Search

Layered van der Waals (vdW) magnets are prominent playgrounds for developing magnetoelectric, magneto‐optic, and spintronic devices. In spintronics, particularly in spincaloritronic applications, low thermal conductivity (κ) is highly desired. Herein, by combining thermal transport measurements with density functional theory calculations, this study demonstrates low κ down to 1 W m−1 K−1 in a typical vdW ferromagnet Cr2Si2Te6. In the paramagnetic state, development of magnetic fluctuations way above Tc = 33 K strongly reduces κ via spin‐phonon scattering, leading to low κ ≈ 1 W m−1 K−1 over a wide temperature range, in comparable to that of amorphous silica. In the magnetically ordered state, emergence of resonant magnon‐phonon scattering limits κ below ≈2 W m−1 K−1, which will be three times larger if magnetic scatterings are absent. Application of magnetic fields strongly suppresses the spin‐phonon scattering, giving rise to large enhancements of κ. This study's calculations well capture these complex behaviors of κ by taking the temperature‐ and magnetic‐field‐dependent spin‐phonon scattering into account. Realization of low κ, which is easily tunable by magnetic fields in Cr2Si2Te6, may further promote spincaloritronic applications of vdW magnets. This study's theoretical approach may also provide a generic understanding of spin‐phonon scattering, which appears to play important roles in various systems. [ABSTRACT FROM AUTHOR]

Although the sealing mechanism of the embedded magnetic fluid seal is unclear, it is an effective way to improve the performance of the ordinary magnetic fluid seal. Embedded magnetic seals can be divided into diverging and converging embedded magnetic fluid seals, according to the direction of leakage of the sealed medium. This article mainly focuses on presenting a sealing device that can observe the change in the shape of the magnetic fluid film and investigate the mechanism of diverging and converging embedded magnetic fluid seals. The pressure transfer mechanism of the embedded magnetic fluid seal with a large gap was studied through experiments. Numerical analysis of the magnetic field distribution in the seal gap and calculation of the theoretical pressure capacity of the embedded magnetic fluid seal are produced on the basis of embedded magnetic fluid seal theory. The experimental pressure capacity is compared with the theoretical pressure capacity to verify the correctness of the embedded magnetic fluid seal pressure capacity theory. The research has investigated the effect of the number of magnetic fluid film ruptures on the self-restoring capacity of embedded magnetic fluid seals, compared with the self-restoring capacity of diverging and converging embedded magnetic fluid seals, and analyzed the data. The results illustrated that the experimental pressure capacity of the embedded magnetic fluid seal matched well with the theoretical pressure capacity, which verifies the correctness of the embedded magnetic fluid seal theory. The pressure transfers from one chamber to another when the pressure difference between the two sides of the magnetic fluid film under the pole tooth is larger than the pressure capacity of the magnetic fluid seal, and the air will enter from the high-pressure side seal chamber to the low-pressure side seal chamber, in turn. As the inlet pressure increases, the pressure trend in the radial chamber of the embedded magnetic fluid seal differs from that in the axial chamber. When the seal fails, the magnetic fluid shows microleakage and complete leakage. As the number of magnetic fluid film ruptures increases, the self-restoring capacity first decreases and then increases. The self-restoring capacity of the converging embedded magnetic fluid seals is better than that of the diverging embedded magnetic fluid seals. [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]

In order to solve the leakage problem of rotating machinery under the condition of large clearance, a new type of divergent magnetic fluid sealing device with secondary magnetic source was designed. The magnetic field distribution in the clearance of the magnetic fluid seal was simulated by the finite element method of magnetic field, and the theoretical value of the sealing pressure resistance was calculated according to the pressure resistance theory of the divergent magnetic fluid seal. The influences of the volume of magnetic fluid injection, the number of teeth, the clearance, and the eccentricity of the rotating shaft on the pressure resistance abilities of divergent magnetic fluid seal were studied by experimental method and compared with the pressure resistance experimental value of ordinary magnetic fluid seal. The results showed that when the injection volume of magnetic fluid is more than 3 ml, the sealing pressure resistance ability of the magnetic fluid does increase greatly and tends to be stable gradually. The saturated magnetic fluid injection volume of divergent magnetic fluid seal with large clearance is 3 ml. With the increase of radial teeth, the pressure resistance ability of magnetic fluid seal first increases and then decreases. With the increase of axial teeth, the pressure resistance ability of magnetic fluid seal also increases. With the increase of radial clearance, the pressure resistance value of magnetic fluid seal first increases and then decreases. With the increase of axial clearance, the pressure resistance value of magnetic fluid seal decreases. The pressure resistance ability of divergent magnetic fluid seal is significantly higher than that of ordinary magnetic fluid seal. [ABSTRACT FROM AUTHOR]

