Natural circulation double-channel visual experimental analysis device

Abstract

The application relates to a natural circulation double-channel visualized experimental analysis device, which comprises a circulating pump, a preheater, a parallel-channel visualized experimental section, a condenser and a back pressure valve connected in sequence to form a circulating loop and an analysis system; the circulating mode is natural circulation established by using the preheater as a heat source and the condenser as a cold source; the visualized experimental section comprises two flow channels with different materials, at least two communication channels between the parallel flow channels, visual windows with different light transmittances and a heating device for heating the flowing working medium in the two flow channels; the analysis system is used for observing the macroscopic characteristics of the flowing working medium in the parallel-channel visualized experimental section through the visualized observation window; flow field information is collected, the collected data are optimized and screened; based on the screened data, a natural circulation instability occurrence boundary graph is obtained by using related software, a database is established, and a mathematical model of instability flow is obtained; the experimental device is a visualized, double-channel and intelligent analysis platform for medium-high pressure natural circulation, and the working medium can be mixed between the two channels, and the inclination angle of the experimental section can be swung.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear energy technology or mechanical equipment, in particular to a natural circulation double-channel visualized experimental analysis device. BACKGROUND

[0002] Natural circulation is an energy transmission mode that can drive fluid circulation flow only by the driving force generated by the density difference between cold and hot fluids. Without an additional power source, the system can reduce the dependence on external power supply, effectively improve the safety of the running system, and is the main circulation cooling mode for advanced nuclear reactors in operation, and is also an important means for emergency cooling after a shutdown accident. However, two-phase flow is very easy to cause large amplitude oscillation of flow, pressure drop and cross-section steam content due to small disturbance, similar to the vibration phenomenon in mechanical systems. Continuous flow oscillation can cause forced mechanical vibration of the equipment, causing resonance phenomenon, and flow oscillation can also greatly affect the local heat transfer performance, greatly reduce the critical heat flux density, and seriously endanger the safety of system operation.

[0003] Miniaturization and integration are important directions for the development of two-phase systems. The narrow rectangular channel in the natural circulation system has the characteristics of compact structure, enhanced heat transfer, flexible design and application, and the parallel narrow rectangular channels with various arrangements can better protect the reactor. However, the hydraulic diameter of the narrow rectangular channel is small, the allowable heat flux density is large, and the bubbles are more easily deformed under the influence of narrow space effect. Therefore, flow instability phenomenon is more likely to occur in the channel, and the generation mechanism and fluctuation rule of various flow instabilities are different from those of conventional channels. At the same time, in the small and integrated nuclear reactor, there are a large number of parallel narrow rectangular channels in the non-active safety measures due to the small space. When these channels occur unstable flow, they will affect each other and appear more intense unstable flow, which seriously affects the normal work of the equipment.

[0004] At present, the natural circulation experiments at home and abroad are mainly aimed at single channel in the normal pressure range, Yang Ruichang, Salah and others respectively studied the natural circulation instability flow through experiments, and the criterion relationship obtained is in good agreement in the lower pressure range. But in the above experiments, the channel type is mostly circular pipe, and the pressure range involved in the experiment is extremely limited. With the gradual improvement of the requirements of equipment on working environment pressure, temperature and other requirements, the exploration of the natural circulation characteristics in a higher pressure range is needed. The existing parallel channels are mainly used in the nuclear submarine with compact structure, so the experiment is mainly based on the swing condition in the sea. Yin Chaoxing, Otsuji and others respectively explored the influence of amplitude, period and other factors on the two-phase flow pressure drop and CHF point occurrence position under the external swing condition. The above experiments are mostly from external influence, and the influence of internal instability flow of the channel is less studied. Zhou Tao, Fang Xiaolu, Cheng and others have carried out natural circulation experiment of single channel in normal pressure narrow rectangle, but they mainly focus on the process of bubble generation and the change of heat transfer characteristics, and lack of division and research on instability flow in medium and high pressure. At the same time, Zhou Tao and others in the applicant team have applied for a patent of single channel supercritical / subcritical water natural circulation experiment platform, and have built an experimental platform to carry out some research, but the physical properties of supercritical fluid are quite different from those of conventional fluid, and the experimental platform is only for a single vertical channel, so the applicability is poor. With the development of small integrated nuclear reactor, the importance of narrow rectangular parallel channel begins to stand out, and the angle of channel assembly also becomes various with the demand of equipment, but there is a lack of instability experiment in medium and high pressure at present. Therefore, the applicant believes that it is necessary to carry out detailed research on the instability of natural circulation flow in narrow rectangular parallel channel, and find the stable boundary of safe operation. SUMMARY

