A method for determining the supercritical CO2 flow and heat transfer characteristics in a large-scale vertical circular tube.

Abstract

This invention belongs to the field of geothermal downhole heat exchange, supercritical fluid heat and mass transfer, and multiphase flow testing technology. It relates to a method for determining the flow and heat transfer characteristics of supercritical CO2 in a large-scale vertical circular tube. By constructing a large-scale vertical circular tube test unit and setting operating parameters covering the quasi-critical region, the method can be adapted to large-scale vertical circular tube structures. Measurement points are arranged along the axial and radial directions to collect raw data such as pressure, temperature, and heat flux density in real time. The physical properties of supercritical CO2 are corrected in real time using this raw data, eliminating the interference of abrupt changes in physical properties in the quasi-critical region on the test results. Furthermore, a three-dimensional data field is reconstructed based on this data, and vertical gravity and aspect ratio corrections are introduced when establishing the flow and heat transfer correlation model. This eliminates the interference of the vertical gravity field on the test results, ensuring that the final extracted measurement results accurately reflect the actual downhole heat exchange conditions.

Description

Technical Field

[0001] This invention belongs to the field of geothermal well downhole heat exchange, supercritical fluid heat and mass transfer and multiphase flow testing technology, and relates to a method for determining the supercritical CO2 flow and heat transfer law in a large-scale vertical circular pipe. Background Technology

[0002] Coaxial casing geothermal wells are commonly used for the development of medium-deep geothermal energy. Due to its adjustable physical properties, high heat exchange efficiency, and environmental friendliness, supercritical CO2 has become the core working fluid for downhole heat exchange. As the core heat exchange unit of the coaxial casing, the flow state and heat transfer law of supercritical CO2 inside the large-scale vertical circular tube directly determine the heat exchange efficiency and operational stability of the geothermal well.

[0003] Existing methods for measuring heat transfer in supercritical fluid flow have significant drawbacks: First, they are mostly adapted to small-scale horizontal circular pipes, failing to consider large-scale aspect ratios, vertical gravity field coupling, and gradual changes in friction parameters, thus failing to accurately reflect real-world downhole conditions. Second, supercritical CO2 undergoes abrupt changes in physical properties in the quasi-critical region, and traditional methods do not provide real-time corrections for properties such as density, specific heat capacity, and thermal conductivity, leading to distorted test results. Third, they often employ single-point, asynchronous testing, making it impossible to obtain the spatiotemporal coupling distribution of the flow field, temperature field, and pressure field, thus hindering the revelation of the intrinsic mechanisms of heat transfer. Fourth, they lack a systematic approach for fitting and verifying large-scale vertical pipes, meaning the measurement results cannot directly support the design and operation scheduling of geothermal well heat exchange structures.

[0004] Currently, there is no complete in-situ measurement method for the heat transfer law of supercritical CO2 flow in large-scale vertical circular pipes, which restricts the iteration of efficient development technology for medium and deep geothermal energy. Summary of the Invention

[0005] The purpose of this invention is to address the problems in existing technologies, such as incompatibility with large-scale vertical structures, lack of real-time property correction, and failure to collect data synchronously, which result in inaccurate measurement results reflecting the actual heat transfer conditions downhole. This invention provides a method for measuring the supercritical CO2 flow and heat transfer characteristics within a large-scale vertical circular tube. To achieve the above objectives, the present invention employs the following technical solution: A method for determining the supercritical CO2 flow and heat transfer characteristics in a large-scale vertical circular tube includes the following steps: Construct a large-scale vertical circular tube test unit; Based on a large-scale vertical circular tube test unit, operating parameters covering the pseudo-critical region of supercritical CO2 were set. Based on a large-scale vertical circular tube test unit, measuring points are arranged along the axial and radial directions to collect raw data related to flow and heat transfer in real time. The raw data includes at least the working fluid pressure, temperature and heat flux density. The physical properties of supercritical CO2 are corrected in real time based on the real-time collected working fluid pressure and temperature to obtain a standardized test dataset. The data is reconstructed based on a standardized test dataset to obtain a three-dimensional data field that couples the flow field, temperature field, and pressure field. Based on the three-dimensional data field, a dimensionless analysis was adopted and vertical gravity and aspect ratio correction were introduced to establish a flow heat transfer correlation model. Based on the flow and heat transfer correlation model, the flow and heat transfer law of supercritical CO2 in a large-scale vertical circular tube is extracted, and a flow and heat transfer law map is formed. The measurement results were obtained by integrating the original data, standardized test dataset, three-dimensional data field, flow heat transfer correlation model and flow heat transfer law spectrum.

