Design of a parabolic valve core in a flow control valve and flow calculation method

Abstract

The present invention belongs to the technical field related to fluid regulating valves, and discloses a design and flow calculation method for a parabolic valve core in a flow regulating valve. The method comprises: S1 constructing a relational expression of the flow area of ​​the flow regulating valve corresponding to different valve core displacements; S2 constructing a geometric relational expression of the flow area according to the geometric structure of the throttle valve and the valve core, and obtaining a relational expression satisfied by the cross-sectional profile of the valve core; S3 discretizing the displacement ratio into multiple values, calculating the flow area corresponding to different displacement ratios, calculating the coordinates of the points on the valve core profile at different displacement ratios, fitting the points on the valve core profile at all displacement ratios into a parabola, and the parabola rotates around the central axis of the valve core to obtain the required rotational parabolic curve of the valve core. The present invention also discloses the application of the above method. Through the present invention, the deformation problem of the valve stem under the radial impact force of the fluid and the problem of inconsistent flow regulation resolution at different valve stem positions of the regulating valve are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field related to fluid regulating valves, and more specifically, relates to a design of a parabolic valve core in a flow regulating valve and a flow calculation method. Background Art

[0002] In the field of fluid control, it is usually necessary to adjust the flow rate of a certain fluid, such as a device for adjusting the refrigerant flow rate in the refrigeration system of industrial equipment. Refrigerant plays a key role in heat exchange in the refrigeration system. According to the temperature of the equipment, the refrigerant flow rate needs to be changed to adjust the refrigeration effect to prevent the equipment from failing or even being damaged due to high temperature. The regulation and control accuracy of the refrigerant flow rate directly affects the safety of industrial equipment. Carbon dioxide, as a natural medium, is green, environmentally friendly, non-toxic and pollution-free. In the supercritical state, it has the advantages of high density, low viscosity, small flow loss, and good heat transfer effect. More importantly, supercritical carbon dioxide has large latent heat and high phase transition heat, which can achieve higher heat exchange efficiency and better cooling performance. Therefore, carbon dioxide is widely used in refrigeration systems as a new refrigerant.

[0003] In the invention patent publication specification CN101655173A, a regulating valve is disclosed, which is particularly used for regulating the flow of fluid in a refrigeration system. The regulating valve inserts the valve body into the connecting opening of the pipeline, and the piston is driven by an electric motor to adjust between the open position and the blocked position of the connecting opening. At the same time, there are multiple small holes on the front surface of the piston to balance the pressure applied to the front surface by the fluid. The flow channel of this flow regulating valve is relatively complex, and turbulence is easily generated when carbon dioxide flows through the small holes at the piston of this regulating valve, resulting in a large pressure loss, causing uncontrollable phase change of carbon dioxide, affecting the flow regulation accuracy and refrigeration effect. Therefore, it is not suitable for flow regulation of carbon dioxide medium.

[0004] Invention patent CN113175532A discloses an adjustable cavitation venturi for flow control equipment. This flow control valve includes a venturi, a differential voltage displacement sensor, a drive mechanism and a controller. The valve core passes through the flow channel and abuts against the sensing end of the differential voltage displacement sensor, and the drive mechanism is arranged at the other end of the valve core. The controller causes the drive mechanism to drive the valve core to move, and at the same time uses the displacement sensor to obtain the position information of the valve core in real time to achieve closed-loop control of the displacement of the valve core. Invention patent CN112211751A also discloses an adjustable venturi device. This adjustable venturi divides the valve body into two parts. The first valve body fixes the drive motor, the first section of the valve stem is connected to the drive motor, the second section of the valve stem is cylindrical, passes through the first valve body and enters the flow channel, and the third section of the valve stem is conical and can be inserted into the venturi of the second valve body. The drive motor is used to move the valve core axially to achieve the control of the fluid flow rate.

[0005] The venturi flow control device reduces the pressure of the fluid at the throat through the contraction and expansion structure, generating a cavitation zone. The cavitation zone can isolate the influence of downstream pressure fluctuations on upstream pressure, while maintaining the flow rate stable. However, in the above two adjustable venturi flow control devices, firstly, the device only relies on the limit mechanism or through hole on the valve body to support the valve stem. For the relatively slender structure of the valve stem, when the fluid flows in from the inlet on the side of the valve body, it will produce a large radial impact force on the valve stem, causing the valve stem to deform, and then the valve stem will deviate from the axial position at the throat of the venturi, changing the symmetry of the valve port flow area and the flow channel, and even causing it to get stuck and unable to work. Secondly, the valve stems of the regulating devices are all designed to be conical. The minimum flow area of ​​this shape at the venturi valve port is nonlinearly related to the valve stem displacement, making the flow regulation resolution of different valve stem positions inconsistent, which is not conducive to the high-precision regulation of the flow control device. Therefore, it is necessary to design a flow control valve whose flow area changes linearly with the valve core displacement to improve the flow control accuracy. The flow calculation formula of the existing flow control valve is as follows:

[0006]

