Supercritical carbon dioxide flow heat transfer dissimilation experimental device and experimental method

Abstract

The application discloses a supercritical carbon dioxide flow heat transfer differentiation experiment device and an experiment method.The device comprises a main circulation loop which is composed of a liquid storage tank, a filter, a plunger pump, a bladder accumulator, a mass flow meter, a preheating section, an experiment section, a jacketed condenser, a back pressure valve and related pipes and equipment, a condensing system which is composed of the jacketed condenser, a refrigerator and related pipes and equipment, and an electric heating system which is composed of a direct current power supply and related equipment.The application also provides an experiment method of the device.The application can meet the needs of the heat transfer differentiation characteristic experiment research of supercritical carbon dioxide in different flow directions in a vertical circular pipe under forced circulation and natural circulation.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor thermal hydraulics, specifically to an experimental apparatus and method for supercritical carbon dioxide flow heat transfer dissimilarity. Background Technology

[0002] Supercritical carbon dioxide Brayton cycle power generation systems, with their advantages of high flexibility, high power generation efficiency, compact equipment, complete decoupling of thermoelectricity, and ability to meet rapid peak-shaving requirements, represent a major strategic frontier technology poised for a disruptive breakthrough in replacing the currently widely used steam power conversion technology. Meanwhile, advanced nuclear energy systems based on supercritical carbon dioxide Brayton cycles, characterized by high reactor power density, low fuel consumption, zero emissions, simple and compact gas turbine structure, high system efficiency, and low construction costs, have become a key focus of current advanced nuclear reactor research.

[0003] Supercritical carbon dioxide can also be used as a coolant for nuclear reactors. Supercritical carbon dioxide gas-cooled fast reactor coolant has excellent properties, low cost, high safety, good economy, low noise, and compact structure. When combined with supercritical carbon dioxide Brayton cycle, it can achieve higher energy conversion efficiency, making it suitable for nuclear-powered submarines and inland nuclear power plants.

[0004] Supercritical carbon dioxide fluid exhibits drastic property changes at the pseudo-critical point, which, while advantageous for improving cycle efficiency, also introduces phenomena such as heat transfer distortion and flow instability. For example, near the critical point, supercritical carbon dioxide has a high specific heat. Due to the dramatic changes in its properties with pressure and temperature, heat transfer pinch points can form inside the heat exchanger, hindering heat transfer and limiting the improvement of heat transfer efficiency. However, existing research is insufficient, and a reasonable mechanistic explanation for the heat transfer distortion phenomenon has not yet been found. Summary of the Invention

[0005] The purpose of this invention is to provide an experimental apparatus and method for studying the heat transfer dissimilarity phenomenon of supercritical carbon dioxide flow. The experimental apparatus of this invention can conduct experiments on the heat transfer deterioration mechanism of supercritical carbon dioxide in a vertical circular tube under forced circulation and natural circulation conditions, and study the influence of system pressure, mass flow rate, heat flux density, flow direction and inlet temperature on the heat transfer of supercritical carbon dioxide flow.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An experimental apparatus for supercritical carbon dioxide flow heat transfer dissimilatory reaction includes a main circulation loop, a condensation system and an electric heating system;

[0008] The main circulation loop includes a storage tank 1, a first filter 2, a plunger pump 3, a bladder accumulator 4, a first back pressure valve V1, a mass flow meter 5, a regulating valve 16, a preheating section 6, an experimental section 7, a shell-and-tube condenser 8, a second filter 9, a second back pressure valve V2, a first shut-off valve 14, a second shut-off valve 15, a third shut-off valve 17, a fourth shut-off valve 18, a fifth shut-off valve 19, and a sixth shut-off valve 20. The bottom of the storage tank 1 is connected to one end of the first shut-off valve 14 and the second shut-off valve 15. The other end of the first shut-off valve 14 is connected to one end of the first filter 2, and the other end of the first filter 2 is connected to the inlet of the plunger pump 3. The plunger pump 3 outlet is equipped with a bladder accumulator 4, and the other end of the second shut-off valve 15 is connected to the outlet of the bladder accumulator 4. The outlet pipeline of the plunger pump 3 is divided into a main line and a bypass line via the bladder accumulator 4. The outlet bypass is connected to the lower side of the storage tank 1 via the first back pressure valve V1; the mass flow meter 5 is connected to one end of the regulating valve 16; the other end of the regulating valve 16 is connected to the inlet of the preheating section 6; the outlet of the preheating section 6 is connected to the two vertical rising sections and the experimental section 7 via the third shut-off valve 17 and the fourth shut-off valve 18, the two vertical rising sections are connected in parallel with the experimental section 7, the fifth shut-off valve 19 is installed on the first vertical rising section connected to the outlet of the third shut-off valve 17, and the sixth shut-off valve 20 is installed between the outlet of the second vertical rising section connected to the outlet of the first vertical rising section and the outlet of the fourth shut-off valve 18; the outlet of the experimental section 7 is connected to the tube-side inlet of the shell-and-tube condenser 8 via the sixth shut-off valve 20, and the tube-side outlet of the shell-and-tube condenser 8 is connected to the bottom of the storage tank 1 via the second filter 9 and the second back pressure valve V2 in sequence;

