Gas diffusion coefficient testing device and method based on multi-component gas diffusion theory

Abstract

The invention discloses a gas diffusion coefficient testing device and method based on a multi-component gas diffusion theory. The device comprises diffusion double chambers, a heat preservation box, a temperature sensor, a gas pipe, a gas cylinder and the like. The multi-component gas diffusion coefficient testing method comprises the following steps: placing sample soil in diffusion double chambers, controlling the temperature through a heat tracing band and a temperature sensor, injecting to-be-tested gas, sampling and detecting the concentration of each component gas at regular time, obtaining the diffusion coefficient through a multi-component gas model, and simulating the diffusion coefficients under different gas components and working conditions. Compared with a traditional gas diffusion device and a diffusion theory based on the Fick law, the device has the advantages of being simple in structure, easy and convenient to operate, good in gas tightness, controllable in temperature and capable of detecting the diffusion coefficient of multi-component gas, and has great popularization and research value under the background of seeking economic, green and sustainable development and improving the atmospheric environment.

Description

Technical Field

[0001] The invention belongs to the field of water conservancy engineering and geotechnical engineering measurement facilities, in particular to a gas diffusion coefficient testing device and method based on multi-component gas diffusion theory. Background Art

[0002] The diffusion and migration of gas in porous media involves many fields, such as the diffusion of natural gas as a clean energy in underground porous rock formations, the migration of landfill gas in landfill cover systems, and the diffusion of toxic and harmful gases in complex terrain after gas field leakage. Therefore, it is particularly important to master the diffusion and migration mechanism of gas. At the same time, the diffusion gas mostly exists in the form of multi-component gas. For example, landfill gas is composed of methane, carbon dioxide, ammonia, VOCs and other gases.

[0003] At present, the gas diffusion coefficient is mainly obtained through indoor gas diffusion experiments based on Fick's law. For example, the advection diffusion model (ADM) is most commonly used to describe gas migration in porous media. ADM is a linear superposition of the convection flux calculated based on Darcy's law and the diffusion flux calculated based on Fick's law. The Fick's law used is applicable to the description of gas diffusion in a two-component gas system. However, traditional detection devices have limitations such as poor airtightness, complex use, and inability to control temperature. Moreover, Fick's law is only applicable to diffusion in two-component gases, which is inconsistent with the actual situation of multi-component gases and has low prediction accuracy. Therefore, seeking measurement technology for the diffusion coefficient of multi-component gases is of great significance for improving the atmospheric environment for human survival and has great value for the sustainable development of the economy and society. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a gas diffusion coefficient testing device and method based on multi-component gas diffusion theory.

[0005] The present invention firstly discloses a gas diffusion coefficient testing device based on multi-component gas diffusion theory, which comprises an insulated box, a diffusion double chamber arranged inside the insulated box and a gas cylinder;

[0006] The interior of the diffusion double chamber has a vertically arranged cylindrical chamber, and the main body of the diffusion double chamber includes an upper chamber, a sample ring and a lower chamber from top to bottom; wherein the sample ring is used to fill the soil sample; sampling tubes are arranged on the upper chamber and the lower chamber, and the sampling tubes are used for multi-component gas sampling, collecting gas samples, flushing the gas chamber or connecting a gas pressure gauge for air tightness detection; sealing rings are arranged at the connection between the upper chamber and the lower chamber and the sample ring for sealing;

[0007] The thermal insulation box is divided into a first semi-cylindrical box body, a second semi-cylindrical box body and a base; wherein the bottom of the diffusion double chamber is installed on the base; the first semi-cylindrical box body and the second semi-cylindrical box body are mutually buckled and installed on the base; the sampling tube on the diffusion double chamber extends out of the thermal insulation box; the lower chamber is connected to the gas cylinder through an air pipe.

[0008] The present invention also discloses a method for testing the multi-component gas diffusion coefficient of the device, which comprises the following steps:

[0009] S1. After the soil sample is prepared, it is loaded into the sample ring. The upper chamber, lower chamber, sample ring and porous plate are connected by bolts. O-rings are placed in the groove at the bottom of the upper chamber and the inner groove of the lower chamber. The diffusion double chamber and the base are fixed. The diffusion double chamber device is connected to the gas cylinder through the air pipe. All parts are connected and fixed to ensure the air tightness of the device.

