Method for measuring sizes of bubbles in liquid metal based on ultrasonic waves

Abstract

The invention discloses a method for measuring the size of bubbles in liquid metal based on ultrasonic waves. The method comprises the following five steps: 1, determining working parameters and physical parameters of a secondary side heat exchange medium and the liquid metal; 2, experimental structure design and optimization analysis; 3, arranging an ultrasonic emitting electrode, a receiving electrode, a signal conversion device and a silencing material on the experimental structure; 4, applying an excitation signal by the ultrasonic emitting electrode, and recording a signal of the receiving electrode; and 5, calculating the bubble size according to the ultrasonic signal, and counting the deviation with the bubble design size. According to the invention, non-immersion measurement of the size of high-temperature and high-pressure liquid metal bubbles in a complex geometric container can be realized, normal work of an ultrasonic probe in a conventional environment is ensured, a sound field structure is not obviously changed, high measurement precision is achieved, and key test data can be provided for data reconstruction and software development verification.

Description

Technical Field

[0001] This invention belongs to the field of nuclear energy development and new energy technology, and specifically relates to a method for measuring the size of bubbles in liquid metal based on ultrasonic waves. Background Technology

[0002] Liquid metal fast reactors, as one of the most promising energy solutions among fourth-generation nuclear reactor technologies, use liquid lead-bismuth alloy, liquid sodium, or liquid lead as the primary coolant. Heat is transferred to the secondary coolant via an intermediate heat exchanger to drive the turbine generator unit. However, due to the design with a pressure difference exceeding 10 MPa between the primary and secondary loops, long-term erosion and abrasion of the cooling and heat transfer media can easily lead to heat transfer tube rupture. This can cause the high-temperature, high-pressure heat transfer medium in the secondary loop to be ejected into the high-temperature liquid metal in the primary loop, resulting in temperature and pressure fluctuations that endanger the reactor system's structural safety. Furthermore, the drastic pressure and temperature changes during the ejection process may cause a phase change in the secondary heat transfer medium, leading to bubble migration within the reactor and introducing a positive voiding coefficient, posing a significant safety hazard. Therefore, a precise bubble measurement method is needed to address the bubble migration phenomenon caused by high-temperature, high-pressure heat transfer tube rupture accidents in liquid metal fast reactors. Currently, existing methods for measuring bubbles include acquiring bubble images through a pressure-resistant window and calculating the volume using processing algorithms; however, the opacity of liquid metal makes this method difficult to implement. X-ray tomography is another method, but the equipment is extremely expensive, and high-density lead-bismuth requires a strong radiation source, limiting its field application. Therefore, there is an urgent need to develop a method capable of measuring the size of high-temperature, high-pressure liquid metal bubbles in complex geometric containers, thereby providing crucial experimental data for data reconstruction and software development verification. Summary of the Invention

[0003] To overcome the problems existing in the prior art, the present invention aims to provide a method for measuring the size of bubbles in liquid metal based on ultrasound. The present invention can realize non-immersion measurement of the size of bubbles in high-temperature and high-pressure liquid metal in complex geometric containers, ensuring that the ultrasonic probe can work normally in a normal environment without significantly changing the sound field structure. It has high measurement accuracy and can provide key experimental data for data reconstruction and software development verification.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for measuring bubble size in liquid metal based on ultrasound includes the following steps:

[0006] Step 1: Determine the operating parameters and physical properties of the secondary heat exchange medium and liquid metal: Under the condition of heat transfer tube rupture at the pressure boundary between the secondary and primary sides of the heat exchanger, the high-pressure fluid medium on the secondary side jets into the liquid metal medium on the primary side. The operating temperature of the high-pressure fluid medium on the secondary side is between 100-800℃, and the operating pressure is between 0.1-20MPa. Under these operating parameters, the sound velocity is higher than 100m / s. Under the condition of heat transfer tube rupture, bubbles will be generated on the primary side. The operating temperature of the liquid metal medium on the primary side is between 125-800℃, and the operating pressure is between 0.1-20MPa. Under these operating parameters, the sound velocity is higher than 1000m / s.

