Two-phase steam condensation water hammer experiment device, scaling design method and experiment method

Abstract

The invention discloses a two-phase steam condensation water hammer experiment device, a scaling design method and an experiment method, and relates to the technical field of nuclear power, and the experiment device comprises a steam supply unit which is used for providing steam for an experiment; a steam flow channel is arranged in the experiment section, an inlet of the steam flow channel is connected with the steam supply unit through a steam pipeline, and an electric quick-closing valve is arranged on the steam pipeline; the bottom of the experiment section is provided with a cooling water flow channel, and the cooling water flow channel and the steam flow channel are arranged at an interval; an outlet of the condensate water supply unit is communicated with the steam flow channel of the experiment section, and the condensate water supply unit is used for providing condensate water for the experiment; and the discharge unit is communicated with an outlet of the steam flow channel of the experiment section through a discharge pipeline, and an atmosphere discharge valve and a first pressure reducing valve are arranged on the discharge pipeline. The experimental device can simulate real working conditions and research the two-phase steam condensation water hammer phenomenon caused by the fact that steam makes contact with condensed water accumulated at the bottom of a pipeline in the flowing process.

Description

Technical Field

[0001] This invention relates to the field of nuclear power technology, specifically to a two-phase steam condensate water hammer experimental device, a scaled-down design method, and an experimental method. Background Technology

[0002] Two-phase steam condensate hammer in nuclear power plant pipelines is a phenomenon that can occur in the steam system of a nuclear power plant. In a nuclear power plant, when steam comes into direct contact with subcooled water, the steam condenses rapidly due to the significant temperature and density differences between the vapor and liquid. During this process, the steam is trapped within the subcooled water, forming independent vapor bubbles. The rapid condensation of these bubbles creates a negative pressure or vacuum in the area they occupy. Under the combined effects of pressure difference and condensation, the subcooled water is instantly accelerated towards this negative pressure zone, causing a huge pressure fluctuation and forming a condensate hammer.

[0003] In the existing technology, most CIWH (Condensation Induced Water Hammer) experiments focus on the CIWH phenomenon that occurs when steam and subcooled water come into direct contact. There are very few studies on the CIWH phenomenon caused by changes in fluid flow pattern when steam comes into contact with condensate accumulated at the bottom of the pipe during the flow process.

[0004] However, in actual production, a small amount of condensate may exist at the bottom of the steam pipes in the secondary loop main steam system of a nuclear power plant due to the failure of the steam trap or other reasons. When the opening of the atmospheric vent valve in the steam pipe changes, the steam flow rate in the pipe changes rapidly, further accelerating the flow of fluid in the pipe, thereby triggering the two-phase steam condensate hammer (CIWH) phenomenon. Summary of the Invention

[0005] In view of this, the present invention provides a two-phase steam condensation water hammer experimental device, a scaled-down design method, and an experimental method to solve the problem that existing two-phase steam condensation water hammer experimental devices lack research on the two-phase steam condensation water hammer phenomenon caused by steam contacting condensate accumulated at the bottom of the pipe during the flow process.

[0006] The two-phase steam condensate water hammer experimental apparatus provided by this invention includes:

[0007] Steam supply unit, used to provide steam for experiments;

[0008] The experimental section has a steam flow channel inside, and the inlet of the steam flow channel is connected to the steam supply unit through a steam pipe. The steam pipe is equipped with an electric quick-closing valve. The bottom of the experimental section has a cooling water flow channel, which is spaced apart from the steam flow channel.

[0009] A condensate supply unit is provided, with its outlet connected to the steam flow channel of the experimental section. The condensate supply unit is used to provide condensate for the experiment.

[0010] The emission unit is connected to the outlet of the steam flow channel of the experimental section through an emission pipe, which is equipped with an atmospheric emission valve and a first pressure reducing valve.

[0011] The technical solution of this invention can simulate real working conditions and study the two-phase steam condensation water hammer phenomenon caused by steam coming into contact with condensate accumulated at the bottom of the pipe during the flow process.

[0012] Specifically, the steam supply unit provides experimental steam, ensuring a stable supply of steam with specific parameters to the steam channels within the experimental section, thereby accurately simulating the steam conditions within pipelines during actual nuclear power plant operation. A cooling water channel, spaced from the steam channels, is located at the bottom of the experimental section. The cooling water flowing within this channel controls the temperature of the condensate at the bottom of the experimental section. The experimental setup provided in this embodiment focuses on studying the impact of changes in two key parameters—condensate volume and condensate bottom temperature—on the two-phase steam condensation hammer phenomenon. The discharge unit is connected to the outlet of the experimental section's steam channels. The pressure difference between the experimental section and the downstream discharge unit accelerates fluid flow within the experimental section, further triggering the two-phase steam condensation hammer phenomenon.

[0013] Optionally, the system further includes a reducing device having a small opening and a large opening. The small opening is connected to the steam pipe, and the large opening is connected to the inlet of the steam channel in the experimental section. The bottom of the small opening is higher than the bottom of the large opening. In this design, the small opening being higher than the large opening effectively prevents condensate in the experimental section from flowing back into the steam pipe. During the experiment, the condensate in the steam channel of the experimental section will naturally flow downwards. The inclined structure of the reducing device makes it easier for the condensate to flow into the experimental section without flowing back into the steam pipe, ensuring the purity and normal delivery of steam in the steam pipe and maintaining the stability and accuracy of the experiment. Furthermore, through the above design, when steam flows from the small opening to the large opening, the steam velocity decreases and the pressure increases due to the increased cross-sectional area of ​​the channel. During diffusion at the large opening, the steam can more comprehensively cover the inlet cross-section of the steam channel in the experimental section, preventing steam from concentrating in a certain area and ensuring the uniformity of steam flow within the experimental section.

[0014] Optionally, the top of the small end of the variable diameter device is flush with the top of the large end, or the top of the small end is higher than the top of the large end.

[0015] In the above scheme, when the tip of the small end of the reducing device is flush with the tip of the large end, the steam can flow into the experimental section relatively evenly after passing through the reducing device. However, when the tip of the small end is higher than the tip of the large end, the downward flow of steam will be enhanced, resulting in a relatively high steam concentration at the bottom of the experimental section inlet.

[0016] Both the flush-top design and the higher top of the smaller end further enhance the ability to prevent condensate from flowing back into the steam pipe. This is because the reducing device is tilted overall, and the scientifically designed top height makes it easier for condensate to flow into the experimental section under the influence of gravity. Especially when the top of the smaller end is higher than the top of the larger end, the difficulty of condensate flowing back into the steam pipe increases significantly, effectively preventing condensate from adversely affecting the steam pipe and steam supply unit. This not only ensures the stable operation of the steam supply system but also maintains the stability of steam parameters during the experiment, thereby improving the reliability of the experimental data.

[0017] Optionally, the experimental section is externally encased in a sleeve, forming a cooling water channel between the sleeve and the outer wall of the experimental section. With this configuration, the cold water in the cooling water channel can create a significant temperature difference with the steam in the steam channel of the experimental section, facilitating heat exchange through the pipe wall of the experimental section. By adjusting parameters such as the flow rate and temperature of the cooling water in the cooling water channel, a large temperature gradient can be maintained in the condensate, facilitating the study of the influence of different condensate temperatures on water hammer phenomena.

[0018] Optionally, the experimental section is a horizontally positioned cylindrical shape, with the sleeve enclosing the lower semi-circular region of the experimental section. In this design, the sleeve enclosing the lower semi-circular region results in a larger contact area between the cooling water channel and the experimental section at the bottom, enhancing the heat exchange efficiency in this area. Since condensate accumulates at the bottom due to gravity when steam flows in the horizontal pipe, this cooling water channel effectively cools the condensate. This helps in studying the effect of condensate on water hammer at different temperatures.

[0019] Optionally, the sleeve covers the lower half-arc region of the experimental section at an angle of 120°±10°. In the above scheme, the sleeve covers the lower half-arc region of the experimental section at an angle of 120°±10°. This specific angle design achieves precise control over the heat exchange area and intensity. At this angle, the contact area between the cooling water channel and the experimental section is moderate, enabling effective heat exchange with the condensate within the experimental section.

[0020] Optionally, the discharge pipe is inclined and connected to the upper semi-circular region of the experimental section. This design accurately simulates the steam emission process during actual operation of a nuclear power plant, providing reliable experimental conditions for studying the impact of steam emissions on condensate hammer. Furthermore, because the experimental section is horizontally positioned and has a cooling water channel at the bottom, condensate mainly forms and accumulates in the lower half of the experimental section. The inclined discharge pipe prevents condensate from directly entering the discharge pipe, thus achieving effective separation of steam and condensate within the experimental section.

[0021] Optionally, the system further includes a condensate draining unit connected to the steam channel of the experimental section, used to drain condensate from the steam channel. The addition of the condensate draining unit can simulate the condition of condensate continuously accumulating in the steam pipeline of a nuclear power plant due to a condensate draining pipeline malfunction. Furthermore, the condensate draining unit can also be used to drain any remaining liquid from the steam channel after the experiment, for use in the next experiment.

