A gas-liquid two-phase flow cross-sectional imaging device

Abstract

A gas-liquid two-phase flow cross-sectional imaging device, in which a vertical conductive wire mesh and a horizontal capacitive wire mesh form a set of measurement units for measuring the projection of the gas-liquid phase distribution in the horizontal direction, and a vertical capacitive wire mesh and a horizontal conductive wire mesh form another set of measurement units for measuring the projection of the gas-liquid phase distribution in the vertical direction. By reconstructing the projections in both the horizontal and vertical directions, real-time imaging of the gas-liquid two-phase distribution can be achieved. The advantages of the present invention are that the present invention can simultaneously measure the capacitance values of all capacitive wires in contact with the wires, and accurately calculate the length of the liquid film in contact with the capacitive wires through the capacitance values, thereby greatly improving the imaging speed and accuracy.

Description

Technical Field:

[0001] The present invention belongs to the technical field of multiphase flow measurement, and particularly relates to a gas-liquid two-phase flow cross-sectional imaging device. Background Art:

[0002] Gas-liquid two-phase flows widely exist in engineering fields such as petroleum, chemical industry, energy and power. With different gas-liquid flow velocities, different distribution forms will appear in the cross-section of the gas-liquid two-phase pipe, namely, stratified flow, wavy flow, slug flow, annular flow and other flow patterns. Accurately measuring the gas-liquid phase distribution is a prerequisite for studying the multiphase flow law and monitoring the operation status of the multiphase flow system.

[0003] Currently, the measurement methods for gas-liquid phase distribution mainly include ray absorption method, conductivity probe method, and tomography method, etc. The ray method requires the use of a radioactive source, which is expensive and has radiation risks.

[0004] Chinese Patent with application number 200610042792.4, "Single-wire capacitance probe measurement system for phase holdup and phase interface in multiphase pipe flow", proposes a single-wire capacitance probe in the pipe to measure the phase fraction of the multiphase flow pipe cross-section. This invention only vertically places a capacitance probe in the pipe, so it can only measure the local phase fraction of the multiphase flow pipe and cannot represent the phase fraction of the entire pipe.

[0005] A Chinese patent with an application number (not provided in the original text) published a new type of capacitance-based gas-liquid two-phase separated flow liquid film distribution measurement device, which can accurately measure the circumferential distribution of the liquid film. However, it needs to use a cyclone to rectify the inlet flow pattern, and the obtained is the average liquid holdup, and it cannot measure the gas-liquid phase distribution in the natural state.

[0006] The tomography method can obtain the real-time gas-liquid distribution on the pipe cross-section. Among them, X-ray and γ-ray tomography technologies are the most widely used. Its detection principle is to perform imaging based on the attenuation (absorbed or scattered by the medium) generated when the radiation penetrates the measured two-phase / multiphase fluid. However, its disadvantages are poor real-time performance, high cost, and poor safety.

[0007] US Patent US6314373 proposed another new method of electrical capacitance tomography. The conductivity sensitive array consists of two layers of mutually perpendicular parallel electrodes. The electrodes are bare wires with a diameter equal to 0.12 mm. The layer spacing is 1.5 mm, and the distance between adjacent parallel electrodes is equal to 3 mm. This device uses the cross nodes (spatial intersections) formed by the horizontal and vertical electrodes to form a kind of local conductivity "probe". The conductivity between the two electrodes mainly depends on the two-phase medium distribution at the nodes. By sequentially measuring the conductivity between each cross electrode, the local phase distribution of each node area on the flow cross-section can be directly obtained without complex image reconstruction operations. The measurement accuracy of this imaging method depends on the distance between two adjacent electrodes. If the distance between the wires is reduced, the interference to the flow field will increase. If the wire spacing is increased, the measurement error will increase.

