CN106769667B

CN106769667B - Nanoscale gas flow rule experiment system and method

Info

Publication number: CN106769667B
Application number: CN201611183952.7A
Authority: CN
Inventors: 王登科; 魏建平; 姚邦华; 刘勇; 李波; 王洪磊; 刘淑敏; 夏玉玲
Original assignee: Henan University of Technology
Current assignee: Henan University of Technology
Priority date: 2016-12-20
Filing date: 2016-12-20
Publication date: 2023-03-10
Anticipated expiration: 2036-12-20
Also published as: CN106769667A

Abstract

The invention discloses a nanoscale gas flow law experiment system which comprises a clamp holder, a pressure control system, a vacuum pumping system, a pressure difference measuring system, a pressure stabilizing system, a flow measuring system and a data acquisition control system, wherein the clamp holder, the pressure control system, the vacuum pumping system, the pressure difference measuring system, the pressure stabilizing system, the flow measuring system and the data acquisition control system are arranged in a constant temperature box; the pressure control system comprises an inlet pressure control unit and an outlet pressure control unit; the vacuum pumping system comprises a vacuum pump and a vacuum pumping pipeline; the pressure differential pressure measuring system comprises a precision pressure sensor and a differential pressure sensor; the flow measurement system comprises a first branch, a second branch and a third branch which are connected in parallel; the pressure stabilizing system comprises a pressure buffer tank and a pressure stabilizing container, and the data acquisition control system comprises a computer and a signal circuit; the invention also discloses a method for carrying out experiments by using the system. The system and the method are very convenient to switch the experiment types and the experiment conditions, meet the requirement of researching the flow rule of the nanoscale gas from multiple angles, simulate the geological field conditions of various shale gas reservoirs and provide theoretical guidance for exploitation of the shale gas.

Description

Nanoscale gas flow rule experiment system and method

Technical Field

The invention relates to the technical field of shale gas development, in particular to a system and a method for testing a nanoscale gas flow rule, which are mainly used for researching the nanoscale gas flow rule and the nanoscale gas flow rule with different rarefaction degrees under different pressure difference conditions.

Background

Shale gas reservoirs are ultra-low permeability reservoirs with abundant nanoscale pores, and the nanoscale pores inside the reservoirs are extremely developed. The average free path of gas molecules (the average value of each free path which is possible by one gas molecule between two continuous collisions and refers to the average distance which is passed by the collision of the particles and other particles, which is represented by the symbol lambda and is expressed by meters) is equivalent to the size of pores, under the condition, the number of Knudsen is large, and the gas flow has various flow mechanisms such as seepage, slip and diffusion, so that the gas production mechanism of the shale gas reservoir with low seepage characteristics is very complex, and the research on the flow characteristics of the nanoscale gas has important significance for the development of the shale gas.

The anodic alumina film has uniform pore distribution and controllable pore diameter, and the pore diameter of each alumina film is uniform, so that the invention provides a method for carrying out nano-scale gas flow rule research by taking the anodic alumina film with uniform pore diameter and nano pores as a sample for simplifying the research.

Disclosure of Invention

The invention aims to provide a nanoscale gas flow law experiment system which can stably and reliably clamp a sample, can perform normal-pressure experiments and negative-pressure experiments conveniently, can test nanoscale gas flow characteristics under different pressure difference conditions, and can realize nanoscale gas flow law experiments with different rarefaction degrees.

In order to achieve the above object, the present invention provides a system for testing a flow law of a nanoscale gas, comprising: the device comprises a clamp holder, a pressure control system, a vacuum pumping system, a pressure difference measuring system, a pressure stabilizing system, a flow measuring system and a data acquisition control system which are arranged in a constant temperature box;

the clamp holder comprises a left tank body and a right tank body, wherein a left connecting disc is arranged at the right end of the left tank body in a protruding mode along the radial direction, a right connecting disc is arranged at the right end of the right tank body in a protruding mode along the radial direction, and the left connecting disc and the right connecting disc are detachably pressed together through bolts; a left clamping groove is formed in the right end face of the left connecting disc, a right clamping groove is formed in the left end face of the right connecting disc, and the left clamping groove and the right clamping groove correspond to each other and form an orifice plate clamping groove; an orifice plate structure is clamped in the orifice plate clamping groove;

the pore plate structure comprises a left pore plate and a right pore plate which are in clamping fit, the radial outer end parts of the left pore plate and the right pore plate are clamped in the pore plate clamping grooves, air holes are correspondingly formed in the middle parts of the left pore plate and the right pore plate, and the air holes in the left pore plate and the air holes in the right pore plate are correspondingly communicated and penetrate through the left pore plate and the right pore plate left and right; a round sample made of an anodic aluminum oxide film is pressed between the left pore plate and the right pore plate; the orifice plate structure divides the inner cavity of the holder into a left cavity and a right cavity;

the pressure control system comprises an inlet pressure control unit and an outlet pressure control unit; the inlet pressure control unit comprises a high-pressure gas cylinder for storing natural gas, a pressure reducing valve, an inlet pressure gauge and an inlet speed regulating valve; the outlet of the high-pressure gas cylinder is sequentially connected with the pressure reducing valve, the inlet pressure gauge and the inlet speed regulating valve from back to front by taking the airflow direction as the front direction;

the outlet pressure control unit comprises a pressure vacuum meter, an outlet speed regulating valve and a first manual valve which are sequentially connected through a pipeline from back to front;

the vacuumizing system comprises a vacuum pump, a suction inlet of the vacuum pump is connected with a vacuumizing pipeline, and a second manual valve is arranged on the vacuumizing pipeline;

the pressure differential pressure measuring system comprises a precise pressure sensor and a differential pressure sensor, one end of the differential pressure sensor is communicated with the left cavity through a measuring tube, and the other end of the differential pressure sensor is communicated with the right cavity through the measuring tube;

the flow measurement system comprises a first branch, a second branch and a third branch which are connected in parallel; the first branch is connected with a first electromagnetic valve and a first mass flowmeter with the range of 0 to 100SCCM in series, the second branch is connected with a second electromagnetic valve and a second mass flowmeter with the range of 0 to 500SCCM in series, and the third branch is connected with a third electromagnetic valve and a third mass flowmeter with the range of 0 to 5000SCCM in series;

the pressure stabilizing system comprises a pressure buffer tank and a pressure stabilizing container, the pressure buffer tank is connected with the pressure stabilizing container through a communicating pipe, the pressure stabilizing container is connected with a fourth electromagnetic valve for emptying negative pressure, and a first pressure sensor and a temperature sensor are arranged on the pressure buffer tank;

the data acquisition control system comprises a computer and a signal line connected with the computer;

