Experimental device and experimental method for two-phase steam condensation water hammer

Abstract

The invention discloses an experimental device and an experimental method of a two-phase steam condensation water hammer, and relates to the technical field of nuclear power, and the experimental device of the two-phase steam condensation water hammer comprises a water supply unit, an inlet experimental section, a heat exchanger, an outlet experimental section and a drainage unit. The water supply unit is used for providing cold water; the inlet experiment section is provided with a first U-shaped pipeline, and the first U-shaped pipeline is connected with the water supply unit through a first valve; a temperature detection device and a pressure detection device are arranged on the heat exchanger; the outlet experiment section is provided with a second U-shaped pipeline, one end of the second U-shaped pipeline is connected with the water outlet end of the heat exchanger, the other end of the second U-shaped pipeline is provided with a second valve, and the first U-shaped pipeline and the second U-shaped pipeline are respectively provided with a temperature detection device and a pressure detection device; according to the technical scheme, the inlet pipeline at the upstream of the heat exchanger and the outlet pipeline at the downstream of the heat exchanger are both designed into a part of the experimental section, and the water hammer phenomenon generated in the heat exchanger can be researched more comprehensively.

Description

Technical Field

[0001] The present invention relates to the field of nuclear power technology, and in particular to an experimental device and an experimental method for two-phase steam condensation water hammer. Background Art

[0002] Water hammer, caused by two-phase steam condensation in nuclear power plant pipelines, is a phenomenon that can occur in nuclear power plant steam systems. Nuclear power plants utilize numerous heat exchangers, of which the waste heat removal heat exchanger is particularly important. The tube side of this heat exchanger carries the primary coolant, while the shell side carries the equipment cooling water. Under certain power plant operating conditions, the waste heat removal heat exchanger is responsible for cooling the primary coolant.

[0003] Accident records at nuclear power plants reveal a specific operating condition in waste heat removal heat exchangers: after the cold water end is isolated, the remaining cold water in the heat exchanger continues to be heated and pressurized by the hot water in the primary circuit. If power plant operators inject cold water directly into the heat exchanger during this condition, the cold water will come into direct contact with the high-temperature, high-pressure water, causing it to vaporize and form steam. This steam and cold water then come into direct contact within the pipes, triggering severe water hammer in the heat exchanger's inlet and outlet pipes or within the heat exchanger itself, causing pressure fluctuations and potentially damaging the equipment. Because the primary coolant in the heat exchanger's pipes is radioactive, large pressure fluctuations within the heat exchanger could potentially damage the primary circuit pressure boundary. This equipment safety issue is something nuclear power plants strive to avoid.

[0004] In traditional two-phase water hammer experiments, the research focus is mainly on the impact of physical parameters on two-phase water hammer, while relatively little research is conducted on human operation or valve movement in real-world settings. Therefore, it is very necessary to develop a water hammer test device for heat exchanger pipelines. Summary of the Invention

[0005] In view of this, the present invention provides an experimental device and an experimental method for two-phase steam condensation water hammer to solve the problem of how to study the two-phase steam condensation water hammer phenomenon in the heat exchanger pipeline.

[0006] The present invention provides an experimental device for two-phase steam condensation water hammer, comprising:

[0007] a water supply unit for providing cold water;

[0008] an inlet experimental section, comprising a first U-shaped pipe, one end of which is provided with a first valve, and the first U-shaped pipe is connected to the water supply unit via the first valve;

[0009] A heat exchanger, the water inlet end of which is connected to the other end of the first U-shaped pipe of the inlet experimental section, and the heat exchanger is provided with a temperature detection device and a pressure detection device;

[0010] The outlet experimental section comprises a second U-shaped pipe, one end of the second U-shaped pipe is connected to the water outlet of the heat exchanger, and the other end is provided with a second valve, and the first U-shaped pipe and the second U-shaped pipe are respectively provided with a temperature detection device and a pressure detection device;

[0011] The hydrophobic unit is connected to the second U-shaped pipe of the outlet experimental section through the second valve.

[0012] The technical solution of the present invention designs the inlet pipe upstream of the heat exchanger and the outlet pipe downstream as part of the experimental section, which can more comprehensively study the water hammer phenomenon generated in the heat exchanger.

[0013] In other words, the present invention incorporates the inlet and outlet piping as part of the experimental section, more closely resembling actual accident conditions in nuclear power plants. Nuclear power plant piping systems are complex, and when an accident occurs, water hammer is often not limited to the heat exchanger itself but also spreads and develops throughout the connected pipes. The design of this experimental setup can realistically replicate this complex physical process, making the experimental results more credible and convincing, and providing a more reliable reference for actual nuclear power plant operations.

[0014] Specifically, the present invention utilizes the first U-shaped pipe upstream of the heat exchanger as part of the inlet experimental section, effectively simulating the scenario of water hammer caused by the re-injection of cold water after steam accumulates in the inlet pipe during an accident. In actual nuclear power plant operation, when a system anomaly occurs, steam may accumulate in the inlet pipe. Subsequent cold water injection rapidly contacts the high-temperature steam, causing condensation and a sudden localized pressure change, which in turn triggers water hammer. This experimental setup accurately replicates this process, enabling in-depth research into the mechanisms, influencing factors, and propagation characteristics of water hammer within the inlet pipe.

[0015] Incorporating a second U-shaped pipe downstream of the heat exchanger into the outlet experimental section simulates the water hammer caused by slug flow impacting the pipe after the valve is opened. In nuclear power plant steam systems, when a valve is opened, the steam-water mixture in the pipe may flow in the form of a slug flow. The slug flow impacts the pipe wall or other components, causing water hammer. This design of the experimental device can simulate the process of slug flow-induced water hammer under different conditions (such as different steam-water ratios and valve opening speeds), study the intensity and frequency of water hammer, and its impact on the piping system. This provides an experimental basis for optimizing pipeline layout and valve control strategies in nuclear power plants to reduce the damage caused by water hammer.

