Method for monitoring bubbles in gas-liquid two-phase flow based on electromagnetic tomography

Abstract

The invention discloses a method for monitoring bubbles in a gas-liquid two-phase flow based on electromagnetic tomography. A double-layer electromagnetic tomography sensor is designed, induction coil measurement data obtained under high-frequency excitation is processed, a three-dimensional reconstruction image of bubbles is obtained by using an image reconstruction algorithm, and the movement speed of the bubbles is calculated through measurement values of two layers of coils. The method has the beneficial effects that the obtained measurement data is very accurate, the accuracy of a monitoring result is ensured, the whole measurement process is carried out based on an electromagnetic induction principle, image reconstruction and rate estimation of a target can be realized under the condition that a pipeline and a measured object are not contacted, fluid pollution and sensor damage are avoided, and the measurement accuracy is improved. The method is mainly suitable for monitoring bubbles in gas-liquid two-phase flow in industrial production links, including bubble image reconstruction and rate estimation.

Description

Technical Field

[0001] This invention relates to a method for monitoring bubbles in a gas-liquid two-phase flow based on electromagnetic tomography (EMT), belonging to the field of non-contact fluid monitoring technology using electromagnetic tomography (EMT). Background Technology

[0002] Gas-liquid two-phase flow refers to the fluid phenomenon where gas and liquid coexist in a pipeline, and it is widely present in many industrial scenarios, such as the chemical, petroleum, and nuclear industries. Monitoring the fluid state and dynamic changes is crucial for overall process control and ensuring the required production efficiency. Existing methods for monitoring gas-liquid two-phase flow mainly use optical detection, X-ray detection, and electrode detection. However, all of these methods have certain limitations: optical detection is limited by the transparency of the pipeline and is not suitable for opaque pipelines; X-ray detection poses certain safety hazards due to its radioactivity; and electrode detection requires the probe to be in direct contact with the fluid being measured, which can lead to probe corrosion and fluid contamination.

[0003] Electromagnetic tomography (EMT) is characterized by its non-invasive, non-contact, and non-radioactive nature. This technology exhibits high detection sensitivity for conductive or magnetic materials. Utilizing the principle of electromagnetic induction, it obtains the electromagnetic property distribution of the sample by interacting with the magnetic field generated by an excitation coil. Furthermore, the entire detection process can be completed without contact with the object, avoiding damage and contamination to the sensor and the sample. However, accurately monitoring gas-liquid two-phase flows using this technology remains a critical technical challenge. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for monitoring bubbles in gas-liquid two-phase flow based on electromagnetic tomography, which can accurately monitor gas-liquid two-phase flow using electromagnetic tomography.

[0005] To address the aforementioned technical problems, the present invention provides a method for monitoring bubbles in a gas-liquid two-phase flow based on electromagnetic tomography. This method designs a dual-layer electromagnetic tomography sensor, processes the measurement data of the induction coils obtained under high-frequency excitation, uses an image reconstruction algorithm to obtain a three-dimensional reconstructed image of the bubble, and calculates the bubble's velocity using the measurement values ​​from the two layers of coils.

[0006] The dual-layer electromagnetic tomography sensor consists of eight capsule-shaped coils on the top and bottom, with each coil wound with seven turns of copper wire. The major axis is 50 mm long, the minor axis is 30 mm long, the distance between the centers of the two layers of coils is 58 mm, the imaging area diameter is 100 mm, and the sensor's longitudinal height is 140 mm.

[0007] The specific analysis steps are as follows:

[0008] (1) The electromagnetic tomography instrument is configured by computer to generate a high-frequency AC excitation signal. Each coil of the electromagnetic tomography sensor is sequentially supplied with the excitation signal to generate an excitation magnetic field.

[0009] (2) The remaining coils act as induction coils to generate induced voltage, and all induction coil measurement values ​​are collected and sent to the computer for processing;

[0010] (3) The measured values ​​of the induction coil are used to obtain a reconstructed image of the bubble through an image reconstruction algorithm;

[0011] (4) Use the cross-correlation method to analyze the original signal of each layer of coil and estimate the rate v of bubble rise.

