Gas volume calibration method and system based on critical flow venturi nozzle

Abstract

The invention discloses a gas volume calibration method and system based on a critical flow venturi nozzle, and relates to the technical field of gas flow, and the method comprises the following steps: constructing a volume calibration device comprising a gas source, a switch valve, the critical flow venturi nozzle and a container to be measured; the container to be measured is vacuumized to a target value, the switch valve is opened, gas in the gas source enters the container to be measured through the critical flow venturi nozzle, and the volume calibration device enters a critical flow state; obtaining the state parameter of the gas source outlet during the critical flow state, and the pressure rise amount and the average temperature of the to-be-measured container; obtaining the total mass of gas flowing into the to-be-detected container based on the state parameters; and obtaining a volume calibration result of the to-be-measured container based on the pressure rise amount, the average temperature and the total gas mass. And high-efficiency, low-cost and high-precision calibration of the volume of the gas container is realized.

Description

Technical Field

[0001] This invention relates to the field of gas flow technology, and more specifically to a gas volume calibration method and system based on a critical flow Venturi nozzle. Background Technology

[0002] As key equipment for gas storage, transportation, and use, the accuracy of gas container volume parameters directly affects the fairness of trade settlement, the reliability of special equipment safety assessments, and the accuracy of metrological traceability. With the rapid development of gas energy applications, increasingly stringent safety regulations for special equipment, and continuously improving scientific research precision standards, the industry has an urgent need for "high efficiency, low cost, and high precision" in gas container volume calibration. Currently, gas container volume calibration technologies mainly include the water volume method, the traditional gas expansion method, and the traditional critical flow nozzle method.

[0003] However, the aforementioned existing technologies generally suffer from the following technical problems in practical applications: First, complex operation and low calibration efficiency: The water volume method requires repeated filling, venting, and weighing operations, and the container needs to be dried after calibration. The entire process is time-consuming and labor-intensive, with a long calibration cycle; the traditional gas expansion method has a cumbersome operation process, requiring multiple pressure balancing and temperature stabilization waits; the traditional critical flow nozzle method has many operation steps and many human intervention links, resulting in low overall efficiency; Second, measurement accuracy is greatly affected by environmental and operational factors: The measurement results of the water volume method are easily affected by factors such as water temperature changes, residual bubbles, and adhesion to the inner wall of the container; the gas expansion method has extremely high requirements for temperature stability, and temperature fluctuations during pressure exchange will significantly affect the accuracy of the measurement results; the traditional critical flow nozzle method relies on the operator's experience and judgment, which easily introduces subjective errors and has poor measurement repeatability; Third, high equipment cost and difficult maintenance: Traditional gas expansion methods require multiple high-precision standard containers of various specifications as reference standards, resulting in significant upfront investment. Some high-precision equipment relies on imports, leading to high procurement costs and long delivery cycles. The equipment is subject to stringent environmental requirements, resulting in high daily maintenance costs and short calibration cycles, further increasing operating costs. Fourth, the applicability is limited: water volumetric methods cannot be used for containers susceptible to water or corrosion, such as those made of special materials or containing precision components. Traditional gas expansion methods are poorly adaptable to large-volume or complex-structure containers. Traditional critical flow nozzle methods have strict requirements for operating conditions, limiting their applicability and making it difficult to meet the calibration needs of various scenarios. Fifth, automation and rapid calibration are difficult to achieve: existing calibration methods largely rely on manual intervention, resulting in cumbersome processes and low automation levels. This fails to meet the demands of modern industrial testing and research scenarios for "rapid, automated, and batch calibration," making integration into intelligent testing systems difficult and hindering the industry's digital transformation. In summary, existing gas container volumetric calibration technologies cannot achieve a balance between accuracy, efficiency, and cost, exhibiting core bottlenecks such as contradictions between accuracy and efficiency, cost and performance, and versatility and specialization.

[0004] Therefore, how to achieve efficient, low-cost, and high-precision calibration of gas container volume is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide a gas volume calibration method and system based on a critical flow Venturi nozzle that overcomes or at least partially solves the above problems, thereby achieving efficient, low-cost, and high-precision calibration of gas container volume.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, embodiments of the present invention provide a gas volume calibration method based on a critical flow Venturi nozzle, comprising: Construct a volume calibration device that includes a gas source, a switching valve, a critical flow Venturi nozzle, and a container to be tested; The container under test is evacuated to the target value, the switch valve is opened, and the gas in the gas source enters the container under test through the critical flow venturi nozzle, and the volume calibration device enters the critical flow state. Acquire the state parameters of the gas source outlet during the critical flow state, as well as the pressure rise and average temperature of the container under test; The total mass of gas flowing into the container under test is obtained based on the state parameters; The volume calibration result of the container under test is obtained based on the pressure rise, the average temperature, and the total mass of the gas.

