A liquid nitrogen cold immersion real-time temperature measurement and strain measurement system and its usage method

Abstract

The present invention provides a real-time temperature measurement and strain measurement system for cryogenic immersion in liquid nitrogen, which includes a liquid nitrogen tank, an incubator, a controller, a multi-channel data recorder, an acoustic emission detector, and an infrared scanning thermal imager, and is applicable to studying the temperature transfer evolution law and strain law of coal and rock masses under cryogenic immersion in liquid nitrogen. By performing steps such as drilling, grinding, drying, pasting strain gauges and acoustic emission sensors on coal samples, turning on the controller and testing the system, injecting liquid nitrogen into the incubator and conducting data acquisition, and recording the recovery characteristics of the temperature and strain of coal samples under normal temperature environment after the liquid nitrogen injection is completed, real-time temperature monitoring can be carried out on coal samples of different sizes under different numbers of cryogenic immersions in liquid nitrogen, as well as the temperature field response and crack evolution characteristics of coal samples of the same size under the action of different numbers of cryogenic immersions in liquid nitrogen, so as to study the damage mechanism of cryogenic immersion in liquid nitrogen to coal.

Description

Technical Field

[0001] The present invention relates to the field of coal liquid nitrogen cold soaking, and particularly relates to a real-time temperature measurement and strain measurement system for liquid nitrogen cold soaking and a method for using the same. Background Art

[0002] In the coal field, with the increase in the depth and intensity of coal resource mining, the gas pressure and gas reserves also increase, while the coal permeability gradually decreases. Therefore, improving coal permeability is the main challenge in coalbed methane development and efficient natural gas extraction. Subsequently, the liquid nitrogen cold soaking method is proposed, which utilizes the principle of liquid nitrogen refrigeration to increase the cracks in coal samples and thus increase the coal body permeability. However, the current method cannot reflect the strain of coal samples when liquid nitrogen is injected and the temperature drops, making it difficult to master the strain of coal samples during actual application research, and thus making correct judgments. In order to study and understand the effects of the number of liquid nitrogen cold soaking times, metamorphic degree, and coal sample size on the coal temperature distribution and strain, and to explore the damage mechanism of coal under liquid nitrogen cold soaking, based on actual needs, those skilled in the art are committed to inventing a real-time temperature measurement and strain measurement system for liquid nitrogen cold soaking.

[0003] Chinese Patent Application CN109307558A discloses a coal sample liquid nitrogen temperature transfer test device and a test method. This method provides a coal sample liquid nitrogen temperature transfer test device to study the change law of coal sample temperature after continuous injection of liquid nitrogen into the coal sample. However, this method only proposes how to measure the coal sample temperature when liquid nitrogen is injected into the coal sample and monitor the change law of the coal sample temperature, and does not propose the strain of the coal sample after continuous injection of liquid nitrogen and temperature reduction, as well as the damage of the coal sample under liquid nitrogen cold soaking. In actual application, it cannot reflect the strain and damage of the coal sample as the temperature decreases; moreover, the thermocouple thermometer provided by this method cannot accurately and quickly measure the change of the temperature field and reflect the distribution of the temperature field in an ultra-low temperature environment; it cannot achieve a perfect effect in actual application.

[0004] Therefore, the prior art needs a method that can measure the change of coal sample strain when liquid nitrogen is injected into the coal sample to solve the problem of being unable to master the coal sample strain when liquid nitrogen is injected into the coal sample, and a test system that can simultaneously and accurately measure the temperature field distribution, strain, and crack field evolution of coal samples during liquid nitrogen cold soaking to improve the efficiency of actual application and the understanding of the temperature field distribution, crack field evolution, and strain change of coal samples when liquid nitrogen is injected. Summary of the Invention

[0005] The purpose of the present invention is to study the temperature field distribution, strain, and crack field evolution of coal and rock masses under freeze-thaw conditions, and to provide a real-time temperature measurement and strain measurement system for liquid nitrogen cold soaking and a method for using the same.

