A dynamic measurement method and system based on parallel differential pressure analysis

Abstract

The application provides a dynamic measurement method and system based on parallel differential pressure analysis, and relates to the technical field of gas-liquid mass transfer measurement. The method adopts a measurement unit and a control unit in parallel, a first closed container of the measurement unit containing liquid and gas, and the initial volume of the gas phase in a second closed container of the control unit being the same as the volume of the gas in the first closed container. After the pressure of the two containers is synchronously and suddenly increased to the initial pressure P0 by synchronous pressure excitation, the system is closed, and the pressure decay curves P1(t) and P2(t) in the two containers are synchronously collected. After differential processing, the influence of system leakage is eliminated, and the net pressure decay curve ΔP(t) is obtained. Based on the ideal gas state equation, the change amount of the dissolved gas mass with time is inversed, and the dissolution kinetics data are obtained. The application can dynamically and accurately measure the gas dissolution process, effectively eliminates the leakage interference, and provides key dissolution kinetics data for gas-liquid mass transfer engineering.

Description

Technical Field

[0001] This invention relates to the field of gas-liquid mass transfer measurement technology, and in particular to a dynamic measurement method and system based on parallel differential pressure analysis. Background Technology

[0002] The dissolution of gases in liquids is a widespread phenomenon in energy, chemical, and environmental engineering fields, such as compressed air energy storage systems, liquid piston compression systems, and gas-liquid reaction devices. In these systems, gas dissolution not only affects system efficiency but also causes gas loss.

[0003] In existing technologies, gas solubility is typically measured based on the principle of thermodynamic equilibrium, such as using Henry's law to determine solubility by measuring the gas concentration or pressure at equilibrium. However, this type of method has the following main problems: (1) It can only obtain steady-state solubility and cannot reflect the dynamic process of gas dissolution; (2) It is difficult to capture rapid dissolution behavior within a short timescale; (3) During the measurement process, both gas leakage and gas dissolution will cause pressure changes, making it difficult to distinguish the effects of the two. (4) It is difficult to directly measure the mass of dissolved gas, and the measurement accuracy is low.

[0004] Therefore, it is necessary to provide a novel measuring device and method that can realize dynamic measurement of gas dissolution and eliminate the effects of system leakage. Summary of the Invention

[0005] This invention proposes a dynamic measurement method and system based on parallel differential pressure analysis, aiming to solve the problems of existing technologies where gas solubility measurement is limited to static equilibrium, cannot distinguish between dissolution and leakage, is difficult to capture rapid dissolution behavior within a short time scale, and has low measurement accuracy.

[0006] Firstly, a dynamic measurement method based on parallel differential pressure analysis is provided, which employs a measurement system including a measurement unit and a control unit to perform the following steps: System preparation steps: Inject a predetermined volume of liquid into the first sealed container; and close the first control valve and the second control valve; then start the first gas source and the second gas source and the data acquisition and processing unit; and then store the gas from the first gas source and the second gas source in the first gas storage tank and the second gas storage tank respectively through the first gas source regulator and the second gas source regulator. Synchronous pressure excitation steps: Gas is synchronously introduced into the first sealed container of the measuring unit and the second sealed container of the control unit. The first control valve and the second control valve are synchronously opened, so that the gas from the first gas storage tank and the second gas storage tank rush into the first sealed container and the second sealed container respectively within a millisecond time. When the first high-frequency pressure sensor and the second high-frequency pressure sensor detect that the pressure in both containers has reached and stabilized at the preset initial pressure P0, the first control valve and the second control valve are immediately and synchronously closed, so that the two containers form an independent closed system. The first sealed container contains a predetermined volume of liquid and gas, and the initial volume of the gas phase in the second sealed container is the same as the volume of gas in the first container. Synchronous attenuation monitoring steps: The data acquisition and processing unit begins to synchronously acquire the first attenuation curve P1(t) of the gas pressure change over time in the first sealed container and the second attenuation curve P2(t) of the gas pressure change over time in the second sealed container. The differential and inversion calculation steps are as follows: Subtract the second attenuation curve P2(t) from the first attenuation curve P1(t) to obtain the net pressure attenuation curve ΔP(t) after eliminating the influence of system leakage; Based on the ideal gas law, ΔP(t) is converted into the change in gas mass lost due to gas dissolution in the first closed container over time, Δm(t), to obtain the dynamic dissolution amount and dissolution kinetics data of the gas in the liquid.

