Supercritical CO2 mixed working medium heat transfer experiment system and operation method thereof

Abstract

The invention provides a supercritical CO2 mixed working medium heat transfer experiment system and an operation method thereof.The supercritical CO2 mixed working medium heat transfer experiment system comprises a mixed working medium injection module and a working medium circulation heat exchange module which operate independently, and the mixed working medium injection module is connected with the working medium circulation heat exchange module. The system has the beneficial effects that the mixed working medium injection module is used for preparing and filling a supercritical CO2 mixed working medium, the working medium circulation heat exchange module is used for a mixed working medium heat transfer experiment, and the two modules operate independently and do not influence each other, so that the problems that in the prior art, working medium mixing is not uniform, the pressure is difficult to regulate and control, and the flow is unstable can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of supercritical fluids, and in particular to a supercritical CO 2 Mixed working fluid heat transfer experimental system and operation method thereof. Background Art

[0002] 1.1 Supercritical fluid heat transfer experimental system

[0003] Supercritical fluid is the energy transfer and work fluid in the power cycle operation process of thermal power generation system, waste heat recovery system, refrigeration system, etc. 2 The mixed working fluid power cycle has flexible operation and high cycle thermal efficiency, and has good development prospects. Supercritical fluid heat transfer experiments are used to study the flow and heat transfer characteristics of supercritical fluids, analyze related heat transfer mechanisms, and provide basic data for the control and operation of supercritical fluid power cycle systems and the development and design of key equipment. At present, most of the existing supercritical working fluid heat transfer experimental systems are based on pure working fluids, while the supercritical fluid heat transfer experimental system for CO 2 There are few experimental systems for mixed working fluids. Unlike pure working fluids, the physical properties of the components of mixed working fluids vary greatly, and the components are not easy to mix evenly. In addition, the pressure, temperature, component concentration and other parameters are coupled, and small changes in state parameters will lead to changes in flow state and physical property parameters, which can easily cause inaccurate heat transfer measurement data. For the development of efficient mixed working fluid power cycle systems, it is urgent to invent a method to study supercritical CO 2 The experimental system and method for the heat transfer characteristics of mixed working fluids not only ensures that the working fluid components are fully mixed, but also ensures the stability and flexible regulation of parameters such as pressure, temperature, and flow rate during the test.

[0004] 1.2 However, supercritical CO 2 In the experimental system and method for the heat transfer characteristics of mixed working fluids, the inventors found that there are still many shortcomings:

[0005] (1) Uneven mixing of working fluid

[0006] In the existing experimental system, the mixed working fluid storage tank is located in the experimental system circulation loop, which is easy to affect the experimental measurement. When the mixed working fluid in the storage tank is not completely filled with liquid phase, it is very easy to have gas-liquid two phases. For the mixed working fluid, the concentrations of the gas phase and liquid phase components are often inconsistent. When the temperature and pressure of the storage tank change, the gas-liquid two-phase ratio, the concentration of the liquid phase mixed working fluid components, etc. will change accordingly, which will easily lead to inconsistent concentrations of working fluid components in the circulation loop, affecting the accuracy of the experimental data.

[0007] (2) Difficult to regulate pressure and poor stability

[0008] Existing supercritical mixed fluid experimental systems mostly increase the pressure of the test section by jointly adjusting the bypass and back pressure valves. Any adjustment will not only change the system pressure, but also the flow rate of the test section, which is extremely difficult to control. In addition, most booster pumps are positive displacement pumps, which have strong pulsations and can easily cause unstable system pressure. The temperature and pressure changes before the pump affect the flow changes of the high-pressure test section after the pump, resulting in poor stability.

[0009] Terminology explanation:

[0010] 1. Supercritical fluid: A supercritical fluid is a fluid whose temperature and pressure are higher than its critical value, such as the critical temperature of water T = 374 ° C, the critical pressure P = 22.1 MPa, the critical temperature of carbon dioxide T = 31.26 ° C, the critical pressure Pc = 7.29 MPa. When the temperature and pressure are higher than these values, it becomes a supercritical fluid.