[0007] Among them, Q m is the mass flow rate, C d is the flow coefficient, A is the flow area, ΔP is the difference between the inlet pressure and the saturated vapor pressure, and ρ is the fluid density. Therefore, when the flow area changes linearly with the valve core displacement, the mass flow rate is also linearly related to the valve core displacement, which is conducive to the precise control of the flow rate. However, this flow formula is only applicable to ideal incompressible fluids. For carbon dioxide, this medium has strong compressibility in the supercritical state, and its physical properties will also change dramatically when flowing through the venturi linear flow control valve. The traditional mass flow calculation method is not applicable to this type of flow control valve. This problem will have a great impact on the control accuracy of the flow control valve. Therefore, there is an urgent need for a device and method that can solve the above problems. Summary of the invention

[0008] In response to the above defects or improvement needs of the prior art, the present invention provides a design and flow calculation method of a parabolic valve core in a flow control valve to solve the deformation problem of the valve stem under the radial impact force of the fluid, and the problem of inconsistent flow control resolution at different valve stem positions of the control valve.

[0009] To achieve the above object, according to one aspect of the present invention, a method for designing a parabolic valve core in a flow control valve is provided, the method comprising the following steps:

[0010] S1 sets the displacement ratio of the valve core in the regulating valve, constructs the relationship between the flow area and the valve core displacement in the flow regulating valve, and the boundary conditions satisfied when the valve core is at the maximum and minimum displacements in the flow regulating valve, thereby obtaining the relationship between the flow area of ​​the flow regulating valve corresponding to different valve core displacements;

[0011] S2 constructs a geometric relationship of the flow area according to the geometric structure of the throttle valve and the valve core, and obtains a relationship satisfied by the cross-sectional profile of the valve core from the geometric relationship of the flow area;

[0012] S3 discretizes the displacement ratio into multiple values, and uses the relationship between the flow area corresponding to the valve core displacement obtained in step S1 to calculate the flow area corresponding to different displacement ratios, and brings the flow area into the cross-sectional profile of the valve core in step S2 to calculate the coordinates of the points on the valve core surface at different displacement ratios. The points on the valve core surface at all displacement ratios are fitted into a parabola, and the parabola rotates around the central axis of the valve core once to obtain the desired rotational parabola curve of the valve core.

[0013] Further preferably, in step S1, the relationship between the flow area and the valve core displacement is as follows:

[0014]

[0015] Among them, A is the flow area; x is the valve core displacement; k and b are linear characteristic parameters, A max is the maximum flow area.

[0016] Further preferably, in step S1, the boundary conditions are as follows:

[0017]

[0018] Among them, A min , A max 、x min 、x max They are minimum flow area, maximum flow area, minimum valve core displacement, and maximum valve core displacement respectively.

[0019] Further preferably, in step S1, the relationship between the flow area of ​​the flow control valve corresponding to different valve core displacements is as follows:

[0020] A=[(t-1)·k+1]·A max

[0021] Among them, A is the flow area; t is the displacement ratio, that is, the ratio of the current valve core displacement to the maximum valve core displacement; k is the linear characteristic parameter, and Amax is the maximum flow area.

[0022] Further preferably, the expression satisfied by the envelope is performed as follows:

[0023]

[0024] Where f(l, α) is the equation of the equal-area curve, l is the radial distance between a point on the valve core profile and the throat; α is the angle between a perpendicular line drawn from any point on the intersection of the contraction section and the throat of the Venturi flow channel and the valve core profile and the plane where the intersection line lies; D is the throat diameter; and A is the flow area.

[0025] According to another aspect of the present invention, there is provided a valve core obtained by the method described above, wherein the front end of the valve core is a rotating parabola.

[0026] According to another aspect of the present invention, a flow control valve having the valve core described above is provided, wherein the flow control valve comprises a linear motor, a main valve body, a valve core and a venturi, wherein:

[0027] The linear motor, the main valve body and the venturi are connected in sequence, the valve core is arranged in the main valve body, one end of the valve core is connected to the output shaft of the linear motor, and the other end is matched with the venturi, the main valve body is provided with a fluid inlet and a fluid channel, the fluid channel is connected to the venturi, the fluid enters the fluid channel from the fluid inlet, and flows out from the venturi;

[0028] The valve core cooperates with the venturi tube in the fluid channel, and the linear motor drives the valve core to perform linear motion to adjust the gap between the venturi tube and the valve core, thereby adjusting the opening of the fluid outflow point, thereby achieving control of the fluid flow rate.

[0029] According to another aspect of the present invention, there is provided a method for calculating the mass flow of the flow control valve as described above, the method comprising the following steps:

[0030] (a) Based on the mass flow formula and the fluid velocity formula at the valve port interface, the flow model of the flow control valve is constructed;

[0031] (b) constructing a relationship between the density and pressure of the fluid in the cross section at the inlet or outlet of the venturi according to the geometric structure of the venturi, and substituting the relationship between the density and pressure of the fluid into the flow model to obtain the required mass flow.

[0032] Further preferably, in step (a), the traffic model is performed according to the following relationship:

[0033]

[0034]

[0035] Wherein, Qm is the mass flow rate; Cd is the flow coefficient; ρ is the fluid density; A(x) is the flow area, which is a function of the valve core displacement x; P1 is the fluid pressure at the inlet; T1 is the fluid temperature at the inlet; P2 is the fluid pressure at the valve port; T2 is the fluid temperature at the valve port; F(P,T) is the indefinite integral of the reciprocal of the fluid density with respect to the pressure.

