An adaptive device for improving the loop flow rate and stability of an open natural circulation system.

Abstract

This invention discloses an adaptive device for improving the circulation flow and stability of an open-loop natural circulation system. The device consists of four parts: a bubble generating needle, a self-locking hinge, a flash evaporation initiation point positioning slide rail, and a slide rail housing. This invention features a simple structure and high reliability. By arranging a bubble generating needle inside the pipe, which acts as a vaporization core and agitates the fluid, it promotes the flash evaporation of the mainstream liquid. This invention can automatically locate the flash evaporation initiation point in the rising section of an open-loop natural circulation system, promoting earlier flash evaporation within the pipe and thus solving the problem of pipe vibration caused by circulation flow instability.

Description

Technical Field

[0001] This invention relates to an adaptive device for improving the circulation flow and stability of an open natural circulation system, belonging to the field of enhanced natural circulation technology. Technical Background

[0002] Open-loop natural circulation systems are typically complex nonlinear systems, characterized by large variations in the physical properties of the flowing medium, relatively low operating pressure, and a tendency for flash evaporation to occur within the rising channel. When the fluid in the rising section passes through the heat exchanger and reaches a certain temperature, the static pressure gradually decreases as the fluid flows upwards along the channel. When the fluid saturation temperature at the local pressure is lower than the fluid temperature, flash evaporation occurs within the channel.

[0003] As the fluid flashes, the density difference in the loop increases, and the circulation flow increases. The increased circulation flow at the next moment will cause the heat exchanger outlet temperature to decrease, the flashing initiation point to rise, the two-phase section to decrease again, the density difference in the loop to decrease, and the circulation flow to decrease. This process repeats itself, causing fluctuations in the system flow, which may lead to severe mechanical vibration in the rising pipe.

[0004] Currently, many scholars have summarized methods to reduce the instability of natural circulation flow rates, such as increasing system pressure, reducing inlet subcooling, decreasing outlet resistance of the heating section, and increasing system circulation flow rate. However, for open natural circulation systems, increasing system circulation flow rate by arranging inserts to reduce flow instability is one of the more suitable solutions.

[0005] The following is an example experiment. The insert is a solid cylinder with an outer diameter of 2 mm, and the inner diameter of the riser pipe is 50 mm. The system's circulating flow rate is measured. Observation. Figure 3 It can be seen that without an insert in the pipeline, the system is in an unstable flow state. After inserting an insert into the system pipeline, the change in flow rate within the pipeline is observed. Figure 3 It can be seen that when the flow inside the pipe changes from an unstable state to a stable state, the time-averaged value of the system's circulating flow rate is significantly improved compared to the case without the insertion. Regarding the depth of the insertion, the deeper the insertion, the better the effect. Regarding the location of the insertion, the closer it is to the flash evaporation initiation point, the better the suppression of flow instability; the farther away from the flash evaporation initiation point, the worse the suppression effect. Summary of the Invention

[0006] The technical problem this application aims to solve is that flow fluctuations in an open-loop natural circulation system can adversely affect the system's heat exchange efficiency and stability. To address this problem, the technical solution provided in this application is an adaptive device for improving the circulation flow and stability of an open-loop natural circulation system. The adaptive bubble generator is characterized by being arranged in the rising flash evaporation section of the system loop, and comprises four parts: a bubble generating needle, a self-locking hinge, a flash evaporation initiation point positioning slide rail, and a slide rail housing.

[0007] This invention is achieved through the following technical solution:

[0008] The bubble generating needle is connected to the positioning slider via a self-locking device. The positioning slider can slide freely along the axial direction of the pipe on the positioning slide rail. The slide rail housing covers the self-locking hinge, the positioning slide rail, and the positioning slider. Since the positioning slider needs to move together with the bubble generating needle, grooves are arranged on the side of the slide rail housing that is in contact with the fluid.

[0009] When the open natural circulation system is not in operation, the bubble generating needle is in a free-hanging state, and the positioning slider is located at the top of the slide rail. After the device is put into operation, the bubble generating needle changes from a free-hanging state to a horizontal state due to the propulsion of the fluid. After reaching the horizontal state, the self-locking hinge locks it in the horizontal position. Since the effect of suppressing flow instability is better closer to the flash evaporation initiation point, the positioning slider will drive the bubble generating needle to automatically find the flash evaporation initiation point.

