Cavitation control device for drain pipeline of nuclear power station

Abstract

The invention particularly relates to a cavitation control device for a drain pipeline of a nuclear power station, and belongs to the technical field of corrosion prevention of inner walls of pipelines. The throttling orifice plate is used for connecting the tail end of the drain pipeline with the head end of the flash tank in a welding manner; a sleeve is arranged outside the drainage pipeline; the central axis of the throttling orifice plate coincides with the central axis of the drainage pipeline, a first through hole is formed in the center of the throttling orifice plate, and second through holes are symmetrically formed in the two ends, perpendicular to the diameter direction of the central axis, of the throttling orifice plate. The throttling orifice plate is formed by cutting and trepanning a whole forge piece, and design parameters of the throttling orifice plate are simulated and optimized through CFD of the drainage pipeline. By improving the design and installation of the throttling orifice plate, the situations that the pipe wall is gradually thinned due to the fact that cavitation impacts the pipe wall and the drainage pipeline is impacted due to the fact that water flow impacts accumulated water are avoided, the design parameters of the throttling orifice plate are subjected to CFD simulation optimization of the drainage pipeline, and it is ensured that the design parameters of the throttling orifice plate meet the design requirements; and the running safety of the drainage pipeline is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of anti-corrosion of pipeline inner walls, and particularly to a cavitation control device for drain pipelines in nuclear power plants. Background Art

[0002] During the operation of a nuclear power plant, the steam turbine drain system in the nuclear power plant undertakes the task of draining the steam extracted from the steam turbine. The steam turbine drain system in the nuclear power plant mainly consists of a steam trap, a drain pipeline, and a flash tank.

[0003] The steam trap completes the separation of water and gas in the steam extracted from the steam turbine, and the generated drain water is discharged to the flash tank through the drain pipeline. The water-gas separation effect of the steam trap ensures that the steam in the steam extracted from the steam turbine does not enter the flash tank, thereby maintaining a low-pressure environment in the flash tank.

[0004] A fixed orifice plate is installed in the drain pipeline. The orifice plate has a central opening and is fixed in the drain pipeline by welding. The orifice plate forms a constriction by reducing the aperture at an appropriate position in the drain pipeline. When the drain water flows through the constriction in the drain pipeline, it becomes thinner or contracts. When the drain water flows in the drain pipeline, due to the local resistance of the orifice plate, the pressure of the drain water downstream of the orifice plate decreases and energy is lost. The vibration of the drain pipeline and the erosion and perforation of the pipe fittings behind the orifice plate will cause many problems during the operation of the nuclear power plant, directly affecting the safety and economy of the nuclear power plant operation.

[0005] During the actual service process of the steam turbine drain system in the nuclear power plant, the drainage method of the steam trap is intermittent drainage, and the design structure of the orifice plate is only to open a through hole in the center of the orifice plate, which causes the drain pipeline upstream of the orifice plate to be very easy to accumulate water. The continuous impact of the water flow on the accumulated water generates oscillation, which will cause a large impact on the drain pipeline; the gas-liquid two-phase flow generated after the drain water passes through the orifice plate for throttling and pressure reduction forms an eddy current at the back of the orifice plate, eroding the pipe wall at the eddy current, making the pipe wall at the eddy current gradually thinner. These factors seriously threaten the service life of the steam turbine drain system in the nuclear power plant, reduce the economic benefits of the nuclear power plant, and increase the difficulty of equipment maintenance. Summary of the Invention

[0006] One of the purposes of the present invention is to provide a cavitation control device for drain pipelines in nuclear power plants, to solve the problem that the drain pipeline downstream of the existing orifice plate is cavitated and impacts the pipe wall, resulting in the pipe wall gradually thinning. By improving the design and installation of the orifice plate, cavitation of the drain pipeline is avoided, thereby avoiding the pipe wall being thinned due to cavitation impact on the pipe wall.

[0007] A second object of the present invention is to provide a cavitation control device for a nuclear power plant's drain pipeline, which solves the problems that the drainer drains intermittently, the upstream drain pipeline of the existing orifice plate is prone to water accumulation, and the water flow impacts the accumulated water to generate oscillation and impact on the drain pipeline. By improving the design and installation of the orifice plate, water accumulation in the upstream drain pipeline of the orifice plate is avoided, thereby avoiding the impact on the drain pipeline caused by the water flow impacting the accumulated water to generate oscillation.

[0008] To achieve the above object, the present invention provides the following technical solutions: A cavitation control device for a nuclear power plant's drain pipeline includes an orifice plate; the orifice plate connects the end of the drain pipeline and the head of the flash tank together by welding; a sleeve is provided outside the drain pipeline; The central axis of the orifice plate coincides with the central axis of the drain pipeline. A first through hole is opened in the center of the orifice plate, and second through holes are symmetrically opened at both ends in the diameter direction perpendicular to the central axis of the orifice plate; The orifice plate is formed by cutting and opening a whole forging, and the design parameters of the orifice plate are optimized through CFD simulation of the drain pipeline.

[0009] As one realizable way, both the first through hole and the second through hole are circular through holes; the design parameters of the orifice plate include the diameter of the first through hole, the diameter of the second through hole, and the fluid flow rate under the rated working condition at the inlet of the orifice plate; the design parameters of the orifice plate are optimized through CFD simulation of the drain pipeline, including the following steps: Step 101: Perform CFD solution for the drain pipeline 3 according to the initial design parameters of the orifice plate to obtain the fluid flow rate under the solved working condition of the drain pipeline; When the difference between the fluid flow rate under the solved working condition of the drain pipeline and the fluid flow rate under the rated working condition at the inlet of the orifice plate is outside the given deviation range, it indicates that the initial design parameters of the orifice plate are unreasonable, and enter Step 102; When the difference between the fluid flow rate under the solved working condition of the drain pipeline and the fluid flow rate under the rated working condition at the inlet of the orifice plate is within the given deviation range, enter Step 103; Step 102: Adjust the design parameters of the orifice plate; perform CFD solution according to the adjusted design parameters of the orifice plate to obtain the fluid flow rate under the solved working condition of the drain pipeline; repeat the above steps multiple times until the difference between the fluid flow rate under the solved working condition of the drain pipeline and the fluid flow rate under the rated working condition at the inlet of the orifice plate is within the given deviation range; Step 103: When the difference between the fluid flow rate under the solved working condition of the drain pipeline and the fluid flow rate under the rated working condition at the inlet of the orifice plate is within the given deviation range, it indicates that the corresponding design parameters of the orifice plate are reasonable, and take them as the final design parameters of the orifice plate.

[0010] As one of the achievable ways, perform CFD solution according to the design parameters of the orifice plate to obtain the fluid flow rate under the solution conditions of the drain pipe, including the following steps: Step 201: Establish a CFD solution grid for the drain pipe; Step 202: Establish the boundary conditions, fluid type, and fluid flow model for the CFD solution of the drain pipe; Step 203: Perform CFD iterative solution on the CFD solution grid of the drain pipe according to the boundary conditions, fluid type, and fluid flow model for the CFD solution of the drain pipe to obtain the CFD iterative solution result of the drain pipe; Step 204: According to the CFD iterative solution result of the drain pipe, perform finite element analysis on the fluid of the vertical middle plane of the drain pipe through finite element analysis software to obtain the fluid velocity field diagram and fluid pressure field diagram of the vertical middle plane of the drain pipe; Step 205: Determine the fluid flow rate under the solution conditions of the drain pipe according to the fluid pressure field diagram of the vertical middle plane of the drain pipe and the calculation formula for the flow capacity of the steam trap.

