Flow metering system under all working conditions and venturi flow meter thereof

Abstract

This invention relates to a flow metering system under all operating conditions and its Venturi tube flow meter. The system includes a Venturi tube flow meter and a corresponding flow calculation unit. The flow calculation unit constructs a flow coefficient prediction model based on the calibration data of the Venturi tube flow meter to calculate the flow rate. The flow coefficient prediction model is configured to: acquire the flow rate, Reynolds number, and flow coefficient data calibrated by the Venturi tube flow meter under normal temperature and pressure; set a boundary Reynolds number and divide the calibration data according to the boundary Reynolds number; perform cubic polynomial fitting with X as the variable based on the low Reynolds number region data to obtain a partitioned model; and calculate fixed prediction coefficient values ​​based on the high Reynolds number region data. This invention overcomes the limitations of a single model, especially in the extrapolation region, by using a dual-region coupled model that combines "accurate cubic polynomial fitting in the low Reynolds number region" with "extrapolation of the mean of the stability coefficient in the high Reynolds number region".

Description

Technical Field

[0001] This invention relates to the field of flow measurement technology, and in particular to a flow measurement system under all operating conditions and its Venturi tube flow meter. Specifically, it relates to a high-precision flow measurement system and its Venturi tube flow meter based on segmented modeling and extrapolation under all operating conditions, which is suitable for high-precision flow monitoring of liquids such as deionized water in nuclear power, chemical industry and other fields. Background Technology

[0002] In industrial sectors such as petrochemicals, thermal power generation, nuclear power, and new energy, high-precision flow measurement of fluids in high-temperature and high-pressure pipelines is a core component for ensuring the safe and stable operation of production processes, achieving refined energy efficiency management, and meeting trade measurement compliance requirements. Especially in scenarios such as power plant boiler feedwater and the transportation of high-pressure chemical reaction media, there is a common need to measure small flow rates (typically 0.2-2.0 m³ / h) of media under harsh conditions such as 15.5 MPa and 350℃ superheated water. The accuracy of this measurement directly affects the calculation of unit thermal efficiency, closed-loop control of process parameters, and equipment safety protection, placing extremely high demands on the long-term stability, adaptability to operating conditions, and measurement accuracy of flow meters.

[0003] Among the aforementioned flow measurement solutions for demanding operating conditions, the Venturi flow meter has become the preferred flow measurement device in industrial settings due to its significant advantages, including simple structure, low pressure loss, resistance to erosion and wear, strong anti-interference ability, and adaptability to high temperature, high pressure, and complex media conditions. Compared to orifice plate flow meters, Venturi tubes offer superior flow characteristics and exhibit less accuracy degradation over long-term use. Compared to velocity flow meters such as turbine and vortex flow meters, it has no moving parts, resulting in greater reliability and service life under high temperature and high pressure conditions. Therefore, it has been widely used in flow measurement under demanding conditions in the energy and chemical industries.

[0004] The metering accuracy of Venturi flow meters is highly dependent on the instrument coefficient obtained from actual flow calibration. Only through traceable actual flow calibration can the metering error under application conditions be guaranteed to meet standard requirements. However, the calibration capabilities of mainstream domestic and international metrology institutions are currently significantly limited: due to limitations in the pressure resistance, temperature tolerance, and construction costs of calibration equipment, most legal metrology institutions can only conduct actual flow calibration under normal temperature and pressure water conditions, and cannot perform actual flow calibration for the full range and the full Reynolds number range under high temperature and high pressure conditions. Taking a typical small-flow Venturi tube as an example, the highest Reynolds number that can be covered by normal temperature and pressure calibration is about 83,000, while under actual operating conditions of 15.5 MPa and 350℃ superheated water, the highest Reynolds number can reach 120,000. The Reynolds number range covered by calibration is far lower than the Reynolds number range of actual operating conditions, forming a significant calibration coverage blind spot.

[0005] To address the aforementioned calibration blind zone issue, the traditional industry approach is to directly extrapolate the calibration curve obtained under normal temperature and pressure to the high Reynolds number range of actual operation, using this as the basis for flow calculation under high operating conditions. However, this method has a fatal technical flaw: the instrument coefficient of the Venturi tube exhibits a strong nonlinear correlation with the Reynolds number. In the low Reynolds number range, the instrument coefficient fluctuates significantly with changes in the Reynolds number; only when the Reynolds number reaches a certain threshold does the instrument coefficient tend to stabilize. The traditional single-curve extrapolation method cannot accurately fit the nonlinear characteristics of the low Reynolds number range, nor can it guarantee the accuracy of the coefficient in the high Reynolds number extrapolation range. It is highly susceptible to introducing significant extrapolation errors, ultimately resulting in the flowmeter failing to achieve a measurement accuracy better than 0.5% across the entire range. In fact, the relative error in the high Reynolds number extrapolation range can exceed 1%, completely failing to meet the high-precision metering requirements under high temperature and high pressure conditions.

[0006] To address the extrapolation error problem, several improvement solutions have emerged in the industry: First, computational fluid dynamics (CFD) numerical simulation is used to correct the flow coefficient in the high Reynolds number region. However, the simulation results are greatly affected by boundary conditions, turbulence models, and mesh accuracy, resulting in inherent deviations from the actual flow characteristics and failing to achieve metrological-grade accuracy. Second, custom-built high-temperature and high-pressure actual flow calibration devices are used. While this solution can achieve calibration under all operating conditions, the construction cost of such devices can easily reach millions of yuan, with long calibration cycles and extremely high maintenance costs. This makes it suitable only for a very limited number of laboratory scenarios and cannot be widely applied in industrial settings. Third, multi-segment linear fitting is used to process the calibration data. However, its fitting accuracy in the low Reynolds number nonlinear region is insufficient, and the coefficient drift problem in the high Reynolds number extrapolation region remains unresolved, making it difficult to achieve high-precision measurement across the entire range.

