Device and method for testing three-dimensional heat conductivity coefficient of rock under true three-dimensional stress condition

Abstract

The invention relates to the technical field of rock heat conductivity coefficient testing, in particular to a rock three-dimensional heat conductivity coefficient testing device and method under the true three-dimensional stress condition, and the rock three-dimensional heat conductivity coefficient testing device comprises a testing assembly, a steady-state heat flow generating assembly, an elastic pressure fixing assembly, an environment temperature control assembly and a true three-dimensional stress applying assembly. The steady-state heat flow generation assembly comprises a heat source and a cold source, and the length of the pressure transmission structural member is smaller than or equal to the axial length of the test chamber. The environment temperature control assembly comprises a heat preservation shell, and the elastic pressure assembly is covered with the heat preservation shell. The length of the axial direction formed by the test structural member, the cold source and the heat source is shortened, so that the space structure of the test device is compact, and the accuracy of the heat conductivity coefficient can be ensured. In addition, the axial direction is shortened, and larger pressure can be applied in the axial direction, so that the pressure stabilizing heat flow generation assembly is prevented from being stressed and bent, and the bearable pressure level is higher. And continuous and accurate testing of the heat conduction coefficients in all directions under high-temperature and high-pressure conditions can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of rock thermal conductivity testing, and particularly to a device and method for testing the three-dimensional thermal conductivity of rocks under true triaxial stress conditions. Background Technique

[0002] The thermal conductivity of rocks is an important parameter used to characterize the heat conduction ability of rocks, and it has extensive applications in many fields such as deep geothermal exploitation and utilization, deep engineering construction, nuclear waste storage, and oil and gas development.

[0003] The existing rock thermal conductivity tests generally adopt the Chinese patent "CN114813385B - A device and method for steady-state test of rock thermal anisotropy under true triaxial stress". This patent arranges true triaxial stress application modules, steady-state heat flux generation modules, heat insulation modules, and distributed temperature test pieces on the six end faces of the rock specimen respectively. The two opposite end faces are in direct contact with the heat source and the cold source respectively to provide a stable heat flux for the specimen, and the other faces are heat-insulated during measurement; by measuring the temperature and heat flux when the rock reaches the steady state, the thermal conductivity of the rock in a certain direction is measured, and by switching the heat flux direction, the thermal conductivities in each direction are measured.

[0004] In the process of the existing rock thermal conductivity test, the rock specimen is placed in the test chamber, and stress is applied to the steady-state heat flux generation module by the true triaxial stress application module. At this time, the heat flux meters on both sides of the cold source and the heat source in the steady-state heat flux generation module together act as pressure transmission rods to transfer the pressure to the rock specimen, and the heat source or the cold source is located between the heat flux meter and the true triaxial stress application module. The heat flux is transferred to the radiator through the two heat flux meters and the rock specimen and discharged by the radiator. During the heat flux transfer process, there will be a temperature change in the transfer direction from the heat source to the cold source. Since there is an accuracy error in the sensor itself, the relative error is smaller when the temperature difference between the two sensors is larger. In order to achieve an obvious temperature difference on the temperature sensor, the existing pressure transmission rod for rock thermal conductivity measurement is relatively long, and four temperature sensors are arranged on one side of the heat flux meter, and there are distance requirements between each temperature sensor. Therefore, the axial direction of the pressure transmission rod is a slender rod shape, and at the same time, the overall size of the equipment is too large.

[0005] After deep rock masses are subjected to high temperatures and high stresses, their thermal conductivity changes profoundly and complexly, posing many challenges for accurately studying the thermal environment, rock mass deformation, fracture, etc. of deep rock mass engineering. Therefore, accurately measuring the thermal conductivity of rocks under high-temperature true triaxial stress conditions has very important practical significance. If we want to reproduce the high-temperature environment of rock specimens, we need a heat preservation box that can provide heating and heat preservation functions. Once the test device is too large, resulting in an overly large structure of the heat preservation box, it places very high requirements on the heating and heat preservation capabilities, exponentially increasing the difficulty of restoring the high-temperature environment, driving up the overall cost of the equipment, and for the slender rod-shaped force transmission structure, it is difficult to avoid the buckling effect and difficult to achieve large stress loading on rock specimens. Summary of the Invention

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a test device and test method for the three-dimensional thermal conductivity of rocks under true triaxial stress conditions, which solves the technical problems that the buckling effect of the slender stress transmission structure is obvious, resulting in the inability to apply large stresses; the structure of the heat preservation box is too large, placing very high requirements on the heating and heat preservation capabilities, driving up the cost of the equipment, and it is difficult to achieve a high-temperature environment.

