Device and method for realizing transcritical phase change and flow measurement of fluid with high CO2 content

Abstract

The invention discloses a device and a method for realizing transcritical phase change and flow measurement of a fluid with high CO2 content. A gas supply device, a booster pump, a temperature regulation buffer device, a test section, a flow meter and a gas recovery device are sequentially arranged along the flow direction of the fluid; the test section comprises three Venturi tubes which are the same in structure and are connected in series, controllable transcritical phase change of the high-CO2-content fluid from a supercritical state to a gas state is achieved through stepped pressure reduction, the technical bottleneck that phase change of single-stage throttling near a critical point is uncontrollable is solved, and a standardized platform is provided for throttling characteristic research of the fluid near the critical point; a multi-sensor array is arranged at an inlet and an outlet of each stage of Venturi tube, and a high-speed data acquisition system is combined, so that real-time accurate calculation of the scorch soup coefficient is facilitated; a flow and pressure drop semi-empirical formula considering the influence of an expansion coefficient and density is adopted, outflow coefficients suitable for different working conditions are obtained through linear fitting, and a flow measurement system can be constructed by being matched with a Venturi tube.

Description

Technical Field

[0001] This invention relates to the field of fluid throttling and flow measurement technology, specifically to a device and method for realizing transcritical phase change and flow measurement of fluids with high CO2 content. Background Technology

[0002] High-CO2 fluids are widely generated in industrial processes such as fossil fuel combustion, chemical synthesis, metallurgy, building materials, and bio-fermentation. Injecting high-CO2 fluids into underground reservoirs through throttling devices to displace crude oil offers the dual benefits of carbon emission reduction and enhanced oil and gas recovery. To regulate the pressure and flow rate injected into the reservoir, throttling devices need to be installed at multiple locations, both at the wellhead and downhole. Venturi tube throttling devices offer advantages such as low pressure loss and minimal fluid disturbance, and can be adapted to different flow ranges and fluid properties, demonstrating significant application potential.

[0003] However, the J / T coefficient is sensitive to temperature and pressure changes near the critical point, and the fluid density changes drastically during transcritical conditions. Existing single-stage throttling devices (such as orifice plates and single-stage venturi tubes) suffer from uncontrollable phase transition processes when handling transcritical phase transitions in high-CO2-content fluids, and the phase transition monitoring system lacks accuracy. Traditional differential pressure flowmeters rarely use temperature and pressure compensation for density correction, resulting in significant measurement errors during transcritical conditions. Existing multi-stage throttling device designs (such as orifice plates in series) suffer from large pressure losses and poor adaptability.

[0004] Therefore, there is an urgent need to develop a multi-stage throttling device that enables controllable transcritical phase change, high-precision parameter monitoring, and dynamic density compensation, in order to overcome the limitations of existing technologies in transcritical throttling and flow measurement of high CO2-content fluids. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a device and method for realizing transcritical phase change and flow measurement of high CO2-content fluids. A multi-stage throttling device composed of three Venturi tubes is used to achieve the transition of high CO2-content fluids from a supercritical state to a gaseous state. The correlation between throttling temperature drop, pressure drop, and flow rate of high CO2-content fluids near the critical point within the Venturi tubes is studied. By monitoring the pressure and temperature before and after the throttling section, the location of the phase change is determined. Multiple inlet conditions are set to explore their impact on outlet temperature and pressure changes. A temperature-pressure prediction method for the throttling process of high CO2-content fluids is derived based on theoretical analysis. Taking into full account the density changes at the fluid inlet and outlet, an outlet coefficient applicable to different operating conditions is obtained, and a semi-empirical formula meeting the accuracy requirements is fitted.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a device for realizing transcritical phase change and flow measurement of high CO2-content fluids, comprising a gas supply device, a booster pump, a temperature control buffer device, a test section, a flow meter, and a gas recovery device connected sequentially along the gas flow direction; the test section includes three identical Venturi tubes connected in series, a pressure sensor is installed at the inlet of the test section, and thermocouples and differential pressure sensors are installed at the inlet and outlet of each Venturi tube.