[0016] Because real-time changes in temperature and pressure are closely linked to water hammer, once water hammer occurs, the pressure in the pipe increases dramatically in an instant. This pressure change, coupled with the conversion of fluid mechanical energy, can also cause temperature changes. By capturing these sudden changes in pressure and temperature using detection equipment, researchers can gain insight into the mechanisms that cause water hammer.

[0017] Therefore, in the first U-shaped pipe at the inlet experimental section, the present invention uses a temperature detection device to monitor the temperature changes of the cold water before it enters the heat exchanger, and a pressure detection device to reflect the pressure of the cold water during its flow. In the second U-shaped pipe at the outlet experimental section, these detection devices can monitor the temperature and pressure dynamics of steam or steam-water mixtures in real time during their flow. For example, the temperature drop and pressure fluctuations that occur during the condensation process can be detected, providing key data support for studying steam condensation characteristics and water hammer.

[0018] By installing temperature and pressure sensors on the first and second U-shaped pipes, as well as on the heat exchanger, we were able to comprehensively monitor temperature and pressure changes at various locations during the experiment. During the experiment, the data collected by these temperature and pressure sensors, combined with the simultaneous monitoring of water hammer within the heat exchanger and the inlet and outlet pipes, enabled in-depth analysis of the water hammer process.

[0019] Optionally, a first electric valve is provided on the first U-shaped pipe, and a second electric valve is provided on the second U-shaped pipe.

[0020] The first electric valve on the first U-shaped pipe can precisely control the flow of cold water into the water supply unit. By adjusting the opening of the regulating valve, the rate at which cold water enters the heat exchanger can be flexibly changed according to experimental requirements. The second electric valve on the second U-shaped pipe not only controls the flow of steam or steam-water mixture, but also provides fine-tuning of the outlet pressure. In the experiment, steam flows and condenses in the second U-shaped pipe. By changing the opening of the second electric valve, the steam flow resistance can be changed, thereby adjusting the outlet pressure and flow. Studying the condensation characteristics of steam under different pressure and flow conditions and the occurrence of water hammer will help to deepen the understanding of the role of steam pressure and flow in steam systems and provide experimental support for pressure and flow control in nuclear power plants.

[0021] The two electric control valves enable simulation of various complex nuclear power plant operating conditions. Cold water flow, steam pressure, and flow rate vary significantly during different operational phases of a nuclear power plant, such as startup, normal operation, and shutdown. Using electric control valves, the experimental setup can accurately simulate the fluid states under these diverse operating conditions. Researchers can observe and analyze the steam condensation process and the characteristics of water hammer under various conditions, providing comprehensive experimental data support for nuclear power plants to cope with diverse operating conditions and helping to optimize their operational strategies and procedures.

[0022] Proper adjustment of the electric control valve can avoid water hammer caused by sudden changes in flow or pressure. Specifically, by controlling the rate of change of flow and pressure, so that the fluid enters and flows out of the experimental section smoothly, the risk of water hammer can be effectively reduced, the safe operation of the experimental device can be guaranteed, and a safe environment can be created for the smooth progress of the experiment. In other words, during the start and stop phases of the experiment, the opening of the electric control valve should be slowly adjusted to avoid large instantaneous changes in the flow of cold water or steam, thereby preventing the occurrence of water hammer.

[0023] Optionally, a variable-power heating rod is provided in the heat exchanger. The variable-power heating rod is used to replace the tube-side hot water in the original heat exchanger, and different heat exchanger load experiments are achieved by changing the power of the heating rod. Specifically, three layers of heating rods are arranged in such a way that 2 on the upper layer, 3 in the middle layer, and 2 on the lower layer replace approximately 1,000 heat exchange tubes in the heat exchanger. Due to the large number of heat exchange tubes in the nuclear power plant heat exchanger, it is impossible to accurately simulate all of them. At the same time, in order to ensure the accuracy of the experiment and ensure that the temperature distribution inside the experimental section is similar to the temperature distribution inside the power plant heat exchanger, this experimental device is arranged according to the above-mentioned heating rods, which can accurately simulate the situation of continuous heating inside the heat exchanger after the cold end of the power plant heat exchanger is isolated. This arrangement reduces the number of heating rods and ensures that the temperature distribution in the experimental section is similar to the temperature distribution in the power plant heat exchanger when the heating rods are working.

[0024] Optionally, a transparent window is provided on the side of the water inlet of the heat exchanger, which can be used with a camera to observe the water inlet of the heat exchanger and record the water level data inside the heat exchanger.

[0025] Optionally, the heat exchanger is arranged horizontally, and the water inlet and / or water outlet of the heat exchanger are located at the top of the side wall of the heat exchanger. This arrangement can more realistically simulate the flow characteristics of steam in the heat exchanger and subsequent pipelines under accident conditions. The flow direction, velocity distribution, and interaction of steam with condensed water in the horizontal heat exchanger are closer to the actual situation during a nuclear power plant accident. In addition, because the water inlet of the heat exchanger is at the top, there is a situation where steam accumulates in the inlet pipeline under accident conditions. In this case, two-phase water hammer may occur at the inlet after the cold water is injected, so the inlet U-shaped pipe is also designed as part of the experimental section. Because the water outlet of the heat exchanger is at the top, there is a situation where steam accumulates in the outlet pipeline under accident conditions. At this time, if the downstream valve is opened, a slug flow may hit the pipeline and cause water hammer, so the outlet U-shaped pipe is also designed as part of the experimental section.

[0026] Optionally, the heat exchanger includes a plurality of baffles. The baffles at both ends near the water inlet and outlet are designed according to the prototype scale of the heat exchanger, while the baffles in the middle section away from the water inlet and outlet are simplified. Specifically, the number of baffles in the middle section of the heat exchanger is simplified to three. This ensures the accuracy of phenomena at key locations in the water inlet and outlet experiments, ensures the vertical flow of fluid within the heat exchanger, and reduces experimental costs.

[0027] Since the cold end of the heat exchanger in this experimental device is in an isolated state, the baffle has little effect on the experiment. However, considering that the flow state of the inlet and outlet water in a short period of time will have a certain impact on the occurrence of water hammer after the cold water is connected again, the baffles at the inlet and outlet water are designed according to the prototype proportions, and the middle section is only to make the fluid flow roughly similar to that of the heat exchanger prototype, so only three layers are chosen to replace it.

