Coal contact angle testing device under high pressure load conditions

Abstract

The coal contact angle testing device under high-pressure bearing conditions includes a methane filling system, a helium filling calibration system, a vacuum pumping system, a liquid injection system, a visual loading kettle system, an imaging test system and a constant temperature system. The methane outlet of the methane filling system and the helium outlet of the helium filling calibration system are connected in parallel with the gas inlet of the visual loading kettle system. The gas outlet of the visual loading kettle system is connected to the gas inlet of the vacuum pumping system. The liquid outlet of the liquid injection system is connected to the liquid inlet of the visual loading kettle system. The imaging test system is arranged on one side of the visual loading kettle system and is photographed toward the visual loading kettle system. Some components of the methane filling system, the helium filling calibration system, the visual loading kettle system and the imaging test system are all arranged inside the constant temperature system. The present invention can simulate the actual occurrence conditions of different coal seams in a similar manner and accurately test the contact angle between coal and liquid in the loaded coal-gas-liquid three-phase system.

Description

Technical Field

[0001] The invention relates to the technical field of coal mine safety, in particular to a coal body contact angle testing device under high pressure bearing conditions. Background Art

[0002] With the increase in the depth and intensity of coal mining in my country, gas and dust hazards are gradually increasing. Gas hazards lead to coal and gas outbursts, gas explosions, and gas over-limit. Dust hazards lead to dust explosions, pneumoconiosis, etc., which seriously affect the occupational health of workers. Coal seam water injection is a comprehensive disaster control measure. The effect of coal seam water injection on wetting the coal body is closely related to the effects of gas control, dust prevention, and outburst prevention. The contact angle is an important parameter to measure the wetting effect of liquid on the coal body. When the contact angle is less than 90°, the solid surface is hydrophilic; when the contact angle is greater than 90°, the solid surface is hydrophobic.

[0003] The most commonly used method to measure the contact angle is the fixed drop method, and then the contact angle is obtained by the method of shape image analysis. At present, most of the tests on the contact angle between coal and liquid are carried out in the coal-air-liquid three-phase system or the coal-gas-liquid three-phase system. In fact, during the wetting process of the coal body under in-situ conditions, the bearing stress of the coal body and the gas in the coal body affect the size of the contact angle between the coal and the liquid. Therefore, the contact angle between the coal body and the liquid under in-situ conditions should be tested in the liquid-gas-loaded coal body three-phase system. Because the surface energy of the pores will decrease after the coal body adsorbs gas, and the pore and fracture structure of the coal body is different when it is in a loaded state, these differences will cause the contact angle between the coal and the liquid in the coal-air-liquid three-phase system to be different from the contact angle formed by the loaded coal and the liquid in the loaded coal-gas-liquid three-phase system, which will lead to inaccurate evaluation of the wetting effect of coal seam water injection.

[0004] Therefore, in order to accurately evaluate the wetting effect of liquid on loaded gas-containing coal, it is necessary to design a coal contact angle test device under high-pressure loading conditions to provide parameter support for in-depth research on coal seam water injection for gas control, dust prevention, and outburst prevention. Summary of the invention

[0005] The purpose of the present invention is to provide a coal contact angle testing device under high-pressure loading conditions. The present invention can similarly simulate the actual occurrence conditions of different coal seams and accurately test the contact angle between coal and liquid in a loaded coal-gas-liquid three-phase system.

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

[0007] A coal contact angle testing device under high-pressure bearing conditions includes a methane filling system, a helium filling calibration system, a vacuum system, a liquid injection system, a visual loading kettle system, an imaging test system and a constant temperature system. The methane outlet of the methane filling system and the helium outlet of the helium filling calibration system are connected in parallel with the gas inlet of the visual loading kettle system, the gas outlet of the visual loading kettle system is connected with the gas inlet of the vacuum system, the liquid outlet of the liquid injection system is connected with the liquid inlet of the visual loading kettle system, the imaging test system is arranged at one side of the visual loading kettle system and shoots toward the visual loading kettle system, and some components of the methane filling system, the helium filling calibration system, the visual loading kettle system and the imaging test system are arranged inside the constant temperature system.

[0008] The methane filling system includes a methane storage bottle and a methane reference tank. The methane outlet of the methane storage bottle is connected to the methane inlet of the methane reference tank through a first gas pipeline. The methane outlet of the methane reference tank is connected to a second gas pipeline. The other end of the second gas pipeline is connected to the outside atmosphere. A methane pressure regulating valve and a first gas valve are sequentially arranged on the upper side of the first gas pipeline in the direction of gas flow. A first precision pressure gauge, a second gas valve, a second precision pressure gauge, a gas injection pipeline and a third gas valve are sequentially arranged on the upper side of the second gas pipeline in the direction of gas flow. The other end of the gas injection pipeline is connected to the gas inlet of the visual loading kettle system.

[0009] The helium-filled calibration system includes a helium storage bottle and a helium reference tank. The helium outlet of the helium storage bottle is connected to the helium inlet of the helium reference tank through a third gas pipeline. The helium outlet of the helium reference tank is connected to a fourth gas pipeline. The other end of the fourth gas pipeline is connected to the second gas pipeline located between the second gas valve and the second precision pressure gauge. A helium pressure regulating valve and a fourth gas valve are sequentially arranged along the gas flow direction of the third gas pipeline. A third precision pressure gauge and a fifth gas valve are sequentially arranged along the gas flow direction of the fourth gas pipeline.

[0010] The vacuum system includes a vacuum pump, the gas inlet of the vacuum pump is connected to the gas outlet of the visual loading kettle system through a vacuum pipeline, a sixth gas valve and a vacuum gauge are sequentially arranged along the gas flow direction of the vacuum pipeline, and the gas outlet of the vacuum pump is connected to the outside atmosphere.

[0011] The liquid injection system includes a first water cup, a high-pressure micro-flow liquid injection pump and a capillary dropper. The bottom of the first water cup is connected to the liquid inlet of the high-pressure micro-flow liquid injection pump through a first liquid pipeline. The capillary dropper is vertically fixed in the liquid inlet of the visualization loading kettle system. The upper end of the capillary dropper is connected to the liquid outlet of the high-pressure micro-flow liquid injection pump through a second liquid pipeline. The lower end of the capillary dropper extends into the visualization loading kettle system. A first liquid valve is arranged on the first liquid pipeline. A second liquid valve, a fourth precision pressure gauge and a one-way valve are sequentially arranged on the second liquid pipeline along the liquid flow direction. The liquid flow direction in the one-way valve is the direction in which the liquid flows from the high-pressure micro-flow liquid injection pump to the capillary dropper.