[0008] In one embodiment, entering the critical flow state specifically involves: The container under test is evacuated to the target value and forms a high vacuum state far below the critical back pressure. After the back pressure ratio is <0.1, a significant pressure difference is formed between it and the gas source. The switch valve is opened, and the gas in the gas source enters the critical flow venturi nozzle. The opening of the valve automatically and instantly establishes and maintains the stable critical flow state.

[0009] In one embodiment, the critical flow state includes a state start time and a state end time; The state start time is the opening time of the switching valve; The state end time is the time required to reach a preset pressure threshold, a time threshold, or to actively close the switching valve.

[0010] In one embodiment, the method for obtaining the state parameters is as follows: Acquire multiple pressure and temperature data points at the gas source outlet as time decreases during the critical flow state; Calibration is performed based on the acquisition timestamps of the pressure data and the temperature data to ensure that the pressure data and the temperature data correspond at the same time, thereby obtaining calibrated pressure data and calibrated temperature data. Based on the average values ​​of the calibration pressure data and the calibration temperature data, the upstream total pressure and upstream total temperature are obtained accordingly. The upstream total pressure and the upstream total temperature together constitute the state parameters.

[0011] In one embodiment, the method for obtaining the pressure increase is as follows: The pressure value at the start time of the critical flow state of the container under test is obtained as the starting pressure; The pressure value at the end time of the critical flow state of the container under test is obtained as the end pressure; The pressure increase is based on the difference between the ending pressure and the starting pressure.

[0012] In one embodiment, the method for obtaining the average temperature is as follows: The temperature value at the start time of the critical flow state of the container under test is obtained as the starting temperature; The temperature value at the end time of the critical flow state of the container under test is obtained as the end temperature; The average temperature is obtained by averaging the starting temperature and the ending temperature.

[0013] In one embodiment, the method for obtaining the total mass of the gas is as follows: The critical flow mass flow rate is obtained based on the upstream total pressure, the upstream total temperature, and the structural parameters of the critical flow Venturi nozzle. The effective flow time is obtained based on the state start time and the state end time; The total mass of gas is obtained by multiplying the critical flow mass rate by the effective flow time.

[0014] In one embodiment, the critical flow mass flow rate Specifically: ; in, This represents the throat area of ​​the critical flow Venturi nozzle. This represents the discharge coefficient of the critical flow Venturi nozzle. This represents the critical flow function for a real gas. Indicates the total upstream pressure. Represents the gas constant. Indicates molar mass. This indicates the total upstream temperature.

[0015] In one embodiment, the volume calibration result of the container under test Specifically: ; in, Indicates the total mass of the gas. Indicates average temperature. Indicates the amount of pressure increase. This indicates the gas compressibility factor.

[0016] In a second aspect, embodiments of the present invention provide a gas volume calibration system based on a critical flow Venturi nozzle, which applies a gas volume calibration method based on a critical flow Venturi nozzle as described in any of the first aspects, including: a calibration device construction module, a critical state establishment module, a critical parameter acquisition module, a gas mass acquisition module, and a volume result output module; The calibration device construction module is used to construct a volume calibration device including a gas source, a switching valve, a critical flow Venturi nozzle, and a container to be tested. The critical state establishment module is used to evacuate the container under test to the target value, open the switch valve, and allow the gas in the gas source to enter the container under test through the critical flow venturi nozzle, and the volume calibration device enters the critical flow state. The critical parameter acquisition module is used to acquire the state parameters of the gas source outlet during the critical flow state, as well as the pressure rise and average temperature of the container under test. The gas mass acquisition module is used to obtain the total mass of gas flowing into the container to be tested based on the state parameters; The volume result output module is used to obtain the volume calibration result of the container under test based on the pressure rise, the average temperature and the total mass of the gas.

[0017] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a gas volume calibration method and system based on a critical flow Venturi nozzle, which has the following beneficial effects: 1. A leap in efficiency, from "adjustment and waiting" to "instant results upon valve opening": This invention utilizes the huge and stable pressure difference formed by the downstream pre-evacuation high vacuum and the upstream atmospheric pressure, eliminating the traditional dynamic adjustment process. Simply open the valve quickly, and the nozzle will automatically and inevitably enter the optimal critical flow state within milliseconds. This reduces the critical flow establishment time from several minutes to almost zero, shortening the single effective calibration time by more than 70%, and achieving truly high-throughput and high-efficiency calibration.

