A design parameter optimization method for the throttle orifice plate of a nuclear power plant drain pipe cavitation control device

Abstract

The present invention specifically relates to a method for optimizing the design parameters of a throttle orifice plate in a cavitation control device for a drain pipe in a nuclear power plant, belonging to the technical field of pipeline inner wall corrosion protection. The method comprises a throttle orifice plate; the throttle orifice plate connects the end of the drain pipe to the head end of a flash tank by welding; a sleeve is provided on the outside of the drain pipe; the central axis of the throttle orifice plate coincides with the central axis of the drain pipe, a first through-hole is provided in the center of the throttle orifice plate, and second through-holes are symmetrically provided at both ends of the diametrical direction perpendicular to the central axis of the throttle orifice plate; the throttle orifice plate is formed by cutting and opening holes in a single forging, and the design parameters of the throttle orifice plate are optimized through CFD simulation of the drain pipe. By improving the design and installation of the throttle orifice plate, the present invention avoids the thinning of the pipe wall caused by cavitation impact and the impact of water flow on the drain pipe caused by accumulated water. The design parameters of the throttle orifice plate are optimized through CFD simulation of the drain pipe, ensuring that the design parameters of the throttle orifice plate meet the design requirements and improving the safety of the drain pipe operation.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline inner wall anti-corrosion, in particular to a design parameter optimization method for a throttling orifice plate of a cavitation control device for a drain pipeline of a nuclear power plant. Background Art

[0002] The nuclear power plant gas turbine drain system is responsible for draining the gas turbine during operation. The system mainly consists of a drain trap, drain piping, and a flash tank.

[0003] The steam trap separates steam from the turbine exhaust, discharging the resulting steam through a drain pipe into the flash tank. The steam trap's water-gas separation function prevents steam from entering the flash tank, maintaining a low-pressure environment within the flash tank.

[0004] A throttling orifice plate is fixed within the drain pipe. The orifice plate has a central opening and is welded to the drain pipe. The orifice plate is designed to create a constriction at an appropriate location within the drain pipe. As drain flows through the constriction, it becomes thinner or constricted. As drain flows through the constriction, the localized resistance of the orifice plate reduces the pressure downstream of the orifice, leading to energy loss. Vibration in the drain pipe and erosion and perforation of the pipe fittings behind the orifice plate can cause numerous operational problems in nuclear power plants, directly impacting their safety and economic efficiency.

[0005] In the actual service life of nuclear power plant gas turbine drain systems, the steam traps drain intermittently, and the orifice design features only a through-hole in the center of the orifice. This results in water accumulation in the drain pipe upstream of the orifice. The constant impact of the water on the accumulated water creates oscillations, which significantly impacts the drain pipe. Furthermore, the gas-liquid two-phase flow generated by the drain after throttling and reducing the pressure through the orifice creates vortices behind the orifice, which erode the pipe wall at the vortex, gradually thinning the pipe wall. These factors seriously threaten the service life of nuclear power plant gas turbine drain systems, 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 method for optimizing the design parameters of a throttling orifice plate of a cavitation control device for a drain pipe of a nuclear power plant, so as to solve the problem that cavitation occurs in the drain pipe downstream of the existing throttling orifice plate, impacting the pipe wall and causing the pipe wall to become thinner. By improving the design and installation of the throttling orifice plate, cavitation is avoided in the drain pipe, thereby preventing cavitation from impacting the pipe wall and causing the pipe wall to become thinner.

[0007] A second object of the present invention is to provide a method for optimizing the design parameters of a throttling orifice plate of a nuclear power plant drain pipe cavitation control device, thereby resolving the problem of intermittent drainage of the drain trap, water accumulation in the drain pipe upstream of the existing throttling orifice plate, and oscillation caused by the impact of water flow on the accumulated water, which in turn impacts the drain pipe. By improving the design and installation of the throttling orifice plate, water accumulation in the drain pipe upstream of the throttling orifice plate is avoided, thereby preventing the impact of water flow on the drain pipe, which in turn impacts the drain pipe, caused by oscillation.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A method for optimizing design parameters of a throttle orifice plate of a cavitation control device for a drain pipe of a nuclear power plant comprises a throttle orifice plate; the throttle orifice plate connects the end of the drain pipe to the head end of a flash tank by welding; a casing is provided on the outside of the drain pipe;

[0010] The central axis of the throttling orifice coincides with the central axis of the drain pipe, a first through hole is provided in the center of the throttling orifice, and second through holes are symmetrically provided at both ends of the throttling orifice in a diameter direction perpendicular to the central axis;

[0011] The throttle orifice plate is made by cutting a hole in a whole forging, and the design parameters of the throttle orifice plate are optimized through CFD simulation of the drain pipe.

[0012] In one achievable method, the first through hole and the second through hole are both 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 rated working condition fluid flow rate of the orifice plate inlet; the design parameters of the orifice plate are optimized through CFD simulation of the drain pipe, including the following steps:

[0013] Step 101: Perform 3CFD solution of the drain pipe according to the initial design parameters of the throttle orifice plate to obtain the fluid flow rate of the drain pipe under the working condition;

[0014] When the difference between the calculated working condition fluid flow rate of the drain pipe and the rated working condition fluid flow rate of the orifice plate inlet is outside the given deviation range, it indicates that the initial design parameters of the orifice plate are unreasonable, and the process goes to step 102;

[0015] When the difference between the fluid flow rate of the drain pipe under the working condition and the fluid flow rate of the rated working condition at the orifice plate inlet is within a given deviation range, step 103 is entered;

[0016] Step 102: Adjust the design parameters of the orifice plate; perform CFD solution based on the adjusted design parameters of the orifice plate to obtain the fluid flow rate of the drain pipe under the working condition; repeat the above steps multiple times until the difference between the fluid flow rate of the drain pipe under the working condition and the rated fluid flow rate of the orifice plate inlet under the working condition is within a given deviation range;

[0017] Step 103: When the difference between the calculated working condition fluid flow rate of the drain pipe and the rated working condition fluid flow rate of the orifice plate inlet is within a given deviation range, it indicates that the design parameters corresponding to the orifice plate are reasonable, and the difference is used as the final design parameters of the orifice plate.

[0018] As one of the feasible methods, CFD solution is performed based on the design parameters of the orifice plate to obtain the fluid flow rate of the drain pipe working condition, including the following steps:

[0019] Step 201: Establishing a CFD solution grid for the drainage pipeline;

[0020] Step 202: Establish boundary conditions, fluid types, and fluid flow models for CFD solution of the drainage pipeline;

[0021] Step 203: performing CFD iterative solution 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;

[0022] Step 204: Based on the CFD iterative solution results of the drain pipe, a finite element analysis is performed on the fluid on the vertical mid-plane of the drain pipe 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;

[0023] Step 205: Determine the fluid flow rate of the drain pipe in the working condition according to the fluid pressure field diagram of the vertical median plane of the drain pipe and the calculation formula of the flow capacity of the steam trap.