[0005] The purpose of the present application is to solve the problems in the background art, and to provide a natural circulation double-channel visualized experimental analysis device, which is used for observing the distribution of bubbles and the change characteristics of flow pattern in the channel when instability occurs by using visualized means, and obtaining the main characteristics of instability occurrence.

[0006] The technical scheme of the present application is a natural circulation double-channel visualized experimental analysis device, which comprises a circulation loop composed of a circulating pump, a preheater, a parallel-channel visualized experimental section, a condenser and a back pressure valve connected in sequence, and an analysis system, characterized in that the circulation loop is a natural circulation loop established by using the preheater as a heat source and the condenser as a cold source; a storage tank is used for storing liquid or gas, flow meters and temperature tables are arranged at the inlet and outlet ends of the parallel-channel visualized experimental section, and a pressure gauge is connected in parallel between the inlet and outlet ends of the parallel-channel visualized experimental section.

[0007] The analysis system comprises an image acquisition device and a data acquisition and analysis system; the image acquisition device is used for observing the mesoscopic characteristics of the flowing working medium in the parallel channel visualized experimental section through a visual window, including temperature, pressure, pulsation frequency, period, amplitude and steam quality after the occurrence of unstable flow; the collected data are screened and optimized by using an artificial intelligence algorithm; based on the screened data, a natural circulation instability occurrence boundary graph is obtained by using existing software origin, a database is established to obtain an unstable flow mathematical model, a prediction model is constructed based on artificial intelligence learning, and model prediction results are obtained through virtual experiments;

[0008] The structure of the parallel channel visualized experimental section comprises at least two parallel flow channels arranged in parallel, visual windows arranged on the side walls of the at least two flow channels respectively, and a heating device for heating the flowing working medium in the at least two flow channels; the two flow channels are arranged in parallel, cross or herringbone shape, and the cross section of each flow channel is a narrow rectangle with a large aspect ratio.

[0009] Preferably, the roughness of the inner walls of the two flow channels is different, and each is provided with a protruding part capable of independent control of up and down movement; the number, height and size of the protruding part are controlled by a controller; the protruding part forms a vortex generator in the flow channel for disturbing the working medium in the flow channel;

[0010] Preferably, two communication channels are arranged between the two parallel flow channels and at both ends of the parallel flow channels respectively, for mixing the working medium in the two flow channels; valves are arranged on the two parallel flow channels and the two communication channels; the two ends of the parallel flow channels are respectively provided with electric valves which are opened and closed by electric control to realize the connection of any one or both flow channels to the circulation loop; the two communication channels are respectively provided with valves composed of beta-lithia-silicon carbide composite thermal sensitive material and photosensitive material; the opening and closing of the valves are controlled by a passive way to control the mixing of the working medium in the two flow channels. The aforementioned valve is a passive component, which means that it does not rely on external input to perform functions. There is generally no moving part in the passive component, and its function is completed after sensing the change of a certain parameter such as pressure, temperature or flow. In this application, the opening and closing of the valve are controlled by the change of temperature and light.

[0011] Preferably, the at least two flow channels are respectively located at both sides of a cover plate, and the visual windows are sealed and installed on the side of the flow channels by locking members; a heating device for indirectly heating the working medium in the flow channels is installed in the middle of the cover plate; the heating device is an electric heating sheet or a heat pipe, which is fixed by a high-temperature-resistant material gasket; or a transparent heating film is used to cover the visual window for indirect heating.

[0012] The material of the visual window is quartz glass, aluminum-silicon glass, sapphire or high-silica glass;

[0013] The flow channel material is titanium or magnesium alloy;

[0014] The cover plate material is high-strength steel;

[0015] The high-temperature-resistant sealing gasket is a asbestos gasket, a flexible graphite gasket, a metal composite gasket or a polytetrafluoroethylene gasket.