[0007] Step 2: Experimental Structure Design and Optimization Analysis: Under the experimental parameter settings, a geometric model of the experimental container was constructed in COMSOL software. A solid mechanics module was added, and linear elastic materials and boundary loads were set. The Young's modulus, Poisson's ratio, and density of the linear elastic material were determined. Temperature and absolute pressure were input, and von Mises stress and principal stresses were calculated for the experimental container, thus achieving mechanical verification of the experimental container. For the same experimental container geometric model, solid and fluid heat transfer modules and a laminar flow module were added in COMSOL software. Temperature and velocity boundary conditions were set, and ultrasonic waves of different frequencies were applied to the ultrasonic transmitter of the ultrasonic device. A nonlinear programming equation system was constructed for the waveguide rod to calculate the temperature of the ultrasonic transmitter at different emission frequencies and waveguide rod lengths. The temperature field distribution and the maximum allowable waveguide rod length at different frequencies obtained from the numerical calculation results were used to guide the design of the ultrasonic device and the pressure resistance limit of the experimental container. Small circular spheres were pre-set inside the experimental container to simulate actual bubbles.

[0008] Sub-step 1: Conduct static verification of the experimental container using the solid mechanics module:

[0009] In COMSOL software, construct the geometric model of the experimental container, add the solid mechanics module, linear elastic material and boundary load, set the Young's modulus, Poisson's ratio and density of the linear elastic material, input the temperature and absolute pressure, add rigid body motion suppression to the experimental container, and calculate the von Mises stress and principal stress of the experimental container.

[0010] Sub-step 2: Calculation of waveguide rod length for ultrasonic device:

[0011] (1) Let the frequency of the excitation wave be f, then the excitation period T = 1 / f, the number of excitations be n, and the total excitation time be T. n =n / f, calculate the excitation wavelength as Where L is the excitation wavelength and c is the sound velocity of the material, to ensure that the complete excitation wavelength does not cause significant self-interference within the experimental container wall, the excitation wavelength needs to be no greater than the container thickness L ≤ L. RV ;

[0012] (2) The time it takes for the ultrasound to first reach the outer wall of the container is L G c represents the length of the waveguide rod. S Indicates the speed of sound in the experimental container;

[0013] (3) When the ultrasonic wave reaches the surface of the experimental container, part of it is reflected back to the waveguide rod, and the other part is transmitted into the wall of the experimental container. The time it takes for the ultrasonic wave to reach the outer wall of the container for the second time is... L RV Indicates the thickness of the experimental container;

[0014] (4) Due to the echo rebound within the waveguide rod, it is conservatively estimated that the distance between the leading edge of the rebound wave within the waveguide rod and the surface of the experimental container is L within time t2. G,1 =t2c S ;

[0015] (5) The ultrasonic wave travels through the liquid metal in the experimental container to the bubble and is reflected back to the inner wall. Estimate the round-trip time of the ultrasonic wave in the liquid metal. L liquid c represents the thickness of the liquid metal. liquid R represents the speed of sound in liquid metal. bubble R represents the bubble radius. in Indicates the inner radius of the experimental container;

[0016] (6) In the same time interval, the distance traveled by the reflected wave inside the waveguide rod is L. G,2 =t3c S ;

[0017] (7) The time required for the ultrasound to reach the outer wall of the experimental container again is

[0018] (8) In the same time interval, the distance traveled by the reflected wave inside the waveguide rod is L. G,3 =t4c S ;

[0019] (9) To avoid t = t1 + t2 + t liquid Within the time interval +t4, the ultrasonic waves reflected from inside the waveguide interfere with the waves in the liquid metal, interfering with the measurement results. Therefore, the waveguide length needs to meet certain conditions.

[0020] Therefore, by constructing a set of nonlinear programming equations, the length of the waveguide rod can be calculated based on the wall thickness of the experimental container, the inner radius of the experimental container, the radius of the bubble, the sound velocity of the experimental container and the liquid metal, as well as the excitation frequency and wavenumber.

[0021]

[0022] Sub-step 3: Temperature check of the waveguide rod in the ultrasonic device:

[0023] Add solid and fluid heat transfer modules and laminar flow module to COMSOL software, set temperature and velocity boundary conditions, apply ultrasonic waves of different frequencies to the ultrasonic transmitter of the ultrasonic device, and perform temperature verification on the waveguide rod. Calculate the temperature of the ultrasonic transmitter at different emission frequencies and waveguide rod lengths in sub-step 2. Use the streamlined windward-crosswind diffusion finite element method to solve the Navier-Stokes equations, heat conduction equation, and convection equation to calculate the temperature of the waveguide rod. Compare the calculated temperature at the end face of the waveguide rod, i.e., the temperature at the location of the ultrasonic transmitter, with the allowable temperature to verify whether the waveguide rod design meets the requirements.