[0006] To achieve the object of the present invention, the following technical solutions are adopted:

[0007] A liquid nitrogen cold immersion real-time temperature measurement and strain measurement system, characterized in that it includes a liquid nitrogen tank, an incubator, a controller, a multi-channel data recorder, an acoustic emission detector and an infrared scanning thermal imager;

[0008] The controller is a computer, and temperature real-time recording software and acoustic wave analysis software are installed in the computer. The computer is respectively connected to the multi-channel data recorder and the acoustic emission detector through connecting wires;

[0009] The liquid nitrogen tank is connected to the incubator through a liquid nitrogen injection pipe, and an automatic valve is arranged at the liquid nitrogen outlet. A coal sample is placed in the incubator, an acoustic emission sensor is placed on the coal sample, and the acoustic emission sensor is connected to a preamplifier through a multi-channel conversion line. The preamplifier is connected to the acoustic emission detector through a coaxial cable, and the infrared scanning thermal imager is connected to the multi-channel data recorder through a conversion line.

[0010] Preferably, the whole incubator is a transparent body. The processed square coal sample is placed inside the incubator. There is a drill hole in the center of the upper surface of the coal sample, and the drill hole extends to the middle and lower part of the coal sample. A semiconductor resistance thermometer is inserted at the drill hole. The acoustic emission sensor is placed on the right side of the drill hole on the upper surface of the coal sample. Strain gauges are pasted on the surface of the coal sample, and every four strain gauges form a multi-axial 45° strain rosette, that is, a four-axial 45° strain rosette.

[0011] Preferably, strain gauges are pasted on any three surfaces of the coal sample, and the surface without the pasted strain gauge is closely attached to the front surface of the incubator.

[0012] Preferably, the infrared scanning thermal imager is placed outside the front surface of the incubator, and its lens faces the side of the incubator close to the coal sample, and the lens can rotate 360°. The infrared recorder is used to scan and record the surface temperature and strain evolution of the coal sample and transmit the data to the multi-channel data recorder.

[0013] Preferably, before the strain gauges are pasted, they are first connected to a strain conversion line, and the strain conversion line is connected to a multi-channel conversion line. The acoustic emission sensor and the strain gauges share a multi-channel conversion line. Two sets of independent lines in the multi-channel conversion line are respectively connected to the acoustic emission sensor and the strain gauges, and the line of the multi-channel conversion line connected to the strain gauges is connected to the multi-channel data recorder.

[0014] Preferably, the incubator includes an upper cover and a box body. One side edge of the upper cover is connected to the top end of one side surface of the box body. There is an injection hole on the left side of the upper cover, which is the channel for the liquid nitrogen injection pipe to insert into the incubator. The liquid nitrogen injection pipe is arranged at an equal distance from the coal sample. A temperature measurement opening is provided in the middle of the upper cover, which is opposite to the drilling hole on the upper surface of the coal sample. It is the channel for the probe of the semiconductor resistance thermometer to insert into the incubator and then into the bottom of the drilling hole. The other end of the semiconductor resistance thermometer is connected to a multi-channel data recorder through a temperature conversion line. A connection hole is provided on the right side wall of the box body, which is the channel for the multi-channel conversion line to connect from inside the box to the outside.

[0015] Preferably, on the bottom end surface inside the incubator, a liquid level controller is vertically placed to measure the height of the liquid nitrogen injected into the incubator. Its range value is greater than the height value of the coal sample. The liquid level controller is placed closely against the right side wall of the incubator. The liquid level controller is also made of a transparent material.

[0016] A usage method of a liquid nitrogen cold immersion real-time temperature measurement and strain measurement system, applying the above liquid nitrogen cold immersion real-time temperature measurement and strain measurement system, specifically includes the following steps:

[0017] Step 1. Treatment of the coal sample: Process the coal sample to obtain a cube-shaped coal sample. Drill a hole in the center of the upper surface of the coal sample with a drill. The drilling extends to the middle and lower part of the coal sample. Then place the coal sample in a constant temperature drying oven until the weight remains unchanged to reduce the influence of water on the experimental coal sample. Polish it and then put it into a sealed bag for standby.

[0018] Step 2. Pasting and connection of strain gauges and acoustic emission sensors, placing the coal sample: Install strain gauges on any three surfaces of the coal sample in Step 1. After the installation of the strain gauges is completed, install the acoustic emission sensor on the upper surface of the coal sample near the drilling hole. Then open the upper cover of the incubator, pick up the coal sample vertically, and gently place it at a position close to the center of the incubator, so that the surface of the coal sample without installed strain gauges is tightly attached to the front surface of the incubator.

