阅读说明：本技术 强磁场下液态金属速度场高时空精度的测量系统及方法 (System and method for measuring high space-time precision of liquid metal velocity field under strong magnetic field ) 是由 倪明玖 吕泽 阳倦成 于 2019-12-13 设计创作，主要内容包括：强磁场下液态金属速度场高时空精度的测量系统及方法,测量系统包括集成在通道壁面上的微探针阵列及其集线器,浸入式探针及其三维位移装置,多通道高精度同步电压采集系统；浸入式探针位置由计算机通过其位移装置自动化控制；壁面微针阵列和浸入式探针的信号接入同步电压采集系统；基于该系统实现液态金属速度场的精确测量；以管道流为例,给出了测试步骤和数据处理方法；运用多种形式的探针结构测量多点局部速度分量,亦可测量近壁面速度、主流速度、主流涡度等速度场信息；本发明克服了液态金属速度场不易测量的难点,具有实用性强,测量效果好的特点。(The measuring system comprises a microprobe array and a concentrator thereof, an immersion probe and a three-dimensional displacement device thereof, and a multi-channel high-precision synchronous voltage acquisition system, wherein the microprobe array and the concentrator thereof are integrated on the wall surface of a channel; the position of the immersion probe is automatically controlled by a computer through a displacement device of the immersion probe; signals of the wall surface microneedle array and the immersion probe are connected into a synchronous voltage acquisition system; the system is used for realizing accurate measurement of the liquid metal velocity field; taking pipeline flow as an example, a testing step and a data processing method are given; the probe structure in various forms is used for measuring the multipoint local velocity component, and the velocity field information such as the near wall surface velocity, the main flow vorticity and the like can also be measured; the invention overcomes the difficulty that the liquid metal velocity field is difficult to measure, and has the characteristics of strong practicability and good measuring effect.)

1. The high-space-time precision measuring system of the liquid metal velocity field under the strong magnetic field is characterized by comprising a wall surface detector (3), wherein an immersion probe (4) is arranged in a main flow area of a channel, the immersion probe (4) is fixed on a displacement device (5), and signal ends of the wall surface detector (3) and the immersion probe (4) are connected to a multi-channel high-precision synchronous voltage acquisition system (6).

2. The system for measuring the high space-time precision of the liquid metal velocity field under the high magnetic field according to claim 1, wherein the immersion probes (4) are spaced by 1-5mm in pairs, are single immersion probes, and comprise a plurality of copper wires with insulating layers and diameters of 0.1-0.5mm, the copper wires penetrate into a hollow copper tube body or a stainless steel tube body with diameters of 2-5mm after being bound, the copper wires exceed 10-30mm of the tube body, the tube body is fixed by filling glue, the insulating layers are coated on the whole tube body, the fact that the whole probe is not in electric contact with liquid after being immersed is guaranteed, and only the tips of the copper wires are in electric contact with the liquid metal.

3. The system for measuring the high space-time precision of the velocity field of the liquid metal under the strong magnetic field according to claim 1, wherein the wall surface detector (3) comprises micro probe arrays (3-1), the distance between the arrays is 1-5mm, one end of each micro probe array (3-1) is inserted into a wall surface micropore reserved on the wall surface of a channel and penetrates through the wall surface of the channel to be vertically welded on a circuit board (3-2), the micro probe arrays (3-1) are all covered with an insulating coating, and only probe tips at the other end of each micro probe array (3-1) are kept in electrical contact with a fluid; the wall surface micropores are filled with insulating glue, so that liquid is prevented from leaking, and the probe is electrically insulated from the wall surface. The circuit board (3-2) is provided with a prefabricated circuit, and the probes are matched to form a voltage signal positive electrode and a voltage signal negative electrode to form a line concentration plug (3-3).

4. The system for measuring the high space-time precision of the velocity field of the liquid metal in the high magnetic field according to claim 1, wherein the multichannel high-precision synchronous voltage acquisition system (6) is connected with the wall surface detector (3) and the immersion probe (4) through shielded signal lines to acquire and store voltage signals; the synchronous acquisition capacity of 200 channels or more of analog signals is provided; acquisition speeds of 500S/S or more can be achieved.