[0010] Preferably, the bubble generating needle is a solid cylinder. The diameter d of the bubble generating needle should be selected to be as small as possible while ensuring the structural strength of the needle. In this way, the resistance introduced into the natural circulation loop due to the presence of the needle can be ignored.

[0011] Preferably, to ensure that the inertial force of the fluid on the bubble generating needle has a component in the tangential direction of the motion trajectory when the device is put into operation, the self-locking hinge has an angle limit, which restricts the bubble generating needle to a position with an angle of 5° in the vertical direction when it is hanging freely, and locks it in the horizontal position after it is swung to a horizontal position.

[0012] Preferably, after the bubble generating needle is raised to a horizontal position, the total length l of the bubble generating needle and the positioning slider should be slightly less than the inner diameter D of the flow channel, and the length difference should be controlled within a small range.

[0013] Preferably, the width s of the groove in the slide rail housing is slightly larger than the diameter of the needle. In order to minimize the inertial force caused by the impact of the fluid on the positioning slider, the groove width should be as small as possible while ensuring that the bubble generating needle can move freely in the groove.

[0014] Preferably, the bubble generating needle and the positioning slider are made of a buoyancy material with a certain density, whose average density is comparable to that of the liquid in the natural circulation loop. Considering that the natural circulation fluid will exert a certain inertial force on the positioning slider, it is recommended that the density of the positioning slider be slightly greater than the liquid density, i.e., 100%-105% of the liquid density. When flash evaporation occurs in the fluid in the loop, the flash evaporation area will be a vapor-liquid mixture with a density lower than that of the single-phase liquid. Since the density of the positioning slider is comparable to that of the liquid, the positioning slider will automatically move to the starting position of the flash evaporation (i.e., the junction area between the vapor-liquid mixture and the single-phase liquid).

[0015] The present invention has the following advantages:

[0016] Compared with the prior art, the present invention starts from the mechanism of flash evaporation heterogeneous nucleation, and sets bubble generating needles in the flash evaporation generation section to increase the local disturbance of the fluid and provide a large number of vaporization nuclei, thereby inducing the early occurrence of flash evaporation, thereby eliminating flow instability and increasing the natural circulation flow rate of the system, providing a new idea and solution for strengthening natural circulation.

[0017] In this invention, the slide rail housing covers the positioning slider and the slide rail, thereby minimizing the inertial force exerted on the slider by the fluid and preventing the fluid inertial force from interfering with the automatic search for the flash point. Consequently, this device, when arranged inside the pipeline, will not cause significant resistance to the fluid flow within the loop.

[0018] This invention employs adaptive passive turbulence technology, requiring no external energy drive. The bubble generating needle can be driven by a positioning slider to automatically find the flash evaporation starting point on the positioning slide rail, allowing the bubble generating needle to function in the most suitable position.

[0019] This invention features a simple structure, easy installation, and convenient maintenance, and can be directly modified into existing natural circulation system pipelines. Attached Figure Description

[0020] Figure 1 The present invention provides an adaptive device for improving the loop circulation flow of an open natural circulation system. In the figure, the state of the bubble generating needle (a) is the state before the device is started, and the state (b) is the state after the device is put into operation.

[0021] Figure 2 This is a front view of an adaptive device for increasing the loop circulation flow of an open natural circulation system, as shown in the embodiment.

[0022] Figure 3 This is a graph showing the change in system circulation flow over time.

[0023] Label Explanation:

[0024] 1-PCS rising section pipe, 2-fluid inlet, 3-fluid outlet, 4-bubble generating needle, 5-self-locking hinge, 6-flash evaporation starting point positioning slide rail, 7-slide rail housing, d-outer diameter of bubble generating needle, D-inner diameter of flow pipe, l-total length of bubble generating needle and positioning slider, s-width of slot in slide rail housing. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0026] Example

[0027] This embodiment provides an adaptive device for increasing the loop circulation flow of an open natural circulation system, such as... Figure 1 As shown, the device consists of four parts: a bubble generating needle, a self-locking hinge, a flash evaporation initiation point positioning slide rail, and a slide rail housing.