[0036] Further preferably, in step (b), the relationship between the fluid density and the pressure is as follows:

[0037]

[0038] Wherein, ρ is the fluid density; e is the natural index; k, a, and b are the fitting parameters of the fluid density-pressure relationship, and the specific values ​​should be determined by fitting based on the fluid temperature corresponding to the inlet of the flow control valve.

[0039] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0040] 1. The front end of the valve core in the present invention is designed as a rotating parabola. This rotating parabola valve core can make the flow area linearly related to the valve core displacement. It can be seen from the flow formula that when the pressure and temperature conditions are constant, if the flow area changes linearly with the valve core displacement, the mass flow rate also changes linearly with the valve core displacement. This design reduces the difficulty of flow control, is conducive to high-precision control of flow, and improves the problem of inconsistent flow regulation resolution in different displacement ranges of existing conical valve cores.

[0041] 2. The carbon dioxide venturi linear flow control valve provided by the present invention moves the valve core axially through a linear motor, thereby changing the minimum flow area between the valve core curved surface and the throat, thereby realizing the regulation function of the carbon dioxide flow. The internal flow channel of the flow control valve is designed as a venturi tube, which reduces flow resistance and pressure loss. Carbon dioxide undergoes cavitation at the throat of the venturi tube, so that downstream pressure fluctuations will not affect upstream pressure, thereby avoiding the influence of downstream load pressure fluctuations on flow regulation.

[0042] 3. The carbon dioxide venturi linear flow control valve provided by the present invention is internally provided with a valve sleeve structure to provide additional support and guiding effects on the valve core, thereby improving the displacement accuracy of the valve core. The profile of the regulating section of the valve core of the flow control valve is calculated by the envelope method to obtain a rotating parabola, and specific calculation steps are given. This method can make the displacement of the valve core of the control valve linearly related to the flow area, so that the flow control resolution within the working range of the control valve remains consistent, thereby improving the flow control accuracy of the flow control valve.

[0043] 4. Aiming at the characteristics of carbon dioxide in liquid and supercritical states, which has drastic changes in physical properties and strong compressibility, the present invention uses the Euler equation to derive the general Bernoulli equation, and then obtains the mass flow formula applicable to compressible fluids. By fitting and integrating the relationship between carbon dioxide density and pressure, a flow model applicable to carbon dioxide medium is obtained. This model can calculate and predict the mass flow through the regulating valve according to the flow area and state parameters such as pressure and temperature, thereby improving the control accuracy of the regulating valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the three-dimensional structure of a carbon dioxide venturi linear flow control valve constructed according to an embodiment of the present invention;

[0045] Figure 2 It is constructed according to the embodiment of the present invention Figure 1 A cross-sectional view of a carbon dioxide venturi linear flow control valve;

[0046] Figure 3 It is a schematic diagram of the three-dimensional structure of the main valve sleeve of the carbon dioxide venturi linear flow control valve constructed according to an embodiment of the present invention;

[0047] Figure 4 It is constructed according to the embodiment of the present invention Figure 2 A local enlarged schematic diagram of the middle A;

[0048] Figure 5 It is constructed according to the embodiment of the present invention Figure 2 A partial enlarged schematic diagram of point B in the middle;

[0049] Figure 6 It is a schematic diagram of the valve port structure of a carbon dioxide venturi linear flow control valve constructed according to an embodiment of the present invention;

[0050] Figure 7 It is a schematic diagram of the physical parameters of the inlet, throat and outlet of the carbon dioxide venturi linear flow control valve constructed according to an embodiment of the present invention.

[0051] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0052] 10-linear motor; 20-limit valve sleeve; 30-main valve body; 31-first sealing ring; 32-first sealing retaining ring; 40-valve core; 41-valve core curved portion; 50-main valve sleeve; 60-venturi; 61-contraction section; 62-throat; 63-expansion section; 64-second sealing ring; 65-second sealing retaining ring; D-throat diameter; d-valve core diameter at the valve port; l-radial distance between point M on the valve core profile and the throat; α-angle between PM and PQ; x-valve core displacement; x'-axial distance between MN and the right end of the curved portion. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0054] See also Figures 1 to 7 As shown, this embodiment provides a carbon dioxide venturi linear flow control valve, which is applied in the field of fluid control and is used to regulate the flow of carbon dioxide refrigerant in a refrigeration system.

[0055] See also Figures 1 to 3 As shown. The carbon dioxide venturi linear flow control valve provided in this embodiment includes a linear motor 10, a limit valve sleeve 20, a main valve body 30, a valve core 40, a main valve sleeve 50, and a venturi 60. Among them, the linear motor 10 and the limit valve sleeve 20 are fixed to the upper end of the main valve body 30 in sequence, and the venturi 60 is fixed to the lower end of the main valve body 30. The linear motor 10 has an output shaft, and the valve core 40 is fixed to the output shaft of the linear motor 10 by threaded connection. The other end of the valve core 40 passes through the through hole of the main valve body 30 to enter the internal flow channel. When the output shaft of the linear motor 10 moves linearly, the valve core 40 will also move axially accordingly, thereby controlling the flow of the regulating valve. The main valve sleeve 50 is installed inside the main valve body, and the valve core 40 passes through the central through hole of the main valve sleeve 50 and enters the flow channel of the venturi 60.