[0010] S2. The first cylindrical box and the second semi-cylindrical box are fixed to the base by bolts, and then the first cylindrical box and the second semi-cylindrical box are connected by snaps;

[0011] S3. Wrap the heating tape and insulation cloth outside the insulation box, set the required temperature through the temperature controller, and control the internal temperature to the required temperature through the temperature sensor inside the insulation box;

[0012] S4. Use a syringe to slowly inject the gas to be tested into the lower chamber and the upper chamber through the first lower chamber sampling port and the first upper chamber sampling port respectively;

[0013] S5. After the gas is injected, the gas is immediately collected through the second upper chamber sampling port and the second lower chamber sampling port with a syringe as the initial gas sample and the sampling time is recorded; sampling is performed at the set time after the experiment starts; the concentration of each component in the gas sample is analyzed by a gas chromatograph;

[0014] S6. Repeat the above S4 and S5 processes through the test parameters or test conditions of multi-component gas diffusion to achieve the diffusion performance study of multi-component gas under different working conditions;

[0015] S7. After the experiment, the multi-component gas diffusion coefficient is obtained through the multi-component gas diffusion model.

[0016] According to a preferred embodiment of the present invention, S7 is specifically:

[0017] Assuming that the gas contains n components, the diffusion of multi-component gas in porous media is described by the dust-gas model (DGM), as shown in equation (4). The multi-component gas diffusion model is established by the mass conservation equation (3) of the multi-component gas and the dust-gas model equation (4). The boundary conditions are shown in equations (5) to (7):

[0018]

[0019]

[0020] Among them, θ g is the gas pore volume ratio of the soil sample; R is the ideal gas constant; T is the absolute temperature; p i is the partial pressure of gas component i; t is time; N i is the diffusion flux of component i gas, calculated by formula (4); z is the depth; τ is the tortuosity coefficient; D ij is the binary diffusion coefficient of bulk diffusion of component i and component j in air; D iK is the Knudsen diffusion coefficient of component i;

[0021] At the initial moment, the concentration of each component gas in the soil is the concentration in the air:

[0022] C s =C air t=0 (5)

[0023] The gas concentration boundaries at the top and bottom of the soil column adopt integral boundaries; assuming that the gas in the air chamber is evenly mixed, the gas concentration at the top boundary or the bottom boundary at time t is equal to the gas concentration in the air chamber at time t, and the boundary condition at the top of the soil column is:

[0024]

[0025] In the formula, C 0,top is the initial concentration of the gas in the top air chamber at the initial moment; the boundary condition at the bottom of the soil column is:

[0026]

[0027] In the formula, C 0,bottom is the initial concentration of the gas in the bottom chamber at the initial moment;

[0028] Substituting the experimental data into equations (3)-(7) we can obtain the multi-component gas diffusion coefficient.

[0029] By adopting the testing device and method of the present invention, the influence of factors such as different soil sample characteristics, soil compaction degree, soil moisture content, soil particle gradation, gas components, gas component ratio, temperature, etc. on the multi-component gas diffusion coefficient can be obtained. Compared with the traditional gas diffusion coefficient testing device, it has the advantages of simple structure, easy use, controllable temperature, good airtightness and easy detection; compared with the traditional single-component gas diffusion coefficient detection method, this method has the innovation of being able to obtain multi-component gas diffusion coefficients, and has guiding significance for the diffusion and prevention of polluted gas under the background of increasingly serious impact of polluted gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the use of a gas diffusion coefficient test device based on multi-component gas diffusion theory;

[0031] Figure 2 Schematic diagram of the upper chamber of the gas diffusion coefficient test device based on the multi-component gas diffusion theory; wherein, (a) is a front view, and (b) is a top view;

[0032] Figure 3 Schematic diagram of a sample ring of a gas diffusion coefficient test device based on multi-component gas diffusion theory; wherein, (a) is a front view, and (b) is a top view;

[0033] Figure 4 Schematic diagram of the lower chamber of a gas diffusion coefficient test device based on multi-component gas diffusion theory; wherein, (a) is a front view, and (b) is a top view;

[0034] Figure 5 Schematic diagram of the semi-cylindrical boxes A and B of the gas diffusion coefficient test device based on the multi-component gas diffusion theory; wherein, (a) is a front view, and (b) is a top view;

[0035] Figure 6 This is a partial schematic diagram of the connection between the semi-cylindrical boxes A and B of the gas diffusion coefficient test device based on the multi-component gas diffusion theory;

[0036] Figure 7 Schematic diagram of the lower chamber of a gas diffusion coefficient test device based on multi-component gas diffusion theory; wherein, (a) is a front view, and (b) is a top view;

[0037] Figure 8 This is a comparison chart of the O2, CH4 and CO2 mixed gas diffusion experiment and model results based on multi-component gas diffusion theory; among them, (a) O2 concentration in the gas chamber, (b) CH4 concentration in the gas chamber, (c) CO2 concentration in the gas chamber.