[0008] Patent 200410026282.9 disclosed a wire mesh capacitance tomography method. The wire mesh capacitance sensor performs a high-speed rotational scan on the two-phase fluid in the pipeline to obtain the projection information of the two-phase fluid in all directions on the pipeline cross-section, and through image reconstruction operations, a real-time image of the two-phase flow is obtained. However, the disadvantage of this method is that the capacitance sensor needs to rotate to achieve measurement, the measurement system is complex, and it is difficult to work continuously for a long time. In addition, the rotation of the electrodes will interfere with the flow field, and bubbles and droplets may deviate from their original positions under the action of the rotating wire mesh, thereby causing measurement errors. Summary of the Invention:

[0009] A gas-liquid two-phase flow cross-section imaging device, characterized in that it mainly includes a vertical conductive wire mesh (1), a horizontal capacitance wire mesh (2), a vertical capacitance wire mesh (3), a horizontal conductive wire mesh (4), a terminal block (5), a control and acquisition module (6), and an acquisition computer (7). The vertical conductive wire mesh (1), the horizontal capacitance wire mesh (2), the vertical capacitance wire mesh (3), and the horizontal conductive wire mesh (4) are arranged in sequence along the pipeline axis direction, and the mesh surface is kept perpendicular to the pipeline axis direction, with a spacing of 0.5 mm - 1.5 mm between each other. The wire meshes of the vertical capacitance wire mesh (3) and the horizontal conductive wire mesh (4) are all connected to the terminal block (5), the terminal block (5) is connected to the control and acquisition module (6), and the control and acquisition module (6) is connected to the acquisition computer (7);

[0010] The vertical conductive wire mesh (1) is formed by arranging a number of metal wires at equal intervals in the vertical direction. The horizontal conductive wire mesh (4) is formed by arranging a number of metal wires at equal intervals in the horizontal direction. The horizontal capacitive wire mesh (2) is formed by arranging a number of capacitive wires (10) at equal intervals in the horizontal direction. The vertical capacitive wire mesh (3) is formed by arranging a number of capacitive wires (10) at equal intervals in the vertical direction. The vertical conductive wire mesh (1), the horizontal capacitive wire mesh (2), the vertical capacitive wire mesh (3), and the horizontal conductive wire mesh (4) have the same number of wires. For the same wire mesh, the distance between the wires is also the same. The metal wire is a metal wire with an exposed surface layer, and its diameter is 0.1 - 0.2 mm. The capacitive wire (10) has a double-layer structure. The middle core wire is a conductive metal core (12), and there is an insulating layer (13) on the surface. The diameter of the conductive metal core (12) is 0.1 - 0.2 mm, and the thickness of the insulating layer (13) is 1% - 5% of the diameter of the conductive metal core (12).

[0011] The control and acquisition module (6) consists of a power supply (14), a timing control circuit (15), and a capacitance acquisition circuit (16). The power supply (14) is connected to the timing control circuit (15) to provide electrical energy for the operation of the circuit system. The timing control circuit (15) is connected to the metal wires of the vertical conductive wire mesh (1) and the horizontal conductive wire mesh (4) through a terminal block (5), and the conduction and disconnection of the circuit are controlled through the timing control circuit (15). The capacitance acquisition circuit (16) is connected to the metal wires at the upper ends of the capacitive wires (10) of the horizontal capacitive wire mesh (2) and the vertical capacitive wire mesh (3), and the capacitance values measured on each capacitive wire (10) are converted into voltages and input to the acquisition computer.

[0012] The vertical conductive wire mesh (1) and the horizontal capacitive wire mesh (2) form a set of measurement units for measuring the projection of the gas-liquid phase distribution in the horizontal direction. The vertical capacitive wire mesh (3) and the horizontal conductive wire mesh (4) form another set of measurement units for measuring the projection of the gas-liquid phase distribution in the horizontal direction. The projections of the two are reconstructed to perform real-time imaging of the gas-liquid two-phase distribution.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) There are no moving parts, the response speed is fast, and real-time measurement of the gas-liquid phase cross-sectional distribution can be achieved;

[0015] (2) The measurement resolution depends on the thickness of the insulating layer of the capacitive wire, which is far better than that of traditional grid sensors. (3) The measurement results are not affected by changes in parameters such as the salt content and temperature of the measurement medium, and can be used in a wide range of flow patterns BRIEF DESCRIPTION OF THE DRAWINGS:

[0016] Figure 1 Schematic structural diagram of the present invention

[0017] Figure 2 Schematic diagram of vertical conductive wire mesh;

[0018] Figure 3 Schematic diagram of horizontal conductive wire mesh;

[0019] Figure 4 Schematic diagram of horizontal capacitive wire mesh;

[0020] Figure 5 Schematic diagram of vertical capacitive wire mesh;

[0021] Figure 6 Schematic diagram of insulating wire structure;

[0022] Figure 7 Schematic diagram of insulating wire cross-section;

