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Due to the complexity of working conditions and physical fields, the clearance flow field of the magnetic fluid sealing device for the main shaft of hydraulic turbine has always been a difficult point in the research of magnetic fluid seal. To study the flow characteristics of magnetic fluid in the clearance of the magnetic fluid sealing device for the main shaft of a hydraulic turbine, a numerical model of the flow field in the seal clearance of the main shaft was established and verified through experiments. The influence of the seal clearance, the width of the pole tooth, the height of the pole tooth and the width of the pole tooth slot on the flow of the magnetic fluid was studied by numerical calculation. The results show that the magnetic fluid near the pole tooth is not affected by the structural parameters and basically remains stationary. When the seal clearance is less than 0. 6 mm, the magnetic fluid in the clearance basically does not flow. When the seal clearance exceeds 0. 6 mm, the magnetic fluid near the pole slot and permanent magnet increases with the increase of the seal clearance, and the speed increases linearly. The flow of magnetic fluid near the pole tooth slot and permanent magnet decreases with the increase of the width of the pole tooth, and the velocity decreases linearly at first, decreases sharply at the width of the pole tooth from 3. 0 mm to 3. 5 mm, and finally tends to be stable. With the gradual increase of the height of the pole teeth and the width of the pole tooth slot, the magnetic fluid flow near the pole teeth and the permanent magnet will weaken. The magnetic fluid velocity near the pole teeth and slots will decrease sharply at the the height of the pole tooth from 1. 0 mm to 3. 5 mm and the width of the pole teeth from 3. 0 mm to 12 mm and finally become stable, while the magnetic fluid velocity near the permanent magnet has been decreasing linearly. [ABSTRACT FROM AUTHOR]

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The advantages of magnetic fluid seals, such as low friction moment, high tightness, and high durability, have been known for many years. However, they are used particularly in air or vacuum environments and the application of this type of seal in water still remains a problem. This is mainly due to the friction occurring between the two fluids and interfacial instability. This publication focuses on investigating the influence of magnetic fluid properties on the mechanism of pressure transfer between sealing stages. The main aim was to better understand the leak mechanism in this type of seal and to be able to select ferrofluids (FFs) resistant to water for long-term operation after short-term testing. The tested seals rotated over 4.3 million times without failure. The results of the research carried out are recommendations for the selection of magnetic fluid, sealing stage width, and FF volume. [ABSTRACT FROM AUTHOR]

[Display omitted] • The research progress of magnetic fluid in vacuum, gas, liquid and dust prevention is reviewed. • The magnetic fluid component materials are introduced, including sealing characteristics, liquid–liquid interface stability, simulation analysis and structural design. • The future development in the field of magnetic fluid seals is envisioned. Magnetic fluids(MF) are stable colloidal solution systems consisting of a mixture of nanoscale magnetic particles, surfactants, and a base carrier fluid. Magnetic fluid sealing(MFS) technology has been widely used in gas and vacuum conditions, and research on liquid seals is also receiving increasing attention. Magnetic fluid seals have many advantages, such as "zero" leakage, green environmental protection, long service life, reliability and stability. The current review on the subject is limited to the form of magneto-fluidic applications, and there is no clear description of the specific structure and classification. In this paper, the research progress of magnetic fluid in the field of vacuum, gas, liquid and dust prevention is reviewed, and the magnetic fluid component materials are introduced in a categorized and summarized way, including sealing characteristics, liquid–liquid interface stability, simulation analysis and structural design. Finally, the future development in the field of magnetic fluid seals is envisioned. In the future, the magnetic fluid sealing technology is expected to further innovate and develop, bringing more breakthrough solutions to the sealing field. [ABSTRACT FROM AUTHOR]

