Measuring device for calibrating gas mass flow and calibration method

Abstract

The invention discloses a measuring device and method for calibrating gas mass flow, and belongs to the technical field of flow measurement. The device comprises a gas inlet pipe provided with a pressure regulating valve; the stagnation container is communicated with the air inlet pipe; the plurality of sonic nozzles are respectively arranged on the stagnation container, and each sonic nozzle is provided with an upstream end communicated with the stagnation container and a downstream end communicated with the collection container; a collection container; the exhaust pipe is communicated with the collecting container; the pressure measuring piece I, the temperature measuring piece I and the humidity measuring piece are connected to the stagnation container; and the second pressure measuring piece is connected to the collection container. The calibration method comprises the following steps: opening the pressure regulating valve and regulating until each sonic nozzle is in a critical flow state; and after the measured data is stable, collecting and calculating the standard flow. According to the gas mass flow metering device, the field gas source can be directly utilized, measurement can be conveniently and rapidly carried out, the field calibration problem of the gas mass flow metering device can be solved, it is guaranteed that the flow value of the gas mass flow metering device is accurate, and meanwhile the gas mass flow metering device can be used under the laboratory condition.

Description

Technical Field

[0001] The present application relates to the field of flow measurement technology, and in particular to a measuring device and a calibration method for calibrating gas mass flow. Background Art

[0002] The measuring device for calibrating gas mass flow is used for the transfer of measurement values of gas mass flow metering devices to ensure that the flow measurement data is accurate and reliable. At present, with the continuous development of semiconductors, aerospace technology, biopharmaceuticals, new energy and other fields, gas mass flow metering devices have been widely used in the industry as important equipment for monitoring parameters of production lines in related fields. If unqualified flow meters are used, it will cause safety hazards and product quality problems. Therefore, in order to ensure the accuracy and reliability of gas mass flow measurement, the flow meter needs to be inspected regularly. When inspected, the flow meter generally needs to be disassembled and sent to the laboratory of the metrology and calibration agency. The inspection cycle of this method is as short as ten days and as long as one or two months. Therefore, it causes inconvenience to users in using the flow meter, long-term shutdown of the production line and other problems, wasting a lot of manpower, financial resources and time. Therefore, users have an urgent need for on-site calibration of flow measurement.

[0003] At present, most gas mass flowmeter calibration devices used by most measurement institutions are gas bell-type or pVTt-type gas flow standard devices, but they are large in mass and volume, are all fixed, and lack portability and maneuverability. On the other hand, to ensure the calibration accuracy, it is necessary to measure data under multiple sets of different parameters, which will lead to the overall structure of the calibration equipment being complex and large in volume, making it difficult to meet the on-site calibration needs of gas mass flowmeters. Summary of the Invention

[0004] The present application aims to at least to some extent solve the technical problem that current calibration devices are difficult to meet on-site calibration requirements. To this end, the present application provides a measuring device and calibration method for calibrating gas mass flow. By using this device, the on-site gas source can be directly utilized to perform measurements conveniently and quickly, which can solve the on-site calibration problem of gas mass flow metering devices to ensure the accuracy of the flow value of such equipment. At the same time, the device can also be used under laboratory conditions.

[0005] In a first aspect, an embodiment of the present application provides a measuring device for calibrating gas mass flow, comprising:

[0006] An air inlet pipe is used to communicate with the air source and is provided with a pressure regulating valve;

[0007] a stagnation container, connected to the air inlet pipe;

[0008] a plurality of sonic nozzles, each disposed in the stagnation container, the sonic nozzles having an upstream end and a downstream end, the plurality of upstream ends being in communication with the interior of the stagnation container;

[0009] a collecting container, communicating with a plurality of downstream ends;

[0010] an exhaust pipe, connected to the collecting container, for connecting to the flow metering device to be tested and for introducing the gas exhausted from the collecting container into the exhaust pipe;

[0011] A pressure measuring device 1, a temperature measuring device 1 and a humidity measuring device are connected to the stagnation container and are used to detect the pressure P0, temperature T0 and humidity RH upstream of the sonic nozzle respectively;

[0012] The second pressure measuring device is connected to the collecting container and is used to detect the pressure P downstream of the sonic nozzle.

[0013] In some embodiments, further comprising:

[0014] The third pressure measuring component is connected to the exhaust pipe and is used to detect the pressure P1 before entering the flow metering device to be tested.

[0015] In some embodiments, a second temperature measuring element is further included, which is connected to the exhaust pipe and is used to detect the temperature T1 before entering the flow metering device to be tested.

[0016] In some embodiments, a plurality of downstream pipes are further included, with both ends of the downstream pipes being connected to the downstream end and the collecting container respectively, and the downstream pipes are arranged in a one-to-one correspondence with the sonic nozzles.