[0007] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] In a first aspect, an embodiment of the present invention provides a test device for the three-dimensional thermal conductivity of rocks under true triaxial stress conditions, including a test component, a steady-state heat flux generation component, an elastic pressure fixation component, an ambient temperature control component, and a true triaxial stress application component;

[0009] The test component includes test structural members located at six end faces of the specimen, and each test structural member is respectively used to monitor the temperature of the end face of the specimen;

[0010] The steady-state heat flux generation component includes three heat sources and three cold sources. Among them, one heat source corresponds to one cold source on the other side along the axial direction of the specimen. The heat source or the cold source is located at the end of the test structural member far from the end face of the specimen, and the heat source or the cold source is fixedly connected to the test structural member to form six test bodies. The six test bodies enclose a test chamber for placing the specimen. In one direction, the heat source and the cold source form a pressure transmission structural member with the test structural member. The total axial length of the pressure transmission structural member is the pressure transmission structure length, and the length of the pressure transmission structural member is less than or equal to the axial length of the test chamber;

[0011] The elastic pressure fixation component covers the outside of the six test bodies and is fixedly connected to each test body;

[0012] The environmental temperature control component includes a heat-insulating housing, and the heat-insulating housing covers the outside of the elastic pressure component;

[0013] The true triaxial stress application component includes six stress application structural members. Each stress application structural member is installed on the outside of the heat-insulating housing, and the driving end of the stress application structural member passes through the heat-insulating housing and is connected to one end face of the elastic pressure fixing component, and applies stress to the specimen through the elastic pressure fixing component, the steady-state heat flux generation component and the test component.

[0014] Optionally, the test structural member includes two temperature test pieces and a reference thermal resistance disposed between the two temperature test pieces, and the reference thermal resistance has a first end face close to the specimen and a second end face far from the specimen;

[0015] The temperature test piece includes a metal sheet of high thermal conductivity material and a temperature sensor disposed in the inner cavity of the metal sheet;

[0016] One end faces of the two metal sheets are respectively fixedly connected to the first end face and the second end face of the reference thermal resistance. The other end face of the metal sheet connected to the first end face is in contact with the specimen, and the metal sheet connected to the second end face is in contact with the cold source or the heat source. The temperature sensor located on the heat source side and far from the specimen is used to measure the temperature T1 of the second end face of the reference thermal resistance. The temperature sensor located on the heat source side and close to the specimen is used to measure the temperature of the first end face of the reference thermal resistance and the heat source temperature of the specimen, both of which are T2. The temperature sensor located on the cold source side and close to the specimen is used to measure the temperature of the first end face of the reference thermal resistance and the cold source temperature of the specimen, both of which are T3. The temperature sensor located on the cold source side and far from the specimen is used to measure the temperature of the second end face of the reference thermal resistance as T4, and T1 - T2 is the temperature difference of the reference thermal resistance on the heat source side, T3 - T4 is the temperature difference of the reference thermal resistance on the cold source side, and T2 - T3 is the temperature difference of the specimen.

[0017] Optionally, the area ratio of the metal sheet, the reference thermal resistance and the test chamber is 1:1:1.

[0018] Optionally, the material of the reference thermal resistance is a high thermal resistance material with stable temperature and pressure, that is, the thermal conductivity of the reference thermal resistance is less than 0.5 W / m*K.

[0019] Optionally, the metal sheet is made of a copper alloy material with a thermal conductivity greater than 300 W / m*K, and the thickness of the metal sheet can accommodate the temperature sensor.

[0020] Optionally, it further includes a heat insulation component, which includes six heat insulation structural members. Three of the heat insulation structural members are respectively installed between three of the heat sources and the metal sheets close to the heat sources, and the other three heat insulation structural members are respectively installed between three of the cold sources and the metal sheets close to the cold sources. And the heat insulation structural members are heated by heaters for heat insulation;

[0021] In the measurement direction, the heat insulation structural member installed on the heat source is integrally formed with the heat source to form a heater, the heat insulation structural member installed on the cold source is not heated, and the heat insulation structural members on the other four end faces are heated.

[0022] Optionally, the heat source uses a heater, a heating resistor is arranged in the heater, the cold source uses a radiator, and a cooling circulation system is provided in the radiator. The heater and the radiator both use shells made of high-strength alloy materials.

[0023] Optionally, the ambient temperature control component further includes a thermoelectric device arranged in the heat insulation shell, and the electric heater is used to heat the chamber where the heat insulation shell is located.

[0024] Optionally, it further includes a control system, which is used to control the temperatures of the heat source and the cold source and the temperature inside the heat insulation shell cavity, and can also collect and record the temperatures measured by the temperature sensors.

[0025] In a second aspect, a method for testing the three-dimensional thermal conductivity of rock under true triaxial stress conditions, the testing method is based on the testing device for the three-dimensional thermal conductivity of rock under true triaxial stress conditions;

[0026] The testing method includes the following steps:

[0027] S1. Process the irregular rock specimens collected on site into cube shapes with matching specifications;

[0028] S2. Turn on the elastic pressure fixing component, apply a layer of thermal grease to the six end faces of the cube rock specimens processed in S1, and place them in the test chamber;

[0029] S3. Close the elastic pressure fixing component, start the true triaxial stress applying component, and provide a small pre-tightening force in three directions of the specimen respectively to make the test component contact with the six end faces of the specimen;

[0030] S4. Turn on the thermoelectric device of the ambient temperature control component to raise the temperature of the inner cavity of the heat insulation shell until it reaches a predetermined temperature and remains stable;

[0031] S5. According to the original in-situ stress conditions of the specimen, use the true triaxial stress applying component to apply stress to the specimen;

[0032] S6. Turn on the heat source and cold source in the measurement direction (taking the X direction as an example), set the temperatures of the heat source and cold source, and form a steady-state heat flux along the measurement direction; and turn on the heaters of the thermal insulation components in the Y direction and Z direction so that the set temperature of the thermal insulation components is the average value of the specimen temperature.