• The process of rivalry between diffusion and magnetophoresis was studied, taking into account the dependence on concentration. • Establishing the equilibrium distribution of particles in a magnetic fluid seal may require from two weeks to six months. • The duration of establishing equilibrium is affected by the parameters of the magnetic field and the properties of the fluid. • An area with close packing particles is formed in the fluid volume. In this paper, the unsteady process of particle concentration distribution in a magnetic fluid is studied. Diffusion and the effect of a high-gradient magnetic field in a magnetic fluid seal (MFS) are taken into consideration. It is crucial to take into account how particle mobility and diffusion coefficient vary on particle concentration in order to determine the possibility and time of the formation of a close packing of particles. The Carnaghan-Starling approximation was employed. It is demonstrated numerically that the geometry of the MFS, namely its gap width and pole base width, as well as the magnitude of the magnetic field strength under the pole tooth of the MFS, both influence the time of the formation of a close packing of particles. This period can be regarded as the MFS's uptime. Depending on the design of the working gap, the uptime seal for magnetic fluid based on vacuum oil may require between two weeks and six months. The uptime seal also becomes shorter when the carrier fluid's viscosity decreases. [ABSTRACT FROM AUTHOR]

To investigate the failure mechanism of the magnetic fluid seal (MFS) with opposite pole teeth (OPT) in gas and vacuum environments, a sealing device was designed to directly observe the surface shape of the magnetic fluid film. The failure mechanism and sealing performance of the MFS-OPT in different environments were investigated and discussed with the ordinary MFS. Numerical analysis was conducted to study the magnetic field distribution of the sealing device. The self-healing ability of the MFS-OPT in different environments was investigated. The results indicate that the pressure transfer process of sealing device occurs in a step-by-step manner. When the sealing device fails, it will go through two consecutive stages of microleakage and complete leakage. On the other hand, when the ordinary MFS fails, it first goes through a bubble stage. The magnetic fluid in the sealing device leaks from the middle location of the opposing pole teeth. The sealing device exhibits higher pressure resistance in a gas environment than that in a vacuum environment. Both gas and vacuum environments have a higher pressure resistance for MFS-OPT compared to ordinary MFSs. • The MFS-OPT device can visualize the change of MF film shape. • In the MFS-OPT, the leakage channel occurs in the middle of the opposing PT. • In a gas environment, the gas bubbles are not produced by MF film during failure. • Pressure resistance and self-healing ability of the MFS-OPT are superior to the ordinary MFS. [ABSTRACT FROM AUTHOR]

Magnetic fluid seal(MFS) is one of the most mature applications of magnetic fluid(MF) and is widely used in numerous fields. The permanent magnet is an integral component of the classic MFS and provides a stable and robust magnetic field. However, this leads to a high initial torque requirement and a noticeable separation between ferromagnetic particles and the base liquid in the presence of such a strong magnetic field. This situation results in starting difficulties and impedes the normal device startup, particularly in low-temperature environments. Moreover, a constant magnetic field fails to address fluctuating pressure. To address these issues, we have introduced a novel design for the field-controlled MFS. Through theoretical and finite element analyses(FEA), we derived the magnetic field distribution within the seal gap. Additionally, we established the theoretical range for the sealing capacity of the field-control MFS. Experimental results demonstrate that the magnetic field, sealing capacity, and starting torque all increase with higher coil currents. The reduction in starting torque is particularly pronounced at lower temperatures. By manipulating the magnetic field, the starting torque can be reduced by over 50%. The field-controlled MFS exhibits a 0.24 MPa sealing capacity without requiring cooling equipment, representing a 33% improvement in sealing capacity compared to the classic MFS without a coil. [ABSTRACT FROM AUTHOR]