[0012] In step (3), the measured values ​​are used to obtain slice images and three-dimensional images of the bubble through an image reconstruction algorithm. The image reconstruction algorithm uses the Landweber iterative method, and the iterative steps are as follows:

[0013]

[0014]

[0015] In step (4), when the object under test is placed between a pair of opposing excitation-induction coils, if the object under test is weakly disturbed by the excitation magnetic field, that is, the skin depth of the excitation magnetic field is much larger than the size of the object under test, the electromagnetic response signal of the induction coil is:

[0016]

[0017] In the formula, V is the measurement signal of the induction coil in the absence of a field, ΔV is the measured change in the relative field when the object being measured is present, ω is the angular frequency, and μ0 and μ r These represent the vacuum permeability and the relative permeability of the measured object, respectively, ∈0 and ∈ r Here, σ is the vacuum permittivity and the relative permittivity of the test object, respectively; P and Q are constants related to the shape of the test object.

[0018] Analyzing the relative changes in the imaginary part of the coil measurement signal, each layer of the electromagnetic tomography sensor has four pairs of opposing coil combinations. Therefore, the measurement signal of each layer can be represented by the average measurement value of each pair of opposing coil combinations in each layer.

[0019]

[0020] In the formula, and V represents the relative change of the imaginary part of the measurement signal between the lower and upper coils, respectively. p(p+4)The induced voltage generated by coil (p+4) under the excitation of coil p, and the cross-correlation coefficient of the signals from the two coil layers can be expressed as:

[0021]

[0022] In the formula, T is the total sampling time, and the cross-correlation coefficient R is the cross-correlation coefficient when the variable τ = τ0. cc (τ) reaches its maximum value, therefore the bubble rising rate can be expressed as:

[0023]

[0024] In the formula, D is the distance between the two layers of coils.

[0025] The beneficial effects of this invention are:

[0026] Electromagnetic tomography (EMT) is used to monitor bubbles in gas-liquid two-phase flow, obtaining reconstructed images of the bubbles and their movement velocities. A dual-layer EMT sensor is specifically designed to process induction coil measurement data obtained under high-frequency excitation. Simultaneously, through corresponding analysis methods, the bubble velocity is calculated using the measurements from both layers of coils, ensuring highly accurate measurement data and guaranteeing the accuracy of the monitoring results. The entire measurement process is based on the principle of electromagnetic induction, enabling image reconstruction and velocity estimation of the target without contact with the pipe or the object being measured, avoiding fluid contamination and sensor damage. It is primarily applicable to the monitoring of bubbles in gas-liquid two-phase flow in industrial production processes, including bubble image reconstruction and velocity estimation. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the dual-layer electromagnetic tomography sensor in this invention;

[0028] Figure 2 This is a schematic diagram of the coil structure in this invention;

[0029] Figure 3 This is a schematic diagram of the monitoring process of the present invention;

[0030] Figure 4 This is a schematic diagram of the test sample for the monitoring method of the present invention;

[0031] Figure 5 This is a schematic diagram of the system experiment for the monitoring method of the present invention;

[0032] Figure 6 This is a schematic diagram illustrating the image reconstruction effect of the monitoring method of the present invention on the rising process of a 30mm diameter bubble in 4% saline solution;

[0033] Figure 7This is a schematic diagram of the experimental results of the monitoring method of the present invention for measuring the signal of two-layer coils during the rising process of a 30mm diameter bubble in 4% saline solution;

[0034] Figure 8 This is a schematic diagram illustrating the image reconstruction effect of the monitoring method of the present invention on the rising process of a 40mm diameter bubble in 4% saline solution;

[0035] Figure 9 This is a schematic diagram of the experimental results of the monitoring method of the present invention for measuring the signal of two-layer coils during the rising process of a 40mm diameter bubble in 4% saline solution;

[0036] Figure labeling: 1. 4% saline solution; 2. 40mm hollow plastic bubble ball; 3. 30mm hollow plastic bubble ball; 4. Computer; 5. Double-layer electromagnetic tomography sensor; 6. Electromagnetic tomography instrument; 7. Experimental test sample. Detailed Implementation

[0037] The following detailed description of the method for monitoring bubbles in gas-liquid two-phase flow based on electromagnetic tomography, in conjunction with the accompanying drawings and specific embodiments, further illustrates the present invention.

[0038] As shown in the figure, the method for monitoring bubbles in a gas-liquid two-phase flow based on electromagnetic tomography of the present invention, by designing a dual-layer electromagnetic tomography sensor, processes the measurement data of the induction coils obtained under high-frequency excitation, uses an image reconstruction algorithm to obtain a three-dimensional reconstructed image of the bubble, and calculates the bubble's velocity using the measurement values ​​of the two layers of coils. Figure 1 and Figure 2 As shown, in this embodiment, the dual-layer electromagnetic tomography sensor consists of eight capsule-shaped coils on the top and bottom. Each coil is wound with seven turns of copper wire, with a major axis length of 50 mm, a minor axis length of 30 mm, a center-to-center distance of 58 mm between the two layers of coils, an imaging area diameter of 100 mm, and a sensor longitudinal height of 140 mm.