[0009] The condensation system includes a shell-and-tube condenser 8, a refrigerator 10, and a coolant regulating valve 21; the outlet of the refrigerator 10 is connected to the shell-side inlet of the shell-and-tube condenser 8 and is provided with a bypass connected by the coolant regulating valve 21, and the other end of the bypass and the shell-side outlet of the shell-and-tube condenser 8 are connected to the inlet of the refrigerator 10.

[0010] The electric heating system includes a preheating section DC power supply 28 and an experimental section DC power supply 29, located on a flat ground; the preheating section DC power supply 28 provides three-point DC heating for the preheating section 6; the experimental section DC power supply 29 provides two-point DC heating for the experimental section 7.

[0011] Preferably, the temperature at which carbon dioxide returns to the storage tank 1 after condensation is controlled by adjusting the cooling temperature of the refrigerator 10 and the coolant regulating valve 21 on the bypass.

[0012] Preferably, the main circulation loop is fixed by a truss structure, the shell-and-tube condenser 8 has a height difference with the experimental section 7, and the shell-and-tube condenser 8 has a height difference with the preheating section 6, resulting in strong natural circulation driving force.

[0013] Preferably, the main circulation loop forms a natural circulation through the driving force generated by the height difference between the cold source jacketed condenser 8 and the heat source preheating section 6 and the experimental section 7, as well as the carbon dioxide density difference. Specifically, the plunger pump 3, the first shut-off valve 14 and the first back pressure valve V1 are closed, and the second shut-off valve 15 is opened, so that the experimental device can switch from forced circulation to natural circulation mode.

[0014] Preferably, the main circulation loop allows supercritical carbon dioxide to flow vertically upward in the experimental section 7 by opening the third shut-off valve 17 and the sixth shut-off valve 20 and closing the fourth shut-off valve 18 and the fifth shut-off valve 19; the main circulation loop also allows supercritical carbon dioxide to flow vertically downward in the experimental section 7 by closing the third shut-off valve 17 and the sixth shut-off valve 20 and opening the fourth shut-off valve 18 and the fifth shut-off valve 19.

[0015] Preferably, the experimental section 7 is a circular tube experimental section, which is directly heated by the DC power supply 29 of the experimental section, and the power control sensitivity is high; T-type patch thermocouples 30 are arranged at preset intervals on the wall of the experimental section 7 to measure the wall temperature, and T-type armored thermocouples 31 are inserted at the center of the inlet and outlet of the experimental section 7 to measure the fluid temperature, so as to monitor the temperature status of the experimental section wall and the fluid in real time; the experimental section 7 can be quickly replaced by quick-release insulating flanges 32 to realize the study of the flow thermal characteristics of experimental sections of different sizes.

[0016] Preferably, the pipes and valves of the main circulation loop and condensation system are wrapped with aerogel insulation cotton for effective heat preservation.

[0017] Preferably, the top of the liquid storage tank 1 is provided with a first safety valve 26, and the outlet of the experimental section 7 is provided with a second safety valve 25, so as to prevent the danger caused by accidental overpressure of the liquid storage tank 1 and the experimental section 7 and ensure personnel safety.

[0018] The experimental method corresponding to the experimental device involves filling the experimental device with water for leak detection, water pressure test, and air tightness test before the experiment begins to ensure that there is no leakage in the circuit under high pressure.

[0019] Before the experiment begins, open all valves in the main circulation loop, turn on the vacuum pump 22 to discharge the gas in the main circulation loop, turn off the vacuum pump 22, close the vacuum pump shut-off valve 11, open the first pressure reducing valve 12, and inject carbon dioxide gas into the storage tank 1 through the carbon dioxide cylinder 23. After the pressure of the carbon dioxide cylinder is balanced with the pressure of the main circulation loop, close the first pressure reducing valve 12 and disconnect the carbon dioxide cylinder 23.

