CN106769689B - Device and method for measuring diffusion coefficient of gas in liquid under variable volume and constant pressure - Google Patents

Abstract

The invention discloses the measuring devices and method of a kind of diffusion coefficient in a liquid of gas under variable volume constant pressure, and device mainly includes gaseous sample bottle, air chamber, diffusion chamber, thermostat, valve, vacuum pump, pressure reducing valve, pressure control gas cylinder, displacement sensor, pressure sensor, platinum resistance thermometer, data collection system.The diffusion chamber uses the visual window construction with quartz glass；The diffusion chamber is equipped with pressure sensor and displacement sensor；The diffusion chamber keeps its pressure in diffusion process constant by moveable piston with pressure control gas cylinder；Moving distance of the moveable piston in measurement process is obtained by displacement sensor.The diffusion coefficient of gas in a liquid is calculated according to Fick second law.The present invention realizes the measurement of the diffusion coefficient in a liquid of gas under constant pressure, has the advantages that device is simple, at low cost, easy to operate, system is stable.

Description

Device and method for measuring diffusion coefficient of gas in liquid under variable volume and constant pressure

technical field

The invention belongs to the fields of chemical engineering and fluid thermophysical property measurement, in particular to a device and method for measuring the diffusion coefficient of gas in liquid under variable volume and constant pressure.

Background technique

As one of the three major migration properties of fluids, diffusion coefficient is the basic parameter for studying the movement and transfer phenomena of fluid molecules, for example, it is the limiting factor for the mixing and separation process of solutions and chemical reactions. At present, there are many reports on the measurement methods of gas diffusion coefficient in liquid, mainly including: pressure decay method, gravity balance method, time delay method, dynamic light scattering method, real-time concentration measurement method, etc. Among them, the pressure decay method is the most widely used. It mainly obtains the diffusion coefficient by measuring the relationship between pressure and time during the diffusion process of gas in liquid under constant volume. This method has simple experimental equipment, low cost and easy operation. However, at a constant volume, the pressure in the diffusion chamber decreases as the gas dissolves, and it is difficult to measure the diffusion coefficient at a certain constant pressure with this method.

Contents of the invention

The purpose of the present invention is to provide a device and method for measuring the diffusion coefficient of gas in liquid under variable volume and constant pressure, so as to solve the defect that the pressure decay method cannot measure the diffusion coefficient of gas in liquid under constant pressure.

In order to achieve the above object, the present invention adopts the following technical solutions:

A device for measuring the diffusion coefficient of gas in liquid under variable volume and constant pressure, the device includes a gas chamber, a diffusion chamber, a constant temperature tank and a pressure control cylinder, the gas chamber and the diffusion chamber are set in the constant temperature tank, and the gas chamber is set There is a first pressure sensor used to detect the pressure in the gas chamber. A piston that can move up and down within a limited range is arranged in the diffusion chamber. The piston divides the diffusion chamber into an upper chamber above the piston and a lower chamber below the piston. Partly, the pressure control gas cylinder is connected to the upper chamber of the diffusion chamber through a pipeline with a pressure reducing valve, and the second pressure sensor for detecting the pressure of the lower chamber and a displacement sensor for detecting the change of the piston position are arranged on the diffusion chamber. The gas chamber is connected to the lower chamber of the diffusion chamber through a pipeline with a sampling valve.

The diffusion chamber is provided with a visual window for observing the change of the liquid surface position of the liquid to be measured and the gas diffusion process.

An upper bracket and a lower bracket are arranged in the diffusion chamber, and the movement of the piston is restricted between the upper and lower brackets.

The device also includes a first valve, a second valve, a third valve, an exhaust valve, a vacuum pump and a gas sample bottle, the third valve is connected to the gas cavity, the second valve is arranged on the connecting pipeline between the vacuum pump and the third valve, The first valve is arranged on the connection pipeline between the gas sample bottle and the third valve, and the exhaust valve communicates with the upper chamber of the diffusion chamber through the pipeline with the pressure reducing valve.

The device also includes a data acquisition and analysis system. The first and second pressure sensors, displacement sensors and thermometers for detecting the temperature of the constant temperature bath are respectively connected with the data acquisition and analysis system.

The data acquisition and analysis system calculates the spatial average concentration of the gas diffused in the liquid at different times according to the piston displacement collected during the process of gas diffusion to the liquid under constant temperature and constant pressure, and then calculates the spatial average concentration equation obtained by solving according to Fick's second theorem Nonlinear fitting to obtain the diffusion coefficient of gas in liquid.

