Research system for influence rule of heat transfer coefficient of water in cooling pipeline of water-turbine generator set

Abstract

The invention discloses a research system for a water heat transfer coefficient influence rule in a water-turbine generator set cooling pipeline, and belongs to the technical field of water-turbine generator set cooling, and the research system comprises a water supply system which is used for providing a circulating working medium with controllable parameters; the preheating system is used for preheating the circulating working medium conveyed by the water supply system, so that the working medium reaches a set inlet temperature; the visual experiment system is used for receiving the working medium preheated by the preheating system, heating the working medium at specific power to induce and maintain a controllable boiling process, and synchronously completing visual observation and multi-parameter measurement of a heat transfer process; and the condensation recovery system is used for condensing the high-temperature working medium experimented by the visual experiment system and constructing a working medium circulation loop. According to the method, the problems that a micro transient phenomenon is difficult to capture by a heat exchange characteristic analysis method and a theoretical rule is difficult to accurately and quantitatively research by an experimental visualization method can be simultaneously solved, so that comprehensive and accurate research is realized.

Description

Technical Field

[0001] This invention relates to the field of cooling technology for hydro-generator sets, specifically to a research system for studying the influence of the heat transfer coefficient of water in the cooling pipes of hydro-generator sets. Background Technology

[0002] In the operation of large hydropower stations, water-cooled generator sets are one of the core pieces of equipment, and the performance of their cooling systems directly affects the safe, stable operation and service life of the units. Differences in the fluid characteristics of the water flow within the cooling system significantly influence the heat transfer efficiency of the water, thus having a significant impact on the heat dissipation effect and equipment temperature of the turbine unit. Therefore, in-depth research into the evolution of the heat transfer coefficient of water within the cooling system piping is of great significance for optimizing cooling system design and improving the operational reliability of the units.

[0003] In the existing technology, two representative methodological systems have been mainly formed for the above-mentioned research: One approach is the heat transfer characteristic analysis method. This method comprehensively considers key parameters in the heat transfer process, including experimentally measured heat transfer characteristics (such as the Nusselt number Nu) and experimentally measured resistance characteristics (such as the friction coefficient f), and uses heat transfer correlations for prediction and fitting. The aim is to systematically reveal the evolution of the water heat transfer coefficient with varying operating conditions (such as temperature, flow rate, and heat flux density). This method primarily focuses on revealing theoretical patterns and numerical calculations. Its advantage lies in establishing universal correlation models, but its disadvantage is that it is difficult to directly capture and deeply reveal microscopic and transient phenomena such as the evolution of supercooled boiling bubbles under special operating conditions (such as transient processes, local hot spots, or complex flow patterns).

[0004] Another approach is the experimental visualization method. This method focuses on directly observing microscopic phenomena during the boiling process. Its core lies in using high-speed imaging and other technologies to capture and analyze the dynamic behaviors of bubbles, such as nucleation, growth, detachment, and aggregation, in real time. Simultaneously, it combines this with the calculation or prediction of the critical heat flux (CHF) to correlate this visualization information with macroscopic heat transfer performance, thereby exploring the evolution of the water heat transfer coefficient, especially near the critical state. Its core advantage is the ability to directly and dynamically observe the actual boiling evolution process. However, its limitation is that it is difficult to conduct precise quantitative research and effective theoretical calculations for evolution under highly idealized or simplified conditions (such as undisturbed ideal boiling models based on purely theoretical assumptions), as the observation results are easily affected by the complexity of actual experimental conditions.

