System and method for testing water-ice phase change frost heaving force in liquid nitrogen cold impact coal rock

Abstract

The invention discloses a system and method for testing water-ice phase change frost heaving force in liquid nitrogen cold impact coal rock, a liquid nitrogen injection device accurately controls the cooling rate of a sample, and it is ensured that stable temperature change is maintained in the freezing process; the sample testing device monitors flow, temperature, deformation quantity and frost heaving force parameters of a sample in the freezing process in real time, and the data acquisition and control device is responsible for synchronously collecting data; through cooperative work of multiple devices, high precision and synchronism of the measurement process are guaranteed, multi-parameter synchronous measurement at any moment in the freezing process is achieved, and therefore complete and accurate experimental data are provided for research of complex physical phenomena such as water-ice phase change frost heaving force in the liquid nitrogen environment. Besides, through real-time dynamic monitoring of the cooling process, frost heaving deformation of the sample can be accurately evaluated, and generation of measurement errors and time delay in the traditional technology is avoided. The device is not only suitable for static measurement, but also can meet dynamic experiment requirements, and the accuracy and efficiency of experiments are greatly improved.

Description

Technical Field

[0001] The present invention relates to a testing system and method, in particular to a system and method for testing the frost heave force of water-ice phase change in coal rock during liquid nitrogen cold shock, belonging to the technical field of mine gas prevention and control. Background Art

[0002] Currently, gas management in my country's soft, low-permeability coal seams is difficult, and gas disasters still occur frequently. This is primarily due to the fact that soft coal seams are rich in clay minerals, which expand upon absorption of water, making hydraulic permeability enhancement measures ineffective. Consequently, gas extraction to reduce the gas content in these seams is impossible. However, there is currently a lack of effective alternative permeability enhancement technologies.

[0003] Liquid nitrogen, as a low-temperature (-196°C) anhydrous fluid, prevents the minerals from absorbing water and expanding during cold shock, thereby blocking cracks. This effectively addresses the drawback of hydraulic fracturing technology, which is difficult to apply to soft, low-permeability coal seams. Furthermore, since coal generally contains water, the low-temperature cold shock of liquid nitrogen causes the water in the coal to transform into ice, resulting in a 9% volume expansion. The force generated by this expansion can continuously expand the pores in the coal seam until they become cracks, providing pathways for gas migration and extraction within the coal.

[0004] However, moisture within coal is typically stored in tiny pores and fissures, making it difficult to directly measure the frost heave force of water-ice phase transitions within these pores and fissures using conventional methods. Furthermore, significant differences exist in the temperature reduction rate and heat transfer patterns between coal samples placed in a standard cooling environment and a liquid nitrogen environment. Therefore, how to conduct stable tests in different liquid nitrogen environments and effectively measure the frost heave force of coal samples during the water-ice phase transition remain pressing challenges that hinder the further application of liquid nitrogen permeability enhancement.

[0005] The research direction of this invention is to provide a testing system and method that can meet the requirements of simultaneous testing of multiple parameters of coal rock samples in static and dynamic liquid nitrogen environments, and then measure the frost heave force of water-ice phase change in coal rock under liquid nitrogen environment, and establish a quantitative relationship between the temperature, displacement and frost heave force of water-ice phase change of coal rock samples, so as to provide theoretical guidance for liquid nitrogen injection for coal seam permeability enhancement in the future. Summary of the Invention

[0006] In response to the problems existing in the above-mentioned prior art, the present invention provides a system and method for testing the frost heave force of water-ice phase change in coal rock caused by liquid nitrogen cold shock, which can effectively solve the above-mentioned technical problems.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is: a system for testing the frost heave force of water ice phase change in coal rock under liquid nitrogen cold shock, comprising a liquid nitrogen injection device, a sample testing device, and a data acquisition and control device;

[0008] The liquid nitrogen injection device includes a nitrogen cylinder, a liquid nitrogen storage tank and a waste liquid storage tank. Liquid nitrogen is contained in the liquid nitrogen storage tank. An inlet and an outlet are provided at the top of the liquid nitrogen storage tank. One end of a low-temperature resistant pipeline extends from the outlet into the liquid nitrogen storage tank and is close to the bottom thereof. The nitrogen cylinder is connected to the inlet of the liquid nitrogen storage tank through a pipeline and is used to inject nitrogen into the liquid nitrogen storage tank to apply pressure, thereby causing the liquid nitrogen to enter the low-temperature resistant pipeline from the liquid nitrogen storage tank and be discharged. The low-temperature resistant pipeline outside the liquid nitrogen storage tank is equipped with a first flow control valve for regulating the flow of liquid nitrogen in the pipeline, a mass flow meter for detecting the flow of liquid nitrogen in the pipeline, and an electronic current stabilizer for stabilizing the flow of liquid nitrogen in the pipeline. The waste liquid storage tank is located below the electronic current stabilizer. The electronic current stabilizer discharges waste liquid generated by the stable flow through the pipeline to the waste liquid storage tank for recovery.