[0007] Furthermore, the second sealed container of the control unit is an empty container, the geometric volume of which is equal to the gas volume in the first sealed container, and the initial gas phase volume of which is equal to its geometric volume.

[0008] Furthermore, the second sealed container of the control unit is provided with a flexible airbag, which is filled with gas and has a liquid on its outside; the gas volume in the flexible airbag is equal to the gas volume in the first sealed container, and the geometric volume of the second sealed container is not less than the gas volume in the flexible airbag.

[0009] Furthermore, a separator structure is provided at the gas-liquid interface within the first sealed container of the measuring unit.

[0010] Furthermore, in the synchronous pressure excitation step, the first control valve and the second control valve located in the gas circuit are controlled to open and close synchronously. The control valve is a solenoid valve or a piezoelectric ceramic valve, and the opening time is in the millisecond range.

[0011] Furthermore, the first attenuation curve P1(t) and the second attenuation curve P2(t) are acquired by a high-frequency dynamic pressure sensor with a response frequency of not less than 500Hz.

[0012] Furthermore, Δm(t) in the difference and inversion calculation steps is calculated using the following formula: Δm(t) = ΔP(t) * V / (R * T); Where V is the initial volume of the gas phase in the first sealed container, m is the gas mass, R is the ideal gas constant, and T is the thermodynamic temperature of the system.

[0013] Furthermore, the differential and inversion calculation steps also include: fitting the curve of the net pressure decay curve ΔP(t) or the curve of the gas mass change Δm(t) over time to extract the time constant, initial dissolution rate and final equilibrium dissolution amount of the gas dissolution process.

[0014] Secondly, the present invention also provides a dynamic measurement system based on parallel differential pressure analysis for implementing the above method. The dynamic measurement system includes a measurement unit, a control unit, and a data acquisition and processing unit.

[0015] The measuring unit includes a first sealed container, a first gas source connected to the first sealed container, a first control valve disposed in the connected gas path, and a first high-frequency pressure sensor disposed on the first sealed container. The first sealed container contains a predetermined volume of liquid and gas.

[0016] The control unit includes a second sealed container, a second gas source connected to the second sealed container, a second control valve disposed in the connected gas path, and a second high-frequency pressure sensor disposed on the second sealed container. The initial gas volume in the second sealed container is the same as the gas volume in the first sealed container.

[0017] The data acquisition and processing unit is connected to the signals of the first high-frequency pressure sensor and the second high-frequency pressure sensor.

[0018] Furthermore, the second sealed container of the control unit is an empty container, and its geometric volume is equal to the gas volume in the first sealed container; or, the second sealed container of the control unit is provided with a flexible airbag, the gas volume in the flexible airbag is equal to the gas volume in the first sealed container, and the geometric volume of the second sealed container is not less than the gas volume; the first sealed container of the measuring unit is also provided with a separator structure at the gas-liquid interface.

[0019] Compared with the prior art, the present invention has the following advantages: 1. Achieving dynamic measurement of gas dissolution process: Unlike traditional static methods that can only obtain equilibrium solubility, this invention can continuously and in real time record the entire process of gas dissolution in liquid, including dissolution behavior in the unsteady state stage, providing complete data support for the study of dissolution kinetics.

[0020] 2. High time resolution: Employing a millisecond-level synchronous control valve and a high-frequency dynamic pressure sensor with a response frequency of no less than 500Hz, it can capture rapid dissolution events within a short timescale, making it suitable for gas-liquid mass transfer studies under high pressure and transient conditions.

[0021] 3. Effectively eliminates system leakage interference: Through the parallel setting of the control unit, the initial volume of the gas phase inside is the same as the gas volume of the measuring unit, and no gas dissolution occurs in the control unit (empty container or flexible airbag isolation). The leakage error shared by the two containers is accurately deducted in the differential calculation, which significantly improves the measurement accuracy and solves the problem that traditional methods cannot distinguish between dissolution and leakage.

