A nitrogen fixation and high efficiency heat pipe refrigeration unit for air electric propulsion superconducting electric machines

Abstract

The application discloses a nitrogen fixation and cold storage high-efficiency heat pipe refrigeration unit for an aviation electric propulsion superconducting motor, comprising a Dewar, a nitrogen fixation cavity, a refrigerator cold head, a liquid nitrogen heat pipe, fins, a superconducting magnet and a cold shield. The liquid nitrogen heat pipe is a closed two-phase heat pipe. The top end of the heat pipe is located in the nitrogen fixation cavity and exchanges heat with the nitrogen fixation directly through the fins. The bottom end of the heat pipe is in close contact with the surface of the superconducting magnet for heat conduction and heat exchange. The high-efficiency heat exchange capacity of the two-phase heat pipe rapidly transfers the cold energy in the nitrogen fixation cavity to the superconducting magnet, realizing high-power heat transfer. After the superconducting magnet works, the refrigerator cold head can be lifted, reducing the heat leakage of the refrigeration unit and making the refrigeration unit only rely on the nitrogen fixation in the nitrogen fixation cavity to provide cold energy. The refrigeration unit can be applied to the aviation electric propulsion superconducting motor, can provide the superconducting magnet with low-temperature working conditions of hours, greatly reduces the weight of the on-board low-temperature refrigeration system and guarantees the effective working time of the superconducting motor.

Description

Technical Field

[0001] This invention is a high-efficiency nitrogen-fixed heat pipe cooling unit for superconducting motors used in aerospace electric propulsion. Specifically, it is a high-efficiency nitrogen-fixed heat pipe cooling unit that utilizes the large cold storage capacity of nitrogen to provide an hourly low-temperature environment for high-temperature superconducting magnets. Background Technology

[0002] The aviation industry is developing towards green, efficient, and intelligent directions. In recent years, high-power electric propulsion technology has undoubtedly been one of the most watched new technologies in the aviation power market, providing new ideas for aircraft and propulsion system design. High-power aviation electric propulsion has significant characteristics such as distributed propulsion, flexible maneuverability, high efficiency, and low pollution. Its development requires the support of high-power-density special electric system technologies, among which superconducting motors have gradually gained favor among researchers.

[0003] However, unlike traditional motors, superconducting motors require cryogenic cooling, and their operation heavily depends on the properties of superconducting materials and the cryogenic stability of the wound magnets. External heat leakage and high-frequency heat generation within the motor pose significant challenges to the stability of the superconducting magnets and cryogenic protection conditions. Whether through cryogenic liquid immersion cooling or cryogenic conduction cooling, the size and mass of the cryogenic cooling structure and cryogenic protection system are substantial, often becoming a burden in the design of superconducting motor systems.

[0004] Considering the application environment of aerospace electric propulsion, there is a high demand for reducing the size and weight of the motor system. This invention uses a two-phase copper heat pipe with gas and liquid nitrogen for conductive cooling of the superconducting magnet, significantly improving the thermal conductivity of the magnet region and the cold source region, thus achieving better magnet cooling sensitivity and stability. Liquid nitrogen is stored and cooled in the nitrogen-fixing chamber to form solid nitrogen, and the strong heat capacity of solid nitrogen provides sufficient cryogenic cold storage to ensure the thermal stability of the superconducting magnet itself after it is removed from the cooling equipment. A retractable cold head is used to minimize heat leakage at the cold head location and smoothly transition to the cryogenic maintenance stage of nitrogen-fixed cold storage of the superconducting magnet. Finally, the heat exchange between the hot and cold ends of the closed liquid nitrogen heat pipe ensures the effective working time of the superconducting magnet on the order of hours. Summary of the Invention

[0005] The purpose of this invention is to provide a nitrogen-fixed cold storage high-efficiency heat pipe cooling unit for aero-electric propulsion superconducting motors. This system can be applied to aero-electric propulsion superconducting motors to provide a low-temperature environment on the order of hours for superconducting magnets, ensuring the effective working time of the superconducting motor and increasing the loiter time of the aircraft.