[0009] The sample testing device includes a test sealed cavity, a test tube, a test cage and a test rod. The inner wall of the test sealed cavity is covered with an insulation layer for reducing the heat transfer efficiency between the inside of the test sealed cavity and the outside. One end of the test tube extends into the test sealed cavity from the top of the test sealed cavity. The test cage is installed at one end of the test tube, and the test sample is placed inside the test cage. The test cage includes a base and multiple connecting rods. The base is connected to one end of the test tube through the multiple connecting rods, and a gap is left between two adjacent connecting rods. The test rod is installed in the test tube, and one end of the test rod is in close contact with the top of the test sample. An inlet and an outlet are provided on the side of the test sealed cavity. The other end of the low-temperature resistant pipeline is connected to the inlet of the test sealed cavity for injecting liquid nitrogen into the test sealed cavity and allowing the liquid nitrogen to contact the side of the test sample through the gap to perform a low-temperature liquid nitrogen cold shock test. The outlet of the test sealed cavity is connected to a second flow control valve and an evaporator through a pipeline for discharging liquid nitrogen and nitrogen gas inside the test sealed cavity from the outlet and forming nitrogen gas through the evaporator. The second flow control valve is used to control the flow between the outlet of the test sealed cavity and the evaporator.

[0010] The data acquisition and control device includes a computer, a deformation or force data detection device and a temperature detection device. The deformation or force data detection device is installed at the other end of the test rod and is used to obtain real-time deformation force data of the test sample during the test through the test rod; the temperature detection device is installed between the base and the test sample and is used to obtain real-time temperature data of the test sample during the test; the computer is connected to the first flow control valve, the second flow control valve, the mass flow meter, the electronic stabilizer, the deformation or force data detection device and the temperature detection device, and is used to control the first flow control valve, the second flow control valve and the electronic stabilizer, and obtain data fed back by the mass flow meter, the deformation or force data detection device and the temperature detection device.

[0011] Furthermore, the test sealed chamber includes a dynamic test sealed chamber and a static test sealed chamber. The dynamic test sealed chamber and the static test sealed chamber have identical structures, differing only in that the inlet of the dynamic test sealed chamber is higher than its outlet in the vertical direction, while the inlet of the static test sealed chamber is lower than its outlet in the vertical direction. This arrangement ensures smooth injection and discharge of liquid nitrogen during static and dynamic tests, meeting the requirements of each test.

[0012] Furthermore, a pressure relief gauge is installed on the pipeline between the nitrogen cylinder and the liquid nitrogen storage tank for adjusting the pressure of nitrogen entering the liquid nitrogen storage tank from the nitrogen cylinder; a first liquid level gauge is installed on the liquid nitrogen storage tank for monitoring the liquid level of liquid nitrogen in the liquid nitrogen storage tank; and a second liquid level gauge is installed on the test sealing cavity for monitoring the liquid level of liquid nitrogen in the test sealing cavity.

[0013] Furthermore, the test tube, test cage, and test rod are all made of quartz glass. Since quartz glass undergoes minimal volume changes in hot and cold environments, the deformation or force data detection device accurately measures the deformation and force of the test specimen during the test, facilitating the accuracy of subsequent data analysis.

[0014] Furthermore, the deformation or force data detection device is a displacement micrometer or a force sensor. If it is a force sensor, when the test sample is deformed after being affected by liquid nitrogen cold shock, it will apply pressure to the test rod, and the test rod will then transmit the pressure to the force sensor, thereby measuring the deformation force of the test sample. If it is a displacement micrometer, it can detect the deformation amount of the test sample after being affected by liquid nitrogen cold shock. The required data is obtained by replacing the two sensors.

[0015] Furthermore, the temperature detection device is a thermocouple temperature sensor, which is used because of its stable operation and wide temperature measurement range, and can ensure the acquisition of required test data.

[0016] The working method of the system for testing the frost heave force of water ice phase change in coal rock by liquid nitrogen cold shock is as follows:

[0017] A. First, select the coal rock mass to be tested and make multiple test samples of the same size. The test samples are divided into two groups, one group is the saturated state test samples after soaking in water, and the other group is the dry state test samples after drying. Then, assemble the liquid nitrogen injection device, the sample testing device, and the data acquisition and control device. The test sealing cavity of the sample testing device, if a static liquid nitrogen environment test is performed, select the static test sealing cavity and proceed to step B; if a dynamic liquid nitrogen environment test is performed, select the dynamic test sealing cavity and proceed to step C.