[0023] Figure 8 Principle diagram of single-wire capacitance measurement;

[0024] Figure 9 Schematic diagram of vertical measurement of gas-liquid distribution

[0025] Figure 10 Schematic diagram of horizontal measurement of gas-liquid distribution;

[0026] Figure 11 Schematic diagram of the composition of the control and acquisition module

[0027] 1. Vertical conductive wire mesh; 2. Horizontal capacitive wire mesh; 3. Vertical capacitive wire mesh; 4. Horizontal conductive wire mesh 5. Wiring terminal; 6. Control and acquisition module; 7. Acquisition computer; 8. Pipeline; 9 Wire; 10. Capacitance wire; 11. Pipe wall; 12. Conductive metal core; 13. Insulating layer; 14. Power supply; 15. Timing control circuit; 16. Capacitance acquisition circuit; 17 Liquid mass Specific implementation method:

[0028] As Figure 1 This is the structural schematic diagram of the present invention. It mainly includes a vertical conductive wire mesh 1, a horizontal capacitive wire mesh 2, a vertical capacitive wire mesh 3, a horizontal conductive wire mesh 4, a wiring terminal 5, a control and acquisition module 6, and an acquisition computer 7. The vertical conductive wire mesh 1, the horizontal capacitive wire mesh 2, the vertical capacitive wire mesh 3, and the horizontal conductive wire mesh 4 are arranged in sequence along the pipeline axis direction, and the mesh surface is perpendicular to the pipeline axis direction, with a distance of 0.5 mm - 1.5 mm between them. The mesh wires of the vertical capacitive wire mesh 3 and the horizontal conductive wire mesh 4 are all connected to the wiring terminal 5, the wiring terminal 5 is connected to the control and acquisition module 6, and the control and acquisition module 6 is connected to the acquisition computer 7.

[0029] The vertical conductive wire mesh 1 is formed by arranging a number of metal wires at equal intervals in the vertical direction. The horizontal conductive wire mesh 4 is formed by arranging a number of metal wires at equal intervals in the horizontal direction. The horizontal capacitive wire mesh 2 is formed by arranging a number of capacitive wires (10) at equal intervals in the horizontal direction. The vertical capacitive wire mesh 3 is formed by arranging a number of capacitive wires (10) at equal intervals in the vertical direction. The vertical conductive wire mesh 1, the horizontal capacitive wire mesh 2, the vertical capacitive wire mesh 3, and the horizontal conductive wire mesh 4 have the same number of wires, and for the same wire mesh, the distance between the wires is also the same.

[0030] As Figure 2 is a schematic diagram of the vertical conductive wire mesh. The vertical conductive wire mesh 1 is formed by arranging a number of metal wires at equal intervals in the vertical direction, and each metal wire is located on the same plane. As Figure 3 is a schematic diagram of the horizontal conductive wire mesh 4. The horizontal conductive wire mesh 4 is formed by arranging a number of metal wires at equal intervals in the horizontal direction, and each metal wire is located on the same plane. The wires 9 of the vertical conductive wire mesh 1 and the horizontal conductive wire mesh 4 are bare metal wires without an insulating layer 13 covering the surface.

[0031] As Figure 4 is a schematic diagram of the horizontal capacitive wire mesh. The horizontal capacitive wire mesh 2 is formed by arranging a number of capacitive wires 10 at equal intervals in the horizontal direction, and each capacitive wire 10 is located on the same plane. As Figure 5 is a schematic diagram of the vertical capacitive wire mesh 3. The vertical capacitive wire mesh 3 is formed by arranging a number of capacitive wires 10 at equal intervals in the vertical direction, and each capacitive wire 10 is located on the same plane.

[0032] As Figure 6 、 Figure 7 shown, the capacitive wire 10 is a double-layer structure, with a conductive metal core 12 in the center and a layer of insulating layer 13 evenly coated on the outside. The insulating layer 13 is a non-conductive thin film, and its thickness is less than 1.0% of the diameter of the conductive metal core 12. When the capacitive probe contacts the conductive liquid, the conductive liquid and the conductive metal core 12 form a cylindrical capacitor, and the insulating layer 13 acts as the dielectric of the capacitor. The capacitance of the cylindrical capacitor can be calculated by Equation (1):

[0033]

[0034] In the formula: L is the thickness of the liquid film contacted by the probe; d is the diameter of the capacitive wire 10; δ is the thickness of the insulating layer 13; ε is the dielectric constant of the insulating layer 13.

