Magnetofluid dynamic sealing structure suitable for rotary superconducting induction heating system

Abstract

The invention relates to a magnetofluid dynamic sealing structure suitable for a rotary superconducting induction heating system. The magnetofluid dynamic sealing structure comprises a static magnetofluid inner layer, a rotary magnetofluid shell, a magnetofluid sealing unit, a thermal stress compensation mechanism and an integrated gas transmission and thermal management subsystem. By adopting the low-temperature compatible magnetic fluid, the invar alloy thermal compensation ring, the flexible supporting element and the multi-level heat insulation structure, the problems of sealing gap instability, carrier liquid solidification, serious heat leakage and the like in the large-shaft-diameter and high-rotating-speed working condition under the liquid helium temperature area are effectively solved. According to the application, sufficient heat insulation between a 4.2-8K working environment and a magnetofluid dynamic sealing area in a superconducting cooling area can be realized, the flowability of the magnetofluid is ensured while long-term zero-leakage sealing is realized, low-temperature failure is avoided, meanwhile, smoothness of a gas helium circulation channel is ensured, the refrigeration load is remarkably reduced, and the operation reliability of a system is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of superconducting heating, in particular to the technical field of combination of superconducting technology and cryogenic engineering. BACKGROUND

[0002] Superconducting technology, with its unique physical properties such as zero resistance and complete diamagnetism, has shown irreplaceable application value in energy transmission, medical imaging, and high-end industrial heating. In particular, in a rotating superconducting induction heating system, by integrating a superconducting coil into a hollow rotor structure and driving it to rotate at high speed to form a dynamic alternating magnetic field, efficient and uniform heating of the workpiece to be processed is achieved, which has become a key path to improve the quality and energy efficiency of material heat treatment. However, the core challenge of such a system is how to maintain the superconducting coil in an extremely low temperature environment (usually in the liquid helium temperature range of 4.2K to 8K) while ensuring long-term, stable and zero-leakage dynamic sealing between rotating parts and stationary cooling circuits. This requirement is directly related to the continuous maintenance of superconducting state, optimization of system thermal efficiency, and overall operation reliability.

[0003] In the existing technical system, magnetic fluid sealing has been widely used in high vacuum rotary sealing scenes at room temperature and small shaft diameters due to its non-contact, wear-free and theoretically "zero leakage" advantages. Its basic principle is to use permanent magnets or electromagnets to build a strong gradient magnetic field at the sealing gap, so that the carrier liquid containing nanoscale magnetic particles is tightly bound to the small annular area between the pole shoes and the shaft, forming a multi-stage liquid "O" ring seal, thereby effectively blocking the cross-interface migration of gas or liquid medium. This technology performs excellently under normal working conditions, especially for low linear speed, small shaft diameter and stable temperature environment. However, when it is tried to be introduced into a superconducting rotating system with large diameter (200mm-500mm), high linear speed (30-50m / s) and extremely low temperature (4.2K-8K), its inherent technical limitations are exposed and a series of deep-seated physical contradictions are triggered.

[0004] At its root, the existing magnetic fluid sealing technology faces two big mutually coupled and difficult to reconcile technical bottlenecks. One of them, the oil-based or water-based carrier liquid relied on by the conventional magnetic fluid will rapidly solidify in the liquid helium temperature zone, not only losing fluidity and leading to complete failure of the sealing function, but also possibly causing irreversible damage to the precision sealing structure due to volume expansion during the phase change. The second, even if there is a low-temperature compatible magnetic fluid formula, the superposition effect of large shaft diameter and high speed will seriously weaken the sealing performance: on the one hand, the large diameter rotor inevitably brings greater radial runout, forcing the designer to increase the sealing gap to avoid mechanical interference between the pole shoe and the rotating shaft; while the expansion of the gap directly weakens the restraining ability of the magnetic field to the magnetic fluid, resulting in a significant decrease in single-stage pressure resistance; on the other hand, the centrifugal force and viscous shear friction caused by high linear speed will generate a large amount of heat, which is difficult to dissipate in time even in a vacuum environment, causing the local temperature rise to further exacerbate the deterioration of the stability of the magnetic fluid, forming a vicious cycle of "heat generation-performance degradation-sealing failure". More complex is that in the process of cooling from room temperature to 4.2K, different materials (such as stainless steel shaft, soft magnetic pole shoe, shell) will produce uneven shrinkage due to the difference in thermal expansion coefficient, which is easy to cause the distortion or even closure of the preset micron-level sealing gap, and then cause structural stress concentration or sealing failure.