[0033] When the four temperature sensors on the test structural components on the two end faces in the measurement direction reach a stable state, and the temperature sensors on the test structural components on any one of the four end faces in the Y direction and Z direction are equal, it indicates that a one-dimensional steady state has been achieved.

[0034] S7. After the temperature sensors reach temperature stability, by recording the temperatures of the temperature sensors in the X direction, the sensor temperatures from the heat source to the cold source are respectively denoted as T1 - T4, and through the thermal resistance of the reference thermal resistance material and the thickness of the reference thermal resistance, the thermal conductivity of the specimen can be calculated. The specific formula is as follows:

[0035]

[0036] In the formula, R ref represents the thermal resistance of the reference thermal resistance material, T1, T2, T3, and T4 respectively represent the sensor temperatures from the heat source to the cold source, and R contact represents the system thermal resistance.

[0037] S8. After the measurement of the thermal conductivity in the X direction is completed, stop the operation of the heat source and cold source in this direction. Until the temperatures of the opposite temperature sensors are equal, it is regarded as being in a new temperature equilibrium state.

[0038] S9. Keep the pressure unchanged, turn on the heat source and cold source in the next direction (taking the Y direction as an example) to form a stable heat flux in the Y direction, while insulating in the X and Z directions, and measure the thermal conductivity in the Y direction; similarly, the thermal conductivity in the Z direction can be measured.

[0039] S10. According to the engineering disturbance situation, design a true triaxial stress path, adjust the stress unloading path of the specimen, and repeat S6 - S10.

[0040] S11. After the tests of the thermal conductivities of the rock in all directions under different working conditions are completed, unload the triaxial stress, discharge the heat in the cavity of the thermal insulation shell, open the elastic pressure fixing component and take out the specimen, and the test ends.

[0041] The beneficial effects of the present invention are as follows: a three-dimensional thermal conductivity test device and test method for rocks under true triaxial stress conditions of the present invention can make the overall test device space structure compact by shortening the length in the axial direction formed by the test structure, the cold source and the heat source, while also ensuring the accuracy of its thermal conductivity. In addition, the shortening in the axial direction can also apply greater pressure in the axial direction, so that the pressure-stabilized heat flux generation component can avoid the stress-buckling effect, can withstand a higher pressure level, and effectively reduce the size of the equipment. It can achieve continuous and accurate testing of the thermal conductivity in all directions under the conditions of uniform loading of 3000KN pressure in all directions and long-term maintenance from room temperature to 400°C, and the size of the test device is controllable.

[0042] The technical problems that the stress caused by the slender force transmission structure is difficult to load, the insulation box structure is too large, high requirements are put forward for heating and insulation capacity, the equipment cost is increased, and it is difficult to achieve a high temperature environment are solved. It is ensured that the thermal conductivity of the deep rock mass undergoes profound and complex changes after being subjected to high temperature and high stress, which brings many challenges to the accurate study of the thermal environment of deep rock mass engineering, rock mass deformation, fracture, etc. Therefore, the present invention can accurately measure the thermal conductivity of rock under high temperature true triaxial stress conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the overall structure of the rock three-dimensional thermal conductivity testing device under true triaxial stress conditions of the present invention;

[0044] Figure 2 for Figure 1 The hidden part structure in the test body will show the schematic diagram of the structure;

[0045] Figure 3 for Figure 1 A schematic diagram of the structure of the elastic pressure fixing component and its interior;

[0046] Figure 4 for Figure 3 Schematic diagram of the exploded structure of the heat source end portion in the Y direction;

[0047] Figure 5 for Figure 4 Schematic diagram of the decomposed structure of the test structure.

[0048] Description of Reference Numerals

[0049] 1. Test structure; 11. Temperature test piece; 111. Metal sheet; 112. Temperature sensor; 12. Reference thermal resistance; 121. First end face; 122. Second end face; 2. Heat source; 3. Cold source; 4. Test chamber; 5. Metal connecting belt; 6. Elastic pressure plate; 7. Ambient temperature control assembly; 71. Insulation shell; 8. Stress applying structure; 9. Insulation structure; 100. Test specimen. Detailed implementation manners

[0050] For better explaining the present invention for easy understanding, the present invention will be described in detail below in conjunction with the accompanying drawings through specific implementation manners.

[0051] See Figures 1-5 As shown, a three-dimensional thermal conductivity testing device for rock under true triaxial stress conditions proposed in an embodiment of the present invention includes a testing component, a steady-state heat flux generating component, an elastic pressure fixing component, an environmental temperature control component 7, and a true triaxial stress applying component.

[0052] The testing component includes testing structural members 1 located on six end faces of the specimen 100, and each testing structural member 1 is respectively used to monitor the temperature of the end face of the specimen 100.

