Method and structure for dynamically calibrating sonic nozzle by adopting pVTt gas flow standard device

Abstract

The invention relates to a method and a structure for dynamically calibrating a sonic nozzle by adopting a pVTt gas flow standard device. The method comprises the following steps: placing a standard container in a constant temperature box; the standard container is inflated once; in the inflation process, the air pressure and temperature in the standard container and the wall surface temperature of the standard container are continuously collected to obtain a first pressure value and a first average temperature value at a first time point in the standard container and obtain a second pressure value and a second average temperature value at a second time point in the standard container, so that the instantaneous mass flow rate is obtained; the method is high in standard accuracy and short in time consumption, and does not need to depend on a large amount of experimental data.

Description

Technical Field

[0001] The invention relates to the technical field of flow measurement, and in particular to a method and structure for dynamically calibrating a sonic nozzle by using a pVTt gas flow standard device. Background Art

[0002] The pVTt gas flow standard device (hereinafter referred to as the pVTt device) is a primary (the highest level) flow standard device that indirectly measures mass flow. It is used to calibrate secondary (transfer) standards. The secondary (transfer) standard for domestic gas flow generally refers to the critical flow Venturi nozzle (also known as the sonic nozzle). The pVTt device is directly traceable to basic physical quantities. Its working principle is: within a certain time interval t, the gas flows into or out of a standard container with a volume of V. According to the changes in the absolute pressure p and thermodynamic temperature T of the gas in the standard container, the mass flow rate of the gas can be obtained, that is, the density change in the standard container is combined with time to calculate the mass flow rate.

[0003] However, the current flow calibration method using the pVTt device includes a static calibration method. The static calibration method requires measuring the temperature and pressure before and after the standard container is filled with gas when the gas is in a stable equilibrium state, and then calculating the density. However, calibrating a small flow sonic nozzle is quite time-consuming, and due to the small size of the container, it is impossible to install a forced convection fan or agitator, resulting in uneven temperature distribution in the container space, and a deviation between the average temperature and the actual temperature of the gas in the container.

[0004] Therefore, it is necessary to improve the prior art to overcome the above defects in the prior art. Summary of the invention

[0005] In view of this, the embodiment of the present application provides a method for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device to solve at least one problem existing in the background technology, the method comprising:

[0006] Place the standard container in a thermostatic box containing thermostatic fluid;

[0007] After the standard container is pumped to a first preset pressure by a first vacuum pump, the first vacuum pump is then turned off;

[0008] The sonic nozzle and the second vacuum pump are connected via a fast three-way switching valve, and the second vacuum pump is started to make the airflow through the sonic nozzle reach a critical state;

[0009] The fast three-way switching valve quickly connects the standard container and the sonic nozzle, and at the same time triggers the timer to start timing;

[0010] After the air pressure in the standard container rises to the second preset pressure, the fast three-way switching valve connects the second vacuum pump to the sonic nozzle, and at the same time triggers the timer to stop timing, completing one inflation;

[0011] During the inflation process, the air pressure and temperature in the standard container and the wall temperature of the standard container are continuously collected to obtain the first pressure value and the first average temperature value at the first time point in the standard container, and the second pressure value and the second average temperature value at the second time point in the standard container. The instantaneous mass flow rate q flowing into the standard container through the sonic nozzle is calculated according to the following formula: md

[0012]

[0013] Where V is the volume of the standard container, V pipe is the volume of the pipe connecting the quick three-way switching valve and the standard container, t end -t start is the time period between the second time point and the first time point, ρ end (P end ,T end )-ρ start (P start ,T start ) is the change in the air density of the standard container between the second time point and the first time point.

[0014] Optionally, in the above method of dynamically calibrating a sonic nozzle using a pVTt gas flow standard device, the method for obtaining the average temperature value is:

[0015] Divide the internal space of the standard container into n non-overlapping unit cells, each with a volume of V i , the temperature of the gas inside each unit cell is T i ;

[0016] The average temperature at each time point Calculated by the following formula:

[0017]

[0018] Where V is the volume of the entire container, V i is the volume of the ith unit cell, and Ti is the temperature of the ith unit cell.