[0007] Furthermore, each venturi tube segment includes a contraction section, a throat, and an expansion section. Each venturi tube segment has a throat diameter of 1.1 mm, a throat length of 5 mm, an inner diameter of 4 mm, and both the contraction angle and the expansion angle are 30°.

[0008] Furthermore, the thermocouples, pressure sensors, differential pressure sensors, and flow meters are connected to a data acquisition system, which is connected to a computer.

[0009] Furthermore, the gas supply device is a first gas cylinder filled with a gas to be tested with a defined composition, or the gas supply device is multiple gas cylinders filled with different gases, each gas cylinder is connected to a mixer, and the outlet of the mixer or the outlet of the first gas cylinder is connected to a temperature regulating buffer device via a booster pump.

[0010] Furthermore, the temperature regulating buffer device is provided with a space for containing the mixed gas, and a temperature regulating device is provided outside the space, and a regulating valve is provided at the outlet of the temperature regulating buffer device.

[0011] Furthermore, the space for containing the mixed gas includes a second gas cylinder and a third gas cylinder, and the temperature control device includes a water bath, with the second and third gas cylinders disposed in the water bath.

[0012] Furthermore, the outlet of the test section is connected in sequence to a valve and a safety valve. The outlet of the safety valve is connected to a gas recovery device, and a pressure gauge is installed on the gas recovery device.

[0013] Furthermore, the gas supply device is used to provide a mixed fluid of CO2 and CH4 containing different volume fractions of CO2.

[0014] Secondly, this invention provides a method for measuring transcritical phase change and flow rate of high CO2-content fluid. A gas supply device and a booster pump inject fluid at a set pressure into a temperature-regulating buffer device. The temperature-regulating buffer device adjusts the fluid temperature. The mixed fluid enters a test section with a set composition, pressure, and temperature. A pressure sensor, thermocouple, and differential pressure sensor monitor the pressure entering the test section, the temperature passing through each venturi tube segment, and the pressure difference between the inlet and outlet of the two venturi tubes, respectively. A flow meter measures the flow rate through the test section. A gas recovery device recovers the fluid after the test is completed.

[0015] Furthermore, the volume fraction of CO2 in the fluid was 90%~100%, the inlet pressure of the test section was 8MPa~9MPa, and the inlet temperature of the test section was 35℃~45℃.

[0016] Furthermore, combining semi-empirical formulas Calculate the outflow coefficient CD In the formula, q m is the mass flow rate, Δ P For pressure difference, β The diameter ratio is defined as the diameter of the venturi throat. With pipe inner diameter The ratio, A The area of ​​the throat of the Venturi tube. A =π d 2 / 4, r The fluid density at the inlet. e The coefficient of expansion is determined by the formula. Solve e For mass flow q m and related parameters By performing linear fitting, slopes applicable to different operating conditions can be obtained. k , The structural dimensions of the Venturi tube are determined, and k Substituting into the semi-empirical formula yields the outflow coefficient. CD ; the pressure difference Δ P Substitution Combined with the obtained outflow coefficient CD The calculated mass flow rate is obtained. q m1.

[0017] Compared with existing technologies, this invention has at least the following beneficial effects: This invention constructs a three-stage Venturi tube series structure, which realizes the controllable transcritical phase transition of high CO2-containing fluid from the supercritical state to the gaseous state through step-by-step pressure reduction, solving the technical bottleneck of uncontrollable phase transition near the critical point in single-stage throttling, and providing a standardized platform for the study of throttling characteristics of fluids near the critical point; at the same time, it provides a high-precision phase transition monitoring system, which adopts a multi-sensor array deployed at the inlet and outlet of each stage of Venturi tube combined with a high-speed data acquisition system, which helps to realize the real-time accurate calculation of the Joule-Thomson coefficient, with the error between the measured value and the theoretical value being <5%.