[0028] Optionally, diverter plates are provided at the water inlet and the water outlet in the heat exchanger, respectively, and the diverter plates are designed according to the prototype proportions of the heat exchanger. Designing the diverter plates according to the prototype proportions helps to ensure the consistency of the heat exchange efficiency in the experiment with that of the actual nuclear power plant heat exchanger. The size and position of the diverter plates will affect the residence time of the fluid in the heat exchanger, the degree of mixing, and the contact area with the heating or cooling medium. Diverter plates with the same proportions as the prototype can make the heat exchange process in the experiment follow physical laws similar to those in reality, and accurately simulate the changes in heat exchange efficiency under different operating conditions. This is crucial for studying the performance of nuclear power plant heat exchangers under normal operation and accident conditions, and provides a reliable basis for evaluating and optimizing the heat exchange efficiency of actual heat exchangers.

[0029] Optionally, the water supply unit has a water supply tank, the outlet of which is connected to the inlet experimental section via a water supply pipe, and the water supply pipe is provided with a water supply pump and a flow meter. The water supply unit simulates the cold water supply link in the actual operation of a nuclear power plant. The flow meter on the water supply pipe can monitor the cold water flow in real time, and the water supply pump can accurately adjust the flow according to experimental requirements. In a two-phase steam condensation water hammer experiment, different cold water flow rates will significantly affect the heat exchange process, steam generation, and subsequent water hammer phenomenon in the heat exchanger. By adjusting the power of the water supply pump and based on the real-time data fed back by the flow meter, researchers can accurately set the cold water flow rate, conduct in-depth analysis of the impact of flow changes on the steam condensation rate, steam pressure, and the frequency and intensity of water hammer, and provide key experimental data for the optimization of the steam system of nuclear power plants.

[0030] Optionally, the water supply unit also has a pressurized gas cylinder, and the outlet of the pressurized gas cylinder is connected to the water supply tank. The pressurized gas cylinder is connected to the water supply tank, and the pressure of the water supply system can be flexibly adjusted. Precise control of the water supply pressure helps to conduct in-depth research on the impact of pressure on the entire experimental process. A higher water supply pressure will cause cold water to enter the heat exchanger faster, changing the rate and mode of heat exchange, thereby affecting the amount, temperature and pressure of steam generated. By adjusting the pressure of the pressurized gas cylinder, researchers can quantify these effects, analyze the relationship between water supply pressure and steam temperature, and how changes in water supply pressure trigger changes in water hammer. This is crucial to understanding the mechanism of action of pressure factors in the steam system of nuclear power plants, and provides a theoretical basis for optimizing the design and operation of nuclear power plants.

[0031] The present invention also provides an experimental method for two-phase steam condensation water hammer, comprising the following steps:

[0032] Supply water to the heat exchanger through the water supply unit;

[0033] After a period of time, the first valve and the second valve are closed to stop supplying water to the heat exchanger, and the cold water in the heat exchanger is heated;

[0034] When the temperature and pressure in the heat exchanger reach the set values, cold water is injected into the heat exchanger again to cause two-phase steam condensation water hammer;

[0035] After the pressure stabilizes, the hot water in the inlet experimental section, heat exchanger and outlet experimental section is transported to the drain unit;

[0036] Adjust the temperature and pressure in the heat exchanger, the cold water temperature, pressure and flow rate of the water supply unit, repeat the above steps to conduct experiments and collect experimental data.

[0037] The technical solution of this invention accurately simulates the scenario of two-phase steam condensation water hammer that can trigger heat exchanger piping in nuclear power plants. Repeating the above steps for the experiment allowed researchers to replicate the water hammer phenomenon multiple times, thereby more comprehensively studying its characteristics. During each experiment, by adjusting parameters such as the temperature and pressure within the heat exchanger and the cold water temperature, pressure, and flow rate of the water supply unit, the changing patterns of water hammer under different conditions could be observed. Studying the effect of steam condensation rate at different temperatures and pressures on water hammer intensity and frequency provides rich data support for a deeper understanding of water hammer, helping nuclear power plants develop more effective water hammer prevention and response measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 Schematic diagram of the overall structure of an experimental device for two-phase steam condensation water hammer according to an embodiment of the present invention;

[0040] Figure 2 for Figure 1 Schematic diagram of the heat exchanger and its internal baffles and sensor distribution locations shown;

[0041] Figure 3 for Figure 2 Side view of the arrangement of heating rods in the heat exchanger;

[0042] Figure 4 It is the pressure fluctuation curve in the first U-shaped pipe of the inlet experimental section under a certain working condition.

[0043] Description of reference numerals:

[0044] 1. Water supply unit; 2. Inlet test section; 3. Heat exchanger; 4. Outlet test section; 5. Drain unit; 6. First U-shaped pipe; 7. First valve; 8. Second U-shaped pipe; 9. Second valve; 10. First electric valve; 11. Second electric valve; 12. Heating rod; 13. Water inlet; 14. Transparent window; 15. Water outlet; 16. Baffle; 17. Diverter plate; 18. Water supply tank; 19. Water supply pump; 20. Flow meter; 21. Pressurized gas cylinder; 22. Drain tank. DETAILED DESCRIPTION

[0045] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0046] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0047] In the description of the present invention, it should be noted that, unless otherwise specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections; and they may refer to direct connections or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0048] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0049] Since the interior of the heat exchanger 3 is the main location for steam generation, and cold water is also injected into the interior of the heat exchanger 3 after entering, it is generally believed that water hammer occurs inside the heat exchanger 3 and is not easily connected to upstream and downstream pipelines.

[0050] After fully considering the experimental background, it was found that the steam in heat exchanger 3 did accumulate in the pipeline. In this case, the two-phase water hammer fluctuations generated in the upstream and downstream pipelines are also worthy of analysis.