[0006] The technical solution adopted by this invention to achieve its objective is as follows: It includes a Dewar flask, a nitrogen-fixing chamber, a refrigerator cold head mounted on top of the Dewar flask, a liquid nitrogen heat pipe, fins, a superconducting magnet, and a cold shield; the superconducting magnet is installed in the liquid nitrogen heat pipe interlayer, the lower end of the liquid nitrogen heat pipe is installed in the cold shield, and the upper end of the liquid nitrogen heat pipe is installed in the nitrogen-fixing chamber; the nitrogen-fixing chamber is installed in the Dewar flask; Its characteristic is that the liquid nitrogen heat pipe is a closed heat pipe, and the interior of the liquid nitrogen heat pipe has a two-phase flow of liquid nitrogen and nitrogen gas; the top end of the liquid nitrogen heat pipe is located in the nitrogen-fixing chamber, and the top end of the liquid nitrogen heat pipe... The fins directly exchange heat with the nitrogen in the nitrogen-fixing chamber; the bottom of the liquid nitrogen heat pipe only contacts the surface of the superconducting magnet, and heat is exchanged through heat conduction; the liquid nitrogen heat pipe is a closed copper heat pipe with gas and liquid nitrogen phases to conduct heat to cool the superconducting magnet, which greatly improves the thermal conductivity between the magnet area and the cold source area, and achieves better magnet cooling sensitivity and stability; the cold head of the refrigerator is a retractable cold head. After the superconducting magnet starts working, the retractable mechanism is activated to detach the cold head from the upper wall of the nitrogen-fixing chamber. This cooling system relies solely on the nitrogen in the nitrogen-fixing chamber to provide cooling.

[0007] The working principle of this invention is:

[0008] When the superconducting magnet is working, it generates heat, which is transferred to the lower end of the liquid nitrogen heat pipe through thermal conduction. Therefore, the lower end of the liquid nitrogen heat pipe is the hot end. The liquid nitrogen inside the heat pipe absorbs heat and turns into nitrogen gas. The nitrogen gas rises to the nitrogen-fixing chamber at the top of the liquid nitrogen heat pipe. The fins at the top of the liquid nitrogen heat pipe transfer heat to the solid nitrogen in the nitrogen-fixing chamber. The nitrogen gas releases heat when it cools and turns back into liquid nitrogen. Since this invention uses a closed heat pipe, the liquid nitrogen will flow back to the lower end of the liquid nitrogen heat pipe under the action of gravity. The cold head of the refrigerator is raised by a telescopic mechanism, so that the cold head is separated from the upper wall of the nitrogen-fixing chamber. The refrigeration unit then operates in a closed loop, with the solid nitrogen in the nitrogen-fixing chamber providing the cooling capacity. This provides a stable low-temperature environment for the superconducting magnet, ensuring its long-term operation.

[0009] Compared with the prior art, the beneficial effects of the present invention are:

[0010] I. This invention employs a fully enclosed heat pipe filled with liquid nitrogen. During operation, the heat pipe exhibits a two-phase flow of nitrogen gas and liquid nitrogen. The liquid nitrogen heat pipe contacts the surface of the superconducting magnet, and heat exchange occurs via conduction. Compared to immersion cooling of the superconducting magnet, conduction cooling effectively avoids the structural instability and leakage problems associated with immersion cooling, thus improving the structural reliability of the magnet cooling. Using copper, with its high thermal conductivity, as the material for the liquid nitrogen heat pipe enables rapid heat transfer to the vapor-liquid two-phase working fluid within the heat pipe, achieving high-power heat conversion.

[0011] Second, this invention employs a retractable cold head and nitrogen-fixing refrigeration technology. When in operation, the cold head is in close contact with the upper wall of the nitrogen-fixing chamber. After all the liquid nitrogen in the nitrogen-fixing chamber has been converted into solid nitrogen, the cold head of the refrigeration unit can be lifted. After the cold head is detached from the upper wall of the nitrogen-fixing chamber, the operator can disconnect the connection between the cold head of the refrigeration unit and the compressor. The refrigeration unit then enters closed-loop operation, relying solely on the solid nitrogen in the nitrogen-fixing chamber to provide a stable low-temperature working environment for the superconducting magnet on an hourly basis, thereby achieving the goal of low-temperature refrigeration without the participation of a compressor, reducing the carrying mass of the airborne cryogenic system, and meeting the requirements of aerospace electric propulsion systems for low volume and low mass of superconducting motors.

[0012] Third, the side of the cooling screen has high / low voltage feed ports for connecting current leads and other sensor leads, which can effectively reduce heat leakage of the cooling unit. While ensuring the stable operation of the superconducting magnet, the working status of the superconducting magnet can also be observed and detected in real time. Attached Figure Description

[0013] Figure 1 This is a front view of the overall structure of an embodiment of the present invention.