[0011] As one of the achievable ways, in Step 201, select the part where the drain pipe, casing, and flash tank are connected as the CFD solution flow field of the drain pipe, and establish a CFD solution grid for the drain pipe; the fluid flow outlet of the CFD solution grid of the drain pipe is cylindrical.

[0012] As one of the achievable ways, in Step 201, the CFD solution grid of the drain pipe is a structured hexahedral grid; the grid density of the CFD solution grid of the drain pipe on the walls of the drain pipe, casing, and flash tank and in the areas before and after the orifice plate is greater than that of other areas of the CFD solution grid of the drain pipe.

[0013] As one of the achievable ways, in Step 202, the boundary conditions for the CFD solution of the drain pipe include the inlet boundary condition of the steam trap, the inlet boundary condition of the orifice plate, and the outlet boundary condition of the orifice plate; Among them, the inlet boundary condition of the steam trap includes the inlet fluid pressure of the steam trap and the saturated water enthalpy of the inlet fluid of the steam trap; The inlet boundary condition of the orifice plate includes the rated working condition fluid flow rate at the inlet of the orifice plate, the fluid flow direction at the inlet of the orifice plate, the assumed initial value of the fluid temperature at the inlet of the orifice plate, and the assumed initial value of the fluid dryness at the inlet of the orifice plate; the fluid flow direction at the inlet of the orifice plate is perpendicular to the wall of the orifice plate; The outlet boundary condition of the orifice plate includes the fluid boundary at the outlet of the orifice plate, the fluid pressure at the outlet of the orifice plate, and the fluid temperature at the outlet of the orifice plate; the fluid boundary at the outlet of the orifice plate is a free open boundary, that is, the fluid can both flow in and flow out; The fluid type for the CFD solution of the hydrophobic pipeline is wet steam; the fluid flow model for the CFD solution of the hydrophobic pipeline includes a heat transfer model, a turbulence equation, and a wall function. Among them, the heat transfer model is the total energy model, the turbulence equation is the K-Epsilon equation, and the wall function is the adaptive wall function.

[0014] As one possible implementation, in step 203, the CFD iterative solution of the hydrophobic pipeline CFD solution grid is performed according to the boundary conditions, fluid type, and fluid flow model of the hydrophobic pipeline CFD solution, and the hydrophobic pipeline CFD iterative solution result is obtained, including the following steps: Perform multiple CFD solutions of the hydrophobic pipeline on the CFD solution grid of the hydrophobic pipeline according to the boundary conditions, fluid type, and fluid flow model of the hydrophobic pipeline CFD solution; the initial condition for the next CFD solution of the hydrophobic pipeline is the result of the previous CFD solution of the hydrophobic pipeline; the CFD solution result of the hydrophobic pipeline includes the fluid pressure at the inlet of the orifice plate, the fluid temperature at the inlet of the orifice plate, and the fluid dryness at the inlet of the orifice plate. When the deviation of the fluid pressure at the inlet of the orifice plate between the next and the previous CFD solutions of the hydrophobic pipeline is within the given deviation range, the convergence of the CFD iterative solution of the hydrophobic pipeline is achieved, and the CFD iterative solution result of the hydrophobic pipeline is obtained; the CFD iterative solution result of the hydrophobic pipeline includes the converged fluid pressure at the inlet of the orifice plate, the fluid temperature at the inlet of the orifice plate, and the fluid dryness at the inlet of the orifice plate.

[0015] As one possible implementation, in step 205, the calculation formula for the flow capacity of the steam trap is the linear relationship between the pressure drop of the steam trap and the flow capacity; Determine the fluid pressure at the outlet of the steam trap according to the fluid pressure field diagram of the vertical mid-plane of the hydrophobic pipeline; the fluid pressure at the inlet of the steam trap is the boundary condition of the CFD solution of the hydrophobic pipeline; the difference between the fluid pressure at the inlet of the steam trap and the fluid pressure at the outlet of the steam trap is the pressure drop of the steam trap; Substitute the pressure drop of the steam trap into the calculation formula for the flow capacity of the steam trap to obtain the flow capacity of the steam trap; determine the fluid flow rate at the outlet of the steam trap according to the flow capacity of the steam trap, and the fluid flow rate at the outlet of the steam trap is the fluid flow rate of the hydrophobic pipeline under the solution condition.

[0016] As one possible implementation, it further includes: step 104, checking the fluid flow rate of the hydrophobic pipeline under the solution condition corresponding to the final design parameters of the orifice plate; Checking the fluid flow rate of the hydrophobic pipeline under the solution condition corresponding to the final design parameters of the orifice plate includes the following steps: Select a suitable two-phase flow empirical calculation formula to calculate the fluid flow rate of the hydrophobic pipeline according to the fluid dryness at the inlet of the orifice plate in the CFD iterative solution result of the hydrophobic pipeline, and obtain the fluid flow rate of the hydrophobic pipeline under the calculation condition; If the difference between the fluid flow rate under the calculation condition and the fluid flow rate under the solution condition of the drain pipe is within a reasonable deviation range, it is determined that the fluid flow rate under the solution condition of the drain pipe passes the verification.

[0017] As one of the realizable ways, it further includes: Step 105, designing the maximum flow capacity of the drain pipe; Step 105, designing the maximum flow capacity of the drain pipe, includes the following steps: performing iterative solution according to the two-phase flow empirical calculation formula and the flow capacity calculation formula of the steam trap, so that the fluid pressure at the inlet of the steam trap satisfies the boundary conditions.

[0018] The beneficial technical effects of the present invention: The cavitation control device for the drain pipe of the nuclear power plant of the present invention improves the design and installation of the orifice plate. The orifice plate is vertically installed at the end of the drain pipe, a first through hole is opened in the center, and second through holes are symmetrically opened at both ends in the diameter direction perpendicular to the central axis. In this way, cavitation and water accumulation in the drain pipe downstream of the orifice plate are avoided, thereby avoiding the gradual thinning of the pipe wall caused by the cavitation impact on the pipe wall downstream of the orifice plate and the impact on the drain pipe caused by the water flow impact on the accumulated water.

[0019] For the cavitation control device of the drain pipe of the nuclear power plant of the present invention, the design parameters of the orifice plate are optimized through CFD simulation of the drain pipe, and at the same time, the CFD simulation results of the drain pipe are checked by the two-phase flow empirical formula, ensuring that the design parameters of the orifice plate meet the design requirements and improving the safety of the drain pipe operation. Brief Description of the Drawings

[0020] Figure 1 It is an installation cross-sectional view of an embodiment of the cavitation control device for the drain pipe of the nuclear power plant of the present invention; Figure 2 It is a curve graph of the fluid flow velocity and pressure change of the drain pipe; Figure 3 It is a curve graph of the fluid pressure change of the drain pipe; Figure 4 It is a schematic diagram of the CFD solution grid of an embodiment of the drain pipe; Figure 5 It is a schematic diagram of the CFD solution grid of an embodiment of the drain pipe; Figure 6 It is a schematic diagram of the CFD solution grid of an embodiment of the drain pipe; Figure 7 It is a schematic diagram of the fluid pressure field of the vertical middle plane of an embodiment of the drain pipe; Figure 8 It is a schematic diagram of the fluid pressure field of the vertical middle plane of an embodiment of the drain pipe; Figure 9Schematic diagram of the fluid pressure field on the vertical mid - plane of an embodiment of a hydrophobic pipeline; Figure 10 Schematic diagram of the fluid velocity field on the vertical mid - plane of an embodiment of a hydrophobic pipeline; Figure 11 Schematic diagram of the fluid velocity field on the vertical mid - plane of an embodiment of a hydrophobic pipeline; Figure 12 Schematic diagram of the fluid velocity field on the vertical mid - plane of an embodiment of a hydrophobic pipeline; Figure 13 Graph of the relationship between the pressure drop and the flow - through capacity of a steam trap.

