Method for testing convective heat transfer coefficient in crack of hot dry rock
By applying mechanical stress in the cracks of dry hot rock and measuring the temperature and flow rate, the dynamic thermal conductivity is calculated, which solves the problem of determining the thermal conductivity in the existing technology, improves the accuracy and prediction ability of the model, and provides a better solution for the utilization of geothermal energy. Reliable data support.
Patent Information
- Application Number
- CN202411474916.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-22
- Publication Date
- 2025-01-21
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
When testing the internal convection heat transfer coefficient of dry-heat rock fractures, the thermal conductivity coefficient is regarded as a constant value and cannot reflect the dynamic changes in actual production, resulting in insufficient model accuracy and prediction capabilities.
By applying mechanical stresses of different sizes and directions in the experimental device, measuring the temperature distribution and fluid flow rate inside the crack, and calculating the changes in the dynamic thermal conductivity, a more accurate convection heat transfer coefficient can be obtained.
It improves the accuracy and predictive capabilities of the model, enhances the understanding of rock and fracture materials under actual operating conditions, and provides more reliable data support for geothermal energy utilization and engineering design.
Smart Images
Figure CN119335006A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of hot dry rock development, and in particular relates to a method for testing the convection heat transfer coefficient inside a hot dry rock crack. Background Art
[0002] Hot dry rock is a hot rock mass buried 3 to 10 km from the surface, with a rock temperature of 150 to 650°C, almost no water or steam in the rock layer, and extremely low porosity and permeability. When extracting thermal energy from hot dry rock, hydraulic fracturing and other technical means are usually used to transform the reservoir with low permeability, construct heat exchange channels in the reservoir, and use heat extraction fluids to extract heat from the reservoir for power generation and other purposes. Therefore, testing the convective heat transfer coefficient of heat extraction fluids in the cracks of hot dry rocks is the basis for studying the flow and heat transfer laws of heat extraction fluids in rock cracks.
[0003] However, the existing technology still has major deficiencies, such as:
[0004] In the prior art, when testing the convection heat transfer coefficient inside hot dry rock cracks, the thermal conductivity may change with factors such as temperature, pressure, and material state, and the thermal conductivity in the existing model is a fixed value, which cannot represent the actual production situation. To this end, we provide a method for testing the convection heat transfer coefficient inside hot dry rock cracks to solve the above problems. Summary of the invention
[0005] The purpose of the present invention is to provide a method for testing the convective heat transfer coefficient inside dry hot rock fractures. By reflecting the dynamic change of thermal conductivity, the problem that the thermal conductivity will change and the thermal conductivity of the existing model is a fixed value and cannot represent the actual production situation is solved.
[0006] To solve the above technical problems, the present invention is achieved through the following technical solutions:
[0007] The present invention provides a method for testing the convection heat transfer coefficient inside a hot dry rock crack, comprising the following steps:
[0008] S1. Sample preparation: Prepare rock samples with fracture structures, while ensuring that the sample size and shape meet the experimental requirements and have well-defined fracture morphology and size;
[0009] S2. Laboratory setup: Design and build the experimental setup, including the sample holder and a device capable of applying mechanical stress;
[0010] S3. Basic test: Basic test is performed without applying stress to measure the temperature distribution and fluid flow rate inside the crack;
[0011] S4. Apply mechanical stress: Use equipment to apply mechanical stress of different magnitudes and directions to the rock sample;
[0012] S5. Experimental data acquisition: While applying stress, the thermal sensor and flow rate measuring device are used to obtain data and record the temperature distribution and fluid flow rate inside the crack in real time;
[0013] S6, stress adjustment and repeated testing: adjust the magnitude and direction of the applied stress and repeat the experiment to obtain multiple data points;
[0014] S7. Data analysis and comparison: Compare the temperature gradient and fluid flow rate data under different stress conditions, and use these data to calculate and analyze the convection heat transfer coefficient inside the crack.
