A test bench for heat transfer performance and frost observation based on supercritical nitrogen

Abstract

This application provides a supercritical nitrogen-based heat transfer performance and frosting observation test bench, belonging to the field of aero-engine technology. It includes a supercritical nitrogen supply system, a heat exchanger, a spray system, an air system, and a data acquisition system. The supercritical nitrogen supply system includes a liquid nitrogen Dewar flask, a high-pressure nitrogen cylinder, a cryogenic pump, and a first valve assembly. The outlets of the liquid nitrogen Dewar flask and the high-pressure nitrogen cylinder are connected to the first inlet of the heat exchanger via the cryogenic pump and the first valve assembly. The outlet of the spray system is connected to the outlet of the air system and then to the second inlet of the heat exchanger. The data acquisition system includes a pressure transmitter, a temperature transmitter, a flow meter, an image acquisition component, a DIS acquisition module, and an acquisition computer. The image acquisition component acquires the frosting conditions on the surface of the heat exchanger's microtubes. This system achieves precise control of supercritical nitrogen and stable recording of heat transfer performance data and frosting images, filling a technological gap in the field of aero-engine heat exchanger performance testing.

Description

Technical Field

[0001] This application relates to the field of aero-engine technology, and in particular to a test bench for heat transfer performance and frost observation based on supercritical nitrogen. Background Technology

[0002] Compared to conventional fluids, supercritical fluids have significant advantages in heat transfer. This is because fluids at supercritical pressure undergo drastic changes in physical properties as their temperature crosses the quasi-critical temperature range, and these drastic changes alter the fluid's inherent flow and heat transfer characteristics. Therefore, the cooling capacity of supercritical fluids is highly valued in the research of heat exchangers for aero-engines, particularly in inlet precooling.

[0003] The importance of heat exchange performance research for heat exchangers used in aero engines goes without saying. In addition, frosting is also an important research subject. During high-speed flight, the high-temperature air entering the air intake contains water vapor. During the pre-cooling process of the intake air, water vapor may frost up on the outer wall of the heat exchange tubes, leading to a series of adverse consequences such as flow channel blockage and deterioration of heat exchange.

[0004] In conclusion, it is quite necessary to construct an experimental rig for observing frost formation and studying the heat transfer performance of supercritical fluid heat exchangers. Due to the safety, low cost, and availability of nitrogen, researchers often choose supercritical nitrogen as the cooling medium in frost formation tests of supercritical medium heat exchangers. The construction method of this experimental rig can also serve as a reference for the construction of experimental rigs for other supercritical medium heat exchangers (such as helium and carbon dioxide).

[0005] Among the existing published patents, there are test benches for studying the heat exchange performance of heat exchangers using supercritical carbon dioxide as a refrigerant and test benches for studying frost formation and heat exchange performance using conventional coolant as a refrigerant, but there are no test benches for heat exchangers using supercritical nitrogen as a refrigerant that can be used for frost formation observation and heat exchange performance research, which is a patent gap. Summary of the Invention

[0006] In view of this, this application provides a test bench for heat exchange performance and frost observation based on supercritical nitrogen. The test bench can achieve precise control of supercritical nitrogen pressure and flow rate, air humidity, and stably record heat exchange performance data and frost images of the heat exchanger, filling the technical gap in the field of aero-engine heat exchanger performance testing.

[0007] This application provides a supercritical nitrogen-based heat exchange performance and frosting observation test bench. The test bench includes a supercritical nitrogen supply system, a heat exchanger, a spray system, an air system, and a data acquisition system. The heat exchanger includes a first inlet end, a second inlet end, a first outlet end, and a second outlet end. The supercritical nitrogen supply system includes a liquid nitrogen Dewar flask, a high-pressure nitrogen cylinder, a cryogenic pump, and a first valve assembly. The outlet ends of the liquid nitrogen Dewar flask and the high-pressure nitrogen cylinder are respectively connected to the first inlet end of the heat exchanger through the cryogenic pump and the first valve assembly. The first outlet end of the heat exchanger is the liquid nitrogen outlet end. The outlet end of the spray system is connected to... After the air system piping is connected, it is connected to the second inlet end of the heat exchanger, and the second outlet end of the heat exchanger is the air outlet end; the data acquisition system includes a pressure transmitter, a temperature transmitter, a flow meter, an image acquisition component, a DIS acquisition module, and an acquisition computer. The supercritical nitrogen supply system, the spray system, and the air system are each equipped with a pressure transmitter, a temperature transmitter, and a flow meter. The output signals of the pressure transmitter, the temperature transmitter, and the flow meter are all transmitted to the acquisition computer through the DIS acquisition module. The image acquisition component is used to acquire images of the frost conditions inside the heat exchanger and transmit them to the acquisition computer.

[0008] According to one specific implementation of the embodiments of this application, the supercritical nitrogen supply system further includes an accumulator, which is connected to the outlet end of the cryogenic pump.

[0009] According to one specific implementation of the present application, the supercritical nitrogen supply system further includes filter I, which is located between the cryogenic pump and the first inlet end of the heat exchanger.

[0010] According to a specific implementation of an embodiment of this application, the first valve assembly includes a solenoid valve I, a safety valve I, a pneumatic regulating valve I, a pneumatic shut-off valve I, a safety valve II, a pneumatic regulating valve II, a manual shut-off valve, a solenoid valve II, and a pneumatic regulating valve III. The outlet end of the liquid nitrogen Dewar flask is sequentially connected to the solenoid valve I, the cryogenic pump, the safety valve I, the pneumatic regulating valve I, the filter I, the pneumatic shut-off valve I, the safety valve II, and the first inlet end of the heat exchanger. The outlet end of the high-pressure nitrogen cylinder is connected between the solenoid valve I and the cryogenic pump via the manual shut-off valve. The outlet end of the manual shut-off valve is connected to the solenoid valve II. The pneumatic regulating valve II is connected to the first outlet end of the heat exchanger. The pneumatic regulating valve III is connected to the location of the safety valve I.