[0021] In the figure, 1. Flash tank; 2. Throttling orifice plate; 3. Hydrophobic pipeline; 4. First through - hole; 5. Second through - hole; p1. Fluid pressure upstream of the throttling orifice plate; p2. Fluid pressure downstream of the throttling orifice plate; p vc 、Fluid pressure at the vena contracta; v1. Fluid velocity upstream of the throttling orifice plate; v2. Fluid velocity downstream of the throttling orifice plate; p v 、Fluid saturated vapor pressure; p. Fluid velocity. Detailed implementation mode

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used in the description of this application in the specification are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0023] Reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0024] In the description of the present invention, unless otherwise clearly specified and limited, terms such as "set", "installed", "connected", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific situations.

[0025] The orientation or positional relationship indicated by terms such as "upper", "lower", "front", "rear", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the inventive product is customarily placed during use. It is only for the convenience of description and to simplify the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention.

[0026] Terms such as "first", "second", etc. are only used to distinguish elements with similar attributes, rather than indicating or implying relative importance or a specific order.

[0027] The term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion. In addition to the elements listed, it may also include other elements not specifically listed.

[0028] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings and specific embodiments.

[0029] The nuclear power plant steam turbine drainage system mainly consists of a steam trap, drainage pipes and a flash tank; the head end of the drainage pipe is connected to the steam trap, the tail end of the drainage pipe is inserted into the flash tank and welded to the inner wall of the flash tank, and a sleeve is provided outside the drainage pipe section. The steam extraction from the steam turbine undergoes gas-liquid separation by the steam trap to generate a large amount of drainage, which enters the flash tank through the drainage pipe. A fixed orifice plate is provided inside the drainage pipe. The orifice plate has a central opening and is fixed inside the drainage pipe by welding.

[0030] The drainage pipe downstream of the orifice plate is prone to cavitation. The cavitation impacts the pipe wall, resulting in local thinning of the pipe wall. The drainage mode of the steam trap is intermittent drainage, and the design structure of the orifice plate is only to open a through hole in the center of the orifice plate, which causes the drainage pipe upstream of the orifice plate to be very prone to water accumulation. The continuous impact of the water flow on the accumulated water generates oscillation, which will cause a greater impact on the drainage pipe.

[0031] Figure 2 It is a graph of the flow velocity and pressure changes of the fluid in the drainage pipe. The function of the orifice plate is to reduce the aperture to form a constriction at an appropriate position in the drainage pipe. When the fluid passes through the constriction, it will become thinner or contract. When the fluid flows in the drainage pipe, due to the local resistance of the orifice plate, the pressure of the fluid decreases and the energy is dissipated. The minimum cross-section of the fluid appears downstream of the constriction, which is called the contracted flow section.

[0032] At the contracted flow section, the flow velocity of the fluid is the maximum and the pressure is the lowest. When the fluid expands into a larger area, the flow velocity of the fluid decreases and the pressure increases, but the fluid pressure downstream of the orifice plate will not fully recover to the fluid pressure upstream. This is due to the result of larger internal turbulence and energy consumption.

[0033] Figure 3 It is a pressure change curve graph of the fluid in the hydrophobic pipeline. If the pressure P of the fluid at the throttling section vc drops below the saturated vapor pressure P of the fluid at the corresponding temperature v , vapor and gas dissolved in the fluid will escape in the fluid, forming bubbles mixed with vapor and gas. The lower the pressure of the fluid at the throttling section, the more bubbles there are. If the pressure P2 of the fluid downstream of the orifice plate is still lower than the saturated vapor pressure P of the fluid at the corresponding temperature v , bubbles will continue to be generated in the hydrophobic pipeline downstream of the orifice plate, and the liquid-gas two-phase mixture exists. This phenomenon is called flashing.

[0034] If the pressure P2 of the fluid downstream of the orifice plate returns to be higher than the saturated vapor pressure P of the fluid at the corresponding temperature v , the bubbles will quickly condense and burst under the action of high pressure. At the moment when the bubbles burst, local cavities are generated. The high-pressure fluid around the original bubbles flows at an extremely high speed into the space occupied by these original bubbles, forming an impact force. Since the gas and vapor in the bubbles cannot be completely dissolved and condensed in an instant, under the action of the impact force, they are divided into bubbles again, and then compressed and condensed by the high-pressure fluid around the bubbles. This process repeats many times, generating a noise similar to that of sand and gravel flowing through the hydrophobic pipeline. This phenomenon is called cavitation.

[0035] There are two ways to avoid cavitation in the hydrophobic pipeline downstream of the orifice plate: One is to improve the design and installation of the orifice plate, control the pressure P of the fluid at the throttling section vc , and keep the pressure P of the fluid at the throttling section vc not lower than the saturated vapor pressure P of the fluid at the corresponding temperature v . In this way, bubbles will not be generated in the fluid at the throttling section, thus preventing cavitation in the hydrophobic pipeline downstream of the orifice plate; The other is to reduce the pressure P2 of the fluid downstream of the orifice plate, so that the pressure P2 of the fluid downstream of the orifice plate is lower than the saturated vapor pressure P of the fluid at the corresponding temperature v , but the pressure difference between the front and back of the hydrophobic pipeline is not large, and it is unlikely to use the multi-stage pressure reduction method to make the pressure P2 of the fluid downstream of the orifice plate lower than the saturated vapor pressure P of the fluid at the corresponding temperature v .

[0036] Therefore, the first way must be adopted to avoid cavitation in the hydrophobic pipeline downstream of the orifice plate. And adopting the first way requires verifying whether the design parameters of the orifice plate meet the design requirements, and taking appropriate measures during the installation of the orifice plate to ensure that there is no incorrect installation or misalignment.

[0037] For this reason, refer to Figure 1, the present invention provides a cavitation control device for the drain pipe of a nuclear power plant, including an orifice plate 2; the orifice plate 2 connects the end of the drain pipe 3 and the head end of the flash tank 1 together by welding; a sleeve is provided outside the drain pipe 3; The central axis of the orifice plate 2 coincides with the central axis of the drain pipe 3. A first through hole 4 is opened in the center of the orifice plate 2, and second through holes 5 are symmetrically opened at both ends in the diameter direction perpendicular to the central axis of the orifice plate 2; The orifice plate 2 is formed by cutting holes in a solid forging with a design length that meets the requirements. The design parameters of the orifice plate 2 are optimized through CFD simulation of the drain pipe.

[0038] The cavitation control device for the drain pipe of the nuclear power plant according to the present invention avoids cavitation of the drain pipe by improving the design and installation of the orifice plate, thereby avoiding the gradual thinning of the pipe wall caused by cavitation impact on the pipe wall; by improving the design and installation of the orifice plate, the accumulation of water in the drain pipe upstream of the orifice plate is avoided, thereby avoiding the impact on the drain pipe caused by the oscillation generated by the water flow impacting the accumulated water; the orifice plate 2 connects the end of the drain pipe 3 and the head end of the flash tank 1 together by welding, avoiding the formation of a connection weld by inserting the end of the drain pipe 3 into the interior of the flash tank 1 and welding it to the inner wall of the flash tank 1; the design parameters of the orifice plate 2 are optimized through CFD simulation of the drain pipe, ensuring that the design parameters of the orifice plate 2 meet the design specifications and improving the safety of the operation of the drain pipe 3.

