CN110794164B - System and method for measuring high space-time precision of liquid metal speed field under strong magnetic field - Google Patents
System and method for measuring high space-time precision of liquid metal speed field under strong magnetic field Download PDFInfo
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- CN110794164B CN110794164B CN201911279604.3A CN201911279604A CN110794164B CN 110794164 B CN110794164 B CN 110794164B CN 201911279604 A CN201911279604 A CN 201911279604A CN 110794164 B CN110794164 B CN 110794164B
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- 229910001338 liquidmetal Inorganic materials 0.000 title claims abstract description 41
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 16
- 229910052802 copper Inorganic materials 0.000 claims description 16
- 239000010949 copper Substances 0.000 claims description 16
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- 239000007788 liquid Substances 0.000 claims description 11
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- 238000007405 data analysis Methods 0.000 claims description 5
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- 238000009851 ferrous metallurgy Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
- G01P5/08—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring variation of an electric variable directly affected by the flow, e.g. by using dynamo-electric effect
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M10/00—Hydrodynamic testing; Arrangements in or on ship-testing tanks or water tunnels
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
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- General Physics & Mathematics (AREA)
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Abstract
The measuring system comprises a microprobe array integrated on the wall surface of a channel, a concentrator thereof, an immersed probe, a three-dimensional displacement device thereof and a multichannel high-precision synchronous voltage acquisition system; the position of the immersion probe is automatically controlled by a computer through a displacement device of the immersion probe; the signals of the wall microneedle array and the immersion probe are connected to a synchronous voltage acquisition system; based on the system, accurate measurement of the liquid metal speed field is realized; taking a pipeline flow as an example, a test step and a data processing method are given; the multi-point local velocity component is measured by using various probe structures, and velocity field information such as near wall surface velocity, main stream vorticity and the like can also be measured; the invention overcomes the difficulty that the liquid metal speed field is difficult to measure, and has the characteristics of strong practicability and good measuring effect.
Description
Technical Field
The invention belongs to the technical field of fluid measurement, and particularly relates to a system and a method for measuring high space-time precision of a liquid metal speed field under a strong magnetic field.
Background
The liquid metal flow phenomenon can be understood as the combination of electromagnetic and hydrodynamic characteristics, has rich basic research significance, and also has important engineering application scenes in the ferrous metallurgy industry and the magnetic confinement fusion reactor. In particular fusion stacks involve a number of physical and engineering problems with liquid metal flow heat exchange. Liquid metal flow is extremely challenging to study because of its trans-scale, multi-field coupling, opaque, high temperature characteristics, many traditional measurement means are not applicable. From the development history of magnetohydrodynamics, the liquid metal flow field measurement technology plays a major role in the subject development.
According to literature investigation, 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 remain in good electrical contact therewith. The method has the advantages of high time resolution, very small probe and space design to measure local speed, and convenient expansion into an array to obtain abundant transient flow field information.
2. The permanent magnet probe method is to tightly attach a tiny permanent magnet and a potential probe and immerse the tiny permanent magnet and the potential probe in fluid. The principle is similar to the potentiometric probe method, but is only applicable to flow rate measurements without background magnetic fields.
3. The resistance probe method is commonly used for measuring the two-phase flow of liquid metal. The principle is that the measured resistance drops significantly as the liquid phase passes through the probe region, while the resistance rises sharply as the gas phase passes through. This approach must carefully tailor the electrical contact properties of the probe with the liquid.
4. Hotline anemometers are the same technology as traditional hotline 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 peripheral liquid flow rate.
5. Pressure measurement (pitot tube) is a traditional immersed measurement scheme used in liquid metal for the measurement of the main flow velocity.
6. Precision opto-mechanical methods are based on the mechanical force of a fluid on an immersed tiny probe. The requirement on the installation precision is very high.
7. The pulse ultrasonic velocimetry and the branches thereof are widely applied to liquid metal measurement. The probe transmits a single-directional 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 sending and receiving time difference, and the speed 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 emitting direction. In the pulsed ultrasonic method, the probe can be installed on the wall surface without immersing in liquid, and has no influence on the flow field.
