Device and method for measuring induced magnetic field data of liquid metal

Abstract

The invention provides a device and a method for measuring induced magnetic field data of liquid metal, and belongs to the technical field of magnetic variable measurement. According to the scheme, an excitation magnetic field generation device and a magnetic field sensor array are arranged outside an experiment section containing liquid metal, two initial magnetic fields in different directions are sequentially applied in a measurement section, and two groups of corresponding secondary induced magnetic field data are collected by the sensor array. According to the invention, at least two initial magnetic fields in different directions are alternately applied, and two groups of linear independent measurement data can be provided, so that the richness, accuracy and stability of acquired data are remarkably improved; a distributed detection array is formed by high-precision fluxgate sensors to detect the size of an induced magnetic field at an nT level, and a flowing development section is arranged at at least one of the upstream and the downstream of a measurement section to eliminate the influence of local disturbance, so that the precision of induced magnetic field data detection is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic variable measurement, in particular to a device and method for measuring liquid metal induced magnetic field data. BACKGROUND

[0002] In the thermal-hydraulic research of advanced nuclear reactors, such as lead-cooled fast reactors, accurately grasping the velocity field distribution of the coolant, such as liquid lead-bismuth alloy, is the key to safety analysis and optimal design. However, liquid metals such as liquid lead-bismuth have physical and chemical properties of high temperature, opacity, and strong corrosion, which brings great challenges to traditional flow measurement techniques. On the one hand, invasive measurement methods, such as using a probe to directly insert into the fluid, will face serious material compatibility problems, and the probe is easy to be corroded and damaged, and its own existence will also disturb the original flow field. On the other hand, non-contact optical measurement methods, such as laser Doppler velocimetry and particle image velocimetry, rely on light penetration and are completely unsuitable for opaque liquid metal media.

[0003] CIFT (contactless induction flow tomography) technology is a flow measurement technology that can realize the visualization of the overall flow in conductive fluid. This method is based on the principle of motion induction: under the influence of the main excitation magnetic field, the fluid motion produces a very weak induced magnetic field, and then the flow field of the fluid is reconstructed according to the induced magnetic field. It can be seen that accurate measurement of the induced magnetic field is the basis for flow field reconstruction and analysis of the fluid. However, this technology has not been applied to the measurement of liquid lead-bismuth pipes. The main application difficulties are: the liquid lead-bismuth three-pipe is in a three-dimensional distributed non-uniform flow state, and the data collected by the traditional method is not sufficient for subsequent flow field analysis; the induced magnetic field data of liquid lead-bismuth is in the order of nT, which is easily disturbed by external magnetic fields, in addition, the disturbance of the upstream and downstream regions of the pipe will also affect the measurement results of the measurement region. SUMMARY

[0004] In view of the defects in the prior art, the purpose of the present application is to provide a device and method for measuring liquid metal induced magnetic field data.

[0005] According to the device for measuring liquid metal induced magnetic field data provided by the present application, the device comprises: a fluid circuit comprising a pipe for containing the flow of the liquid metal; an experimental section connected in series to the fluid circuit, the experimental section comprising a measurement section, an electromagnetic shield outside the experimental section; an excitation magnetic field generating device arranged outside the experimental section and configured to apply at least two initial magnetic fields of different directions in the fluid region of the measurement section; a magnetic field sensor array arranged outside the measurement section for collecting secondary induced magnetic field data generated by the liquid metal flowing cutting the initial magnetic field; The experimental section is arranged at least one of upstream and downstream of the measurement section.

[0006] Further, the liquid metal is liquid lead-bismuth alloy.

[0007] Further, the excitation magnetic field generating device comprises two pairs of Helmholtz coils, the axes of which are orthogonal to each other, for alternately applying two initial magnetic fields of different directions.

[0008] Further, the magnetic field sensor array is composed of a plurality of fluxgate sensors.

[0009] Further, the magnetic field sensor array comprises at least two detection sections arranged along the axial direction of the measurement section, and a plurality of magnetic field sensors are uniformly distributed in the circumferential direction on each detection section.

[0010] Further, the width-height ratio of the measurement section is 1:1.

[0011] Further, a processing unit is further included, which is electrically connected with the magnetic field sensor array, for receiving the secondary induced magnetic field data and inversely reconstructing the velocity field distribution in the measurement section based on the data.

