Simulation test device for measuring fracture seepage heat transfer characteristics and construction method

Abstract

The invention discloses a simulation test device for measuring fracture seepage heat transfer characteristics and a construction method for measuring the fracture seepage heat transfer characteristics by adopting the simulation test device. According to the simulation test device for fracture seepage heat transfer characteristic measurement and the construction method, the effective value of a convective heat transfer coefficient between hot water and surrounding rock can be effectively obtained, and then ground temperature distribution is effectively predicted in a numerical simulation mode. The simulation test device comprises a seepage simulation system and a fracture sample model, the fracture sample model at least comprises a fault simulation assembly and a surrounding rock simulation assembly, and the surrounding rock simulation assembly covers the outer side of the fault simulation assembly. Constant-temperature seepage needed by the fracture sample model is provided through the seepage simulation system according to specified requirements, and heat transfer characteristics of the constant-temperature seepage are recorded. According to the construction method, parameters of flow conduction heat of seepage water with at least three different flows in a fractured rock mass under at least three different temperature conditions are recorded, and then a convective heat transfer coefficient value is obtained through extension and deduction.

Description

Technical Field

[0001] The present invention relates to a simulation test device, in particular to a simulation test device for measuring fracture seepage heat transfer characteristics, belonging to the field of geological exploration test process equipment design and manufacturing technology. The present invention also relates to a construction method for measuring fracture seepage heat transfer characteristics using the simulation test device for measuring fracture seepage heat transfer characteristics. Background Art

[0002] Faults control the migration of most groundwater and are also the main channels for deep hot water to migrate to the shallow surface. Since the temperature of hot water in the channel is higher than the temperature of the shallow surrounding rock, the hot water transfers a large amount of heat to the surrounding rock, causing the surrounding rock temperature to rise sharply. It is currently believed that in addition to the heat generated by geothermal flow and radioactive elements, the seepage heat flow during the hot water overflow process is also an important way to cause the surrounding rock temperature to rise. When tunnel construction frequently passes through hydrothermal activity areas and disturbs geothermal systems, the heat damage caused by high rock temperature will also become one of the problems that need to be solved in engineering tunnel construction.

[0003] In the preliminary investigation of tunnel construction, in order to find out the characteristics of thermal damage in the tunnel site, the layout of geological boreholes is a relatively more effective and direct method. This method analyzes the geothermal data of multiple boreholes to judge the geothermal characteristics of the tunnel site, so as to roughly determine the scope of influence of thermal damage. However, drilling not only consumes a lot of manpower and material resources, but is also greatly affected by terrain factors and takes a lot of time. In contrast, it is faster and more time-saving to judge the characteristics of thermal damage by numerical simulation of the heat transfer between the main water-controlling and heat-controlling fractures and the surrounding rock of the hot water seepage heat transfer in the tunnel site. However, the prediction results obtained in general numerical simulations are often unsatisfactory. Summary of the invention

[0004] The technical problem to be solved by the present invention is: to provide a simulation test device for measuring the heat transfer characteristics of fracture seepage, which can effectively obtain the effective value of the convective heat transfer coefficient between hot water and surrounding rock, and then effectively predict the geothermal distribution through numerical simulation, and a construction method for measuring the heat transfer characteristics of fracture seepage using the simulation test device for measuring the heat transfer characteristics of fracture seepage.

[0005] The technical solution adopted to solve the above technical problems is: a simulation test device for measuring fracture seepage heat transfer characteristics, the simulation test device includes a seepage simulation system and a fracture sample model, the fracture sample model at least includes a fault simulation component and a surrounding rock simulation component, the surrounding rock simulation component is coated on the outside of the fault simulation component, the constant temperature seepage required by the fracture sample model is provided by the seepage simulation system according to the specified requirements and its heat transfer characteristics are recorded.

[0006] Furthermore, the fracture specimen model also includes a model shell and a rubber sleeve structure. The fault simulation component and the surrounding rock simulation component are filled in the rubber sleeve structure according to the specified pressure and position. The rubber sleeve structure is surrounded by the model shell to form a rectangular block with a length, width and height of 50cm×40cm×50cm respectively. The seepage simulation system is connected with the fault simulation component through the model shell with the cooperation of the rubber sleeve structure.

[0007] A preferred embodiment of the above scheme is that a model shell composed of hard resin is inlaid with nylon material at the position connected to the hot water input end of the seepage simulation system; the fault simulation component includes a fracture zone and a fault core sandwiched in the fracture zone, the fault core is a fault rock filling body including fault mud, mylonite and crushed rock, the fracture zone is a peripheral fault subordinate structure including secondary faults, fissures and fault fold development zones, the fault rock filling body has a thickness of 5 cm, a width of 15 cm and a height of 50 cm, and the surrounding rock simulation component is coated on the outside of the fracture zone.

[0008] Furthermore, the seepage simulation system at least includes a constant temperature hot water storage mechanism, a seepage flow state simulation mechanism and a monitoring and control component. The liquid in the constant temperature hot water storage mechanism runs according to the set seepage flow state in the fault simulation component and the surrounding rock simulation component through the seepage flow state simulation mechanism with the cooperation of the monitoring and control component; the heat transfer characteristics of the seepage liquid running in the fault simulation component are obtained through the monitoring and control component.