[0011] 2. Supercritical CO 2 Mixed working fluid: CO 2 The mixture formed with other working fluids (such as R134a, R41, water, etc.) is in a supercritical state. The mixed working fluid can be used as a new type of power system or equipment energy or power conversion working fluid, and has the characteristics of high cycle efficiency and strong operability. Summary of the invention

[0012] In view of this, the present invention provides a supercritical CO 2 A mixed working fluid heat transfer experimental system and its operation method are used to solve the problem of uneven working fluid mixing.

[0013] The embodiments of this specification provide the following technical solutions: a supercritical CO 2 The mixed working fluid heat transfer experimental system comprises a mixed working fluid injection module and a working fluid circulation heat exchange module which operate independently of each other, and the mixed working fluid injection module is connected with the working fluid circulation heat exchange module.

[0014] Furthermore, the mixed working fluid injection module includes: a first high-pressure gas cylinder; an injector, one end of which is connected to the first high-pressure gas cylinder, and a pressure reducing valve and an exhaust valve are provided on the connecting pipeline between the first high-pressure gas cylinder and the injector; the other end of the injector is connected to the working fluid circulation heat exchange module, and a gas source shut-off valve and a filling shut-off valve are provided on the connecting pipeline between the other end of the injector and the working fluid circulation heat exchange module.

[0015] Furthermore, the working fluid circulation heat exchange module includes a circulation pump, a filter, a main circulation loop and a bypass. The outlet of the circulation pump is respectively connected to the main circulation loop and the bypass, and the main circulation loop and the bypass are connected to the inlet of the filter. The outlet of the filling stop valve and the outlet of the filter are both connected to the inlet of the circulation pump.

[0016] Furthermore, the main circulation loop includes: a pressure control unit, one end of which is connected to the outlet of the circulation pump; a preheater, an inlet of which is connected to the other end of the pressure control unit, and a mass flow meter is provided on the connecting pipeline between the preheater and the pressure control unit; a test unit, an inlet of which is connected to the outlet of the preheater, and the outlet of the test unit is connected to the outlet of the bypass and both are connected to the inlet of the filter.

[0017] Furthermore, the pressure control unit includes: a pressure controller, which is provided with a mixed working fluid inlet, a mixed working fluid outlet and a gas connecting port, the mixed working fluid inlet is connected to the outlet of the circulation pump, the mixed working fluid outlet is connected to the inlet of the preheater, and the gas connecting port is placed at the top of the pressure controller; a second high-pressure gas cylinder is connected to the gas connecting port, and a pressure reducing valve and an exhaust valve are provided on the connecting pipeline between the second high-pressure gas cylinder and the gas connecting port.

[0018] Furthermore, the pressure controller includes: a cylinder having an inner cavity; a second movable piston, which is placed inside the cylinder and divides the cylinder into a high-pressure gas chamber and a mixed working fluid chamber, the mixed working fluid inlet and the mixed working fluid outlet are both connected to the mixed working fluid chamber, and the gas connection port is connected to the high-pressure gas chamber.

[0019] Furthermore, a stop ring is provided in the mixed working medium chamber and is located above the mixed working medium inlet and the mixed working medium outlet.

[0020] Furthermore, the experimental test unit includes: a test pipeline, connected to a DC power supply, the inlet of the test pipeline is connected to the outlet of the preheater, the outlet of the test pipeline is connected to the outlet of the bypass and both are connected to the inlet of the filter; an insulating flange is symmetrically arranged at the inlet and outlet of the test pipeline.

[0021] Furthermore, supercritical CO 2 The mixed working medium heat transfer experimental system also includes: a cooler, the inlet of the cooler is connected with the outlet of the test pipeline and the outlet of the bypass; a buffer, the inlet of the buffer is connected with the outlet of the cooler, and the outlet of the buffer is connected with the inlet of the filter.

[0022] Furthermore, a cooling jacket is provided on the outside of the injector; the cooler is connected to the cooling jacket via a chiller for heat exchange.