[0038] The reference numerals in the figure are: diffusion double chamber 1, insulation box 2, temperature sensor 3, air pipe 4, gas cylinder 5, bolts 6-7, upper chamber 8, first upper chamber sampling tube 8-1, second upper chamber sampling tube 8-2, upper chamber bolt hole 8-3, upper chamber bottom groove 8-4, sample ring 9, lower chamber 10, first lower chamber sampling tube 10-1, second lower chamber sampling tube 10-2, lower chamber bolt hole 10-3, lower chamber air inlet 10-4, lower chamber internal groove 10-5, lower chamber bottom groove 10-6, first A semi-cylindrical box 11, a first bottom bolt hole 11-1, a first bottom groove 11-2, an air inlet pipe interface 11-3, sampling tube interfaces 11-4 to 11-5, a second semi-cylindrical box 12, a sensor interface 12-1, a second bottom groove 12-2, sampling tube interfaces 12-3 to 12-5, a second bottom bolt hole 12-4, a base 13, a base protrusion 13-1, a base groove 13-2, a base bolt hole 13-3, a buckle 14, a barometer 15, and a porous plate 16. DETAILED DESCRIPTION

[0039] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0040] This embodiment provides a diffusion coefficient test device for a multi-component gas. This embodiment is described using the diffusion coefficient test of three gas components, CH4, O2 and CO2, as a specific application scenario. It should be noted that the test device provided by the present invention can be used for diffusion coefficient tests of multi-component gases of other components, and the number of components of the multi-component gas is not limited to three. The test device of this embodiment is as follows:

[0041] like Figure 1 , which is a schematic diagram of a gas diffusion coefficient testing device based on the multi-component gas diffusion theory of this embodiment, the device mainly includes a diffusion double chamber 1, an insulation box 2, a thermal sensor 3, a gas pipe 4 and a gas cylinder 5.

[0042] like Figure 2-7 As shown, the diffusion double chamber 1 is a hollow cylindrical structure with upper and lower sealed ends, and its main structure is composed of an upper chamber 8, a sample ring 9 and a lower chamber 10. Figure 3 As shown, the sample ring 9 is used to load the soil sample required for the test, the loading height of the porous medium is the same as the top of the sample ring 9, and a lower porous plate 16 is arranged at the bottom of the sample ring 9, and the porous plate 16 is used to carry the soil sample. In a specific embodiment of the present invention, the sample ring 9 is a hollow cylindrical structure, and a convex edge is arranged outwardly around the top of the cylinder, which is called the sample ring convex edge.

[0043] like Figure 2As shown, the upper chamber 8 is a cylindrical structure with a sealed top and an open bottom. A circle of upper chamber flange is arranged outward at the bottom of the upper chamber 8, and the entire upper chamber 8 is in the shape of a hat. An annular positioning hole for matching the size of the sample ring flange is arranged on the upper chamber flange; the flange of the sample ring 9 is installed in the annular positioning hole. The side wall of the upper chamber 8 is provided with a first upper chamber sampling tube 8-1 and a second upper chamber sampling tube 8-2 in the horizontal direction, and 4 upper chamber bolt holes 8-3 are arranged on the upper chamber flange. An upper chamber bottom groove 8-4 for installing an O-ring is reserved in the annular positioning hole. The inner diameter of the upper chamber 8 is the same as the inner diameter of the sample ring 9.