[0005] Therefore, how to build a new sealing structure that can effectively suppress heat leakage and maintain the functional activity of the magnetic fluid while having the ability of thermal deformation self-adaptation under the multiple constraints of large diameter, high speed and extreme low temperature has become an urgent task for those skilled in the art. SUMMARY

[0006] The purpose of the present application is to provide a magnetic fluid dynamic sealing structure suitable for a rotary superconducting induction heating system, in order to solve the technical defects of the conventional magnetic fluid sealing in the rotary superconducting induction heating system under the working conditions of liquid helium temperature zone (4.2K-8K), high linear speed (30-50m / s) and large shaft diameter (200mm-500mm), such as carrier liquid solidification, thermal deformation mismatch, serious heat leakage and uncontrollable sealing gap, which lead to the difficulty in maintaining zero leakage.

[0007] To achieve the above purpose, the present application provides a magnetic fluid dynamic sealing structure suitable for a rotary superconducting induction heating system, comprising a stationary inner layer assembly, a rotating outer layer assembly, a magnetic fluid sealing unit and an integrated gas transmission and thermal management subsystem. The stationary inner layer assembly is a magnetic fluid inner layer, which is uniformly provided with a plurality of independent helium gas transmission channels in the circumferential direction, each channel penetrating the entire length of the magnetic fluid inner layer in the axial direction, and one end of the magnetic fluid inner layer is connected with the outer wall of the heating channel through a radial rolling bearing. The rotating outer layer assembly is a magnetic fluid shell, one end of which is rigidly connected to the side wall of the hollow rotor assembly through a flange, and an annular sealed working gap is formed between the inner wall of the magnetic fluid shell and the outer surface of the magnetic fluid inner layer; The magnetic fluid sealing unit is arranged in the annular space between the magnetic fluid inner layer and the magnetic fluid shell; The integrated gas transmission and thermal management subsystem includes a double concentric annular gas transmission ring, a multilayer heat shield, a composite cold shield and a vacuum heat insulation structure; The double concentric annular gas transmission ring is arranged on the side of the magnetic fluid sealing structure away from the heating channel, the outer ring is a gas helium input ring, the inner ring is a gas helium output ring, and the gas helium input ring and the gas helium output ring are respectively communicated with the gas helium transmission channel in the magnetic fluid inner layer through radial pipelines; the inner wall and both sides of the gas helium transmission channel are covered with multilayer heat shields; The gas helium input pipeline is additionally provided with three layers of composite cold shields, which are aluminized polyester film, terylene fiber mesh and stainless steel thin shell from inside to outside; The gas helium output pipeline adopts double-layer vacuum heat shields, the inner layer is an aluminized composite film, and the outer layer is a vacuumized stainless steel interlayer.

[0008] Further, the magnetic fluid sealing unit sequentially comprises a pair of symmetrically arranged annular pole shoes, a radially magnetized annular permanent magnet, a low-temperature compatible magnetic fluid, a retaining ring and a bearing set; the annular permanent magnet is clamped between the two pole shoes and is magnetized in the radial direction, and together with the two side pole shoes forms a closed magnetic circuit to generate a magnetic field at the sealing gap; the low-temperature compatible magnetic fluid is filled in the sealing gap between the pole shoes and the magnetic fluid inner layer, the retaining ring is arranged at the outer axial position of the pole shoes, and the bearing set is arranged outside the retaining ring.