[0018] 2. Fundamentally Enhanced Accuracy and Stability: This invention employs "instantaneous criticality" to eliminate the uncertainty of manual adjustment; and uses "negative pressure drive" to provide an extremely stable differential pressure environment far exceeding the critical value. Each test begins with exactly the same differential pressure conditions, ensuring 100% reproducibility of the critical flow state establishment process, completely eliminating batch errors caused by differences in the adjustment process; under critical flow conditions, the flow rate is immune to downstream pressure fluctuations. In this invention, the downstream is a high-vacuum cavity with extremely low pressure, and changes in pressure have no impact on flow rate calculation, resulting in extremely strong system robustness; the rapid establishment of a stable state ensures that the flow throughout the entire acquisition period is an ideal critical flow, with a data utilization rate approaching 100%, providing the purest data source for backend calculations.

[0019] 3. Simplified System and Significantly Improved Reliability: This invention replaces the complex regulating valve with a simple switching valve and the real-time feedback control loop with deterministic preset vacuum conditions; it reduces key moving parts and control levels, thereby lowering system complexity and manufacturing costs; the switching valve is more reliable and has a longer lifespan than the regulating valve, and system stability no longer depends on sophisticated control algorithms and rapid servo response; the most technically challenging step of "establishing and maintaining critical flow" is transformed into the simplest operation of "starting the vacuum pump and pressing the start button," reducing reliance on operator skills and avoiding human error.

[0020] 4. Significant overall benefits: Electricity is consumed only during the vacuuming stage, and the testing process itself does not require additional energy for compressing or regulating the gas; it is particularly suitable for calibrating medium to large containers ranging from tens to thousands of liters, because the negative pressure method makes it easier to establish and maintain sufficient vacuum in large volumes; the entire process (vacuuming, valve switching, data acquisition, and calculation) can be easily fully automated in sequence, making it an ideal solution for building unmanned, intelligent calibration laboratories or online testing stations. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0022] Figure 1 This is a flowchart of a gas volume calibration method based on a critical flow Venturi nozzle provided in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the volume calibration device provided in an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of a gas volume calibration system based on a critical flow Venturi nozzle provided in an embodiment of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1 like Figure 1As shown, this embodiment of the invention discloses a gas volume calibration method based on a critical flow Venturi nozzle, including the following steps. For ease of description, these steps are numbered S1 to S5, and these numbers are not intended to limit the sequential relationship between the various steps of this invention: The S1 construct includes a volume calibration device comprising a gas source, a switching valve, a critical flow venturi nozzle, and the container under test.

[0027] Furthermore, such as Figure 2 As shown, the volume calibration device includes: an upstream gas source unit, a central control and data acquisition unit, a high-speed switching valve, a critical flow venturi nozzle, a vacuum generation unit, and a downstream measured unit; The upstream gas source unit includes: a gas source, which is an atmospheric environment or a stable gas source, a high-precision pressure sensor P_up, and a high-precision temperature sensor T_up; A high-precision pressure sensor, P_uP, is used to monitor the absolute pressure upstream of the nozzle (at the gas source) in real time. The high-precision temperature sensor T_uP is used to monitor the gas temperature upstream of the nozzle (at the gas source) in real time.

[0028] The central control and data acquisition unit includes: a synchronous data acquisition card, an industrial computer, and control software; the synchronous data acquisition card is used to receive all sensor signals and ensure the synchronization and timing accuracy of the acquisition; the industrial computer and control software are responsible for process control, parameter setting, data processing, and human-machine interaction.

[0029] The high-speed switching valve responds to the instructions of the central control and data acquisition unit to realize the rapid opening and closing of the gas source to the critical flow venturi nozzle pipeline, and is the key actuator for "instantaneous establishment of critical flow".

[0030] The critical flow Venturi nozzle serves as the flow reference for the system, and its throat area... A nt and outflow coefficient It requires separate high-precision calibration, and the gas flows through this point to reach the speed of sound.

[0031] The vacuum generation unit includes a vacuum pump and a vacuum valve. The vacuum pump is used to evacuate the container under test to a high vacuum before testing, creating an initial large pressure difference condition. The vacuum valve connects the vacuum pump and the container under test, and is opened when evacuating and closed during calibration testing to isolate the vacuum pump.