[0007] In summary, current Venturi flowmeters designed for low-flow-rate measurements under high-temperature and high-pressure conditions have consistently failed to resolve the core contradiction between "limited calibration capabilities at ambient temperature and pressure" and "the need for high-precision measurement under high Reynolds number conditions." There is a lack of intelligent flow measurement systems that can reliably predict flow rates across the entire high-temperature and high-pressure operating range using limited ambient temperature and pressure calibration data, achieve full-range accuracy better than 0.5%, have low calibration costs, and are easily implemented in engineering. This has become a common industry challenge restricting high-precision flow measurement under harsh conditions in the energy and chemical industries.

[0008] Furthermore, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the applicant studied a large number of documents and patents when making this invention, but due to space limitations, not all details and contents were listed in detail. However, this does not mean that the present invention does not possess the features of these prior art. On the contrary, the present invention already possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a flow metering system operating under all conditions. The system includes a Venturi tube flow meter and a corresponding flow calculation unit. The flow calculation unit constructs a flow coefficient prediction model based on the calibration data of the Venturi tube flow meter to calculate the flow rate. The flow coefficient prediction model is configured as follows:

[0010] S1: Obtain the flow rate, Reynolds number, and flow coefficient data of the venturi tube flow meter calibrated at room temperature and pressure;

[0011] S2: Set the boundary Reynolds number and divide the calibration data according to the boundary Reynolds number. Based on the low Reynolds number area data, perform cubic polynomial fitting with X as the variable to obtain the partition model. Calculate the fixed prediction coefficient value based on the high Reynolds number area data.

[0012] S3: In actual measurements under full operating conditions, the real-time Reynolds number is calculated iteratively;

[0013] S3: Based on the relationship between the boundary Reynolds number and the real-time Reynolds number, select either the zoning model or the fixed prediction coefficient value to determine the flow coefficient for flow calculation.

[0014] According to a preferred embodiment, steps S1 and S2 are the model building and calibration stages for the flow calculation unit;

[0015] Steps S3 and S4 are the operational phases in which the flow calculation unit performs real-time measurement and iterative calculation on the Venturi tube flow meter.

[0016] According to a preferred embodiment, the steps for obtaining the flow rate, Reynolds number, and flow coefficient data of a Venturi tube flow meter calibrated at room temperature and pressure include:

[0017] Obtain the flow rate from Q1 to Q in water at normal temperature and pressure using a Venturi tube flow meter. n Data from n calibration points, including flow rate, Reynolds number, and instrument coefficient for each calibration point.

[0018] According to a preferred embodiment, the step of setting a boundary Reynolds number and dividing the calibration data according to the boundary Reynolds number includes:

[0019] Divide the modeling interval: Set a boundary Reynolds number, and divide the calibration data into set A and set B according to the boundary Reynolds number; where,

[0020] Set A represents the set of data points for all calibration points whose Reynolds number is less than or equal to the threshold Reynolds number, corresponding to the nonlinear range of the instrument coefficient as the Reynolds number changes.

[0021] Set B represents the set of data from several highest flow calibration points where the calibration point Reynolds number is greater than the threshold Reynolds number, corresponding to a stable range where the rate of change of the instrument coefficient tends to level off.

[0022] According to a preferred embodiment, the step of performing a cubic polynomial fitting on low Reynolds number region data with X as the variable to obtain a partitioning model includes:

[0023] For the data in set A, let X = log 10 With the Reynolds number at the calibration point as the independent variable and the instrument coefficient as the dependent variable, a cubic polynomial is used for fitting, and the formula is as follows:

[0024]

[0025] Where Intercept, B1, B2, and B3 are constants obtained by fitting calibration data; C is the flow coefficient.

[0026] According to a preferred embodiment, the step of performing cubic polynomial fitting on low Reynolds number region data with X as the variable to obtain a partitioning model further includes:

[0027] For the data in set B, the arithmetic mean of the instrument coefficients is calculated and used as the fixed prediction coefficient value for the high Reynolds number region; where the fixed prediction coefficient value is the arithmetic mean of the flow coefficients of several calibration points in the calibration data where the Reynolds number is greater than the boundary Reynolds number.

[0028] According to a preferred embodiment, in actual measurements under full operating conditions, the step of iteratively calculating the real-time Reynolds number includes:

[0029] The real-time differential pressure, temperature, and pressure of the Venturi tube flow meter are collected, and the fluid density and viscosity are calculated based on the real-time temperature and pressure.

[0030] According to a preferred embodiment, the step of the flow calculation unit executing the iterative algorithm includes:

[0031] S321: Assume an initial flow coefficient;

[0032] S322: The formula for calculating real-time traffic is as follows:

[0033]

[0034] Q temp For real-time traffic; C old ρ is the initial flow coefficient; K is the instrument coefficient; ΔP is the real-time differential pressure; ρ is the fluid density.

[0035] S323: The formula for calculating the real-time Reynolds number is as follows:

[0036]

[0037] Among them, Re temp denoted as the real-time Reynolds number, d as the throat diameter, and μ as the fluid viscosity.

[0038] S324: Compare the real-time Reynolds number with the pre-stored boundary Reynolds number; if the real-time Reynolds number is less than or equal to the boundary Reynolds number, calculate the new flow coefficient C based on the fitted polynomial. new The fitting polynomial is C new =f(log 10 (Re temp If the real-time Reynolds number is greater than the threshold Reynolds number, then set the new flow coefficient to the fixed prediction coefficient value.