the left cavity of the holder is communicated with an air inlet pipe, the air inlet pipe is connected with the inlet speed regulating valve, a first three-way valve is connected to the air inlet pipe in series, a third interface of the first three-way valve is connected with the precise pressure sensor, and the precise pressure sensor, the differential pressure sensor, the first to fourth electromagnetic valves, the first to third mass flow meters, the first pressure sensor and the temperature sensor are respectively connected with the computer through signal lines;

the right cavity of the clamp holder is communicated with an air outlet pipe, and the air outlet pipe is connected with a pressure vacuum meter of the outlet pressure control unit; a second three-way valve is arranged on the air outlet pipe, and a third interface of the second three-way valve is connected with the vacuumizing pipeline;

a first four-way valve is arranged between the flow measuring system and the outlet pressure control unit, and a second four-way valve is arranged at the gas outflow end of the flow measuring system;

the rear ends of the first branch, the second branch and the third branch are respectively connected with an interface of the first four-way valve by taking the airflow direction as the forward direction, and a fourth interface of the first four-way valve is connected with the front end of the pipeline of the outlet pressure control unit;

the front ends of the first branch, the second branch and the third branch are respectively connected with one interface of the second four-way valve, the fourth interface of the second four-way valve is connected with a third three-way valve, the other two interfaces of the third three-way valve are respectively connected with an emptying pipe and a pressure-stabilizing air inlet pipe, and a third manual valve is arranged on the emptying pipe; and the pressure stabilizing air inlet pipe is connected with the pressure buffer tank, and a fourth manual valve is arranged on the pressure stabilizing air inlet pipe.

The radial outer ends of the left pore plate and the right pore plate are pressed together through bolts; the middle part of left side orifice plate is protruding to be equipped with the ka tai right, the middle part of right side orifice plate be equipped with the recess of ka tai looks adaptation, ka tai card is gone into the recess, just the sample crimping is between the tank bottom of ka tai and recess.

A fifth manual valve is arranged on the communicating pipe; the volume of the pressure buffer tank is more than or equal to 5 liters, and the volume of the pressure stabilizing container is more than or equal to 15 liters.

An annular left sealing groove is formed in the left side surface of the left pore plate on the radial outer side of the clamping table, and a left sealing ring is arranged in an annular space defined by the left sealing groove and the left connecting disc in a pressing mode;

a middle sealing groove is formed in the left side surface of the right pore plate on the radial outer side of the groove, and a middle sealing ring is pressed in an annular space formed by the left pore plate and the middle sealing groove in an enclosed mode;

the right side surface of the right orifice plate on the radial outer side of the groove is provided with a right sealing groove, and a right sealing ring is pressed in an annular space formed by the right connecting disc and the middle sealing groove.

The invention also aims to provide a method for carrying out the normal pressure experiment by using the nano-scale gas flow law experiment system, which sequentially comprises the following steps:

the first step is a sample loading and connecting step, firstly, all valves are closed, a round sample is loaded between a left pore plate and a right pore plate of a clamp holder, the left pore plate and the right pore plate are pressed together through bolts, a pore plate structure consisting of the left pore plate and the right pore plate is loaded into a pore plate clamping groove, then a left tank body and a right tank body are pressed together through bolts, an air inlet pipe and an air outlet pipe are respectively connected to the left end and the right end of the clamp holder, and the good sealing of the connection part is ensured;

the second step is a vacuumizing step; firstly, opening an inlet speed regulating valve, an outlet speed regulating valve, a first manual valve, a second manual valve and first to third electromagnetic valves, starting a vacuum pump to perform degassing treatment on a system, judging whether the vacuum degree requirement of an experiment is met or not according to the reading of a pressure vacuum meter, closing the inlet speed regulating valve, the outlet speed regulating valve, the first manual valve, the second manual valve and the first to third electromagnetic valves when the reading of the pressure vacuum meter is 0, and closing the vacuum pump;

the third step is a temperature adjustment step; adjusting the temperature of the thermostat to a range set by an experiment to ensure that the experiment system is in a constant temperature state;

the fourth step is a ventilation step; opening the pressure reducing valve, the third manual valve, the first manual valve and the outlet speed regulating valve, regulating the inlet speed regulating valve according to the indication of the precise pressure sensor, and regulating the air inlet pressure of the clamp holder to the value set by the experiment; gas in the high-pressure gas cylinder enters the left cavity of the clamp holder through the gas inlet pipe, then sequentially passes through the left pore plate, the sample and the right cavity, and flows out of the clamp holder through the gas outlet pipe;

the fifth step is a metering step; adjusting an outlet speed regulating valve according to the design requirements of the test so as to regulate the gas pressure difference at two sides of the sample to a preset value, and continuously acquiring and recording pressure data transmitted by a precision pressure sensor and pressure difference data transmitted by a pressure difference sensor by a computer;

according to the size of the gas flow, the mass flow meter with the range larger than the actual gas flow and the range closest to the actual gas flow is the best-matched mass flow meter, the electromagnetic valve on the branch of the best-matched mass flow meter is opened, so that the gas mass flow under the normal pressure condition and the specific pressure difference condition is accurately measured through the first mass flow meter, the second mass flow meter or the third mass flow meter, and the gas is discharged after passing through the third three-way valve, the emptying pipe and the third manual valve after passing through the flow measurement system; the computer continuously collects and records the gas flow data transmitted by the mass flowmeter; after the gas flow is stable and unchanged, the computer records pressure data, pressure difference data and gas flow data under a steady flow state, and completes a test under normal pressure and specific pressure difference;

repeatedly carrying out the fifth step, and regulating the gas pressure difference at two sides of the sample to different preset values by regulating the outlet speed regulating valve when carrying out the fifth step each time, thereby completing the nano-scale gas flow rule experiment under the conditions of normal pressure and different pressure differences;

after the experiment is finished, all the valves are closed in sequence from back to front by taking the direction of the airflow as the front direction, so that a complete sample experiment is finished;

and in the sixth step, samples with different pore diameters are replaced, and the first step, the second step and the third step are repeated to complete the nano-scale gas flow rule experiment under different pore conditions.

