Replaceable laval tube differential pressure measurement device and control method thereof

Abstract

The present application relates to a kind of replaceable Laval nozzle differential pressure measuring device, including measuring device support (1), inlet pipe section (2), differential pressure measuring module (3), replaceable Laval tube and throat area adjusting module (4), Laval tube cavity (5) and outlet pipe section (6). Laval tube cavity (5) top is provided with rectangular air flow channel (504) with rectangular inner cavity communication;Differential pressure measuring module (3) includes the gear (305) driven by motor (302), rack (307), fixed flat plate (310) and measuring flat plate (311);The bottom of Laval tube cavity (5) is provided with base embedding slot (508), replaceable Laval tube embedding cavity (506) is set in base embedding slot (508).The present application also provides a kind of control method of the replaceable Laval nozzle differential pressure measuring device described.

Description

Technical Field

[0001] This invention belongs to the field of supersonic two-phase condensation flow measurement, and specifically relates to a differential pressure measuring device and its control method that can replace Laval tubes of different profiles and has an adjustable throat area. Background Technology

[0002] As the global energy system gradually transitions from a carbon-intensive system to one of deep decarbonization, net-zero emissions, and renewable energy, clean, low-carbon natural gas has become a major alternative to traditional oil and coal. Laval tubes are widely used in natural gas flow metering and supersonic dehydration. Under actual operating conditions, condensation occurs when moist natural gas flows through the nozzle, significantly impacting natural gas metering and supersonic dehydration. Existing research indicates that the pressure difference along the flow path is a crucial parameter directly reflecting condensation characteristics. Researchers have measured the pressure along the flow path of Laval tubes using various measuring devices, primarily employing multi-point discrete measurements on a single Laval tube. However, this discrete-point measurement method cannot accurately reflect the true pressure changes within the flow field, especially the dynamic pressure changes at non-equilibrium condensation sites. Furthermore, current practical measurements use theoretically designed throat position parameters as the actual experimental throat position. However, due to factors such as manufacturing errors, the actual throat position deviates from the designed position, leading to significant measurement errors and failing to accurately reflect the actual condensation location and characteristics. Therefore, when measuring the pressure difference along the pipe of a Laval nozzle, it is necessary to meet the requirements of rapid replacement of nozzles with different profiles and precise adjustment of the throat area. The throat position of the actual Laval nozzle should be accurately obtained through experimental means to achieve accurate measurement of the pressure difference parameters along the pipe of Laval nozzles with different profiles and flow rates, reduce measurement errors, and accurately reflect the condensation position and characteristics inside the Laval nozzle.

[0003] Based on this, a replaceable Laval tube differential pressure measurement device was designed, and corresponding control methods and experimental control strategies were proposed. This not only enabled the rapid replacement of multi-shaped Laval tubes and precise adjustment of the throat area, but also accurately located the throat position of the actual Laval tube using the proposed control methods and experimental control strategies, and precisely measured the friction differential pressure change in the flow field. Summary of the Invention

[0004] The purpose of this invention is to provide a replaceable Laval tube differential pressure measuring device capable of precisely adjusting the throat area and applicable to different working conditions. Furthermore, this invention also provides an active disturbance rejection control method to achieve accurate positioning of the actual throat position of the Laval tube and accurate measurement of the differential pressure parameters along the pressure line. The technical solution is as follows:

[0005] A replaceable Laval nozzle differential pressure measuring device is characterized in that it includes a measuring device support 1, an inlet pipe section 2, a differential pressure measuring module 3, a replaceable Laval pipe and throat area adjustment module 4, a Laval pipe cavity 5, and an outlet pipe section 6; the Laval pipe cavity 5 is placed on the device support 1, and its two ends are connected to the external air circuit through the inlet pipe section 2 and the outlet pipe section 6.

[0006] The inner cavity of the Laval tube body 5 is a rectangular inner cavity, and a rectangular airflow channel 504 communicating with the rectangular inner cavity is opened at its top.