[0022] 4. No need to directly measure dissolved gas, reducing experimental difficulty: The mass of dissolved gas can be obtained simply by inverting pressure data and the ideal gas law, avoiding complex operations such as direct sampling, separation or weighing of dissolved gas, thus simplifying the measurement process.

[0023] 5. Complete dissolution kinetic parameters can be obtained: By fitting the net pressure decay curve or the dissolution mass change curve, the time constant, initial dissolution rate and final equilibrium dissolution amount of the gas dissolution process can be extracted, providing a direct basis for efficiency evaluation of engineering systems, gas loss calculation and process parameter optimization.

[0024] 6. Wide applicability and strong scalability: The control unit can be either an empty container or have an internal flexible airbag, suitable for conventional control and gas-liquid isolation control, respectively; the measurement unit can be equipped with a separator structure, which controls the dissolution rate by adjusting the gas-liquid contact area, facilitating the study of dissolution behavior under different confined conditions. By changing the gas source and liquid, this method can also be applied to the dissolution kinetics measurement of various gas-liquid combinations.

[0025] 7. Significant support value for engineering applications: The dynamic dissolution data provided by this invention can provide key experimental evidence for engineering systems involving gas-liquid mass transfer, such as compressed air energy storage, liquid piston compressors, chemical reactors, and deep-sea resource development. It helps to optimize operating parameters, improve system efficiency, and guide the research and development of new absorbents or membrane materials. Attached Figure Description

[0026] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, with the same or corresponding reference numerals denoteing the same or corresponding parts, wherein: Figure 1 This is a schematic diagram of the structure of the gas dissolution dynamic measurement device of the present invention; Figure 2 This is a schematic diagram of an embodiment of a flexible airbag structure; Figure 3 This is a schematic diagram of an embodiment of the separator structure.

[0027] In the diagram: 1. First gas storage tank; 2. First sealed container; 3. First control valve; 4. First high-frequency pressure sensor; 5. First gas source; 6. First gas source regulator; 7. Liquid; 8. Second gas storage tank; 9. Second sealed container; 10. Second high-frequency pressure sensor; 11. Second control valve; 12. Second gas source regulator; 13. Second gas source; 14. Data acquisition and processing unit; 15. Flexible airbag; 16. Separator structure. Detailed Implementation

[0028] The exemplary embodiments disclosed in this application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of this application and to fully convey the scope of this application to those skilled in the art. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0029] like Figure 1 As shown, this invention provides a dynamic measurement method based on parallel differential pressure analysis, which employs a measurement system including a measurement unit and a control unit to perform the following steps: System preparation steps: Inject a predetermined volume of liquid 7 into the first sealed container 2; close the first control valve 3 and the second control valve 11; start the first gas source 5 and the second gas source 13 and the data acquisition and processing unit 14; store the gas in the first gas source 5 and the second gas source 13 in the first gas storage tank 1 and the second gas storage tank 8 respectively through the first gas source regulator 6 and the second gas source regulator 12.

[0030] Synchronous pressure excitation and closure steps: The first control valve 3 and the second control valve 11 are opened synchronously, so that the high-pressure gas from the first gas storage tank 1 and the second gas storage tank 8 rushes into the first sealed container 2 and the second sealed container 9 respectively within a millisecond time; when the first high-frequency pressure sensor 4 and the second high-frequency pressure sensor 10 detect that the pressure in the two containers has reached and stabilized at the preset initial pressure P0, the first control valve 3 and the second control valve 11 are immediately closed synchronously, so that the two containers are isolated from the gas source and form an independent closed test system.

[0031] Synchronous pressure decay monitoring steps: After the first control valve 3 and the second control valve 11 are closed, the data acquisition and processing unit 14 begins to synchronously and at high speed acquire and record the first pressure decay data P1(t) from the first high-frequency pressure sensor 4 and the second pressure decay data P2(t) from the second high-frequency pressure sensor 10, and continues to monitor until the pressure change tends to level off or reaches the predetermined time.

[0032] Differential calculation and quality inversion steps: In the data acquisition and processing unit 14, the following calculation process is performed: a) Differential processing: Subtract the second pressure decay data P2(t) from the first pressure decay data P1(t) in real time to obtain the net pressure decay curve ΔP(t) that eliminates the common leakage error of the two systems.