Based on the above device, the present invention also proposes a method for measuring the diffusion coefficient of gas in liquid under variable volume and constant pressure, comprising the following steps:

1) Inject the liquid to be measured with a mass of m into the part below the piston in the diffusion chamber, then place the diffusion chamber in a constant temperature tank and connect it to the gas chamber in the constant temperature tank, and then vacuumize the liquid injected into the diffusion chamber Degassing treatment, and at the same time make the piston in the diffusion chamber move to the lower limit position by vacuuming;

2) Inject the gas in the gas chamber into the cavity between the liquid level in the diffusion chamber and the piston, and calculate the molar amount Δn of the gas injected into the diffusion chamber according to the pressure change in the gas chamber before and after injection;

3) After stopping the injection of gas, use the exhaust valve to adjust the pressure of the part above the piston in the diffusion chamber to the target pressure. Under the condition that the pressure of the part above the piston in the diffusion chamber is maintained at the target pressure by using the pressure reducing valve and the pressure control cylinder, record The displacement L ₂ of the piston at any time during the gas diffusion process in the liquid, the molar amount of the gas diffused into the liquid is calculated according to the pressure of the part below the piston in the diffusion chamber and the displacement of the piston at the corresponding time according to Calculate the spatial average concentration <C> of the gas diffused into the liquid at the corresponding moment;

4) Using the calculated spatial average concentration at multiple moments under the target pressure, nonlinear fitting is performed on the spatial average concentration equation obtained by solving Fick's second theorem to obtain the diffusion coefficient of the gas in the liquid.

said Calculated as follows:

V _g =V _D -V ₁

V _D ＝V _E +πr ² (L ₁ -L ₂ )

Wherein, n _g is the molar amount of gas in the cavity, V is the volume _of liquid injected into the diffusion chamber, _VE is the volume of the diffusion chamber below the piston when the piston moves to the lower limit position, and ρ _g is the volume of the diffusion chamber at the corresponding time The density of the gas in the cavity, M _g is the molar mass of the gas, V _D is the volume of the diffusion cavity below the piston at the corresponding time, V _g is the volume of the cavity at the corresponding time, r is the radius _of the piston section, and L is The distance from the displacement sensor to the piston at the top of the diffusion chamber when the piston moves to the lower limit position.

The spatial average concentration is calculated as follows:

where V1 is the volume _of liquid injected into the diffusion chamber.

The space average concentration equation is expressed as:

Among them, λ _n =(n+1/2)π/L; D is the diffusion coefficient; t is the diffusion time; L is the thickness of the liquid in the diffusion chamber; C ₀ is the initial concentration of the gas in the liquid, C _S is a constant Saturated dissolved concentration of gas in liquid under pressure and temperature; n is the number of fitting terms.

Compared with the prior art, the beneficial effects of the present invention are reflected in:

The invention can adjust and keep constant the pressure of the gas in the diffusion chamber through the pressure-controlling gas cylinder and the movable piston, uses a constant temperature tank to keep the temperature constant during the diffusion process, and realizes the measurement of the gas diffusion coefficient in the liquid under constant pressure. The invention uses less liquid and gas, and has simple experimental measurement, low required cost and convenient operation.

Furthermore, the present invention facilitates observation of the position of the liquid level in the diffusion chamber and the real-time diffusion of the gas in the liquid by adding a viewing window.

Description of drawings

Fig. 1 is the structure schematic diagram of gas diffusion coefficient measuring device in liquid under variable volume constant pressure;

Fig. 2 is a schematic diagram of the structure of a diffusion chamber; wherein, (a) is a top view, and (b) is a side view;

Fig. 3 is a sectional view of a diffusion chamber;

In the figure: 1. Gas sample bottle; 2. Vacuum pump; 3. First valve; 4. Second valve; 5. Third valve; 6. Gas cavity; 7. First pressure sensor; 8. Fourth valve; 9 1. Displacement sensor; 10. Diffusion cavity; 11. Constant temperature tank; 12. Thermometer; 13. Data acquisition system; 14. Second pressure sensor; 15. Fifth valve; , bolts; 19, constant pressure air source inlet; 20, displacement sensor installation interface; 21, diffusion chamber top cover; 22, viewing window; 23, pressure sensor installation interface; 24, diffusion chamber air inlet; 1 sealing ring; 26, quartz glass; 27, upper bracket; 28, second sealing ring; 29, lower bracket; 30, movable piston.