[0039] S325: Determine if the absolute value of the difference between the new flow coefficient and the initial flow coefficient is less than the convergence threshold; if not, set the initial flow coefficient equal to the current new flow coefficient and return to step S322; if yes, the iteration ends, and the final real-time flow Q is output. temp .

[0040] This invention also relates to a Venturi tube flow meter, employing the aforementioned full-condition flow metering system, comprising a Venturi tube body. The Venturi tube body includes an inlet section, a contraction section, a throat, a diffuser section, and an extension section connected in sequence. The ratio of the throat diameter to the inlet section diameter ranges from 0.55 to 0.65.

[0041] According to a preferred embodiment, the inlet section, constriction section, throat, diffuser section, and extension section are all circumferentially covered by the wall. A low-pressure tap connected to the throat and a high-pressure tap connected to the extension section are provided on the wall. Each of the low-pressure and high-pressure taps has an annular chamber structure near the wall end for averaging the pressure at the taps to suppress fluid eddies and lateral flow interference. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0043] Figure 1 This is a simplified hardware topology diagram of a flow metering system under all operating conditions according to a preferred embodiment of the present invention;

[0044] Figure 2 This is a simplified logic flow diagram of a flow metering system under all operating conditions according to a preferred embodiment of the present invention.

[0045] Figure 3 This is a simplified structural diagram of a Venturi tube flow meter according to a preferred embodiment of the present invention;

[0046] Figure 4 This is a simplified structural diagram of a venturi tube flow meter after being cut open, according to a preferred embodiment of the present invention.

[0047] List of reference numerals

[0048] 100: Venturi tube body; 101: Inlet section; 102: Contraction section; 103: Throat; 104: Diffusion section; 105: Wall; 106: Extension section; 107: Low-pressure tap; 108: High-pressure tap; 109: Annular chamber structure; 110: Conical self-cleaning tap. Detailed Implementation

[0049] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments, and therefore should not be construed as limiting this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0050] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or server that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0051] Example 1

[0052] The following is an explanation of the technical terms used in this application.

[0053] Reynolds number: The Reynolds number is a core dimensionless similarity criterion number in fluid mechanics, characterizing the state of fluid flow. Its physical essence is the ratio of inertial force to viscous force during fluid flow. It is used to quantitatively determine the flow pattern of a fluid and is also a key parameter relating the metering characteristics of flow measurement equipment to the fluid flow state. When the Reynolds number is small, the fluid viscous force dominates, and fluid particles flow in a regular parallel layer along the pipe axis without lateral disturbance; this is called laminar flow. When the Reynolds number is large, the fluid inertial force dominates, and the flow trajectory of fluid particles is turbulent, with strong lateral pulsations and eddies; this is called turbulent flow. For fluid flow in industrial pipelines, the critical Reynolds number (approximately 2300) is usually used as the boundary between laminar and turbulent flow, and the stable operating range of a Venturi flowmeter is usually in a turbulent state.

[0054] In this invention, the Reynolds number is the key criterion, permeating the entire process of calibration modeling, real-time measurement, and iterative calculation, and is the core parameter for achieving high-precision flow prediction. As a dimensionless number, the Reynolds number eliminates the influence of changes in temperature, pressure, and media properties, enabling similarity benchmarking of fluid flow characteristics under different operating conditions. This patent utilizes this characteristic to reliably predict the flow coefficient under high-temperature, high-pressure, and high-Reynolds-number operating conditions through the Reynolds number mapping relationship obtained from calibration at room temperature and pressure, completely solving the industry pain point of being unable to perform actual flow calibration under harsh operating conditions.

[0055] High temperature and high pressure: In this invention, it refers to pipelines that require testing in the energy and chemical industries and possess the characteristics of high temperature and high pressure. This is especially true for superheated water operating under environmental parameters of 15.5 MPa and 350°C.

[0056] Venturi flow meters are a common choice for low-flow-rate media. However, typical metrology systems for Venturi flow meters can only perform actual flow calibration for water at normal temperature and pressure. This involves allowing actual fluid to flow through the calibrated flow meter and comparing the result with a standard flowmeter to determine the flow meter's measurement error. But under extreme conditions, the Reynolds number range calibrated by the metrology system is far lower than the Reynolds number under actual operating conditions. Current technology, by directly extrapolating the calibration curve to the unknown high Reynolds number region in this situation, introduces significant errors, making it difficult to achieve a measurement accuracy better than 0.5% across the entire flow range.

[0057] To address this challenge of Venturi flowmeters and their metering mechanisms under the aforementioned operating conditions, there is an urgent need in the field for a Venturi flowmeter with small flow rates under high temperature and high pressure conditions. In particular, there is a need for a high-precision intelligent flow measurement system that can predict flow rates from high temperature and high pressure to all operating conditions using limited calibration data at normal temperature and pressure.

[0058] The purpose of this invention is to provide a Venturi flow metering system with high accuracy and low calibration cost. It uses a segmented prediction algorithm configured in the flow calculation unit to achieve accurate prediction of flow under higher Reynolds number operating conditions using limited ambient temperature and pressure calibration data, with a full-range accuracy better than 0.5%.

[0059] The technical solutions of the embodiments of this application will be described in detail below, such as... Figure 1 As shown, this invention discloses a flow metering system under all operating conditions, and more particularly, a flow metering system for a Venturi tube flow meter under all operating conditions. Specifically, it discloses a high-precision flow metering system for a Venturi tube flow meter based on segmented modeling and extrapolation under all operating conditions.

