Kunio Shimada

Natural convection of magnetic fluid in a rectangular box

Abstract The natural convection of a magnetic fluid in a two dimensional cell, whose aspect ratio is one, is studied experimentally and numerically. Result obtained from experiment and numerical analysis revealed that the vertically imposed magnetic field has destabilizing influence and at the super critical state the flow mode becomes quit different from that without the magnetic field.

Heat transfer characteristics of magnetic fluid in a partitioned rectangular box

Abstract The natural convection of a magnetic fluid in a square cavity with four rigid walls, in which a portion of partition exists (partitioned square cavity), is studied numerically for an externally imposed magnetic field. It is found that the convection state may be largely affected by improving heat transfer characteristics at higher Rayleigh number when a strong magnetic field is imposed.

Characteristics of magnetic compound fluid (MCF) in a rotating rheometer

As a new intelligent or smart fluid, we propose a magnetic compound fluid (MCF). This fluid has nm size magnetite and μm size iron particles in a solvent. The magnetic field effect on flow characteristics of MCF can demonstrate midpoint between magnetic fluid (MF) and magneto-rheological fluid (MRF). For example, the magnitude of shear stress to shear rate under a steady magnetic field in MCF can be larger than MRF by varying the compound rate of the magnetite and iron particles. This report shows an experimental data of shear stress to shear rate of MCF in rotating rheometers of cone and concentric cylinder types under transverse and longitudinal magnetic fields.

Effect of magnetic cluster and magnetic field on polishing using magnetic compound fluid (MCF)

Using the magnetic compound fluid (MCF) developed by one of the authors in this paper, we performed polishing under various intensities of steady and fluctuating magnetic fields. We determined the optimal intensity of both types of magnetic field in order to produce the most effective polishing effect. The optimal intensity is related to the produced magnetic clusters in the MCF.

New microscopic polishing with magnetic compound fluid (MCF)

We propose a magnetic compound fluid (MCF) as a new smart fluid. This fluid includes nm size magnetite and mm size iron particles in a solvent. The magnetic effect can be expected to demonstrate between the magnetic fluid (MF) and magneto-rheological fluid (MRF). Moreover, the magnitude of the shear stress to the shear rate under steady magnetic field can be larger than MRF by varying the compound rate of the MF and MRF. This report shows an experimental application of microscopic polishing with the MCF. We examined the surface roughness of flat titanium material to the attached rotating plate with 15 rpm under magnetic field. By comparing the roughness between the MCF and the MR, the polished plate is more uniformly over the plate with the MCF than the MR. Further the roughness of Ry and Ra are larger under fluctuating magnetic field than steady magnetic field. The more effective polishing can be explained with the cluster model of particles.

Magnetic Rubber Having Magnetic Clusters Composed of Metal Particles

For the purpose of assembling metal particles on a nano- or microscale, in a previous investigation the authors had succeeded in extracting magnetic clusters from an intelligent fluid responsive to a magnetic field. The clusters are shaped like rods or needles and range from macroscopic to microscopic in size. In the present paper, a method for producing silicon rubber that contains the magnetic clusters is presented and its magnetic, mechanical, and physical properties are discussed. This new material shows superpara and anisotropic magnetization. In addition, the tensile strain of the material in relation to normal stress changes due to the existence of the magnetic clusters is studied. This material can be used in engineering applications.

Extraction of magnetic particle clusters self-assembled by a magnetic field

For the purpose of particle assembly on a nano- or microscale produced by metal particles, we proposed a method of extracting magnetic clusters in the shapes of rods or needles that have been produced in sizes ranging from macroscopic to microscopic. We also succeeded in freely controlling the scale of the magnetic cluster in this size range, with the form remaining stable without the presence of a magnetic field through the use of hydrophilic monomers of oleic acid. We discovered an algebraic rule governing the relation between the scale of the magnetic cluster and the strength of the applied magnetic field.

A new float-polishing technique with large clearance utilising magnetic compound fluid

This report described a new float-polishing technique with large clearance utilising a newly developed magnetic responsive fluid, Magnetic Compound Fluid (MCF) developed by one of the authors, Shimada, in 2001. Before the present study, a clearance of up to 0.1 mm had been obtained through the use of MCF in float polishing. MCF was then improved by the addition of α-cellulose. A clearance as large as 8 mm could then be achieved in float polishing. The polishing results showed a finely polished, and mirror-like surface with a nm-order Ra for various kinds of polished material was obtained. The mechanism of our proposed polishing technique was explained in terms of a magnetic cluster model by using the experimental results regarding polished surface roughness under the abrasive particles condition of the MCF. The results obtained by this polishing technique were also compared to those obtained by utilising ordinary magnetic responsive fluids, that is, Magnetic Fluid (MF) or magnetorheological fluid.

MEASUREMENT OF INTERACTIVE SURFACE FORCE OF SUSPENDED PARTICLES IN ER AND MR SUSPENSIONS UNDER ELECTRIC AND MAGNETIC FIELD

Interactive surface force between each particle in suspension is very important to explain the dispersion and flocculation phenomena in fluid. The new equipment has been developed to measure the interactive surface force of particles, which was calculated by using Derjaguins formula, in Electro-Rheological (ER) Fluid and Magneto-Rheological (MR) Suspensions/fluids under electric and magnetic fields, respectively. Firstly, the interactive force of particles in ER fluid dispersed by melamine particles under electric fields was measured. Secondly, the interactive force of particles in MR suspensions dispersed by carbonyl iron particles under magnetic field was investigated. Considering the measurement of interactive surface force of ER and MR fluids, they have a original characteristic frequency due to the attractive and repulsive force of particles interactions initiated by the electric, magnetic and compressive force. Moreover, clusters formed according to the size of particles, particles movement model and formation are estimated by the characteristic frequency of ER fluid and MR suspensions under various electrical and magnetic fields. It indicates that these estimation models might be lead to the interaction kinetics of suspended particles in ER/MR under electrical and magnetic fields.

Experimental investigation of the effect of the MPL (magnetic polishing liquid) on surface finishing

We investigated the polishing effect of magnetic polishing liquid (MPL) made of abrasive particles and a newly developed magnetic responsive fluid, magnetic compound fluid (MCF) as intelligent or smart fluid. By applying steady and fluctuating magnetic fields, we investigated the polishing effects of the magnetic fields, varying the kinds of polishing material and the components of the MPL. In order to explain the cause of the experimental results, we investigated the apparent viscosity of the MCF and MPL, and used microscopic to investigate behavior of the particles in the MCF and MPL. We clarified the mechanisms governing the polishing effects through the use of a model based on the observation of the particles.