The invention also aims to provide a method for carrying out a negative pressure experiment by using the nanoscale gas flow law experiment system, which sequentially comprises the following steps:

the second step is a vacuumizing step; firstly, opening an inlet speed regulating valve, an outlet speed regulating valve, a first manual valve, a second manual valve, a third manual valve, a fourth manual valve and a fifth manual valve, starting a vacuum pump to degas a system, judging whether the vacuum degree requirement of an experiment is met or not according to the reading of a pressure vacuum meter, and closing the inlet speed regulating valve, the outlet speed regulating valve, the first manual valve, the second manual valve, the fourth manual valve, the fifth manual valve and the third manual valve when the reading of the pressure vacuum meter reaches a preset negative pressure; closing the vacuum pump;

the fourth step is a ventilation step; opening a pressure reducing valve, adjusting an inlet speed regulating valve according to the indication number of a precise pressure sensor, adjusting the air inlet pressure of the holder to the range set by the experiment, allowing the gas in the high-pressure gas cylinder to enter a left cavity of the holder through an air inlet pipe, then sequentially passing through a left pore plate, a sample and a right cavity, and allowing the gas to flow out of the holder through an air outlet pipe;

the fifth step is a metering step; adjusting an outlet speed regulating valve according to the design requirements of the test so as to regulate the gas pressure difference at two sides of the sample to a preset value, and continuously acquiring and recording pressure data at an inlet transmitted by a precision pressure sensor and pressure difference data transmitted by a pressure difference sensor by a computer;

opening a first manual valve, a fourth manual valve and a fifth manual valve, according to the size of gas flow, enabling a mass flow meter with a measuring range larger than the actual gas flow and the measuring range closest to the actual gas flow to be a best-matched mass flow meter, opening an electromagnetic valve on a branch of the best-matched mass flow meter, accurately measuring the gas mass flow under a negative pressure condition and a specific pressure difference condition through the first mass flow meter, the second mass flow meter or the third mass flow meter, enabling the gas to enter a pressure buffer tank through a third three-way valve and the fourth manual valve after passing through a flow measuring system, and then entering a pressure stabilizing container through a communicating pipe; the computer continuously collects and records gas flow data transmitted by the mass flow meter, pressure data of the pressure buffer tank transmitted by the first pressure sensor and temperature data transmitted by the temperature sensor; after the gas flow is stable and unchanged, the computer records pressure data at an inlet, pressure data of the pressure buffer tank, pressure difference data and gas flow data under a steady flow state, and completes a negative pressure specific pressure difference experiment;

repeatedly carrying out the fifth step, and regulating the gas pressure difference at two sides of the sample to different preset values by regulating the outlet speed regulating valve when carrying out the fifth step each time, thereby completing the nano-scale gas flow rule experiment under the conditions of negative pressure and different pressure differences;

closing other valves except the fifth manual valve, then opening the fourth electromagnetic valve, and emptying the gas in the pressure buffer tank and the pressure stabilizing container to complete a complete sample experiment;

and the sixth step is to replace the samples with different pore diameters, repeat the first to fifth steps and complete the nano-scale gas flow law experiment under different pore conditions and negative pressure conditions.

The invention also aims to provide a method for carrying out gas experiments with different rarefaction degrees by using the nanoscale gas flow law experiment system, which sequentially comprises the following steps:

the first step is a sample loading and connecting step, firstly, all valves are closed, a round sample is loaded between a left pore plate and a right pore plate of a holder, the left pore plate and the right pore plate are pressed together through bolts, a pore plate structure consisting of the left pore plate and the right pore plate is loaded into a pore plate clamping groove, then a left tank body and a right tank body are pressed together through bolts, an air inlet pipe and an air outlet pipe are respectively connected to the left end and the right end of the holder, and the good sealing of the connection part is ensured;

the third step is a temperature adjustment step; adjusting the temperature of the thermostat to a range set by an experiment, and ensuring that the experiment system is in a constant temperature state;

according to the size of the gas flow, the mass flow meter with the range larger than the actual gas flow and the range closest to the actual gas flow is the best-matched mass flow meter, the electromagnetic valve on the branch of the best-matched mass flow meter is opened, so that the gas mass flow under the normal pressure condition and the specific pressure difference condition is accurately measured through the first mass flow meter, the second mass flow meter or the third mass flow meter, and the gas is discharged after passing through the third three-way valve, the emptying pipe and the third manual valve after passing through the flow measurement system; the computer continuously collects and records the gas flow data transmitted by the mass flowmeter;

in the process of the fifth step, continuously adjusting the outlet speed regulating valve, and keeping the gas pressure difference on the two sides of the sample unchanged during the fifth step;

after the gas flow is stable and unchanged, the computer records pressure data, pressure difference data and gas flow data under a steady flow state, and completes a test under normal pressure and constant pressure difference;

repeatedly carrying out the fifth step, and regulating the air inlet pressure of the clamp holder to different preset values by regulating the inlet speed regulating valve when carrying out the fifth step each time, thereby completing the nanoscale gas flow law experiment of different rarefactions under the constant pressure difference state under normal pressure;

and in the sixth step, samples with different pore diameters are replaced, and the first step to the fifth step are repeated to complete the nanoscale gas flow rule experiment with different pore conditions and different rarefaction degrees under constant pressure difference.

The invention has the following advantages:

the nanoscale gas flow law experiment system is simple in structure, convenient to connect various systems, convenient to install and replace samples and convenient to operate, and the clamp holder can stably and reliably fix the samples and has good sealing performance. By using the invention, the experimental data can be monitored in real time and automatically collected, so that the experimental result has more comprehensiveness and reliability. The invention can test the flow rule of the gas with different rarefaction degrees under the same pressure difference condition in the nanometer scale. The pressure stabilizing system has the volume matched with the gas flow in the experiment, can keep stable negative pressure in the system in the negative pressure experiment, and simultaneously does not excessively increase the volume of the pressure stabilizing system.

The nanoscale gas flow law experiment system and method can realize multiple types of experiments such as normal pressure experiments, negative pressure experiments, constant pressure difference and the like by opening and closing each valve and adjusting the opening degree of each valve, can perform experiments under different air inlet pressure conditions, different pressure difference conditions and different pore conditions, have rich functions, are very convenient to switch experiment types and experiment conditions, can meet the requirement of researching nanoscale gas (natural gas) flow laws from multiple angles, can simulate geological field conditions of various shale gas mineral reservoirs, and provide theoretical guidance for exploitation of shale gas.

Specifically, the method for performing the normal pressure experiment by using the nanoscale gas flow law experiment system can complete the nanoscale gas flow law experiment under the conditions of normal pressure and different pressure differences under the constant temperature condition, and can simulate different pore conditions by conveniently replacing samples with different pore diameters, thereby facilitating the multi-group variable pressure difference experiment under different preset temperature conditions.

The method for performing the negative pressure experiment by using the nanoscale gas flow law experiment system can complete the nanoscale gas flow law experiment under different negative pressure and pressure difference states under the conditions of negative pressure and constant temperature, conveniently simulate different pore conditions and conveniently perform a multi-group variable pressure difference experiment under different preset negative pressure and temperature conditions.