[0056] See also Figure 1 and Figure 2As shown, a square flange is provided at the upper end of the main valve body 30, and the limit valve sleeve 20 and the linear motor 10 are fixed on the main valve body in sequence. The lower side of the square flange is a cylindrical cavity, which can accommodate the limit valve sleeve 20 and the output shaft of the linear motor 10, and can also meet the space requirements for the axial displacement of the valve core 40. An inlet pipe joint and an inlet flow channel are provided on one side of the outer circumference of the main valve body 30, and the carbon dioxide medium flows into the flow regulating valve through this inlet flow channel. The outer circumference of the inlet pipe joint is provided with a thread, and a frustum is provided on the inner side. This frustum can cooperate with the spherical joint of the refrigeration system pipeline to achieve surface sealing and avoid carbon dioxide leakage. A through hole is provided on the upper side of the inlet flow channel of the main valve body 30, and the valve core 30 can pass through this through hole to enter the internal flow channel of the regulating valve. This through hole has a supporting, radial positioning and guiding effect on the valve core 30. The main valve body 30 is provided with two cylindrical flow channels, the upper cylindrical flow channel is connected to the inlet flow channel, so that the flow direction of carbon dioxide changes from radial to axial. The diameter of the lower cylindrical flow channel is slightly larger than that of the upper section, presenting a stepped structure. This structure can play a positioning role for the main valve sleeve 50. The main valve sleeve 50 is inserted into the lower cylindrical flow channel from the lower opening of the main valve body 30. A circular flange is provided at the lower end of the main valve body 30, and the venturi 60 is fixed to the main valve body 30 through the flange.

[0057] Further, in this embodiment, see Figure 4 As shown, a sealing groove is provided on the circumferential surface of the through hole of the main valve body 30, and a first sealing ring 31 and a first sealing retaining ring 32 are installed in the sealing groove, which can realize dynamic sealing during the axial movement of the valve core 40; the first sealing ring 31 is installed on the side close to the internal flow channel of the main valve body 30, that is, the pressure-bearing side, and the first sealing retaining ring 32 is installed on the side away from the internal flow channel of the main valve body 30, that is, the non-pressure-bearing side. This installation method can avoid the first sealing ring 31 from being extruded due to a large fluid pressure, thereby increasing the maximum sealing pressure of the sealing structure here.

[0058] In this embodiment, the material of the first sealing ring 32 can be polytetrafluoroethylene.

[0059] As an alternative embodiment, see Figure 1 and Figure 2 As shown, a fixing plate is also provided on the circumferential surface of the rear side of the main valve body 30 near the square flange, and a mounting hole is provided on the fixing plate. When the carbon dioxide venturi linear flow control valve is assembled in a refrigeration system, the flow control valve can be fixed on other tables or brackets through the fixing plate to avoid the pipeline bearing the entire weight of the flow control valve.

[0060] The limit valve sleeve 20 is a stepped cylindrical structure, which can be divided into a first cylindrical section on the upper side and a second cylindrical section on the lower side. A square flange is provided at the upper end of the limit valve sleeve 20, which can be fixed on the main valve body 30. A through hole is provided at the bottom of the second cylindrical section of the limit valve sleeve 20, and the output shaft of the linear motor 10 extends from this through hole for axial movement. The lower end surface of the second cylindrical section has a limiting effect. On the one hand, it can limit the upward displacement of the valve core 40 to not exceed the maximum opening displacement; on the other hand, when the valve core 40 is at the maximum opening displacement and the flow regulating valve discharges excess carbon dioxide upstream at the maximum working pressure, this lower end surface can bear the vertical upward fluid pressure on the valve core 40 and transmit it to the main valve body 30, so as to avoid the fluid pressure from directly acting on the linear motor 10 through the valve core 40, causing the linear motor 10 to be overloaded and damaged;

[0061] Specifically, in this embodiment, when assembling the flow regulating valve, the lower end face of the second cylindrical section of the limit valve sleeve 20 faces the main valve body 30 and is inserted into the interior thereof. At this time, the outer circumferential surface of the first cylindrical section and the inner circumferential surface of the cylindrical cavity of the main valve body 30 are interference fit to limit the radial displacement of the limit valve sleeve 20.

[0062] The linear motor 10 plays a driving and controlling role in the carbon dioxide venturi linear flow control valve. A square flange surface is provided at the lower end of the linear motor 10, and this flange surface can be connected to the limit valve sleeve 20, and thereby indirectly fixed to the main valve body 30. The linear motor 10 has a cylindrical output shaft at one end close to the square flange surface, and this output shaft can make linear motion along the axial direction. An external thread is provided on the outer circumferential surface of the output shaft, and this external thread can be connected to the valve core 40, so that the valve core 40 is fixedly connected to the output shaft of the linear motor 10. When the output shaft of the linear motor 10 moves, it will drive the valve core 40 to make axial linear motion, and control the valve core 40 to stop and remain at the required valve core displacement. As a result, the minimum flow area at the valve port is changed to a certain specific value, thereby realizing the function of flow regulation.

