Method and device for measuring flow heat exchange characteristic of supercritical carbon dioxide in tiny circular channel

Abstract

The invention provides a method and a device for measuring the flowing heat exchange characteristic of supercritical carbon dioxide in a tiny circular channel, and belongs to the field of research on the flowing heat exchange characteristic of supercritical fluid. The problem that parameters such as temperature, pressure and flow velocity in a tiny circular channel are difficult to measure by traditional measuring means is solved. The invention discloses a method for measuring the flowing heat exchange characteristic of supercritical carbon dioxide in a tiny circular channel. The method comprises the following steps: enabling the supercritical carbon dioxide to flow into a testing section of the tiny circular channel at preset pressure and flow; measuring temperature, pressure and flow velocity data of different positions of the micro circular channel test section in real time; according to the data, supercritical carbon dioxide flow heat exchange characteristic parameters are calculated through a pre-established model; and changing the working condition of the supercritical carbon dioxide supply system to obtain the flow heat exchange characteristic parameters of the supercritical carbon dioxide under different working conditions. The device is mainly used for measuring the flow heat exchange characteristic.

Description

Technical Field

[0001] This invention belongs to the field of supercritical fluid flow heat transfer characteristics research, and in particular relates to a method and apparatus for measuring the flow heat transfer characteristics of supercritical carbon dioxide in a tiny circular channel. Background Technology

[0002] With the continuous development of energy technology, supercritical carbon dioxide, due to its excellent thermodynamic properties, has shown great application potential in energy power, refrigeration and other fields. Micro-circular channels, due to their compact structure and high heat exchange efficiency, are widely used in compact heat exchangers and other equipment. Studying the flow and heat transfer characteristics of supercritical carbon dioxide within micro-circular channels is of great significance for optimizing the design and operation of related equipment.

[0003] However, there are currently many difficulties in measuring the heat transfer characteristics of supercritical carbon dioxide flow in tiny circular channels. The small size of these channels makes it difficult to accurately measure parameters such as temperature, pressure, and flow rate using conventional methods. Furthermore, the physical properties of supercritical carbon dioxide vary complexly under different operating conditions, and traditional measurement methods cannot meet the requirements for high-precision measurement. This results in large errors in existing measurement results, failing to provide reliable data support for related research and engineering applications. Summary of the Invention

[0004] In view of this, the present invention aims to provide a method and apparatus for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a small circular channel, so as to solve the problem that traditional measurement methods are difficult to measure parameters such as temperature, pressure and flow rate in a small circular channel.

[0005] To achieve the above objectives, the present invention employs the following technical solution: According to one aspect of the present invention, a method for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a micro-circular channel is provided, comprising the following steps: Supercritical carbon dioxide was introduced into the test section of a tiny circular channel at a predetermined pressure and flow rate. After the supercritical carbon dioxide flow and heat exchange in the micro-circular channel test section reach a stable state, the temperature, pressure and flow rate data at different locations in the micro-circular channel test section are measured in real time. Based on the data, the flow heat transfer characteristics of supercritical carbon dioxide in a tiny circular channel were calculated using a pre-established mathematical model. By changing the operating conditions of the supercritical carbon dioxide supply system and repeating the above steps, the flow and heat transfer characteristics of supercritical carbon dioxide in the test section of the micro-circular channel under different operating conditions can be obtained.

[0006] Furthermore, the mathematical model includes a calculation model for the heating efficiency of the micro-circular channel test section, a calculation model for the local fluid enthalpy, a calculation model for the inner wall temperature, a calculation model for the local heat transfer coefficient, and / or a calculation model for the friction factor.

[0007] Furthermore, the model formula for calculating the heating efficiency is as follows: In the formula, U is the heating voltage and I is the heating current. The supercritical carbon dioxide heat flux density, The heating area is given; the heat flux density q is calculated as follows: In the formula For quality flux; Inner diameter; The heating area; and The fluid enthalpy at the outlet and inlet of the test section of the tiny circular channel is given; the heating area is calculated as follows: In the formula This refers to the heating length.

