Magnetic Fluid Column Research Articles

Capillary ascension of magnetic fluids

The equilibrium of a magnetic fluid column inside a cylindrical capillary is investigated in the presence of the external uniform magnetic field. It is found that due to the fluid meniscus deformation, the surface pressure drop in the fluid decreases in the fields longitudinal and transverse to the capillary axis.

502 磁場保持される磁性流体液柱の動的圧力応答(O.S.5-1 磁性流体)(O.S.5 機能性流体とシステム化)

502 磁場保持される磁性流体液柱の動的圧力応答(O.S.5-1 磁性流体)(O.S.5 機能性流体とシステム化)

B5 軸方向加振される磁性流体液柱の共振現象

B5 軸方向加振される磁性流体液柱の共振現象

Large-Amplitude Axisymmetric Mode Oscillations of a Magnetic Fluid Column Supported by a Magnetic Field

Large-Amplitude Axisymmetric Mode Oscillations of a Magnetic Fluid Column Supported by a Magnetic Field

Oscillating Characteristics of Magnetic Fluid Column in the Magnetic Field. An Estimate from Transient Response.

Magnetic fluids are known as a typical example of functional fluids in the magnetic field. Fundamental studies are conducted to develop engineering devices, in which the motion of magnetic fluid column is utilized. Since the oscillating characteristics should be crucial for the device performance, the motion of the liquid column in a U-tube is observed using step response method. In the experimental work, the effects of the magnetic field strength and the position of the column surface on the damping characteristics are examined for a variety of conditions. The damping ratio that is used in the case of forced vibration increases with the magnetic field strength. The natural frequency with damping oncreases with the magnetic field intensity and with the rise of the fluid column position. Numerical calculation is also carried out using conditions similar to the experiment. The predicted results agree qualitatively with measured values.

Dynamic characteristics of a magnetic fluid column formed by magnetic field

This paper examines the dynamic characteristics of liquid columns when lateral sinusoidal vibration is applied. The first, second and third resonant frequencies shift to a higher frequency region as the magnetic field intensity increases. For a magnetic fluid column, the second and third resonant frequencies show interesting behaviour as the magnetic field is varied.

The stability of a rigidly rotating magnetic fluid column effect of a periodic azimuthal magnetic field

The stability of an infinitely long magnetic fluid column of weak viscous effects is investigated. The column is subjected to a periodic azimuthal magnetic field and a rigid-body rotation. Non-axisymmetric two-dimensional perturbations are considered in this investigation. Linear analysis leads to a Mathieu equation with complex coefficients. The analytical results show that the constant magnetic field plays a stabilizing role and can be used to suppress the instability due to the rotation. When the field has been oscillating, the stabilizing role of the amplitude of the magnetic field decreases somewhat due to the applied frequency . The oscillating magnetic field plays a dual role in the stability criterion. The increase of the azimuthal wavenumber decreases the unstable region due to the increase of the column radius. A small viscosity plays a destabilizing effect due to the influence of the angular velocity in the presence of a constant or an oscillating magnetic field. A magnetic column can be stabilized at a given azimuthal wavenumber by a suitable choice of the angular velocity, the density and viscosity for the outer fluid being greater than the corresponding parameters for the inside fluid.

On magnetization relaxation in ferrofluids and acousto-electromagnetic conversion

A theoretical picture of electromagnetic oscillations excitation by an acoustic wave in a magnetic fluid and an experimental testing of it are presented and analysed. It is shown that the main cause of the excitation of electromagnetic oscillations is the disturbance of fluid magnetization, due to its density and its temperature oscillations in the acoustic field. The amplitude of this disturbance is evaluated for two geometries: when the wave vector is parallel to the magnetic field intensity, the magnetization disturbances are compensated by those of the magnetic field intensity, while when these two vectors are perpendicular the annihilation does not take place. Experimental data are obtained by means of a two-coil system in which an electromotive force is induced. The experimental data confirm qualitatively the theoretical prediction. The increase of applied magnetic field intensity leads to a monotonic increase of the induced voltage. For magnetic field intensities exceeding 10 3 A m −1 a saturation tendency is noticed, the induced voltage amplitude saturation occurring in the same range of applied magnetic field intensity as the saturation of the magnetic fluid magnetization. As an explanation for the data for the first configuration, it is shown that the elastic deformation of a magnetic fluid column can induce disturbances of the demagnetizing factor and hence of the demagnetizing field, these being able to excite electromagnetic oscillations.