[0019] Step 3. Preparation and testing of the liquid nitrogen cold immersion real-time temperature measurement and strain measurement system: Turn on the computer, multi-channel data recorder, infrared scanning thermal imager, acoustic emission detector, and multi-channel data recorder. Open the temperature real-time recording software and acoustic wave analysis software installed in the computer, set the time interval for collecting data, and test whether the temperature measurement and strain measurement system is running normally.

[0020] Step 4. Inject liquid nitrogen into the incubator and conduct data acquisition: When the temperature measurement system and the strain measurement system are normal, keep the systems turned on, cover the upper lid of the incubator, insert the liquid nitrogen injection tube through the injection hole to the bottom of the incubator, and place the liquid nitrogen injection tube at a certain distance from the coal sample; insert the probe of the semiconductor resistance thermometer through the temperature measurement opening on the lid of the incubator and further into the borehole of the coal sample. At the same time, visually observe the contact degree between the probe and the coal sample to ensure that the probe gently touches the bottom of the coal sample borehole; pass the multi-channel conversion line through the connection hole on the right side to connect the multi-channel data recorder and the acoustic emission detector; keep the incubator in a sealed state;

[0021] Open the automatic valve at the outlet of the liquid nitrogen tank, inject liquid nitrogen into the incubator through the liquid nitrogen injection tube. The purity of the liquid nitrogen is 99.99%. At the same time, click "Acquire" in the computer software to start real-time synchronous data acquisition;

[0022] Observe the liquid level controller at the position equal to the height of the coal sample on the side of the incubator, and always control the liquid nitrogen at the same height as the coal sample;

[0023] Step 5. After the liquid nitrogen injection ends, record the recovery characteristics of the temperature and strain of the coal sample at room temperature: When the temperature of the coal sample remains stable, close the automatic valve of the liquid nitrogen tank, stop injecting liquid nitrogen, and the liquid nitrogen cold soaking ends. Vertically lift out the liquid nitrogen injection tube and the probe of the semiconductor resistance thermometer, open the upper lid of the incubator, and then insert the probe of the semiconductor resistance thermometer into the borehole of the coal sample for testing;

[0024] Keep the system turned on, wait for the coal sample to warm up in the external room temperature environment, and record the changes in the temperature field distribution and the characteristics of the strain during the warming of the coal sample;

[0025] Step 6. Export data: After the coal sample returns to room temperature and reaches the equilibrium state, click "Stop" in the computer software to stop data acquisition, and export or calculate the experimental data;

[0026] Step 7: End this coal sample experiment and conduct continuous testing.

[0027] Preferably, in Step 3, the set time interval for data acquisition is 1 - 10 seconds, and it is advisable to set the time interval to 2 seconds. Generally, it is set according to the needs of the test. Whether the test system is running normally includes: observing whether the measured temperature inside and outside the incubator is the room temperature and whether the acoustic wave value is approximately 0 to check whether the temperature measurement system and the acoustic emission device are running normally; at the same time, gently touch the strain gauge with an extremely slight force with your finger, observe the state of the strain force curve in the strain module on the screen of the multi-channel data recorder, whether there is a fluctuation, and observe whether the acoustic wave curve on the computer screen fluctuates to check whether the strain measurement system is normal, and ensure that the temperature measurement system and the strain measurement system are normal.

[0028] Preferably, the temperature real-time recording software and acoustic wave analysis software in the computer preset calculation formulas. When the strain gauge is deformed by an external force, its resistance value R will increase or decrease accordingly. The relationship between the stress ε and the change in the resistance value ΔR of the strain gauge is as follows:

[0029] ΔR÷R=GF*ε

[0030] Among them, the strain coefficient GF is a coefficient representing the sensitivity of the strain gauge;

[0031] The acoustic emission sensor can receive the acoustic emission signals on the surface and inside of the coal sample when strain occurs, convert the mechanical vibration generated by the acoustic emission source on the surface of the coal sample into an electrical signal, and then amplify and transmit the electrical signal to the acoustic emission detector through noise reduction and filtering by the preamplifier to understand the damage situation of the coal sample. The functional relationship is as follows:

[0032] V(t,x)=U(t,x)*T(t)

[0033] Among them, t is time, x is the surface displacement of the coal sample, V(t,x) is the output voltage, U(t,x) is the surface displacement wave, and T(t) is the response function, that is, the output voltage V(t,x) is the convolution of the surface displacement wave U(t,x) and its response function T(t).

