A stagnation channel heat cycle experiment system and method

Abstract

The application discloses a stagnation pipeline thermal cycle experiment system and method, which comprises a heating pipeline (3a) and an experiment pipeline (3b) arranged in parallel, and the experiment pipeline (3b) comprises a main pipe (1) and a branch pipe (2). The branch pipe (2) comprises a first pipe section, a second pipe section and a third pipe section, the branch pipe (2) is connected to the main pipe (1) through the first pipe section, the first pipe section is connected to one end of the second pipe section, and the third pipe section is connected to the other end of the second pipe section. The pipe diameter D1 of the main pipe (1) is greater than the pipe diameter D2 of the branch pipe (2). The experiment method comprises adjusting the water temperature and pressure of experimental water in the system to target values through the heating pipeline (3a). The experimental water is controlled to flow into the main pipe (1) and the branch pipe (2), and the simple experiment system can be quickly adjusted to obtain experimental parameters in different conditions, so that the stagnation pipeline thermal cycle experiment system is more adaptable and practical.

Description

Technical Field

[0001] This invention relates to the field of thermal cycling experiments in nuclear power pipelines, and specifically to a thermal cycling experimental system and method for stagnant pipelines. Background Technology

[0002] During the operation of a nuclear power plant, the heat generated by the reactor needs to be transferred through a piping system. The fluid movement within these pipes can become highly complex due to their unique structure, such as the turbulent infiltration-induced thermal cycling phenomenon in the downstream horizontal stagnant branch pipes. This phenomenon is characterized by reciprocating thermal fluctuations at the interface between hot and cold elements. These temperature fluctuations, when transmitted to the pipe walls, cause periodic intensifications and deteriorations of thermal stratification, leading to localized fatigue loads at critical locations within the pipes. This exacerbates crack initiation, shortens the lifespan of critical pipes, and poses a potential threat to the operational safety of nuclear power facilities. Because thermal cycling is a dynamic phenomenon, it is difficult to monitor directly in engineering. Therefore, targeted experiments are needed to measure the impact of parameters such as mainstream velocity, mainstream temperature, and the main-to-branch pipe diameter ratio on the thermal cycling phenomenon.

[0003] Currently, there are relevant measures for experiments on thermal stratification in fluctuating pipes; however, they lack flexibility in adjusting parameters such as pipe diameter ratio, temperature difference, and flow rate, and there is limited data acquisition for strain. Secondly, existing heat dissipation devices often cannot effectively consider the complex heat dissipation conditions of thermal cycling. During thermal cycling experiments on pipelines, there is no comprehensive monitoring system or method to accurately obtain data on the pipeline's temperature and deformation status. Furthermore, current deformation detection of pipelines mainly uses digital image correlation (DIC) technology, which has the following problems: DIC technology has certain requirements for ambient light and surface texture; in outdoor or poorly lit environments, additional lighting equipment may be needed to ensure image quality; DIC technology requires good texture features on the surface of the measured object to track feature points in the image. For pipelines with smooth surfaces or indistinct textures, additional surface treatments, such as spraying random speckle patterns, may be needed to improve measurement accuracy; DIC technology mainly uses a single camera and can only measure two-dimensional deformation data, unable to measure three-dimensional deformation.

[0004] Patent document CN116066654B discloses a pipeline system for eliminating thermal fatigue in nuclear power plant pipelines. The system includes a main pipeline and branch pipelines connected to it. Each branch pipeline includes a vertical section and a horizontal section. The vertical section is connected to the main pipeline, and the horizontal section is connected to the end of the vertical section furthest from the main pipeline. The horizontal section has a sensitive area. The axial heat transfer system for mitigating thermal stratification in nuclear power plant pipelines includes: a heat pipe device extending axially along the lower outer wall of the main and branch pipelines to transport heat to the sensitive area to eliminate or mitigate the thermal stratification effect; and a temperature measuring device located on the outer periphery of the horizontal section at the sensitive area to detect the temperature of the sensitive area. This pipeline system for eliminating thermal fatigue in nuclear power plant pipelines reduces the occurrence of thermal stratification, thermal cycling, and thermal oscillation in nuclear power plant pipelines, thus lowering the probability of pipeline fatigue. However, it does not solve the problem of monitoring pipeline temperature, deformation state, and strain in current pipeline thermal fatigue tests.