[0018] This invention further proposes a transcritical flow measurement algorithm based on density dynamic compensation. By using the measured fluid temperature and pressure at the inlet and outlet of the throttling tube, the specific volume and density at the inlet and outlet are obtained using the equation of state. The expandability coefficient is then obtained to correct the influence of gas volume changes caused by pressure variations on flow measurement. This significantly reduces the measurement error of traditional differential pressure flowmeters when density fluctuates drastically. The flow rate is calculated using a semi-empirical formula with a relative error of ≤15%.

[0019] Furthermore, this invention verified the applicability of the device under actual operating conditions by controlling CO2 volume fraction (90%-100%), inlet pressure (8-9 MPa), temperature (35-45℃), and flow rate variables. A transcritical temperature and pressure prediction model was established, revealing that increased CO2 purity leads to a 20% increase in temperature drop and increased pressure causes an earlier shift in the critical phase transition position, providing real data support for the design of oil displacement injection parameters under field operating conditions.

[0020] Furthermore, the device described in this invention integrates a working fluid circulation and data measurement system, adopts a compact design, is easy to operate, can realize the recycling of the working fluid, and combines experimental cost-effectiveness with operational safety.

[0021] Furthermore, the water bath provides a constant temperature and heat capacity environment for the gas cylinder. Water has a high specific heat capacity, which can effectively absorb or release heat and buffer fluctuations in the ambient temperature. When it is necessary to change the set temperature, the water can transfer heat to the gas cylinder or absorb heat from the gas cylinder more quickly, shortening the time required to reach the target temperature and improving efficiency. In addition, the water makes the temperature very uniform through convection, ensuring that the entire gas cylinder is at the same temperature.

[0022] Furthermore, the gas supply device is a first gas cylinder filled with the test gas of a defined composition, or the gas supply device is multiple gas cylinders filled with different gases, each gas cylinder is connected to a mixer, and the outlet of the mixer or the outlet of the first gas cylinder is connected to a temperature regulating buffer device via a booster pump; any proportion of mixed gas can be customized according to experimental or process requirements, and the booster pump will increase the gas pressure from the gas cylinder or mixer to the required higher working pressure. After the booster pump is connected to the temperature regulating buffer device, it effectively suppresses the small pulses and pressure fluctuations that may be generated during the booster pumping process, providing a stable pressure source for the test section. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the device of the present invention; Figure 2a This is a schematic diagram of the overall structure of the test section; Figure 2b This is a schematic diagram of a Venturi tube structure; Figure 3 Transcritical phase transition diagram for fluids with high CO2 content; Figure 4 This is a graph showing the results of the linear fitting. In the diagram: 1-First gas cylinder, 2-Second gas cylinder, 3-Third gas cylinder, 4-Fourth gas cylinder, 5-Booster pump, 6-Water bath, 7-Regulating valve, 8-Test section, 9-K-type thermocouple, 10-Pressure sensor, 11-Differential pressure sensor, 12-Data acquisition system, 13-Computer, 14-Flow meter, 15-Safety valve, 16-Pressure gauge, 17-Contraction section, 18-Throat, 19-Expansion section. Detailed Implementation

[0024] 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, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The present invention provides a device for realizing transcritical phase change and flow measurement of high CO2 fluid, comprising a gas supply device, a booster pump, a temperature control buffer device, a test section, a flow meter, and a gas recovery device connected sequentially along the gas flow direction; the test section includes three venturi tubes with the same structure connected in series, a pressure sensor is installed at the inlet of the test section, and thermocouples and differential pressure sensors are installed at the inlet and outlet of each venturi tube.

[0026] As an optional embodiment, the gas supply device is a first gas cylinder filled with a gas to be tested with a determined composition, or the gas supply device is multiple gas cylinders filled with different gases, each gas cylinder is connected to a mixer, and the outlet of the mixer or the outlet of the first gas cylinder is connected to a temperature regulating buffer device via a booster pump; the gas ratio can be flexibly configured at any time.

[0027] The space for containing the mixed gas includes a second gas cylinder and a third gas cylinder. The temperature control device includes a water bath. The second gas cylinder and the third gas cylinder are arranged in the water bath. The second gas cylinder and the third gas cylinder can be filled with a gas filling chamber, which is arranged in the water bath.