[0023] The present invention also provides an operation method, using the supercritical CO 2 The mixed working fluid heat transfer experiment system is carried out, and the operation method includes the following steps:

[0024] Step 1: liquefying the gaseous working fluid in the injector to form a mixed working fluid;

[0025] Step 2: injecting the mixed working fluid into the working fluid circulation heat exchange module;

[0026] Step 3: Perform a precooling cycle, so that the mixed working fluid passes through the circulation pump, the pressure control unit, the mass flow meter, the preheater, the test unit, the cooler and the buffer in sequence and then returns to the circulation pump;

[0027] Step 4: Perform preheater regulation, system pressure regulation and experimental operating condition regulation to make the mixed working fluid in the test unit meet the experimental numerical requirements, and collect and record heat transfer data.

[0028] Compared with the prior art, the beneficial effects achieved by at least one of the above technical solutions adopted in the embodiments of this specification include at least: the mixed working fluid injection module is used for supercritical CO 2 Mixed working fluid preparation and filling, working fluid circulation heat exchange module is used for mixed working fluid heat transfer experiment, the two modules operate independently without affecting each other, thus solving the problems of uneven working fluid mixing, difficult pressure control and unstable flow in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 The supercritical CO provided in the embodiment of the present application 2 Schematic diagram of the mixed working fluid heat transfer experimental system;

[0031] Figure 2 A schematic diagram of a pressure controller provided in an embodiment of the present application;

[0032] Figure 3 The supercritical CO provided in the embodiment of the present application 2 Schematic diagram of the operation method of the mixed working fluid heat transfer experimental system;

[0033] 1. The first high-pressure gas cylinder; 2. The first pressure reducing valve; 3. The first discharge valve; 4. The injector; 41. The movable piston; 42. The gas phase region; 43. The liquid phase region; 5. The cooling jacket; 6. The gas source shut-off valve; 7. The filling shut-off valve; 8. The filter; 9. The circulating pump; 10. The bypass valve; 11. The pressure controller; 12. The second discharge valve; 13. The second pressure reducing valve; 14. The second high-pressure gas cylinder; 15. The mass flow meter; 16. The preheater; 17. The insulating flange; 18. The heat transfer experimental section; 19. The cooler; 20. The chiller; 21. The working fluid discharge valve; 22. The buffer; 110. The cylinder; 111. The high-pressure gas chamber; 112. The mixed working fluid chamber; 113. The mixed working fluid inlet; 114. The mixed working fluid outlet; 115. The gas connection port; 116. The movable piston; 117. The sealing ring; 118. The stop ring. DETAILED DESCRIPTION

[0034] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0035] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0036] like Figure 1 to Figure 2 As shown, the embodiment of the present invention provides a supercritical CO 2 The mixed working fluid heat transfer experimental system comprises a mixed working fluid injection module and a working fluid circulation heat exchange module which operate independently of each other, and the mixed working fluid injection module is connected with the working fluid circulation heat exchange module.

[0037] Mixed Fluid Injection Module for Supercritical CO 2 Mixed working fluid preparation and filling, working fluid circulation heat exchange module is used for mixed working fluid heat transfer experiment, the two modules operate independently without affecting each other, thus solving the problems of uneven working fluid mixing, difficult pressure control and unstable flow in the prior art.

[0038] Specifically, the mixed working fluid injection module includes a first high-pressure gas cylinder 1 and an injector 4. One end of the injector 4 is connected to the first high-pressure gas cylinder 1, and a first pressure reducing valve 2 and a first discharge valve 3 are provided on the connecting pipeline between the first high-pressure gas cylinder 1 and the injector 4; the other end of the injector 4 is connected to the working fluid circulation heat exchange module, and a gas source stop valve 6 and a filling stop valve 7 are provided on the connecting pipeline between the other end of the injector 4 and the working fluid circulation heat exchange module.

[0039] It should be noted that the first discharge valve 3 is arranged on the side road of the connecting pipeline between the first pressure reducing valve 2 and the injector 4; the gas source stop valve 6 is arranged on the side road of the connecting pipeline between the injector 4 and the filling stop valve 7.