[0019] Optionally, in the above method of dynamically calibrating a sonic nozzle using a pVTt gas flow standard device, a method for obtaining the temperature at each location in the standard container at each time point includes:

[0020] Introducing the dimensionless energy equation, the dimensionless energy equation is:

[0021]

[0022] Among them, three-dimensional dimensionless spatial coordinates (X, Y, Z), ξ is dimensionless temperature, τ is dimensionless time, is the Laplace operator, L is the preset characteristic length, λ is the thermal conductivity of air, R is the gas constant, q m is the mass flow rate, V is the internal volume of the standard container;

[0023] Taking the wall temperature of the standard container as the boundary condition and the stable air temperature in the standard container before inflation as the initial condition, solve formula (3) in the internal space of the standard container to obtain the distribution of the dimensionless temperature ξ in the space at each time point;

[0024] The dimensionless temperature ξ and dimensionless time τ are converted into dimensional temperature T and dimensional time t by formula (4);

[0025]

[0026] Among them, the three-dimensional space coordinates (x, y, z), thermodynamic temperature T, time t, T * is the temperature of the gas filled into the standard container, c v is the constant volume specific heat capacity of air, λ is the thermal conductivity of air, ρ is the air density, and L is the preset characteristic length.

[0027] Optionally, in the above method of dynamically calibrating a sonic nozzle using a pVTt gas flow standard device, the mass flow rate q m The acquisition method is:

[0028] By converting the instantaneous mass flow rate q md Substituting q into the dimensionless equation multiple times m , until q md No noticeable changes are occurring.

[0029] Optionally, in the above-mentioned method of dynamically calibrating a sonic nozzle using a pVTt gas flow standard device, the volume of the standard container satisfies that the inflation time at the maximum flow rate is not less than 30 s.

[0030] Optionally, in the above-mentioned method of dynamically calibrating a sonic nozzle using a pVTt gas flow standard device, the standard container is connected to at least a first pressure sensor through a pressure measuring hole, and the first pressure sensor is used to detect the pressure value in the standard container, and the first pressure sensor is a high-frequency response dynamic pressure sensor with a dynamic frequency response of 5000 Hz.

[0031] Optionally, the above method of dynamically calibrating a sonic nozzle using a pVTt gas flow standard device uses a digital pressure gauge to detect the pressure fluctuation amplitude outside the thermostat, and performs the first operation or the second operation according to the detection result;

[0032] The first operation is to connect one end of the differential pressure transmitter to the pressure measuring hole of the standard container and the other end to the atmospheric pressure;

[0033] The second operation is to connect one end of the differential pressure transmitter to the pressure measuring hole of the standard container, and the other end to the constant pressure cavity arranged in the constant temperature box.

[0034] Optionally, in the above method of dynamically calibrating a sonic nozzle using a pVTt gas flow standard device, the flow range of the sonic nozzle is 0.016-0.8m 3 / h.

[0035] Optionally, in the above method of dynamically calibrating a sonic nozzle using a pVTt gas flow standard device, the time measurement uncertainty of the timer is no more than 0.01%, k=2, and the resolution is no more than 1 ms.

[0036] The present application also provides a structure for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device, comprising:

[0037] A thermostatic box storing a constant temperature liquid;

[0038] A standard container, located in the constant temperature liquid;

[0039] The vacuum pump assembly includes a first vacuum pump, a second vacuum pump, a pneumatic ball valve and a three-way switching valve. The first vacuum pump is connected to the standard container through the pneumatic ball valve. The first end of the three-way switching valve is connected to the second vacuum pump, the second end is connected to the standard container, and the third end is connected to the sonic nozzle.

[0040] Compared with the prior art, the present application has the following beneficial effects: by continuously collecting the pressure and average temperature values ​​in the standard container for multiple times during an inflation process, the first pressure value and the first average temperature at the first time point and the second pressure value and the second average temperature at the second time point are obtained, and the instantaneous mass flow rate is obtained through the relevant formula to realize the calibration of the small flow sonic nozzle; compared with the static calibration method in the prior art, this method can implement calibration during the inflation stage, and multiple mass flow values ​​can be obtained during an inflation process, while the static measurement method can only obtain the mass flow value after the inflation is completed, and can only obtain one mass flow value, without waiting for the inflation process and the stabilization process, reducing the working time and improving the calibration efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the structure of the dynamic calibration sonic nozzle of the pVTt gas flow standard device shown in this embodiment;

[0042] Figure 2 Another embodiment is shown Figure 1The shown diagram is a partial structural schematic diagram of the pVTt gas flow standard device for dynamically calibrating the sonic nozzle.