[0035] As can be seen from the formula, since d, δ, and ε are all constants, the liquid film thickness has a linear relationship with the probe capacitance value. In addition, since the thickness of the insulating layer 13 is much smaller than the diameter d of the conductive metal core 12, that is, δ << d, thus ln((d + 2δ) / d) is very small, so 2πε / ln((d + 2δ) / d) is very large, indicating that this method has high sensitivity. In addition, since ε is the dielectric constant of the insulating layer 13, its value depends only on the material of the insulating layer 13 and has nothing to do with the properties of the fluid itself. Therefore, the measured value only depends on the length of the liquid film in contact with the capacitance wire 10 and is not affected by fluctuations in parameters such as the ion content, temperature, and pressure of the fluid itself.

[0036] Figure 9 It is a schematic diagram of the composition of the control and acquisition module. The control and acquisition module 6 is composed of a power supply 14, a timing control circuit 15, a capacitance acquisition circuit 16, etc. The power supply 14 provides electrical energy for the control and acquisition module 6 to drive the relevant circuits to work. The timing control circuit 15 is used to control the sequential connection of the metal wires of the vertical conductive wire mesh 1 or the horizontal conductive wire mesh 4 to the circuit, thereby providing a closed circuit for measuring the capacitance value on the capacitance wire 10 intersecting with the wire. The function of the capacitance acquisition 16 module is to measure the capacitance value of each insulating wire and send it to the acquisition computer 7. The acquisition computer 7 can inversely calculate the corresponding liquid phase lengths in the horizontal and vertical directions through formula (1), and then realize the cross-sectional imaging of the gas-liquid phase distribution.

[0037] Figure 10 It is a schematic diagram of the measurement of the gas-liquid horizontal distribution. The wires 9 arranged along the vertical direction of the vertical conductive wire mesh 1 and the capacitance wires 10 arranged along the horizontal direction of the horizontal capacitance wire mesh 2 are perpendicular to each other, forming a mesh structure covering the cross-section of the measurement pipeline. During measurement, through the timing control circuit 15 of the control and acquisition module 6, each wire on the vertical conductive wire mesh 1 is sequentially connected to the measurement system to obtain the capacitance values on all the capacitance wires 10 intersecting with the current wire 9. If the wire 9 is not in contact with the liquid phase, the measured capacitance value is close to 0. If the wire 9 is in contact with a liquid mass 17, the capacitance value on the capacitance wire 10 passing through the liquid mass 17 will change, and its capacitance value is proportional to the length of the contact between the liquid mass 17 and the capacitance wire 10. If the capacitance wire 10 is not in contact with the liquid mass 17, the measured capacitance value of the capacitance wire 10 remains close to 0. Therefore, through the combination of the vertical conductive wire mesh 1 and the horizontal capacitance wire mesh 2, the accurate horizontal distribution of the gas-liquid at the pipeline interface can be obtained.

[0038] From Figure 10 Through the combination of the vertical conductive wire mesh 1 and the horizontal capacitance wire mesh 2, the accurate horizontal distribution of the liquid mass 17 can be obtained. However, for the vertical direction, its resolution depends on the distance between two capacitance wires 10, with a large error, and it needs to be improved by measuring through the combination of the horizontal conductive wire mesh 4 and the vertical capacitance wire mesh 3.

[0039] Figure 11It is a schematic diagram for measuring the vertical distribution of gas-liquid. The wires 9 arranged horizontally on the horizontal conductive wire mesh 4 and the capacitance wires 10 arranged vertically on the vertical capacitance wire mesh 3 are perpendicular to each other, forming a mesh structure covering the cross-section of the measurement pipeline. Through the timing control circuit 15 of the control and acquisition module 6, each wire on the horizontal conductive wire mesh 4 is sequentially connected to the measurement system, and the capacitance values on all the capacitance wires 10 intersecting with the conductance wire are obtained. If the wire 9 is not in contact with the liquid mass 17, the measured capacitance value is close to 0. If the wire is in contact with a certain liquid mass 17, the capacitance value on the capacitance wire 10 of the liquid mass 17 will change, and its capacitance value is proportional to the length of contact between the liquid mass 17 and the capacitance wire 10. If the capacitance wire 10 is not in contact with the liquid mass 17, the capacitance value on the capacitance wire 10 still approaches 0.