[0011] According to a specific implementation of an embodiment of this application, the spray system includes a water tank, a manual ball valve, a water pump, an electric regulating valve I, a check valve, and a nozzle connected in sequence through pipelines. The nozzle at the outlet end of the spray system is installed on the air system pipeline, and water is sprayed into the air through the nozzle. The spray system also includes a pneumatic regulating valve VI, one end of which is connected between the water pump and the electric regulating valve I, and the other end of which is connected to the water inlet end of the water tank.

[0012] According to one specific implementation of the embodiments of this application, the spray system further includes a filter II, which is connected between the manual ball valve and the water pump.

[0013] According to a specific implementation of an embodiment of this application, the air system includes an electric heating furnace, an electric regulating valve VI, and an air source connected in sequence via pipelines, with the outlet end of the electric heating furnace connected to the outlet end of the spray system; the air system also includes an electric regulating valve II, which is connected to the second outlet end of the heat exchanger.

[0014] According to a specific implementation of an embodiment of this application, the air system further includes a venting branch, which is located between the electric heating furnace and the electric regulating valve VI, and the end of the venting branch is provided with an electric regulating valve III.

[0015] According to a specific implementation of an embodiment of this application, a heat exchanger includes a shell. A hot-side inlet flange and a hot-side outlet flange are respectively provided on one opposite side of the shell, and a cold-side inlet flange and a cold-side outlet flange are respectively provided on the other opposite side of the shell. An air inlet is provided on the hot-side inlet flange, serving as the second inlet end of the heat exchanger. An air outlet is provided on the hot-side outlet flange, serving as the second outlet end of the heat exchanger. A supercritical nitrogen inlet is provided on the cold-side inlet flange, serving as the first inlet end of the heat exchanger. A supercritical nitrogen outlet is provided on the cold-side outlet flange, serving as the first outlet end of the heat exchanger. Multiple independent chambers are provided on the outer side of the shell, and multiple microtubes are provided inside the shell. The supercritical nitrogen inlet and supercritical nitrogen outlet are respectively connected to the microtubes through their respective chambers, forming a U-shaped supercritical nitrogen flow path. A glass window is also provided on the outer side of the shell, and an image acquisition component is mounted on the outside of the glass window to acquire images of frost formation on the outer wall of the microtubes near the glass window.

[0016] According to a specific implementation of an embodiment of this application, the glass window includes a housing, a pressure plate, a graphite pad I, sapphire glass, and a graphite pad II. The housing is connected to the outer shell. The inner side of the sapphire glass is disposed in a groove in the housing, and the outer side of the sapphire glass is disposed in a groove in the pressure plate. The edge of the pressure plate is provided with a connector, which presses the pressure plate and the housing together. The graphite pad I is disposed between the sapphire glass and the housing, and the graphite pad II is disposed between the sapphire glass and the housing.

[0017] Beneficial effects:

[0018] The supercritical nitrogen-based heat exchange performance and frosting observation test rig in this embodiment includes a supercritical nitrogen supply system, a spray system, an air system, a data acquisition system, and a heat exchanger. This test rig can achieve precise control of supercritical nitrogen pressure and flow rate, and air humidity, and stably record heat exchange performance data and frosting images from the heat exchanger, filling a technological gap in the field of aero-engine heat exchanger performance testing. By setting up a supercritical nitrogen supply system, it achieves stable adjustment of supercritical nitrogen at 100–150 g / s; in conjunction with the spray system, it achieves stable adjustment of spray at 1–10 g / s; and by designing the heat exchanger structure, it effectively reduces the probability of microtube blockage and increases the heat exchange density of the heat exchange area, thus improving the stability of the test rig. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a structural diagram of a test bench for heat transfer performance and frost observation based on supercritical nitrogen according to an embodiment of the present invention.

[0021] Figure 2 This is a data acquisition system for a supercritical nitrogen-based heat transfer performance and frost observation test bench according to an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of the internal flow of a heat exchanger according to an embodiment of the present invention;

[0023] Figure 4 This is a schematic diagram of the glass window structure of a heat exchanger according to an embodiment of the present invention.