[0012] Further, the way of inversely reconstructing the velocity field distribution in the measurement section comprises constructing and solving a regularized least square equation to obtain the velocity field distribution.

[0013] According to the present application, a method for measuring liquid metal induced magnetic field data is provided, which adopts the device for measuring liquid metal induced magnetic field data, and comprises the following steps: flowing the liquid metal in a fluid circuit comprising an experimental section; applying an initial magnetic field of a first direction in the measurement section; collecting a first group of secondary induced magnetic field data; applying an initial magnetic field of a second direction different from the first direction in the measurement section; collecting a second group of secondary induced magnetic field data.

[0014] Further, the method further comprises inversely reconstructing the velocity field distribution in the measurement section based on the first group and the second group of secondary induced magnetic field data, and the way of inversely reconstructing the velocity field distribution in the measurement section comprises constructing and solving a regularized least square equation to obtain the velocity field distribution.

[0015] Compared with the prior art, the present application has the following beneficial effects: The present application realizes the complete non-invasive measurement of liquid metal by deploying excitation magnetic field generating device and magnetic field sensor array outside the pipeline. The whole measurement system has no physical contact with high-temperature and strongly corrosive liquid metal, fundamentally solving the problems of material corrosion, sealing difficulty and short service life faced by the prior art using contact components such as electrodes, and also avoiding the interference to the flow field, significantly improving the reliability and long-term stability of the measurement system. By alternately applying at least two initial magnetic fields in different directions, two sets of linearly independent measurement data can be provided, thereby significantly improving the richness, accuracy and stability of the collected data. The nT-level induced magnetic field size is detected by the high-precision fluxgate sensor constituting a distributed detection array, and a flow development section is arranged at least at one of the upstream and downstream of the measurement section to eliminate the influence of local disturbance, thereby greatly improving the accuracy of the induced magnetic field data detection. BRIEF DESCRIPTION OF DRAWINGS

[0016] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings: Figure 1 The system working principle block diagram provided for the embodiment of the present application is shown in the figure; Figure 2 The overall structure schematic diagram of the experimental device provided for the embodiment of the present application is shown in the figure; Figure 3 The experimental section structure schematic diagram provided for the embodiment of the present application is shown in the figure; Figure 4 The fluxgate sensor array layout schematic diagram provided for the embodiment of the present application is shown in the figure; Figure 5 The measurement section cross section and magnetic field direction schematic diagram provided for the embodiment of the present application is shown in the figure; Figure 6 The velocity field reconstruction method flow chart provided for the embodiment of the present application is shown in the figure; Figure 7 The inversion velocity and reference velocity comparison diagram provided for the embodiment of the present application is shown in the figure; Figure 8 The corresponding velocity field vector distribution is shown in the figure. Figure 7

[0017] Wherein, the main figure mark explanations are as follows: 1-electromagnetic pump; 2-valve; 3-electromagnetic shield; 4-experimental section; 5-filter circuit; 6-PC; 7-Helmholtz coil; 8-front development section; 9-measurement section; 10-back development section; 11-fluxgate sensor. DETAILED DESCRIPTION

[0018] ​The application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the application. These are within the scope of protection of the application.

[0019] Example 1 The present embodiment provides a liquid metal inductive magnetic field data measurement device based on inductive flow tomography and a corresponding measurement method, aiming to fully demonstrate a basic scheme capable of non-invasively measuring high-temperature, opaque, and highly corrosive liquid metal (specifically liquid lead-bismuth alloy in the present embodiment).

[0020] In combination Figure 1 With Figure 2 As shown in the figure, Figure 1 The system working principle block diagram provided in the embodiment of the present application, Figure 2 The overall structure of the experimental device provided in the embodiment of the present application is shown in the figure. The device of the present embodiment is mainly constructed as a closed-loop fluid circuit system, and integrates a non-contact electromagnetic excitation and measurement system and a data processing system. The flow field of the liquid metal is analyzed by collecting secondary induction magnetic field data.