The method for carrying out the gas experiments with different rarefaction degrees by using the nanoscale gas flow law experiment system can complete the nanoscale gas flow law experiments under the constant pressure and constant temperature conditions at the normal pressure, conveniently simulate different pore conditions, conveniently simulate gas environments with different rarefaction degrees at different temperatures and under different pore conditions, and carry out multiple groups of constant pressure difference experiments.

Drawings

FIG. 1 is a schematic structural diagram of a nanoscale gas flow law experimental system of the present invention;

FIG. 2 is a schematic view of the structure of the holder;

FIG. 3 is an enlarged view at A in FIG. 2;

FIG. 4 is a schematic view of the structure of the left orifice plate;

FIG. 5 is a schematic diagram of a right orifice plate;

fig. 6 is a schematic cross-sectional view of a chuck.

Detailed Description

The direction of the arrows in fig. 1 is the direction of flow of the fluid there.

As shown in fig. 1 to 6, the nanoscale gas flow law experiment system of the present invention comprises a holder 9, a pressure control system, a vacuum pumping system, a pressure differential measurement system, a pressure stabilization system, a flow measurement system and a data acquisition control system, which are arranged in a thermostat 8; incubator 8 is conventional in the art, and preferably employs a thermostatic water bath structure to maintain a constant temperature state, and the specific structure will not be described in detail.

The clamp holder 9 comprises a left tank body 51 and a right tank body 52, the right end of the left tank body 51 is provided with a left connecting disc 53 in a protruding mode along the radial direction, the right end of the right tank body 52 is provided with a right connecting disc 54 in a protruding mode along the radial direction, and the left connecting disc 53 and the right connecting disc 54 are detachably connected together in a pressing mode through bolts; a left clamping groove 55 is formed in the right end face of the left connecting disc 53, a right clamping groove 56 is formed in the left end face of the right connecting disc 54, and the left clamping groove 55 and the right clamping groove 56 correspond to each other to form an orifice plate clamping groove; an orifice plate structure is clamped in the orifice plate clamping groove;

the pore plate structure comprises a left pore plate 57 and a right pore plate 58 which are in clamping fit, the radial outer end parts of the left pore plate 57 and the right pore plate 58 are clamped in pore plate clamping grooves, air holes 59 are correspondingly formed in the middle parts of the left pore plate 57 and the right pore plate 58, the air holes 59 in the left pore plate 57 are correspondingly communicated with the air holes 59 in the right pore plate 58, and the left pore plate 57 and the right pore plate 58 are communicated in a left-right mode; a round sample 60 made of an anodized aluminum film is pressed between the left orifice plate 57 and the right orifice plate 58; the left orifice plate 57 and the right orifice plate 58 may be prepared in various models with different pore diameters according to experimental design, and the pore diameters of the air holes 59 of the left orifice plate 57 and the right orifice plate 58 with different models are different. The orifice plate structure divides the inner cavity of the holder 9 into a left cavity 61 and a right cavity 62; a variety of left and

right orifice plates

57, 58 having different pore diameters of the air holes 59 may be fabricated according to different experimental designs.

The pressure control system comprises an inlet pressure control unit and an outlet pressure control unit; the inlet pressure control unit comprises a high-pressure gas bottle 1 for storing natural gas, a pressure reducing valve 2, an inlet pressure gauge 3 and an inlet speed regulating valve 4; the outlet of the high-pressure gas bottle 1 is sequentially connected with the pressure reducing valve 2, the inlet pressure gauge 3 and the inlet speed regulating valve 4 from back to front by taking the airflow direction as the front direction;

the outlet pressure control unit comprises a pressure vacuum gauge 17, an outlet speed regulating valve 18 and a first manual valve 19 which are connected in sequence through pipelines from back to front;

the vacuumizing system comprises a vacuum pump 16, a vacuumizing pipeline 71 is connected to a suction inlet of the vacuum pump 16, and a second manual valve 15 is arranged on the vacuumizing pipeline 71;

the pressure differential pressure measuring system comprises a precision pressure sensor 6 and a differential pressure sensor 12, one end of the differential pressure sensor 12 is communicated with the left cavity 61 through a measuring pipe 72, and the other end of the differential pressure sensor 12 is communicated with the right cavity 62 through the measuring pipe 72;

the flow measurement system comprises a first branch 73, a second branch 74 and a third branch 75 connected in parallel; the first branch 73 is connected with a first electromagnetic valve 21 and a first mass flowmeter 24 with the range of 0 to 100SCCM in series, the second branch 74 is connected with a second electromagnetic valve 22 and a second mass flowmeter 25 with the range of 0 to 500SCCM in series, and the third branch 75 is connected with a third electromagnetic valve 23 and a third mass flowmeter 26 with the range of 0 to 500SCCM in series; SCCM is the volume flow unit, i.e., standard condition milliliters per minute.

The pressure stabilizing system comprises a pressure buffer tank 31 and a pressure stabilizing container 35, the pressure buffer tank 31 is connected with the pressure stabilizing container 35 through a communicating pipe 76, the pressure stabilizing container 35 is connected with a fourth electromagnetic valve 36 for emptying negative pressure, and the pressure buffer tank 31 is provided with a first pressure sensor 32 and a temperature sensor 33;

the data acquisition control system comprises a computer 37 and a signal line 77 connected with the computer 37;

the left cavity 61 of the clamp 9 is communicated with an air inlet pipe 7, the air inlet pipe 7 is connected with the inlet speed regulating valve 4, the air inlet pipe 7 is connected with a first three-way valve 5 in series, a third interface of the first three-way valve 5 is connected with the precision pressure sensor 6, and the precision pressure sensor 6, the differential pressure sensor 12, the first to fourth

electromagnetic valves

21, 22, 23 and 36, the first to third

mass flow meters

24, 25 and 26, the first pressure sensor 32 and the temperature sensor 33 are respectively connected with the computer 37 through the signal lines 77;

the right cavity 62 of the clamp holder 9 is communicated with an air outlet pipe 13, and the air outlet pipe 13 is connected with a pressure vacuum meter 17 of the outlet pressure control unit; a second three-way valve 14 is arranged on the gas outlet pipe 13, and a third interface of the second three-way valve 14 is connected with the vacuum-pumping pipeline 71;

a first four-way valve 20 is arranged between the flow measurement system and the outlet pressure control unit, and a second four-way valve 27 is arranged at the gas outflow end of the flow measurement system;

the rear ends of the first branch 73, the second branch 74 and the third branch 75 are respectively connected with an interface of the first four-way valve 20 by taking the airflow direction as the forward direction, and the fourth interface of the first four-way valve 20 is connected with the front end of the pipeline of the outlet pressure control unit;

the front ends of the first branch 73, the second branch 74 and the third branch 75 are respectively connected to one interface of the second four-way valve 27, the fourth interface of the second four-way valve 27 is connected to the third three-way valve 28, the other two interfaces of the third three-way valve 28 are respectively connected to the evacuation pipe 78 and the pressure-stabilizing air inlet pipe 79, and the evacuation pipe 78 is provided with the third manual valve 29; the pressure-stabilizing intake pipe 79 is connected to the pressure surge tank 31, and the fourth manual valve 30 is provided on the pressure-stabilizing intake pipe 79.

