CN111610229B - Gas-liquid two-phase flow monitoring device, system and method - Google Patents

Abstract

The invention discloses a gas-liquid two-phase flow monitoring device, a system and a method, comprising a main control module, an excitation module, a silk screen sensor and a receiving module; the silk screen sensor is respectively and electrically connected with the excitation module and the receiving module; the excitation module comprises a polarity conversion circuit, a gating circuit and an amplifying circuit, and the polarity conversion circuit and the gating circuit are respectively and electrically connected with the main control module; the gating circuit is also electrically connected with the polarity conversion circuit and the amplifying circuit respectively; the receiving module comprises a transimpedance amplifying circuit, a first digital potentiometer circuit, a voltage amplifying circuit, a second digital potentiometer circuit and a signal acquisition circuit; the first digital potentiometer circuit is electrically connected with the transimpedance amplifying circuit and the main control module respectively; the voltage amplifying circuit is electrically connected with the transimpedance amplifying circuit; the second digital potentiometer circuit is electrically connected with the voltage amplifying circuit and the main control module respectively; the signal acquisition circuit is respectively and electrically connected with the voltage amplifying circuit and the main control module. The invention can realize the rapid and accurate measurement of the gas-liquid two-phase flow.

Description

Gas-liquid two-phase flow monitoring device, system and method

Technical Field

The present invention belongs to the technical field of gas-liquid two-phase flow monitoring, and in particular relates to a gas-liquid two-phase flow monitoring device, system and method.

Background Art

The measurement of gas-liquid two-phase flow velocity, flow rate, flow pattern, pressure, and phase holdup parameters can generally be summarized into the following three categories:

① Direct measurement technology

Direct measurement technology is mainly used to measure specific two-phase flow parameters, including flow pattern, flow velocity, gas content, etc. Among them, in the measurement of gas content, the traditional method is to use the fast closing valve method, which will seriously interfere with the flow field and has high requirements for the control of the threshold. With the continuous development of scientific and technological progress, more and more new measurement methods are applied to the flow parameter measurement of gas-liquid two-phase flow, such as electrical method, ray method, optical method, etc.

The optical method mainly uses the principles of scattering and attenuation of light when it passes through two-phase fluids for measurement. The light changes are obtained by using optical sensors, and the relevant parameters of the gas-liquid two-phase flow are measured based on the output signal of the sensor. This method can measure parameters such as bubble size and velocity in gas-liquid two-phase flow. The optical method is a typical non-contact measurement, but there are problems such as high cost of the data acquisition system and high requirements for the measurement environment. At present, the optical method is difficult to apply and promote in industry.

The ray method mainly uses the principle of attenuation or Compton scattering of rays after passing through the medium for measurement. Since different media have different attenuation or scattering conditions for rays, by detecting the change in the radiation intensity of the rays after passing through the measured medium, the distribution information of the measured medium can be obtained, and then the flow type can be determined. The ray method is a non-contact measurement, but the protection cost is high when using it.

The electrical method is a widely used and mature method. Based on the principle of obvious difference in conductivity or dielectric constant of gas-liquid two-phase flow, a sensor is used to convert non-electrical measured information changes into electrical signal changes, and the measured information is obtained by collecting electrical signals. According to different principles, it can be divided into conductivity measurement method and capacitance measurement method. For example, the capacitance-based cavitation meter can measure bubble velocity, which is mainly used for the measurement of tiny channels. The conductivity-based probe can measure local gas content, bubble size, interface concentration, bubble apparent velocity and other related parameters. Due to its simple structure, low cost and good response characteristics, the electrical method plays an important role in the field of two-phase flow detection.

②Indirect measurement technology (soft measurement)

Indirect measurement technology is to apply various modern information processing technologies to the field of gas-liquid two-phase flow, establish the relationship between easy-to-measure process variables and process variables to be measured, and indirectly realize the measurement of process variables to be measured through various theoretical calculations and estimation methods. This method is based on simple measurement parameters to estimate difficult measurements, and can be used to solve the problem of parameter measurement of nonlinear and complex two-phase flow systems. In the field of multiphase flow measurement, commonly used processing methods mainly include neural networks, pattern recognition, spectrum analysis, wavelet analysis, spectrum analysis, fuzzy control soft measurement and other methods. This type of method is often used in a cross- and fusion manner, and is mainly used for parameter measurement and two-phase flow mechanism research.

③Visual measurement technology

Visual measurement technology is a two-dimensional or three-dimensional imaging measurement of gas-liquid two-phase flow, which can extract characteristic parameters from the measurement results. It mainly includes particle image velocimetry, high-speed camera method, process tomography (PT), etc.

Particle image velocimetry is a measurement method based on flow field display and image analysis technology, mainly used for measuring fluid velocity field. This method has low image clarity due to uneven distribution of tracer particles, image noise such as camera noise and optical noise, and the growth, aggregation, and breakage of bubbles during the flow process.

High-speed photography uses a high-speed camera to quickly take pictures to obtain images, and uses image processing algorithms to extract gas-liquid two-phase flow information in the images. This method can only be used for measurements in transparent pipes. In addition, the amount of image information collected by high-speed cameras is too much, and image analysis and processing are relatively difficult.

Therefore, it is necessary to develop a new gas-liquid two-phase flow monitoring device, system and method.

Summary of the invention

The object of the present invention is to provide a gas-liquid two-phase flow monitoring device, system and method, which can realize rapid and accurate measurement of the gas-liquid two-phase flow.

In a first aspect, the gas-liquid two-phase flow monitoring device of the present invention comprises a main control module, an excitation module, a wire mesh sensor, a receiving module, a communication module and a power module; the main control module is electrically connected to the excitation module, the receiving module, the communication module and the power module respectively; the wire mesh sensor is electrically connected to the excitation module and the receiving module respectively;

The incentive module comprises:

A polarity conversion circuit for converting a unipolar square wave signal generated by the main control module into a bipolar square wave excitation signal, the polarity conversion circuit being electrically connected to the main control module;

A gating circuit for realizing continuous sequential multiplexing of bipolar square wave excitation signals, the gating circuit being electrically connected to the main control module and the polarity conversion circuit respectively;

and an amplifier circuit for amplifying the signal output by the gating circuit, the amplifier circuit being electrically connected to the gating circuit and the excitation end of the wire mesh sensor respectively;

The receiving module comprises:

A trans-resistance amplifier circuit for converting a received current signal into a voltage signal, the trans-resistance amplifier circuit being electrically connected to an output terminal of the wire mesh sensor;

A first digital potentiometer circuit for adjusting the gain of the trans-impedance amplifier circuit, the first digital potentiometer circuit being electrically connected to the trans-impedance amplifier circuit and the main control module respectively;

A voltage amplifier circuit for amplifying a voltage signal output by the trans-impedance amplifier circuit, the voltage amplifier circuit being electrically connected to the trans-impedance amplifier circuit;

A second digital potentiometer circuit for adjusting the gain of the voltage amplifier circuit, the second digital potentiometer circuit being electrically connected to the voltage amplifier circuit and the main control module respectively;

And a signal acquisition circuit for acquiring the voltage signal amplified by the voltage amplifier circuit, the signal acquisition circuit is electrically connected to the voltage amplifier circuit and the main control module respectively.