[0022] Optionally, it further includes: a cooling water supply unit and a cooling water return unit, wherein the cooling water supply unit is connected to the inlet of the cooling water channel, and the cooling water return unit is connected to the outlet of the cooling water channel;

[0023] The cooling water supply unit includes a temperature detection device, a flow detection device, and a regulating valve;

[0024] The cooling water return unit has a regulating valve and a temperature detection device.

[0025] In the above scheme, both the cooling water supply unit and the cooling water return unit are equipped with temperature detection devices, which can monitor the cooling water temperature in real time. In the cooling water supply unit, the information fed back by the temperature detection device allows for precise control of the cooling water temperature entering the cooling water channel using a regulating valve. The cooling water return unit is equipped with a temperature detection device to monitor the temperature of the cooling water flowing out of the cooling water channel, further understanding the heat exchange effect of the cooling process, providing a reference for adjusting the supply water temperature, and ensuring that the cooling process is stable and meets experimental requirements.

[0026] The flow detection device and regulating valve of the cooling water supply unit work together to achieve precise control of the cooling water flow rate. Specifically, the flow detection device monitors the flow data in real time, and adjusts the opening of the regulating valve according to experimental requirements to precisely control the cooling water flow rate entering the cooling water channel. Different steam condensation processes may require different cooling water flow velocities to simulate. Through precise flow control, the influence of cooling water flow velocity on steam condensation rate, condensation location, and water hammer phenomenon can be studied.

[0027] Optionally, temperature detection devices are also installed at the inlet and outlet of the cooling water channel. This setup allows for real-time and accurate acquisition of cooling water temperature data as it enters and exits the channel. By comparing the inlet and outlet temperatures, the heat exchange during the cooling water flow through the experimental section can be accurately calculated. Based on the inlet and outlet temperature data, the regulating valves of the cooling water supply and return units can be adjusted more precisely. If the temperature difference between the inlet and outlet of the cooling water channel is too large, it indicates that the cooling effect is too strong, potentially leading to over-cooling of the steam. In this case, the cooling water flow rate can be appropriately reduced or the supply temperature increased by adjusting the valves to achieve a more suitable cooling level. Conversely, if the temperature difference is too small, the opposite operation can be performed. This precise adjustment based on actual temperature feedback ensures that the cooling process remains in the ideal state required for the experiment, thereby improving the accuracy and reliability of the experimental results.

[0028] Optionally, multiple temperature detection devices are sequentially installed along the steam flow channel on the experimental section. These devices are multi-point thermocouples used to detect the temperature within the steam flow channel. Each multi-point thermocouple detects multiple areas at different heights within the same horizontal position within the steam flow channel. In this scheme, multiple temperature detection devices (multi-point thermocouples) are installed along the steam flow channel on the experimental section to accurately reflect the temperature stratification of the condensate within the experimental section. Since multi-point thermocouples can detect multiple areas at different heights within the same horizontal position, researchers can obtain detailed temperature distribution information within the steam flow channel. This data clearly shows the temperature changes of steam during its flow, from the steam inlet to the outlet, and at different heights within the same cross-section. This is significant for in-depth research on the heat transfer process of steam within the experimental section and the heat exchange effect between steam and cooling water flow channels, accurately capturing the spatial variation of steam temperature.

[0029] Optionally, the experimental section is also equipped with a pressure detection device for detecting the pressure within the steam flow channel. Combined with the existing multiple temperature detection devices on the experimental section, the pressure detection device allows for more comprehensive monitoring of the operating conditions within the steam flow channel. Pressure and temperature are two key parameters describing the state of steam. By simultaneously acquiring temperature and pressure data at different locations within the steam flow channel, researchers can more accurately grasp the thermodynamic state of the steam.

[0030] This invention also provides a scaled-down design method for a two-phase steam condensate water hammer experimental device. For a circular pipe, the dimensionless conversion standard between stratified flow and intermittent flow or annular dispersed flow states is:

[0031]

[0032] Where Fr is the vapor phase corrected Froude number:

[0033]

[0034] In the formula, ρG and ρL represent the gas phase fluid density and liquid phase fluid density, respectively (kg / m3); vG represents the gas phase fluid velocity (m / s); g represents the acceleration due to gravity (m / s2); D represents the pipe inner diameter (m); and θ represents the pipe inclination angle (°).

[0035] That is The function where H L The liquid level height (m) in the pipeline is given by equation (2-1). It can be seen that the flow pattern transformation model mainly reflects the similarity of the relative liquid level height and the vapor phase corrected Froude number.

[0036] π2=(Fr G ) R =1 (2-4)

[0037] Equations (2-3) and (2-4) are two sets of dimensionless transformation relationships for scaled-down design of two-phase water hammer in horizontal pipes, involving the similarity modeling of fluid flow patterns. In the above equations, the subscript R refers to the ratio between the experimental device and the prototype. Under the condition that the gravitational acceleration is equal and the pipes of both the prototype and the experimental device are horizontal, we can obtain from equations (2-2) and (2-4):

[0038]

[0039] The key to achieving similar flow pattern transitions within a pipeline lies in ensuring that the similarity between the relative height of the liquid phase fluid and the flow velocity of the gas phase fluid is maintained.

[0040] For the prototype steam pipe, its relative liquid level height is:

[0041]

[0042] To meet the requirements of equation (2-3), the height of the liquid fluid in the experimental section is controlled as follows:

[0043] H L，t =0.5×D t

[0044] The vapor phase fluid velocity within the experimental section, according to equation (2-5), is related to both the physical properties of the two-phase fluid and the experimental pipe diameter:

[0045]

[0046] Among them, v G，p The steam flow rate inside the prototype pipe;

[0047] Substituting the relevant values ​​into the calculation, the steam velocity v is obtained. G，t This invention's scaled-down design method, through a clearly defined dimensionless transformation standard, enables precise simulation of the similarity in flow patterns between the experimental setup and the prototype. For circular pipes, it ensures accurate reproduction of flow patterns such as stratified flow, intermittent flow, or annular dispersed flow within the prototype pipe in the scaled-down experimental setup. This is crucial for studying water hammer phenomena in two-phase steam condensation, as different flow patterns significantly affect the occurrence mechanism, intensity, and frequency of water hammer. Under stratified and intermittent flow conditions, the interaction between steam and condensate differs, leading to different manifestations of water hammer. By accurately simulating flow pattern similarity, researchers can more realistically observe and analyze the intrinsic relationship between water hammer phenomena and flow patterns in the experimental setup, providing a reliable theoretical basis for the design and operation of nuclear power plant steam piping systems.

[0048] Specifically, this scaled-down design method comprehensively considers multiple factors affecting flow pattern conversion, including gas phase fluid density, liquid phase fluid density, gas phase fluid velocity, pipe inner diameter, and pipe inclination angle. During the scaled-down design process, dimensionless transformation formulas are used to reasonably scale these factors between the prototype and experimental setup, ensuring that the experimental setup accurately reflects the physical characteristics of the prototype. This provides specific and operational guidance for the design of two-phase steam condensation water hammer experimental setups. Researchers only need to substitute relevant parameters of the prototype steam pipe (such as pipe inner diameter, fluid properties, and steam velocity) into the corresponding formulas to calculate the height of the liquid phase fluid and the velocity of the vapor phase fluid in the experimental section, thereby determining the key design parameters of the experimental setup. This greatly simplifies the design process of the experimental setup and reduces the risk of inaccurate experimental results due to unreasonable design. When designing the experimental setup, researchers do not need to conduct extensive trial-and-error experiments to determine suitable parameters; instead, they can directly calculate them using this method, improving design efficiency and the success rate of experiments. At the same time, clear design guidance also helps different research teams compare and verify experimental results, promoting the development of research in this field.

[0049] This invention also provides a method for conducting a two-phase steam condensate water hammer test, comprising the following steps:

[0050] First, a reference experiment was conducted in the first stage. Before the experiment began, a certain amount of condensate was injected into the experimental section.

[0051] The steam supply unit is started to generate high-pressure steam. The electric quick-closing valve, atmospheric exhaust valve and first pressure reducing valve are opened to allow steam to slowly enter the experimental section.

[0052] The study investigated the changes in liquid phase temperature and vapor phase pressure over time in the experimental section under conditions of external cooling and without external cooling. When there was no external cooling, after all air was exhausted, the electric quick-closing valve, atmospheric vent valve, and first pressure-reducing valve were closed, and the changes in liquid phase temperature and vapor phase pressure over time in the pipeline under these conditions were investigated. When external cooling was present, after all air was exhausted, the electric quick-closing valve, atmospheric vent valve, and pressure-reducing valve were closed, allowing cooling water to flow through the cooling water channel to cool the liquid in the lower layer of the experimental section. The changes in liquid phase temperature and vapor phase pressure over time in the pipeline under conditions of external cooling were investigated and recorded.

[0053] Then, the second phase of formal experiments was conducted; two major types of differential pressure driving experiments were designed according to the two types of differential pressure driving methods for comparative analysis.