[0060] Preferably, the system includes a venturi flow meter, a differential pressure transmitter, a temperature sensor, a pressure sensor, and a flow calculation unit. The flow calculation unit uses an embedded microprocessor (MCU) or a programmable logic controller (PLC) as its hardware carrier, and has a built-in non-volatile memory module and a calculation module. It pre-stores a flow coefficient prediction model and iterative calculation method based on specific calibration data. Core parameters such as the boundary Reynolds number, cubic polynomial fitting coefficients, fixed prediction coefficient values, instrument constant K, and venturi throat diameter d can be pre-stored in the memory module. At the same time, the iterative calculation program is fixed to meet the requirements of stable operation under harsh industrial conditions.

[0061] Preferably, such as Figure 1 and Figure 2 As shown, the flow coefficient prediction model is configured as follows:

[0062] S1: Obtain the calibrated flow rate, Reynolds number, and flow coefficient data under normal temperature and pressure;

[0063] S2: Set the boundary Reynolds number and divide the calibration data according to the boundary Reynolds number. Based on the low Reynolds number area data, perform cubic polynomial fitting with X as the variable to obtain the partition model. Calculate the fixed prediction coefficient value based on the high Reynolds number area data.

[0064] S3: In actual measurements under full operating conditions, the real-time Reynolds number is calculated iteratively;

[0065] S4: Based on the relationship between the boundary Reynolds number and the real-time Reynolds number, select either the zoning model or the fixed prediction coefficient value to determine the flow coefficient for flow calculation.

[0066] In this invention, steps S1 and S2 are the model construction and calibration stages, and steps S3 and S4 are the real-time measurement and iterative calculation operation stages. The fixed prediction coefficient value is the calculated flow coefficient.

[0067] In step S1, preferably, the steps of obtaining the calibrated flow rate, Reynolds number, and flow coefficient data under normal temperature and pressure include:

[0068] S11: Obtain the flow rate from Q1 to Q in water at normal temperature and pressure. n Data from n calibration points, including flow rate, Reynolds number, and instrument coefficient for each calibration point.

[0069] In this invention, Q1 to Q n Corresponding to Reynolds numbers Re1 to Re n .

[0070] Preferably, the steps of setting the boundary Reynolds number and dividing the calibration data according to the boundary Reynolds number include:

[0071] S21: Divide the modeling interval: Set a boundary Reynolds number, and divide the calibration data into set A and set B according to the boundary Reynolds number; where...

[0072] Set A represents the set of data points for all calibration points whose Reynolds number is less than or equal to the threshold Reynolds number, corresponding to the nonlinear range of the instrument coefficient as the Reynolds number changes.

[0073] Set B represents the set of data from several highest flow calibration points where the calibration point Reynolds number is greater than the threshold Reynolds number, corresponding to a stable range where the rate of change of the instrument coefficient tends to level off.

[0074] The core setting rule for the boundary Reynolds number is as follows: the Reynolds number corresponding to the turning point where the rate of change of the instrument coefficient in the calibration data tends to flatten out can be adaptively determined according to the different Venturi throat ratio, structural form, and fluid medium, rather than being set randomly by humans. This ensures from the model structure that the low Reynolds number fitting region fully covers the nonlinear change segment of the coefficient, and the high Reynolds number extrapolation region corresponds to the stable segment of the coefficient, thus avoiding extrapolation errors at the source.

[0075] Preferably, the step of performing a cubic polynomial fitting on the low Reynolds number region data with X as the variable to obtain the partitioning model includes:

[0076] S22: Establish a partitioning model.

[0077] Specifically, in some exemplary embodiments, step S22 includes:

[0078] S221: For the data in set A, let X = log 10 The Reynolds number at the calibration point is the independent variable, and the instrument coefficient (i.e., the flow coefficient) is the dependent variable. A cubic polynomial is used for fitting, and its formula is as follows:

[0079]

[0080] Where Intercept, B1, B2, and B3 are constants obtained by fitting calibration data; C is the flow coefficient.

[0081] S222: For the data in set B, calculate the arithmetic mean of its instrument coefficients, which serves as the fixed prediction coefficient value for the high Reynolds number region. The fixed prediction coefficient value is the arithmetic mean of the flow coefficients at several calibration points where the Reynolds number is greater than the boundary Reynolds number in the calibration data.

[0082] Preferably, the calibration point Reynolds number, fitting polynomial coefficients, fixed prediction coefficient values, and instrument coefficients are pre-stored in the flow calculation unit.

[0083] In step S3, preferably, in actual measurements under full operating conditions, the step of iteratively calculating the real-time Reynolds number includes:

[0084] S31: Collect real-time differential pressure, temperature, and pressure from the Venturi tube flow meter, and calculate fluid density and viscosity based on the real-time temperature and pressure;

[0085] S32: Execute the iterative algorithm.

[0086] Specifically, in some exemplary embodiments, step S32 includes:

[0087] S321: Assume an initial flow coefficient;

[0088] S322: The formula for calculating real-time traffic is as follows:

[0089]

[0090] Q temp For real-time traffic; C old ρ is the initial flow coefficient; K is the instrument coefficient; ΔP is the real-time differential pressure; ρ is the fluid density.

[0091] S323: The formula for calculating the real-time Reynolds number is as follows:

[0092]

[0093] Among them, Re temp denoted as the real-time Reynolds number, d as the throat diameter, and μ as the fluid viscosity.

[0094] S324: Compare the real-time Reynolds number with the pre-stored boundary Reynolds number; if the real-time Reynolds number is less than or equal to the boundary Reynolds number, calculate the new flow coefficient C based on the fitted polynomial. new The fitting polynomial is C new =f(log 10 (Re temp If the real-time Reynolds number is greater than the threshold Reynolds number, then set the new flow coefficient to the fixed prediction coefficient value.

[0095] S325: Determine if the absolute value of the difference between the new flow coefficient and the initial flow coefficient is less than the convergence threshold; if not, set the initial flow coefficient equal to the current new flow coefficient and return to step S322; if yes, the iteration ends, and the final real-time flow Q is output. temp .