To improve the pressure capability of ferrofluid seals with small clearance, a converging ferrofluid seal with double magnetic sources was designed. The magnetic field distribution in the clearances of the converging ferrofluid seal was studied by employing the finite-element method, and the theoretical pressure capability of the seal is calculated. The effects of ferrofluid injection volume, radial clearance, axial clearance, and the numbers of radial pole teeth and axial pole teeth on the pressure capabilities of converging ferrofluid seal device were investigated by experimental methods and compared with the experimental pressure capability of the stepless ferrofluid seal. The results show that the experimental and theoretical pressure capabilities of the converging ferrofluid seal are in good agreement. The saturated ferrofluid injection volume of the converging ferrofluid seal device is 1 mL. The experimental pressure capability of the converging ferrofluid seal does not decrease with increasing clearance or decreasing number of pole teeth. The pressure capability of the converging ferrofluid seal is related not only to the size of the clearance but also to the number of pole teeth. The pressure capability of the converging ferrofluid seal is better than that of the stepless ferrofluid seal. [ABSTRACT FROM AUTHOR]

• The influence of four factors on the pressure resistance of the parts was studied. • Orthogonal experiments are used in this paper. • The optimal combination of four factors was obtained. • This study provides important guidance for the design of seal pressure resistance. In order to improve the pressure resistance(PR) of magnetic fluid reciprocating seal(MFRS) suitable for vacuum coating machines, effects of sealing gap(SG), number of pole teeth(PT), height of PT and thickness of magnet on the PR of the seal were investigated. L 16 (4 5) orthogonal test was designed to optimize the reciprocating seal structure, and the magnetic field distribution of each test in the four-factor, four-level orthogonal test was analyzed. The statistical analyses of the results of the orthogonal tests were compared between the method of range analysis and the analysis of variance (ANOVA). The results show that the data obtained by ANOVA are more accurate, and the PR of MFRS increases by 455 kPa under the optimization of this scheme, and the optimal PR value is 318 kPa after considering the interference and limitations of practical applications, which is in line with the requirements of the PR of practical applications. [ABSTRACT FROM AUTHOR]

The stepped magnetofluid seal is an effective method for improving the pressure ability of ordinary magnetofluid seals (OMS) with large clearance. At present, the research on stepped magnetofluid seal with less than 0.4 mm small clearance has not been carried out yet. The equivalent magnetic circuit design of converging stepped magnetofluid seal (CSMS) with small clearance has been carried out and verified by magnetic field finite element method based on the CSMS theory and magnetic circuit theory. The effects of the width of the axial seal position, the height of the radial seal position, the number of the pole tooth in the axial seal position, and the number of the pole tooth in the radial seal position on the theoretical pressure ability of the CSMS are investigated by numerical simulation. The calculation results are analyzed and discussed. The results show that the magnetic flux leakage at the junction of the permanent magnet and pole piece causes the higher pressure ability of the CSMS structure designed by the equivalent magnetic circuit method than that calculated by the magnetic field finite element method. When the width of the axial seal position is greater than the height of the radial seal position and the number of pole teeth in the axial seal position is less than the number of pole teeth in the radial seal position, the CSMS has the best effect. Compared with OMS with small clearance, CSMS has greater advantages. [ABSTRACT FROM AUTHOR]

In order to improve the pressure capability of the ferrofluid seal under the condition of large sealing gap, a diverging stepped ferrofluid seal with a large gap and two magnetic sources was designed. The magnetic field distributions in the gap of the ferrofluid seal were calculated by finite element method. The effects of the pole teeth number, the height of the pole teeth and the sealing gap on the pressure capabilities of the diverging stepped ferrofluid seal are studied and compared with ordinary ferrofluid seal. The results show that the change of the radial pole teeth number has little effect on the pressure capability of the stepped ferrofluid seal. The pressure capability of stepped ferrofluid seal decreases with the increase of the axial pole teeth number. The pressure capability of the stepped ferrofluid seals reach maximum when the radial and axial pole teeth height is 0.6 mm. The pressure capability of stepped ferrofluid seal decreases as the radial sealing gap increases. The pressure capability of stepped ferrofluid seal decreases firstly and then increases with the increase of the axial sealing gap. Comparing with ordinary ferrofluid seal, the stepped ferrofluid seal has better pressure capability. [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]