[0009] Further, it further comprises a thermal stress compensation mechanism, the thermal stress compensation mechanism comprises a thermal compensation ring and a flexible support element; the thermal compensation ring is sleeved on the outer periphery of the magnetic fluid inner layer and is located at the mounting base of the pole shoe; the flexible support element is arranged between the mounting base of the permanent magnet or the pole shoe and the magnetic fluid inner layer.

[0010] Further, it further comprises an integrated gas transmission and thermal management subsystem; the integrated gas transmission and thermal management subsystem comprises a double concentric annular gas transmission ring, a multilayer heat shield, a composite cold shield and a vacuum heat insulation structure; The double concentric annular gas transmission ring is arranged on the side of the magnetic fluid sealing structure away from the heating channel, the outer ring is a gas helium input ring, the inner ring is a gas helium output ring, and the gas helium input ring and the gas helium output ring are respectively communicated with the gas helium transmission channel in the magnetic fluid inner layer through radial pipelines; the inner wall and both sides of the gas helium transmission channel are covered with multilayer heat shields; The gas helium input pipeline is additionally provided with three layers of composite cold shields, which are aluminized polyester film, terylene fiber mesh and stainless steel thin shell from inside to outside; The gas helium output pipeline adopts double-layer vacuum heat insulation screen, the inner layer is aluminized composite film, and the outer layer is vacuumized stainless steel interlayer.

[0011] Further, the multilayer heat insulation screen is formed by alternately winding aluminized polyester film and terylene fiber filaments.

[0012] Further, the low-temperature compatible magnetic fluid has a perfluoropolyether or fluoroether organic solvent as a carrier liquid matrix, and has Fe3O4 nano magnetic particles with a particle size of 5-15 nm as a dispersed phase, and a volume fraction of 3%-8%.

[0013] Further, the magnetic fluid sealing structure is provided with a magnetic fluid injection port and an exhaust port at the axial ends of the sealing gap.

[0014] Compared with the prior art, the advantages of the present application are that the above-mentioned technical solutions work together to solve the core problem of long-term zero-leakage dynamic sealing under the conditions of extremely low temperature, large diameter and high speed in the prior art.

[0015] In the present application, based on the design structure of adding three-layer composite cold screen to the gas helium input pipeline and adopting double-layer vacuum heat insulation screen for the gas helium output pipeline, and the design of the multilayer heat insulation screen of the gas helium transmission channel, the sealing of the low-temperature medium transmission is ensured, the leakage is fully avoided, and the working environment of the low-temperature medium and the magnetic fluid is fully insulated, and the overall radiant thermal resistance of the gas helium transmission channel is 1.2*10 4 K / W, so that the working environment temperature of the magnetic fluid can be stabilized at 300K or above, so as to ensure the fluidity of the magnetic fluid and avoid the failure of the magnetic fluid.

[0016] The present application further selects a low-temperature compatible magnetic fluid composed of a fluoroether carrier liquid matrix and Fe3O4 nano particles, which is safer and has higher performance, and overcomes the problem of solidification failure of traditional oil-based / water-based magnetic fluids due to low temperature resistance in the case of a small amount of leakage of low-temperature medium.

[0017] 3, the present application precisely controls the sealing gap under low-temperature working conditions by the combination of the thermal compensation ring and the flexible support element, so that the sealing gap is stabilized in the effective sealing interval of 15-30μm.

[0018] 4, by the multilayer heat insulation screen, the composite cold screen and the vacuum interlayer structure, the total heat leakage is suppressed to be less than 0.5W, and the refrigeration machine load is significantly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is the overall structure schematic diagram of the rotating superconducting induction heating system in the embodiment of the present application; Figure 2 is the cross-sectional view of the magnetic fluid dynamic sealing structure in the embodiment of the present application; Figure 3 It is a schematic diagram of the overall structure of the magnetic fluid dynamic sealing structure in the embodiment of the present application. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the present application more clear, the technical scheme of the present application will be further described below.

