共查询到10条相似文献,搜索用时 156 毫秒
1.
根据铁磁流体磁化后会受到磁力,退磁后不存在任何磁滞的超顺磁性质,提出了铁磁流体的动态控制方法,对喷射在空气域中的铁磁流体液柱直接添加电磁场实现其动态偏转驱动。在修正后的纳维-斯托克斯(N-S) 控制方程中加入表面张力、重力及磁力,并结合磁感应方程,建立了铁磁流体动力学(FHD)模型。利用二次开发的Fluent流体仿真软件建立了铁磁流体在空气域中喷射的流体体积函数(VOF)多相流模型,仿真了在不同磁场强度下铁磁流体的液相分布及分散状况,分析了磁性对其动力学行为的影响。结果表明,随着磁场强度和喷射距离的增大,铁磁流体沿磁场方向速度及偏移量增大,其发散情况逐渐明显。 相似文献
2.
M. Pinho B. Brouard J.M. Génevaux N. Dauchez O. Volkova H. Mézière P. Collas 《Journal of magnetism and magnetic materials》2011,323(18-19):2386-2390
The use of ferrofluid seals in mechanical systems can lead to viscous damping that affects their dynamic behavior. This paper describes an investigation into local viscous properties in the case of an axial harmonic force. The influence of magnetic field level, shear stress amplitude and frequency are studied. Even for ferrofluid particles in a highly saturated magnetic field, it is shown that viscosity increases with magnetic intensity, decreases with the frequency of harmonic excitation and is not sensitive to shear rate amplitude. Viscosity is lower for oscillatory flows than for steady flows. 相似文献
3.
The transmission light intensity method is carried out on a classical platform to study the reciprocity of Faraday effect in water-based Fe3O4 ferrofluid and its diluents. Setting the polarization direction of the analyzer at an angle of 45° to that of the polarizer, the switchable DC magnetic field and the alternating magnetic field are imposed to ferrofluid. The ferrofluid film is replaced by magneto-optical glass for contrastive experiments. The results indicate that ferrofluid is different with magneto-optical glass. Even though the direction of magnetic field is reversed, the rotation direction of the polarized light does not change for ferrofluid. The theoretical model of magneto-optical rotation was used to describe the origin of the reciprocity of Faraday effect in ferrofluid and the non-reciprocity in magneto-optical glass. These findings suggest that the magnetic moments of nanoparticles in ferrofluid tend to the same orientation with the magnetic field because of the rotation of particles. 相似文献
4.
Based on a lognormal particle size distribution, this paper makes a model analysis on the polydispersity effects on the magnetization behaviour of diluted ferrofluids. Using a modified Langevin relationship for the lognormal dispersion, it first performs reduced calculations without material parameters. From the results, it is extrapolated that for the ferrofluid of lognormal polydispersion, in comparison with the corresponding monodispersion, the saturation magnetization is enhanced higher by the particle size distribution. It also indicates that in an equivalent magnetic field, the lognormally polydispersed ferrofluid is magnetically saturated faster than the corresponding monodispersion. Along the theoretical extrapolations, the polydispersity effects are evaluated for a typical ferrofluid of magnetite, with a dispersity of σ =0.20. The results indicate that the lognormal polydispersity leads to a slight increase of the saturation magnetization, but a noticeable increase of the speed to reach the saturation value in an equivalent magnetic field. 相似文献
5.
Habib Aminfar 《Journal of magnetism and magnetic materials》2011,323(15):1963-1972
In this paper, results of applying a non-uniform magnetic field on a ferrofluid (kerosene and 4 vol% Fe3O4 ) flow in a vertical tube have been reported. The hydrodynamics and thermal behavior of the flow are investigated numerically using the two phase mixture model and the control volume technique. Two positive and negative magnetic field gradients have been examined. Based on the obtained results the Nusselt number can be controlled externally using the magnetic field with different intensity and gradients. It is concluded that the magnetic field with negative gradient acts similar to Buoyancy force and augments the Nusselt number, while the magnetic field with positive gradient decreases it. Also with the negative gradient of the magnetic field, pumping power increases and vice versa for the positive gradient case. 相似文献
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7.
In this paper, relaxation behavior of transmitted light through thin ferrofluid film under an applied magnetic field is measured.
The results show that the intensity of transmitted light through a ferrofluid film increases quickly as soon as an external
magnetic field is applied then weakens with time. If uniformity of the field is poor, the transmission of light continuously
decreases in a measured duration. Otherwise, the transmission of light will tend increasingly towards a stable value after
it decreases to a minimum value while the gradient of the field is low. The relaxation time would increase to an order of
some hundreds seconds magnitude and is dependent on the strength of magnetic field and viscosity of the ferrofluids. The field-induced
relaxation behaviors of transmitted light through ferrofluids correspond to anisotropic microstructure of the ferrofluids
under applied magnetic field.
PACS 75.50.Mm; 78.20.Ls 相似文献
8.
本文运用Lattice-Boltzmann(LB)方法建立了宏观静止磁流体模型,提出磁性聚集体概念,充分考虑了磁性颗粒受到的各种内力与外力包括重力、布朗力、vanderWaals相互作用及静磁相互作用,对无外加磁场及外加竖直均匀磁场时磁流体的结构进行了模拟,并分析了磁能与热能之比对磁流体系统中粒子分布形态的影响。模拟结果表明:无外加磁场时磁流体结构易失去稳定性,外加均匀磁场时磁流体粒子沿外磁场方向排列,随着磁热能比例的增大,外磁场对粒子分布的影响逐渐明显。 相似文献
9.
This paper presents a numerical investigation of the hydro-thermal behavior of a ferrofluid (sea water and 4 vol% Fe3O4) in a rectangular vertical duct in the presence of different magnetic fields, using two-phase mixture model and control volume technique. Considering the electrical conductivity of the ferrofluid, in addition to the ferrohydrodynamics principles, the magnetohydrodynamics principles have also been taken into account. Three cases for magnetic field have been considered to study mixed convection of the ferrofluid: non-uniform axial field (negative and positive gradient), uniform transverse field and another case when both fields are applied simultaneously. The results indicate that negative gradient axial field and uniform transverse field act similarly and enhance both the Nusselt number and the friction factor, while positive gradient axial field decreases them. It is also concluded that, under the influence of both fields by increasing the intensity of uniform transverse field the effect of non-uniform axial fields decrease. 相似文献