[0096] Preferably, in this invention, the dividing Reynolds number corresponds to the turning point where the rate of change of the instrument coefficient in the calibration data tends to level off.

[0097] This invention overcomes the limitations of a single model, especially in the extrapolation region, by combining a dual-region coupled model that integrates "accurate fitting of cubic polynomials in the low Reynolds number region" with "extrapolation of the mean stability coefficient in the high Reynolds number region," and possesses the following core technical advantages:

[0098] Breakthrough improvement in measurement accuracy: Verified by actual data and high temperature and high pressure conditions, the maximum relative error of flow prediction is less than 0.48% and the average absolute error is about 0.2% in the full range of 0.2-2.0 m³ / h, achieving a stable measurement accuracy of better than 0.5%, and completely solving the error divergence problem of traditional extrapolation methods in the high Reynolds number region.

[0099] Overcoming core engineering pain points in the industry: A complete technical path of "limited calibration data at ambient temperature and pressure - flow prediction under wide Reynolds number conditions" has been creatively constructed, which has completely broken through the industry bottleneck that metrology institutions can only carry out actual flow calibration at ambient temperature and pressure and cannot cover high temperature, high pressure and high Reynolds number operating conditions. It has solved the long-standing problem that small flow media in high temperature and high pressure pipelines in industries such as energy and chemical industry cannot achieve high-precision actual flow calibration throughout the entire process.

[0100] Significantly reduces calibration and application costs: There is no need to build an expensive high-temperature and high-pressure actual flow calibration device. Only conventional room temperature and pressure calibration is required to complete the construction of a high-precision model, which significantly reduces the calibration cost and cycle of the flow meter. At the same time, the algorithm logic is rigorous and the amount of calculation is small. It can be directly embedded in the embedded flow calculation unit without adding extra hardware costs, making it very easy to promote and apply on a large scale in industrial fields.

[0101] Extremely strong adaptability and versatility: The boundary Reynolds number, fitting coefficient, and fixed prediction coefficient can all be adaptively adjusted through calibration data. It can adapt to Venturi tubes with different throat ratios and different structural forms. At the same time, it can adapt to flow measurement of different fluid media and different temperature and pressure conditions, and has extremely strong versatility and field adaptability.

[0102] Example 2

[0103] This embodiment is a further supplement to the above embodiments.

[0104] Specifically, to further illustrate the model construction method and iterative algorithm calculation method of the system of the present invention, the specific actual working conditions are given as 15.5MPa, 350℃ superheated water, and the measured differential pressure ΔP is a certain value.

[0105] Preferably, taking a Venturi tube with a throat diameter ratio β=0.5 as an example, its calibration data for normal temperature and pressure water is shown in the following table (excerpt):

[0106] Table 1. Calibration data of Venturi tubes with throat diameter ratio β=0.5 at normal temperature and pressure.

[0107] Serial Number Flow rate Q (m³ / h) Reynolds number Re Instrument coefficient C 1 0.2029 8443.69 0.9494 ... ... ... ... 8 1.6041 66957.26 0.9992 9 1.7970 74886.93 1.0018 10 2.0011 82664.34 1.0028

[0108] Specifically, the boundary Reynolds number corresponds to the turning point where the rate of change of the instrument coefficient in the calibration data tends to level off. As shown in the table above, in some embodiments, as the flow rate in a Venturi tube with a throat ratio β=0.5 increases, the rate of change (slope) of its instrument coefficient tends to level off at the 8th calibration point. Therefore, the Reynolds number at the 8th calibration point is selected as the boundary Reynolds number. In the above-described actual operating conditions of the present invention, the boundary Reynolds number is 66957.26. It is understood that the boundary Reynolds number varies depending on the throat ratio, the Venturi tube structure, and the fluid medium. It is the Reynolds number at the point where the rate of change of the instrument coefficient corresponding to the calibrated value levels off, and will not be listed here.

[0109] More preferably, Intercept, B1, B2 and B3 are constants obtained by fitting the calibration data, so the fitting coefficients are: Intercept=7.30817, B1=-4.53521, B2=1.06416, B3=-0.08191.

[0110] For set A, in this invention, since the boundary Reynolds number corresponds to the 8th calibration point, the data for the first 8 points (where the calibration point Reynolds number is less than or equal to the boundary Reynolds number) are represented by X = log 10 (Re) performs a cubic polynomial fit on the variables to obtain the accurate model:

[0111] C=7.30817-4.53521*X+1.06416*X²- 0.08191*X³.

[0112] For set B, in this invention, preferably, the fixed prediction coefficient value is the arithmetic mean of the flow coefficients of multiple calibration points in the calibration data where the Reynolds number is greater than the threshold Reynolds number. Set B is the arithmetic mean of the flow coefficients of the last three calibration points (where the Reynolds number is greater than the threshold Reynolds number) selected for technical analysis. As shown in the table above, its flow coefficients (i.e., instrument coefficients) are 0.999196368, 1.001799146, and 1.002798795, according to the formula:

[0113]

[0114] The calculated fixed prediction coefficient value C high_avg The value is 1.00126477.

[0115] Preferably, the flow calculation unit begins iterative calculation according to the following method:

[0116] Set the initial flow coefficient to the instrument coefficient C at the 8th calibration point. old =0.99, according to the formula:

[0117]

[0118]

[0119] Calculate the real-time traffic Q temp and real-time Reynolds number Re temp .

[0120] Preferably, if the real-time Reynolds number Re calculated in this iteration is... temp =80000>Boundary Reynolds Number Re th Then the new flow coefficient C new =C high_avg =1.00126477.