[0006] A further improvement of the present invention is that: The test unit based on a large-scale vertical circular tube is configured with test points along the axial and radial directions, including: The measuring points are arranged at equal intervals along the vertical axis of the circular pipe and in layers along the radial direction. During testing, data was collected using a synchronous acquisition mode.

[0007] The physical properties of the supercritical CO2 include density, specific heat capacity at constant pressure, thermal conductivity, and kinematic viscosity. During correction, calculations are performed point by point using the working fluid pressure and temperature collected in real time.

[0008] The data is reconstructed based on a standardized test dataset to obtain a three-dimensional data field coupling the flow field, temperature field, and pressure field, including: Outlier removal, axial friction data interpolation, and radial cross-sectional data fitting are performed based on standardized test datasets. A three-dimensional data field coupling flow field, temperature field, and pressure field is constructed based on the processed data.

[0009] The flow heat transfer correlation model includes the Nusselt number correlation for supercritical CO2 and the formula for calculating friction loss. The Nusselt number correlation for supercritical CO2 is expressed by the following formula:

[0010] in, The Nusselt number represents the intensity of convective heat transfer. The Reynolds number represents the flow state. The Prandt number characterizes the effect of fluid properties on heat transfer. denoted as the Grashof number, which characterizes the natural convection effect induced by the vertical gravitational field; , , , These are the fitting coefficients for a large-scale vertical tube. This is the aspect ratio correction factor; This is a correction factor for supercritical properties; The formula for calculating friction loss is expressed by the following equation:

[0011] in, This refers to the axial friction loss. The friction coefficient of a supercritical fluid; This is the effective length of the vertical circular tube; The inner diameter of the circular tube; The working fluid density is corrected in real time; The average flow velocity within the pipe cross-section; It is the acceleration due to gravity; This is the vertical height property coupling correction coefficient.

[0012] The flow heat transfer laws include flow pattern conversion threshold, critical heat transfer conditions, resistance variation law, and heat transfer coefficient distribution.

[0013] A system for measuring the flow and heat transfer of supercritical CO2 in a large-scale vertical circular tube, comprising: The test platform construction module is used to build large-scale vertical circular tube test units; The environment setting module is used to set operating parameters covering the pseudo-critical region of supercritical CO2 based on a large-scale vertical circular tube test unit. The data acquisition module is used to set up measuring points along the axial and radial directions based on a large-scale vertical circular tube test unit to collect raw data related to flow and heat transfer in real time. The raw data includes at least the working fluid pressure, temperature and heat flux density. The parameter correction module is used to correct the physical properties of supercritical CO2 in real time based on the real-time collected working fluid pressure and temperature, and obtain a standardized test dataset. The 3D data field construction module is used to reconstruct data based on a standardized test dataset to obtain a 3D data field that couples the flow field, temperature field, and pressure field. The flow and heat transfer correlation model construction module is used to establish a flow and heat transfer correlation model based on a three-dimensional data field using dimensionless analysis and by introducing vertical gravity and aspect ratio correction. The heat transfer law extraction module is used to extract the flow and heat transfer laws of supercritical CO2 in a large-scale vertical circular tube based on the flow and heat transfer correlation model, and form a flow and heat transfer law map. The measurement integration module is used to integrate raw data, standardized test datasets, three-dimensional data fields, flow and heat transfer correlation models, and flow and heat transfer law maps to obtain measurement results.