[0005] In summary, the two existing research methods each have their own focus in revealing the influence of water heat transfer coefficient in the cooling system pipes of hydro-generator units, but they also have certain limitations and cannot fully and accurately meet the relevant research needs. Therefore, there is an urgent need for a technical solution that can overcome the above-mentioned defects. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a system for studying the influence of water heat transfer coefficient in the cooling pipes of a hydro-generator unit. It aims to simultaneously solve the problems that heat transfer characteristic analysis methods struggle to capture microscopic transient phenomena and that experimental visualization methods are insufficient for accurately quantifying theoretical laws, thereby achieving comprehensive and precise research. To achieve the above objectives, this invention provides the following technical solution: A research system on the influence of water heat transfer coefficient in the cooling pipes of hydro-generator units includes: A water supply system is used to provide circulating working fluid with controllable parameters; A preheating system is used to preheat the circulating working fluid supplied by the water supply system so that the working fluid reaches the set inlet temperature. A visualization experimental system is used to receive the working fluid after it has been preheated by the preheating system, to heat the working fluid with a specific power to induce and maintain a controllable boiling process, and to simultaneously complete the visualization observation and multi-parameter measurement of the heat transfer process. A condensation recovery system is used to condense the high-temperature working fluid after the experiment conducted by the visualization experimental system and to construct a working fluid circulation loop. The water supply system, preheating system, visualization experimental system, and condensate recovery system are connected sequentially through pipelines.

[0007] Furthermore, the water supply system includes a high-pressure constant flow pump; the high-pressure constant flow pump is used to provide circulating working fluid and to set and maintain the flow rate and pressure of the circulating medium.

[0008] Furthermore, a valve and a mass flow meter are sequentially installed on the pipeline between the water supply system and the preheating system; the mass flow meter is used to measure the mass flow rate of the working fluid at the inlet end of the preheating system.

[0009] Furthermore, the preheating system includes a preheating pipe and an electric heater; the inlet of the preheating pipe is connected to the outlet of the water supply system, and the outlet of the preheating pipe is connected to the inlet of the visualization experimental system; the electric heater is used to preheat the working fluid flowing through the preheating pipe.

[0010] Furthermore, the visualization experimental system includes an experimental pipe, a heating element, a high-speed camera, and a data acquisition module; the inlet of the experimental pipe is connected to the outlet of the preheating system, and the outlet of the experimental pipe is connected to the inlet of the condensation recovery system; the pipe wall of the experimental pipe is provided with a visualization window; the heating element is located on the outer wall of the experimental pipe and is used to heat the working fluid at a specific power to induce and maintain a controllable boiling process; the high-speed camera is positioned facing the visualization window and is used to capture and record the nucleation, growth, detachment, and aggregation behavior of bubbles during the boiling process in real time; the data acquisition module is electrically connected to the high-speed camera.

[0011] Furthermore, the experimental pipeline has a composite layered structure; the experimental pipeline includes an intermediate layer and two reinforcing layers; the intermediate layer has visibility characteristics, and a flow channel for the working fluid is opened inside the intermediate layer; the two reinforcing layers are respectively attached and fixed to the outside of the intermediate layer, and are fastened together by connectors; one of the two reinforcing layers has an inlet and an outlet communicating with the flow channel, and one of the two reinforcing layers has a visibility window; the heating element is a heating plate, and the heating plate is attached and fixed to the outer wall of one of the reinforcing layers.

[0012] Furthermore, the intermediate layer includes two parallel and oppositely arranged polycarbonate plates, each with a groove on its contact surface, and the grooves of the two polycarbonate plates correspondingly form flow channels; the fixing layer is a stainless steel plate.

[0013] Furthermore, temperature sensors are installed at both the inlet and outlet of the experimental pipeline; differential pressure gauges and pressure gauges are connected to both ends of the experimental pipeline; the pressure gauges, differential pressure gauges, and temperature sensors are all electrically connected to the data acquisition module.

[0014] Furthermore, the condensation recovery system includes a condenser and a water storage tank connected in sequence; the inlet of the condenser is connected to the outlet of the visualization experimental system; and the outlet of the water storage tank is connected to the inlet of the water supply system.

[0015] Furthermore, a back pressure valve is provided on the pipeline between the condenser and the water storage tank.