[0015] The present invention is further configured that the dynamic thermal conductivity changes inside the cracks in S1-S7 are obtained by the following steps:
[0016] Step 1: Data collection and temperature gradient analysis;
[0017] Step 2: Calculation of dynamic thermal conductivity;
[0018] Step 3: Data analysis and verification.
[0019] The present invention is further configured such that, in step 1, the thermal sensors in S3 and S5 are used to measure the temperature distribution at different positions inside the crack, and the changes in temperature data are recorded before and after the mechanical stress is applied.
[0020] The present invention is further configured to calculate the temperature gradient between different positions inside the crack at each time point and under each applied stress condition through the data recorded in S3 and S5.
[0021] The present invention is further configured that the calculation formula of the temperature gradient is as follows:
[0022] Temperature gradient = T(x_j,t)-T(x_i,t)(x_j-x_i)
[0023] Where (T(x_i,t)) and (T(x_j,t)) are the temperatures at locations (x_i) and (x_j), and (t) is the time.
[0024] The present invention is further configured that the step 2 uses the equation of convective heat transfer to infer the change of dynamic thermal conductivity based on the measured temperature gradient data, wherein the convective heat transfer coefficient (h) is related to the dynamic thermal conductivity by the following formula, which is:
[0025] h=k / L
[0026] Where h is the convective heat transfer coefficient, k is the dynamic thermal conductivity, and L is the thickness or radius of the fluid.
[0027] The present invention is further configured such that step three compares the temperature gradient data obtained under different stress conditions with the theoretical model, infers the trend of the dynamic thermal conductivity inside the crack changing with the mechanical stress, and then performs statistical analysis and trend analysis to verify whether the inferred dynamic thermal conductivity change is consistent with the experimental observation, and evaluates its accuracy and reliability.
[0028] The present invention is further configured such that the calculation of the mechanical stress applied to the rock sample in S4 generally involves determining the magnitude and direction of the applied force, and the mechanical stress applied to the rock sample is pressure, shear force and tensile force respectively.
[0029] The present invention is further configured such that the direction of the applied force is determined in S4, the pressure is the pressure perpendicular to the sample surface, the shear force is the shear force parallel to the sample surface, and the tensile force is the tensile force applied along the tensile direction of the sample.
[0030] The present invention is further configured as follows: the calculation formula for the pressure is P=F1 / A1, wherein P is pressure, F1 is the force applied to the rock, and A1 is the area of action of the applied force; the calculation formula for the shear force is τ=F2 / A2, wherein τ is the shear stress, F2 is the shear force applied to the rock, and A2 is the area of action of the applied force; the calculation formula for the tensile force is σ=F3 / A3, wherein σ is the tensile stress, F3 is the tensile force applied to the rock, and A3 is the area of action of the applied force.
[0031] The present invention has the following beneficial effects:
[0032] The present invention not only improves the accuracy and predictive ability of the model by reflecting the dynamic change of thermal conductivity and testing the convective heat transfer coefficient inside the dry hot rock fracture, but also enhances the understanding of rock and fracture materials under actual operating conditions, providing more reliable data support for geothermal energy utilization and engineering design.
[0033] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS
[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.