[0021] As Figure 1 shown, the low-temperature large-diameter magnetic fluid dynamic sealing structure of the present application is installed in the annular axial transition area between the hollow rotor assembly 6 and the heating channel 7 in the rotary superconducting induction heating system, for realizing long-term zero-leakage dynamic sealing of the two under the working conditions of extremely low temperature (4.2K-8K), high vacuum, high rotation speed (linear speed 30-50m / s) and large shaft diameter (200-500mm), and at the same time ensuring the smoothness of the low-temperature helium circulation channel. The sealing structure as a whole is in the form of a tubular interface, and its core is composed of a stationary inner layer assembly, a rotating outer layer assembly, a magnetic fluid sealing unit, a thermal stress compensation mechanism and an integrated gas transmission and thermal management subsystem.

[0022] Specifically, the working principle of the rotary superconducting induction heating system is as follows: rotation is generated between the hollow stator assembly 12 and the hollow rotor assembly 6 based on traditional electromagnetic interaction, the rotor rotates to drive the heating channel 7 to rotate synchronously, the superconducting coil on the surface of the heating channel 6 generates a rotating dynamic magnetic field to cut the metal rod ingot inside the heating channel, thereby heating the metal rod ingot, and realizing efficient metal heating. The superconducting coil needs to be in an extremely low-temperature environment to ensure working efficiency; the low-temperature medium circulating device 15 passes through the 4.2K input pipeline, penetrates into the low-temperature dewar formed between the inner wall of the hollow rotor and the outer wall of the heating channel through the magnetic fluid dynamic sealing structure, and circulates the heat-absorbed gas to the low-temperature medium circulating device 15 for repeated circulation through the 5.6.K output pipeline.

[0023] As Figure 2 and Figure 3 shown, the stationary inner layer assembly is a magnetic fluid inner layer 1, which is integrally turned by Invar 36 alloy, and its thermal expansion coefficient is not more than 1.2×10 -6 / K in the temperature range of 4.2K to 300K, effectively inhibiting low-temperature shrinkage deformation. The magnetic fluid inner layer 1 is uniformly provided with six independent helium transmission channels 9 along its circumferential direction, each channel penetrating the entire length of the magnetic fluid inner layer 1 along the axial direction, for conveying 4.2K input helium or discharging 5.6K backflow helium. One end of the magnetic fluid inner layer 1 is connected to the outer wall of the heating channel 7 through a radial rolling bearing 8, and the radial rolling bearing 8 adopts a full-ceramic structure, and the rolling body and the inner and outer rings are made of silicon nitride, avoiding metal cold welding and blocking the heat conduction path, thereby ensuring that the magnetic fluid inner layer 1 remains in an absolutely stationary state during high-speed rotation of the hollow rotor assembly 6.

[0024] The rotating outer layer assembly is a magnetic fluid shell 2, which is integrally processed by thick-walled cylinder of austenitic stainless steel 316L, and is rigidly connected with the side wall of the hollow rotor assembly 6 through a flange plate 18 at one end, and rotates synchronously with the rotor. The inner wall of the magnetic fluid shell 2 and the outer surface of the magnetic fluid inner layer 1 form an annular sealed working gap, and the initial assembly gap is set to 25±5μm. The gap is controlled by precision machining and assembly tolerance at room temperature, and is maintained in the effective sealing interval of 15-30μm by a thermal stress compensation mechanism at low temperature working condition.