Abstract In this study, an ionic liquid (IL)-based magnetic fluid (MF) (IMF; IL-based MF) and dispersant was synthesized to create MF seals for rotational mechanisms in high-vacuum chambers, such as those in rotational electron beam mastering systems. The synthesized dispersant dispersed magnetite nanoparticles in pyridinium ionic liquid that is stable under magnetic fields. The outgassing from the IMF was investigated using a quadrupole mass spectrometer during a sliding test under high-vacuum conditions with a pressure of 10−6 Pa. The fragmentation pattern of the outgassing from the IMF was very similar to that of the base IL. Pollution-causing fragments were not detected under vacuum conditions on the order of 10−9 Pa. On the basis of our findings, we anticipate that the IMF is suitable for use in MF seals required in clean, high-vacuum conditions. Highlights • An ionic liquid-based magnetic fluid (IMF) using a new dispersant was synthesized. • The IMF generated low outgassing under friction in high-vacuum conditions. • Few fragments from the new dispersant were detected by Q-mass. • The usefulness of the IMF under high-vacuum conditions was shown. [ABSTRACT FROM AUTHOR]

A novel symmetrical embedded magnetic fluid seal (SEMFS) structure was designed with the aim of enhancing the pressure resistance of the magnetic fluid (MF) seal with small gap under vacuum condition. The magnetic field distribution in the sealing gap (SG) was studied by numerical simulation, and the theoretical pressure resistant-withstanding of the SEMFS was obtained by combining the pressure resistance theories of stepped MFS. An experimental study was conducted to investigate the effects of magnetic fluid injection volume (MFIV), number of pole teeth, SG, and rotational speed of the rotating shaft on the seal's pressure resistance. The pressure resistant-withstanding values obtained were compared with those theoretically projected for the (SEMFS) and the ordinary magnetic fluid seal (OMFS), based on numerical analysis. The results indicate that the measured pressure value for the SEMFS matches well with the calculated pressure value. Furthermore, the SEMFS exhibits superior pressure resistance capabilities compared to the OMFS when subjected to the same parameters, which fully reflects the superiority of SEMFS structure. With an augment in the injection volume of MF, the pressure-withstanding performance of the SEMFS exhibits an initial upward trend followed by a gradual stabilization. Moreover, the pressure-withstanding performance of the SEMFS demonstrates a progressive enhancement with an increase in the number of radial pole teeth (RPT) and a corresponding increment in the number of axial pole teeth (APT). The ability to resist pressure of SEMFS decreases as the radial sealing gap (RSG) and axial sealing gap (ASG) increase. At low shaft speeds, the SEMFS's pressure resistance capability is not impacted by rotational speed and can be considered similar to a static seal. • A novel symmetrical embedded magnetic fluid seal structure was designed. • A sealing test bench was designed to conduct experimental studies on the sealing performance. • The symmetrical embedded magnetic fluid seal structure exhibits superior pressure resistance capabilities compared to the traditional sealing structure. • The increase of the magnetic fluid volume will cause the sealing pressure resistance to rise first and then stabilize. • The more the teeth, the smaller the seal gap and the greater the pressure value. The low speed has almost no effect on the pressure resistance. [ABSTRACT FROM AUTHOR]

• Based on the requirements of the working conditions, a magnetic fluid seal device applicable to rotating shafts was designed in this study using magnetic field simulation analysis and experimental verification. • The relationships between several structural variables and seal pressure were analyzed, and the fitting curve and equation were derived via fitting analysis. • The magnetic field simulation results showed that sealing pressure decreased with an increase in the sealing gap, increased with the number of pole teeth, and increased and then decreased with an increase in the pole teeth angle. • The experimental results showed that the best sealing performance was achieved when the amount of magnetic fluid was 3 m L. • The sealing pressure significantly decreased with an increase in the rotational speed. Magnetic fluid seals are a new type of seal with zero leakage. Based on the requirements of the working conditions, a magnetic fluid seal device applicable to rotating shafts was designed in this study using magnetic field simulation analysis and experimental verification. The relationships between several structural variables and seal pressure were analyzed, and the fitting curve and equation were derived via fitting analysis. The magnetic field simulation results showed that sealing pressure decreased with an increase in the sealing gap, increased with the number of pole teeth, and increased and then decreased with an increase in the pole teeth angle. The trapezoidal pole teeth exhibited the best sealing performance. The experimental results showed that the best sealing performance was achieved when the amount of magnetic fluid was 3 m L. The sealing pressure significantly decreased with an increase in the rotational speed. [ABSTRACT FROM AUTHOR]