[0034] Compared with the prior art, the advantages of the present invention are as follows:

[0035] This system can perform real-time temperature monitoring on coal samples of different sizes under different numbers of liquid nitrogen cold soaking conditions, study the size effect of the temperature field change of different coal qualities under the action of liquid nitrogen cold soaking, as well as the temperature field response and crack evolution characteristics of coal samples of the same size under different numbers of liquid nitrogen cold soaking, qualitatively and quantitatively characterize the evolution characteristics of the crack structure of coal under liquid nitrogen cold soaking, reveal the influence of the number of liquid nitrogen cold soaking, metamorphic degree and coal sample size on the temperature distribution and strain of coal, and study the damage mechanism of liquid nitrogen cold soaking on coal. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic structural diagram of a liquid nitrogen cold soaking real-time temperature measurement and strain measurement system of the present invention;

[0037] Figure 2 It is an enlarged view of the acoustic emission sensor of a liquid nitrogen cold soaking real-time temperature measurement and strain measurement system of the present invention;

[0038] Figure 3 It is a flowchart of a liquid nitrogen cold soaking real-time temperature measurement and strain measurement system of the present invention.

[0039] In the figure, 1 is a liquid nitrogen tank; 2 is an automatic valve; 3 is a liquid nitrogen injection pipe; 4 is an injection hole; 5 is an incubator; 6 is a temperature measurement opening; 7 is a temperature conversion line; 8 is a connection hole; 9 is a multi-channel conversion line; 10 is a computer; 11 and 12 are connection lines; 13 is a multi-channel data recorder; 14 is an acoustic emission detector; 15 is a coaxial cable; 16 is a conversion line; 17 is a liquid level controller; 18 is a strain gauge; 19 is a semiconductor resistance thermometer; 20 is a coal sample; 21 is a transparent incubator; 22 is an infrared scanning thermal imager; 23 is an acoustic emission sensor; 24 is a preamplifier. Detailed implementation mode

[0040] The attached drawings are only for illustrative purposes and should not be construed as limitations on the present invention; for better illustration of this embodiment, some components in the attached drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, some well-known structures and their descriptions in the attached drawings may be omitted; the orientation or positional relationships indicated by the terms "upper", "lower", "front", "rear", "one end", "the other end", "top", "bottom", "inner", "outer", "side", "vertical", etc. are based on the orientation or positional relationships shown in the attached drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limitations on the present invention.

[0041] In the present invention, unless otherwise clearly defined and limited, the terms "installation", "connection", "connection" and other terms should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral body; it can be a mechanical connection, an electrical connection or communication with each other; it can be a direct connection, or an indirect connection through a medium, and can be the internal communication of two components or the interaction relationship between two components. Unless otherwise clearly defined, for those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] The following will make a specific description in conjunction with the attached drawings.

[0043] As Figure 1 shown,

[0044] A liquid nitrogen cold immersion real-time temperature measurement and strain measurement system, characterized in that it includes a liquid nitrogen tank 1, an incubator 5, a controller 10, a multi-channel data recorder 13, an acoustic emission detector 14 and an infrared scanning thermal imager 22;

[0045] The controller 10 is a computer, and temperature real-time recording software and acoustic wave analysis software are installed in the computer. The computer is respectively connected to the multi-channel data recorder and the acoustic emission detector through connection lines;

[0046] The liquid nitrogen tank 1 is connected to the incubator 5 through a liquid nitrogen injection pipe 3. An automatic valve 2 is provided at the liquid nitrogen outlet. A coal sample 20 is placed in the incubator 5. A acoustic emission sensor 23 is placed on the right side of the drilled hole on the upper surface of the coal sample 20. The acoustic emission sensor 23 is connected to a preamplifier 24 through a multiplexing line 9. The preamplifier 24 is connected to an acoustic emission detector 14 through a coaxial cable 15. An infrared scanning thermal imager 22 is connected to a multi-channel data recorder 13 through a conversion line 16.

[0047] The incubator 5 is entirely made of a transparent material. The treated coal sample 20 is placed inside the incubator 5. There is a drilled hole at the center of the upper surface of the coal sample 20, and the drilled hole extends to the middle and lower part of the coal sample 20. A semiconductor resistance thermometer 19 is inserted into the drilled hole. The acoustic emission sensor 23 is placed on the right side of the drilled hole. Strain gauges 18 are pasted on the surface of the coal sample 20. Every four strain gauges 18 form a multi-axial 45° strain rosette, that is, a four-axial 45° strain rosette, and the included angle between each strain gauge 18 is 45°.

