To improve the performance of rotary ferrofluid (FF) sealing devices, a structure featuring stepped grooved pole teeth (SGPTs) and zigzag sealing clearances (SCs) was designed in this paper. Since existing research lacks studies on the pressure transmission mechanism and sealing performance of this special pole tooth (PT) structure, a sealing device with an SC of 0.5 mm was developed. Seven sealing chambers formed by the structure were separately connected to pressure transmitters to monitor pressure transmission characteristics, and a digital electron microscope was adopted to record the status of FF films. Finally, the pressure transmission and failure mechanisms of the sealing device, together with the effects of pressurization modes and step dimensions on sealing performance, were systematically investigated. The results show noticeable pressure fluctuations within SGPT cavities once micro-leakage occurs in the downstream FF film. In cyclic pressurization and pressurization failure experiments, the second-stage FF film exhibits the most severe sealing performance degradation. Its critical leakage threshold decreases by 47.1% after the sixth failure cycle, and premature leakage emerges in the third failure cycle. Furthermore, increasing the width of the first step of the SGPTs from 1.4 mm to 2.2 mm can effectively enhance the magnetic flux concentration capacity of the entire sealing structure, and the pressure resistance of the seal increases by approximately 17.8%.

This study investigates magnetic fluid seal mechanisms and failure modes in end-face interleaved teeth structures. An integrated optimization, simulation, and experimental framework reveals macro-scale dynamics and introduces sealing constraint coefficients to characterize clearance-tooth height synergy. Orthogonal tests show both clearance and height significantly impact pressure resistance, with optimization yielding a 20% improvement. Experiments indicate constraint coefficients don't alter macro pressure transfer; pressure resistance and self-healing rates peak and then decline with tooth width and increase with reduced clearance. Microscopically, varying coefficients induce differing pole tooth friction marks, caused by magnetic particles contacting and moving relative to the surface. Results provide a quantitative basis for designing and predicting failures in highreliability magnetic fluid seals.

This study investigates magnetization relaxation effects in ferrofluids using a coupled molecular dynamics and Lattice Boltzmann simulation framework. The model incorporates dipole-dipole and short-range (Lennard-Jones) interactions between particles, couples hydrodynamic interactions, and employs a bidisperse model for particle distribution. The magnetization component along the magnetic field direction, M-x*, increases and saturates with the Langevin parameter alpha L. However, larger shear rates gamma* or pressure differences P* (beyond a threshold) slow this saturation due to the greater difficulty larger particles face in aligning with the magnetic field. The off-field magnetization component M-y*, arising from relaxation, exhibits a non-monotonic dependence on alpha L, first increasing and then decreasing under shear and pressure difference. This behavior is attributed to the evolving chain-like microstructures within the ferrofluid at different field intensities. Higher particle concentrations phi m or dipole coupling parameters lambda lead to larger maximum values of M-y*. The competition between the magnetic field and shear flow, along with shear-rate-dependent chain size distributions, leads to a larger gamma* requires a stronger magnetic field for M-y* to peak, and the peak value itself increases with gamma*. The pressure difference P* influences magnetization by modifying the local shear rate distribution, with its hydrodynamic effects becoming significant only after P* exceeds a critical value.

Surface modification treatments are widely employed to enhance the performance of materials, often resulting in layered mechanical properties along the material’s height. The majority of research into friction and wear of materials relies on finite element methods (FEM). However, when accounting for topography of very thin surface layers, FEM encounters specific constraints. This paper introduces a novel approach for predicting the wear morphology evolution of layered materials subsequent to surface modification, specifically under ball-on-disk contact conditions. This methodology discretizes the surface into cells, considering the wear process of the cells from a microscopic perspective. The stress distribution within the contacting area is computed based on a balance of forces between the ball and the discretized surface, with the equivalent elastic modulus serving as a proxy for the substrate’s elastic modulus. Additionally, the model is made more realistic by incorporating the effects of boundary lubrication via a load-sharing approach and plastic deformation of surface asperities. Leveraging the Archard’s model, a wear equation for discrete surface cells is formulated to ascertain the wear volume. The availability of this method is substantiated by comparing simulation outcomes with experimental data for carburized 16Cr3, carburized followed by shot-peened 16Cr3, and carburized, shot peened, and subsequently coated 16Cr3 materials subjected to different temperature conditions, revealing a maximum discrepancy of 17.1

The maintenance of railway rails relies heavily on accurate profiling and wear assessment. In this research, a rail profile detection system using line-structured light machine vision technology is developed. Traditional image processing algorithms for rail profile measurement involve Zhang's camera calibration, radial distortion correction, Gaussian filtering, and the iterative closest point (ICP) algorithm for point cloud registration. Building upon these conventional algorithms, an integrated error correction framework comprising projective transformation and system offset compensation is proposed. We introduce a method to dynamically determine the direction vector of the rail alignment and the angle between the laser plane and the rail cross-section for the projective transformation. Compared to the same hardware system without error correction, this method improves measurement accuracy from 0.0686 to ±0.015mm at the lateral wear measurement points and from 0.0678 to ±0.020mm at the vertical wear measurement points in profile detection.