[0018] B. Static liquid nitrogen environment test of coal rock mechanical data: select a saturated state test sample from step A and place it in the test cage, and set the liquid nitrogen flow value; open the nitrogen bottle, and control the nitrogen pressure delivered to the liquid nitrogen storage tank through the pressure relief gauge. After the nitrogen enters, it drives the liquid nitrogen in the liquid nitrogen storage tank into one end of the low-temperature resistant pipeline near the bottom, and then the computer controls the opening of the first flow control valve to allow the liquid nitrogen to pass through the mass flow meter in the low-temperature resistant pipeline to reach the electronic flow stabilizer, and adjust the opening of the first flow control valve according to the mass flow meter until the liquid nitrogen flow reaches the set liquid nitrogen flow value; the electronic flow stabilizer stabilizes the liquid nitrogen, and the liquid nitrogen before the stabilization is completed is transported to the waste liquid storage tank for recovery. After the stabilization is completed, the liquid Nitrogen is injected into the static test chamber until the liquid nitrogen level exceeds the top of the test specimen. The computer then controls the second flow control valve to open, allowing excess liquid nitrogen to evaporate from the outlet through the evaporator and be discharged into the air. Once the liquid level stabilizes, the first and second flow control valves are closed, halting the injection and discharge of liquid nitrogen. At this point, a deformation or force data detection device and a temperature detection device collect mechanical or deformation data and temperature data from the test specimen at different time points in the static liquid nitrogen environment and feed them back to the computer for storage. The temperature data is used to determine the sample's real-time temperature, which continuously changes during freezing. It is a key parameter that dynamically and real-timely reflects the freezing process. Temperature changes directly affect physical state transitions within the test specimen, such as water freezing and ice crystal formation and expansion, and thus influence the generation and development of frost heave forces (deformation). In the present invention, temperature data determines the time the sample is tested in liquid nitrogen, that is, the test process is completed when the temperature data monitors that the test sample has dropped to the liquid nitrogen temperature. After the test is completed, the liquid nitrogen in the static test sealed cavity is discharged to the waste liquid storage tank through the electronic current stabilizer, and the test tube is removed. After the test sample returns to room temperature, it is removed from the test cage to complete the static liquid nitrogen environment cold shock test of the test sample. Then, a dry state test sample is selected from step A and placed in the test cage. This step is repeated with the same test parameters as the saturated state test sample to complete the static liquid nitrogen environment cold shock test of the dry state test sample.

[0019] C. Dynamic liquid nitrogen environment test of coal rock mechanical data: select a saturated state test sample from step A and place it in the test cage, and set the liquid nitrogen flow value; open the nitrogen bottle, and control the nitrogen pressure delivered to the liquid nitrogen storage tank through the pressure relief gauge. After the nitrogen enters, it drives the liquid nitrogen in the liquid nitrogen storage tank into one end of the low-temperature resistant pipeline near the bottom, and then the computer controls the first flow control valve to open, so that the liquid nitrogen passes through the mass flow meter in the low-temperature resistant pipeline to reach the electronic flow stabilizer, and adjust the opening of the first flow control valve according to the mass flow meter until the liquid nitrogen flow reaches the set liquid nitrogen flow value; the electronic flow stabilizer stabilizes the liquid nitrogen, and the liquid nitrogen before the stabilization is completed is transported to the waste liquid storage tank for recovery. After the stabilization is completed, the liquid nitrogen is injected into the dynamic test sealing cavity, and the computer controls the second flow control valve to open. After the liquid nitrogen enters, it contacts the side of the test sample in the dynamic test sealing cavity for cold shock, and then the liquid nitrogen is discharged from the outlet and evaporated into nitrogen through the evaporator and discharged into the air. ; Maintain the current dynamic liquid nitrogen environment, and at this time collect the mechanical or deformation data and temperature data of the test sample at different time points in the dynamic liquid nitrogen environment through the deformation or force data detection device and the temperature detection device, and feed them back to the computer for storage; after the test is completed, the liquid nitrogen in the dynamic test sealing cavity is discharged to the waste liquid storage tank through the electronic current stabilizer, the test tube is taken out, and after the test sample returns to room temperature, it is taken out of the test cage to complete the dynamic liquid nitrogen environment cold shock test of the saturated state test sample; then select a dry state test sample from step A and put it into the test cage, and repeat this step with the same test parameters as the saturated state test sample to complete the dynamic liquid nitrogen environment cold shock test of the dry state test sample; select multiple saturated state and dry state test samples from step A and set different liquid nitrogen flow rates, and repeat this step respectively, so as to obtain the mechanical data and temperature data of the saturated state and dry state test samples in the dynamic liquid nitrogen environment with different liquid nitrogen flow rates.

[0020] D. Data analysis: Analyze and process the static liquid nitrogen environment data and dynamic liquid nitrogen environment data obtained in step B and step C respectively:

[0021] The force variation curve of the saturated state test specimen under the same environment is obtained as F 饱 (t); and the force variation curve of the dry state test specimen is F 干 (t); then the variation curve of the frost heave force of water ice phase change is F(t)=F 饱 (t)-F 干 (t);

[0022] Since the frost heave force of water-ice phase change is a variable force, the maximum frost heave force of water-ice phase change F max (t1) taken from At this moment, the deformation of the coal body due to the water-ice phase transition is also the largest, which is L max (t1); Obtain different coal rock porosity in the same environmental test The deformation L of the coal rock mass caused by the water-ice phase transition corresponding to the liquid nitrogen injection rate V max (t1) and the maximum water ice phase change frost heave force F max (t1), and then establish the linear relationship between the three as follows:

[0023]

[0024] Through the above formula, the porosity of coal rock mass is realized. The two parameters of liquid nitrogen injection rate V are used to predict the maximum deformation and maximum frost heave force caused by water-ice phase change in the static liquid nitrogen environment of coal rock mass and the dynamic liquid nitrogen environment with different liquid nitrogen flow rates.