[0048] Strain gauges 18 are pasted on any three surfaces of the coal sample 20. The surface without the pasted strain gauges 18 is in close contact with the front surface of the incubator 5, and the lower surface is in contact with the upper end surface of the bottom of the incubator 5. Any three of the remaining surfaces can be pasted.

[0049] The infrared scanning thermal imager 22 is placed outside the front surface of the incubator 5, and its lens faces the side of the incubator 5 in close contact with the coal sample. The lens can rotate 360°.

[0050] Before the strain gauges 18 are pasted, they are first connected to a strain conversion line, and through the strain conversion line, they are connected to the multiplexing line 9. The acoustic emission sensor 23 and the strain gauges 18 share a multiplexing line 9. Inside the multiplexing line 9, two sets of independent lines are respectively connected to the acoustic emission sensor 23 and the strain gauges 18. The line of the multiplexing line 9 connected to the strain gauges 18 is connected to the multi-channel data recorder 13.

[0051] The incubator 5 includes an upper cover and a box body. One side edge of the upper cover is connected to the top end of one side surface of the box body by screws; there is an injection hole 4 on the left side of the upper cover, which is the channel for the liquid nitrogen injection pipe 3 to insert into the incubator 5. The liquid nitrogen injection pipe 3 is arranged at an equal distance from the coal sample 20; there is a temperature measurement opening 6 in the middle of the upper cover, facing the drilled hole on the upper surface of the coal sample 20, which is the channel for the probe of the semiconductor resistance thermometer 19 to insert into the incubator 5 and then into the bottom of the drilled hole. The other end of the semiconductor resistance thermometer 19 is connected to the multi-channel data recorder 13 through a temperature conversion line 7; there is a connection hole 8 on the right side wall of the box body, which is the channel for the multiplexing line 9 to connect from inside the box to the outside.

[0052] On the bottom end face on the right side of the coal sample 20 in the incubator 5, a liquid level controller 17 is vertically placed. Its range value is greater than the height value of the coal sample 20, and the liquid level controller 17 is placed close to the right side wall of the incubator 5. The liquid level controller 17 is also made of transparent material.

[0053] Embodiment

[0054] Step 1. Treatment of the coal sample 20: Select three coal samples 20 with different degrees of coal metamorphism, and the degrees of coal body metamorphism are anthracite, bituminous coal, and lignite respectively. Among them, the moisture content grade of the coal sample 20 is controlled by a drying oven; prepare a coal sample 20 that is adapted to the aperture size of the rotary drill according to industrial standards, and drill the coal sample 20 with a drill; according to the requirements of the standard of GB / T212 - 2008 "Methods for the Proximate Analysis of Coal", process a cylindrical coal sample with a diameter of about 80 mm and a length of about 100 mm into a cube coal sample with a side length of 60 mm; use a drill with a diameter of 6 mm and a depth of 55 mm to drill a hole in the center of one surface of the coal sample, and take the surface of this hole as the upper surface; in order to facilitate the installation of the acoustic emission sensor 23, polish the surface of the coal sample 20 with sandpaper, remove the polishing dust and then place it in a constant temperature oven for drying until the weight remains unchanged to reduce the influence of water on the experimental coal sample, and then put it into a sealed bag for standby.

[0055] Step 2. Paste and connect the strain gauges 18 and the acoustic emission sensors 23, and place the coal sample 20: Install the strain gauges 18 on any three surfaces of the coal sample 20 in Step 1. Four strain gauges form a multi - axial strain rosette. Then paste the strain rosette with 610 type epoxy phenolic resin adhesive. Before pasting the strain gauges 18, connect them to the strain conversion wires first, and connect the multi - path conversion wires 9 through the strain conversion wires.

[0056] After the installation of the strain gauges 18 is completed, apply the coupling agent to the place near the hole in the center of the upper surface of the coal sample, and then gently place the acoustic emission sensor 23 on it. After placing the acoustic emission sensor 23, gently translate it to make the coupling agent evenly distributed, and connect the acoustic emission sensor 23 to the multi - path conversion wires 9. The length of the multi - path conversion wires 9 is generally not less than 1.5 meters, and it can also be set according to actual needs.