[0043] Reference numerals:

[0044] 1- Constant temperature box, 2- Standard container, 3- Pneumatic ball valve, 4- Three-way switching valve, 5- First vacuum pump, 6- Second vacuum pump, 7- Sonic nozzle, 8- Digital pressure gauge, 9- Differential pressure transmitter, 10- Constant temperature chamber. DETAILED DESCRIPTION

[0045] The exemplary embodiments disclosed in the present application will be described in more detail below. In the following description, a large number of specific details are given in order to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features well known in the art are not described; that is, all features of the actual embodiments are not described here, and known functions and structures are not described in detail.

[0046] It should be understood that when an element or layer is referred to as "on ...", "adjacent to ...", "connected to" or "coupled to" other elements or layers, it can be directly on, adjacent to, connected to or coupled to other elements or layers, or there can be intervening elements or layers. On the contrary, when an element is referred to as "directly on ...", "directly adjacent to ...", "directly connected to" or "directly coupled to" other elements or layers, there is no intervening element or layer. It should be understood that although the terms first, second, third, etc. can be used to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or part from another element, component, region, layer or part. Therefore, without departing from the teachings of the present application, the first element, component, region, layer or part discussed below can be represented as the second element, component, region, layer or part. And when the second element, component, region, layer or part is discussed, it does not indicate that the present application necessarily has the first element, component, region, layer or part.

[0047] Spatially relative terms such as "under", "beneath", "below", "under", "over", "above", etc., may be used herein for convenience of description to describe the relationship of one element or feature to other elements or features shown in the figures. It should be understood that the spatially relative terms are intended to encompass different orientations of the device in use and operation in addition to the orientation shown in the figures.

[0048] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present application. When used herein, the singular forms "a", "an" and " / the" are also intended to include plural forms, unless the context clearly indicates another way. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0049] In order to thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solution of the present application. The preferred embodiments of the present application are described in detail below, but in addition to these detailed descriptions, the present application may also have other implementation methods.

[0050] The pVTt gas flow standard device (hereinafter referred to as the pVTt device) is a primary (the highest level) flow standard device that indirectly measures mass flow. It is used to calibrate secondary (transfer) standards. The secondary (transfer) standard for domestic gas flow generally refers to the critical flow Venturi nozzle (also known as the sonic nozzle). The pVTt device is directly traceable to basic physical quantities. Its working principle is: within a certain time interval t, the gas flows into or out of a standard container with a volume of V. According to the changes in the absolute pressure p and thermodynamic temperature T of the gas in the standard container, the mass flow rate of the gas can be obtained, that is, the density change in the standard container is combined with time to calculate the mass flow rate.

[0051] However, the pVTt method is a static calibration method that requires obtaining the state parameters of the gas under relatively stable static conditions. Therefore, the filling and stabilization processes are time-consuming, especially for small flow rates. For example, a 34L standard container is used to calibrate 6×10 -5 m 3 / h flowmeter, it takes 24 days to inflate the container from 0.02kPa to 100kPa. Small flow sonic nozzles are widely used in the calibration devices of household (membrane / ultrasonic) gas meters. Each device is generally equipped with 7 to 13 small flow sonic nozzles. Each gas meter needs to pass factory calibration on such devices. This leads to the problem of long time and low efficiency when calibrating small flow sonic nozzles using static calibration method, and the calibration accuracy is insufficient due to inaccurate temperature measurement.

[0052] In addition, related technologies also include the rate of rise method, which uses the density at multiple moments to determine the rate of change of gas mass over time. The problem is that the temperature of the gas in the container cannot be accurately obtained. This method is limited to 0.012m 3 / h or less flow rate calibration, under this limit, the temperature measurement error is relatively small. The developer of the rate of rise method attributed the temperature measurement error to a dimensionless ratio of the heat exchange between the gas and the environment and the heat generated by the gas compression, and then analyzed the uncertainty of the measurement result. From the relevant measurement results, it can be seen that the temperature measurement error increases with the increase of flow rate, so there is a 0.012m 3 / h or less, and my country's small flow sonic nozzles are widely used in household (membrane / ultrasonic) gas meter calibration devices. The lower limit of the range of household gas meters is 0.016m 3 / h, so the rate of rise method is not widely applicable in our country.