Further, the main control module adopts the STM32 minimum system, and the STM32 minimum system is connected to the input port of the excitation module through an IO pin with a timer function, and the timer register is configured to realize the square wave signal output, so as to drive the excitation module;

The STM32 minimum system is electrically connected to the first digital potentiometer circuit and the second digital potentiometer circuit through the SPI interface, respectively, and the gain multiple of the mutual resistance amplifier circuit is regulated by adjusting the resistance value of the first digital potentiometer circuit, and the gain multiple of the voltage amplifier circuit is regulated by adjusting the resistance value of the second digital potentiometer circuit;

The STM32 minimum system is electrically connected to the signal acquisition circuit through the FSMC interface to achieve efficient acquisition of multi-channel data;

The STM32 minimum system is electrically connected to the communication module via the RMII interface to realize the network communication function between the embedded end and the computer end.

Furthermore, the polarity conversion circuit includes a capacitor C32, a capacitor C35 and a resistor R12, one end of the capacitor C32 is electrically connected to the main control module, the other end of the capacitor C32 is grounded after passing through the resistor R12, and the connection point between the capacitor C32 and the resistor R12 is also grounded through the capacitor C35.

Further, the gating circuit includes an analog switch U7, resistors R4 to R11, capacitors C7, C9, and C22 to C29;

The analog switch U7 adopts the MAX4581CEE+ chip, and the 7th pin of the analog switch U7 is grounded through the capacitor C9; the 16th pin of the analog switch U7 is grounded through the capacitor C7; the 13th pin of the analog switch U7 is grounded through the resistor R4, and the capacitor C22 is connected in parallel with the resistor R4; the 14th pin of the analog switch U7 is grounded through the resistor R5, and the capacitor C23 is connected in parallel with the resistor R5; the 15th pin of the analog switch U7 is grounded through the resistor R6, and the capacitor C24 is connected in parallel with the resistor R6; Pin 12 of the analog switch U7 is grounded via resistor R7, and capacitor C25 is connected in parallel with resistor R7; pin 1 of the analog switch U7 is grounded via resistor R8, and capacitor C26 is connected in parallel with resistor R8; pin 5 of the analog switch U7 is grounded via resistor R9, and capacitor C27 is connected in parallel with resistor R9; pin 2 of the analog switch U7 is grounded via resistor R10, and capacitor C28 is connected in parallel with resistor R10; pin 4 of the analog switch U7 is grounded via resistor R11, and capacitor C29 is connected in parallel with resistor R11;

Pin 3 of the analog switch U7 is electrically connected to the polarity conversion circuit;

Pins 12 to 15 of the analog switch U7 are also electrically connected to the amplifier circuit respectively.

In a second aspect, the gas-liquid two-phase flow monitoring system of the present invention comprises a computer terminal and the gas-liquid two-phase flow monitoring device of the present invention;

The excitation module of the gas-liquid two-phase flow monitoring device adopts a cyclic scanning strategy, and sends a bipolar voltage excitation signal to an electrode wire at the excitation end of the wire mesh sensor in sequence each time. All response signals at the receiving end are converted from current to voltage, amplified by voltage, and processed by AD conversion, so that the data collection of one electrode wire in the wire mesh sensor is completed; then the excitation, reception, and processing are performed again, and so on, until the excitation of all electrode wires in the wire mesh sensor is completed, thereby obtaining a voltage matrix that can reflect the two-dimensional distribution of the conductivity at the cross section of the measured flow channel, that is, obtaining the phase state information of a complete cross-sectional point, and sending the phase state information to the computer end in real time through the communication module;

The computer terminal is configured to: perform data analysis, data storage and cross-sectional data imaging processing on the phase state information of each complete cross-sectional point received, display the two-phase distribution characteristics of the flow field cross section, and calculate and display the cross-sectional gas content.

Furthermore, in the cross-sectional data imaging process, the intersection points of the screen sensor are taken as pixel points, the measured values are taken as corresponding pixel values, an interpolation algorithm is used to increase the pixel points of the image, and a median filter is used to filter the image.

Furthermore, the cubic spline interpolation method is used to increase the pixel points of the image.

Further, the method for calculating the cross-sectional air void fraction is as follows:

Convert the voltage value matrix into a gas phase gas fraction matrix:

Wherein, ε(i,j,k) represents the local gas content at coordinate (i,j) in the k-th frame data, u _gas (i,j) represents the calibration voltage value when all the measuring points at coordinate (i,j) are passed by gas, u _liquid (i,j) represents the calibration voltage value when all the measuring points at coordinate (i,j) are passed by liquid, and u(i,j,k) represents the voltage value of the measuring point at coordinate (i,j) in the k-th frame data;

Calculate the cross-sectional air content:

为截面含气率；a_i,j表示坐标为(i,j)的测点的测量值对应的权重值；in,

is the cross-sectional gas content; a _i,j represents the weight value corresponding to the measured value of the measuring point with coordinates (i, j);

Where A _sensor represents the total area of the circular cross section, and A _i,j represents the effective area corresponding to ε _i,j .

Furthermore, the computer terminal is also configured to: view historical data, including table display and view display; wherein the front view and side view in the view use data projection method to reconstruct the view information of the measuring pipeline; the front view and side view are used to display the position of the bubble relative to the pipe wall.

In a third aspect, the gas-liquid two-phase flow monitoring method of the present invention adopts the gas-liquid two-phase flow monitoring system of the present invention, and the method comprises the following steps:

Step 1: Install the wire mesh sensor on the section perpendicular to the flow direction;

Step 2: The excitation module adopts a cyclic scanning strategy, and sends a bipolar voltage excitation signal to an electrode wire at the excitation end of the wire mesh sensor in sequence each time. All response signals at the receiving end are converted from current to voltage, amplified, and processed by AD conversion, thus completing the data acquisition of one electrode wire in the wire mesh sensor; then excitation, receiving, and processing are performed again, and so on, until the excitation of all electrode wires in the wire mesh sensor is completed, thereby obtaining a voltage matrix that can reflect the two-dimensional distribution of the conductivity at the cross section of the measured flow channel, that is, obtaining the phase state information of a complete cross-sectional point, and sending the phase state information to the computer end in real time through the communication module;

Step 3: The computer performs data analysis, data storage and cross-sectional data imaging processing on the phase state information of each complete cross-sectional point received, displays the two-phase distribution characteristics of the flow field cross section, and calculates and displays the cross-sectional gas content.