[0054] The first type of pressure difference driven experiment: a pressure difference experiment between the test section and the upstream steam pipeline. This type of test is a mechanism experiment used to study the mechanism of two-phase steam condensation water hammer phenomenon and to compare and analyze it with the second type of power plant prototype reproduction experiment; specifically, it includes the following steps:

[0055] Cooling water is injected into the experimental section to a predetermined volume through the cooling water supply unit;

[0056] Start the steam supply unit to generate high-pressure steam, and set the saturated steam pressure value of the steam supply unit to be slightly larger than the steam pressure value of the experimental section in the formal experiment;

[0057] Open the electric quick-closing valve, atmospheric vent valve, and first pressure reducing valve to allow steam to slowly enter the experimental section; after all the air has been expelled, close the electric quick-closing valve, atmospheric vent valve, and first pressure reducing valve.

[0058] After readjusting the steam pressure of the steam supply unit to the predetermined parameters, turn on the cooling water to allow the cooling water to flow through the cooling water channel and cool the lower layer of liquid in the test section.

[0059] When the parameters of the gas and liquid in the experimental section reach the preset values, the electric quick-closing valve is quickly opened to start the experiment; within a very short time, a complex gas-liquid two-phase steam condensation water hammer phenomenon will occur in the experimental section.

[0060] The second type of differential pressure driven experiment: This involves a differential pressure experiment between the experimental section and the downstream atmospheric emission valve pipeline. This type of test operates under conditions similar to those of a power plant prototype, designed to replicate the actual operating conditions of the power plant. Specifically, it includes the following steps:

[0061] First, set the pressure value of the saturated steam in the steam supply unit to be equal to the steam pressure value of the experimental section in the formal experiment;

[0062] Open the electric quick-closing valve and the atmospheric discharge valve, and adjust the opening of the first pressure reducing valve to allow steam to slowly enter the experimental section;

[0063] Turn on the cooling water to allow it to flow through the cooling water channel and cool the lower layer of liquid in the test section.

[0064] After all the air in the test section has been expelled, close the atmospheric exhaust valve.

[0065] Once the flow pattern in the experimental section stabilizes, the opening of the atmospheric discharge valve is quickly adjusted to the predetermined value. Within a very short time, a complex gas-liquid two-phase steam condensation water hammer phenomenon will occur in the experimental section.

[0066] The experimental method of this invention comprehensively examines the changes in liquid phase temperature and vapor phase pressure over time within the experimental section by setting up two conditions in the first-stage reference experiment: one with external cooling and one without. This comparative analysis helps researchers gain a deeper understanding of the influence mechanism of external cooling on steam condensation and pressure changes. Specifically, without external cooling, the condensation and pressure evolution process of steam under natural conditions can be observed; while with external cooling, it is possible to explore how the cooling effect accelerates steam condensation and changes the pressure change trend, thus providing multi-dimensional data support for understanding the intrinsic mechanism of water hammer phenomenon in two-phase steam condensation.

[0067] The entire experimental method was divided into two phases: a reference experiment and a formal experiment. Multiple parameters were recorded at each phase. In the reference experiment, changes in liquid phase temperature and vapor phase pressure over time were recorded with and without external cooling. In the formal experiment, for two types of pressure difference-driven experiments, steam pressure, temperature, flow rate, changes in flow pattern within the experimental section, and various parameters related to the occurrence of steam condensation water hammer in the two-phase system were recorded. This multi-stage, multi-parameter data collection provides a rich data foundation for in-depth analysis of the two-phase steam condensation water hammer phenomenon. Researchers can comprehensively analyze the interrelationships between different parameters, establish more accurate physical models, and further understand the nature of steam condensation water hammer.

[0068] In the formal experiments, a Type I pressure differential-driven experiment was used to specifically investigate the mechanism of the pressure difference between the experimental section and the upstream steam pipeline. By setting the steam pressure in the steam supply unit to be slightly higher than the steam pressure in the experimental section, specific pressure differential conditions were simulated, allowing researchers to deeply analyze the occurrence mechanism of two-phase steam condensation water hammer. Comparative analysis with the Type II power plant prototype replication experiment clarified the relationship and differences between the mechanistic factors and actual power plant operating conditions. This comparison revealed which mechanisms play a dominant role in actual power plants and which factors change due to the complexity of actual operating conditions, providing a theoretical basis for the optimized design and operation of nuclear power plants.

[0069] The second type of differential pressure driven experiment focuses on the pressure difference between the experimental section and the downstream atmospheric discharge valve, aiming to reproduce the actual operating conditions of the power plant. By setting the saturated steam pressure of the steam supply unit to be equal to the steam pressure of the experimental section in the formal experiment, and simulating a series of operations such as steam entering the experimental section, air discharge, stabilizing the flow pattern, and rapidly adjusting the opening of the atmospheric discharge valve, the scenario that may cause two-phase steam condensation water hammer in actual power plant operation can be highly reproduced. This allows researchers to observe and study complex situations that occur in actual power plants in the laboratory, providing direct experimental data and response strategies for nuclear power plants to cope with actual operating conditions. Optionally, the two-phase steam condensation water hammer determination method includes the following steps:

[0070] Based on the steam flow rate, the dimensionless number (Fr-Froude number) is obtained as follows:

[0071]

[0072] Where Fr is the Froude number, g is the acceleration due to gravity, L is the characteristic length of the fluid flow, and v is the fluid velocity;

[0073] Based on the temperature difference, the dimensionless number (Ja-Jabber number) is obtained as follows:

[0074]

[0075] Where, ρ L ρ represents the density of the liquid phase. V C represents the density of the gas phase. PL ΔT represents the specific heat of the liquid phase at atmospheric pressure, L is the latent heat of vaporization, and ΔT is the temperature difference between the saturated vapor and the bottom of the liquid phase space in the experimental section.

[0076] Based on the amount of condensate in the experimental section, the dimensionless number (H / D - ratio of liquid level to diameter) is as follows:

[0077]

[0078] Where H is the water level in the condensate pipe at the bottom of the test section, and D is the inner diameter of the pipe in the test section;

[0079] Based on the above steps, the three dimensionless numbers are calculated. The judgment criteria shown in the table below are used to determine whether the two-phase steam condensation water hammer phenomenon has occurred:

[0080] CIWH does not occur H / D<0.1; Fr<0.3; Yes ​ CIWH occurred H / D>0.1 CIWH occurred Fr>0.3 CIWH occurred Ja>A .

[0081] The determination method of this invention introduces three dimensionless numbers—Froude number (Fr), Jacobi number (Ja), and the level-to-diameter ratio (H / D)—to quantitatively describe experimental conditions from different physical dimensions. The Froude number reflects the relative magnitude of fluid inertial force and gravity, demonstrating the influence of steam velocity on the flow state; the Jacobi number characterizes the ratio of sensible heat to latent heat of vaporization, highlighting the role of temperature difference in the steam condensation process; and the level-to-diameter ratio visually demonstrates the degree of condensate accumulation within the experimental section. This multi-dimensional quantification method allows for a more comprehensive and in-depth analysis of the water hammer phenomenon in two-phase steam condensation.

[0082] Based on these three dimensionless numbers calculated and combined with the given criteria, it is possible to accurately determine whether water hammer has occurred in two-phase steam condensation. This criterion comprehensively considers key factors such as steam flow characteristics, heat exchange, and condensate distribution, significantly improving the accuracy and reliability of the determination compared to methods relying on a single parameter. Specifically, in actual steam transmission pipeline experiments, by calculating these three dimensionless numbers in real time and comparing them with the criteria, it is possible to promptly and accurately determine whether water hammer is about to occur or has already occurred, providing a scientific basis for taking appropriate measures to prevent or address water hammer hazards. Attached Figure Description

[0083] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0084] Figure 1 This is a front view of a two-phase steam condensate water hammer experimental apparatus according to an embodiment of the present invention;

[0085] Figure 2 for Figure 1 The front view of the experimental section shown;

[0086] Figure 3 for Figure 2 The right-side view of the experimental section shown;

[0087] Figure 4 for Figure 2 The internal front view of the experimental section shown;

[0088] Figure 5 for Figure 4 The right-side view.

[0089] Explanation of reference numerals in the attached figures:

[0090] 1. Steam supply unit; 2. Steam pipeline; 3. Test section; 4. Condensate supply unit; 5. Discharge unit; 6. Cooling water supply unit; 7. Cooling water return unit; 8. Drainage unit; 9. Steam flow channel; 10. Cooling water flow channel; 11. Variable diameter device; 12. Discharge pipeline; 13. First temperature detection device; 14. Second temperature detection device; 15. Third temperature detection device; 16. Fourth temperature detection device; 17. Fifth temperature detection device; 18. Sixth temperature detection device; 19. Seventh temperature detection device 20. First pressure detection device; 21. First flow detection device; 22. Second flow detection device; 23. First regulating valve; 24. Second regulating valve; 25. Third regulating valve; 26. Electric quick-closing valve; 27. Atmospheric vent valve; 28. Second pressure detection device; 29. ​​Third pressure detection device; 30. Third flow detection device; 31. Fourth pressure detection device; 32. Eighth temperature detection device; 33. Second pressure reducing valve; 34. First pressure reducing valve; 35. Drain valve; 36. Drain collection box. Detailed Implementation

[0091] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0092] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0093] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0094] Furthermore, 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.