[0024] Step 3: Arrange ultrasonic transmitter, ultrasonic receiver, signal conversion device and sound-absorbing material on the experimental structure: Based on the experimental container structure and ultrasonic device structure verified in Step 2, arrange thermal insulation material on the outer surface of the experimental container, install ultrasonic receiver on the surface of the experimental container, and arrange sound-absorbing material around it; the ultrasonic receiver is connected to the surface of the experimental container by a waveguide rod as the sound wave transmission carrier, and an ultrasonic transmitter is installed at the end of the waveguide rod away from the experimental container, and connected to the signal conversion device together with the receiver.

[0025] Step 4: Apply an excitation signal to the ultrasonic transmitter and record the signal from the ultrasonic receiver: Based on the structure in Step 3, select pressure acoustics and explicit time-domain model in COMSOL software. Set the impedance model in COMSOL software on the outer surface of the experimental container and the ultrasonic transmitter to achieve surface silencing. Set a hard acoustic field boundary on the outer surface of the waveguide rod. Apply an excitation signal to the ultrasonic transmitter, perform numerical simulation, and record the intensity of the ultrasonic signal received by the ultrasonic receiver at different times. Use the recorded times with obvious peak values ​​for the calculation of bubble size.

[0026] Step 5: Calculate the bubble size based on the ultrasonic signal and calculate the deviation from the designed bubble size: Based on the time with obvious peak recorded in Step 4, and according to the different sound velocities in the experimental container, liquid metal, and bubble, as well as the waveguide rod length, experimental container thickness, and liquid metal thickness, construct equation (2) to solve for the bubble size, and calculate the deviation according to equation (3):

[0027]

[0028] Among them, L RV L represents the thickness of the experimental container. liquid R represents the thickness of the liquid metal inside the experimental container. bubble R is the calculated bubble radius. design R is the designed bubble radius. in Let c be the inner radius of the experimental container. liquidFor the speed of sound in liquid metal, c s Let t be the speed of sound in the experimental container, t1 be the time it takes for the ultrasonic wave to reach the outer wall of the container for the first time, t2 be the time it takes for the ultrasonic wave to reach the outer wall of the container for the second time, and t3 be the time it takes for the ultrasonic wave to reach the outer wall of the container for the third time.

[0029] The high-pressure fluid medium on the secondary side is the working fluid in the power cycle system, which can be water, carbon dioxide or helium, and has good heat exchange characteristics and high thermal cycle efficiency.

[0030] The primary side liquid metal medium is made of liquid lead-bismuth or liquid sodium, which has good heat exchange capacity and a low melting point, allowing it to operate at lower pressures.

[0031] The ultrasonic device includes an ultrasonic transmitter, a waveguide rod, an ultrasonic receiver, and a signal conversion device.

[0032] The ultrasonic transmitter is made of piezoelectric ceramic material, which has high energy conversion efficiency and stability. It is installed at the end of the waveguide rod away from the experimental container. The waveguide rod is made of 316 stainless steel, which has good thermal conductivity and signal fidelity. It can provide a good physical carrier for the acoustic system and protect the stability and reliability of the acoustic components at high temperatures. The waveguide rod is connected to the surface of the experimental container through an ultrasonic receiver. The ultrasonic transmitter and ultrasonic receiver are connected to the signal conversion device.

[0033] The maximum allowable temperature of the ultrasonic emitter is 200℃, which ensures the stable and efficient operation of the piezoelectric ceramic material.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] 1. High temperature, high pressure and non-immersion measurement: This invention is a non-immersion measurement. It only requires the ultrasonic transmitter, waveguide rod and ultrasonic receiver to be installed outside the experimental container. The intensity of the transmission and reception frequencies is outside the vibration frequency of the jet. The non-immersion measurement method ensures that the acoustic signal inside the container is not interfered with to a large extent. Since the sound-absorbing material and heat-insulating material are arranged outside the container and the container itself is strong enough, non-immersion measurement can be carried out in harsh environments such as high temperature and high pressure.