[0033] b) Calculation of dissolved mass: Based on the ideal gas law, using the formula: Δm(t) = ΔP(t) * V / (R * T); Where m is the gas mass, V is the initial volume of the gas phase in the first sealed container 2, R is the ideal gas constant, and T is the thermodynamic temperature of the system.

[0034] The net pressure decay curve ΔP(t) is transformed to calculate the cumulative mass Δm(t) of gas dissolved from the gas phase of the first sealed container 2 into the liquid 7 within time t.

[0035] c) Extraction of kinetic parameters: Analyze the curve of net pressure decay ΔP(t) or the curve of gas cumulative mass Δm(t) changing with time to obtain the time constant, initial dissolution rate and final equilibrium dissolution amount of the gas dissolution process, thereby fully characterizing the dissolution kinetic behavior of the gas in the liquid 7.

[0036] In one specific embodiment, the second sealed container 9 of the control unit is an empty container, the geometric volume of which is equal to the gas volume in the first sealed container 2, and the initial gas phase volume is equal to its geometric volume.

[0037] In one specific implementation, such as Figure 2 As shown, the second sealed container 9 of the control unit is provided with a flexible airbag 15, which is filled with gas and has a liquid 7 on the outside; thereby achieving complete isolation between the gas and the liquid; the gas volume in the flexible airbag 15 is equal to the gas volume in the first sealed container 2, and the geometric volume of the second sealed container 9 is not less than the gas volume in the flexible airbag 15.

[0038] It should be noted that the geometric volume of the second sealed container 9 in the two embodiments described above can be different: in the empty container scheme, its geometric volume is equal to the gas volume in the first sealed container 2; in the flexible airbag 15 scheme, its geometric volume is not less than the gas volume in the flexible airbag 15; since both schemes can ensure that the initial gas phase volume is equal, the geometric volume of the container can be flexibly set according to actual needs, which will not be elaborated here.

[0039] Specifically, the flexible airbag 15 has a bag-like, sac-like, or flexible membrane structure, and its shape can be designed to match the structure of the second sealed container 9, including cylindrical, spherical, or irregular shapes. The wall thickness of the flexible airbag 15 is 0.5mm to 5mm to ensure both flexibility and good pressure resistance. During gas injection, the flexible airbag 15 expands under pressure, thereby compressing the external liquid 7 and creating a pressure change process inside the system similar to that of an actual gas-liquid system 7. Since the gas is confined inside the flexible airbag 15, there is no direct contact between the gas and the liquid 7, thus effectively suppressing the gas dissolution process, making the gas mass change mainly originate from system leakage. Based on these characteristics, the flexible airbag 15 can be used to construct a control measurement condition to obtain pressure change data caused by system leakage and provide a benchmark for calculating the amount of gas dissolved. Compared with measurement conditions involving direct gas-liquid contact, this structure can effectively distinguish the contribution of gas dissolution and system leakage to pressure changes, thereby significantly improving measurement accuracy.

[0040] In one specific implementation, such as Figure 3 As shown, a separator structure 16 is provided in the first sealed container 2 of the measuring unit at the gas-liquid interface to adjust the contact state between the gas and the liquid 7.

[0041] Specifically, the separator structure 16 can be a plate-like structure, a mesh-like structure, a porous structure, or a combination of the above structures, and its material is preferably stainless steel, aluminum alloy, or high-strength non-metallic material; the separator structure 16 is installed on the inner wall of the first sealed container 2 by a fixing device, or is set at the gas-liquid interface position by a support structure; a gap is provided between the separator structure 16 and the inner wall of the first sealed container 2, and the width of the gap is preferably 0.1mm to 10mm, so that the gas and liquid 7 can have restricted contact through the gap; during the gas injection process, the gas mainly contacts the liquid 7 through the gap area, from This significantly reduces the effective gas-liquid contact area. By changing the parameters of the separator structure 16, the gas dissolution behavior can be adjusted, including: changing the size parameters of the separator structure 16; changing the porosity or pore size of the separator structure 16; and changing the gap width between the separator structure 16 and the inner wall of the container. When the gas-liquid contact area decreases, the gas dissolution rate decreases significantly, and the duration of the dissolution process is prolonged, which is beneficial for fine analysis of the gas dissolution kinetics. In addition, the separator structure 16 can be used to simulate different confined gas-liquid contact conditions, thereby expanding the application of this invention in different engineering scenarios.