[0028] Example 1, as Figure 1This invention discloses a device for measuring transcritical phase change and flow rate of high CO2-containing fluids. The device includes a gas supply and storage module, a test section 8, and a data acquisition module. The gas supply and storage module comprises a first gas cylinder 1, a booster pump 5, a second gas cylinder 2, a third gas cylinder 3, a water bath 6, a regulating valve 7, and a fourth gas cylinder 4. The first gas cylinder 1 stores a mixture of CO2 and CH4. To investigate the effects of different components on the throttling temperature drop and pressure drop characteristics of the fluid, the CO2 volume fractions are 90%, 95%, and 100%. After being pressurized by the booster pump 5 (model STD25CL), the mixture is delivered to the second gas cylinder 2 and the third gas cylinder 3, which are placed in the water bath 6 to regulate the temperature. Based on the dimensions of other components, the water bath 6 in this embodiment has a length of 1.6m, a width of 0.5m, and a height of 0.5m. To investigate the effects of changes in inlet pressure and temperature on the throttling temperature drop and pressure drop characteristics, the fluid must reach the set inlet pressure and temperature before flowing through the test section 8. When the inlet temperature is 40℃, the inlet pressure is changed to 8MPa, 8.5MPa, and 9MPa. When the inlet pressure is 8MPa, the inlet temperature is changed to 35℃, 40℃, and 45℃.

[0029] The mixed fluid enters the test section 8 via regulating valve 7, and after throttling, it enters the fourth gas cylinder 4 for recycling. The effect of mass flow rate on the throttling temperature drop and pressure drop characteristics is investigated. Six mass flow rates are selected for experiments under each component, pressure, and temperature condition. When the pressure in the gas supply and storage equipment and pipelines exceeds the set safety value, safety valve 15 automatically opens to release pressure. Pressure gauges 16 are installed at the outlets of the first gas cylinder 1 and the fourth gas cylinder 4 to determine the remaining fluid in the cylinders, whether the pipelines are blocked or leaking, etc., providing a reference for system maintenance and fluid replenishment. All the above components are connected by stainless steel flexible hoses, increasing the flexibility of space between devices. Threaded connections are used at the joints, and PTFE tape is wrapped around the threads to ensure increased airtightness.

[0030] Reference Figure 2a and Figure 2b As shown, test section 8 consists of three venturi tubes connected in series, with adjacent venturi tubes connected by a clamp. Each venturi tube includes a contraction section 17, a throat 18, and an expansion section 19, with structural parameters of 50 mm in length, 1.1 mm in diameter of throat 18, 5 mm in length of throat 18, 4 mm in inner diameter of the tube, and both the contraction angle and the expansion angle are 30°.

[0031] Test section 8 is equipped with multiple K-type thermocouples 9, pressure sensors 10, and differential pressure sensors 11, installed at the inlet and outlet of each venturi section, respectively, for measuring temperature, pressure, and differential pressure. The K-type thermocouples have a measurement range of 0-200℃ and an accuracy of ±0.5℃; the Rosemount pressure sensors have a range of 0-20MPa and an accuracy of ±0.075%; and the Rosemount differential pressure sensors have a range of 0-1MPa and an accuracy of ±0.075%, accurately capturing parameter changes during the throttling process. A flow meter is located at the outlet of the test section, using a RHEONIK Coriolis mass flow meter 14 with a range of 0-0.17 kg / s to measure fluid flow rate, with an accuracy of ±0.1%.

[0032] The data acquisition module includes an NI data acquisition system 12 and a computer 13, with a sampling frequency of 100Hz and a sampling duration of 30s. The data acquisition system 12 connects to each sensor and transmits the acquired data to the computer 13 for real-time recording using LabVIEW software.

[0033] As described above, the feasible experimental parameters are as follows: the volume fraction of CO2 in the fluid is 90% to 100%, the inlet pressure of test section 8 is 8 MPa to 9 MPa, and the inlet temperature of test section 8 is 35°C to 45°C.