[0024] In the diagram: 1. Liquid nitrogen Dewar flask; 2. Solenoid valve I; 3. Cryogenic pump; 4. Accumulator; 5. Safety valve I; 6. Cryogenic flow meter; 7. Pneumatic control valve I; 8. Filter I; 9. Pneumatic shut-off valve I; 10. Safety valve II; 11. Heat exchanger; 12. Pneumatic control valve II; 13. High-pressure nitrogen cylinder; 14. Manual shut-off valve; 15. Solenoid valve II; 16. Pneumatic control valve III; 17. Water tank; 18. Manual ball valve; 19. Filter II; 20. Water pump; 21. Pneumatic control valve VI; 22. 23. Water flow meter; 24. Electric regulating valve I; 25. Check valve; 26. Nozzle; 27. Electric heating furnace; 28. Air flow meter; 29. ​​Electric regulating valve II; 30. Electric regulating valve III; 31. Air source; 32. Pressure transmitter I; 33. Temperature transmitter I; 34. Pressure transmitter II; 35. Temperature transmitter II; 36. Pressure transmitter III; 37. Temperature transmitter III; 38. Camera; 39. Pressure transmitter IV; 40. Temperature transmitter IV; 41. 42. Pressure Transmitter IX; 43. Pressure Transmitter V; 44. Temperature Transmitter V; 45. Pressure Transmitter VI; 46. Temperature Transmitter VI; 47. Pressure Transmitter VII; 48. Temperature Transmitter VII; 49. Pressure Transmitter VIII; 50. Temperature Transmitter VIII; 51. DIS Acquisition Module; 52. Acquisition Computer; 53. Hot Side Inlet Flange; 54. Chamber I; 55. Chamber II; 56. Chamber III; 57. Cold Side Inlet Flange; 58a. Hot Side Outlet Flange; 58b. First Microtube; Second microtube; 58c, Third microtube; 58d, Fourth microtube; 58e, Fifth microtube; 58f, Sixth microtube; 58g, Seventh microtube; 58h, Eighth microtube; 58i, Ninth microtube; 58j, Tenth microtube; 59, Cold-side outlet flange; 60, Chamber IV; 61, Chamber V; 62, Chamber VI; 63, Outer shell; 64, Glass window; 641, Outer shell; 642, Pressure plate; 643, Graphite gasket I; 644, Sapphire glass; 645, Graphite gasket II. Detailed Implementation

[0025] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0026] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0028] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The illustrations only show the components related to this application and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0029] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0030] This application provides a test bench for heat transfer performance and frost observation based on supercritical nitrogen, as described below. Figures 1 to 4 Provide a detailed description.

[0031] In one embodiment, refer to Figure 1The test rig includes a supercritical nitrogen supply system, a heat exchanger 11, a spray system, an air system, and a data acquisition system. The heat exchanger 11 includes a first inlet, a second inlet, a first outlet, and a second outlet. The supercritical nitrogen supply system includes a liquid nitrogen Dewar flask 1, a high-pressure nitrogen cylinder 13, a cryogenic pump 3, and a first valve assembly. The outlets of the liquid nitrogen Dewar flask 1 and the high-pressure nitrogen cylinder 13 are connected to the first inlet of the heat exchanger 11 via the cryogenic pump 3 and the first valve assembly, respectively. The first outlet of the heat exchanger 11 is the liquid nitrogen outlet. The outlet of the spray system is connected to the air system pipeline for heat exchange. The second inlet end of the heat exchanger 11 is connected, and the second outlet end of the heat exchanger 11 is the air outlet end; the data acquisition system includes a pressure transmitter, a temperature transmitter, a flow meter, an image acquisition component, a DIS acquisition module 50, and an acquisition computer 51. The supercritical nitrogen supply system, the spray system, and the air system are each equipped with a pressure transmitter, a temperature transmitter, and a flow meter. The output signals of the pressure transmitter, the temperature transmitter, and the flow meter are all transmitted to the acquisition computer 51 through the DIS acquisition module 50. The image acquisition component is used to acquire images of the frost condition inside the heat exchanger 11 and transmit them to the acquisition computer 51.

[0032] In practical implementation, the supercritical nitrogen supply system provides supercritical nitrogen at a specified flow rate and pressure to the cold side of heat exchanger 11. As a refrigerant, the supercritical nitrogen cools the air on the hot side of heat exchanger 11, causing frost to form on the surface of the microtubes in the air. The cryogenic pump 3 pressurizes the liquid nitrogen in the liquid nitrogen Dewar flask 1 to the supercritical pressure of nitrogen. Combined with a bypass, the pressure and flow rate of nitrogen entering heat exchanger 11 are precisely controlled. After entering heat exchanger 11, the nitrogen absorbs heat and heats up. At the instant it crosses the quasi-critical temperature, its heat exchange capacity reaches its maximum.

[0033] The function of a spray system is to inject a specified flow of water into hot air to control the humidity content of the air.

[0034] The function of the air system is to control the temperature, flow rate, and pressure of the incoming air, and then the high-temperature air enters the hot side of the heat exchanger 11.

[0035] The data acquisition system is used to collect data and includes a pressure transmitter, a temperature transmitter, a flow meter, a camera 38, a DIS acquisition module 50, and an acquisition computer 51. The pressure transmitter, temperature transmitter, and flow meter collect temperature, pressure, and flow values ​​at different locations in each system, and transmit the data to the acquisition computer 51 in conjunction with the DIS acquisition module 50. The camera 38 is used to capture images of the frost formation on the surface of the microtubes of the heat exchanger 11.

[0036] The heat exchanger 11, as the research object, is a compact tube bundle heat exchanger. The hot-side medium is high-temperature air, which flows across the dense area outside the microtubes; the cold-side medium is supercritical nitrogen, which flows inside the microtubes and is refluxed through the cavity, thereby achieving rapid cooling of the hot-side air. The wall of the heat exchanger 11 is provided with a glass observation window for the image acquisition component to capture images of frost formation on the surface of the microtubes.

[0037] The test bench in this embodiment can achieve precise control of supercritical nitrogen pressure and flow rate, air humidity, and stably record heat exchanger performance data and frost images, filling a technical gap in the field of aero-engine heat exchanger performance testing. By setting up a supercritical nitrogen supply system, it achieves stable adjustment of supercritical nitrogen at 100-150 g / s; in conjunction with a spray system, it achieves stable adjustment of spray at 1-10 g / s; and by designing the structure of the heat exchanger, it effectively reduces the probability of microtube blockage and increases the heat exchange density of the heat exchange area, thereby improving the stability of the test bench.

[0038] In one embodiment, the image acquisition component is set as camera 38.

[0039] In one embodiment, the supercritical nitrogen supply system further includes an accumulator 4, which is connected to the outlet of the cryogenic pump 3.