[0014] 1-Refrigerator, 2-Vacuum port, 3-Dewar, 4-Nitrogen fixation chamber, 5-Fin, 6-Feeding port, 7-Cold shield, 8-Liquid nitrogen heat pipe, 9-Superconducting magnet

[0015] Figure 2 This is a side view of the overall structure of an embodiment of the present invention.

[0016] 6-Feedout port, 8-Liquid nitrogen heat pipe, 9-Superconducting magnet, 10-Liquid nitrogen inlet, 11-Liquid nitrogen outlet Detailed Implementation

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and implementation guidelines.

[0018] Figure 1As shown, one specific embodiment of the present invention discloses a high-efficiency heat pipe refrigeration unit for nitrogen storage in superconducting motors for aerospace electric propulsion, comprising a Dewar (3), a nitrogen-fixing chamber (4), a refrigeration cold head (1) mounted on the top of the Dewar, a liquid nitrogen heat pipe (8), fins (5), a superconducting magnet (9), and a cold shield (7); characterized in that: the liquid nitrogen heat pipe (8) is a closed heat pipe, and the liquid nitrogen heat pipe (8) has a two-phase flow of nitrogen gas and liquid nitrogen inside when it is working; in this example, the liquid nitrogen heat pipe (8) is a closed heat pipe, and the top of the liquid nitrogen heat pipe (8) is located in the nitrogen-fixing chamber, and the liquid nitrogen heat pipe (8) is a liquid nitrogen heat pipe with a nitrogen-fixing chamber. The top of the nitrogen heat pipe (8) exchanges heat directly with the nitrogen in the nitrogen-fixed cavity (4) through the fins (5); the bottom of the liquid nitrogen heat pipe (8) is in close contact with the radial surface of the superconducting magnet (9) and exchanges heat through heat conduction; the liquid nitrogen heat pipe (8) is made of copper with high thermal conductivity, which can quickly transfer the cold energy in the nitrogen-fixed cavity (4) to the superconducting magnet (9), thereby achieving high-power heat conversion; the refrigerator cold head (1) is a retractable cold head, and the refrigerator cold head (1) is raised after the superconducting magnet (9) starts working. The cooling system relies solely on the nitrogen in the nitrogen-fixed cavity (4) to provide the cooling energy.

[0019] Figure 2 This is a side view of the overall structure of an embodiment of the present invention. The cold screen (7) and the Dewar (3) are an integral structure. The interior of the cold screen (7) and the Dewar (3) is evacuated through the vacuum port (2). The top of the nitrogen-fixing chamber (4) is connected to the liquid nitrogen inlet (10) and the liquid nitrogen outlet (11) pipelines, and the liquid nitrogen inlet (10) and the liquid nitrogen outlet (11) pipelines extend to the top of the Dewar (3). The side of the cold screen (7) has a strong / weak current feed port (6).