[0121] Preferably, based on the real-time Reynolds number Re temp With the boundary Reynolds number Re th The steps for determining the accurate flow coefficients for the final flow calculation, based on the magnitude relationship between the flow coefficients and the selection of a partitioned model or fixed prediction coefficient values, include:

[0122] The real-time Reynolds number Re is calculated based on real-time iteration. temp With the pre-stored boundary Reynolds number Re th Compare; if the real-time Reynolds number Re temp ≤ Boundary Reynolds Number Re th Then, a cubic polynomial function with the logarithm of the Reynolds number as the variable is called to calculate the flow coefficient; if the real-time Reynolds number Re temp >Boundary Reynolds Number Re th In this case, a pre-stored fixed coefficient value is directly used as the flow coefficient.

[0123] Preferably, the new flow coefficient C is compared. new With the initial flow coefficient C old If the convergence condition is not met, then the new flow coefficient C is used. new Use this as the starting point for the next iteration.

[0124] Preferably, in this invention, the convergence condition is the flow coefficient calculated in two consecutive iterations (|new flow coefficient C) new -Initial flow coefficient C old |) The difference is less than 1×10⁻ 6 .

[0125] In this invention, convergence is typically achieved after 3-5 iterations, and the final flow rate value is output.

[0126] Full-range simulation verification shows that the maximum relative error between the predicted flow rate and the theoretical value is less than 0.5%, meeting the requirements for high-precision measurement.

[0127] Verification through examples shows that within the flow rate range of 0.2-2.0 m³ / h, the maximum relative error of flow rate prediction is less than 0.48%, and the average absolute error is about 0.2%, consistently better than the 0.5% accuracy target.

[0128] Example 3

[0129] This embodiment is a further supplement to the above embodiments.

[0130] Specifically, this invention discloses a Venturi tube flow meter, and more particularly a Venturi tube flow meter suitable for high temperature, high pressure, and low flow measurement scenarios, which can be used for high-precision flow monitoring of liquids such as deionized water in fields such as nuclear power and chemical industry.

[0131] The Venturi tube flow meter of the present invention monitors flow based on the differential pressure principle, and calculates the flow rate by measuring the pressure difference before and after the throttling. Existing venturi flowmeters have significant shortcomings when applied to specific extreme conditions, including: poor adaptability to high temperature and high pressure; conventional materials (such as 304 stainless steel) will creep and decrease in strength under long-term conditions of 380℃ and 20MPa, leading to tube deformation or changes in the size of the measuring cavity, which seriously affects measurement accuracy and safety; low measurement accuracy at low flow rates; in the small flow range of 0.15-1.5t / h, the generated differential pressure signal is very weak (may only a few kPa), and the accuracy of conventional differential pressure transmitters and the signal-to-noise ratio of sensors are difficult to meet the 0.5-level accuracy requirement; thermal expansion compensation issues; at high temperatures, the thermal expansion of key components such as the contraction section and throat of the venturi tube will change the geometric dimensions, thereby changing the flow coefficient and introducing significant measurement errors, and existing designs lack effective compensation mechanisms; and clogging and corrosion of the pressure taps; when measuring media such as deionized water, traditional pressure taps are prone to clogging due to media vaporization or impurity precipitation, and corrosion under high temperature and high pressure will affect the accuracy of pressure tapping.

[0132] In summary, the present invention aims to provide a novel Venturi tube flow meter that can be used in conjunction with a flow metering system under all operating conditions as described in the above embodiments, thereby achieving high-precision use of the Venturi tube flow meter under all operating conditions.

[0133] Preferably, the Venturi tube flow meter of the present invention includes a Venturi tube body 100. For example... Figure 3 and Figure 4As shown, the Venturi tube body 100 includes an inlet section 101, a contraction section 102, a throat 103, and a diffuser section 104 connected in sequence. Each section is an integral forged structure without splicing welds, improving the overall structure's pressure resistance and sealing performance, and adapting to extreme working conditions of high temperature and high pressure. The inlet section 101, contraction section 102, throat 103, and diffuser section 104 are all circumferentially covered by a wall surface 105. The inlet section 101, contraction section 102, throat 103, and diffuser section 104 are coaxially arranged, and the ratio of the diameter of the throat 103 to the diameter of the inlet section 101 ranges from 0.55 to 0.65. The preferred ratio is 0.6. This size design can generate a sufficiently large and easily measurable differential pressure signal in a small flow range of 0.15-1.5 t / h, solving the problem of weak differential pressure signals in traditional flowmeters at small flow rates, and laying the foundation for high-precision measurement.

[0134] According to a preferred embodiment, an extension section 106 is further provided at the end of the diffuser section 104 away from the throat 103. The extension section 106 is coaxially integrated with the diffuser section 104, providing a stable pressure tapping environment for the high-pressure tapping port 108, ensuring that the pressure tapping point is in the stable fluid flow channel region, and avoiding interference from fluid backflow in the diffuser section on the pressure tapping accuracy. A low-pressure tapping port 107 connected to the throat 103 and a high-pressure tapping port 108 connected to the extension section 106 are provided on the wall surface 105. The high-pressure tapping port 108 and the low-pressure tapping port 107 form a reasonable differential pressure tapping range in the flow channel, accurately capturing the pressure change after the fluid flows through the throat throttling, and improving the accuracy of differential pressure detection. The high-pressure tap 108 and the low-pressure tap 107 are located on the wall surface 105 instead of being directly connected to the chamber surfaces of the corresponding throat 103 and extension 106. This not only forms a symmetrical dual tap, suppressing fluid eddy interference, but also leaves space for the subsequent annular chamber structure 109, further improving detection accuracy.

[0135] According to a preferred embodiment, the low-pressure tap 107 is located at the connection between the contraction section 102 and the throat 103. This location is a critical node where the fluid velocity increases sharply and the pressure drops sharply. It can accurately collect the low-pressure signal of the throat, reproduce the true pressure state of the fluid after throttling to the greatest extent, and reduce the measurement error caused by the deviation of the tap position.