[0040] The working fluid circulation heat exchange module includes a circulation pump 9, a filter 8, a main circulation loop and a bypass. The outlet of the circulation pump 9 is connected to the main circulation loop and the bypass respectively, and the main circulation loop and the bypass are connected to the inlet of the filter 8. The outlet of the filling stop valve 7 and the outlet of the filter 8 are both connected to the inlet of the circulation pump 9.

[0041] A first movable piston 41 is provided inside the injector 4, dividing the injector into two areas, namely a gas phase area 42 and a liquid phase area 43. A temperature and pressure sensor is installed inside the liquid phase area 43. A cooling jacket 5 is provided on the outside of the injector 4. The cooling jacket 5 is provided with a cooling water inlet and outlet, which are respectively connected to the inlet and outlet of the chiller 20 through pipelines.

[0042] The main circulation loop includes a pressure control unit, a preheater 16 and a test unit. One end of the pressure control unit is connected to the outlet of the circulation pump 9; the inlet of the preheater 16 is connected to the other end of the pressure control unit, and a mass flow meter 15 is provided on the connecting pipeline between the preheater 16 and the pressure control unit; the inlet of the test unit is connected to the outlet of the preheater 16, and the outlet of the test unit is connected to the outlet of the bypass and both are connected to the inlet of the filter 8.

[0043] Specifically, the pressure control unit includes a pressure controller 11 and a second high-pressure gas cylinder 14. The pressure controller 11 is provided with a mixed working medium inlet 113, a mixed working medium outlet 114 and a gas connection port 115, the mixed working medium inlet 113 is connected to the outlet of the circulation pump 9, the mixed working medium outlet 114 is connected to the inlet of the mass flow meter 15, and the gas connection port 115 is placed at the top of the pressure controller 11; the second high-pressure gas cylinder 14 is connected to the gas connection port 115, and the second pressure reducing valve 13 and the second discharge valve 12 are provided on the connecting pipeline between the second high-pressure gas cylinder 14 and the gas connection port.

[0044] Furthermore, the pressure controller 11 includes a cylinder 110 and a second movable piston 116. The cylinder 110 has an inner cavity; the second movable piston 116 is disposed inside the cylinder 110 and divides the cylinder 110 into a high-pressure gas chamber 111 and a mixed medium chamber 112, the mixed medium inlet 113 and the mixed medium outlet 114 are both connected to the mixed medium chamber 112, and the gas connection port 115 is connected to the high-pressure gas chamber 111.

[0045] like Figure 2 As shown, in the embodiment of the present invention, a stop ring 118 is provided in the mixed medium chamber, located above the mixed medium inlet 113 and the mixed medium outlet 114. The stop ring 118 is a hollow ring, forming an integral structure with the cylinder 110, and is located above the mixed medium inlet 113 and the mixed medium outlet 114, in order to prevent the moving piston 116 from falling into the bottom of the cylinder 110 and blocking the flow channel.

[0046] It should be noted that the second movable piston 116 is a solid cylindrical structure, and an O-ring 117 is provided on the outer side of its circumference. The material of the O-ring 117 is a corrosion-resistant swelling material, such as polytetrafluoroethylene or perfluororubber.

[0047] The pressure controller of the present invention can not only adjust the system pressure, but also realize uniform mixing of the working fluid, and can maintain the working fluid in a single-phase state during the entire circulation process, making the test more accurate; the present invention can be applied to micro-channel and large-scale mixed working fluid circulation heat exchange experiments, and has a wide range of applications.

[0048] The preheater 16 in the embodiment of the present invention adopts one or more preheating devices including resistance Joule heat release, oil bath and water bath, and the inlet and outlet of the preheater 16 are both provided with temperature measuring thermocouples or thermal resistors.

[0049] Furthermore, if Figure 1 As shown, the test unit includes a heat transfer test section 18 and an insulating flange 17. The heat transfer test section 18 is connected to a DC power supply to form a current loop, the inlet of the heat transfer test section 18 is connected to the outlet of the preheater 16, the outlet of the heat transfer test section 18 is connected to the outlet of the bypass and both are connected to the inlet of the filter 8; the insulating flange 17 is symmetrically arranged at the inlet and outlet of the heat transfer test section 18. Instruments for measuring inlet and outlet temperature, pressure and pressure difference are arranged on the outside of the insulating flange 17.