[0007] The differential pressure measurement module 3 includes a gear 305 driven by a motor 302, a rack 307, a fixed plate 310, and a measuring plate 311. The fixed plate 310 has a U-shaped structure and is fixed to the upper part of the Laval cavity 5. The fixed plate 310 has a slot along its axis through which the rack 307 can pass, and the position of the slot corresponds to the rectangular airflow channel 504. The rack 307 is fixedly connected to the measuring plate 311 and meshes with the gear 305. A pressure tapping hole is provided on the measuring plate 311. The differential pressure measurement module 3 measures the differential pressure parameters in the rectangular cavity of the Laval cavity 5 through the pressure tapping hole. The measuring plate 311 moves along the rectangular airflow channel 504 under the drive of the fixed plate 310. The fixed plate 310 and the upper part of the Laval cavity 5 are dynamically sealed.

[0008] The bottom of the Laval tube cavity 5 is provided with a base embedding groove 508, and a replaceable Laval tube embedding cavity 506 communicating with the rectangular inner cavity is provided in the base embedding groove 508; a ball screw nut 507 is also connected to the bottom of the Laval tube cavity 5.

[0009] The replaceable Laval tube and throat area adjustment module 4 includes a base 404, a replaceable Laval tube insert 401, a stepper motor 402, and a ball screw 403. The replaceable Laval tube insert 401 is fixed on the base 404 and extends into the rectangular inner cavity of the Laval tube cavity 5 through the replaceable Laval tube insertion cavity 506. The outer surface of the replaceable Laval tube insert 401 mates with the rectangular inner cavity. The base 404 is located in the base insertion groove. The base 404 is dynamically sealed to the embedded groove 508 of the base 404; the stepper motor 402 is used to drive the ball screw 403; at least three sets of stepper motors and ball screw adjustment mechanisms are symmetrically arranged at the bottom of the base 404, and each ball screw 403 is matched with the ball screw nut 507 at the corresponding position at the bottom of the Laval tube cavity 5. The position of the base 404 and the replaceable Laval tube insert 401 is adjusted by the stepper motor and the ball screw adjustment mechanism, thereby realizing the adjustment of the throat area.

[0010] Furthermore, a groove 505 is provided axially at the top of the Laval tube cavity, and the rectangular airflow channel 504 is formed in the groove 505.

[0011] Furthermore, a planar sealing groove 503 for accommodating an O-ring is provided around the outer surface of the rectangular airflow channel 504. By applying a certain pre-tightening force, the fixed plate 310 compresses the O-ring assembled in the planar sealing groove 503 to achieve dynamic sealing and ensure the translation of the measuring plate 311 in the groove 505.

[0012] Furthermore, an annular sealing groove 509 for accommodating O-rings is provided on the inner wall of the base embedding groove 508 and the annular sealing groove 509, thereby achieving a dynamic sealing connection between the base 404 and the base embedding groove 508 at the bottom of the Laval tube cavity 5.

[0013] The present invention also provides a control method for the replaceable Laval nozzle differential pressure measurement device, characterized in that, based on the ADRC controller, according to the differential pressure parameters collected by the differential pressure measurement module 3, the differential pressure change gradient is used as the judgment index to achieve accurate positioning of the Laval nozzle throat position, thereby realizing continuous and accurate measurement of differential pressure parameters along the nozzle. Attached Figure Description

[0014] Figure 1 3D model of a replaceable Laval tube differential pressure measuring device

[0015] Figure 2 Front sectional view of the replaceable Laval tube differential pressure measuring device

[0016] Figure 3 Experimental apparatus support structure diagram

[0017] Figure 4 Differential pressure measurement module structure diagram

[0018] Figure 5 : Structural diagram of replaceable Laval tube and throat area adjustment module

[0019] Figure 6 Laval lumen structure diagram

[0020] Figure 7 ADRC control system structure diagram

[0021] Figure 8 Flowchart of Experimental Control for Replaceable Laval Tube Differential Pressure Measurement Device Detailed Implementation

[0022] The interchangeable Laval nozzle differential pressure measuring device of the present invention includes a device support, an inlet pipe section, a differential pressure measuring module, an interchangeable Laval tube and a throat area adjustment module, a Laval tube cavity, and an outlet pipe section, wherein the inlet pipe section and the outlet pipe section are connected to an external gas path. The experimental gas enters the rectangular Laval tube cavity through the inlet pipe section and flows out of the rectangular Laval tube cavity through the outlet pipe section. The differential pressure parameter is measured using the pressure tapping hole built into the movable plate at the top.