[0012] The visual loading kettle system includes a visual kettle and two sets of loading devices. The visual kettle is a cubic box structure with an open top. The top of the visual kettle is detachably fixedly connected to a kettle cover by bolts. The front side plate and the rear side plate of the visual kettle are both provided with front and rear corresponding and transparent windows. The front side plate and the rear side plate of the visual kettle are both detachably fixedly connected to sapphire glass windows embedded in the corresponding windows by bolts. The first O-rings are pressed between the four sides of the kettle cover and the upper port of the visual kettle and between the four sides of the inner side of the sapphire glass window and the window. A support platform is fixedly provided in the middle of the inner bottom surface of the visual kettle. The two sets of loading devices have the same structure and are symmetrically installed on the left and right sides of the visualized kettle body. An air inlet is opened on the left side of the kettle cover, a liquid inlet is opened in the middle part of the kettle cover, and an air exhaust port is opened on the right side of the kettle cover. The other end of the air injection pipeline is connected to the air inlet, and the capillary droplet tube is vertically penetrated and connected to the liquid inlet. The lower end of the capillary droplet tube extends into the visualized kettle body and is located directly above the support platform. The capillary droplet tube is fixedly connected to the kettle cover through a pressure cap which is sleeved on the outer circumference of its upper and lower parts. The upper pressure cap is fixed on the outer surface of the kettle cover, and the lower pressure cap is fixed on the inner surface of the kettle cover. The air inlet end of the vacuum pipeline is connected to the air exhaust port.

[0013] The loading device on the left side includes a loading plate, a loading cylinder, a loading piston, a second water cup and a high-pressure injection pump. The loading plate is vertically arranged in the front-to-back direction on the left side of the visualization kettle body and on the left side of the support platform. The lower side of the loading plate is flush with the upper surface of the support platform. The loading cylinder body is horizontally arranged in the left-right direction. A flange plate is integrally formed on the outer circumference of the right end of the loading cylinder body. The flange plate is fixedly connected to the middle part of the left side surface of the left side plate of the visualization kettle body by a plurality of bolts. The loading piston is sealingly and slidably connected in the loading cylinder body. A piston rod is concentrically arranged in the loading cylinder body. The left end of the piston rod is integrally and fixedly connected to the middle part of the right side surface of the loading piston. The piston rod extends to the right from the right end of the loading cylinder body and passes through the middle part of the left side plate of the visualization kettle body. The right end of the piston rod extends into the interior of the visualization kettle body and is fixedly connected with the middle part of the left side surface of the loading plate through a thread. The piston rod is sealingly and slidably connected to the right side plate of the loading cylinder body and the left side plate of the visualization kettle body respectively. Two portions are fixedly embedded on the outer circumference of the loading piston and are arranged at intervals on the left and right and slide with the inner wall of the loading cylinder body. A second O-ring in dynamic contact, a third O-ring sleeved on the outer circumference of the piston rod is fixedly embedded in the right side plate of the loading cylinder body and the left side plate of the visualization kettle body, a pressurized liquid injection port located on the left side of the loading piston is opened in the middle of the left side plate of the loading cylinder body, and a pressure relief liquid injection port located on the right side of the loading piston is opened on the upper side wall of the right end of the loading cylinder body. The bottom of the second water cup is connected to the liquid inlet of the high-pressure liquid injection pump through the third liquid pipeline, and the liquid outlet of the high-pressure liquid injection pump is connected to the pressurized liquid injection port through the fourth liquid pipeline. A third liquid valve is arranged on the third liquid pipeline, and a fifth liquid pipeline, a fourth liquid valve, a fifth precision pressure gauge and a first liquid discharge pipeline are arranged in sequence along the liquid flow direction on the fourth liquid pipeline. The other end of the fifth liquid pipeline is connected to the pressure relief liquid injection port, and a fifth liquid valve, a sixth precision pressure gauge and a second liquid discharge pipeline are arranged in sequence along the liquid flow direction on the fifth liquid pipeline. A sixth liquid valve is arranged on the first liquid discharge pipeline, and a seventh liquid valve is arranged on the second liquid discharge pipeline.

[0014] The imaging test system includes a high-speed camera, a computer and a cold light source. The high-speed camera is connected to the computer through a signal wire. The high-speed camera is set in front of the visualization kettle body and shoots towards the sapphire glass window on the front side. The cold light source is set behind the visualization kettle body and irradiates towards the sapphire glass window on the rear side.

[0015] The constant temperature system includes a constant temperature box, and a methane reference tank, a helium reference tank, a visualization kettle, a high-speed camera and a cold light source are all arranged in the constant temperature box.

[0016] Using the above technical solution, a method for testing the contact angle of loaded gas-containing coal specifically comprises the following steps:

[0017] (1) Assemble the coal contact angle test device under high pressure load conditions;

[0018] (ii) preparing coal samples and placing the prepared coal samples into the visual loading kettle system;

[0019] (III) Conduct air tightness test on the coal contact angle test device under high pressure load conditions;

[0020] (iv) The coal sample is squeezed and loaded to the set loading stress through the visual loading kettle system to simulate the bearing stress of the coal seam;

[0021] (V) Calibrate the dead volume between the helium filling calibration system, the methane filling system, the liquid injection system and the visual loading kettle system through the helium filling calibration system;

[0022] (VI) Methane filling system: methane is filled into the visual loading kettle system to make the coal sample adsorb methane until adsorption equilibrium is reached, thus completing the simulation of the actual occurrence conditions of the coal seam and calculating the amount of gas adsorbed by the coal sample when adsorption equilibrium is reached;

[0023] (VII) The liquid injection system drips distilled water or modified water into the visual loading kettle system onto the coal sample, and the contact angle between the gas-containing coal and the distilled water or modified water is measured by the imaging test system;

[0024] (VIII) After the test, the coal sample is unloaded and taken out from the visual loading kettle system;

[0025] (IX) Repeat steps (II) to (VIII) and change the experimental conditions to measure the contact angle between gas-containing coal and distilled water or modified water under different adsorption equilibrium pressures, different adsorbed gas amounts and different load stress conditions.