[0017] In some embodiments, a plurality of branch valves are further included, which are arranged in the downstream pipe, and the number of the branch valves corresponds to the number of the sonic nozzles.

[0018] In some embodiments, a data acquisition component is further included. The data acquisition component is electrically connected to the pressure measuring component 1, the pressure measuring component 2, the temperature measuring component 1 and the humidity measuring component, and is used to collect pressure and temperature data.

[0019] In some embodiments, the data acquisition component is also electrically connected to the third pressure measuring component and the second temperature measuring component, and is used to collect pressure and temperature data.

[0020] In some embodiments, the data acquisition component has a built-in method for calculating the gas mass flow rate under the critical state of a sonic nozzle. When the gas source contains CO2 and water vapor, the gas mass flow rate is:

[0021]

[0022] Where q m,atmos is the corrected mass flow rate, kg / s; is the mole fraction of CO2 in the air. If unknown, it is determined as 0.0004. RH is the relative humidity. A and B are both intermediate calculation parameters, A=0.127828τ 3 -0.789422τ2 +1.63166τ-1.12818, B=-0.000288749π 2 -0.00191022π+0.00569536-0.0719995π -1 , p c is the critical parameter, 3.786MPa; T c is the critical parameter, 132.5306K.

[0023] In a second aspect, an embodiment of the present application provides a gas mass flow calibration method, which uses the above-mentioned measuring device for calibrating gas mass flow, and the calibration method includes:

[0024] Connect the air inlet pipe to the air source, connect the exhaust pipe to the flow metering device to be tested, select at least one sonic nozzle to participate in the test, and ensure that the sonic nozzle is connected to the collecting container;

[0025] Open the pressure regulating valve to allow the gas to flow through the stagnation container, sonic nozzle, collecting container, exhaust pipe and flow metering device to be tested in sequence, and adjust the pressure regulating valve until each sonic nozzle is in the critical flow state;

[0026] After the monitored pressure, temperature and humidity are stable, collect the pressure, temperature and humidity data and calculate the standard flow rate.

[0027] In some embodiments, the standard flow rate is calculated using a gas mass flow rate calculation formula when the sonic nozzle is in a critical flow state.

[0028] It can be seen from the above technical solution that the beneficial effects of this application are:

[0029] 1. The present application forms the main part for detecting the gas mass flow rate between the gas source and the flow metering device to be tested by arranging an air inlet pipe, a stagnation container, a sonic nozzle, a collecting container and an exhaust pipe. The stagnation container and the collecting container provide a buffer and airflow space when the gas source enters and discharges multiple sonic nozzles. The pressure, temperature, humidity upstream of the sonic nozzle, or the pressure downstream can be determined by a pressure measuring device 1, a temperature measuring device 1, a humidity measuring device 2, or a pressure measuring device 2, thereby reducing the number of measuring devices and simplifying the structure. At the same time, the pressure measuring device 1, the temperature measuring device 1 and the humidity measuring device are used to detect the pressure P0, temperature T0 and humidity RH upstream of the sonic nozzle, and the pressure measuring device 2 is used to detect the pressure P downstream of the sonic nozzle. In this way, the four parameters can be substituted into the formula of the critical flow state to determine whether the sonic nozzle is in the critical state, and subsequent calculations can be performed to determine the gas mass flow rate. In this way, the device can directly use the on-site gas source to perform measurements conveniently and quickly, which can solve the on-site calibration problem of gas mass flow metering devices to ensure the accuracy of the flow value of such equipment. At the same time, the device can also be used under laboratory conditions.

[0030] 2. This application uses the above-mentioned calibration device to adjust the pressure in the stagnation container by opening the regulating valve, and adjusts the airflow through the regulating valve. Each sonic nozzle is in a critical flow state. The pressure and temperature values measured in the critical flow state can be substituted into the calculation formula of the standard flow to obtain the gas mass flow result. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other embodiments and drawings can be obtained based on these drawings without creative work. The flowcharts shown in the drawings are only exemplary illustrations and do not necessarily include all the content and operations / steps, nor do they have to be executed in the order described. For example, some operations / steps can be decomposed, while some operations / steps can be combined or partially combined, so the actual execution order may change according to the actual situation.