[0051] like Figure 1 As shown, a specific embodiment of the experimental device for two-phase steam condensation water hammer provided in this embodiment includes: a water supply unit 1, an inlet experimental section 2, a heat exchanger 3, an outlet experimental section 4, and a drain unit 5. The water supply unit 1 is used to provide cold water; the inlet experimental section 2 has a first U-shaped pipe 6, one end of which has a first valve 7, and the first U-shaped pipe 6 is connected to the water supply unit 1 through the first valve 7; the water inlet end of the heat exchanger 3 is connected to the other end of the first U-shaped pipe 6 of the inlet experimental section 2, and the heat exchanger 3 is provided with a temperature detection device and a pressure detection device; the outlet experimental section 4 has a second U-shaped pipe 8, one end of which is connected to the water outlet end of the heat exchanger 3 and the other end is provided with a second valve 9, and the first U-shaped pipe 6 and the second U-shaped pipe 8 are respectively provided with a temperature detection device and a pressure detection device; the drain unit 5 is connected to the second U-shaped pipe 8 of the outlet experimental section 4 through the second valve 9.

[0052] Specifically, in this example, the experimental section piping is made of high-pressure resistant 304 stainless steel, ensuring it can withstand the severe pressure and temperature fluctuations required by the experimental parameters. To reduce heat loss during steam transportation, the inlet experimental section 2, heat exchanger 3, and outlet experimental section 4 are all wrapped with insulation.

[0053] In an accident, steam may accumulate in the inlet and outlet pipes. When cold water is reinjected, two-phase water hammer is likely to occur first in the inlet pipe. Opening the valve downstream of heat exchanger 3 could also cause slug flow to strike the pipes, triggering water hammer.

[0054] In the experimental device for two-phase steam condensation water hammer provided in this embodiment, both the upstream inlet pipe and the downstream outlet pipe of the heat exchanger 3 are designed as part of the experimental section, which can more comprehensively study the water hammer phenomenon generated in the heat exchanger 3.

[0055] In other words, this embodiment designed the inlet and outlet pipes as part of the experimental section, more closely resembling actual accident conditions in nuclear power plants. Nuclear power plant piping systems are complex, and when an accident occurs, water hammer is often not limited to heat exchanger 3 but also spreads and develops in connected pipes. The design of this experimental setup can realistically reproduce this complex physical process, making the experimental results more credible and convincing, and providing a more reliable reference for the actual operation of nuclear power plants.

[0056] Specifically, this embodiment uses the first U-shaped pipe 6 upstream of the heat exchanger 3 as part of the inlet experimental section 2, effectively simulating the scenario of water hammer caused by the re-injection of cold water after steam accumulates in the inlet pipe during an accident. In actual nuclear power plant operation, when a system anomaly occurs, steam may accumulate in the inlet pipe. Subsequent cold water injection causes rapid contact between the cold water and the high-temperature steam, leading to condensation and a sudden localized pressure change, which in turn triggers water hammer. This experimental setup accurately replicates this process, enabling in-depth research into the mechanisms, influencing factors, and propagation characteristics of water hammer within the inlet pipe.

[0057] Incorporating the second U-shaped pipe 8 downstream of the heat exchanger 3 into the outlet experimental section 4 simulates the water hammer caused by a slug flow impacting the pipe after the valve is opened. In a nuclear power plant steam system, when a valve is opened, the steam-water mixture in the pipe may flow in the form of a slug flow. The slug flow impacts the pipe wall or other components, causing water hammer. This design of the experimental device can simulate the process of slug flow-induced water hammer under different conditions (such as different steam-water ratios and valve opening speeds), study the intensity and frequency of water hammer, and its impact on the piping system. This provides an experimental basis for optimizing pipeline layout and valve control strategies in nuclear power plants, thereby reducing the damage caused by water hammer to the system.

[0058] Because real-time changes in temperature and pressure are closely linked to water hammer, once water hammer occurs, the pressure in the pipe increases dramatically in an instant. This pressure change, coupled with the conversion of fluid mechanical energy, can also cause temperature changes. By capturing these sudden changes in pressure and temperature using detection equipment, researchers can gain insight into the mechanisms that cause water hammer.

[0059] Therefore, in this embodiment, in the first U-shaped pipe 6 of the inlet experimental section 2, a temperature detection device can monitor the temperature changes of the cold water before it enters the heat exchanger 3, and a pressure detection device can reflect the pressure of the cold water during its flow. In the second U-shaped pipe 8 of the outlet experimental section 4, these detection devices can monitor the temperature and pressure dynamics of the steam or steam-water mixture in real time during its flow. For example, the temperature drop and pressure fluctuations that occur during the condensation process of steam can be detected, providing key data support for studying steam condensation characteristics and water hammer.

[0060] By installing temperature and pressure detection devices on the first U-shaped pipe 6, the second U-shaped pipe 8, and the heat exchanger 3, it was possible to comprehensively monitor temperature and pressure changes at different locations during the experiment. During the experiment, data collected by the temperature and pressure detection devices, combined with simultaneous monitoring of water hammer within the heat exchanger 3 and the inlet and outlet pipes, enabled in-depth analysis of the water hammer generation process.

[0061] like Figure 1 As shown, in the experimental device for two-phase steam condensation water hammer provided in this embodiment, a first electric valve 10 is provided on the first U-shaped pipe 6 , and a second electric valve 11 is provided on the second U-shaped pipe 8 .

[0062] The first electric valve 10 on the first U-shaped pipe 6 precisely controls the flow of cold water into the water supply unit 1. By adjusting the valve opening, the rate at which cold water enters the heat exchanger 3 can be flexibly varied according to experimental requirements. In this implementation, the inlet experimental section 2 is part of the main experimental section. The inlet pipeline in this section is designed based on the actual inlet pipeline of a nuclear power plant. During the experiment, the right side of the first electric valve 10 carries the high-temperature, high-pressure water or steam within the heat exchanger 3, and the left side carries the upstream cold water. Because the valve of the heat exchanger 3 is not directly located at the inlet, but rather on a U-shaped bend some distance from the inlet, the point where the cold water and steam come into direct contact after the cold water end is de-isolated (after the valve is opened) is in the inlet experimental section 2. Therefore, temperature and pressure sensors are installed on the inlet pipeline to accurately record the pressure fluctuations caused by water hammer. The inlet experimental section 2 is equipped with an electric regulating valve to simulate the effects of different valve operation speeds and opening variations on two-phase water hammer in a power plant, providing a basis for mitigating two-phase water hammer in the heat exchanger 3.

