Published papers

Propagation of waves on the free surface of magnetic fluid is experimentally investigated. It is found that the surface velocity of the magnetic fluid depends on the intensity and frequency of traveling magnetic fields, and depth of the channel contained with the magnetic fluid. Theoretical investigation is also carried out in order to clarify the phenomena.

Natural convection of a magnetic fluid in concentric annuli was investigated experimentally. A thermosensitive liquid crystal was utilized for temperature visualization instead of flow visualization. When there was no magnetic field, developments of ordinary natural convection were observed. When a magnetic field was applied in the same direction of the gravity, wall-temperature distribution was observed as if an apparent gravity increased. But the clear influence of the magnetic field was not found. If a magnetic field was applied in the opposite direction of the gravity, the reverse natural convection was observed. Consequently, even if the intensity of the applied magnetic field was small, it played an important role in natural convection and heat transfer of a magnetic fluid. It was recognized that natural convection of a magnetic fluid could be controlled by the applied magnetic field.

Dynamic behaviors of a magnetic fluid in three different containers were experimentally studied. Experiments were carried out for rectangular, cylindrical and spherical containers, respectively. These containers were laterally oscillated. The vertical non-uniform magnetic field was applied by permanent magnets which were fitted underneath the container. Test liquid was a magnetic fluid with 33\% weight concentration of fine magnetite particles in a water carrier. It was found that harmonic wave motion, swirling waves and flow pattern of surface waves were influenced by the magnetic fields. The resonant frequency of the fluid-container system moved toward high frequency region with the magnetic field intensity. This behavior was also examined by the linear approximate theory. Theoretical results were qualitatively in good agreement with experimental results.

Laminar natural convection heat transfer of a magnetic fluid in a cubic enclosure is examined experimentally. Wall-temperature distributions are visualized by thermosensitive liquid crystal sheets. The effect of the magnetic field on the transient temperature distributions, and the local and averaged Nusselt numbers are discussed.

The dynamic behavior of a magnetic fluid in a laterally oscillating rectangular container was experimentally studied. A vertical non-uniform magnetic field was applied to the container. The resonant frequency of the fluid-container system moved toward the high frequency region with the magnetic field intensity. An experiment was also carried out for a two-phase liquid of magnetic fluid and kerosene.

Natural convection of a magnetic fluid in concentric annuli was investigated experimentally. A magnetic field was applied to the cylinders using a permanent magnet. When there was no magnetic field, ordinary natural convection was observed. When a magnetic field gradient was applied in the same direction as the gravity, a wall-temperature distribution was observed, as if an apparent gravity had increased; however, the clear influence of the magnetic field was not found. When a magnetic field gradient was applied in the opposite direction of the gravity, the reverse natural convection was observed. Consequently, even if the intensity of the applied magnetic field was small, it played an important role in natural convection and heat transfer of a magnetic fluid. It was recognized that natural convection of a magnetic fluid could be controlled by the application of a magnetic field.

Natural convection of a magnetic fluid is driven by the buoyancy force due to the difference in the fluid density and by the magnetic force. The purpose of this investigation is to examine the effect of uniformed and ununiformed magnetic fields on natural convection heat transfer of a magnetic fluid in a vertical square cavity. The vertical magnetic fields are applied uniformly and ununiformly using a permanent magnet and an electromagnet. Temperature distributions on a front wall is visualized by a thermosensitive liquid crystal sheet. The horizontal temperature distributions in the central cross-section of the cavity were measured with copper-constantan thermocouples.

The authors studied a shear flow of a water-based magnetic fluid between concentric annuli experimentally. The outer cylinder is rotates at the constant speed(0-160 rpm). The inner cylinder is hung by the small stainless wire. Magnetic field was applied by a two pole three-phase induction motor. Experiments are largely divided into two parts. One is to clarify the rheological properties without magnetic field. The other is to make it clear how large the moment, which is acting on the inner cylinder, becomes under the magnetic field. Experimental results were discussed using power law theory and micro-polar theory.

We report that thermomagnetic convection of a magnetic fluid in concentric annuli made of two isothermal horizontal cylinders. Rotating magnetic field was applied by a three-phase induction motor. A thermosensitive liquid crystal was utilized in order to visualize wall-temperature distributions. A new parameter was introduced to understand heat transfer mechanism of the thermomagnetic convection. Influences of rotating magnetic field on distributions of the wall-temperature and Nusselt numbers were investigated precisely and characteristics of heat transfer of a magnetic fluid were discussed.