[0009] The preferred embodiment of the above scheme is that the constant temperature hot water storage mechanism is composed of a constant temperature hot water tank, the seepage flow simulation mechanism is composed of a variable frequency constant pressure jet pump, the monitoring and control component includes at least a water temperature monitoring component group, a fracture specimen model temperature monitoring component group and a control module, the two ends of the variable frequency constant pressure jet pump are respectively connected to the constant temperature hot water tank and the rubber sleeve structure through PVC pipes, the fracture specimen model temperature monitoring component group is arranged in the surrounding rock simulation component, the water temperature monitoring component group is connected in series to the PVC pipe at the output end of the variable frequency constant pressure jet pump, and at least the control end of the water temperature monitoring component group is connected to the control module.

[0010] Furthermore, the seepage simulation system also includes a tailwater collection component, which includes a tailwater container, a stopwatch and a water pressure gauge, a water temperature monitoring component group includes at least two groups of water temperature sensors, and a fracture specimen model temperature monitoring component group includes a paperless recorder and at least three groups of platinum electrodes. The stopwatch is arranged on the tailwater container, and the tailwater container is connected to the rubber sleeve structure of the fracture specimen model through a PVC pipe. A water pressure gauge and at least one group of water temperature sensors are respectively arranged on the PVC pipe between the tailwater container and the rubber sleeve structure, and at least one group of water temperature sensors is arranged on the PVC pipe between the output end of the variable frequency constant pressure jet pump and the rubber sleeve structure. Each group of platinum electrodes inserted in the surrounding rock simulation component at an interval is respectively connected to the paperless recorder, and at least the control end of the water temperature sensor, the stopwatch and the water pressure gauge is connected to the control module.

[0011] A construction method for measuring fracture seepage heat transfer characteristics by using the simulation test device for measuring fracture seepage heat transfer characteristics, wherein the construction method first connects a constant temperature hot water tank, a variable frequency constant pressure jet pump, a fracture sample model and a tail water collection assembly in sequence, and arranges a water temperature sensor and a water pressure gauge on the PVC pipes at both ends of the fracture sample model, arranges a stopwatch on the tail water container, arranges each group of platinum electrodes on the fracture sample model, and then starts the variable frequency constant pressure jet pump to input seepage water of a specified temperature, a specified flow rate and a specified flow state into the fracture sample model, and records corresponding data when the temperature change of the surrounding rock tends to be stable, and finally performs extended deduction based on the recorded corresponding data to obtain a convective heat transfer coefficient value close to the actual hot water seepage condition,

[0012] Among them, when the seepage water of the specified temperature, specified flow rate and specified flow state is input into the fracture specimen model, at least three seepage waters of different flow rates under three different temperature conditions are included. Each input is completed after the last seepage water input is completed and the corresponding data is recorded. After the surrounding rock temperature drops to normal temperature, the next seepage water input and recording step is performed.

[0013] The corresponding data recorded include at least the inlet hot water temperature Ta and the outlet hot water temperature Tb, the temperature Tg of the solid side of the heat exchange surface and the temperature Tl of the fluid on the heat exchange surface.

[0014] Furthermore, the temperatures of the hot water sequentially input into the fracture specimen model include four temperatures of 30°C, 40°C, 50°C and 60°C, and the flow rates of the hot water sequentially input include four flow rates of 170ml / min, 340ml / min, 500ml / min and 600ml / min. The specific simulation input process is as follows:

[0015] First, the hot water flow rate in the fracture is controlled at a flow rate of 170 ml / min and kept constant. Then, the hot water inlet temperature is adjusted to 30°C, 40°C, 50°C and 60°C in turn, and input into the fracture specimen model respectively. The data of each temperature under the flow condition is recorded. After the surrounding rock temperature change tends to be stable, the hot water flow rate is changed to a constant flow rate of 340 ml / min, 500 ml / min and 600 ml / min in turn, and input into the fracture specimen model under four temperature conditions of 30°C, 40°C, 50°C and 60°C, and the data of each flow rate and each temperature condition are recorded respectively. This process is repeated to obtain a total of 16 sets of data on the relationship between the various data of hot water in the fault simulation component under four flow rates and four temperature conditions and the changing relationship between the hot water inlet temperature and the hot water test. The simulation test is completed.

[0016] The preferred embodiment of the above scheme is that the seepage water of the specified flow state is input into the fracture sample model by a variable frequency constant pressure jet pump, and at least the seepage water of the laminar flow state is inputted. The seepage water of the laminar flow state is realized by controlling the flow rate q of the hot water, and the Reynolds number Re in the dimensionless number is used to determine the flow state of the water flow. When Re<2300, it is laminar flow, wherein the water flow velocity U is expressed by formula (1), and the Reynolds number Re is expressed by formula (2),

[0017]

[0018] Where: U is the water flow velocity, m / s; q is the hot water flow, m 3 / s; V is the kinematic viscosity of water, m 2 / s; X is the length of the crack, m; Y is the width of the crack, m.