[0063] In this embodiment, see Figure 2 , Figure 5 and Figure 6As shown, a through flow channel is arranged inside the venturi 60 along the axial direction. The through flow channel can be divided into four parts along the flow direction of carbon dioxide, namely, a contraction section 61, a throat 62, an expansion section 63 and an outlet section. Each section of the flow channel is connected in sequence. The contraction section 61 is a truncated cone-shaped flow channel, whose cone angle is set to 60°, and the diameter gradually decreases along the flow direction of carbon dioxide until it becomes the same as the diameter at the beginning of the throat. When carbon dioxide flows through this section of the flow channel, the flow velocity increases and the pressure decreases; the throat 62 is a cylindrical flow channel, whose diameter remains unchanged. Carbon dioxide forms a cavitation zone in this section of the flow channel, which is a key area of ​​the flow control valve; the expansion section 63 is also a truncated cone-shaped flow channel, whose cone angle is set to 6°, and the diameter gradually increases along the flow direction of carbon dioxide. When carbon dioxide flows through this section of the flow channel, the flow velocity decreases, the pressure increases, the cavitation zone disappears, and the carbon dioxide returns to a liquid or supercritical state; the outlet section is a transition section between the venturi 60 and the downstream pipeline. This section is provided with an outlet pipe joint. Carbon dioxide flows out of the flow control valve from this section of the flow channel. The truncated cone surface of the outlet section can also cooperate with the pipeline joint to achieve surface sealing.

[0064] Specifically, in this embodiment, when assembling the flow control valve, the contraction section 61 of the venturi tube 60 faces the main valve body 30 and is inserted therein, so that the internal flow channel of the venturi tube 60 is connected with the internal flow channel of the main valve body 30 and is on the same axis. The carbon dioxide fluid flows into the venturi tube 60 from the contraction section 61, passes through each section of the flow channel in sequence, and then flows out of the venturi tube 60 from the outlet section. A circular flange is provided on the outer circumferential surface of the venturi tube 60, which can be fixed on the main valve body 30.

[0065] Further, in this embodiment, see Figure 2 and Figure 5 As shown, a sealing groove is provided on the side of the outer circumference of the venturi tube 60 close to the contraction section 61, and a second sealing ring 64 and a second sealing retaining ring 65 are installed in the sealing groove to prevent carbon dioxide from leaking into the external environment; the second sealing ring 64 is installed on the side close to the contraction section of the venturi tube, that is, the pressure-bearing side, and the second sealing retaining ring 65 is installed on the side away from the contraction section of the venturi tube, that is, the non-pressure-bearing side. This installation method can also avoid the second sealing ring 64 from being squeezed out due to a large fluid pressure, thereby increasing the maximum sealing pressure of the sealing structure here.

[0066] In this embodiment, the material of the second sealing ring 65 can be polytetrafluoroethylene.

[0067] In this embodiment, see Figure 2 and Figure 3As shown, the main valve sleeve 50 is a cylindrical structure, and the interior thereof is a cylindrical flow channel, and the diameter of this flow channel is the same as the diameter of the upper cylindrical flow channel of the main valve body 30. This structure can avoid large local pressure loss of carbon dioxide due to sudden change of the flow channel cross section. A Y-shaped bracket is provided at the upper end of the main valve sleeve 50, and a through hole along the axial direction is provided at the center of the Y-shaped bracket, which can support the radial positioning of the valve core and the auxiliary valve core 40, and has a certain guiding effect. The valve core 40 can pass through this through hole with clearance fit and extend into the venturi tube 60.

[0068] Further, in this embodiment, see Figure 2 and Figure 5 As shown, a main valve sleeve limiting groove is provided on the outer circumferential surface of the venturi tube 60 near the contraction section 61, and the limiting groove has a certain width and depth, which can fix the main valve sleeve 50 in the axial and radial directions. When assembling the flow control valve, the lower end of the main valve sleeve 50 is inserted into the main valve sleeve limiting groove with interference fit; then, the main valve sleeve 50 is inserted into the main valve body 30 with clearance fit along with the venturi tube 60. At this point, the inlet flow channel of the main valve body 30, the upper cylindrical flow channel of the main valve body 30, the cylindrical flow channel of the main valve sleeve 50 and the internal flow channel of the venturi tube 60 are completely connected, and are combined together to form a complete flow channel inside the flow control valve.

[0069] In this embodiment, see Figures 2 to 6 As shown, the valve core 40 is composed of a connecting section, a first supporting section, a second supporting section, and an adjusting section in the axial direction. The end face of the connecting section is provided with an internal threaded hole, which can be connected with the external thread of the output shaft of the linear motor 10, so that the valve core 40 can be fixed on the output shaft of the linear motor 10, so that the valve core 40 can generate axial displacement with the movement of the output shaft; the outer circumferential surface of the connecting section is provided with a hexagonal boss, and this structure can play a role in tightening the threaded connection between the valve core 40 and the output shaft of the linear motor 10; an end face perpendicular to the axial direction is provided between the connecting section of the valve core 40 and the first supporting section, and when this end face contacts the outer end face on one side of the through hole of the main valve body 30, it is the displacement zero point of the valve core 40. The first supporting section is cylindrical and passes through the through hole of the main valve body 30 with clearance fit. The second supporting section is also cylindrical and is connected to the first supporting section through a 45° chamfer, and the second supporting section passes through the through hole of the main valve sleeve 50 with clearance fit.