[0039] In the present invention, as one realizable manner, both the first through hole 4 and the second through hole 5 are circular through holes; the design parameters of the orifice plate 2 include the diameter of the first through hole 4, the diameter of the second through hole 5, and the fluid flow rate under the rated working condition at the inlet of the orifice plate; the design parameters of the orifice plate 2 are optimized through CFD simulation of the drain pipe, including the following steps: Step 101: Perform CFD solution of the drain pipe according to the initial design parameters of the orifice plate 2 to obtain the fluid flow rate under the solution working condition of the drain pipe; When the difference between the fluid flow rate under the solution working condition of the drain pipe and the fluid flow rate under the rated working condition at the inlet of the orifice plate is outside the given deviation range, it indicates that the initial design parameters of the orifice plate 2 are unreasonable, and enter step 102; When the difference between the fluid flow rate under the solution working condition of the drain pipe and the fluid flow rate under the rated working condition at the inlet of the orifice plate is within the given deviation range, enter step 103; Step 102: Adjust the design parameters of the orifice plate 2; perform CFD solution of the drain pipe according to the adjusted design parameters of the orifice plate 2 to obtain the fluid flow rate under the solution working condition of the drain pipe; repeat the above steps multiple times until the difference between the fluid flow rate under the solution working condition of the drain pipe and the fluid flow rate under the rated working condition at the inlet of the orifice plate is within the given deviation range; Step 103: When the difference between the fluid flow rate under the solution condition of the drain pipe and the rated fluid flow rate at the inlet of the orifice plate is within the given deviation range, it indicates that the design parameters corresponding to the orifice plate 2 are reasonable, and these parameters are taken as the final design parameters of the orifice plate 2.

[0040] In the present invention, as one possible implementation, performing CFD solution for the drain pipe according to the design parameters of the orifice plate 2 to obtain the fluid flow rate under the solution condition of the drain pipe includes the following steps: Step 201: Establish a CFD solution grid for the drain pipe; Step 202: Establish the boundary conditions, fluid type, and fluid flow model for the CFD solution of the drain pipe; Step 203: Perform iterative CFD solution for the drain pipe on the CFD solution grid of the drain pipe according to the boundary conditions, fluid type, and fluid flow model for the CFD solution of the drain pipe to obtain the iterative CFD solution result of the drain pipe 3; Step 204: According to the iterative CFD solution result of the drain pipe, perform finite element analysis on the fluid of the vertical mid-plane of the drain pipe through finite element analysis software to obtain the fluid velocity field diagram and fluid pressure field diagram of the vertical mid-plane of the drain pipe; Step 205: Determine the fluid flow rate under the solution condition of the drain pipe according to the fluid pressure field diagram of the vertical mid-plane of the drain pipe and the calculation formula for the flow capacity of the steam trap.

[0041] In the present invention, as one possible implementation, in Step 201, select the part where the drain pipe 3, the casing, and the flash tank 1 are connected as the flow field for the CFD solution of the drain pipe, and establish a CFD solution grid for the drain pipe; The fluid flow outlet of the CFD solution grid of the drain pipe is cylindrical. The cylindrical fluid flow outlet is selected because when the fluid flows out of the orifice plate 2, it has a large inertia to continue flowing forward. Therefore, a longer area is selected in the fluid flow direction to establish the CFD solution grid for the drain pipe.

[0042] In the present invention, as one possible implementation, in Step 201, establish a CFD solution grid for the drain pipe through CFD modeling and mesh generation software; the CFD modeling and mesh generation software is a general software in the art, including but not limited to ICEM.

[0043] In the present invention, as one possible implementation, in Step 201, the CFD solution grid of the drain pipe is a structured hexahedral grid; the mesh density of the CFD solution grid of the walls of the drain pipe 3, the casing, and the flash tank 1 and the areas before and after the orifice plate 2 is greater than that of other areas of the CFD solution grid of the drain pipe; the number of the CFD solution grid of the drain pipe is 380,000, and the number of nodes of the CFD solution grid of the drain pipe is 360,000.

[0044] The CFD solution mesh of the condensate drain pipe is the basis for the CFD solution of the condensate drain pipe. A sufficient density of the CFD solution mesh of the condensate drain pipe is the guarantee for the CFD solution accuracy of the condensate drain pipe. However, an overly dense CFD solution mesh of the condensate drain pipe will significantly increase the time and difficulty of the CFD solution convergence of the condensate drain pipe; a relatively dense CFD solution mesh of the condensate drain pipe is set in the area near the wall and where the fluid velocity changes rapidly, and a relatively sparse CFD solution mesh of the condensate drain pipe is set in other areas, which can meet the requirements of the CFD solution accuracy of the condensate drain pipe.

[0045] In the present invention, as one of the feasible ways, in step 202, the boundary conditions for the CFD solution of the condensate drain pipe include the inlet boundary condition of the steam trap, the inlet boundary condition of the orifice plate, and the outlet boundary condition of the orifice plate; Among them, the inlet boundary condition of the steam trap includes the inlet fluid pressure of the steam trap and the saturated water enthalpy of the inlet fluid of the steam trap; The inlet boundary condition of the orifice plate includes the rated working condition fluid flow rate at the inlet of the orifice plate, the fluid flow direction at the inlet of the orifice plate, the assumed initial value of the fluid temperature at the inlet of the orifice plate, and the assumed initial value of the fluid dryness at the inlet of the orifice plate; the fluid flow direction at the inlet of the orifice plate is perpendicular to the wall of the orifice plate 2; The outlet boundary condition of the orifice plate includes the fluid boundary at the outlet of the orifice plate, the fluid pressure at the outlet of the orifice plate, and the fluid temperature at the outlet of the orifice plate; the fluid boundary at the outlet of the orifice plate is a free open boundary, that is, the fluid can both flow in and flow out; The fluid type for the CFD solution of the condensate drain pipe is wet steam, which belongs to gas-liquid two-phase flow; the fluid flow model for the CFD solution of the condensate drain pipe includes a heat transfer model, a turbulence equation, and a wall function. Among them, the heat transfer model is the total energy model, the turbulence equation is the K-Epsilon equation, and the wall function is the adaptive wall function.

[0046] In the present invention, as one of the feasible ways, in step 203, the CFD iterative solution of the CFD solution mesh of the condensate drain pipe is carried out according to the boundary conditions, fluid type, and fluid flow model of the CFD solution of the condensate drain pipe to obtain the CFD iterative solution result of the condensate drain pipe, including the following steps: The CFD solution mesh of the condensate drain pipe is subjected to multiple CFD solutions of the condensate drain pipe 3 according to the boundary conditions, fluid type, and fluid flow model of the CFD solution of the condensate drain pipe; the initial condition for the next CFD solution of the condensate drain pipe is the result of the previous CFD solution of the condensate drain pipe; the CFD solution result of the condensate drain pipe includes the fluid pressure at the inlet of the orifice plate, the fluid temperature at the inlet of the orifice plate, and the fluid dryness at the inlet of the orifice plate; When the deviation of the fluid pressure at the inlet of the throttle orifice in the next hydrophobic pipeline CFD solution from that in the previous one is within the given deviation range, the convergence of the iterative CFD solution of the hydrophobic pipeline is achieved, and the iterative CFD solution result of the hydrophobic pipeline is obtained. The iterative CFD solution result of the hydrophobic pipeline includes the fluid pressure at the inlet of the throttle orifice after convergence, the fluid temperature at the inlet of the throttle orifice, and the fluid dryness at the inlet of the throttle orifice. The deviation of the fluid pressure at the inlet of the throttle orifice in the next hydrophobic pipeline CFD solution from that in the previous one is within 1E-4, the convergence of the iterative CFD solution of the hydrophobic pipeline is achieved, and the iterative CFD solution result of the hydrophobic pipeline is obtained.