The radial outer ends of the left orifice plate 57 and the right orifice plate 58 are pressed together through bolts; thereby holding the sample 60 more tightly. The middle part of left side orifice plate 57 is protruding to the right and is equipped with card platform 63, the middle part of right side orifice plate 58 be equipped with the recess 64 of card platform 63 looks adaptation, card platform 63 card is gone into recess 64, just sample 60 crimping is between the tank bottom of card platform 63 and recess 64.

The communication pipe 76 is provided with a fifth manual valve 34. So that the negative pressure state can be maintained at the pressure surge tank 31 by closing the fifth manual valve 34 when the fourth electromagnetic valve 36 is opened to evacuate the negative pressure in the surge tank 35. The volume of the pressure buffer tank 31 is not less than 5 liters, and the volume of the pressure stabilizing vessel 35 is not less than 15 liters. Therefore, a relatively stable negative pressure state can be maintained in the system under the air flow condition of the normal experiment (the air flow data of the normal experiment is 2-5 liters).

The pressure vacuum gauge 17, the high-pressure gas cylinder 1, the pressure reducing valve 2, the inlet pressure gauge 3, the pressure vacuum gauge 17, the speed regulating valves, the electromagnetic valves, the precision pressure sensor 6, the differential pressure sensor 12, the mass flow meters, the pressure buffer tank 31, the computer 37 and the like are all conventional devices, and the specific structures are not detailed.

An annular left sealing groove 65 is formed in the left side surface of the left hole plate 57 on the radial outer side of the clamping table 63, and a left sealing ring 66 is pressed in an annular space defined by the left sealing groove 65 and the left connecting disc 53;

a middle sealing groove 67 is formed in the left side surface of the right pore plate 58 on the radial outer side of the groove 64, and a middle sealing ring 68 is pressed in an annular space formed by the surrounding of the left pore plate 57 and the middle sealing groove 67;

the right side surface of the right pore plate 58 at the radial outer side of the groove 64 is provided with a right sealing groove 69, and an annular space enclosed by the right connecting disc 54 and the middle sealing groove 67 is internally provided with a right sealing ring 70 in a pressing manner.

The arrangement of the three sealing rings greatly enhances the sealing performance of the clamp holder 9, thereby better ensuring the normal operation of the experiment.

Since the three-way valves and the four-way valves are always in communication, when the term "close all the valves" is used in describing the experimental method, it is easily understood by those skilled in the art that this does not mean that the three-way valves or the four-way valves can be closed.

The invention also discloses a method for carrying out normal pressure experiment by using the nano-scale gas flow law experiment system, which comprises the following steps in sequence:

the first step is a sample loading connection step, firstly, all valves are closed, and a round sample 60 is loaded between the left orifice plate 57 and the right orifice plate 58 of the clamp 9, specifically, clamped between the clamping table 63 and the groove 64; the left and

right orifice plates

57, 58 are crimped together by bolts, thereby clamping the test piece 60. The pore plate structure consisting of the left pore plate 57 and the right pore plate 58 is arranged in the pore plate clamping groove, then the left tank body 51 and the right tank body 52 are pressed together through bolts, and then the air inlet pipe 7 and the air outlet pipe 13 are respectively connected to the left end and the right end of the clamp 9, and the good sealing of the connection part is ensured;

the second step is a vacuum pumping step; firstly, opening an inlet speed regulating valve 4, an outlet speed regulating valve 18, a first manual valve 19, a second manual valve 15 and first to third

electromagnetic valves

21, 22 and 23, starting a vacuum pump 16 to perform degassing treatment on the system, judging whether the vacuum degree requirement of the experiment is met or not according to the reading of a pressure vacuum meter 17, closing the inlet speed regulating valve 4, the outlet speed regulating valve 18, the first manual valve 19, the second manual valve 15 and the first to third

electromagnetic valves

21, 22 and 23 when the reading of the pressure vacuum meter 17 is 0, and closing the vacuum pump 16;

the third step is a temperature adjustment step; adjusting the temperature of the constant temperature box 8 to the range set by the experiment to ensure that the experiment system is in a constant temperature state;

the fourth step is a ventilation step; opening the pressure reducing valve 2, the third manual valve 29, the first manual valve 19 and the outlet speed regulating valve 18, regulating the inlet speed regulating valve 4 according to the indication of the precise pressure sensor 6, and regulating the air inlet pressure of the clamp 9 to the value set by the experiment; the gas in the high-pressure gas cylinder 1 enters a left cavity 61 of the clamp holder 9 through a gas inlet pipe 7, then sequentially passes through a left pore plate 57, a sample 60 and a right cavity 62, and flows out of the clamp holder 9 through a gas outlet pipe 13;

the fifth step is a metering step; the outlet speed regulating valve 18 is adjusted according to the design requirements of the test so as to regulate the gas pressure difference between two sides of the sample 60 (namely the gas pressure difference between the left cavity 61 and the right cavity 62) to a preset value, and the computer 37 continuously collects and records the pressure data transmitted by the precision pressure sensor 6 and the pressure difference data transmitted by the pressure difference sensor 12;

according to the magnitude of the gas flow, a mass flow meter (one of the first to third mass flow meters) with a range larger than the actual gas flow and a range closest to the actual gas flow is a best-matching mass flow meter, a solenoid valve (one of the first to third solenoid valves) on a branch where the best-matching mass flow meter is located is opened, so that the gas mass flow under the normal pressure condition and the specific pressure difference condition is accurately measured through the first, second or third mass flow meter, and the gas is discharged after passing through the flow measuring system and passing through the third three-way valve 28, the emptying pipe 78 and the third manual valve 29; the computer 37 continuously collects and records the gas flow data transmitted by the mass flow meter; after the gas flow is stable and unchanged, the computer 37 records the pressure data, the pressure difference data and the gas flow data under the steady flow state, and completes a test under the normal pressure and the specific pressure difference;

repeating the fifth step, and when the fifth step is carried out each time, adjusting the outlet speed regulating valve 18 to adjust the gas pressure difference at the two sides of the sample 60 to different preset values so as to complete the nano-scale gas flow rule experiment under the conditions of normal pressure and different pressure differences; the number of repetitions of the fifth step is predetermined by the designer of the experiment.

