A method for measuring liquid metal temperature cross section

Abstract

The present invention discloses a liquid metal temperature cross-section measurement method, which relates to the liquid metal experimental measurement technology field, and comprises the following steps: uniformly arranging multiple measuring points in a certain cross-section of a pipeline with liquid metal inside, collecting the electric potential of any two measuring points; calculating the dimensionless number Ri according to the flow rate of the liquid metal; when Ri<0.1, arranging multiple temperature values ​​to obtain temperature gradients along different directions, wherein polynomial interpolation is performed on the temperature gradient of nonlinear distribution, and linear interpolation is performed on the temperature gradient of linear distribution, to obtain a temperature cloud map; when Ri>0.1, increasing the number of measuring points, collecting the temperature value of each measuring point, wherein spline interpolation is used to interpolate the temperature distribution, to obtain a temperature cloud map. Based on the dimensionless number Ri, the present invention changes the number of measuring points in different situations, and uses different interpolation methods to interpolate the temperature gradients of different distribution situations, thereby greatly improving the accuracy of measurement.

Description

Technical Field

[0001] The invention relates to the technical field of liquid metal experimental measurement, and in particular to a liquid metal temperature cross-section measurement method. Background Art

[0002] Liquid metal refers to an amorphous metal. Liquid metal can be regarded as a mixture of positive ion fluid and free electron gas. For some high-temperature applications, such as nuclear energy, aerospace, etc., liquid metal may be used as a coolant or heat transfer medium. Accurately measuring the temperature of high-temperature liquid metal is a key factor in ensuring the safety and reliability of system engineering. Too high or too low temperature may cause equipment damage or performance degradation, so timely monitoring and control of temperature is crucial.

[0003] In the liquid metal pipeline flow experiment, the fluidity of liquid metal makes the measurement of velocity field extremely difficult because its viscosity and rheological properties may change significantly with temperature. At the same time, there are unique challenges in measuring flow fields compared to transparent liquids, especially when applying methods such as PIV (Particle Image Velocimetry). Transparent liquids usually allow light to pass through and form clear images, so that the velocity field of the fluid can be accurately measured by observing particle trajectories. However, due to its metallic properties, liquid metal is opaque and has strong reflective ability, so that traditional PIV technology cannot produce clear images on its surface. Therefore, when conducting flow field measurements in liquid metal, advanced optical technologies and precision measurement methods specially designed for high temperature and high pressure environments are required to overcome the challenges posed by the opacity of metals. Secondly, the high temperature characteristics of liquid metal increase the difficulty of temperature field measurement. Conventional temperature measurement techniques may fail under extreme high temperature conditions, and the distribution of temperature fields may be very uneven in the dynamic environment of liquid metal. Therefore, selecting appropriate sensors and measurement methods to ensure accurate capture of temperature field changes in high-temperature liquid metal is a challenging engineering task.

[0004] The existing temperature cross-section measurement technology directly inserts a circle of thermocouples around the pipeline, converges them at a certain cross-section of the pipeline, and draws the cross-section temperature through interpolation between points. However, this method uses a unified interpolation method in all directions of the cross-section, which may cause inaccurate measurements in areas with sparse data. Summary of the invention

[0005] The present invention provides a liquid metal temperature cross-section measurement method, which solves the technical problem that the existing temperature cross-section measurement adopts a unified interpolation method in all directions of the cross-section, and may cause inaccurate measurement in data sparse areas.