[0053] Alternatively, researchers obtain relevant calibration methods through lumped parameter models of a large amount of experimental data and computational fluid dynamics methods, but this method often relies on a large amount of experimental data or has complex calculation methods.

[0054] In order to solve the above technical problems, refer to Figure 1 As shown, a structure for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device as shown in a preferred embodiment of the present application is used to calibrate a small flow sonic nozzle. The calibration method implemented by this structure is a dynamic calibration method, which can not only perform calibration during the inflation process, reducing the time waiting for inflation and waiting for the gas to stabilize, but also the measured temperature average value is more accurate, and there is no need to rely on a large amount of experimental data and complex calculation methods.

[0055] The structure includes a thermostatic box 1 storing a constant temperature liquid, a standard container 2 located in the constant temperature liquid, and a vacuum pump assembly. The vacuum pump assembly includes a first vacuum pump 5, a second vacuum pump 6, a pneumatic ball valve 3, and a three-way switching valve 4. The first vacuum pump 5 is connected to the standard container 2 through the pneumatic ball valve 3. The first end of the three-way switching valve 4 is connected to the second vacuum pump 6, the second end is connected to the standard container 2, and the third end is connected to the sonic nozzle 7. It should be noted that in this embodiment, the flow range of the sonic nozzle 7 is 0.016-0.8m 3 / h.

[0056] Furthermore, a thermometer is provided on the thermostat 1, which is used to measure the temperature of the thermostat liquid, so as to control the temperature uniformity of the liquid in the thermostat 1 by detecting the temperature of the thermostat liquid.

[0057] ±0.02℃.

[0058] In an optional embodiment, the structure also includes a standard container connected to at least a first pressure sensor and a second pressure sensor through a pressure measuring hole, which is used to monitor the pressure in the standard container in real time. In this embodiment, pressure measuring holes are provided above and below the standard container, and the first pressure sensor and the second pressure sensor are respectively connected to the two pressure measuring holes to monitor the pressure thereof. It should be noted that in this embodiment, since the sonic nozzle is a small flow sonic nozzle, its flow rate is relatively low, so the pressure at various locations of the standard container is almost the same, and any monitoring value of the first pressure sensor and the second pressure sensor can be used for subsequent calculations. In this embodiment, the first pressure sensor and the second pressure sensor are both high-frequency response dynamic pressure sensors with a dynamic frequency response of 5000Hz.

[0059] In an optional embodiment, the structure further includes at least one first temperature sensor, a second temperature sensor and a third temperature sensor, the first temperature sensor is used to detect the gas temperature in the standard container 2, the second temperature sensor is used to detect the temperature of the wall of the standard container 2, and the third temperature sensor is used to measure the temperature of the air flow flowing through the sonic nozzle 7. It should be noted that the uncertainty of the first temperature sensor, the second temperature sensor and the third temperature sensor is U=0.05°C, k=2.

[0060] In an optional embodiment, the structure further includes a digital pressure gauge 8 disposed outside the thermostatic box 1 , and the digital pressure gauge 8 is used to detect the pressure fluctuation amplitude outside the thermostatic box 1 , and the digital pressure gauge 8 is of 0.01 level.

[0061] In an alternative embodiment, referring to Figure 2 As shown, the structure also includes a constant pressure chamber 10 disposed in the thermostat 1, and the constant pressure chamber 10 is connected to two pressure measuring holes in the standard container 2 through two differential pressure transmitters 9, respectively, to provide a stable air pressure for the thermostat 1 to prevent the large fluctuation of the air pressure in the external operating environment from affecting the calibration. Among them, both differential pressure transmitters are 0.05 level.

