磁性液体传感器一阶悬浮力的理论计算和仿真分析

一阶悬浮力是磁性液体传感器的设计关键。利用任意多物理场直接耦合分析软件COMSOL multiphysics仿真分析了磁性液体一阶悬浮力,一阶悬浮力在最大偏心距纵坐标为-2.5mm,横坐标在-20~25mm的范围内呈周期分布,其平均值为38.43N。同时对没考虑磁场和流场耦合情况下的一阶悬浮力进行了理论计算,仿真和理论计算均表明一阶悬浮力与偏心距离间存在非线性关系,一阶悬浮力的理论计算结果大于仿真分析结果,偏心距越大,理论计算与仿真分析的结果相差越大。磁性液体传感器的设计应该考虑磁场和流场的耦合作用。     

旋转轴的磁性流体密封

本文根据电磁学和流体力学对磁性流体密封进行了理论分析。推导出磁性流体内部压强和边界压差公式,进而得出密封压差公式。同时提出了减小离心力作用的方法。对静止和旋转密封进行了数值计算,分析了磁性流体量和转速对密封能力的影响。     

磁流体技术及发展方向综述

本文综述了磁流体制备和应用技术的新进展，并对现阶段我国磁流体制备和应用中存在的问题及将来的发展方向进行了探讨。     

Chemically reactive and radiative flow of ferro-aluminum (AA7075) hybrid nanofluid past a stretching cylinder

The present investigation throws light on the heat transfer behavior of hybridized (ferro-aluminum alloy [AA7075]) nanofluid. In addition to that, influences of thermal radiation, magnetic effect, and chemical reaction are also considered for the exploration. Here, the flow is deliberated due to a porous stretching cylinder. The equations that portray the fluid flow are transfused to simple ordinary differential equations by applying similarity elements. Then, the procured equations have been solved by adopting the Runge–Kutta–Fehlberg 4th–5th order tool. The extracted solution are exported to plot graphs for velocity, thermal, and solutal profiles with the concerned parameters, and using these plots, the discussion has been produced for the behavior of all flow fields. The behavior of the thermal profile shows substantial enhancement with an increase in the solid volume fraction of hybrid nanofluid. The velocity and concentration panel de-escalates for larger values of Reynolds number. A significant discussion on the skin friction drag, Nusselt number, and Sherwood number has been produced.     

Swarming Microdroplets to a Dexterous Micromanipulator

Many astonishing biological collective behaviors exist in nature, and artificial microrobotic swarms have been developed by emulating these scenarios. However, these microswarms typically have single structures and lack the adaptability that many biological swarms exhibit to thrive in complex environments. Inspired by viscoelastic fire ant aggregations and using a combination of experiment and simulation, a strategy to trigger ferrofluid droplets into forming microswarms exhibiting both liquid-like and solid-like behaviors is reported. By spatiotemporally programming an applied magnetic field, microswarms can be liquefied to implement reversible elongation with a high aspect ratio and solidified into entireties to perform overturning and bending behaviors. It is demonstrated that reconfigurability enables the microswarm to be a mobile dexterous micromanipulator, acting not only as a soft “octopus arm” to explore a confined environment and grasp a targeted object but also adaptively navigate multiple terrains, such as uneven surfaces, curved grooves, complex mazes, high steps, narrow channels, and even wide gaps. This microrobotic swarm can reconfigure both shapes and tasks based on the demands of the environment, presenting novel solutions for a variety of applications.     

Heat transfer enhancement in oscillatory two-phase flow of Casson and ferrofluid comprising differently shaped nanoparticles in a horizontal composite channel

The most commonly discussed topic at the present time is the fluid flow in a channel having a porous area, as it is of practical importance for petroleum extraction, frequently isolated irrigation, coolant circulation, biofluid transportation in living organisms, and industrial cleaning systems. An investigation of heat transfer characteristics of unsteady magnetohydrodynamics oscillatory two-immiscible fluid flow of Casson fluid (CF) and ferrofluid (FF) in a long-infinite horizontal composite channel is performed analytically. The channel is divided into two regions. Region I is occupied by a porous region with CF, while Region II is a clear region filled with FF. The mathematical system of coupled partial differential equations is solved analytically considering the two-term periodic and nonperiodic functions. The influences of physical parameters such as CF parameter, porosity parameter, nanoparticles volume fraction, Hartmann number, periodic frequency parameter, oscillations amplitude, and pressure on momentum as well as heat transfer are presented through graphical illustrations (two-dimensional along with three-dimensional) and in tabular form using the MATHEMATICA program. Four different shaped nano-size ferroparticles are used in this study. The investigation of four different nanosized ferroparticles exhibits that the momentum transfer is higher when brick-shaped nanosized ferroparticles are added to the base fluid, water. It is also observed that thermal performance enhances in the case of brick-shaped nanosized ferroparticles compared to the blade, cylinder, and platelet-shaped nanosized ferroparticles. It is observed that the dispersion of brick-shaped nanosized ferroparticles is recommended in base fluid water for greater thermal performance through a horizontal channel.     

Frequency Characteristics of Stiffness and Damping Effect of a Ferrofluid Bearing

Damping characteristics and frequency characteristics of a ferrofluid bearing spindle were measured using a high-frequency vibration base driven by a piezo actuator. They show that ferrofluid bearing spindles have effective damping. In this experiment, the damping effect became larger with higher spindle rotational speed.     

磁场作用下的Fe3 O4磁流体承载能力的试验研究

通过对MS-800四球机油杯的改进,在测试区域内产生可调磁场,利用该改进后的油杯在四球机上对磁场作用下Fe3O4磁流体承载能力进行测定。试验结果表明,磁流体润滑膜在外加磁场作用下,综合承载能力得到了很大的提高,最大可提高至原来的1.3倍。结合Rosensweig理论模型,通过对磁场下磁流体粘度的测定,分析得出磁流体的粘度变化是引起综合承载能力发生变化的主要原因。