[0024] As one of the feasible ways, in step 201, the connection part of the drain pipe, the casing and the flash tank is 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.

[0025] As one of the feasible ways, in step 201, the drain pipe CFD solution grid is a structured hexahedral grid; the drain pipe, the wall of the casing and the flash tank, and the drain pipe CFD solution grid density in the area before and after the throttle orifice plate is greater than the drain pipe CFD solution grid in other areas.

[0026] As one possible implementation, in step 202, the boundary conditions of the steam trap CFD solution include the steam trap inlet boundary condition, the orifice plate inlet boundary condition, and the orifice plate outlet boundary condition;

[0027] Among them, the boundary conditions of the steam trap inlet include the steam trap inlet fluid pressure and the steam trap inlet fluid saturated water enthalpy;

[0028] The boundary conditions of the orifice plate inlet include the rated working condition fluid flow rate of the orifice plate inlet, the flow direction of the fluid at the orifice plate inlet, the assumed initial value of the fluid temperature at the orifice plate inlet, and the assumed initial value of the fluid dryness at the orifice plate inlet; the flow direction of the fluid at the orifice plate inlet is perpendicular to the orifice plate wall;

[0029] The orifice plate outlet boundary conditions include the orifice plate outlet fluid boundary, orifice plate outlet fluid pressure, and orifice plate outlet fluid temperature. The orifice plate outlet fluid boundary is a free open boundary, that is, the fluid can flow in and out.

[0030] 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 a heat transfer model, a turbulence equation, and a wall function. Among them, the heat transfer model is a total energy model, the turbulence equation is a K-Epsilon equation, and the wall function is an adaptive wall function.

[0031] As one possible implementation, in step 203, performing CFD iterative solution on the drain pipe CFD solution grid according to the boundary conditions, fluid type, and fluid flow model of the drain pipe CFD solution to obtain the drain pipe CFD iterative solution result includes the following steps:

[0032] Multiple CFD solutions are performed on the CFD grid of the drain pipe according to the boundary conditions, fluid type, and fluid flow model of the drain pipe. The initial conditions of the next CFD solution of the drain pipe are the results of the previous CFD solution of the drain pipe. The CFD solution results of the drain pipe include the fluid pressure at the inlet of the throttle orifice plate, the fluid temperature at the inlet of the throttle orifice plate, and the fluid dryness at the inlet of the throttle orifice plate.

[0033] When the deviation of the fluid pressure at the throttle plate inlet obtained from the previous CFD solution of the drain pipe is within a given deviation range, the convergence of the CFD iterative solution of the drain pipe is achieved, and the CFD iterative solution results of the drain pipe are obtained; the CFD iterative solution results of the drain pipe include the converged fluid pressure at the throttle plate inlet, the fluid temperature at the throttle plate inlet, and the fluid dryness at the throttle plate inlet.

[0034] As one possible implementation, in step 205, the steam trap flow capacity calculation formula is a linear relationship between the steam trap pressure drop and the flow capacity;

[0035] Determine the steam trap outlet fluid pressure based on the fluid pressure field diagram of the vertical midplane of the steam trap pipeline. The steam trap inlet fluid pressure is the boundary condition for the steam trap pipeline CFD solution. The difference between the steam trap inlet fluid pressure and the steam trap outlet fluid pressure is the steam trap pressure drop.

[0036] 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. The steam trap outlet fluid flow rate is the fluid flow rate of the steam trap pipeline working condition solution.

[0037] As one possible implementation method, the method further includes: step 104, verifying the fluid flow rate of the drain pipe working condition corresponding to the final design parameters of the throttling orifice plate;

[0038] Verify the fluid flow rate of the drain pipe solution corresponding to the final design parameters of the throttling orifice plate, including the following steps:

[0039] According to the fluid dryness at the orifice inlet in the drain pipe CFD iterative solution results, the appropriate two-phase flow empirical calculation formula is selected to calculate the fluid flow rate in the drain pipe, and the fluid flow rate under the calculated working condition of the drain pipe is obtained;

[0040] When the difference between the fluid flow rate of the calculated working condition of the drain pipe and the fluid flow rate of the solved working condition of the drain pipe is within a reasonable deviation range, it is determined that the fluid flow rate of the solved working condition of the drain pipe has passed the verification.

[0041] As one possible implementation method, the method further includes: step 105, designing the maximum flow capacity of the drain pipe;

[0042] Step 105, designing the maximum flow capacity of the steam trap pipeline, includes 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 meets the boundary conditions.

[0043] Beneficial technical effects of the present invention:

[0044] The design parameter optimization method of the throttle orifice plate of the nuclear power plant drain pipe cavitation control device of the present invention improves the design and installation of the throttle orifice plate. The throttle orifice plate is vertically installed at the end of the drain pipe, a first through hole is provided in the center, and second through holes are symmetrically provided at both ends in the diameter direction perpendicular to the central axis. This avoids cavitation and water accumulation in the drain pipe downstream of the throttle orifice plate, thereby avoiding the gradual thinning of the pipe wall due to the impact of cavitation on the pipe wall of the drain pipe downstream of the throttle orifice plate and the impact of water flow on the drain pipe caused by the impact of the accumulated water.

[0045] The present invention provides a method for optimizing the design parameters of a throttling orifice plate of a cavitation control device for a nuclear power plant drain pipe. The design parameters of the throttling orifice plate are optimized through CFD simulation of the drain pipe. Simultaneously, the CFD simulation results of the drain pipe are verified using a two-phase flow empirical formula, thereby ensuring that the design parameters of the throttling orifice plate meet the design requirements and improving the safety of drain pipe operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1This is a cross-sectional view of an installation embodiment of a nuclear power plant drain pipe cavitation control device according to the present invention;

[0047] Figure 2 It is a curve diagram of fluid flow rate and pressure change in the drain pipe;

[0048] Figure 3 It is a curve diagram of fluid pressure change in the drain pipe;

[0049] Figure 4 A schematic diagram of a CFD solution grid for a drain pipe embodiment;

[0050] Figure 5 A schematic diagram of a CFD solution grid for a drain pipe embodiment;

[0051] Figure 6 A schematic diagram of a CFD solution grid for a drain pipe embodiment;

[0052] Figure 7 A schematic diagram of a fluid pressure field on a vertical median plane of an embodiment of a drain pipe;

[0053] Figure 8 A schematic diagram of a fluid pressure field on a vertical median plane of an embodiment of a drain pipe;

[0054] Figure 9 A schematic diagram of a fluid pressure field on a vertical median plane of an embodiment of a drain pipe;

[0055] Figure 10 A schematic diagram of a fluid velocity field on a vertical median plane of an embodiment of a drain pipe;

[0056] Figure 11 A schematic diagram of a fluid velocity field on a vertical median plane of an embodiment of a drain pipe;

[0057] Figure 12 A schematic diagram of a fluid velocity field on a vertical median plane of an embodiment of a drain pipe;

[0058] Figure 13 This is the relationship diagram between the pressure drop and flow capacity of the steam trap.