[0036] 2. Non-immersion ultrasonic bubble size measurement: This invention overcomes the opaque nature of liquid metal. By utilizing the differences in the absorption and reflection characteristics of ultrasonic waves by different materials, the bubble size can be calculated by the signal intensity received at different times. It adopts pressure acoustics and a time-domain explicit model to calculate the bubble size in liquid metal. It has high fidelity in transient response and high solution efficiency of large-scale models, and can maximize the balance between calculation efficiency and calculation accuracy. Attached Figure Description

[0037] Figure 1This is a schematic diagram of a method for measuring the size of bubbles in liquid metal based on ultrasonic waves, provided in a specific embodiment of the present invention.

[0038] Figure 2 This is a cross-sectional view of the numerical calculation model used to verify this method.

[0039] Figure 3 This is the result of the static calibration of the experimental container.

[0040] Figure 4 This is the result of steady-state temperature verification of the ultrasonic emitter piezoelectric ceramic end face.

[0041] Figure 5 It is the acoustic signal result calculated using pressure acoustics and an explicit time-domain model. Detailed Implementation

[0042] This invention provides a method for measuring the size of bubbles in liquid metal based on ultrasound. The invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0043] like Figure 1 As shown, the present invention discloses a method for measuring bubble size in liquid metal based on ultrasonic waves, comprising the following five steps: 1. Determining the operating parameters and physical properties of the secondary heat exchange medium and the liquid metal; 2. Experimental structure design and optimization analysis; 3. Arranging an ultrasonic transmitter, receiver, signal conversion device, and sound-absorbing material on the experimental structure; 4. Applying an excitation signal to the ultrasonic transmitter and recording the signal from the receiver; 5. Calculating the bubble size based on the ultrasonic signal and statistically analyzing the deviation from the designed bubble size.

[0044] Step 1: Determine the operating parameters and physical properties of the secondary heat exchange medium and liquid metal: Under the condition of heat transfer tube rupture at the pressure boundary between the secondary and primary sides of the heat exchanger, the high-pressure fluid medium on the secondary side jets into the liquid metal medium on the primary side. The high-pressure fluid medium on the secondary side is usually the working fluid in the power cycle system, including but not limited to water, carbon dioxide, and helium, with an operating temperature between 100-800℃ and an operating pressure between 0.1-20MPa. Under the operating parameters, the sound velocity is higher than 100m / s, and bubbles will be generated on the primary side under the condition of heat transfer tube rupture. The liquid metal medium on the primary side includes but is not limited to liquid lead-bismuth and liquid sodium, with an operating temperature between 125-800℃ and an operating pressure between 0.1-20MPa. Under the operating parameters, the sound velocity is higher than 1000m / s.

[0045] Step 2, Experimental Structure Design and Optimization Analysis: Under the experimental parameter settings, a geometric model of the experimental container was constructed in COMSOL software. A solid mechanics module was added, and linear elastic materials and boundary loads were set. The Young's modulus, Poisson's ratio, and density of the linear elastic material were determined. Temperature and absolute pressure were input, and von Mises stress and principal stresses were calculated for the experimental container to achieve mechanical verification. For the same experimental container geometric model, solid and fluid heat transfer modules, as well as a laminar flow module, were added in COMSOL software. Temperature and velocity boundary conditions were set, and ultrasonic waves of different frequencies were applied to the ultrasonic transmitter of the ultrasonic device. A nonlinear programming equation system was constructed for the waveguide rod to calculate the temperature of the ultrasonic transmitter under different emission frequencies and waveguide rod lengths. The temperature field distribution and the maximum allowable waveguide rod length at different frequencies obtained from the numerical calculation results were used to guide the design of the ultrasonic device and the pressure resistance limit of the experimental container. A small circular sphere was preset inside the experimental container to simulate actual bubbles. The specific design and optimization steps are as follows: The experimental container material was selected as 316 stainless steel, the liquid metal was determined to be liquid lead-bismuth (LBE), and the bubble was set as carbon dioxide with a design radius of 0.08 m.