5. The method for measuring the high space-time precision of the liquid metal velocity field under the strong magnetic field according to any one of the preceding claims, characterized by comprising the following steps:

firstly, an immersion probe (4) measures to obtain a voltage signal which is proportional to flow speed, and based on the basic principle of ohm's law, the liquid metal flowing in a magnetic field can generate an induced potential difference which is vertical to the flowing direction:

where j is the current density, σ is the liquid metal conductivity,

wherein dz is the separation of two points of the potential probe in a direction perpendicular to the magnetic field and the flow plane; the immersion probe (4) is fixed on the displacement device (5), the immersion probe (4) measures the local speed of each position by displacing to each position on the flow section, the data analysis method of the immersion probe (4) comprises the corresponding relation of the potential difference and the speed component in different directions of the same position, the three-dimensional speed information of the same position in space is reflected, and according to ohm's law, two speed components vertical to the direction of the magnetic field (2) are positively correlated with the electric potential thereof, namely u is u_x～dφ_7,8＝φ₇-φ₈，u_z～dφ_9,10＝φ₉-φ₁₀；

The principle of the wall surface detector (3) is consistent with that of the immersion probe (4), the wall surface detector (3) integrates an array formed by a plurality of micro-needles, a group of voltage signals are formed between every two adjacent micro-needles of the array, and the local flow velocity corresponds to one group of voltage signals, so that the wall surface detector (3) can measure multipoint velocities to form a velocity distribution result;

thirdly, determining the probe spacing, selecting the probe spacing, wherein the distance between every two immersion probes (4) and the spacing between the microprobe arrays (3-1) are 1-5 mm;

fourthly, determining a sampling speed, wherein the sampling speed is higher than 500S/S;

and fifthly, the signals of the wall surface detector (3) and the immersion probe (4) are jointly analyzed, and the correlation of local speeds at different spatial positions reflects the whole flow structure.

Technical Field

The invention belongs to the technical field of fluid measurement, and particularly relates to a high-space-time-precision measurement system and method for a liquid metal velocity field in a strong magnetic field.

Background

The liquid metal flow phenomenon can be understood as the combination of electromagnetic and hydrodynamic properties, has rich fundamental research significance, and also has important engineering application scenes in the ferrous metallurgy industry and the magnetic confinement fusion reactor. In particular, fusion reactors involve physical and engineering problems with the flow heat transfer of large quantities of liquid metal. Due to the characteristics of cross-scale, multi-field coupling, light tightness and high temperature of the liquid metal flow, a plurality of traditional measurement means cannot be suitable, and the research is very challenging. From the history of development of magnetohydrodynamics, the liquid metal flow field measurement technology is important to the development of disciplines.

According to literature research, the existing liquid metal local flow field measurement scheme is summarized as follows:

1. potential probe method. It measures the potential difference perpendicular to the direction of the magnetic field generated by the fluid in a constant magnetic field. The probe is immersed in the liquid and must maintain good electrical contact therewith. The advantage is that the time resolution is high, the probe and the space can be designed to be very small to measure the local speed, and the development into an array is facilitated to obtain rich transient flow field information.

2. The permanent magnet probe method is to closely attach the tiny permanent magnet and the potential probe and immerse the tiny permanent magnet and the potential probe into fluid. The principle is similar to the potentiometric probe method, but is only applicable to flow rate measurements without a background magnetic field.

3. The resistance probe method is commonly used for measuring the two-phase flow of the liquid metal. The principle is that the resistance measured when the liquid phase passes through the probe region drops significantly, while the resistance rises sharply when the gas phase passes. This solution necessitates careful adjustment of the electrical contact properties of the probe with the liquid.

4. Hot wire anemometers are the same technology as traditional hot wire anemometers. Based on the heat exchange between the resistance wire and the flow field in the heating state, the temperature of the resistance wire is linearly related to the flow velocity of the peripheral liquid.