[0042] In one specific embodiment, the synchronous pressure excitation step is achieved by controlling the first control valve 3 and the second control valve 11 located in the gas path to open and close synchronously. The control valve is a solenoid valve or a piezoelectric ceramic valve, and the opening time is on the order of milliseconds.

[0043] In one specific embodiment, the first attenuation curve P1(t) and the second attenuation curve P2(t) are acquired by a high-frequency dynamic pressure sensor with a response frequency of not less than 500Hz.

[0044] Secondly, the present invention also provides a system for implementing the above method, comprising: a measurement unit, a comparison unit, and a data acquisition and processing unit 14.

[0045] The measuring unit includes a first sealed container 2, a first gas source 5 connected to the first sealed container 2, a first control valve 3 disposed in the connected gas path, and a first high-frequency pressure sensor 4 disposed on the first sealed container 2. The first sealed container 2 contains a predetermined volume of liquid 7 and gas.

[0046] The control unit includes a second sealed container 9, a second gas source 13 connected to the second sealed container 9, a second control valve 11 disposed in the connected gas path, and a second high-frequency pressure sensor 10 disposed on the second sealed container 9. The initial gas volume in the second sealed container 9 is the same as the gas volume in the first sealed container 2.

[0047] The data acquisition and processing unit 14 is connected to the first high-frequency pressure sensor 4 and the second high-frequency pressure sensor 10, and is configured to perform the differential and inversion calculation steps described above.

[0048] In one specific embodiment, the second sealed container 9 of the control unit is an empty container, and its geometric volume is equal to the gas volume in the first sealed container 2.

[0049] In one specific embodiment, the second sealed container 9 of the control unit is provided with a flexible airbag 15, the gas volume in the flexible airbag 15 is equal to the gas volume in the first sealed container 2, and the geometric volume of the second sealed container 9 is not less than the gas volume.

[0050] In one specific embodiment, a separator structure 16 is further provided inside the first sealed container 2 of the measuring unit at the gas-liquid interface.

[0051] In one specific embodiment, the first air source 5 and the second air source 13 include an air compressor, and a first air storage tank 1 and a second air storage tank 8 for stabilizing the output pressure. The measuring unit and the control unit are respectively connected to the first air storage tank 1 and the second air storage tank 8 through parallel pipelines, and the first air source 5 and the second air source 13 have the same output pressure.

[0052] In one specific embodiment, the liquid 7 is located in the lower part of the first sealed container 2, and the gas is located in the upper part of the first sealed container 2, forming a clear gas-liquid interface.

[0053] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A dynamic measurement method based on parallel differential pressure analysis, characterized in that, The following steps are performed using a measurement system that includes a measurement unit and a control unit: System preparation steps: Inject a predetermined volume of liquid (7) into the first sealed container (2); and close the first control valve (3) and the second control valve (11); then start the first gas source (5) and the second gas source (13) and the data acquisition and processing unit (14); then store the gas in the first gas source (5) and the second gas source (13) in the first gas storage tank (1) and the second gas storage tank (8) respectively through the first gas source regulator (6) and the second gas source regulator (12); Synchronous pressure excitation steps: Gas is synchronously introduced into the first sealed container (2) of the measuring unit and the second sealed container (9) of the control unit. The first control valve (3) and the second control valve (11) are synchronously opened, so that the gas from the first gas storage tank (1) and the second gas storage tank (8) are injected into the first sealed container (2) and the second sealed container (9) respectively within a millisecond time. When the first high-frequency pressure sensor (4) and the second high-frequency pressure sensor (10) detect that the pressure in the two containers has reached and stabilized at the preset initial pressure P0, the first control valve (3) and the second control valve (11) are immediately closed synchronously, so that the two containers form an independent closed system. The first sealed container (2) contains a predetermined volume of liquid (7) and gas, and the initial volume of the gas phase in the second sealed container (9) is the same as the volume of gas in the first sealed container (2). Synchronous attenuation monitoring steps: The data acquisition and processing unit (14) starts to synchronously acquire the first attenuation curve P1(t) of the gas pressure in the first sealed container (2) and the second attenuation curve P2(t) of the gas pressure in the second sealed container (9) over time. Differential and inversion calculation steps: Subtract the second attenuation curve P2(t) from the first attenuation curve P1(t) to obtain the net pressure attenuation curve ΔP(t) after eliminating the influence of system leakage; Based on the ideal gas law, convert ΔP(t) into the change of gas mass lost due to gas dissolution in the first closed container (2) over time Δm(t) to obtain the dynamic dissolution amount and dissolution kinetic data of gas in liquid (7).