Detailed ways

The present invention will be further described in detail below in conjunction with the drawings and embodiments, and the embodiments described here are only used to explain the present invention, and are not intended to limit the present invention.

As shown in Figure 1, a device for measuring the diffusion coefficient of gas in liquid under variable volume and constant pressure, the device includes: a gas sample bottle 1, a vacuum pump 2, a first valve 3, a second valve 4, a third valve 5, Gas chamber 6, first pressure sensor 7, fourth valve 8 (sampling valve), displacement sensor 9, diffusion chamber 10, constant temperature tank 11, platinum resistance thermometer 12, data acquisition system 13, second pressure sensor 14, fifth Valve 15 (exhaust valve), pressure reducing valve 16 and pressure-controlling cylinder 17. The gas chamber 6 is connected to the gas sample bottle 1 and the vacuum pump 2 through a pipeline with a valve (the specific connection mode is: the third valve 5 is connected to the gas chamber 6, and the second valve 4 is arranged at the junction of the vacuum pump 2 and the third valve 5 On the connecting pipeline, the first valve 3 is arranged on the connecting pipeline between the gas sample bottle 1 and the third valve 5), and a first pressure sensor 7 is installed on the top of the gas cavity 6 . The diffusion chamber 10 is connected to the gas chamber 6 through a pipeline with a fourth valve 8, a movable piston 30 is installed inside the diffusion chamber, a second pressure sensor 14 is installed on the side of the diffusion chamber 10, and a displacement sensor is installed on the top of the diffusion chamber 10. sensor9. The gas chamber 6 and the diffusion chamber 10 are placed in a constant temperature bath 11 with high precision temperature control. The temperature of the constant temperature tank 11 is measured by a platinum resistance thermometer 12 . The pressure control gas bottle 17 is connected with the diffusion chamber 10 through a pipeline with a pressure reducing valve 16 . A fifth valve 15 is connected to this pipeline. The pressure in the gas chamber 6 and the pressure at the outlet of the pressure reducing valve 16 are measured by the first pressure sensor 7 and the second pressure sensor 14 . Described data collection system 13 comprises Keithley 2007 digital multimeter and computer, and described Keithley 2007 digital multimeter collects the electric current or the voltage signal of thermometer and pressure sensor, then transmits in the computer, obtains the measured value of temperature and pressure by conversion, the displacement sensor The detection signal is collected by computer, and the data collection system is automatically controlled and collected by Labview programming.

As shown in Figures 2 and 3, the diffusion chamber 10 is composed of a diffusion chamber body and a diffusion chamber top cover 21 arranged on the diffusion chamber body through fixing bolts 18, and a first sealing ring is installed at the joint 25 to ensure tightness. The movable piston 30 installed in the diffusion chamber divides the entire diffusion chamber into upper and lower parts, which are called upper chamber and lower chamber respectively. The upper bracket 27 and the lower bracket 29, and the movable piston 30 is provided with a second sealing ring 28 in contact with the inner wall of the diffusion chamber, so that the upper and lower parts separated by the movable piston 30 are not connected. The top cover 21 of the diffusion chamber is provided with a constant-pressure gas source inlet 19 communicating with the upper chamber. One end of the pipeline with a pressure reducing valve 16 is connected to the constant-pressure gas source inlet 19, and the other end is connected to a pressure-controlling gas cylinder. 17 interface connection, the side wall of the diffusion chamber 10 is provided with a pressure sensor installation interface 23 communicating with the lower chamber and a diffusion chamber air inlet 24, the second pressure sensor 14 is arranged on the pressure sensor installation interface 23, with a fourth One end of the pipeline of the valve 8 is connected to the gas chamber 6 , and the other end is connected to the gas inlet 24 of the diffusion chamber. Through the pressure reducing valve 16 and the second pressure sensor 14, the pressure in the upper chamber can be precisely adjusted and kept constant during the movement of the movable piston 30. The top cover 21 of the diffusion chamber also has a displacement sensor installation interface 20, which is equipped with a displacement sensor 9 for real-time measurement of the moving distance of the above-mentioned piston. The diffusion chamber 10 is provided with a high-pressure viewing window 22, and a quartz glass 26 with good light transmission is installed in the high-pressure viewing window. The quartz glass is fixed by the flange through bolts and sealing gaskets. The viewing window is conducive to observing the gas in the diffusion chamber. Diffusion in a liquid in real time.