[0025] As shown in Figure 2 The magnetic fluid sealing unit is arranged in the annular space between the magnetic fluid inner layer 1 and the magnetic fluid shell 2, and sequentially comprises: a pair of symmetrically arranged annular pole shoes 3, a radially magnetized annular permanent magnet 4, a low-temperature compatible magnetic fluid, a check ring 5 and a bearing set 16. The pole shoes 3 are made of permalloy (78% Ni-Fe), and the saturation magnetic induction Bs≥1.5T. The inner side working surface is processed with a rectangular sealing groove with a depth of 10μm and a width of 0.5mm, which is used to enhance the residence capacity of the magnetic fluid under the action of the magnetic field. The permanent magnet 4 is clamped between the two pole shoes 3, which is made of samarium-cobalt material, and is magnetized in the radial direction, and together with the two side pole shoes 3 forms a closed magnetic circuit, generating a strong gradient magnetic field of 0.35T at the sealing gap, and the magnetic field gradient reaches 1.2×10 5 T / m. The low-temperature compatible magnetic fluid filled between the pole shoes 3 and the magnetic fluid inner layer 1 has a full fluoropolyether (PFPE) as a carrier liquid matrix, and a Fe3O4 nano-magnetic particle with a particle size of 10nm as a dispersed phase, with a volume fraction of 5%, which has no phase change and no gelation at-70°C to +200°C, and maintains good fluidity and magnetic response stability. In the case of a small amount of leakage of the low-temperature medium, the problem of solidification failure of traditional oil-based / water-based magnetic fluid due to poor low-temperature resistance is overcome; the check ring 5 is arranged at the outer side of the axial position of the pole shoe 3. The bearing set 16 is arranged outside the check ring 5 and is composed of two back-to-back configured angular contact ceramic bearings, which is used to support the radial and axial load of the magnetic fluid shell 2, and isolate the transmission of rotating friction heat to the sealing area.

[0026] As shown in Figure 3 The thermal stress compensation mechanism includes a thermal compensation ring 13 and a flexible support element 14. The thermal compensation ring 13 is sleeved on the outer periphery of the magnetic fluid inner layer 1 and is located at the mounting base of the pole shoe 3, which is made of Invar 36 alloy, and its axial length matches that of the pole shoe 3. The thermal shrinkage amount can offset the relative displacement difference of about 18μm between the austenitic stainless steel rotating shaft and the soft magnetic pole shoe 3 during cooling from 300K to 4.2K, so that the actual sealing gap is stabilized at 22μm at low temperature working condition. The flexible support element 14 is arranged between the mounting base of the permanent magnet 4 and the magnetic fluid inner layer 1, which adopts a 316L stainless steel metal bellows structure with a wall thickness of 0.2mm, and the axial flexibility is 6×10-6 m / N, for absorbing micron-level thermal deformation, avoiding excessive stress in the structure, leading to sealing failure.

[0027] As shown in Figure 2 , the integrated gas transmission and thermal management subsystem includes a double concentric annular gas transmission ring, a multilayer heat shield 17, a composite cold shield, and a vacuum insulation structure. The double concentric annular gas transmission ring is arranged on the side of the magnetic fluid sealing structure away from the heating channel 7, the outer ring is a 4.2K helium input ring 10, and the inner ring is a 5.6K helium output ring 11. The helium input ring 10 and the output ring 11 are respectively communicated with the six helium transmission channels 9 in the magnetic fluid inner layer 1 through six radial pipes, in which three channels 9 are used for inputting 4.2K helium to the low-temperature Dewar, and the other three are used for outputting 5.6K backflow helium. The inner wall and both sides of the helium transmission channel 9 are covered with a multilayer heat shield 17, which is made of 10 layers of 5μm thick aluminized polyester film and 15μm diameter polyester fiber filaments alternately wound, and the overall radiation thermal resistance is 1.2×10 4 K / W. For the 4.2K helium input pipe 19, three layers of composite cold shield are added, from inside to outside: the first layer is aluminized polyester film, the second layer is polyester fiber mesh, and the third layer is 0.2mm thick 304 stainless steel shell. The cold shield is actively connected to the 4.2K cryostat through a flexible stainless steel hose to realize cold energy extraction to suppress pipe heat leakage; for the 5.6K helium output pipe 20, a double-layer vacuum heat shield is used, the inner layer is aluminized composite film, and the outer layer is vacuumized stainless steel interlayer, the interlayer vacuum degree is ≤10 -3 Pa, passive and efficient heat insulation is achieved. Through the above thermal management measures, the total heat leakage of the whole sealing device under 4.2K working condition is controlled at 0.42W; the design of the integrated gas transmission and thermal management subsystem makes the working environment of the low-temperature medium and the magnetic fluid fully insulated, the overall radiation thermal resistance of the helium transmission channel is 1.2×10 4 K / W, so as to ensure that the working environment temperature of the magnetic fluid is stable above 300K, so as to ensure the fluidity of the magnetic fluid and avoid the failure of the magnetic fluid.