[0136] According to a preferred embodiment, both the low-pressure tap 107 and the high-pressure tap 108 are provided with annular chamber structures 109 near the wall surface 105 to average the pressure at the taps and suppress interference from fluid eddies and lateral flow. The annular chamber structure 109 is an annular pressure equalization cavity that can average the pressure taps in symmetrical directions, offsetting pressure fluctuations caused by eddies and lateral flow generated during fluid flow, resulting in a more stable differential pressure signal transmitted to the differential pressure transmitter and improving the signal-to-noise ratio.

[0137] According to a preferred embodiment, the Venturi tube body 100 also includes a differential pressure transmitter. This differential pressure transmitter is a high-precision transmitter adapted for small flow rate measurements, meeting the 0.5-level accuracy requirement, and can accurately identify weak differential pressure signals of a few kPa. The differential pressure transmitter is connected to the pressure tapping pipe of the low-pressure tapping port 107 and / or the pressure tapping pipe of the high-pressure tapping port 108 via a capillary tube and a remote flange to isolate the differential pressure transmitter from the high-temperature and high-pressure environment. The capillary tube is a sealed tube resistant to high temperature and high pressure, and the remote flange achieves physical isolation between the pressure tapping end and the transmitter, preventing the core components of the transmitter from directly contacting extreme conditions of 380℃ and 20MPa, preventing component damage, and improving the service life and operational stability of the transmitter.

[0138] It should be noted that the differential pressure transmitter used in this invention is a conventional choice for venturi tube flow meters. However, this differential pressure transmitter employs a full-condition flow measurement system as described in the above embodiment. Specifically, the differential pressure transmitter integrates a signal processing unit and a temperature sensor (Pt100). The temperature sensor is in contact with the wall 105 of the venturi tube body 100, enabling real-time monitoring of the tube's operating temperature. The signal processing unit pre-stores the thermal expansion coefficient and temperature-flow correction curve of the nickel-based alloy used in this invention. Based on the real-time monitored temperature data, it can perform real-time temperature compensation calculations on the collected differential pressure value, eliminating measurement errors introduced by thermal expansion changes in the throat area 103 caused by temperature variations. This achieves accurate compensation for thermal expansion errors and further improves flow measurement accuracy.

[0139] According to a preferred embodiment, at least two annular chamber structures 109 are located inside the diffusion section 104 and the extension section 106, respectively, and are connected to the pressure tapping pipe of the low-pressure tapping port 107 and / or the high-pressure tapping port 108 via capillary tubes and remote transmission flanges, respectively. The built-in design of the annular chamber structures 109 avoids interference from external structures on the pressure tapping flow channel, while shortening the pressure transmission path, reducing the attenuation of the pressure signal during transmission, and ensuring the transmission efficiency and authenticity of the differential pressure signal.

[0140] According to a preferred embodiment, a conical self-cleaning pressure tap 110 is installed at both the low-pressure tap 107 and the high-pressure tap 108. The pressure tap and the tap have a sealed snap-fit ​​structure, which facilitates disassembly and maintenance and is suitable for the stringent requirements of nuclear power, chemical and other fields.

[0141] According to a preferred embodiment, the side of the conical self-cleaning pressure tap 110 facing the fluid is provided with a smooth conical surface to prevent impurities from adhering to the wall. The smooth conical surface transitions flush with the flow channel wall, without protrusions or dead corners, forming a smooth flow field when the fluid flows through, preventing impurities in the medium from depositing and adhering to the wall at the pressure tap. The side of the conical self-cleaning pressure tap 110 facing away from the fluid is provided with a pressure tapping orifice for using hydrostatic pressure to achieve pressure tapping and reduce the risk of clogging. The pressure tapping orifice is a small-diameter hydrostatic pressure tapping orifice, transmitting pressure signals only through hydrostatic pressure, avoiding direct impact of the medium on the channel, and effectively preventing channel blockage caused by medium vaporization or impurity precipitation, thus improving the anti-clogging capability of the pressure tap.

[0142] According to a preferred embodiment, the venturi tube body 100 is integrally forged from a nickel-based alloy. Preferably, it is a 316L or Inconel 625 nickel-based alloy, which possesses excellent high-temperature strength, creep resistance, and corrosion resistance. Under long-term operating conditions of 380℃ and 20MPa, it exhibits no significant deformation, ensuring the stability of the venturi tube body's geometric dimensions and preventing changes in flow coefficient and decreased measurement accuracy due to tube deformation. Simultaneously, it can withstand high-temperature and high-pressure corrosion from media such as deionized water, improving the equipment's corrosion resistance and service life.

[0143] It should be noted that the specific embodiments described above are exemplary. Those skilled in the art can devise various solutions inspired by the disclosure of this invention, and these solutions all fall within the scope of this invention and its protection. Those skilled in the art should understand that this specification and its accompanying drawings are illustrative and do not constitute a limitation on the claims. The scope of protection of this invention is defined by the claims and their equivalents. This specification contains multiple inventive concepts; phrases such as "preferred" or "according to a preferred embodiment" indicate that the corresponding paragraph discloses an independent concept. The applicant reserves the right to file divisional applications based on each inventive concept. Throughout the text, the feature introduced by "preferred" is only an optional mode and should not be construed as mandatory. Therefore, the applicant reserves the right to abandon or delete relevant preferred features at any time.