[0053] The steady-state heat flux generating component includes three heat sources 2 and three cold sources 3. Among them, one heat source 2 corresponds to one cold source 3 on the other side in the axial direction of the specimen 100. The heat source 2 or the cold source 3 is located at one end face of the testing structural member 1 far from the specimen 100, and the heat source 2 or the cold source 3 is fixedly connected to the testing structural member 1 to form six testing bodies. The six testing bodies enclose to form a testing chamber 4 for placing the specimen 100. In one direction, the heat source 2 and the cold source 3 form a pressure transmission structural member with the testing structural member 1. The total axial length of the pressure transmission structural member along the specimen 100 is the pressure transmission structure length, and the length of the pressure transmission structural member is less than or equal to the axial length of the testing chamber 4. The steady-state heat flux generating component also plays a role in transmitting pressure, contacting the true triaxial stress applying component at the rear end and contacting the specimen 100 at the front end.

[0054] In this embodiment, further, the heat source 2 adopts a heater, a heating resistor is arranged in the heater, the cold source 3 adopts a radiator, and a cooling circulation system is arranged in the radiator. The heater and the radiator both adopt a housing made of high-strength alloy material, for example: a housing made of chrome-manganese alloy material. Among them, the heat source and the cold source adopt a layered design. The heater is equipped with a resistance wire, and the radiator is equipped with a coolant circulation system. The heat source and the radiator are respectively installed on both sides of the specimen. Both the heater and the radiator adopt a firm housing design and can withstand the test pressure.

[0055] The elastic pressure fixing component covers the outside of six test bodies and is fixedly connected to each test body. The elastic pressure fixing component includes six elastic pressure plates 6 and twelve highly elastic metal connecting bands 5. At least 12 highly elastic metal connecting bands 5 connect the six elastic pressure plates 6 together to form an elastic pressure box, avoiding stress concentration. The elastic pressure box functions to fix the specimen 100. Inside the elastic pressure box, there are 3 pairs of heat sources and cold sources, and inside the steady-state heat flow generating component, there is a test component. One heat source 2 or cold source 3 and the test structural member form a test body, which has the functions of simultaneously transmitting pressure and generating heat flow, and is in close contact with the six faces of the cubic specimen 100 in the X, Y, and Z directions respectively.

[0056] The ambient temperature control component 7 includes a heat-insulating outer shell 71, and the heat-insulating outer shell 71 covers the outside of the elastic pressure component.

[0057] The true triaxial stress application component includes six stress application structural members 8. Each stress application structural member 8 is installed outside the heat-insulating outer shell 71, and the driving end of the stress application structural member 8 passes through the heat-insulating outer shell 71 and is connected to one end face of the elastic pressure fixing component, and applies stress to the specimen 100 through the elastic pressure fixing component, the steady-state heat flow generating component, and the test component. The stress application structural member 8 is six hydraulic servo actuators, all of which are connected to the control system and can be independently controlled for pressure. In particular, a triaxial six-direction stress loading system is used to apply stress to the cubic specimen 100. The triaxial six-direction stress loading system includes six hydraulic actuators, and the output ends of the 6 hydraulic actuators are respectively docked with the outer ends of one of the docked elastic pressure plates 6.

[0058] Further, the test structural member 1 includes two temperature test members 11 and a reference thermal resistance 12 disposed between the two temperature test members 11. The reference thermal resistance 12 has a first end face 121 close to the specimen 100 and a second end face 122 away from the specimen 100. The temperature test member 11 includes a metal sheet 111 made of a high thermal conductivity material and a temperature sensor 112 disposed in the inner cavity of the metal sheet 111. One end face of the two metal sheets 111 is fixedly connected to the first end face 121 and the second end face 122 of the reference thermal resistance 12 respectively. The other end face of the metal sheet 111 connected to the first end face 121 contacts the specimen 100. The metal sheet 111 connected to the second end face 122 contacts the cold source 3 or the heat source 2. The temperature sensor 112 located on the side of the heat source 2 and away from the specimen 100 is used to measure the temperature T1 of the second end face 122 of the reference thermal resistance 12. The temperature sensor 112 located on the side of the heat source 2 and close to the specimen 100 is used to measure that the temperature of the first end face 121 of the reference thermal resistance 12 and the temperature of the heat source 2 of the specimen 100 are both T2. The temperature sensor 112 located on the side of the cold source 3 and close to the specimen 100 is used to measure that the temperature of the first end face 121 of the reference thermal resistance 12 and the temperature of the cold source 3 of the specimen 100 are both T3. The temperature sensor 112 located on the side of the cold source 3 and away from the specimen 100 is used to measure the temperature T4 of the second end face 122 of the reference thermal resistance 12. And T1 - T2 is the temperature difference of the reference thermal resistance 12 on the side of the heat source 2, T3 - T4 is the temperature difference of the reference thermal resistance 12 on the side of the cold source 3, and T2 - T3 is the temperature difference of the specimen 100.