[0062] As described above, in this embodiment, the method of dynamically calibrating a sonic nozzle using a pVTt gas flow standard device includes:

[0063] Place the standard container in a thermostatic box containing thermostatic fluid;

[0064] After the standard container is pumped to a first preset pressure by a first vacuum pump, the first vacuum pump is then turned off;

[0065] The sonic nozzle and the second vacuum pump are connected via a fast three-way switching valve, and the second vacuum pump is started to make the airflow through the sonic nozzle reach a critical state;

[0066] The fast three-way switching valve quickly connects the standard container and the sonic nozzle, and at the same time triggers the timer to start timing;

[0067] After the air pressure in the standard container rises to the second preset pressure, the fast three-way switching valve connects the second vacuum pump to the sonic nozzle, and at the same time triggers the timer to stop timing, completing one inflation;

[0068] It should be noted that the time measurement uncertainty of the timer is no more than 0.01%, k = 2, and the resolution is no more than 1ms;

[0069] During the inflation process, the air pressure and temperature in the standard container and the wall temperature of the standard container are continuously collected to obtain the first pressure value and the first average temperature value in the standard container at the first time point, and the second pressure value and the second average temperature value in the standard container at the second time point. The instantaneous mass flow rate q is calculated according to the following formula md

[0070]

[0071] Where V is the volume of the standard container, V pipe is the volume of the pipe connecting the quick three-way switching valve and the standard container, t end -t start is the time period between the second time point and the first time point, ρ end (P end ,T end )-ρ start (P start ,T start ) is the change in the air density of the standard container between the second time point and the first time point.

[0072] It can be understood that the first pressure value P is obtained by detecting the pressure value in the standard container at the first time point through the first pressure sensor or the second pressure sensor. start The first pressure sensor or the second pressure sensor detects the pressure value in the standard container at the second time point to obtain the second air pressure value P end .

[0073] It can be understood that the temperature of the gas in the standard container is monitored by the first temperature sensor.

[0074] It can be understood that by collecting the pressure and average temperature in the standard container for multiple consecutive times, the instantaneous mass flow rate flowing into the standard container through the sonic nozzle can be calculated by the above formula (1), thereby realizing the calibration of the small flow sonic nozzle. Compared with the static calibration method, there is no need to wait for the inflation process and the process of waiting for the airflow to stabilize. Calibration can be performed during the inflation stage, which reduces the calibration time and improves the calibration efficiency. Compared with the static calibration method that can only obtain one mass flow value, the calibration method of this embodiment can obtain multiple mass flow values.

[0075] It should be noted that during the inflation process, the gas temperature changes and cannot be accurately measured. The reasons are: first, the measured value measured by the temperature sensor is different from the change of the air temperature during the inflation process, that is, it has a lag; second, the temperature in different places in the standard container is inconsistent. Therefore, in this embodiment, the average temperature value of the standard container is obtained by the following method:

[0076] In an optional embodiment, the method for obtaining the average temperature value is:

[0077] Divide the standard container into n non-overlapping unit cells, each with a volume of V i , the temperature of the gas inside each unit cell is T i ;

[0078] Average temperature Calculated by the following formula:

[0079]

[0080] Where V is the volume of the entire container, V i is the volume of the ith unit cell, and Ti is the temperature of the ith unit cell.

[0081] It can be understood that by dividing the interior of the standard container into n non-overlapping unit bodies, and obtaining the temperature value of each unit body at each time point, the average temperature value at each time point can be obtained. For example, at time point T1, the temperatures of the n unit bodies in the standard container are T 11 , T 12 , T 13 ……T 1n At time point T2, the temperatures of the n units in the standard container are T 21 , T 22 , T 23 ……T 2n , the average temperature value in the standard container at time point T1 or T2 can be obtained by calculation. This can avoid the influence of temperature measurement error caused by the hysteresis of the temperature sensor and the temperature difference of each part of the standard container on the accuracy of calibration. Moreover, this grid division method to obtain the average temperature in the standard container at each time point is not limited by the shape and size of the standard container. (Just for better understanding: For modern CAD and CAE technology, space grid division is almost done at once while designing the container, and a useful byproduct is obtained at the same time - the volume V of each unit body i )

[0082] In this embodiment, the method for obtaining the temperature at each location in the standard container at each time point includes:

[0083] Introducing the dimensionless energy equation, the dimensionless energy equation is:

[0084]