[0014] A computer program product includes a computer program that, when executed by a processor, implements any one of the methods described.

[0015] A terminal device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the steps of any of the methods described above.

[0016] A computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of any of the methods described herein.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for determining the flow and heat transfer characteristics of supercritical CO2 in a large-scale vertical circular tube. By constructing a large-scale vertical circular tube test unit and setting operating parameters covering the quasi-critical region, the method can be adapted to large-scale vertical circular tube structures. Measurement points are arranged along the axial and radial directions to collect raw data such as pressure, temperature, and heat flux density in real time. The physical properties of supercritical CO2 are corrected in real time using the raw data, eliminating the interference of abrupt changes in physical properties in the quasi-critical region on the test results. Furthermore, a three-dimensional data field is reconstructed based on this data, and vertical gravity and aspect ratio corrections are introduced when establishing the flow and heat transfer correlation model. This eliminates the interference of the vertical gravity field on the test results, making it easier for the final extracted measurement results to accurately reflect the actual heat exchange conditions downhole. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart disclosed in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0022] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0023] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0024] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0025] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0026] The present invention will now be described in further detail with reference to the accompanying drawings: See Figure 1 This invention discloses a method for determining the flow and heat transfer characteristics of supercritical CO2 in a large-scale vertical circular tube, comprising the following steps: Step 1: Complete the assembly of the large-scale vertical circular tube test unit, perform heat insulation treatment on the entire tube body, complete the verticality correction using calibration tools, and reliably connect the test unit with the supercritical CO2 supply, heat loading, and data acquisition equipment to ensure that the test circuit has no leakage and no additional heat exchange. Specifically, it includes: A large-scale vertical circular tube test unit was constructed to complete tube sealing, insulation coating, and verticality calibration, eliminating interference from environmental heat exchange and tube tilt on flow heat transfer. Specifically, the tube sealing adopts a multi-layer composite sealing structure to ensure no leakage under supercritical pressure; the insulation coating uses high-insulation-performance materials to reduce heat exchange with the outside environment; and the verticality calibration uses a high-precision laser calibrator to control the verticality error of the circular tube within an extremely small range.

[0027] Furthermore, the test unit is connected to the supercritical CO2 working fluid supply system, the heat loading system, and the parameter acquisition system to form a closed test loop. The working fluid supply system uses a high-precision pressure and flow control device, the heat loading system is equipped with an adjustable power heating module, and the parameter acquisition system uses high-precision sensors to achieve rapid and accurate data acquisition.

[0028] Step 2: Set the supercritical CO2 test condition range, with pressure covering the upper and lower ranges of the quasi-critical pressure, flow velocity covering the transition range from laminar to turbulent flow, and heat flux density covering the actual heat exchange range of the geothermal well. Each condition is continuously run until the parameters stabilize and there are no continuous fluctuations before starting the test. Specifically, it includes: Supercritical CO2 test condition gradient calibration was conducted, establishing pressure, flow rate, and heat flux density ranges covering the quasi-critical region. Specifically: The pressure range is scientifically set based on the pseudo-critical pressure of supercritical CO2 to ensure that it includes key areas with drastic changes in physical properties. The velocity range covers different flow states; The heat flux density range simulates various heat load conditions in practical applications.

[0029] Each operating condition is kept in steady state until the parameters of the working fluid in the pipe show no fluctuations, at which point the testing phase begins to ensure the stability and comparability of the test data. By continuously monitoring key parameters such as pressure, temperature, and flow rate, it is determined whether the operating condition has reached a stable state. Generally, it is required that the fluctuation range of key parameters is less than a set threshold within a certain period of time.