[0032] The downstream measured unit includes: a gas container under test, a high-precision pressure sensor P_down, and a high-precision temperature sensor T_down. Before calibration begins, the gas container under test is evacuated to a "high vacuum state" by a vacuum pump. At this time, the pressure value collected by the pressure sensor P_down deployed in the gas container under test is P1 (close to 0 Pa, such as ≤10 Pa), which serves as the reference value for pressure change. The end value of P_down is P2: when the calibration meets the end conditions (such as the back pressure ratio being close to 0.528 or the preset pressure threshold), the pressure value inside the gas container under test collected by P_down in real time is P2. The high-precision temperature sensor T_down deployed in the gas container under test has an accuracy of ≤±0.10℃ and continuously collects the gas temperature inside the gas container under test throughout the entire calibration process (from the end of evacuation to the end of calibration).

[0033] The gas container being tested, also known as the test container, is a sealed container whose internal geometric volume is to be calibrated. It needs to be evacuated to a high vacuum before calibration.

[0034] Furthermore, the key actuators connecting the tested container, nozzle, and vacuum system have extremely fast response times (typically on the order of milliseconds) to ensure that the valve opening action is strictly synchronized with the start of data acquisition and to achieve "instantaneous establishment of critical flow." High-frequency, high-speed ball valves or butterfly valves, either pneumatic or electric, are used, forming a pressure-bearing and airtight flow channel together with sealed pipelines and flanges.

[0035] Furthermore, the temperature sensor is a high-response platinum resistance thermometer (PT100 or PT1000), installed in the upstream pipeline of the nozzle to accurately measure the gas temperature.

[0036] High-precision timer: Typically powered by a temperature-controlled crystal oscillator in the data acquisition card (DAQ), it accurately measures the gas flow time Δ from valve opening to closing. t All sensor signals are connected to the synchronous data acquisition unit to ensure that the start time of pressure, temperature and time signal acquisition is strictly consistent, eliminating system errors caused by asynchrony.

[0037] Furthermore, the central control and data acquisition unit typically consists of an industrial computer (IPC), a programmable logic controller (PLC), and dedicated control software. It automatically executes the test process of "vacuuming → valve opening command → valve closing command → data acquisition termination." It has a built-in calculation engine that, based on the acquired data... P , T Δ t Data, real-time access to the gas property database and the calibration coefficients of the selected nozzle. The calculation is performed according to the standardized critical flow formula. A human-machine interface (HMI) is provided, allowing users to set parameters, start the test, monitor the process, and directly read the final volume calibration results. V And measurement uncertainty report.

[0038] Further, based on the design volume of the container under test, a critical flow venturi nozzle with a suitable range is selected from the nozzle group and connected to the system; all valves are closed, the vacuum pump is started, and the downstream pipeline is evacuated to the preset high vacuum target value, which is confirmed by a high-precision pressure sensor P_down. Dry air or nitrogen is introduced into the upstream gas source to near atmospheric pressure, and its pressure and temperature are monitored by an upstream pressure / temperature sensor.

[0039] S2 evacuates the container under test to the target value, opens the switch valve, and the gas in the gas source enters the container under test through the critical flow venturi nozzle, and the volume calibration device enters the critical flow state.

[0040] Furthermore, it enters the critical flow state, specifically as follows: After the container under test is evacuated to the target value and forms a high vacuum state (pressure 5% lower than atmospheric pressure) far below the critical back pressure, a significant pressure difference is formed between it and the gas source. When the switch valve is opened, the gas in the gas source enters the critical flow Venturi nozzle. The pressure ratio between the inlet and outlet of the critical flow Venturi nozzle is much smaller than its critical back pressure ratio (back pressure ratio < 0.1). The airflow is instantly accelerated to the throat speed of sound. When the valve is opened, a stable critical flow state is automatically and instantly established and maintained.

[0041] Furthermore, before calibration, the vacuum pump is started to evacuate the downstream of the nozzle (including the tested container and downstream pipeline) to the preset value. The downstream pressure is monitored in real time using a high-precision pressure sensor. After confirming that the pressure is stable at the target pressure value, the vacuum valve is closed, and then the vacuum pump is turned off. Since the downstream is already in an extremely low absolute pressure state, opening the valve at this time can instantly reach the preset pressure ratio, realizing the instantaneous start of the critical flow state. At the same time, the system has a built-in pressure stability monitoring module that continuously monitors the downstream pressure throughout the calibration process. If an abnormal pressure rise occurs, the protection mechanism is immediately triggered to ensure the continuous stability of the critical flow state and guarantee the consistency of flow measurement.

[0042] Furthermore, the critical flow state is: the pressure ratio before and after the nozzle is ≤ the critical back pressure ratio. In this embodiment, the critical back pressure ratio is set to 0.528 (the critical condition of back pressure ratio ≤ 0.528, the specific value of which varies slightly depending on the nozzle model and the characteristics of the gas medium).