[0023] To ensure reliable fixation of the device support and various modules, this invention designs an aluminum alloy profile support, a motor mounting bracket, and a reducer mounting bracket. All connection parts are fixed using hexagonal bolts and angle brackets.

[0024] To achieve accurate measurement of the pressure difference along the Laval tube, a combination of a DC servo motor and a reducer is used to drive the rack and pinion mechanism, enabling continuous reciprocating movement and precise positioning of the top pressure tap. A fixed flat plate is used to compress a flat O-ring, ensuring reliable sealing while maintaining the movement of the measuring plate.

[0025] To enable quick replacement of Laval tubes with different profiles, a rectangular cavity and corresponding Laval tube inserts with different profiles were designed. The Laval tube inserts are nested in the rectangular cavity, and the Laval tube inserts are assembled with the base by tightening or loosening bolts.

[0026] To meet the experimental measurement requirements under various flow rates and achieve precise adjustment of the Laval tube throat area, this invention applies drive by fixing a stepper motor to the Laval tube insert base. A ball screw is fixed to the stepper motor output shaft via a coupling, and the ball screw nut is fixed at a corresponding position on the cavity. The stepper motor drives the ball screw to rotate, controlling the relative position between the base and the cavity, thus achieving precise adjustment of the Laval tube throat area. Furthermore, an O-ring within the mounting groove of the base below the cavity ensures a reliable seal between the base and the cavity.

[0027] To address the challenges of accurately locating the actual Laval throat and precisely adjusting the measurement position under real-world operating conditions, which are affected by internal and external disturbances, an ADRC controller was designed. A corresponding experimental control strategy was proposed. Based on actively suppressing system disturbances, the control device uses the pressure difference gradient as a judgment index to achieve accurate positioning of the Laval throat and ultimately completes continuous and accurate measurement of the pressure difference parameters along the pipe.

[0028] To further understand the features, technical means, and specific objectives and functions achieved by the present invention, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0029] like Figure 1The image shown is a 3D model of the replaceable Laval nozzle differential pressure measurement device. Figure 2 The diagram shows a cross-sectional view of its mechanical structure, which includes a measuring device support 1, an inlet pipe section 2, a differential pressure measuring module 3, a replaceable Laval tube and throat area adjustment module 4, a Laval tube cavity 5, and an outlet pipe section 6. The inlet pipe section 2 and the outlet pipe section 6 are rigidly connected to the experimental gas path via flanges or pneumatic quick-connect couplings. The Laval tube cavity 5 is fixed to the device support 1 using angle brackets and bolts.

[0030] Figure 3 The diagram shows the structure of the measuring device support, which includes an aluminum alloy profile support 101, a motor mounting bracket 102, and a reducer mounting bracket 103. Each part is fixed by hexagonal bolts and angle brackets.

[0031] Figure 4 This is a structural diagram of the differential pressure measurement module 3, which includes a fixing screw 301, a DC servo motor 302, a gear reducer 303, a flat key 304, a cylindrical spur gear 305, a fastening screw 306, a rack 307, a rack fixing screw 308, a pressure tapping hole quick connector 309, a fixing plate 310, and a measuring plate 311.

[0032] The DC servo motor 302 and the gear reducer 303 are bolted together and fixed to corresponding positions on the motor mounting bracket 102 and reducer mounting bracket 103 of the measuring device bracket 1, respectively. A flat key is used to fix the radial relative position between the output shaft of the DC servo motor 302 and the input shaft of the gear reducer 303, ensuring power output. A flat key 304 limits the rotational freedom of the cylindrical spur gear 305 to the output shaft of the gear reducer, and a fastening screw 306 fixes it to the end of the gear reducer output shaft, ensuring that the gear reducer output shaft can synchronously drive the cylindrical spur gear 305. A rack 307 is fixed to one end of the measuring plate 311 by rack fixing screws 308 and meshes with the cylindrical spur gear 305. The measuring plate 311 has miniature pressure holes and is connected to quick connectors 309. The fixed plate 310 has a U-shaped structure design with internal slots for the rack to pass through, while also serving as a limiter. The fixed plate 310 is fixed to the Laval tube cavity 5 by screws 301. By applying a certain pre-tightening force, the O-ring installed in the flat sealing groove 503 is compressed to achieve sealing, while ensuring the translation of the measuring plate 311 in the groove 505.