[0047] The fluid in the flow field of the hydrophobic pipeline CFD solution is a gas-liquid two-phase flow. The CFD solution of the gas-liquid two-phase flow is much more complex than that of the single-phase flow. When setting the fluid flow rate at the inlet of the throttle orifice as the boundary condition, the fluid temperature at the inlet of the throttle orifice and the fluid dryness at the inlet of the throttle orifice must be given, and both of these two parameters are related to the fluid pressure at the inlet of the throttle orifice. Therefore, CFD iterative solution is required. First, assume the initial values of the fluid temperature at the inlet of the throttle orifice and the fluid dryness at the inlet of the throttle orifice, and then correct the assumed initial values of the fluid temperature at the inlet of the throttle orifice and the fluid dryness at the inlet of the throttle orifice according to the fluid pressure at the inlet of the throttle orifice obtained by the CFD solution. Perform CFD iterative solution multiple times until the deviation of the fluid pressure at the inlet of the throttle orifice obtained by the previous and the next CFD solutions is within the given deviation range.

[0048] In the present invention, as one of the realizable ways, in step 204, according to the iterative CFD solution result of the hydrophobic pipeline, perform finite element analysis on the fluid of the vertical mid-plane of the hydrophobic pipeline by using finite element analysis software to obtain the velocity field diagram and pressure field diagram of the fluid on the vertical mid-plane of the hydrophobic pipeline. The finite element analysis software is a general software in the art, including but not limited to ANSYS. Determine the maximum flow velocity of the fluid on the vertical mid-plane of the hydrophobic pipeline according to the velocity field diagram of the fluid on the vertical mid-plane of the hydrophobic pipeline. Determine the change of the flow velocity and pressure of the fluid on the vertical mid-plane of the hydrophobic pipeline according to the velocity field diagram and pressure field diagram of the fluid on the vertical mid-plane of the hydrophobic pipeline.

[0049] Figure 13 For the relationship diagram of the pressure drop and flow capacity of the steam trap, in the present invention, as one of the realizable ways, the steam trap is a DN50 FT44-32 steam trap. In step 205, the calculation formula for the flow capacity of the steam trap is: Where is the flow capacity of the steam trap, with the unit of kg / h; is the pressure drop of the steam trap, with the unit of kPa; and are both fitting coefficients. is 2.13, is -7.31; Determine the fluid pressure at the outlet of the steam trap according to the fluid pressure field diagram of the vertical mid-plane of the hydrophobic pipeline; the fluid pressure at the inlet of the steam trap is the boundary condition for the CFD solution of the hydrophobic pipeline; the difference between the fluid pressure at the inlet of the steam trap and the fluid pressure at the outlet of the steam trap is the pressure drop of the steam trap. ; Substitute the pressure drop of the steam trap into the calculation formula for the flow capacity of the steam trap to obtain the flow capacity of the steam trap. ; Determine the fluid flow rate at the outlet of the steam trap according to the flow capacity of the steam trap , and the fluid flow rate at the outlet of the steam trap is the fluid flow rate under the solution condition of the hydrophobic pipeline.

[0050] In the present invention, as one of the realizable ways, it further includes: Step 104, check the fluid flow rate under the solution condition of the hydrophobic pipeline corresponding to the final design parameters of the orifice plate 2. Checking the fluid flow rate under the solution condition of the hydrophobic pipeline corresponding to the final design parameters of the orifice plate 2 includes the following steps: Select a suitable two-phase flow empirical calculation formula to calculate the fluid flow rate of the hydrophobic pipeline according to the dryness of the fluid at the inlet of the orifice plate in the CFD iterative solution result of the hydrophobic pipeline, and obtain the fluid flow rate under the calculation condition of the hydrophobic pipeline; When the difference between the fluid flow rate under the calculation condition of the hydrophobic pipeline and the fluid flow rate under the solution condition of the hydrophobic pipeline is within a reasonable deviation range, it is determined that the fluid flow rate under the solution condition of the hydrophobic pipeline passes the check.

[0051] In the present invention, as one of the realizable ways, the two-phase flow empirical calculation formula is the Lin Zonghu calculation formula; the Lin Zonghu calculation formula is: Wherein, is the fluid flow rate under the calculation condition of the hydrophobic pipeline, with the unit of kg / s; is the thermal expansion coefficient of the orifice plate 2; is the discharge coefficient of single-phase flow; is the diameter of the first through hole 4 of the orifice plate 2, with the unit of m; D is the inner diameter of the hydrophobic pipeline 3, with the unit of m; is the orifice ratio, equal to / D; is the pressure difference of gas-liquid two-phase flow, with the unit of Pa; is the liquid phase density, with the unit of kg / m 3 ; is the gas phase density, with the unit of kg / m 3 ; is the dryness of the fluid at the inlet of the orifice plate; is the two-phase correction coefficient of the orifice plate.

[0052] Most of the coefficients in Lin Zonghu's calculation formula can be directly calculated. However, for the determination of the single-phase flow discharge coefficient, the Reader-Harria / Gellagher formula published by ISO in 1998 is adopted. The single-phase flow discharge coefficient in this formula is a function of the pipe flow Reynolds number and the orifice diameter ratio, and the Reynolds number is a function of the flow rate. Therefore, this formula requires iterative solution by a program. In the solution process, in addition to the basic calculation formula, the calculation of the thermophysical properties of the working fluid is also required. Since the thermophysical properties of wet steam are all in the two-phase region, according to the relevant formulas in the saturated line and two-phase region of the fourth zone in the IF97 series standards published by the International Association for the Properties of Water and Steam (IAPWS), a calculation program for the thermodynamic properties of water vapor is compiled.

[0053] Using the compiled calculation program for the thermodynamic properties of water vapor, setting the inlet fluid pressure of the orifice plate in the CFD iterative solution result of the drain pipe as the initial condition, the fluid flow rate under the calculation conditions of the drain pipe is obtained. The difference between the fluid flow rate under the calculation conditions of the drain pipe and the fluid flow rate under the solution conditions of the drain pipe is about 20%. This deviation is not large for the calculation results of wet steam two-phase flow. The main reasons are as follows: First of all, the applicable range of Lin Zonghu's calculation formula is that the outlet fluid pressure of the orifice plate is 0.8 - 19.8 MPa, and the orifice diameter ratio is between 0.25 and 0.75; while the outlet fluid pressure and orifice diameter ratio of the orifice plate in the CFD simulation of the drain pipe are both outside the applicable range of Lin Zonghu's calculation formula, resulting in certain errors in the calculation results of Lin Zonghu's calculation formula; Secondly, Lin Zonghu's calculation formula is for orifice plate flowmeters. Orifice plate flowmeters are generally installed according to ISO or GB standards, and the installation pressure ratio of general orifice plate flowmeters is relatively large, often above 0.75; while the installation pressure ratio of the orifice plate in the CFD simulation of the drain pipe is below 0.75, resulting in certain errors in Lin Zonghu's calculation formula; Lin Zonghu's calculation formula is not only applicable to wet steam, but also to two-phase flows of air and water. There is no phase change in the formula. When there is a phase change, the density of the two-phase flow will sharply decrease due to more steam generated by the phase change, making the mass flow rate smaller, resulting in certain deviations in Lin Zonghu's calculation formula.