[0059] Further, the area ratio of the metal sheet 111, the reference thermal resistance 12 and the test chamber 4 is 1:1:1. Specifically, the metal sheet 111 and the reference thermal resistance 12 completely cover the test chamber 4, so as to have a larger contact area with the measured specimen 100, and further make the temperature measured by the temperature sensor 112 on the end face of the specimen 100 more accurate. And further make the measured thermal conductivity more accurate.

[0060] It should also be noted that in this embodiment, the heat source 2 and the cold source 3 in the X direction are completely symmetric with respect to the upper and lower structures of the test chamber 4. When measuring in the X direction, it is ensured that the heat is transferred evenly, thereby improving the measurement accuracy. The same is true for the Y direction and the Z direction.

[0061] Furthermore, the material of the reference thermal resistance 12 is a high-thermal-resistance material with stable temperature and pressure, that is, the thermal conductivity of the reference thermal resistance 12 is less than 0.5 W / m*K. The reference thermal resistance 12 is a high-thermal-resistance material with a known thickness and thermal resistance. Temperature difference test modules are respectively arranged on both sides of the reference thermal resistance 12 material, which is composed of a copper alloy high-thermal-conductivity material and a temperature sensor 112. By measuring the temperature difference and using the known thermal resistance of the reference material, the thermal conductivity of the specimen is calculated. In this embodiment, the reference thermal resistance 12 uses a high-thermal-resistance material to replace the heat transfer component, enabling a large temperature difference to be achieved without a long heat transfer component, reducing the equipment size, avoiding the buckling effect of the heat transfer component, thus greatly reducing the equipment cost and allowing a large stress to be applied.

[0062] Furthermore, the metal sheet 111 is made of a copper alloy material with a thermal conductivity greater than 300 W / m*K, and the thickness of the metal sheet 111 can accommodate the temperature sensor 112. The greater the thermal conductivity of the metal sheet 111, the closer the temperature measured in the internal temperature sensor 112 is to the surface of the metal sheet 111.

[0063] Furthermore, a thermal insulation component is further included. The thermal insulation component includes six thermal insulation structural members 9. Three of the thermal insulation structural members 9 are respectively installed between the three heat sources 2 and the metal sheet 111 close to the heat sources 2, and the other three thermal insulation structural members 9 are respectively installed between the three cold sources 3 and the metal sheet 111 close to the cold sources 3, and the thermal insulation structural members 9 are heated by heaters for thermal insulation. In the measurement direction, the thermal insulation structural member 9 installed on the heat source 2 is integrally formed with the heat source 2 to form a heater, the thermal insulation structural member 9 installed on the cold source 3 is not heated, and the thermal insulation structural members 9 on the other four end faces are heated.

[0064] It should also be noted that one end of the steady-state heat flux generation component in any direction, such as the X direction, is equipped with a heater, and the other end is installed with a radiator and a heater at the same time. When measuring the thermal conductivity of a rock mass in a certain direction, such as the X direction, the heater and radiator in this direction are respectively heated and cooled to form a stable temperature difference, and the heaters in the other directions perform heat compensation. When the temperature sensors 112 on both sides of the reference thermal resistance 12 measure equal temperatures by the temperature sensors 112 in the corresponding direction, it is considered that there is no heat leakage in this direction. When measuring the thermal conductivity in a certain direction, the heat source is turned on to heat one side of the specimen, the radiator is turned on for heat dissipation, and the heater modules in the other directions perform heat compensation to ensure that the lateral heat leakage rate is not higher than 5%. The measurement accuracy of the temperature is further improved, that is, while the axial length of the measurement body is shortened, the heat leakage rates in the other four directions are further ensured through the thermal insulation structural members 9, thereby improving the measurement accuracy.

[0065] Furthermore, the environmental temperature control component 7 also includes a thermoelectric device arranged in the heat-insulating shell 71, and the electric heater is used to heat the chamber where the heat-insulating shell 71 is located. The electric heater is used to heat the sample 100 to provide a high-temperature environment, and the heat-insulating shell 71 is insulated. The elastic pressure fixing component, the test component, the steady-state heat flow generation group and the sample in the heat-insulating shell 71 are further insulated to provide a real-time high-temperature environment. The interior of the heat-insulating shell 71 is first heated by the environmental temperature control component 7 to reach the test temperature of the sample 100, and then the heater and the radiator in the steady-state heat flow are used for heating and cooling to achieve a counter temperature difference.

[0066] Furthermore, it also includes a control system, which is used to control the temperature of the heat source 2 and the cold source 3 and the temperature of the inner cavity of the heat-insulating outer shell 71, and can also collect the temperature measured by the temperature sensor 112 for recording.