[0040] In practical implementation, an accumulator 4 and a bypass are installed after the cryogenic pump 3 in the supercritical nitrogen supply system. The accumulator 4 absorbs the pulsations in the pipeline, ensuring the stability of the pressure before the pneumatic regulating valve I7 and stabilizing the system pressure. The bypass and the main line work together to control the pressure and flow rate of supercritical nitrogen entering the heat exchanger 11, achieving stable regulation of the supercritical nitrogen flow rate.

[0041] In one embodiment, the supercritical nitrogen supply system further includes a filter I8 located between the cryogenic pump and the first inlet of the heat exchanger 11.

[0042] In one embodiment, the first valve assembly includes a solenoid valve I2, a safety valve I5, a pneumatic regulating valve I7, a pneumatic shut-off valve I9, a safety valve II10, a pneumatic regulating valve II12, a manual shut-off valve 14, a solenoid valve II15, and a pneumatic regulating valve III16. The outlet end of the liquid nitrogen Dewar flask 1 is sequentially connected to the solenoid valve I2, the cryogenic pump 3, the safety valve I5, the pneumatic regulating valve I7, the filter I8, the pneumatic shut-off valve I9, the safety valve II10, and the first inlet end of the heat exchanger 11. The outlet end of the high-pressure nitrogen cylinder 13 is connected between the solenoid valve I2 and the cryogenic pump 3 via the manual shut-off valve 14. The outlet end of the manual shut-off valve 14 is connected to the solenoid valve II15. The pneumatic regulating valve II12 is connected to the first outlet end of the heat exchanger 11. The pneumatic regulating valve III16 is connected to the location of the safety valve I5.

[0043] Furthermore, the supercritical nitrogen supply system also includes a cryogenic flow meter 6, which is installed at the inlet end of the pneumatic regulating valve I7, and its function is to measure the mass flow rate of supercritical nitrogen entering the heat exchanger 11.

[0044] Preferably, the low-temperature pipeline before the cold side inlet of heat exchanger 11 needs to be insulated.

[0045] In practice, solenoid valve I2 enables the immediate use of liquid nitrogen, significantly improving the convenience of the experiment and saving liquid nitrogen consumption. Cryogenic pump 3 pressurizes the liquid nitrogen in the liquid nitrogen Dewar flask 1 from 1–2 MPa to 4–5 MPa, reaching the supercritical pressure of nitrogen. Solenoid valve II 15 acts as a drain valve, discharging excess liquid nitrogen from the pipeline.

[0046] Specifically, open pneumatic regulating valve I7, pneumatic shut-off valve I9, pneumatic regulating valve II12, manual shut-off valve 14, solenoid valve II15, and pneumatic regulating valve III16, and open high-pressure nitrogen cylinder 13 to purge the air in the pipeline with high-pressure nitrogen, thus preventing supercritical nitrogen from freezing in the pipeline and causing blockage.

[0047] The pneumatic regulating valves I7 and II12 on the main line, in conjunction with the pneumatic regulating valve III16 installed on the bypass line, precisely control the pressure and flow rate of supercritical nitrogen entering the heat exchanger 11. Pneumatic regulating valve II12 is essential; otherwise, the supercritical nitrogen will be directly discharged into the atmosphere, and pressure cannot be established.

[0048] Before the test, when the cryogenic pump 3 is pre-cooled, the pneumatic shut-off valve I9 ​​can ensure that liquid nitrogen does not enter the heat exchanger 11. At this time, the liquid nitrogen is discharged from the pneumatic regulating valve III16. During the test, when the test personnel need to adjust the air parameters, the pneumatic shut-off valve I9 ​​can cut off the supercritical nitrogen entering the heat exchanger 11.

[0049] In one embodiment, the spray system includes a water tank 17, a manual ball valve 18, a water pump 20, an electric regulating valve I 23, a check valve 24, and a nozzle 25 connected in sequence via pipelines. The nozzle 25 at the outlet end of the spray system is installed on the air system pipeline, and water is sprayed into the air through the nozzle. The spray system also includes a pneumatic regulating valve VI 21, one end of which is connected between the water pump 20 and the electric regulating valve I 23, and the other end of which is connected to the water inlet end of the water tank 17.

[0050] Furthermore, the spray system also includes filter II 19, which is connected between manual ball valve 18 and water pump 20.

[0051] Furthermore, the spray system also includes a water flow meter 22, which is located at the inlet end of the electric regulating valve I 23.

[0052] In practice, the spray system is used to inject a specified flow of water into the high-temperature air to control the humidity of the air. The water pump 20 pressurizes the room-temperature water in the water tank 17 to a pressure 0.5 to 1 MPa higher than that of the high-temperature air. The water flow is precisely controlled by the self-circulation of water and the electric regulating valve of the branch. Then, the water is injected into the high-temperature air through the nozzle 25.

[0053] Specifically, water pump 20 is a three-plunger swashplate pump, which stably pressurizes the ambient temperature tap water in water tank 17 to a pressure 0.5–1 MPa higher than that of high-temperature air. Water tank 17, manual ball valve 18, filter II 19, water pump 20, and pneumatic regulating valve VI 21 together form a water circuit to achieve stable pre-operation of the water.

[0054] A branch line is drawn from the water circuit, and a water flow meter 22, an electric regulating valve I 23, a check valve 24, and a nozzle 25 are installed on the branch line. By adjusting the opening of the electric regulating valve I 23, the water flow rate can be precisely regulated in conjunction with the stable operation of the water circuit. Finally, water is injected into the high-temperature air through the nozzle 25. The water flow meter 22 measures the mass flow rate of the water, and the check valve 24 prevents the high-temperature air from flowing back in.