[0044] like Figure 4 As shown, the top of the lower chamber 10 is open, and the upper part of the lower chamber 10 is a sample ring installation section, the inner diameter of the sample ring installation section is the same as the outer diameter of the sample ring, and the length of the sample ring installation section is the same as the length of the sample ring excluding the flange section; the inner diameter of the rest of the lower chamber 10 is the same as the inner diameter of the upper chamber 8. A first lower chamber sampling tube 10-1 and a second lower chamber sampling tube 10-2 are arranged horizontally on the side wall of the lower chamber 10, and an air inlet 10-4 is arranged at the bottom, and the air inlet 10-4 is connected to the gas cylinder 5 through the air pipe 4. A circle of lower chamber flanges is arranged on the side of the lower chamber 10, and 4 lower chamber bolt holes 10-3 are reserved on the lower chamber flanges, which correspond to and are connected to the upper chamber bolt holes 8-3 one by one through bolts 6. The bottom of the sample ring installation section of the lower chamber 10 is reserved with a lower chamber internal groove 10-5 for installing an O-ring, and the bottom of the lower chamber 10 is provided with 3 lower chamber bottom grooves 10-6.

[0045] The heat preservation box 2 is a hollow cylindrical structure, which can be divided into three parts: a first semi-cylindrical box body 11, a second semi-cylindrical box body 12 and a base 13. Figure 5 As shown, the first semi-cylindrical box 11 has a first bottom bolt hole 11-1 at the bottom, sampling tube interfaces 11-4 and 11-5 for placing the second upper chamber sampling tube 8-2 and the second lower chamber sampling tube 10-2 respectively, and an air intake pipe interface 11-3 connected to the lower chamber air intake pipe 10-4, and a first bottom groove 11-2 at the bottom; the second semi-cylindrical box 12 has a sensor interface 12-1 for connecting the temperature sensor 3 at the top, sampling tube interfaces 12-5 and 12-6 for placing the first upper chamber sampling tube 8-1 and the first lower chamber sampling tube 10-1 respectively on the side, and a second bottom groove 12-2 and a bottom bolt hole 12-4 at the bottom; as shown Figure 7 As shown, the base 13 is provided with three base protrusions 13-1, a base groove 13-2 and a base bolt hole 13-3, and the base 13 is connected to the first semi-cylindrical box 11 and the second semi-cylindrical box 12 by bolts 7. After the diffusion double chamber 1 is connected to the heat preservation box 2, the air pipe 4 is used to connect to the gas cylinder 5.

[0046] In a specific embodiment of the present invention, the diffusion double chamber 1 is composed of only two parts, the upper chamber 8 and the lower chamber 10, which are assembled with the sample ring 9, thereby reducing the number of parts and components and reducing the probability of air leakage in the device. At the same time, O-rings are placed at the connection between the upper chamber 8 and the lower chamber 10 and the sample ring 9 to enhance the sealing of the device.

[0047] In a specific embodiment of the present invention, the diffusion double chamber 1 is placed in an insulation box 2, and a temperature sensor 3 is provided in the insulation box. The temperature of the device can be controlled by adding an external heating belt and insulation materials.

[0048] In a specific embodiment of the present invention, the sample ring 9 is of a pull-and-release type and can be directly used for sample preparation, facilitating rapid replacement of test soil samples.

[0049] In a specific embodiment of the present invention, the first semi-cylindrical box body 11 and the second semi-cylindrical box body 12 of the thermal insulation box 2 have openings 11-7 and 12-7 on the side edges respectively, and are connected by a buckle 14, so that the thermal insulation box can be quickly disassembled and assembled. In addition, the bottom has a first bottom groove 11-2 and a second bottom groove 12-2 and a first bottom bolt hole 11-1 and a second bottom bolt hole 12-4, which are fixed to the base 13 by screws 7.

[0050] In a specific embodiment of the present invention, the first upper chamber sampling tube 8-1, the second upper chamber sampling tube 8-2, the first lower chamber sampling tube 10-1, and the second lower chamber sampling tube 10-2 can be used for flushing the gas chamber before the experiment and for connecting the gas pressure gauge 15 to achieve accurate judgment of the air tightness of the device, and can also be used for injection and sampling of the gas to be tested during the experiment.

[0051] The gas diffusion coefficient test method based on multi-component gas diffusion theory is:

[0052] S1. Sample filling and device air tightness test. After the soil sample is prepared, fill it into the sample ring 9, connect the upper chamber 8, the lower chamber 10, the sample ring 9 and the porous plate 16 through bolts 6, and place O-rings in the groove 8-4 at the bottom of the upper chamber and the groove 10-5 inside the lower chamber. The groove 10-6 at the bottom of the diffusion double chamber 1 and the base protrusion 13-1 of the insulation box base 13 are installed one by one to fix the diffusion double chamber 1 and the base 13. Connect the diffusion double chamber device 1 to the gas cylinder 5 through the air pipe 4, and connect and fix all parts to achieve airtightness. Pass the experimental gas, and observe that the reading of the barometer 15 does not change within 2 hours to ensure the air tightness of the device.