[0008] Furthermore, the local fluid enthalpy calculation model is as follows: In the formula For local heating length, For heating length, and The fluid enthalpy at the outlet and inlet of the test section of the tiny circular channel.

[0009] Furthermore, the inner wall temperature calculation model is as follows: In the formula T w,i and T w,o The inner and outer wall temperatures of the test section of the tiny circular channel; Inner diameter Outer diameter; is the thermal conductivity.

[0010] Furthermore, the calculation model for the local heat transfer coefficient is as follows: In the formula T b The temperature of the fluid within the test section of the tiny circular channel.

[0011] Furthermore, the friction factor calculation model is as follows: In the formula, This refers to the frictional pressure drop within the test section of a tiny circular channel. The length of the tiny circular channel test segment. For the density of the fluid, The velocity of the fluid.

[0012] According to another aspect of the present invention, an apparatus is provided for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a small circular channel as described above, comprising: A carbon dioxide cylinder has its outlet connected to the inlet of a heater via a pump. The heater outlet is connected to the inlet of a micro-circular channel test section via a first gas regulating valve and a carbon dioxide flow meter. A second gas regulating valve is installed at the outlet of the micro-circular channel test section. The micro-circular channel test section has thermocouples and pressure sensors installed at both its inlet and outlet, with several pairs of thermocouples arranged opposite each other on its outer wall. The power supply is connected to the tiny circular channel test section; The data acquisition and processing system, connected to thermocouples and pressure sensors, is used to acquire and process data.

[0013] Furthermore, the thermocouples on the outer wall of the tiny circular channel test section are fixed with insulating high-temperature tape.

[0014] Furthermore, the interval between each pair of adjacent thermocouples is 5 cm.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This method, through the design of "predetermined pressure and flow rate," can strictly control the initial state parameters (such as pressure and flow rate) of supercritical carbon dioxide, ensuring the repeatability and comparability of experimental conditions. This lays the foundation for studying the flow and heat transfer laws under different operating conditions and avoids experimental errors caused by parameter fluctuations. Measuring data after the flow and heat transfer have reached a steady state can avoid interference from unsteady-state processes. Temperature, pressure, and flow rate data under steady-state conditions can better reflect the true characteristics of supercritical carbon dioxide under specific operating conditions, improving the reliability of the data.

[0016] 2. This method measures temperature, pressure, and flow rate data in a small circular channel test section, and calculates flow heat transfer characteristic parameters using a model. This transforms experimental data into quantifiable and comparable physical indicators, improving the accuracy and efficiency of parameter calculation and providing experimental verification for theoretical research.

[0017] 3. By changing the operating conditions of the supply system, the flow and heat transfer characteristics under different conditions can be obtained, covering the parameter range of supercritical carbon dioxide in practical applications. This helps to reveal parameter sensitivity and provide reference data under multiple operating conditions for engineering design.

[0018] 4. The flow and heat transfer mechanism of supercritical fluids in microchannels differs significantly from that on a macroscopic scale. This technology can improve relevant theoretical models through systematic experimental data, especially for the analysis of complex phenomena such as phase change heat transfer and resistance characteristics of supercritical carbon dioxide at the microscale, providing support for the establishment of more accurate engineering calculation models.

[0019] 5. By measuring the temperature on the outside of the test section of the micro-circular channel and converting it using a model, the problem of traditional sensors being unable to be effectively used in micro-channel conditions can be solved, providing a new approach for the study of microchannel flow characteristics. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the structure of a device for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a tiny circular channel, as described in this invention.

[0021] 1. Carbon dioxide cylinder; 2. Pump; 3. Heater; 4. First gas regulating valve; 5. Carbon dioxide flow meter; 6. Micro-circular channel test section; 7. Second gas regulating valve. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other, and the described embodiments are only some embodiments of the present invention, not all embodiments.