[0019] Furthermore,

[0020] According to the recorded corresponding data, the convective heat transfer system value of rock fracture seepage is calculated according to the following steps:

[0021] The convective heat transfer coefficient is calculated using Newton's law of cooling,

[0022] Q=S×r×|T g -T l | (3),

[0023] (3) Where S is the contact surface area, m 2 ; r is the convective heat transfer coefficient, W / (m 2 ℃); T g is the temperature of the solid side of the heat exchange surface, °C; T l is the temperature of the fluid on the heat exchange surface, °C;

[0024] Because the convective heat transfer Q can be calculated by the inlet and outlet temperature difference of hot water, the total convective heat transfer and the inlet and outlet temperatures of hot water satisfy the formula,

[0025] Q=c w ×m w ×(T a -T b ) (4),

[0026] (4) In the formula, c w is the specific heat capacity of the convective heat transfer fluid, kJ / (kg·℃); m w is the mass flow rate of the convective heat transfer fluid, kg / s; T a is the fluid inlet temperature, °C; T b is the fluid outlet temperature, °C;

[0027] Combining formula (1) and formula (2), we get the expression of convective heat transfer coefficient:

[0028]

[0029] In formula (5): q w is the hot water flow rate, m 3 / s;ρ w is the fluid density, kg / m 3 .

[0030] The beneficial effect of the present invention is as follows: the technical solution provided by the present application is to set up a set of simulation test devices including a seepage simulation system and a fracture sample model, and set the fracture sample model to a structure including at least a fault simulation component and a surrounding rock simulation component, and then cover the surrounding rock simulation component on the outside of the fault simulation component, and then in the simulation test, the constant temperature seepage required by the fracture sample model is provided by the seepage simulation system according to the specified requirements and its heat transfer characteristics are recorded, and finally, based on the corresponding recorded data, an extended deduction is performed to obtain a convective heat transfer coefficient value close to the actual hot water seepage condition. The technical problems in the prior art that a large amount of manpower and material resources are required to drill multiple holes for geothermal data analysis and the prediction effect is not as good as that of personnel are solved. At the same time, the simulation test configuration of the present application can effectively obtain the effective value of the convective heat transfer coefficient between hot water and surrounding rock, and then effectively predict the geothermal distribution through numerical simulation, so as to reduce the probability of engineering construction encountering heat damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a simplified structural schematic diagram of a simulation test device for measuring fracture seepage heat transfer characteristics of the present invention;

[0032] Figure 2 A schematic diagram of the three-dimensional structure of a fracture sample model involved in a simulation test device for measuring fracture seepage heat transfer characteristics of the present invention;

[0033] Figure 3 It is a schematic diagram of the fault simulation components involved in the simulation test device for measuring the fracture seepage heat transfer characteristics of the present invention.

[0034] Marked in the figure are: surrounding rock simulation component 1, model shell 2, rubber sleeve structure 3, fracture zone 4, fault core 5, constant temperature hot water tank 6, variable frequency constant pressure jet pump 7, PVC pipe 8, tailwater container 9, stopwatch 10, water pressure gauge 11, water temperature sensor 12, paperless recorder 13, platinum electrode group 14, fault simulation component 15. DETAILED DESCRIPTION

[0035] like Figure 1 , Figure 2 as well as Figure 3The present invention shows a simulation test device for measuring fracture seepage heat transfer characteristics, which can effectively obtain the effective value of the convective heat transfer coefficient between hot water and surrounding rock, and then effectively predict the geothermal distribution through numerical simulation, and a construction method for measuring fracture seepage heat transfer characteristics using the simulation test device for measuring fracture seepage heat transfer characteristics. The simulation test device includes a seepage simulation system and a fracture sample model, the fracture sample model at least includes a fault simulation component 15 and a surrounding rock simulation component 1, the surrounding rock simulation component 1 is coated on the outside of the fault simulation component 15, and the constant temperature seepage required by the fracture sample model is provided by the seepage simulation system according to the specified requirements and its heat transfer characteristics are recorded. The technical solution provided by the present application is to set up a set of simulation test devices including a seepage simulation system and a fracture sample model, and set the fracture sample model to a structure including at least a fault simulation component 15 and a surrounding rock simulation component, and then cover the surrounding rock simulation component on the outside of the fault simulation component 15, and then in the simulation test, the constant temperature seepage required by the fracture sample model is provided by the seepage simulation system according to the specified requirements and its heat transfer characteristics are recorded, and finally, based on the recorded corresponding data, an extended deduction is performed to obtain a convective heat transfer coefficient value close to the actual hot water seepage condition. The technical problems in the prior art that a large amount of manpower and material resources are required to drill multiple holes for geothermal data analysis and the prediction effect is not as good as that of personnel are solved. At the same time, the simulation test configuration of the present application can effectively obtain the effective value of the convective heat transfer coefficient between hot water and surrounding rock, and then effectively predict the geothermal distribution through numerical simulation, so as to reduce the probability of engineering construction encountering heat damage.