[0095] Condensate at the bottom of the steam pipe moves downstream under the impetus of steam. A significant amount of condensate accumulates at the closed valve at the end of the pipe. The fluid flow within the pipe exhibits a stratified flow pattern: saturated steam is located above the pipe, the surface layer in contact with the steam is saturated water, and undersaturated condensate is located below – a stratified flow. When the atmospheric vent valve is opened, the increased steam velocity further accelerates the fluid flow within the pipe. This can cause the condensate flow to change from a stratified flow to a slug flow, potentially trapping steam bubbles within the water column. The rapid condensation of these steam bubbles can trigger the CIWH phenomenon.

[0096] This embodiment provides a two-phase steam condensation water hammer experimental device.

[0097] like Figure 1 As shown, the system includes: a steam supply unit 1, an experimental section 3, a condensate supply unit 4, and a discharge unit 5. The steam supply unit 1 is used to provide experimental steam. The experimental section 3 has a steam flow channel 9 inside, and the inlet of the steam flow channel 9 is connected to the steam supply unit 1 through a steam pipe 2. The steam pipe 2 is equipped with an electric quick-closing valve 26. The bottom of the experimental section 3 has a cooling water flow channel 10, which is spaced apart from the steam flow channel 9. The outlet of the condensate supply unit 4 is connected to the steam flow channel 9 of the experimental section 3, and the condensate supply unit 4 is used to provide experimental condensate. The discharge unit 5 is connected to the outlet of the steam flow channel 9 of the experimental section 3 through a discharge pipe 12, and the discharge pipe 12 is equipped with an atmospheric discharge valve 27 and a first pressure reducing valve 34.

[0098] Specifically, in this embodiment, the steam supply unit 1 is used to provide experimental steam, enabling the steam flow channel 9 in the experimental section 3 to stably obtain steam with specific parameters, thereby accurately simulating the steam conditions in the pipeline during actual operation of a nuclear power plant. The outlet of the condensate supply unit 4 is connected to the steam flow channel 9 in the experimental section 3 to provide experimental condensate. This allows for the study of the frequency and intensity changes of water hammer generated during steam condensation under different condensate injection volumes, providing a theoretical basis for preventing water hammer hazards in nuclear power plants.

[0099] The bottom of the experimental section 3 is provided with a cooling water channel 10, which is spaced apart from the steam channel 9. The cooling water flowing in the cooling water channel 10 controls the temperature of the bottom condensate in the experimental section 3. The experimental apparatus provided in this embodiment can focus on studying the impact of changes in two key parameters—the volume of condensate and the temperature of the bottom condensate—on the two-phase steam condensation water hammer phenomenon. The discharge unit 5 is connected to the outlet of the steam channel 9 in the experimental section 3. The pressure difference between the experimental section 3 and the downstream discharge unit 5 can accelerate the flow of fluid in the experimental section 3, further triggering the two-phase steam condensation water hammer phenomenon.

[0100] The key driving force of this experimental setup is pressure difference, and the focus is on studying the impact of changes in this key parameter on the two-phase steam condensation water hammer phenomenon. This experimental setup mainly designs two types of pressure difference driving forces for comparative experiments. The first type of pressure difference driving force is the pressure difference between experimental section 3 and upstream steam supply unit 1. This type of test condition is a mechanistic test used to study the mechanism of two-phase steam condensation water hammer phenomenon and to compare it with the second type of power plant prototype reproduction experiment. The second type of pressure difference driving force is the pressure difference between experimental section 3 and downstream emission unit 5. This type of test condition is a reproduction test similar to the power plant prototype, used to reproduce the actual operating conditions of the power plant.

[0101] The experimental section 3 of this apparatus can be made of high-pressure resistant 304 stainless steel, ensuring that it can withstand severe pressure and temperature fluctuations under the required experimental parameters. To reduce heat loss during steam transport, the entire exterior of experimental section 3 is wrapped with insulating cotton.

[0102] The technical solution provided in this embodiment can simulate real working conditions and study the two-phase steam condensation water hammer phenomenon caused by the contact between steam and condensate accumulated at the bottom of the pipe during the flow process.

[0103] It should be noted that the steam supply unit 1 in this embodiment can provide saturated steam to focus on studying the impact of changes in the key parameter of saturated steam in experimental section 3 on the water hammer phenomenon, thereby simulating the flow state of the steam working medium in the main steam pipeline 2 when two-phase steam condensation water hammer occurs in the nuclear power plant pipeline. Furthermore, since the two-phase steam condensation water hammer phenomenon in the nuclear power plant pipeline occurs under high pressure conditions, if experimental conditions permit, it is necessary to design experiments under high pressure conditions and conduct experiments to reproduce the operating conditions under the same pressure and working medium as the nuclear power plant steam pipeline. If experimental conditions do not permit, low-pressure experiments can be used to replace high-pressure experiments in the experimental design. After the mechanistic study of the low-pressure experiment, further extended operating conditions of the low-pressure experiment can be designed. Subsequently, if conditions permit, extrapolation experiments under the same pressure and working medium conditions can be conducted.

[0104] The experimental apparatus provided in this embodiment has also been optimized to address interference factors that may affect the water hammer experiment. Specific interference factors include: during the experiment, condensate in experimental section 3 may flow back to steam pipe 2; direct pressure relief and release of high-pressure steam in experimental section 3 may cause severe critical flow conditions; condensate in experimental section 3 may not be able to maintain a large temperature gradient under the drive of high-pressure steam; a large temperature gradient of condensate may prevent temperature measurements from accurately reflecting the true temperature gradient; and the control of some key influencing factors during the formal experiment may not be able to be accurately adjusted.

[0105] like Figure 2 As shown, the two-phase steam condensation water hammer experimental apparatus provided in this embodiment further includes: a reducing device 11, which is a reducing connector with a small end and a large end. The small end is connected to the steam pipe 2, and the large end is connected to the inlet of the steam flow channel 9 of the experimental section 3. The bottom of the small end is higher than the bottom of the large end. In the above scheme, the design of the small end being higher than the large end effectively prevents the condensate in the experimental section 3 from flowing back into the steam pipe 2. During the experiment, the condensate in the steam channel of the experimental section 3 will naturally flow downwards. The inclined structure of the reducing device 11 makes it easier for the condensate to flow into the experimental section 3 without flowing back into the steam pipe 2, ensuring the purity and normal delivery of the steam in the steam pipe 2, and maintaining the stability and accuracy of the experiment. In addition, through the above settings, when the steam flows from the small end to the large end, the steam velocity decreases and the pressure increases due to the increase in the cross-sectional area of ​​the flow channel. During the diffusion process at the large opening, the steam can more comprehensively cover the inlet section of the steam channel 9 in experimental section 3, avoiding the steam from concentrating in a certain area and thus ensuring the uniformity of steam flow within experimental section 3.

[0106] like Figure 2 As shown, in the two-phase steam condensation water hammer experimental apparatus provided in this embodiment, the top of the small-mouth end of the reducing device 11 is flush with the top of the large-mouth end. When the top of the small-mouth end of the reducing device 11 is flush with the top of the large-mouth end, the steam can flow into the experimental section 3 relatively evenly after passing through the reducing device. In addition, in some alternative embodiments, the top of the small-mouth end is higher than the top of the large-mouth end. When the top of the small-mouth end is higher than the top of the large-mouth end, the downward flow tendency of the steam will be enhanced, thereby forming a distribution state with a relatively high bottom steam concentration at the inlet of the experimental section 3.

[0107] It should be noted that both the flush-top design and the higher top of the smaller end further enhance the ability to prevent condensate from flowing back into steam pipe 2. This is because the reducing device 11 is tilted as a whole, and the height of its top is scientifically and reasonably set, making it easier for condensate to flow into the experimental section 3 under the influence of gravity. In particular, when the top of the smaller end is higher than the top of the larger end, the difficulty of condensate flowing back into steam pipe 2 increases significantly, which effectively avoids adverse effects of condensate on steam pipe 2 and steam supply unit 1. In this way, not only can the steam supply system operate stably, but the stability of steam parameters can also be maintained during the experiment, thereby improving the reliability of experimental data.

[0108] like Figure 3 As shown, in the two-phase steam condensation water hammer experimental apparatus provided in this embodiment, the experimental section 3 is externally wrapped with a sleeve, and a cooling water channel 10 is formed between the sleeve and the outer wall of the experimental section 3. Through this arrangement, the cold water in the cooling water channel 10 can form a large temperature difference with the steam in the steam channel 9 of the experimental section 3, and heat exchange occurs through the pipe wall of the experimental section 3. By adjusting parameters such as the flow rate and temperature of the cooling water in the cooling water channel 10, a large temperature gradient can be maintained in the condensate, facilitating the study of the influence of different condensate temperatures on the water hammer phenomenon. Of course, the above description is not limiting; in some alternative embodiments, the cooling water channel 10 can also be arranged in other ways, such as being formed inside the experimental section 3.