The method for using the measuring device for the diffusion coefficient of gas in liquid under variable volume and constant pressure includes the following steps:

1) preparation

a. Measure the volume of the gas chamber 6 and the volume of the lower part of the movable piston in the diffusion chamber 10 . Fill the two containers to be measured with water respectively at a constant temperature, and then weigh the mass difference before and after the water is injected to obtain the measured volume V _G , _VE , where V _G is the volume of the gas chamber 6, including The volume of the connecting pipeline (the pipeline from the fourth valve 8 to the gas chamber 6), _VE is the diffusion chamber volume of the lower part of the piston when the above-mentioned piston moves to the lower bracket 29, including the connecting pipeline (the fourth valve 8 to the diffusion chamber). The volume of the pipeline of chamber 10).

b. The air tightness of the testing device. Open the second valve 4, the third valve 5 and the fourth valve 8, and use the vacuum pump 2 to evacuate the device to less than 1kPa. If the pressure in the device is still lower than 1kPa after half an hour, then open the first valve 3 to pass the gas sample. Bottle 1 is injected with a gas with a pressure of 10MPa. If the pressure in the device does not drop after half an hour, it can be considered that the airtightness of the experimental system is good.

c. Use a precision electronic balance to measure the quality of the reagent bottle containing the liquid to be tested, then inject a certain amount of liquid into the lower chamber of the diffusion chamber 10, and measure the quality of the reagent bottle again. The quality difference between the two measurements is the diffusion chamber The mass m of the liquid in 10, and connect the diffusion chamber filled with the measured liquid to the experimental system.

2) measure

a. Adjust the constant temperature tank 11 to the target temperature, open the second valve 4, the third valve 5 and the fourth valve 8, use the vacuum pump 2 to evacuate the device, and degas the liquid to be measured.

B, close the second valve 4 and the fourth valve 8, open the first valve 3, the gas in the gas sample bottle 1 is charged in the gas chamber 6, until the gas chamber pressure is about 2 times of the target pressure (guarantee that the gas chamber can After supplying target pressure gas to the diffusion chamber), the first valve 3 and the third valve 5 are closed. After the pressure in the gas chamber 6 stabilizes, record the pressure of the gas chamber and the temperature of the constant temperature tank 11 at this time. Then open the pressure reducing valve 16 to adjust to the target pressure. Finally, the fourth valve 8 is opened, and it is quickly closed after a few seconds, and the pressure in the gas chamber 6 and the temperature of the constant temperature tank 11 are recorded at this time. The pressure in the diffusion chamber 10 at any time t after the fourth valve 8 is closed, the moving distance of the movable piston 30 and the temperature of the constant temperature tank 11 are automatically recorded and saved by the data acquisition system 13 .

After a measurement is finished, the fifth valve 15 is used to exhaust gas.

3) calculate

The volume V1 _of the measured liquid can be calculated by the following formula:

Where m is the mass of the liquid and ρ is the mass density of the liquid. The volume of the dissolved liquid will change as the gas dissolves, and the camera is used to measure the change of the liquid level through the high _- pressure visible window, and V1 is corrected.

The total molar amount Δn of the gas in the diffusion chamber before the diffusion starts is:

Δn=n ₁ -n ₂ (2)

Among them, n ₁ and n ₂ are the molar quantities of gas in the gas chamber before and after the gas measured in the gas chamber is released into the lower chamber of the diffusion chamber, which are calculated from the density ρ ₁ and ρ ₂ of the gas in the gas chamber and the volume V _G of the gas chamber respectively get:

Where M _g is the molar mass of the gas, the density ρ ₁ and ρ ₂ of the gas in the gas container at different temperatures and pressures can be accurately calculated by using the REFPROP software.