[0036] Accordingly, in order to improve the authenticity of the simulation of the fault simulation component 15 and the surrounding rock simulation component 1, the fracture specimen model of the present application also includes a model shell 2 and a rubber sleeve structure 3. The fault simulation component 15 and the surrounding rock simulation component 1 are filled in the rubber sleeve structure 3 according to the specified pressure and position. The rubber sleeve structure 3 is surrounded by the model shell 2 to form a rectangular parallelepiped with a length, width and height of 50cm×40cm×50cm respectively. The seepage simulation system is connected to the fault simulation component 15 through the model shell in cooperation with the rubber sleeve structure. At this time, the fault simulation component 15 preferably includes a fracture zone 4 and a fault core 5 sandwiched in the fracture zone 4. Further, the fault core 5 is set as a fault rock filling body including fault mud, mylonite and crushed powder rock. The fracture zone 4 is set as a peripheral fault subordinate structure including secondary faults, fractures and fault fold development zones, and the fault rock filling body is set as a regular cubic structure with a thickness of 5cm, a width of 15cm and a height of 50cm. The surrounding rock simulation component 1 is coated on the outside of the fracture zone 4. At least the model shell 2 is printed by 3D modeling.

[0037] Furthermore, in order to improve the seepage state of the seepage hot water, the model shell composed of hard resin in the present application is inlaid with nylon material at the position connected to the hot water input end of the seepage simulation system; the seepage simulation system of the present application at least includes a constant temperature hot water storage mechanism, a seepage flow state simulation mechanism and a monitoring and control component, and the liquid in the constant temperature hot water storage mechanism runs according to the set seepage flow state in the fault simulation component 15 and the surrounding rock simulation component 1 through the seepage flow state simulation mechanism with the cooperation of the monitoring and control component; the heat transfer characteristics of the seepage liquid running in the fault simulation component 15 are obtained through the monitoring and control component. A more specific structure is that the constant temperature hot water storage mechanism is composed of a constant temperature hot water tank 6, the seepage flow simulation mechanism is composed of a variable frequency constant pressure jet pump 7, the monitoring and control component at least includes a water temperature monitoring component group, a fracture specimen model temperature monitoring component group and a control module, the two ends of the variable frequency constant pressure jet pump 7 are respectively connected to the constant temperature hot water tank 6 and the rubber sleeve structure 3 through a PVC pipe 8, the fracture specimen model temperature monitoring component group is arranged in the surrounding rock simulation component 1, the water temperature monitoring component group is serially connected to the PVC pipe 8 at the output end of the variable frequency constant pressure jet pump, and at least the control end of the water temperature monitoring component group is connected to the control module. At the same time, the seepage simulation system of the present application also includes a tailwater collection component, which includes a tailwater container 9, a stopwatch 10 and a water pressure gauge 11, a water temperature monitoring component group includes at least two groups of water temperature sensors 12, and a fracture sample model temperature monitoring component group includes a paperless recorder 13 and at least three groups of platinum electrodes 14. The stopwatch 10 is arranged on the tailwater container 9, and the tailwater container 9 is connected to the rubber sleeve structure 3 of the fracture sample model through a PVC pipe 8. The PVC pipe 8 between the tailwater container 9 and the rubber sleeve structure 3 is respectively arranged with a water pressure gauge 11 and at least one group of water temperature sensors 12, and at least one group of water temperature sensors 12 is arranged on the PVC pipe 8 between the output end of the variable frequency constant pressure jet pump and the rubber sleeve structure 3. The groups of platinum electrodes 14 that are spaced apart and inserted in the surrounding rock simulation component 1 are respectively connected to the paperless recorder 13, and at least the control ends of the water temperature sensor 12, the stopwatch 10 and the water pressure gauge 11 are connected to the control module.

[0038] Thus, the fracture seepage heat transfer characteristics can be measured by using the simulation test device of the present application according to the following steps:

[0039] First, the constant temperature hot water tank, variable frequency constant pressure jet pump, fracture sample model and tail water collection assembly are connected in sequence, and water temperature sensors and water pressure gauges are arranged on the PVC pipes at both ends of the fracture sample model, a stopwatch is arranged on the tail water container, and each group of platinum electrodes is arranged on the fracture sample model. Then, the variable frequency constant pressure jet pump is started to input seepage water of specified temperature, specified flow rate and specified flow state into the fracture sample model, and the corresponding data are recorded when the temperature change of the surrounding rock tends to be stable. Finally, based on the recorded corresponding data, an extended deduction is carried out to obtain the convective heat transfer coefficient value close to the actual hot water seepage condition.

[0040] Among them, when the seepage water of the specified temperature, specified flow rate and specified flow state is input into the fracture specimen model, at least three seepage waters of different flow rates under three different temperature conditions are included. Each input is completed after the last seepage water input is completed and the corresponding data is recorded. After the surrounding rock temperature drops to normal temperature, the next seepage water input and recording step is performed.

[0041] The corresponding data recorded include at least the inlet hot water temperature Ta and the outlet hot water temperature Tb, the temperature Tg of the solid side of the heat exchange surface and the temperature Tl of the fluid on the heat exchange surface.