8. High-energy ray imaging is mainly used for researching liquid metal two-phase flow. There are applications of gamma rays, X-rays and neutron rays in liquid metal flow field measurements in the literature. From the image, rich two-dimensional flow field information can be analyzed. However, the limitation is that the radiation decays very rapidly in the fluid, and its depth of measurement along the radiation direction is typically only in the order of centimeters. On the other hand, increasing its time resolution, or improving to 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 resistive, conductive or capacitive 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 inversely based on the magnetic field signal.
10. Lorentz force velocimetry is also a method based on an induced magnetic field. It measures the reaction force of the induced magnetic field generated by the fluid to the magnetic source (i.e., permanent magnet). Its spatial resolution is limited to the size of the permanent magnet (down to the millimeter scale) and its temporal resolution is limited to the mechanical structural characteristics of the sensor.
In summary, method 2 is not suitable for strong background magnetic field environments; the methods 3 and 8 are mainly used for two-phase flow; method 4 is not suitable for use in a thermal environment; method 5 is used for main flow measurement, and local speed is difficult to measure; method 6 has insufficient time resolution; method 7 is still a spatial averaging method on the ultrasound scale; the signals of the methods 9 and 10 are dependent on the integration effect of electromagnetic action in local space, and the spatial resolution is poor.
Disclosure of Invention
In order to make up the defects of the prior art, the invention aims to provide a high-space-time precision measuring system and method for a liquid metal speed field under a strong magnetic field, and designs various probe arrangement, signal acquisition systems and data analysis methods based on the potential probe principle so as to solve the problem of high-precision measurement of a liquid metal local flow field under the strong magnetic field.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
The measuring system with high space-time precision for the liquid metal velocity field under the strong magnetic field comprises a wall 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 the wall detector 3 and a signal end of the immersion probe 4 are connected with a multichannel high-precision synchronous voltage acquisition system 6.
The immersed probe 4 is a single immersed probe with a distance of 1-5mm, and comprises a plurality of copper wires with the diameter of 0.1-0.5mm and an insulating layer, wherein the copper wires are bound and then penetrate into a hollow copper pipe body or a stainless steel pipe body with the diameter of 2-5mm, the copper wires exceed the pipe body by 10-30mm, the inside of the pipe body is filled with glue and fixed, the insulating layer is coated on the whole pipe body, the whole immersed probe is ensured not to be in electrical contact with liquid, and only the tips of the copper wires are kept in electrical contact with liquid metal.
The wall detector 3 comprises a micro probe array 3-1, the distance between the arrays is 1-5mm, one end of the micro probe array 3-1 is inserted into a wall micropore reserved on the wall surface of a channel and penetrates through the wall surface of the channel to be vertically welded on the circuit board 3-2, the whole micro probe array 3-1 is covered with an insulating cladding, and only the probe tip at the other end of the micro probe array 3-1 is kept in electrical contact with fluid; the micropores on the wall surface are filled with insulating glue, so that liquid is prevented from leaking, and the probes and the prefabricated circuits on the wall surface electric insulation circuit board 3-2 are matched to form voltage signal positive and negative electrodes to form the line concentration plug 3-3.
The multichannel high-precision synchronous voltage acquisition system 6 is connected with the wall detector 3 and the immersion probe 4 through shielding signal wires and is used for acquiring and storing voltage signals; the synchronous acquisition capability of 200 channels or more of analog signals is provided; the acquisition speed of 500S/S or more can be achieved.