[0005] Patent document CN116221525A discloses an axial heat transfer system for mitigating thermal stratification effects in nuclear power plant pipelines. The system includes a main pipeline and branch pipelines connected to it. Each branch pipeline comprises a vertical section and a horizontal section. The vertical section is connected to the main pipeline, and the horizontal section is connected to the end of the vertical section furthest from the main pipeline. The horizontal section has a sensitive area. The axial heat transfer system includes a heat pipe device that extends axially along the lower outer wall of the main and branch pipelines to transfer heat to the sensitive area to eliminate or mitigate the thermal stratification effect. This system can reduce the probability of pipeline fatigue and improve the availability of nuclear power units. However, it does not solve the problem of monitoring pipeline temperature, deformation state, and strain in current pipeline thermal fatigue tests.

[0006] In summary, neither of the two existing patents mentioned above has solved the problem of monitoring pipeline temperature, deformation state, and strain in current pipeline thermal fatigue tests. Summary of the Invention

[0007] Based on the above-mentioned technical problems, this invention proposes a stagnant pipeline thermal cycle test system and method to solve the problem of monitoring pipeline temperature, deformation state and strain in current pipeline thermal fatigue tests.

[0008] To achieve the above objectives, this invention proposes a stagnant pipe thermal circulation experimental system.

[0009] A stagnant pipeline thermal circulation test system includes a heating pipeline and a test pipeline, wherein the heating pipeline and the test pipeline are connected in parallel, and the test pipeline includes a main pipe and branch pipes;

[0010] The branch pipe includes a first pipe section, a second pipe section, and a third pipe section. The branch pipe is connected to the main pipe through the first pipe section. The first pipe section is connected to one end of the second pipe section, and the third pipe section is connected to the other end of the second pipe section.

[0011] The diameter D1 of the main pipe is larger than the diameter D2 of the branch pipe.

[0012] Furthermore, the variable diameter section is located at both ends of the main pipe. The distance between the outlet of the variable diameter section at the inflow end of the main pipe and the center of the contact surface between the branch pipe and the main pipe is 10D1-20D1, and the distance between the inlet of the variable diameter section at the outflow end of the main pipe and the center of the contact surface between the branch pipe and the main pipe is 5D1-10D1.

[0013] Furthermore, the first pipe segment is connected perpendicular to the main pipe, and the second pipe segment is arranged parallel to the main pipe, and the second pipe segment is an L-shaped pipe segment.

[0014] Furthermore, the branch pipe includes multiple temperature measuring points and multiple thermocouples, with the multiple temperature measuring points arranged at different radial angle positions of the branch pipe; each thermocouple corresponds to one temperature measuring point.

[0015] The thermocouple is inserted radially into the wall of the branch pipe at a distance of 1mm-3mm from the inner wall of the branch pipe.

[0016] Furthermore, multiple temperature measuring points are located on the same measuring section of the branch pipe and are arranged at radial positions of the branch pipe at intervals of 44°-46°, and the branch pipe includes multiple measuring sections.

[0017] Furthermore, the branch pipe includes multiple high-temperature speckle spray points, which are located on the second pipe section.

[0018] Furthermore, the branch pipe includes a cooling flange, which is located at the end of the third pipe section that is not connected to the second pipe section.

[0019] Furthermore, it also includes a water chiller and an electric valve, wherein the water chiller is connected to the cooling flange via a pipe, and the electric valve is located on the pipe between the water chiller and the cooling flange.

[0020] Furthermore, it also includes a cooling duct, which is located outside the branch pipe.

[0021] Furthermore, it also includes a thermal insulation layer, which is filled between the cooling air duct and the branch pipe, and the thickness of the thermal insulation layer is 5mm-15mm.

[0022] Furthermore, it also includes a blower, which is connected to the cooling duct via a flexible hose.

[0023] Furthermore, the diameter D1 of the main pipe ranges from 15cm to 40cm;

[0024] The diameter D2 of the branch pipe ranges from 3cm to 20cm.

[0025] Furthermore, it also includes a water storage tank, which is connected to the heating pipeline and the experimental pipeline.

[0026] Furthermore, it also includes a heating pipe section, which, together with the heating pipeline, forms a heating circuit.

[0027] Furthermore, the heating pipe section also includes a filter, a variable frequency pump, a flow meter, an electric heater, and a voltage regulator. The filter is located upstream of the variable frequency pump to prevent impurities from entering the variable frequency pump.

[0028] The filter, the variable frequency pump, the flow meter, the electric heater, and the voltage regulator are sequentially connected and installed in the heating pipe section.

[0029] Furthermore, the experimental pipeline also includes a speedometer, which is located upstream of the main pipe in the experimental pipeline.