Motion of Liquid Column Driven by Magnetic Fluid in a Circular Tube.

The motion of a liquid column in a circular tube, driven by the motion of a magnetic fluid under an oscillating magnetic field in the axial direction, is studied experimentally. Nondiluted hydrocarbon-based magnetic fluid and a kind of fluorocarbon are employed as working fluids. The displacement of the magnetic fluid column becomes larger than that reported in the previous work. However, the magnetic fluid column is separated. from the driven liquid at the interface in the frequency range where the displacement is expected to increase. For a U-tube of constant diameter, the time variation of displacement shows a distorted waveform in the lower frequency range due to smaller hydraulic loss, although the displacement is considerably large even in the case of rather weak input current to the solenoid. Numerical analyses are also carried out using conditions similar to those of the experiments. The predicted results agree well with experimental data in the case of no separation at the interface.

Oscillating flow driven by a magnetic fluid column under fluctuating magnetic field

Abstract Oscillatory pipe flow driven by reciprocating motion of magnetic fluid column is studied experimentally and theoretically. The governing equation is expressed as a nonlinear ordinary differential equation and calculated under similar conditions to the experiment. Computational results agree well with data obtained from the experiment.

Application of Magnetic Fluids as a Driving Source of Fluid Motion. 2nd Report. Effects of Waveform of Magnetic Field on Vibrating Characteristics.

The characteristics of oscillatory pipe flow driven by the reciprocating motion of a magnetic fluid column are examined mainly under the conditions where the waveform of the oscillating magnetic field is rectangular. The displacement of the fluid column for the rectangular waveform of the magnetic field is larger than that for the sinusoidal waveform. The phase difference between the magnetic field and the displacement of the fluid column increases with the frequency of the applied magnetic field in the lower frequency region. However, it decreases with the frequency in the higher frequency region, in contrast to the sinusoidal waveform. Experimental data on the vibrating characteristics agree qualitatively with the predicted results. The response of the fluid column to sudden change of the magnetic field strength is also examined.

An Application of Magnetic Fluids as a Driving Source of Fluid Motion.

Studies of oscillatory pipe flow driven by the reciprocating motion of a magnetic fluid column are carried out as fundamental work toward an application to a driving source of fluid motion. In the present experiment, the motion is induced by a sinusoidal oscillating magnetic field. A system of pipes of different sizes is employed to examine the characteristics of the oscillatory flow. Larger displacement is attained in the case where the upper surface of the magnetic fluid column is initially set below the center of the magnetic field. In order to predict the characteristics of the pipe flow driven by the magnetic fluid motion, a numerical analysis is also conducted. The governing equation, in which frictional resistance of laminar flow and other flow losses are included, is expressed as a nonlinear ordinary differential equation and calculated numerically under conditions similar to those of the experiment. Computational results agree well with data obtained from the experiment.

Reversible, field induced agglomeration in magnetic colloids

Reversible agglomeration of magnetic particles (20–300-Å diameter) in a colloidal suspension has been induced by applying various magnetic fields: nonuniform static fields and uniform ac or dc fields of magnitudes from 2.5 to 230 Oe. A sensitive Colpitts oscillator circuit monitored the spatial and temporal variations in magnetization in a vertical 11-cm column of magnetic fluid. The results are consistent with the hypothesis that spherical agglomerates of 10 7–10 9 particles are formed and settle gravitationally. The agglomeration was most pronounced in a commercially available water-base, 200-G ferrofluid; 20% of the particles formed agglomerates of ≥ 10 7 particles and settled out in 1 hr in a 230-Oe uniform ac or dc field. This effect was present to a lesser extent in other fluids (200-G ester base, 3% of the particles agglomerate in 1 hr; 200-G hydrocarbon base, ∼ 0.05% in 2 hr). Electron micrograph studies indicate that all sizes of particles participate in the agglomeration. Centrifuge experiments show that the agglomerates are not limited by close packing upon settling to the bottom of the tube. The Colpitts oscillator should be useful in determining the stability of magnetic fluids used in applications such as magnetic ink printers, metal separation, etc. It may also be useful in experimental investigation of agglomeration hypotheses because the extent of the agglomeration can be conveniently controlled via the applicatioa of magnetic fields.