5. Pressure measurement (pitot tube) is a conventional immersion measurement scheme used in liquid metal for measurement of the main flow velocity.

6. Precision opto-mechanical methods are based on the mechanical force of a fluid on an immersed microscopic probe. The requirement on the mounting accuracy is high.

7. The pulse ultrasonic velocity measurement method and the branch thereof are widely applied to the measurement of liquid metal. The probe sends a unidirectional ultrasonic pulse into the fluid and receives signals that are progressively reflected by fluid micelles at different distances. The space position of the fluid micro-cluster is calculated through the time difference of sending and receiving, and the velocity of the fluid micro-cluster is calculated through the Doppler frequency shift of sending and receiving, so that the signal can calculate the one-dimensional flow field information of the ultrasonic wave transmitting direction. In the pulse ultrasonic method, the probe can be installed on the wall surface without being immersed in liquid, and has no influence on the flow field.

8. The high-energy ray imaging is mainly used for researching liquid metal two-phase flow. The application of gamma rays, X rays and neutron rays in the measurement of the liquid metal flow field is already known in the literature. Abundant two-dimensional flow field information can be analyzed from the image. The limitation is however that the radiation is attenuated very rapidly in the fluid, and its measurement depth in the direction of the radiation is usually only in the order of centimeters. On the other hand, increasing its temporal resolution, or improving it into a three-dimensional measurement system, still faces a number of technical challenges.

9. Some local flow field measurement methods based on secondary induced magnetic fields. Such as electromagnetic imaging (imaging techniques based on resistance, conductance or capacitance measurements), induction coil methods. Such methods are based on induced magnetic field feedback of the fluid under an external alternating (or constant) magnetic field. Flow field information is derived in reverse based on the magnetic field signals.

10. A lorentz force velocimeter is also a method based on an induced magnetic field. It measures the reaction force of the induced magnetic field generated by the fluid against the magnetic source (i.e., the permanent magnet). Its spatial resolution is limited to the size of the permanent magnet (down to the millimeter level) and its temporal resolution is limited to the mechanical structural properties of the sensor.

In conclusion, method 2 is not suitable for a strong background magnetic field environment; methods 3, 8 are primarily for two-phase flow; method 4 is not applicable in hot environments; method 5 is used for mainstream measurement, and local velocity is difficult to measure; method 6 is insufficient in time resolution; method 7 remains a spatial averaging method on the ultrasound scale; the signals of the methods 9 and 10 both depend on the integral effect of the electromagnetic action on the local space, and the spatial resolution is deficient.

Disclosure of Invention

In order to make up for the defects of the prior art, the invention aims to provide a system and a method for measuring the high space-time precision of a liquid metal velocity field in a strong magnetic field.

In order to achieve the purpose, the technical scheme of the invention is as follows:

the high-space-time precision measuring system of the liquid metal velocity field under the strong magnetic field comprises a wall surface detector 3, an immersion probe 4 is arranged in a main flow area of a channel, the immersion probe 4 is fixed on a displacement device 5, and signal ends of the wall surface detector 3 and the immersion probe 4 are connected to a multi-channel high-precision synchronous voltage acquisition system 6.

The immersion probes 4 are spaced by 1-5mm in pairs, are single immersion probes and comprise a plurality of copper wires with insulating layers, the diameter of each copper wire is 0.1-0.5mm, the copper wires penetrate into a hollow copper pipe body or a stainless steel pipe body with the diameter of 2-5mm after being bound, the copper wires exceed the pipe body by 10-30mm, glue is filled and fixed in the pipe body, the insulating layers are coated on the whole pipe body, the fact that the probe is not in electric contact with liquid after being immersed is guaranteed, and only the tips of the copper wires are in electric contact with the liquid metal.