[0020] Open the exhaust valve 27, and close the exhaust valve 27 when the pressure in the main circulation loop is greater than atmospheric pressure. Open the vacuum pump shut-off valve 11, start the vacuum pump 22 again, and discharge the carbon dioxide gas in the main circulation loop. Close the vacuum pump shut-off valve 11 and close the vacuum pump 22. Repeat the above three gas replacement operations.

[0021] Open the second pressure reducing valve 13 and use the liquid carbon dioxide bottle 24 with a siphon tube to fill the storage tank 1 with liquid carbon dioxide until the pressure of the liquid carbon dioxide bottle with the siphon tube is balanced with the pressure of the main circulation loop.

[0022] Turn on the refrigeration unit 10, adjust the refrigeration temperature of the refrigeration unit 10 and the coolant regulating valve 21, and wait until the main circulation loop is full of liquid carbon dioxide. Then close the second pressure reducing valve 13 and disconnect the connection with the liquid carbon dioxide bottle 24 with the siphon tube.

[0023] Open the exhaust port of plunger pump 3 to release carbon dioxide gas, then close the exhaust port of plunger pump.

[0024] Turn on plunger pump 3, adjust the working frequency of plunger pump, adjust the first back pressure valve V1, so that part of the liquid carbon dioxide returns to the storage tank 1 through the plunger pump outlet bypass, and adjust the regulating valve 16 and the second back pressure valve V2 in the main circulation loop so that the carbon dioxide mass flow rate and system pressure in the main circulation loop are at the experimental target conditions.

[0025] Turn on the electric heating system, start the DC power supply 28 of the preheating section, and gradually and slowly increase the heating power of the preheating section 6, ensuring that each increase in power does not exceed 5% of the current heating power;

[0026] Once the wall temperature of experimental section 7 has stabilized, proceed with the next operation to increase the heating power of preheating section 6 until the inlet fluid temperature of experimental section 7 reaches the target operating temperature.

[0027] Start the DC power supply 29 for the experimental section and gradually and slowly increase the heating power of the experimental section 7, ensuring that each increase does not exceed 5% of the current heating power; once the wall temperature of the experimental section 7 has stabilized, perform the next increase in the heating power of the experimental section 7 until the experimental section 7 reaches the heat flux density of the experimental target operating condition.

[0028] Liquid carbon dioxide is heated through preheating section 6 and experimental section 7. In experimental section 7, the critical temperature of carbon dioxide is reached and the pressure of the main circulation loop is greater than the critical pressure of carbon dioxide. Liquid carbon dioxide is transformed into supercritical carbon dioxide. When the experimental device reaches stability, a local temperature peak appears on the wall temperature of experimental section 7, that is, the phenomenon of supercritical carbon dioxide heat transfer deterioration occurs, and experimental data is recorded.

[0029] Adjust the refrigeration temperature of the refrigeration unit 10 and the coolant regulating valve 21 to ensure that supercritical carbon dioxide is condensed into liquid by the shell-and-tube condenser 8.

[0030] Proceed to the next experimental condition and record the experimental data.

[0031] Compared with existing technologies, the present invention has the following advantages:

[0032] 1. The experimental apparatus and method described in this invention realize the supercritical carbon dioxide flow heat transfer dissimilarity experiment under forced circulation conditions and natural circulation conditions, and the flow direction of supercritical carbon dioxide in the experimental section can be changed by controlling the opening and closing of the shut-off valve.

[0033] 2. Using a refrigeration unit as the cold source, it can provide a minimum temperature of -25℃, which expands the lower limit of the inlet temperature of the experimental section compared to traditional water-cooled chillers; the main circulation loop can achieve a high pressure of up to 20MPa, thereby expanding the operating range for studying the flow heat transfer characteristics of supercritical carbon dioxide.

[0034] 3. The experimental section is heated by a DC power supply, with high power control sensitivity; the experimental section can be quickly replaced by a quick-release insulating flange, enabling the study of flow thermal characteristics of experimental sections of different sizes.