[0063] The second electric valve 11 on the second U-shaped pipe 8 can not only control the flow of steam or steam-water mixture, but also fine-tune the outlet pressure. The outlet experimental section 4 is similar to the inlet experimental section 2. Since the actual outlet valve of the nuclear power plant heat exchanger 3 is also designed on a U-shaped elbow at a certain distance from the heat exchanger 3, if an accident occurs, the high-temperature and high-pressure water generated in the heat exchanger 3 may also come into contact with the downstream cold water after the downstream valve is opened, causing severe water hammer. Therefore, temperature and pressure sensors are also arranged on the outlet experimental section 4 to ensure that the water hammer fluctuations at the outlet can be collected. The outlet experimental section 4 is equipped with a second electric regulating valve to simulate the effects of different valve operation speeds and different opening changes on two-phase water hammer in the power plant, providing a basis for alleviating the two-phase water hammer of the heat exchanger 3. In the experiment, steam flows and condenses in the second U-shaped pipe 8. By changing the opening of the second electric valve 11, the steam circulation resistance can be changed, and the outlet pressure and flow rate can be adjusted. The condensation characteristics of steam under different pressure and flow conditions and the occurrence law of water hammer phenomenon are studied, which helps to deeply understand the role mechanism of steam pressure and flow in the steam system and provide experimental support for pressure and flow control in nuclear power plants.

[0064] The two electric control valves enable simulation of various complex nuclear power plant operating conditions. Cold water flow, steam pressure, and flow rate vary significantly during different operational phases of a nuclear power plant, such as startup, normal operation, and shutdown. Using electric control valves, the experimental setup can accurately simulate the fluid states under these diverse operating conditions. Researchers can observe and analyze the steam condensation process and the characteristics of water hammer under various conditions, providing comprehensive experimental data support for nuclear power plants to cope with diverse operating conditions and helping to optimize their operational strategies and procedures.

[0065] Proper adjustment of the electric control valve can avoid water hammer caused by sudden changes in flow or pressure. Specifically, by controlling the rate of change of flow and pressure, so that the fluid enters and flows out of the experimental section smoothly, the risk of water hammer can be effectively reduced, the safe operation of the experimental device can be guaranteed, and a safe environment can be created for the smooth progress of the experiment. In other words, during the start and stop phases of the experiment, the opening of the electric control valve should be slowly adjusted to avoid large instantaneous changes in the flow of cold water or steam, thereby preventing the occurrence of water hammer.

[0066] like Figure 2As shown, in the experimental apparatus for two-phase steam condensation water hammer provided in this embodiment, the heat exchanger 3 is equipped with three sets of temperature detection devices, all of which are multi-point temperature sensors. Each temperature sensor has three measuring points, which respectively detect the temperatures at the top, middle, and bottom locations within the heat exchanger 3. The three sets of temperature detection devices are sequentially arranged at different positions along the length of the heat exchanger 3 to record the temperature distribution within the heat exchanger 3. The heat exchanger 3 is also equipped with three pressure detection devices to monitor pressure fluctuations within the heat exchanger 3. The redundant design ensures the accuracy of the experimental measurement data.

[0067] like Figure 2 、 Figure 3 As shown, in the experimental setup for two-phase steam condensation water hammer provided in this embodiment, variable-power heating rods 12 are installed within the heat exchanger 3. Variable-power heating rods 12 replace the tube-side hot water in the original heat exchanger 3. By varying the power of heating rods 12, different load tests on the heat exchanger 3 can be performed. This setup overcomes the difficulties encountered in heating the heat exchanger 3 by using hot water supplied by the heating rods and the difficulty in controlling the actual heat exchange power. By replacing the heat exchange tubes in the prototype heat exchanger 3 with variable-power heating rods 12, the heat exchange power of the heat exchanger 3 can be varied by varying the power of the heating rods 12, enabling simple testing of the heat exchanger 3 under different loads. Specifically, three layers of heating rods 12 are used, with two in the upper layer, three in the middle layer, and two in the lower layer, to replace the approximately 1,000 heat exchange tubes in the heat exchanger 3. This reduces the number of heating rods 12 while ensuring that, when the heating rods 12 are operating, the temperature distribution within the experimental section is similar to that within the power plant heat exchanger 3. Optionally, the three-layer heating rod 12 can be inserted from the outlet side of the heat exchanger 3 and fixed in the middle by partitions, deflectors 16, etc.

[0068] like Figure 2 As shown, in the experimental apparatus for two-phase steam condensation water hammer provided in this embodiment, a transparent window 14 is provided on the side of the water inlet of the heat exchanger 3. Specifically, the transparent window 14 can be made of pressure-bearing glass. When used with a camera, the water inlet of the heat exchanger 3 can be observed and the water level data inside the heat exchanger 3 can be recorded.

[0069] like Figure 1 、 Figure 2As shown, in the experimental setup for two-phase steam condensation water hammer provided in this embodiment, the heat exchanger 3 is arranged horizontally, with the water inlet 13 and / or water outlet 15 of the heat exchanger 3 located at the top of the sidewall of the heat exchanger 3. This arrangement more realistically simulates the flow characteristics of steam in the heat exchanger 3 and subsequent pipelines under accident conditions. The steam flow direction, velocity distribution, and interaction with condensed water within the horizontal heat exchanger 3 are more consistent with actual conditions during nuclear power plant accidents. Furthermore, because the water inlet 13 of the heat exchanger 3 is located at the top, steam may accumulate in the inlet pipeline during an accident. In this case, two-phase water hammer may initially occur at the inlet after cold water injection. Therefore, the inlet U-shaped pipe is also designed as part of the experimental section. Because the water outlet 15 of the heat exchanger 3 is located at the top, steam may accumulate in the outlet pipeline during an accident. In this case, if the downstream valve is opened, slug flow may impact the pipeline, causing water hammer. Therefore, the outlet U-shaped pipe is also designed as part of the experimental section.