After the experiment is finished, all the valves are closed in sequence from back to front by taking the direction of the airflow as the front direction (so that the system is in a normal pressure state after the system is closed), and a complete sample experiment is finished;

the sixth step is to replace the sample 60 with different pore sizes (i.e., the anodized aluminum film with different pore sizes) to simulate different pore conditions, and repeat the first to fifth steps to complete the nanoscale gas flow law experiment under different pore conditions.

The computer 37 is used for observing, collecting and recording experimental data in real time in the experimental process, so that the recorded data are accurate and reliable, and errors caused by artificial reading to experimental results are reduced.

The experimental method disclosed by the invention is simple and convenient in steps, can be used for carrying out normal pressure experiments under different pressure difference conditions and different pore conditions through simple repetition, and is higher in experimental efficiency.

The invention also discloses a method for carrying out negative pressure experiments by using the nanoscale gas flow law experiment system, which comprises the following steps in sequence:

the first step is a sample loading connection step in which all valves are closed, and a round sample 60 is loaded between the left and

right orifice plates

57 and 58 of the holder 9 (specifically, between the chuck 63 and the recess 64), and the left and

right orifice plates

57 and 58 are pressed together by bolts, thereby clamping the sample 60. A pore plate structure consisting of a left pore plate 57 and a right pore plate 58 is arranged in a pore plate clamping groove, then the left tank body 51 and the right tank body 52 are pressed together through bolts, and then the air inlet pipe 7 and the air outlet pipe 13 are respectively connected to the left end and the right end of the clamp 9, and the good sealing of the connection part is ensured;

the second step is a vacuumizing step; firstly, opening an inlet speed regulating valve 4, an outlet speed regulating valve 18, a first manual valve 19, a second manual valve 15, first to third

electromagnetic valves

21, 22 and 23, a fourth manual valve 30 and a fifth manual valve 34, starting a vacuum pump 16 to degas the system, judging whether the vacuum degree requirement of the experiment is met or not according to the reading of a pressure vacuum meter 17, and closing the inlet speed regulating valve 4, the outlet speed regulating valve 18, the first manual valve 19, the second manual valve 15, the fourth manual valve 30, the fifth manual valve 34 and the first to third

electromagnetic valves

21, 22 and 23 when the reading of the pressure vacuum meter 17 reaches a preset negative pressure; turning off the vacuum pump 16;

the fourth step is a ventilation step; opening the reducing valve 2, adjusting the inlet speed regulating valve 4 according to the indication number of the precise pressure sensor 6, adjusting the inlet pressure of the holder 9 to the range set by the experiment, allowing the gas in the high-pressure gas cylinder 1 to enter a left cavity 61 of the holder 9 through a gas inlet pipe 7, then sequentially passing through a left orifice plate 57, a sample 60 and a right cavity 62, and allowing the gas to flow out of the holder 9 through a gas outlet pipe 13;

the fifth step is a metering step; the outlet speed regulating valve 18 is adjusted according to the design requirements of the test so as to regulate the gas pressure difference between the two sides of the sample 60 (namely the gas pressure difference between the left cavity 61 and the right cavity 62) to a preset value, and the computer 37 continuously collects and records the pressure data at the inlet transmitted by the precision pressure sensor 6 and the pressure difference data transmitted by the pressure difference sensor 12;

opening a first manual valve 19, a fourth manual valve 30 and a fifth manual valve 34, according to the size of the gas flow, a mass flow meter with a range larger than the actual gas flow and the range closest to the actual gas flow is a best-matched mass flow meter, opening an electromagnetic valve on a branch of the best-matched mass flow meter, so that the gas mass flow under the negative pressure condition and the specific pressure difference condition is accurately measured through the first, second or third mass flow meter, and after passing through a flow measurement system, the gas enters a pressure buffer tank 31 through a third three-way valve 28 and the fourth manual valve 30 and then enters a pressure stabilizing container 35 through a communication pipe 76; the computer 37 continuously collects and records the gas flow data transmitted by the mass flow meter, the pressure data of the pressure buffer tank 31 transmitted by the first pressure sensor 32 and the temperature data transmitted by the temperature sensor 33; after the gas flow is stable and unchanged, the computer 37 records the pressure data at the inlet, the pressure data of the pressure buffer tank 31, the pressure difference data and the gas flow data under the steady flow state, and completes the experiment under the negative pressure specific pressure difference;

repeating the fifth step, and when the fifth step is carried out each time, adjusting the outlet speed regulating valve 18 to adjust the gas pressure difference at the two sides of the sample 60 to different preset values to complete the nanoscale gas flow rule experiment under the conditions of negative pressure and different pressure differences; the number of repetitions of the fifth step is predetermined by the designer of the experiment.

Closing other valves except the fifth manual valve 34, then opening the fourth electromagnetic valve 36, and exhausting the gas in the pressure buffer tank 31 and the pressure stabilizing container 35 to complete a complete sample experiment;

the sixth step is to replace the sample 60 with different pore sizes (i.e. anodic alumina membranes with different pore sizes), simulate different pore conditions, and repeat the first to fifth steps to complete the nano-scale gas flow law experiment under different pore conditions and negative pressure conditions.

In the experimental process, the computer 37 is used for observing, collecting and recording experimental data in real time, and the recorded data is accurate and reliable, so that errors caused by artificial reading to experimental results are reduced.

The experiment method disclosed by the invention is simple and convenient in steps, can be used for carrying out negative pressure experiments under different pressure difference conditions and different pore conditions through simple repetition, and is higher in experiment efficiency.