[0059] In the figure, 1, flash tank; 2, throttling orifice; 3, drain pipe; 4, first through hole; 5, second through hole; p1, fluid pressure upstream of throttling orifice; p2, fluid pressure downstream of throttling orifice; p vc , fluid pressure at the contraction section; v1, fluid velocity upstream of the throttle orifice; v2, fluid velocity downstream of the throttle orifice; p v , fluid saturated vapor pressure; p, fluid flow rate. DETAILED DESCRIPTION

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used in the specification of the application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0061] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0062] In the description of the present invention, unless otherwise specified or limited, the terms "disposed," "installed," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; and direct or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of these terms based on the specific circumstances.

[0063] The directions or positional relationships indicated by terms such as "upper", "lower", "front", "back", "inside", and "outside" are based on the directions or positional relationships shown in the accompanying drawings, or are the directions or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience and simplification of description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, they should not be understood as limiting the present invention.

[0064] The terms "first," "second," and the like are merely used to distinguish between elements of similar nature and do not indicate or imply relative importance or a particular order.

[0065] The terms "comprises," "comprising," or any other variations thereof, are intended to cover a non-exclusive inclusion of elements other than the listed elements and may also include additional elements not specifically listed.

[0066] The technical solution of the present invention is described clearly and completely below with reference to the accompanying drawings and specific embodiments.

[0067] The steam turbine drain system in a nuclear power plant primarily consists of a steam trap, a drain pipe, and a flash tank. The drain pipe's head end connects to the steam trap, while its tail end is inserted into the flash tank and welded to its inner wall. A casing is installed on the outside of the drain pipe. Turbine exhaust air is separated into water and gas in the steam trap, producing a large amount of drain water, which enters the flash tank through the drain pipe. A throttling orifice plate is fixed within the drain pipe. The orifice plate has a central opening and is welded to the drain pipe.

[0068] The drain pipe downstream of the orifice plate is prone to cavitation, which impacts the pipe wall and causes localized thinning. The steam trap uses intermittent drainage, while the orifice plate design only features a through hole in the center. This makes it very easy for water to accumulate in the drain pipe upstream of the orifice plate. The constant impact of the water on the accumulated water creates oscillations, which significantly impacts the drain pipe.

[0069] Figure 2 This graph shows the flow rate and pressure changes of a fluid in a drain pipe. The function of an orifice is to reduce the aperture at an appropriate location in the drain pipe, forming a constriction. As the fluid passes through the constriction, it becomes thinner or constricted. As the fluid flows through the drain pipe, the localized resistance of the orifice reduces its pressure and causes energy loss. The minimum cross-sectional area of ​​the fluid occurs downstream of the constriction, known as the contraction.

[0070] At the contraction section, the fluid velocity is the highest and the pressure is the lowest. As the fluid expands into a larger area, the velocity decreases and the pressure increases. However, the fluid pressure downstream of the orifice does not fully recover to the upstream fluid pressure. This is the result of greater internal turbulence and energy consumption.

[0071] Figure 3 The pressure change curve of the fluid in the drain pipe is shown in Figure 2. If the pressure of the fluid at the contraction section is P vc Drop to the saturated vapor pressure P at the corresponding temperature of the fluid v Below this point, steam and gas dissolved in the fluid will escape from the fluid, forming bubbles of steam and gas mixture. The lower the pressure of the fluid at the contraction section, the more bubbles there are. If the fluid pressure P2 downstream of the throttling orifice is still lower than the saturated vapor pressure P at the corresponding temperature of the fluid, v , bubbles will continue to be generated in the drain pipe downstream of the throttling orifice plate, and the liquid and gas phases will mix. This phenomenon is called flash evaporation.

[0072] If the fluid pressure P2 downstream of the throttling orifice plate returns to a level higher than the saturated vapor pressure P corresponding to the fluid temperature, v Under the action of high pressure, bubbles quickly condense and burst, creating a local cavity at the moment of bubble rupture. The high-pressure fluid surrounding the original bubbles flows at a very high speed into the space occupied by these bubbles, creating an impact force. Because the gas and vapor in the bubbles do not have time to completely dissolve and condense instantly, the impact force causes them to separate into bubbles. These bubbles are then compressed and condensed by the high-pressure fluid surrounding them. This repeated process produces a noise similar to that of sand and gravel flowing through a drain pipe. This phenomenon is called cavitation.

[0073] There are two ways to avoid cavitation in the drain pipe downstream of the orifice:

[0074] One is to improve the design and installation of the throttle orifice plate to control the fluid pressure P at the contraction section. vc , maintain the fluid pressure P at the contraction section vc Not lower than the saturated vapor pressure P at the corresponding temperature of the fluid v , so that the fluid at the contraction section will not generate bubbles, thereby preventing cavitation from occurring in the drain pipe downstream of the throttle orifice plate;

[0075] The other is to reduce the fluid pressure P2 downstream of the throttle orifice plate so that the fluid pressure P2 downstream of the throttle orifice plate is lower than the saturated vapor pressure P at the corresponding temperature of the fluid. v However, the pressure difference before and after the drain pipe is not large, and it is unlikely to use a multi-stage pressure reduction method to make the fluid pressure P2 downstream of the throttling orifice lower than the saturated vapor pressure P at the corresponding temperature of the fluid. v .

[0076] Therefore, the first approach must be adopted to avoid cavitation in the drain pipe downstream of the orifice plate. Taking the first approach requires verifying whether the design parameters of the orifice plate meet the design requirements and taking appropriate measures to ensure that the orifice plate is not installed incorrectly or misaligned.

[0077] For this, see Figure 1 The present invention provides a method for optimizing design parameters of a throttle orifice plate of a cavitation control device for a drain pipe of a nuclear power plant, comprising a throttle orifice plate 2; the throttle orifice plate 2 connects the end of a drain pipe 3 to the head end of a flash tank 1 by welding; a casing is provided on the outside of the drain pipe 3;

[0078] 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 in the center of the throttling orifice plate 2. 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.

[0079] The throttling orifice plate 2 is formed by cutting a hole through a whole forging piece that meets the design length. The design parameters of the throttling orifice plate 2 are optimized through CFD simulation of the drain pipe.