[0067] A device and method for testing thermal conductivity of rocks under true triaxial stress conditions of high temperature and high pressure. In this embodiment, the length of the axial direction formed by the test structure 1, the cold source and the heat source is shortened, which can make the overall test device space structure compact and ensure the accuracy of its thermal conductivity. In addition, the shortening of the axial direction can also apply greater pressure in the axial direction, so that the pressure-stabilizing heat flow generating component can avoid the stress-buckling effect, can withstand a higher pressure level, and effectively reduce the size of the equipment. It can achieve uniform loading of 3000KN pressure in each direction, and continuous and accurate testing of the thermal conductivity in all directions under the conditions of long-term maintenance from room temperature to 400℃, and the size of the test device is controllable. It solves the technical problems that the stress caused by the slender force transmission structure is difficult to load, resulting in an overly large structure of the insulation box, high requirements for heating and insulation capacity, and high equipment cost, and it is difficult to achieve a high temperature environment. It ensures that the thermal conductivity of deep rock mass undergoes profound and complex changes after being subjected to high temperature and high stress, which brings many challenges to the accurate study of the deep rock mass engineering thermal environment, rock mass deformation, and fracture. Therefore, the present invention can accurately measure the thermal conductivity of rock under high temperature true triaxial stress conditions.

[0068] Moreover, the full-contact voltage-stabilized heat flux generating component and testing component used in this embodiment are independently designed from the stress application module, so that the stress and heat flux can be coupled and applied evenly in the same spatial direction, avoiding disturbance of the heat flux, so that the sample 100 can completely restore the stress and heat conduction process of deep engineering, the experimental conditions are more in line with actual engineering and the test accuracy is higher.

[0069] The invention discloses a method for testing the three-dimensional thermal conductivity of rocks under true triaxial stress conditions. The testing method is based on a device for testing the three-dimensional thermal conductivity of rocks under true triaxial stress conditions.

[0070] The test method includes the following steps:

[0071] S1. Process the irregular rock specimen 100 collected on-site into a cube shape with a matching specification.

[0072] S2. Turn on the elastic pressure fixing component, apply a layer of thermal conductive silicone grease to the six end faces of the cube rock specimen 100 processed in S1, and place it into the test chamber 4.

[0073] S3. Turn off the elastic pressure fixing component, start the true triaxial stress applying component, and provide a small pre-tightening force in three directions for the specimen 100 respectively, so that the test component contacts the six end faces of the specimen 100.

[0074] S4. Turn on the thermoelectric device of the ambient temperature control component 7, heat up the inner cavity of the heat preservation housing 71 until it reaches the predetermined temperature and remains stable.

[0075] S5. According to the original in-situ stress conditions of the specimen 100, use the true triaxial stress applying component to apply stress to the specimen 100. Specifically, the stress application uses pressure servo to control the magnitude of the stress.

[0076] S6. Turn on the heat source 2 and the cold source 3 in the measurement direction (taking the X direction as an example), set the temperatures of the heat source 2 and the cold source 3 to form a steady-state heat flow along the measurement direction; and turn on the heaters of the heat preservation components in the Y direction and the Z direction so that the set temperature of the heat preservation components is the average value of the temperature of the specimen 100.

[0077] When the four temperature sensors 112 on the test structural parts 1 on the two end faces in the measurement direction reach a stable state, and the temperature sensors 112 on the test structural parts 1 on any one of the four end faces in the Y direction and the Z direction are equal, it indicates that a one-dimensional steady-state state is achieved.

[0078] S7. After the temperature sensors 112 reach temperature stability, by recording the temperatures of the temperature sensors 112 in the X direction, the sensor temperatures from the heat source 2 to the cold source 3 are respectively denoted as T1 - T4, and through referring to the thermal resistance of the reference thermal resistance 12 material and the thickness of the reference thermal resistance 12, the thermal conductivity of the specimen 100 can be calculated. The specific formula 1 is as follows:

[0079]

[0080] In formula 1, R ref represents the thermal resistance of the reference thermal resistance 12 material, T1, T2, T3, and T4 respectively represent the sensor temperatures from the heat source 2 to the cold source 3, and R contact represents the system thermal resistance.

[0081] Furthermore, R contact can be obtained through system correction. From the above formula, the specimen thermal resistance can be linearly expressed. By measuring the thermal resistances of multiple specimens with known thermal resistances, a graph of R rock-T curve to determine R contact value.

[0082] Furthermore, the thermal conductivity of the specimen can be obtained by the following formula (2):

[0083] In formula (2), L rock is the length of the specimen, S rock is the cross-sectional area of the specimen, and λ is the thermal conductivity of the specimen.

[0084] In this embodiment, compared with the prior art solution, the thermal conductivity can be calculated without using a heat flux sensor in this embodiment. Therefore, the usage condition limitations and error accumulation caused by the heat flux sensor are avoided, making the applicable range of the device wider, and the test accuracy theoretically reaching ±2%.

[0085] S8. After the measurement of the thermal conductivity in the X direction is completed, stop the operation of the heat source 2 and the cold source 3 in this direction. Until the temperatures of the relative temperature sensors 112 are equal, it is regarded as being in a new temperature equilibrium state.

[0086] S9. Keep the pressure unchanged, turn on the heat source 2 and the cold source 3 in the next direction (taking the Y direction as an example) to form a stable heat flux in the Y direction. At the same time, perform heat insulation in the X and Z directions, and measure the thermal conductivity in the Y direction; similarly, the thermal conductivity in the Z direction can be measured.

[0087] S10. According to the engineering disturbance situation, design a true triaxial stress path, adjust the stress unloading path of the specimen 100, and repeat S6 - S10.