A convergent monolithic embedded ferromagnetic fluid seal structure is proposed and designed to improve the reliability of the seal under vacuum conditions. The capacity for self-healing and critical pressure were experimentally investigated for different axial sealing clearance, radial sealing clearance, number of radial teeth of the pole shoe, number of axial teeth of the pole shoe, and pole tooth height. The results show that when the axial or radial sealing gap is gradually increased to 0.4 mm, the self-healing performance of the convergent monolithic embedded ferromagnetic fluid seals shows the same pattern of enhancing and then weakening. As the number of radial teeth of the pole shoe increases, the self-healing performance of the convergent monolithic embedded ferromagnetic fluid seal first weakens and then strengthens before weakening. As the number of axial teeth in the pole shoe increases, the convergent monolithic embedded ferromagnetic fluid seal structure's ability to mend itself is initially strengthened and subsequently impaired. The self-healing performance of the convergent monolithic embedded ferromagnetic fluid seal structure increases with the increase in pole tooth height.

The idea of ferrofluid pumping in pipes is extended to scenarios where a uniform magnetic field gradient is employed, yet without a pressure difference between the inlet and outlet of the pipe. The governing equations, including the phenomenological magnetization equation for ferrofluid pipe flow, are solved by a custom-developed OpenFOAM solver. After the validation of this solver, ferrofluid pipe flows under the application of a magnetic field gradient are numerically predicted. The findings reveal that both pumping volume and pressure distribution can be adjusted by varying the reference magnetic field intensity and field gradient. A stronger reference magnetic field and a steeper field gradient result in higher flow rates and accelerated pressure increases along the field gradient direction. In a circular tube with a radius of 1 mm, when the dimensionless magnetic field gradient is 0.1 and the magnetic Reynolds number is 1000, the maximum velocity can attain 10.2 μm/s, the flow rate can reach 0.016 μL/s, and the equivalent average pressure gradient achieves 0.15 Pa/s. Notably, in a gradient magnetic field, the effective viscosity of a ferrofluid flowing in a pipe can be significantly reduced, achieving approximately 70% of its intrinsic viscosity in this study. These promising results lay the groundwork for the design of ferrohydrodynamic pumps that harness the potential of constant magnetic fields.

Computational simulation serves as an effective method for elucidating the pristine microstructures within ferrofluids, yet the choice of dispersion model can significantly influence the outcomes of these simulations. This study identifies the criteria for equivalence among polydisperse, bidisperse, and monodisperse models in ferrofluid systems. Through molecular dynamics simulations, a comparative analysis of the particle chain characteristics in equivalent ferrofluid systems is conducted. The findings reveal that both the monodisperse and bidisperse models tend to underestimate the quantity of chains present in the ferrofluid when compared to the polydisperse model, with the monodisperse model exhibiting the most pronounced underestimation, reaching up to 86% within the studied parameter range. Moreover, the monodisperse system fails to produce long chains as densely populated as those in the polydisperse system. In the absence of a magnetic field, the bidisperse model tends to underestimate the average chain length, whereas the monodisperse model does the same at lower dipolar coupling parameters and overestimates at higher values. Under the influence of a magnetic field, both the bidisperse and monodisperse models underestimate the average chain length, and this underestimation becomes more pronounced with increasing ferrofluid concentration, reaching a maximum of approximately 38.6% within the examined parameter range. These insights provide guidance for the selection of appropriate dispersion models in the investigation of microstructural phenomena within ferrofluids.

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.

We conducted a study on the surface compound modification of shot peening and pure carbon DLC coating to simultaneously meet the requirements of wear resistance and fatigue resistance of spline structure. The effects of surface compound modification were investigated on the surface morphology, residual stress profile, microstructure, and nano-indentation hardness of 16Cr3NiWMovNbE gear steel, and conducted a comparative study on fatigue performance. The results show that the surface compound modification inherits the surface morphology and compressive residual stress gradient of shot peening, while the surface residual stress is slightly smaller than that of shot peening. In addition, surface compound modification still reflects the characteristics of high hardness and high fracture resistance of DLC coatings. Under the bending load based on spline tooth root, compared to the original specimen, the fatigue life after shot peening, pure carbon DLC coating, and surface compound modification is increased by 3.68, 2.35, and 3.36 respectively. Although the compound modified surface still maintains the shot peening morphology with a increasing surface roughness and stress concentration coefficient, the 100μm-depth compressive residual stress profile and the subgrain refinement layer introduced, as well as the hard surface layer with good load-bearing capacity, have played the role of fatigue strengthening.