[0016] Preferably, the flowing working medium in the circulation loop is deionized water, the working temperature is 20-600 DEG C, and the working pressure is 0.1-14.2 MPa.

[0017] The preheater adopts an indirect heating mode to preheat the flowing working medium; and the cold side of the condenser is cooling water.

[0018] The pressure stabilizing tank is also included, which is connected in series in the circulation loop and located downstream of the condenser, for pressure stabilization of the circulation loop.

[0019] The inlet and outlet ends of the parallel channel visualized experimental section are respectively provided with arc-shaped connectors, a plurality of interfaces are arranged on the arc-shaped connectors in the direction of the circular arc, the inlet and outlet of the parallel channel visualized experimental section are connected with different interfaces, and the inclination angle of the entire parallel channel visualized experimental section is adjusted to perform experiments at different inclination angles.

[0020] A natural circulation unstable flow measurement method of the natural circulation double-channel visualized experimental analysis device as described above, comprising:

[0021] The outlet end pressure booster pump of the storage tank is opened, deionized water is injected into the circulation loop, when the pressure reaches the set value, the circulation pump is started;

[0022] The preheater and the condenser are opened to form a heat source and a cold source respectively to form a natural circulation;

[0023] The vortex generator arranged in the flow channel is opened, the number, height and size of the protrusions in the flow channel are controlled by the upper computer according to the working medium flow condition, and the working medium is disturbed;

[0024] During the circulation of the deionized water, the heating temperature and the light irradiation of the working medium in the parallel channel visualized experimental section are adjusted to introduce heat disturbance; the two intermediate valves are contracted to open the communication channels in the two parallel flow channels and mix the flowing working medium in the two flow channels;

[0025] The flow field information in the loop is collected by the data acquisition and analysis system, including the pulsation frequency, period, amplitude, steam quality, temperature, pressure and other information after the occurrence of unstable flow;

[0026] The image acquisition device collects the image of the fluid flow pattern and bubble development information in the flow channel of the parallel channel visualized experimental section through the visual window;

[0027] Obtain the unstable flow phenomenon in the flow channel through the collected image information;

[0028] A learning model is first constructed by using the BP neural network, then the collected data are input to train the model, the model is perfected, and the result closest to the expected output value is obtained; the neural network is directly used to optimize and screen out unreasonable data from the collected flow field information in the parallel channel visualization experimental section 8; the existing software origin is used to obtain the natural circulation instability occurrence boundary graph through the screened flow field information, a database is constructed, and finally a prediction model is learned and constructed based on artificial neural networks, such as convolutional neural network CNN or graph neural network GNN; the subsequent experiment can obtain the model prediction result in a virtual experiment mode.

[0029] Compared with the prior art, the present application has the following beneficial technical effects:

[0030] The present application can simulate the flow instability phenomenon in the natural circulation system by building a narrow rectangular parallel channel natural circulation experimental device under medium and high pressure conditions, and obtain the main characteristics of instability occurrence and the stability boundary by using visualization means, image acquisition, data acquisition and analysis, thereby solving the problem of hazards caused by the flow instability in the natural circulation system as a passive safety system of a nuclear reactor.

[0031] Other features and advantages of the present application will be set forth in the subsequent description, and in part will become apparent to those skilled in the art from the description, or will be learned from practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The present application is a structure schematic diagram of an embodiment.

[0033] Figure 2 The present application is a three-dimensional structure schematic diagram of a parallel channel visualization experimental section of an embodiment.

[0034] Figure 3 The present application is a cross-sectional view of a parallel channel visualization experimental section of an embodiment.

[0035] Figure 4 The present application is a structure schematic diagram of a convex part of an embodiment.