[0054] Since there is no more accurate empirical formula for verification in the international scope of the research on wet steam two-phase flow, the verification of general calculation results usually relies on experiments. However, due to the limitations of the gas source and measurement tools, the cost and complexity of experiments with steam working fluids are quite high. CFD simulation has become a relatively efficient, fast, and flexible alternative estimation method.

[0055] In the present invention, as one of the feasible implementation manners, it further includes: step 105, designing the maximum flow capacity of the hydrophobic pipeline 3. Designing the maximum flow capacity of the hydrophobic pipeline 3 includes the following steps: performing iterative solution according to Lin Zonghu's calculation formula and the calculation formula for the flow capacity of the steam trap, so that the fluid pressure at the inlet of the steam trap meets the boundary conditions.

[0056] In one embodiment, Figure 4 For the CFD solution grid of the hydrophobic pipeline in this embodiment, the blue part in the figure is the pipe wall of the hydrophobic pipeline 3, the pipe wall of the casing or the head end of the flash tank 1, the green part is the inlet of the hydrophobic pipeline 3, and the red part is the fluid flow boundary in the flash tank 1. The fluid flow boundary in the flash tank 1 can allow fluid to flow in and out. In the CFD solution flow field of the hydrophobic pipeline, the hydrophobic pipeline 3 is a DN100 pipeline; in the final design parameters of the orifice plate 2, the diameter of the first through hole 4 is 18 mm, and the diameter of the second through hole 5 is 4 mm. In the boundary conditions of the CFD solution of the hydrophobic pipeline, the fluid pressure at the inlet of the steam trap is 2.790 MPa, the saturated water enthalpy of the fluid at the inlet of the steam trap is 989.587 kJ / (kg·K), the rated working condition fluid flow rate at the inlet of the orifice plate is 1.03 kg / s, the assumed initial value of the fluid dryness at the inlet of the orifice plate is 0.14, the assumed initial value of the fluid temperature at the inlet of the orifice plate is 145 °C, the fluid pressure at the outlet of the orifice plate is 0.92 bar, and the fluid temperature at the outlet of the orifice plate is 176.29 °C. The results of the iterative solution of the CFD of the hydrophobic pipeline are: the fluid pressure at the inlet of the orifice plate is 0.65 MPa, the fluid temperature at the inlet of the orifice plate is 161.986 °C, and the fluid dryness at the inlet of the orifice plate is 0.15. Figure 7 For the flow velocity field diagram of the fluid on the vertical middle plane of the hydrophobic pipeline in this embodiment, Figure 10 For the pressure field diagram of the fluid on the vertical middle plane of the hydrophobic pipeline in this embodiment; according to Figure 7 , it is determined that the highest flow velocity of the fluid on the vertical middle plane of the hydrophobic pipeline is 248 m / s. From Figure 7 It can be seen that the fluid flow velocity and flow direction of the inlet part of the hydrophobic pipeline 3 are relatively uniform. When reaching the second through hole 5, the change in the fluid flow velocity direction begins to occur, and the fluid flow velocity reaches the maximum at the first through hole 4; after the fluid exits the orifice plate 2, due to inertia, it still maintains a relatively high flow velocity within a certain range; as the fluid flow further expands, the fluid flow velocity gradually decreases; the fluid coming out of the second through hole 5 impacts the inner surface of the blue sleeve and finally flows deep into the flash tank 1. From Figure 10 It can be seen that a large gradient appears in the fluid pressure at the orifice plate 2, while it is basically uniform at the end of the hydrophobic pipeline 3 and inside the flash tank 1. According to Figure 10 , determine the fluid pressure at the outlet of the steam trap; the pressure drop of the steam trap is 2.05 MPa; according to Figure 7 , determine the fluid velocity in front of the orifice plate to be 7.45 m / s; the flow capacity of the steam trap is 3.11 kg / s; perform CFD solution for the condensate pipeline according to the final design parameters of the orifice plate 2, and obtain the fluid flow rate of the condensate pipeline under the solution condition to be 1.03 kg / s; The fluid flow rate of the condensate pipeline under the calculation condition is 1.37 kg / s, and the deviation between the fluid flow rate of the condensate pipeline under the calculation condition and the fluid flow rate of the condensate pipeline under the solution condition is within 25%; the fluid pressure at the outlet of the orifice plate in the CFD simulation of the condensate pipeline is 0.092 MPa, and the aperture ratio is 0.18. The installation pressure ratio of the orifice plate = fluid pressure at the outlet of the orifice plate / fluid pressure at the inlet of the orifice plate = 0.092 MPa / 0.65 MPa = 0.14; In step 105, the boundary conditions satisfied by the fluid pressure at the inlet of the steam trap are: the actual fluid flow rate of the condensate pipeline is 75% of the fluid flow rate of the condensate pipeline under the calculation condition, the fluid pressure at the inlet of the orifice plate is 1.48 MPa, the pressure drop of the steam trap is 1.31 MPa, the flow capacity of the condensate pipeline 3 is 2.53 kg / s, and the safety factor is 2.5.

[0057] In one of the embodiments, Figure 5 is the CFD solution grid of the condensate pipeline for this embodiment. In the figure, the blue part is the wall of the condensate pipeline 3, the wall of the casing, or the head end of the flash tank 1, the green part is the inlet of the condensate pipeline 3, and the red part is the fluid flow boundary in the flash tank 1. The fluid flow boundary in the flash tank 1 can allow fluid to flow in and out; In the CFD solution flow field of the condensate pipeline, the condensate pipeline 3 is a DN80 pipeline; in the final design parameters of the orifice plate 2, the diameter of the first through hole 4 is 9 mm, and the diameter of the second through hole 5 is 3 mm; In the boundary conditions of the CFD solution of the condensate pipeline, the fluid pressure at the inlet of the steam trap is 2.734 MPa, the saturated water enthalpy of the fluid at the inlet of the steam trap is 986.416 kJ / (kg·K), the rated fluid flow rate at the inlet of the orifice plate is 0.12 kg / s, the assumed initial value of the fluid dryness at the inlet of the orifice plate is 0.14, the assumed initial value of the fluid temperature at the inlet of the orifice plate is 145 °C, the fluid pressure at the outlet of the orifice plate is 0.92 bar, and the fluid temperature at the outlet of the orifice plate is 176.29 °C; The results of the iterative CFD solution of the condensate pipeline are: the fluid pressure at the inlet of the orifice plate is 0.34 MPa, the fluid temperature at the inlet of the orifice plate is 138.36 °C, and the fluid dryness at the inlet of the orifice plate is 0.19; Figure 8It is the flow velocity field diagram of the fluid on the vertical mid - plane of the hydrophobic pipeline for this embodiment, Figure 11 and it is the pressure field diagram of the fluid on the vertical mid - plane of the hydrophobic pipeline for this embodiment; According to Figure 8 , it is determined that the maximum flow velocity of the fluid on the vertical mid - plane of the hydrophobic pipeline is 254 m / s; From Figure 8 it can be seen that the fluid flow velocity and flow direction in the inlet part of the hydrophobic pipeline 3 are relatively uniform. When reaching the second through - hole 5, the change in the fluid flow velocity direction starts to occur, and the fluid flow velocity reaches the maximum at the first through - hole 4; After the fluid exits the orifice plate 2, due to inertia, it still maintains a relatively high flow velocity within a certain range; As the fluid flow further expands, the fluid flow velocity gradually decreases; The fluid coming out from the second through - hole 5 impacts the inner surface of the blue sleeve and finally flows deep into the flash tank 1; From Figure 11 it can be seen that a large gradient of fluid pressure appears at the orifice plate 2, while it is basically uniform at the end of the hydrophobic pipeline 3 and inside the flash tank 1; According to Figure 11 , the fluid pressure at the outlet of the steam trap is determined; The pressure drop of the steam trap is 2.36 MPa; According to Figure 8 , the fluid flow velocity before the orifice plate is determined to be 3.08 m / s; The flow - through capacity of the steam trap is 0.25 kg / s; According to the final design parameters of the orifice plate, CFD solution of the hydrophobic pipeline is carried out, and the fluid flow rate of the hydrophobic pipeline under the solution condition is 0.12 kg / s; The fluid flow rate of the hydrophobic pipeline under the calculation condition is 0.16 kg / s, and the deviation between the fluid flow rate of the hydrophobic pipeline under the calculation condition and the fluid flow rate of the hydrophobic pipeline under the solution condition is 23%; The fluid pressure at the outlet of the orifice plate in the CFD simulation of the hydrophobic pipeline is 0.092 MPa, and the aperture ratio is 0.1125. The installation pressure ratio of the orifice plate = fluid pressure at the outlet of the orifice plate / fluid pressure at the inlet of the orifice plate = 0.092 MPa / 0.34 MPa = 0.27; In step 105, the boundary conditions satisfied by the fluid pressure at the inlet of the steam trap are: The actual fluid flow rate of the hydrophobic pipeline is 77% of the fluid flow rate of the hydrophobic pipeline under the calculation condition, the fluid pressure at the inlet of the orifice plate is 0.69 MPa, the pressure drop of the steam trap is 2.11 MPa, the flow - through capacity of the hydrophobic pipeline 3 is 0.23 kg / s, and the safety multiple is 1.9.