[0021] Specifically, the device includes a fluid circuit composed of a pipeline, an electromagnetic pump 1 for driving the flow of the liquid metal working medium, and a valve 2 for accurately adjusting the flow rate. In the present embodiment, the pipeline is made of stainless steel material with high temperature resistance and corrosion resistance, and its inner diameter is 200 millimeters. The working medium flowing in the pipeline is a liquid lead-bismuth alloy used as a coolant in advanced nuclear reactors, and its working temperature is maintained at about 500K. The electromagnetic pump 1 drives the flow of the liquid metal using the principle of Lorentz force. Its characteristics of not containing mechanical moving parts enable it to be well compatible with high-temperature liquid metal and achieve smooth fluid driving. The valve 2 can be a gate valve or a ball valve with manual or automatic adjustment. Its function is to adjust and stabilize the flow rate in the circuit to the preset target value before the experiment starts, for example, to make the average velocity of the inlet of the measurement region reach 1.6 meters per second.

[0022] On the fluid circuit, an experimental section 4 is arranged in series. The experimental section 4 is the core area for electromagnetic induction measurement. In order to ensure the accuracy of the measurement and reduce the interference of the external electromagnetic environment on the weak induction magnetic field signal, the outside of the entire experimental section 4 is wrapped by an electromagnetic shielding cover 3 made of high magnetic permeability material (such as permalloy).

[0023] Further, referring to Figure 3The detailed structure of the experimental section 4 is shown in the figure. The total length of the experimental section 4 is 800 mm, which is composed of three parts. In the center is a measuring section 9 with a length of 200 mm, which is the target area for reconstructing the actual velocity field. Upstream of the measuring section 9, a pre-development section 8 with a length of 300 mm is arranged. Correspondingly, downstream of the measuring section 9, a post-development section 10 with a length of 300 mm is also arranged. The pre-development section 8 and the post-development section 10 are arranged to ensure that the liquid lead-bismuth flow field flowing through the measuring section 9 can be fully developed, so as to eliminate the local disturbance caused by the upstream elbow or valve 2 and other components, thereby forming a relatively stable and predictable flow profile, providing high-quality flow field conditions for accurate velocity field measurement and reconstruction.

[0024] Around the outside of the experimental section 4, a magnetic field excitation device is arranged. As an implementation, the device is specifically two pairs of Helmholtz coils 7. Helmholtz coil is a special coil pair that can generate a highly uniform magnetic field near the central axis. As shown in Figure 3 and Figure 5 The axes of the two pairs of Helmholtz coils 7 are orthogonal to each other, and are used to generate initial magnetic fields Bx and By in the first and second directions in the fluid region of the measuring section 9, respectively. Specifically, the axis of the first pair of Helmholtz coils is in the x direction, and the axis of the second pair of Helmholtz coils is in the y direction, both of which are perpendicular to the axis of the pipe (i.e. the flow direction z). The inner diameter of the two pairs of coils is 300 mm, so as to ensure that the uniform magnetic field region generated thereby can completely cover the measuring section 9 with an inner diameter of 200 mm. The center distance of the two pairs of coils is 480 mm. The two pairs of coils are powered by an external large current excitation source (as shown in Figure 1 ), which can provide adjustable direct current of 20 to 50 amperes. In operation, the excitation source alternately powers the two pairs of coils at a preset period (for example, 5 seconds), so as to alternately apply a uniform initial magnetic field with a strength of millitesla level and in the directions of Bx and By in the measuring section 9. It should be noted that the strategy of applying at least two initial magnetic fields in different directions is a key technical means for solving the underdetermination of the electromagnetic inverse problem in induced flow tomography, which can provide two sets of linearly independent measurement data, thereby significantly improving the accuracy and stability of the velocity field inversion reconstruction.

[0025] In order to realize non-contact acquisition of the secondary induction magnetic field generated by the liquid lead-bismuth flow, the device is also configured with a magnetic field sensor array. Referring to Figure 4The magnetic field sensor array layout is shown. The array is arranged outside the measurement section 9 and consists of a total of 48 high-precision, high-sensitivity fluxgate sensors 11. The fluxgate sensor is a kind of vector magnetometer capable of measuring weak magnetic fields, which is extremely suitable for detecting weak secondary induced magnetic fields generated by fluid flow. Specifically, the 48 fluxgate sensors 11 are arranged in a specific three-dimensional array: along the axial direction of the measurement section 9, they are arranged equidistantly on 4 parallel detection sections, and the distance between adjacent detection sections (i.e. the interlayer spacing) is 50 mm; on each detection section, 12 fluxgate sensors 11 are uniformly distributed in the circumferential direction. The radial distance between the probes of all sensors and the outer wall of the pipeline is kept at 40 mm, and the gap is filled with thermal insulation materials such as thermal insulation cotton to protect the sensors from the high temperature of the pipeline while not affecting the penetration of the magnetic field. It can be understood that such an array layout distributed in the axial and circumferential directions enables the system to synchronously collect distribution information of the secondary induced magnetic field from multiple spatial positions, providing necessary and rich measurement data for reconstructing the velocity field with three-dimensional spatial structure.