[0016] The beneficial effects of this invention are: 1. This invention establishes a mutual feedback verification mechanism between theoretical research and experimental observation through deep coupling, opening up a channel between the predicted laws of theoretical models and the laws revealed by experimental observations, enabling mutual verification, complementarity, and iterative optimization. This fusion method effectively overcomes the limitations of single methods, compensating for the deficiency of purely theoretical methods in capturing transient microscopic phenomena, and solving the problem of purely experimental methods in accurately quantifying the laws of idealized models. This greatly enhances the reliability and confidence of the obtained evolution law of water heat transfer coefficient under complex and variable operating conditions.

[0017] 2. This invention can integrate and correlate research data from heat transfer characteristic analysis and experimental visualization methods, changing the situation where the data of the two methods are fragmented and difficult to analyze together. It provides more comprehensive data support for revealing the influence law of heat transfer coefficient and helps to deeply explore the hidden laws behind the data from multiple dimensions.

[0018] 3. This invention addresses the special structures that may exist in the cooling system of hydro-generator units, such as irregularly shaped pipes and curved pipes. Through targeted structural design and parameter control, the system achieves in-depth research on the heat transfer law under special pipe structures, making up for the shortcomings of existing technologies in the study of special pipe structures. At the same time, with the help of multi-parameter coordinated control and monitoring, it can effectively study the heat transfer law under the coupled effect of multiple operating parameters such as temperature, flow rate, and heat flux density, solving the problem of the difficulty of research in multi-operating-condition coupled scenarios in existing methods, and making the research more in line with actual operating conditions.

[0019] 4. This invention can obtain accurate and comprehensive laws governing the influence of water heat transfer coefficient, providing a scientific basis for cooling system pipeline design and parameter setting, helping to optimize cooling system performance, improve the operational reliability and efficiency of hydro-generator units, reduce equipment failure risks, and has significant practical application value. Attached Figure Description

[0020] Figure 1 A schematic diagram of the overall structure of the research system provided by this invention; Figure 2 This is a schematic diagram of the experimental pipeline provided by the present invention; The attached diagram is labeled as follows: 1. High-pressure constant flow pump; 2. Valve; 3. Mass flow meter; 4. Preheating pipe; 5. Experimental pipe; 6. High-speed camera; 7. Temperature sensor; 8. Differential pressure gauge; 9. Pressure gauge; 10. Condenser; 11. Water storage tank; 12. Back pressure valve; 13. Stainless steel plate; 14. Inlet; 15. Outlet; 16. Visualization window; 17. Polycarbonate plate; 18. Groove; 19. Heating plate. Detailed Implementation

[0021] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore merely examples and should not be used to limit the scope of protection of the present invention. Those skilled in the art should understand that the present invention can be implemented even without certain specific details. In some other embodiments, methods, means, equipment, and steps well known to those skilled in the art are not described in detail in order to highlight the spirit of the present invention.

[0022] Unless otherwise specified, in this invention, terms such as "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," "x-direction," "y-direction," and "z-direction" 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 this invention and 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, the terms used to describe orientation or positional relationships in this invention are for illustrative purposes only and should not be construed as limiting this patent. For those skilled in the art, the specific meaning of the above terms can be understood in conjunction with the accompanying drawings and according to the specific circumstances.

[0023] Example 1 See attached Figures 1-2 This embodiment provides a system for studying the influence of water heat transfer coefficient in the cooling pipes of a hydro-generator unit. It includes four subsystems: a water supply system, a preheating system, a visualization experimental system, and a condensation recovery system. These systems are connected by pipelines, forming a complete closed-loop circuit. The specific functions and connections are as follows: The water supply system provides a controllable circulating working fluid, which can be water. Specifically, the water supply system includes a high-pressure constant flow pump 1, which provides the circulating working fluid and sets and maintains the flow rate and pressure of the circulating medium. The high-pressure constant flow pump 1 can be a plunger-type precision high-pressure constant flow pump. The output end of the water supply system is the outlet of the high-pressure constant flow pump 1, which is connected to the input end of the preheating system via a pipeline. On the connecting pipeline, a valve 2 and a mass flow meter 3 are installed in series along the flow direction of the working fluid. The valve 2 controls the flow of the working fluid from the water supply system to the preheating system, while the mass flow meter 3 is installed close to the inlet of the preheating pipe 4 of the preheating system to measure the mass flow rate of the working fluid entering the preheating system in real time, ensuring that the working fluid parameters are monitorable. The valve 2 can be a stainless steel manual shut-off valve; the mass flow meter 3 can be a Coriolis mass flow meter.