[0036] Figure numerals: 1. Storage tank; 2. Circulation pump; 3. Preheater; 4. Flow meter; 5. Thermometer; 6. Differential pressure gauge; 7. Arc connector; 8. Parallel channel visualization experiment section; 9. Condenser; 10. Pressure regulating tank; 11. Back pressure valve; 12. Booster pump; 13. Data processing and control terminal; 14. High-speed camera; 15. Data acquisition instrument; 16. Cover plate; 17. Class I roughness narrow rectangular flow channel; 18. Visual window; 19. Locking piece; 20. High-temperature resistant sealing gasket; 21. Heating device; 22. Class II roughness narrow rectangular flow channel; 23. Fastening pin; 24. Housing; 25 Connecting channel. DETAILED DESCRIPTION

[0037] Example 1

[0038] like Figure 1 As shown, the natural circulation dual-channel visualization experimental analysis device of this embodiment includes a circulation loop and an analysis system composed of a circulation pump 2, a preheater 3, a parallel channel visualization experimental section 8, a condenser 9 and a back pressure valve 11 connected in sequence;

[0039] The inlet end of the circulation pump 2 is connected to the outlet end of the storage tank 1, and the outlet end of the storage tank 1 is provided with a booster pump 12 and a control valve;

[0040] The circulation loop is a natural circulation established by using a preheater 3 as a heat source and a condenser 9 as a cold source. The storage tank 1 is used to store liquid or gas. The inlet and outlet ends of the parallel channel visualization experiment section 8 are both provided with a flow meter 4 and a temperature meter 5. A pressure gauge 6 is connected in parallel between the inlet and outlet ends of the parallel channel visualization experiment section 8.

[0041] The structure of the parallel channel visualization experiment section 8 includes two flow channels arranged in parallel, visual windows 18 respectively arranged on the side walls of the two flow channels, four connecting channels between the two flow channels, and a heating device for heating the flowing working medium in at least two flow channels;

[0042] For details, see Figure 2 and Figure 3 The two flow channels (the narrow rectangular flow channel 17 with Class I roughness and the narrow rectangular flow channel 22 with Class II roughness) are located on both sides of the cover plate 16. The two flow channels are arranged in parallel, cross or herringbone shape. There are four connecting channels 25 between the two flow channels. The connecting channels can promote the mixing of the working fluids of the two flow channels; the viewing window 18 is sealed and installed on the side of the flow channel by the fastening pin 23, and the viewing window 18 is fixed on the outside by the outer shell 24 and the locking member 19.

[0043] An electric heating plate 21 or heat pipe is installed in the middle of the cover plate 16 for indirectly heating the working medium in the flow channel. The electric heating plate 21 or heat pipe is fixed by a high-temperature resistant material gasket 20; or a transparent heating film is used to cover the viewing window 18 for indirect heating;

[0044] Specifically, a plurality of armored thermocouple probes are provided in the cover plate 16 in an area adjacent to the flow along the length direction thereof.

[0045] The roughness of the inner walls of the two flow channels is different; both have convex parts. Figure 4 As shown, the protrusion can be set to a chimney shape; by adjusting the height, the position entering the flow channel can be adjusted; preferably, the raising and lowering of the protrusion can be controlled by hydraulic control; two relatively sealed cavities are set on the inner wall of the flow channel, and the raising and lowering of the entire protrusion is controlled by controlling the oil pressure of the hydraulic oil entering the upper or lower cavity; in this embodiment, the inside of the protrusion is connected to the controller, and the number, height and size of the protrusions are intelligently controlled by the host computer according to the flow conditions of the working fluid; specifically, first, a BP neural network is used to construct a learning model, and the image acquisition device in the analysis system is used to collect the original data of the fluid disturbance, and the signal is transmitted to the data acquisition and analysis system. The constructed BP neural network model is used to calculate the relevant parameters of the fluid flow, such as the pulsation frequency, amplitude and other parameters. If the parameter is too high or too low, an intelligent control instruction is output, and the height and number of the protrusions are increased or decreased by the controller; in this way, the model is trained to make it tend to be perfect; at this time, when the neural network receives a signal with a small pulsation frequency and a small amplitude of the working fluid, the number and height of the protrusions are intelligently increased to enhance the disturbance in the tube, and vice versa.

[0046] The two flow channels are arranged in parallel, cross or herringbone shape.

[0047] The cross-sections of the two flow channels are narrow rectangles with a large aspect ratio;

[0048] The preferred dimensions of the flow channel are: length 1000 mm, width 40 mm, and height 2 mm.

[0049] The preferred diameter of other pipelines in the circulation loop is DN25.

[0050] Valves are provided at the inlet and outlet of the two flow channels to connect either or both flow channels to the circulation loop.