[0025] Compared with the prior art, the present invention adopts a combination of a liquid nitrogen injection device, a sample testing device, and a data acquisition and control device to achieve the function of dynamic and static measurement of liquid nitrogen cold shock on the test sample. Through the liquid nitrogen injection device, the cooling rate of the sample can be accurately controlled to ensure that a stable temperature change is maintained during the freezing process; the sample testing device monitors the flow rate, temperature, deformation, water ice phase change frost heave force and other physical parameters of the sample in the freezing process in real time through high-precision sensors, and the data acquisition and control device is responsible for synchronously collecting these data to ensure that each parameter can be accurately obtained at the same time point. This invention ensures the high precision and synchronization of the measurement process through the collaborative work of multiple devices, and can achieve multi-parameter synchronous measurement at any time during the freezing process, thereby providing complete and accurate experimental data for the study of complex physical phenomena such as frost heave force. In addition, by real-time dynamic monitoring of the cooling process, the frost heave deformation of the sample can also be accurately evaluated, avoiding the measurement errors and time lags in traditional technologies. Therefore, the present invention is not only suitable for static measurement, but also meets the needs of dynamic experiments, greatly improving the accuracy and efficiency of the experiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 2. It is a schematic structural diagram of the present invention for conducting a static liquid nitrogen cold shock test;

[0027] Figure 2 2. It is a schematic structural diagram of the present invention for conducting a dynamic liquid nitrogen cold shock test;

[0028] Figure 3 It is a structural schematic diagram of the test cage in the present invention.

[0029] In the figure: 1-nitrogen cylinder; 2-liquid nitrogen storage tank; 3-liquid nitrogen; 4-first liquid level gauge; 5-pressure relief gauge; 6-low-temperature resistant pipeline; 7-first flow control valve; 8-mass flow meter; 9-electronic current stabilizer; 10-waste liquid storage tank; 11-test sealing cavity; 12-insulation layer; 13-second liquid level gauge; 14-deformation or force data detection device; 15-test tube; 16-test rod; 17-test sample; 18-test cage; 19-thermocouple temperature sensor; 20-second flow control valve; 21-evaporator; 22-computer. DETAILED DESCRIPTION

[0030] The present invention will be further described below.

[0031] like Figure 1 and 2 As shown, a system for testing the frost heave force of water-ice phase change in coal rock during liquid nitrogen cold shock includes a liquid nitrogen injection device, a sample testing device, and a data acquisition and control device;

[0032] The liquid nitrogen injection device includes a nitrogen cylinder 1, a liquid nitrogen storage tank 2 and a waste liquid storage tank 10. Liquid nitrogen 3 is contained in the liquid nitrogen storage tank 10. An inlet and an outlet are provided at the top of the liquid nitrogen storage tank 2. One end of a low-temperature resistant pipeline 6 extends from the outlet into the liquid nitrogen storage tank 2 and is close to its bottom. The nitrogen cylinder 1 is connected to the inlet of the liquid nitrogen storage tank 2 through a pipeline, and is used to inject nitrogen into the liquid nitrogen storage tank 2 to apply pressure, thereby causing the liquid nitrogen to enter the low-temperature resistant pipeline 6 from the liquid nitrogen storage tank 2 and be discharged; the low-temperature resistant pipeline 6 outside the liquid nitrogen storage tank 2 is equipped with a first flow control valve 7 for regulating the flow of liquid nitrogen in the pipeline, a mass flowmeter 8 for detecting the flow of liquid nitrogen in the pipeline, and an electronic current stabilizer 9 for stabilizing the flow of liquid nitrogen in the pipeline. The waste liquid storage tank 10 is located below the electronic current stabilizer 9. The electronic current stabilizer 9 discharges the waste liquid generated by the stable flow through the pipeline to the waste liquid storage tank 2 for recovery.

[0033] The sample testing device includes a test sealed cavity 11, a test tube 15, a test cage 18 and a test rod 16. The inner wall of the test sealed cavity 11 is covered with an insulation layer 12 to reduce the heat transfer efficiency between the inside of the test sealed cavity 11 and the outside. One end of the test tube 15 extends into the test sealed cavity 11 from the top of the test sealed cavity 11. The test cage 18 is installed at one end of the test tube 15, and the test sample 17 is placed inside the test cage. Figure 3As shown, the test cage 18 includes a base and multiple connecting rods, the base is connected to one end of the test tube through the multiple connecting rods, and a gap is left between two adjacent connecting rods; the test rod 16 is installed in the test tube 15, and one end of it is in close contact with the top of the test sample 17; an inlet and an outlet are provided on the side of the test sealing cavity 11, and the other end of the low-temperature resistant pipeline 6 is connected to the inlet of the test sealing cavity 11 for injecting liquid nitrogen 3 into the test sealing cavity 11 and making the liquid nitrogen 3 contact the side of the test sample 17 through the gap to perform a low-temperature liquid nitrogen cold shock test; the outlet of the test sealing cavity 11 is connected to the second flow control valve 20 through a pipeline. The test tube 15 is connected to the evaporator 21, allowing the liquid nitrogen 3 and nitrogen gas within the test sealed chamber 11 to be discharged from the outlet and formed into nitrogen gas through the evaporator 21. The second flow control valve 20 is used to control the flow rate between the outlet of the test sealed chamber 11 and the evaporator 21. The test sealed chamber 11 includes a dynamic test sealed chamber and a static test sealed chamber. The dynamic test sealed chamber and the static test sealed chamber have the same structure, differing only in that the inlet of the dynamic test sealed chamber is higher than its outlet in the vertical direction, while the inlet of the static test sealed chamber is lower than its outlet in the vertical direction. This arrangement ensures smooth injection and discharge of liquid nitrogen during static and dynamic tests, meeting the requirements of each test. The test tube 15, test cage 18, and test rod 16 are all made of quartz glass. Because quartz glass undergoes minimal volume changes in hot and cold environments, it ensures the accuracy of the deformation and force measurements of the test specimen during the test, facilitating the accuracy of subsequent data analysis.