[0032] Figure 1 A schematic diagram of an embodiment of a measuring device for calibrating gas mass flow rate according to the present invention is shown;

[0033] Figure 2 A schematic diagram showing the principle of an embodiment of a measuring device for calibrating gas mass flow rate according to the present invention is shown;

[0034] Figure 3 A schematic diagram of an embodiment of an electrical device portion of the present invention is shown;

[0035] Figure numerals: 100, pipe component part; 110, air inlet pipe; 120, stagnation container; 130, sonic nozzle; 140, collecting container; 150, downstream pipe; 160, exhaust pipe; 170, measuring component; 171, pressure measuring component one; 172, pressure measuring component two; 173, pressure measuring component three; 174, temperature measuring component one; 175, temperature measuring component two; 176, humidity measuring component; 180, valve; 181, pressure regulating valve; 182, branch valve; 200, electrical component part; 210, power supply component; 220, data acquisition component. DETAILED DESCRIPTION

[0036] The following will be combined with the accompanying drawings corresponding to the specific embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. The following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection. The described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, various different configurations can be arranged and designed. All other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] The present application is described below with reference to specific embodiments and with reference to the accompanying drawings:

[0038] Please refer to Figure 1 and Figure 2 In the first aspect of the present application, an embodiment provides a measuring device for calibrating gas mass flow, which includes a pipe device part 100, specifically including an inlet pipe 110, a stagnation container 120, multiple sonic nozzles 130, a collecting container 140, an exhaust pipe 160, and a measuring component. The measuring component includes devices for measuring pressure, temperature and humidity, wherein the sonic nozzle 130 is a device with an inlet aperture gradually narrowing to the throat and gradually expanding after passing through the throat, which is used to measure gas flow. The sonic nozzle 130 used in this application is a standard specification part, and sonic nozzles 130 of different specifications can also be used, such as different apertures, different lengths of each section, etc., which are all suitable for the calibration device of this application. The stagnation container 120 and the collecting container 140 can adjust the structural dimensions according to actual use; the connection of the following pipe device part 100 refers to the connection between the pipeline and the equipment, and the connection between the pipeline and the pipeline, which is a conventional connection method, and the following valve 180 is also a conventional setting method.

[0039] One end of the air inlet pipe 110 is connected to the outside for communicating with the air source, and the other end of the air inlet pipe 110 is connected to the stagnation container 120. The air inlet pipe 110 is provided with a pressure regulating valve 181, which is a high-precision pressure regulating valve. The stagnation container 120 provides a buffer and a uniform airflow space for entering the multiple sonic nozzles 130. The stagnation container 120 can adopt a horizontal tank structure of a certain length, such as a cylindrical container with an outer diameter of 150 mm, a height of 500 mm, and a wall thickness of 4 mm placed horizontally. The number of sonic nozzles 130 is based on the number of sonic nozzles 130. According to the detection and accuracy requirements, multiple sonic nozzles 130 are respectively provided in the stagnation container 120. The sonic nozzles 130 can be embedded in the side wall openings of the stagnation container 120, or multiple sonic nozzles 130 can be placed in the stagnation container 120. One end of the sonic nozzle 130 can be placed in the stagnation container 120 and the other end can be located outside it. For example, one end of six sonic nozzles 130 is fixedly installed in the stagnation container 120. Specifically, six mounting bases are provided in the stagnation container 120, and the sonic nozzles 130 are fixed by using a pressure plate and a bolt. 130 is installed in the stagnation container 120; the sonic nozzle 130 has an upstream end and a downstream end, the upstream ends of the multiple sonic nozzles 130 are connected to the interior of the stagnation container 120, and the downstream ends of the multiple sonic nozzles 130 are connected to the collection container 140; the collection container 140 also adopts a horizontal tank structure of a certain length, an outer diameter of 30mm, a height of 500mm, and a cylindrical container with a wall thickness of 3mm and is placed horizontally, and the collection container 140 is provided with multiple inlets, each of which is connected to the port at the downstream end of the sonic nozzle 130, and can also be connected to the sonic nozzle 130. A pipe is installed between the downstream end of the speed nozzle 130 and the corresponding inlet for connection; through the design of the above-mentioned stagnation container 120 and the collecting container 140, the number of instruments for measuring pressure and temperature can be reduced; the exhaust pipe 160 is connected to the collecting container 140, one end of the exhaust pipe 160 is connected to the collecting container 140, and the other end is used to connect to the flow metering device to be tested, and the gas discharged from the collecting container 140 is introduced into the flow meter device to be tested through the exhaust pipe 160; the flow metering device to be tested is a metering device used on site, which is relatively conventional, such as a gas mass flow meter.

[0040] The measurement assembly 170 of the present application utilizes existing pressure measuring devices, temperature measuring devices, and humidity measuring devices. For example, pressure measurement utilizes a pressure transmitter, pressure sensor, or other conventional pressure detection device; temperature measurement utilizes a temperature transmitter, temperature sensor, or other conventional temperature detection device; and humidity measurement utilizes a humidity transmitter, dew point meter, or other conventional humidity detection device. The measurement assembly 170 includes: a first pressure measuring device 171, a second pressure measuring device 172, a first temperature measuring device 174, and a humidity measuring device 176. The first pressure measuring device 171, the first temperature measuring device 174, and the humidity measuring device 176 are connected to the stagnation container 120, specifically by being installed in an opening in the side wall of the stagnation container 120, and are used to respectively detect the pressure P0, temperature T0, and relative humidity RH upstream of the sonic nozzle 130. The second pressure measuring device 172 is connected to the collection container 140, specifically by being installed in an opening in the side wall of the collection container 140, and is used to detect the pressure P downstream of the sonic nozzle 130. The measurement range can be extended and the accuracy level can be improved by increasing the number of sonic nozzles 130 and selecting a measurement component 170 with a high accuracy level, thereby further enhancing the calibration capability of the gas mass flow meter.