[0050] Supercritical CO 2 The mixed working fluid heat transfer experimental system also includes a cooler 19 and a buffer 22. The inlet of the cooler 19 is connected to the outlet of the heat transfer experimental section 18 and the outlet of the bypass; the inlet of the buffer 22 is connected to the outlet of the cooler 19, and the outlet of the buffer 22 is connected to the inlet of the filter 8. The outlet of the bypass is set between the inlet of the cooler 19 and the outlet of the heat transfer experimental section 18.

[0051] The buffer 22 is composed of a cylindrical high-pressure pipeline with an inner diameter larger than the main circulation route. The two ends of the buffer 22 are respectively connected to the cooler 19 and the filter 8. A working medium discharge valve 21 is provided on the side between the buffer 22 and the cooler 19, and a mixed working medium injection module connecting pipeline is provided on the side between the buffer 22 and the filter 8. The function of the buffer 22 is that the buffer 22 is essentially a small container, which increases the flow of the working medium inside it, which is conducive to further mixing of the circulating mixed working medium.

[0052] Furthermore, the cooler 19 is connected to the cooling jacket 5 through a water chiller 20 for heat exchange.

[0053] It should be noted that the first high-pressure gas cylinder 1 and the second high-pressure gas cylinder 14 contain high-pressure N 2 It or other high-pressure inert gas, the gas pressure is higher than the fluid pressure required for the experiment.

[0054] In the embodiment of the present invention, a buffer, a variable frequency circulation pump and a pressure controller are provided in the circulation heat exchange module, which play a role in stabilizing the flow and uniformly mixing the working fluid, and the system pressure can be flexibly adjusted.

[0055] The present invention also provides an operating method, using the above-mentioned supercritical CO 2 The mixed working fluid heat transfer experiment system is carried out, and the operation method includes the following steps:

[0056] Step 1: liquefy the gaseous working medium in the injector 4 to form a mixed working medium;

[0057] Step 2: injecting the mixed working fluid into the working fluid circulation heat exchange module;

[0058] Step 3: Perform a precooling cycle, so that the mixed working medium passes through the circulation pump 9, the pressure control unit, the mass flow meter 15, the preheater 16, the test unit, the cooler 19 and the buffer 22 in sequence and then returns to the circulation pump 9;

[0059] Step 4: Control the preheater 16, the system pressure and the experimental working conditions so that the mixed working fluid in the test unit meets the experimental numerical requirements, and collect and record the heat transfer data.

[0060] Take a specific embodiment as an example. Figure 3 As shown:

[0061] Before the experiment begins, the mixed working fluid is prepared. 2 Mix the working fluid components and calculate the mass filling ratio of each working fluid. In addition, the injector 4 and the auxiliary pipelines and the flow pipelines of the working fluid circulation heat exchange module need to be evacuated. Then, the gas working fluid storage tank is connected to the gas source shut-off valve 6 of the mixed working fluid injection module in turn. The injector 4 is temperature-controlled by the circulating cooling water delivered by the chiller 20. The gas working fluid is liquefied in the injector 4 to form a mixed working fluid. By measuring the mass reduction of the gas working fluid storage tank, the liquefied amount of each working fluid component is calculated to ensure CO 2 The mixed working fluid components are mixed according to the set ratio, and the pressure and temperature of the mixed working fluid liquid are obtained through the temperature and pressure transmitter installed in the injector 4. After the working fluid is mixed, the gas source stop valve 6 is closed, all valves of the main and bypass of the working fluid circulation heat exchange module are opened, the second discharge valve 12 of the pressure control unit is opened, the cold water pipeline of the cooler 19 is opened, and then the filling stop valve 7 and the first pressure reducing valve 2 are opened. CO 2 The mixed working fluid enters the flow pipeline of the working fluid circulation heat exchange module through the connecting pipeline. During the filling process, the circulation pump 9 can be turned on at a low speed, and the bypass valve 10 can be adjusted to accelerate the injection of the mixed working fluid into the circulation system. After the filling is completed, the filling stop valve 7 is closed.