[0035] Figure 1 A step diagram of a method for testing the convection heat transfer coefficient inside a hot dry rock fracture. DETAILED DESCRIPTION
[0036] The technical solutions in the embodiments of the present invention will be described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Specific embodiments
[0038] See also Figure 1 , a method for testing the convection heat transfer coefficient inside a hot dry rock fracture, comprising the following steps:
[0039] S1. Sample preparation: Prepare rock samples with fracture structures, while ensuring that the sample size and shape meet the experimental requirements and have well-defined fracture morphology and size;
[0040] S2. Laboratory setup: Design and build the experimental setup, including the sample holder and a device capable of applying mechanical stress;
[0041] S3. Basic test: Basic test is performed without applying stress to measure the temperature distribution and fluid flow rate inside the crack;
[0042] S4. Apply mechanical stress: Use equipment to apply mechanical stress of different magnitudes and directions to the rock sample;
[0043] S5. Experimental data acquisition: While applying stress, the thermal sensor and flow rate measuring device are used to obtain data and record the temperature distribution and fluid flow rate inside the crack in real time;
[0044] S6, stress adjustment and repeated testing: adjust the magnitude and direction of the applied stress and repeat the experiment to obtain multiple data points;
[0045] S7. Data analysis and comparison: Compare the temperature gradient and fluid flow rate data under different stress conditions, and use these data to calculate and analyze the convection heat transfer coefficient inside the crack.
[0046] The dynamic thermal conductivity changes inside the cracks in S1-S7 are obtained by the following steps:
[0047] Step 1: Data collection and temperature gradient analysis;
[0048] Step 2: Calculation of dynamic thermal conductivity;
[0049] Step 3: Data analysis and verification.
[0050] Step 1: Use the thermal sensors in S3 and S5 to measure the temperature distribution at different locations inside the crack, and record the changes in temperature data before and after applying mechanical stress.
[0051] The temperature gradient between different positions inside the crack at each time point and each applied stress condition is calculated using the data recorded in S3 and S5.
[0052] The temperature gradient is calculated as follows:
[0053] Temperature gradient = T(x_j,t)-T(x_i,t)(x_j-x_i)
[0054] Where (T(x_i,t)) and (T(x_j,t)) are the temperatures at locations (x_i) and (x_j), and (t) is the time.
[0055] Step 2 uses the equation for convective heat transfer to infer the change in dynamic thermal conductivity based on the measured temperature gradient data, where the convective heat transfer coefficient (h) is related to the dynamic thermal conductivity by the following formula:
[0056] h=k / L
[0057] Where h is the convective heat transfer coefficient, k is the dynamic thermal conductivity, and L is the thickness or radius of the fluid.
[0058] Step three compares the temperature gradient data obtained under different stress conditions with the theoretical model to infer the trend of the dynamic thermal conductivity inside the crack with mechanical stress, and then performs statistical analysis and trend analysis to verify whether the inferred dynamic thermal conductivity change is consistent with the experimental observation and to evaluate its accuracy and reliability.
[0059] Calculating the mechanical stress applied to the rock sample in S4 generally involves determining the magnitude and direction of the applied force, and the mechanical stresses applied to the rock sample are pressure, shear force, and tension force.
[0060] In S4, the direction of the applied force is determined, the pressure is the pressure perpendicular to the sample surface, the shear force is the shear force parallel to the sample surface, and the tensile force is the tensile force applied along the tensile direction of the sample.
[0061] The calculation formula for pressure is P=F1 / A1, where P is pressure, F1 is the force applied to the rock, and A1 is the area of action of the applied force. The calculation formula for shear force is τ=F2 / A2, where τ is the shear stress, F2 is the shear force applied to the rock, and A2 is the area of action of the applied force. The calculation formula for tensile force is σ=F3 / A3, where σ is the tensile stress, F3 is the tensile force applied to the rock, and A3 is the area of action of the applied force.
[0062] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to specific implementation methods. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that technicians in the relevant technical field can better understand and utilize the present invention.
Claims
1. A method for testing the convection heat transfer coefficient inside a hot dry rock crack, characterized in that: The following steps are involved: S1. Sample preparation: Prepare rock samples with fracture structures, while ensuring that the sample size and shape meet the experimental requirements and have well-defined fracture morphology and size; S2. Laboratory setup: Design and build the experimental setup, including the sample holder and a device capable of applying mechanical stress; S3. Basic test: Basic test is performed without applying stress to measure the temperature distribution and fluid flow rate inside the crack; S4. Apply mechanical stress: Use equipment to apply mechanical stress of different magnitudes and directions to the rock sample; S5. Experimental data acquisition: While applying stress, the thermal sensor and flow rate measuring device are used to obtain data and record the temperature distribution and fluid flow rate inside the crack in real time; S6, stress adjustment and repeated testing: adjust the magnitude and direction of the applied stress and repeat the experiment to obtain multiple data points; S7. Data analysis and comparison: Compare the temperature gradient and fluid flow rate data under different stress conditions, and use these data to calculate and analyze the convection heat transfer coefficient inside the crack.