After the gas in the gas chamber enters the diffusion chamber, the pressure of the lower part of the movable piston is greater than the pressure of the upper part of the movable piston at the beginning, and the piston will move upward for a certain distance rapidly. At this time, the fifth valve 15 is opened to reduce the pressure of the upper part of the piston. Adjust to target pressure. Then, due to the gradual dissolution of the gas into the liquid, the piston will slowly move downwards, and the displacement at any time t is L ₂ , then the volume V _D in the diffusion chamber of the lower part of the movable piston at time t is (take the diffusion chamber The body is cylindrical as an example, the lower surface of the piston is flat, and the radius of the cross-sectional circle is r):

V _D ＝V _E +πr ² (L ₁ -L ₂ ) (5)

Wherein, _VE is the volume of the lower part of the piston when the movable piston moves to the lower bracket, and L is the distance from the displacement sensor to the piston when the piston moves to the lower bracket ₂₉ , then the gas part in the lower chamber of the diffusion chamber at any time t The volume V _g is:

V _g =V _D -V ₁ (6)

The molar mass _ng of gas in the lower chamber of the diffusion chamber (that is, the molar mass of gas not dissolved in the liquid in the diffusion chamber) is calculated by the following formula:

ρ _g is the density of the gas in the lower chamber of the diffusion chamber at any time t.

For time t, the molar amount of gas dissolved in the liquid in the diffusion chamber is:

In the time t, the concentration of the gas diffused into the liquid is defined as the spatial average concentration <C>, which is calculated by the following formula:

Through the above formulas, the final expression of <C> is:

The diffusion of gas in the liquid in the lower chamber of the diffusion chamber can be regarded as one-dimensional free diffusion, and the following assumptions are made: the diffusion of gas in the liquid is a one-dimensional diffusion process without convective effects; there is a thin gap between the gas phase and the liquid phase The contact surface is in an equilibrium state, and the dissolution of gas in the liquid at the contact surface is in a saturated state; the temperature and pressure in the diffusion chamber remain constant. During the whole process of gas diffusion in the liquid, the solution is regarded as a dilute solution, and its corresponding thermophysical properties do not change.

Then according to Fick's second theorem:

Initial condition: when t=0, 0<z<L, C=C ₀ (12)

Boundary conditions: when t>0, z=0, C=C _S (13)

When z=L,

Among them, D is the diffusion coefficient, which is assumed to be a constant; C is the concentration of the gas dissolved in the liquid, which is a function of the diffusion time t and the position z; L is the thickness of the liquid in the diffusion chamber (that is, the height, the liquid in the diffusion chamber The height L is measured by the altimeter through the visible window); z = 0 is the gas-liquid contact surface; C ₀ is the initial concentration of the gas in the liquid; C _S is the saturation of the gas dissolved in the liquid at the target pressure p and temperature T concentration of the state.

Through initial conditions and boundary conditions, formula (11) can be solved to get:

where λ _n =(n+1/2)π/L. During time t, the spatial average concentration <C> of the gas in the liquid can be calculated by the following formula:

Under constant temperature and pressure, C ₀ and L are known, and the relationship between measured <C> and time t is used for nonlinear fitting, and the diffusion coefficient D and saturation concentration C _S can be calculated. Although the above formula contains a summation formula with infinite items, in fact, only some of the previous items have an impact on the fitting result of the above formula, and an appropriate number of items n can be selected during the fitting process.

Claims (9)