[0070] like Figure 2 As shown, in the experimental apparatus for two-phase steam condensation water hammer provided in this embodiment, the heat exchanger 3 is provided with a plurality of baffles 16. The baffles 16 at both ends near the water inlet 13 and the water outlet 15 are designed according to the prototype proportions of the heat exchanger 3, while the baffles 16 in the middle section away from the water inlet 13 and the water outlet 15 are simplified. Specifically, the middle section of the baffles 16 in the heat exchanger 3 is simplified to three, which not only ensures the accuracy of the phenomena at the key experimental locations of the water inlet and outlet 15, but also achieves the vertical flow of the fluid within the heat exchanger 3, while reducing experimental costs.

[0071] Since the cold end of the heat exchanger 3 in this experimental device is in an isolated state, the baffle 16 has little effect on the experiment. However, considering that the flow state of the water inlet and outlet 15 in a short period of time after the cold water is connected again has a certain impact on the occurrence of water hammer, the baffle 16 of the water inlet and outlet 15 is designed according to the prototype proportions, and the middle section is only to make the fluid flow roughly similar to that of the heat exchanger 3 prototype, so only three layers are chosen to replace it.

[0072] like Figure 2As shown, in the experimental device for two-phase steam condensation water hammer provided in this embodiment, diverter plates 17 are respectively provided at the water inlet 13 and the water outlet 15 in the heat exchanger 3, and the diverter plates 17 are designed according to the prototype proportion of the heat exchanger 3. Designing the diverter plates 17 according to the prototype proportion helps to ensure the consistency of the heat exchange efficiency in the experiment with the actual nuclear power plant heat exchanger 3. The size and position of the diverter plates 17 will affect the residence time, mixing degree and contact area of ​​the fluid in the heat exchanger 3 and the heating or cooling medium. The diverter plates 17 with the same proportion as the prototype can make the heat exchange process in the experiment follow physical laws similar to those in reality, and accurately simulate the changes in heat exchange efficiency under different working conditions. This is crucial for studying the performance of nuclear power plant heat exchangers 3 under normal operation and accident conditions, and provides a reliable basis for evaluating and optimizing the heat exchange efficiency of the actual heat exchanger 3.

[0073] like Figure 1 As shown, in the experimental setup for two-phase steam condensation water hammer provided in this embodiment, the water supply unit 1 includes a water supply tank 18. The outlet of the water supply tank 18 is connected to the inlet experimental section 2 via a water supply pipeline. The water supply pipeline is equipped with a water supply pump 19 and a flow meter 20. The water supply unit 1 simulates the cold water supply process in actual nuclear power plant operation. The flow meter 20 on the water supply pipeline monitors the cold water flow in real time, and the water supply pump 19 precisely adjusts the flow rate based on experimental requirements. In two-phase steam condensation water hammer experiments, different cold water flow rates significantly affect the heat exchange process, steam generation, and subsequent water hammer phenomena within the heat exchanger 3. Researchers can precisely set the cold water flow rate by adjusting the power of the water supply pump 19 based on real-time data feedback from the flow meter 20. This allows for in-depth analysis of the impact of flow rate changes on steam condensation rate, steam pressure, and the frequency and intensity of water hammer, providing key experimental data for optimizing nuclear power plant steam systems.

[0074] like Figure 1As shown, in the experimental setup for two-phase steam condensation water hammer provided in this embodiment, the water supply unit 1 also includes a pressurized gas cylinder 21, the outlet of which is connected to the water supply tank 18. Therefore, the water supply tank 18 is a pressure-bearing device. To ensure experimental safety, a safety valve is installed on the top of the water supply tank 18 to prevent overpressure. Furthermore, to control the water temperature inside the tank, the water supply tank 18 is equipped with a heater 12 and a PID (proportional-integral-differential) temperature control device to maintain the tank temperature within a certain range. Temperature and pressure sensors are also installed on the tank to monitor the tank temperature and pressure in real time. The pressurized gas cylinder 21 is connected to the water supply tank 18, allowing for flexible adjustment of the water supply system pressure. Precise control of the water supply pressure facilitates in-depth study of the impact of pressure on the entire experimental process. Higher water supply pressure causes cold water to enter the heat exchanger 3 more quickly, changing the rate and pattern of heat exchange, and thus affecting the amount, temperature, and pressure of steam generated. By adjusting the pressure in pressurized gas cylinder 21, researchers can quantify these effects, analyze the relationship between water supply pressure and steam temperature, and how changes in water supply pressure trigger changes in water hammer. This is crucial for understanding the mechanism of pressure factors in nuclear power plant steam systems and provides a theoretical basis for optimizing nuclear power plant design and operation.

[0075] It should be noted that, in this embodiment, for the accuracy of the experimental data, the performance of the pressure sensors all adopts high frequency to ensure that the pressure fluctuations generated by the water hammer can be fully captured.

[0076] like Figure 1 As shown, in the experimental apparatus for two-phase steam condensation water hammer provided in this embodiment, the drain unit 5 includes a drain tank 22. During the experiment, a large amount of cold water is stored in the drain tank 22 to condense the high-temperature, high-pressure water discharged from the heat exchanger 3 and to alleviate pressure fluctuations generated in the upstream experimental section. To ensure the condensation effect, the water level in the drain tank 22 must be sufficiently high, and the outlet 15 of the drain line is inserted below the internal water level of the drain tank 22. This prevents the high-temperature, high-pressure water from evaporating into the atmospheric pressure environment and generating a large amount of steam.