[0024] The preheating system is used to preheat the circulating working fluid supplied by the water supply system to reach the set inlet temperature. Specifically, the preheating system includes a preheating pipe 4 and an electric heater. The preheating pipe 4 can be made of 304 stainless steel, and the electric heater can be a wound tubular electric heater. The input end of the preheating system is the inlet of the preheating pipe 4, which is connected to the outlet of the high-pressure constant flow pump 1 through a pipeline; the output end of the preheating system is the outlet of the preheating pipe 4, which is connected to the input end of the visualization experimental system through a pipeline. The electric heater is used to preheat the working fluid flowing through the preheating pipe 4.

[0025] The visualization experimental system receives the working fluid preheated by the preheating system, heats it to a specific power to induce and maintain a controllable boiling process, and simultaneously performs visualized observation and multi-parameter measurement of the heat transfer process. Specifically, the visualization experimental system includes an experimental pipe 5, a heating element, a high-speed camera 6, and a data acquisition module. The input end of the visualization experimental system is the inlet 14 of the experimental pipe 5, which is connected to the output end of the preheating pipe 4 via a pipeline; the output end of the visualization experimental system is the outlet 15 of the experimental pipe 5, which is connected to the input end of the condensation recovery system via a pipeline. The pipe wall of the experimental pipe 5 has a visualization window 16. The heating element is located on the outer wall of the experimental pipe 5 and is used to heat the working fluid to a specific power to induce and maintain a controllable boiling process. The high-speed camera 6 is positioned directly opposite the visualization window 16 to capture and record the nucleation, growth, detachment, and aggregation behavior of bubbles during the boiling process in real time. Temperature sensors 7 are installed at both the inlet and outlet of the experimental pipe 5. Differential pressure gauges 8 and pressure gauges 9 are connected to both ends of the experimental pipe 5. The high-speed camera 6, pressure gauges 9, differential pressure gauges 8 and temperature sensors 7 are all electrically connected to the data acquisition module. The visualized image data recorded by the high-speed camera 6 and the macroscopic operating condition data collected by the multi-source sensors are synchronized in time, correlated, and processed in depth in the later stage to reveal the dynamic evolution law of the heat transfer coefficient under different conditions. The high-speed camera 6 can be a Phantom V2512 model with a resolution of 1920×1080, a frame rate of 1000fps, and a 100mm fixed-focus lens; the temperature sensor 7 can be a K-type thermocouple; the differential pressure gauge 8 can be a Rosemount 3051CD differential pressure transmitter; the pressure gauge 9 can be a Rosemount 3051TG pressure transmitter; the data acquisition module can be an NICDAQ-9178 data acquisition card, equipped with an eight-channel analog input module, a sampling frequency of 1kHz, and can simultaneously receive image data from the high-speed camera 6 and signals from various sensors to achieve time-synchronous acquisition of multi-source data with a synchronization accuracy of 1ms. Preferably, the research system also includes a human-machine interface control unit, which is electrically connected to the high-pressure constant current pump 1, electric heater, heating plate 19, high-speed camera 6, and other equipment in the four subsystems. For example, a 10-inch touchscreen industrial all-in-one machine can be selected, with built-in system control software. It can set and monitor parameters such as water flow rate, system pressure, preheating temperature, and heating power of experimental pipe 5 through the touchscreen, and generate standardized experimental operation procedures to reduce operation complexity. It also has experimental data storage and export functions, supporting data formats including Excel, CSV, and image formats.