[0026] Step (ii) is specifically as follows: the coal sample retrieved from the coal mining face is cut and polished into a hexahedral coal sample, and then the coal sample is placed in a drying oven for drying until the mass of the coal sample does not change, which is considered to be the end of drying, the mass of the coal sample is weighed and recorded as m, and then the coal sample is placed from the upper port of the visualization kettle body to the support platform inside the visualization kettle body, and then the kettle cover is fixedly connected to the top of the visualization kettle body by bolts, thereby closing the upper port of the visualization kettle body;

[0027] Step (iii) is specifically as follows: close all valves, that is, close the first gas valve, the second gas valve, the third gas valve, the fourth gas valve, the fifth gas valve, the sixth gas valve, the first liquid valve, the second liquid valve, and the third liquid valve, the fourth liquid valve, the fifth liquid valve, the sixth liquid valve, and the seventh liquid valve in the two loading devices, then turn on the power of the thermostat, set the temperature in the thermostat to meet the temperature required for the test, then open the valve of the helium storage bottle, and at the same time adjust the outlet pressure of the helium pressure regulating valve to p, open the fourth gas valve, and the helium storage bottle will fill the helium reference tank with a certain pressure of helium through the third gas pipeline, close the valve of the helium storage bottle and the fourth gas valve, and record the reading of the third precision pressure gauge after the reading of the third precision pressure gauge stabilizes. p , then open the fifth gas valve and observe the indication of the second precision pressure gauge. If the indications of the second precision pressure gauge and the third precision pressure gauge can remain stable for a certain period of time, it means that the overall device is leaking and has good air tightness. Otherwise, it is leaking. When it is measured that the overall device is leaking, open the third gas valve, and release the helium in the second gas pipeline, helium reference tank, fourth gas pipeline, gas injection pipeline and visualization kettle body to the outside atmosphere through the second gas pipeline, and then close the third gas valve and the fifth gas valve.

[0028] Step (IV) is as follows: operate two sets of loading devices at the same time to realize extrusion loading of the coal sample. The operation process of the two sets of loading devices is the same. Here, the loading device on the left is used as an example to illustrate: open the high-pressure injection pump and the third liquid valve. After the high-pressure injection pump sucks the water in the second water cup, close the third liquid valve and set the loading stress. s , open the fourth liquid valve and the seventh liquid valve, then the water in the high-pressure injection pump is injected into the left side of the inner cavity of the loading cylinder through the fourth liquid pipeline and the pressurized liquid injection port and pushes the loading piston to the right, and the air or water in the inner cavity of the loading cylinder on the right side of the loading piston is discharged through the second liquid discharge pipeline, so that the piston rod pushes the loading plate on the left side to the right, and the right side of the loading plate on the left side squeezes the left side of the coal sample, and the coal sample is squeezed and loaded until the fifth precision pressure gauge reaches the set loading stress s Then, the high-pressure injection pump is controlled to stop injecting liquid, and the fourth liquid valve and the seventh liquid valve are closed. In this way, the coal sample can be squeezed and loaded to the set loading stress. s , similarly simulates the bearing stress of the coal seam.

[0029] Step (V) is as follows: Open the valve of the helium storage bottle and adjust the outlet pressure of the helium pressure regulating valve to p 1. Open the fourth gas valve, and the helium storage bottle will fill the helium reference tank with a certain pressure of helium through the third gas pipeline. Close the valve of the helium storage bottle and the fourth gas valve. After the reading of the third precision pressure gauge stabilizes, record the reading of the third precision pressure gauge. p 1. Then open the fifth gas valve and wait for the reading of the second precision pressure gauge to stabilize, then record the reading of the second precision pressure gauge. p 2, where the volume between the fourth gas valve and the fifth gas valve V 1 It has been pre-calibrated before the experiment starts, according to the formula p 1 V 1 / Z 1=p 2 V 2 / Z 2 can be calculated V 2, Z 1. Z 2 are p 1. p 2 compressibility factor under pressure, V 2- V 1 is the dead volume between the fifth gas valve, the second gas valve, the third gas valve, the one-way valve and the visualization kettle. After calibration, open the third gas valve, release the helium in the second gas pipeline, the helium reference tank, the fourth gas pipeline, the gas injection pipeline and the visualization kettle to the outside atmosphere through the second gas pipeline, and then close the third gas valve and the fifth gas valve.

[0030] Step (six) is as follows: open the vacuum pump and the sixth gas valve, and the vacuum pump evacuates the inside of the visual kettle until the reading of the vacuum gauge is less than 20Pa, which is considered to be the end of vacuuming. Then, close the vacuum pump and the sixth gas valve, and then open the valve of the methane storage bottle. At the same time, adjust the outlet pressure of the methane pressure regulating valve to p 3. Open the first gas valve, and the methane storage bottle will fill a certain pressure of methane into the methane reference tank through the first gas pipeline. Close the first gas valve, and record the reading of the first precision pressure gauge after the reading of the first precision pressure gauge stabilizes. p 3. Then open the second gas valve, and the methane in the methane reference tank will be filled into the visual kettle through the second gas pipeline and the gas injection pipeline. Then close the second gas valve and record the reading of the first precision pressure gauge. p 4. After the coal sample has absorbed methane for a period of time, observe whether the reading on the second precision pressure gauge reaches the adsorption equilibrium pressure required for the experiment. P If it is not reached, open the second gas valve to continue to fill the visual kettle with methane gas and record the reading of the first precision pressure gauge. p n Until the reading on the second precision pressure gauge reaches the adsorption equilibrium pressure required for the experiment P In this way, the actual occurrence conditions of the coal seam can be simulated similarly, and the amount of gas adsorbed by the experimental coal sample is ,in Z 3. Z n , Z are p 3. p n , p The compressibility factor under pressure, V 1 is known, V 2- V1 is the dead volume between the fifth gas valve, the second gas valve, the third gas valve, the one-way valve and the visualized kettle.

[0031] Step (VII) is specifically as follows: turn on the computer, the high-speed camera and the cold light source, then add distilled water or modified water of a certain concentration into the first water cup, turn on the high-pressure micro-flow injection pump and the first liquid valve, and the high-pressure micro-flow injection pump starts to suck the water in the first water cup. After the water is sucked, close the first liquid valve and open the second liquid valve. When a very small pressure difference is formed at both ends of the one-way valve, the pressure difference is related to the accuracy of the one-way valve. When the one-way valve is opened, the liquid enters the capillary droplet through the second liquid pipeline. The liquid drips down to the upper surface of the coal sample through the capillary droplet. The cold light source illuminates the sapphire glass window on the rear side to visualize the interior of the kettle. At the same time, the high-speed camera captures the shape of the droplet through the sapphire glass window on the front side. The high-speed camera transmits the captured image to the computer through the signal wire. The contact angle between the liquid and the solid in the captured image is measured by the image analysis software of the computer, and the adsorption equilibrium pressure can be obtained. P , the amount of adsorbed gas is Q x The load stress is s Contact angle of gas-containing coal with distilled water or modified water under different conditions.