[0028] This device is installed in the rising flash evaporation section of the open natural circulation system loop. When the open natural circulation system is not in operation, the system loop is filled with fluid, but the flow velocity is almost zero. Under the combined action of gravity and buoyancy, the bubble generating needle hangs freely, and the positioning slider is located at the top of the slide rail.

[0029] After the system starts operating, the fluid velocity within the system loop gradually increases. Under the influence of fluid inertia, the bubble generating needle gradually swings upward along the hinge from a free-hanging state, eventually stopping at a horizontal position. Once horizontal, the self-locking hinge locks it in place. After the bubble generating needle is locked, flash evaporation begins to occur in the rising section as the system continues to operate. Driven by the positioning slider, the bubble generating needle automatically finds the flash evaporation initiation point on the positioning rail and stops at that point.

[0030] The principle is explained as follows:

[0031] After flashing occurs in the rising loop, the fluid density in the two-phase section is significantly lower than that in the single-phase section. Through mechanical balance, the positioning slider and bubble generating needle automatically locate the flashing initiation point within the flashing section on the positioning track. Within the flashing section, as the fluid flows past the bubble generating needle, it disturbs the mainstream liquid, preventing overheating. The bubble generating needle also reduces the local static pressure of the nearby fluid. When the fluid temperature exceeds its saturation temperature at the current pressure, local flashing occurs, causing water to vaporize and form tiny bubbles. These tiny bubbles, carried by the mainstream fluid, are carried downstream in the system pipeline. They provide vaporization nuclei for the flashing of the superheated mainstream liquid, making the flashing point of the mainstream liquid relatively stable and ensuring the flow stability of the open natural circulation system. Because the flow in the rising section of the system is relatively stable, the average flow rate of the system increases, and flow fluctuations are significantly reduced, thereby reducing pipeline vibration.

[0032] In summary, the specific embodiments described above are only for further explanation of the purpose, design scheme, and advantages of the present invention, and are not intended to limit the scope of protection of the present invention. Depending on the actual parameters of different initial natural circulation systems, this application may select materials of different densities and component sizes, but the basic principle of the device remains the same.

[0033] This invention discloses an adaptive device for improving the circulation flow and stability of an open-loop natural circulation system. The device consists of four parts: a bubble generating needle, a self-locking hinge, a flash evaporation initiation point positioning slide rail, and a slide rail housing. This invention features a simple structure and high reliability. By arranging a bubble generating needle inside the pipe, which acts as a vaporization core and agitates the fluid, it promotes the flash evaporation of the mainstream liquid. This invention can automatically locate the flash evaporation initiation point in the rising section of an open-loop natural circulation system, promoting earlier flash evaporation within the pipe and thus solving the problem of pipe vibration caused by circulation flow instability.

Claims

1. An adaptive device for improving the circulation flow and stability of an open natural circulation system, characterized in that: The device is arranged in the flash section of the open natural circulation system loop; it includes four parts: a bubble generating needle, a self-locking hinge, a positioning slide rail, and a slide rail housing; the bubble generating needle is connected to the positioning slider through the self-locking hinge, and the positioning slider can slide freely along the axial direction of the pipe on the positioning slide rail. After the device is put into operation, the bubble generating needle changes from a free hanging state to a horizontal state due to the push of the fluid. After reaching the horizontal state, the self-locking hinge locks it in the horizontal position, and the positioning slider drives the bubble generating needle to automatically find the flash point on the positioning slide rail.

2. The adaptive device for improving the loop flow rate and stability of an open natural circulation system according to claim 1, characterized in that: The self-locking hinge has an angle limit, and its rotation range is from 5° to 90° with respect to the vertical direction.

3. The adaptive device for improving the loop flow rate and stability of an open natural circulation system according to claim 1, characterized in that: The bubble generating needle and the positioning slider should be made of a buoyancy material with a certain density, and its average density should be 100%-105% of the fluid density.

4. The adaptive device for improving the loop flow rate and stability of an open natural circulation system according to claim 1, characterized in that: The slide rail housing covers the self-locking hinge, positioning slider, and positioning slide rail. The surface of the housing has a groove on the side of the bubble generating needle. The width s of the groove is slightly larger than the diameter of the needle to reduce the inertial force caused by the fluid impacting the positioning slider.

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