[0042] According to the test requirements, in order to obtain the closest relevant parameters, the number of tests must be guaranteed. The parameters of one time are obviously too random, and too many times may significantly increase the test cost. For this reason, the temperature of the hot water sequentially input into the fracture specimen model of the present application includes four temperatures of 30°C, 40°C, 50°C and 60°C, and the flow rate of the hot water sequentially input includes four flow rates of 170ml / min, 340ml / min, 500ml / min and 600ml / min. The specific simulation input process is as follows: first, the hot water flow rate in the fracture is controlled at a flow rate of 170ml / min and kept constant, and then the hot water inlet temperature is adjusted in sequence to be divided into 3 Four temperatures of 0℃, 40℃, 50℃ and 60℃ were respectively input into the fracture specimen model, and the data of each temperature under the flow condition were recorded. After the temperature change of the surrounding rock tended to be stable, the hot water flow rate was changed to a constant temperature of 340ml / min, 500ml / min and 600ml / min in turn, and the hot water flow rate was input into the fracture specimen model under four temperature conditions of 30℃, 40℃, 50℃ and 60℃, and the data of various flow rates and temperature conditions were recorded respectively. This was repeated to obtain a total of 16 sets of data on the relationship between the various data of hot water in the fault simulation component under four flow rates and four temperature conditions and the changing relationship with the hot water inlet temperature, and the simulation test was completed. At the same time, in order to obtain a laminar flow state that meets the requirements, the present application uses a variable frequency constant pressure jet pump to input seepage water of a specified flow state into the fracture sample model, including at least seepage water of a laminar flow state. The seepage water of a laminar flow state is achieved by controlling the flow rate q of hot water, and the Reynolds number Re in the dimensionless number is used to determine the flow state of the water flow. When Re<2300, it is laminar flow, where the water flow velocity U is expressed by formula (1), and the Reynolds number Re is expressed by formula (2).

[0043]

[0044] Where: U is the water flow velocity, m / s; q is the hot water flow, m 3 / s; V is the kinematic viscosity of water, m 2 / s; X is the length of the crack, m; Y is the width of the crack, m.

[0045] Accordingly, according to the recorded corresponding data, the convective heat transfer system value of rock fracture seepage is calculated according to the following steps:

[0046] The convective heat transfer coefficient is calculated using Newton's law of cooling,

[0047] Q=S×r×|T g -T l | (3),

[0048] (3) Where S is the contact surface area, m 2 ; r is the convective heat transfer coefficient, W / (m 2 ℃); T g is the temperature of the solid side of the heat exchange surface, °C; T l is the temperature of the fluid on the heat exchange surface, °C;

[0049] Because the convective heat transfer Q can be calculated by the inlet and outlet temperature difference of hot water, the total convective heat transfer and the inlet and outlet temperatures of hot water satisfy the formula,

[0050] Q=c w ×m w ×(T a -T b ) (4),

[0051] (4) In the formula, c w is the specific heat capacity of the convective heat transfer fluid, kJ / (kg·℃); m w is the mass flow rate of the convective heat transfer fluid, kg / s; T a is the fluid inlet temperature, °C; T b is the fluid outlet temperature, °C;

[0052] Combining formula (1) and formula (2), we get the expression of convective heat transfer coefficient:

[0053]

[0054] In formula (5): q w is the hot water flow rate, m 3 / s;ρ w is the fluid density, kg / m 3 .

[0055] In summary, the technical solution provided by this application also has the following advantages:

[0056] 1. The present invention provides a fracture seepage heat transfer characteristic test model, which includes a water supply system, a water flow system and a tail water collection system.

[0057] 2. The present invention provides a fracture seepage heat transfer characteristic test model, including a 3D printing mold for constructing a fracture surrounding rock system that simulates the actual fracture.

[0058] 3. The present invention provides a fracture seepage heat transfer characteristic test model, including a fault zone simulation method, wherein the fault core is mainly a fault rock filling part such as fault mud, mylonite, crushed powder rock, etc., and the permeability is relatively low; the fracture zone refers to the fault subordinate structure outside the fault core, such as secondary faults, fissures, and fault fold development zones, and the permeability is relatively high. Based on the above-mentioned fault zonation, different particle size fillers are used for layered filling during filling to simulate the spatial heterogeneity of the fault permeability coefficient.

[0059] 4. The present invention provides a fracture seepage heat transfer characteristic test model, the convective heat transfer coefficient of which can be extended and deduced based on the law of the convective heat transfer coefficient, hot water temperature and flow rate obtained through the experiment, so as to obtain a convective heat transfer coefficient value close to the actual hot water seepage conditions.

[0060] The technical solution of the present application is further described below through specific embodiments:

[0061] Embodiment 1

[0062] Technical solutions to technical problems:

[0063] A fracture seepage heat transfer characteristic test and simulation method: The experimental system is mainly composed of three parts. The first part is the water supply system, including: a constant temperature hot water device and a high-pressure water injection pump. The second part is the water flow system, including: a temperature measurement part 203, a fracture sample model, a temperature sensor, and a tail water pressure measurement part. The third part is the tail water collection system, including a tail water container and a stopwatch, which is used to detect the hot water flow in the simulated fracture and provide a reference for flow regulation. PVC pipes are used to connect the first, second and third parts.