The present invention has the following advantages: the wire mesh sensor imaging technology has the advantages of simple principle, low R&D cost, fast imaging speed, multiple measurable parameters and uniform spatial resolution. The gas-liquid two-phase flow monitoring system based on the wire mesh sensor can realize fast and accurate measurement of the gas-liquid two-phase flow, and has the characteristics of wide dynamic measurement range, low cost and small volume. The gas-liquid two-phase flow monitoring based on the wire mesh sensor belongs to contact measurement, so compared with indirect measurement, it has the advantages of simple equipment, low cost and strong anti-interference ability. However, compared with the traditional contact measurement, this new measurement method has a small contact surface and the flow field is disturbed very little. This device is suitable for various occasions such as laboratories and industries, and has the advantage of wide application. Due to the realization of self-adaptation, the present invention can accurately measure the conductivity ≤0.1μS/cm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a functional block diagram of the present embodiment;

FIG2 is a circuit diagram of a main control module in this embodiment;

FIG3 is a circuit diagram of a polarity conversion circuit in this embodiment;

FIG4 is a circuit diagram of a gating circuit in this embodiment;

FIG5 is a circuit diagram of an amplifier circuit in this embodiment;

FIG6 is a circuit diagram of a mutual resistance amplifier circuit and a first digital potentiometer circuit in this embodiment;

FIG7 is a circuit diagram of a voltage amplifier circuit and a second digital potentiometer circuit in this embodiment;

FIG8 is a circuit diagram of a signal acquisition circuit in this embodiment;

FIG9 is a circuit diagram of a communication module in this embodiment;

FIG10 is an architecture diagram of the device-side software and the computer-side software in this embodiment;

FIG11 is a flowchart of reconstructing an image display in this embodiment;

FIG12 is a schematic diagram of the region of the measured values in this embodiment;

FIG13 is a flow chart showing the cross-sectional gas content rate in this embodiment;

FIG14 is a schematic diagram of data projection of one frame in this embodiment;

FIG15 is a static measurement imaging effect diagram of this embodiment;

FIG16 is a cross-sectional imaging effect at different bubble sizes in this embodiment;

In the figure: 1. main control module, 2. excitation module, 2a. polarity conversion circuit, 2b. selection circuit, 2c. amplifier circuit, 3. silk screen sensor, 4. receiving module, 4a. mutual resistance amplifier circuit, 4b. first digital potentiometer circuit, 4c. voltage amplifier circuit, 4d. second digital potentiometer circuit, 4e. signal acquisition circuit, 5. power module, 6. communication module, 7. computer terminal.

DETAILED DESCRIPTION

The present invention will be further described below in conjunction with the accompanying drawings.

As shown in Figure 1, a gas-liquid two-phase flow monitoring device includes a main control module 1, an excitation module 2, a wire mesh sensor 3, a receiving module 4, a communication module 6 and a power module 5; the main control module 1 is electrically connected to the excitation module 2, the receiving module 4, the communication module 6 and the power module 5 respectively; the wire mesh sensor 3 is electrically connected to the excitation module 2 and the receiving module 4 respectively.

As shown in FIG1 , in this embodiment, the excitation module 2 mainly realizes the sequential control of the bipolar voltage excitation signal of the multi-channel stable amplitude, so as to complete the orderly excitation of the wire mesh sensor 3. The excitation module 2 includes a polarity conversion circuit 2a, a gating circuit 2b and an amplifier circuit 2c. Among them, the polarity conversion circuit 2a is composed of a high-pass filter circuit, which is used to convert the unipolar square wave signal generated by the main control module 1 into a bipolar square wave excitation signal, and the polarity conversion circuit 2a is electrically connected to the main control module 1. The gating circuit 2b is composed of a multiplexed analog switch, which is used to realize the continuous sequence multiplexing of the bipolar square wave excitation signal, and the gating circuit 2b is electrically connected to the main control module 1 and the polarity conversion circuit 2a respectively. The amplifier circuit 2c is mainly composed of a constant gain amplifier chip, which is used to amplify the signal output by the gating circuit 2b, enhance the driving ability of the excitation signal and reduce the influence of the load, and the amplifier circuit 2c is electrically connected to the gating circuit 2b and the excitation end of the wire mesh sensor 3 respectively.

In this embodiment, a bipolar square wave voltage signal is selected to excite the transmitting electrode. Common voltage excitations include DC signals, bipolar sine wave signals, and bipolar square wave signals. If the transmitting electrode is activated by a DC voltage, polarization will occur in the dielectric electrode, thereby introducing errors in the conductivity measurement. In addition, if the transmitting electrode is activated by an alternating sinusoidal wave voltage signal, the circuit will require a complex and time-consuming demodulation process, thereby reducing the speed of system data acquisition. The bipolar square wave voltage signal can protect the electrode from polarization because its two adjacent half-cycles have the same amplitude and opposite polarity. In the half cycle of the measurement, the transmitting electrode can be regarded as being excited by a constant DC voltage signal, and the receiving electrode does not need to undergo more complex signal conditioning processes such as amplification, filtering, and rectification, so a bipolar voltage excitation signal is selected to drive the excitation module.

As shown in FIG1 , in this embodiment, the receiving module 4 is mainly used to realize the quantitative acquisition of multi-channel weak current response signals; the receiving module 4 includes a mutual resistance amplifier circuit 4a, a first digital potentiometer circuit 4b, a voltage amplifier circuit 4c, a second digital potentiometer circuit 4d and a signal acquisition circuit 4e. The mutual resistance amplifier circuit 4a is used to convert the received current signal into a voltage signal, and the mutual resistance amplifier circuit 4a is electrically connected to the output end of the wire mesh sensor 3. The first digital potentiometer circuit 4b is used to adjust the gain of the mutual resistance amplifier circuit 4a, and the first digital potentiometer circuit 4b is electrically connected to the mutual resistance amplifier circuit 4a and the main control module 1 respectively. The voltage amplifier circuit 4c is used to amplify the voltage signal output by the mutual resistance amplifier circuit 4a, and the voltage amplifier circuit 4c is electrically connected to the mutual resistance amplifier circuit 4a. The second digital potentiometer circuit 4d is used to adjust the gain of the voltage amplifier circuit 4c, and the second digital potentiometer circuit 4d is electrically connected to the voltage amplifier circuit 4c and the main control module 1 respectively. The signal acquisition circuit 4e is used to acquire the voltage signal amplified by the voltage amplifier circuit 4c. The signal acquisition circuit 4e is electrically connected to the voltage amplifier circuit 4c and the main control module 1 respectively.

In this embodiment, the gain control of the amplifier circuit is realized by changing the feedback resistance by using a digital potentiometer. The mutual resistance amplifier circuit can avoid the integral error caused by the operational amplifier input offset voltage, input bias current and offset current, and also avoid the error caused by the capacitor leakage current, and avoid the measurement error of nano-scale conductivity, thereby effectively improving the measurement accuracy.