[0070] See also Figure 2 and Figure 3The valve core 40 is supported at two places in the flow control valve. The first place is the support of the first support section of the valve core 40 by the through hole of the main valve body 30, and the second place is the support of the Y-shaped bracket of the main valve sleeve 50 by the second support section of the valve core 40. The two supports are respectively located on the upper and lower sides of the inlet flow channel. This structural form can prevent the valve core 40 from being greatly deformed and offset when the carbon dioxide flows into the inlet flow channel and causes radial fluid impact on the valve core 40, and can also guide the valve core 40. In addition, after the carbon dioxide flows through the two support sections, due to the influence of the cylindrical flow channel inside the control valve, the flow direction of the carbon dioxide inside the control valve changes from radial flow to uniform axial flow. Therefore, outside the two support sections, the valve core 40 is almost not affected by the radial fluid impact, which is conducive to keeping the valve core 40 on the axis of the flow channel, ensuring the symmetry of the flow channel, and reducing the error of the valve port flow area and the occurrence of the jamming problem.

[0071] Furthermore, the regulating section is connected to the second supporting section by a 60° chamfer, and the regulating section includes a cylindrical portion and a curved portion in sequence along the fluid flow direction, the diameter of the cylindrical portion is the same as the diameter of the venturi throat 62, and there is a clearance fit between the two. When the valve core 40 is at the zero displacement point, the cylindrical portion can be partially inserted into the venturi throat 62. The diameter of the upper end of the curved portion is the same as the diameter of the cylindrical portion, and then the diameter gradually decreases to 0 along the axial fluid flow direction; the outer profile of the curved portion is a rotational parabola, and the rotational parabola cooperates with the venturi throat 62 to form the minimum flow area of ​​the flow control valve, and this flow area is linearly related to the linear displacement of the valve core 40. Changing the displacement of the valve core 40 can linearly change this flow area, thereby realizing a precise flow regulation function.

[0072] In this embodiment, the material of the metal parts of the regulating valve can be PH 17-4 stainless steel.

[0073] Further, in this embodiment, see Figure 2 , Figure 5 and Figure 6 The design method of the rotating parabola of the curved surface of the regulating section of the valve core 40 uses the flow characteristics of the regulating valve and the mathematical characteristics of the envelope, and mainly includes the following steps:

[0074] Step 1: Make the valve core displacement x and the flow area A have a linear relationship. Then the flow control valve should have a linear area characteristic. The expression satisfied by this linear area characteristic within the maximum stroke range of the valve core is:

[0075]

[0076] Where A is the flow area; x is the valve core displacement; k and b are both linear characteristic parameters and are unknown quantities. In order to obtain the values ​​of k and b, the working conditions when the valve core 40 is at the minimum and maximum displacements are substituted, and the boundary conditions satisfied by equation (1) at the minimum and maximum displacements of the valve core 40 can be obtained:

[0077]

[0078] Among them, A min , A max 、x min 、x max These are all known control valve design parameters and are specific values.

[0079] Solve equation (2) to obtain the values ​​of linear characteristic parameters k and b:

[0080]

[0081] Among them, R is the adjustable ratio: When the pressure difference before and after the regulating valve remains unchanged and the flow coefficient is constant, the flow rate of the regulating valve is related to the flow area, and the two are proportional, that is, R satisfies:

[0082]

[0083] Step 2: In order to simplify the calculation and solution of the equation, the flow control valve core displacement x and the maximum valve core displacement x max The ratio is defined as the displacement ratio t of the flow control valve. From the geometric relationship, the expression satisfied by the displacement ratio t can be obtained:

[0084]

[0085] Among them, x' is the axial distance between MN and the right end of the curved surface; l is the radial distance between point M on the valve core profile and the throat; α is the angle between PM and PQ. From equations (1) to (5), the expression of the flow area A of the flow control valve under different valve core displacements x is obtained, which is also another expression of the linear area characteristic of equation (1):

[0086] A=[(t-1)·k+1]·A max (6)

[0087] In this embodiment, see Figure 6 , the flow area A is the side area of ​​the truncated cone PMNQ, from which the expression of its geometric form is obtained:

[0088]

[0089] Among them, A is the flow area, α is the angle between PM and PQ, PM is the generatrix of the frustum PMNQ in the valve port cross section, PQ is the diameter of the throat in the valve port cross section; l is the radial distance between point M on the valve core profile and the throat; D is the throat diameter. From formula (7), after transformation, the equation of the equal area curve can be obtained in the valve port cross section:

[0090]

[0091] All points (l, α) on the equal-area curve determined by this equation can be calculated to obtain the same flow area A, that is, the surface area formed by the line segment connecting point P and point (l, α) rotating around the axis of the valve core 40 is a constant.