Claims

1. A flow metering system under all operating conditions, characterized in that, The system includes a Venturi tube flow meter and a corresponding flow calculation unit. The flow calculation unit constructs a flow coefficient prediction model based on the calibration data of the Venturi tube flow meter to perform flow calculation. The flow coefficient prediction model is configured as follows: S1: Obtain the flow rate, Reynolds number, and flow coefficient data of the Venturi tube flow meter calibrated at room temperature and pressure; S2: Set the boundary Reynolds number and divide the calibration data according to the boundary Reynolds number. Based on the low Reynolds number region data, perform cubic polynomial fitting with X as the variable to obtain the partition model. Calculate the fixed prediction coefficient value based on the high Reynolds number region data. S3: In actual measurements under full operating conditions, the real-time Reynolds number is calculated iteratively; S3: Based on the relationship between the boundary Reynolds number and the real-time Reynolds number, select either the partition model or the fixed prediction coefficient value to determine the flow coefficient for flow calculation.

2. The flow metering system under all operating conditions according to claim 1, characterized in that, Steps S1 and S2 are the model construction and calibration stages for the flow calculation unit; Steps S3 and S4 are the operational phases in which the flow calculation unit performs real-time measurement and iterative calculation on the Venturi tube flow meter.

3. The flow metering system under all operating conditions according to claim 1, characterized in that, The steps for obtaining the flow rate, Reynolds number, and flow coefficient data of the Venturi tube flow meter calibrated at room temperature and pressure include: Obtaining n calibration point data of the Venturi flowmeter in normal temperature and pressure water, including flow rate, Reynolds number and meter coefficient of each calibration point. n Obtaining n calibration point data of the Venturi flowmeter in normal temperature and pressure water, including flow rate, Reynolds number and meter coefficient of each calibration point.

4. The flow metering system under all operating conditions according to claim 1, characterized in that, The step of setting the boundary Reynolds number and dividing the calibration data according to the boundary Reynolds number includes: Divide the modeling interval: Set a boundary Reynolds number, and divide the calibration data into set A and set B according to the boundary Reynolds number; wherein, Set A represents the set of data points for all calibration points whose Reynolds number is less than or equal to the threshold Reynolds number, corresponding to the nonlinear interval of the instrument coefficient as the Reynolds number changes. Set B represents a set of data from several highest flow rate calibration points where the calibration point Reynolds number is greater than the threshold Reynolds number, corresponding to a stable range where the rate of change of the instrument coefficient tends to level off.

5. The flow metering system under all operating conditions according to claim 4, characterized in that, The step of performing a cubic polynomial fitting on the low Reynolds number region data with X as the variable to obtain the partitioning model includes: For the data of set A, with X = log 10 The instrument coefficient as a function of the calibration point Reynolds number is fitted with a cubic polynomial whose formula is: Wherein, Intercept, B1, B2, and B3 are constants obtained by fitting the calibration data; C is the flow coefficient.

6. The flow metering system under all operating conditions according to claim 4, characterized in that, The step of performing a cubic polynomial fitting on the low Reynolds number region data with X as the variable to obtain the partitioning model further includes: For the data in set B, the arithmetic mean of the instrument coefficients is calculated as the fixed prediction coefficient value for the high Reynolds number region; wherein, the fixed prediction coefficient value is the arithmetic mean of the flow coefficients of several calibration points in the calibration data where the Reynolds number is greater than the boundary Reynolds number.

7. The flow metering system under all operating conditions according to claim 1, characterized in that, The steps for iteratively calculating the real-time Reynolds number in actual measurements under full operating conditions include: The real-time differential pressure, temperature, and pressure of the Venturi tube flow meter are collected, and the fluid density and viscosity are calculated based on the real-time temperature and real-time pressure.

8. The flow metering system under all operating conditions according to claim 1, characterized in that, The steps by which the flow calculation unit executes the iterative algorithm include: S321: Assume an initial flow coefficient; S322: The formula for calculating real-time traffic is as follows: Q temp For real-time traffic; C old ρ is the initial flow coefficient; K is the instrument coefficient; ΔP is the real-time differential pressure; ρ is the fluid density. S323: The formula for calculating the real-time Reynolds number is as follows: Among them, Re temp denoted as the real-time Reynolds number, d as the throat diameter, and μ as the fluid viscosity. S324: Compare the real-time Reynolds number with the pre-stored boundary Reynolds number; if the real-time Reynolds number is less than or equal to the boundary Reynolds number, calculate the new flow coefficient C based on the fitted polynomial. new The fitting polynomial is C new =f(log 10 (Re temp If the real-time Reynolds number is greater than the boundary Reynolds number, then the new flow coefficient is set to equal the fixed prediction coefficient value. S325: Determine if the absolute value of the difference between the new flow coefficient and the initial flow coefficient is less than the convergence threshold; if not, set the initial flow coefficient equal to the current new flow coefficient and return to step S322; if yes, the iteration ends, and the final real-time flow Q is output. temp .

9. A venturi tube flow meter, characterized in that, The Venturi tube flow meter employing the full-condition flow measurement system as described in any one of claims 1-8 includes a Venturi tube body (100), wherein the Venturi tube body (100) includes an inlet section (101), a contraction section (102), a throat (103), a diffuser section (104), and an extension section (106) connected in sequence, wherein, The ratio of the diameter of the throat (103) to the diameter of the inlet section (101) is in the range of 0.55-0.

65.

10. The Venturi tube flow meter according to claim 9, characterized in that, The inlet section (101), the constriction section (102), the throat (103), the diffusion section (104), and the extension section (106) are all circumferentially covered by the wall surface (105), wherein, The wall surface (105) is provided with a low-pressure tap (107) connected to the throat (103) and a high-pressure tap (108) connected to the extension section (106). The low-pressure tap (107) and the high-pressure tap (108) are each provided with an annular chamber structure (109) at the end near the wall surface (105) for averaging the pressure of the tap to suppress fluid eddies and lateral flow interference.

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