[0035] 4. T-type patch thermocouples are arranged at preset intervals on the wall surface of the experimental section to measure the wall temperature, eliminating the influence of DC voltage and local oxidation of welding on temperature measurement. The dense arrangement of thermocouples makes the starting point of heat transfer distortion more accurate. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the overall experimental setup.

[0037] Figure 2 This is a schematic diagram of the experimental section of the experimental setup. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and examples:

[0039] As attached Figure 1As shown, this invention relates to a supercritical carbon dioxide flow heat transfer dissimilarity experimental device, including a main circulation loop, a condensation system, and an electric heating system; the main circulation loop includes a storage tank 1, a first filter 2, a plunger pump 3, a bladder accumulator 4, a first back pressure valve V1, a mass flow meter 5, a regulating valve (16), a preheating section 6, an experimental section 7, a shell-and-tube condenser 8, a second filter 9, a second back pressure valve V2, a first shut-off valve 14, a second shut-off valve 15, a third shut-off valve 17, a fourth shut-off valve 18, a fifth shut-off valve 19, and a sixth shut-off valve 20; wherein the bottom of the storage tank 1 is connected to one end of the first shut-off valve 14 and the second shut-off valve 15, the other end of the first shut-off valve 14 is connected to one end of the first filter 2, and the other end of the first filter 2 is connected to the inlet of the plunger pump 3; the outlet of the plunger pump 3 is provided with a bladder accumulator 4, and the other end of the second shut-off valve 15 is connected to the outlet of the bladder accumulator 4; the outlet of the plunger pump 3 ... The outlet pipeline is divided into a main line and a bypass line via the bladder accumulator 4. The outlet main line is connected to the mass flow meter 5, and the outlet bypass is connected to the lower side of the storage tank 1 via the first back pressure valve V1. The mass flow meter 5 is connected to one end of the regulating valve (16). The other end of the regulating valve (16) is connected to the inlet of the preheating section 6. The outlet of the preheating section 6 is connected to the two vertical rising sections and the experimental section 7 via the third shut-off valve 17 and the fourth shut-off valve 18. The two vertical rising sections are connected in parallel with the experimental section 7. The fifth shut-off valve 19 is installed on the first vertical rising section connected to the outlet of the third shut-off valve 17. The sixth shut-off valve 20 is installed between the outlet of the second vertical rising section connected to the outlet of the fourth shut-off valve 18 and the outlet of the first vertical rising section. The outlet of the experimental section 7 is connected to the tube side inlet of the shell-and-tube condenser 8 via the sixth shut-off valve 20. The tube side outlet of the shell-and-tube condenser 8 is connected to the bottom of the storage tank 1 via the second filter 9 and the second back pressure valve V2 in sequence.

[0040] The condensation system includes a shell-and-tube condenser 8, a refrigerator 10, and a coolant regulating valve 21. The outlet of the refrigerator 10 is connected to the shell-side inlet of the shell-and-tube condenser 8 and is equipped with a bypass connected by the coolant regulating valve 21. The other end of the bypass and the shell-side outlet of the shell-and-tube condenser 8 are connected to the inlet of the refrigerator 10. The height difference between the shell-and-tube condenser 8 and the preheating section 6 is 5.5m, and the height difference between the shell-and-tube condenser 8 and the center position of the experimental section 7 is 2.9m, resulting in strong natural circulation driving force. The electric heating system includes a DC power supply 28 for the preheating section and a DC power supply 29 for the experimental section, both located on a flat ground. The DC power supply 28 for the preheating section provides three-point DC heating for the preheating section 6, and the DC power supply 29 for the experimental section provides two-point DC heating for the experimental section 7.

[0041] like Figure 2As shown, experimental section 7 is a circular tube experimental section, which is directly heated by the DC power supply 29 of the experimental section, and the power control sensitivity is high. T-type patch thermocouples 30 are arranged at equal intervals of 40mm on the wall surface of experimental section 7 to measure the wall temperature. T-type armored thermocouples 31 are inserted at the center position of the inlet and outlet of experimental section 7 to measure the fluid temperature. The fluid and wall temperature status of experimental section 7 can be monitored in real time. Experimental section 7 can be quickly replaced by quick-release insulating flange 32 to realize the study of flow thermal characteristics of experimental sections of different sizes.