[0034] Example 2: This invention provides a method for measuring transcritical phase change and flow rate of high CO2-content fluid. A gas supply device and a booster pump 5 inject fluid at a set pressure into a temperature-regulating buffer device. The temperature-regulating buffer device adjusts the fluid temperature. The mixed fluid enters test section 8 with a set composition, pressure, and temperature. Pressure sensor 10, thermocouple 9, and differential pressure sensor 11 monitor the pressure entering test section 8, the temperature passing through each venturi tube segment, and the pressure difference between the inlet and outlet of the two venturi tubes, respectively. Flow meter 14 measures the flow rate through test section 8. A gas recovery device recovers the fluid after the test is completed. The specific process is as follows: First, replace the first gas cylinder 1 with an argon cylinder. Use argon to purge the air from the pipeline and bring the overall pipeline pressure to above 9 MPa. Close the first gas cylinder 1 and check for leaks at the pipeline connections with soapy water. If no bubbles are generated at the pipeline connections and the pipeline pressure remains stable for one hour, the system is well-sealed. Then, replace the first gas cylinder 1 with a CO2 and CH4 mixture cylinder. Connect the vacuum pump (VRD-8) to the pipeline and extract the argon from the pipeline. Open the first gas cylinder 1 and use the booster pump 5 to fill the second gas cylinder 2 and the third gas cylinder 3 with gas, while simultaneously filling and heating the water bath 6 with water. When the gas pressure and temperature in the second gas cylinder 2 and the third gas cylinder 3 reach the required inlet conditions, close the first gas cylinder 1. Adjust the opening of valve 7 to control the fluid flow rate, allowing the fluid to pass through test section 8. After collecting pressure, differential pressure, temperature, and flow rate data, begin the next operating condition and repeat the above steps.

[0035] By mapping the temperature and pressure at different measuring points to a three-phase diagram, the phase change pattern of the fluid can be intuitively presented. When the CO2 volume fraction is 95%, the three-phase diagram of the mixed fluid is as follows: Figure 3 As shown, when the inlet conditions are 8 MPa and 40℃, the fluid flows through the test section at different mass flow rates, and the temperature and pressure at four measuring points are obtained. Plotting these values ​​onto a three-phase diagram visually illustrates the fluid phase change pattern. When the flow rate is low, the decrease in fluid pressure and temperature is limited, and the fluid remains in a supercritical state after multiple throttling operations. As the flow rate continues to increase, the supercritical fluid gradually transforms into a gaseous state after multiple throttling operations. Multi-stage throttling precisely controls the phase change path of the supercritical fluid through progressive pressure reduction, allowing it to bypass the gas-liquid two-phase region and directly and smoothly transition to a single-phase gaseous state. This controllability fundamentally avoids a series of engineering risks such as liquid precipitation, ice blockage, erosion, and flow instability caused by crossing the two-phase region during single-stage drastic throttling. Simultaneously, distributing the significant temperature drop across multiple stages makes the entire testing process gentler, effectively protecting equipment safety. This is a superior solution for achieving safe and reliable throttling control of complex fluids.

[0036] Because of the high fluid velocity and small heat exchange area in the pipeline, the fluid flow through test section 8 approximates an adiabatic throttling process. The Jørn-Thomson coefficient is often used to describe the relationship between temperature and pressure changes during isenthalpic (adiabatic and without external work) throttling of a fluid. Based on the definition of the Jørn-Thomson coefficient... In the formula, m JT is the scorch coefficient; T For temperature, P For pressure, H This represents an isenthalpic process. By fitting the linear relationship between temperature drop and pressure drop during the throttling process, the scorch coefficient is obtained under different working fluid compositions, test section inlet temperatures, and test section inlet pressures.