[0030] To achieve the above objectives, the present invention also proposes an experimental method using the above-mentioned stagnant pipe thermal circulation system.

[0031] A method for conducting thermal cycling experiments in a stagnant pipe, characterized by comprising:

[0032] S1: Adjust the temperature and pressure of the experimental water in the system to the target value through the heating pipeline;

[0033] S2: Control the flow of experimental water into the main pipe and the branch pipe.

[0034] Further, step S1 includes:

[0035] The water temperature and pressure of the experimental water in the system are adjusted to the target values ​​using an electric heater and a voltage regulator.

[0036] Further, step S2 includes:

[0037] Close the electric regulating valve of the heating pipeline, open the electric regulating valve of the experimental pipeline to allow experimental water to flow into the main and branch pipes, and detect the flow rate of the experimental pipeline using a speed meter.

[0038] Based on the experimental parameters, the electric regulating valve in the experimental pipeline was adjusted to input different waveforms and opening degrees to the experimental water. The formula for calculating the flow rate y is as follows:

[0039] y = F(x, T)

[0040] Where x is the opening degree of the electric regulating valve in the experimental pipeline, and T is time. The flow curve is obtained based on the flow rate, and the output waveform and opening degree of the electric regulating valve in the experimental pipeline are adjusted according to the flow curve.

[0041] Furthermore, step S2 also includes:

[0042] Start the blower, electric valve, and water cooler. Set the two strain monitoring lenses at different positions 30cm-50cm away from the second pipe section so that both strain monitoring lenses can capture the high-temperature speckle spray points. Obtain temperature data through thermocouples. Turn on the two strain monitoring lenses to capture the deformation position of the high-temperature speckle spray points to obtain three-dimensional strain field data.

[0043] Based on the above technical solution, the present invention has at least the following beneficial effects:

[0044] 1. This invention proposes a stagnant pipe thermal circulation experimental system and method. By adjusting the flow system and replacing the experimental pipe section, the experimental system of this invention can simulate thermal circulation phenomena under different operating conditions, including variables such as different main pipe temperatures, pipe diameters, main-branch pipe diameter ratios, and flow velocities. This invention improves the flexibility of pipe thermal circulation experiments, enabling the experimental system to adapt to a wide range of experimental needs, improving experimental efficiency and system availability, while also saving economic costs. The stagnant pipe thermal circulation experimental method proposed in this invention allows for rapid adjustment of the simple experimental system to obtain experimental parameters under different conditions, making it more adaptable and practical.

[0045] 2. This invention proposes an experimental system and method for thermal cycling in stagnant pipes. By setting temperature measuring points on the outer side of multiple cross-sections of the branch pipes and strain measuring points at bends in the experimental system, along with a non-contact strain measurement system, the experimental system can effectively measure temperature and strain information during the experiment. Multiple strain monitoring lenses, combined with an optical measurement system, capture speckle patterns to obtain a three-dimensional strain field. This precise data acquisition capability makes the experimental results more reliable, providing accurate data support for subsequent analysis and research.

[0046] 3. This invention proposes a stagnant pipe thermal circulation experimental system and method. By wrapping a cooling duct around the outside of the branch pipe's insulation cotton and controlling the heat exchange conditions at the end of the branch pipe using experimental water, the experimental device can effectively cope with complex thermal circulation phenomena, ensuring the heat dissipation boundary conditions of the branch pipe, thereby effectively controlling the thermal circulation phenomenon during the experiment. This ability to adjust heat dissipation conditions not only improves the accuracy of the experiment but also enhances its safety, as it effectively prevents local overheating or pressure anomalies caused by thermal circulation, protecting the experimental device and operators. The design of the experimental device allows for the adjustment of multiple parameters to simulate different operating conditions, increasing the flexibility and adaptability of the experiment, enabling the experimental device to operate stably under different experimental conditions, further ensuring the safety and reliability of the experiment. Attached Figure Description

[0047] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0048] Figure 1 A schematic diagram of a stagnant pipe thermal circulation experimental system according to one embodiment is shown;

[0049] Figure 2 A schematic diagram of a branch pipe section structure of one embodiment is shown.