[0057] Open the upper cover of the incubator 5, pick up the coal sample 20 vertically, and gently place it at the center position of the incubator 5, so that the surface of the coal sample 20 without the installed strain gauges 18 is close to the front surface of the incubator 5;

[0058] Step 3. Detection and testing of the liquid nitrogen cold immersion real-time temperature measurement and strain measurement system: Turn on the computer, multi-channel data recorder 13, infrared scanning thermal imager 22, and acoustic emission detector 14. Open the temperature real-time recording software and acoustic wave analysis software installed on the computer, and set the data acquisition time interval to 2 s. It can also be set according to the actual needs of each test experiment. Check and test whether the temperature measurement and strain measurement systems are operating normally, including: observing whether the measured temperature inside and outside the incubator 5 is room temperature and whether the acoustic wave value is approximately 0 to check whether the temperature measurement system and the acoustic emission detector 14 are operating normally; at the same time, gently touch the strain gauge 18 with a finger with an extremely slight force, and observe the state of the strain force curve in the strain module on the screen of the multi-channel data recorder 13 to check whether the strain measurement system is normal, and finally ensure that the temperature measurement system and the strain measurement system are normal.

[0059] Step 4. Inject liquid nitrogen into the incubator 5 and collect various data: When the temperature measurement system and the strain measurement system are normal, keep the system on, cover the upper cover of the incubator 5, insert the liquid nitrogen injection tube 3 from the injection hole 4 to the bottom of the incubator 5, and place the liquid nitrogen injection tube 3 at a certain distance from the coal sample 20; insert the probe of the semiconductor resistance thermometer 19 into the incubator through the temperature measurement opening 6 on the upper cover of the box and continue to insert it into the drill hole of the coal sample 20. At the same time, visually observe the contact degree between the probe and the coal sample to ensure that the probe gently touches the bottom of the drill hole of the coal sample 20; the multi-channel conversion line 9 passes through the connection hole 8 on the right side to connect the multi-channel data recorder 13 and the acoustic emission detector 14. Keep the incubator 5 in a sealed state, and the various holes and the upper cover can be sealed by setting sealing rings.

[0060] Open the automatic valve 2 at the outlet of the liquid nitrogen tank 1, inject liquid nitrogen into the incubator 5 through the liquid nitrogen injection tube 3. The purity of the liquid nitrogen is 99.99%. At the same time, click "Collect" in the computer software to start real-time synchronous data collection;

[0061] Due to the gasification of liquid nitrogen, part of the gasified liquid nitrogen enters the cracks of the coal sample, further enlarging the cracks and accelerating the crack development, thereby causing strain in the coal sample;

[0062] Observe the liquid nitrogen level displayed on the liquid level controller 17 placed on the right side of the incubator 5, and always control the liquid nitrogen at the same height as the coal sample 20.

[0063] Step 5. Record the recovery characteristics of the temperature and strain of the coal sample 20 at room temperature after the liquid nitrogen injection ends: When the temperature of the coal sample 20 remains stable, close the automatic valve 2 of the liquid nitrogen tank 1 to stop injecting liquid nitrogen. The liquid nitrogen cold immersion ends. Vertically lift out the liquid nitrogen injection tube 3, vertically lift out the probe of the semiconductor resistance thermometer 19, open the upper cover of the incubator 5, and then insert the probe of the semiconductor resistance thermometer 19 into the drill hole of the coal sample 20 in the same way as inserting into the drill hole in Step 4;

[0064] Keep the system on and wait for the coal sample 20 to warm up in the external room temperature environment, and record the changes in the temperature field distribution and the characteristics of the strain during the warming of the coal sample.

[0065] Step Six. Export data: After the coal sample 20 returns to room temperature and reaches the equilibrium state, click "Stop" in the computer software to stop data acquisition. The data of the multi-channel data recorder, acoustic emission detector, and infrared scanning thermal imager can all be transmitted to the software in the computer, and the experimental data can be exported, or the results can be calculated according to the preset formula.

[0066] Step Seven: End the experiment on the coal sample 20 this time. If you continue to conduct measurement experiments with different numbers of liquid nitrogen cold soaking times and measurement experiments on coal samples with other degrees of metamorphism, just repeat the above steps two to six.

[0067] If the experiment is completely ended, turn off the switches of each instrument and device, take out the probe of the semiconductor resistance thermometer 19, and remove the conversion wires and connection wires between each component; vertically take out the coal sample 20, remove the acoustic emission sensor, and organize and store all the instruments and devices.