The diverging stepped magnetic fluid seal based on stepped labyrinth seal was an effective method to improve the capability of usual magnetic fluid seal with large gap. Pressure theory of the diverging stepped magnetic fluid seal was presented and a diverging magnetic fluid sealing with two magnetic sources was designed. The leakage location hypothesis in the diverging stepped magnetic fluid seal has been made. The magnetic field distributions in the radial and axial sealing gaps have been calculated by means of the finite element method of magnetic field and its maximum sealing capabilities have been calculated based on its pressure theory. The effects of radial and axial sealing gaps on the diverging stepped magnetic fluid seal have been obtained. The numerical and experimental results were analyzed and discussed. The results show that the theoretical pressure-resistant capabilities of the diverging stepped magnetic fluid seal with two magnetic sources agree well with its experimental pressure-resistant capabilities. The leakage path in the axial sealing gap located at its center position and the leakage path in the radial sealing gap located in the vicinity of the shaft. [ABSTRACT FROM AUTHOR]

To improve the pressure capability of ordinary ferrofluid seals with a large gap, a novel type of converging stepped ferrofluid seals was proposed. The leakage positions and the magnetic field distributions in the sealing gaps of the new device are studied computationally by means of the finite-element method. The theoretical pressure capabilities of the seal are calculated based on a new expression introduced for the particular new seal geometry and for different sealing gaps. Computational results for effects of the radial and axial sealing gaps on the pressure capabilities of the seal are compared to the experimental results obtained from measurements employing a prototype of the proposed new seal. A good agreement between theoretical and experimental results is obtained. It is found that the pressure capabilities of the new seal depend on the height of the radial sealing gap and on the width of the axial sealing gap. [ABSTRACT FROM AUTHOR]

In order to meet the high cleanliness and high vacuum requirements of the working environment of the silicon conveyer robot, a new type of concentric biaxial stepped ferrofluid sealing structure is proposed based on the original universal ferrofluid sealing structure. The two dimensional simplified physical model of concentric biaxial stepped structure under axisymmetric condition is established by using the magnetic field finite element method. The nonlinear magnetic field distributions in the ferrofluid sealing structure are calculated and analyzed. The influences of the sealing gap, the width of the pole teeth, the ratio of the permanent magnet length to its height on the its sealing capabilities were studied. The calculation results were also analyzed and discussed. The results show that the pressure resistances of the concentric biaxial stepped ferrofluid seals significantly decrease with the increase of the sealing gap. Their pressure resistances firstly increased and then decreased with the increase of tooth width. The pressure resistance of the outer diverging stepped ferrofluid seal in the concentric biaxial stepped ferrofluid seal firstly increased and then decreased with the increase of the ratio of the permanent magnet length to its height; Their pressure resistances of inner converging stepped ferrofluid seal firstly decrease and then increase with the increase of the ratio of the permanent magnet length to its height. [ABSTRACT FROM AUTHOR]

Magnetic fluid seal (MFS) has been widely applied in the vacuum environment, but its pressure transfer mechanism has been less studied. This paper investigates the pressure transfer mechanism of MFS in the vacuum environment by designing an experimental device of MFS mechanism, which can observe the change of liquid film during the pressure transfer. Meanwhile, the pressure transfer mechanism of the designed device in the vacuum environment is compared with the that of MFS in the gas environment. The self-repairing performance of MFS in both vacuum and gas environments is investigated. Based on the MFS theory, the magnetic field distribution of the experimental device is analyzed numerically, and the theoretical pressure resistance is calculated and compared with the experimental value. The results show that the pressure transfer mechanism of MFS in the vacuum environment is similar to that in the gas environment with different forms. The pressure transfer form in the vacuum environment is magnetic fluid liquid film to produce a leakage channel. It is concluded that the self-repairing performance of MFS in the vacuum environment is better than that in the gas environment. • Using a comparative study approach. • The pressure transfer mechanism of MFS in the vacuum environment is similar to that in the gas environment. • The pressure transfer of MFS in the vacuum environment is the form of leakage channels generated in magnetic fluid film. • The self-repairing performance of MFS in the vacuum environment is better than that in the gas environment. [ABSTRACT FROM AUTHOR]