[0037] Referring to Table 1, based on the comparison between the experimental and theoretical values ​​of the scorch-Thomson coefficient of the device described in this application, the experimental scorch-Thomson coefficient values ​​agree well with the theoretical calculation values, with an error of less than 5%. The scorch-Thomson coefficient increases with increasing CO2 volume fraction and decreasing inlet pressure of the test section. With increasing inlet temperature of the test section, the scorch-Thomson coefficient first increases and then decreases. Near the critical point, the scorch-Thomson coefficient is sensitive to changes in temperature and pressure, mainly due to the sudden increase in isobaric specific heat capacity. The scorch-Thomson coefficient can be used for transcritical temperature and pressure prediction.

[0038] Table 1 Comparison of experimental scorch coefficient and theoretical value

[0039] For a steady-state fluid flowing through a Venturi tube, according to Bernoulli's equation and the continuity equation, the mass flow rate and pressure difference have the following relationship: In the formula,q m is the mass flow rate. CD The outflow coefficient, Δ, takes into account the difference between the actual flow rate and the theoretical flow rate. P For pressure difference, β The diameter ratio is defined as the diameter of the venturi throat. With pipe inner diameter The ratio, A The area of ​​the throat of the Venturi tube. A =π d 2 / 4, r 1 represents the fluid density at the inlet of the test section. e The coefficient of expansion is _____. e Used to correct for the effect of gas volume changes due to pressure variations on flow rate measurement; through the formula Solve e In the formula, v 1. v 2. r 1. r 2 represents the specific volume and density of the fluid at the inlet and outlet of the test section, respectively. The temperatures of the fluid at the inlet and outlet of the test section have been measured using the instrument. T 1. T 2 and pressure P 1. P 2. Then, the state equations (such as the Penn-Robinson equation and the Soawe-Redlich-Kuang equation) can be used to obtain the result. v 1. v 2. r 1. r 2. Near the critical point, the specific volume of CO2 is sensitive to changes in temperature and pressure. Volume expansion is more significant than in ideal gases. Unlike other phases, the expansibility coefficient of CO2 in the high-pressure near-critical and supercritical states is greater than 1. The experimentally obtained expansibility coefficient range for supercritical high-CO2 fluids is 1-1.2. The three throttling tubes have identical internal structures and equal fluid mass flow rates. Data from the first throttling tube with mass flow rates of 0.005-0.025 kg / s are selected for detailed analysis. At some high flow rates, the fluid undergoes a transcritical process. Assuming that the influence of the expansibility coefficient and the inlet density of the test section is fully considered, an outflow coefficient applicable to different operating conditions can be obtained, i.e., the outflow coefficient is a constant. Because the dimensions of the Venturi tube structure are fixed, i.e. A and β If it is a constant, then Can be rewritten as ,in .according to Relevant parameters under different working fluid compositions, test section inlet temperature, and test section inlet pressure. With mass flow q By performing linear fitting on m, a slope applicable to different operating conditions can be obtained.k .according to ,Will k Substituting into the above formula yields the outflow coefficient. CD .

[0040] The fitting results are as follows Figure 4 As shown, each data point has a high degree of fit with the fitted line, and the goodness of fit R0 is high. 2 It approaches 1. Assuming this holds, a unique slope can be obtained. k =615992 is suitable for different working conditions. The slope can be determined based on the structural dimensions of the venturi tube. k Substitute into the formula The outflow coefficient can be obtained. CD =0.91. The pressure difference Δ P Substitution Combined with the obtained outflow coefficient CD The calculated mass flow rate is obtained. q m1. The actual value of mass flow rate. q m and calculated value q Comparative analysis using m1 showed that, excluding a few outlier data points (all at low flow rates), the relative error for 95% of the data points was within 15%. The semi-empirical formula fully considers the impact of changes in fluid inlet and outlet density on the accuracy of flow measurement. This measurement method can achieve accurate flow measurement under transcritical conditions.

[0041] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A device for realizing transcritical phase change and flow rate measurement of high CO2-content fluids, characterized in that, The gas supply device, booster pump (5), temperature control buffer device, test section (8), flow meter (14) and gas recovery device are connected in sequence along the gas flow direction; the test section (8) includes three venturi tubes with the same structure connected in series, and a pressure sensor (10) is installed at the inlet of the test section (8), and thermocouples (9) and differential pressure sensors (11) are installed at the inlet and outlet of each venturi tube.