[0023] It should be noted that the descriptions of "left," "right," "left side," "right side," "upper part," "lower part," "top," and "bottom" in this invention are defined based on the orientation or positional relationships shown in the accompanying drawings. They are merely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the described structure must be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0024] In the description of this invention, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" 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 direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] Referring to the accompanying drawings, this embodiment provides a method for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a small circular channel, comprising the following steps: S1. First, a measurement device needs to be built, which includes a supercritical carbon dioxide supply system, a micro-circular channel test section 6, a parameter measurement system, and a data acquisition and processing system. The supercritical carbon dioxide supply system is used to provide supercritical carbon dioxide at a stable pressure and flow rate; the micro-circular channel test section 6 is the core component for conducting flow heat transfer experiments; the parameter measurement system includes temperature and pressure sensors arranged at different locations in the micro-circular channel test section to measure the temperature and pressure parameters of the supercritical carbon dioxide; the data acquisition and processing system is used to collect data from the parameter measurement system and perform calculations and analysis.

[0026] S2, adjust the supercritical carbon dioxide supply system to the required operating conditions, so that supercritical carbon dioxide flows into the micro-circular channel test section 6 at a predetermined pressure and flow rate; S3. After the supercritical carbon dioxide flow and heat exchange in the micro-circular channel test section 6 reach a stable state, the temperature, pressure and flow rate data at different locations in the micro-circular channel test section 6 are measured in real time through the parameter measurement system. S4. Based on the data, calculate the flow heat transfer characteristics parameters of supercritical carbon dioxide in the micro-circular channel using a pre-established mathematical model. S5. Change the operating conditions of the supercritical carbon dioxide supply system and repeat steps S2-S4 to obtain the flow and heat transfer characteristics parameters of supercritical carbon dioxide in the micro-circular channel test section 6 under different operating conditions.

[0027] In this embodiment, the mathematical model includes a calculation model for the heating efficiency of the micro-circular channel test section 6, a calculation model for the local fluid enthalpy, a calculation model for the inner wall temperature, a calculation model for the local heat transfer coefficient, and / or a calculation model for the friction factor. Unless otherwise specified, all parameters involved are specific to the micro-circular channel test section 6.

[0028] In this embodiment, the model calculation formula for the heating efficiency is: In the formula, U is the heating voltage in volts (V), and I is the heating current in amperes (A). The supercritical carbon dioxide heat flux density, The heating area is expressed in square meters (m²). 2 Carbon dioxide heat flux density The calculation is as follows: In the formula, G is the carbon dioxide mass flux, in kg / (m³). 2 ·s); A is the inner diameter; A is the heating area, in meters. 2 ; and The fluid enthalpy at the outlet and inlet of test section 6 of the micro-circular channel is given in J / kg; the heating area is calculated as follows: In the formula The heating length is in meters (m).

[0029] In this embodiment, the local fluid enthalpy calculation model is as follows: In the formula The length of the localized heating section is in meters. Heating length, in meters. and The fluid enthalpy at the outlet and inlet of the micro-circular channel test section 6 is expressed in J / kg.

[0030] In this embodiment, the inner wall temperature calculation model is as follows: In the formula T w,i and T w,o The inner and outer wall temperatures of the test section 6 of the micro-circular channel are given in Kelvin. Inner diameter, unit: meters (m). Outer diameter, in meters (m); is the thermal conductivity, in W / (m·K).

[0031] In this embodiment, the local heat transfer coefficient calculation model is as follows: In the formula T b The temperature of the fluid within section 6 of the tiny circular channel test is measured in Kelvin.

[0032] In this embodiment, the friction factor calculation model is as follows: In the formula, L is the frictional pressure drop within the micro-circular channel test section 6, in Pa; L is the length of the micro-circular channel test section 6, in meters. The density of the fluid, in kg / m³ 3 , The velocity of the fluid is expressed in m / s.

[0033] This method measures temperature, pressure, and flow velocity data in a micro-circular channel test section, and calculates flow and heat transfer characteristic parameters using a model, transforming experimental data into quantifiable and comparable physical indicators. This improves the accuracy and efficiency of parameter calculations, providing experimental verification for theoretical research. By measuring temperature on the outside of the micro-circular channel test section and converting it using a model, the method overcomes the limitation of traditional sensors in microchannel conditions, offering a new approach to studying microchannel flow characteristics. This makes the measurement of various parameters possible.