[0033] Before the experiment, the DC servo motor 302 is first controlled to drive the gear reducer 303 to rotate, simultaneously causing the spur gear 305 to rotate synchronously. This allows the rack 307, which meshes with the gear reducer, and the measuring plate 311 to translate along the groove 505 to their initial positions. At this point, the pressure measured at the pressure tap on the measuring plate 311 serves as the reference pressure. When experimental parameters need to be measured, the DC servo motor 302 is controlled to drive the measuring plate 311 to translate along the groove 505 towards the throat. The system outputs the relative pressure difference value based on the pressure measured at different pressure tap positions.

[0034] The structure of the replaceable Laval tube and throat area adjustment module 4 is as follows: Figure 5 As shown, it includes a replaceable Laval tube insert 401, a stepper motor 402, a ball screw 403, and a base 404. The Laval tube insert 401 has a threaded hole at its bottom end and is bolted to the base 404. The stepper motor is fixed to a corresponding position on the base 404 with screws, and its output shaft is fixed to the ball screw 403 via a miniature coupling to ensure synchronous power output. Four sets of stepper motors and ball screw adjustment mechanisms are symmetrically arranged at the bottom of the base, and each ball screw 403 mates with a corresponding ball screw nut 507 on the Laval tube cavity 5.

[0035] Before the experiment, when it is necessary to replace the Laval tube with a different profile, firstly, the four stepper motors on the base 404 are synchronously controlled to drive the ball screws to rotate, removing the entire module from the base embedding groove 508 of the Laval tube cavity 5. The original Laval tube insert 401 is manually removed, and the Laval tube insert 401 of the required profile is replaced and fixed to the base 404 with fixing bolts. Then, the entire module is aligned with the base embedding groove 508, and each ball screw 403 is engaged with the corresponding ball screw nut 507 on the Laval tube cavity 5. The stepper motors are controlled to rotate, driving the ball screws 403 to rotate, embedding the entire module into the Laval tube cavity 5. This allows the Laval tube insert 401 to be embedded into the replaceable Laval tube embedding cavity 506, and the base 404 to be embedded into the base embedding groove 508. An O-ring is installed in the base embedding groove 508 to ensure a reliable seal when the base and cavity slide relative to each other.

[0036] During the experiment, when it is necessary to adjust the throat area of ​​the Laval tube, four sets of stepper motors symmetrically arranged at the bottom of the base 404 drive the ball screw 403 to rotate synchronously, so that the replaceable Laval tube and the throat area adjustment module 4 slide up and down along the replaceable Laval tube embedding cavity 506 and the base embedding groove 508, thereby achieving precise adjustment of the throat area.

[0037] Laval lumen 5 structure as follows Figure 6 As shown, it features an inlet 501, a threaded hole 502, a planar sealing groove 503, a rectangular airflow channel 504, a groove 505, a replaceable Laval tube embedded cavity 506, a ball screw nut 507, a base embedded groove 508, an annular sealing groove 509, and an outlet 510. O-rings are fitted in the planar sealing groove 503 and the annular sealing groove 509 to achieve sealing.

[0038] Due to factors such as manufacturing errors, the throat position during the experiment deviated from the designed position. The pressure difference for the actual Laval tube airflow is shown in the equation.

[0039] p d =p m -p in (1)

[0040] Where, p m This is the measurement value for the current location.

[0041] The pressure gradient is expressed as shown in the equation.

[0042]

[0043] At a certain inlet pressure p in Under, when the export pressure p out When the flow rate is at an appropriate value, the Laval tube will be in a critical flow state, with a throat Mach number of Ma. t =1, Exit Mach number Ma t <1, p d The pressure difference gradually decreases along the nozzle axis in the convergence section and reaches its minimum value at the throat. After passing the throat, the pressure difference p d It gradually increases within the expansion segment and eventually tends to a constant value p. e =p out -p in That is, the pressure gradient at the throat of the Laval tube changes from negative (grad(p)<0) to positive (grad(p)>0). The pressure difference is at a minimum at the throat of the Laval tube, with a gradient of grad(p)=0.