[0051] The material of the viewing window is quartz glass, high silica glass, sapphire or borosilicate glass; the flow channel material is titanium or magnesium alloy; the cover material is high-strength steel; the high-temperature resistant sealing gasket is asbestos gasket, flexible graphite gasket, metal composite gasket or polytetrafluoroethylene gasket.

[0052] The analysis system includes:

[0053] An image acquisition device is configured to observe the mesoscopic characteristics of the flowing working medium in the parallel channel visualized experimental section 8 through the visualizing observation window, including the generation and development of bubbles and the transition of flow patterns in the unstable flow state.

[0054] A data acquisition and analysis system is configured to first build a learning model by using a BP neural network, then input the artificially collected data to train the model, and make the model perfect to obtain the result closest to the expected output value. The neural network is directly used to optimize and filter out unreasonable data from the collected flow field information in the parallel channel visualized experimental section 8, including the temperature, pressure, fluctuation frequency, cycle, amplitude, steam quality and circulation flow rate of the flowing working medium after the occurrence of unstable flow. An unstable flow prediction model is built based on a convolutional neural network CNN or a graph neural network GNN. The subsequent experiment can obtain the prediction result of the model by using a virtual experiment method. The model inputs the heating power of the experimental section, the loop pressure, the inlet subcooling degree and other possible influencing variables in the natural circulation system, and outputs the information of the unstable flow starting position, flow pattern, unstable flow type and stage under the condition, and displays the loop cloud map visually, so as to reflect the overall temperature, pressure and flow field state of the system more directly.

[0055] The flow rate-pressure drop curve when the flow instability occurs is compared with the image 0 taken by the high-speed camera, and the relevant data obtained are combined to further analyze the flow instability mechanism in the narrow rectangular channel.

[0056] The image acquisition device can specifically adopt a high-speed camera 14. The data acquisition and analysis system specifically includes a data processing and control terminal 13 and a data acquisition instrument 15.

[0057] The flowing working medium in the circulating loop of the embodiment is deionized water, and the working temperature is 20-600 DEG C, and the working pressure is 0.1-14.2 MPa.

[0058] The preheater 3 adopts an indirect heating mode to preheat the flowing working medium.

[0059] The cold side of the condenser 9 is cooling water.

[0060] The stable pressure tank 10 is further included, which is connected in series in the circulating loop and located downstream of the condenser 9, and is used for pressure stabilization of the circulating loop.

[0061] The stable pressure tank 10 can specifically adopt a nitrogen tank, and an adjusting valve and a pressure reducing valve are arranged on the tank.

[0062] As an optimization mode, the inlet and outlet ends of the parallel channel visualization experimental section 8 are respectively provided with arc-shaped connectors 7, a plurality of interfaces are arranged on the arc-shaped connectors 7 in the arc direction, the inlet and outlet of the parallel channel visualization experimental section 8 are connected with different interfaces, the inclination angle of the entire parallel channel visualization experimental section 8 is adjusted, and experiments at different inclination angles are realized.

[0063] The working method of the natural circulation visualization experimental device in the embodiment is as follows: deionized water is stored in the storage tank, two flow channels with different roughness are opened at the same time, and the working method of the natural circulation visualization experimental device in the embodiment is as follows:

[0064] The booster pump at the outlet end of the storage tank is opened, deionized water is injected into the circulating loop, when the pressure reaches the set value, the circulating pump is started;

[0065] The preheater 3 and the condenser 9 are opened to form a heat source and a cold source respectively to form natural circulation.

[0066] The vortex generator arranged in the flow channel is opened, the number and size of the protrusions in the flow channel are controlled according to the flow condition of the working medium, and the working medium is disturbed.

[0067] During the circulation of the deionized water, the heating temperature and the light of the working medium in the parallel channel visualization experimental section 8 are adjusted, heat disturbance is introduced, and the two valves in the middle are contracted, so as to open the communication channel 25 in the two parallel flow channels and mix the flow working medium in the two flow channels.

[0068] The data acquisition instrument 15 collects the flow field information in the loop, including the pulsation frequency, period, amplitude, steam quality, temperature, pressure and other information after the occurrence of unstable flow, wherein the sampling period is 0.1-5 seconds, which can be manually set according to the needs of different stages of the experiment; the locking part is opened to manually replace the flow channel material, and the above steps are repeated to collect the flow field information; the flow channel material is various, and a plurality of experimental data can be obtained by manually replacing the flow channel material.

