Dynamic pVTt flow standard device based on instantaneous temperature field prediction of spherical cavity

Abstract

The invention relates to the technical field of gas flow metering, and discloses a dynamic pVTt flow standard device based on the prediction of the instantaneous temperature field of a spherical cavity, comprising a spherical cavity, a vent pipe, a diffusion joint, a plurality of temperature measuring units and a pressure measuring unit. The vent pipe is connected to the spherical cavity, the vent pipe is used for external gas to flow into the spherical cavity or for internal gas of the spherical cavity to flow out, one end of the vent pipe is exposed to the spherical cavity, a vent is formed at the other end of the vent pipe, the diffusion joint is fixedly connected to the vent, the diffusion joint is used for making the gas evenly enter or evenly discharge the spherical cavity so that the internal temperature of the spherical cavity changes in layers along the radial direction, the temperature measuring units are distributed along the length direction of the vent pipe and are used for measuring the gas temperature, the pressure measuring unit is arranged on the inner wall of the spherical cavity and is used for detecting the gas pressure, and is used for realizing fast and accurate measurement of the internal temperature of the standard cavity, thereby improving the efficiency and accuracy of flow detection.

Description

Technical Field

[0001] The invention relates to the technical field of gas flow measurement, and in particular to a dynamic pVTt flow standard device based on instantaneous temperature field prediction of a spherical cavity. Background Art

[0002] A flow standard device refers to a measuring device that can provide accurate flow values, and it is the basis of flow measurement. The pVTt method gas flow standard device is an important primary gas flow standard device, which has the advantages of high device accuracy, simple and easy maintenance, and low requirements for gas source pressure. The pVTt method determines the mass flow rate by measuring the gas pressure p, temperature T, and time t inside the standard container (volume V) before and after inflation (exhaustion). Therefore, as long as the volume of the standard container is accurately calibrated and high-precision temperature and pressure measurement equipment is used, a higher accuracy can be achieved in theory.

[0003] Improving the measurement accuracy of the temperature T and pressure p in the standard container is one of the keys to ensure that the pVTt method device achieves high accuracy. However, in practical applications, after the pVTt method device is inflated (exhausted), the temperature and pressure distribution of the gas inside the cavity are not uniform, which increases the difficulty of measurement. Among them, the change in pressure propagates faster, and the use of a pressure sensor with higher accuracy and stability can meet the design requirements of the device. However, temperature is a slow variable, and the temperature field needs to wait for a long process to reach a stable state, which not only makes the verification efficiency of this method low, but also increases the uncertainty of the measurement results.

[0004] In order to improve the accuracy of temperature measurement results and the efficiency of verification, some existing research methods attempt to make the temperature field inside the cavity reach a stable and uniform state in a shorter time. For example, the standard container is placed in a constant temperature bath and cooled in a water bath or oil bath, or a fan is installed inside to allow the gas to flow fully. However, the above methods still require waiting for a certain period of time for the inside of the container to stabilize, and the waiting time is unstable, so the measurement efficiency cannot be guaranteed. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a dynamic pVTt flow standard device based on the prediction of the instantaneous temperature field of a spherical cavity, which is used to quickly and accurately measure the internal temperature of the standard cavity, thereby improving the efficiency and accuracy of flow detection.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A dynamic pVTt flow standard device based on the prediction of the instantaneous temperature field of a spherical cavity, comprising:

[0008] Spherical cavity,

[0009] A vent pipe is connected to the spherical cavity, the vent pipe allows external gas to flow into the spherical cavity or allows internal gas of the spherical cavity to flow out, one end of the vent pipe is exposed to the spherical cavity, and the other end of the vent pipe is formed with a vent,

[0010] A diffusion joint, the diffusion joint is fixedly connected to the vent, and the diffusion joint is used to allow gas to enter or exit the spherical cavity evenly so that the temperature inside the spherical cavity changes in layers along the radial direction.

[0011] A plurality of temperature measuring units, which are distributed along the length of the ventilation pipe and are used to measure the gas temperature.

[0012] A pressure measuring unit is arranged on the inner wall of the spherical cavity and is used to detect the gas pressure.

[0013] Furthermore, the shape of the diffusion joint is set to be spherical, and the center of the diffusion joint coincides with the center of the spherical cavity. A plurality of exhaust ports are distributed on the surface of the diffusion joint. The interior of the diffusion joint is filled with a porous structural material, and the exterior of the diffusion joint is covered with a sponge sleeve.

