Y~(3+)掺杂对Mn-Zn铁氧体结构和性能的影响及正己烷磁流体的制备

用改进的化学共沉淀法首次合成了稀土钇离子掺杂的Mn0.8Zn0.2YxFe2-xO4(其中x=0、0.02、0.04、0.06、0.08、0.1)铁氧体纳米颗粒,利用X射线粉末衍射(XRD)和振动样品磁强计(VSM)研究了温度和Y3+掺杂量对磁性纳米颗粒结构和磁性能的影响。通过加入十二烷基硫酸钠(SDS)控制纳米颗粒的大小,并用油酸作为表面改性剂,制备了稳定的Mn0.8Zn0.2Y0.02Fe1.98O4正己烷磁流体,使用红外光谱(FTIR)、热重(TGA)和透射电镜(TEM)研究了p H值对油酸包裹的影响。研究发现:通过对化学共沉淀法进行改进,在沸腾的情况下制备出了目前饱和磁化强度最高的Mn0.8Zn0.2Fe2O4纳米磁性颗粒(Ms=63.8 A?m2?kg?1),适当掺杂Y3+不会破坏铁氧体的尖晶石结构并且随着掺杂量的增加,饱和磁化强度Ms先增加后减小,当x=0.02时Ms最大;在p H=5的乙醇-水体系中进行改性,油酸的包裹量最大,制备出的Mn0.8Zn0.2Y0.02Fe1.98O4正己烷磁流体长期放置不会分层。     

磁性流体的制备及在扬声器中的应用

用化学共沉淀法制备粒径10nm的Fe3O4作磁粉,在表面活性剂的作用和适当温度条件下通过高速搅拌制备出聚烃基磁性流体。通过加入抗氧剂等微量添加剂提高其化学稳定性和磁稳定性。调节好粘度和磁饱和强度,得到扬声器用磁性流体。通过实际应用,检测磁性流体在扬声器中的应用效果。     

Magnetically induced agitation in liquid‐liquid‐magnetic nanoparticle emulsions: Potential for process intensification

Microscopic mixing using magnetic nanoparticles (MNP) unveils exciting ramifications for process intensification in chemical engineering. This study explores the use of oil‐in‐water MNP emulsions to achieve mixing in a nonmagnetic continuous phase tantamount to that occurring in equivalent dilute ferrofluid suspensions. To assess the technique, measurements of the torque exerted by ferrofluid emulsions and suspensions of equal magnetic content were performed in rotating, oscillating, and static magnetic fields. Results show that momentum transfer is fairly alike in amplitude and proportionality for the two types of systems of equal magnetic content under the three types of magnetic fields. This implies that momentum of spinning nanoparticles in the emulsions is transferable to the oil droplets containing them which, in return is then transferred to surrounding nonmagnetic liquid. The magnitude of the resulting mixing allows for the foresight of a versatile MNP mixing technology completely separated from the target phase being mixed. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1176–1181, 2014     

Unsteady flow and heat transfer of a ferrofluid between two rotating,vertical moving and stretching disks

Unsteady flow and heat transfer of a magnetic fluid between two rotating disks is investigated. Both the disks are stretchable and the lower disk moves in the vertical direction. A new approach of similarity transformation is adopted to transform the equation of continuity, momentum, and the energy equation into ordinary nonlinear coupled differential equations. The numerical solution of the converted nonlinear differential equations is obtained using the finite element method. The effects of magnetization force, rotational viscosity, Prandtl number, and Eckert number on the velocity and temperature distributions are studied. The impact of stretching, movement, and rotation of the disk is also considered in this computational study. The skin friction coefficients and heat transfer rate on the lower disk for different physical parameters are calculated. Different types of motion of the disks and the magnetization force are crucial aspects in the stress distribution and heat transfer rate near the lower disk.     

磁性液体合成装置的研制及其应用

分析了现有磁性液体合成装置的弊端,并进行针对性改装和部分设计。改装后的合成装置主要由脉冲电源、冷却、温控、搅拌、进料和调节等六部分组成。利用新改制的合成装置,对气-液两相介质进行脉冲活化和电离,通过适当控制脉冲频率、脉冲电压、工作电流等放电参数和反应过程的温度,只需2h左右即可合成性能较好的磁性液体,极大地缩短了制备周期。利用SEM,VSM和电子天平等技术手段对产品进行检测分析,构成磁性液体的磁性颗粒平均粒径为10nm,密度为1.025g/cm3,磁饱和磁化强度达3×105A/m,没有磁滞现象。并根据磁性液体场致效应明显特性,研制出"封闭式磁性液体立体磁场观察器"。     

FHD flow and heat transfer over a porous rotating disk accounting for Coriolis force along with viscous dissipation and thermal radiation

The prime concern of the current findings includes the effect of viscous dissipation and nonlinear thermal radiation on the study of ferrofluid flow and heat transfer past a porous rotating disk. The time-independent flow of incompressible ferrofluid is modeled for the considered geometry, and via similarity transformations, the given system is converted to a dimensionless system of the nonlinear ordinary differential equations. Here, the findings are explored computationally with help of Maple software. The study exhibits the effect of the involved emerging parameters: the interaction parameter $B$, Prandtl number $Pr$, rotation parameter $R$, radiation parameter $Qr$, Eckert number $Ec$, and these are discussed graphically. Moreover, the numerical values of heat transfer rate and skin frictions are also presented in tabular form. From the perspective of numerical findings, it is perceived that the radial flow is dominant when we increase the rotation of the disk. Furthermore, the magnitude of magnetic-fluid temperature is enhanced with the surge in the magnetic field, viscous dissipation, and thermal radiation mechanism. Finally, the current research can successfully fill a gap in the existing literature.     

指向性控制和恒指向性号筒综述

介绍了指向性因数和指向性指数的定义、计算式。按历史次序讨论了多格号筒、径向号筒、CE号筒、曼塔莱号筒的指向性特性。还简要讨论了号筒内的失真,以及一个恒指向性号筒的实例,给出了实测的水平和垂直的极坐标响应、波束宽度,及指向性因数和指向性指数与频率的关系。最后,简单介绍了磁液在压缩驱动器中的应用。     

磁性液体性能及运行工况对密封耐压值的影响

为研究不同种类磁性液体及密封工况对密封效果的影响,以Fe3O4为磁性颗粒,以链状氟醚油为基液,制备一系列不同颗粒含量、基液分子量的磁性液体,对磁性颗粒及磁性液体的结构、性能进行表征,在搭建的密封试验台上测试磁性液体种类及运行工况对密封耐压效果的影响。结果表明：制备的磁性颗粒粒径为纳米级,呈近球形形貌,具有较高的饱和磁化强度,磁性液体具有较好的分散稳定性;随颗粒含量增加、基液分子量增大,密封耐压值先增大后减小;在颗粒质量分数为30%、基液分子量为4 600 g/mol时,密封耐压值最高;随主轴转速增大,密封耐压值逐渐减小;随密封时间延长,密封耐压值先减小后趋于稳定。     

磁性流体多极－多级密封

分析了磁性流体多级密封中存在的问题，提出了实现高压差密封的方法，对多极－多级密封的特性进行了分析，提出了控制压差形成的方法，进一步提高了密封压差，密封压差达到２．５ＭＰａ。