[0064] The constant temperature hot water device in the first part is used to maintain the temperature of the hot water used in the test process to be constant at a fixed value; the high-pressure water injection pump is used to apply different pressures to the hot water in the hot water device to ensure that the hot water can enter the test at different pressures. The high-pressure water injection pump uses a variable frequency constant pressure jet pump as a device for providing the test hot water head, reducing the test data fluctuation caused by the unstable tap water pressure during the test. Through the combination of the constant pressure pump and the valve, the test conditions of keeping the hot water head constant and the flow stable during the test are achieved.

[0065] The temperature measurement part of the water flow system in the second part uses a temperature automatic recording device composed of a paperless recorder and RTD (platinum resistance) to measure the surrounding rock temperature. The water thermometer is used to measure the hot water temperature at both ends of the sample inlet and outlet. The fracture sample model includes a mold shell boundary part, a fault part, a rubber sleeve part, and a surrounding rock part. The mold shell boundary part includes a 3D printed mold, which is used to construct a simulated actual fracture surrounding rock system; the fault zone consists of two parts: the fault core and the fracture zone. The fault core part is mainly a fault rock filling part such as fault mud, mylonite, and crushed powder rock, and the permeability is relatively low; the fracture zone refers to the fault subordinate structure outside the fault core, such as secondary faults, fractures, and fault fold development zones, and the permeability is relatively high. Based on the above-mentioned fault zonation, different particle size fillers are used for layered filling during filling to simulate the spatial inhomogeneity of the fault permeability coefficient. A reserved hole for temperature measuring thermocouples is reserved inside the fault for loading temperature sensors, which are inserted into the sample to measure and monitor the temperature of the surrounding rock sample simulating the fracture. The rubber sleeve part is used to wrap the fault part to prevent the temperature inside the fault part from diffusing. The casting materials used in the surrounding rock part are appropriately proportioned to be close to the thermal conductivity of the actual surrounding rock in the working area. The tailwater water pressure measurement part is used to measure the water pressure at the outlet of the measurement sample.

[0066] The 3D printed mold used in the experiment was first made into a 3D stereoscopic model of the mold through 3D modeling. Among them, the mold mainly consists of three parts: the mold shell part; the fracture filling part; and the reserved hole part for the thermocouple. Except for the hot water inlet at the bottom of the mold shell, which is made of nylon material that is more resistant to high temperature and has higher hardness, the rest is hard resin. The overall length, width and height of the mold are a rectangular parallelepiped of 50cm×40cm×50cm, respectively. The size of the hot water flow fracture in the middle is a rectangle of 5cm×15cm, and the size of the reserved thermocouple placement hole in the mold shell is a circular hole with a diameter of 5mm. In order to reduce the influence of the reserved temperature measuring holes on the heat transfer results, the number of reserved temperature measuring holes should not be too many. According to symmetry, the temperature measurement result at a can be symmetrical to b, and the surrounding rock temperature of a certain section on one side of the fracture can be measured. The average of the temperatures obtained by the three channels of the thermometer on the a side is taken as the temperature on the solid side of the heat exchange surface, and the average of the temperatures obtained by the three channels of the thermometer on the b side is taken as the temperature on the solid side of the heat exchange surface.

[0067] The water supply system, water flow system and tailwater collection system of the test system are connected, and PVC pipes are used in the middle to ensure that there is no leakage between the devices, to check the accuracy of the inlet and outlet temperature meters and the surrounding rock data acquisition system, as well as the ability of the test system to work continuously. The first, second and third parts are connected with each other.

[0068] In order to ensure that the hot water seepage in the crack is in a laminar state, the flow rate q of the hot water needs to be controlled. For the fracture seepage in non-circular pipes, the Reynolds number (Re) in the dimensionless number is usually used to determine the flow state of the water flow. When Re < 2300, it is laminar flow, where the water flow velocity U can be expressed by formula (1), so the Reynolds number (Re) can be described as formula (2):

[0069]

[0070] Where: U is the water flow velocity, m / s; q is the hot water flow, m 3 / s; V is the kinematic viscosity of water, m 2 / s; X is the length of the crack, m; Y is the width of the crack, m.

[0071] Control the hot water temperature at the inlet to be stable, adjust different hot water flow rates in turn, and record various data at each flow rate at this temperature, including the inlet and outlet hot water temperatures (Ta and Tb), the temperatures of the solid side of the heat exchange surface and the fluid on the heat exchange surface (Tg and Tl). When the surrounding rock temperature changes tend to be stable, end the recording, wait for the surrounding rock temperature to drop to normal temperature, set the inlet hot water to other temperatures, and record various data under the above flow conditions again. Repeat this step 3 times to obtain the relationship between the data and the flow rate under 4 constant temperature conditions, a total of 16 sets of data.

[0072] The hot water flow rate in the fracture was controlled to be constant at 170 ml / min, and the hot water inlet temperature was adjusted to 30, 40, 50, and 60 °C in turn. The data of each temperature under this flow rate condition were recorded. When the temperature change of the surrounding rock tended to be stable, the hot water flow rate was changed to 340 ml / min, 500 ml / min, and 600 ml / min in turn, and the data of each temperature were recorded again. This process was repeated to obtain the relationship between the data under 4 constant flow conditions and the hot water inlet temperature, for a total of 16 sets of data.