[0042] like Figure 1As shown, the experimental method of the supercritical carbon dioxide flow heat transfer dissimilarity experimental device of the present invention is as follows: Before the experiment, each loop is filled with water for leak detection, water pressure test, and air tightness test to ensure that there is no leakage in the loop under the conditions of flow rate of 1000 kg / h and pressure of 20 MPa; before the experiment, all valves of the main circulation loop are opened, vacuum pump 22 is turned on, vacuum pump shut-off valve 11 is closed, first pressure reducing valve 12 is opened to discharge the gas in the main circulation loop, vacuum pump 22 is turned off, and carbon dioxide gas is injected into the storage tank 1 through carbon dioxide cylinder 23. After the pressure of the carbon dioxide cylinder is balanced with the pressure of the main circulation loop, the first pressure reducing valve 12 is closed and the connection of carbon dioxide cylinder 23 is disconnected; the exhaust valve 27 is opened and the pressure of the main circulation loop is 0.At 15MPa, close the exhaust valve 27, open the vacuum pump shut-off valve 11, restart the vacuum pump 22 to expel carbon dioxide gas from the main circulation loop, close the vacuum pump shut-off valve 11, and turn off the vacuum pump 22. Repeat the above three gas replacement operations. Open the second pressure reducing valve 13 and use the liquid carbon dioxide bottle 24 with a siphon tube to fill the storage tank 1 with liquid carbon dioxide until the pressure of the liquid carbon dioxide bottle with the siphon tube is balanced with the pressure of the main circulation loop. Turn on the refrigerator 10, adjust the refrigeration temperature of the refrigerator 10 and the coolant regulating valve 21, and wait until the pressure in the main circulation loop is balanced. Fill the container with liquid carbon dioxide, close the second pressure reducing valve 13, and disconnect the liquid carbon dioxide bottle 24 with the siphon tube; open the exhaust port of the plunger pump 3 to discharge carbon dioxide gas, and close the exhaust port of the plunger pump; turn on the plunger pump 3, adjust the operating frequency of the plunger pump, adjust the first back pressure valve V1 to allow some liquid carbon dioxide to return to the storage tank 1 through the plunger pump outlet bypass, adjust the regulating valve 16 and the second back pressure valve V2 in the main circulation loop to make the carbon dioxide mass flow rate and system pressure in the main circulation loop meet the experimental target conditions; turn on the electric heating system and start the DC power supply 2 in the preheating section. 8. Gradually and slowly increase the heating power of preheating section 6, ensuring that each increase does not exceed 5% of the current heating power; once the wall temperature of experimental section 7 stabilizes, perform the next increase of heating power in preheating section 6 until the inlet fluid temperature of experimental section 7 reaches the target operating temperature; start the DC power supply 29 of experimental section 7 and gradually and slowly increase the heating power of experimental section 7, ensuring that each increase does not exceed 5% of the current heating power; once the wall temperature of experimental section 7 stabilizes, perform the next increase of heating power in experimental section 7 until experimental section 7 reaches the target operating heat flux density; liquid carbon dioxide, after being heated by preheating section 6 and experimental section 7, reaches the critical temperature of carbon dioxide in experimental section 7, and the pressure in the main circulation loop exceeds the critical pressure of carbon dioxide, causing liquid carbon dioxide to transform into supercritical carbon dioxide. Once the experimental system stabilizes, a local temperature peak appears on the wall temperature of experimental section 7, indicating that the supercritical carbon dioxide heat transfer deterioration phenomenon has occurred, and experimental data recording begins; adjust the refrigeration temperature of the refrigerator 10 and the coolant regulating valve 21 to ensure that the supercritical carbon dioxide is condensed into liquid by the shell-and-tube condenser 8; proceed to the next experimental condition and record experimental data.