[0032] Step (eight) is specifically as follows: after the test is completed, close the second liquid valve, open the third gas valve, release the methane in the second gas pipeline, methane reference tank, gas injection pipeline and visualization kettle body to the outside atmosphere through the second gas pipeline, then close the second gas valve and the third gas valve, and then operate the two sets of loading devices at the same time to relieve the pressure and loosen the coal sample. The operation process of the two sets of loading devices is the same. Here, the loading device on the left is used as an example for explanation: open the high-pressure injection pump and the third liquid valve. After the high-pressure injection pump has finished sucking the water in the second water cup, close the third liquid valve, open the fifth liquid valve and the sixth liquid valve, and the water in the high-pressure injection pump is released through the fifth liquid valve. The body pipeline and the oblique pressure injection port are injected into the right side of the inner cavity of the loading cylinder and push the loading piston to move to the left. The water in the inner cavity of the loading cylinder on the left side of the loading piston is discharged through the first discharge pipeline, and then the piston rod pulls the loading plate on the left to the left, so that the right side of the loading plate on the left is separated from the left side of the coal sample, and the coal sample is depressurized and released until the loading piston returns to the initial position. The high-pressure injection pump is then controlled to stop injecting liquid, and the fifth liquid valve and the sixth liquid valve are closed. In this way, the coal sample can be depressurized and released, and then the bolts connecting the kettle cover and the visual kettle body are unscrewed, the kettle cover is removed from the top of the visual kettle body, and the coal sample can be taken out from the visual kettle body.

[0033] The present invention can fully consider the actual occurrence conditions of coal seams and similarly simulate the actual occurrence conditions of different coal seams, that is, it can similarly simulate coal samples under different adsorption equilibrium pressures, different adsorbed gas amounts and different load stress conditions, and accurately test the contact angle between coal and liquid in the loaded coal-gas-liquid three-phase system, effectively solving the problem of inaccurate contact angle tested in the coal-gas-liquid or coal-air-liquid three-phase system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the overall structure of the coal contact angle testing device under high pressure bearing conditions of the present invention.

[0035] Figure 2 It is a structural schematic diagram of the visual loading kettle system of the present invention.

[0036] Figure 3 It is a right side view of the arrangement of the visualization kettle body, high-speed camera and cold light source of the present invention. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are further described below with reference to the accompanying drawings.

[0038] like Figure 1-3 As shown, a coal contact angle testing device under high-pressure loading conditions includes a methane filling system, a helium filling calibration system, a vacuum system, a liquid injection system, a visual loading kettle system, an imaging test system and a constant temperature system. The methane outlet of the methane filling system and the helium outlet of the helium filling calibration system are connected in parallel with the gas inlet of the visual loading kettle system, the gas outlet of the visual loading kettle system is connected to the gas inlet of the vacuum system, the liquid outlet of the liquid injection system is connected to the liquid inlet of the visual loading kettle system, the imaging test system is arranged on one side of the visual loading kettle system and shoots toward the visual loading kettle system, and some components of the methane filling system, the helium filling calibration system, the visual loading kettle system and the imaging test system are all arranged inside the constant temperature system.

[0039] The methane filling system includes a methane storage bottle 1 and a methane reference tank 2. The methane outlet of the methane storage bottle 1 is connected to the methane inlet of the methane reference tank 2 through a first gas pipeline 3. The methane outlet of the methane reference tank 2 is connected to a second gas pipeline 4. The other end of the second gas pipeline 4 is connected to the outside atmosphere. A methane pressure regulating valve 5 and a first gas valve 6 are sequentially arranged on the first gas pipeline 3 along the gas flow direction. A first precision pressure gauge 7, a second gas valve 8, a second precision pressure gauge 9, a gas injection pipeline 10 and a third gas valve 11 are sequentially arranged on the second gas pipeline 4 along the gas flow direction. The other end of the gas injection pipeline 10 is connected to the gas inlet of the visual loading kettle system.

[0040] The helium-filled calibration system includes a helium storage bottle 12 and a helium reference tank 13. The helium outlet of the helium storage bottle 12 is connected to the helium inlet of the helium reference tank 13 through a third gas pipeline 14. The helium outlet of the helium reference tank 13 is connected to a fourth gas pipeline 15. The other end of the fourth gas pipeline 15 is connected to the second gas pipeline 4 located between the second gas valve 8 and the second precision pressure gauge 9. The third gas pipeline 14 is provided with a helium pressure regulating valve 16 and a fourth gas valve 17 in sequence along the gas flow direction. The fourth gas pipeline 15 is provided with a third precision pressure gauge 18 and a fifth gas valve 19 in sequence along the gas flow direction.

[0041] The vacuum pump system includes a vacuum pump 20, the gas inlet of the vacuum pump 20 is connected to the gas outlet of the visual loading kettle system through a vacuum pump pipeline 21, and a sixth gas valve 22 and a vacuum gauge 23 are sequentially arranged on the vacuum pump pipeline 21 along the gas flow direction, and the gas outlet of the vacuum pump 20 is connected to the outside atmosphere;

[0042] The liquid injection system includes a first water cup 24, a high-pressure micro-flow liquid injection pump 25 and a capillary dropper 26. The bottom of the first water cup 24 is connected to the liquid inlet of the high-pressure micro-flow liquid injection pump 25 through a first liquid pipeline 27. The capillary dropper 26 is vertically fixedly installed in the liquid inlet of the visualization loading kettle system. The upper end of the capillary dropper 26 is connected to the liquid outlet of the high-pressure micro-flow liquid injection pump 25 through a second liquid pipeline 28. The lower end of the capillary dropper 26 extends into the visualization loading kettle system. A first liquid valve 29 is arranged on the first liquid pipeline 27. A second liquid valve 30, a fourth precision pressure gauge 31 and a one-way valve 32 are arranged in sequence on the second liquid pipeline 28 along the liquid flow direction. The liquid flow direction in the one-way valve 32 is the direction in which the liquid flows from the high-pressure micro-flow liquid injection pump 25 to the capillary dropper 26.