[0026] The condensation recovery system is used to condense the high-temperature working fluid after experiments conducted by the visualization experimental system and to construct a working fluid circulation loop. Specifically, the condensation recovery system includes a condenser 10 and a water storage tank 11 connected in sequence. The condenser 10 can be a shell-and-tube condenser, and the water storage tank 11 can be a 100L water storage tank. The output end of the condensation recovery system is the outlet of the water storage tank 11, which is connected to the inlet of the high-pressure constant flow pump 1 of the water supply system through a pipeline, forming a complete and reusable closed-loop circulation system. A back pressure valve 12 is also installed on the pipeline between the outlet of the water storage tank 11 and the inlet of the high-pressure constant flow pump 1 to prevent backflow of the working fluid when the high-pressure constant flow pump 1 stops, ensuring system safety. The outlet of the water storage tank 11 can be higher than the inlet of the high-pressure constant flow pump 1, using gravity to assist the working fluid in flowing into the high-pressure constant flow pump 1, reducing the pump's suction resistance. The pipeline interface can use quick-connect couplings for easy pipeline disassembly during system maintenance, and the quick-connect couplings have built-in sealing rings to ensure no leakage during the working fluid delivery process.

[0027] Experimental pipe 5 serves as the core section of the visualization experimental system. Here, the water flow is electrically heated to a specific power, inducing and maintaining a controllable boiling process. The specific structure of experimental pipe 5 is as follows: like Figure 2 As shown, the experimental pipe 5 has a composite layered structure. Specifically, the experimental pipe 5 includes an intermediate layer and two reinforcing layers. The two reinforcing layers are respectively attached and fixed to the outside of the intermediate layer and fastened together by bolts or other connectors, serving as the outer reinforcing structure. The intermediate layer has visibility characteristics, and a flow channel for the working fluid is formed inside the intermediate layer. Preferably, the intermediate layer includes two parallel and oppositely arranged polycarbonate plates 17, each with a groove 18 on its contact surface. The groove 18 extends along the length of the polycarbonate plate 17, and the grooves 18 of the two polycarbonate plates 17 correspondingly form flow channels. One of the two reinforcing layers has an inlet 14 and an outlet 15 communicating with the flow channel, and another of the two reinforcing layers has a visibility window 16. Preferably, the fixing layer is a 304 stainless steel plate 13. The heating element is a heating plate 19, which is attached and fixed to the outer wall of one of the reinforcing layers. The heating plate 19 can be a ceramic heating plate 19, which is attached and fixed to the outer wall of the stainless steel plate 13, and the heating power is precisely controlled by a voltage regulator.

[0028] This invention constructs a closed-loop research system to control and monitor the water flow parameters and thermal conditions within the cooling system pipes of a hydro-generator unit, thereby studying their impact on the evolution of the heat transfer coefficient. The specific workflow is as follows: 1. High-voltage constant current drive.

[0029] Turn on the high-pressure constant flow pump 1 in the water supply system to provide a stable and controllable circulating water flow for the entire experimental pipeline; use the high-pressure constant flow pump 1 to precisely adjust and set the target parameters, including the working fluid flow rate and pressure in the cooling system pipeline of the water turbine generator set, to ensure that the working fluid flow parameters remain stable throughout the experiment.

[0030] 2. Preheating.

[0031] The water flow driven by the water supply system passes through valve 2 and mass flow meter 3 in sequence, and then enters the preheating pipe 4 of the preheating system. The electric heater matched with the preheating pipe 4 is started to preheat the water flow with precise temperature control until the working medium reaches the inlet temperature set in the experiment. A temperature sensor 7 can be installed on the preheating pipe 4 to monitor the working medium temperature in real time.

[0032] 3. Experimental section boiling heating, simultaneous multi-parameter measurement and visualization observation.