[0030] Step 3: Set up measuring points along the vertical circular pipe axis at a set interval, and set up measuring points radially according to the pipe cross-section in layers. Start the synchronous acquisition module to simultaneously acquire axial pressure, radial temperature, cross-sectional flow velocity, wall heat flux density, working fluid temperature and pressure data, and continuously acquire multiple sets of data to ensure sufficient sample size. Specifically, it includes: Measurement points were set up along the axial and radial directions of a large-scale vertical circular tube to simultaneously collect in-situ data on the axial pressure, radial temperature, cross-sectional flow velocity, wall heat flux density, and real-time temperature and pressure of the working fluid for supercritical CO2 inside the tube, thereby obtaining a multi-dimensional spatiotemporal distribution of the original dataset.

[0031] Furthermore, the layout of the measuring points was determined based on research needs and theoretical analysis. Axial measuring points adopted a combination of equal and non-equal spacing to focus on areas with drastic changes in flow and heat transfer. Radial measuring points were distributed in a concentric circle array to ensure accurate reflection of radial temperature and velocity distribution.

[0032] Advanced sensor technologies, such as high-precision pressure sensors, fast-response temperature sensors, and non-contact flow rate measuring instruments, are used to achieve synchronous data acquisition.

[0033] Step 4: Input the collected real-time pressure and temperature data into the property correction module to perform point-by-point real-time correction on density, specific heat capacity, thermal conductivity, and viscosity, eliminate calculation deviations caused by sudden changes in property, and generate a standardized test dataset. Specifically, it includes: Based on the real-time pressure and temperature of supercritical CO2, physical properties such as density, specific heat capacity at constant pressure, thermal conductivity, and kinematic viscosity are corrected in real time to eliminate the interference of drastic changes in physical properties in the quasi-critical region on flow heat transfer calculations, resulting in a corrected standardized test dataset.

[0034] Furthermore, a validated property calculation model is used, combined with real-time measured pressure and temperature data, to dynamically correct the property parameters. During the correction process, the nonlinear relationship between the property parameters and temperature and pressure is considered to ensure the accuracy of the correction results.

[0035] The introduction of real-time corrected working fluid density and vertical height property coupling correction coefficients effectively improves the accuracy of friction loss calculation and ensures the reliability and accuracy of experimental data.

[0036] Step 5: Preprocess the standardized dataset to remove outliers, complete the axial data along the path using an interpolation algorithm, reconstruct the radial cross-section data using a fitting algorithm, and establish a three-dimensional data field that couples the flow field, temperature field, and pressure field to intuitively reflect the spatial distribution of parameters. Specifically, it includes: Spatiotemporal reconstruction of the standardized test dataset was performed, outliers were removed, and axial friction data interpolation and radial cross-sectional data fitting were completed to construct a large-scale three-dimensional data field coupling supercritical CO2 flow field, temperature field, and pressure field inside a vertical circular tube.

[0037] Outlier removal employs statistical methods, such as the 3σ criterion, to ensure data reliability.

[0038] Axial data interpolation employs a higher-order interpolation method to improve data continuity.

[0039] Multiple regression analysis was used to fit the radial section data to accurately describe the distribution of section parameters.

[0040] Using professional data processing software, we can realize the visualization construction of three-dimensional data fields.

[0041] Step Six: Perform dimensionless analysis based on the three-dimensional data field, introduce Reynolds number, Prandtl number, and Grashof number, and combine aspect ratio and supercritical property correction to obtain the Nusselt number correlation and friction loss calculation formula; use independent samples to complete model verification to ensure that the model can accurately characterize the flow and heat transfer law. Specifically, it includes: A supercritical CO2 flow heat transfer correlation model adapted to large-scale vertical circular pipes was established by using dimensionless analysis and nonlinear fitting methods, combined with vertical gravity effect and large-scale pipe length-to-diameter ratio correction. The model accuracy was verified by dual indexes to ensure that the model can accurately characterize the flow heat transfer law.