[0043] The visual loading kettle system includes a visual kettle 33 and two sets of loading devices. The visual kettle 33 is a cubic box structure with an open top. The top of the visual kettle 33 is detachably fixedly connected to a kettle cover 34 by bolts. The front side plate and the rear side plate of the visual kettle 33 are both provided with front and rear corresponding and transparent windows. The front side plate and the rear side plate of the visual kettle 33 are both detachably fixedly connected to sapphire glass windows 35 embedded in the corresponding windows by bolts. The first O-rings 36 are pressed between the four sides of the kettle cover 34 and the upper port of the visual kettle 33 and between the four sides of the inner side of the sapphire glass window 35 and the window. A support platform 37 is fixedly provided in the middle of the inner bottom surface of the visual kettle 33. The two sets of loading devices have the same structure. And they are symmetrically installed on the left and right sides of the visualized kettle body 33, an air inlet 38 is opened on the left side of the kettle cover 34, a liquid inlet 39 is opened in the middle part of the kettle cover 34, and an air extraction port 40 is opened on the right side of the kettle cover 34, the other end of the gas injection pipeline 10 is connected to the air inlet 38, the capillary droplet tube 26 vertically penetrates and is connected to the liquid inlet 39, the lower end of the capillary droplet tube 26 extends into the visualized kettle body 33 and is located directly above the support platform 37, the capillary droplet tube 26 is fixedly connected to the kettle cover 34 through a pressure cap 41 which is sleeved on the outer circumference of its upper and lower parts, the upper pressure cap 41 is fixed to the outer surface of the kettle cover 34, the lower pressure cap 41 is fixed to the inner surface of the kettle cover 34, and the air inlet end of the vacuum pumping pipeline 21 is connected to the air extraction port 40.

[0044] The loading device on the left side includes a loading plate 42, a loading cylinder 43, a loading piston 44, a second water cup 45 and a high-pressure injection pump 46. The loading plate 42 is vertically arranged in the front-to-back direction at the left side of the visualization kettle body 33 and is located on the left side of the support platform 37. The lower side of the loading plate 42 is flush with the upper surface of the support platform 37. The loading cylinder 43 is horizontally arranged in the left-right direction. A flange plate 47 is integrally formed on the outer circumference of the right end of the loading cylinder 43. The flange plate 47 is fixedly connected to the middle of the left side surface of the left side plate of the visualization kettle body 33 by a plurality of bolts. The loading piston 44 is sealingly slidably connected in the loading cylinder 43. A piston rod 48 is co-centerably provided in the loading cylinder 43, and the left end of the piston rod 48 is integrally formed and fixedly connected with the middle part of the right side surface of the loading piston 44. The piston rod 48 extends to the right from the right end of the loading cylinder 43 and passes through the middle part of the left side plate of the visualization kettle body 33. The right end of the piston rod 48 extends into the interior of the visualization kettle body 33 and is fixedly connected with the middle part of the left side surface of the loading plate 42 through a thread. The piston rod 48 is respectively sealed and slidably connected with the right side plate of the loading cylinder 43 and the left side plate of the visualization kettle body 33. Two piston rods are fixedly embedded on the outer circumference of the loading piston 44 and are arranged at intervals on the left and right sides and are in sliding contact with the inner wall of the loading cylinder 43. The second O-ring 49 is contacted, the right side plate of the loading cylinder 43 and the left side plate of the visualization kettle 33 are both fixedly embedded with a third O-ring 50 sleeved on the outer circumference of the piston rod 48 in the same center, the middle of the left side plate of the loading cylinder 43 is provided with a pressurized liquid injection port 51 located on the left side of the loading piston 44, and the upper side wall of the right end of the loading cylinder 43 is provided with a pressure relief liquid injection port 52 located on the right side of the loading piston 44. The bottom of the second water cup 45 is connected to the liquid inlet of the high-pressure liquid injection pump 46 through a third liquid pipeline 53, and the liquid outlet of the high-pressure liquid injection pump 46 is connected to the pressurized liquid injection port 51 through a fourth liquid pipeline 54. The third liquid pipeline 53 is connected with a third liquid valve 55, and the fourth liquid pipeline 54 is provided with a fifth liquid pipeline 56, a fourth liquid valve 57, a fifth precision pressure gauge 58 and a first liquid discharge pipeline 59 in sequence along the liquid flow direction. The other end of the fifth liquid pipeline 56 is connected to the pressure relief liquid injection port 52, and the fifth liquid pipeline 56 is provided with a fifth liquid valve 60, a sixth precision pressure gauge 61 and a second liquid discharge pipeline 62 in sequence along the liquid flow direction. The first liquid discharge pipeline 59 is provided with a sixth liquid valve 63, and the second liquid discharge pipeline 62 is provided with a seventh liquid valve 68;

[0045] The imaging test system includes a high-speed camera 64, a computer 65 and a cold light source 66. The high-speed camera 64 is connected to the computer 65 through a signal wire. The high-speed camera 64 is arranged in front of the visualization kettle body 33 and shoots toward the sapphire glass window 35 on the front side. The cold light source 66 is arranged in the rear of the visualization kettle body 33 and irradiates toward the sapphire glass window 35 on the rear side.

[0046] The constant temperature system includes a constant temperature box 69 , in which the methane reference tank 2 , the helium reference tank 13 , the visualization kettle 33 , the high-speed camera 64 and the cold light source 66 are all arranged.

[0047] Using the above technical solution, a method for testing the contact angle of loaded gas-containing coal specifically comprises the following steps:

[0048] (1) Assemble the coal contact angle test device under high pressure load conditions;

[0049] (ii) preparing a coal sample 67, and placing the prepared coal sample 67 into a visual loading kettle system;

[0050] (III) Conduct air tightness test on the coal contact angle test device under high pressure load conditions;

[0051] (iv) Extrusion loading the coal sample 67 to a set loading stress through a visual loading kettle system, similarly simulating the bearing stress of the coal seam;

[0052] (V) Calibrate the dead volume between the helium filling calibration system, the methane filling system, the liquid injection system and the visual loading kettle system through the helium filling calibration system;

[0053] (VI) Methane filling system: methane is filled into the visual loading kettle system to make coal sample 67 adsorb methane until adsorption equilibrium is reached, thus completing the similar simulation of the actual occurrence conditions of the coal seam and calculating the amount of gas adsorbed by coal sample 67 when adsorption equilibrium is reached;

[0054] (VII) The liquid injection system drips distilled water or modified water into the visual loading kettle system onto the coal sample 67, and measures the contact angle between the gas-containing coal and the distilled water or modified water through the imaging test system;

[0055] (VIII) After the test, the coal sample 67 is unloaded and taken out from the visual loading kettle system;

[0056] (IX) Repeat steps (II) to (VIII) and change the experimental conditions to measure the contact angle between gas-containing coal and distilled water or modified water under different adsorption equilibrium pressures, different adsorbed gas amounts and different load stress conditions.