[0014] Furthermore, the dynamic pVTt flow standard device is equipped with an average temperature calculation strategy, and the average temperature calculation strategy specifically includes the following formula:

[0015] ,

[0016] ,

[0017] Among them, r represents the distance from the temperature measuring unit to the center of the spherical cavity, The temperature values ​​measured by multiple measurement units are fitted. represents the temperature at a distance r from the center of the spherical cavity at time t, represents the average temperature inside the spherical cavity at time t, R represents the inner diameter of the spherical cavity, d is the differential symbol of the integral formula, and dr represents taking r as the integral variable.

[0018] Furthermore, considering the influence of the vent pipe and diffusion joint inside the cavity on the volume, the average temperature calculation strategy is modified to obtain the modified average temperature formula:

[0019] ,

[0020] Where R1 is the inner diameter of the spherical cavity, R2 is the outer diameter of the diffusion joint, and R3 is the outer diameter of the vent pipe. In this formula, d is the differential symbol of the integral formula, and dr means taking r as the integral variable.

[0021] Furthermore, the dynamic pVTt flow standard device is equipped with a gas mass flow calculation strategy, and the gas mass flow calculation strategy includes the following formula:

[0022] ,

[0023] ,

[0024] Where m represents the mass of the gas inside the cavity at a certain moment, p represents the gas pressure inside the spherical cavity, T represents the temperature inside the spherical cavity, and V represents the volume of the spherical cavity. It indicates the change in the gas mass inside the cavity between the two moments of gas mass flow detection. Represents the time difference used for gas mass flow detection, R g represents the gas constant of the gas used in the spherical cavity; q represents the calculated gas mass flow rate, t1 and t2 are the two moments for gas mass flow rate detection, p1 represents the gas pressure inside the spherical cavity at moment t1, p2 represents the gas pressure inside the spherical cavity at moment t2, T ave,t1 represents the average temperature inside the spherical cavity calculated at time t1, T ave,t2 represents the average temperature inside the spherical cavity calculated at time t2.

[0025] Beneficial effects of the present invention:

[0026] The present invention arranges a spherical cavity and a diffusion joint, and during the inflation process, the gas diffuses uniformly from the center of the sphere to the inside of the spherical cavity, so that the temperature field in the spherical cavity presents a specific distribution law, specifically, the temperature changes in layers with the distance from the center of the sphere, and a plurality of temperature measuring units are arranged in the radial direction at the same time, and the average temperature inside the spherical cavity is estimated according to the plurality of temperature measuring units. During the calibration process, the gas mass inside the spherical cavity can be calculated according to the gas pressure p inside the spherical cavity measured at a certain moment, the temperature T inside the spherical cavity and the volume V of the spherical cavity, and the gas mass flow rate flowing through the time period between the two moments can be calculated by arbitrarily selecting the measurement results at two moments. The measurement process is simple, and the flow calculation can be completed during the intake process without waiting for the temperature field to be stable, and the measurement efficiency is high. By integrating the measurement results of multiple time periods, a more stable calculation result can be obtained, and the calculation result is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0028] Figure 2 is a schematic diagram of the cross-sectional structure of the diffusion joint in the present invention;

[0029] Figure 3 It is a schematic diagram of the temperature distribution inside the spherical cavity in the present invention;

[0030] Figure 4 It is a distribution diagram of the temperature measuring unit and the pressure measuring unit in the present invention.

[0031] Figure numerals: 1, spherical cavity; 2, ventilation pipe; 3, diffusion joint; 301, exhaust port; 31, sponge cover; 32, porous material; 33, threaded interface; 4, temperature measuring unit; 5, pressure measuring unit. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may also be a component centered. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may also be a component centered. When a component is considered to be "set on" another component, it may be directly set on the other component or there may also be a component centered. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0035] like Figure 1-Figure 4 As shown, a dynamic pVTt flow standard device based on the instantaneous temperature field prediction of a spherical cavity in this embodiment includes a spherical cavity 1, a vent pipe 2, a diffusion joint 3, a plurality of temperature measuring units 4 and a pressure measuring unit 5.