[0028] In this embodiment, a magnetic fluid injection port and an exhaust port are respectively arranged at the axial ends of the sealing gap, which are used for injecting magnetic fluid and exhausting residual gas during assembly.

[0029] The actual operation process of the present application is as follows: before the system starts, the low-temperature compatible magnetic fluid is injected into the sealed gap between the pole shoe 3 and the magnetic fluid inner layer 1 through the magnetic fluid injection port 17, and the air is discharged through the exhaust port 18, ensuring that there is no gas residue in the sealed cavity. Subsequently, the low-temperature medium circulating device 15 sends 4.2K helium into the 4.2K helium input ring 10 through the 4.2K helium input pipeline, enters the hollow rotor 6 through the three helium transmission channels 9, and enters the low-temperature dewar between the inner wall of the hollow rotor 6 and the outer wall of the heating channel 7, and cools the superconducting coil. The 5.6K helium after heat absorption is collected into the 5.6K helium output ring 11 through another three helium transmission channels 9, and is returned to the low-temperature medium circulating device through the 5.6K helium output pipeline. In this process, the hollow rotor assembly 6 rotates at high speed, driving the magnetic fluid shell 2 to rotate synchronously, while the magnetic fluid inner layer 1 is connected with the heating channel 7 through the radial rolling bearing 8 and remains stationary. The strong gradient magnetic field formed by the permanent magnet 4 and the pole shoe 3 tightly binds the magnetic fluid in the sealed gap, forming a multi-stage liquid "O" ring seal, effectively blocking the gas migration between the high vacuum cavity and the low-temperature dewar. The thermal compensation ring 13 and the flexible support element 14 work together to compensate for the thermal shrinkage difference of different materials during the cooling process, and maintain the sealed gap within the effective range. The multi-layer thermal insulation structure significantly inhibits heat leakage and reduces the load of the refrigerator.

[0030] The above is only the preferred embodiment of the present application, and does not limit the present application in any way. Any person skilled in the art can make any form of equivalent replacement, modification or change to the technical solutions and technical content disclosed by the present application without departing from the scope of the technical solutions of the present application, which still belongs to the protection scope of the present application.

Claims

1. A magnetohydrodynamic sealing structure suitable for a rotary superconducting induction heating system, characterized in that, It includes a stationary inner layer assembly, a rotating outer layer assembly, a magnetohydrodynamic sealing unit, and an integrated gas transport and thermal management subsystem; The stationary inner layer component is a magnetic fluid inner layer (1). The magnetic fluid inner layer (1) is provided with multiple independent gas-helium transmission channels (9) evenly distributed along the circumference. Each channel runs through the entire length of the magnetic fluid inner layer (1) along the axial direction. One end of the magnetic fluid inner layer (1) is connected to the outer wall of the heating channel (7) through a radial rolling bearing (8). The rotating outer layer assembly is a magnetic fluid shell (2), one end of which is rigidly connected to the side wall of the hollow rotor assembly (6) through a flange. The inner wall of the magnetic fluid shell (2) and the outer surface of the magnetic fluid inner layer (1) form an annular sealed working gap. The magnetic fluid sealing unit is disposed in the annular space between the magnetic fluid inner layer (1) and the magnetic fluid outer shell (2); The integrated gas transmission and thermal management subsystem includes a double concentric annular gas transmission ring, a multi-layer thermal insulation screen, a composite cold screen, and a vacuum thermal insulation structure. The double concentric annular gas transmission ring is located on the side of the magnetic fluid sealing structure away from the heating channel (7). The outer ring is a gas helium input ring (10), and the inner ring is a gas helium output ring (11). The gas helium input ring (10) and the gas helium output ring (11) are respectively connected to the gas helium transmission channel (9) in the inner layer (1) of the magnetic fluid through radial pipes. The inner wall and both sides of the gas helium transmission channel (9) are covered with the multi-layer heat insulation screen. The gas helium input pipeline is equipped with a three-layer composite cold shield, consisting of an aluminized polyester film, a polyester fiber mesh, and a stainless steel thin shell from the inside out. The gas helium output pipeline uses a double-layer vacuum heat shield, with an inner layer of aluminum-plated composite film and an outer layer of vacuum-sealed stainless steel interlayer.