[0068] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for using a real-time temperature and strain measurement system with liquid nitrogen cold immersion, which uses a real-time temperature and strain measurement system with liquid nitrogen cold immersion, and is characterized in that, The system includes a liquid nitrogen tank, an incubator, a controller, a multi-channel data recorder, an acoustic emission detector, and an infrared scanning thermal imager; The controller is a computer, and temperature real-time recording software and acoustic wave analysis software are installed in the computer. The computer is respectively connected to the multi-channel data recorder and the acoustic emission detector through connecting wires; The method specifically includes the following steps: Step 1. Processing of coal samples: Process the coal samples to obtain cube-shaped coal samples. Drill holes in the center of the upper surface of the coal samples with a drill, and the holes extend to the middle and lower parts of the coal samples. After grinding the coal samples, place them in a constant temperature drying oven until the weight remains unchanged to reduce the influence of water on the experimental coal samples, and then put them into a sealed bag for standby; Step 2. Pasting and connecting strain gauges and acoustic emission sensors, placing coal samples: Install strain gauges on any three surfaces of the coal samples in Step 1. After the installation of the strain gauges is completed, install the acoustic emission sensors on the upper surface of the coal samples near the drilled holes, and then place the coal samples at the center position of the incubator, with the surface without the installed strain gauges closely attached to the front surface of the incubator; Step 3. Preparation and testing of the liquid nitrogen cold soaking real-time temperature measurement and strain measurement system: Turn on the computer, multi-channel data recorder, infrared scanning thermal imager, and acoustic emission detector. For the multi-channel data recorder, turn on the temperature real-time recording software and acoustic wave analysis software installed in the computer, set the time interval for collecting data, and test whether the temperature measurement and strain measurement systems are operating normally; Step 4. Inject liquid nitrogen into the incubator and collect data: When the temperature measurement system and the strain measurement system are normal, keep the systems on, cover the upper cover of the incubator, insert the liquid nitrogen injection tube into the bottom of the incubator through the injection hole, and place the liquid nitrogen injection tube at a certain distance from the coal samples; Insert the probe of the semiconductor resistance thermometer into the incubator through the temperature measurement opening on the upper cover of the incubator and continue to insert it into the drilled hole of the coal sample. At the same time, visually observe the contact degree between the probe and the coal sample to ensure that the probe gently touches the bottom of the drilled hole of the coal sample; The multi-channel conversion line passes through the connection hole on the right side to connect the multi-channel data recorder and the acoustic emission detector; Keep the incubator in a sealed state; Open the automatic valve at the outlet of the liquid nitrogen tank, inject liquid nitrogen into the incubator through the liquid nitrogen injection tube. The purity of the liquid nitrogen is 99.99%. At the same time, click "Collect" in the computer software to start real-time synchronous data collection; Observe the liquid level controller at the position equal to the height of the coal sample on the side of the incubator, and always control the liquid nitrogen at the same height as the coal sample; Step 5. Record the recovery characteristics of the temperature and strain of the coal sample at room temperature after the liquid nitrogen injection ends: When the temperature of the coal sample remains stable, close the automatic valve of the liquid nitrogen tank, stop injecting liquid nitrogen, and the liquid nitrogen cold soaking ends. Vertically lift out the liquid nitrogen injection tube and the probe of the semiconductor resistance thermometer, open the upper cover of the incubator, and then insert the probe of the semiconductor resistance thermometer into the drilled hole of the coal sample for testing; Keep the systems on, wait for the coal sample to warm up in the external room temperature environment, and record the changes in the temperature field distribution and the characteristics of the strain when the coal sample is warming up; Step 6. Export data: After the coal sample returns to room temperature and reaches the equilibrium state, click "Stop" in the computer software to stop data collection, and export or calculate the experimental data; Step 7: End the current coal sample experiment and proceed with further testing.