[0062] After the filling is completed, the mixed working fluid heat transfer experiment working condition adjustment is carried out. The first step is pre-cooling cycle. Turn on the circulation pump 9, CO 2 The mixed working medium passes through the circulation pump 9, bypass and pressure controller 11, mass flow meter 15, preheater 16, heat transfer experimental section 18, cooler 19, buffer 22 in pure liquid state or gas-liquid two-phase in sequence, and finally returns to the inlet of the circulation pump 9; the second step is preheater regulation, adjusting the preheater 16 to heat the mixed working medium so that the inlet temperature of the heat transfer experimental section 18 reaches the value required by the experimental working condition; the third step is system pressure regulation, closing the second discharge valve 12 of the pressure control unit, adjusting the second pressure reducing valve 13 to inflate the high-pressure gas phase cavity of the pressure controller, and the piston moves. When the system pressure reaches the value near the value required by the experimental working condition, stop inflating and close the second high-pressure gas cylinder 14; the fourth step is experimental working condition regulation, comprehensively regulating the frequency converter and bypass valve 10 of the circulation pump 9, regulating the working medium flow of the main circulation pipeline of the system, so that the CO in the heat transfer experimental section 18 2 The mixed working fluid flow rate reaches the value required by the experimental conditions; the heating DC power supply of the heat transfer experimental section 18 is turned on, and the heating power is adjusted to reach the value required by the experimental conditions, and then the pressure controller 11, the inverter circulating pump 9 and the preheater 16 are comprehensively adjusted, and finally the CO in the heat transfer experimental section 18 is 2 The mixed working fluid inlet temperature, pressure, flow rate and heating heat flux reach the values ​​required by the experiment, and the data acquisition system records the heat transfer data; repeat steps 2 to 4 to carry out the next working condition test.

[0063] After the experimental conditions are completed, the heating power supply of the heat transfer experimental section 18, the heating switch of the preheater 16, the water cooler 20 and the circulating pump 9 are turned off in sequence. After the experimental system pipeline returns to room temperature, the experiment is ended by discharging the mixed working fluid in the system.

[0064] The supercritical CO 2 Mixed working fluid heat transfer experimental operation method can be used for different types of CO 2 Heat transfer test under mixed working fluid and different heating experimental pipeline conditions.

[0065] The above is only a specific embodiment of the present invention, and cannot be used to limit the scope of the invention. Therefore, the replacement of equivalent components, or equivalent changes and modifications made according to the scope of protection of the patent of the present invention, should still fall within the scope of this patent. In addition, the technical features of the present invention can be freely combined with each other, with each other, and with each other.

Claims

1. A supercritical CO2 mixed working fluid heat transfer experimental system, characterized in that: It comprises a mixed working fluid injection module and a working fluid circulation heat exchange module which operate independently of each other, and the mixed working fluid injection module is connected to the working fluid circulation heat exchange module.

2. The supercritical CO2 mixed working fluid heat transfer experimental system according to claim 1 is characterized in that: The mixed working fluid injection module comprises: A first high-pressure gas cylinder (1); An injector (4) is connected at one end to the first high-pressure gas cylinder (1), and a first pressure reducing valve (2) and a first discharge valve (3) are provided on the connecting pipeline between the first high-pressure gas cylinder (1) and the injector (4); the other end of the injector (4) is connected to the working fluid circulation heat exchange module, and a gas source stop valve (6) and a charging stop valve (7) are provided on the connecting pipeline between the other end of the injector (4) and the working fluid circulation heat exchange module.

3. The supercritical CO2 mixed working fluid heat transfer experimental system according to claim 2 is characterized in that: The working fluid circulation heat exchange module comprises a circulation pump (9), a filter (8), a main circulation loop and a bypass, the outlet of the circulation pump (9) is connected to the main circulation loop and the bypass respectively, and the main circulation loop and the bypass are connected to the inlet of the filter (8), and the outlet of the filling stop valve (7) and the outlet of the filter (8) are both connected to the inlet of the circulation pump (9).