Magnetic fluid seal(MFS) is one of the most mature applications of MF and is widely used in numerous fields. Magnet is an essential part in MFS, which create magnetic field gradient to held MFs at the sealing stage to resist pressure. We summarize the MFS mechanisms and the formation mechanisms of magnetic field. Here, we provide an comprehensive comparison with the theory analyses and diverse applications of different magnet type in MFS from two categories, permanent magnet and electromagnet. And their respective strengths and weaknesses were analyzed. We find that the electromagnet has an important role in many working conditions. Then we provide an in-depth, comprehensive insight into the applications of MFS with both permanent magnets and electromagnets, such as application to reduce breakaway torque, to re-magnetize permanent magnets without disassembly and to explore the magnetic saturation principle of magnetic materials. At the end of the paper, the present challenges and future prospects in the progress of electromagnets in MFS are also outlined. [ABSTRACT FROM AUTHOR]

• A coupling numerical simulation method of magnetic-flow field and diffusion equation is proposed to obtain the concentration distribution of magnetic particles. • Nonuniform magnetic particle concentration distribution enhances the magnetic volume force and magnetizing pressure at the pole tooth tip. • The aggregation of magnetic particles promotes the sealing performance with a rotating shaft. Magnetic fluid is used for sealing because of its strong magnetic response. However, magnetic particles are aggregated at the pole tooth in the nonuniform magnetic field, which results in a change in sealing performance. This paper uses the coupling simulation of the magnetic-flow field and the diffusion equation to solve the magnetic particle concentration distribution with the different rotating speeds. The sealing performance of different magnetic particle concentration distributions is calculated using the multi-physical field coupling and the dynamic mesh method. The results show that the particle concentration inhomogeneity degree is influenced by rotating speed, particle size, and volume fractions. Besides, the increasing particle concentration inhomogeneity degree increases the sealing performance. [ABSTRACT FROM AUTHOR]

• Based on the static pressure curves, the microstructure models of different magnetic powders in the sealing gap are proposed. • The dynamic sealing capability of powders with different proportions also prove the rationality of the microstructure hypothesis. • It is concluded that different microstructures have different fracture and recombination abilities under the action of shear stress and external magnetic field. • The thermal effect caused by the friction between the shaft and magnetic powder makes the magnetism of magnetic powder decrease and reduces the sealing ability. The focus of the paper is the experimental study of static and dynamic magnetic powder sealing by preparing micro-nano hybrid magnetic powders with different proportions. The magnetization curves of the magnetic powders are measured, and the formula for calculating saturation magnetization of mixed magnetic particles is fitted. In the static seal test, the maximum pressure resistances of magnetic powders are studied. It can be concluded that the nanoparticles can achieve a stable pressure resistance under low pressure and the micron particles have higher pressure resistance, but there is a small amount of leakage due to the microcavities between particles. The nanoparticles are introduced into the micron particles' microcavities to form a hybrid magnetic powder, which significantly improves the pressure resistance. The microstructure models of magnetic powders in the sealing gap are proposed based on the static pressure curves. However, in the dynamic magnetic powder seal test, its pressure characteristic curve is different from that of the magnetic fluid seal. The relationship between the pressure resistance and the rotational speed of the shaft is studied. It is concluded that different microstructures' fracture and recombination abilities under shear stress and external magnetic field in seal clearance are different. The thermal effect caused by the friction between the shaft and magnetic powder makes the magnetism of magnetic powder decrease and reduces the sealing ability. Experimental studies prove the application potential of magnetic powder seal. [ABSTRACT FROM AUTHOR]