[0085] Among them, three-dimensional dimensionless spatial coordinates (X, Y, Z), ξ is dimensionless temperature, τ is dimensionless time, is the Laplace operator, L is the preset characteristic length, λ is the thermal conductivity of air, R is the gas constant, q m is the mass flow rate, V is the internal volume of the standard container;

[0086] Taking the wall temperature of the standard container as the boundary condition and the stable air temperature in the standard container before inflation as the initial condition, solve formula (3) in the internal space of the standard container to obtain the distribution of the dimensionless temperature ξ in the space at each time point;

[0087] The dimensionless temperature ξ and dimensionless time τ are converted into dimensional temperature T and dimensional time t by formula (4);

[0088]

[0089] Among them, the three-dimensional space coordinates (x, y, z), thermodynamic temperature T, time t, T * is the temperature of the gas filled into the standard container, c v is the constant volume specific heat capacity of air, λ is the thermal conductivity of air, ρ is the air density, and L is the preset characteristic length.

[0090] It can be understood that in this embodiment, the temperature of the wall of the standard container is monitored to ensure that the temperature change of the wall of the standard container is extremely small, thereby providing a stable boundary condition for solving the dimensionless equation.

[0091] In an optional embodiment, the first pressure sensor and the second pressure sensor are set as high-frequency response dynamic pressure sensors with a dynamic frequency response of 5000 Hz, so that the high-frequency response dynamic pressure sensor can quickly capture pressure changes, and the response frequency is as high as 5000 Hz. The reason for setting it as a high-frequency response dynamic pressure sensor is that it can monitor the transient pressure changes during the inflation process in real time, thereby improving the accuracy and reliability of the measurement.

[0092] In an optional embodiment, the mass flow rate q in formula (3) is m The acquisition method is:

[0093] By converting the instantaneous mass flow rate q md Substituting q into the dimensionless equation multiple times m , until q md No noticeable changes are occurring.

[0094] In an optional embodiment, the standard container volume satisfies that the inflation time at the maximum flow rate is not less than 30 seconds.

[0095] Understandably, this setting is to ensure that the inflation time is long enough at the maximum flow rate to ensure that the measurement system can record data more accurately. A longer inflation time helps the system achieve a more stable temperature and pressure distribution, and can better reflect the dynamic characteristics of gas flow, thereby improving the accuracy of the experiment, data stability and dynamic response capabilities.

[0096] In an optional embodiment, a digital pressure gauge is used to detect the pressure in the laboratory environment or inside the constant pressure chamber, and the first operation or the second operation is performed according to the detection result;

[0097] The first operation is to connect one end of the differential pressure transmitter to the pressure measuring hole of the standard container and the other end to the atmospheric pressure;

[0098] The second operation is to connect one end of the differential pressure transmitter to the pressure measuring hole of the standard container, and the other end to the constant pressure cavity arranged in the constant temperature box.

[0099] Understandably, it can be flexibly selected according to the experimental environment, that is, the pressure fluctuation amplitude measured outside the constant temperature box. If the fluctuation amplitude is small, the atmospheric pressure is directly used as the reference pressure without the need for an additional constant pressure device. This design simplifies the system structure and reduces cost and complexity. If the fluctuation amplitude is large, a constant pressure chamber is selected to provide a stable reference pressure environment. Even if the laboratory environment pressure fluctuates greatly, it will not affect the measurement accuracy. The differential pressure transmitter measures the difference between the pressure in the standard container and the pressure in the constant pressure chamber, eliminating the influence of atmospheric pressure fluctuations on the measurement results. This design can significantly improve the stability and repeatability of the measurement.

[0100] The above is only a specific implementation of the present application, and any other improvements made based on the concept of the present application are deemed to be within the protection scope of the present application.