[0080] The method for optimizing the design parameters of the throttle orifice plate of the cavitation control device of the nuclear power plant drain pipe of the present invention avoids cavitation in the drain pipe by improving the design and installation of the throttle orifice plate, thereby avoiding the cavitation impacting the pipe wall and causing the pipe wall to become thinner; by improving the design and installation of the throttle orifice plate, water accumulation in the drain pipe upstream of the throttle orifice plate is avoided, thereby avoiding the oscillation caused by the water flow impacting the accumulated water and causing the drain pipe to be impacted by the oscillation; the throttle orifice plate 2 connects the end of the drain pipe 3 with the head end of the flash tank 1 by welding, thereby avoiding the end of the drain pipe 3 being inserted into the interior of the flash tank 1 and welded to the inner wall of the flash tank 1 to form a connecting weld; the design parameters of the throttle orifice plate 2 are optimized through CFD simulation of the drain pipe, thereby ensuring that the design parameters of the throttle orifice plate 2 meet the design specifications and improving the safety of the operation of the drain pipe 3.

[0081] In the present invention, as one of the possible implementations, the first through hole 4 and the second through hole 5 are both 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 rated working condition fluid flow rate of the orifice plate inlet; the design parameters of the orifice plate 2 are optimized by CFD simulation of the drain pipe, including the following steps:

[0082] Step 101: Perform CFD solution for the drain pipe according to the initial design parameters of the orifice plate 2 to obtain the fluid flow rate of the drain pipe under the working condition;

[0083] When the difference between the calculated working condition fluid flow rate of the drain pipe and the rated working condition fluid flow rate of the orifice plate inlet is outside the given deviation range, it indicates that the initial design parameters of the orifice plate 2 are unreasonable, and the process goes to step 102;

[0084] When the difference between the fluid flow rate of the drain pipe under the working condition and the fluid flow rate of the rated working condition at the orifice plate inlet is within a given deviation range, step 103 is entered;

[0085] Step 102: Adjust the design parameters of the orifice plate 2; perform a CFD solution for the drain pipe based on the adjusted design parameters of the orifice plate 2 to obtain a calculated working condition fluid flow rate for the drain pipe; repeat the above steps multiple times until the difference between the calculated working condition fluid flow rate for the drain pipe and the rated working condition fluid flow rate at the orifice plate inlet is within a given deviation range;

[0086] Step 103: When the difference between the calculated working condition fluid flow rate of the drain pipe and the rated working condition fluid flow rate of the orifice plate inlet is within a given deviation range, it indicates that the design parameters corresponding to the orifice plate 2 are reasonable, and the difference is used as the final design parameters of the orifice plate 2.

[0087] In the present invention, as one of the feasible methods, a CFD solution of the drain pipe is performed according to the design parameters of the throttle orifice plate 2 to obtain the fluid flow rate of the drain pipe under the working condition, including the following steps:

[0088] Step 201: Establishing a CFD solution grid for the drainage pipeline;

[0089] Step 202: Establish boundary conditions, fluid types, and fluid flow models for CFD solution of the drainage pipeline;

[0090] Step 203: Perform 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 to obtain a 3CFD iterative solution result of the drain pipe;

[0091] Step 204: Based on the CFD iterative solution results of the drain pipe, a finite element analysis is performed on the fluid on the vertical mid-plane of the drain pipe 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;

[0092] Step 205: Determine the fluid flow rate of the drain pipe in the working condition according to the fluid pressure field diagram of the vertical median plane of the drain pipe and the calculation formula of the flow capacity of the steam trap.

[0093] In the present invention, as one of the possible implementation methods, in step 201, the drain pipe 3, the connecting portion 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;

[0094] The fluid flow outlet of the hydrophobic pipe CFD solution grid is cylindrical. The cylindrical fluid flow outlet is chosen because the fluid has a large inertia to continue flowing forward when flowing out of the throttling orifice plate 2. Therefore, a longer area in the fluid flow direction is selected to establish the hydrophobic pipe CFD solution grid.

[0095] In the present invention, as one of the achievable methods, in step 201, a CFD solution grid for the drain pipe is established by using CFD modeling and meshing software; the CFD modeling and meshing software is general software in the field, including but not limited to ICEM.

[0096] In the present invention, as one of the feasible methods, in step 201, the hydrophobic pipe CFD solution grid is a structured hexahedral grid; the hydrophobic pipe 3, the wall of the casing and the flash tank 1, and the hydrophobic pipe CFD solution area before and after the throttle orifice 2 have a greater density than the hydrophobic pipe CFD solution grid in other areas; the number of hydrophobic pipe CFD solution grids is 380,000, and the number of nodes in the hydrophobic pipe CFD solution grid is 360,000.

[0097] The hydrophobic pipe CFD solution grid is the basis of the hydrophobic pipe CFD solution. Sufficient density of the hydrophobic pipe CFD solution grid is the guarantee of the hydrophobic pipe CFD solution accuracy. However, an overly dense hydrophobic pipe CFD solution grid will greatly increase the time and difficulty of convergence of the hydrophobic pipe CFD solution. Setting a denser hydrophobic pipe CFD solution grid near the wall and in areas where the fluid flow rate changes rapidly, and setting a relatively sparse hydrophobic pipe CFD solution grid in other areas can meet the hydrophobic pipe CFD solution accuracy requirements.

[0098] In the present invention, as one of the possible implementations, in step 202, the boundary conditions of the steam trap CFD solution include the steam trap inlet boundary condition, the orifice plate inlet boundary condition, and the orifice plate outlet boundary condition;

[0099] Among them, the boundary conditions of the steam trap inlet include the steam trap inlet fluid pressure and the steam trap inlet fluid saturated water enthalpy;

[0100] The boundary conditions of the orifice plate inlet include the rated working condition fluid flow rate of the orifice plate inlet, the flow direction of the fluid at the orifice plate inlet, the assumed initial value of the fluid temperature at the orifice plate inlet, and the assumed initial value of the fluid dryness at the orifice plate inlet; the flow direction of the fluid at the orifice plate inlet is perpendicular to the wall surface of the orifice plate 2;

[0101] The orifice plate outlet boundary conditions include the orifice plate outlet fluid boundary, orifice plate outlet fluid pressure, and orifice plate outlet fluid temperature. The orifice plate outlet fluid boundary is a free open boundary, that is, the fluid can flow in and out.

[0102] The fluid type solved by CFD for the drain pipe is wet steam, which belongs to gas-liquid two-phase flow; the fluid flow model solved by CFD for the drain pipe includes a heat transfer model, a turbulence equation, and a wall function. Among them, the heat transfer model is a total energy model, the turbulence equation is the K-Epsilon equation, and the wall function is an adaptive wall function.

[0103] In the present invention, as one of the possible implementation methods, in step 203, performing CFD iterative solution on the drain pipe CFD solution grid according to the boundary conditions, fluid type, and fluid flow model of the drain pipe CFD solution to obtain the drain pipe CFD iterative solution result includes the following steps:

[0104] Multiple 3CFD solutions are performed on the CFD grid of the drain pipe according to the boundary conditions, fluid type, and fluid flow model of the drain pipe CFD solution. The initial conditions of the next CFD solution of the drain pipe are the results of the previous CFD solution of the drain pipe. The CFD solution results of the drain pipe include the fluid pressure at the inlet of the throttle orifice plate, the fluid temperature at the inlet of the throttle orifice plate, and the fluid dryness at the inlet of the throttle orifice plate.