[0026] The device also includes a data processing system composed of a signal conditioning circuit electrically connected to the magnetic field sensor array and a processing unit. In this embodiment, the signal conditioning circuit is a multi-channel filter circuit 5 (as shown in Figure 2 It can be a combination of analog amplification filter circuit and digital filter circuit (as shown in Figure 1 Its function is to amplify and filter the original, weak secondary induced magnetic field signals collected by the 48 fluxgate sensors 11, to filter out power frequency interference, high frequency noise and transient interference caused by excitation magnetic field switching, thereby significantly improving the signal-to-noise ratio. The processing unit is a personal computer (PC) 6. The digital signals processed by the filter circuit 5 are transmitted to the PC 6 through data cables. The PC 6 runs a pre-set software program to receive two sets of secondary induced magnetic field data collected under different initial magnetic fields, and based on these data, performs complex inversion calculation to finally reconstruct the three-dimensional velocity field distribution in the measurement section 9.

[0027] This embodiment also provides a liquid metal flow field measurement method based on the above device. The working process and data processing flow can be understood in combination with the method flow chart shown in Figure 6

[0028] Before the measurement starts, the preparation work is carried out first. The electromagnetic pump 1 is started to drive the liquid lead-bismuth alloy at a temperature of 500 K to circulate in the closed loop pipeline. By adjusting the valve 2, the average flow velocity in the pipeline is stabilized at the target value, for example, the inlet velocity is 1.6 m / s.

[0029] ​Subsequently, the formal data acquisition process begins, which alternates to acquire two sets of independent data. In step S101, an initial magnetic field in the first direction is applied. Specifically, an external high-current excitation source supplies power to the first pair of Helmholtz coils 7, establishing a stable, uniform initial magnetic field along the Bx direction inside the measurement section 9. In step S102, the first set of secondary magnetic field data is acquired. When the conductive liquid lead-bismuth fluid flows through the Bx magnetic field at a velocity v, according to the law of electromagnetic induction, the charged particles inside the fluid are subjected to the Lorentz force, generating an induced current j. This induced current j, according to the Biot-Savart law, generates a secondary induced magnetic field b in the space outside the fluid. The distribution and intensity of this secondary induced magnetic field b are closely related to the velocity field v distribution inside the fluid. At this time, 48 fluxgate sensors 11 arranged outside the measurement section 9 synchronously and non-contactly measure and acquire the vector component data of the secondary induced magnetic field b at their respective spatial positions, forming the first set of secondary induced magnetic field data. In step S103, an initial magnetic field in the second direction is applied. After the first excitation cycle (e.g., 5 seconds) ends, the excitation source automatically switches, stopping power supply to the first pair of coils and instead supplying power to the second pair of mutually orthogonal Helmholtz coils 7, thereby establishing an equally stable and uniform initial magnetic field within the measurement section 9, but with the direction changed to By. In step S104, a second set of secondary magnetic field data is acquired. Similar to step S102, a secondary induced magnetic field is also generated when the fluid flows through the By magnetic field. The fluxgate sensor array 11 synchronously acquires the data again, obtaining the second set of secondary induced magnetic field data corresponding to the By magnetic field. After acquiring the two sets of original analog signals, they are filtered in step S105. The two sets of original analog signals acquired above are transmitted to the filtering circuit 5, which amplifies the signals and filters out various noise interferences. Then, they are converted into digital signals by an analog-to-digital converter and transmitted to the PC 6. Step S106 is the core calculation step of this method, which involves constructing and solving the regularized least squares equation. After receiving the two sets of filtered secondary induced magnetic data, the PC 6 starts the internal inversion reconstruction program. The theoretical basis of this procedure is that, under the assumption of a low magnetic Reynolds number (Rm << 1) (this assumption usually holds true in laboratory-scale flows of liquid metals), the secondary induced magnetic field b generated by the fluid motion is much smaller than the initial magnetic field B0. Therefore, the total magnetic field B can be approximated as the initial magnetic field B0. At this point, the governing equation for the motion of the conductive fluid, i.e., the induction term of Ohm's law, can be written as: in, It is the induced current density. It is the conductivity of liquid lead bismuth. It is the velocity field of the fluid. It is electric potential. It is a potential difference. According to the Biot-Savart law, the induced current j produces a secondary induced magnetic field at the sensor position r. for: in It is the vacuum permeability. Pi is the mathematical constant of a circle, and V is the fluid volume. It is the differential form of a volume integral. A vector in three-dimensional Euclidean space ( , ∈ ).