[0036] See also Figure 1 The ventilation pipe 2 is connected to the spherical cavity 1, and the ventilation pipe 2 allows external gas to flow into the spherical cavity 1 or allows internal gas of the spherical cavity 1 to flow out. One end of the ventilation pipe 2 is exposed to the spherical cavity 1, and a ventilation port is formed at the other end of the ventilation pipe 2.

[0037] See also Figure 2 , the diffusion joint 3 is fixedly connected to the vent, and the diffusion joint 3 is used to make the gas enter or discharge the spherical cavity 1 evenly so that the temperature inside the spherical cavity 1 changes in layers along the radial direction. The shape of the diffusion joint 3 is set to be spherical, and the center of the diffusion joint 3 coincides with the center of the spherical cavity 1. A threaded interface is formed on the diffusion joint 3, so that the diffusion joint 3 is threadedly connected to the vent pipe 2. The threaded connection is convenient for controlling the installation position between the vent pipe 2 and the spherical joint, and has good sealing performance. There are multiple exhaust ports 301 distributed on the surface of the diffusion joint, and the exhaust ports 301 are evenly distributed. In addition, the interior of the diffusion joint 3 is filled with a porous structural material, and the exterior of the diffusion joint 3 is covered with a sponge cover. The setting of the spherical joint is used to make the gas diffuse evenly. The porous structural material and the sponge cover can both play a role in reducing the initial velocity of the gas, thereby causing the initial velocity of the gas to approach 0 when entering the spherical cavity 1, reducing the influence of the initial velocity of the airflow on the detection results, and causing the temperature field inside the spherical cavity 1 to be distributed according to the expected conditions. Inside the spherical cavity 1, part of the kinetic energy of the gas will be converted into thermal energy, causing the temperature field to change. When the gas velocity field satisfies the uniform distribution, its temperature field also conforms to the ideal layered distribution characteristics, that is, the temperature at the same radius in all directions is approximately the same. Figure 3 As shown, points with equal distances from the center of the sphere are regarded as isothermal layers, and the temperature values ​​of points on the same isothermal layer are regarded as the same.

[0038] like Figure 4 As shown, the temperature measuring unit 4 is distributed along the length direction of the ventilation pipe 2 and is used to measure the gas temperature, and the pressure measuring unit 5 is arranged on the inner wall of the spherical cavity 1 and is used to detect the gas pressure. Further, the dynamic pVTt flow standard device is equipped with an average temperature calculation strategy, which specifically includes the following formula:

[0039] ,

[0040] ,

[0041] Among them, r represents the distance from the temperature measuring unit to the center of the spherical cavity, The temperature values ​​measured by multiple measurement units are fitted. represents the temperature at a distance r from the center of the spherical cavity at time t, represents the average temperature inside the spherical cavity at time t, R represents the inner diameter of the spherical cavity, and d is the differential symbol of the integral formula. As the integrand, dr means taking r as the integration variable.

[0042] Furthermore, considering the influence of the vent pipe and diffusion joint inside the cavity on the volume, the average temperature calculation strategy is modified to obtain the modified average temperature formula:

[0043] ,

[0044] Where R1 is the inner diameter of the spherical cavity, R2 is the outer diameter of the diffusion joint, R3 is the outer diameter of the vent pipe, and d is the differential symbol of the integral formula. As the integrand, dr means taking r as the integration variable.

[0045] Furthermore, the dynamic pVTt flow standard device is equipped with a gas mass flow calculation strategy, which includes the following formula:

[0046] ,

[0047] ,

[0048] Where m represents the mass of the gas inside the cavity at a certain moment, p represents the gas pressure inside the spherical cavity, T represents the temperature inside the spherical cavity, and V represents the volume of the spherical cavity. It indicates the change in the gas mass inside the cavity between the two moments of gas mass flow detection. Represents the time difference used for gas mass flow detection, R g represents the gas constant of the gas used in the spherical cavity; q represents the calculated gas mass flow rate, t1 and t2 are the two moments for gas mass flow rate detection, p1 represents the gas pressure inside the spherical cavity at moment t1, p2 represents the gas pressure inside the spherical cavity at moment t2, T ave,t1 represents the average temperature inside the spherical cavity calculated at time t1, T ave,t2 represents the average temperature inside the spherical cavity calculated at time t2.