[0006] The present invention provides a liquid metal temperature cross-section measurement method, which is applied to a liquid metal pipeline flow experiment and comprises the following steps:

[0007] Multiple measuring points are evenly arranged in a certain cross section of a pipeline with liquid metal inside, and the electric potential of any two measuring points is collected; the horizontal distance and vertical distance between the two measuring points are not zero;

[0008] The flow rate of the liquid metal is calculated based on the potential of the two measuring points, and the dimensionless number Ri is calculated based on the flow rate of the liquid metal;

[0009] When Ri<0.1, reduce the number of measuring points, collect the temperature value of each measuring point, and arrange multiple temperature values ​​to obtain temperature gradients along different directions; perform nonlinear interpolation on the temperature gradient of nonlinear distribution, and perform linear interpolation on the temperature gradient of linear distribution to obtain the temperature cloud map;

[0010] When Ri>0.1, increase the number of measuring points, collect the temperature value of each measuring point, arrange multiple temperature values ​​to obtain the temperature distribution, use spline interpolation to interpolate the temperature distribution, and obtain the temperature cloud map.

[0011] Preferably, a thermocouple close to the Seebeck effect of liquid metal is arranged at each measuring point, and the potentials of the two thermocouples are collected.

[0012] Preferably, the flow rate of the liquid metal is calculated according to the potential of the two measuring points, specifically:

[0013]

[0014] In the formula, u x is the fluid velocity in the x direction, is the potential value at point a, is the potential value at point b, c1 is the conductivity of the fluid, B0 is the magnetic field strength of the environment, Δl y is the distance between the two measuring points in the y direction, Δl x is the distance u between the two measuring points in the x direction y is the fluid velocity in the y direction.

[0015] Preferably, the dimensionless number Ri is calculated by the following formula:

[0016]

[0017] in,

[0018]

[0019] Where Gr is the Grashof number, Re is the Reynolds number, U is the flow velocity, a is the characteristic length, v is the viscosity, g is the acceleration of gravity, α is the thermal expansion coefficient, q is the heat flux, d is the characteristic length, and λ is the thermal conductivity.

[0020] Preferably, a plurality of positioning tubes perpendicular to the pipeline are arranged in a certain cross section of the pipeline, and a plurality of openings are opened on each of the positioning tubes along the height direction, and the positions of the plurality of openings are the positions of a plurality of measuring points; a plurality of thermocouples are respectively arranged on each opening, and the hot ends of the plurality of thermal couples are exposed to the liquid metal, and the cold ends are placed in a constant temperature bath through thermocouple wires.

[0021] Preferably, the number of measuring points is adjusted by replacing positioning tubes with different opening spacings and changing the number of positioning tubes.

[0022] Preferably, it also includes:

[0023] Before collecting data, place the standard thermistor and the thermocouple of the same type at the measuring point in a constant temperature bath;

[0024] By setting the temperature of the thermostat, collecting the potential of the thermocouple at different temperatures, finding the corresponding relationship between the potential and the temperature, the temperature is obtained through the standard thermistor;

[0025] When conducting a pipeline flow experiment, the potential of the thermocouple at each measuring point is collected, and the potential is substituted into the corresponding relationship to obtain the corresponding temperature value.

[0026] Preferably, the cross section of the positioning tube is V-shaped.

[0027] Preferably, two adjacent positioning tubes are connected via a fixing tube.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention first collects the electric potential of any two measuring points of a certain cross section of a pipeline with liquid metal, calculates the flow rate of the liquid metal according to the electric potential of the two measuring points, and calculates the dimensionless number Ri according to the flow rate of the liquid metal; when Ri<0.1, multiple temperature values ​​are arranged to obtain temperature gradients along different directions, wherein polynomial interpolation is performed on the temperature gradient of nonlinear distribution, and linear interpolation is performed on the temperature gradient of linear distribution to obtain a temperature cloud map; when Ri>0.1, the number of measuring points is increased, and the temperature value of each measuring point is collected, wherein spline interpolation is used to interpolate the temperature distribution to obtain a temperature cloud map. Based on the dimensionless number Ri, the present invention changes the number of measuring points in different situations, and uses different interpolation methods to interpolate the temperature gradients of different distribution situations, which greatly improves the accuracy of measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 It is a flow chart of a method for measuring the temperature cross section of liquid metal according to the present invention;

[0032] Figure 2 Schematic diagram of the structure of a measuring device according to an embodiment of the present invention.