[0044] Based on this principle, a control system was designed and an experimental control strategy was formulated by utilizing the pressure gradient changes at the throat position. The measurement position was adjusted promptly based on the positive or negative value of the feedback pressure gradient, with a zero pressure gradient serving as the criterion for accurate positioning of the actual throat. Furthermore, in actual system control, the system is inevitably subject to external disturbances, requiring the control system to achieve precise control of the measurement position while resisting these disturbances.

[0045] Based on this, a DC servo motor is used as the controlled object. The motor output shaft feeds back the actual distance information y to the control system via an encoder, with the desired value v as the system input. A design is then implemented as follows: Figure 7 The ADRC control system shown here contains a nonlinear tracking differentiator (NTD) as shown in the equation.

[0046]

[0047] In the formula, r is the velocity factor that determines the tracking speed, h is the integration step size, and h0 is the filtering factor that performs the filtering function; the nonlinear function fhan(e,v2,r,h) is:

[0048]

[0049] In the formula, sign(a) is the sign function, and fsg(a,d) is shown in the formula:

[0050] fsg(a,d)=[sign(a+d)-sign(ad)] / 2 (5)

[0051] a and d are shown in the formula:

[0052]

[0053] The parameters a, h, and h0 are undetermined parameters in NTD.

[0054] The Extended State Observer (ESO) is shown in the equation. The ESO treats all disturbances inside and outside the system as a total disturbance and expands it into a state information of the system for observation.

[0055]

[0056] in:

[0057]

[0058] β 01 ,β 02 ,β 03 b0 and b0 are system parameters to be tuned, and δ is the width of the linear interval of the nonlinear function fal near the zero point. Its value is selected according to the error range of the system, and is generally taken as δ = 0.1.

[0059] The nonlinear state error feedback control law (NLSEF), as shown in the equation, can effectively suppress uncertain disturbances in the system.

[0060]

[0061] Where 0≤α 01 ≤1≤α 02 α is usually taken01 =0.25,α 02 =1.5; δ0 is a parameter related to the range and control accuracy of the controlled variable, and is generally taken as δ0 = 0.02. k p and k d These are the parameters to be tuned.

[0062] Through disturbance compensation, the control variable u is obtained as follows:

[0063]

[0064] Where b0 is a parameter to be determined.

[0065] This controller can treat all disturbances as state variables, observe them through ESO, and actively use control signals to eliminate disturbances, effectively suppressing various internal and external disturbances and improving the control accuracy of the system.

[0066] Precisely locate the throat position and measure the differential pressure experimental control process as follows: Figure 8 As shown, before starting the experiment, the Laval tube insert of the required profile must be replaced, and the reliability of the device assembly must be checked. After starting, the device is first initialized to ensure the measurement position is at the theoretically designed starting point. Then, experimental gas is introduced into the front end, and the experimental operating conditions are adjusted to meet the critical flow parameters of the Laval tube. The motor is then driven to rotate forward, while simultaneously collecting and recording differential pressure data. The system automatically calculates the differential pressure gradient and judges its value in real time. If it is less than 0, the motor continues to rotate forward, and the pressure measurement position continues to move forward; if it is greater than 0, the motor is driven to rotate in reverse, and the measurement position moves backward; if the differential pressure gradient is determined to be 0, the motor automatically stops, and the system records the current position as the actual throat position. Using this position as a reference, the motor is controlled to rotate in reverse, moving the measurement position to the Laval tube inlet position. The operating conditions are adjusted to meet the experimental requirements, and then the motor is controlled to rotate forward to start the experiment, measuring and recording the differential pressure data. After the measurement position moves to the Laval tube outlet, the motor stops, and the experiment ends.

[0067] The above-described specific embodiments provide a detailed explanation of the theoretical innovations and implementation schemes of this invention. This invention is not limited to the above-described embodiments. For those skilled in the art, any improvements or substitutions made based on the above principles and spirit are within the scope of protection of this invention.