[0050] The above figures include the following reference numerals:

[0051] 1. Main pipe; 2. Branch pipe; 3a. Heating pipeline; 3b. Experimental pipeline; 4. Check valve; 5a. Water storage tank; 5b. Electric regulating valve for water storage tank; 6. Filter; 7. Variable frequency pump; 8. Flow meter; 9. Electric heater; 10. Voltage regulator; 11. Electric regulating valve for heating pipeline; 12. Electric regulating valve for experimental pipeline; 13. Speed ​​meter; 14. Cooling flange; 15. Cooling duct; 16. Blower; 17. Electric valve; 18. Water chiller; 19. Strain monitoring lens;

[0052] 2a. Temperature measuring point; 2b. Thermocouple; 2c. High-temperature speckle spraying point. Detailed Implementation

[0053] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0054] The present invention will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention. The term "comprising" indicates the presence of a feature, but does not exclude the presence or addition of one or more other features. The terms "lateral," "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the purpose of description, and do not indicate or imply that the system or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0055] In this description, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0056] Example

[0057] This invention proposes a stagnant pipe thermal circulation experimental system, such as... Figure 1 The diagram shows a heating pipeline and an experimental pipeline, which are connected in parallel. The experimental pipeline includes a main pipe and branch pipes.

[0058] The branch pipe includes a first pipe section, a second pipe section, and a third pipe section. The branch pipe is connected to the main pipe through the first pipe section. The first pipe section is connected to one end of the second pipe section, and the third pipe section is connected to the other end of the second pipe section.

[0059] The diameter D1 of the main pipe is larger than the diameter D2 of the branch pipe.

[0060] Furthermore, the composition of branch pipe 2 is as follows: Figure 2 As shown, the first section of branch pipe 2 is vertically connected to the main pipe 1, the other end of the first section is connected to the second section, and the third section is connected to the first section through the second section. The bending angle of the second section is 90°, the length of the first section is 0.5m, and the length of the third section is 1.2m. The first section, the second section and the third section together form the main structure of branch pipe 2.

[0061] Furthermore, a cooling flange 14 is installed at the end of the third pipe section. The cooling flange 14 has multiple layers of guide vanes inside, and an inlet and an outlet are respectively provided on both sides of the cooling flange 14 for connecting to the water chiller 18. The temperature of the water in the branch pipe 2 flowing into the water chiller 18 through the cooling flange 14 is controlled to be maintained between 35℃ and 80℃.

[0062] Furthermore, the outer side of the branch pipe 2 is provided with insulation cotton, and the outer side of the insulation cotton is provided with a cooling air duct 15 to wrap the branch pipe 2. A blower 16 is provided outside the branch pipe 2, and the blower 16 is connected to the cooling air duct 15 through a flexible hose.

[0063] Furthermore, two strain monitoring lenses 19 are respectively set outside the second pipe section, so that the two sets of strain monitoring lenses 19 can capture and detect as many high-temperature speckle spray points 2c on the second pipe section as possible.

[0064] To achieve the above objectives, the present invention also proposes a method for conducting thermal cycling experiments on stagnant pipes, using the thermal cycling experimental system for stagnant pipes described above, comprising the following steps:

[0065] S1: Adjust the temperature and pressure of the experimental water in the system to the target value through heating pipeline 3a;

[0066] S2: Control the flow of experimental water into the main pipe 1 and the branch pipe 2.

[0067] Further, step S1 includes:

[0068] The water temperature and pressure of the experimental water in the system are adjusted to the target values ​​by using electric heater 9 and voltage regulator 10.

[0069] Furthermore, open the electric regulating valve 11 of the heating pipeline 3a, close the electric regulating valve 12 of the experimental pipeline 3b, adjust the variable frequency pump 7, and observe the circuit flow through the flow meter 8. Preferably, the water temperature in the heating pipeline 3a is raised to 300°C and the pressure is raised to 9 MPa through the electric heater 9 and the pressure regulator 10. The electric heater 9 and the pressure regulator 10 work alternately to ensure that all parts of the system are stable and do not boil.

[0070] Further, step S2 includes:

[0071] By opening the electric regulating valve 12 of the experimental pipeline, experimental water flows into the main pipe 1 and the branch pipe 2, and the temperature boundary on the outside of the branch pipe 2 is kept stable by the water chiller 18 and the blower 16.

[0072] Furthermore, by adjusting the experimental pipeline regulating valve 12, a sine wave, triangular wave, square wave, or trapezoidal wave is input to the experimental water according to the experimental parameter requirements. At the same time, the flow curve is obtained based on the opening degree and time of the experimental pipeline regulating valve 12, and the experimental pipeline regulating valve 12 is further adjusted based on the obtained flow curve.