[0105] When the deviation of the fluid pressure at the orifice plate inlet obtained from the previous CFD solution of the drain pipe is within a given deviation range, the CFD iterative solution of the drain pipe is converged and the CFD iterative solution results of the drain pipe are obtained. The CFD iterative solution results of the drain pipe include the converged fluid pressure at the orifice plate inlet, the fluid temperature at the orifice plate inlet, and the fluid dryness at the orifice plate inlet.

[0106] The deviation of the fluid pressure at the inlet of the throttling orifice plate between the next and the previous CFD solutions of the drain pipe is within 1E-4, achieving the convergence of the CFD iterative solution of the drain pipe and obtaining the CFD iterative solution result of the drain pipe.

[0107] The fluid in the flow field of the hydrophobic pipe CFD solution is a gas-liquid two-phase flow. The CFD solution of gas-liquid two-phase flow is much more complicated than the CFD solution of single-phase flow. When setting the fluid flow rate at the throttle orifice inlet as a boundary condition, the fluid temperature at the throttle orifice inlet and the fluid dryness at the throttle orifice inlet must be given. Both of these parameters are related to the fluid pressure at the throttle orifice inlet. Therefore, CFD iterative solution is required. First, set the assumed initial value of the fluid temperature at the throttle orifice inlet and the assumed initial value of the fluid dryness at the throttle orifice inlet. Then, use the throttle orifice inlet fluid pressure obtained by CFD solution to correct the assumed initial value of the fluid temperature at the throttle orifice inlet and the assumed initial value of the fluid dryness at the throttle orifice inlet. CFD iterative solution is performed multiple times until the deviation of the fluid pressure at the throttle orifice inlet obtained by the previous step and the next step CFD solution is within the given deviation range.

[0108] In the present invention, as one of the achievable methods, in step 204, based on the CFD iterative solution results of the drain pipe, a finite element analysis is performed on the fluid on the vertical mid-plane of the drain pipe using finite element analysis software to obtain a velocity field diagram and a pressure field diagram of the fluid on the vertical mid-plane of the drain pipe; the finite element analysis software is a general software in the art, including but not limited to ANSYS;

[0109] According to the velocity field diagram of the fluid on the vertical mid-plane of the drain pipe, the maximum velocity of the fluid on the vertical mid-plane of the drain pipe is determined; according to the velocity field diagram and pressure field diagram of the fluid on the vertical mid-plane of the drain pipe, the velocity and pressure changes of the fluid on the vertical mid-plane of the drain pipe are determined.

[0110] Figure 13 is a relationship diagram between the pressure drop and flow capacity of a steam trap. In the present invention, as one of the possible implementations, the steam trap is a DN50 FT44-32 steam trap. In step 205, the flow capacity of the steam trap is calculated as follows:

[0111] log 10 Δp=K L *log 10 Q m +B L

[0112] Among them, Q m is the flow capacity of the steam trap, in kg / h; Δp is the pressure drop of the steam trap, in kPa; K L and B L are fitting coefficients, K L is 2.13, B L is -7.31;

[0113] Determine the steam trap outlet fluid pressure based on the fluid pressure field diagram of the vertical midplane of the steam trap pipeline. The steam trap inlet fluid pressure is the boundary condition for the steam trap pipeline CFD solution. The difference between the steam trap inlet fluid pressure and the steam trap outlet fluid pressure is the steam trap pressure drop Δp.

[0114] Substitute the steam trap pressure drop Δp into the steam trap flow capacity calculation formula to obtain the steam trap flow capacity Q m ; According to the flow capacity Q of the steam trap m , determine the fluid flow rate at the steam trap outlet, which is the fluid flow rate of the steam trap pipeline working condition solution.

[0115] In the present invention, as one of the possible implementation methods, the method further includes: step 104, checking the fluid flow rate of the drain pipe working condition corresponding to the final design parameters of the throttle orifice plate 2;

[0116] The fluid flow rate of the drain pipe working condition corresponding to the final design parameters of the throttle orifice plate 2 is checked, including the following steps:

[0117] According to the fluid dryness at the orifice inlet in the drain pipe CFD iterative solution results, the appropriate two-phase flow empirical calculation formula is selected to calculate the fluid flow rate in the drain pipe, and the fluid flow rate under the calculated working condition of the drain pipe is obtained;

[0118] When the difference between the fluid flow rate of the calculated working condition of the drain pipe and the fluid flow rate of the solved working condition of the drain pipe is within a reasonable deviation range, it is determined that the fluid flow rate of the solved working condition of the drain pipe has passed the verification.

[0119] In the present invention, as one of the feasible methods, the empirical calculation formula for two-phase flow is the Lin Zonghu calculation formula; the Lin Zonghu calculation formula is:

[0120]

[0121] Among them, q mTP Calculate the working fluid flow rate for the drain pipe in kg / s; F a is the thermal expansion coefficient of the orifice plate 2; C is the outflow coefficient of the single-phase flow; d is the diameter of the first through hole 4 of the orifice plate 2, in m; D is the inner diameter of the drain pipe 3, in m; β is the aperture ratio, which is equal to d / D; Δp TPis the pressure difference of gas-liquid two-phase flow, unit is Pa; ρ l is the liquid density, in kg / m 3 ρ g is the gas phase density, in kg / m 3 ; x is the fluid dryness at the throttle orifice inlet; θ0 is the two-phase correction coefficient of the throttle orifice.

[0122] Most of the coefficients in Lin Zonghu's calculation formula can be calculated directly, but the determination of the single-phase flow discharge coefficient uses the Reader-Harria / Gellagher formula published by ISO in 1998. The single-phase flow discharge coefficient in this formula is a function of the pipe flow Reynolds number and aperture ratio, and the Reynolds number is a function of the flow rate, so the formula requires an iterative program solution. In addition to the basic calculation formulas, the calculation of the thermal properties of the working fluid is also required during the solution process. Since the thermal properties of wet steam are all in the two-phase region, a water vapor thermodynamic property calculation program was written based on the relevant formulas for the saturation line and two-phase region in the fourth zone of the IF97 series of standards published by the International Association for the Properties of Water and Water Vapor (IAPWS).