[0034] The data acquisition and control device includes a computer 22, a deformation or force data detection device 14 and a temperature detection device. The deformation or force data detection device is installed at the other end of the test rod 16, and is used to obtain real-time deformation force data of the test sample 17 during the test through the test rod 16; the temperature detection device is installed between the base and the test sample 17, and is used to obtain real-time temperature data of the test sample 17 during the test; the computer 22 is connected to the first flow control valve 7, the second flow control valve 20, the mass flow meter 8, the electronic stabilizer 9, the deformation or force data detection device 14 and the temperature detection device, and is used to control the first flow control valve 7, the second flow control valve 20 and the electronic stabilizer 9, and obtain the data fed back by the mass flow meter 8, the deformation or force data detection device and the temperature detection device.

[0035] As an improvement of the present invention, a pressure relief gauge 5 is installed on the pipeline between the nitrogen cylinder 1 and the liquid nitrogen storage tank 2, which is used to adjust the pressure of nitrogen entering the liquid nitrogen storage tank 2 from the nitrogen cylinder 1; a first liquid level gauge 4 is installed on the liquid nitrogen storage tank 2, which is used to monitor the liquid level of liquid nitrogen in the liquid nitrogen storage tank 2; and a second liquid level gauge 13 is installed on the test sealed cavity 11, which is used to monitor the liquid level of liquid nitrogen in the test sealed cavity 11.

[0036] As another improvement to the present invention, the deformation or force data detection device 14 is a displacement micrometer or a force sensor. If it is a force sensor, when the test sample is deformed after being affected by the liquid nitrogen cold shock, it will apply pressure to the test rod, and then the test rod transmits the pressure to the force sensor, thereby measuring the deformation force of the test sample. If it is a displacement micrometer, it can detect the deformation amount of the test sample after being affected by the liquid nitrogen cold shock. The required data is obtained by replacing the two sensors. The temperature detection device is a thermocouple temperature sensor. This sensor is used because it is stable in operation and has a wide temperature range of measurement, which can ensure that the required test data can be obtained.

[0037] The working method of the system for testing the frost heave force of water ice phase change in coal rock by liquid nitrogen cold shock is as follows:

[0038] A. First, select the coal rock mass to be tested and make multiple test samples 17 of the same size. Then divide the test samples 17 into two groups, one group is the saturated state test samples after soaking in water, and the other group is the dry state test samples after drying. Then assemble the liquid nitrogen injection device, the sample testing device, and the data acquisition and control device. The test sealing chamber 11 of the sample testing device is a static test sealing chamber if a static liquid nitrogen environment test is performed. Figure 1 As shown, and go to step B; if dynamic liquid nitrogen environment test is performed, select the dynamic test sealing cavity as shown Figure 2 As shown, and go to step C.

[0039] B. Static liquid nitrogen environment test of coal rock mechanical data: select a saturated state test sample from step A and place it in the test cage 18, and set the liquid nitrogen flow value; open the nitrogen bottle 1, and control the nitrogen pressure delivered to the liquid nitrogen storage tank 2 through the pressure relief gauge 5. After the nitrogen enters, it drives the liquid nitrogen 3 in the liquid nitrogen storage tank 2 into one end of the low-temperature resistant pipeline 6 near the bottom, and then the computer 22 controls the first flow control valve 7 to open, so that the liquid nitrogen 3 passes through the mass flow meter 8 in the low-temperature resistant pipeline 6 to reach the electronic flow stabilizer 9, and adjust the opening of the first flow control valve 7 according to the mass flow meter 8 until the liquid nitrogen flow reaches the set liquid nitrogen flow value; the electronic flow stabilizer 9 stabilizes the liquid nitrogen 3, and the liquid nitrogen 3 before the stabilization is completed is transported to the waste liquid storage tank 10 for recovery. After the stabilization is completed, the liquid nitrogen 3 is injected into the static test sealing cavity until the liquid nitrogen After the liquid level in the static test sealed chamber exceeds the top of the test specimen, the computer 22 controls the second flow control valve 20 to open, allowing excess liquid nitrogen 3 to evaporate from the outlet through the evaporator 21 and be discharged into the air. After the liquid level stabilizes, the first flow control valve 7 and the second flow control valve 20 are controlled to close, stopping the injection and discharge of liquid nitrogen 3. At this time, the deformation or force data detection device 14 and the temperature detection device collect mechanical or deformation data (mechanical data is measured using a force sensor, and deformation data is measured using a displacement micrometer, with one data point obtained for each test) and temperature data of the test specimen at different time points in the static liquid nitrogen environment and feed them back to the computer for storage. The temperature data is used to determine the real-time temperature of the sample, which continuously changes during the freezing process. It is a key parameter that dynamically and real-timely reflects the freezing process. Temperature changes directly affect the physical state transformations within the test specimen, such as the freezing of water, the formation and expansion of ice crystals, and thus affect the generation and development of frost heave forces (deformation). In the present invention, the temperature data determines the time the sample is tested in liquid nitrogen, that is, the test process is completed when the temperature data monitors that the test sample has dropped to the liquid nitrogen temperature. After the test is completed, the liquid nitrogen 3 in the static test sealed cavity is discharged to the waste liquid storage tank 10 through the electronic current stabilizer 9, and the test tube 15 is taken out. After the test sample 17 returns to room temperature, it is taken out of the test cage 18 to complete the static liquid nitrogen environment cold shock test of the saturated state test sample 17. Then, a dry state test sample is selected from step A and placed in the test cage 18. This step is repeated with the same test parameters as the saturated state test sample to complete the static liquid nitrogen environment cold shock test of the dry state test sample.