[0073] Furthermore, step S2 also includes:

[0074] Two strain monitoring lenses were placed at different positions 40cm away from the second pipe section, so that both lenses could acquire images of the high-temperature speckle spray point 2c on the second pipe section. The blower 16 was started and the electric valve 17 was opened. Temperature data of various temperature measuring points 2a on different sections were obtained through thermocouples 2b on the experimental pipe section. The second pipe section was photographed by strain monitoring lenses 19 at different angles to capture the high-temperature speckle spray point 2c and obtain three-dimensional strain field data.

[0075] Furthermore, when it is necessary to conduct experiments under different experimental conditions, after the experimental pipeline 3b stops draining, the main pipe 1 and the branch pipe 2 are removed. By replacing the main pipe 1 and the branch pipe 2 with different diameters, the ratio of the diameters of the main pipe 1 and the branch pipe 2 is adjusted. Preferably, the diameter D1 of the main pipe 1 is 20cm, the diameter D2 of the branch pipe 2 is 10cm, and the ratio of D1 to D2 is 2:1.

[0076] In summary, as can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0077] 1. This invention proposes a stagnant pipe thermal circulation experimental system and method. By adjusting the flow system and replacing the experimental pipe section, the experimental system of this invention can simulate thermal circulation phenomena under different operating conditions, including variables such as different main pipe temperatures, pipe diameters, main-branch pipe diameter ratios, and flow velocities. This invention improves the flexibility of pipe thermal circulation experiments, enabling the experimental system to adapt to a wide range of experimental needs, improving experimental efficiency and system availability, while also saving economic costs. The stagnant pipe thermal circulation experimental method proposed in this invention allows for rapid adjustment of the simple experimental system to obtain experimental parameters under different conditions, making it more adaptable and practical.

[0078] 2. This invention proposes an experimental system and method for thermal cycling in stagnant pipes. By setting temperature measuring points on the outer side of multiple cross-sections of the branch pipes and strain measuring points at bends in the experimental system, along with a non-contact strain measurement system, the experimental system can effectively measure temperature and strain information during the experiment. Multiple strain monitoring lenses, combined with an optical measurement system, capture speckle patterns to obtain a three-dimensional strain field. This precise data acquisition capability makes the experimental results more reliable, providing accurate data support for subsequent analysis and research.

[0079] 3. This invention proposes a stagnant pipe thermal circulation experimental system and method. By wrapping a cooling duct around the outside of the branch pipe's insulation cotton and controlling the heat exchange conditions at the end of the branch pipe using experimental water, the experimental device can effectively cope with complex thermal circulation phenomena, ensuring the heat dissipation boundary conditions of the branch pipe, thereby effectively controlling the thermal circulation phenomenon during the experiment. This ability to adjust heat dissipation conditions not only improves the accuracy of the experiment but also enhances its safety, as it effectively prevents local overheating or pressure anomalies caused by thermal circulation, protecting the experimental device and operators. The design of the experimental device allows for the adjustment of multiple parameters to simulate different operating conditions, increasing the flexibility and adaptability of the experiment, enabling the experimental device to operate stably under different experimental conditions, further ensuring the safety and reliability of the experiment.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0081] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0082] It should be noted that, in the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A stagnant pipe thermal circulation experimental system, characterized in that, This includes heating lines (3a) and experimental lines (3b). The heating pipeline (3a) and the experimental pipeline (3b) are connected in parallel. The experimental pipeline (3b) includes a main pipe (1) and a branch pipe (2). The branch pipe (2) includes a first pipe section, a second pipe section and a third pipe section. The branch pipe (2) is connected to the main pipe (1) through the first pipe section. The first pipe section is connected to one end of the second pipe section, and the third pipe section is connected to the other end of the second pipe section. The diameter D1 of the main pipe (1) is greater than the diameter D2 of the branch pipe (2); The first pipe section is connected perpendicular to the main pipe (1), the third pipe section is set parallel to the main pipe (1), and the second pipe section is an L-shaped pipe section; The branch pipe (2) includes multiple temperature measuring points (2a) and multiple thermocouples (2b). The multiple temperature measuring points (2a) are set at different radial angles of the branch pipe (2). Each thermocouple (2b) corresponds to one temperature measuring point (2a). The thermocouple (2b) is inserted into the wall of the branch pipe (2) radially along the branch pipe (2) and at a distance of 1mm-3mm from the inner wall of the branch pipe (2). The branch pipe (2) includes multiple high-temperature speckle spray points (2c), and the multiple high-temperature speckle spray points (2c) are located in the second pipe section.