[0057] Step (ii) specifically includes: cutting and grinding the coal sample 67 retrieved from the coal mining face into a hexahedral coal sample 67, and then placing the coal sample 67 in a drying oven to dry until the mass of the coal sample 67 does not change, which is considered to be the end of drying, weighing the mass of the coal sample 67 and recording it as m, and then placing the coal sample 67 from the upper port of the visualized kettle body 33 onto the support platform 37 in the visualized kettle body 33, and then fixing the kettle cover 34 to the top of the visualized kettle body 33 by bolts, thereby closing the upper port of the visualized kettle body 33;

[0058] Step (iii) specifically includes: closing all valves, namely, closing the first gas valve 6, the second gas valve 8, the third gas valve 11, the fourth gas valve 17, the fifth gas valve 19, the sixth gas valve 22, the first liquid valve 29, the second liquid valve 30, and the third liquid valve 55, the fourth liquid valve 57, the fifth liquid valve 60, the sixth liquid valve 63 and the seventh liquid valve 68 in the two sets of loading devices, and then turning on the power of the thermostat 69, setting the temperature in the thermostat 69 to meet the temperature required for the test, and then opening the valve of the helium storage bottle 12, and at the same time adjusting the outlet pressure of the helium pressure regulating valve 16 to p , open the fourth gas valve 17, and the helium storage bottle 12 will fill the helium reference tank 13 with a certain pressure through the third gas pipeline 14, close the valve of the helium storage bottle 12 and the fourth gas valve 17, and record the reading of the third precision pressure gauge 18 after the reading is stable. p , then open the fifth gas valve 19 and observe the indication of the second precision pressure gauge 9. If the indications of the second precision pressure gauge 9 and the third precision pressure gauge 18 can remain stable for a certain period of time, it means that the overall device is leaking and has good air tightness. Otherwise, it is leaking. When it is measured that the overall device is leaking, open the third gas valve 11, and release the helium in the second gas pipeline 4, the helium reference tank 13, the fourth gas pipeline 15, the gas injection pipeline 10 and the visual kettle body 33 to the outside atmosphere through the second gas pipeline 4, and then close the third gas valve 11 and the fifth gas valve 19.

[0059] Step (iv) is as follows: operate two sets of loading devices at the same time to realize extrusion loading of the coal sample 67. The operation process of the two sets of loading devices is the same. Here, the loading device on the left is used as an example for explanation: open the high-pressure injection pump 46 and the third liquid valve 55. After the high-pressure injection pump 46 finishes sucking the water in the second water cup 45, close the third liquid valve 55 and set the loading stress s , open the fourth liquid valve 57 and the seventh liquid valve 68, then the water in the high-pressure injection pump 46 is injected into the left side of the inner cavity of the loading cylinder 43 through the fourth liquid pipeline 54 and the pressurized injection port 51 and pushes the loading piston 44 to move rightward, and the air or water in the inner cavity of the loading cylinder 43 on the right side of the loading piston 44 is discharged through the second liquid discharge pipeline 62, so that the piston rod 48 pushes the left loading plate 42 to the right, and the right side of the left loading plate 42 squeezes the left side of the coal sample 67, and the coal sample 67 is squeezed and loaded until the fifth precision pressure gauge 58 reaches the set loading stress s Then, the high pressure injection pump 46 is controlled to stop injecting liquid, and the fourth liquid valve 57 and the seventh liquid valve 68 are closed. In this way, the coal sample 67 can be squeezed and loaded to the set loading stress. s, similarly simulates the bearing stress of the coal seam.

[0060] Step (V) is as follows: open the valve of the helium storage bottle 12 and adjust the outlet pressure of the helium pressure regulating valve 16 to p 1. Open the fourth gas valve 17, and the helium storage bottle 12 will fill the helium reference tank 13 with a certain pressure through the third gas pipeline 14. Close the valve of the helium storage bottle 12 and the fourth gas valve 17. After the reading of the third precision pressure gauge 18 stabilizes, record the reading of the third precision pressure gauge 18. p 1. Then open the fifth gas valve 19, and after the reading of the second precision pressure gauge 9 stabilizes, record the reading of the second precision pressure gauge 9. p 2, wherein the volume between the fourth gas valve 17 and the fifth gas valve 19 V 1 It has been pre-calibrated before the experiment starts, according to the formula p 1 V 1 / Z 1= p 2 V 2 / Z 2 can be calculated V 2, Z 1. Z 2 are p 1. p 2 compressibility factor under pressure, V 2- V 1 is the dead volume between the fifth gas valve 19, the second gas valve 8, the third gas valve 11, the one-way valve 32 and the visualization kettle 33. After calibration, open the third gas valve 11, release the helium in the second gas pipeline 4, the helium reference tank 13, the fourth gas pipeline 15, the gas injection pipeline 10 and the visualization kettle 33 to the outside atmosphere through the second gas pipeline 4, and then close the third gas valve 11 and the fifth gas valve 19.

[0061] Step (six) is as follows: the vacuum pump 20 and the sixth gas valve 22 are turned on, and the vacuum pump 20 evacuates the interior of the visual kettle 33 until the reading of the vacuum gauge 23 is less than 20Pa, which is considered to be the end of the evacuation. The vacuum pump 20 and the sixth gas valve 22 are turned off, and then the valve of the methane storage bottle 1 is opened, and at the same time, the outlet pressure of the methane pressure regulating valve 5 is adjusted to p 3. Open the first gas valve 6, and the methane storage bottle 1 will fill the methane reference tank 2 with a certain pressure of methane through the first gas pipeline 3. Close the first gas valve 6, and after the reading of the first precision pressure gauge 7 stabilizes, record the reading of the first precision pressure gauge 7. p3, then open the second gas valve 8, the methane in the methane reference tank 2 is filled into the visual kettle 33 through the second gas pipeline 4 and the gas injection pipeline 10, then close the second gas valve 8, and record the reading of the first precision pressure gauge 7 p 4. After the coal sample 67 has absorbed methane for a period of time, observe whether the reading of the second precision pressure gauge 9 reaches the adsorption equilibrium pressure required for the experiment. P If it is not reached, open the second gas valve 8 to continue to fill the visual kettle 33 with methane gas, and record the reading of the first precision pressure gauge 7. p n Until the reading of the second precision pressure gauge 9 reaches the adsorption equilibrium pressure required for the experiment P In this way, the actual occurrence conditions of the coal seam can be simulated similarly, and the amount of gas adsorbed by the experimental coal sample 67 is ,in Z 3. Z n , Z are p 3. p n , p The compressibility factor under pressure, V 1 is known, V 2- V 1 is the dead volume between the fifth gas valve 19 , the second gas valve 8 , the third gas valve 11 , the one-way valve 32 and the visualized kettle 33 .