As shown in Figure 2, in this embodiment, the main control module 1 adopts the STM32 minimum system, and the STM32 minimum system is connected to the input port of the excitation module 2 through the IO pin with a timer function, and the timer register is configured to realize the square wave signal output, and the excitation module 2 is driven. The STM32 minimum system is electrically connected to the first digital potentiometer circuit 4b and the second digital potentiometer circuit 4d through the SPI interface, respectively, and the gain multiple of the mutual resistance amplifier circuit 4a is regulated by adjusting the resistance value of the first digital potentiometer circuit 4b, and the gain multiple of the voltage amplifier circuit 4c is regulated by adjusting the resistance value of the second digital potentiometer circuit 4d. The STM32 minimum system is electrically connected to the signal acquisition circuit 4e through the FSMC interface to achieve efficient acquisition of multi-channel data. The STM32 minimum system is electrically connected to the communication module 6 through the RMII interface to realize the network communication function between the embedded end (i.e., the device end) and the computer end.

As shown in Figure 3, in this embodiment, the polarity conversion circuit 2a includes a capacitor C32, a capacitor C35 and a resistor R12, one end of the capacitor C32 is electrically connected to the main control module 1, the other end of the capacitor C32 is grounded after passing through the resistor R12, and the connection point between the capacitor C32 and the resistor R12 is also grounded through the capacitor C35.

As shown in Figure 4, in this embodiment, the gating circuit 2b includes an analog switch U7, resistors R4 to R11, capacitors C7, capacitors C9, capacitors C22 to C29. The analog switch U7 adopts the MAX4581CEE+ chip, and the 7th pin of the analog switch U7 is grounded after capacitor C9. The 16th pin of the analog switch U7 is grounded after capacitor C7. The 13th pin of the analog switch U7 is grounded after resistor R4, and capacitor C22 is connected in parallel with resistor R4. The 14th pin of the analog switch U7 is grounded after resistor R5, and capacitor C23 is connected in parallel with resistor R5. The 15th pin of the analog switch U7 is grounded after resistor R6, and capacitor C24 is connected in parallel with resistor R6. The 12th pin of the analog switch U7 is grounded after resistor R7, and capacitor C25 is connected in parallel with resistor R7. The 1st pin of the analog switch U7 is grounded after resistor R8, and capacitor C26 is connected in parallel with resistor R8. Pin 5 of the analog switch U7 is grounded via resistor R9, and capacitor C27 is connected in parallel with resistor R9. Pin 2 of the analog switch U7 is grounded via resistor R10, and capacitor C28 is connected in parallel with resistor R10. Pin 4 of the analog switch U7 is grounded via resistor R11, and capacitor C29 is connected in parallel with resistor R11. Pin 3 of the analog switch U7 is electrically connected to the polarity conversion circuit 2a. Pins 12 to 15 of the analog switch U7 are also electrically connected to the amplifier circuit 2c, respectively.

As shown in FIG5 , in this embodiment, the amplifier circuit 2c includes an amplifier U2, a capacitor C1 and a capacitor C5. The amplifier U2 uses a max4022eee chip, and the 4th pin of the amplifier U2 is grounded through the capacitor C1, and the 13th pin of the amplifier U2 is grounded through the capacitor C5. The 3rd pin, the 4th pin, the 12th pin and the 14th pin of the amplifier U2 are electrically connected to the selection circuit 2b respectively.

As shown in Figure 6, the mutual resistance amplifier circuit 4a includes an operational amplifier U21, a capacitor C108, a capacitor C120, a capacitor C124 and a capacitor C128. The operational amplifier U21 adopts an OPA4132UA chip, one end of the capacitor C108 is connected to pin 1 of the operational amplifier U21, and the other end of the capacitor C108 is connected to pin 2 of the operational amplifier U21. One end of the capacitor C120 is connected to pin 6 of the operational amplifier U21, and the other end of the capacitor C120 is connected to pin 7 of the operational amplifier U21. One end of the capacitor C124 is connected to pin 9 of the operational amplifier U21, and the other end of the capacitor C124 is connected to pin 8 of the operational amplifier U21. One end of the capacitor C128 is connected to pin 13 of the operational amplifier U21, and the other end of the capacitor C128 is connected to pin 14 of the operational amplifier U21.

As shown in FIG7 , the voltage amplifier circuit 4c includes an operational amplifier U22 and a peripheral circuit, wherein the peripheral circuit includes a capacitor C109, a capacitor C121, a capacitor C125, a capacitor C129, a resistor R32, a resistor R34, a resistor R36, a resistor R38, a resistor R40, a resistor R45, and a resistor R46. The operational amplifier U22 adopts an OPA4820IPWT chip, one end of the capacitor C109 is connected to pin 1 of the operational amplifier U22, and the other end of the capacitor C109 is connected to pin 2 of the operational amplifier U22. One end of the capacitor C121 is connected to pin 6 of the operational amplifier U22, and the other end of the capacitor C121 is connected to pin 7 of the operational amplifier U22. One end of the capacitor C125 is connected to pin 9 of the operational amplifier U22, and the other end of the capacitor C125 is connected to pin 8 of the operational amplifier U22. One end of the capacitor C129 is connected to the pin 13 of the operational amplifier U22, and the other end of the capacitor C129 is connected to the pin 14 of the operational amplifier U22.

As shown in FIG. 6 , in this embodiment, the first digital potentiometer circuit 4 b includes a digital potentiometer U19 and peripheral circuits, and the model of the digital potentiometer U19 is AD5263BRZ200.

As shown in FIG. 7 , in this embodiment, the second digital potentiometer circuit 4 d includes a digital potentiometer U20 and peripheral circuits, and the model of the digital potentiometer U20 is AD5263BRZ200.

As shown in FIG. 8 , in this embodiment, the signal acquisition circuit 4 e includes an analog-to-digital converter U4 and peripheral circuits. The model of the analog-to-digital converter U4 is AD7606BSTZ.

As shown in FIG. 9 , in this embodiment, the communication module 6 is mainly composed of a network communication circuit. The communication module 6 includes a PHY chip and peripheral circuits. The model of the PHY chip is DP838481VV.

In this embodiment, the power supply module 5 is composed of a voltage stabilizing circuit, which mainly provides different power supply voltages inside the system.

In this embodiment, a gas-liquid two-phase flow monitoring system includes a computer terminal and a gas-liquid two-phase flow monitoring device as described in this embodiment.

The excitation module of the gas-liquid two-phase flow monitoring device adopts a cyclic scanning strategy, and sends a bipolar voltage excitation signal to an electrode wire at the excitation end of the wire mesh sensor in sequence each time. All response signals at the receiving end are converted from current to voltage, amplified by voltage, and processed by AD conversion, thereby completing the data acquisition of one electrode wire in the wire mesh sensor; then the excitation, reception, and processing are performed again, and so on, until the excitation of all electrode wires in the wire mesh sensor is completed, thereby obtaining a voltage matrix that can reflect the two-dimensional distribution of the conductivity at the cross section of the measured flow channel, that is, obtaining the phase state information of a complete cross-sectional point, and sending the phase state information to the computer end in real time through the communication module.