[0020] First, the staff filled the liquid nitrogen heat pipe (8) with liquid nitrogen. Then, they fixed the upper end of the liquid nitrogen heat pipe (8) and the fins (5). They installed the fins (5) and the upper end of the liquid nitrogen heat pipe (8) in the nitrogen-fixing chamber (4), installed the superconducting magnet (9) in the lower end of the liquid nitrogen heat pipe (8), installed the lower end of the liquid nitrogen heat pipe (8) and the superconducting magnet (9) in the cold screen (7), and installed the nitrogen-fixing chamber (4) in the Dewar (3). They connected the vacuum port pipe (2) at the top of the Dewar (3), started the vacuum machine, and emptied the cold screen (7) and the inside of the Dewar (3). Vacuum the interior and, once the required vacuum level is reached, shut down the vacuum machine and disconnect the vacuum port pipeline. Connect the liquid nitrogen inlet (10) and liquid nitrogen outlet (11) pipelines at the top of the Dewar (3), start the refrigerator, and keep the refrigerator cold head pressed against the upper wall of the nitrogen-fixing chamber (4). Once the temperature inside the nitrogen-fixing chamber (4) drops to the liquid nitrogen temperature, inject liquid nitrogen into the liquid nitrogen inlet (10) at the top of the Dewar (3). The liquid nitrogen enters the nitrogen-fixing chamber (4) through the pipeline. When liquid nitrogen overflows from the liquid nitrogen outlet (11), stop injecting liquid nitrogen and seal the liquid nitrogen inlet and outlet pipelines. The cold head (1) continues to work to cool the nitrogen-fixing chamber (4) until all the liquid nitrogen in the nitrogen-fixing chamber (4) is converted into solid nitrogen; the superconducting magnet (9) is energized to put the superconducting magnet (9) into working condition; since the superconducting magnet (9) generates heat during operation, the lower end of the liquid nitrogen heat pipe (8) is the hot end, and the superconducting magnet (9) will transfer heat to the liquid nitrogen heat pipe (8) through heat conduction. The liquid nitrogen in the heat pipe (8) absorbs heat and is converted into nitrogen gas. The nitrogen gas rises to the nitrogen-fixing chamber (4) at the top of the liquid nitrogen heat pipe (8), and the fins at the top of the liquid nitrogen heat pipe (8) are... (5) Heat is transferred to nitrogen fixation in nitrogen fixation chamber (4). Nitrogen gas is cooled and converted into liquid nitrogen. Under the action of gravity, it flows back to the lower end of liquid nitrogen heat pipe (8). After the refrigeration unit is stable, the cold head (1) of the refrigeration machine is lifted by the telescopic mechanism so that the cold head (1) is separated from the upper wall of nitrogen fixation chamber (4). The refrigeration machine pipeline and its power supply are disconnected. The refrigeration unit will switch to closed-loop operation. The nitrogen fixation in nitrogen fixation chamber (3) provides cooling capacity and provides a stable low temperature environment for superconducting magnet (9) to ensure long-term operation of superconducting magnet (9).

Claims

1. A nitrogen-fixing cold storage heat pipe refrigeration unit for use in aerospace electric propulsion superconducting motors, characterized in that: The system includes a vacuum-insulated Dewar (3), a nitrogen-fixing chamber (4), a refrigerator cold head (1) installed on top of the vacuum-insulated Dewar (3), a liquid nitrogen heat pipe (8), fins (5), a superconducting magnet (9), and a cold shield (7); the superconducting magnet (9) is installed in the lower interlayer of the liquid nitrogen heat pipe (8), the lower end of the liquid nitrogen heat pipe (8) is installed in the cold shield (7), the upper end of the liquid nitrogen heat pipe (8) is installed in the nitrogen-fixing chamber (4), and the nitrogen-fixing chamber (4) is installed in the vacuum-insulated Dewar (3). The nitrogen-fixing chamber (4) is used to store liquid nitrogen and cool it to form solid nitrogen. The liquid nitrogen heat pipe (8) is a closed copper heat pipe. The heat transfer between the hot and cold ends is achieved through the two-phase heat exchange of liquid nitrogen and nitrogen gas in the nitrogen heat pipe (8). The top of the liquid nitrogen heat pipe (8) exchanges heat with the solid nitrogen in the nitrogen-fixing chamber (4) through the fins (5). The bottom of the liquid nitrogen heat pipe (8) is in close contact with the radial surface of the superconducting magnet (9) and heat exchange is carried out through heat conduction. The cold head (1) of the refrigerator adopts a telescopic structure. After all the liquid nitrogen in the nitrogen-fixing chamber (4) is converted into solid nitrogen, the cold head (1) of the refrigerator is lifted through the telescopic structure, so that the cold head (1) of the refrigerator is separated from the upper wall of the nitrogen-fixing chamber (4) and the solid nitrogen in the nitrogen-fixing chamber (4) provides the cooling capacity.

2. The nitrogen-fixing cold storage heat pipe refrigeration unit as described in claim 1, characterized in that, The top fins (5) of the liquid nitrogen heat pipe (8) are made of copper.

3. The nitrogen-fixing cold storage heat pipe refrigeration unit as described in claim 1, characterized in that, The cold shield (7) and the vacuum insulation Dewar (3) adopt an integrated structure. When working, a vacuum is required to isolate the internal and external environment of the refrigeration unit, reduce the influence of room temperature on the refrigeration unit, and control system heat leakage. The cold shield (7) has a feed through port (6) on its side, and the vacuum insulation Dewar (3) has a vacuum port (2), a liquid nitrogen pipeline outlet (11), and a liquid nitrogen pipeline inlet (10) on its top. The feed through port (6), the vacuum port (2), the liquid nitrogen pipeline outlet (11), and the liquid nitrogen pipeline inlet (10) all adopt a vacuum insulation structure to compress heat leakage.

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