[0109] like Figure 2 , Figure 3 As shown, in this embodiment, the experimental section 3 is a horizontally arranged cylindrical shape, and the sleeve wraps around the lower semi-circular area of ​​the experimental section 3. This arrangement results in a larger contact area between the cooling water channel 10 and the experimental section 3 at the bottom, enhancing the heat exchange efficiency in this area. Since condensate accumulates at the bottom due to gravity when steam flows in the horizontal pipe, the cooling water channel 10 here can more effectively cool the condensate. This helps in studying the effect of condensate on water hammer at different temperatures.

[0110] Specifically, in this embodiment, the angle at which the sleeve covers the lower half-arc region of the experimental section 3 is 120°±10°. This specific angle design achieves precise control over the heat exchange area and intensity. At this angle, the contact area between the cooling water channel 10 and the experimental section 3 is moderate, enabling effective heat exchange with the condensate within the experimental section 3. Of course, the above description is not limiting; in some alternative embodiments, the angle at which the sleeve covers the lower half-arc region of the experimental section 3 can be other angles, such as 180°.

[0111] like Figure 2 , Figure 3 As shown, in this embodiment, the discharge pipe 12 is inclinedly connected to the upper semi-arc region of the experimental section 3. Specifically, from the main view, the discharge pipe 12 is inclined in the opposite direction to the steam flow direction in the steam channel 9. This design of the inclined discharge pipe 12 helps to better separate condensate and steam. Due to the different densities of steam and condensate, condensate tends to move downwards under the influence of gravity during steam flow. The inclination of the discharge pipe 12 in the opposite direction to the steam flow makes it easier for condensate to separate from the steam under gravity during the upward discharge process, flowing back to the bottom of the experimental section 3. This efficient separation process reduces the instability of the vapor-liquid two-phase flow in the discharge pipe 12, lowers the risk of water hammer caused by two-phase flow impact, and also facilitates the study of the separation characteristics of steam and condensate in the experimental section 3 and its impact on water hammer. Specifically, in this embodiment, the steam discharge pipe 12 is connected to the experimental section 3 by welding, with the right end of the experimental section 3 closed and the left end connected to the steam pipe 2 via a reducing joint.

[0112] In addition, such as Figure 3 As shown, viewed from the right, the discharge pipe 12 is inclined towards one side of the vertical plane. This setting aims to ensure geometric similarity to the prototype nuclear power plant, allowing the experimental setup to more accurately simulate the actual situation of a nuclear power plant's steam emission system. The geometry of pipes in a nuclear power plant plays a crucial role in the flow characteristics of steam and condensate. By replicating this geometric feature, the flow, separation, and pressure changes of steam and condensate within the discharge pipe 12 will more closely resemble the real-world scenario. In other words, using the above setup, the steam emission process during actual nuclear power plant operation can be accurately simulated, providing reliable experimental conditions for studying the impact of steam emission on condensate hammer phenomena. Furthermore, since the experimental section 3 is horizontally positioned and has a cooling water channel 10 at its lower part, condensate mainly forms and accumulates in the lower half of the experimental section 3. The inclined discharge pipe 12 prevents condensate from directly entering the discharge pipe 12, thereby achieving effective separation of steam and condensate within the experimental section 3.

[0113] like Figure 1 As shown, the two-phase steam condensate water hammer experimental apparatus provided in this embodiment further includes a condensate draining unit 8, which is connected to the steam channel 9 of the experimental section 3. The condensate draining unit 8 is used to drain the condensate from the steam channel 9. The addition of the condensate draining unit 8 can simulate the condition of condensate continuously accumulating in the steam pipeline of a nuclear power plant due to a condensate draining pipeline malfunction. Furthermore, the condensate draining unit 8 can also be used to drain the remaining liquid in the steam channel 9 after the experiment, for use in the next experiment. Of course, the above description is not limiting; in some alternative embodiments, the condensate draining unit 8 can be omitted.

[0114] like Figure 1 As shown, the two-phase steam condensate water hammer experimental apparatus provided in this embodiment further includes: a cooling water supply unit 6 and a cooling water return unit 7. The cooling water supply unit 6 is connected to the inlet of the cooling water channel 10, and the cooling water return unit 7 is connected to the outlet of the cooling water channel 10. In use, the cooling water supply unit 6 supplies cooling water to the cooling water channel 10, and the cooling water return unit 7 receives the cooling water in the cooling water channel 10, thereby allowing the coolant in the cooling water channel 10 to flow.

[0115] like Figure 1 , Figure 2 As shown, the cooling water supply unit 6 has a temperature detection device, a flow detection device, and a regulating valve; the cooling water return unit 7 has a regulating valve and a temperature detection device. In other words, both the cooling water supply unit 6 and the return unit are equipped with temperature detection devices, thus enabling real-time monitoring of the cooling water temperature.

[0116] Specifically, the cooling water supply unit 6 includes a first temperature detection device 13, a first flow rate detection device 21, and a first regulating valve 23. Based on the information fed back from the first temperature detection device 13 and the first flow rate detection device 21, the first regulating valve 23 can precisely control the temperature of the cooling water entering the cooling water channel 10. The cooling water return unit 7 is equipped with a second temperature detection device 14 and a second regulating valve 24. The second temperature detection device 14 can monitor the temperature of the cooling water flowing out of the cooling water channel 10, further understanding the heat exchange effect of the cooling process, providing a reference for adjusting the supply water temperature, and ensuring that the cooling process is stable and meets experimental requirements.

[0117] The first flow detection device 21 monitors the flow data in real time and adjusts the opening of the first regulating valve 23 according to experimental requirements to precisely control the flow rate of cooling water entering the cooling water channel 10. Different steam condensation processes may require different cooling water flow rates to simulate. Through precise flow control, the influence of cooling water flow rate on steam condensation rate, condensation location, and water hammer phenomenon can be studied.

[0118] like Figure 1 , Figure 2 As shown, in this embodiment, the inlet and outlet of the cooling water channel 10 are respectively equipped with temperature detection devices. Specifically, the inlet of the cooling water channel 10 is equipped with a third temperature detection device 15, and the outlet of the cooling water channel 10 is equipped with a fourth temperature detection device 16.

[0119] This setup allows for real-time and precise acquisition of cooling water temperature data as it enters and exits the cooling water channel 10. By comparing the inlet and outlet temperatures, the heat exchange during the cooling water flow through experimental section 3 can be accurately calculated. Based on the inlet and outlet temperature data, the regulating valves of the cooling water supply unit 6 and the return unit can be adjusted more precisely. If the temperature difference between the inlet and outlet of the cooling water channel 10 is too large, it indicates that the cooling effect is too strong, which may lead to over-cooling of the steam. In this case, the cooling water flow rate can be appropriately reduced or the supply water temperature increased by adjusting the valve to achieve a more suitable cooling level. Conversely, if the temperature difference is too small, the opposite operation can be performed. This precise adjustment based on actual temperature feedback ensures that the cooling process is always maintained in the ideal state required for the experiment, thereby improving the accuracy and reliability of the experimental results.

[0120] like Figure 1 , Figure 2 As shown, in this embodiment, multiple temperature detection devices are sequentially arranged along the steam channel 9 on the experimental section 3. These multiple temperature detection devices are used to detect the temperature within the steam channel 9. Each of the multiple temperature detection devices is a multi-point thermocouple, used to detect multiple points at different heights within the steam channel 9 at the same horizontal position. Specifically, the experimental section 3 has three temperature detection devices: a fifth temperature detection device 17, a sixth temperature detection device 18, and a seventh temperature detection device 19, all of which are multi-point thermocouples with four temperature measurement points.

[0121] In the above scheme, multiple temperature detection devices (multi-point thermocouples) are installed along the steam flow channel 9 in experimental section 3, which can accurately reflect the temperature stratification of the condensate within experimental section 3. Since multi-point thermocouples can detect multiple areas at different heights on the same horizontal level, researchers can obtain detailed temperature distribution information within the steam flow channel 9. This data provides a clear understanding of the temperature changes of steam during its flow, from the steam inlet to the outlet, and at different heights on the same cross-section. This is of great significance for in-depth research on the heat transfer process of steam within experimental section 3 and the heat exchange effect between steam and the cooling water flow channel 10, accurately capturing the spatial variation of steam temperature.

[0122] like Figure 1 , Figure 2As shown in this embodiment, the experimental section 3 is also equipped with a pressure detection device, specifically a first pressure detection device 20, which is used to detect the pressure within the steam flow channel 9. Combined with the existing multiple temperature detection devices on the experimental section 3, the first pressure detection device 20 allows for more comprehensive monitoring of the operating conditions within the steam flow channel 9. Pressure and temperature are two key parameters describing the state of steam. By simultaneously acquiring temperature and pressure data at different locations within the steam flow channel 9, researchers can more accurately grasp the thermodynamic state of the steam.

[0123] like Figure 1 As shown, in this embodiment, the condensate supply unit 4 includes a second flow detection device 22 and a third regulating valve 25. The second flow detection device 22 and the third regulating valve 25 work together to precisely regulate the flow rate of the condensate supplied to the steam channel 9 of the experimental section 3. The second flow detection device 22 monitors the condensate flow rate data in real time, providing feedback information to the third regulating valve 25. According to experimental requirements, researchers can precisely control the condensate flow rate by adjusting the opening of the third regulating valve 25.