[0041] The calibration devices of the existing technology are difficult to meet the requirements of on-site calibration. The measuring devices currently used to calibrate gas mass flow are divided into bell-shaped type, soap film type, piston type, pVTt type, mt type and standard meter type according to the structural composition. For example, the standard meter type has problems such as limited measurement range, poor repeatability and stability, and high requirements for gas flow rate distribution. Since flow is not a basic physical quantity, but a derived quantity. Gas flow metering devices can be divided into primary standard devices and secondary standard devices according to their accuracy. The primary standard device measures basic quantities (mass, length, time, temperature, pressure, etc.) to calculate the flow value. Therefore, the primary standard generally has a complex structure and is only used in fixed places such as laboratories. The secondary standard device is generally a standard meter device. Based on the principle of the continuity equation of fluid mechanics, the fluid continuously passes through the calibrated flow meter and the standard flow meter, and the technical indicators of the calibrated flow meter are obtained by comparison.

[0042] The present application belongs to a secondary standard device. Through the arrangement of the air inlet pipe 110, the stagnation container 120, the sonic nozzle 130, the collecting container 140 and the exhaust pipe 160, the main part of the gas mass flow detection can be formed between the gas source and the flow metering device to be detected. The stagnation container 120 and the collecting container 140 provide a buffer and airflow space when the gas source enters and exits the multiple sonic nozzles 130. Through a pressure measuring piece 171, a temperature measuring piece 174 and a humidity measuring piece 176, the pressure, temperature and humidity upstream of the sonic nozzle 130 can be determined; through a pressure measuring piece 172, the pressure, temperature and humidity upstream of the sonic nozzle 130 can be determined. The pressure downstream of the sonic nozzle 130 is determined, reducing the number of measuring devices and simplifying the structure. Pressure measuring device 1 171, temperature measuring device 1 174, and humidity measuring device 176 are used to detect pressure P0, temperature T0, and humidity RH upstream of the sonic nozzle 130, while pressure measuring device 2 172 is used to detect pressure P downstream of the sonic nozzle 130. These four parameters can then be substituted into the critical flow state formula to determine whether the sonic nozzle 130 is in a critical state, allowing subsequent calculations to determine the gas mass flow rate. This is a conventional method for determining the critical state using the critical flow state formula. This device can directly utilize an on-site gas source for convenient and quick measurement, solving the problem of on-site calibration of gas mass flow metering devices and ensuring accurate flow values for such equipment. The device can also be used under laboratory conditions.

[0043] The present application is used to calibrate gas mass flow meters. It is relatively convenient and quick, which is also reflected in its portability. Taking the product actually manufactured and used by the applicant as an example, the weight of the calibration device is less than 28 kg and the dimensions are 650 mm × 482 mm × 198 mm. With the calibration device of the present application, the user no longer needs to return the flow meter to the laboratory for measurement. As long as the gas source can be provided on site, the on-site measurement of the flow meter can be completed using this device. Therefore, the device is more convenient and efficient than the traditional traceability method. At the same time, the device can also be used in the laboratory. Compared with the mainstream gas flow standard device, the device has the advantages of small footprint, high accuracy, good stability and repeatability. In order to further reduce the weight and volume of the device, the stagnation container 120, the collecting container 140 and the connecting pipeline of the calibrated gas flow meter (the measuring component includes a set of pressure measurement, temperature measurement and humidity measurement devices) are designed in an integrated modular manner, and finally a standard module of the sonic nozzle 130 device is formed.

[0044] Please refer to Figure 2In some embodiments, the measurement assembly 170 further includes a third pressure measuring element 173. This pressure measuring element 173 can also be a pressure transmitter, pressure sensor, or the like. The third pressure measuring element 173 is connected to the exhaust pipe 160. Since the exhaust pipe 160 is connected to the flow metering device to be tested, the third pressure measuring element 173 is used to detect the pressure P1 before the flow metering device enters the test device. In some embodiments, the measurement assembly 170 further includes a second temperature measuring element 175. The second temperature measuring element 175 is connected to the exhaust pipe 160 and is used to detect the temperature T1 before the flow metering device enters the test device. The arrangement of the first pressure measuring element 171, the second pressure measuring element 172, the third pressure measuring element 173, the first temperature measuring element 174, the second temperature measuring element 175, and the humidity measuring element 176 is similar to the arrangement of conventional measuring instruments installed on a pipeline.