[0040] C. Dynamic liquid nitrogen environment test of coal rock mechanical data: Select a saturated state test sample from step A and place it in the test cage 18, and set the liquid nitrogen flow value; open the nitrogen bottle 1, and control the nitrogen pressure delivered to the liquid nitrogen storage tank 2 through the pressure relief gauge 5. After the nitrogen enters, it drives the liquid nitrogen 3 in the liquid nitrogen storage tank 2 into one end of the low-temperature resistant pipeline 6 near the bottom, and then the computer 22 controls the first flow control valve 7 to open, so that the liquid nitrogen 3 passes through the mass flow meter 8 in the low-temperature resistant pipeline 6 to reach the electronic flow stabilizer 9, and adjusts the opening of the first flow control valve 7 according to the mass flow meter 8 until the liquid nitrogen flow reaches the set liquid nitrogen flow value; the electronic flow stabilizer 9 stabilizes the flow of the liquid nitrogen 3, and the liquid nitrogen 3 before the stabilization is completed is transported to the waste liquid storage tank 10 for recovery. After the stabilization is completed, the liquid nitrogen 3 is injected into the dynamic test sealing cavity, and at the same time, the computer 22 controls the second flow control valve 20 to open. After the liquid nitrogen 3 enters, it contacts the side of the test sample 17 in the dynamic test sealing cavity for cold shock, and then the liquid nitrogen 3 is discharged from the outlet and evaporated through the evaporator 21 The nitrogen is discharged into the air; the current dynamic liquid nitrogen environment is maintained, and the mechanical or deformation data and temperature data of the test sample at different time points in the dynamic liquid nitrogen environment are collected by the deformation or force data detection device 14 and the temperature detection device, and fed back to the computer for storage; after the test is completed, the liquid nitrogen in the dynamic test sealing cavity is discharged to the waste liquid storage tank 10 through the electronic current stabilizer 9, the test tube 15 is taken out, and after the test sample 17 returns to room temperature, it is taken out from the test cage 18 to complete the dynamic liquid nitrogen environment cold shock test of the saturated state test sample; then, a dry state test sample is selected from step A and placed in the test cage 18, and this step is repeated with the same test parameters as the saturated state test sample to complete the dynamic liquid nitrogen environment cold shock test of the dry state test sample; multiple saturated state and dry state test samples are selected from step A and different liquid nitrogen flow rates are set, and this step is repeated respectively, so that the mechanical data and temperature data of the saturated state and dry state test samples in the dynamic liquid nitrogen environment with different liquid nitrogen flow rates can be obtained.

[0041] D. Data analysis: Analyze and process the static liquid nitrogen environment data and dynamic liquid nitrogen environment data obtained in step B and step C respectively:

[0042] The force variation curve of the saturated state test specimen under the same environment is obtained as F 饱 (t); and the force variation curve of the dry state test specimen is F 干 (t); then the variation curve of the frost heave force of water ice phase change is F(t)=F 饱 (t)-F 干 (t);

[0043] Since the frost heave force of water-ice phase change is a variable force, the maximum frost heave force of water-ice phase change F max (t1) taken from At this moment, the deformation of the coal body due to the water-ice phase transition is also the largest, which is L max (t1); Obtain different coal rock porosity in the same environmental test The deformation L of the coal rock mass caused by the water-ice phase transition corresponding to the liquid nitrogen injection rate V max (t1) and the maximum water ice phase change frost heave force F max (t1), and then establish the linear relationship between the three as follows:

[0044]

[0045]

[0046] Through the above formula, the porosity of coal rock mass is realized. The two parameters of liquid nitrogen injection rate V are used to predict the maximum deformation and maximum frost heave force caused by water-ice phase change in the static liquid nitrogen environment of coal rock mass and the dynamic liquid nitrogen environment with different liquid nitrogen flow rates.