4. The supercritical CO2 mixed working fluid heat transfer experimental system according to claim 3 is characterized in that: The main circulation loop comprises: A pressure control unit, one end of which is connected to the outlet of the circulation pump (9); A preheater (16), the inlet of which is connected to the other end of the pressure control unit, and a mass flow meter (15) is provided on the connecting pipeline between the preheater (16) and the pressure control unit; The inlet of the test unit is connected to the outlet of the preheater (16), and the outlet of the test unit is communicated with the outlet of the bypass and both are communicated with the inlet of the filter (8).

5. The supercritical CO2 mixed working fluid heat transfer experimental system according to claim 4 is characterized in that: The pressure control unit comprises: The pressure controller (11) is provided with a mixed working fluid inlet, a mixed working fluid outlet and a gas connection port, wherein the mixed working fluid inlet is connected to the outlet of the circulation pump (9), the mixed working fluid outlet is connected to the inlet of the preheater (16), and the gas connection port is disposed at the top of the pressure controller (11); A second high-pressure gas cylinder (14) is connected to the gas connection port, and a second pressure reducing valve (13) and a second discharge valve (12) are provided on the connection pipeline between the second high-pressure gas cylinder (14) and the gas connection port.

6. The supercritical CO2 mixed working fluid heat transfer experimental system according to claim 5, characterized in that: The pressure controller (11) comprises: A cylinder (110) having an inner cavity; The second movable piston (116) is disposed inside the cylinder (110) and divides the cylinder (110) into a high-pressure gas chamber and a mixed working fluid chamber, the mixed working fluid inlet and the mixed working fluid outlet are both connected to the mixed working fluid chamber, and the gas connection port is connected to the high-pressure gas chamber.

7. The supercritical CO2 mixed working fluid heat transfer experimental system according to claim 6, characterized in that: A stop ring (118) is provided in the mixed working medium chamber and is located above the mixed working medium inlet and the mixed working medium outlet.

8. The supercritical CO2 mixed working fluid heat transfer experimental system according to claim 4, characterized in that: The experimental test unit comprises: A heat transfer test section (18) is connected to a DC power supply, the inlet of the heat transfer test section (18) is connected to the outlet of the preheater (16), the outlet of the heat transfer test section (18) is connected to the outlet of the bypass and both are connected to the inlet of the filter (8); The insulating flange (17) is symmetrically arranged at the inlet and outlet of the heat transfer experimental section (18).

9. The supercritical CO2 mixed working fluid heat transfer experimental system according to claim 8, characterized in that: The supercritical CO2 mixed working fluid heat transfer experimental system also includes: A cooler (19), wherein the inlet of the cooler (19) is connected to the outlet of the heat transfer experimental section (18) and the outlet of the bypass; The inlet of the buffer (22) is connected to the outlet of the cooler (19), and the outlet of the buffer (22) is connected to the inlet of the filter (8).

10. The supercritical CO2 mixed working fluid heat transfer experimental system according to claim 9, characterized in that: A cooling jacket (5) is provided outside the injector (4); The cooler (19) is connected to the cooling jacket (5) via a water chiller (20) for heat exchange.

11. An operating method, using the supercritical CO2 mixed working fluid heat transfer experimental system according to any one of claims 1 to 10, characterized in that: The operation method comprises the following steps: Step 1: liquefying the gaseous working medium in the injector (4) to form a mixed working medium; Step 2: injecting the mixed working fluid into the working fluid circulation heat exchange module; Step 3, performing a precooling cycle, so that the mixed working fluid passes through the circulation pump (9), the pressure control unit, the mass flow meter (15), the preheater (16), the test unit, the cooler (19) and the buffer (22) in sequence and then returns to the circulation pump (9); Step 4: Control the preheater (16), the system pressure and the experimental working conditions so that the mixed working fluid in the test unit meets the experimental numerical requirements, and collect and record heat transfer data.

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