[0045] In this application, it is necessary to measure the pressure, temperature, humidity at the inlet of each sonic nozzle 130, the pressure downstream of each sonic nozzle 130, and the temperature and pressure at the inlet of the calibrated gas mass flowmeter. The pressure P0, temperature T0 and humidity RH upstream of each sonic nozzle 130 can be measured by the pressure measuring component 171, the temperature measuring component 174 and the humidity measuring component 176, and the pressure P downstream of the sonic nozzle 130 can be measured by the pressure measuring component 2 172. In this way, the formula for the critical flow state can be used to determine whether the sonic nozzle 130 has reached the critical flow state. This formula is existing; and this application uses the pressure measuring component 2 172, the pressure measuring component 3 173 and the temperature measuring component 2 175 to measure the pressure P1 and temperature T1 at the front end of the gas flowmeter to be inspected for conversion between operating flow rate and standard flow rate.

[0046] In some embodiments, the system further includes multiple downstream pipes 150. Each downstream pipe 150 is a conventional pipe, with one end connected to the downstream end of the sonic nozzle 130 and the other end connected to the inlet of the manifold 140. The two ends of the downstream pipe 150 respectively connect the downstream end and the manifold 140. The downstream pipes 150 are arranged in a one-to-one correspondence with the sonic nozzles 130, that is, each downstream pipe 150 corresponds to a sonic nozzle 130. In some embodiments, the system further includes multiple branch valves 182. Each branch valve 182 is a conventional valve 180, such as a ball valve. The branch valves 182 are arranged on the downstream pipes 150. The number of branch valves 182 corresponds to the number of sonic nozzles 130, that is, one branch valve 182 controls the airflow through one sonic nozzle 130.

[0047] In some embodiments, the valve 180 may be a manual valve, an electric valve, or a pneumatic valve, for example, the pressure regulating valve 181 may be a manual valve, the branch valve 182 may be a ball valve, an electric valve, or a pneumatic valve, and each valve 180 may be set separately.

[0048] Please refer to Figure 3In some embodiments, an electrical device portion 200 is further included. The electrical device portion 200 is combined with the pipe device portion 100 to form the present device. The electrical device portion 200 includes a data acquisition component 220. The data acquisition component 220 is electrically connected to the pressure measuring component 1 171, the pressure measuring component 2 172, the pressure measuring component 3 173, the temperature measuring component 1 174, the temperature measuring component 2 175, and the humidity measuring component 176, respectively, and is used to collect pressure P0, P, P1, temperature T0, T1 and humidity RH data. The data acquisition component 220 is then electrically connected to a terminal device. The terminal device can receive data from the data acquisition component 220 and use it for analysis and judgment, and is configured with a display for displaying data and results. The data acquisition component 220 can use a 16-channel data acquisition card to collect the analog output of each measuring component 170. Corresponding software can also be compiled in the data acquisition card to calculate the automatic collection of standard flow under standard conditions. In some embodiments, the electrical device portion 200 further includes a power module, which is used to power a data acquisition card and a measurement component 170 for measuring pressure, temperature, and humidity. In this application, the power module and the data acquisition card can also be combined together to form a power supply and data acquisition box, and the box can be used to package the power module and the data acquisition card into one.

[0049] In some embodiments, the data acquisition component 220 has a built-in method for calculating the gas mass flow rate under the critical state of the sonic nozzle 130. When the gas source contains CO2 and water vapor, the gas mass flow rate is:

[0050]

[0051] Where q m,atmos is the corrected mass flow rate, kg / s; is the mole fraction of CO2 in the air. If unknown, it is determined as 0.0004. RH is the relative humidity. A and B are both intermediate calculation parameters, A=0.127828τ 3 -0.789422τ 2 +1.63166τ-1.12818, B=-0.000288749π 2 -0.00191022π+0.00569536-0.0719995π -1 , p c is the critical pressure parameter, 3.786MPa; T c is the critical temperature parameter, 132.5306K.

[0052] The present application may also include a terminal device having a memory, a processor, and software stored in the memory and executable on the processor. The software includes the calculation method described above, and the processor implements the relevant calculation process when executing the computer program in the software. It should be understood that the calculations involved in the various data in the present application can be implemented based on the memory and the processor, each memory being used to store the computer program for executing the above-mentioned method of the present application, and the processor executing the above-mentioned computer program, so that the measurement device / terminal device for calibrating gas mass flow rate implements the methods of the above-mentioned embodiments.