[0043] Furthermore, this invention employs a negative pressure method, pre-evacuating the container under test to a high vacuum, with the upstream environment being atmospheric. This ensures that at the moment of connection, the pressure ratio before and after the nozzle is much greater than the critical value, automatically and instantly establishing the critical flow state upon valve opening, eliminating the need for dynamic adjustment and significantly improving calibration speed and reliability.

[0044] Furthermore, this invention enables rapid and efficient calibration: the "negative pressure method" combined with the "critical point upon valve opening" design eliminates the need for dynamic adjustment stabilization time. The single test cycle is short, typically completed within minutes from preparation to result, greatly improving calibration efficiency and making it suitable for rapid testing of large batches of containers in laboratories.

[0045] S3 acquires the state parameters of the gas source outlet during the critical flow state, as well as the pressure rise and average temperature of the container under test.

[0046] Furthermore, the critical flow state includes the state start time and the state end time; The state start time is the opening time of the switching valve; The state end time is the time required to reach the preset pressure threshold, time threshold, or to actively close the switching valve.

[0047] Furthermore, the method for obtaining the state parameters is as follows: Acquire multiple pressure and temperature data points at the gas source outlet as time decreases during the critical flow state; Calibration is performed based on the acquisition timestamps of pressure and temperature data to ensure that pressure and temperature data correspond at the same time, thus obtaining calibrated pressure and temperature data. The upstream total pressure and upstream total temperature are obtained by taking the average values ​​of the calibration pressure data and calibration temperature data, respectively. The upstream total pressure and upstream total temperature together constitute the state parameters.

[0048] Furthermore, high-precision temperature sensors (measurement accuracy ≤ ±0.10℃) and pressure sensors (measurement accuracy ≤ 0.05%FS) are deployed in the upstream gas pipeline and downstream port of the measured container to simultaneously collect real-time temperature and pressure parameters from both upstream and downstream, eliminating the influence of pipeline temperature gradients and pressure losses on the data. For timing control, a central control unit triggers a synchronous acquisition command. The parameter acquisition and timing module is simultaneously activated the instant the critical flow state is established, achieving millisecond-level timing accuracy. This ensures a strict correspondence between temperature and pressure data and the gas flow duration, avoiding flow calculation errors caused by timing deviations. A data filtering algorithm is implemented during the acquisition process to eliminate abnormal fluctuations in data, further improving the reliability of the parameter data.

[0049] Furthermore, to eliminate interference signals in the raw acquired data and ensure the accuracy of the computational input, the core parameters need to be preprocessed: Based on the time base signal of a high-precision timer (typically a 10MHz isothermal crystal oscillator with an accuracy ≤1ppm), the acquisition timestamps of the pressure and temperature data are calibrated to ensure strict correspondence between pressure and temperature data at the same moment, avoiding flow calculation errors caused by time deviations. During the critical flow stability period, the average upstream pressure is calculated as the upstream total pressure, and the average upstream temperature is calculated as the upstream total temperature, serving as the basic input parameters for subsequent flow calculations, reducing the impact of instantaneous fluctuations on the results.

[0050] Furthermore, the method for obtaining the pressure increase is as follows: The pressure value at the start time of the test vessel in the critical flow state is obtained. The test vessel is in a high vacuum state with a pressure close to 0 Pa, which is used as the starting pressure. P 1; The pressure value at the end time of the critical flow state of the container under test is obtained as the termination pressure. P 2, much larger than P 1. Approaching the preset threshold; Based on termination pressure P 2 and initial pressure P The difference of 1 is taken as the pressure increase Δ P = P 2- P 1.

[0051] Furthermore, the method for obtaining the average temperature is as follows: The temperature value at the start time of the state of the container under test in the critical flow state is obtained as the starting temperature. T 1; The temperature value at which the container under test reaches the end of its critical flow state is obtained and used as the end temperature. T 2; The average temperature is obtained by averaging the initial and final temperatures.

[0052] Furthermore, based on the initial temperature T 1 and the final temperature T 2. The average temperature is obtained by using arithmetic mean or integral mean. T avg .

[0053] S4 obtains the total mass of gas flowing into the container under test based on the state parameters.

[0054] Furthermore, the method for obtaining the total gas mass is as follows: The critical flow mass flow rate is obtained based on the upstream total pressure, upstream total temperature, and the structural parameters of the critical flow Venturi nozzle. The effective flow time is obtained based on the state start time and state end time; The total gas mass is obtained by multiplying the critical flow mass rate by the effective flow time.