[0053] S2. Connecting the heat preservation device: The first cylindrical box 11 and the second semi-cylindrical box 12 are fixed to the base by bolts 7 , and then the first cylindrical box 11 and the second semi-cylindrical box 12 are connected by buckles 14 .

[0054] S3. Temperature setting. Wrap the heating tape and insulation cloth outside the insulation box, set the required temperature through the temperature controller, and control the internal temperature to the required temperature through the temperature sensor 3 inside the box.

[0055] S4. Injection of the gas to be tested. Use a syringe to slowly inject 50 mL of a mixed gas of CO2 and CH4 into the lower chamber 10 through the first lower chamber sampling port 10-1; inject 50 mL of O2 into the upper chamber 8 through the first upper chamber sampling port 8-1 to replace the air in the gas chamber.

[0056] S5. Gas sampling. Immediately after the gas is injected, 1 mL of gas is collected as the initial gas sample through the second upper chamber sampling port 8-2 and the second lower chamber sampling port 10-2 with a syringe and the sampling time is recorded; sampling is performed every minute within 10 minutes before the start of the experiment; sampling is performed every 5 minutes from 10 to 60 minutes; and sampling is performed every 20 minutes thereafter until 2 hours. If the saturation is high, the sampling interval can be appropriately extended. The concentrations of CH4, CO2 and O2 in the gas sample are analyzed by gas chromatography.

[0057] S6. Repeat the experiment. Repeat the above process through the test parameters or test conditions of multi-component gas diffusion to achieve the diffusion performance study of multi-component gas under different working conditions.

[0058] S7. Calculation of diffusion coefficient. Equation (3) is the mass conservation equation of multi-component gas. The gas contains three components, CH4, CO2 and O2. The diffusion of multi-component gas in porous media can be described by the dust-gas model (DGM), as shown in equation (4). The numerical model is established by equations (3) and (4), and the boundary conditions are shown in equations (5-7):

[0059]

[0060]

[0061] Among them, θ g is the gas pore volume ratio of the soil sample; R(m 3 / Pa·K / mol) is the ideal gas constant; T(K) is the absolute temperature; p i (Pa) is the partial pressure of gas component i; t(s) is the time; N i (mol / m 2 / s) is the diffusion flux of the i-component gas, which can be calculated by formula (4); z(m) is the depth; τ is the tortuosity coefficient; D ij (m 2 / s) is the binary diffusion coefficient of bulk diffusion of component i and component j in air; D iK (m 2 / s) is the Knudsen diffusion coefficient of component i.

[0062] At the initial moment, the concentration of each component gas in the soil is the concentration in the air:

[0063] C s =C air t=0 (5)

[0064] The gas concentration boundaries at the top and bottom of the soil column use integral boundaries. Assuming that the gas in the air chamber is evenly mixed, the gas concentration at the top boundary (or bottom boundary) at time t is equal to the gas concentration in the air chamber at time t, which can be calculated by adding (or subtracting) the gas flux flowing into (or out of) the air chamber during the time period t from the gas concentration at the initial time. The boundary condition at the top of the soil column is:

[0065]

[0066] In the formula, C 0,top is the initial concentration of the gas in the top air chamber at the initial moment. The boundary condition at the bottom of the soil column is:

[0067]

[0068] In the formula, C 0,bottom is the initial concentration of the gas in the bottom chamber at the initial moment.

[0069] After the experiment, the data obtained from the experiment were substituted into equations (3)-(7) to obtain the multi-component gas diffusion coefficient.