2. The dynamic measurement method based on parallel differential pressure analysis according to claim 1, characterized in that, The second sealed container (9) of the control unit is an empty container, and its geometric volume is equal to the gas volume in the first sealed container (2), and its initial gas phase volume is equal to its geometric volume.

3. The dynamic measurement method based on parallel differential pressure analysis according to claim 1, characterized in that, The second sealed container (9) of the control unit is provided with a flexible airbag (15), which is filled with gas and has a liquid (7) on the outside; the gas volume in the flexible airbag (15) is equal to the gas volume in the first sealed container (2), and the geometric volume of the second sealed container (9) is not less than the gas volume in the flexible airbag (15).

4. The dynamic measurement method based on parallel differential pressure analysis according to claim 1, characterized in that, Inside the first sealed container (2) of the measuring unit, a separator structure (16) is provided at the gas-liquid interface.

5. The dynamic measurement method based on parallel differential pressure analysis according to claim 1, characterized in that, In the synchronous pressure excitation step, the first control valve (3) and the second control valve (11) located in the gas path are controlled to open and close synchronously. The control valve is a solenoid valve or a piezoelectric ceramic valve, and the opening time is in the millisecond range.

6. The dynamic measurement method based on parallel differential pressure analysis according to claim 1, characterized in that, The first attenuation curve P1(t) and the second attenuation curve P2(t) are acquired by a high-frequency dynamic pressure sensor with a response frequency of not less than 500Hz.

7. The dynamic measurement method based on parallel differential pressure analysis according to claim 1, characterized in that, The Δm(t) mentioned in the difference and inversion calculation steps is calculated using the following formula: Δm(t) = ΔP(t) * V / (R * T); Where V is the initial volume of the gas phase in the first sealed container (2), m is the gas mass, R is the ideal gas constant, and T is the thermodynamic temperature of the system.

8. The dynamic measurement method based on parallel differential pressure analysis according to claim 1, characterized in that, The differential and inversion calculation steps also include: fitting the curve of the net pressure decay curve ΔP(t) or the curve of the gas mass change Δm(t) over time to extract the time constant, initial dissolution rate and final equilibrium dissolution amount of the gas dissolution process.

9. A dynamic measurement system based on parallel differential pressure analysis for implementing the dynamic measurement method based on parallel differential pressure analysis as described in claim 1, characterized in that, The dynamic measurement system includes: a measurement unit, a control unit, and a data acquisition and processing unit (14). The measuring unit includes a first sealed container (2), a first gas source (5) connected to the first sealed container (2), a first control valve (3) provided in the connected gas path, and a first high-frequency pressure sensor (4) provided on the first sealed container (2). The first sealed container (2) contains a predetermined volume of liquid (7) and gas. The control unit includes a second sealed container (9), a second gas source (13) connected to the second sealed container (9), a second control valve (11) provided in the connected gas path, and a second high-frequency pressure sensor (10) provided on the second sealed container (9). The initial volume of the gas phase in the second sealed container (9) is the same as the gas volume in the first sealed container (2). The data acquisition and processing unit (14) is connected to the first high-frequency pressure sensor (4) of the measurement unit and the second high-frequency pressure sensor (10) of the control unit.

10. The dynamic measurement system based on parallel differential pressure analysis according to claim 9, characterized in that, The second sealed container (9) of the control unit is an empty container, and its geometric volume is equal to the gas volume in the first sealed container (2); or, the second sealed container (9) of the control unit is provided with a flexible airbag (15), the gas volume in the flexible airbag (15) is equal to the gas volume in the first sealed container (2), and the geometric volume of the second sealed container (9) is not less than the gas volume; the first sealed container (2) of the measuring unit is also provided with a separator structure (16) at the gas-liquid interface.

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