[0040] In the present invention, the vertical conductive wire mesh 1, the horizontal capacitance wire mesh 2, the vertical capacitance wire mesh 3, and the horizontal conductive wire mesh 4 are arranged in sequence along the pipeline. The vertical conductive wire mesh 1 and the horizontal capacitance wire mesh 2 form a set of measurement units for measuring the projection of the gas-liquid phase distribution in the horizontal direction. The vertical capacitance wire mesh 3 and the horizontal conductive wire mesh 4 form another set of measurement units for measuring the projection of the gas-liquid phase distribution in the horizontal direction. By reconstructing the projections in the horizontal and vertical directions, real-time imaging of the gas-liquid two-phase distribution is performed.

[0041] The present invention can simultaneously measure the capacitance values on all the capacitance wires 10 in contact with the wire 9, and accurately calculate the length of the liquid film in contact with the capacitance wire 10 through the capacitance values. Therefore, compared with the traditional method of obtaining the grid imaging of the gas-liquid distribution in the cross-section by measuring the conductance or capacitance at the intersection points of the wires, the cross-section imaging speed and accuracy are greatly improved.

Claims

1. A gas-liquid two-phase flow cross-sectional imaging device, characterized in that: It mainly includes a vertical conductive wire mesh (1), a horizontal capacitive wire mesh (2), a vertical capacitive wire mesh (3), a horizontal conductive wire mesh (4), a terminal (5), a control and acquisition module (6), and an acquisition computer (7). The vertical conductive wire mesh (1), the horizontal capacitive wire mesh (2), the vertical capacitive wire mesh (3), and the horizontal conductive wire mesh (4) are arranged in sequence along the pipeline axis direction, with the mesh surfaces perpendicular to the pipeline axis direction, and the distance between each other is 0.5 mm - 1.5 mm. The wire meshes of the vertical capacitive wire mesh (3) and the horizontal conductive wire mesh (4) are all connected to the terminal (5), the terminal (5) is connected to the control and acquisition module (6), and the control and acquisition module (6) is connected to the acquisition computer (7). The vertical conductive wire mesh (1) is formed by arranging a number of metal wires at equal intervals in the vertical direction. The horizontal conductive wire mesh (4) is formed by arranging a number of metal wires at equal intervals in the horizontal direction. The horizontal capacitive wire mesh (2) is formed by arranging a number of capacitive wires (10) at equal intervals in the horizontal direction. The vertical capacitive wire mesh (3) is formed by arranging a number of capacitive wires (10) at equal intervals in the horizontal direction. The vertical conductive wire mesh (1), the horizontal capacitive wire mesh (2), the vertical capacitive wire mesh (3), and the horizontal conductive wire mesh (4) have the same number of wires, and for the same wire mesh, the distance between the wires is also the same. The metal wire is a metal wire with an exposed surface layer, and its diameter is 0.1 - 0.2 mm. The capacitive wire (10) has a double-layer structure, with a conductive metal core (12) in the middle and an insulating layer (13) on the surface. The diameter of the conductive metal core (12) is 0.1 - 0.2 mm, and the thickness of the insulating layer (13) is 1% - 5% of the diameter of the conductive metal core (12). The control and acquisition module (6) consists of a power supply (14), a timing control circuit (15), and a capacitance acquisition circuit (16). The power supply (14) is connected to the timing control circuit (15) to provide electrical energy for the operation of the circuit system. The timing control circuit (15) is connected to the metal wires of the vertical conductive wire mesh (1) and the horizontal conductive wire mesh (4) through the terminal (5), and controls the on and off of the circuit through the timing control circuit (15). The capacitance acquisition circuit (16) is connected to the metal wires at the upper ends of the capacitive wires (10) of the horizontal capacitive wire mesh (2) and the vertical capacitive wire mesh (3), and converts the measured capacitance values of each capacitive wire (10) into voltage and inputs it into the acquisition computer. The vertical conductive wire mesh (1) and the horizontal capacitive wire mesh (2) form a set of measurement units for measuring the horizontal direction gas-liquid phase distribution projection. The vertical capacitive wire mesh (3) and the horizontal conductive wire mesh (4) form another set of measurement units for measuring the horizontal direction gas-liquid phase distribution projection, reconstruct the projections of the two, and perform real-time imaging of the gas-liquid two-phase distribution.

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