[0092] From the mathematical relationship, we can get the expression that the cross-sectional profile of the valve core, that is, the envelope of the valve core, satisfies:

[0093]

[0094] The cross-sectional profile of the curved portion of the valve core 40 is the envelope of the equal-area curve corresponding to the flow area A under different displacement ratios t. Therefore, the displacement ratio t is uniformly discretized into n+1 values ​​t in the interval [0,1]. 0 , t 1 , ..., t n , index number is i, according to the linear area characteristic obtained by formula (6), each discrete displacement ratio t is obtained i The corresponding flow area A i , thus we get n+1 groups of displacement ratios t i With flow area A i From formula (9), we get the point set {l i , α i}, all points on this point set are located on the envelope line, that is, the cross-sectional profile of the curved portion of the valve core 40.

[0095] Step 3: For the envelope point set {l i , α i} Perform quadratic fitting to obtain a parabola; rotate this parabola about the axis of the valve core 40 to obtain a rotating parabola on the curved surface of the valve core 40. This rotating parabola makes the valve core displacement x and the flow area A have a linear relationship and satisfies the linear flow characteristic expressed in formula (1). The profile obtained by this method can make the flow control resolution within the working range of the control valve consistent, thereby improving the flow control accuracy of the flow control valve.

[0096] In this embodiment, a flow model suitable for compressible media is proposed, which can be used for mass flow calculation of a flow control valve, including the general Bernoulli equation and an improved mass flow formula.

[0097] Preferably, the flow model in this embodiment is suitable for calculating the mass flow rate of the carbon dioxide medium when it flows through the flow regulating valve, so as to meet special working conditions such as the drastic change in the physical properties of the medium when the carbon dioxide flows through the flow regulating valve and the strong compressibility in the supercritical state.

[0098] In this embodiment, see Figure 7 , where P is the fluid pressure, v is the fluid flow rate, z is the relative height, subscript 1 represents the flow channel inlet cross section, subscript 2 represents the valve port cross section at the junction of the contraction section 61 and the throat 62, and subscript 3 represents the flow channel outlet cross section.

[0099] According to the physical properties of carbon dioxide, the viscosity of carbon dioxide in liquid and supercritical state is only about one tenth of that of water, so carbon dioxide is regarded as an ideal fluid without viscosity. From the Euler equation and fluid streamline equation of the ideal fluid, the differential equation satisfied by each fluid particle on the streamline when the ideal fluid is in steady flow is as follows:

[0100]

[0101] Wherein, ρ is the fluid density; P is the fluid pressure; v is the fluid velocity; g is the gravitational acceleration; and z is the relative height. Formula (10) is a universal Bernoulli equation, which is applicable to compressible and incompressible ideal fluids, and is therefore applicable to the carbon dioxide medium in this embodiment.

[0102] Integrate equation (10) along the streamline from the flow channel inlet section to the valve port section. Ignore the height change of carbon dioxide when flowing in the flow control valve during integration, and approximate the flow rate of carbon dioxide at the flow channel inlet section of the flow control valve to zero.

[0103] Furthermore, in this embodiment, considering the strong compressibility of the carbon dioxide medium in the supercritical state, the density is regarded as a function of pressure and temperature, expressed as: ρ(P, T). Then the fluid flow rate expression at the valve port section is as follows:

[0104]

[0105] Where v is the fluid velocity; ρ is the fluid density; P is the fluid pressure; T is the fluid temperature; subscript 1 represents the physical parameters of the flow channel inlet section, and subscript 2 represents the physical parameters of the valve port section. In formula (11), let the indefinite integral of the integral term be: Another form of the expression for the fluid velocity at the valve port section is obtained:

[0106]

[0107] Substitute into the mass flow formula: Qm =ρvA, and consider the flow coefficient C d , and the following traffic model is obtained:

[0108]

[0109] Among them, Q m is the mass flow rate; C d is the flow coefficient; ρ is the density of carbon dioxide; A(x) is the flow area; is a function of the valve core displacement x; P is the fluid pressure; T is the fluid temperature; see Figure 7 As shown, subscript 1 represents the physical parameters of the flow channel inlet section, subscript 2 represents the physical parameters of the valve port section; F(P,T) is the indefinite integral of the reciprocal of the fluid density with respect to the pressure.

[0110] Since the integral object in equation (11) is only pressure, we can consider the inlet section temperature T 1 Under known conditions, the relationship between density and pressure is fitted. According to the physical properties of carbon dioxide, the following carbon dioxide density-pressure relationship is obtained:

[0111]

[0112] Wherein, e is the natural index; ρ is the density of carbon dioxide; P is the pressure of carbon dioxide; k, a, and b are the fitting parameters of the carbon dioxide density-pressure relationship, and the specific values ​​should be determined according to the medium temperature corresponding to the inlet of the flow control valve. The meaning and value of the parameter symbols described in formula (14) are not related to the symbols in the design method of the rotating parabola of the valve core curved surface 41. Substituting the density-pressure relationship expressed by formula (14) into formula (13) for integration, the flow model suitable for the flow of carbon dioxide medium in the flow control valve is obtained:

[0113]

[0114] Among them, Q m is the mass flow rate; C d is the flow coefficient; ρ is the carbon dioxide density; A(x) is the flow area, which is a function of the valve core displacement x; P is the fluid pressure; T is the fluid temperature; see Figure 7 As shown, subscript 1 represents the physical parameters of the flow channel inlet section, subscript 2 represents the physical parameters of the valve port section; e is the natural index; k, a, and b are constants, which are the fitting parameters of the carbon dioxide density-pressure relationship.