• Based on the divergent seal theory, a new structure, the divergent magnetic fluid seal with stepped pole piece, is proposed. • Through sealing structure design, magnetic field analysis, theoretical calculation and experimental study, the reliability of the designed sealing structure is verified. • In numerical and experimental aspects, the influences of magnetic fluid injection, step number, step height, radial clearance and axial clearance are studied in order to know the influence of these factors on the pressure resistance of the new structure. • It presents the theoretical and experimental basis for the design of stepped magneto-fluidic seals with high sealing performance. It is crucial that the pressure resistance of ordinary magnetic fluid seals is under small clearance conditions. Therefore, a new structure for magnetic fluid seals, i. e. a dispersion type with stepped pole pieces, is proposed in this paper to further improve the pressure resistance under such operating conditions. For the divergent magnetic fluid seal with stepped pole piece, the magnetic field distribution in the clearance can be calculated, as well as the theoretical pressure resistance of the new seal structure. In this paper, it is calculated the magnetic field distribution and theoretical pressure resistance utilizing the magnetic field finite element method based on the theory of divergent magnetic fluid seals, investigated the influence of the amount of injected magnetic fluid, the number of steps, the height of the steps and the sealing gap on the pressure resistance of the new sealing structure of stepped magnetic fluid seals, as well as compared and analyzed with that of ordinary magnetic fluid seals and normal magnetic fluid seals. The results show that the pressure resistance of the normal magnetic fluid seal is significantly worse than that suggested by the split magnetic fluid seal. The pressure resistance of the stepped magnetic fluid seal increases as the number of steps increases, while the pressure resistance of the proposed structure decreases and then increases as the height of the steps increases; and the pressure resistance of the proposed structure increases and then decreases as the radial clearance increases, while the pressure resistance of the proposed structure decreases as the axial clearance increases. [ABSTRACT FROM AUTHOR]

Layered van der Waals (vdW) magnets are prominent playgrounds for developing magnetoelectric, magneto‐optic, and spintronic devices. In spintronics, particularly in spincaloritronic applications, low thermal conductivity (κ) is highly desired. Herein, by combining thermal transport measurements with density functional theory calculations, this study demonstrates low κ down to 1 W m−1 K−1 in a typical vdW ferromagnet Cr2Si2Te6. In the paramagnetic state, development of magnetic fluctuations way above Tc = 33 K strongly reduces κ via spin‐phonon scattering, leading to low κ ≈ 1 W m−1 K−1 over a wide temperature range, in comparable to that of amorphous silica. In the magnetically ordered state, emergence of resonant magnon‐phonon scattering limits κ below ≈2 W m−1 K−1, which will be three times larger if magnetic scatterings are absent. Application of magnetic fields strongly suppresses the spin‐phonon scattering, giving rise to large enhancements of κ. This study's calculations well capture these complex behaviors of κ by taking the temperature‐ and magnetic‐field‐dependent spin‐phonon scattering into account. Realization of low κ, which is easily tunable by magnetic fields in Cr2Si2Te6, may further promote spincaloritronic applications of vdW magnets. This study's theoretical approach may also provide a generic understanding of spin‐phonon scattering, which appears to play important roles in various systems. [ABSTRACT FROM AUTHOR]

• Ferrofluids Couette–Poiseuille flows in three time-varying magnetic fields are analyzed. • Ferrohydrodynamic equations are solved with regular perturbation method. • Assumption of zero spin viscosity leads to exaggerated effect of magnetic fields. • Ferrofluid flows behave non-Newtonian characteristics in time-varying magnetic fields. We analyze the fully developed Couette–Poiseuille flows of ferrofluids between two parallel flat walls subject to three types of time-varying magnetic fields. In these scenarios, ferrofluids exhibit diverse non-Newtonian characteristics such as distinct flow velocity distribution, apparent viscosity and shear stress compared to ordinary Couette–Poiseuille flows. The influence of spin viscosity is explored first through the solution of the governing equations with zero and non-zero spin viscosities. It shows that although the value of the spin viscosity is very small, its inviscid limit would have great influence over the velocity and spin velocity distributions. The assumption of zero spin viscosity leads to an exaggerated non-Newtonian behavior induced by time-varying magnetic fields in the ferrofluid Couette–Poiseuille flows. Then the solutions of equations with non-zero spin viscosity are utilized to delve into non-Newtonian behaviors of ferrofluid Couette–Poiseuille flow under the application of the three time-varying magnetic fields. The results indicate that negative rotational viscosity will occur if the dimensionless frequency lies in the range 1–10, which is a distinguishing feature compared with Newtonian flows. At this point, non-Newtonian flow induced by magnetic field arises, although this effect is very tiny. Within the same frequency range, reversed tangential stress appears in strong uniform alternating magnetic fields. The minimum negative rotational viscosity may arrive at up to 20 % of the intrinsic viscosity in the rotating magnetic field when the magnetization relaxation time is 4 ms. [ABSTRACT FROM AUTHOR]