[0046] Sub-step 1: Conduct static verification of the experimental container using the solid mechanics module:

[0047] In COMSOL software, construct the geometric model of the experimental container, add a solid mechanics module, set the linear elastic material and boundary loads, set the Young's modulus, Poisson's ratio, and density of the linear elastic material, input the temperature and absolute pressure, add rigid body motion suppression to the experimental container, and calculate... Figure 2 The experimental vessel is shown to exhibit von Mises stress and principal stress. The vessel is designed to withstand a pressure of not less than 16 MPa and a temperature of not less than 500℃. Figure 3 The results of the static calibration of the experimental vessel show the von Mises stress, with a maximum value of 82.2 MPa, which is lower than the allowable stress of 316 stainless steel at 500℃ (approximately 107 MPa), proving that the strength of the experimental vessel meets the design requirements.

[0048] Sub-step 2: Calculation of waveguide rod length for ultrasonic device:

[0049] (1) Let the frequency of the excitation wave be f, then the excitation period T = 1 / f, the number of excitations be n, and the total excitation time be T. n =n / f, the excitation wavelength can be calculated as Where L is the excitation wavelength and c is the sound velocity of the material, to ensure that the complete excitation wavelength does not cause significant self-interference within the experimental container wall, the excitation wavelength needs to be no greater than the container thickness L ≤ L. RV ;

[0050] (2) The time it takes for the ultrasound to first reach the outer wall of the container is L G c represents the length of the waveguide rod. S This indicates the sound velocity of 316 stainless steel.

[0051] (3) When the ultrasonic wave reaches the surface of the experimental container, part of it is reflected back to the waveguide rod, and the other part is transmitted into the wall of the experimental container. The time it takes for the ultrasonic wave to reach the outer wall of the container for the second time is... L RV Indicates the thickness of the experimental container;

[0052] (4) Due to the echo rebound within the waveguide rod, it is conservatively estimated that the distance between the leading edge of the rebound wave within the waveguide rod and the surface of the experimental container is L within time t2. G,1 =t2c S ;

[0053] (5) The ultrasonic wave travels through the lead-bismuth to the CO2 bubble and is reflected back to the inner wall. The estimated round-trip time of the ultrasonic wave in the lead-bismuth is: L LBE c represents the lead-bismuth thickness. LBE R represents the speed of sound in lead-bismuth. CO2 R represents the radius of the carbon dioxide bubble. in Indicates the inner radius of the experimental container;

[0054] (6) In the same time interval, the distance traveled by the reflected wave inside the waveguide rod is L. G,2 =t3c S ;

[0055] (7) The time required for the ultrasound to reach the outer wall of the experimental container again is

[0056] (8) In the same time interval, the distance traveled by the reflected wave inside the waveguide rod is L. G,3 =t4c S ;

[0057] (9) To avoid interference between the ultrasonic waves reflected from the waveguide rod and the waves in the lead-bismuth alloy during the time interval t = t1 + t2 + t3 + t4, thus preventing interference with the measurement results, the length of the waveguide rod needs to meet the following requirements.

[0058] Therefore, by constructing a set of nonlinear programming equations, the waveguide length can be calculated based on the experimental container wall thickness, inner radius, carbon dioxide bubble radius, sound velocity of 316 stainless steel and lead-bismuth, as well as the excitation frequency and wavenumber.

[0059]

[0060] Table 1 shows the parameters and results used for frequency and length verification of the waveguide rod. A waveguide rod with a length of about 0.5m can be selected first, as it can distinguish the characteristics of the acoustic wave. Considering the attenuation of high-frequency acoustic waves, 100kHz or 200kHz ultrasonic transmitting probes are preferred, which can control the generation of 2 or 4 excitation waves respectively for bubble distance detection.

[0061] Table 1: Waveguide rod frequency and length verification parameters and results.