1. A measuring device for the diffusion coefficient of gas in liquid under variable volume and constant pressure, characterized in that: the device comprises a gas chamber (6), a diffusion chamber (10), a constant temperature bath (11), and a pressure control cylinder (17) And a data acquisition and analysis system, the gas chamber (6) and the diffusion chamber (10) are arranged in the constant temperature tank (11), and the gas chamber (6) is provided with a first pressure for detecting the pressure in the gas chamber (6) The sensor (7), the diffusion chamber (10) is provided with a piston that can move up and down within a limited range, and the piston divides the diffusion chamber (10) into two parts: an upper chamber above the piston and a lower chamber below the piston, The pressure control gas cylinder (17) is connected to the upper chamber of the diffusion chamber (10) through a pipeline with a pressure reducing valve (16), and the diffusion chamber (10) is provided with a second pressure sensor ( 14) and a displacement sensor (9) for detecting changes in the position of the piston, the gas chamber (6) is connected to the lower chamber of the diffusion chamber (10) through a pipeline with a sampling valve; The data acquisition and analysis system calculates the spatial average concentration of gas diffused in the liquid at different times according to the piston displacement collected during the gas diffusion to the liquid under constant temperature and constant pressure, and then solves the spatial average concentration equation obtained according to Fick's second theorem Perform nonlinear fitting to obtain the diffusion coefficient of gas in liquid. 2. The device for measuring the diffusion coefficient of gas in liquid under a variable volume and constant pressure according to claim 1, characterized in that: the diffusion chamber (10) is provided with a device for observing the change of the liquid level position of the liquid to be measured and Visibility window (22) for the gas diffusion process. 3. A device for measuring the diffusion coefficient of gas in liquid under variable volume and constant pressure according to claim 1, characterized in that: an upper bracket (27) and a lower bracket (29) are arranged in the diffusion chamber (10) , the movement of the piston is limited between the upper and lower brackets. 4. A measuring device for the diffusion coefficient of gas in liquid under variable volume and constant pressure according to claim 1, characterized in that: said device also includes a first valve (3), a second valve (4), a third Valve (5), exhaust valve, vacuum pump (2) and gas sample bottle (1), the third valve (5) is connected with the gas cavity (6), the first valve (3) is arranged on the gas sample bottle (1) and On the connecting pipeline of the third valve (5), the second valve (4) is arranged on the connecting pipeline of the vacuum pump (2) and the third valve (5), and the exhaust valve passes through the pressure reducing valve (16) The pipeline communicates with the upper chamber of the diffusion chamber (10). 5. according to claim 1 said a kind of measuring device of gas diffusion coefficient in liquid under variable volume and constant pressure, it is characterized in that: said first pressure sensor, second pressure sensor, displacement sensor (9) and for detecting The thermometers (12) for the temperature of the constant temperature bath (11) are respectively connected with the data acquisition and analysis system. 6. according to the method for measuring the diffusion coefficient of gas in liquid under the device measurement variable volume constant pressure according to any one of claims 1-5, it is characterized in that: comprise the following steps: 1) Inject the liquid to be measured with mass m into the part below the piston in the diffusion chamber (10), then place the diffusion chamber (10) in the constant temperature tank (11), and connect it with the gas chamber (6) in the constant temperature tank (11) ) is connected, and then the liquid injected into the diffusion chamber (10) is degassed by vacuuming, and at the same time, the piston in the diffusion chamber (10) is moved to the lower limit position by vacuuming; 2) Inject the gas in the gas chamber (6) into the cavity between the liquid level in the diffusion chamber (10) and the piston, and calculate the gas injected into the diffusion chamber (10) according to the pressure change of the gas chamber (6) before and after injection The molar amount Δn; 3) After stopping the injection of gas, use the exhaust valve to adjust the pressure of the part above the piston in the diffusion chamber (10) to the target pressure, and use the pressure reducing valve (16) and the pressure control gas cylinder (17) to reduce the pressure above the piston in the diffusion chamber (10). Part of the pressure is maintained at the target pressure, record the displacement L ₂ of the piston at any time during the diffusion process of the gas in the liquid, and calculate the diffusion into the liquid according to the pressure of the part below the piston in the diffusion chamber and the displacement of the piston at the corresponding time moles of gas according to Calculate the spatial average concentration <C> of the gas diffused into the liquid at the corresponding moment; 4) Using the calculated spatial average concentration at multiple moments under the target pressure, nonlinear fitting is performed on the spatial average concentration equation obtained by solving Fick's second theorem to obtain the diffusion coefficient of the gas in the liquid. 7. The method according to claim 6, characterized in that: the Calculated as follows: V _g =V _D -V ₁ V _D ＝V _E +πr ² (L ₁ -L ₂ ) Wherein, n _g is the molar amount of gas in the cavity, V is the volume _of liquid injected into the diffusion chamber, _VE is the volume of the diffusion chamber below the piston when the piston moves to the lower limit position, and ρ _g is the volume of the diffusion chamber at the corresponding time The density of the gas in the cavity, M _g is the molar mass of the gas, V _D is the volume of the diffusion cavity below the piston at the corresponding time, V _g is the volume of the cavity at the corresponding time, r is the radius _of the piston section, and L is The distance from the displacement sensor to the piston at the top of the diffusion chamber when the piston moves to the lower limit position. 8. The method according to claim 6, characterized in that: the spatial average concentration is calculated in the following manner: where V1 is the volume _of liquid injected into the diffusion chamber. 9. The method according to claim 6, characterized in that: the spatial average concentration equation is expressed as: Among them, λ _n =(n+1/2)π/L; D is the diffusion coefficient; t is the diffusion time; L is the thickness of the liquid in the diffusion chamber; C ₀ is the initial concentration of the gas in the liquid, C _S is a constant Saturated dissolved concentration of gas in liquid under pressure and temperature; n is the number of fitting terms.