[0039] Figure 3 The diagram shows a schematic flow chart of the gas-liquid two-phase flow bubble monitoring method based on electromagnetic tomography according to the present invention. Figure 3 As shown, firstly, electromagnetic tomography (EMT) instrument 6 and dual-layer EMT sensor 5 are used to collect coil measurement data, and the data after IQ demodulation by EMT instrument 6 is transmitted to computer 4. A two-dimensional cross-sectional image and a three-dimensional reconstructed image of the bubble distribution are obtained through image reconstruction algorithms, and the cross-correlation algorithm is used to analyze the signals of the two layers of coils to estimate the bubble's rising rate. The specific analysis steps of this monitoring method are as follows:

[0040] (1) The electromagnetic tomography instrument is configured by computer to generate a high-frequency AC excitation signal. Each coil of the electromagnetic tomography sensor is sequentially fed with the excitation signal to generate an excitation magnetic field. Specifically, after the electromagnetic tomography instrument is configured by computer, it generates a high-frequency AC excitation signal of a specific frequency, which is sequentially fed into each coil of the electromagnetic tomography sensor to generate an excitation magnetic field. The object under test generates eddy currents under the action of the excitation magnetic field, and the eddy currents then generate a secondary magnetic field.

[0041] (2) The remaining coils act as induction coils to generate induced voltages. Under the influence of the excitation magnetic field and the secondary magnetic field, induced voltages are generated. During each working cycle, the electromagnetic tomography instrument collects the voltage values ​​of the induction coils. For example, when coil 1 is excited, the induced voltage values ​​of coils 2, 3, ..., 16 are collected; when coil 2 is excited, the induced voltage values ​​of coils 3, 4, ..., 16 are collected. This allows for the acquisition of... The system collects a set of independent measurement values ​​and then sends them to the computer for processing, thereby achieving the goal of collecting all the measurement values ​​of the induction coils and sending them to the computer for processing.

[0042] (3) The measured values ​​of the induction coil are used to obtain a reconstructed image of the bubble through an image reconstruction algorithm;

[0043] In this step, the computer processes the collected data. 120 sets of measurements are used to obtain slice images and 3D images of the bubble using an image reconstruction algorithm. The image reconstruction algorithm employs the Landweber iterative method, with the following iterative steps:

[0044]

[0045] (4) Analyze the original signal of each layer of coil using the cross-correlation method to estimate the rising speed v of the bubble; in this step (4), when the object under test is placed between a pair of opposing excitation-induction coils, if the object under test has weak disturbance to the excitation magnetic field, that is, the skin depth of the excitation magnetic field is much larger than the size of the object under test, the electromagnetic response signal of the induction coil is:

[0046]

[0047] In the formula, V is the measurement signal of the induction coil in the absence of a field, ΔV is the measured change in the relative field when the object being measured is present, ω is the angular frequency, and μ0 and μ r These represent the vacuum permeability and the relative permeability of the measured object, respectively, ∈0 and ∈ r Here, σ is the vacuum permittivity and the relative permittivity of the test object, respectively; P and Q are constants related to the shape of the test object.

[0048] The above equation shows that in the sensor's measurement space, changes in dielectric constant and permeability cause relative changes in the real part of the induction coil's measurement voltage, while changes in conductivity cause relative changes in the imaginary part of the induction coil's measurement voltage. Gas-liquid two-phase flow primarily causes changes in conductivity; therefore, this invention analyzes the relative changes in the imaginary part of the coil's measurement signal. Each layer of the sensor's coil has four pairs of opposing coil combinations; therefore, the measurement signal of each layer can be represented by the average measurement value of each pair of opposing coil combinations in each layer.

[0049]

[0050] In the formula, and V represents the relative change of the imaginary part of the measurement signal between the lower and upper coils, respectively. p(p+4) The induced voltage generated by coil (p+4) under the excitation of coil p, and the cross-correlation coefficient of the signals from the two coil layers can be expressed as:

[0051]

[0052] In the formula, T is the total sampling time, and the cross-correlation coefficient R is the cross-correlation coefficient when the variable τ = τ0. cc (τ) reaches its maximum value, therefore the bubble rising rate can be expressed as:

[0053]

[0054] In the formula, D is the distance between the two layers of coils.