Claims

1. A supercritical carbon dioxide flow heat transfer dissimilarity experimental device, characterized in that: This includes the main circulation loop, condensation system, and electric heating system; The main circulation loop includes a storage tank (1), a first filter (2), a plunger pump (3), a bladder accumulator (4), a first back pressure valve (V1), a mass flow meter (5), a regulating valve (16), a preheating section (6), an experimental section (7), a shell-and-tube condenser (8), a second filter (9), a second back pressure valve (V2), a first shut-off valve (14), a second shut-off valve (15), a third shut-off valve (17), a fourth shut-off valve (18), and a fifth shut-off valve (19). The sixth shut-off valve (20) is used; the bottom of the storage tank (1) is connected to one end of the first shut-off valve (14) and the second shut-off valve (15), the other end of the first shut-off valve (14) is connected to one end of the first filter (2), and the other end of the first filter (2) is connected to the inlet of the plunger pump (3); the outlet of the plunger pump (3) is equipped with a bladder accumulator (4), and the other end of the second shut-off valve (15) is connected to the outlet of the bladder accumulator (4); the outlet pipeline of the plunger pump (3) is branched into the main pipeline via the bladder accumulator (4). The main outlet path and bypass path are connected to the mass flow meter (5), and the bypass path is connected to the lower side of the storage tank (1) through the first back pressure valve (V1); the mass flow meter (5) is connected to one end of the regulating valve (16); the other end of the regulating valve (16) is connected to the inlet of the preheating section (6); the outlet of the preheating section (6) is connected to the two vertical rising sections and the experimental section (7) through the third shut-off valve (17) and the fourth shut-off valve (18), and the two vertical rising sections are connected in parallel with the experimental section (7), and the third shut-off valve is connected in parallel with the experimental section (7). A fifth shut-off valve (19) is installed on the first vertical rising section connected to the outlet of valve (17). A sixth shut-off valve (20) is installed between the outlet of the second vertical rising section connected to the outlet of the fourth shut-off valve (18) and the outlet of the first vertical rising section. The outlet of the experimental section (7) is connected to the tube-side inlet of the shell-and-tube condenser (8) through the sixth shut-off valve (20). The tube-side outlet of the shell-and-tube condenser (8) is connected to the bottom of the storage tank (1) in sequence through the second filter (9) and the second back pressure valve (V2). The condensation system includes a shell-and-tube condenser (8), a refrigerator (10), and a coolant regulating valve (21); the outlet of the refrigerator (10) is connected to the shell-side inlet of the shell-and-tube condenser (8) and is provided with a coolant regulating valve (21) to connect to a bypass, and the other end of the bypass and the shell-side outlet of the shell-and-tube condenser (8) are connected to the inlet of the refrigerator (10); The electric heating system includes a preheating section DC power supply (28) and an experimental section DC power supply (29), located on a flat ground; the preheating section DC power supply (28) provides three-point DC heating for the preheating section (6); the experimental section DC power supply (29) provides two-point DC heating for the experimental section (7).

2. The supercritical carbon dioxide flow heat transfer dissimilarity experimental device according to claim 1, characterized in that: By adjusting the cooling temperature of the refrigeration unit (10) and the coolant regulating valve (21) on the bypass, the temperature at which carbon dioxide returns to the storage tank (1) after condensation is controlled.

3. The supercritical carbon dioxide flow heat transfer dissimilarity experimental apparatus according to claim 1, characterized in that: The main circulation loop is fixed by a truss structure. There is a height difference between the shell-and-tube condenser (8) and the experimental section (7), and a height difference between the shell-and-tube condenser (8) and the preheating section (6). The natural circulation driving force is strong.

4. The supercritical carbon dioxide flow heat transfer dissimilarity experimental apparatus according to claim 1, characterized in that: The main circulation loop forms a natural circulation through the driving force generated by the height difference between the cold source jacket condenser (8) and the heat source preheating section (6) and the experimental section (7) and the carbon dioxide density difference. Specifically, the plunger pump (3), the first shut-off valve (14) and the first back pressure valve (V1) are closed and the second shut-off valve (15) is opened to realize the experimental device switching from forced circulation to natural circulation mode.

5. The supercritical carbon dioxide flow heat transfer dissimilarity experimental apparatus according to claim 1, characterized in that: The main circulation loop allows supercritical carbon dioxide to flow vertically upward in the experimental section (7) by opening the third shut-off valve (17) and the sixth shut-off valve (20) and closing the fourth shut-off valve (18) and the fifth shut-off valve (19); the main circulation loop allows supercritical carbon dioxide to flow vertically downward in the experimental section (7) by closing the third shut-off valve (17) and the sixth shut-off valve (20) and opening the fourth shut-off valve (18) and the fifth shut-off valve (19).

6. The supercritical carbon dioxide flow heat transfer dissimilarity experimental apparatus according to claim 1, characterized in that: The experimental section (7) is a circular tube experimental section, which is directly heated by the DC power supply (29) of the experimental section, and has high power control sensitivity. T-type patch thermocouples (30) are arranged at preset intervals on the wall of the experimental section (7) to measure the wall temperature. T-type armored thermocouples (31) are inserted at the center of the inlet and outlet of the experimental section (7) to measure the fluid temperature, and the wall and fluid temperature status of the experimental section are monitored in real time. The experimental section (7) can be quickly replaced by quick-release insulating flanges (32) to realize the study of flow thermal characteristics of experimental sections of different sizes.