[0034] In this embodiment, the outlet of carbon dioxide cylinder 1 is connected to the inlet of heater 3 via pump 2. The outlet of heater 3 is connected to the inlet of micro-circular channel test section 6 via a first gas regulating valve 4 and a carbon dioxide flow meter 5. A second gas regulating valve 7 is installed at the outlet of micro-circular channel test section 6. Thermocouples and pressure sensors are installed at both the inlet and outlet of micro-circular channel test section 6, with several pairs of thermocouples arranged opposite each other on the outer wall. Carbon dioxide cylinder 1 stores liquid carbon dioxide. Pump 2 is a high-pressure pump used to pressurize the liquid carbon dioxide and deliver it to heater 3. Heater 3 is a preheater; heating the liquid carbon dioxide through the preheater allows it to reach a supercritical state, providing the prerequisite for subsequent measurement. The first gas regulating valve 4 is used to regulate the pressure of the supercritical carbon dioxide to meet the needs of different experimental conditions. During installation, carbon dioxide cylinder 1 and pump 2 are connected via pipelines to ensure a good seal and prevent leakage. Pump 2 is activated to extract and pressurize carbon dioxide from carbon dioxide cylinder 1, then delivers it to heater 3. Heater 3 must meet predetermined heating and reliability requirements. In heater 3, carbon dioxide is heated to a supercritical state via electric heating. Other types of heaters can also be used as needed, all within the spirit of this invention. After heating to the predetermined state, the first gas regulating valve 4 is adjusted to bring the pressure of the supercritical carbon dioxide to the set value required for the experiment. The output end of heater 3 is connected to the micro-circular channel test section 6 via a pipeline. This pipeline must meet the requirements of high temperature and high pressure resistance. It is also necessary to check whether the micro-circular channel test section 6 is insulated from other pipelines. After ensuring that the micro-circular channel test section 6 can work normally, the DC power supply is turned on, and the heating power is adjusted to the set value to simulate the actual heat exchange conditions. As mentioned above, the supercritical carbon dioxide supply system refers to the combination of carbon dioxide cylinder 1, pump 2, and heater 3.

[0035] The micro-circular channel test section 6 is made of stainless steel, with an inner diameter of 1-2 mm and a length of 550 mm. Copper plates at both ends of the micro-circular channel test section 6 are connected to a DC power supply to heat the supercritical carbon dioxide inside the channel, simulating actual heat exchange conditions. Simultaneously, thermocouples and pressure sensors are placed at the inlet and outlet positions of the micro-circular channel test section 6, respectively, and thermocouples are placed on the outer wall of the channel to measure various parameters of the supercritical carbon dioxide.

[0036] The power supply is connected to the micro-circular channel test section 6; the power supply here is the DC power supply mentioned above, which is connected to both ends of the micro-circular channel test section 6 through a copper plate, and can heat the supercritical carbon dioxide in the channel to simulate the actual heat exchange conditions.

[0037] The data acquisition and processing system, connected to thermocouples and pressure sensors, is used to collect and process data. High-precision K-type thermocouples are used, with a measurement accuracy of 0.5%; diaphragm-type pressure sensors are used, with a measurement accuracy of 0.5%. All sensors are connected to the data acquisition and processing system via signal transmission lines. A high-performance data acquisition card and computer are employed. The data acquisition card collects analog signals transmitted from the parameter measurement system and converts them into digital signals; the computer is equipped with dedicated data processing software capable of real-time display, storage, and analysis of the acquired data. It calculates the flow heat transfer characteristics parameters of supercritical carbon dioxide using a built-in mathematical model and generates corresponding charts and reports.

[0038] In this embodiment, the thermocouple on the outer wall of the micro-circular channel test section 6 is fixed with insulating high-temperature tape. This fixing method is suitable for the working conditions of the micro-circular channel test section 6.