The wall surface detector 3 comprises a micro probe array 3-1, the distance between arrays is 1-5mm, one end of the micro probe array 3-1 is inserted into a wall surface micropore reserved on the wall surface of a channel and penetrates through the wall surface of the channel to be vertically welded on a circuit board 3-2, the micro probe array 3-1 is entirely covered with an insulating cladding, and only the probe tip at the other end of the micro probe array 3-1 keeps electric contact with fluid; the wall surface micropores are filled with insulating glue, so that liquid is prevented from leaking, and the probes are matched with a prefabricated circuit on the wall surface electric insulation circuit board 3-2 to form voltage signal positive and negative electrodes to form a line concentration plug 3-3.

The multi-channel high-precision synchronous voltage acquisition system 6 is connected with the wall surface detector 3 and the immersion probe 4 through a shielding signal line, and acquires and stores voltage signals; the synchronous acquisition capacity of 200 channels or more of analog signals is provided; acquisition speeds of 500S/S or more can be achieved.

The method of the measuring system of the high space-time precision of the liquid metal velocity field under the strong magnetic field comprises the following steps:

firstly, an immersion probe 4 measures a voltage signal which is proportional to the flow velocity, and based on the basic principle of ohm's law, the flow of liquid metal in a magnetic field generates an induced potential difference perpendicular to the flow direction:

where j is the current density, σ is the liquid metal conductivity,the signal is measured as the potential difference, u is the flow velocity, B is the magnetic flux density, under the external strong magnetic field, j/sigma-0, therefore the potential difference between two measuring points is directly related to the velocity, and the fluid velocity is:

where dz is the separation of two points of the potential probe in a direction perpendicular to the magnetic field and the flow plane. The immersion probe 4 is fixed on the displacement device 5, the immersion probe 4 can measure the local speed of each position by displacing to each position on the flow section, the data analysis method of the immersion probe 4 comprises the corresponding relation of the potential difference and the speed component in different directions of the same position, the three-dimensional speed information of the same position in space is reflected, and according to ohm's law, two speed components perpendicular to the direction of the magnetic field 2 are positively correlated with the potential thereof, namely u_x～dφ_7,8＝φ₇-φ₈，u_z～dφ_9,10＝φ₉-φ₁₀；

The principle of the wall surface detector 3 is consistent with that of the immersion probe 4, the wall surface detector 3 integrates an array formed by a plurality of micro-needles, a group of voltage signals are formed between every two adjacent micro-needles of the array, and the voltage signals correspond to a local flow velocity, so that the wall surface detector 3 can measure the speed of multiple points to form a speed distribution result;

thirdly, determining the probe spacing, selecting the probe spacing, wherein the distance between every two immersion probes 4 and the distance between the microprobe arrays 3-1 are 1-5 mm;

fourthly, determining a sampling speed, wherein the sampling speed is higher than 500S/S;

and fifthly, the signals of the wall surface detector 3 and the immersion probe 4 are jointly analyzed, and the correlation of local velocities at different spatial positions reflects the whole flow structure.

Compared with the prior art, the invention has the following advantages:

1. the method is suitable for opaque liquid metal measurement, and compared with other liquid metal measurement means, the local velocity field measured by the method is finer, and the method has excellent time (millisecond level) and space (less than millimeter level) resolution.

2. The probe is thin, the response is fast, and the manufacturing cost is low; the effect on the flow is negligible. The high-temperature-resistant and high-intensity magnetic field sensor can bear high temperature and high magnetic field environment, is not sensitive to fluid conductivity, and has good vibration resistance.

3. The invention has the characteristic of easy expansion, and can arrange a large number of probe measuring points according to the requirement to obtain clear whole field data in a large space range.

Drawings

Fig. 1 illustrates an implementation method of the measurement system by taking a pipeline flow as an example.

FIG. 2 is a schematic diagram of a structure of an immersion probe.

FIG. 3 is a schematic diagram of a micro probe array and a circuit board thereof.

FIG. 4 is a schematic view of the wall mount of the probe array.

Fig. 5 is a signal processing flow.

Detailed Description

The invention relates to a method for measuring a local flow field of liquid metal, which is mainly used for measuring the potential difference formed between microprobes by the flow field. The main measuring components comprise a microprobe array and a concentrator thereof, an immersion probe and a three-dimensional displacement device thereof, and a multi-channel high-precision synchronous voltage acquisition system, which are integrated on the wall surface of a channel.