2. The system according to claim 1, characterized in that, The main pipe (1) includes a variable diameter section. The variable diameter section is located at both ends of the main pipe (1). The distance between the outlet of the variable diameter section at the inflow end of the main pipe (1) and the center of the contact surface between the branch pipe (2) and the main pipe (1) is 10D1-20D1. The distance between the inlet of the variable diameter section at the outflow end of the main pipe (1) and the center of the contact surface between the branch pipe (2) and the main pipe (1) is 5D1-10D1.

3. The system according to claim 1, characterized in that, Multiple temperature measuring points (2a) are located on the same measuring section of the branch pipe (2) and are set at radial positions of the branch pipe (2) at intervals of 44°-46°. The branch pipe (2) includes multiple measuring sections.

4. The system according to claim 1, characterized in that, The branch pipe (2) includes a cooling flange (14). The cooling flange (14) is located at the end of the third pipe section that is not connected to the second pipe section.

5. The system according to claim 4, characterized in that, It also includes a water chiller (18) and an electric valve (17). The water chiller (18) is connected to the cooling flange (14) via a pipe, and the electric valve (17) is located on the pipe between the water chiller (18) and the cooling flange (14).

6. The system according to claim 1, characterized in that, It also includes cooling ducts (15). The cooling duct (15) is located outside the branch pipe (2).

7. The system according to claim 6, characterized in that, It also includes an insulation layer. The insulation layer is filled between the cooling duct (15) and the branch pipe (2), and the thickness of the insulation layer is 5mm-15mm.

8. The system according to claim 6, characterized in that, It also includes blowers (16). The blower (16) is connected to the cooling duct (15) via a hose.

9. The system according to claim 1, characterized in that, The diameter D1 of the main pipe (1) ranges from 15cm to 40cm; The diameter D2 of the branch pipe (2) ranges from 3cm to 20cm.

10. The system according to claim 1, characterized in that, It also includes a water storage tank (5a). The water storage tank (5a) is connected to the heating pipeline (3a) and the experimental pipeline (3b).

11. The system according to claim 1, characterized in that, It also includes heating pipe sections, The heating pipe section and the heating pipeline (3a) form a heating circuit.

12. The system according to claim 11, characterized in that, The heating section also includes a filter (6), a variable frequency pump (7), a flow meter (8), an electric heater (9), and a voltage regulator (10). The filter (6) is located upstream of the variable frequency pump (7) to prevent impurities from entering the variable frequency pump (7). The filter (6), the variable frequency pump (7), the flow meter (8), the electric heater (9), and the voltage regulator (10) are sequentially connected and installed in the heating pipe section.

13. The system according to claim 1, characterized in that, The experimental pipeline also includes a speedometer (13). The speedometer (13) is located upstream of the main pipe (1) in the experimental pipeline.

14. An experimental method using the stagnant pipe thermal circulation experimental system as described in claim 1, characterized in that, include: S1: Adjust the temperature and pressure of the experimental water in the system to the target value through the heating pipeline (3a); S2: Control the flow of experimental water into the main pipe (1) and the branch pipe (2).

15. The method according to claim 14, characterized in that, Step S1 includes: The water temperature and pressure of the experimental water in the system are adjusted to the target values ​​by using an electric heater (9) and a voltage regulator (10).

16. The method according to claim 14, characterized in that, Step S2 includes: Close the electric regulating valve (11) of the heating pipeline, open the electric regulating valve (12) of the experimental pipeline, and let the experimental water flow into the main pipe (1) and the branch pipe (2). Detect the flow rate of the experimental pipeline (3b) by the speed meter (13). Based on the experimental parameters, the electric regulating valve (12) of the experimental pipeline was adjusted to input different waveforms and opening degrees to the experimental water. The flow rate y was calculated using the following formula: Where x is the opening degree of the experimental pipeline electric regulating valve (12), T is time, the flow curve is obtained according to the flow rate, and the output waveform and opening degree of the experimental pipeline electric regulating valve (12) are adjusted according to the flow curve.

17. The method according to claim 14, characterized in that, Step S2 further includes: Start the blower (16), electric valve (17), and water chiller (18). Set the two strain monitoring lenses (19) at different positions 30cm-50cm away from the second pipe section, so that both strain monitoring lenses (19) can capture the high-temperature speckle spray point (2c). Obtain temperature data through thermocouple (2b). Turn on the two strain monitoring lenses (19) to capture the second pipe section and capture the deformation position of the high-temperature speckle spray point (2c) to obtain three-dimensional strain field data.

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