2. The method for using a liquid nitrogen cold immersion real-time temperature and strain measurement system according to claim 1, characterized in that, The liquid nitrogen tank is connected to the incubator through a liquid nitrogen injection pipe. An automatic valve is set at the liquid nitrogen outlet. A coal sample is placed in the incubator. An acoustic emission sensor is placed on the coal sample. The acoustic emission sensor is connected to a preamplifier through a multiplexer cable. The preamplifier is connected to an acoustic emission detector through a coaxial cable. An infrared scanning thermal imager is connected to a multi-channel data recorder through a conversion cable. The incubator is entirely transparent. The treated coal sample is placed inside the incubator. There is a drill hole in the center of the upper surface of the coal sample, which extends to the middle and lower part of the coal sample. A semiconductor resistance thermometer is inserted into the drill hole. The acoustic emission sensor is placed on the right side of the drill hole on the upper surface of the coal sample. Strain gauges are pasted on the surface of the coal sample, and every four strain gauges form a multi-axial 45° strain rosette. Before the strain gauges are pasted, they are first connected to a strain conversion cable, and the strain conversion cable is connected to a multiplexer cable. The acoustic emission sensor and the strain gauges share one multiplexer cable. Inside the multiplexer cable, two independent lines are respectively connected to the acoustic emission sensor and the strain gauges. The other end of the line of the multiplexer cable connected to the strain gauges is connected to a multi-channel data recorder. Strain gauges are pasted on any three surfaces of the coal sample, and the surface without the pasted strain gauges is closely attached to the front surface of the incubator.

3. The usage method of a real-time temperature measurement and strain measurement system with liquid nitrogen cold immersion according to claim 2, characterized in that, The infrared scanning thermal imager is placed outside the front surface of the incubator, and its lens faces the side of the incubator closely attached to the coal sample. The lens can rotate 360°.

4. The method for using a real-time temperature measurement and strain measurement system with liquid nitrogen cold immersion according to claim 2, wherein, The incubator includes an upper cover and a box body. One side edge of the upper cover is connected to the top of one side surface of the box body. There is an injection hole on the left side of the upper cover, which is the channel for the liquid nitrogen injection pipe to insert into the incubator. The liquid nitrogen injection pipe is placed at a certain distance from the coal sample. There is a temperature measurement opening in the middle of the upper cover, which is directly opposite to the drill hole on the upper surface of the coal sample. It is the channel for the probe of the semiconductor resistance thermometer to insert into the incubator and then into the bottom of the drill hole. The other end of the semiconductor resistance thermometer is connected to a multi-channel data recorder through a temperature conversion cable. There is a connection hole on the right side wall of the box body, which is the channel for the multiplexer cable to connect from inside the box to the outside.

5. The method for using a real-time temperature measurement and strain measurement system with liquid nitrogen cold immersion according to claim 4, characterized in that, A liquid level controller is vertically placed on the bottom end surface inside the incubator. Its range value is greater than the height value of the coal sample. The liquid level controller is placed closely against the right side wall of the incubator.

6. The usage method of a liquid nitrogen cold immersion real-time temperature and strain measurement system according to claim 1, characterized in that, In Step 3, the set interval time for collecting data is 1 to 10 seconds. Whether the test system is operating normally includes: observing whether the measured temperature inside and outside the incubator is at room temperature and whether the acoustic wave value is approximately 0, so as to check whether the temperature measurement system and the acoustic emission detector are operating normally; at the same time, gently touch the strain gauges with a finger with extremely slight force, and observe the state of the strain force curve in the strain module on the screen of the multi-channel data recorder to see if there is any fluctuation, and observe whether the acoustic wave curve on the computer screen fluctuates to check whether the strain measurement system is normal, and ensure that the temperature measurement system and the strain measurement system are normal.

7. The method of using a real-time temperature measurement and strain measurement system with liquid nitrogen cold immersion according to claim 1, characterized in that The temperature real-time recording software and acoustic wave analysis software in the computer preset calculation formulas. When the strain gauge is deformed by an external force, its resistance value R will increase or decrease accordingly. The relationship between the stress ε and the change amount △R of the resistance value R of the strain gauge is: △R÷R = GF*ε Among them, the strain coefficient GF is a coefficient representing the sensitivity of the strain gauge; The acoustic emission sensor can receive the acoustic emission signals generated on the surface and inside of the coal sample during strain, convert the mechanical vibration generated by the acoustic emission source on the surface of the coal sample into an electrical signal, and then amplify and transmit the electrical signal to the acoustic emission detector through noise reduction and filtering by the preamplifier to understand the damage condition of the coal sample. The functional relationship is as follows: V(t,x) = U(t,x) * T(t) Where t is time, x is the surface displacement of the coal sample, V(t,x) is the output voltage, U(t,x) is the surface displacement wave, and T(t) is the response function, that is, the output voltage V(t,x) is the convolution of the surface displacement wave U(t,x) and its response function T(t).

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