[0062] Step (VII) is specifically as follows: turn on the computer 65, the high-speed camera 64 and the cold light source 66, then add distilled water or modified water of a certain concentration into the first water cup 24, turn on the high-pressure micro-flow injection pump 25 and the first liquid valve 29, and the high-pressure micro-flow injection pump 25 starts to suck the water in the first water cup 24. After the water is sucked, the first liquid valve 29 is closed and the second liquid valve 30 is opened. When a very small pressure difference is formed at both ends of the one-way valve 32, the pressure difference is related to the accuracy of the one-way valve 32. When the one-way valve 32 is opened, the liquid is discharged. The liquid enters the capillary droplet 26 through the second liquid pipeline 28, and the liquid drips downward to the upper surface of the coal sample 67 through the capillary droplet 26. The cold light source 66 illuminates the sapphire glass window 35 on the rear side to illuminate the interior of the visual kettle 33. At the same time, the high-speed camera 64 captures the shape of the droplet through the sapphire glass window 35 on the front side. The high-speed camera 64 transmits the captured image to the computer 65 through the signal wire. The contact angle between the liquid and the solid in the captured image is measured by the image analysis software of the computer 65, and the adsorption equilibrium pressure can be obtained. P , the amount of adsorbed gas is Q x The load stress is s Contact angle of gas-containing coal with distilled water or modified water under different conditions.

[0063] Step (eight) is specifically as follows: after the test is completed, close the second liquid valve 30, open the third gas valve 11, release the methane in the second gas pipeline 4, the methane reference tank 2, the gas injection pipeline 10 and the visual kettle body 33 to the outside atmosphere through the second gas pipeline 4, then close the second gas valve 8 and the third gas valve 11, and then operate the two sets of loading devices at the same time to relieve the pressure and loosen the coal sample 67. The operation process of the two sets of loading devices is the same. Here, the loading device on the left is used as an example for explanation: open the high-pressure injection pump 46 and the third liquid valve 55. After the high-pressure injection pump 46 has sucked the water in the second water cup 45, close the third liquid valve 55, open the fifth liquid valve 60 and the sixth liquid valve 63, and the water in the high-pressure injection pump 46 is released through the fifth liquid pipeline 56 and The oblique pressure injection port injects water into the right side of the inner cavity of the loading cylinder 43 and pushes the loading piston 44 to move to the left, and the water in the inner cavity of the loading cylinder 43 on the left side of the loading piston 44 is discharged through the first drainage pipe 59, so that the piston rod 48 pulls the left loading plate 42 to the left, so that the right side surface of the left loading plate 42 is separated from the left side surface of the coal sample 67, and the coal sample 67 is depressurized and released until the loading piston 44 returns to the initial position, and then the high-pressure injection pump 46 is controlled to stop injecting liquid, and the fifth liquid valve 60 and the sixth liquid valve 63 are closed. In this way, the coal sample 67 can be depressurized and released, and then the bolts connecting the kettle cover 34 and the visual kettle body 33 are unscrewed, and the kettle cover 34 is removed from the top of the visual kettle body 33, and the coal sample 67 can be taken out of the visual kettle body 33.

[0064] The methane pressure regulating valve 5, the helium pressure regulating valve 16, the vacuum pump 20, the vacuum gauge 23, the high-pressure micro-flow injection pump 25, the one-way valve 32, the high-pressure injection pump 46, the high-speed camera 64, the computer 65, the cold light source 66 and the constant temperature box 69 are all existing conventional devices and can be purchased on the market. The specific structure and working principle will not be elaborated here.

[0065] The present invention can fully consider the actual occurrence conditions of coal seams and similarly simulate the actual occurrence conditions of different coal seams, that is, it can similarly simulate coal sample 67 under different adsorption equilibrium pressures, different adsorbed gas amounts and different load stress conditions, and accurately test the contact angle between coal and liquid in the loaded coal-gas-liquid three-phase system, effectively solving the problem of inaccurate contact angle tested in the coal-gas-liquid or coal-air-liquid three-phase system.

[0066] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A coal contact angle testing device based on high pressure load conditions, characterized in that: It includes a methane filling system, a helium filling calibration system, a vacuum system, a liquid injection system, a visual loading kettle system, an imaging test system and a constant temperature system. The methane outlet of the methane filling system and the helium outlet of the helium filling calibration system are connected in parallel with the gas inlet of the visual loading kettle system. The gas outlet of the visual loading kettle system is connected with the gas inlet of the vacuum system. The liquid outlet of the liquid injection system is connected with the liquid inlet of the visual loading kettle system. The imaging test system is arranged on one side of the visual loading kettle system and shoots toward the visual loading kettle system. Some components of the methane filling system, the helium filling calibration system, the visual loading kettle system and the imaging test system are arranged inside the constant temperature system. The visual loading kettle system includes a visual kettle and two sets of loading devices. The visual kettle is a cubic box structure with an open top. The top of the visual kettle is detachably fixedly connected to a kettle cover by bolts. The front side plate and the rear side plate of the visual kettle are both provided with front and rear corresponding and transparent windows. The front side plate and the rear side plate of the visual kettle are both detachably fixedly connected to sapphire glass windows embedded in the corresponding windows by bolts. The first O-rings are pressed between the four sides of the kettle cover and the upper port of the visual kettle and between the four sides of the inner side of the sapphire glass window and the window. A support platform is fixedly provided in the middle of the inner bottom surface of the visual kettle. The two sets of loading devices have the same structure and are symmetrically installed on the left and right sides of the visualized kettle body. An air inlet is opened on the left side of the kettle cover, a liquid inlet is opened in the middle part of the kettle cover, and an air exhaust port is opened on the right side of the kettle cover. The other end of the air injection pipeline is connected to the air inlet, and the capillary droplet tube is vertically penetrated and connected to the liquid inlet. The lower end of the capillary droplet tube extends into the visualized kettle body and is located directly above the support platform. The capillary droplet tube is fixedly connected to the kettle cover through a pressure cap which is sleeved on the outer circumference of its upper and lower parts. The upper pressure cap is fixed on the outer surface of the kettle cover, and the lower pressure cap is fixed on the inner surface of the kettle cover. The air inlet end of the vacuum pipeline is connected to the air exhaust port.