[0047] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A system for testing the frost heave force of water ice phase change in coal rock during liquid nitrogen cold shock, characterized in that: Including liquid nitrogen injection device, sample testing device, data acquisition and control device; The liquid nitrogen injection device includes a nitrogen cylinder, a liquid nitrogen storage tank and a waste liquid storage tank. Liquid nitrogen is contained in the liquid nitrogen storage tank. An inlet and an outlet are provided at the top of the liquid nitrogen storage tank. One end of a low-temperature resistant pipeline extends from the outlet into the liquid nitrogen storage tank and is close to the bottom thereof. The nitrogen cylinder is connected to the inlet of the liquid nitrogen storage tank through a pipeline and is used to inject nitrogen into the liquid nitrogen storage tank to apply pressure, thereby causing the liquid nitrogen to enter the low-temperature resistant pipeline from the liquid nitrogen storage tank and be discharged. The low-temperature resistant pipeline outside the liquid nitrogen storage tank is equipped with a first flow control valve for regulating the flow of liquid nitrogen in the pipeline, a mass flow meter for detecting the flow of liquid nitrogen in the pipeline, and an electronic current stabilizer for stabilizing the flow of liquid nitrogen in the pipeline. The waste liquid storage tank is located below the electronic current stabilizer. The electronic current stabilizer discharges the waste liquid generated by the stable flow through the pipeline to the waste liquid storage tank for recovery. The sample testing device includes a test sealed cavity, a test tube, a test cage and a test rod. The inner wall of the test sealed cavity is covered with an insulation layer for reducing the heat transfer efficiency between the inside of the test sealed cavity and the outside world. One end of the test tube extends into the test sealed cavity from the top of the test sealed cavity. The test cage is installed at one end of the test tube, and the test sample is placed inside the test cage. The test cage includes a base and multiple connecting rods. The base is connected to one end of the test tube through multiple connecting rods, and a gap is left between two adjacent connecting rods. The test rod is installed in the test tube, and one end of the test rod is in close contact with the top of the test sample. An inlet and an outlet are provided on the side of the test sealed cavity. The other end of the low-temperature resistant pipeline is connected to the inlet of the test sealed cavity for injecting liquid nitrogen into the test sealed cavity and allowing the liquid nitrogen to contact the side of the test sample through the gap to perform a low-temperature liquid nitrogen cold shock test. The outlet of the test sealed cavity is connected to a second flow control valve and an evaporator through a pipeline for discharging liquid nitrogen and nitrogen gas inside the test sealed cavity from the outlet and forming nitrogen gas through the evaporator. The second flow control valve is used to control the flow between the outlet of the test sealed cavity and the evaporator. The data acquisition and control device includes a computer, a deformation or force data detection device and a temperature detection device. The deformation or force data detection device is installed at the other end of the test rod and is used to obtain real-time deformation force data of the test sample during the test through the test rod; the temperature detection device is installed between the base and the test sample and is used to obtain real-time temperature data of the test sample during the test; the computer is connected to the first flow control valve, the second flow control valve, the mass flow meter, the electronic stabilizer, the deformation or force data detection device and the temperature detection device, and is used to control the first flow control valve, the second flow control valve and the electronic stabilizer, and obtain data fed back by the mass flow meter, the deformation or force data detection device and the temperature detection device.

2. The system for testing the frost heave force of water ice phase change in coal rock by liquid nitrogen cold shock according to claim 1, characterized in that: The test sealing chamber includes a dynamic test sealing chamber and a static test sealing chamber. The dynamic test sealing chamber and the static test sealing chamber have the same structure, the only difference being that the inlet of the dynamic test sealing chamber is higher than its outlet in the direction of the vertical horizontal plane; the inlet of the static test sealing chamber is lower than its outlet in the direction of the vertical horizontal plane.

3. The system for testing the frost heave force of water ice phase change in coal rock by liquid nitrogen cold shock according to claim 1, characterized in that: A pressure relief gauge is installed on the pipeline between the nitrogen cylinder and the liquid nitrogen storage tank for adjusting the pressure of nitrogen entering the liquid nitrogen storage tank from the nitrogen cylinder; a first liquid level gauge is installed on the liquid nitrogen storage tank for monitoring the liquid level of liquid nitrogen in the liquid nitrogen storage tank; and a second liquid level gauge is installed on the test sealing cavity for monitoring the liquid level of liquid nitrogen in the test sealing cavity.

4. The system for testing the frost heave force of water ice phase change in coal rock by liquid nitrogen cold shock according to claim 1, characterized in that: The test tube, test cage and test rod are all made of quartz glass.

5. The system for testing the frost heave force of water ice phase change in coal rock by liquid nitrogen cold shock according to claim 1, characterized in that: The deformation or force data detection device is a displacement micrometer or a force sensor.

6. The system for testing the frost heave force of water ice phase change in coal rock by liquid nitrogen cold shock according to claim 1, characterized in that: The temperature detection device is a thermocouple temperature sensor.