[0033] The preheated water is transported to the experimental pipe 5 of the visualization experimental system through the pipeline; the heating element set on the outer wall of the experimental pipe 5 is activated, and heat is provided to the working medium by setting a specific heating power, inducing the water in the experimental pipe 5 to form a boiling state, and continuously maintaining this controllable boiling process to simulate the key thermal working conditions of the water turbine generator cooling system. Start the high-speed camera 6 facing the visualization window 16 of the experimental pipe 5, and capture and record the key microscopic dynamic behaviors of bubbles such as nucleation, growth, detachment and aggregation during boiling in real time and at a resolution of no less than 1920×1080 and a frame rate of 1000fps, forming visualized image data. Turn on the temperature sensor 7 at the inlet / outlet of experimental pipeline 5, the differential pressure gauge 8 and pressure gauge 9 at both ends of the pipeline, and simultaneously, in conjunction with the previously activated mass flow meter 3, collect macroscopic parameters at key locations in the experimental pipeline in real time, including working fluid temperature, pressure, pressure drop along the pipeline, and working fluid flow rate monitored at multiple points. All macroscopic operating condition data (temperature, pressure, differential pressure, flow rate) collected by sensors and components, and microscopic image data captured by high-speed camera 6 are transmitted in real time to the data acquisition module of the visualization experimental system, realizing the time-synchronized integration of multi-source data.

[0034] 4. Data processing and pattern analysis.

[0035] After the experiment, the synchronous data stored in the data acquisition module was post-processed: the microscopic image data and macroscopic parameter data were precisely aligned along the time axis to ensure that the phenomena and parameters at the same moment corresponded one-to-one; through the data association algorithm, the correspondence between the microscopic bubble dynamic behavior (such as bubble density and escape frequency) and the macroscopic heat transfer / flow parameters (such as heat flux density, temperature difference, and flow velocity) was established, and then the dynamic change characteristics of the heat transfer coefficient under different water flow parameters and thermal conditions were quantitatively analyzed to reveal its evolution law.

[0036] 5. Condensation recovery and closed-loop circulation.

[0037] The boiling water, after completing the experimental measurement, flows out from the outlet of the experimental pipe 5 of the visualization experimental system and enters the condenser 10 of the condensation recovery system through the pipeline. After being fully cooled by the condenser 10, the high-temperature working fluid is cooled to below 30°C. The condensed working fluid flows through the pressure relief valve on the pipeline between the condenser 10 and the water storage tank 11. The pressure relief valve stabilizes the system pressure and avoids the risk of overpressure. Then it safely flows into the water storage tank 11. The low-temperature working fluid in the water storage tank 11 flows back to the inlet of the water supply system through the pipeline and re-enters the experimental process of "high-pressure constant flow drive - preheating - experiment and measurement observation", forming a complete and repeatable closed-loop circulation system, realizing the recycling of the working fluid and the continuous conduct of the experiment.

[0038] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. Technical aspects, shapes, and structures not described in detail in this invention are all well-known technologies.

Claims

1. A system for studying the influence of water heat transfer coefficient in cooling pipes of hydro-generator units, characterized in that, include: A water supply system is used to provide circulating working fluid with controllable parameters; A preheating system is used to preheat the circulating working fluid supplied by the water supply system so that the working fluid reaches the set inlet temperature. A visualization experimental system is used to receive the working fluid after it has been preheated by the preheating system, to heat the working fluid with a specific power to induce and maintain a controllable boiling process, and to simultaneously complete the visualization observation and multi-parameter measurement of the heat transfer process. A condensation recovery system is used to condense the high-temperature working fluid after the experiment conducted by the visualization experimental system and to construct a working fluid circulation loop. The water supply system, preheating system, visualization experimental system, and condensate recovery system are connected sequentially through pipelines.

2. The research system for studying the influence of water heat transfer coefficient in the cooling pipes of a hydro-generator unit according to claim 1, characterized in that: The water supply system includes a high-pressure constant flow pump (1); the high-pressure constant flow pump (1) is used to provide circulating working fluid and to set and maintain the flow rate and pressure of the circulating medium.