To address the issue of inadequate sealing performance in ordinary ferromagnetic fluid seals for large-diameter rotating shafts, a convergent staggered pole tooth ferromagnetic fluid sealing (CSPT-FFS) device has been proposed. The influence of critical parameters like size of sealing clearance (SC), number of pole teeth (PT), PT eccentricity distance, and the stepped shaft rotational speed on the sealing performance of CSPT-FFS were experimentally investigated. The results show that both the experimental and theoretical sealing pressure capability (SPC) of the CSPT-FFS device follow the same trend, with its experimental SPC being obviously better than that of the ordinary FFS device. The SPC increased with PT eccentricity distance, and the SPC decreases by approximately 30% when the linear velocity reaches 10.2 m/s.

The focus of this study is on modeling the shape deformation of ferrofluid ring sections and secondary flows in ferrofluid seals with a rectangular polar tooth. These factors determine the sealing capability and homogenization of particles in ferrofluids. The model consists of governing equations for ferrofluid flows, the balance equation of normal stresses on ferrofluid free surfaces, the magnetic field equations and the ferrofluid volume equation. To solve the mathematical model, a method utilizing a combination of boundary element method and finite volume method is proposed. Discretizing the azimuthal velocity equation with boundary element method enables efficient determination of ferrofluid-ring section shape deformation. Furthermore, a discretely fitting method is proposed to solve the issue of lack of analytic expressions for the magnetic field distribution in sealing structures with rectangular polar teeth. Numerical tests of the magnetic field and azimuthal velocity distribution verify the validity and accuracy of the proposed solution method. Numerical experiments conducted on an actual ferrofluid sealing structure show that increasing the rotational speed of the shaft, in conjunction with effect of the centrifugal force, leads to deformation of the ferrofluid-ring section shape and reduces the contact area between the ferrofluid ring and shaft. This results in a decrease in pressure resistance. Typically, at a speed of 10 m/s, the pressure resistance falls by around 20%. The maximum value of secondary-flow velocity is significantly affected by the rotational speed of the shaft, although it does not exceed 0.8% of the linear velocity on the shaft surface in our study.

There is an immediate need for aerosol measuring sensors to monitor the size and concentration of DNA strand aerosols in PCR systems. We evaluate the performance of a previously developed small aerosol sensor for its potential use as a component in measuring DNA strand aerosols in PCR system chambers. A detailed derivation of the working principle is presented along with the principles used to determine the dimensions of the stages and the operational parameters. After characterizing the aerosolized DNA strands, experiments were conducted to identify their relationship with measured currents. The experimental results indicate that for aerosolized Escherichia coli DNA strands, the sensor is capable of measuring concentrations from 102 cm−3 to 105 cm−3 (from 103 cm−3 to 105 cm−3 for particles smaller than 102 nm) and sizes from 100 bp to 1000 bp. There was a slight difference between the results of the sensor and its theoretical model. The sensor exhibited good sensitivity to different concentrations and can detect every 150 bp of strands, indicating its effectiveness in monitoring ultrafine DNA strand aerosols for PCR systems and other applications.

Shot peening is a widely utilized surface modification technique, and the surface morphology of the treated materials plays a crucial role in determining their friction and fatigue properties. Surface morphology generation is a pivotal process in simulating shot-peened surface friction and other performance characteristics. However, there are limited available methods for shot-peened surfaces until now. In this paper, we present a method that directly specifies the height probability distribution and power spectrum to generate shot-peened surfaces. Compared to methods that specify height parameters, this method has more flexibility. This approach replaces the traditional Johnson transformation method with an optimization algorithm to generate height data that follows a high probability distribution, while the power spectrum is derived from the Fourier transform of an exponential autocorrelation function. The results show that this approach can generate shot-peened surfaces using any conventional height parameters, with a maximum difference in height parameters between the reconstructed surface and the original surface of no more than 18.63%. Compared to the Johnson transformation method, this method significantly reduces the errors in skewness and kurtosis of the generated surface. It offers rapid surface generation for shot-peened surfaces, leading to significant time and cost savings in experiments.