[0088] S11. After the measurement of the thermal conductivity in all directions of the rock under different working conditions is completed, unload the triaxial stress, discharge the heat in the cavity of the heat insulation housing 71, open the elastic pressure fixing component, and take out the specimen 100, and the test ends.

[0089] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0090] In the present invention, unless otherwise clearly specified or limited, terms such as "installed", "connected", "coupled", "fixed", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium; it may be the communication inside two elements or the interaction relationship between two elements. 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.

[0091] In the present invention, unless otherwise clearly specified or limited, when the first feature is "on" or "under" the second feature, it may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, when the first feature is "above", "over" and "on top of" the second feature, it may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. When the first feature is "under", "beneath" and "underneath" the second feature, it may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the horizontal height of the first feature is lower than that of the second feature.

[0092] In the description of this specification, the descriptions of terms such as "one embodiment", "some embodiments", "embodiment", "example", "specific example" or "some examples", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0093] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A three-dimensional thermal conductivity testing device for rocks under true triaxial stress conditions, characterized in that: It includes a test component, a steady-state heat flux generation component, an elastic pressure fixation component, an environmental temperature control component (7), and a true triaxial stress application component; The test component includes test structural members (1) located at six end faces of a specimen (100), and each of the test structural members (1) is respectively used to monitor the temperature of the end face of the specimen (100); The steady-state heat flux generation component includes three heat sources (2) and three cold sources (3). Among them, one of the heat sources (2) corresponds to one of the cold sources (3) on the other side along the axial direction of the specimen (100). The heat source (2) or the cold source (3) is located at one end of the test structural member (1) away from the specimen (100), and the heat source (2) or the cold source (3) is fixedly connected to the test structural member (1) to form six test bodies. The six test bodies enclose a test chamber (4) for placing the specimen (100). In one direction, the heat source (2) and the cold source (3) form a pressure transmission structural member with the test structural member (1). The total axial length of the pressure transmission structural member along the specimen (100) is the pressure transmission structure length, and the length of the pressure transmission structural member is less than or equal to the axial length of the test chamber (4); The elastic pressure fixation component covers the outside of the six test bodies and is fixedly connected to each of the test bodies; The environmental temperature control component (7) includes a heat preservation outer shell (71), and the heat preservation outer shell (71) covers the outside of the elastic pressure component; The true triaxial stress application component includes six stress application structural members (8). Each of the stress application structural members (8) is installed outside the heat preservation outer shell (71), and the driving end of the stress application structural member (8) passes through the heat preservation outer shell (71) and is connected to one end face of the elastic pressure fixation component, and applies stress to the specimen (100) through the elastic pressure fixation component, the steady-state heat flux generation component, and the test component.

2. The three-dimensional thermal conductivity testing device for rock under true triaxial stress conditions according to claim 1, wherein: The test structural member (1) includes two temperature test pieces (11) and a reference thermal resistance (12) arranged between the two temperature test pieces (11), and the reference thermal resistance (12) has a first end face (121) close to the specimen (100) and a second end face (122) away from the specimen (100); The temperature test piece (11) includes a metal sheet (111) made of a high thermal conductivity material and a temperature sensor (112) arranged in the inner cavity of the metal sheet (111); One end face of each of the two metal sheets (111) is fixedly connected to the first end face (121) and the second end face (122) of the reference thermal resistance (12). The other end face of the metal sheet (111) connected to the first end face (121) is in contact with the specimen (100). The metal sheet (111) connected to the second end face (122) is in contact with the cold source (3) or the heat source (2). A temperature sensor (112) located on the side of the heat source (2) and away from the specimen (100) is used to measure the temperature T1 of the second end face (122) of the reference thermal resistance (12). A temperature sensor (112) located on the side of the heat source (2) and close to the specimen (100) is used to measure the temperature of the first end face (121) of the reference thermal resistance (12) and the temperature of the heat source (2) of the specimen (100), both of which are T2. A temperature sensor (112) located on the side of the cold source (3) and close to the specimen (100) is used to measure the temperature of the first end face (121) of the reference thermal resistance (12) and the temperature of the cold source (3) of the specimen (100), both of which are T3. A temperature sensor (112) located on the side of the cold source (3) and away from the specimen (100) is used to measure the temperature of the second end face (122) of the reference thermal resistance (12) as T4. And T1 - T2 is the temperature difference of the reference thermal resistance (12) on the side of the heat source (2), T3 - T4 is the temperature difference of the reference thermal resistance (12) on the side of the cold source (3), and T2 - T3 is the temperature difference of the specimen (100).

3. The three-dimensional thermal conductivity testing device for rock under true triaxial stress conditions according to claim 2, wherein: The area ratio of the metal sheet (111), the reference thermal resistance (12), and the test chamber (4) is 1:1:

1.

4. The three-dimensional thermal conductivity testing device for rock under true triaxial stress conditions according to claim 3, characterized in that: The material of the reference thermal resistance (12) is a high-thermal-resistance material with stable temperature and pressure, that is, the thermal conductivity of the reference thermal resistance (12) is less than 0.5 W / m·K.