The computer terminal is configured to: perform data analysis, data storage and cross-sectional data imaging processing on the phase state information of each complete cross-sectional point received, display the two-phase distribution characteristics of the flow field cross section, and calculate and display the cross-sectional gas content.

In this embodiment, in order to facilitate the user to control the equipment and view information such as measurement data, a software is developed for system parameter setting and imaging display, and the UDP protocol is selected to achieve rapid interaction between the gas-liquid two-phase flow monitoring device and the computer.

As shown in Figure 10, the software on the device side mainly completes the quantitative acquisition of voltage signals at each measuring point in the measured area and the rapid transmission of the result data. In order to achieve the above functions, it is necessary to implement analog switch control, signal acquisition and processing, digital potentiometer control, parameter storage and network communication functions on the embedded platform.

(1) Analog switch control: A binary weighted method is used to control the orderly switching of analog switches to achieve time-division multiplexing of excitation signals.

(2) Signal acquisition and processing: The STM32 minimum system is used to drive the acquisition chip to achieve rapid quantitative acquisition of voltage signals at each measuring point in the measured area.

(3) Digital potentiometer control: Sending commands via the SPI bus to adjust the output resistance of the digital potentiometer (i.e., the first digital potentiometer circuit and the second digital potentiometer circuit) to achieve gain setting of the receiving-end programmable amplifier (i.e., the mutual resistance amplifier circuit and the voltage amplifier circuit).

(4) Parameter saving: Considering that the system needs to set the gain of the programmable amplifier after each startup, in order to reduce the user's repeated setting work, the parameter saving function needs to be completed. The system automatically saves the latest op amp gain information. When the system is started next time, it completes the op amp gain setting by reading the saved op amp gain information.

(5) Network communication: Considering the limited storage capacity of the embedded platform, in order to minimize the memory usage of communication, the network communication function is implemented by transplanting the lightweight LWIP protocol stack on the embedded end, and the UDP method is used to achieve fast upload of measurement data.

As shown in Figure 10, the computer software design mainly completes the conversion of the voltage information received from each measuring point, data storage, gas content parameter extraction, cross-sectional image reconstruction and other operations, as well as system parameter settings and historical data viewing. In order to achieve this function, it is necessary to implement system parameter settings, cross-sectional imaging display, gas content display, historical data display and network communication functions in the computer software.

(1) Cross-sectional imaging display: In order to allow users to more intuitively see the cross-sectional phase distribution of the screen sensor at 3 locations, 30 frames are extracted from the measurement data per second for imaging display. The corresponding interpolation algorithm is used to increase the number of pixels in the image and improve the image resolution. The median filter algorithm is used to smooth the image, thereby optimizing the image display quality.

(2) Display of cross-sectional gas content: In order to enable users to more accurately understand the gas-liquid phase information of the pipeline cross section, the cross-sectional gas content parameters are extracted from the measured data and the extracted parameters are displayed.

(3) Data preservation: In order to facilitate the viewing and secondary development of measurement data, the system should have the function of saving measurement data in the form of TXT documents.

(4) System parameter setting: In order to better meet the monitoring system's measurement of various gas-liquid two-phase flows, the system needs to have a system parameter setting function. According to different application scenarios, two setting modes are provided: custom parameter setting mode and adaptive parameter setting mode. The custom parameter setting mode is mainly used for gain debugging of specified channels, and the adaptive parameter setting mode is mainly used for different gas-liquid two-phase flow measurements. In order to improve the efficiency of parameter adjustment of the system when measuring different media, an adaptive algorithm is designed on the embedded end.

(5) Historical data display: In order to facilitate users to view historical data, the system should have the function of displaying historical data in the form of tables and images. In the image display part, a data projection method is designed.

(6) Network communication function: In order to realize the rapid data exchange between the computer and the device, the computer software adopts Socket programming based on UDP protocol. Considering the standardization of the interactive data, a communication protocol is also designed.

In this embodiment, the intersection of the wire mesh sensor is taken as the pixel point, and the measured value is the corresponding pixel value. Direct imaging display can reflect the phase distribution characteristics of the measured area. However, the total number of measuring points of the wire mesh sensor is limited, and there is a certain distance between the measuring points, so the resolution of direct imaging is not high. In order to optimize the image display quality, it is necessary to use a corresponding interpolation algorithm to increase the pixel points of the image to improve the resolution of the image. In order to smooth the edge of the image, the image is filtered by a median filter. Therefore, in this embodiment, the image reconstruction algorithm adopts a method combining an interpolation algorithm with a median filter algorithm. At present, commonly used interpolation algorithms include the nearest neighbor method, bilinear interpolation method, bicubic interpolation method, cubic spline interpolation method, etc. In this embodiment, the cubic spline interpolation method is used to increase the pixel points of the image.

In this embodiment, the following is an explanation using a 16x16 screen sensor as an example. The cubic spline interpolation method also considers the relationship between the point to be interpolated and the surrounding 16 adjacent points, and adjusts S(w) on the basis of the bicubic interpolation method, where S(w) is a cubic spline curve, which is a piecewise function. Assume a＝w ₀ ＜w ₁ ＜…＜ _wn-1 ＜ _wn ＝b, given nodes. If the function S(w) is a cubic polynomial on each small interval [ _wi ,wi ₊₁ ] on the domain [a,b], and satisfies S( _wi )＝ _fi (Note: _fi is a polynomial) and S(w), S'(w) (S'(w) is the derivative of S(w)), S”(w)(S”(w) is the derivative of S'(w)) are continuous on [a,b], then S(w) is called a cubic spline function, and the function is expressed as formula (1):

S _i (w)＝a _i (ww _i ) ³ +b _i (ww _i ) ² +c _i (ww _i )+d _i

i＝0,1,2……,n-1,n (1)

Among them, a _i , b _i , c _i , and d _i are the corresponding coefficients of the corresponding interval polynomial.

The cubic spline interpolation method not only considers the correlation of pixel points within a larger neighborhood of the interpolation point, but also introduces the concept of spline curves to optimize the imaging effect. The transition between pixels is smooth, and the imaging quality is closer to the actual situation.

The cubic spline interpolation method not only considers the correlation of 16 neighboring pixels, but also introduces the concept of curve to optimize the imaging effect, so that the image is close to the real image.

In order to make the image smoother and closer to the real image, in this embodiment, the median filter algorithm is used to smooth the image. Median filtering is a nonlinear smoothing filtering method. The basic idea is to use a sliding window with an odd number of points, sort the gray values in the window, and then assign the median value to the center point. The system cross-section image reconstruction method is to first perform cubic spline interpolation on the data and then perform median filtering.