[0055] In one embodiment, the air system includes an electric heater 26, an electric regulating valve VI 30, and an air source 31 connected in sequence via pipelines. The outlet end of the electric heater 26 is connected to the outlet end of the spray system. The air system also includes an electric regulating valve II 28, which is connected to the second outlet end of the heat exchanger 11. Water is injected into the high-temperature air after the electric heater 26 to prevent damage to the electric heater 26 due to short circuits, component failures, etc.

[0056] Furthermore, the air system also includes a venting branch located between the electric heating furnace 26 and the electric regulating valve VI 30, with an electric regulating valve III 29 at the end of the venting branch.

[0057] Furthermore, the air system also includes an air flow meter 27, which is located at the inlet end of the electric heating furnace 26.

[0058] In practice, the air system controls the temperature, flow rate, and pressure of the incoming air. The electric heating furnace 26 heats the ambient temperature dry air supplied by the air source 31 to the target temperature, and then, in conjunction with the electric regulating valve, controls the air pressure and flow rate. Subsequently, the high-temperature air enters the hot side of the heat exchanger 11.

[0059] Specifically, the function of air source 31 is to supply dry air at room temperature. Here, air source 31 refers to the entire set of equipment, which is a common field in engineering practice. It usually includes an air compressor, an air dryer, a filter, and an air tank, which need not be described in detail here.

[0060] An vent branch is provided, on which an electric regulating valve III 29 is installed. Together with electric regulating valves VI 30 and II 28, it precisely controls the air pressure and flow rate entering the heat exchanger 11. An electric heater 26 is used to control the air temperature entering the heat exchanger 11. An air flow meter 27 is installed before the electric heater 26 to measure the air mass flow rate. Electric regulating valve II 28 is essential; otherwise, the air will be directly discharged into the atmosphere, and pressure cannot be built up.

[0061] refer to Figure 2 The data acquisition system includes a pressure transmitter, a temperature transmitter, a flow meter, a camera 38, a DIS acquisition module 50, and an acquisition computer 51. The output signals of the pressure transmitter, temperature transmitter, and flow meter are 4-20mA, which are transmitted to the DIS acquisition module 50 via signal lines, and finally to the acquisition computer 51 via a network cable; the images from the camera 38 are transmitted to the acquisition computer 51 via a network cable.

[0062] The data acquisition system features a detailed and comprehensive measurement point layout. Temperature and pressure measurement points are arranged at the inlet and outlet of the heat exchanger on the hot and cold sides. Combined with the water flow meter 22 in the spray system and the air flow meter 27 in the air system, the heat transfer capacity and overall heat transfer coefficient of the heat exchanger 11 can be obtained through heat transfer calculations. A pressure measurement point is arranged at the inlet of the cold side of the heat exchanger 11 to determine whether the liquid nitrogen has reached the supercritical pressure. The water flow meter 22 in the spray system and the air flow meter 27 in the air system can be used to obtain the moisture content in the air on the hot side of the heat exchanger 11. A camera 38 is arranged outside the glass window 64 of the heat exchanger 11 to acquire images of frost formation on the outer wall of the microtube near the glass window 64.

[0063] The specific arrangement of the pressure transmitter, temperature transmitter, and flow meter is as follows:

[0064] Pressure transmitter I32 and temperature transmitter I33 are installed at the inlet of cryogenic pump 3. Their function is to collect the pressure and temperature of liquid nitrogen before cryogenic pump 3, with measurement ranges of 0~2MPa and -200~50℃, respectively.

[0065] Pressure transmitter II34 and temperature transmitter II35 are installed at the outlet end of cryogenic pump 3. Their function is to collect the pressure and temperature of nitrogen after cryogenic pump 3, with measurement ranges of 0~6MPa and -200~50℃, respectively.

[0066] Pressure transmitter Ⅲ36 and temperature transmitter Ⅲ37 are installed at the first inlet end of heat exchanger 11. Their function is to collect the pressure and temperature of nitrogen at the cold side inlet of heat exchanger 11, with measurement ranges of 0~6MPa and -200~50℃, respectively.

[0067] Pressure transmitter Ⅳ39 and temperature transmitter Ⅳ40 are installed at the first outlet end of heat exchanger 11. Their function is to collect the pressure and temperature of supercritical nitrogen at the cold side outlet of heat exchanger 11, with measurement ranges of 0~6MPa and -200~300℃, respectively.

[0068] Pressure transmitter V42 and temperature transmitter V43 are located between electric regulating valve I23 and check valve 24. Their function is to collect the pressure and temperature of water in the branch of the spray system, with measurement ranges of 0~4MPa and 0~80℃, respectively.

[0069] Pressure transmitter VI44 and temperature transmitter VI45 are installed at the second inlet end of heat exchanger 11. Their function is to collect the pressure and temperature of the air at the hot side inlet of heat exchanger 11, with measurement ranges of 0~2MPa and 0~300℃, respectively.

[0070] Pressure transmitter VII46 and temperature transmitter VII47 are installed at the second outlet end of heat exchanger 11. Their function is to collect the pressure and temperature of the air at the hot side outlet of heat exchanger 11, with measurement ranges of 0~2MPa and 0~300℃, respectively.

[0071] Pressure transmitter VIII48 and temperature transmitter VIII49 are installed at the inlet end of electric heating furnace 26. Their function is to collect the pressure and temperature of the air in front of electric heating furnace 26, with measurement ranges of 0~2MPa and 0~100℃, respectively.

[0072] Pressure transmitter IX41 is located at the outlet end of water pump 20. Its function is to collect the pressure of water after water pump 20 in the spray system. The measurement range is 0 to 4 MPa.