[0069] The high-speed camera 14 transmits the image of the fluid flow pattern and bubble development in the two flow channels of the parallel channel visualization experimental section 8 through the visualization window; the data collected by the data acquisition instrument 15 and the high-speed camera 14 are transmitted to the data processing and control terminal 13 for further processing: according to the collected image information, the unstable flow phenomena in the narrow rectangular flow channel 17 with type I roughness and the narrow rectangular flow channel 22 with type II roughness are obtained; after the collected data are optimized and screened by the BP neural network, the natural circulation instability occurrence boundary graph is obtained based on reasonable data using the existing software origin, and a database is constructed. Based on the convolutional neural network CNN or the graph neural network GNN, an unstable flow prediction model is constructed, and the model prediction result can be obtained by using virtual experiment.

[0070] Specifically, when the steam quality at the outlet of the parallel channel visualization experimental section 8 is greater than 0.8 and the maximum temperature rise exceeds 15℃ / s, an alarm is issued, the data processing and control terminal 13 executes corresponding protection measures, and the circulating pump is automatically started and the heating of the parallel channel visualization experimental section 8 is stopped.

[0071] Specifically, by connecting different interfaces on the arc-shaped connector at the inlet and outlet of the parallel channel visualization experimental section 8, the inclination angle of the parallel channel visualization experimental section 8 can be adjusted, and experimental data at different inclination angles can be obtained.

[0072] The hydraulic diameter of the narrow rectangular channel is small, the heat flux allowed is large, flow instability phenomena are more likely to occur in narrow space, and the instability is inconsistent with conventional pipes. Therefore, the narrow rectangular parallel channel experimental bench under medium and high pressure conditions is designed to study the occurrence and development of instability flow in the narrow rectangular channel, analyze the mutual interference of instability flow in parallel channels, and analyze the influence of roughness, arrangement angle, and mixing between channels on instability flow. The reference for improving the safety of the natural circulation system is provided, the mathematical model is constructed by collecting data, and the virtual experiment is carried out by using digital twinning and other means to predict the results.

[0073] Those skilled in the art can understand that the above description is only preferred embodiments of the present application and is not used to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments. For those skilled in the art, the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A natural circulation dual-channel visual experimental analysis device, comprising a circulation loop and an analysis system formed by sequentially connecting a circulation pump (2), a preheater (3), a parallel channel visual experimental section (8), a condenser (9) and a back pressure valve (11), and characterized in that: The circulation loop is a natural circulation loop established by using a preheater (3) as a heat source and a condenser (9) as a cold source; the storage tank (1) is used to store liquid or gas, and the inlet and outlet ends of the parallel channel visualization experiment section (8) are both provided with a flow meter (4) and a temperature gauge (5), and a pressure gauge (6) is connected in parallel between the inlet and outlet ends of the parallel channel visualization experiment section (8); The analysis system includes an image acquisition device and a data acquisition and analysis system; the image acquisition device is used to observe the mesoscopic characteristics of the flowing working medium in the parallel channel visualization experimental section (8) through a visual window (18), including the temperature, pressure, pulsation frequency, period, amplitude, and steam content after the unstable flow occurs; the collected data is screened and optimized using an artificial intelligence algorithm; based on the screened data, a natural circulation instability occurrence boundary map is obtained using the existing software origin, and a database is established to obtain an unstable flow mathematical model, and a prediction model is constructed based on artificial intelligence learning to achieve model prediction results through virtual experiments; The structure of the parallel channel visualization experimental section (8) includes at least two parallel flow channels arranged in parallel, visual windows (18) respectively arranged on the side walls of the at least two flow channels, and a heating device (21) for heating the flowing working medium in the at least two flow channels; the two flow channels are arranged in a parallel, cross or herringbone shape, and the cross section of each flow channel is a narrow rectangle with a large length-to-width ratio; Two connecting channels (25) are provided between the two parallel flow channels, and are located at the two ends of the parallel flow channels respectively, for mixing the working fluids in the two flow channels; valves are provided on the two parallel flow channels and the two connecting channels (25); electric valves are provided at the two ends of the parallel flow channels respectively, and are opened and closed by electric control to realize connecting any one or both flow channels to the circulation loop; valves composed of β-eucryptite-silicon carbide composite thermal sensitive material and photosensitive material are provided on the two connecting channels (25), and the opening and closing of the valves are controlled to control the mixing of the working fluids in the two flow channels.