[0039] In this embodiment, the interval between any two adjacent thermocouple pairs is 5 cm. By arranging them at equal intervals, measurements can be performed in segments throughout the entire process, ensuring the authenticity and controllability of the data, preventing large errors, and allowing the data from the sensors to serve as mutual references.

[0040] The sensors, controllers, and control programs mentioned above are all existing technologies and will not be elaborated upon.

[0041] The embodiments of the present invention disclosed above are merely illustrative of the invention. These embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A method for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a tiny circular channel, characterized in that, Includes the following steps: Supercritical carbon dioxide was allowed to flow into the micro-circular channel test section (6) at a predetermined pressure and flow rate. After the supercritical carbon dioxide flow and heat exchange in the micro-circular channel test section (6) reach a stable state, the temperature, pressure and flow rate data at different locations in the micro-circular channel test section (6) are measured in real time. Based on the data, the flow heat transfer characteristics of supercritical carbon dioxide in a tiny circular channel were calculated using a pre-established mathematical model. By changing the operating conditions of the supercritical carbon dioxide supply system and repeating the above steps, the flow heat transfer characteristics parameters of supercritical carbon dioxide in the micro-circular channel test section (6) under different operating conditions can be obtained.

2. The method for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a micro-circular channel according to claim 1, characterized in that: The mathematical model includes a calculation model for the heating efficiency of the micro-circular channel test section (6), a calculation model for the local fluid enthalpy, a calculation model for the inner wall temperature, a calculation model for the local heat transfer coefficient, and / or a calculation model for the friction factor.

3. A method for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a micro-circular channel according to claim 2, characterized in that: The formula for calculating the heating efficiency is as follows: In the formula, U is the heating voltage and I is the heating current. The supercritical carbon dioxide heat flux density, Heating area; heat flux density The calculation is as follows: In the formula For quality flux; Inner diameter; The heating area; and The fluid enthalpy at the outlet and inlet of the micro-circular channel test section (6) is calculated as follows: The heating area is calculated as follows: In the formula This refers to the heating length.

4. The method for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a micro-circular channel according to claim 3, characterized in that: The local fluid enthalpy calculation model is as follows: In the formula For local heating length, For heating length, and The fluid enthalpy at the outlet and inlet of the test section (6) of the tiny circular channel.

5. The method for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a micro-circular channel according to claim 3, characterized in that: The inner wall temperature calculation model is as follows: In the formula T w,i and T w,o The inner and outer wall temperatures of the test section (6) of the micro-circular channel; Inner diameter Outer diameter; is the thermal conductivity.

6. The method for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a micro-circular channel according to claim 5, characterized in that: The local heat transfer coefficient calculation model is as follows: In the formula T b The fluid temperature is measured within the micro-circular channel test section (6).

7. The method for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a micro-circular channel according to claim 2, characterized in that: The friction factor calculation model is as follows: In the formula, The frictional pressure drop within the micro-circular channel test section (6); The length of the tiny circular channel test segment (6) is given. For the density of the fluid, The velocity of the fluid.

8. An apparatus for measuring the heat transfer characteristics of supercritical carbon dioxide flow in a micro-circular channel as described in any one of claims 1-7, characterized in that, include: A carbon dioxide cylinder (1) has its outlet end connected to the inlet end of a heater (3) via a pump (2). The outlet end of the heater (3) is connected to the inlet end of a micro-circular channel test section (6) via a first gas regulating valve (4) and a carbon dioxide flow meter (5). A second gas regulating valve (7) is installed at the outlet end of the micro-circular channel test section (6). Thermocouples and pressure sensors are installed at both the inlet and outlet ends of the micro-circular channel test section (6), and several pairs of thermocouples are arranged opposite each other on the outer wall. The power supply is connected to the micro-circular channel test section (6); The data acquisition and processing system, connected to thermocouples and pressure sensors, is used to acquire and process data.

9. The apparatus according to claim 8, characterized in that: The thermocouples on the outer wall of the tiny circular channel test section (6) are fixed by insulating high-temperature tape.

10. The apparatus according to claim 8, characterized in that: The interval between each pair of thermocouples is 5 cm.

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