[0077] This embodiment also provides an experimental method for two-phase steam condensation water hammer, comprising the following steps:

[0078] Water is supplied to the heat exchanger 3 through the water supply unit 1;

[0079] After a period of time, the first valve 7 and the second valve 9 are closed to stop the water supply to the heat exchanger 3 and heat the cold water in the heat exchanger 3;

[0080] When the temperature and pressure in the heat exchanger 3 reach the set values, cold water is injected into the heat exchanger 3 again to cause two-phase steam condensation water hammer;

[0081] After the pressure stabilizes, the hot water in the inlet experimental section 2, the heat exchanger 3 and the outlet experimental section 4 is transported to the drain unit 5;

[0082] The temperature and pressure in the heat exchanger 3 and the cold water temperature, pressure and flow rate of the water supply unit 1 were adjusted, and the above steps were repeated to conduct experiments and collect experimental data.

[0083] It should be noted that in the above steps, when all upstream and downstream valves of the heat exchanger 3 are closed, the following two situations and corresponding operation methods will occur:

[0084] First, if the water level in heat exchanger 3 is high: First, open the downstream valve to relieve pressure. This prevents excessive pressure in the test section from preventing cold water from being injected. Once the pressure in the test section decreases, open the upstream valve to begin injecting cold water. Once the test section is filled with water again and the temperature has dropped, the water hammer event is considered alleviated.

[0085] Second, the situation where the water level in the heat exchanger 3 is low and the heating rod 12 is exposed and dry-burning: In this case, it is necessary to first open the upstream valve with a small opening. This is because if the downstream valve is opened directly to release the pressure, the high-temperature and high-pressure steam will encounter the residual water in the downstream pipeline, which is very likely to produce a slug flow, thereby causing pipeline vibration. In addition, there is also steam in the upstream U-shaped pipeline. If the valve is opened with a large opening at the beginning, it is easy to cause obvious water hammer in the pipeline. Therefore, first open the upstream valve with a small opening, and after the inlet pipeline of the experimental section is filled with water, adjust the valve opening to a large extent and inject cold water into the heat exchanger 3. During this process, pay close attention to the pressure situation in the heat exchanger 3. When the upstream cold water can no longer be injected, open the downstream valve to circulate the cold water in the heat exchanger 3. In this way, water can be quickly injected into the heat exchanger 3 to achieve cooling of the heat exchanger 3.

[0086] In the above steps, when the upstream valve of the heat exchanger 3 is closed and the downstream valve is connected, the following two situations exist:

[0087] First, if the water level in the heat exchanger 3 is high, water can be injected with a small opening. After the water level in the heat exchanger 3 rises, the normal flow rate can be restored to achieve cooling in the heat exchanger 3.

[0088] Second, if the water level in heat exchanger 3 is low and heater rod 12 is exposed, injecting water through a small opening may cause a small amount of cold water to contact the outer surface of heater rod 12, causing flash evaporation, followed by collapse and pressure fluctuation. Therefore, in this case, water should be injected through a small opening first. Once the first U-shaped tube is filled with water, the valve should be opened wide to quickly cool the heat exchanger 3.

[0089] In the above steps, when the downstream valve of heat exchanger 3 is closed and the upstream valve is open, the interior of heat exchanger 3 will always be full of water. In this case, if the heating time is too long, the hot water in heat exchanger 3 will naturally circulate heat with the upstream cold water. In this case, you only need to open the downstream valve to restore normal forced circulation of cold water.

[0090] In the above steps, when injecting cold water again, the valve is first opened slightly or the water supply pump 19 is adjusted to inject water at a small flow rate, and then returns to normal after a period of time, which can effectively alleviate the occurrence of two-phase water hammer.

[0091] The technical solution in this embodiment accurately simulates the scenario of two-phase steam condensation water hammer that could potentially trigger heat exchanger 3 piping in a nuclear power plant. Repeating the above steps allows researchers to replicate the water hammer phenomenon multiple times, enabling a more comprehensive study of its characteristics. During each experiment, by adjusting parameters such as the temperature and pressure within heat exchanger 3 and the cold water temperature, pressure, and flow rate of water supply unit 1, the variations in the water hammer phenomenon under different conditions can be observed. Studying the effect of steam condensation rates at different temperatures and pressures on water hammer intensity and frequency provides rich data support for a deeper understanding of the water hammer phenomenon, helping nuclear power plants develop more effective water hammer prevention and response measures.

[0092] like Figure 4 Figure 2 shows the pressure fluctuations at the inlet U-shaped tube under certain operating conditions in the experimental setup of this embodiment. Analysis of the pressure fluctuations in the figure reveals that, after the injection of cold water at the start of the experiment, significant pressure fluctuations occur at the inlet within a short period of time, with a large amplitude. This indicates that certain pressure fluctuations do occur within the upstream and downstream U-shaped tubes, and under certain conditions, the pressure fluctuations within the U-shaped tube are even greater. This confirms that two-phase water hammer is prone to occur in the U-shaped tube, and the addition of the U-shaped tube provides a more comprehensive understanding of the water hammer phenomenon occurring within heat exchanger 3.

[0093] After completing the above experiments, the obtained experimental data need to be sorted out and single variable analysis needs to be carried out on these data.

[0094] First, we will summarize the influence of the first category of parameters on water hammer. These parameters include the cold water temperature, the high-temperature water temperature inside heat exchanger 3, the internal pressure of heat exchanger 3, and the water level. Under accident conditions, water hammer cannot be alleviated or avoided by directly adjusting these factors. Therefore, it is necessary to use mechanistic analysis to clarify how these influencing factors affect water hammer. Then, based on the patterns of water hammer changes with these factors, we can determine the parameters of heat exchanger 3 that can best avoid water hammer or minimize the vibration level when water hammer occurs. This can provide guidance to power plants, allowing them to maintain the operating parameters of heat exchanger 3 within this range as much as possible to prevent serious water hammer accidents.

[0095] Next, we will study the mechanisms by which other factors, such as water supply volume, valve operation sequences, and valve actuation speed, influence water hammer. This will help clarify how to avoid water hammer during an emergency. These factors are closely related to the actions taken by personnel during actual power plant operation. By thoroughly studying their specific mechanisms and understanding the impact of different operating procedures on two-phase water hammer, we can address these issues within appropriate regulations and systems, effectively mitigating or preventing water hammer in power plant heat exchangers.