[0073] The convective heat transfer coefficient is calculated using Newton's law of cooling,

[0074] Q=S×r×|T g -T l | (3),

[0075] (3) Where S is the contact surface area, m 2 ; r is the convective heat transfer coefficient, W / (m 2 ℃); T g is the temperature of the solid side of the heat exchange surface, °C; T l is the temperature of the fluid on the heat exchange surface, °C;

[0076] Because the convective heat transfer Q can be calculated by the inlet and outlet temperature difference of hot water, the total convective heat transfer and the inlet and outlet temperatures of hot water satisfy the formula,

[0077] Q=c w ×m w ×(T a -T b ) (4),

[0078] (4) In the formula, c w is the specific heat capacity of the convective heat transfer fluid, kJ / (kg·℃); m w is the mass flow rate of the convective heat transfer fluid, kg / s; T a is the fluid inlet temperature, °C; T b is the fluid outlet temperature, °C;

[0079] Combining formula (1) and formula (2), we get the expression of convective heat transfer coefficient:

[0080]

[0081] In formula (5): q w is the hot water flow rate, m 3 / s;ρ w is the fluid density, kg / m 3 .

[0082] When the thermal conductivity of the surrounding rock, the permeability of the fracture and the hot water flow pattern in the test are close to the actual situation, the convective heat transfer coefficient, hot water temperature and flow rate obtained in the test can be extended and deduced on this basis to obtain a convective heat transfer coefficient value close to the actual hot water seepage conditions. Then, through numerical simulation, the purpose of effectively predicting the ground temperature distribution can be achieved.

Claims

1. A simulation test device for measuring fracture seepage heat transfer characteristics, characterized in that: The simulation test device comprises a seepage simulation system and a fracture sample model, wherein the fracture sample model comprises at least a fault simulation component (15) and a surrounding rock simulation component (1), wherein the surrounding rock simulation component (1) is coated on the outside of the fault simulation component (15), and the constant temperature seepage required by the fracture sample model is provided by the seepage simulation system according to specified requirements and its heat transfer characteristics are recorded.

2. The simulation test device for measuring fracture seepage heat transfer characteristics according to claim 1, characterized in that: The fracture specimen model also includes a model shell (2) and a rubber sleeve structure (3). The fault simulation component (15) and the surrounding rock simulation component (1) are filled in the rubber sleeve structure (3) according to the specified pressure and position. The rubber sleeve structure (3) is surrounded by the model shell (2) to form a rectangular parallelepiped with a length, width and height of 50 cm×40 cm×50 cm respectively. The seepage simulation system is connected to the fault simulation component (15) through the model shell (2) with the cooperation of the rubber sleeve structure (3).

3. The simulation test device for measuring fracture seepage heat transfer characteristics according to claim 2, characterized in that: The model shell (2) made of hard resin is inlaid with nylon material at the position connected to the hot water input end of the seepage simulation system; the fault simulation component (15) includes a fracture zone (4) and a fault core (5) sandwiched in the fracture zone (4), the fault core (5) is a fault rock filling body including fault mud, mylonite and crushed powder rock, the fracture zone (4) is an outer fault subordinate structure including secondary faults, fissures and fault fold development zones, the fault rock filling body has a thickness of 5 cm, a width of 15 cm and a height of 50 cm, and the surrounding rock simulation component (1) is coated on the outside of the fracture zone (4).

4. The simulation test device for measuring fracture seepage heat transfer characteristics according to claim 1, 2 or 3, characterized in that: The seepage simulation system comprises at least a constant temperature hot water storage mechanism, a seepage flow pattern simulation mechanism and a monitoring and control component. The liquid in the constant temperature hot water storage mechanism runs in a fault simulation component (15) and a surrounding rock simulation component (1) according to a set seepage flow pattern through the seepage flow pattern simulation mechanism in cooperation with the monitoring and control component; the heat transfer characteristics of the seepage liquid running in the fault simulation component (15) are obtained through the monitoring and control component.

5. The simulation test device for measuring fracture seepage heat transfer characteristics according to claim 4, characterized in that: The constant temperature hot water storage mechanism is composed of a constant temperature hot water tank (6), the seepage flow simulation mechanism is composed of a variable frequency constant pressure jet pump (7), the monitoring and control component comprises at least a water temperature monitoring component group, a fracture sample model temperature monitoring component group and a control module, the two ends of the variable frequency constant pressure jet pump (7) are respectively connected to the constant temperature hot water tank (6) and the rubber sleeve structure (3) through a PVC pipe (8), the fracture sample model temperature monitoring component group is arranged in the surrounding rock simulation component (1), the water temperature monitoring component group is connected in series to the PVC pipe (8) at the output end of the variable frequency constant pressure jet pump, and at least the control end of the water temperature monitoring component group is connected to the control module.