[0030] Due to charge conservation, the divergence of the current is zero. in It is the divergence operator.

[0031] The electric potential can be obtained by taking the divergence from the governing equations of the motion of the conductive fluid. Poisson's equation: Applying Gaussian divergence theorem, the volume integral of the latter half can be transformed into a surface integral: It is the magnetic induction intensity at measuring point r. It is the boundary potential at the measuring point r. It is the differential form of surface integral. This is a correction form for the surface integral error at measurement point r, determined by the shape of the boundary surface and dependent on the solid angle at position r, where n is the normal vector at the boundary surface. The ratio of b to B0 is related to the magnetic Reynolds number. Proportional, defined as: in and These are the characteristic length and characteristic velocity of the fluid, respectively.

[0032] By discretizing the fluid volume of measurement segment 9 (e.g., dividing it into multiple small cubic units) and simultaneously discretizing the velocity field v and the secondary induced magnetic field b, a data vector of the secondary induced magnetic field measured by all sensor points can be established. With the velocity field vector within all discrete units Linear relationship between them: A is a large coefficient matrix, also known as the sensitivity matrix or Jacobian matrix, which is only related to the geometry of the device, the distribution of the initial magnetic field B0, and the conductivity σ of the fluid. It can be obtained in advance through numerical calculation before measurement. A matrix representing the collected magnetic field data indicating the magnitude of the induced magnetic field at all measuring points. It is a discrete velocity field matrix.

[0033] Since this is a typical electromagnetic inverse problem, it is usually ill-conditioned, and direct solutions often lead to results that are extremely sensitive to noise and unstable. To obtain a stable and physically reasonable solution, this embodiment employs a least-bicycle method based on Tikhonov regularization. Two initial magnetic fields with different directions are given as B... 0x With B 0y The magnitudes of the magnetic fields measured by the sensors are respectively and In order to obtain To address this, the Poisson equation needs to be inverted using the least squares method, and Tikhonov regularization should be used to mitigate the non-uniqueness issue. The following optimization objective function is constructed and solved: In this objective function, the first two terms are data fitting terms, representing the velocity field to be solved. The calculated induced magnetic field under two initial magnetic fields and the actual measured induced magnetic field The difference between them is minimized. The third term is the divergence constraint term, where G is the discrete matrix of the divergence operator. This term forces the reconstructed velocity field to satisfy the physical constraints of incompressible fluids (i.e., the divergence is zero). The fourth term is the Tikhonov regularization term, where D is the regularization matrix, and λ and λg are regularization parameters determined by the L-curve method. This term penalizes excessive norms or gradients in the solution to suppress the influence of noise and ensure the smoothness and stability of the solution.

[0034] The following linear equation is constructed from the above formula. By solving it in real time, the optimal parameters are found to achieve the goal of real-time speed reconstruction.

[0035] Where C is and The sum, with the superscript T indicating transpose. This indicates that the first three terms are summed and combined into one term, making subsequent calculations easier.

[0036] After solving for the inverse matrix, the distribution of the velocity field is obtained. The graph of the L-curve is plotted according to the above method, and the maximum value of the second derivative is found. The optimal regularization parameter is determined by solving the problem multiple times.

[0037] By solving this least-squares problem, a stable and unique discretized velocity field can be obtained. Finally, in step S107, the velocity field distribution is output. PC 6 then processes the calculated discretized velocity field. Visualization processing is performed, such as displaying it on the screen as a vector map, cloud map, or slice map, or saving it as a data file, thereby achieving a complete reconstruction of the three-dimensional velocity field inside measurement segment 9.