The following takes the pipe flow of the liquid metal under the background magnetic field as an example, and further describes the pipe flow with reference to the attached drawings.

As shown in fig. 1, a liquid metal main flow velocity 1, an external magnetic field 2, and a main flow velocity 1 are provided by an external circulation loop system. The external magnetic field 2 may come from a permanent magnet, an electromagnet or a superconducting magnet, providing a stable magnetic field environment for the pipe. The system for measuring the high space-time precision of the liquid metal velocity field under the strong magnetic field comprises a plurality of wall surface detectors 3, and can measure the flow field information close to the wall surface. An immersion probe 4 is arranged in the main flow area of the channel, the immersion probe 4 is fixed on a displacement device 5, and the immersion probe 4 can measure the local speed of each position by displacing to each position on the flow section. The signal ends of the wall surface detector 3 and the immersion probe 4 are connected to a multi-channel high-precision synchronous voltage acquisition system 6, and are used for acquiring and storing potential data and converting the potential data into speed field information.

As shown in fig. 2, the immersion probes 4 are spaced 1-5mm apart from each other, are single immersion probes, and include a plurality of copper wires with insulating layers, the diameter of which is 0.1-0.5mm, the copper wires penetrate into the hollow copper tube body or the stainless steel tube body with the diameter of 2-5mm after being bound, the copper wires exceed the tube body by 10-30mm, the tube body is internally filled with glue for fixation, the insulating layers are coated on the whole tube body, it is ensured that the whole probe is not in electrical contact with liquid after being immersed, and only the tips of the copper wires keep electrical contact with the liquid metal.

As shown in fig. 3, the wall surface detector 3 includes a micro probe array 3-1, the distance between arrays is 1-5mm, one end of the micro probe array 3-1 is inserted into a wall surface micropore reserved on the wall surface of a channel and penetrates through the wall surface of the channel to be vertically welded on a circuit board 3-2, the micro probe array 3-1 is entirely covered with an insulating cladding, and only the probe tip at the other end of the micro probe array 3-1 keeps electrical contact with a liquid fluid; the wall surface micropores are filled with insulating glue, so that liquid is prevented from leaking, and the probe is electrically insulated from the wall surface. The circuit board 3-2 is provided with a prefabricated circuit, and the probes are matched to form a voltage signal anode and a voltage signal cathode to form a line concentration plug 3-3. The multi-channel high-precision synchronous voltage acquisition system 6 is connected with the wall surface detector 3 and the immersion probe 4 through a shielding signal line, and acquires and stores voltage signals; the synchronous acquisition capacity of 200 channels or more of analog signals is provided; the high-voltage-resolution high-precision grounding device has high voltage resolution, the precision reaches microvolt level, and meanwhile, the high-voltage-resolution high-precision grounding device has a good grounding design and reduces signal noise generated by electromagnetic interference. The multi-channel high-precision synchronous voltage acquisition system 6 can achieve the acquisition speed of 500S/S or higher.

A plurality of probe arrays are transversely and longitudinally arranged on the wall surface perpendicular to the direction of the magnetic field, the tips of the probes can be tightly attached to the inner wall of the pipeline or exceed the inner wall by 1-5mm, and two-dimensional velocity field information of the wall surface close to the wall surface and parallel to the wall surface can be obtained based on the same principle as the immersion probe. The method is also suitable for the wall surface of a conductive or non-conductive material. When the wall surface is made of conductive material, the gap between the probe and the wall surface should be filled with insulating material to block the electrical contact between the probe and the wall surface, as shown in fig. 4, 13 to 16 are wall surface probes, and 17 is an insulating sealant filled between the probe and the micropore.