The method of the liquid metal speed field high space-time precision measuring system under the strong magnetic field comprises the following steps:
1. The immersion probe 4 measures a voltage signal proportional to the flow rate, based on the basic principle of ohm's law, the flow of liquid metal in a magnetic field generates an induced electric potential difference perpendicular to the flow direction:
where j is the current density, σ is the liquid metal conductivity, The potential difference is the measured signal, u is the flow velocity, B is the magnetic flux density, j/sigma-0 is carried out under the external strong magnetic field, so that the potential difference between two measuring points is directly related to the velocity, and the fluid velocity is:
Where dz is the distance between the two points of the potential probe in a direction perpendicular to the magnetic field and the flow plane. Since 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 between potential differences in different directions and speed components at the same position, 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～dφ7,8＝φ7-φ8,uz～dφ9,10＝φ9-φ10;
2. the principle of the wall detector 3 is consistent with that of the immersion probe 4, the wall detector 3 integrates an array formed by a plurality of micro-needles, a group of voltage signals is arranged between every two adjacent micro-needles of the array, and a local flow velocity corresponds to the array, so that the wall detector 3 can measure the multi-point velocity to form a velocity distribution result;
3. Determining the probe spacing, wherein regarding the selection of the probe spacing, the distance between every two immersed probes 4 is equal to the spacing between 3-1 arrays of the micro probe arrays, and Deltal is 1-5mm;
4. Determining a sampling speed, wherein the sampling speed is higher than 500S/S;
5. The correlation of the local velocities at different spatial locations reflects the overall flow structure, by signal combination analysis of the wall probe 3 and the immersion probe 4.
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 has excellent time (millisecond level) and space (less than millimeter level) resolution.
2. The probe of the invention is thin, the response is quick, and the manufacturing cost is low; the effect on flow is negligible. Can bear high temperature and strong magnetic field environment, is insensitive to fluid conductivity and has good vibration resistance.
3. The invention has the characteristic of easy expansion, and a large number of probe measuring points can be arranged according to the requirement so as to obtain clear whole field data with a large space range.
Drawings
Fig. 1 illustrates an implementation of the present measurement system, taking a pipe flow as an example.
Fig. 2 is a schematic structural view of an immersion probe.
FIG. 3 is a schematic diagram of the structure of a micro probe array and its circuit board.
FIG. 4 is a wall mounting schematic of a 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 mainly aims at measuring potential difference formed between microprobe by the flow field. The main measuring component comprises a microprobe array and a concentrator thereof which are integrated on the wall surface of the channel, an immersed probe and a three-dimensional displacement device thereof, and a multichannel high-precision synchronous voltage acquisition system.
The pipe flow of the liquid metal under the background magnetic field is taken as an example and further described with reference to the accompanying drawings.
As shown in fig. 1, the liquid metal main flow velocity 1, the external magnetic field 2, the main flow velocity 1 is provided by an external circulation loop system. The external magnetic field 2 may be from a permanent magnet, an electromagnet or a superconducting magnet, providing a stable magnetic field environment for the pipe. The measuring system with high space-time precision for the liquid metal velocity field under the strong magnetic field comprises a plurality of wall surface detectors 3 which can measure the flow field information of the near 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 wall detector 3 and the signal end of the immersion probe 4 are connected with a multichannel high-precision synchronous voltage acquisition system 6, and potential data are acquired and stored and converted into speed field information.
As shown in figure 2, the immersed probe 4 is a single immersed probe with a distance of 1-5mm, and comprises a plurality of copper wires with insulating layers, wherein the diameters of the copper wires are 0.1-0.5mm, the copper wires are bound and then penetrate into a hollow copper pipe body or a stainless steel pipe body with the diameters of 2-5mm, the copper wires exceed the pipe body by 10-30mm, the inside of the pipe body is filled with glue and fixed, the insulating layers are integrally smeared on the pipe body, the whole immersed probe is ensured not to be in electrical contact with liquid, and only the tips of the copper wires are kept in electrical contact with the liquid metal.
As shown in FIG. 3, the wall detector 3 comprises a micro probe array 3-1, the distance between the arrays is 1-5mm, one end of the micro probe array 3-1 is inserted into a wall micropore reserved on the wall surface of a channel and vertically welded on a circuit board 3-2 by penetrating the wall surface of the channel, the whole micro probe array 3-1 is covered with an insulating coating, and only the probe tip at the other end of the micro probe array 3-1 is kept in electrical contact with liquid fluid; the wall micropores are filled with insulating glue, so that the liquid is prevented from leaking, and the probes are electrically insulated from the wall. The prefabricated circuit on the circuit board 3-2 pairs the probes to form the voltage signal positive and negative poles to form the line concentration plug 3-3. The multichannel high-precision synchronous voltage acquisition system 6 is connected with the wall detector 3 and the immersion probe 4 through shielding signal wires and is used for acquiring and storing voltage signals; the synchronous acquisition capability of 200 channels or more of analog signals is provided; the high-voltage-resolution power supply has high voltage resolution, the precision reaches the order of microvolts, and meanwhile, the high-voltage-resolution power supply has good grounding design, and signal noise generated by electromagnetic interference is reduced. The multichannel high-precision synchronous voltage acquisition system 6 can achieve an acquisition speed of 500S/S or higher.