2. The device for realizing transcritical phase change and flow rate measurement of high CO2-content fluid according to claim 1, characterized in that, Each Venturi tube includes a contraction section (17), a throat (18), and an expansion section (19). The throat (18) of each Venturi tube has a diameter of 1.1 mm, a length of 5 mm, an inner diameter of 4 mm, and a contraction angle and an expansion angle of 30°.

3. The device for realizing transcritical phase change and flow rate measurement of high CO2-content fluid according to claim 1, characterized in that, Thermocouple (9), pressure sensor (10), differential pressure sensor (11) and flow meter (14) are connected to data acquisition system (12), which is connected to computer (13).

4. The device for realizing transcritical phase change and flow rate measurement of high CO2-content fluid according to claim 1, characterized in that, The gas supply device is a first gas cylinder (1), which is filled with a gas to be tested with a determined composition, or the gas supply device is a plurality of gas cylinders filled with different gases, each gas cylinder is connected to a mixer, and the outlet of the mixer or the outlet of the first gas cylinder (1) is connected to a temperature regulating buffer device via a booster pump (5).

5. The device for realizing transcritical phase change and flow rate measurement of high CO2-content fluids according to claim 1, characterized in that, The temperature regulating buffer device is provided with a space for containing the mixed gas, and a temperature regulating device is provided outside the space. The outlet of the temperature regulating buffer device is provided with a regulating valve (7).

6. The device for realizing transcritical phase change and flow measurement of high CO2-content fluid according to claim 5, characterized in that, The space for containing the mixed gas includes a second gas cylinder (2) and a third gas cylinder (3), and the temperature control device includes a water bath (6), in which the second gas cylinder (2) and the third gas cylinder (3) are disposed.

7. The device for realizing transcritical phase change and flow rate measurement of high CO2-content fluid according to claim 1, characterized in that, The outlet of the test section (8) is connected to a valve and a safety valve (15) in sequence. The outlet of the safety valve (15) is connected to a gas recovery device, and a pressure gauge (16) is installed on the gas recovery device.

8. The device for realizing transcritical phase change and flow measurement of high CO2-content fluid according to claim 1, characterized in that, The gas supply device is used to provide a mixed fluid of CO2 and CH4 containing different volume fractions of CO2.

9. A method for measuring transcritical phase change and flow rate of high CO2-content fluids, characterized in that, The fluid at a set pressure is supplied to the temperature-regulating buffer device by the gas supply device and the booster pump (5). The temperature-regulating buffer device adjusts the temperature of the fluid. The mixed fluid enters the test section (8) with the set composition, pressure and temperature. The pressure sensor (10), thermocouple (9) and differential pressure sensor (11) monitor the pressure entering the test section (8), the temperature of each venturi tube, and the pressure difference between the inlet and outlet of the two venturi tubes, respectively. The flow meter (14) measures the flow rate through the test section (8). The gas recovery device recovers the fluid after the test is completed.

10. The method for transcritical phase transition and flow rate measurement of high CO2-content fluid according to claim 9, characterized in that, Combining semi-empirical formulas Calculate the outflow coefficient Cd In the formula, q m is the mass flow rate, Δ P For pressure difference, β The diameter ratio is defined as the diameter of the venturi throat. With pipe inner diameter The ratio, A The area of ​​the throat of the Venturi tube. A =π d 2 / 4, ρ The fluid density at the inlet. ε The coefficient of expansion is determined by the formula. Solve ε For mass flow q m and related parameters By performing linear fitting, slopes applicable to different operating conditions can be obtained. k , The structural dimensions of the Venturi tube are determined, and k Substituting into the semi-empirical formula yields the outflow coefficient. Cd ; the pressure difference Δ P Substitution Combined with the obtained outflow coefficient Cd The calculated mass flow rate is obtained. q m1.

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