We have investigated the stability and vibrational response of magnetic liquid columns held by Helmholtz coils. Theoretical resonance frequencies were derived from the linear potential theory prior to the experiment. During the experiment, a small quantity of a kerosene-based magnetic liquid was injected onto a lower pole plate. When the magnetic field was increased. a cylindrical column (height=9.78mm) was vertically formed between the two pole faces of the iron core Helmholtz coils. When the magnetic field was decreased, the column diameter exhibited hysteresis such that the column broke at a smaller diameter than that at formation. The coils holding the liquid column were then excited horizontally and the lowest mode (m=1, n=1) derived theoretically appeared in the measurements. The surface frequency response was measured optically using a CCD camera, a strobovision analyzer and a stroboscope for various magnetic field intensities and aspect ratios (mean diameter/height). We found that the resonance frequency of the mode (m=1, n=1) decreased with increase of the aspect ratio. The experimental resonance frequencies were in qualitative agreement with the theoretical predictions.

磁性流体液柱が振動する場合に液柱表面に生じる表面波動の様子を実験的に調べて，印加磁場と加振周波数との関係を明らかにした。

Dynamic behavior of a magnetic fluid column which is formed between two electromagnets is investigated. An electrodynamic shaker is used to generate a lateral sinusoidal vibration. Experiments are carried out to clarify the influence of magnetic field intensity, column height and fluid volume on the vibration of a magnetic fluid column. A theoretical approach is also taken using linearized wave theory. The first resonant frequency of displacement of the free surface increases with the magnetic field intensity, and decreases with the radius and height of the magnetic fluid column. These results are in good agreement with theoretical results.

The dynamic behavior of a magnetic fluid in a laterally vibrated rectangular container subject to a non-uniform vertical magnetic field has been investigated. Flow behavior was observed using the ultrasound velocity profile measuring technique. The effect of the magnetic field on the resonant frequency of the fluid-container system is discussed. Experimental results are compared with the results obtained from nonlinear theory using the perturbation method.

磁性流体の液柱の軸対称振動におよぼす磁場の効果を調べた。

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 behavior as the magnetic field is varied.

The interfacial impulse response of the axisymmetric mode (0,1) of a finite liquid column in a microgravity environment is simulated using magnetic liquids and random vibration.

円管内振動流をDNSによって解析を行い，特に壁近傍の乱流特性を明らかにした。

Natural thermal convection of different unmixed liquids is quite different from that of a single liquid because of the existence of liquid-liquid interface. In order to clarify this phenomenon, it is necessary to know both flow and temperature fields of different unmixed liquids. In the present paper, natural convection of different unmixed liquids in a cubic enclosure with isothermal hot and cold walls was investigated. Influence of difference of kinematic viscosities and volume ratio of two liquids on flow and temperature fields were experimentally studied. Temperature distribution on a central cross section was visualized by thermosensitive liquid crystal particles. The conclusions derived from the above experiment are as follows: As the thermal movement occur through the interface, The reverse speed of two kind of liquids near the interface was promoted. And beside the main circulation that occurred in the liquids of higher volume ratio and lower viscosity ratio, the secondary circulation was caused in the upper liquid.

Sloshing is a phenomenon that occurs when a liquid with a free surface is severely agitated in a liquid storage container. In an axisymmetric container, even though the excitation is lateral, the liquid oscillates with rotational movement around the central axis of the container. This phenomenon is called swirling and may be unstable swirling or stable swirling. We measure the velocity profile of a sloshing magnetic fluid using an ultrasonic Doppler velocimetry method called UVP, and examine the relationship between internal velocity profiles and swirling phenomena, in particular, stable swirling phenomena. We calculated power spectra from the velocity data using a fast Fourier transform and observed that the most dominant peak in the power spectrum moved to higher frequencies as the magnetic field intensity was increased, whereas a derived peak at a lower frequency moved to lower frequencies as the magnetic field intensity was increased.

Sloshing of a magnetic fluid in a laterally vibrated cylindrical container subject to a non-uniform vertical magnetic field was examined. Internal velocity profiles were measured using ultrasound Doppler velocimetry. The effect of the magnetic field on the resonant frequency of the fluid-container system was examined and the results were compared with theoretical results. The second and third peak of the power spectra of velocity shifted to a low frequency region as the magnetic field was increased. It was observed that these derived frequency peaks were connected with swirling in the cylindrical container.