6. The simulation test device for measuring fracture seepage heat transfer characteristics according to claim 5, characterized in that: The seepage simulation system also includes a tailwater collection component, which includes a tailwater container (9), a stopwatch (10) and a water pressure gauge (11). The water temperature monitoring component group includes at least two groups of water temperature sensors (12). The fracture sample model temperature monitoring component group includes a paperless recorder (13) and at least three groups of platinum electrodes (14). The stopwatch (10) is arranged on the tailwater container (9). The tailwater container (9) is connected to the rubber sleeve structure (3) of the fracture sample model through a PVC pipe (8). The PVC pipes (8) between the structures (3) are respectively provided with a water pressure gauge (11) and at least one group of water temperature sensors (12); at least one group of water temperature sensors (12) is arranged on the PVC pipe (8) between the output end of the variable frequency constant pressure jet pump and the rubber sleeve structure (3); each group of platinum electrodes (14) inserted into the surrounding rock simulation component (1) at intervals are respectively connected to a paperless recorder (13); at least the control end of the water temperature sensor (12), the stopwatch (10) and the water pressure gauge (11) is connected to a control module.

7. A construction method for measuring fracture seepage heat transfer characteristics using the simulation test device for measuring fracture seepage heat transfer characteristics according to claim 6, characterized in that: The construction method first connects a constant temperature hot water tank, a variable frequency constant pressure jet pump, a fracture sample model and a tail water collection assembly in sequence, and arranges a water temperature sensor and a water pressure gauge on the PVC pipes at both ends of the fracture sample model, arranges a stopwatch on the tail water container, arranges each group of platinum electrodes on the fracture sample model, and then starts the variable frequency constant pressure jet pump to input seepage water of a specified temperature, a specified flow rate and a specified flow state into the fracture sample model, and records corresponding data when the temperature change of the surrounding rock tends to be stable, and finally, based on the recorded corresponding data, an extended deduction is performed to obtain a convective heat transfer coefficient value close to the actual hot water seepage condition, Among them, when the seepage water of the specified temperature, specified flow rate and specified flow state is input into the fracture specimen model, at least three seepage waters of different flow rates under three different temperature conditions are included. Each input is completed after the last seepage water input is completed and the corresponding data is recorded. After the surrounding rock temperature drops to normal temperature, the next seepage water input and recording step is performed. The corresponding data recorded at least include the inlet hot water temperature Ta and the outlet hot water temperature Tb, the temperature of the solid side of the heat exchange surface Tg and the temperature of the fluid on the heat exchange surface T l .

8. The construction method according to claim 7, characterized in that: The temperatures of the hot water input into the fracture specimen model include four temperatures of 30°C, 40°C, 50°C and 60°C, and the flow rates of the hot water input include four flow rates of 170ml / min, 340ml / min, 500ml / min and 600ml / min. The specific simulation input process is as follows: First, the hot water flow rate in the fracture is controlled at a flow rate of 170 ml / min and kept constant. Then, the hot water inlet temperature is adjusted to 30°C, 40°C, 50°C and 60°C in turn, and input into the fracture specimen model respectively. The data of each temperature under the flow condition is recorded. After the surrounding rock temperature change tends to be stable, the hot water flow rate is changed to a constant flow rate of 340 ml / min, 500 ml / min and 600 ml / min in turn, and input into the fracture specimen model under four temperature conditions of 30°C, 40°C, 50°C and 60°C, and the data of each flow rate and each temperature condition are recorded respectively. This process is repeated to obtain a total of 16 sets of data on the relationship between the various data of hot water in the fault simulation component under four flow rates and four temperature conditions and the changing relationship between the hot water inlet temperature and the hot water test. The simulation test is completed.

9. The construction method according to claim 8, characterized in that: The seepage water of the specified flow state is input into the fracture sample model through the variable frequency constant pressure jet pump, which includes at least the seepage water of the laminar flow state. The seepage water of the laminar flow state is realized by controlling the flow rate q of the hot water, and the Reynolds number Re in the dimensionless number is used to determine the flow state of the water flow. When Re<2300, it is laminar flow, where the water flow velocity U is expressed by formula (1), and the Reynolds number Re is expressed by formula (2). Where: U is the water flow velocity, m / s; q is the hot water flow, m 3 / s; V is the kinematic viscosity of water, m 2 / s; X is the length of the crack, m; Y is the width of the crack, m.

10. The construction method according to claim 9, characterized in that: According to the recorded corresponding data, the convective heat transfer system value of rock fracture seepage is calculated according to the following steps: The convective heat transfer coefficient is calculated using Newton's law of cooling, Q=S×r×|T g -T l | (3), (3) Where S is the contact surface area, m 2 ; r is the convective heat transfer coefficient, W / (m 2 ℃); T g is the temperature of the solid side of the heat exchange surface, °C; T l is the temperature of the fluid on the heat exchange surface, °C; Because the convective heat transfer Q can be calculated by the inlet and outlet temperature difference of hot water, the total convective heat transfer and the inlet and outlet temperatures of hot water satisfy the formula, Q=c w ×m w ×(T a -T b ) (4), (4) In the formula, c w is the specific heat capacity of the convective heat transfer fluid, kJ / (kg·℃); m w is the mass flow rate of the convective heat transfer fluid, kg / s; T a is the fluid inlet temperature, °C; T b is the fluid outlet temperature, °C; Combining formula (1) and formula (2), we get the expression of convective heat transfer coefficient: In formula (5): q w is the hot water flow rate, m 3 / s;ρ w is the fluid density, kg / m 3 .

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