2. The magnetohydrodynamic sealing structure for a rotary superconducting induction heating system according to claim 1, characterized in that, The magnetic fluid sealing unit sequentially includes a pair of symmetrically arranged annular pole shoes (3), a radially magnetized annular permanent magnet (4), a low-temperature compatible magnetic fluid, a retaining ring (5), and a bearing assembly (16); the annular permanent magnet (4) is sandwiched between the two pole shoes (3) and magnetized in the radial direction, forming a closed magnetic circuit together with the two pole shoes (3) to generate a magnetic field at the sealing gap; the low-temperature compatible magnetic fluid fills the sealing gap between the pole shoes (3) and the inner layer of the magnetic fluid (1), the retaining ring (5) is set at the outer axial position of the pole shoes (3), and the bearing assembly (16) is set outside the retaining ring (5).

3. The magnetohydrodynamic sealing structure for a rotary superconducting induction heating system according to claim 1, characterized in that, It also includes a thermal stress compensation mechanism, which includes a thermal compensation ring (13) and a flexible support element (14); the thermal compensation ring (13) is sleeved on the outer periphery of the magnetic fluid inner layer (1) and located at the mounting base of the pole shoe (3); the flexible support element (14) is disposed between the mounting base of the permanent magnet (4) or the pole shoe (3) and the magnetic fluid inner layer (1).

4. The magnetohydrodynamic sealing structure for a rotary superconducting induction heating system according to claim 1, characterized in that, It also includes an integrated gas transmission and thermal management subsystem; the integrated gas transmission and thermal management subsystem includes a double concentric annular gas transmission ring, a multi-layer thermal insulation screen, a composite cold screen, and a vacuum thermal insulation structure; The double concentric annular gas transmission ring is located on the side of the magnetic fluid sealing structure away from the heating channel (7). The outer ring is a gas helium input ring (10), and the inner ring is a gas helium output ring (11). The gas helium input ring (10) and the gas helium output ring (11) are respectively connected to the gas helium transmission channel (9) in the inner layer (1) of the magnetic fluid through radial pipes. The inner wall and both sides of the gas helium transmission channel (9) are covered with the multi-layer heat insulation screen. The gas helium input pipeline is equipped with a three-layer composite cold shield, consisting of an aluminized polyester film, a polyester fiber mesh, and a stainless steel thin shell from the inside out. The gas helium output pipeline uses a double-layer vacuum heat shield, with an inner layer of aluminum-plated composite film and an outer layer of vacuum-sealed stainless steel interlayer.

5. The magnetohydrodynamic sealing structure for a rotary superconducting induction heating system according to claim 2, characterized in that, The multi-layer heat insulation screen is made of alternating layers of aluminized polyester film and polyester fiber filaments.

6. The low-temperature large-diameter magnetohydrodynamic sealing structure according to claim 1, characterized in that, The low-temperature compatible magnetic fluid has a carrier liquid matrix of perfluoropolyether or fluoroether organic solvent, and a dispersed phase of Fe3O4 nanomagnetic particles with a particle size of 5-15nm and a volume fraction of 3%-8%.

7. The low-temperature large-diameter magnetohydrodynamic sealing structure according to claim 1, characterized in that, The magnetic fluid sealing structure has a magnetic fluid injection port and an exhaust port at both ends of the sealing gap.

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