[0058] In one of the embodiments, Figure 6 it is the CFD solution grid of the hydrophobic pipeline for this embodiment. The blue part in the figure is the pipe wall of the hydrophobic pipeline 3, the pipe wall of the sleeve, or the head end of the flash tank 1. The green part is the inlet of the hydrophobic pipeline 3, and the red part is the fluid flow boundary inside the flash tank 1. The fluid flow boundary inside the flash tank 1 can allow the fluid to flow in and out; In the CFD solution of the hydrophobic pipeline flow field, the hydrophobic pipeline 3 is a DN50 pipeline; in the final design parameters of the orifice plate 2, the diameter of the first through hole 4 is 9 mm, and the diameter of the second through hole 5 is 3 mm; In the boundary conditions of the CFD solution of the hydrophobic pipeline, the fluid pressure at the inlet of the steam trap is 2.781 MPa, the saturated water enthalpy of the fluid at the inlet of the steam trap is 988.76 kJ / (kg·K), the rated fluid flow rate at the inlet of the orifice plate is 0.12 kg / s, the assumed initial value of the fluid dryness at the inlet of the orifice plate is 0.14, the assumed initial value of the fluid temperature at the inlet of the orifice plate is 145 °C, the fluid pressure at the outlet of the orifice plate is 0.92 bar, and the fluid temperature at the outlet of the orifice plate is 176.29 °C; The CFD iterative solution results of the hydrophobic pipeline are: the fluid pressure at the inlet of the orifice plate is 0.36 MPa, the fluid temperature at the inlet of the orifice plate is 139.85 °C, and the fluid dryness at the inlet of the orifice plate is 0.19; Figure 9 is the flow velocity field diagram of the fluid on the vertical middle plane of the hydrophobic pipeline for this embodiment, Figure 12 is the pressure field diagram of the fluid on the vertical middle plane of the hydrophobic pipeline for this embodiment; According to Figure 9 , it is determined that the maximum flow velocity of the fluid on the vertical middle plane of the hydrophobic pipeline is 206 m / s; From Figure 9 it can be seen that the fluid flow velocity and flow direction of the inlet part of the hydrophobic pipeline 3 are relatively uniform. When reaching the second through hole 5, the change in the fluid flow velocity direction begins to occur, and the fluid flow velocity reaches the maximum at the first through hole 4; due to inertia after the fluid exits the orifice plate 2, it still maintains a relatively high flow velocity within a certain range; as the fluid flow further expands, the fluid flow velocity gradually decreases; the fluid coming out of the second through hole 5 impacts the inner surface of the blue sleeve and finally flows deep into the flash tank 1; From Figure 12 it can be seen that a large gradient appears in the fluid pressure at the orifice plate 2, while it is basically uniform at the end of the hydrophobic pipeline 3 and inside the flash tank 1; According to Figure 12 , the fluid pressure at the outlet of the steam trap is determined; the pressure drop of the steam trap is 2.34 MPa; according to Figure 9 , the fluid flow velocity in front of the orifice plate is determined to be 7.96 m / s; the flow capacity of the steam trap is 0.25 kg / s; according to the final design parameters of the orifice plate, the CFD solution of the hydrophobic pipeline 3 is carried out, and the fluid flow rate of the hydrophobic pipeline solution working condition is obtained as 0.12 kg / s; The fluid flow rate of the hydrophobic pipeline calculation working condition is 0.17 kg / s, and the deviation between the fluid flow rate of the hydrophobic pipeline calculation working condition and the fluid flow rate of the hydrophobic pipeline solution working condition is 28%; the fluid pressure at the outlet of the orifice plate in the CFD simulation of the hydrophobic pipeline is 0.092 MPa, and the orifice diameter ratio is 0.18, and the installation pressure ratio of the orifice plate = the fluid pressure at the outlet of the orifice plate / the fluid pressure at the inlet of the orifice plate = 0.092 MPa / 0.36 MPa = 0.25; In step 105, the boundary conditions satisfied by the fluid pressure at the inlet of the steam trap are as follows: the actual working condition fluid flow rate of the steam trap pipeline is 72% of the calculated working condition fluid flow rate of the steam trap pipeline, the fluid pressure at the inlet of the orifice plate is 0.71 MPa, the pressure drop of the steam trap is 2.08 MPa, the flow capacity of the steam trap pipeline 3 is 0.23 kg / s, and the safety multiple is 1.9.

[0059] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent for the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and all of them fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for the present invention shall be subject to the appended claims.

Claims

1. A cavitation control device for a nuclear power plant drain pipe, characterized in that: It comprises a throttling orifice plate (2); the throttling orifice plate (2) connects the end of a drain pipe (3) and the head end of a flash tank (1) together by welding; a sleeve is provided outside the drain pipe (3); The central axis of the throttling orifice plate (2) coincides with the central axis of the drain pipe (3); a first through hole (4) is provided at the center of the throttling orifice plate (2); and second through holes (5) are symmetrically provided at both ends of the throttling orifice plate (2) in a diameter direction perpendicular to the central axis. The throttling orifice plate (2) is formed by cutting and opening a hole in a whole forging, and the design parameters of the throttling orifice plate (2) are optimized by CFD simulation of the drain pipe.