[0038] This invention can reconstruct the velocity field distribution throughout the entire measurement segment, rather than just measuring a single point or average flow velocity. It provides rich and detailed data support for a deeper understanding and analysis of complex flow mechanisms, and experimentally demonstrates the feasibility and accuracy of applying inductive flow tomography to the measurement of liquid metal flow fields.

[0039] Reference Figure 7 The diagram shown here compares the inversion velocity obtained in this embodiment with the reference velocity. Figure 8 To and Figure 7 The corresponding velocity field vector distribution is shown in the figure. The horizontal axis represents 48 different measurement point numbers, and the vertical axis represents the velocity magnitude. In the figure, the data marked with black dots represent the baseline velocity values ​​obtained through computational fluid dynamics software simulation, while the data marked with red dots represent the velocity values ​​obtained through inversion and reconstruction using the device and method of this embodiment. It can be clearly seen from the figure that the red data points and the black data points are highly consistent, and the velocity magnitude error of most measurement points is within 5%. Only in a few near-wall regions or regions with large flow field gradients is the measurement point error around 10%. This comparison result fully demonstrates that the device and method provided in this embodiment can accurately and non-invasively measure the velocity field of liquid lead-bismuth pipeline flow, verifying the feasibility and effectiveness of this technical solution.

[0040] Example 2 This embodiment provides a variant based on Embodiment 1, whose core technical principles, fluid loop, excitation system, and data processing algorithm are basically the same as those of Embodiment 1. The main difference and optimization in this embodiment lies in the adjustment of the layout of the magnetic field sensor array, aiming to explore the impact of different sensor layouts on measurement resolution and accuracy, in order to adapt to different measurement needs or cost considerations.

[0041] As an optional implementation, to achieve higher axial spatial resolution, the array layout of the fluxgate sensor 11 is redesigned in this embodiment. The overall structure of the device, including the electromagnetic pump 1, valve 2, experimental section 4 (including the forward development section 8, measurement section 9, and backward development section 10), and Helmholtz coil 7, is the same as in Embodiment 1. The difference lies in that the total number of sensors in the magnetic field sensor array remains 48, but their distribution is adjusted from "4 axial sections × 12 circumferential sensors" in Embodiment 1 to "6 axial sections × 8 circumferential sensors". This means that along the axis of the measurement section 9, the number of detection sections increases to 6, thereby improving the axial sampling density; correspondingly, the number of circumferential sensors on each section decreases to 8.

[0042] When using this 6x8 layout, the working process is exactly the same as in Example 1, still involving alternating application of initial magnetic fields Bx and By to collect two sets of secondary induced magnetic field data. During the data processing stage, due to the change in the spatial position of the sensor, the PC 6 is used to construct a system of linear equations. The coefficient matrix A needs to be recalculated based on the new sensor coordinates. Due to the increased number of data points along the axial direction, this layout is theoretically better able to capture details of velocity field changes along the flow direction. For example, it enhances the ability to identify axial vortex structures or velocity gradients in the flow field, thereby improving the axial reconstruction resolution of the velocity field.

[0043] Alternatively, in another embodiment, to further improve the overall measurement signal-to-noise ratio and reconstruction accuracy, the total number of sensors can be increased. For example, this embodiment can employ an enhanced array consisting of 72 fluxgate sensors 11, which can adopt a layout of "6 axial sections × 12 circumferential sensors". Compared to the 4x12 layout of Embodiment 1, this layout increases both axial and circumferential sampling density.

[0044] When using a 72-sensor layout, the operation process is the same as in Example 1. However, due to the increase in the number of collected measurement data points from 48 to 72, the data redundancy increases significantly. In solving the inversion problem, more measurement data means stronger constraints on the unknown velocity field, making the least squares-based solution process more robust and more resistant to measurement noise. Therefore, it is foreseeable that this high-density sensor array scheme will further improve the overall accuracy of the reconstructed velocity field distribution compared to Example 1, especially in the reconstruction quality of flow field details and weak signal regions.