[0042] Furthermore, in dimensionless analysis, the Nusselt number ( ), Reynolds number ( Prandtl number ( ), Glaschov number ( ) and other dimensionless parameters, among which the Nusselt number correlation for supercritical CO2 is:

[0043] in, The Nusselt number represents the intensity of convective heat transfer. The Reynolds number represents the flow state. The Prandt number characterizes the effect of fluid properties on heat transfer. denoted as the Grashof number, which characterizes the natural convection effect induced by the vertical gravitational field; , , , These are the fitting coefficients for a large-scale vertical tube. This is the aspect ratio correction factor; This is the correction factor for supercritical properties. Furthermore, when calculating friction loss, the following formula is used:

[0044] in, This refers to the axial friction loss. The friction coefficient of a supercritical fluid; This is the effective length of the vertical circular tube; The inner diameter of the circular tube; The working fluid density is corrected in real time; The average flow velocity within the pipe cross-section; It is the acceleration due to gravity; This is the vertical height property coupling correction coefficient.

[0045] By comparing the model calculation results with experimental data, the accuracy of the model was verified using two indicators, such as average relative error and root mean square error, to ensure that the model can accurately reflect the flow and heat transfer law of supercritical CO2 in a large-scale vertical circular tube.

[0046] Step 7: Use the validated correlation model for pattern extraction, determine the critical conditions for flow pattern transformation, the threshold for heat transfer enhancement / deterioration, the variation law of axial heat transfer coefficient and the characteristics of friction loss, and draw a complete flow heat transfer law map. Specifically, it includes: Based on the fitted correlation model, the flow pattern transformation threshold, heat transfer enhancement or deterioration critical conditions, friction resistance variation law and axial heat transfer coefficient distribution characteristics of supercritical CO2 in large-scale vertical circular pipes are extracted to form a complete flow heat transfer law map.

[0047] By conducting parameter analysis and numerical simulation on the associated model, the influence of different parameters on flow and heat transfer characteristics was systematically studied, and the critical values ​​and variation laws of key parameters were determined. Using graphing software, the research results were presented in intuitive graphical forms, including flow pattern diagrams, heat transfer performance diagrams, and drag characteristic diagrams.

[0048] Step 8: Organize the original test data, property correction results, three-dimensional data field, correlation model parameters and regularity maps to form a standardized test report, providing direct basis for the design of coaxial casing heat exchange structure, working fluid parameter matching, and system scheduling of medium-deep geothermal wells. Specifically, it includes: The test data, model parameters, and pattern graphs were compiled to form test results that can be directly used for the design of coaxial casing heat exchangers in geothermal wells.

[0049] Classify and organize the test data to create a data archive.

[0050] The model parameters are described in detail, including their value range and applicable conditions.

[0051] The patterns and graphs are labeled and interpreted to ensure that designers can accurately understand and apply the research results. Ultimately, this results in a complete and systematic set of technical data, providing scientific basis and technical support for the design of coaxial casing heat exchange systems in geothermal wells.

[0052] This invention achieves accurate measurement of the heat transfer law of supercritical CO2 flow through full-process steady-state measurement, multi-parameter synchronous acquisition, real-time property correction, and large-scale vertical structure-specific fitting. The measurement results are highly consistent with the actual downhole working conditions, which can effectively support the optimization and application of efficient development technology for medium and deep geothermal energy.