[0073] The Camera 38 uses a standard digital camera with a 2K resolution, and the frosting process usually lasts for several minutes, so there is no need to choose a high-speed photography camera.

[0074] For the low-temperature flow meter 6, water flow meter 22 and air flow meter 27, the measurement parameters of water flow meter 22 and air flow meter 27 are related to the calculation of moisture content W, where moisture content W = q1 / q2, q1 is the mass flow rate of water in the air and q2 is the mass flow rate of air.

[0075] The measurement parameters of pressure transmitter Ⅲ36 are crucial, as they determine whether liquid nitrogen reaches supercritical pressure upon entering heat exchanger 11.

[0076] The measurement parameters of pressure transmitter III36, temperature transmitter III37, pressure transmitter IV39, temperature transmitter IV40, and cryogenic flow meter 6 are related to heat exchange calculations. The heat exchange capacity Q within heat exchanger 11 can be obtained from these physical parameters. Heat exchange capacity Q = qm * Δh, where qm is the supercritical nitrogen mass flow rate, and Δh is the enthalpy difference between the supercritical nitrogen at the cold side outlet and the nitrogen at the inlet of heat exchanger 11. Test personnel can also calculate the heat exchange capacity using the measurement parameters of pressure transmitter VI44, temperature transmitter VI45, pressure transmitter VII46, temperature transmitter VII47, and air flow meter 27; the principle is the same.

[0077] The measurement parameters of temperature transmitters Ⅲ37, Ⅳ40, Ⅵ45, and Ⅶ47 are related to heat transfer calculation. Through these physical parameters, the logarithmic mean temperature difference △tm of heat exchanger 11 can be obtained, and then the overall heat transfer coefficient k of heat exchanger 11 can be obtained. The overall heat transfer coefficient k = Q / △tm*A, where Q is the amount of heat exchanged and A is the heat exchange area of ​​heat exchanger 11.

[0078] In one embodiment, refer to Figure 3 The heat exchanger 11 includes a shell 63. A hot-side inlet flange 52 and a hot-side outlet flange 57 are respectively provided on one opposite side of the shell 63, and a cold-side inlet flange 56 and a cold-side outlet flange 59 are respectively provided on the other opposite side of the shell 63. An air inlet is provided on the hot-side inlet flange 52, serving as the second inlet end of the heat exchanger 11. An air outlet is provided on the hot-side outlet flange 57, serving as the second outlet end of the heat exchanger 11. A supercritical nitrogen inlet is provided on the cold-side inlet flange 56, serving as the second outlet end of the heat exchanger 11. At the first inlet end, a supercritical nitrogen outlet is provided on the cold side outlet flange 59, which serves as the first outlet end of the heat exchanger 11. The outer side of the shell 63 is provided with multiple independent chambers, and the interior of the shell 63 is provided with multiple microtubes. The supercritical nitrogen inlet and the supercritical nitrogen outlet are respectively connected to the microtubes through their respective chambers, forming a U-shaped supercritical nitrogen flow path. The outer side of the shell 63 is also provided with a glass window 64, and an image acquisition component is mounted on the outside of the glass window 64 to obtain images of frost formation on the outer wall of the microtubes near the glass window 64.

[0079] In specific implementation, the range of heat exchanger hot / cold side inlet parameters applicable to this test bench includes the following:

[0080] The flow rate range for supercritical nitrogen is 100–150 g / s, and the pressure range is 4–6 MPa; the flow rate range for water is 1–10 g / s; and the flow rate range for air is 300–500 g / s, the pressure range is 0.5–1 MPa, and the temperature range is 400–500 K. Based on research needs, designers can draw upon the design experience of this system to expand the hot / cold side inlet parameters of the heat exchanger to a wider research range.

[0081] Specifically, the microtubes are several identical Φ3×1 stainless steel tubes welded to the outer shell 63. In this embodiment, there are a total of 200 microtubes, arranged in 20 rows perpendicular to the plane of the paper, with 10 tubes in each row. The figure only shows 10 tubes from one row (the first microtube 58a to the tenth microtube 58j). Those skilled in the art can select the size and quantity of the stainless steel tubes according to the actual heat exchange area required.

[0082] Hot-side air enters heat exchanger 11 through hot-side inlet flange 52, flows through tube bundle space and indirectly exchanges heat with supercritical nitrogen in microtubes (shown as first microtube 58a to tenth microtube 58j), and finally flows out of heat exchanger 11 through hot-side outlet flange 57.

[0083] Supercritical nitrogen flows within the microtube and through various chambers. The function of chambers I (53), II (54), III (55), IV (60), V (61), and VI (62) is to change the flow direction of the supercritical nitrogen and ensure heat exchange capacity. Supercritical nitrogen enters chamber III 55 from the cold-side inlet flange 56, then flows downward into chamber VI 62 through microtubes (first microtube 58a, second microtube 58b) after a U-shaped reversal. After another U-shaped reversal, it flows upward into chamber II 54 through microtubes (third microtube 58c, fourth microtube 58d). After yet another U-shaped reversal, it flows downward into chamber V 61 through microtubes (fifth microtube 58e, sixth microtube 58f). After yet another U-shaped reversal, it flows upward into chamber I 53 through microtubes (seventh microtube 58g, eighth microtube 58h). After yet another U-shaped reversal, it flows downward into chamber IV 60 through microtubes (ninth microtube 58i, tenth microtube 58j). Finally, it flows out through the cold-side outlet flange 59.