5. The three-dimensional thermal conductivity testing device for rock under true triaxial stress conditions according to claim 3, characterized in that: The metal sheet (111) is made of a copper alloy material with a thermal conductivity greater than 300 W / m·K, and the thickness of the metal sheet (111) can accommodate the temperature sensor (112).

6. The three-dimensional thermal conductivity testing device for rock under true triaxial stress conditions according to claim 3, wherein: It further includes a heat insulation assembly. The heat insulation assembly includes six heat insulation structural members (9). Among them, three heat insulation structural members (9) are respectively installed between the three heat sources (2) and the metal sheet (111) close to the heat source (2), and the other three heat insulation structural members (9) are respectively installed between the three cold sources (3) and the metal sheet (111) close to the cold source (3), and the heat insulation structural members (9) are heated by heaters for heat insulation; In the measurement direction, the heat insulation structural member (9) installed on the heat source (2) is integrally formed with the heat source (2) to form a heater. The heat insulation structural member (9) installed on the cold source (3) is not heated, and the heat insulation structural members (9) on the other four end faces are heated.

7. The three-dimensional thermal conductivity testing device for rock under true triaxial stress conditions according to claim 6, characterized in that: The heat source (2) is a heater, in which a heating resistor is provided. The cold source (3) is a radiator, in which a cooling circulation system is provided. The heater and the radiator both adopt a housing made of high-strength alloy material.

8. The three-dimensional thermal conductivity testing device for rock under true triaxial stress conditions according to claim 2, wherein: The environmental temperature control component (7) further includes a thermoelectric device disposed in the heat-insulating housing (71). The electric heater is used to heat the chamber where the heat-insulating housing (71) is located.

9. The three-dimensional thermal conductivity testing device for rock under true triaxial stress conditions according to claim 8, wherein: It further includes a control system, which is used to control the temperatures of the heat source (2) and the cold source (3) and the temperature inside the cavity of the heat-insulating housing (71), and can also collect and record the temperatures measured by the temperature sensors (112).

10. A method for testing the three-dimensional thermal conductivity of rock under true triaxial stress conditions, characterized in that: The testing method is based on the testing device for the three-dimensional thermal conductivity of rock under true triaxial stress conditions as described in claim 6; The testing method includes the following steps: S1. Process the irregular rock specimen (100) collected on site into a cube shape with a matching specification; S2. Turn on the elastic pressure fixing component, apply a layer of thermal conductive silicone grease to the six end faces of the cube rock specimen (100) processed in S1, and place it in the test chamber (4); S3. Close the elastic pressure fixing component, start the true triaxial stress applying component, and provide a small pre-tightening force in three directions of the specimen (100) respectively, so that the testing component contacts the six end faces of the specimen (100); S4. Turn on the thermoelectric device of the environmental temperature control component (7) to heat the inner cavity of the heat-insulating housing (71) until it reaches a predetermined temperature and remains stable; S5. According to the original in-situ stress conditions of the specimen (100), apply stress to the specimen (100) by using the true triaxial stress applying component; S6. Turn on the heat source (2) and the cold source (3) in the measurement direction (taking the X direction as an example), set the temperatures of the heat source (2) and the cold source (3) to form a steady-state heat flow along the measurement direction; and turn on the heaters of the heat-insulating components in the Y direction and the Z direction so that the set temperature of the heat-insulating components is the average value of the temperature of the specimen (100); When the four temperature sensors (112) on the test structural members (1) on the two end faces in the measurement direction reach a stable state, and the temperature sensors (112) on the test structural members (1) on each of the four end faces in the Y direction and the Z direction are equal, it indicates that a one-dimensional steady-state state is achieved; S7. After the temperature sensors (112) reach temperature stability, by recording the temperatures of the temperature sensors (112) in the X direction, the sensor temperatures from the heat source (2) to the cold source (3) are respectively recorded as T1 - T4, and through the thermal resistance of the reference thermal resistance (12) material and the thickness of the reference thermal resistance (12), the thermal conductivity of the specimen (100) can be calculated. The specific formula is as follows: wherein, R ref represents the thermal resistance of the reference thermal resistance (12) material, T1, T2, T3, and T4 respectively represent the sensor temperatures from the heat source (2) to the cold source (3), and R contact represents the system thermal resistance; S8. After the measurement of the thermal conductivity in the X direction is completed, stop the operation of the heat source (2) and the cold source (3) in that direction until the temperatures of the opposite temperature sensors (112) are equal, and it is regarded as being in a new temperature equilibrium state; S9. Keep the pressure constant, turn on the heat source (2) and the cold source (3) in the next direction (taking the Y direction as an example) to form a stable heat flow in the Y direction, while insulating in the X and Z directions, and measure the thermal conductivity in the Y direction; similarly, the thermal conductivity in the Z direction can be measured. S10. According to the engineering disturbance situation, design a true triaxial stress path, adjust the stress unloading path of the specimen (100), and repeat S6 - S10. S11. After the measurement of the thermal conductivity of the rock in each direction under different working conditions is completed, unload the triaxial stress, discharge the heat in the cavity of the heat insulation shell (71), open the elastic pressure fixing component to take out the specimen (100), and the test ends.

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