非晶铁合金汞基磁流体的制备和性质

以乙醇为反应介质用NaBH4还原铁金属离子,得到用于制备汞基磁流体的非晶纳米铁合金粒子．用原子吸收光谱、透射电子显微镜、X射线粉末衍射和磁天平等对合金粒子和相应的汞基磁流体的性质进行了表征．铁合金粒子中氧化物的含量（质量分数）为1．2％,粒径12nm,饱和磁化强度16400kA／m．这种磁粒子的氧化物含量低,表面金属性强,能够充分分散于汞中,得到饱和磁化强度为210kA／m、稳定的汞基磁流体（性能保持18个月不变）．     

基于磁流体热透镜耦合光磁效应测量高压电流方法的研究

通过实验和理论分析,提出了将磁流体热透镜耦合光磁效应应用于高压电流测量的新方法,并设计了一套测量系统.该方法最大的特点是不用偏振光,避免了复杂的保偏装置,使得该系统简单、经济,同时又具有光纤传输的优点.     

Effect of Using Current-Carrying-Wire Models in the Design of Hydrodynamic Journal Bearings Lubricated with Ferrofluid

Based on the momentum and continuity equations for ferrofluid under an applied magnetic field, a modified Reynolds equation has been obtained. Assuming linear behavior for the magnetic material of the ferrofluid, the magnetic force was calculated. The magnetic pressure resulting from the magnetic force was incorporated into the Reynolds equation and it was not separately treated. The derived Reynolds equation can be applied for any magnetic field distribution model. Using different magnetic field models, the equation has been solved numerically by the finite difference technique with an appropriate iterative technique and pressure distributions have been obtained. The boundary shapes of the load-carrying active regions and cavitation regions could be then determined. The solution gives the bearing performance characteristics, namely; load-carrying capacity, attitude angle of the journal center, friction coefficient and bearing side leakage. The displaced current-carrying infinitely long wire gives a field distribution with a gradient in the circumferential direction. Two novel field models are introduced. The concentric finite current-carrying-wire model gives an axially symmetric magnetic field with a gradient in the axial direction. Axial and circumferential gradients are obtained using displaced finite wire model. The effect of these magnetic models and their design parameters on the overall bearing performance characteristics has been studied. The results concluded that the magnetic lubrication provides a higher load capacity and a reduced friction coefficient, compared with a conventional lubricated bearing. The other bearing characteristics depends on the applied field model. An axially symmetric applied field, with its sealing magnetic force, leads to a decrease in the side leakage, such that the bearing may operate without side leakage by appropriate design of the field.     

磁流体密封在化工设备中的应用展望

简介了在化工领域极具潜力的新型密封方式———磁流体密封,并以化工设备中常用的泵为例,对磁流体密封在化工行业的应用前景进行了展望。     

Static characteristics of ferrofluid finite journal bearing considering rotational viscosity effect

Considering the rotation of ferromagnetic particles, the present study investigates hydrodynamic lubrication by ferrofluids of finite journal bearings using the Shliomis model. A magnetic field created by displaced finite wire is used. A numerical solution for the modified Reynolds equation using the finite difference method is obtained. Static characteristics of finite journal bearings are analysed using three control parameters: rotational viscosity, magnetization and volume concentration of the ferromagnetic particles. It is shown that the pressure, load capacity, attitude angle and side leakage increase and the friction coefficient decreases when increasing the value of each control parameter. Similar trends are also obtained when increasing values of eccentricity for a fixed value of each control parameter except for the decrease of the attitude angle. Copyright © 2016 John Wiley & Sons, Ltd.     

Ferrofluid squeeze film between curved annular plates including rotation of magnetic particles

The effects of ferrofluid on the curved squeeze film between two annular plates, when the upper plate approaches the lower one normally, are studied including the rotation of the magnetic particles and their magnetic moments. The aim is to study the effects of rotation of the magnetic particles on the characteristics of the squeeze film. The main equation is derived in the Appendix A. Expressions for the pressure, load capacity and response time are obtained. Load capacity and response time are found to increase when the volume concentration of the solid phase, Langevins parameter or the curvature of the upper plate are increased.     

Magnetically textured ferrofluid in a non-magnetic matrix: Magnetic properties

Texturing of two different magnetic fluids were carried out in paraffin wax under the influence of an external magnetic field. The textured samples were characterized using magnetization measurement and a.c. susceptibility techniques. The results are discussed in the light of ratio of anisotropic energy to magnetic and thermal energies.     

磁性液体与加速度传感器的输出特性关系研究

设计了一种由一对磁铁产生回复力的磁性液体加速度传感器.在确定电源电压的峰峰值和频率后,对产生回复力的磁铁在不同距离(80～140 mm)、惯性质量块吸附不同体积的磁性液体(1～2.5 ml)、不同体积分数的磁性液体(0.5%～7%)与输出电压随加速度的变化关系进行了实验和理论研究,输出电压与加速度的关系随着回复距离的增...     

Magnetic dipole effects on non-Newtonian ferrofluid over a stretching sheet

In this study, we analyzed the characteristics of heat transfer in non-Newtonian ferrofluids produced by stretchable sheet. Further, we investigated in this study the effects of Arrhenius activation energy and magnetic dipole. We use in this study, a similarity ansatz to simplify the governing system into a nonlinear coupled ordinary differential equations system. We determined the computational solution of the resulting ordinary differential system by applying method with Runge–Kutta method. The influence of beneficial physical parameters on momentum, energy, and concentration profile are shown through graphs. The major finding of this study, the variation of velocity field is reduces for the higher values of $M$, $\beta$, and $H$. The temperature field increases for higher values of $R$, and reduce for $Pr$. Further, we conclude in this study the arising or reducing in the concentration, temperature, and velocity field for various physical parameters. The impacts of physical quantities namely skin fraction, Nusselt, and Sherwood numbers are examined through numerically via tables.     

Heat transfer performance of thermoelectric cooling integrated with wavy channel heat sink with different magnetic distances

Thermoelectric cooling (TEC) reverses the electrical energy to temperature caused by the Peltier effect, where a temperature difference occurs between two conductors, that is, hot and cold junctions. This article presents the enhanced heat transfer of a TEC module using a TEC1-12710 model integrated with a wavy channel heat sink using ferrofluid as a coolant under continuous and pulsating flows, where the differences in the distance of the magnetic field are considered. Square permanent magnets measuring 30 mm × 20 mm × 4 mm (width × length × height) are used to transmit a magnetic field to the heat sink and then tested under a magnetic distance of 10–30 mm. The test is performed at a water flow rate from 0.0083 to 0.028 kg/s and supplied with a constant TEC voltage of 12 V. By applying a magnetic field to the TEC module with a magnetic distance of 20 mm and a ferrofluid concentration ratio of 0.015%, the cooling efficiency increases by approximately 18.64%. Hence, using pulsating flow may improve thermal efficiency by approximately 23%. The results show an exponential increase in the cooling efficiency when both passive and active cooling techniques are used.