The method of the measuring system of the high space-time precision of the liquid metal velocity field under the strong magnetic field comprises the following steps:

firstly, an immersion probe 4 measures a voltage signal which is proportional to the flow velocity, and based on the basic principle of ohm's law, the flow of liquid metal in a magnetic field generates an induced potential difference perpendicular to the flow direction:

where j is the current density, σ is the liquid metal conductivity,

the signal is measured as the potential difference, u is the flow velocity, B is the magnetic flux density, under the external strong magnetic field, j/sigma-0, therefore the potential difference between two measuring points is directly related to the velocity, and the fluid velocity is:

wherein dz is the potential of the probe at two points perpendicular to the magnetic field and flowPitch in the planar direction. Since the immersion probe 4 is fixed to the displacement device 5, the immersion probe 4 can measure the local velocity at each position by displacing to each position on the flow cross section. Specifically, as shown in FIG. 2, the data analysis method for the immersion probe 4 includes the corresponding relationship between the potential difference and the velocity component in different directions at the same position, reflecting the three-dimensional velocity information at the same position in space, and according to ohm's law, two velocity components perpendicular to the direction of the magnetic field 2 are positively correlated with the potential thereof, i.e. u_x～dφ_7,8＝φ₇-φ₈，u_z～dφ_9,10＝φ₉-φ₁₀。

Secondly, the wall detector 3 is constructed as shown in FIG. 3, and its basic principle is consistent with the immersion probe 4. The difference lies in that the immersion probe 4 only collects the flow velocity of a single space point, and the wall surface detector 3 integrates an array formed by a plurality of micro-needles, and a group of voltage signals are formed between every two adjacent micro-needles of the array, and correspond to a local flow velocity, so that the wall surface detector 3 can measure the multi-point velocity to form a velocity distribution result.

And thirdly, determining the probe distance. Regarding the choice of probe pitch. The distance between every two immersion probes 4 and the distance between every two micro probe arrays 3-1 are close to each other as much as possible when the probes are manufactured, namely delta l is as small as possible. The smaller Δ l, the lower the signal amplitude, and the smaller the signal-to-noise ratio with respect to the ambient noise, the less easily it is measured. As can be seen from the above analysis, the choice of Δ l is always a trade-off for different research objectives. For the measurement of the local velocity of the liquid metal fluid, the range of the measurement signal d phi is about 40 to 4000 microvolts, for example Δ l is 4mm, u is 0.1 to 1m/s, and B is 0.1 to 1T. For liquid metal flow measurements, the invention proposes Δ l to be between 1 and 5 mm.

And fourthly, determining the sampling speed. From the above, the velocity directly measured by the probe is actually the spatial average flow field information on the spatial Δ l scale. In some cases this spatial resolution is not sufficient. Under the condition of stable turbulence, if the sampling speed is high enough, the pulse speed high-frequency information can be obtained by carrying out frequency domain analysis on the pulse speed time sequence signal, and the pulse speed high-frequency information corresponds to the speed pulse with smaller space scale, namely

d phi 'u', u '(high frequency) u' (small spatial dimension)

According to the turbulence structure theory, the frequency domain analysis result corresponds to the flow space scale one by one. The method can establish the relation between the time scale and the space scale of the local speed signal and can obtain the local speed pulsation information under the extremely small space scale. For liquid metal flow measurements, the present invention suggests a sampling speed higher than 500S/S.

And fifthly, jointly analyzing signals of the wall surface detector 3 and the immersion probe 4. The correlation of local velocities at different spatial locations reflects the overall flow structure. The data analysis flow is shown in fig. 5. For example, in the case where the external magnetic field 2 is strong, the liquid metal flows to form a quasi-two-dimensional structure. J is measured from the immersion probe 4_y0, i.e. d phi_11,12＝φ₁₁-φ₁₂0, thus d phi_11,12Is a quantitative index for the conversion of flowing three-dimensional and two-dimensional structures. On the other hand, the velocity measured by the two side wall surface probe arrays 3 and the probe 4 is highly correlated, which also indicates that the flow forms a quasi-two-dimensional structure. It should be noted that, as the external magnetic field is strengthened, the three-dimensional and two-dimensional transformation of the flow is a gradual process, and the detailed research thereof is not sufficient, and it is the research object of the patent technology.