7. The supercritical carbon dioxide flow heat transfer dissimilarity experimental apparatus according to claim 1, characterized in that: The pipes and valves of the main circulation loop and condensation system are wrapped with aerogel insulation cotton for effective heat preservation.

8. The supercritical carbon dioxide flow heat transfer dissimilarity experimental apparatus according to claim 1, characterized in that: The top of the storage tank (1) is equipped with a first safety valve (26), and the outlet of the experimental section (7) is equipped with a second safety valve (25) to prevent the danger caused by accidental overpressure of the storage tank (1) and the experimental section (7) and to ensure personnel safety.

9. The experimental method corresponding to the experimental apparatus according to any one of claims 1 to 8, characterized in that: Before the experiment began, the experimental device was filled with water for leak detection, water pressure test, and air tightness test to ensure that there was no leakage in the circuit under high pressure. Before the experiment begins, open all valves in the main circulation loop, turn on the vacuum pump (22) to discharge the gas in the main circulation loop, turn off the vacuum pump (22), close the vacuum pump shut-off valve (11), open the first pressure reducing valve (12), and inject carbon dioxide gas into the storage tank (1) through the carbon dioxide cylinder (23). When the pressure of the carbon dioxide cylinder is balanced with the pressure of the main circulation loop, close the first pressure reducing valve (12) and disconnect the carbon dioxide cylinder (23). Open the exhaust valve (27), and close the exhaust valve (27) when the pressure of the main circulation loop is greater than atmospheric pressure. Open the vacuum pump shut-off valve (11), start the vacuum pump (22) again, discharge the carbon dioxide gas in the main circulation loop, close the vacuum pump shut-off valve (11), close the vacuum pump (22), and repeat the gas replacement operation three times. Open the second pressure reducing valve (13), and use the liquid carbon dioxide bottle (24) with siphon tube to fill the storage tank (1) with liquid carbon dioxide until the pressure of the liquid carbon dioxide bottle with siphon tube is balanced with the pressure of the main circulation loop. Turn on the refrigeration unit (10), adjust the refrigeration temperature of the refrigeration unit (10) and the coolant regulating valve (21), wait until the main circulation loop is filled with liquid carbon dioxide, close the second pressure reducing valve (13), and disconnect the connection with the liquid carbon dioxide bottle (24) with the siphon tube; Open the exhaust port of the plunger pump (3) to discharge carbon dioxide gas, and close the exhaust port of the plunger pump; Turn on the plunger pump (3), adjust the working frequency of the plunger pump, adjust the first back pressure valve (V1) so that some liquid carbon dioxide returns to the storage tank (1) through the outlet bypass of the plunger pump, adjust the regulating valve (16) and the second back pressure valve (V2) in the main circulation loop so that the carbon dioxide mass flow rate and system pressure in the main circulation loop are the experimental target conditions. Turn on the electric heating system, start the DC power supply (28) of the preheating section, and gradually and slowly increase the heating power of the preheating section (6). Each increase in power should not exceed 5% of the current heating power. Once the wall temperature of the experimental section (7) has stabilized, the heating power of the preheating section (6) will be increased again until the inlet fluid temperature of the experimental section (7) reaches the target operating temperature. Start the DC power supply of the experimental section (29), and gradually and slowly increase the heating power of the experimental section (7). Each increase in power should not exceed 5% of the current heating power. After the wall temperature of the experimental section (7) reaches stability, perform the next increase in the heating power of the experimental section (7) until the experimental section (7) reaches the heat flux density of the experimental target working condition. Liquid carbon dioxide is heated through the preheating section (6) and the experimental section (7). In the experimental section (7), the critical temperature of carbon dioxide is reached. The pressure of the main circulation loop is greater than the critical pressure of carbon dioxide. Liquid carbon dioxide is transformed into supercritical carbon dioxide. When the experimental device reaches stability, the wall temperature of the experimental section (7) shows a local temperature peak, which means that the supercritical carbon dioxide heat transfer deterioration phenomenon has occurred. Experimental data is then recorded. Adjust the refrigeration temperature of the refrigeration unit (10) and the cooling liquid regulating valve (21) to ensure that supercritical carbon dioxide is condensed into liquid through the shell-and-tube condenser (8); Proceed to the next experimental condition and record the experimental data.

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