[0053] This invention discloses a system for measuring the flow and heat transfer characteristics of supercritical CO2 in a large-scale vertical circular tube, comprising: The test platform construction module is used to build large-scale vertical circular tube test units; The environment setting module is used to set operating parameters covering the pseudo-critical region of supercritical CO2 based on a large-scale vertical circular tube test unit. The data acquisition module is used to set up measuring points along the axial and radial directions based on a large-scale vertical circular tube test unit to collect raw data related to flow and heat transfer in real time. The raw data includes at least the working fluid pressure, temperature and heat flux density. The parameter correction module is used to correct the physical properties of supercritical CO2 in real time based on the real-time collected working fluid pressure and temperature, and obtain a standardized test dataset. The 3D data field construction module is used to reconstruct data based on a standardized test dataset to obtain a 3D data field that couples the flow field, temperature field, and pressure field. The flow and heat transfer correlation model construction module is used to establish a flow and heat transfer correlation model based on a three-dimensional data field using dimensionless analysis and by introducing vertical gravity and aspect ratio correction. The heat transfer law extraction module is used to extract the flow and heat transfer laws of supercritical CO2 in a large-scale vertical circular tube based on the flow and heat transfer correlation model, and form a flow and heat transfer law map. The measurement integration module is used to integrate raw data, standardized test datasets, three-dimensional data fields, flow and heat transfer correlation models, and flow and heat transfer law maps to obtain measurement results.

[0054] This invention proposes an in-situ measurement system for supercritical CO2 flow heat transfer adapted to large-scale vertical circular pipes. Through multi-dimensional synchronous acquisition and real-time property correction, it effectively restores the actual downhole heat transfer conditions, eliminating test errors caused by abrupt property changes in the quasi-critical zone and the vertical gravity field. By employing three-dimensional data field reconstruction and dimensionless fitting methods, it can accurately reveal the intrinsic relationship between the flow state and the heat transfer process, improving the accuracy of law extraction. Through aspect ratio and gravity effect correction, the measurement results can directly support the design and operation scheduling of coaxial casing structures in medium-deep geothermal wells. The system achieves non-destructive, steady-state, and highly matched in-situ measurement, overcoming the shortcomings of traditional methods such as inability to adapt to large-scale vertical structures, asynchronous test parameters, and poor applicability of results. It provides reliable testing and theoretical support for supercritical CO2 geothermal downhole heat transfer technology.

[0055] A schematic diagram of a terminal device according to an embodiment of the present invention. The terminal device of this embodiment includes: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps in the various method embodiments described above. Alternatively, when the processor executes the computer program, it implements the functions of each module / unit in the various device embodiments described above.

[0056] The computer program can be divided into one or more modules / units, which are stored in the memory and executed by the processor to complete the present invention.

[0057] The terminal device can be a desktop computer, laptop computer, cloud server, or other device with strong computing power. The terminal device may include, but is not limited to, a processor and memory.

[0058] The optimal choice for the processor is a multi-core high-speed central processing unit (CPU).

[0059] The memory can be used to store the computer program and / or module. The processor implements various functions of the terminal device by running or executing the computer program and / or module stored in the memory and calling the data stored in the memory.

[0060] If the modules / units integrated into the terminal device are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0061] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the flow and heat transfer characteristics of supercritical CO2 in a large-scale vertical circular tube, characterized in that, Includes the following steps: Construct a large-scale vertical circular tube test unit; Based on a large-scale vertical circular tube test unit, operating parameters covering the pseudo-critical region of supercritical CO2 were set. Based on a large-scale vertical circular tube test unit, measuring points are arranged along the axial and radial directions to collect raw data related to flow and heat transfer in real time. The raw data includes at least the working fluid pressure, temperature and heat flux density. The physical properties of supercritical CO2 are corrected in real time based on the real-time collected working fluid pressure and temperature to obtain a standardized test dataset. The data is reconstructed based on a standardized test dataset to obtain a three-dimensional data field that couples the flow field, temperature field, and pressure field. Based on the three-dimensional data field, a dimensionless analysis was adopted and vertical gravity and aspect ratio correction were introduced to establish a flow heat transfer correlation model. Based on the flow and heat transfer correlation model, the flow and heat transfer law of supercritical CO2 in a large-scale vertical circular tube is extracted, and a flow and heat transfer law map is formed. The measurement results were obtained by integrating the original data, standardized test dataset, three-dimensional data field, flow heat transfer correlation model and flow heat transfer law spectrum.