3. The research system for studying the influence of water heat transfer coefficient in the cooling pipes of a hydro-generator unit according to claim 1, characterized in that: A valve (2) and a mass flow meter (3) are sequentially installed on the pipeline between the water supply system and the preheating system; the mass flow meter (3) is used to measure the mass flow rate of the working fluid at the inlet end of the preheating system.

4. The research system for studying the influence of water heat transfer coefficient in the cooling pipes of a hydro-generator unit according to claim 1, characterized in that: The preheating system includes a preheating pipe (4) and an electric heater; the inlet of the preheating pipe (4) is connected to the outlet of the water supply system, and the outlet of the preheating pipe (4) is connected to the inlet of the visualization experimental system; the electric heater is used to preheat the working medium flowing through the preheating pipe (4).

5. The research system for studying the influence of water heat transfer coefficient in the cooling pipes of a hydro-generator unit according to claim 1, characterized in that: The visualization experimental system includes an experimental pipe (5), a heating element, a high-speed camera (6), and a data acquisition module; the inlet of the experimental pipe (5) is connected to the outlet of the preheating system, and the outlet of the experimental pipe (5) is connected to the inlet of the condensation recovery system; the pipe wall of the experimental pipe (5) is provided with a visualization window (16); the heating element is located on the outer wall of the experimental pipe (5) and is used to heat the working fluid with a specific power to induce and maintain a controllable boiling process; the high-speed camera (6) is set facing the visualization window (16) and is used to capture and record the nucleation, growth, detachment, and aggregation behavior of bubbles during the boiling process in real time; the data acquisition module is electrically connected to the high-speed camera (6).

6. The research system for studying the influence of water heat transfer coefficient in the cooling pipes of a hydro-generator unit according to claim 5, characterized in that: The experimental pipe (5) is a composite layered structure; the experimental pipe (5) includes an intermediate layer and two reinforcing layers; the intermediate layer has a visualization feature, and a flow channel for the working fluid is opened inside the intermediate layer; the two reinforcing layers are respectively attached and fixed to the outside of the intermediate layer, and are fastened together by connectors; one of the two reinforcing layers is provided with an inlet (14) and an outlet (15) communicating with the flow channel, and one of the two reinforcing layers is provided with a visualization window (16); the heating element is a heating plate (19), and the heating plate (19) is attached and fixed to the outer wall of one of the reinforcing layers.

7. The system for studying the influence of water heat transfer coefficient in the cooling pipes of a hydro-generator unit according to claim 6, characterized in that: The intermediate layer includes two parallel polycarbonate plates (17) arranged opposite each other. The contact surfaces of the two polycarbonate plates (17) are provided with grooves (18), and the grooves (18) of the two polycarbonate plates (17) form flow channels accordingly. The fixing layer is a stainless steel plate (13).

8. The research system for studying the influence of water heat transfer coefficient in the cooling pipes of a hydro-generator unit according to claim 5, characterized in that: Temperature sensors (7) are provided at both the inlet and outlet of the experimental pipe (5); differential pressure gauges (8) and pressure gauges (9) are connected to both ends of the experimental pipe (5); the pressure gauges (9), differential pressure gauges (8) and temperature sensors (7) are all electrically connected to the data acquisition module.

9. The system for studying the influence of water heat transfer coefficient in the cooling pipes of a hydro-generator unit according to claim 1, characterized in that: The condensation recovery system includes a condenser (10) and a water storage tank (11) connected in sequence; the inlet of the condenser (10) is connected to the outlet of the visualization experimental system; and the outlet of the water storage tank (11) is connected to the inlet of the water supply system.

10. The research system for studying the influence law of water heat transfer coefficient in the cooling pipe of a hydro-generator unit according to claim 9, characterized in that: A back pressure valve (12) is provided on the pipeline between the condenser (10) and the water storage tank (11).

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