2. A method for testing the convection heat transfer coefficient inside a hot dry rock fracture according to claim 1, characterized in that: The dynamic thermal conductivity changes inside the cracks in S1-S7 are obtained by the following steps: Step 1: Data collection and temperature gradient analysis; Step 2: Calculation of dynamic thermal conductivity; Step 3: Data analysis and verification.
3. A method for testing the convection heat transfer coefficient inside a hot dry rock fracture according to claim 2, characterized in that: The step 1 uses the thermal sensors in S3 and S5 to measure the temperature distribution at different positions inside the crack, and records the changes in temperature data before and after the mechanical stress is applied.
4. A method for testing the convection heat transfer coefficient inside a hot dry rock fracture according to claim 2, characterized in that: The temperature gradient between different positions inside the crack at each time point and under each applied stress condition is calculated using the data recorded in S3 and S5.
5. A method for testing the convection heat transfer coefficient inside a hot dry rock fracture according to claim 2, characterized in that: The calculation formula of the temperature gradient is as follows: Temperature gradient = T(x_j,t)-T(x_i,t)(x_j-x_i) Where (T(x_i,t)) and (T(x_j,t)) are the temperatures at locations (x_i) and (x_j), and (t) is the time.
6. A method for testing the convection heat transfer coefficient inside a hot dry rock fracture according to claim 2, characterized in that: The second step uses the equation of convective heat transfer to infer the change of dynamic thermal conductivity based on the measured temperature gradient data, wherein the convective heat transfer coefficient (h) is related to the dynamic thermal conductivity by the following formula: h=k / L Where h is the convective heat transfer coefficient, k is the dynamic thermal conductivity, and L is the thickness or radius of the fluid.
7. A method for testing the convection heat transfer coefficient inside a hot dry rock fracture according to claim 2, characterized in that: The step three compares the temperature gradient data obtained under different stress conditions with the theoretical model, infers the trend of the dynamic thermal conductivity inside the crack with the change of mechanical stress, and then performs statistical analysis and trend analysis to verify whether the inferred dynamic thermal conductivity change is consistent with the experimental observation, and evaluates its accuracy and reliability.
8. The method for testing the convection heat transfer coefficient inside a hot dry rock fracture according to claim 1, characterized in that: The calculation of the mechanical stress applied to the rock sample in S4 generally involves determining the magnitude and direction of the applied force, wherein the mechanical stress applied to the rock sample is pressure, shear force and tensile force.
9. A method for testing the convection heat transfer coefficient inside a hot dry rock fracture according to claim 8, characterized in that: In the above S4, the direction of the applied force is determined, the pressure is the pressure perpendicular to the sample surface, the shear force is the shear force parallel to the sample surface, and the tensile force is the tensile force applied along the tensile direction of the sample.
10. A method for testing the convection heat transfer coefficient inside a hot dry rock fracture according to claim 9, characterized in that: The calculation formula for the pressure is P=F1 / A1, wherein P is pressure, F1 is the force applied to the rock, and A1 is the area of action of the applied force. The calculation formula for the shear force is τ=F2 / A2, wherein τ is the shear stress, F2 is the shear force applied to the rock, and A2 is the area of action of the applied force. The calculation formula for the tensile force is σ=F3 / A3, wherein σ is the tensile stress, F3 is the tensile force applied to the rock, and A3 is the area of action of the applied force.