[0053] The calibration device of the present application is used to calibrate the determined gas mass flow meter, in which 6 sonic nozzles 130 are used. Assuming that the standard pressure is 101.325kPa and the standard temperature is 20°C, this device uses 6 sonic nozzles 130, whose critical back pressure ratios are all greater than 0.5, and their throat diameters are designed according to the design requirements and formula (2). The outflow coefficient is obtained according to the traceability certificate, which records the original parameters of the sonic nozzle 130 product. When in use, taking into account the conditions of the on-site gas source, in order to ensure that the sonic nozzle 130 reaches the critical flow state, the upper and lower limits of the pressure at the inlet of the sonic nozzle 130 are set to 250kPa and 600kPa respectively. Under this condition, the volume flow rate of each nozzle in the device is shown in the following table:

[0054] Table 1 Sonic nozzle flow rate table

[0055]

[0056] As can be seen from Table 1, the device adopts the positive pressure method, and by designing the throat diameter of the sonic nozzle 130, adopting different combinations of sonic nozzles 130 and adjusting the upstream stagnation pressure, it can achieve continuous adjustment of any gas flow rate between (0.7 and 90) L / min.

[0057] In a second aspect of the present application, a method for calibrating gas mass flow is provided, which uses the above-mentioned measuring device for calibrating gas mass flow. The calculations involved in the following calibration method can be built into the above-mentioned software. The calibration method includes:

[0058] S1. Determine the calibration point according to the requirements of the measurement technical specifications corresponding to the gas mass flowmeter. According to the principle of the calibration device, connect the gas pipeline and complete the device debugging. Specifically, connect the air inlet pipe 110 to the gas source, connect the exhaust pipe 160 to the flow metering device to be tested, select at least one sonic nozzle 130 to participate in the test, and ensure that the sonic nozzle 130 is connected to the collection container 140. When determining the selection of the sonic nozzle 130, combine Table (1) to select an appropriate nozzle or multiple nozzle combinations, specifically based on the on-site conditions of the measured flow point.

[0059] S2. Open the pressure regulating valve 181, which regulates the pressure within the stagnation vessel 120. Then, open the branch valve 182 corresponding to the selected sonic nozzle 130, allowing gas to flow sequentially through the stagnation vessel 120, the sonic nozzle 130, the collecting vessel 140, the exhaust pipe 160, and the flow metering device to be tested. Adjust the pressure regulating valve 181 until each sonic nozzle 130 is in a critical flow state. The conditions for determining whether each sonic nozzle 130 is in a critical flow state are: temperature T0 meets the critical flow state requirements. Assuming that the upstream pressure of the sonic nozzle 130 remains constant at P0 and the nozzle outlet pressure is P2, when the back pressure ratio (P2 / P0) is less than the critical value, the gas reaches a critical velocity at the throat. Even if the back pressure ratio is further reduced, the flow velocity remains constant. To determine whether a sonic nozzle 130 is in a critical flow state, the pressure display in the software can be observed. The intuitive indicator in the software can be used to confirm whether the sonic nozzle 130 is in a critical flow state.

[0060] S3. After the monitored pressure, temperature, and humidity stabilize, collect the pressure, temperature, and humidity data. Wait for the values of pressure measuring device 171, pressure measuring device 2, temperature measuring device 172, temperature measuring device 174, temperature measuring device 2, and humidity measuring device 176 to stabilize and no longer change. Then, collect the pressure, temperature, and humidity data and calculate the standard flow rate. This calculation can be determined using the gas mass flow rate formula when the sonic nozzle 130 is in the critical flow state. This completes the calibration of the first calibration point. The pressure in stagnation vessel 120 is then adjusted sequentially, and the appropriate sonic nozzle 130 is reselected. Steps S2-S3 are repeated to complete the calibration of all subsequent calibration points.

[0061] The calibration method of the prior art is, on the one hand, inconvenient to operate due to the large size of the calibration device, and on the other hand, the calibration operation of the relatively small calibration device is relatively cumbersome due to the complex pipeline structure and the large number of detection devices. The present application adopts the above-mentioned calibration device, which adjusts the pressure in the stagnation container 120 by opening the regulating valve, and adjusts the airflow through the regulating valve. Each sonic nozzle 130 is in a critical flow state, and the pressure and temperature values measured in the critical flow state can be substituted into the calculation formula of the standard flow to obtain the result of the gas mass flow rate. It is only necessary to make the sonic nozzle 130 reach the critical state, and the flow flowing through the nozzle will not be affected by the downstream pressure. Moreover, in terms of small flow measurement, the repeatability and stability of the sonic nozzle 130 are unmatched by other flow meters. It has the characteristics of simple structure, stable performance, high accuracy, no moving parts, long traceability cycle, and easy maintenance.