[0045] Example 3 This embodiment discloses another variation of Embodiment 1, the innovation of which lies in changing the application mode of the excitation magnetic field, aiming to explore a more efficient data acquisition method and provide technical support for the study of unsteady flow. The fluid loop, experimental section structure, and magnetic field sensor array (e.g., the 4x12 layout in Embodiment 1) of this embodiment can remain unchanged, the main changes are in the excitation magnetic field generating device and its control and subsequent data processing methods.

[0046] In this embodiment, the application mode of the excitation magnetic field is improved. Specifically, the two pairs of Helmholtz coils 7 in the excitation magnetic field generator are no longer alternately powered by a DC current source, but are driven by a two-phase or three-phase AC power supply. For example, a cosine AC current I can be applied to the coil pair in the x-direction. x =I0cos(ωt), where ω is the angular frequency, and a sinusoidal alternating current I is applied to the coil in the y-direction. y =I0sin(ωt). Thus, an initial magnetic field of constant magnitude but rotating uniformly in the xy plane with an angular velocity ω will be generated inside the measuring segment 9.

[0047] Accordingly, its operating process is also adjusted. After starting the electromagnetic pump 1 to stabilize the flow of liquid lead-bismuth, the AC power supply is turned on, generating a rotating initial magnetic field within the measuring section 9. Since the direction of the initial magnetic field is constantly changing, the secondary induced magnetic field b generated by the fluid cutting the magnetic field lines also changes dynamically with time. Therefore, the fluxgate sensor array 11 needs to continuously acquire data at a sampling rate much higher than the magnetic field rotation frequency (e.g., several times ω / 2π) to capture the complete waveform of the secondary induced magnetic field changing with time.

[0048] The data processing stage also requires corresponding adjustments. PC 6 receives timing signal data from 48 channels. To obtain data equivalent to that acquired under static Bx and By magnetic fields in Example 1, these timing signals need to be phase-locked amplified. Specifically, the signal acquired by each sensor can be mixed and low-pass filtered with reference signals cos(ωt) and sin(ωt), respectively. The processing result related to cos(ωt) corresponds to the secondary induced magnetic field component when the initial magnetic field direction is x (i.e., phase 0 degrees); the processing result related to sin(ωt) corresponds to the secondary induced magnetic field component when the initial magnetic field direction is y (i.e., phase 90 degrees).

[0049] Through the aforementioned lock-in amplification process, two sets of secondary induced magnetic field data, equivalent to two orthogonal static magnetic field excitations, can be extracted from a single continuous acquisition. The subsequent inversion and reconstruction process can completely follow the least squares method based on Tikhonov regularization in Example 1, i.e., solving the same optimization objective function to finally obtain the velocity field distribution.

[0050] The advantages of this embodiment are: firstly, it enables continuous acquisition of flow field information, eliminating the waiting time required for switching the excitation magnetic field in Embodiment 1, thereby improving the overall measurement efficiency; secondly, since it can continuously acquire data, this method has a natural advantage for studying unsteady flow or periodic fluctuation phenomena in the flow field, and has higher time resolution.

[0051] Example 4 This embodiment is another variation of Embodiment 1. Its hardware, including the fluid loop, experimental section 4, excitation magnetic field generator (Helmholtz coil 7), and magnetic field sensor array (fluxgate sensor 11), is identical to that of Embodiment 1. The core difference lies in the inversion reconstruction algorithm used by the processing unit (PC 6) in the data processing system. This embodiment aims to provide a rapid reconstruction scheme that can replace traditional mathematical optimization methods. Specifically, this scheme employs a machine learning method based on artificial intelligence.

[0052] In this embodiment, the PC 6 no longer runs only a least squares solver based on Tikhonov regularization, but instead pre-deploys a fully trained deep neural network model. The role of this model is to directly learn and establish a nonlinear mapping relationship between the input secondary induced magnetic field data and the output velocity field distribution.