The invention also discloses a method for carrying out gas experiments with different rarefied degrees under the same pressure difference condition by using the nanoscale gas flow law experiment system, which sequentially comprises the following steps:

right orifice plates

the second step is a vacuumizing step; firstly, opening an inlet speed regulating valve 4, an outlet speed regulating valve 18, a first manual valve 19, a second manual valve 15 and first to third

electromagnetic valves

the third step is a temperature adjusting step; adjusting the temperature of the constant temperature box 8 to the range set by the experiment to ensure that the experiment system is in a constant temperature state;

the fourth step is a ventilation step; opening the pressure reducing valve 2, the third manual valve 29, the first manual valve 19 and the outlet speed regulating valve 18, regulating the inlet speed regulating valve 4 according to the indication of the precision pressure sensor 6, and regulating the air inlet pressure of the clamp 9 to the value set by the experiment; the gas in the high-pressure gas cylinder 1 enters a left cavity 61 of the holder 9 through a gas inlet pipe 7, then sequentially passes through a left pore plate 57, a sample 60 and a right cavity 62, and flows out of the holder 9 through a gas outlet pipe 13;

according to the size of the gas flow, the mass flow meter with the range larger than the actual gas flow and the range closest to the actual gas flow is the best-matched mass flow meter, the electromagnetic valve on the branch of the best-matched mass flow meter is opened, so that the gas mass flow under the normal pressure condition and the specific pressure difference condition is accurately measured through the first mass flow meter, the second mass flow meter or the third mass flow meter, and the gas passes through the flow measurement system, then passes through the third three-way valve 28, the emptying pipe 78 and the third manual valve 29 and then is discharged; the computer 37 continuously collects and records the gas flow data transmitted by the mass flow meter;

during the process of the fifth step, continuously adjusting the outlet speed regulating valve 18 to keep the gas pressure difference between the two sides of the sample 60 unchanged during the process of the fifth step;

after the gas flow is stable and unchanged, the computer 37 records the pressure data, the pressure difference data and the gas flow data under the steady flow state, and completes the experiment under the constant pressure and the constant pressure difference at one time;

repeatedly carrying out the fifth step, and regulating the air inlet pressure of the clamper 9 to different preset values by regulating the inlet speed regulating valve 4 when carrying out the fifth step each time, thereby completing the flow rule experiment of the gases with different rarefaction degrees in the nano scale under the constant pressure difference state under normal pressure; in the condition where the pressure difference is constant, the lower the intake pressure of the holder 9 is, the thinner the gas passing through the sample 60 is. The number of repetitions of the fifth step is predetermined by the designer of the experiment.

the sixth step is to replace the sample 60 with different pore sizes (i.e. the anodic alumina membranes with different pore sizes), and repeat the first to fifth steps to complete the flow rule experiment of the gas with different rarefaction degrees under different pore conditions and constant pressure difference in the nanoscale.

The experimental method disclosed by the invention is simple and convenient in steps, can be used for carrying out normal pressure experiments under different air inlet pressure conditions, constant pressure difference conditions and different pore conditions through simple repetition, simulating gas environments with different rarefied degrees, and is higher in experimental efficiency.

The invention provides conditions for indoor experimental determination for shale gas development and the like, and the measured flow rule of the nano-pore gas can be applied to on-site shale gas exploitation, thereby providing a basis for shale gas exploitation.

The limitations of the directions of "left", "right", front "and" rear "in the present invention are only for convenience of describing the relative positions of the technical features, and are not intended to specifically limit the structure of the present invention. It will be understood by those skilled in the art that any arrangement of the specific elements which are in a spatial relationship with respect to each other may be made without affecting the proper functioning of the invention, such arrangement being rotationally and symmetrically arranged, and obvious changes in such directions and equivalents of the features of the invention are intended to be covered by the scope of the claims.

Claims

1. The method for performing the normal pressure experiment by using the nanoscale gas flow law experiment system comprises a clamp holder, a pressure control system, a vacuum pumping system, a pressure differential pressure measurement system, a pressure stabilizing system, a flow measurement system and a data acquisition control system which are arranged in a constant temperature box;

the clamp holder comprises a left tank body and a right tank body, wherein a left connecting disc is arranged at the right end of the left tank body in a protruding mode along the radial direction, a right connecting disc is arranged at the right end of the right tank body in a protruding mode along the radial direction, and the left connecting disc and the right connecting disc are detachably connected together in a pressing mode through bolts; a left clamping groove is formed in the right end face of the left connecting disc, a right clamping groove is formed in the left end face of the right connecting disc, and the left clamping groove and the right clamping groove correspond to each other and form an orifice plate clamping groove; the pore plate structure is connected in the pore plate clamping groove in a clamping manner;

the pore plate structure comprises a left pore plate and a right pore plate which are in clamping fit, the radial outer end parts of the left pore plate and the right pore plate are clamped in pore plate clamping grooves, air holes are correspondingly formed in the middle parts of the left pore plate and the right pore plate, and the air holes in the left pore plate and the air holes in the right pore plate are correspondingly communicated and penetrate through the left pore plate and the right pore plate left and right; a round sample made of an anodic aluminum oxide film is pressed between the left pore plate and the right pore plate; the orifice plate structure divides the inner cavity of the holder into a left cavity and a right cavity;

the flow measurement system comprises a first branch, a second branch and a third branch which are connected in parallel; a first electromagnetic valve and a first mass flowmeter with the range of 0 to 100SCCM are connected in series with the first branch, a second electromagnetic valve and a second mass flowmeter with the range of 0 to 500SCCM are connected in series with the second branch, and a third electromagnetic valve and a third mass flowmeter with the range of 0 to 5000SCCM are connected in series with the third branch;

a first four-way valve is arranged between the flow measurement system and the outlet pressure control unit, and a second four-way valve is arranged at the gas outflow end of the flow measurement system;

the front ends of the first branch, the second branch and the third branch are respectively connected with one interface of the second four-way valve, the fourth interface of the second four-way valve is connected with a third three-way valve, the other two interfaces of the third three-way valve are respectively connected with an emptying pipe and a pressure-stabilizing air inlet pipe, and a third manual valve is arranged on the emptying pipe; the pressure stabilizing air inlet pipe is connected with the pressure buffer tank and is provided with a fourth manual valve;

the radial outer ends of the left pore plate and the right pore plate are pressed together through bolts; a clamping table is arranged at the middle part of the left pore plate in a protruding mode towards the right, a groove matched with the clamping table is formed in the middle part of the right pore plate, the clamping table is clamped into the groove, and the sample is pressed between the clamping table and the bottom of the groove;

a fifth manual valve is arranged on the communicating pipe; the volume of the pressure buffer tank is more than or equal to 5 liters, and the volume of the pressure stabilizing container is more than or equal to 15 liters;

the method is characterized by comprising the following steps in sequence:

the fifth step is a metering step; adjusting an outlet speed regulating valve according to the design requirement of the test so as to adjust the gas pressure difference on two sides of the sample to a preset value, and continuously acquiring and recording pressure data transmitted by a precision pressure sensor and pressure difference data transmitted by a pressure difference sensor by a computer;