[0115] According to the above flow model, when the flow control valve is in a certain working condition, changing the valve core displacement can change the flow area, thereby realizing the function of flow regulation.

[0116] The above flow model provided in this embodiment can calculate the mass flow rate of liquid or supercritical carbon dioxide medium flowing through the flow control valve under different working conditions such as pressure, temperature, valve core displacement, etc.

[0117] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for calculating the mass flow of a flow control valve, characterized in that: The calculation method includes the following steps: (a) Based on the mass flow formula and the fluid velocity formula at the valve port interface, the flow model of the flow control valve is constructed; (b) constructing a relationship between the density and pressure of the fluid in the cross section at the inlet or outlet of the venturi according to the geometric structure of the venturi, and substituting the relationship between the density and pressure of the fluid into the flow model to obtain the required mass flow; In step (a), the traffic model is performed according to the following relationship: Where, Qm is the mass flow rate; Cd is the flow coefficient; ρ is the fluid density; A(x) is the flow area, which is a function of the valve core displacement x; P1 is the fluid pressure at the inlet; T1 is the fluid temperature at the inlet; P2 is the fluid pressure at the valve port; T2 is the fluid temperature at the valve port; F(P,T) is the indefinite integral of the reciprocal of the fluid density with respect to the pressure; In step (b), the relationship between fluid density and pressure is as follows: Wherein, ρ is the fluid density; e is the natural index; k, a, and b are the fitting parameters of the fluid density-pressure relationship, and the specific values ​​should be determined by fitting based on the fluid temperature corresponding to the inlet of the flow control valve.

2. A design method for a parabolic valve core in a flow control valve calculated according to the calculation method of claim 1, characterized in that: The design method includes the following steps: S1 sets the displacement ratio of the valve core in the regulating valve, constructs the relationship between the flow area and the valve core displacement in the flow regulating valve, and the boundary conditions satisfied when the valve core is at the maximum and minimum displacements in the flow regulating valve, thereby obtaining the relationship between the flow area of ​​the flow regulating valve corresponding to different valve core displacements; S2 constructs a geometric relationship of the flow area according to the geometric structure of the throttle valve and the valve core, and obtains a relationship satisfied by the cross-sectional profile of the valve core from the geometric relationship of the flow area; S3 discretizes the displacement ratio into multiple values, and uses the relationship between the flow area corresponding to the valve core displacement obtained in step S1 to calculate the flow area corresponding to different displacement ratios, and substitutes the flow area into the cross-sectional profile of the valve core in step S2 to calculate the coordinates of the points on the valve core surface at different displacement ratios, and fits the points on the valve core surface under all displacement ratios into a parabola. The parabola rotates around the central axis of the valve core once to obtain the required rotational parabola curve of the valve core.

3. The design method according to claim 2, characterized in that: In step S1, the relationship between the flow area and the valve core displacement is as follows: Among them, A is the flow area; x is the valve core displacement; k and b are linear characteristic parameters, A max is the maximum flow area, X max is the maximum spool displacement.

4. The design method according to claim 3, characterized in that: In step S1, the boundary conditions are as follows: Among them, A max , A min , X min and X max They are minimum flow area, maximum flow area, minimum valve core displacement, and maximum valve core displacement respectively.

5. The design method according to claim 2 or 4, characterized in that: In step S1, the relationship between the flow area of ​​the flow control valve corresponding to different valve core displacements is as follows: Among them, A is the flow area; t is the displacement ratio, that is, the ratio of the current valve core displacement to the maximum valve core displacement; k is the linear characteristic parameter, and Amax is the maximum flow area.

6. The design method according to claim 2, characterized in that: The cross-sectional profile of the valve core, that is, the envelope of the valve core satisfies the following expression: in, f ( l，α ) is the equation of the equal-area curve, , l is the radial distance between the point on the valve core profile and the throat; α The angle between the perpendicular line drawn from any point on the intersection line of the contraction section and throat of the venturi flow channel and the valve core profile and the plane where the intersection line lies; D is the throat diameter; A is the flow area.

7. A valve core obtained by the method according to claim 2, characterized in that: The front end of the valve core is a rotating parabola.

8. A flow control valve having the valve core according to claim 7, characterized in that: The flow control valve includes a linear motor, a main valve body, a valve core and a venturi tube, wherein: The linear motor, the main valve body and the venturi are connected in sequence, the valve core is arranged in the main valve body, one end of the valve core is connected to the output shaft of the linear motor, and the other end is matched with the venturi, the main valve body is provided with a fluid inlet and a fluid channel, the fluid channel is connected to the venturi, the fluid enters the fluid channel from the fluid inlet, and flows out from the venturi; The valve core cooperates with the venturi tube in the fluid channel, and the linear motor drives the valve core to perform linear motion to adjust the gap between the venturi tube and the valve core, thereby adjusting the opening of the fluid outflow point, thereby achieving control of the fluid flow rate.

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