[0049] Working principle:

[0050] The present application sets a diffusion joint 3 inside the spherical cavity 1 by setting a spherical cavity 1, so that the gas can enter the spherical cavity 1 with an initial velocity of nearly 0, so that the gas diffuses evenly. Part of the kinetic energy of the gas will be converted into thermal energy, causing the temperature field to change, and the temperature field conforms to the ideal layered distribution characteristics, so as to estimate the average temperature inside the spherical cavity 1. Then, by selecting different measurement times, the two measurement times are used to calculate , and calculate the gas mass flow rate q, and the measurement time can be selected during the intake process for calculation, with high measurement efficiency and accuracy, and by integrating the measurement results of multiple time periods, a more stable calculation result can be obtained.

[0051] The above are only preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A dynamic pVTt flow standard device based on the prediction of the instantaneous temperature field of a spherical cavity, characterized by: include Spherical cavity (1), a vent pipe (2), the vent pipe (2) being in communication with the spherical cavity (1), the vent pipe (2) allowing external gas to flow into the spherical cavity (1) or allowing internal gas of the spherical cavity (1) to flow out, one end of the vent pipe (2) being exposed to the outside of the spherical cavity (1), and the other end of the vent pipe (2) being formed with a vent, A diffusion joint (3), the diffusion joint (3) being fixedly connected to the vent, the diffusion joint (3) being used to allow gas to enter or be discharged uniformly from the spherical cavity (1) so that the temperature inside the spherical cavity (1) changes in layers along the radial direction, the shape of the diffusion joint (3) being set to be spherical, and the center of the diffusion joint (3) coincides with the center of the spherical cavity (1), a plurality of exhaust ports (301) are distributed on the surface of the diffusion joint (3), the interior of the diffusion joint (3) is filled with a porous structural material, and the exterior of the diffusion joint (3) is covered with a sponge sleeve, a plurality of temperature measuring units (4), wherein the temperature measuring units (4) are distributed along the length direction of the ventilation pipe (2) and are used to measure the gas temperature, A pressure measuring unit (5) is arranged on the inner wall of the spherical cavity (1) and is used to detect gas pressure.

2. The dynamic pVTt flow standard device based on the prediction of the instantaneous temperature field of the spherical cavity according to claim 1 is characterized in that: The dynamic pVTt flow standard device is equipped with an average temperature calculation strategy, which specifically includes the following formula: ， ， Among them, r represents the distance from the temperature measuring unit to the center of the spherical cavity, The temperature values ​​measured by multiple measurement units are fitted. represents the temperature at a distance r from the center of the spherical cavity at time t, represents the average temperature inside the spherical cavity at time t, R represents the inner diameter of the spherical cavity, d is the differential symbol of the integral formula, and dr represents taking r as the integral variable.

3. The dynamic pVTt flow standard device based on the prediction of the instantaneous temperature field of the spherical cavity according to claim 2 is characterized in that: Taking into account the influence of the vent pipe and diffusion joint inside the cavity on the volume, the average temperature calculation strategy is modified to obtain the modified average temperature formula: ， Where R1 is the inner diameter of the spherical cavity, R2 is the outer diameter of the diffusion joint, and R3 is the outer diameter of the vent pipe. In this formula, d is the differential symbol of the integral formula, and dr means taking r as the integral variable.

4. The dynamic pVTt flow standard device based on the prediction of the instantaneous temperature field of the spherical cavity according to claim 3 is characterized in that: The dynamic pVTt flow standard device is equipped with a gas mass flow calculation strategy, which includes the following formula: ， ， Where m represents the mass of the gas inside the cavity at a certain moment, p represents the gas pressure inside the spherical cavity, T represents the temperature inside the spherical cavity, and V represents the volume of the spherical cavity. It indicates the change in the gas mass inside the cavity between the two moments of gas mass flow detection. Represents the time difference used for gas mass flow detection, R g represents the gas constant of the gas used in the spherical cavity; q represents the calculated gas mass flow rate, t1 and t2 are the two moments for gas mass flow rate detection, p1 represents the gas pressure inside the spherical cavity at moment t1, p2 represents the gas pressure inside the spherical cavity at moment t2, T ave,t1 represents the average temperature inside the spherical cavity calculated at time t1, T ave,t2 represents the average temperature inside the spherical cavity calculated at time t2.

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