[0055] Furthermore, the critical flow mass flow rate Specifically: ; in, This represents the throat area of ​​the critical flow Venturi nozzle. This represents the discharge coefficient of the critical flow Venturi nozzle. This represents the critical flow function for a real gas. Indicates the total upstream pressure. This represents the gas constant, a fundamental constant in physics, approximately 8.314462618 J / (mol·K). Indicates molar mass. This indicates the total upstream temperature.

[0056] Furthermore, the critical flow Venturi nozzle was individually calibrated by a national-level metrology institution to obtain its discharge coefficient. By installing it on a quick-switching valve or nozzle holder, it is easy to quickly select a nozzle with a matching range according to the design volume V of the container being measured, so as to optimize measurement uncertainty.

[0057] Furthermore, the total mass of the gas m for: ; in, Indicates the effective flow time.

[0058] Furthermore, the core principle of this invention lies in overcoming the anti-interference bottleneck of traditional calibration techniques by utilizing the "gas flow stability under critical flow conditions": by simply drawing the pressure downstream of the nozzle to an extremely low absolute pressure and opening the valve, the standby pressure ratio condition can be instantaneously met, allowing the gas velocity at the nozzle throat to reach the speed of sound. At this point, the gas flow rate is determined solely by the upstream temperature, pressure, and nozzle structural parameters, and is completely unaffected by downstream pressure fluctuations. This design, in principle, avoids the error in flow measurement caused by environmental pressure interference, laying the foundation for high-precision volumetric calibration.

[0059] S5 obtains the volume calibration result of the container under test based on the pressure rise, average temperature, and total gas mass.

[0060] Furthermore, according to the law of conservation of mass, the total mass of the gas flowing in through the nozzle... m This is equal to the increase in the mass of the gas inside the container being measured. Combining this with the gas law, the volume can be established. V The solution relationship is given by the total mass of the gas. mSubstitute into the gas law and consider the compressibility factor of the real gas. Z After making corrections, the volume calibration result is obtained. V The general solution formula is as follows: ; in, Indicates the total mass of the gas. Indicates average temperature. Indicates the amount of pressure increase. This represents the gas compressibility factor.

[0061] Furthermore, the volume calibration result V is the actual volume of the container to be tested.

[0062] Furthermore, Substituting into the above formula, we obtain the inverse derivation formula of the core of this invention: .

[0063] Furthermore, the above formula clearly demonstrates the closed-loop logic from "critical flow measurement" to "volume calculation": q m Derived from the critical flow mass flow formula, its calculation depends on calibrated nozzle parameters ( , ) and real-time acquisition of upstream gas state ( , ); Δ t , P 1. P 2 and T avg The data originates from real-time measurements obtained by the high-precision synchronous acquisition module during the calibration process. gas constant R molar mass M and gas compressibility factor Z Based on the gas source type (such as air or nitrogen), the system automatically retrieves the gas from its built-in gas property database. Therefore, this part of the algorithm rigorously constitutes the technical closed loop of the present invention, realizing the core objective of "using traceable critical flow as a benchmark, and solving the geometric volume in reverse by measuring time and state parameters", which is the key to achieving high-precision and automated calibration.

[0064] Furthermore, to avoid human calculation errors and ensure the consistency and reproducibility of the calculation process, the entire data calculation and volume derivation are completed automatically by the system. The specific implementation method is as follows: (1) Automatic parameter retrieval: The system automatically retrieves the outflow coefficient from the database based on the nozzle model and gas type selected by the user. Nozzle throat area A nt Gas constant R Key parameters such as isentropic index do not require manual input.

[0065] (2) Real-time calculation and result output: After the data acquisition is completed, the central control unit (industrial computer + special software) completes the entire process of data preprocessing, mass flow calculation and volume reverse derivation within 1 second, and displays the final volume value in real time on the human-machine interface. V (Unit: m) 3 Or L).

[0066] (3) Data storage and traceability: The system automatically stores the original data collected for each calibration and forms a calibration report with a timestamp to meet the requirements of metrological traceability and facilitate subsequent data query.

[0067] Furthermore, to ensure the accuracy of volume derivation, control measures need to be taken for key error sources in the calculation process: (1) Outflow coefficient error control: The nozzle should be sent to a national metrology institution for recalibration and replacement periodically (it is recommended to do so every 12 months). Values ​​should be set to avoid coefficient deviations caused by nozzle wear. (2) Gas parameter error control: High-precision sensors (pressure sensor accuracy ≤ 0.10%FS, temperature sensor accuracy ≤ 0.1℃) are used and calibrated annually to ensure the acquisition accuracy of P_uP and T_uP; (3) Formula compatibility control: For different calibration scenarios (such as high pressure / low pressure, normal temperature / low temperature), the system automatically determines whether to enable compression factor correction and temperature average correction to avoid errors caused by improper formula compatibility.