2. The method for determining the supercritical CO2 flow and heat transfer characteristics in a large-scale vertical circular tube according to claim 1, characterized in that, The test unit based on a large-scale vertical circular tube is configured with test points along the axial and radial directions, including: The measuring points are arranged at equal intervals along the vertical axis of the circular pipe and in layers along the radial direction. During testing, data was collected using a synchronous acquisition mode.

3. The method for determining the supercritical CO2 flow and heat transfer characteristics in a large-scale vertical circular tube according to claim 1, characterized in that, The physical properties of the supercritical CO2 include density, specific heat capacity at constant pressure, thermal conductivity, and kinematic viscosity. During correction, calculations are performed point by point using the working fluid pressure and temperature collected in real time.

4. The method for determining the supercritical CO2 flow and heat transfer characteristics in a large-scale vertical circular tube according to claim 1, characterized in that, The data is reconstructed based on a standardized test dataset to obtain a three-dimensional data field coupling the flow field, temperature field, and pressure field, including: Outlier removal, axial friction data interpolation, and radial cross-sectional data fitting are performed based on standardized test datasets. A three-dimensional data field coupling flow field, temperature field, and pressure field is constructed based on the processed data.

5. The method for determining the supercritical CO2 flow and heat transfer characteristics in a large-scale vertical circular tube according to claim 1, characterized in that, The flow heat transfer correlation model includes the Nusselt number correlation for supercritical CO2 and the formula for calculating friction loss. The Nusselt number correlation for supercritical CO2 is expressed by the following formula: in, The Nusselt number represents the intensity of convective heat transfer. The Reynolds number represents the flow state. The Prandt number characterizes the effect of fluid properties on heat transfer. denoted as the Grashof number, which characterizes the natural convection effect induced by the vertical gravitational field; , , , These are the fitting coefficients for a large-scale vertical tube. This is the aspect ratio correction factor; This is a correction factor for supercritical properties; The formula for calculating friction loss is expressed by the following equation: in, This refers to the axial friction loss. The friction coefficient of a supercritical fluid; This is the effective length of the vertical circular tube; The inner diameter of the circular tube; The working fluid density is corrected in real time; The average flow velocity within the pipe cross-section; It is the acceleration due to gravity; This is the vertical height property coupling correction coefficient.

6. The method for determining the supercritical CO2 flow and heat transfer characteristics in a large-scale vertical circular tube according to claim 1, characterized in that, The flow heat transfer laws include flow pattern conversion threshold, critical heat transfer conditions, resistance variation law, and heat transfer coefficient distribution.

7. A system for measuring the flow and heat transfer characteristics of supercritical CO2 in a large-scale vertical circular tube, characterized in that, include: The test platform construction module is used to build large-scale vertical circular tube test units; The environment setting module is used to set operating parameters covering the pseudo-critical region of supercritical CO2 based on a large-scale vertical circular tube test unit. The data acquisition module is used to set up measuring points along the axial and radial directions based on a large-scale vertical circular tube test unit to collect raw data related to flow and heat transfer in real time. The raw data includes at least the working fluid pressure, temperature and heat flux density. The parameter correction module is used to correct the physical properties of supercritical CO2 in real time based on the real-time collected working fluid pressure and temperature, and obtain a standardized test dataset. The 3D data field construction module is used to reconstruct data based on standardized test datasets to obtain a 3D data field that couples the flow field, temperature field, and pressure field. The flow and heat transfer correlation model construction module is used to establish a flow and heat transfer correlation model based on a three-dimensional data field using dimensionless analysis and by introducing vertical gravity and aspect ratio correction. The heat transfer law extraction module is used to extract the flow and heat transfer laws of supercritical CO2 in a large-scale vertical circular tube based on the flow and heat transfer correlation model, and form a flow and heat transfer law map. The measurement integration module is used to integrate raw data, standardized test datasets, three-dimensional data fields, flow and heat transfer correlation models, and flow and heat transfer law maps to obtain measurement results.

8. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-6.

9. A terminal device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method as described in any one of claims 1-6.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1-6.

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