Jianqiang Mai

Oscillation of a diamagnetic liquid bubble suspended by magnetic force

Abstract The levitation of the diamagnetic liquid droplet with the strong magnetic field is experimentally simulated, using the magnetic fluid as the surrounding fluid in place of air or gas, and the water bubble is levitated with the conventional permanent magnet. When the stepwise magnetic field is superposed, the suspended bubble behaves as a typical step response with the overshoot and viscous damping. The effects of the volume of the bubble, the strength of the magnetic field and the concentration of the magnetic fluid are investigated.

Hot-film measurements in a two-layer system of a magnetic liquid and a silicone oil

Constant-temperature hot-film anemometry measurements in a two-layer system of a silicone fluid layer over a magnetic fluid layer has been investigated. Complicating factors potentially affecting the measurements were very slow velocities, the unusually high thermal conductivity of the magnetic liquid, the vicinity of solid boundaries, the presence of the interface, and the possibility of magneto-convection in addition to natural convection. All these factors required a calibration procedure combining both experimental calibration and a set of numerical models of the system. The findings obtained during the calibration were that neither natural convection nor magneto-convection were adversely affecting the measurements, probably due to the effects of the solid boundaries and the interface. It was furthermore observed that the fluid interface resulted in an effect analogous to the near-wall effect, but deformations of the interface due to the sensor or its mounting prevented measurements close to the boundary. Spatial variation of the fluid velocities affected the calibration of the sensor noticeably. While a simple calibration, either by moving the probe or by assuming a uniform velocity, can give a qualitatively reasonable velocity profile, it will quantitatively deviate significantly from the true velocities.

Numerical analysis of viscous fluid flow in a magnetic fluid coated duct

Abstract Two-layer fluid flow of a magnetic and a non-magnetic fluid is investigated. The present paper reports numerical results of the interface shape, velocity field, and disturbed magnetic field that are obtained by the volume-of-fluid (VOF) method of two-dimensional flow of a non-magnetic fluid over a shallow layer of a magnetic fluid.

Unstable waves at the interface of a diamagnetic liquid column contained in a magnetic fluid

Abstract A magnetically held pipeless fluid transporting system is a potentially useful noncontact technique in science and technology. Keeping a stable interface between the diamagnetic liquid column and the surrounding magnetic fluid is essential. The present study gives an experimental study on the unstable interfacial wave leading to discontinuity of a liquid column maintained in a magnetic fluid by a non-uniform magnetic field. The experiments were carried out by setting two magnetic north poles in opposite position to produce the magnetic field, using water to form the diamagnetic liquid column, and a diluted kerosene-base magnetic fluid as the surrounding fluid. Unstable interfacial waves were measured. It was found that the magnetic pressure acting on the interface can stabilise the interface. The experimental results agree well with the theoretical stability condition derived from a two-fluids model.

New Actuator Utilizing Phase Change of Functional Fluids

This paper proposes a new actuator utilizing the phase change of the ER fluid. The dielectric coolant was used for the solvent and silica gel particles for the dispersion particle. The dynamic characteristics of the actuator was determined for the several patterns of the working conditions.

Instability of Magnetic Fluid Surface under Horizontal Non-Uniform Alternating Magnetic Field.

Stability of the surface of a magnetic fluid under a horizontal non-uniform alternating magnetic field is investigated experimentally and analytically. Several modes of interfacial waves of the same frequency as that of the applied magnetic field are observed, and the critical strength of the magnetic field at each frequency were obtained. The linear stability theory shows that the system is destabilized with the increase in the magnetic susceptibility and the gradient of the magnetic field, which is in accord with the experimental result. The iron nitride magnetic fluid, which is newly developed and has very high susceptibility and magnetization, was tested under the same condition as W-35 and HC-50. The small disturbance occurred even at very weak magnetic field, and the steady wave was formed in the uniform magnetic field.