In this embodiment, the imaging display adopts a display scheme in which white represents gas and blue represents liquid. The depth of blue is determined by the measured value. The larger the measured value, the deeper the blue. The display function is mainly developed and implemented using the cv2 module. cv2 is the C++ namespace name of opencv, which is used to call the opencv interface developed in C++. The specific process of imaging display is as follows: first call the reshape() function to convert the data into a grayscale image, then call the resize() function in the cv2 module to complete the image scaling, then call the color space conversion function cvtColor() function and the channel splitting function split() function in the cv2 module to complete the blue component extraction, and finally use the setPixmap() function in QLabel to complete the image display.

In this embodiment, the cross-sectional imaging display is divided into two types of displays: original image and reconstructed image. For the original image display, the interpolation parameter of the resize() function in the above display process is assigned to cv2.INTERSECT_NONE. For the reconstructed image display, the interpolation parameter of the resize() function in the above display process is assigned to cv2.INTER_CUBIC representing the cubic spline interpolation method, and the medianBlur() function in the cv2 module is called to complete the median filtering process. The reconstructed image display flow chart is shown in Figure 11. Before imaging display, the measurement data needs to be thresholded. Appropriate thresholding can better describe the gas-liquid two-phase distribution in the cross section of the pipeline. The following will use a frame of measurement data to illustrate the thresholding and reconstructed image processing process. The measurement data is the measurement data when the liquid is continuously flowing through the middle of the screen using the circular pipe of the water pump. In theory, the liquid phase area in the imaging picture should be approximately circular.

In this embodiment, in order to enable users to more accurately grasp the gas-liquid phase information of the pipeline cross section, the cross-sectional gas content display function is implemented. The cross-sectional gas content refers to the ratio between the area occupied by the gas phase on a certain cross section of the pipeline and the total area of the cross section. In the actual calculation process, in order to avoid the influence of the processing error and boundary effect of the wire mesh sensor, it is often necessary to calibrate the measured voltage value to obtain the local conductivity distribution, thereby obtaining the local gas content.

The most commonly used calibration method is to use the voltage values measured at two points when the pipe is completely filled with gas and liquid for calibration. In the specific implementation process, when the pipe is full of liquid, the conductivity is maximum and a unit value is assigned. When the pipe is full of gas, the conductivity is minimum and can be assigned a value of zero. The voltage values at the two points are recorded. The theoretical expression is shown in formula (2).

Among them, i,j represent the coordinate position (grid point number of the wire mesh), k represents the frame of data, ε(i,j,k) represents the local gas content at the coordinate (i,j) in the k-th frame of data, c(i,j,k) represents the conductivity at the coordinate (i,j) in the k-th frame of data, c _gas (i,j) represents the conductivity of the pipe filled with gas (usually 0), and c _liquid (i,j) represents the conductivity of the pipe filled with liquid. Since the measured voltage is linearly related to the conductivity, Formula 2 is converted to Formula 3.

Among them, u _gas (i, j) represents the calibrated voltage value when all the measuring points with coordinates (i, j) are gas flowing through, u _liquid (i, j) represents the calibrated voltage value when all the measuring points with coordinates (i, j) are liquid flowing through, and u (i, j, k) represents the voltage value of the measuring point with coordinates (i, j) in the kth frame data. The voltage value matrix can be converted into the gas phase gas fraction matrix using formula (3).

In this embodiment, a 16x16 wire mesh sensor is used, and each frame of measurement data contains 256 measurement values. Since the sensor electrodes are distributed in the circular pipe cross section, 48 intersections are located outside the cross section, and only the measurement values of 208 intersections are valid measurement values. When calculating the gas content parameter of the pipe cross section, it is necessary to consider whether the measurement point is located in the central area or the boundary area, and different weight values should be given to different areas. The cross-sectional gas content can be calculated according to formula (4).

Wherein, a _i,j represents the weight value corresponding to the measurement value of the measuring point with coordinates (i,j), and its calculation is based on simple geometric area calculation, and its formula is formula (5).

Wherein, A _sensor represents the total area of the circular cross section, and A _i,j represents the effective area corresponding to ε _i,j . The schematic diagram of the measurement area is shown in FIG12. The shaded part in FIG12 represents the effective area corresponding to the measurement value of the point. When the measurement point is located in the center area, A _i,j = Δx·Δy, and when the measurement point is located in the boundary area, A _i,j < Δx·Δy. Since the distance between adjacent electrode wires in the same layer in the sensor is 3 mm, Δx = Δy = 3 mm.

In this embodiment, the corresponding processing function is integrated into the background processing function of the computer software to calculate the cross-sectional gas content and realize the gas content display function. The implementation process is: first, the cross-sectional phase information data collected by the embedded end is obtained through the recvfrom() function, and then the obtained data is parsed and the cross-sectional gas content parameter extraction operation is performed, and finally the cross-sectional gas content parameter is updated to the UI interface. The cross-sectional gas content display flow chart is shown in Figure 13.

In this embodiment, in order to facilitate users to view and analyze historical data, the historical data display function is implemented in the computer software. There are mainly two functions: table and view display. Among them, the front view and side view in the view reconstruct the view information of the measurement pipeline with the help of data projection method. The front view and side view only show the position of the bubble relative to the pipe wall, and do not restore the real size of the bubble. The bubble in the picture may be elongated or flattened.

In this embodiment, the data projection method is a method of projecting based on the maximum values of the rows and columns of the measured values. For the front view projection, the minimum value of the column of the measured value is selected for projection. The specific process of the projection algorithm is: first, read a frame of data from the historical data file, convert the data into a 16×16 matrix, and extract the minimum value of the valid measured value in each column to obtain a 16×1 matrix, and then read another frame of data, perform the same processing on the data, and splice the two projection results to obtain a 16×2 matrix, and then continue to read, project, splice and other operations until the last frame of data. Taking the wire mesh sensor measurement data of 8×8 measuring points as an example, a schematic diagram of the data projection of a frame is shown in Figure 14, where "0" and "1" replace the measured voltage value. The side view display principle is similar to the front view display principle, the difference is that the row data of the measurement value matrix is projected, which will not be explained here.

In this embodiment, a gas-liquid two-phase flow monitoring method is provided, using the gas-liquid two-phase flow monitoring system as described in this embodiment, and the method comprises the following steps:

Step 1: Install the wire mesh sensor on the section perpendicular to the flow direction;

Step 2: The excitation module adopts a cyclic scanning strategy, and sends a bipolar voltage excitation signal to an electrode wire at the excitation end of the wire mesh sensor in sequence each time. All response signals at the receiving end are converted from current to voltage, amplified, and processed by AD conversion, thus completing the data acquisition of one electrode wire in the wire mesh sensor; then excitation, receiving, and processing are performed again, and so on, until the excitation of all electrode wires in the wire mesh sensor is completed, thereby obtaining a voltage matrix that can reflect the two-dimensional distribution of the conductivity at the cross section of the measured flow channel, that is, obtaining the phase state information of a complete cross-sectional point, and sending the phase state information to the computer end in real time through the communication module;

Step 3: The computer performs data analysis, data storage and cross-sectional data imaging processing on the phase state information of each complete cross-sectional point received, displays the two-phase distribution characteristics of the flow field cross section, and calculates and displays the cross-sectional gas content.