2. The natural circulation dual-channel visualization experimental analysis device according to claim 1, characterized in that: The inner walls of the two flow channels have different roughness and are both provided with protrusions that can be independently controlled to move up and down; the number, height and size of the protrusions are controlled by a controller; the protrusions form vortex generators in the flow channels, which are used to disturb the working medium in the flow channels.

3. The natural circulation dual-channel visualization experimental analysis device according to claim 1, characterized in that: At least two flow channels are respectively located on both sides of the cover plate (16), and the visual window (18) is sealed and installed on the side of the flow channel through a locking member (19). A heating device (21) for indirectly heating the working medium in the flow channel is installed in the middle of the cover plate (16); the heating device (21) is an electric heating plate or a heat pipe, and the electric heating plate or the heat pipe is fixed by a high-temperature resistant material gasket; or a transparent heating film is used to cover the visual window (18) for indirect heating.

4. The natural circulation dual-channel visualization experimental analysis device according to claim 1, characterized in that: The material of the visual window (18) is quartz glass, aluminosilicate glass, sapphire or high silica glass; The flow channel material is titanium or magnesium alloy; The cover plate (16) is made of high-strength steel; The high temperature resistant sealing gasket is an asbestos gasket, a flexible graphite gasket, a metal composite gasket or a polytetrafluoroethylene gasket.

5. The natural circulation dual-channel visualization experimental analysis device according to claim 1, characterized in that: The flowing working medium in the circulation loop is deionized water, with an operating temperature of 20°C-600°C and a working pressure of 0.1MPa-14.2MPa.

6. The natural circulation dual-channel visualization experimental analysis device according to claim 1, characterized in that: The preheater (3) preheats the flowing working medium by indirect heating; the cold side of the condenser (9) is cooling water.

7. The natural circulation dual-channel visualization experimental analysis device according to claim 1, characterized in that: It also includes a pressure stabilizing tank (10) which is connected in series in the circulation loop and is located downstream of the condenser (9) for stabilizing the pressure of the circulation loop.

8. The natural circulation dual-channel visualization experimental analysis device according to claim 1, characterized in that: The inlet and outlet ends of the parallel channel visualization experiment section (8) are respectively provided with arc connectors (7), on which a plurality of interfaces are provided along the arc direction. The inlet and outlet of the parallel channel visualization experiment section (8) are connected to different interfaces to adjust the inclination angle of the entire parallel channel visualization experiment section (8) so as to conduct experiments with different inclination angles.

9. A natural circulation unstable flow measurement method of the natural circulation dual-channel visualization experimental analysis device according to any one of claims 1 to 8, characterized in that: include: Turn on the booster pump (12) at the outlet of the storage tank (1) to inject deionized water into the circulation loop. When the pressure reaches the set value, turn on the circulation pump; Turn on the preheater (3) and the condenser (9) to form a heat source and a cold source respectively to form a natural circulation; Turn on the vortex generators arranged in the flow channel, and according to the flow conditions of the working medium, control the number, height and size of the protrusions in the flow channel through the host computer to disturb the working medium; During the circulation of deionized water, the heating temperature and light of the working medium in the parallel channel visualization experimental section (8) are adjusted to introduce thermal disturbances; the two middle valves are contracted to open the connecting channel (25) in the two parallel flow channels to mix the flowing working medium in the two flow channels; The data acquisition and analysis system collects flow field information in the loop, including pulsation frequency, period, amplitude, steam content, temperature, and pressure information after unstable flow occurs; The image acquisition device is used to acquire images of the fluid flow pattern and bubble development information in the flow channel of the parallel channel visualization experimental section (8) through the visual window (18); The unstable flow phenomenon in the flow channel is obtained through the collected image information; The collected flow field information is screened and optimized using an artificial neural network, and then the natural circulation instability boundary map is obtained using the existing software origin to build a database; an unstable flow prediction model is constructed based on artificial neural networks, including convolutional neural networks (CNN) or graph neural networks (GNN). Subsequent experiments can use virtual experiments to obtain model prediction results.

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