[0053] The implementation of this method comprises two main stages: offline training and online measurement. In the offline training stage, a large training dataset needs to be constructed before actual measurements. This dataset is generated through high-precision computational fluid dynamics numerical simulations. Specifically, the simulations assume various possible flow regimes under the same geometry (pipes, measurement sections) and fluid properties (liquid lead-bismuth) as the experimental setup, such as changing the inlet velocity and setting different disturbance sources to generate different velocity field distributions. For each simulated "real" velocity field... Then, through forward calculation (i.e., solving the Biot-Savart law), the secondary induced magnetic field data that should be generated at the 48 sensor positions under this velocity field and the given initial magnetic field (Bx and By) are obtained. In this way, a large number of "magnetic field-velocity field" data pairs were obtained. , Then, using these data pairs, a deep neural network model is trained using supervised learning. The model architecture can be a convolutional neural network suitable for processing spatial data, or a Transformer capable of capturing long-range dependencies. The training goal is to optimize the network's output. As close to reality as possible This means minimizing the error between the predicted velocity field and the actual velocity field. During the online measurement phase, the trained and accurate neural network model is deployed on PC 6 for actual measurement. The online measurement process is exactly the same as the first half of Example 1: the fluid loop is activated, initial magnetic fields in the Bx and By directions are applied alternately, two sets of secondary induced magnetic field data are collected through the fluxgate sensor array 11, and processed by the filter circuit 5. After receiving these two sets of processed magnetic field data, PC 6 concatenates them into a vector or tensor conforming to the neural network input format, and then directly feeds this input into the trained deep neural network model. The model performs a single fast forward propagation calculation to directly output the predicted velocity field distribution. .

[0054] The advantage of this embodiment lies in its reconstruction speed. Once the model training is complete, the online reconstruction process is a single forward propagation computation, which is much faster than the iterative solutions required by traditional regularization methods, thus possessing the potential to achieve near real-time visualization of the velocity field. Furthermore, for the flow regimes and operating conditions covered by the training data, its reconstruction accuracy may rival or even surpass that of traditional regularization methods. Deep learning models sometimes also exhibit better robustness in handling noise and artifacts because they have learned during training how to extract key features from noisy or incomplete inputs.

[0055] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0056] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A device for measuring induced magnetic field data of liquid metal, characterized in that, include: A fluid loop including pipes for containing the flow of the liquid metal; An experimental section, connected in series in the fluid circuit, the experimental section including a measuring section and an electromagnetic shielding enclosure outside the experimental section; An excitation magnetic field generator is disposed outside the experimental section and configured to apply initial magnetic fields in at least two different directions within the fluid region of the measurement section; A magnetic field sensor array is disposed around the outside of the measuring section to collect secondary induced magnetic field data generated by the liquid metal flow cutting the initial magnetic field; The experimental section has a flow development section at least at one of the upstream and downstream locations of the measurement section.

2. The apparatus according to claim 1, characterized in that, The liquid metal is a liquid lead-bismuth alloy.

3. The apparatus according to claim 1, characterized in that, The excitation magnetic field generating device includes two pairs of Helmholtz coils with their axes orthogonal to each other, used to alternately apply two initial magnetic fields in different directions.

4. The apparatus according to claim 1, characterized in that, The magnetic field sensor array consists of multiple fluxgate sensors.

5. The apparatus according to claim 1, characterized in that, The magnetic field sensor array includes at least two detection sections arranged along the axial direction of the measurement section, and each detection section has multiple magnetic field sensors evenly distributed circumferentially.

6. The apparatus according to claim 1, characterized in that, The aspect ratio of the measurement segment is 1:

1.

7. The apparatus according to claim 1, characterized in that, It also includes a processing unit electrically connected to the magnetic field sensor array, used to receive the secondary induced magnetic field data and reconstruct the velocity field distribution within the measurement segment based on the data.

8. The apparatus according to claim 1, characterized in that, The method for reconstructing the velocity field distribution within the measurement segment includes obtaining the velocity field distribution by constructing and solving regularized least squares equations.

9. A method for measuring induced magnetic field data of liquid metal, characterized in that, The method using the apparatus for measuring induced magnetic field data of liquid metal according to any one of claims 1-8 includes the following steps: The liquid metal is allowed to flow in a fluid loop containing the experimental section; An initial magnetic field in a first direction is applied within the measurement section; Collect the first set of secondary induced magnetic field data; An initial magnetic field in a second direction, different from the first direction, is applied within the measurement segment; Collect the second set of secondary induced magnetic field data.

10. The method according to claim 9, characterized in that, Also includes: Based on the first and second sets of secondary induced magnetic field data, the velocity field distribution within the measurement segment is inverted and reconstructed. The method of inverting and reconstructing the velocity field distribution within the measurement segment includes obtaining the velocity field distribution by constructing and solving regularized least squares equations.

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