[0062]

[0063] Sub-step 3: Temperature check of the waveguide rod in the ultrasonic device:

[0064] Add solid and fluid heat transfer modules and a laminar flow module to the COMSOL software, set temperature and velocity boundary conditions, and apply ultrasonic waves of different frequencies to the ultrasonic emitter of the ultrasonic device. Figure 2 Temperature verification was performed on the waveguide rod shown. The temperature of the ultrasonic transmitter was calculated for different emission frequencies and waveguide rod lengths in sub-step 2. In COMSOL software, the inner surface of the experimental container and the waveguide rod were set to a constant temperature of 500℃. The outer surface, except for the area in contact with the waveguide rod, was set to be adiabatic. The waveguide rod was cooled externally by natural convection. The temperature of the waveguide rod was calculated by solving the Navier-Stokes equations, the heat conduction equation, and the convection equation using the streamlined windward-crosswind diffusion finite element method. The waveguide rod end-face temperature is shown below. Figure 4 As shown, under natural convection conditions, the temperature of the waveguide rod end face rapidly decreased from the initial 500℃ to below 25℃, which is far less than the allowable operating temperature limit of 200℃, ensuring the effective operation of the ultrasonic device.

[0065] Step 3: Arrange the ultrasonic transmitter, ultrasonic receiver, signal conversion device, and sound-absorbing material on the experimental structure: Based on the experimental container structure and ultrasonic device structure verified in Step 2, such as... Figure 2 As shown, thermal insulation material is arranged on the outer surface of the experimental container, an ultrasonic receiving electrode is installed on the surface of the experimental container, and sound-absorbing material is arranged around it; the ultrasonic device is connected to the surface of the experimental container by a waveguide rod as the sound wave transmission carrier, and an ultrasonic transmitting electrode is installed at the end of the waveguide rod away from the experimental container, which is connected to the signal conversion device together with the receiving electrode.

[0066] Step 4: Apply an excitation signal to the ultrasonic transmitter and record the signal from the ultrasonic receiver: Based on the structure in Step 3, select pressure acoustics and explicit time-domain model in COMSOL software. Figure 2The experimental container and ultrasonic transmitter were designed with impedance models from COMSOL software to achieve surface noise reduction. A hard acoustic field boundary was applied to the outer surface of the waveguide rod. An excitation signal was applied to the ultrasonic transmitter, and numerical simulations were performed. The intensity of the ultrasonic signal received by the ultrasonic receiver at different times was recorded. Figure 5 As shown, three distinct peaks in ultrasonic intensity can be observed, representing the time and intensity of the ultrasonic waves reaching the ultrasonic receiver electrode three times. The times corresponding to the three recorded peaks are used to calculate the bubble size.

[0067] Step 5: Calculate the bubble size based on the ultrasonic signal and calculate the deviation from the designed bubble size: Based on the times corresponding to the three peaks recorded in Step 4, and according to the different sound velocities in the experimental container, liquid metal, and bubble, as well as the waveguide rod length, experimental container thickness, and liquid metal thickness, construct equation (1) to solve for the bubble size, and calculate the deviation according to equation (2):

[0068]

[0069] Among them, L RV =0.105m is the thickness of the experimental container, L LBE The thickness of the liquid metal inside the experimental container. R is the radius of the carbon dioxide bubble to be calculated. design =0.08m is the designed bubble radius, R in =0.15m is the inner diameter of the experimental container, c LBE =1643 m / s is the speed of sound in lead-bismuth, c s =5066 m / s is the velocity of sound in the 316 stainless steel experimental container, t1 = 1.3125 × 10 -4 The time it takes for the ultrasound to first reach the outer wall of the container is t2 = 1.7688 × 10⁻⁶. -4 The time it takes for the ultrasound to reach the outer wall of the container for the second time is t3 = 2.8938 × 10⁻⁶. -4 The time it takes for the ultrasound to reach the outer wall of the container for the third time is used to calculate the final deviation, which is Δ = 7.33%, indicating high measurement accuracy.

[0070] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of patent protection determined by the submitted claims.