2. The coal contact angle testing device under high pressure load conditions according to claim 1 is characterized in that: The methane filling system includes a methane storage bottle and a methane reference tank. The methane outlet of the methane storage bottle is connected to the methane inlet of the methane reference tank through a first gas pipeline. The methane outlet of the methane reference tank is connected to a second gas pipeline. The other end of the second gas pipeline is connected to the outside atmosphere. A methane pressure regulating valve and a first gas valve are sequentially arranged on the upper side of the first gas pipeline in the direction of gas flow. A first precision pressure gauge, a second gas valve, a second precision pressure gauge, a gas injection pipeline and a third gas valve are sequentially arranged on the upper side of the second gas pipeline in the direction of gas flow. The other end of the gas injection pipeline is connected to the gas inlet of the visual loading kettle system.

3. The coal contact angle testing device under high pressure load conditions according to claim 2 is characterized in that: The helium-filled calibration system includes a helium storage bottle and a helium reference tank. The helium outlet of the helium storage bottle is connected to the helium inlet of the helium reference tank through a third gas pipeline. The helium outlet of the helium reference tank is connected to a fourth gas pipeline. The other end of the fourth gas pipeline is connected to the second gas pipeline located between the second gas valve and the second precision pressure gauge. A helium pressure regulating valve and a fourth gas valve are sequentially arranged along the gas flow direction of the third gas pipeline. A third precision pressure gauge and a fifth gas valve are sequentially arranged along the gas flow direction of the fourth gas pipeline.

4. The coal contact angle testing device under high pressure load conditions according to claim 3 is characterized in that: The vacuum system includes a vacuum pump, the gas inlet of the vacuum pump is connected to the gas outlet of the visual loading kettle system through a vacuum pipeline, a sixth gas valve and a vacuum gauge are sequentially arranged along the gas flow direction of the vacuum pipeline, and the gas outlet of the vacuum pump is connected to the outside atmosphere.

5. The coal contact angle testing device under high pressure load conditions according to claim 4 is characterized in that: The liquid injection system includes a first water cup, a high-pressure micro-flow liquid injection pump and a capillary dropper. The bottom of the first water cup is connected to the liquid inlet of the high-pressure micro-flow liquid injection pump through a first liquid pipeline. The capillary dropper is vertically fixed in the liquid inlet of the visualization loading kettle system. The upper end of the capillary dropper is connected to the liquid outlet of the high-pressure micro-flow liquid injection pump through a second liquid pipeline. The lower end of the capillary dropper extends into the visualization loading kettle system. A first liquid valve is arranged on the first liquid pipeline. A second liquid valve, a fourth precision pressure gauge and a one-way valve are sequentially arranged on the second liquid pipeline along the liquid flow direction. The liquid flow direction in the one-way valve is the direction in which the liquid flows from the high-pressure micro-flow liquid injection pump to the capillary dropper.

6. The coal contact angle testing device under high pressure load conditions according to claim 1 is characterized in that: The loading device on the left side includes a loading plate, a loading cylinder, a loading piston, a second water cup and a high-pressure injection pump. The loading plate is vertically arranged in the front-to-back direction on the left side of the visualization kettle body and on the left side of the support platform. The lower side of the loading plate is flush with the upper surface of the support platform. The loading cylinder body is horizontally arranged in the left-right direction. A flange plate is integrally formed on the outer circumference of the right end of the loading cylinder body. The flange plate is fixedly connected to the middle part of the left side surface of the left side plate of the visualization kettle body by a plurality of bolts. The loading piston is sealingly and slidably connected in the loading cylinder body. A piston rod is concentrically arranged in the loading cylinder body. The left end of the piston rod is integrally and fixedly connected to the middle part of the right side surface of the loading piston. The piston rod extends to the right from the right end of the loading cylinder body and passes through the middle part of the left side plate of the visualization kettle body. The right end of the piston rod extends into the interior of the visualization kettle body and is fixedly connected with the middle part of the left side surface of the loading plate through a thread. The piston rod is sealingly and slidably connected to the right side plate of the loading cylinder body and the left side plate of the visualization kettle body respectively. Two portions are fixedly embedded on the outer circumference of the loading piston and are arranged at intervals on the left and right and slide with the inner wall of the loading cylinder body. A second O-ring in dynamic contact, a third O-ring sleeved on the outer circumference of the piston rod is fixedly embedded in the right side plate of the loading cylinder body and the left side plate of the visualization kettle body, a pressurized liquid injection port located on the left side of the loading piston is opened in the middle of the left side plate of the loading cylinder body, and a pressure relief liquid injection port located on the right side of the loading piston is opened on the upper side wall of the right end of the loading cylinder body. The bottom of the second water cup is connected to the liquid inlet of the high-pressure liquid injection pump through the third liquid pipeline, and the liquid outlet of the high-pressure liquid injection pump is connected to the pressurized liquid injection port through the fourth liquid pipeline. A third liquid valve is arranged on the third liquid pipeline, and a fifth liquid pipeline, a fourth liquid valve, a fifth precision pressure gauge and a first liquid discharge pipeline are arranged in sequence along the liquid flow direction on the fourth liquid pipeline. The other end of the fifth liquid pipeline is connected to the pressure relief liquid injection port, and a fifth liquid valve, a sixth precision pressure gauge and a second liquid discharge pipeline are arranged in sequence along the liquid flow direction on the fifth liquid pipeline. A sixth liquid valve is arranged on the first liquid discharge pipeline, and a seventh liquid valve is arranged on the second liquid discharge pipeline.

7. The coal contact angle testing device under high pressure load conditions according to claim 1 is characterized in that: The imaging test system includes a high-speed camera, a computer and a cold light source. The high-speed camera is connected to the computer through a signal wire. The high-speed camera is set in front of the visualization kettle body and shoots towards the sapphire glass window on the front side. The cold light source is set behind the visualization kettle body and irradiates towards the sapphire glass window on the rear side.

8. The coal contact angle testing device under high pressure load conditions according to claim 7 is characterized in that: The constant temperature system includes a constant temperature box, and a methane reference tank, a helium reference tank, a visualization kettle, a high-speed camera and a cold light source are all arranged in the constant temperature box.

Images