[0033] Among them, 1-thermocouple wire outlet, 2-fixing plate, 3-positioning tube, 4-fixing tube. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The present invention is mainly applied to liquid metal pipeline flow experiments. The present invention provides a liquid metal temperature cross-section measurement method. Figure 1 , specifically including the following steps:

[0036] Step 1: Evenly arrange multiple measuring points in a certain cross section of the pipeline with liquid metal inside, and collect the electric potential of two measuring points in a certain cross section of the liquid metal.

[0037] Specifically, refer to Figure 2 , multiple positioning tubes 3 are set in a certain cross section, and each positioning tube 3 is provided with multiple openings, and the multiple opening positions are multiple measuring point positions. A thermocouple is set on each opening, and the hot ends of the multiple thermal couples are exposed to the liquid metal, and the cold ends are placed in a constant temperature bath through thermocouple wires. The number of measuring points is adjusted by replacing positioning tubes 3 with different opening spacings and changing the number of positioning tubes 3. When the number of measuring points needs to be reduced, holes with a larger distance are re-done on the new positioning tube 3, and further, the number of positioning tubes 3 can be reduced. When the number of measuring points needs to be increased, holes with a smaller distance are re-done on the new positioning tube 3, and further, the number of positioning tubes 3 can be increased.

[0038] In this embodiment, a plurality of thermocouple wire outlets 1 are provided on the fixing plate 2, and the plurality of thermocouple wire outlets 1 are respectively connected to a plurality of positioning tubes 3. The positioning tubes 3 are V-shaped, with an angle less than 30°, and the tip faces the incoming flow direction to reduce the influence on the flow field.

[0039] Place the head of the thermocouple in the hole and fix it with AB glue, arrange the thermocouple wire along the inner side of the V-shaped tube (the side with a small angle), and fix the thermocouple wire with AB glue.

[0040] Finally, the thermocouple wire is led out from outlet 1 and sealed with AB glue to ensure the tightness of the pipeline.

[0041] A square opening is opened on the liquid metal experimental section, and the square opening penetrates the inside of the pipe. A fixing plate 2 is arranged at the position of the square opening. In this embodiment, the fixing plate 2 is a flange. Threads are added to the pipe, and the flange is connected to the pipe by bolts.

[0042] Since the thermocouple measurement point needs to be inserted into the pipe, the two ends of the thermocouple need to be connected to the collector to obtain specific temperature information. In addition, liquid metal is easy to oxidize, so it is necessary to seal the middle line of the thermocouple.

[0043] Two adjacent positioning tubes 3 are connected by a fixing tube 4. To prevent the working fluid flow rate from being too high, and the thermocouple positioning tube 3 needs to be designed to be thinner (to reduce the impact on the flow field), the structural strength of the bottom of the thermocouple positioning tube 3 is reinforced.

[0044] Thermocouple temperature measurement principle is based on temperature difference potential, so usually a collector that can collect potential (NI4309, multimeter) is used to collect the temperature difference potential to obtain the temperature value.

[0045] A standard thermistor (PT100) and a thermocouple to be used are placed in a constant temperature bath. By setting the temperature of the constant temperature bath, the potential values ​​of the thermocouple to be used at different temperatures are collected, and the corresponding relationship between the potential value and the temperature value is found. The temperature value is obtained through the standard thermistor (PT100).

[0046] It is necessary to select a thermocouple that is close to the Seebeck effect of the liquid metal (for example, in the measurement of liquid metal gallium, indium and tin, a copper-constantan thermocouple should be used). Since the liquid metal moves in a magnetic field (a uniform magnetic field is usually applied in liquid metal experiments), a velocity potential is generated. The velocity of the fluid between the thermocouples is calculated based on the following formula:

[0047]

[0048] In the formula, u x is the fluid velocity in the x direction, is the potential value at point a, is the potential value at point b, is the potential value at point c, is the potential value at point d, c1 is the conductivity of the fluid, B0 is the magnetic field strength of the environment, Δl y is the distance between the two measuring points in the y direction, u y is the fluid velocity in the y direction.