[0055] The following examples demonstrate its effectiveness:

[0056] Application Example 1:

[0057] like Figure 5 As shown, during the test, a test sample consisting of a 4% saline solution (1) and a 30mm diameter hollow plastic bubble ball (3) was placed within the imaging area of ​​the dual-layer electromagnetic tomography sensor (5). The 4% saline solution has a conductivity of 5.39 S / m, while the bubble's conductivity can be approximated as 0 S / m. During the experiment, the bubble ball rose linearly from the bottom of the container. Simultaneously, the electromagnetic tomography instrument (6) sequentially applied a 4MHz AC excitation signal to each coil of the dual-layer electromagnetic tomography sensor. The magnetic field generated by the energized excitation coils induced eddy currents in the conductive sample, which in turn generated a secondary magnetic field, causing a change in the measured values ​​of the induction coils. The instrument collected all the measured values ​​of the induction coils throughout the bubble's ascent and transmitted the demodulated data to a computer for processing.

[0058] like Figure 6As shown, using a 4% saline signal as the background signal, the electromagnetic property distribution in space can be reconstructed using the Landweber iterative algorithm. The relevant parameters of the Landweber iterative algorithm are as follows:

[0059] Table 1 Landweber Iterative Algorithm Parameter Configuration

[0060]

[0061] During the entire rise of the bubble, eight representative moments with equal time intervals were selected for 3D reconstruction. The reconstruction result for each moment includes three 2D cross-sectional images and one 3D isosurface image: a longitudinal cross-section through the sensor center, a lower coil plane cross-section, an upper coil plane cross-section, and a 3D isosurface image plotted with a threshold of 0.5 times the maximum reconstructed value. Since the conductivity of the bubble is lower than that of the background saline solution, it is represented by negative pixel values ​​in the reconstruction result, i.e., the area surrounded by a white halo in the cross-sectional image. The rising process of the bubble can be visually observed from the longitudinal cross-sectional image and the 3D isosurface image. Simultaneously, as the bubble rises, the bubble image in the lower coil cross-section gradually becomes clearer and then disappears, while the upper coil cross-section gradually reveals the presence of the bubble. This phenomenon is consistent with the actual movement of the bubble, verifying the accuracy and reliability of the reconstruction results.

[0062] This invention takes the relative change of the imaginary part of the coil measurement signal. Analysis. Each layer of the dual-layer sensor has four pairs of oppositely arranged coil combinations. To improve the representativeness and stability of the signal, the measurement signal of each layer's coils is represented by the average measurement value of each pair of opposite coil combinations:

[0063]

[0064] like Figure 7 As shown, when a 30mm bubble passes through the lower and upper coil planes, the corresponding coil signals on those planes exhibit signal peaks. The cross-correlation coefficients of the two coil signals are then calculated.

[0065]

[0066] The time constant τ0 corresponding to the maximum cross-correlation coefficient is obtained, and the bubble rising rate can be calculated using the following formula:

[0067]

[0068] The rate calculation results for this example are shown in Table 2 below.

[0069] Application Example 2:

[0070] In Application Example 2, the 30mm bubble ball 3 in Application Example 1 is replaced with a 40mm bubble ball 2, and the bubble ball rises from the bottom left side of the container. The remaining experimental procedures are the same as in Experiment 1.

[0071] like Figure 8 As shown, the rising process of a 40mm diameter bubble was dynamically reconstructed, with eight equally timed moments selected during the entire rising process. Similar to Example 1, the reconstruction result for each time point includes three two-dimensional cross-sectional views and one three-dimensional isosurface view. The rising process of the bubble can be intuitively observed from both the cross-sectional views and the three-dimensional reconstructed image, and the reconstruction effect is similar to that of Example 1. Furthermore, the pixel values ​​corresponding to the reconstructed image of the 40mm bubble are generally larger than the pixel values ​​of the image of the 30mm bubble in Example 1, which allows for the qualitative differentiation of the size of bubbles of different dimensions.

[0072] like Figure 9 As shown, when a 40mm bubble passes through the two coil planes, the coil signal on the corresponding plane shows a peak. By repeating the steps described in Example 1, the rate at which the bubble rises can be obtained.

[0073] The table below shows the bubble rate calculation results for each embodiment:

[0074] Table 2 Calculation results of bubble rate

[0075]

[0076] The actual rising rate of the bubble is calculated by the ratio of the rising distance to the actual sampling time, and the calculated rate is obtained through the cross-correlation method described above. According to the results in the table, the rising rate of the bubble calculated by the cross-correlation method is close to the actual speed, with relative errors within 3% and an average relative error of 2.07%. This result indicates that the cross-correlation calculation method used can accurately reflect the true rising speed of the bubble and has high reliability.