[0068] Furthermore, the core of this invention lies in providing an "automatic container volume calibration method based on instantaneous establishment of critical flow using negative pressure," fundamentally revolutionizing the traditional high-precision volume calibration technical approach, solving several long-standing key technical problems, and demonstrating significant advantages. It achieves the following core functions and objectives: (1) Achieving high-precision volume calibration: The system transforms the abstract measurement of "volume" into the measurement of three highly measurable physical quantities: time, pressure, and temperature, and traces them back to the International System of Units (SI). This is achieved by using a separately calibrated reference nozzle ( C d The system can achieve extremely high calibration accuracy (uncertainty can reach 0.3% or even higher), and is often used as a gas metering and transfer standard.

[0069] (2) Achieve rapid and efficient calibration: The "negative pressure method" combined with the "critical valve opening" design eliminates the need for dynamic adjustment and stabilization time. The single test cycle is short, and the process from preparation to obtaining results is usually completed within a few minutes, which greatly improves calibration efficiency and is suitable for rapid testing of large batches of containers in the laboratory.

[0070] (3) Achieve automated and intelligent operation: From vacuuming, valve control, data acquisition to calculation and report generation, the entire process is automatically completed by the central control unit, which minimizes human error and subjective intervention and ensures the consistency and reproducibility of the calibration process.

[0071] (4) Achieving reliable quality assurance and traceability: It provides authoritative volume data for the factory inspection, type testing and periodic verification of products such as pressure vessels, breathing gas cylinders, natural gas storage tanks and automotive fuel evaporative emission systems. This data is the direct basis for calculating filling volume, assessing safety performance and conducting trade settlement, and its traceable measurement chain provides core assurance for product quality and safety.

[0072] Example 2 like Figure 3 As shown, based on the same inventive concept, this embodiment of the invention also provides a gas volume calibration system based on a critical flow Venturi nozzle, including: a calibration device construction module, a critical state establishment module, a critical parameter acquisition module, a gas mass acquisition module, and a volume result output module; The calibration device construction module is used to build a volume calibration device including a gas source, a switching valve, a critical flow Venturi nozzle, and a container under test; The critical state establishment module is used to evacuate the container under test to the target value, open the switch valve, and allow gas from the gas source to enter the container under test through the critical flow Venturi nozzle, thus putting the volume calibration device into the critical flow state. The critical parameter acquisition module is used to acquire the state parameters of the gas source outlet during the critical flow state, as well as the pressure rise and average temperature of the container under test. The gas mass acquisition module is used to obtain the total mass of gas flowing into the container under test based on state parameters; The volume result output module is used to obtain the volume calibration result of the container under test based on the pressure rise, average temperature and total gas mass.

[0073] Furthermore, in this embodiment, the functional implementation methods of each functional module correspond one-to-one with the methods described above, and will not be repeated here.

[0074] Example 3 Based on the same inventive concept, the present invention also provides an electronic device, which includes a processor and a memory. The memory stores instructions, which are loaded and executed by the processor to implement a gas volume calibration method based on a critical flow venturi nozzle as described in Example 1.

[0075] Based on the same inventive concept, the present invention also provides a computer device, including a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory, used to store computer programs; When the processor executes a program stored in the memory, it is able to implement a gas volume calibration method based on a critical flow venturi nozzle, as shown in Example 1.

[0076] The electronic device may include a processor, a communications interface, a memory, and a communication bus, wherein the processor, communications interface, and memory communicate with each other via the communication bus. The processor can call logical instructions in the memory to execute a gas volume calibration method based on a critical flow Venturi nozzle as described in Embodiment 1.

[0077] Furthermore, the logical instructions in the aforementioned memory can be implemented as software functional units and sold or used as independent products, and can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0078] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0079] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A gas volume calibration method based on a critical flow Venturi nozzle, characterized in that, include: Construct a volume calibration device that includes a gas source, a switching valve, a critical flow Venturi nozzle, and a container to be tested; The container under test is evacuated to the target value, the switch valve is opened, and the gas in the gas source enters the container under test through the critical flow venturi nozzle, and the volume calibration device enters the critical flow state. Acquire the state parameters of the gas source outlet during the critical flow state, as well as the pressure rise and average temperature of the container under test; The total mass of gas flowing into the container under test is obtained based on the state parameters; The volume calibration result of the container under test is obtained based on the pressure rise, the average temperature, and the total mass of the gas.