[0049] In this embodiment, in order to make the measured flow rate more accurate, the potentials of multiple different measuring points can be collected for calculation. For example:

[0050]

[0051] In the formula, u x is the fluid velocity in the x direction, is the potential value at point a, is the potential value at point b, is the potential value at point c, is the potential value at point d, c1 is the conductivity of the fluid, B0 is the magnetic field strength of the environment, Δl y is the distance between the two measuring points in the y direction, u y is the fluid velocity in the y direction.

[0052] If you cannot find a thermocouple that is close to the Seebeck of liquid metal, you can get the velocity value through the correlation of the thermocouple. Correlation is a statistical method used to measure the relationship between two variables, mainly used to describe the degree of linear relationship between them. When measuring velocity values, correlation based on temperature signals can help understand the trend and degree of correlation between temperature changes and velocity changes. The principle of correlation includes the following key points:

[0053] Correlation coefficient: Correlation is usually expressed by a correlation coefficient. Common correlation coefficients include the Pearson correlation coefficient and the Spearman correlation coefficient. The Pearson correlation coefficient measures the degree of linear relationship between two variables. Its value range is between -1 and 1. The closer to 1, the stronger the positive correlation. The closer to -1, the stronger the negative correlation. The closer to 0, the no linear relationship.

[0054] Calculation method: For a set of data, the correlation coefficient formula can be used to calculate the correlation. For example, for the Pearson correlation coefficient, the formula is:

[0055]

[0056] Where n is the number of samples, x and y are the values ​​of the two variables, and ∑ represents the sum.

[0057] Based on the calculated correlation coefficient, the relationship between the two variables can be explained. If the correlation coefficient is close to 1, it means that the two variables show a strong positive correlation, that is, when one variable increases, the other variable also increases; if the correlation coefficient is close to -1, it means that the two variables show a strong negative correlation, that is, when one variable increases, the other variable decreases; if the correlation coefficient is close to 0, it means that there is no linear relationship between the two variables. When measuring speed values, the correlation of temperature signals can help determine whether there is a clear correlation between temperature changes and speed changes, thereby deriving an estimate or prediction of speed values.

[0058] Step 2: Calculate the flow rate of the liquid metal based on the potential of the two measuring points, and calculate the dimensionless number Ri based on the flow rate of the liquid metal.

[0059] The dimensionless number Ri is calculated by the following formula:

[0060]

[0061] in,

[0062]

[0063] Where Gr is the Grashof number, Re is the Reynolds number, U is the flow velocity, a is the characteristic length, v is the viscosity, g is the acceleration of gravity, α is the thermal expansion coefficient, q is the heat flux, d is the characteristic length, and λ is the thermal conductivity.

[0064] Step 3: Since thermocouples are often used in mixed convection experiments of liquid metals, heating is performed on the tube wall. According to the dimensionless number Ri in the actual experiment, it is determined how to draw the temperature cloud map.

[0065] When the dimensionless number Ri<0.1, the flow state corresponds to a flow state in which natural convection or buoyancy can be ignored relative to the inertial force. In this case, the temperature distribution is relatively uniform, and the heating surface (bottom surface) has a large temperature gradient, which is a nonlinear distribution. However, there is basically no temperature gradient on the top surface, and the temperature change along the heating surface is small, which is a linear distribution. When interpolating, polynomial interpolation is required along the temperature difference direction of the heating surface (bottom surface). In contrast, linear interpolation can be used in the direction with a smaller temperature gradient. The temperature distribution is simple, so more sparse thermocouple collection points can be arranged, so that the flow field is less affected.