2. The method for carrying out the negative pressure experiment by using the nanoscale gas flow law experiment system comprises a clamp holder, a pressure control system, a vacuum pumping system, a pressure differential pressure measurement system, a pressure stabilizing system, a flow measurement system and a data acquisition control system which are arranged in a constant temperature box;

the left cavity of the clamp holder is communicated with an air inlet pipe, the air inlet pipe is connected with the inlet speed regulating valve, a first three-way valve is connected to the air inlet pipe in series, a third interface of the first three-way valve is connected with the precise pressure sensor, and the precise pressure sensor, the differential pressure sensor, the first solenoid valve, the second solenoid valve, the third solenoid valve, the first mass flow meter, the second mass flow meter, the third mass flow meter, the first pressure sensor and the temperature sensor are respectively connected with the computer through signal lines;

the rear ends of the first branch, the second branch and the third branch are respectively connected with one interface of the first four-way valve by taking the airflow direction as the forward direction, and the fourth interface of the first four-way valve is connected with the front end of the pipeline of the outlet pressure control unit;

the radial outer ends of the left pore plate and the right pore plate are pressed together through bolts; a clamping table is arranged in the middle of the left hole plate in a rightward protruding mode, a groove matched with the clamping table is formed in the middle of the right hole plate, the clamping table is clamped into the groove, and the sample is pressed between the clamping table and the bottom of the groove;

the method is characterized by comprising the following steps in sequence:

the second step is a vacuumizing step; firstly, opening an inlet speed regulating valve, an outlet speed regulating valve, a first manual valve, a second manual valve, first to third electromagnetic valves, a fourth manual valve and a fifth manual valve, starting a vacuum pump to perform degassing treatment on a system, judging whether the vacuum degree requirement of an experiment is met or not according to the reading of a pressure vacuum meter, and closing the inlet speed regulating valve, the outlet speed regulating valve, the first manual valve, the second manual valve, the fourth manual valve, the fifth manual valve and the first to third electromagnetic valves when the reading of the pressure vacuum meter reaches a preset negative pressure; closing the vacuum pump;

the fifth step is a metering step; adjusting an outlet speed regulating valve according to the design requirement of the test so as to adjust the gas pressure difference on two sides of the sample to a preset value, and continuously acquiring and recording pressure data at an inlet transmitted by a precision pressure sensor and pressure difference data transmitted by a pressure difference sensor by a computer;

opening a first manual valve, a fourth manual valve and a fifth manual valve, according to the size of gas flow, taking a mass flow meter with a range larger than the actual gas flow and the range closest to the actual gas flow as a best-matching mass flow meter, opening an electromagnetic valve on a branch where the best-matching mass flow meter is positioned, so that the gas mass flow under a negative pressure condition and a specific pressure difference condition is accurately measured through the first, second or third mass flow meter, and after passing through a flow measurement system, the gas enters a pressure buffer tank through a third three-way valve and the fourth manual valve and then enters a pressure stabilizing container through a communicating pipe; the computer continuously collects and records gas flow data transmitted by the mass flow meter, pressure data of the pressure buffer tank transmitted by the first pressure sensor and temperature data transmitted by the temperature sensor; after the gas flow is stable and unchanged, the computer records pressure data at an inlet, pressure data of the pressure buffer tank, pressure difference data and gas flow data under a steady flow state, and completes a negative pressure specific pressure difference experiment;

closing other valves except the fifth manual valve, then opening the fourth electromagnetic valve, and exhausting the gas in the pressure buffer tank and the pressure stabilizing container to complete a complete sample experiment;

and in the sixth step, samples with different pore diameters are replaced, and the first step, the second step and the third step are repeated to complete the nano-scale gas flow rule experiment under different pore conditions and negative pressure conditions.

3. A method for carrying out gas experiments with different rarefaction degrees under the same pressure difference condition by using a nanoscale gas flow law experiment system,

the nanoscale gas flow law experiment system comprises a clamp holder, a pressure control system, a vacuum pumping system, a pressure difference measurement system, a pressure stabilizing system, a flow measurement system and a data acquisition control system which are arranged in a constant temperature box;

the clamp holder comprises a left tank body and a right tank body, wherein a left connecting disc is arranged at the right end of the left tank body in a protruding mode along the radial direction, a right connecting disc is arranged at the right end of the right tank body in a protruding mode along the radial direction, and the left connecting disc and the right connecting disc are detachably pressed together through bolts; a left clamping groove is formed in the right end face of the left connecting disc, a right clamping groove is formed in the left end face of the right connecting disc, and the left clamping groove and the right clamping groove correspond to each other and form an orifice plate clamping groove; the pore plate structure is connected in the pore plate clamping groove in a clamping manner;

the front ends of the first branch, the second branch and the third branch are respectively connected with one interface of the second four-way valve, the fourth interface of the second four-way valve is connected with a third three-way valve, the other two interfaces of the third three-way valve are respectively connected with an emptying pipe and a pressure-stabilizing air inlet pipe, and a third manual valve is arranged on the emptying pipe; the pressure stabilizing air inlet pipe is connected with the pressure buffer tank, and a fourth manual valve is arranged on the pressure stabilizing air inlet pipe;

the method is characterized by comprising the following steps in sequence:

the second step is a vacuumizing step; firstly, opening an inlet speed regulating valve, an outlet speed regulating valve, a first manual valve, a second manual valve and first to third electromagnetic valves, starting a vacuum pump to perform degassing treatment on the system, judging whether the vacuum degree requirement of the experiment is met or not according to the reading of a pressure vacuum meter, closing the inlet speed regulating valve, the outlet speed regulating valve, the first manual valve, the second manual valve and the first to third electromagnetic valves when the reading of the pressure vacuum meter is 0, and closing the vacuum pump;

the fourth step is a ventilation step; opening the pressure reducing valve, the third manual valve, the first manual valve and the outlet speed regulating valve, regulating the inlet speed regulating valve according to the indication of the precise pressure sensor, and regulating the air inlet pressure of the clamp holder to the value set by the experiment; gas in the high-pressure gas cylinder enters a left cavity of the holder through a gas inlet pipe, then sequentially passes through a left pore plate, the sample and a right cavity, and flows out of the holder through a gas outlet pipe;

according to the size of the gas flow, the mass flow meter with the range larger than the actual gas flow and the range closest to the actual gas flow is the best matching mass flow meter, the electromagnetic valve on the branch where the best matching mass flow meter is located is opened, so that the gas mass flow under the normal pressure condition and the specific differential pressure condition is accurately measured through the first mass flow meter, the second mass flow meter or the third mass flow meter, and the gas is discharged after passing through the flow measuring system, the third three-way valve, the emptying pipe and the third manual valve; the computer continuously collects and records the gas flow data transmitted by the mass flowmeter;

repeatedly carrying out the fifth step, and regulating the air inlet pressure of the holder to different preset values by regulating the inlet speed regulating valve when carrying out the fifth step each time, thereby completing the nanoscale gas flow rule experiment with different rarefaction degrees under the constant pressure difference state under normal pressure;