[0123] Using a program developed to calculate the thermodynamic properties of water vapor, the initial condition was set at the orifice inlet fluid pressure from the CFD iterative solution of the drain pipe. The fluid flow rate for the drain pipe calculation condition differed by approximately 20% from the calculated and solved condition. This discrepancy is not significant for wet steam two-phase flow calculations. The main reasons for this discrepancy are as follows:

[0124] First, the applicable range of Lin Zonghu's calculation formula is 0.8-19.8 MPa for the fluid pressure at the orifice outlet and 0.25-0.75 for the aperture ratio. However, the orifice outlet fluid pressure and aperture ratio β in the drain pipe CFD simulation are both outside the applicable range of Lin Zonghu's calculation formula, resulting in a certain error in the calculation results of Lin Zonghu's calculation formula.

[0125] Secondly, Lin Zonghu's calculation formula is for orifice flowmeters. Orifice flowmeters are generally installed according to ISO or GB standards. The installation pressure ratio of an orifice flowmeter is generally large, often above 0.75. However, the installation pressure ratio of an orifice plate in a drain pipe CFD simulation is below 0.75, resulting in a certain error in Lin Zonghu's calculation formula.

[0126] Third, Lin Zonghu's calculation formula is not only applicable to wet steam, but also to the two-phase flow of air and water. The formula does not contain phase change. When there is a phase change, the density of the two-phase flow will drop sharply due to the phase change of more steam, making the mass flow rate smaller, resulting in a certain deviation in Lin Zonghu's calculation formula.

[0127] Since there is no more accurate empirical formula to verify the research of wet steam two-phase flow internationally, the verification of calculation results generally relies on experiments. However, due to the limitations of gas sources and measurement tools, steam working fluid experiments are quite expensive and complex. CFD simulation has become a relatively efficient, fast, and flexible alternative estimation method.

[0128] In the present invention, as one of the possible implementation methods, the method further includes: step 105, designing the maximum flow capacity of the drain pipe 3;

[0129] Designing the maximum flow capacity of the steam trap pipe 3 includes the following steps: performing iterative solutions according to Lin Zonghu's calculation formula and the steam trap flow capacity calculation formula so that the steam trap inlet fluid pressure meets the boundary conditions.

[0130] In one embodiment, Figure 4 This is the CFD solution mesh for the drain pipe in this embodiment. The blue portion in the figure represents the drain pipe 3 wall, casing pipe wall, or the head end of the flash tank 1. The green portion represents the inlet of the drain pipe 3. The red portion represents the fluid flow boundary within the flash tank 1, which allows fluid to flow in and out.

[0131] In the CFD flow field solution of the drain pipe, the drain pipe 3 is a DN100 pipe. In the final design parameters of the throttle 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.

[0132] The boundary conditions for the CFD solution of the steam trap pipeline are as follows: the steam trap inlet fluid pressure is 2.790 MPa, the steam trap inlet fluid saturation water enthalpy is 989.587 kJ / (kg·K), the rated operating fluid flow rate at the orifice inlet is 1.03 kg / s, the orifice inlet fluid dryness is assumed to be 0.14, the orifice inlet fluid temperature is assumed to be 145°C, the orifice outlet fluid pressure is 0.92 bar, and the orifice outlet fluid temperature is 176.29°C.

[0133] The CFD iterative solution results of the drain pipe are: the fluid pressure at the orifice inlet is 0.65 MPa, the fluid temperature at the orifice inlet is 161.986°C, and the fluid dryness at the orifice inlet is 0.15;

[0134] Figure 7 is the flow velocity field diagram of the fluid in the vertical mid-plane of the drain pipe of this embodiment, Figure 10 The pressure field diagram of the fluid in the vertical mid-plane of the drain pipe of this embodiment; Figure 7 , it is determined that the maximum flow velocity of the fluid in the vertical mid-plane of the drain pipe is 248m / s;

[0135] from Figure 7It can be seen that the fluid flow velocity and flow direction at the inlet of the drain pipe 3 are relatively uniform. The fluid flow velocity direction begins to change when it reaches the second through hole 5, and the fluid flow velocity reaches its maximum at the first through hole 4. After the fluid exits the throttling orifice 2, due to inertia, it still maintains a high flow velocity within a certain range. As the fluid flow further expands, the fluid flow velocity gradually decreases. The fluid exiting the second through hole 5 impacts the inner surface of the blue sleeve and eventually flows into the deep part of the flash tank 1.

[0136] from Figure 10 It can be seen that the fluid pressure has a large gradient at the orifice plate 2, while it is basically uniform at the end of the drain pipe 3 and in the flash tank 1;

[0137] according to Figure 10 , determine the steam trap outlet fluid pressure; steam trap pressure drop Δp is 2.05MPa; according to Figure 7 , determine the fluid velocity before the throttling orifice is 7.45m / s; the flow capacity of the steam trap Q m The flow rate of the drain pipe is 3.11 kg / s. According to the final design parameters of the orifice plate 2, the CFD solution of the drain pipe is obtained, and the fluid flow rate of the drain pipe working condition is 1.03 kg / s.

[0138] The calculated fluid flow rate for the drain pipe is 1.37 kg / s, and the deviation between the calculated and solved fluid flow rates is 25%. The orifice outlet fluid pressure in the CFD simulation of the drain pipe is 0.092 MPa, the aperture ratio β is 0.18, and the orifice installation pressure ratio = orifice outlet fluid pressure / orifice inlet fluid pressure = 0.092 MPa / 0.65 MPa = 0.14.

[0139] In step 105, the boundary conditions satisfied by the steam trap inlet fluid pressure are: the actual operating fluid flow rate of the steam trap pipeline is 75% of the calculated operating fluid flow rate of the steam trap pipeline, the fluid pressure at the orifice inlet is 1.48 MPa, the steam trap pressure drop is 1.31 MPa, the flow capacity of steam trap pipeline 3 is 2.53 kg / s, and the safety factor is 2.5.

[0140] In one embodiment, Figure 5 This is the CFD solution mesh for the drain pipe in this embodiment. The blue portion in the figure represents the drain pipe 3 wall, casing pipe wall, or the head end of the flash tank 1. The green portion represents the inlet of the drain pipe 3. The red portion represents the fluid flow boundary within the flash tank 1, which allows fluid to flow in and out.

[0141] In the CFD flow field solution of the drain pipe, the drain pipe 3 is a DN80 pipe. In the final design parameters of the throttle 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.

[0142] The boundary conditions for the CFD solution of the steam trap pipeline are as follows: the steam trap inlet fluid pressure is 2.734 MPa, the steam trap inlet fluid saturation water enthalpy is 986.416 kJ / (kg·K), the rated operating fluid flow rate at the orifice inlet is 0.12 kg / s, the orifice inlet fluid dryness is assumed to be 0.14, the orifice inlet fluid temperature is assumed to be 145°C, the orifice outlet fluid pressure is 0.92 bar, and the orifice outlet fluid temperature is 176.29°C.