[0066] When the dimensionless number 10>Ri>0.1, inertia and buoyancy are not the main factors. This is the transition state between inertia-dominated flow and gravity-dominated flow. When the dimensionless number Ri>10, the fluid is dominated by buoyancy, and the flow approximates Rayleigh-Bérnard convection. Therefore, the temperature change in the direction of the heating surface shows a trend of first increasing, then decreasing, and then increasing. In order to more accurately measure the cross-sectional temperature distribution, by adding measurement points, or using spline interpolation for the cross-sectional temperature distribution, this interpolation method has the advantages of being smooth and able to fit the data points well, not prone to the Runge phenomenon, and suitable for various data distribution situations.

[0067] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0068] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for measuring the temperature cross section of liquid metal, characterized in that: The measurement method is applied to the pipeline flow experiment of liquid metal and includes the following steps: Multiple measuring points are evenly arranged in a certain cross section of a pipeline with liquid metal inside, and the electric potential of any two measuring points is collected; the horizontal distance and vertical distance between the two measuring points are not zero; The flow rate of the liquid metal is calculated based on the potential of the two measuring points, and the dimensionless number Ri is calculated based on the flow rate of the liquid metal; When Ri<0.1, reduce the number of measuring points, collect the temperature value of each measuring point, and arrange multiple temperature values ​​to obtain temperature gradients along different directions; perform nonlinear interpolation on the temperature gradient of nonlinear distribution, and perform linear interpolation on the temperature gradient of linear distribution to obtain the temperature cloud map; When Ri>0.1, increase the number of measuring points, collect the temperature value of each measuring point, arrange multiple temperature values ​​to obtain temperature distribution, use spline interpolation to interpolate the temperature distribution, and obtain the temperature cloud map; A thermocouple close to the Seebeck effect of liquid metal is set at each measuring point, and the potential of the two thermocouples is collected; The flow rate of the liquid metal is calculated according to the potential of the two measuring points, specifically: In the formula, u x is the fluid velocity in the x direction, is the potential value at point a, is the potential value at point b, c1 is the conductivity of the fluid, B0 is the magnetic field strength of the environment, Δl y is the distance between the two measuring points in the y direction, Δl x is the distance between the two measuring points in the x direction, u y is the fluid velocity in the y direction; The dimensionless number Ri is calculated by the following formula: in, Where Gr is the Grashof number, Re is the Reynolds number, U is the flow velocity, a is the characteristic length, v is the viscosity, g is the acceleration of gravity, α is the thermal expansion coefficient, q is the heat flux, d is the characteristic length, and λ is the thermal conductivity.

2. A method for measuring liquid metal temperature cross section according to claim 1, characterized in that: A plurality of positioning tubes (3) perpendicular to the pipeline are arranged in a certain cross section of the pipeline, and a plurality of openings are opened on each positioning tube (3) along the height direction, and the positions of the plurality of openings are the positions of a plurality of measuring points; a plurality of thermocouples are respectively arranged on each opening, and the hot ends of the plurality of thermocouples are exposed to the liquid metal, and the cold ends are placed in a constant temperature bath through thermocouple wires.

3. A method for measuring liquid metal temperature cross section according to claim 2, characterized in that: The number of measuring points is adjusted by replacing positioning tubes (3) with different hole spacings and changing the number of positioning tubes (3).

4. A method for measuring liquid metal temperature cross section according to claim 1, characterized in that: Also includes: Before collecting data, place the standard thermistor and the thermocouple of the same type at the measuring point in a constant temperature bath; By setting the temperature of the thermostat, collecting the potential of the thermocouple at different temperatures, finding the corresponding relationship between the potential and the temperature, the temperature is obtained through the standard thermistor; When conducting a pipeline flow experiment, the potential of the thermocouple at each measuring point is collected, and the potential is substituted into the corresponding relationship to obtain the corresponding temperature value.

5. A method for measuring liquid metal temperature cross section according to claim 2, characterized in that: The cross section of the positioning tube (3) is V-shaped.

6. A method for measuring liquid metal temperature cross section according to claim 2, characterized in that: Two adjacent positioning tubes (3) are connected via a fixing tube (4).

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