2. The nuclear power plant drain pipe cavitation control device according to claim 1, characterized in that: The first through hole (4) and the second through hole (5) are both circular through holes; the design parameters of the throttling orifice plate (2) include the diameter of the first through hole (4), the diameter of the second through hole (5) and the rated working condition fluid flow rate of the throttling orifice plate inlet; the design parameters of the throttling orifice plate (2) are optimized by CFD simulation of the drain pipe, comprising the following steps: Step 101, performing CFD solution of the drain pipe according to the initial design parameters of the throttling orifice plate (2) to obtain the fluid flow rate of the drain pipe under the working condition; When the difference between the working condition fluid flow rate of the drain pipe and the rated working condition fluid flow rate of the throttling orifice inlet is outside the given deviation range, it indicates that the initial design parameters of the throttling orifice (2) are unreasonable, and the process goes to step 102; When the difference between the fluid flow rate of the drain pipe working condition and the fluid flow rate of the rated working condition at the orifice inlet is within a given deviation range, step 103 is entered; Step 102, adjusting the design parameters of the throttling orifice (2); performing CFD solution of the drain pipe according to the adjusted design parameters of the throttling orifice (2), and obtaining the fluid flow rate of the drain pipe under the solution working condition; Repeat the above steps for several times until the difference between the fluid flow rate of the drain pipe solution working condition and the fluid flow rate of the rated working condition at the throttling orifice inlet is within the given deviation range; Step 103: When the difference between the working condition fluid flow rate of the drain pipe and the rated working condition fluid flow rate at the inlet of the throttling orifice plate is within a given deviation range, it indicates that the design parameters corresponding to the throttling orifice plate (2) are reasonable, and the difference is used as the final design parameters of the throttling orifice plate (2).

3. The nuclear power plant drain pipe cavitation control device according to claim 2, characterized in that: The CFD solution of the drain pipe is performed according to the design parameters of the throttling orifice plate (2) to obtain the fluid flow rate of the drain pipe solution working condition, including the following steps: Step 201, establishing a CFD solution grid for a drainage pipeline; Step 202, establishing boundary conditions, fluid types and fluid flow models for CFD solution of the drainage pipeline; Step 203, performing CFD iterative solution of the drain pipe on the drain pipe CFD solution grid according to the boundary conditions, fluid type and fluid flow model of the drain pipe CFD solution, and obtaining the drain pipe CFD iterative solution result; Step 204: According to the CFD iterative solution result of the drain pipe, a finite element analysis is performed on the fluid on the vertical mid-plane of the drain pipe by using finite element analysis software to obtain a fluid velocity field diagram and a fluid pressure field diagram on the vertical mid-plane of the drain pipe; Step 205: Determine the fluid flow rate of the drain pipe according to the fluid pressure field diagram of the vertical mid-plane of the drain pipe and the calculation formula of the flow capacity of the drain trap.

4. The nuclear power plant drain pipe cavitation control device according to claim 3, characterized in that: In step 201, the drain pipe (3), the connecting part of the casing and the flash tank (1) are selected as the drain pipe CFD solution flow field, and a drain pipe CFD solution grid is established; the fluid flow outlet of the drain pipe CFD solution grid is cylindrical.

5. The nuclear power plant drain pipe cavitation control device according to claim 3, characterized in that: In step 201, the drain pipe CFD solution grid is a structured hexahedral grid; the drain pipe (3), the wall of the casing and the flash tank (1), and the drain pipe CFD solution grid density in the area before and after the throttling orifice plate (2) is greater than the drain pipe CFD solution grid in other areas.

6. The nuclear power plant drain pipe cavitation control device according to claim 3, characterized in that: In step 202, the boundary conditions solved by CFD for the steam trap pipeline include the steam trap inlet boundary conditions, the throttling orifice plate inlet boundary conditions, and the throttling orifice plate outlet boundary conditions; Among them, the boundary conditions at the steam trap inlet include the steam trap inlet fluid pressure and the steam trap inlet fluid saturated water enthalpy; The boundary conditions at the inlet of the throttle orifice plate include the rated working condition fluid flow rate at the inlet of the throttle orifice plate, the flow direction of the fluid at the inlet of the throttle orifice plate, the assumed initial value of the fluid temperature at the inlet of the throttle orifice plate, and the assumed initial value of the fluid dryness at the inlet of the throttle orifice plate; the flow direction of the fluid at the inlet of the throttle orifice plate is perpendicular to the wall surface of the throttle orifice plate (2); The boundary conditions at the throttle orifice outlet include the throttle orifice outlet fluid boundary, the throttle orifice outlet fluid pressure and the throttle orifice outlet fluid temperature; the throttle orifice outlet fluid boundary is a free open boundary; The fluid type solved by CFD for the drain pipe is wet steam; the fluid flow model solved by CFD for the drain pipe includes heat transfer model, turbulence equation and wall function, among which the heat transfer model is the total energy model, the turbulence equation is the K-Epsilon equation, and the wall function is an adaptive wall function.

7. The nuclear power plant drain pipe cavitation control device according to claim 3, characterized in that: In step 203, CFD iterative solution is performed on the CFD solution grid of the drain pipe according to the boundary conditions, fluid type and fluid flow model of the drain pipe CFD solution to obtain the CFD iterative solution result of the drain pipe, including the following steps: According to the boundary conditions, fluid type and fluid flow model of the drain pipe CFD solution, the drain pipe CFD solution grid is subjected to multiple drain pipe CFD solutions; the initial condition of the next drain pipe CFD solution is the result of the previous drain pipe CFD solution; the drain pipe CFD solution results include the throttling orifice inlet fluid pressure, throttling orifice inlet fluid temperature and throttling orifice inlet fluid dryness; When the deviation of the fluid pressure at the throttling orifice inlet obtained by the CFD solution of the drain pipe from the previous time is within a given deviation range, the convergence of the CFD iterative solution of the drain pipe is achieved, and the CFD iterative solution result of the drain pipe is obtained; the CFD iterative solution result of the drain pipe includes the converged fluid pressure at the throttling orifice inlet, the fluid temperature at the throttling orifice inlet, and the fluid dryness at the throttling orifice inlet.

8. The nuclear power plant drain pipe cavitation control device according to claim 6, characterized in that: In step 205, the steam trap flow capacity calculation formula is a linear relationship between the steam trap pressure drop and the flow capacity; According to the fluid pressure field diagram of the vertical midplane of the steam trap, the steam trap outlet fluid pressure is determined; the steam trap inlet fluid pressure is the boundary condition for the steam trap CFD solution; the difference between the steam trap inlet fluid pressure and the steam trap outlet fluid pressure is the steam trap pressure drop; Substitute the steam trap pressure drop into the steam trap flow capacity calculation formula to obtain the steam trap flow capacity; determine the steam trap outlet fluid flow rate based on the steam trap flow capacity, and the steam trap outlet fluid flow rate is the fluid flow rate of the steam trap pipeline working condition solution.

9. The nuclear power plant drain pipe cavitation control device according to claim 7, characterized in that: Also includes: Step 104, checking the fluid flow rate of the drain pipe working condition corresponding to the final design parameters of the throttling orifice plate (2); The fluid flow rate of the drain pipe solution working condition corresponding to the final design parameters of the throttling orifice plate (2) is checked, including the following steps: According to the fluid dryness at the inlet of the throttling orifice plate in the CFD iterative solution results of the drain pipe, a suitable two-phase flow empirical calculation formula is selected to calculate the fluid flow rate of the drain pipe, and the fluid flow rate of the drain pipe calculation condition is obtained; When the difference between the calculated working condition fluid flow of the drain pipe and the solved working condition fluid flow of the drain pipe is within a reasonable deviation range, it is determined that the solved working condition fluid flow of the drain pipe has passed the verification.

10. The nuclear power plant drain pipe cavitation control device according to claim 9, characterized in that: The method also includes: step 105, designing the maximum flow capacity of the drainage pipe (3); Designing the maximum flow capacity of the steam trap pipe (3) comprises the following steps: performing iterative solutions according to the empirical calculation formula for two-phase flow and the calculation formula for the flow capacity of the steam trap, so that the fluid pressure at the steam trap inlet satisfies the boundary conditions.

Images