Shigemitsu Shuchi

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.

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.

Flow boiling heat transfer of binary mixed magnetic fluid

A new type of binary magnetic fluid, which is a mixture of base magnetic fluid with an organic secondary fluid, whose saturation temperature is lower than that of the base magnetic fluid, was introduced. Basic heat-transfer characteristics of the binary magnetic fluid were examined for boiling two-phase flow in a partly heated pipe. It was indicated that continuous boiling was achieved without any deterioration in magnetic properties of the fluid and the heat-transfer rate of the flow was improved remarkably by an applied magnetic field at higher flow rate.

Membrane Formation Process in Magnetic Fluid and Application for Aperture Control

Basic characteristics of the membrane formation process were investigated experimentally and numerically. In the experiment the aperture area of magnetic e uid membrane was recorded for a given volume of magnetic e uid sustained by applying a magnetic e eld in a pipe section. In the numerical analysis the formation process of the magnetic e uid membrane was examined under various magnetic e eld intensities. The theoretical background of the numerical work is based on the static force balance between gravity, magnetic force density, and surface tension on the membrane at the solid contact point. The surface proe le was estimated at an equilibrium stage by numerical analysis and compared to experimental results, where the membrane (sustained by magnetic e uid in a pipe) formed the aperture cone guration. In the results of the present investigation, from both experimental and numerical work, the detailed formation process was verie ed, and it was shown that the aperture area can be controlled by applying a magnetic e eld. Nomenclature F = body force density, N/m 3 fg = gravitational body force density, N/m 3 fm = Kelvin body force density, N/m 3 fs = surfacial force density, N/m 3 g = gravitational acceleration, m/s 2 H = magnetic e eld intensity, A/m H = magnetic e eld vector Hr = intensity of magnetic e eld on r direction, A/m Hz = intensity of magnetic e eld on z direction, A/m H ¤ = nominal value of Hz; the maximum of Hz, A/m I = applied dc current, A k = Boltzmann constant M = magnetization, Wb/m 2 M = magnetization vector, Wb/m 2 MS = saturation magnetization, Wb/m 2 R = surface curvature at interface Rs = representative surface curvature at solid contact r, µ, z = cylindrical coordinates (see Fig. 3), S = aperture area, m 2 T = absolute temperature, K O

Application of magnetic fluid membrane for flow control

To study the application of a magnetic e uid membrane for e ow rate control, an experimental investigation was conducted to obtain the basic characteristics and to verify the feasibility of practical use. The working principle of a magnetically controlled magnetic e uid membrane is based on the magnetic attraction body force exerted on the magnetic e uid, which is sustained in the cross-sectional area of a pipe. In the experiments, rupture pressure was obtained at various conditions for an oil ‐magnetic e uid interface. Also, from the results obtained for the e ow rate ontrol characteristics, it was found that the magnetically controlled membrane has a function similar to that of an ordinary buttere y valve, and it was shown that the membrane would be feasible for controlling lower e ow rates at lower driving pressure gradients. Nomenclature D = circular valve diameter of buttere y valve, m D0 = pipe diameter of buttere y valve, m d = pipe diameter of test section, m H = magnetic e eld intensity, A/m H = magnetic e eld vector Hr = intensity of magnetic e eld in r direction, A/m Hz = intensity of magnetic e eld in z direction, A/m .Hz/max = maximum of Hz, A/m I = applied dc current, A l = pipe length, m le = effective length, m lm = length covered by magnetic e uid, m M = magnetization, Wb/m 2 M = magnetization vector, Wb/m 2 Ploss = pressure loss, Pa ¢s Pr = rupture pressure, Pa ¢s Re = Reynolds number r, µ, z = cyclindrical coordinates (see Fig. 6)

Boiling heat transfer characteristics of binary magnetic fluid flow in a vertical circular pipe with a partly heated region

Abstract An investigation was conducted for heat transfer characteristics of binary magnetic fluid flow in a partly heated circular pipe experimentally. The boiling heat transfer characteristics on the effects of the relative position of the magnetic field to the heated region were particularly considered in the present study. From the experimental verification, the Nusselt number, representing boiling heat transfer characteristics, was obtained for various flow and magnetic conditions which were represented by the non-dimensional parameters of the Reynolds number and the magnetic pressure number. Additionally, the rate of change of the Nusselt number found by applying the magnetic field was also estimated and the optimal position of the field to the partly heated region was discussed. The results indicated that the effect of the magnetic field to the heat transfer rate from the heated wall was mainly subjected to the effect of the vortices induced in the magnetic field region and the possibility of controlling the heat transfer rate by applying an outer magnetic field to utilize the effect.

Hydrodynamic characteristics of steady magnetic fluid flow in a straight tube by taking into account the non-uniform distribution of mass concentration

Abstract We clarify numerically the wall friction coefficient, the distributions of velocity and shear rate, and the number of aggregated particles on steady magnetic fluid flow in a straight tube by taking into account the non-uniform distribution of mass concentration (DMC). Also the effect of DMC is clarified under the uniform and non-uniform transverse steady magnetic field. In comparison with the published data, the numerical results show good agreement with the experimental data.

PRESSURE CHARACTERISTICS OF ER DAMPER WITH DIFFERENT PISTON VELOCITIES

A basic experiment for the gap flow in a closed piston - cylinder system of ER fluid was carried out with regard to engineering application to dampers. The purpose of this study is to gain system characteristics and to elucidate flow behaviors of ER fluid in the piston–cylinder system; the model damper. Pressure, which is the system characteristic, was examined in the present study. The test fluid was a smectite ER fluid in silicone oil base of the 3wt% particle dispersion concentration. In the apparatus the piston moves in the vertical direction at a given speed. Theoretical formula of pressure difference is considered by the one-dimensional analysis of the ER flow in the gap of cylinder. It was shown that the response of the pressure was retarded with strong electric field. In comparison with the theoretical estimation and experimental value, the theoretical pressure difference was in good agreement with experimental data. For a sake of giving an insight to flow phenomena, visualization was also achieved using model Newtonian fluid in the piston-cylinder system, and shown that vorticity generated at the rear corner of the piston plays an important role for the pressure characteristic.

Flow Boiling Heat Transfer Characteristics of a Binary Mixed Magnetic Fluid

Boiling heat transfer characteristics were verified for a temperature sensitive magnetic fluid, to which the organic fluid was mixed, yielding a binary-carrier-fluids magnetic fluid. Substantial increase of heat transport capability was achieved in comparison with an ordinary magnetic fluid. In the present study, n-hexane, which has lower boiling point than that of kerosene (mother carrier fluid), was mixed. It was found that the heat transport capability is surely improved with applying magnetic field to the binary mixed magnetic fluid flow. And the effect of vortices predicted by predicted by previous numerical studies is confirmed in the present study, thus the heat transfer characteristics from the heated wall is strongly affected by the vortices.

Measurement of Void Fraction in Magnetic Fluid Using Electromagnetic Induction

A new technique of measuring void fraction in magnetic fluid using electromagnetic induction was proposed. In order to establish the measuring method, a feasibility study was conducted experimentally with an aid of numerical analysis. From the results of static experiment and numerical analysis, it was obtained that there exists a linear relationship between the void fraction and the measured electromotive force, when induction coils were connected in series for Helmholtz excitation coils, regardless of distribution of air bubbles in magnetic fluid