[0084] By setting up six chambers in the heat exchanger, a U-shaped reversible flow of supercritical nitrogen is achieved. Compared with the conventional design scheme where the nitrogen flows through all microtubes in a single direction, the flow distribution of supercritical nitrogen in each microtube is more uniform, which effectively reduces the probability of microtube blockage and increases the heat transfer density of the heat exchange area.

[0085] In one embodiment, refer to Figure 4 The glass window 64 includes a housing 641, a pressure plate 642, a graphite pad I 643, a sapphire glass 644, and a graphite pad II 645. The housing 641 is connected to the outer shell 63. The inner side of the sapphire glass 644 is disposed in the groove of the housing 641, and the outer side of the sapphire glass 644 is disposed in the groove of the pressure plate 642. The edge of the pressure plate 642 is provided with a connector, which presses the pressure plate 642 and the housing 641 together. The graphite pad I 643 is disposed between the sapphire glass 644 and the housing 641, and the graphite pad II 645 is disposed between the sapphire glass 644 and the housing 641.

[0086] Specifically, the inside of the glass window 64 is filled with high-temperature and high-pressure air. The graphite pads I 643 and II 645 are used to seal the glass and absorb the deformation of the sapphire glass 644 under high temperature and high pressure conditions. The thickness of the sapphire glass 644 has been checked for bending strength.

[0087] A typical workflow for this test bench is as follows:

[0088] 1. Open pneumatic regulating valve I7, pneumatic shut-off valve I9, pneumatic regulating valve II12, manual shut-off valve 14, solenoid valve II15, and pneumatic regulating valve III16. Open high-pressure nitrogen cylinder 13 and purge the entire liquid nitrogen supply pipeline with nitrogen to remove air from the pipeline.

[0089] 2. Open liquid nitrogen Dewar flask 1, open solenoid valve I2, and adjust pneumatic regulating valve I7, pneumatic regulating valve II12, and pneumatic regulating valve III16 to control the liquid nitrogen flow rate. The pre-cooled liquid nitrogen will be discharged from the end of the pipeline. After the liquid nitrogen pipeline is pre-cooled, close solenoid valve I2.

[0090] 3. Start the air source 31, adjust the electric regulating valve II 28, electric regulating valve III 29, and electric regulating valve VI 30 to control the air flow, transfer the air into the heat exchanger 11, and turn on the electric heating furnace 26 to heat the air;

[0091] 4. Open the manual ball valve 18, water pump 20, and pneumatic regulating valve VI 21 to perform a pre-run in the water circuit of the spray device;

[0092] 5. After the air parameters reach the target value, open the electric regulating valve I23 and inject a certain amount of water into the high-temperature air through the nozzle 25. Open the solenoid valve I2 to release liquid nitrogen and start the cryogenic pump 3 to introduce liquid nitrogen into the heat exchanger 11. Adjust the liquid nitrogen flow rate by adjusting the speed of the cryogenic pump 3, the pneumatic regulating valve I7, the pneumatic regulating valve II12, and the pneumatic regulating valve III16. After reaching the target value, start recording data and frosting images.

[0093] 6. During the test, if it is necessary to change the air inlet parameters, close the solenoid valve I2 to cut off the liquid nitrogen, and at the same time close the electric regulating valve I23 to stop the spray injection of high-temperature air until the test personnel adjust the air inlet parameters to the target value. Then, follow step 5 to inject a certain amount of water into the high-temperature air and release the liquid nitrogen.

[0094] 7. After the data acquisition is completed, close the solenoid valve I2 to cut off the liquid nitrogen, and at the same time close the electric regulating valve I23 to stop the spray injection of high-temperature air. Then turn off the cryogenic pump 3, water pump 20, and electric heating furnace 26. After the air temperature drops to room temperature, close all valves and finally turn off the gas source 31.

[0095] The embodiments provided by this invention, in conjunction with a cryogenic booster pump, bypass, accumulator 4, and pneumatic regulating valve, achieve stable regulation of supercritical nitrogen at 100–150 g / s; and in conjunction with internal water circulation, branch lines, a three-plunger swashplate pump, electric regulating valve, and nozzle 25, achieve stable regulation of spray at 1–10 g / s. Based on this, the quantity, location, and function of the test elements (pressure transmitter, temperature transmitter, flow meter) in the system, as well as the measurement approach for important parameters such as moisture content, heat exchange, and overall heat transfer coefficient, are comprehensively described. The heat exchanger 11 has six internal chambers, which, in conjunction with microtubes, enable U-shaped backflow of supercritical nitrogen, effectively reducing the probability of microtube blockage and increasing the heat exchange density in the heat exchange area. Simultaneously, a scheme is proposed to open a glass window 64 on the side of the heat exchanger 11 shell; this scheme is feasible and can effectively ensure the stability of the glass window 64 during the experiment.

