ represents the absolute thickness of the liquid film, and D represents the inner diameter of the pipe;
the above extraction can be used according to the expressions (14) to (17)Characteristic quantity of light intensity distribution of
Figure BDA0002390917410000109
Obtaining a set of relative liquid film thickness estimates (delta/D)i}. Since a group of light intensity distribution values are collected during the process of passing a bubble or a gas bomb, and a series of liquid film thickness estimated values are calculated, the liquid film thickness of N sections (N is determined by the actual sampling frequency, the bubble speed and the size) from the head to the tail of the bubble is obtained, and finally the average value of the above measured results is taken as the liquid film thickness estimated result.
In order to verify the feasibility of the proposed method for estimating the thickness of the liquid film, a confirmatory experiment was carried out in a small transparent pipe with an inner diameter and an outer diameter of 4.82mm and 7.02mm, respectively, the gas-liquid two-phase flow adopted in the experiment consisted of air and deionized water, and the other specific experimental measurement conditions were as listed in table 1.
Table 2 shows the liquid film thickness estimation results obtained by the proposed liquid film thickness estimation method and the deviation statistical results of the liquid film thickness reference values calculated by three prior empirical formulas. It can be seen that the maximum absolute deviations of the liquid film thickness estimation result and the three existing empirical formulas are respectively 4.6 μm, 6.4 μm and 6.5 μm, and the experimental result verifies the feasibility and effectiveness of the proposed method for estimating the thickness of the gas-liquid two-phase liquid film in the small pipeline.
TABLE 1 Experimental measurement conditions
Figure BDA0002390917410000111
TABLE 2 comparison of estimated liquid film thickness with prior empirical formula
Figure BDA0002390917410000112

Claims (6)

1. A small pipeline gas-liquid two-phase flow phase distribution optical detection system is characterized in that: the device comprises a laser (1), a beam expander (2), a slit (3), a spectroscope (4), a first plane mirror (5), a second plane mirror (6), a first high-speed CMOS sensor (7), a second high-speed CMOS sensor (8) and a small pipeline gas-liquid two-phase flow (9); a light beam emitted by a laser (1) sequentially passes through a beam expander (2) and a slit (3) and then is changed into a parallel sheet-shaped light beam, and then is divided into two horizontal and vertical sheet-shaped light beams by a spectroscope (4), wherein the horizontal sheet-shaped light beam is directly and vertically incident to a small-pipeline gas-liquid two-phase flow (9), and the vertical sheet-shaped light beam is reflected by a first plane mirror (5) and a second plane mirror (6) and then is incident to the small-pipeline gas-liquid two-phase flow (9) from the other vertical direction; and finally, the first high-speed CMOS sensor (7) and the second high-speed CMOS sensor (8) are used for respectively measuring the light intensity distribution generated after the two horizontal and vertical sheet-shaped light beams pass through the gas-liquid two-phase flow.
2. A small pipeline gas-liquid two-phase flow phase distribution optical measurement method based on the geometrical optics principle is characterized by comprising the following steps:
1) obtaining the light intensity distribution of the small pipeline gas-liquid two-phase flow: the detection system of claim 1 is adopted to synchronously acquire light intensity distribution data generated after parallel flaky incident light beams with mutually perpendicular angles pass through a small pipeline gas-liquid two-phase flow;
2) extracting light intensity distribution characteristic quantity: extracting the length of the relative missing part and the central offset of the relative missing part from the light intensity distribution acquired in the step 1) by combining the light intensity distribution data when the pipeline is filled with water, and normalizing the length and the central offset as final light intensity distribution characteristic quantity;
3) establishing a small pipeline gas-liquid two-phase flow phase distribution measurement model: describing the distribution condition of gas-liquid two-phase flow in the section of the small pipeline as an ellipse with variable central position and half-axis length, recording the central coordinates of the ellipse as (x, y), and the horizontal and vertical half-axis lengths of the ellipse as a and b respectively, and establishing a phase distribution measurement model related to gas-liquid phase distribution parameters (x, y, a and b) and light intensity distribution characteristic quantity of the section;
4) identifying model parameters of the phase distribution measurement model obtained in the step 3): under the experimental parameter condition in the step 1), obtaining theoretical light intensity distribution generated by section gas-liquid phase distribution parameters (x, y, a, b) under different value conditions according to a geometrical optics principle, and extracting theoretical light intensity distribution characteristic quantity; substituting the extracted theoretical light intensity distribution characteristic quantity into the phase distribution measurement model in the step 3) to obtain a measurement result of the gas-liquid phase distribution parameters of the section; finally, obtaining model parameters of the phase distribution measurement model by adopting a least square method;
5) measuring the gas-liquid two-phase flow phase distribution of the small pipeline: obtaining light intensity distribution in two mutually perpendicular directions within a period of sampling time according to the steps 1) to 2), extracting light intensity distribution characteristic quantity, substituting the light intensity distribution characteristic quantity and the model parameters obtained by identification in the step 4) into a phase distribution measurement model, and obtaining a measurement result of gas-liquid phase distribution parameters of the section.