[0143] The CFD iterative solution results of the drain pipe are as follows: the fluid pressure at the orifice inlet is 0.34 MPa, the fluid temperature at the orifice inlet is 138.36°C, and the fluid dryness at the orifice inlet is 0.19;

[0144] Figure 8 The flow velocity field diagram of the fluid in the vertical mid-plane of the drain pipe of this embodiment is shown in FIG. Figure 11 The pressure field diagram of the fluid in the vertical mid-plane of the drain pipe of this embodiment; Figure 8 , it is determined that the maximum flow velocity of the fluid in the vertical mid-plane of the drain pipe is 254m / s;

[0145] from Figure 8 It can be seen that the fluid flow velocity and flow direction at the inlet of the drain pipe 3 are relatively uniform. The fluid flow velocity direction begins to change when it reaches the second through hole 5, and the fluid flow velocity reaches its maximum at the first through hole 4. After the fluid exits the throttling orifice 2, due to inertia, it still maintains a high flow velocity within a certain range. As the fluid flow further expands, the fluid flow velocity gradually decreases. The fluid exiting the second through hole 5 impacts the inner surface of the blue sleeve and eventually flows into the deep part of the flash tank 1.

[0146] from Figure 11 It can be seen that the fluid pressure has a large gradient at the orifice plate 2, while it is basically uniform at the end of the drain pipe 3 and in the flash tank 1;

[0147] according to Figure 11 , determine the outlet fluid pressure of the steam trap; the pressure drop Δp of the steam trap is 2.36MPa; according to Figure 8 , determine the fluid velocity before the throttling orifice is 3.08m / s; the flow capacity of the steam trap Q m The flow rate of the drain pipe is 0.25 kg / s. According to the final design parameters of the orifice plate, the CFD solution of the drain pipe is performed, and the fluid flow rate of the drain pipe working condition is 0.12 kg / s.

[0148] The calculated working condition fluid flow rate of the drain pipe is 0.16 kg / s, and the deviation between the calculated working condition fluid flow rate and the solved working condition fluid flow rate is 23%. The orifice plate outlet fluid pressure of the drain pipe CFD simulation is 0.092 MPa, the aperture ratio β is 0.1125, and the orifice plate installation pressure ratio = orifice plate outlet fluid pressure / orifice plate inlet fluid pressure = 0.092 MPa / 0.34 MPa = 0.27.

[0149] In step 105, the boundary conditions satisfied by the steam trap inlet fluid pressure are: the actual operating fluid flow rate of the steam trap pipeline is 77% of the calculated operating fluid flow rate of the steam trap pipeline, the fluid pressure at the orifice inlet is 0.69 MPa, the steam trap pressure drop is 2.11 MPa, the flow capacity of steam trap pipeline 3 is 0.23 kg / s, and the safety factor is 1.9.

[0150] In one embodiment, Figure 6 This is the CFD solution mesh for the drain pipe in this embodiment. The blue portion in the figure represents the drain pipe 3 wall, casing pipe wall, or the head end of the flash tank 1. The green portion represents the inlet of the drain pipe 3. The red portion represents the fluid flow boundary within the flash tank 1, which allows fluid to flow in and out.

[0151] In the CFD flow field solution of the drain pipe, the drain pipe 3 is a DN50 pipe. In the final design parameters of the throttle 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.

[0152] The boundary conditions for the CFD solution of the steam trap pipeline are as follows: the steam trap inlet fluid pressure is 2.781 MPa, the steam trap inlet fluid saturation water enthalpy is 988.76 kJ / (kg·K), the rated operating fluid flow rate at the orifice inlet is 0.12 kg / s, the orifice inlet fluid dryness is assumed to be 0.14, the orifice inlet fluid temperature is assumed to be 145°C, the orifice outlet fluid pressure is 0.92 bar, and the orifice outlet fluid temperature is 176.29°C.

[0153] The CFD iterative solution results of the drain pipe are as follows: the fluid pressure at the orifice inlet is 0.36 MPa, the fluid temperature at the orifice inlet is 139.85°C, and the fluid dryness at the orifice inlet is 0.19;

[0154] Figure 9 is the flow velocity field diagram of the fluid in the vertical mid-plane of the drain pipe of this embodiment, Figure 12 The pressure field diagram of the fluid in the vertical mid-plane of the drain pipe of this embodiment; Figure 9 , it is determined that the maximum flow velocity of the fluid in the vertical mid-plane of the drain pipe is 206m / s;

[0155] from Figure 9It can be seen that the fluid flow velocity and flow direction at the inlet of the drain pipe 3 are relatively uniform. The fluid flow velocity direction begins to change when it reaches the second through hole 5, and the fluid flow velocity reaches its maximum at the first through hole 4. After the fluid exits the throttling orifice 2, due to inertia, it still maintains a high flow velocity within a certain range. As the fluid flow further expands, the fluid flow velocity gradually decreases. The fluid exiting the second through hole 5 impacts the inner surface of the blue sleeve and eventually flows into the deep part of the flash tank 1.

[0156] from Figure 12 It can be seen that the fluid pressure has a large gradient at the orifice plate 2, while it is basically uniform at the end of the drain pipe 3 and in the flash tank 1;

[0157] according to Figure 12 , determine the outlet fluid pressure of the steam trap; the pressure drop Δp of the steam trap is 2.34MPa; according to Figure 9 , determine the fluid velocity before the throttling orifice is 7.96m / s; the flow capacity of the steam trap Q m The flow rate of the drain pipe is 0.25 kg / s. The 3CFD solution of the drain pipe is performed based on the final design parameters of the orifice plate, and the fluid flow rate of the drain pipe working condition is 0.12 kg / s.

[0158] The calculated working condition fluid flow rate of the drain pipe is 0.17 kg / s, and the deviation between the calculated working condition fluid flow rate and the solved working condition fluid flow rate is 28%. The orifice plate outlet fluid pressure of the drain pipe CFD simulation is 0.092 MPa, the aperture ratio β is 0.18, and the orifice plate installation pressure ratio = orifice plate outlet fluid pressure / orifice plate inlet fluid pressure = 0.092 MPa / 0.36 MPa = 0.25.

[0159] In step 105, the boundary conditions satisfied by the steam trap inlet fluid pressure are: the actual operating fluid flow rate of the steam trap pipeline is 72% of the calculated operating fluid flow rate of the steam trap pipeline, the fluid pressure at the orifice inlet is 0.71 MPa, the steam trap pressure drop is 2.08 MPa, the flow capacity of steam trap pipeline 3 is 0.23 kg / s, and the safety factor is 1.9.