[0124] like Figure 1 As shown, in this embodiment, the steam pipeline 2 is equipped with an electrically operated quick-closing valve 26. In two-phase steam condensation water hammer experiments in nuclear power plant pipelines, various unforeseen situations may occur, such as equipment malfunctions, abnormal data detection, or water hammer exceeding safe limits. The electrically operated quick-closing valve 26 can close quickly, immediately stopping steam from entering the experimental section 3, preventing more serious consequences from continuous steam supply. Besides handling emergencies, the electrically operated quick-closing valve 26 can also be used for precise control of the experimental process. In some experimental scenarios, researchers may need to stop the steam supply at specific times to observe phenomena within the experimental section 3 after steam flow stops, such as the subsequent flow of condensate and pressure decay. The electrically operated quick-closing valve 26 can accurately cut off the steam at a set time point according to the experimenter's instructions, providing a powerful tool for studying the changes in steam condensation water hammer after steam supply is stopped, and contributing to a deeper understanding of the physical mechanisms of the entire process.

[0125] like Figure 1 As shown, in this embodiment, the gas supply unit can be a high-pressure steam boiler, and a second pressure-reducing valve 33 is provided at the outlet of the high-pressure steam boiler. During the experiment, the high-pressure steam required for the experiment is provided by adjusting the high-pressure steam boiler and the second pressure-reducing valve 33, and then the high-temperature steam at the predetermined pressure is injected into the experimental section 3 through the steam pipeline 2. In the two-phase steam condensate hammer experiment in the nuclear power plant pipeline, a stable steam pressure that meets the experimental requirements is crucial. The second pressure-reducing valve 33 can adjust the steam pressure output by the gas supply unit to the precise value required for the experiment, avoiding interference with the experimental results due to steam pressure fluctuations.

[0126] like Figure 1 As shown, in this embodiment, the emission unit 5 includes an atmospheric emission valve 27, a second pressure detection device 28, a third pressure detection device 29, a first pressure reducing valve 34, a third flow detection device 30, a fourth pressure detection device 31, and an eighth temperature detection device 32. The second pressure detection device 28 and the third pressure detection device 29 are located upstream and downstream of the atmospheric emission valve 27, respectively. The first pressure reducing valve 34 is located downstream of the third pressure detection device 29. The third flow detection device 30, the fourth pressure detection device 31, and the eighth temperature detection device 32 are all located downstream of the first pressure reducing valve 34.

[0127] The abundant control and detection devices in emission unit 5 enable experiments to simulate various complex operating conditions of nuclear power plant steam emissions. By adjusting the fifth regulating valve and the first pressure reducing valve 34, combined with precise monitoring of pressure, flow rate, and temperature, the actual situation of nuclear power plant steam emissions under different loads and operating stages can be simulated.

[0128] Specifically, through the coordinated operation of the fifth regulating valve, the second pressure detection device 28, and the third pressure detection device 29, precise regulation of the discharge pressure is achieved. The second pressure detection device 28 monitors the pressure upstream of the fifth regulating valve in real time, while the third pressure detection device 29 monitors the downstream pressure. Based on these two pressure data, the operator can precisely adjust the opening of the fifth regulating valve.

[0129] The second pressure detection device 28 and the third pressure detection device 29 are not only used for regulation, but also for real-time monitoring of abnormal pressure conditions. If the pressure upstream or downstream of the fifth regulating valve exceeds the normal range, an alarm can be issued in a timely manner to prompt the operator to take measures. For example, a sudden increase in pressure may indicate a blockage in the discharge pipe 12 or a malfunction inside the experimental section 3. Timely detection and handling of these abnormalities can effectively prevent damage to the experimental device due to excessive pressure and ensure the safe conduct of the experiment.

[0130] The first pressure-reducing valve 34 is located downstream of the third pressure detection device 29, serving a further regulatory and protective function. When the pressure still does not meet requirements after adjustment by the fifth regulating valve, or in the event of a sudden pressure surge, the first pressure-reducing valve 34 can automatically activate to lower the pressure to a safe range. This provides double protection for the experimental setup, ensuring that the discharge pressure remains under control, especially when simulating high-pressure steam discharge conditions in a nuclear power plant, effectively preventing safety accidents caused by pressure runaway.

[0131] The third flow detection device 30 is located downstream of the first pressure reducing valve 34 and can accurately measure the flow rate of the discharged steam. Accurate flow data is crucial for studying the steam discharge process and its relationship with other parameters.

[0132] The eighth temperature detection device 32 is located downstream of the first pressure reducing valve 34 and monitors the temperature of the discharged steam in real time. Temperature is one of the important parameters of steam state and is of great significance for studying steam condensation process, heat exchange, and water hammer phenomenon. By accurately measuring the temperature of the discharged steam, we can further understand the energy changes and state transitions of steam during the discharge process.

[0133] In addition, during the experiment, a certain pressure difference was created before and after the experimental section 3 by adjusting the opening of the atmospheric discharge valve 27, thereby driving the flow of the working fluid in the experimental section 3 and inducing water hammer. The first pressure reducing valve 34 was adjusted to limit the severe critical flow situation that might be caused by the direct release of high-pressure steam, thus avoiding significant noise pollution and impacting the surrounding environment.

[0134] like Figure 1 As shown, in this embodiment, the condensate collection unit 8 has a condensate collection tank 36, and a condensate trap 35 is installed on the inlet pipe of the condensate collection tank 36. The condensate collection tank 36 serves as a centralized collection point for condensate, effectively collecting the condensate discharged from the steam channel 9 of the experimental section 3. The condensate trap 35, installed on the inlet pipe of the condensate collection tank 36, can precisely control the flow rate and timing of condensate entering the collection tank.

[0135] Within the steam flow channel 9 of the experimental section 3, such as Figure 4 As shown, u G For: steam velocity; u L For: liquid velocity; τ wg For: the shear stress between the wall and the steam; τ wl τ is the shear stress between the wall and the liquid. i For: Shear stress at the vapor-liquid interface.

[0136] like Figure 5 As shown, S G S represents the length of the gas phase boundary. L S represents the length of the liquid phase perimeter. i For: the perimeter length of the vapor-liquid interface; A G For: cross-sectional area of ​​the gas phase; A L For: cross-sectional area of ​​the liquid phase; H L Here: liquid level; D: pipe diameter.

[0137] The two-phase steam condensate water hammer experimental apparatus provided in this embodiment is constructed according to a specific scale and design method to reproduce the two-phase condensate water hammer phenomenon occurring in the main steam pipe 2 of the secondary loop of a nuclear power plant. By exploring the effects of different influencing factors on the two-phase water hammer phenomenon, this apparatus can provide experimental data support for guiding the design of scaled-down test benches, verifying relevant calculation models, and accurately understanding the steam water hammer phenomenon.

[0138] This embodiment provides a scaling analysis method for designing experimental apparatus on a scaled-down basis.

[0139] For a circular pipe, the dimensionless conversion criterion between stratified flow and intermittent or annular dispersed flow states is:

[0140]

[0141] Where Fr is the vapor phase corrected Froude number:

[0142]

[0143] In the formula, ρG and ρL are the densities of the gas phase fluid and the liquid phase fluid, respectively (kg / m3); vG is the velocity of the gas phase fluid (m / s); g is the acceleration due to gravity (m / s2); D refers to the inner diameter of the pipe (m); and θ refers to the inclination angle of the pipe (°).

[0144] That is The function of H. L This refers to the liquid level height (m) within the pipe. As shown in equation (2-1), the flow pattern transformation model mainly reflects the similarity in relative liquid level height and the vapor phase corrected Froude number:

[0145] π2=(Fr G ) R =1 (2-4)

[0146] Equations (2-3) and (2-4) are two sets of dimensionless transformation relationships for scaled-down design of two-phase water hammer in horizontal pipes, involving the similarity modeling of fluid flow patterns. In the above equations, the subscript R refers to the ratio between the experimental device and the prototype. Assuming equal gravitational acceleration and that the pipes of both the prototype and the experimental device are horizontal, equations (2-2) and (2-4) yield the following:

[0147]

[0148] The key to achieving similar flow pattern transitions within a pipeline lies in ensuring that the similarity between the relative height of the liquid phase fluid and the flow velocity of the gas phase fluid is maintained.

[0149] For the prototype steam pipe, its relative liquid level height is:

[0150]

[0151] Given the limited space at the experimental site and the specifications and pressure resistance of existing pressure-bearing pipelines, this study selected a stainless steel pipe section with an inner diameter of 40 mm, an outer diameter of 60 mm, and a design pressure of 9 MPa as experimental section 3. To meet the requirements of equation (2-3), the height of the liquid phase fluid in experimental section 3 needs to be accurately calculated and controlled as follows:

[0152] H L，t =0.5×D t =20mm (2-7).