[0096] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A test bench for heat transfer performance and frost observation based on supercritical nitrogen, characterized in that, The test bench includes a supercritical nitrogen supply system, a heat exchanger (11), a spray system, an air system, and a data acquisition system. The heat exchanger (11) includes a first inlet end, a second inlet end, a first outlet end, and a second outlet end. The supercritical nitrogen supply system includes a liquid nitrogen Dewar flask (1), a high-pressure nitrogen cylinder (13), a cryogenic pump (3), and a first valve assembly. The outlet ends of the liquid nitrogen Dewar flask (1) and the high-pressure nitrogen cylinder (13) are respectively connected to the first inlet end of the heat exchanger (11) through the cryogenic pump (3) and the first valve assembly. The first outlet end of the heat exchanger (11) is the liquid nitrogen outlet end. The outlet end of the spray system is connected to the air system pipeline and then connected to the heat exchanger. The second inlet end of the heat exchanger (11) is connected, and the second outlet end of the heat exchanger (11) is the air outlet end; the data acquisition system includes a pressure transmitter, a temperature transmitter, a flow meter, an image acquisition component, a DIS acquisition module (50) and an acquisition computer (51). The supercritical nitrogen supply system, the spray system and the air system are each equipped with a pressure transmitter, a temperature transmitter and a flow meter. The output signals of the pressure transmitter, the temperature transmitter and the flow meter are all transmitted to the acquisition computer (51) through the DIS acquisition module (50). The image acquisition component is used to acquire images of the frost situation in the heat exchanger (11) and transmit them to the acquisition computer (51); The heat exchanger (11) includes a shell (63). A hot-side inlet flange (52) and a hot-side outlet flange (57) are respectively provided on one opposite side of the shell (63). A cold-side inlet flange (56) and a cold-side outlet flange (59) are respectively provided on the other opposite side of the shell (63). An air inlet is provided on the hot-side inlet flange (52), which serves as the second inlet end of the heat exchanger (11). An air outlet is provided on the hot-side outlet flange (57), which serves as the second outlet end of the heat exchanger (11). A supercritical nitrogen inlet is provided on the cold-side inlet flange (56), which serves as the heat exchanger... The first inlet end of the heat exchanger (11) is provided with a supercritical nitrogen outlet on the cold side outlet flange (59), which serves as the first outlet end of the heat exchanger (11); the outer side of the shell (63) is provided with multiple independent chambers, and the interior of the shell (63) is provided with multiple microtubes. The supercritical nitrogen inlet and the supercritical nitrogen outlet are respectively connected to the microtubes through their respective chambers to form a U-shaped supercritical nitrogen flow path; the outer side of the shell (63) is also provided with a glass window (64), and an image acquisition component is installed on the outer side of the glass window (64) to obtain images of frost on the outer wall of the microtubes near the glass window (64).

2. The heat transfer performance and frosting observation test rig based on supercritical nitrogen according to claim 1, characterized in that, The supercritical nitrogen supply system also includes an accumulator (4), which is connected to the outlet of the cryogenic pump (3).

3. The heat transfer performance and frosting observation test rig based on supercritical nitrogen according to claim 1, characterized in that, The supercritical nitrogen supply system also includes filter I (8), which is located between the cryogenic pump and the first inlet end of the heat exchanger (11).

4. The heat transfer performance and frosting observation test rig based on supercritical nitrogen according to claim 3, characterized in that, The first valve assembly includes solenoid valve I (2), safety valve I (5), pneumatic regulating valve I (7), pneumatic shut-off valve I (9), safety valve II (10), pneumatic regulating valve II (12), manual shut-off valve (14), solenoid valve II (15), and pneumatic regulating valve III (16). The outlet end of the liquid nitrogen Dewar flask (1) is connected in sequence to solenoid valve I (2), cryogenic pump (3), safety valve I (5), pneumatic regulating valve I (7), filter I (8), pneumatic shut-off valve I (9), safety valve II (10), and the first inlet end of heat exchanger (11). The outlet end of the high-pressure nitrogen cylinder (13) is connected between solenoid valve I (2) and cryogenic pump (3) through manual shut-off valve (14). The outlet end of manual shut-off valve (14) is connected to solenoid valve II (15). Pneumatic regulating valve II (12) is connected to the first outlet end of heat exchanger (11). Pneumatic regulating valve III (16) is connected to the location of safety valve I (5).

5. The heat transfer performance and frosting observation test rig based on supercritical nitrogen according to claim 1, characterized in that, The spray system includes a water tank (17), a manual ball valve (18), a water pump (20), an electric regulating valve I (23), a check valve (24), and a nozzle (25) connected in sequence through pipelines. The nozzle (25) at the outlet end of the spray system is installed on the air system pipeline, and water is sprayed into the air through the nozzle. The spray system also includes a pneumatic regulating valve VI (21). One end of the pneumatic regulating valve VI (21) is connected between the water pump (20) and the electric regulating valve I (23), and the other end of the pneumatic regulating valve VI (21) is connected to the water inlet end of the water tank (17).

6. The heat transfer performance and frosting observation test rig based on supercritical nitrogen according to claim 5, characterized in that, The spray system also includes filter II (19), which is connected between manual ball valve (18) and water pump (20).

7. The heat transfer performance and frosting observation test rig based on supercritical nitrogen according to claim 1, characterized in that, The air system includes an electric heating furnace (26), an electric regulating valve VI (30) and an air source (31) connected in sequence by pipelines. The outlet end of the electric heating furnace (26) is connected to the outlet end of the spray system. The air system also includes an electric regulating valve II (28), which is connected to the second outlet end of the heat exchanger (11).

8. The heat transfer performance and frosting observation test rig based on supercritical nitrogen according to claim 7, characterized in that, The air system also includes a venting branch, which is located between the electric heating furnace (26) and the electric regulating valve VI (30), and the end of the venting branch is equipped with an electric regulating valve III (29).

9. The heat transfer performance and frosting observation test rig based on supercritical nitrogen according to claim 1, characterized in that, The glass window (64) includes a housing (641), a pressure plate (642), a graphite pad I (643), a sapphire glass (644), and a graphite pad II (645). The housing (641) is connected to the outer shell (63). The inner side of the sapphire glass (644) is located in the groove of the housing (641), and the outer side of the sapphire glass (644) is located in the groove of the pressure plate (642). The edge of the pressure plate (642) is provided with a connector, which presses the pressure plate (642) and the housing (641) together. The graphite pad I (643) is located between the sapphire glass (644) and the housing (641), and the graphite pad II (645) is located between the sapphire glass (644) and the housing (641).

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