2. The gas volume calibration method based on a critical flow Venturi nozzle as described in claim 1, characterized in that, Entering the critical flow state, specifically: The container under test is evacuated to the target value and forms a high vacuum state far below the critical back pressure. After the back pressure ratio is <0.1, a significant pressure difference is formed between it and the gas source. The switch valve is opened, and the gas in the gas source enters the critical flow venturi nozzle. The opening of the valve automatically and instantly establishes and maintains the stable critical flow state.

3. The gas volume calibration method based on a critical flow Venturi nozzle as described in claim 1, characterized in that, The critical flow state includes the state start time and the state end time; The state start time is the opening time of the switching valve; The state end time is the time required to reach a preset pressure threshold, a time threshold, or to actively close the switching valve.

4. The gas volume calibration method based on a critical flow Venturi nozzle as described in claim 3, characterized in that, The method for obtaining the state parameters is as follows: Acquire multiple pressure and temperature data points at the gas source outlet as time decreases during the critical flow state; Calibration is performed based on the acquisition timestamps of the pressure data and the temperature data to ensure that the pressure data and the temperature data correspond at the same time, thereby obtaining calibrated pressure data and calibrated temperature data. Based on the average values ​​of the calibration pressure data and the calibration temperature data, the upstream total pressure and upstream total temperature are obtained accordingly. The upstream total pressure and the upstream total temperature together constitute the state parameters.

5. The gas volume calibration method based on a critical flow Venturi nozzle as described in claim 4, characterized in that, The method for obtaining the pressure increase is as follows: The pressure value at the start time of the critical flow state of the container under test is obtained as the starting pressure; The pressure value at the end time of the critical flow state of the container under test is obtained as the end pressure; The pressure increase is based on the difference between the ending pressure and the starting pressure.

6. The gas volume calibration method based on a critical flow Venturi nozzle as described in claim 5, characterized in that, The method for obtaining the average temperature is as follows: The temperature value at the start time of the critical flow state of the container under test is obtained as the starting temperature; The temperature value at the end time of the critical flow state of the container under test is obtained as the end temperature; The average temperature is obtained by averaging the starting temperature and the ending temperature.

7. The gas volume calibration method based on a critical flow Venturi nozzle as described in claim 6, characterized in that, The method for obtaining the total mass of the gas is as follows: The critical flow mass flow rate is obtained based on the upstream total pressure, the upstream total temperature, and the structural parameters of the critical flow Venturi nozzle. The effective flow time is obtained based on the state start time and the state end time; The total mass of gas is obtained by multiplying the critical flow mass rate by the effective flow time.

8. The gas volume calibration method based on a critical flow Venturi nozzle as described in claim 7, characterized in that, The critical flow mass flow rate Specifically: ； in, This represents the throat area of ​​the critical flow Venturi nozzle. This represents the discharge coefficient of the critical flow Venturi nozzle. This represents the critical flow function for a real gas. Indicates the total upstream pressure. Represents the gas constant. Indicates molar mass. This indicates the total upstream temperature.

9. The gas volume calibration method based on a critical flow Venturi nozzle as described in claim 8, characterized in that, The volume calibration result of the container under test Specifically: ； in, Indicates the total mass of the gas. Indicates average temperature. Indicates the amount of pressure increase. This represents the gas compressibility factor.

10. A gas volume calibration system based on a critical flow Venturi nozzle, used to perform a gas volume calibration method based on a critical flow Venturi nozzle as described in any one of claims 1-9, characterized in that, include: The system includes a calibration device construction module, a critical state establishment module, a critical parameter acquisition module, a gas mass acquisition module, and a volume result output module. The calibration device construction module is used to construct a volume calibration device including a gas source, a switching valve, a critical flow Venturi nozzle, and a container to be tested. The critical state establishment module is used to evacuate the container under test to the target value, open the switch valve, and allow the gas in the gas source to enter the container under test through the critical flow venturi nozzle, and the volume calibration device enters the critical flow state. The critical parameter acquisition module is used to acquire the state parameters of the gas source outlet during the critical flow state, as well as the pressure rise and average temperature of the container under test. The gas mass acquisition module is used to obtain the total mass of gas flowing into the container to be tested based on the state parameters; The volume result output module is used to obtain the volume calibration result of the container under test based on the pressure rise, the average temperature and the total mass of the gas.

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