[0070] Figure 8 (a)-(c) in the figure respectively give the experimental data of O2, CH4 and CO2 concentrations in the upper and lower chambers measured by the double-chamber diffusion device (red squares and blue dots in the figure). Substitute the parameters of the experimental device (sample ring height, diameter, etc.) and the parameters of the test soil (porosity, water content, dry density, etc.) into the DGM model and Fick's law model, and obtain the concentration curve that best fits the experimental data by changing the tortuosity coefficient τ in the model (if τ takes other values, the simulated concentration curve will have a greater deviation from the experimental data points), as shown in Figure 8 As shown, the red solid line and dashed line are the gas concentration curves to be measured in the upper chamber, and the blue dotted line and dashed line are the gas concentration curves to be measured in the lower chamber. The simulation results show that the tortuosity coefficient τ of the sample soil obtained by the DGM model and the Fick law model is 0.1 (then the diffusion coefficient of each gas is τD ij ). At the same time, from Figure 8It can be seen that the experimental test data points are more evenly and closely distributed near the concentration curve obtained by the DGM model, indicating that the simulation performed by the DGM model is closer to the actual situation. The gas migration flux obtained by the Fick law describing gas diffusion is larger. At 20 minutes, the CH4 and CO2 concentrations in the top gas chamber obtained by the Fick law describing the gas diffusion model are 1.5 times the results of the multi-component gas diffusion model. Comparing the above results, it can be concluded that ignoring the interaction in the multi-component diffusion process may lead to large deviations in the prediction of multi-component gas concentrations. Using the DGM model can obtain more accurate prediction results.

[0071] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A gas diffusion coefficient testing device based on multi-component gas diffusion theory, characterized in that: It comprises an insulated box (2), a diffusion double chamber (1) arranged inside the insulated box, and a gas cylinder (5); The diffusion double chamber (1) has a vertically arranged cylindrical chamber inside, and the main body of the diffusion double chamber (1) includes an upper chamber (8), a sample ring (9) and a lower chamber (10) in sequence from top to bottom; wherein the sample ring (9) is used to fill soil samples; sampling tubes are arranged on the upper chamber (8) and the lower chamber (10), and the sampling tubes are used for multi-component gas sampling, collecting gas samples, gas chamber flushing or connecting a gas pressure gauge for air tightness detection; sealing rings are arranged at the connection between the upper chamber (8) and the lower chamber (10) and the sample ring (9) for sealing; The heat preservation box (2) is divided into a first semi-cylindrical box body (11), a second semi-cylindrical box body (12) and a base (13); wherein the bottom of the diffusion double chamber (1) is mounted on the base (13); the first semi-cylindrical box body (11) and the second semi-cylindrical box body (12) are mutually buckled and mounted on the base (13); the sampling tube on the diffusion double chamber (1) extends out of the heat preservation box (2); The lower chamber (10) is connected to the gas cylinder (5) via an air pipe (4).

2. The gas diffusion coefficient testing device based on multi-component gas diffusion theory according to claim 1, characterized in that: The sample ring (9) is a hollow cylindrical structure. A porous plate (16) for carrying soil samples is arranged at the bottom of the sample ring. A convex edge for installation and positioning is arranged outwardly at the top of the sample ring (9).

3. The gas diffusion coefficient testing device based on multi-component gas diffusion theory according to claim 2, characterized in that: The top of the upper chamber is sealed and the bottom is open. A circle of upper chamber convex edges is arranged outward at the bottom of the upper chamber. An annular positioning hole for installing the sample ring convex edge is arranged on the upper chamber convex edge. An upper chamber bottom groove (8-4) for installing an O-ring is reserved in the annular positioning hole. The side wall of the upper chamber is provided with a first upper chamber sampling tube (8-1) and a second upper chamber sampling tube (8-2) in the horizontal direction. A plurality of bolt holes are arranged on the upper chamber convex edge. The inner diameter of the upper chamber (8) is the same as the inner diameter of the sample ring (9).

4. The gas diffusion coefficient testing device based on multi-component gas diffusion theory according to claim 3 is characterized in that: The top of the lower chamber (10) is open, and an enlarged sample ring installation section is provided at the upper part of the lower chamber (10). The inner diameter of the sample ring installation section is the same as the outer diameter of the sample ring, and the length of the sample ring installation section is the same as the length of the sample ring excluding the convex edge section. A first lower chamber sampling tube (10-1) and a second lower chamber sampling tube (10-2) are provided on the side wall of the lower chamber (10) in the horizontal direction, and an air inlet (10-4) is provided at the bottom, and the air inlet (10-4) is connected to the gas cylinder (5) through the air pipe (4). A lower chamber internal groove (10-5) for installing an O-ring is reserved on the bottom installation surface of the sample ring installation section.