At present, most gas-liquid two-phase flow monitoring is based on "soft field" measurement, with uneven electric field distribution, complex image reconstruction algorithm and low imaging accuracy. The wire mesh sensor measurement method based on "hard field" measures the phase distribution of gas-liquid two-phase flow at the moment of contact with the sensor. It has the advantages of simple structure, simple image reconstruction algorithm and high imaging accuracy, which is of great significance for the visual measurement of gas-liquid two-phase flow. It can meet the requirements for system sampling rate and imaging accuracy that are increasing due to the increasing needs of the industrial field.

The following tests are conducted on the two performance indicators of the device: acquisition speed and stability:

①Acquisition speed test

The acquisition speed test is to collect statistics on the data sent by the embedded end and obtain the acquisition speed. The sampling speed statistics table is shown in Table 1.

Table 1 Collection speed statistics:

From the data in the table, we can see that the average sampling speed of the system is 625 frames/s, and the sampling speed meets the expected requirements.

② Operation stability test

The system can work stably under multiple 24-hour tests. During continuous operation, it can normally complete the acquisition, transmission, processing and storage of flow field cross-section phase information according to the set system parameters.

System parameters:

In this embodiment, in order to verify the imaging effect experiment of the system, two measurement schemes, static measurement and dynamic measurement, are formulated according to whether the phase distribution changes.

Static measurement refers to the measurement of the wire mesh sensor in a constant gas-liquid two-phase distribution environment. The height of the liquid is controlled to just reach the wire mesh, and the pipeline is tilted 45 degrees, so that half of the wire mesh sensor area is immersed in water and the other half is exposed to the air, forming a static gas-liquid two-phase distribution environment.

Dynamic measurement refers to the measurement of the screen sensor in a constantly changing gas-liquid two-phase distribution environment. There are two types of test experiments: one is to use a water pump to circulate liquid into the screen, and the image is reconstructed using the measurement data when the liquid just contacts the screen sensor; the other is to use an air pump to continuously provide flowing bubbles to the pipeline, and the image is reconstructed using the measurement data when the bubbles just contact the screen sensor. Before the experiment, a set of data measurements were completed in the full liquid environment and the full gas environment respectively. The data is used to calibrate the measured values to avoid the influence of the screen sensor's boundary effect and processing errors.

For static measurement, a static gas-liquid two-phase distribution environment is formed by tilting the experimental section 45 degrees along the electrode wire direction. Different test liquids are selected for experiments, including primary deionized water, secondary deionized water, tertiary deionized water, and tap water. When the test liquid is primary deionized, the static measurement imaging effect diagram is shown in Figure 15, where the blue part represents liquid and the white part represents gas. The experimental data is shown in Table 2.

Table 2:

It can be seen from the above test results that the system can measure liquids with a conductivity range of 0.1-125μS/cm; in the measurement laboratory, the boundary between the gas and liquid phases is obvious in the imaging results, and the angle of the boundary line is basically consistent with the inclination angle. Therefore, the system can better distinguish the gas and liquid phases within the detection range, so it can meet the design requirements.

For dynamic measurement, in the experiment, a water pump was used to circulate liquid into the wire mesh sensor, and the contact area of the water column on the wire mesh sensor was changed by constantly moving the pipe position and squeezing the pipe, and the contact area was compared with the liquid shape and position in the cross-sectional imaging of the computer software. After testing, the position where the water column contacted the wire mesh and the position of the liquid in the imaging picture can be matched in real time, and the shape of the blue figure in the imaging picture changes with the shape of the water column.

It can be seen from the test results that the cross-sectional imaging results can better reflect the real situation when the water column just contacts the wire mesh sensor. Single bubbles of different sizes are generated by the air pump, and the measurement data of the bubbles just contacting the sensor are extracted, and the data is used to reconstruct the display. The system uses a camera to record the photos of the bubbles before entering the wire mesh sensor. The proportion of the bubbles to the pipe diameter can be measured through the real photos, which is used to compare the bubble size in the cross-sectional imaging pictures and verify the imaging effect of the system measurement data. In the experiment, the test liquid is first-grade deionized water, and the maximum bubble speed does not exceed 0.5m/s. After testing, the shape of the bubbles in the imaging picture is similar to the shape of the bubbles in the photo. The cross-sectional imaging effect under different bubble sizes is shown in Figure 16. The blue part in the figure represents liquid and the white part represents gas.

It can be seen from the experiment that in the moving single bubble experimental environment, the cross-sectional imaging results can better reflect the actual situation at the moment the bubble contacts the sensor. The shape of the white area is similar to the shape of the real bubble, and the size of the white area changes with the size of the bubble, so the system can meet the design requirements.

Claims (5)