[0062] In some embodiments, the standard flow rate is calculated using a gas mass flow rate calculation formula when the sonic nozzle 130 is in a critical flow state, where the critical mass flow rate q flowing through the sonic nozzle 130 under actual conditions is m It can be calculated by formula (2):

[0063]

[0064] Where q m is the mass flow rate, kg / s; A nt is the cross-sectional area of the nozzle throat, m 2 ; C d' is the outflow coefficient, which is 1; C * is the critical flow function of the actual gas, 1; P0 is the absolute stagnation pressure of the gas at the nozzle inlet, Pa; R is the universal gas constant, J / (mol×kg); M is the molar mass, kg / mol; T0 is the stagnation temperature of the gas at the nozzle inlet, K.

[0065] According to formula (2), it is only necessary to put the sonic nozzle 130 in a critical flow state. By measuring the pressure (P0), temperature (T0) at the inlet of the sonic nozzle 130, and the throat diameter and outflow coefficient related to the sonic nozzle 130, the gas mass flow rate through the sonic nozzle 130 can be accurately calculated. The gas mass flow rate q calculated by formula (2) is m is the mass flow rate of dry air excluding CO2. In the actual use conditions of this application, the gas source contains CO2 and water vapor, which can be determined according to formula (1).

[0066] The sonic nozzle 130 is the main standard of the portable gas mass flowmeter calibration device. When calibrating the gas mass flowmeter, one or more parallel sonic nozzles 130 are required to obtain flow points that meet the calibration requirements. The key design of the sonic nozzle 130 is how to select a relatively small number of sonic nozzles 130 to meet the flow regulation of the calibration point and achieve continuous adjustment within the measurement range. The key parameter of the sonic nozzle 130 is the throat diameter. According to GB / T21188-2007 "Gas Flow Measurement Using Critical Flow Venturi Nozzles" and formula (2), the throat diameter d of the sonic nozzle 130 can be calculated according to formula (3):

[0067]

[0068] The displayed value of the gas mass flow meter is generally the volume flow rate q under certain temperature and pressure conditions (standard conditions). L To calibrate the gas mass flowmeter, the mass flow calculated by formula (2) needs to be converted to the volume flow under standard conditions. The volume flow under standard conditions is calculated according to the following formula:

[0069]

[0070] Where q L is the volume flow rate under standard conditions; L / min; ρ ɑis the air density under standard conditions, m 3 / kg; the air density under standard conditions is calculated according to formula (5):

[0071]

[0072] Where p is the standard pressure, kPa; RH is the relative humidity; t is the standard temperature, °C.

[0073] The following is a calibration test of a certain type of gas mass flow meter. The calibration device of this application is used and the calibration method is referred to. The implementation steps of the calibration are as follows:

[0074] A1. Based on the principles of the calibration device, connect the flowmeter to be calibrated and preheat the device. Adjust the gas flow rate to 8-10 L / min and allow it to flow for at least 5 minutes until the gas temperature, pressure, and flow rate stabilize. According to the regulations, select 1 L / min, 2 L / min, 5 L / min, and 10 L / min as calibration points.

[0075] A2. When calibrating at 1 L / min, use a sonic nozzle 130 with a throat diameter of 0.179 mm. Use precision pressure regulating valve 181 to adjust the internal pressure of stagnation container 120 to a gas flow rate of approximately 1 L / min. Observe the pressure and temperature in the software until the gas stabilizes. Record the stagnation pressure as 378.4 kPa and the stagnation temperature as 20.3°C. At this point, the flowmeter under test displays a value of 0.97 L / min. Software calculations reveal that under standard conditions (pressure of 101.325 kPa and temperature of 0°C), the volumetric flow rate of the standard device is 0.998 L / min. Repeat the above calibration process twice for this calibration point, recording the values of the calibrated flowmeter and the standard device to complete the calibration of the first flow point.

[0076] A3. Adjust the pressure in the stagnation container 120 in sequence, reselect a suitable sonic nozzle 130, and complete the verification of subsequent calibration points according to step A2.

[0077] Where, the reference error E of the flowmeter at the i-th calibration point is i Use the following formula to calculate:

[0078]

[0079] Where, E i is the reference error of the flowmeter at the i-th calibration point; E ij is the reference error of the flowmeter at the jth calibration point i; q ij is the flow meter reading at the i-th calibration point, the j-th time, L / min; (q s ) ij—Indication of the calibration device at the jth calibration point, L / min; q max —The upper measurement limit of the calibrated flowmeter, L / min.

[0080] The repeatability index of the i-th calibration point is calculated using the following formula:

[0081]

[0082] The calibration data of the flow meter calibrated using this device is shown in the following table:

[0083] Table 2 Calibration data table

[0084]

[0085]

[0086] Regarding the specific implementation of this application, it should be noted that:

[0087] In the description of this application, reference to the terms "some embodiments", "optional embodiments", "examples", "specific examples", "optional examples" or "optional embodiments" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of this application, but does not mean that these embodiments illustrate and describe all possible forms of the invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0088] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. The above description is illustrative, not exhaustive, and is not limited to the disclosed embodiments; the above description cannot be understood as a limitation of the present invention. The technical solutions between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by this application. Although the embodiments of the present application have been shown and described, these embodiments can be subjected to various changes, modifications, substitutions and variations without departing from the principles and purposes of the present application. Ordinary technicians in this field can understand that various other specific changes and combinations of embodiments that do not depart from the essence of the present application are made according to the technical inspirations disclosed in this application, and are still within the scope of protection defined by the claims of the present invention and its equivalent technical solutions.