[0153] Calculations show that the steam velocity v inside the prototype pipe is... G，p = 5.41 m / s. As for the vapor phase fluid velocity within experimental section 3, according to equation (2-5), it is related to the physical properties of both phases and the experimental pipe diameter:

[0154]

[0155] Substituting the relevant values ​​into the calculation, the appropriate steam flow rate can be obtained as v. G，t =1.252m / s

[0156] When conducting scaled-down design, the actual dimensions and parameters of the research object must first be considered (in this experiment, the research object is the steam pipeline before the main steam isolation valve of the secondary loop of a nuclear power plant). Secondly, the actual experimental conditions must be considered (such as the existing experimental site, experimental conditions, and the specifications and pressure resistance of the pressure-bearing pipeline in experimental section 3). Finally, several scaling standards obtained through proportional analysis should be referenced for the scaled-down and simplified design of the experimental setup. It is important to note that the scaling standards used in this experiment are based on theoretical formulas and may not achieve precise dynamic similarity between the prototype system and the scaled-down test bench under scaled-down conditions. Furthermore, not all scaling standards can be simultaneously satisfied; therefore, appropriate selection based on the importance of different factors is necessary when designing the experiment. Experimental section 3 is the location where two-phase steam condensation water hammer occurs in the entire experimental setup. The selection of the geometric dimensions of experimental section 3 is crucial to the experiment, so it is necessary to ensure the geometric similarity between experimental section 3 and the prototype pipeline of the nuclear power plant. The scaled-down design of this experimental setup ensures geometric similarity to the nuclear power plant prototype in parameters such as the length, diameter, slope, length-to-diameter ratio (the ratio of pipe length to pipe diameter) of the experimental section 3 and the steam exhaust pipe 12, as well as the location and angle of the steam exhaust pipe 12.

[0157] This embodiment provides a method for testing water hammer caused by two-phase steam condensation.

[0158] First, a reference experiment was conducted in the first stage. Before the experiment began, a certain amount of condensate was injected into experimental section 3.

[0159] Start the steam supply unit 1 to generate high-pressure steam, open the electric quick-closing valve 26, the atmospheric discharge valve 27 and the first pressure reducing valve 34 to allow steam to slowly enter the experimental section 3;

[0160] The changes in liquid phase temperature and vapor phase pressure over time were investigated under both external cooling and non-external cooling conditions. When there was no external cooling, after all air was exhausted, the electric quick-closing valve 26, atmospheric vent valve 27, and the first pressure-reducing valve 34 were closed. The changes in liquid phase temperature and vapor phase pressure over time in the pipe under these conditions were then investigated. When external cooling was present, after all air was exhausted, the electric quick-closing valve 26, atmospheric vent valve 27, and pressure-reducing valve were closed, allowing cooling water to flow through the cooling water channel 10 to cool the lower layer of liquid in experimental section 3. The changes in liquid phase temperature and vapor phase pressure over time in the pipe under external cooling conditions were then investigated and recorded.

[0161] Then, the second phase of formal experiments was conducted. Two major types of differential pressure driving experiments were designed for comparative analysis, based on the two different differential pressure driving methods.

[0162] The first type of pressure difference driven experiment: the pressure difference experiment between test section 3 and upstream steam pipeline 2. This type of test is a mechanism experiment, used to conduct a mechanistic study of the two-phase steam condensation water hammer phenomenon, and to compare and analyze it with the second type of power plant prototype reproduction experiment; specifically, it includes the following steps:

[0163] Cooling water is injected into the experimental section 3 to a predetermined volume through the cooling water supply unit 4;

[0164] Start steam supply unit 1 to generate high-pressure steam, and set the saturated steam pressure value of steam supply unit 1 to be slightly larger than the steam pressure value of experimental section 3 in the formal experiment.

[0165] Open the electric quick-closing valve 26, the atmospheric vent valve 27, and the first pressure reducing valve 34 to allow steam to slowly enter the experimental section 3; after all the air has been expelled, close the electric quick-closing valve 26, the atmospheric vent valve 27, and the first pressure reducing valve 34.

[0166] After readjusting the steam pressure of the steam supply unit 1 to the predetermined parameters, turn on the cooling water to allow the cooling water to flow through the cooling water channel 10 and cool the lower layer of liquid in the experimental section 3.

[0167] When the parameters of the gas and liquid in experimental section 3 reach the preset values, the electric quick-closing valve 26 is quickly opened to start the experiment. Within a very short time, a complex gas-liquid two-phase steam condensation water hammer phenomenon will occur in experimental section 3.

[0168] The second type of differential pressure driven experiment: This involves a differential pressure experiment between test section 3 and the downstream atmospheric emission valve 27. This type of test is a replication test similar to that of the power plant prototype, used to reproduce the actual operating conditions of the power plant. Specifically, it includes the following steps:

[0169] First, set the saturated steam pressure value of steam supply unit 1 to be equal to the steam pressure value of experimental section 3 in the formal experiment.

[0170] Open the electric quick-closing valve 26 and the atmospheric discharge valve 27, and adjust the opening of the first pressure reducing valve 34 to allow steam to slowly enter the experimental section 3.

[0171] Turn on the cooling water to allow it to flow through the cooling water channel 10 and cool the lower layer of liquid in the experimental section 3.

[0172] After all the air in experimental section 3 is expelled, close the atmospheric exhaust valve 27.

[0173] Once the flow pattern in experimental section 3 stabilizes, the opening of atmospheric discharge valve 27 is quickly adjusted to the predetermined value. Within a very short time, a complex gas-liquid two-phase steam condensation water hammer phenomenon will occur in experimental section 3.

[0174] The above experimental method examines the relationship between liquid phase temperature and vapor phase pressure and time in experimental section 3 through the first-stage reference experiment. Based on the data from the first-stage reference experiment, the analysis guides the more precise adjustment of key parameters under different operating conditions in the second-stage formal experiment.

[0175] During the above experiments, carefully observe parameter changes and save data promptly. If any anomalies are found, record them and repair them after the experiment. If the anomalies have a direct impact on the operating conditions, the experiment needs to be repeated.

[0176] After the two-phase water hammer effect ends, close the electric quick-closing valve 26, the atmospheric discharge valve 27 and the first pressure reducing valve 34, open the drain valve 35, weigh the drain collection box 36, and save the experimental data.

[0177] During the experiment, the steam pressure inside the pipe of experimental section 3 can be measured by the first pressure detection device 20 on experimental section 3; by using multiple multi-point thermocouples (each thermocouple is equipped with four temperature measuring points to measure the temperature at different heights at the same location: measuring point 1 is located in the upper gas space of experimental section 3; measuring point 2 is located at the gas-liquid interface in the middle of experimental section 3; measuring points 3 and 4 are located in the liquid phase space to measure the liquid phase temperature stratification in experimental section 3), the steam temperature parameters of the gas space, gas-liquid interface, and liquid phase space in experimental section 3 at different times can be recorded simultaneously.

[0178] This embodiment also provides a criterion for determining two-phase steam condensate hammer in nuclear power plant pipelines.

[0179] Includes the following steps:

[0180] Based on the steam flow rate, the dimensionless number (Fr-Froude number) is obtained as follows:

[0181]

[0182] Where Fr is the Froude number, g is the acceleration due to gravity, L is the characteristic length of the fluid flow, and v is the fluid velocity, determined from the experimental data mentioned above.

[0183] Based on the temperature difference, the dimensionless number (Ja-Jabber number) is obtained as follows:

[0184]

[0185] Where, ρ L ρ represents the density of the liquid phase. V c represents the gas phase density. PL ΔT represents the specific heat of the liquid phase at atmospheric pressure, L represents the latent heat of vaporization, and ΔT represents the temperature difference between the saturated vapor and the bottom of the liquid phase space in experimental section 3, which is determined by the experimental data obtained above.

[0186] Based on the volume of condensate in experimental section 3, the dimensionless number (H / D - ratio of liquid level to diameter) is as follows:

[0187]

[0188] Where H is the water level in the condensate pipe at the bottom of the test section, and D is the inner diameter of the pipe in the test section.

[0189] Based on the above steps, the three dimensionless numbers are calculated. The judgment criteria shown in the table below are used to determine whether two-phase steam condensate hammer phenomenon has occurred in the steam pipeline of the nuclear power plant:

[0190] CIWH does not occur H / D<0.1; Fr<0.3; Yes ​ CIWH occurred H / D>0.1 CIWH occurred Fr>0.3 CIWH occurred Ja>A

[0191] It should be noted that the above judgment criteria are based on the geometric and boundary conditions under which the prototype accident occurred at this nuclear power plant. The water hammer test device was constructed after appropriate simplification and scaling down of the prototype using proportional analysis methods. The conclusions were drawn from relevant experimental research and subsequent iterative analysis using numerical simulations. This research background must be considered when using these judgment criteria.

[0192] The experimental focus of this invention is to study the effects of different parameter conditions (such as the amount of condensate, temperature, steam pressure, steam pressure difference between the steam source and the experimental section 3, and steam pressure difference between the experimental section 3 and the downstream pipeline) on two-phase water hammer, while ensuring safety. The invention aims to study the occurrence phenomenon and load changes of condensate water hammer under specific experimental conditions, and to provide experimental data for a correct understanding of steam water hammer phenomena and to verify relevant models and procedures.

[0193] Although embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations all fall within the scope defined by the present invention.