[0096] In order to explore effective measures to alleviate water hammer, the specific operations are as follows:

[0097] First, experimental research focused on factors related to human operation under actual nuclear power plant accident conditions. These factors, including water supply, valve opening and closing sequence, and valve actuation speed, are closely related to power plant operators' actions and directly linked to the two-phase water hammer phenomenon, providing precise and effective guidance for mitigating or preventing water hammer.

[0098] Secondly, a sensitivity analysis was conducted on other parameters, such as physical properties and the operating conditions of heat exchanger 3. This analysis clarified the severity of two-phase water hammer under different parameter conditions. This allowed us to avoid extreme operating conditions of heat exchanger 3 as much as possible during actual nuclear power plant operation, thereby reducing the possibility of water hammer.

[0099] Specifically, the first step considered the scenario of isolating all upstream and downstream valves. Based on different influencing factors, three different valve operation methods were implemented: opening only the upstream valve; opening only the downstream valve; and opening both upstream and downstream valves simultaneously. During this process, combined with the internal parameters of heat exchanger 3 and the changes in valve actuation speed, water hammer pressure fluctuation data under these conditions was obtained. The underlying mechanism of pressure fluctuation as a function of these parameters was then analyzed. Subsequently, the safest valve operation method was selected from these three valve operation sequences and determined as the optimal option in the event of an accident.

[0100] The second step involved conducting experiments with only the upstream valve closed, varying upstream valve opening speeds and three heat exchanger parameters. The results revealed the dynamics of water hammer pressure fluctuations under these conditions. By analyzing the experimental data, the optimal valve action was determined for these conditions.

[0101] In the third step, when the downstream valve is closed, experiments are conducted with varying downstream valve opening speeds and heat exchanger parameters to determine how the water hammer pressure fluctuations change under these conditions. Similarly, the optimal valve action under these conditions is determined from data analysis.

[0102] Through these three different types of experiments, we can obtain data on water hammer fluctuations caused by corresponding operations under corresponding conditions. This data not only helps to deeply analyze the mechanism of water hammer, but also provides important guidance for power plant operators, helping them to determine how to minimize the occurrence of water hammer.

[0103] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations shall all fall within the scope defined by the present invention.

Claims

1. An experimental device for two-phase steam condensation water hammer, characterized in that: include: A water supply unit (1) for providing cold water; an inlet experimental section (2), comprising a first U-shaped pipe (6), one end of which is provided with a first valve (7), and the first U-shaped pipe (6) is connected to the water supply unit (1) via the first valve (7); A heat exchanger (3), the water inlet end of which is connected to the other end of the first U-shaped pipe (6) of the inlet experimental section (2), and the heat exchanger (3) is provided with a temperature detection device and a pressure detection device; The outlet experimental section (4) has a second U-shaped pipe (8), one end of the second U-shaped pipe (8) is connected to the water outlet end of the heat exchanger (3), and the other end is provided with a second valve (9), and the first U-shaped pipe (6) and the second U-shaped pipe (8) are respectively provided with a temperature detection device and a pressure detection device; The hydrophobic unit (5) is connected to the second U-shaped pipe (8) of the outlet experimental section (4) via the second valve (9).

2. The experimental device for two-phase steam condensation water hammer according to claim 1, characterized in that: The first U-shaped pipe (6) is provided with a first electric valve (10), and the second U-shaped pipe (8) is provided with a second electric valve (11).

3. The experimental device for two-phase steam condensation water hammer according to claim 1, characterized in that: A heating rod (12) with variable power is provided in the heat exchanger (3).

4. The experimental device for two-phase steam condensation water hammer according to claim 1, characterized in that: The side of the water inlet end of the heat exchanger (3) is provided with a transparent window (14).

5. The experimental device for two-phase steam condensation water hammer according to claim 1, characterized in that: The heat exchanger (3) is arranged horizontally, and the water inlet (13) and / or the water outlet (15) of the heat exchanger (3) are located at the top of the side wall of the heat exchanger (3).

6. The experimental device for two-phase steam condensation water hammer according to claim 5, characterized in that: The heat exchanger (3) has a plurality of baffles (16) therein. The baffles (16) are designed according to the prototype proportions of the heat exchanger (3) at both ends close to the water inlet (13) and the water outlet (15), and are simplified in the middle section away from the water inlet (13) and the water outlet (15).

7. The experimental device for two-phase steam condensation water hammer according to claim 6, characterized in that: The heat exchanger (3) is provided with a diverter plate (17) at the water inlet (13) and the water outlet (15), respectively. The diverter plate (17) is designed according to the prototype proportion of the heat exchanger (3).

8. The experimental device for two-phase steam condensation water hammer according to any one of claims 1 to 7, characterized in that: The water supply unit (1) has a water supply tank (18), the outlet of the water supply tank (18) is connected to the inlet experimental section (2) through a water supply pipe, and the water supply pipe is provided with a water supply pump (19) and a flow meter (20).

9. The experimental device for two-phase steam condensation water hammer according to claim 8, characterized in that: The water supply unit (1) further comprises a pressurized gas cylinder (21), the outlet of which is connected to the water supply tank (18).

10. An experimental method for two-phase steam condensation water hammer, characterized in that: The following steps are involved: supplying water to the heat exchanger (3) through the water supply unit (1); After a period of time, the first valve (7) and the second valve (9) are closed to stop the water supply to the heat exchanger (3), and the cold water in the heat exchanger (3) is heated; When the temperature and pressure in the heat exchanger (3) reach set values, cold water is injected into the heat exchanger (3) again to cause two-phase steam condensation water hammer; After the pressure is stabilized, the hot water in the inlet experimental section (2), the heat exchanger (3) and the outlet experimental section (4) is transported to the drain unit (5); The temperature and pressure in the heat exchanger (3), the cold water temperature, pressure and flow rate of the water supply unit (1) are adjusted, and the above steps are repeated to conduct experiments and collect experimental data.

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