Claims

1. A method for measuring the size of bubbles in liquid metal based on ultrasonic waves, characterized in that: Includes the following steps: Step 1: Determine the operating parameters and physical properties of the secondary heat exchange medium and liquid metal: Step 2: Experimental Structure Design and Optimization Analysis: Under the experimental parameter settings, a geometric model of the experimental container was constructed in COMSOL software. A solid mechanics module was added, and linear elastic materials and boundary loads were set. The Young's modulus, Poisson's ratio, and density of the linear elastic material were determined. Temperature and absolute pressure were input, and von Mises stress and principal stresses were calculated for the experimental container, thus achieving mechanical verification of the experimental container. For the same experimental container geometric model, solid and fluid heat transfer modules and a laminar flow module were added in COMSOL software. Temperature and velocity boundary conditions were set, and ultrasonic waves of different frequencies were applied to the ultrasonic transmitter of the ultrasonic device. A nonlinear programming equation system was constructed for the waveguide rod to calculate the temperature of the ultrasonic transmitter at different emission frequencies and waveguide rod lengths. The temperature field distribution and the maximum allowable waveguide rod length at different frequencies obtained from the numerical calculation results were used to guide the design of the ultrasonic device and the pressure resistance limit of the experimental container. Small circular spheres were pre-set inside the experimental container to simulate actual bubbles. Step 3: Arrange ultrasonic transmitter, ultrasonic receiver, signal conversion device and sound-absorbing material on the experimental structure: Based on the experimental container structure and ultrasonic device structure verified in Step 2, arrange thermal insulation material on the outer surface of the experimental container, install ultrasonic receiver on the surface of the experimental container, and arrange sound-absorbing material around it; the ultrasonic receiver is connected to the surface of the experimental container by a waveguide rod as the sound wave transmission carrier, and an ultrasonic transmitter is installed at the end of the waveguide rod away from the experimental container, and connected to the signal conversion device together with the receiver. Step 4: Apply an excitation signal to the ultrasonic transmitter and record the signal from the ultrasonic receiver: Based on the structure in Step 3, select pressure acoustics and explicit time-domain model in COMSOL software. Set the impedance model in COMSOL software on the outer surface of the experimental container and the ultrasonic transmitter to achieve surface silencing. Set a hard acoustic field boundary on the outer surface of the waveguide rod. Apply an excitation signal to the ultrasonic transmitter, perform numerical simulation, and record the intensity of the ultrasonic signal received by the ultrasonic receiver at different times. Use the recorded times with obvious peak values ​​for the calculation of bubble size. Step 5: Calculate the bubble size based on the ultrasonic signal and calculate the deviation from the designed bubble size: Based on the time with obvious peak recorded in Step 4, and according to the different sound velocities in the experimental container, liquid metal, and bubble, as well as the waveguide rod length, experimental container thickness, and liquid metal thickness, construct equation (2) to solve for the bubble size, and calculate the deviation according to equation (3): Among them, L RV L represents the thickness of the experimental container. liquid R represents the thickness of the liquid metal inside the experimental container. bubble R is the calculated bubble radius. design R is the designed bubble radius. in Let c be the inner radius of the experimental container. liquid For the speed of sound in liquid metal, c s Let t be the speed of sound in the experimental container, t1 be the time it takes for the ultrasonic wave to reach the outer wall of the container for the first time, t2 be the time it takes for the ultrasonic wave to reach the outer wall of the container for the second time, and t3 be the time it takes for the ultrasonic wave to reach the outer wall of the container for the third time.

2. The method for measuring bubble size in liquid metal based on ultrasonic waves according to claim 1, characterized in that: Step 1 is as follows: When a heat transfer tube ruptures at the pressure boundary between the secondary and primary sides of the heat exchanger, a jet of high-pressure fluid medium from the secondary side enters the liquid metal medium from the primary side. The operating temperature of the high-pressure fluid medium on the secondary side is between 100-800℃, and the operating pressure is between 0.1-20MPa. Under these operating parameters, the sound velocity is higher than 100m / s. Under the condition of heat transfer tube rupture, bubbles will be generated on the primary side. The operating temperature of the liquid metal medium on the primary side is between 125-800℃, and the operating pressure is between 0.1-20MPa. Under these operating parameters, the sound velocity is higher than 1000m / s.