A plurality of probe arrays are horizontally and longitudinally arranged on the wall surface perpendicular to the magnetic field direction, the probe tip can be clung to the inner wall of a pipeline or exceed the inner wall by 1-5mm, and based on the same principle as an immersed probe, the two-dimensional speed field information of the wall surface parallel to the wall surface can be obtained. This method is also applicable to materials where the walls are conductive or non-conductive. 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 insulating sealant filled between the probe and the micro holes.
The method of the liquid metal speed field high space-time precision measuring system under the strong magnetic field comprises the following steps:
1. The immersion probe 4 measures a voltage signal proportional to the flow rate, based on the basic principle of ohm's law, the flow of liquid metal in a magnetic field generates an induced electric potential difference perpendicular to the flow direction:
where j is the current density, σ is the liquid metal conductivity, The potential difference is the measured signal, u is the flow velocity, B is the magnetic flux density, j/sigma-0 is carried out under the external strong magnetic field, so that the potential difference between two measuring points is directly related to the velocity, and the fluid velocity is:
Where dz is the distance between the two points of the potential probe in a direction perpendicular to the magnetic field and the flow plane. Since the immersion probe 4 is fixed to the displacement device 5, the immersion probe 4 can measure the local velocity of each location by displacement to each location on the flow cross section. Specifically, as shown in fig. 2, the data analysis method of the immersion probe 4 includes the correspondence between potential differences and velocity components in different directions at the same position, reflecting 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 their potentials, i.e., u x～dφ7,8＝φ7-φ8,uz～dφ9,10＝φ9-φ10.
2. The wall probe 3 is constructed as shown in fig. 3, and its basic principle is identical to that of the immersion probe 4. The difference is that the immersion probe 4 only collects the flow velocity of a single space point, and the wall detector 3 integrates an array composed of a plurality of micro-needles, wherein a group of voltage signals is arranged between every two adjacent micro-needles of the array, and corresponds to a local flow velocity, so that the wall detector 3 can measure the multi-point velocity to form a velocity distribution result.
3. The probe spacing is determined. Regarding the selection of probe spacing. The distance between every two immersed probes 4 and the distance between the arrays of the micro probe arrays 3-1 are as close as possible, namely, deltal is as small as possible when the probes are manufactured. And the smaller the Δl, the lower the signal amplitude, the smaller its signal-to-noise ratio relative to ambient noise, and the less easily measured. From the above analysis, it can be seen that the choice of Δl is always a trade-off for different study objectives. For the measurement of the local velocity of the liquid metal fluid, taking al=4mm, u=0.1-1 m/s, b=0.1-1T as an example, the measurement signal dΦ ranges from about 40 to 4000 microvolts. For liquid metal flow measurements, the invention suggests Δl of 1-5mm.
4. The sampling rate is determined. From the bar, the directly measured velocity of the probe is actually the spatially averaged flow field information on the spatial Δl scale. In some cases this spatial resolution is not yet sufficient. In the case of steady turbulence, if the sampling speed is high enough, frequency domain analysis of the pulse speed timing signal can obtain pulse speed high frequency information corresponding to smaller spatial scale speed pulses, i.e
Dphi 'to u', u '(high frequency) to u' (small spatial scale)
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 connection between the time scale and the space scale of the local velocity signal, and can obtain the local velocity pulsation information under the extremely small space scale. For liquid metal flow measurements, the invention suggests sampling speeds higher than 500S/S.