Claims

1. A removable Laval nozzle differential pressure measuring device characterized by, The device includes a measuring device support (1), an inlet pipe section (2), a differential pressure measurement module (3), a replaceable Laval tube and throat area adjustment module (4), a Laval tube cavity (5) and an outlet pipe section (6); the Laval tube cavity (5) is arranged on the device support (1), and both ends of the Laval tube cavity (5) are connected with the outside air path through the inlet pipe section (2) and the outlet pipe section (6); The inner cavity of the Laval tube cavity (5) is a rectangular inner cavity, and a rectangular air flow channel (504) is arranged at the top of the rectangular inner cavity and communicates with the rectangular inner cavity. The differential pressure measurement module (3) comprises a gear (305) driven by a motor (302), a rack (307), a fixed plate (310) and a measurement plate (311); the fixed plate (310) is in a U-shaped structure and is fixed on the upper part of the Laval tube cavity (5); the fixed plate (310) is provided with a slot along the axis, and the slot is provided for the rack (307) to pass through; the slot is located corresponding to the rectangular air flow channel (504); the rack (307) is fixedly connected with the measurement plate (311) and is engaged with the gear (305); the measurement plate (311) is provided with a pressure guiding hole; the differential pressure measurement module (3) measures the differential pressure parameter in the rectangular inner cavity of the Laval tube cavity (5) through the pressure guiding hole; the measurement plate (311) is driven by the fixed plate (310) to translate along the rectangular air flow channel (504); the fixed plate (310) is in dynamic sealing connection with the upper part of the Laval tube cavity (5); The bottom of the Laval tube cavity (5) is provided with a base embedding groove (508), and a replaceable Laval tube embedding cavity (506) communicating with the rectangular inner cavity is arranged in the base embedding groove (508); the bottom of the Laval tube cavity (5) is further connected with a ball screw nut (507); The replaceable Laval tube and throat area adjustment module (4) comprises a base (404), a replaceable Laval tube embedding body (401), a stepping motor (402) and a ball screw (403); the replaceable Laval tube embedding body (401) is fixed on the base (404) and extends into the rectangular inner cavity of the Laval tube cavity (5) through the replaceable Laval tube embedding cavity (506); the outer surface of the replaceable Laval tube embedding body (401) cooperates with the rectangular inner cavity; the base (404) is located in the base embedding groove (508) and is in dynamic sealing connection with the base embedding groove (508); the stepping motor (402) is used to drive the ball screw (403); the base (404) is symmetrically provided with at least three sets of stepping motor and ball screw adjustment mechanisms at the bottom; each ball screw (403) cooperates with the ball screw nut (507) at the corresponding position of the bottom of the Laval tube cavity (5); the position of the base (404) and the replaceable Laval tube embedding body (401) is adjusted through the stepping motor and ball screw adjustment mechanism, so as to realize the adjustment of the throat area.

2. The removable Laval nozzle differential pressure measurement device of claim 1, wherein, A groove (505) is arranged at the top of the Laval tube cavity along the axial direction, and the rectangular air flow channel (504) is arranged in the groove (505).

3. The removable Laval nozzle differential pressure measurement device of claim 2, wherein, The flat sealing groove (503) for accommodating the O-shaped sealing ring is arranged on the periphery of the outer surface of the rectangular air flow channel (504), and the dynamic sealing is realized by applying a certain pre-tightening force to compress the O-shaped sealing ring assembled in the flat sealing groove (503) through the fixed flat plate (310), and the translation of the measuring flat plate (311) in the groove (505) is ensured.

4. The removable Laval nozzle differential pressure measurement device of claim 1, wherein, The annular sealing groove (509) for accommodating the O-shaped sealing ring is arranged on the inner wall of the base embedding groove (508) and the annular sealing groove (509), so that the dynamic sealing connection between the base (404) and the bottom base embedding groove (508) of the Laval tube cavity (5) is realized.

5. The control method of the replaceable Laval nozzle differential pressure measuring device according to any one of claims 1 to 4, characterized by, Based on the ADRC controller, the pressure difference parameter collected by the pressure difference measurement module (3) is used as the judgment index of the pressure difference change gradient, the precise positioning of the Laval tube throat position is realized, and the continuous and accurate measurement of the pressure difference parameter is realized.

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