Claims

1. A method for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device, characterized in that: The method comprises: Place the standard container in a thermostatic box containing thermostatic liquid; After the standard container is pumped to a first preset pressure by a first vacuum pump, the first vacuum pump is then turned off; The sonic nozzle and the second vacuum pump are connected via a fast three-way switching valve, and the second vacuum pump is started to make the airflow through the sonic nozzle reach a critical state; The fast three-way switching valve quickly connects the standard container and the sonic nozzle, and at the same time triggers the timer to start timing; After the air pressure in the standard container rises to the second preset pressure, the fast three-way switching valve connects the second vacuum pump to the sonic nozzle, and at the same time triggers the timer to stop timing, completing one inflation; During the inflation process, the air pressure and temperature in the standard container and the wall temperature of the standard container are continuously collected to obtain the first pressure value and the first average temperature value at the first time point in the standard container, and the second pressure value and the second average temperature value at the second time point in the standard container. The instantaneous mass flow rate q flowing into the standard container through the sonic nozzle is calculated according to the following formula: md Where V is the volume of the standard container, V pipe is the volume of the pipe connecting the quick three-way switching valve and the standard container, t end -t start is the time period between the second time point and the first time point, ρ end (P end ,T end )-ρ start (P start ,T start ) is the change in the air density of the standard container between the second time point and the first time point.

2. The method for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device according to claim 1, characterized in that: The method for obtaining the average temperature value is: Divide the internal space of the standard container into n non-overlapping unit cells, each with a volume of V i , the temperature of the gas inside each unit cell is T i ; The average temperature at each time point Calculated by the following formula: Where V is the volume of the entire container, V i is the volume of the ith unit cell, and Ti is the temperature of the ith unit cell.

3. The method for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device according to claim 2, characterized in that: The method for obtaining the temperature at each location in the standard container at each time point includes: Introducing the dimensionless energy equation, the dimensionless energy equation is: Among them, three-dimensional dimensionless spatial coordinates (X, Y, Z), ξ is dimensionless temperature, τ is dimensionless time, is the Laplace operator, L is the preset characteristic length, λ is the thermal conductivity of air, R is the gas constant, q m is the mass flow rate, V is the internal volume of the standard container; Taking the wall temperature of the standard container as the boundary condition and the stable air temperature in the standard container before inflation as the initial condition, solve formula (3) in the internal space of the standard container to obtain the distribution of the dimensionless temperature ξ in the space at each time point; The dimensionless temperature ξ and dimensionless time τ are converted into dimensional temperature T and dimensional time t by formula (4); Among them, the three-dimensional space coordinates (x, y, z), thermodynamic temperature T, time t, T * is the temperature of the gas filled into the standard container, c v is the constant volume specific heat capacity of air, λ is the thermal conductivity of air, ρ is the air density, and L is the preset characteristic length.

4. The method for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device according to claim 3, characterized in that: Mass flow rate q m The acquisition method is: By converting the instantaneous mass flow rate q md Substituting q into the dimensionless calculation equation multiple times m , until q md No noticeable changes are occurring.

5. The method for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device according to claim 1, characterized in that: The standard container capacity satisfies that the inflation time at the maximum flow rate is not less than 30s.

6. The method for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device according to claim 1, characterized in that: The standard container is connected to at least a first pressure sensor through a pressure measuring hole. The first pressure sensor is used to detect the pressure value in the standard container. The first pressure sensor is a high-frequency response dynamic pressure sensor with a dynamic frequency response of 5000 Hz.

7. The method for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device according to claim 6, characterized in that: Use a digital pressure gauge to detect the fluctuation amplitude of the pressure outside the thermostatic box, and perform the first operation or the second operation according to the detection result; The first operation is to connect one end of the differential pressure transmitter to the pressure measuring hole of the standard container and the other end to the atmospheric pressure; The second operation is to connect one end of the differential pressure transmitter to the pressure measuring hole of the standard container, and the other end to the constant pressure cavity arranged in the constant temperature box.

8. The method for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device according to claim 1, characterized in that: The flow rate range of the sonic nozzle is 0.016-0.8m 3 / h.

9. The method for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device according to claim 1, characterized in that: The time measurement uncertainty of the timer is no greater than 0.01%, k=2, and the resolution is no greater than 1 ms.

10. A structure for dynamically calibrating a sonic nozzle using a pVTt gas flow standard device, characterized in that: include: A thermostatic box storing a constant temperature liquid; a standard container, located in the constant temperature liquid; The vacuum pump assembly includes a first vacuum pump, a second vacuum pump, a pneumatic ball valve and a three-way switching valve. The first vacuum pump is connected to the standard container through the pneumatic ball valve. The first end of the three-way switching valve is connected to the second vacuum pump, the second end is connected to the standard container, and the third end is connected to the sonic nozzle.

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