Claims

1. A two-phase steam condensate water hammer experimental apparatus, characterized in that, include: Steam supply unit (1) is used to provide steam for experiments; The experimental section (3) has a steam flow channel (9) inside. The inlet of the steam flow channel (9) is connected to the steam supply unit (1) through a steam pipe (2). An electric quick-closing valve (26) is provided on the steam pipe (2). The bottom of the experimental section (3) has a cooling water flow channel (10). The cooling water flow channel (10) and the steam flow channel (9) are spaced apart. The condensate supply unit (4) has its outlet connected to the steam flow channel (9) of the experimental section (3). The condensate supply unit (4) is used to provide condensate for the experiment. The discharge unit (5) is connected to the outlet of the steam flow channel (9) of the experimental section (3) through the discharge pipe (12), which is equipped with an atmospheric discharge valve (27) and a first pressure reducing valve (34).

2. The two-phase steam condensate water hammer experimental apparatus according to claim 1, characterized in that, Also includes: A reducing device (11) has a small end and a large end. The small end is connected to the steam pipe (2), and the large end is connected to the inlet of the steam flow channel (9) of the experimental section (3). The bottom end of the small end is higher than the bottom end of the large end.

3. The two-phase steam condensate water hammer experimental apparatus according to claim 1, characterized in that, The experimental section (3) is wrapped with a sleeve, and the cooling water channel (10) is formed between the sleeve and the outer wall of the experimental section (3).

4. The two-phase steam condensate water hammer experimental apparatus according to claim 3, characterized in that, The experimental section (3) is a horizontally set cylindrical shape, and the sleeve wraps around the lower half-arc region of the experimental section (3).

5. The two-phase steam condensate water hammer experimental apparatus according to claim 4, characterized in that, The sleeve covers the lower half-arc region of the experimental section (3) at an angle of 120°±10°.

6. The two-phase steam condensate water hammer experimental apparatus according to any one of claims 1-5, characterized in that, Also includes: The hydrophobic unit (8) is connected to the steam channel (9) of the experimental section (3) and is used to drain the condensate in the steam channel (9).

7. The two-phase steam condensate water hammer experimental apparatus according to any one of claims 1-5, characterized in that, Also includes: Cooling water supply unit (6) and cooling water return unit (7), wherein the cooling water supply unit (6) is connected to the inlet of the cooling water channel (10) and the cooling water return unit (7) is connected to the outlet of the cooling water channel (10); The cooling water supply unit (6) has a temperature detection device, a flow detection device and a regulating valve; The cooling water return unit (7) has a regulating valve and a temperature detection device; Temperature detection devices are also provided at the inlet and outlet of the cooling water channel (10).

8. A scaled-down design method for a two-phase steam condensate water hammer experimental apparatus according to any one of claims 1-7, characterized in that, For a circular pipe, the dimensionless conversion criterion between stratified flow and intermittent or annular dispersed flow states is: Where Fr is the vapor phase corrected Froude number: In the formula, ρG and ρL represent the gas phase fluid density and liquid phase fluid density, respectively (kg / m3); vG represents the gas phase fluid velocity (m / s); g represents the gravitational acceleration (m / s2); D represents the pipe inner diameter (m); and θ represents the pipe inclination angle (°). That is The function where H L The liquid level height (m) in the pipeline is given by equation (2-1). It can be seen that the flow pattern transformation model mainly reflects the similarity of the relative liquid level height and the vapor phase corrected Froude number. π2＝(Fr G ) R ＝1 (2-4) Equations (2-3) and (2-4) are two sets of dimensionless transformation relationships for scaled-down design of two-phase water hammer in horizontal pipes, involving the similarity modeling of fluid flow patterns. In the above equations, the subscript R refers to the ratio between the experimental device and the prototype. Under the condition that the gravitational acceleration is equal and the pipes of both the prototype and the experimental device are horizontal, we can obtain from equations (2-2) and (2-4): The key to achieving similar flow pattern transitions within a pipeline lies in ensuring that the similarity between the relative height of the liquid phase fluid and the flow velocity of the gas phase fluid is maintained. For the prototype steam pipe, its relative liquid level height is: To meet the requirements of equation (2-3), the height of the liquid fluid in the experimental section is controlled as follows: H L，t =0.5×D t The vapor phase fluid velocity within the experimental section, according to equation (2-5), is related to both the physical properties of the two-phase fluid and the experimental pipe diameter: Among them, v G，p The steam flow rate inside the prototype pipe; Substituting the relevant values ​​into the calculation, the steam velocity v is obtained. G，t .

9. A method for testing water hammer in two-phase steam condensation, characterized in that, Includes the following steps: First, a reference experiment was conducted in the first stage. Before the experiment began, a certain amount of condensate was injected into the experimental section (3). Start the steam supply unit (1) to generate high-pressure steam, open the electric quick-closing valve (26), the atmospheric discharge valve (27) and the first pressure reducing valve (34) to allow the steam to slowly enter the experimental section (3); The relationship between liquid phase temperature and vapor phase pressure in experimental section (3) and time was investigated under external cooling conditions and without external cooling conditions. When there was no external cooling, the electric quick-closing valve (26), atmospheric discharge valve (27) and first pressure reducing valve (34) were closed after all the air was discharged. The relationship between liquid phase temperature and vapor phase pressure in the pipeline and time was investigated under the condition without external cooling. When there was external cooling, the electric quick-closing valve (26), atmospheric discharge valve (27) and pressure reducing valve were closed after all the air was discharged. Cooling water was allowed to flow through the cooling water channel (10) to cool the liquid in the lower layer of experimental section (3). The relationship between liquid phase temperature and vapor phase pressure in the pipeline and time was investigated and recorded under the condition with external cooling. Then, the second phase of formal experiments was conducted; two major types of differential pressure driving experiments were designed according to the two types of differential pressure driving methods for comparative analysis. The first type of pressure difference driven experiment: the pressure difference experiment between the experimental section (3) and the upstream steam pipeline (2). This type of test condition is a mechanism test, used to conduct a mechanistic study of the two-phase steam condensation water hammer phenomenon, and to compare and analyze with the second type of power plant prototype reproduction experiment; specifically, it includes the following steps: Cooling water is injected into the experimental section (3) to a predetermined volume through the cooling water supply unit (4); Start the steam supply unit (1) to generate high-pressure steam, and set the pressure value of the saturated steam of the steam supply unit (1) to be slightly larger than the steam pressure value of the experimental section (3) in the formal experiment; Open the electric quick-closing valve (26), the atmospheric exhaust valve (27) and the first pressure reducing valve (34) to allow steam to slowly enter the experimental section (3); after all the air is exhausted, close the electric quick-closing valve (26), the atmospheric exhaust valve (27) and the first pressure reducing valve (34); After adjusting the steam pressure of the steam supply unit (1) to the predetermined parameters again, turn on the cooling water to allow the cooling water to flow through the cooling water channel (10) to cool the lower layer of liquid in the experimental section (3). When the parameters of the gas and liquid in the experimental section (3) reach the preset value, the electric quick-closing valve (26) is quickly opened to start the experiment; in a very short time, a complex gas-liquid two-phase steam condensation water hammer phenomenon will occur in the experimental section (3). The second type of differential pressure driven experiment: the differential pressure experiment between the experimental section (3) and the pipeline where the downstream atmospheric discharge valve (27) is located. This type of test condition is a reproduction test similar to the power plant prototype, used to reproduce the actual operating conditions of the power plant; specifically, it includes the following steps: First, set the pressure value of the saturated steam of the steam supply unit (1) to be equal to the steam pressure value of the experimental section (3) in the formal experiment; Open the electric quick-closing valve (26) and the atmospheric discharge valve (27), and adjust the opening of the first pressure reducing valve (34) to allow steam to slowly enter the experimental section (3); Turn on the cooling water to allow it to flow through the cooling water channel (10) and cool the lower layer of liquid in the experimental section (3); After all the air in the experimental section (3) is exhausted, close the atmospheric exhaust valve (27); Once the flow pattern in the experimental section (3) is stable, the opening of the atmospheric discharge valve (27) is quickly adjusted to the predetermined value. In a very short time, a complex gas-liquid two-phase steam condensation water hammer phenomenon will occur in the experimental section (3).

10. The two-phase steam condensate water hammer test method according to claim 9, characterized in that, Method for determining two-phase steam condensate hammer: Based on the steam flow rate, the dimensionless number (Fr-Froude number) is obtained as follows: Where Fr is the Froude number, g is the acceleration due to gravity, L is the characteristic length of the fluid flow, and v is the fluid velocity; Based on the temperature difference, the dimensionless number (Ja-Jabber number) is obtained as follows: Where, ρ L ρ represents the density of the liquid phase. V c represents the gas phase density. PL ΔT represents the specific heat of the liquid phase at normal pressure, L represents the latent heat of vaporization, and ΔT represents the temperature difference between the saturated steam and the bottom of the liquid phase space in the experimental section (3). Based on the amount of condensate in the experimental section (3), the dimensionless number (H / D - ratio of liquid level to diameter) is as follows: Where H is the water level in the condensate pipe at the bottom of the test section, and D is the inner diameter of the pipe in the test section; Based on the above steps, the three dimensionless numbers are calculated. The judgment criteria shown in the table below are used to determine whether the two-phase steam condensation water hammer phenomenon has occurred: 。

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