5. The gas diffusion coefficient testing device based on multi-component gas diffusion theory according to any one of claims 1 to 4, characterized in that: A temperature sensor (3) is arranged in the heat preservation box, and the temperature of the device is controlled by adding a heating belt and heat preservation material.

6. The gas diffusion coefficient testing device based on multi-component gas diffusion theory according to claim 4, characterized in that: A circle of lower chamber convex edges is arranged on the side of the lower chamber (10), and a plurality of lower chamber bolt holes (10-3) are reserved on the lower chamber convex edges, which correspond to and are connected to the upper chamber bolt holes one by one through bolts.

7. The gas diffusion coefficient testing device based on multi-component gas diffusion theory according to claim 4, characterized in that: The bottom of the lower chamber (10) is provided with a plurality of lower chamber bottom grooves (10-6); the base (13) is provided with base protrusions (13-1) that cooperate with the lower chamber bottom grooves; the base (13) is connected to the first semi-cylindrical box body (11) and the second semi-cylindrical box body (12) by bolts.

8. A method for testing gas diffusion coefficient based on the device of claim 4, characterized in that The steps include: S1. After the soil sample is prepared, it is loaded into the sample ring (9), the upper chamber (8), the lower chamber (10), the sample ring (9) and the porous plate (16) are connected by bolts, and O-rings are placed in the groove (8-4) at the bottom of the upper chamber and the groove (10-5) inside the lower chamber. The diffusion double chamber (1) and the base (13) are fixed, and the diffusion double chamber device (1) is connected to the gas cylinder (5) through the air pipe (4), and the various parts are connected and fixed to ensure the airtightness of the device; S2. The first cylindrical box (11) and the second semi-cylindrical box (12) are fixed to the base by bolts, and then the first cylindrical box (11) and the second semi-cylindrical box (12) are connected by a buckle (14); S3. Wrap the heating tape and insulation cloth outside the insulated box, set the required temperature through the temperature controller, and control the internal temperature to the desired temperature through the temperature sensor (3) in the insulated box (2); S4. Use a syringe to slowly inject the gas to be tested into the lower chamber and the upper chamber through the first lower chamber sampling port (10-1) and the first upper chamber sampling port (8-1), respectively; S5. After the gas is injected, the gas is immediately collected through the second upper chamber sampling port (8-2) and the second lower chamber sampling port (10-2) with a syringe as the initial gas sample and the sampling time is recorded; sampling is performed at the set time after the experiment starts; the concentration of each component in the gas sample is analyzed by a gas chromatograph; S6. Repeat the above S4 and S5 processes through the test parameters or test conditions of multi-component gas diffusion to achieve the diffusion performance study of multi-component gas under different working conditions; S7. After the experiment, the multi-component gas diffusion coefficient is obtained through the multi-component gas diffusion model.

9. The gas diffusion coefficient testing method according to claim 8, characterized in that: The S7 is specifically: Assuming that the gas contains n components, the diffusion of multi-component gas in porous media is described by the dust-gas model (DGM), as shown in equation (4). The multi-component gas diffusion model is established by the mass conservation equation (3) of the multi-component gas and the dust-gas model equation (4). The boundary conditions are shown in equations (5) to (7): Among them, θ g is the gas pore volume ratio of the soil sample; R is the ideal gas constant; T is the absolute temperature; p i is the partial pressure of gas component i; t is time; N i is the diffusion flux of component i gas, calculated by formula (4); z is the depth; τ is the tortuosity coefficient; D ij is the binary diffusion coefficient of bulk diffusion of component i and component j in air; D iK is the Knudsen diffusion coefficient of component i; At the initial moment, the concentration of each component gas in the soil is the concentration in the air: C s =C air t=0 (5) The gas concentration boundaries at the top and bottom of the soil column adopt integral boundaries; assuming that the gas in the air chamber is evenly mixed, the gas concentration at the top boundary or the bottom boundary at time t is equal to the gas concentration in the air chamber at time t, and the boundary condition at the top of the soil column is: In the formula, C 0,top is the initial concentration of the gas in the top air chamber at the initial moment; the boundary condition at the bottom of the soil column is: In the formula, C 0,bottom is the initial concentration of the gas in the bottom chamber at the initial moment; Substitute the experimental data into equations (3)-(7) to obtain the multi-component gas diffusion coefficient.

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