1. A gas-liquid two-phase flow monitoring device, characterized in that: comprising a main control module (1), an excitation module (2), a wire mesh sensor (3), a receiving module (4), a communication module (6) and a power supply module (5); the main control module (1) is electrically connected with the excitation module (2), the receiving module (4), the communication module (6) and the power supply module (5) respectively; the wire mesh sensor (3) is respectively Electrically connected with the excitation module (2) and the receiving module (4); Described excitation module (2) comprises: The polarity conversion circuit (2a) is used to convert the unipolar square wave signal generated by the main control module (1) into a bipolar square wave excitation signal. The polarity conversion circuit (2a) and the main control module (1) electrical connection; The gating circuit (2b) is used to realize the multiplexing of the continuous order of the bipolar square wave excitation signal, and the gating circuit (2b) is electrically connected to the main control module (1) and the polarity conversion circuit (2a) respectively. connect; The amplifying circuit (2c) is used to amplify the signal output by the gating circuit (2b), and the amplifying circuit (2c) is electrically connected to the gating circuit (2b) and the excitation terminal of the screen sensor (3) respectively; The receiving module (4) includes: A transimpedance amplifying circuit (4a), used for converting the received current signal into a voltage signal, the transimpedance amplifying circuit (4a) is electrically connected to the output terminal of the wire mesh sensor (3); The first digital potentiometer circuit (4b) is used to adjust the gain of the transimpedance amplifying circuit (4a), and the first digital potentiometer circuit (4b) is electrically connected to the transimpedance amplifying circuit (4a) and the main control module (1) respectively. connect; A voltage amplifying circuit (4c), configured to amplify the voltage signal output by the transimpedance amplifying circuit (4a), the voltage amplifying circuit (4c) being electrically connected to the transimpedance amplifying circuit (4a); The second digital potentiometer circuit (4d) is used to adjust the gain of the voltage amplifying circuit (4c), and the second digital potentiometer circuit (4d) is electrically connected to the voltage amplifying circuit (4c) and the main control module (1) respectively; The signal acquisition circuit (4e) is used to collect the voltage signal amplified by the voltage amplifier circuit (4c), and the signal acquisition circuit (4e) is electrically connected to the voltage amplifier circuit (4c) and the main control module (1) respectively; The main control module (1) adopts the minimum system of STM32, and the minimum system of the STM32 is connected with the input port of the excitation module (2) through the IO pin with timer function, and configures the timer register to realize the square wave signal output. Module (2) is driven; The STM32 minimum system is electrically connected to the first digital potentiometer circuit (4b) and the second digital potentiometer circuit (4d) respectively through the SPI interface, and realizes mutual pairing by adjusting the resistance value of the first digital potentiometer circuit (4b) The gain multiple of the resistance amplifying circuit is regulated, and the gain multiple of the voltage amplifying circuit is regulated by adjusting the resistance value of the second digital potentiometer circuit (4d); The STM32 minimum system is electrically connected with the signal acquisition circuit (4e) through the FSMC interface to realize efficient acquisition of multi-channel data; The STM32 minimum system is electrically connected to the communication module (6) through the RMII interface; The polarity conversion circuit (2a) includes a capacitor C32, a capacitor C35 and a resistor R12, one end of the capacitor C32 is electrically connected to the main control module (1), the other end of the capacitor C32 is grounded through the resistor R12, and the capacitor C32 is connected to the resistor R12. The connection point of R12 is also grounded through the capacitor C35; The gating circuit (2b) includes an analog switch U7, a resistor R4 to a resistor R11, a capacitor C7, a capacitor C9, and a capacitor C22 to a capacitor C29; The analog switch U7 adopts MAX4581CEE+ chip, the 7 pins of the analog switch U7 are grounded after passing through the capacitor C9; the 16 pins of the analog switch U7 are grounded after passing through the capacitor C7; the 13 pins of the analog switch U7 are grounded after passing through the resistor R4, and the capacitor C22 and the resistor R4 Parallel connection; pin 14 of analog switch U7 is grounded after resistor R5, capacitor C23 is connected in parallel with resistor R5; pin 15 of analog switch U7 is grounded after resistor R6, capacitor C24 is connected in parallel with resistor R6; pin 12 of analog switch U7 is connected after resistor R7 Ground, capacitor C25 is connected in parallel with resistor R7; pin 1 of analog switch U7 is grounded after resistor R8, capacitor C26 is connected in parallel with resistor R8; pin 5 of analog switch U7 is grounded after resistor R9, capacitor C27 is connected in parallel with resistor R9; analog switch U7 The pin 2 of the analog switch U7 is grounded after passing through the resistor R10, and the capacitor C28 is connected in parallel with the resistor R10; the pin 4 of the analog switch U7 is grounded after passing through the resistor R11, and the capacitor C29 is connected in parallel with the resistor R11; Pin 3 of the analog switch U7 is electrically connected to the polarity conversion circuit (2a); Pins 12 to 15 of the analog switch U7 are also electrically connected to the amplifier circuit (2c). 2. A gas-liquid two-phase flow monitoring system, characterized in that: comprising a computer terminal and the gas-liquid two-phase flow monitoring device according to claim 1; The excitation module of the gas-liquid two-phase flow monitoring device adopts a cyclic scanning strategy, and sends a bipolar voltage excitation signal to an electrode wire at the excitation end of the screen sensor sequentially each time, and all response signals at the receiving end are converted from current to voltage, and the voltage Amplification and AD conversion processing, that is, to complete the data collection of one electrode wire in the wire mesh sensor; then stimulate, receive, and process again, and so on, until the excitation of all electrode wires in the wire mesh sensor is completed, thus obtaining a data that can reflect the Measure the voltage matrix of the two-dimensional distribution of conductivity at the cross-section of the flow channel, that is, obtain the phase information of a complete cross-section point, and send the phase information to the computer terminal in real time through the communication module; The computer terminal is configured to: perform data analysis, data storage and cross-section data imaging processing on the received phase information of each complete cross-section point, display the two-phase distribution characteristics of the flow field cross-section, and calculate and display the gas content of the cross-section Rate; In the imaging processing of cross-section data, the intersection point of the screen sensor is used as the pixel point, and the measured value is the corresponding pixel value. The pixel point of the image is increased by the interpolation algorithm, and the image is filtered by the median filter; The pixel points of the image are increased by the cubic spline interpolation method. 3. The gas-liquid two-phase flow monitoring system according to claim 2, characterized in that: the method for calculating the cross-sectional gas fraction is as follows: Transform the voltage value matrix into a gas phase gas holdup matrix:

Among them, ε(i,j,k) indicates the local gas fraction with coordinates (i,j) in the kth frame data, and u _gas (i,j) indicates that when all the measuring points with coordinates (i,j) are The calibration voltage value when the gas flows through, u _liquid (i,j) indicates the calibration voltage value when all the measuring points with coordinates (i,j) are liquid flow, u(i,j,k) indicates the kth frame data The voltage value of the measuring point whose middle coordinate is (i,j); Calculate the cross-sectional gas fraction:

in,

is the cross-section gas fraction; a _i,j represents the weight value corresponding to the measured value of the measuring point whose coordinates are (i,j);

Among them, A _sensor represents the total area of the circular section, and A _i,j represents the effective area corresponding to ε _i,j . 4. The gas-liquid two-phase flow monitoring system according to claim 3, characterized in that: the computer terminal is also configured to: be used to view historical data, including table display and view display; wherein, in the view, the front view and the side view The view uses the data projection method to reconstruct the view information of the measuring pipe; the front view and side view are used to display the position of the bubble relative to the pipe wall. 5. A gas-liquid two-phase flow monitoring method, characterized in that: using the gas-liquid two-phase flow monitoring system according to any one of claims 2 to 4, the method comprises the following steps: Step 1. Install the wire mesh sensor on a section perpendicular to the flow direction; Step 2. The excitation module adopts a circular scanning strategy, and sends a bipolar voltage excitation signal to an electrode wire at the excitation end of the screen sensor in sequence each time. All response signals at the receiving end are converted from current to voltage, voltage amplification, and AD conversion. Complete the data acquisition of one electrode wire in the wire mesh sensor; then stimulate, receive, and process again, and so on, until the excitation of all the electrode wires in the wire mesh sensor is completed, thus obtaining a data that can reflect the conductivity at the cross-section of the measured flow channel The voltage matrix of the two-dimensional distribution, that is, to obtain the phase information of a complete cross-section point, and send the phase information to the computer terminal in real time through the communication module; Step 3. The computer terminal performs data analysis, data storage and cross-section data imaging processing on the received phase information of each complete cross-section point, displays the two-phase distribution characteristics of the flow field cross-section, and calculates and displays the gas fraction of the cross-section.

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