3. The method for optical measurement of phase distribution of a small pipeline gas-liquid two-phase flow based on the geometrical optics principle according to claim 2, wherein the step 2) is specifically as follows:
1) measuring and recording the light intensity distribution in two mutually perpendicular directions when the pipeline is filled with water, and respectively recording the light intensity distribution lengths in the two directions as delta lh、Δlv；
2) When bubbles pass through the pipeline, the corresponding light intensity distribution generates a missing part, the light intensity distribution at the moment is differed from the light intensity distribution when the pipeline is filled with water, and the length delta l of the light intensity missing part is further obtained by an edge detection method1And the central offset Deltal of the light intensity missing part2；
3) The intensity distributions in two mutually perpendicular directions are characterized by (Δ l)1h,Δl2h) And (Δ l)1v,Δl2v) Normalizing to obtain final characteristic quantity of light intensity distribution
Figure FDA0002390917400000021
Wherein:
Figure FDA0002390917400000022
in the formula (I), the compound is shown in the specification,
Figure FDA0002390917400000023
and
Figure FDA0002390917400000024
the length of the light intensity missing portion in the horizontal direction and the central offset amount,
Figure FDA0002390917400000025
and
Figure FDA0002390917400000026
the length of the light intensity missing portion in the vertical direction and the central offset amount, respectively.
4. The method for optical measurement of phase distribution of a small pipeline gas-liquid two-phase flow based on the geometrical optics principle according to claim 2, wherein the step 3) is specifically as follows:
approximately describing gas-liquid phase distribution conditions in the section of a small pipeline by adopting an ellipse with variable central position and half-axis length, recording central coordinates of the ellipse as (x, y), horizontal and vertical half-axis lengths of the ellipse as a and b respectively, establishing a plane rectangular coordinate system by taking the center of the section of the pipeline as an origin and taking the horizontal and vertical directions as horizontal and vertical coordinate axes, and recording the outer radius and the inner radius of the pipeline as R, R respectivelycThe refractive indexes of the channel, the gas phase and the liquid phase are respectively nc，ngAnd nlRecording the vertical distance between the optical detection boundary and the center of the pipeline as L; according to the geometrical optics theory, the parameters (x, y, a, b) of the gas-liquid phase distribution and the characteristic quantity of the light intensity distribution of the cross section are established
Figure FDA0002390917400000027
Phase distribution measurement model of (2):
Figure FDA0002390917400000028
Figure FDA0002390917400000031
Figure FDA0002390917400000032
in the formula, A1,A2,B1,B2,C1,C2,α1,α2,β1,β2,γ1,γ2To identify the model parameters, R, Rc、nc、ng、nlAnd L is an experimental parameter,
Figure FDA0002390917400000033
is a dimensionless gas-liquid phase distribution parameter of the section.
5. The method for optical measurement of phase distribution of a small pipeline gas-liquid two-phase flow based on the geometrical optics principle according to claim 2, wherein the step 4) is specifically as follows:
converting the phase distribution measurement model established in the step 3) into:
P＝M-1N (5)
Figure FDA0002390917400000034
Figure FDA0002390917400000035
Figure FDA0002390917400000036
obtaining theoretical light intensity distribution of gas-liquid phase distribution parameters (x, y, a, b) of cross section under different values according to geometric optics principle, and calculating parameter R, Rc、nc、ng、nlL is the same as the experimental parameters in the step 1); extracting the characteristic quantity of the theoretical light intensity distribution
Figure FDA0002390917400000037
Recording the gas-liquid phase distribution parameters of corresponding preset cross sections
Figure FDA0002390917400000038
N represents the number of sets of sectional gas-liquid phase distribution parameters (x, y, a, b), i.e. the number of sections;
on this basis, the loss function L (θ) is defined as:
Figure FDA0002390917400000039
Figure FDA00023909174000000310
in the formula, θ represents a set of model parameters A to be identified1,A2,B1,B2,C1,C2,α1,α2,β1,β2,γ1,γ2；
Figure FDA00023909174000000311
Calculating the preset result of the gas-liquid phase distribution parameter of the corresponding section for the ith group of theories, PiThe method is a measurement result of section gas-liquid phase distribution parameters obtained by substituting the ith group of theoretical light intensity distribution characteristic quantities into phase distribution measurement model expressions (5) to (8);
model parameter theta to be identified in phase distribution measurement model*Comprises the following steps:
Figure FDA0002390917400000041
6. a liquid film thickness estimation method based on the small pipeline gas-liquid two-phase flow of claim 2, characterized in that a group of light intensity distribution characteristic quantity extraction methods of the step 2) is obtained by using the light intensity distribution measurement result in the horizontal direction in a period of sampling timeCharacteristic quantity of light intensity distribution
Figure FDA0002390917400000042
Substituting the model parameters identified in the step 4) into a phase distribution measurement model to further obtain gas-liquid phase distribution parameters of the cross section
Figure FDA0002390917400000043
Characteristic quantity of light intensity distribution
Figure FDA0002390917400000044
The relationship between:
Figure FDA0002390917400000045
in the formula, A1,A2,C1,C2,α1,α2,γ1,γ2As the parameters of the model to be identified,
Figure FDA0002390917400000046
gas-liquid phase distribution parameters of a dimensionless section;
according to the definition of relative liquid film thickness:
Figure FDA0002390917400000047
wherein δ represents the absolute thickness of the liquid film, and D represents the inner diameter of the pipe;
using extracted characteristic quantity of light intensity distribution
Figure FDA0002390917400000048
A set of relative liquid film thickness estimates (delta/D) can be obtainediAnd taking the average value as the final liquid film thickness estimation result.
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