[0160] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for optimizing design parameters of a throttle orifice plate of a cavitation control device for a drain pipe of a nuclear power plant, characterized in that: A nuclear power plant drain pipe cavitation control device 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) by welding; a sleeve is provided on the outside of 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 a second through hole (5) is provided in the throttling orifice plate (2) perpendicular to the diameter direction of the central axis; the throttling orifice plate (2) is formed by cutting and opening a hole in a whole forging piece; The design parameters of the orifice plate (2) are optimized by CFD simulation of the drain pipe, including the following steps: Step 101, performing CFD solution of the drain pipe according to the initial design parameters of the throttle orifice plate (2), and obtaining 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 orifice plate inlet is outside the given deviation range, it indicates that the initial design parameters of the orifice plate (2) are unreasonable, and the process goes to step 102; When the difference between the fluid flow rate of the drain pipe under the working condition and the fluid flow rate of the rated working condition at the orifice plate 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 working condition; Repeat the above steps several times until the difference between the working condition fluid flow rate of the drain pipe and the rated working condition fluid flow rate of the 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 of the orifice plate inlet is within a given deviation range, it indicates that the design parameters corresponding to the orifice plate (2) are reasonable, and the difference is used as the final design parameters of the orifice plate (2); Step 104, checking the fluid flow rate of the drain pipe working condition corresponding to the final design parameters of the throttling orifice (2); Step 101, performing CFD solution of the drain pipe according to the design parameters of the throttle orifice plate (2) to obtain the fluid flow rate of the drain pipe solution working condition, includes the following steps: Step 201: Establishing a CFD solution grid for the drainage pipeline; Step 202: Establish boundary conditions, fluid types, and fluid flow models for CFD solution of the drainage pipeline; Step 203: performing an iterative CFD solution for 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 to obtain a CFD iterative solution result for the drain pipe; Step 204: Based on the CFD iterative solution results of the drain pipe, a finite element analysis is performed on the fluid on the vertical mid-plane of the drain pipe 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 under the working condition according to the fluid pressure field diagram of the vertical mid-plane of the drain pipe and the flow capacity calculation formula of the steam trap; In step 205, the steam trap flow capacity is calculated using the following linear relationship between steam trap pressure drop and flow capacity: log 10 Δp=K L *log 10 Q m +B L Among them, Q m is the flow capacity of the steam trap, in kg / h; Δp is the pressure drop of the steam trap, in kPa; K L and B L are fitting coefficients, K L is 2.13, B L is -7.31; Determine the steam trap outlet fluid pressure based on the fluid pressure field diagram of the vertical midplane of the steam trap pipeline. The steam trap inlet fluid pressure is the boundary condition for the steam trap pipeline 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. The steam trap outlet fluid flow rate is the fluid flow rate of the steam trap pipeline to solve the working condition; Step 104, checking the fluid flow rate of the drain pipe working condition corresponding to the final design parameters of the throttling orifice (2), includes the following steps: According to the fluid dryness at the orifice inlet in the drain pipe CFD iterative solution results, the 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 rate of the drain pipe and the working condition fluid flow rate of the drain pipe solution is within a reasonable deviation range, it is determined that the working condition fluid flow rate of the drain pipe solution has passed the verification; The empirical calculation formula for two-phase flow is Lin Zonghu's calculation formula: Among them, q mTP Calculate the working fluid flow rate for the drain pipe in kg / s; F a is the thermal expansion coefficient of the throttling orifice (2); C is the outflow coefficient of the single-phase flow; d is the diameter of the first through hole (4) of the throttling orifice (2), in m; D is the inner diameter of the drain pipe (3), in m; β is the aperture ratio, which is equal to d / D; Δp TP is the pressure difference of gas-liquid two-phase flow, unit is Pa; ρ l is the liquid density, in kg / m 3 ρ g is the gas phase density, in kg / m 3 ; x is the fluid dryness at the orifice inlet; θ0 is the two-phase correction coefficient of the orifice.

2. The design parameter optimization method for the orifice plate of 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 at the throttling orifice plate inlet.

3. The design parameter optimization method for the throttle orifice plate of the nuclear power plant drain pipe cavitation control device according to claim 1, characterized in that: In step 201, the connection portion of the drain pipe (3), the casing and the flash tank (1) is 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.

4. The design parameter optimization method for the orifice plate of the cavitation control device of the nuclear power plant drain pipe according to claim 1 is 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 area before and after the throttling orifice (2) have a higher density than the drain pipe CFD solution grid in other areas.

5. The design parameter optimization method for the orifice plate of the cavitation control device of the nuclear power plant drain pipe according to claim 1, characterized in that: In step 202, the boundary conditions of the steam trap CFD solution include the steam trap inlet boundary condition, the orifice plate inlet boundary condition, and the orifice plate outlet boundary condition; Among them, the boundary conditions of the steam trap inlet include the steam trap inlet fluid pressure and the steam trap inlet fluid saturated water enthalpy; The boundary conditions of the orifice plate inlet include the rated working condition fluid flow rate of the orifice plate inlet, the flow direction of the fluid at the orifice plate inlet, the assumed initial value of the fluid temperature at the orifice plate inlet, and the assumed initial value of the fluid dryness at the orifice plate inlet; the flow direction of the fluid at the orifice plate inlet is perpendicular to the wall of the orifice plate (2); The boundary conditions at the orifice plate outlet include the orifice plate outlet fluid boundary, orifice plate outlet fluid pressure, and orifice plate outlet fluid temperature; the orifice plate 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 a heat transfer model, a turbulence equation, and a wall function. Among them, the heat transfer model is a total energy model, the turbulence equation is a K-Epsilon equation, and the wall function is an adaptive wall function.

6. The design parameter optimization method for the orifice plate of the nuclear power plant drain pipe cavitation control device according to claim 1, characterized in that: In step 203, a 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 drain pipe CFD iterative solution result, including the following steps: Multiple CFD solutions are performed on the CFD grid of the drain pipe according to the boundary conditions, fluid type, and fluid flow model of the drain pipe. The initial conditions of the next CFD solution of the drain pipe are the results of the previous CFD solution of the drain pipe. The CFD solution results of the drain pipe include the fluid pressure at the inlet of the throttle orifice plate, the fluid temperature at the inlet of the throttle orifice plate, and the fluid dryness at the inlet of the throttle orifice plate. When the deviation of the fluid pressure at the throttle plate inlet obtained from the previous CFD solution of the drain pipe is within a given deviation range, the convergence of the CFD iterative solution of the drain pipe is achieved, and the CFD iterative solution results of the drain pipe are obtained; the CFD iterative solution results of the drain pipe include the converged fluid pressure at the throttle plate inlet, the fluid temperature at the throttle plate inlet, and the fluid dryness at the throttle plate inlet.

7. The method for optimizing design parameters of a throttle orifice plate of a cavitation control device for a drain pipe of a nuclear power plant according to claim 1, characterized in that: The method further comprises: step 105, designing the maximum flow capacity of the drain pipe (3); The maximum flow capacity of the steam trap pipe (3) is designed, comprising the following steps: performing iterative solutions according to the empirical calculation formula of two-phase flow and the calculation formula of steam trap flow capacity, so that the steam trap inlet fluid pressure meets the boundary conditions.

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