7. A method for operating a system for testing the frost heave force of water ice phase change in coal rock under liquid nitrogen cold shock according to any one of claims 1 to 6, characterized in that: The specific steps are: A. First, select the coal and rock mass to be tested and make multiple test samples of the same size. The test samples are divided into two groups: one group is the saturated state test samples after soaking in water, and the other group is the dry state test samples after drying. Then, assemble the liquid nitrogen injection device, the sample testing device, and the data acquisition and control device. The test sealing chamber of the sample testing device is selected as the static test sealing chamber if a static liquid nitrogen environment test is performed, and proceed to step B; if a dynamic liquid nitrogen environment test is performed, select the dynamic test sealing chamber and proceed to step C. B. Static liquid nitrogen environment test of coal rock mechanical data: select a saturated state test sample from step A and place it in the test cage, and set the liquid nitrogen flow value; open the nitrogen bottle, and control the nitrogen pressure delivered to the liquid nitrogen storage tank through the pressure relief gauge. After the nitrogen enters, it drives the liquid nitrogen in the liquid nitrogen storage tank into one end of the low-temperature resistant pipeline near the bottom, and then the computer controls the first flow control valve to open, so that the liquid nitrogen passes through the mass flow meter in the low-temperature resistant pipeline to reach the electronic flow stabilizer, and adjust the opening of the first flow control valve according to the mass flow meter until the liquid nitrogen flow reaches the set liquid nitrogen flow value; the electronic flow stabilizer stabilizes the flow of liquid nitrogen, and the liquid nitrogen before the stabilization is completed is transported to the waste liquid storage tank for recovery. After the stabilization is completed, the liquid nitrogen is injected into the static test sealing cavity until the liquid nitrogen level in the static test sealing cavity exceeds the top of the test sample, and the computer controls the second flow control valve to open. The excess liquid nitrogen is evaporated from the outlet through the evaporator into nitrogen and discharged into the air; after the liquid level stabilizes, the first flow control valve and the second flow control valve are controlled to close to stop the injection and discharge of liquid nitrogen; at this time, the mechanical or deformation data and temperature data of the test sample at different time points in the static liquid nitrogen environment are collected by the deformation or force data detection device and the temperature detection device, and the data are fed back to the computer for storage; after the test is completed, the liquid nitrogen in the static test sealing cavity is discharged to the waste liquid storage tank through the electronic current stabilizer, the test tube is removed, and after the test sample returns to room temperature, it is removed from the test cage to complete the static liquid nitrogen environment cold shock test of the saturated state test sample; then, a dry state test sample is selected from step A and placed in the test cage, and this step is repeated with the same test parameters as the saturated state test sample to complete the static liquid nitrogen environment cold shock test of the dry state test sample; C. Dynamic liquid nitrogen environment test of coal rock mechanical data: select a saturated state test sample from step A and place it in the test cage, and set the liquid nitrogen flow value; open the nitrogen bottle, and control the nitrogen pressure delivered to the liquid nitrogen storage tank through the pressure relief gauge. After the nitrogen enters, it drives the liquid nitrogen in the liquid nitrogen storage tank into one end of the low-temperature resistant pipeline near the bottom, and then the computer controls the first flow control valve to open, so that the liquid nitrogen passes through the mass flow meter in the low-temperature resistant pipeline to reach the electronic flow stabilizer, and adjust the opening of the first flow control valve according to the mass flow meter until the liquid nitrogen flow reaches the set liquid nitrogen flow value; the electronic flow stabilizer stabilizes the liquid nitrogen, and the liquid nitrogen before the stabilization is completed is transported to the waste liquid storage tank for recovery. After the stabilization is completed, the liquid nitrogen is injected into the dynamic test sealing cavity, and the computer controls the second flow control valve to open. After the liquid nitrogen enters, it contacts the side of the test sample in the dynamic test sealing cavity for cold shock, and then the liquid nitrogen is discharged from the outlet and evaporated into nitrogen through the evaporator and discharged into the air. ; Maintain the current dynamic liquid nitrogen environment, and at this time collect the mechanical or deformation data and temperature data of the test sample at different time points in the dynamic liquid nitrogen environment through the deformation or force data detection device and the temperature detection device, and feed them back to the computer for storage; after the test is completed, the liquid nitrogen in the dynamic test sealing cavity is discharged to the waste liquid storage tank through the electronic current stabilizer, the test tube is taken out, and after the test sample returns to room temperature, it is taken out of the test cage to complete the dynamic liquid nitrogen environment cold shock test of the saturated state test sample; then select a dry state test sample from step A and put it into the test cage, and repeat this step with the same test parameters as the saturated state test sample to complete the dynamic liquid nitrogen environment cold shock test of the dry state test sample; select multiple saturated state and dry state test samples from step A and set different liquid nitrogen flow rates, and repeat this step respectively, so as to obtain the mechanical data and temperature data of the saturated state and dry state test samples in the dynamic liquid nitrogen environment with different liquid nitrogen flow rates; D. Data analysis: Analyze and process the static liquid nitrogen environment data and dynamic liquid nitrogen environment data obtained in step B and step C respectively: The force variation curve of the saturated state test specimen under the same environment is obtained as F 饱 (t); and the force variation curve of the dry state test specimen is F 干 (t); then the variation curve of the frost heave force of water ice phase change is F(t)=F 饱 (t)-F 干 (t); Since the frost heave force of water-ice phase change is a variable force, the maximum frost heave force of water-ice phase change F max (t1) taken from At this moment, the deformation of the coal body due to the water-ice phase transition is also the largest, which is L max (t1); Obtain different coal rock porosity in the same environmental test The deformation L of the coal rock mass caused by the water-ice phase transition corresponding to the liquid nitrogen injection rate V max (t1) and the maximum water ice phase change frost heave force F max (t1), and then establish the linear relationship between the three as follows: Through the above formula, the porosity of coal rock mass is realized. The two parameters of liquid nitrogen injection rate V are used to predict the maximum deformation and maximum frost heave force caused by water-ice phase change in the static liquid nitrogen environment of coal rock mass and the dynamic liquid nitrogen environment with different liquid nitrogen flow rates.

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