3. The method for measuring bubble size in liquid metal based on ultrasound according to claim 1, characterized in that: Step 2 specifically includes the following sub-steps: Sub-step 1: Conduct static verification of the experimental container using the solid mechanics module: In COMSOL software, construct the geometric model of the experimental container, add the solid mechanics module, linear elastic material and boundary load, set the Young's modulus, Poisson's ratio and density of the linear elastic material, input the temperature and absolute pressure, add rigid body motion suppression to the experimental container, and calculate the von Mises stress and principal stress of the experimental container. Sub-step 2: Calculation of waveguide rod length for ultrasonic device: (1) Let the frequency of the excitation wave be f, then the excitation period T = 1 / f, the number of excitations be n, and the total excitation time be T. n =n / f, calculate the excitation wavelength as Where L is the excitation wavelength and c is the sound velocity of the material, to ensure that the complete excitation wavelength does not cause significant self-interference within the experimental container wall, the excitation wavelength needs to be no greater than the container thickness L ≤ L. RV ; (2) The time it takes for the ultrasound to first reach the outer wall of the container is L G c represents the length of the waveguide rod. S Indicates the speed of sound in the experimental container; (3) When the ultrasonic wave reaches the surface of the experimental container, part of it is reflected back to the waveguide rod, and the other part is transmitted into the wall of the experimental container. The time it takes for the ultrasonic wave to reach the outer wall of the container for the second time is... L RV Indicates the thickness of the experimental container; (4) Due to the echo rebound within the waveguide rod, it is conservatively estimated that the distance between the leading edge of the rebound wave within the waveguide rod and the surface of the experimental container is L within time t2. G,1 =t2c S ; (5) The ultrasonic wave travels through the liquid metal in the experimental container to the bubble and is reflected back to the inner wall. Estimate the round-trip time of the ultrasonic wave in the liquid metal. L liquid c represents the thickness of the liquid metal. liquid R represents the speed of sound in liquid metal. bubble R represents the bubble radius. in Indicates the inner radius of the experimental container; (6) In the same time interval, the distance traveled by the reflected wave inside the waveguide rod is L. G,2 =t3c S ; (7) The time required for the ultrasound to reach the outer wall of the experimental container again is (8) In the same time interval, the distance traveled by the reflected wave inside the waveguide rod is L. G,3 =t4c S ; (9) To avoid t = t1 + t2 + t liquid Within the time interval +t4, the ultrasonic waves reflected from inside the waveguide interfere with the waves in the liquid metal, interfering with the measurement results. Therefore, the waveguide length needs to meet certain conditions. Therefore, by constructing a set of nonlinear programming equations, the length of the waveguide rod can be calculated based on the wall thickness of the experimental container, the inner radius of the experimental container, the radius of the bubble, the sound velocity of the experimental container and the liquid metal, as well as the excitation frequency and wavenumber. Sub-step 3: Temperature check of the waveguide rod in the ultrasonic device: Add solid and fluid heat transfer modules and a laminar flow module to the COMSOL software, set temperature and velocity boundary conditions, apply ultrasonic waves of different frequencies to the ultrasonic transmitter of the ultrasonic device, and perform temperature verification on the waveguide rod. Calculate the temperature of the ultrasonic transmitter at different emission frequencies and waveguide rod lengths in sub-step 2. Use the streamlined upwind-crosswind diffusion finite element method to solve the Navier-Stokes equations, heat conduction equation, and convection equation to calculate the temperature of the waveguide rod. Compare the calculated temperature at the end face of the waveguide rod, i.e., the temperature at the location of the ultrasonic transmitter, with the allowable temperature to verify whether the waveguide rod design meets the requirements.

4. The method for measuring bubble size in liquid metal based on ultrasonic waves according to claim 1, characterized in that: The high-pressure fluid medium on the secondary side is the working fluid in the power circulation system, and can be water, carbon dioxide, or helium.

5. The method for measuring bubble size in liquid metal based on ultrasonic waves according to claim 1, characterized in that: The primary side liquid metal medium is either liquid lead-bismuth or liquid sodium.

6. The method for measuring bubble size in liquid metal based on ultrasonic waves according to claim 1, characterized in that: The ultrasonic device includes an ultrasonic transmitter, a waveguide rod, an ultrasonic receiver, and a signal conversion device.

7. The method for measuring bubble size in liquid metal based on ultrasound according to claim 6, characterized in that: The ultrasonic transmitter is made of piezoelectric ceramic material and is installed at the end of the waveguide rod away from the experimental container. The waveguide rod is made of 316 stainless steel and is connected to the surface of the experimental container through an ultrasonic receiver. The ultrasonic transmitter and ultrasonic receiver are connected to a signal conversion device.

8. The method for measuring bubble size in liquid metal based on ultrasonic waves according to claim 6, characterized in that: The maximum permissible temperature of the ultrasonic emitter is 200℃.

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