5. The wall probe 3 is analyzed in combination with the signal of 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. Taking the case of strong external magnetic field 2 as an example, the liquid metal flows to form a quasi-two-dimensional structure. From the immersion probe 4 j y -0, i.e. dφ 11,12＝φ11-φ12 -0, can be measured, so dφ 11,12 is a quantitative indicator of the conversion of the flow three-dimensional and two-dimensional structure. On the other hand, the velocity of the two sidewall probe arrays 3 and the velocity of the probes 4 show a high correlation, which also indicates that the flow forms a quasi-two-dimensional structure. It should be noted that, with the enhancement of the external magnetic field, the three-dimensional two-dimensional transformation of the flow is a gradual process, and the detail is not fully studied, which is the research objective of the technology of this patent.
Claims (2)
1. The method for measuring the high space-time precision of the liquid metal velocity field under the strong magnetic field is characterized in that the measurement system 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 the signal ends of the wall surface detector (3) and the immersion probe (4) are connected with a multichannel high-precision synchronous voltage acquisition system (6); the measuring method comprises the following steps:
1. The immersion probe (4) measures a voltage signal proportional to the flow rate, based on the basic principle of ohm's law, the flow of liquid metal in a magnetic field generates an induced electric potential difference perpendicular to the flow direction:
where j is the current density, σ is the liquid metal conductivity, The potential difference is the measured signal, u is the flow velocity, B is the magnetic flux density, j/sigma is approximately equal to 0 under the external strong magnetic field, so that the potential difference between two measuring points is directly related to the velocity, and the fluid velocity is:
wherein dz is the distance between two points of the potential probe in the direction perpendicular to the magnetic field and the flow plane; because 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 between potential differences and speed components in different directions at the same position, 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 related to the potential of the two speed components, namely u x～dφ7,8＝φ7-φ8,uz～dφ9,10＝φ9-φ10;
2. The principle of the wall detector (3) is consistent with that of the immersion probe (4), the wall detector (3) integrates an array formed by a plurality of micro-needles, a group of voltage signals is arranged between every two adjacent micro-needles of the array, and a local flow velocity corresponds to the array, so that the wall detector (3) can measure the multi-point velocity to form a velocity distribution result;
3. Determining the probe spacing, wherein regarding the selection of the probe spacing, the distance between every two immersed probes (4) and the distance between the arrays of the micro probe arrays (3-1) are 1-5mm;
4. Determining a sampling speed, wherein the sampling speed is higher than 500S/S;
5. The signals of the wall detector (3) and the immersion probe (4) are analyzed in a combined way, and the correlation of local speeds of different spatial positions reflects the whole flow structure;
The immersed probe (4) is a single immersed probe with a distance of 1-5mm, comprises a plurality of copper wires with the diameter of 0.1-0.5mm and provided with insulating layers, the copper wires are bound and then penetrate into a hollow copper pipe body or a stainless steel pipe body with the diameter of 2-5mm, the copper wires exceed the pipe body by 10-30mm, the inside of the pipe body is filled with glue and fixed, the insulating layers are integrally coated on the pipe body, the whole immersed probe is prevented from being electrically contacted with liquid, and only the tips of the copper wires are kept in electrical contact with the liquid metal;
The wall detector (3) comprises a micro probe array (3-1), the distance between the arrays is 1-5mm, one end of the micro probe array (3-1) is inserted into a wall micropore reserved on the wall surface of a channel, and penetrates through the wall surface of the channel to be vertically welded on the circuit board (3-2), the whole micro probe array (3-1) is covered with an insulating cladding, and only the probe tip at the other end of the micro probe array (3-1) is kept in electrical contact with fluid; the wall micropores are filled with insulating glue, so that liquid is prevented from leaking, and the probes are electrically insulated from the wall; the prefabricated circuit on the circuit board (3-2) pairs the probes to form positive and negative poles of the voltage signal to form the line concentration plug (3-3).
2. The method for measuring the high space-time precision of the liquid metal velocity field under the strong magnetic field according to claim 1, wherein the multichannel high-precision synchronous voltage acquisition system (6) is connected with the wall detector (3) and the immersion probe (4) through shielding signal wires and is used for acquiring and storing voltage signals; the synchronous acquisition capability of 200 channels or more of analog signals is provided; the acquisition speed of 500S/S or more can be achieved.
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