[0077] As demonstrated in the above application examples, this invention, through a dual-layer electromagnetic tomography sensor, can achieve three-dimensional image reconstruction of bubbles in a gas-liquid two-phase flow and calculation of bubble rise rates. The above application examples conducted monitoring and reconstruction experiments on bubbles of different sizes and positions, and the results verified the effectiveness and applicability of the method of this invention. The application scope of this invention is not limited to the sample conditions used in the above application examples; adjustments to the sensor structure, bubble size, and related parameters can be made according to actual needs, and these adjustments still fall within the protection scope of this invention.

Claims

1. A method for monitoring bubbles in a gas-liquid two-phase flow based on electromagnetic tomography, characterized in that: By designing a dual-layer electromagnetic tomography sensor, the measurement data of the induction coil obtained under high-frequency excitation is processed. An image reconstruction algorithm is used to obtain a three-dimensional reconstructed image of the bubble, and the velocity of the bubble is calculated by the measurement values ​​of the two layers of coils.

2. The method for monitoring bubbles in a gas-liquid two-phase flow based on electromagnetic tomography according to claim 1, characterized in that: The dual-layer electromagnetic tomography sensor consists of eight capsule-shaped coils on the top and bottom, with each coil wound with seven turns of copper wire. The major axis is 50 mm long, the minor axis is 30 mm long, the distance between the centers of the two layers of coils is 58 mm, the imaging area diameter is 100 mm, and the sensor's longitudinal height is 140 mm.

3. The method for monitoring bubbles in a gas-liquid two-phase flow based on electromagnetic tomography according to claim 1 or 2, characterized in that: The specific analysis steps are as follows: (1) The electromagnetic tomography instrument is configured by computer to generate a high-frequency AC excitation signal. Each coil of the electromagnetic tomography sensor is sequentially supplied with the excitation signal to generate an excitation magnetic field. (2) The remaining coils act as induction coils to generate induced voltage, and all induction coil measurement values ​​are collected and sent to the computer for processing; (3) The measured values ​​of the induction coil are used to obtain a reconstructed image of the bubble through an image reconstruction algorithm; (4) Use the cross-correlation method to analyze the original signal of each layer of coil and estimate the rate v of bubble rise.

4. The method for monitoring bubbles in a gas-liquid two-phase flow based on electromagnetic tomography according to claim 3, characterized in that: In step (3), the measured values ​​are used to obtain slice images and three-dimensional images of the bubble through an image reconstruction algorithm. The image reconstruction algorithm uses the Landweber iterative method, and the iterative steps are as follows:

5. The method for monitoring bubbles in a gas-liquid two-phase flow based on electromagnetic tomography according to claim 3, characterized in that: In step (4), when the object under test is placed between a pair of opposing excitation-induction coils, if the object under test is weakly disturbed by the excitation magnetic field, that is, the skin depth of the excitation magnetic field is much larger than the size of the object under test, the electromagnetic response signal of the induction coil is: In the formula, V is the measurement signal of the induction coil in the absence of a field, ΔV is the measured change in the relative field when the object being measured is present, ω is the angular frequency, and μ0 and μ r These represent the vacuum permeability and the relative permeability of the measured object, respectively, ∈0 and ∈ r Here, σ is the vacuum permittivity and the relative permittivity of the test object, respectively; P and Q are constants related to the shape of the test object.

6. The method for monitoring bubbles in a gas-liquid two-phase flow based on electromagnetic tomography according to claim 5, characterized in that: Analyzing the relative changes in the imaginary part of the coil measurement signal, each layer of the electromagnetic tomography sensor has four pairs of opposing coil combinations. Therefore, the measurement signal of each layer can be represented by the average measurement value of each pair of opposing coil combinations in each layer. In the formula, and V represents the relative change of the imaginary part of the measurement signal between the lower and upper coils, respectively. p(p+4) The induced voltage generated by coil (p+4) under the excitation of coil p, and the cross-correlation coefficient of the signals from the two coil layers can be expressed as: In the formula, T is the total sampling time, and the cross-correlation coefficient R is the cross-correlation coefficient when the variable τ = τ0. cc (τ) reaches its maximum value, therefore the bubble rising rate can be expressed as: In the formula, D is the distance between the two layers of coils.

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