Claims

1. A measuring device for calibrating gas mass flow, characterized in that include: An air inlet pipe (110) is used for communicating with an air source, and the air inlet pipe (110) is provided with a pressure regulating valve (181); a stagnation container (120) in communication with the air inlet pipe (110); A plurality of sonic nozzles (130) are respectively provided in the stagnation container (120), the sonic nozzles (130) having an upstream end and a downstream end, and the plurality of upstream ends are in communication with the interior of the stagnation container (120); a collecting container (140) in communication with the plurality of downstream ends; an exhaust pipe (160) in communication with the collecting container (140) and used for connecting to a flow metering device to be tested and for introducing the gas exhausted from the collecting container (140) therein; A pressure measuring element (171), a temperature measuring element (174), and a humidity measuring element (176), connected to the stagnation container (120), and used to detect the pressure P0, temperature T0, and relative humidity RH upstream of the sonic nozzle (130), respectively; The second pressure measuring device (172) is connected to the collecting container (140) and is used to detect the pressure P downstream of the sonic nozzle (130).

2. The measuring device for calibrating gas mass flow according to claim 1, characterized in that Also includes: The third pressure measuring component (173) is connected to the exhaust pipe (160) and is used to detect the pressure P1 before entering the flow metering device to be tested.

3. The measuring device for calibrating gas mass flow according to claim 2, characterized in that: It also includes a second temperature measuring component (175) connected to the exhaust pipe (160) and used to detect the temperature T1 before entering the flow metering device to be tested.

4. The measuring device for calibrating gas mass flow according to claim 1, characterized in that It also includes a plurality of downstream pipes (150), both ends of which are connected to the downstream end and the collecting container (140), and the arrangement of the downstream pipes (150) corresponds one to one to the sonic nozzles (130).

5. The measuring device for calibrating gas mass flow according to claim 4, characterized in that: It also includes a plurality of branch valves (182) disposed on the downstream pipe (150), wherein the number of the branch valves (182) corresponds to the number of the sonic nozzles (130).

6. The measuring device for calibrating gas mass flow according to claim 1, characterized in that The device further comprises a data acquisition component (220), wherein the data acquisition component (220) is electrically connected to the first pressure measuring component (171), the second pressure measuring component (172), the first temperature measuring component (174) and the humidity measuring component (176), respectively, and is used to collect pressure, temperature and humidity data.

7. The measuring device for calibrating gas mass flow according to claim 6, characterized in that: The data acquisition component (220) is also electrically connected to the third pressure measuring component (173) and the second temperature measuring component (175), and is used to collect pressure and temperature data.

8. The measuring device for calibrating gas mass flow according to claim 7, characterized in that: The data acquisition component (220) has a built-in gas mass flow calculation method for the sonic nozzle (130) under the critical state. When the gas source contains CO2 and water vapor, the gas mass flow is: Where q m,atmos is the corrected mass flow rate, kg / s; is the mole fraction of CO2 in the air. If unknown, it is determined as 0.0004. RH is the relative humidity. A and B are both intermediate calculation parameters. A=0.127828τ 3 -0.789422t 2 +1.63166t-1.12818, B＝-0.000288749π 2 -0.00191022π+0.00569536-0.0719995π -1 ， p c is the critical pressure parameter, 3.786MPa; T c is the critical temperature parameter, 132.5306K.

9. A gas mass flow calibration method, characterized in that: Using the measuring device for calibrating gas mass flow according to any one of claims 1 to 8, the calibration method includes: Connecting the air inlet pipe (110) to an air source, connecting the air outlet pipe (160) to a flow metering device to be tested, selecting at least one sonic nozzle (130) to participate in the test, and ensuring that the sonic nozzle (130) is connected to the collecting container (140); Opening the pressure regulating valve (181) to allow the gas to flow sequentially through the stagnation container (120), the sonic nozzle (130), the collecting container (140), the exhaust pipe (160), and the flow metering device to be inspected, and adjusting the pressure regulating valve (181) until each of the sonic nozzles (130) is in a critical flow state; After the monitored pressure, temperature and humidity are stable, collect the pressure, temperature and humidity data and calculate the standard flow rate.

10. The gas mass flow calibration method according to claim 9, characterized in that: The standard flow rate is calculated using a gas mass flow rate calculation formula when the sonic nozzle (130) is in a critical flow state.

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