Author(s)

M. Shinohara

Abstract

An investigation has been made of the dynamic behaviour of a magnetic fluid drop settling in a viscous fluid inside a vertical cylinder in response to impressed magnetic fields. Two coils were placed so as their axes coincided with the cylinder axis in order to provide the magnetic field for the tests. The Reynolds number Re (Re = avz /ν) is in the range of 0.001–0.037. Here, a is the scale of the magnetic fluid drop, vz is the settling velocity of the drop and ν is the kinematic viscosity of the machine oil. Near the upper coil, the centre of the drop is forced upwards, but the velocity of the drop is not always decreased. At the middle point between the two coils, the drop tends to extend along the field. Due to the change of the shape of the drop, the drag on the drop is reduced and the velocity of the drop is increased. Keywords: low Reynolds number, magnetic fluid, cylindrical wall, viscous fluid. 1 Introduction A magnetic fluid is a homogeneous colloidal suspension of magnetic particles in a solvent. Various physical phenomena relating to the flows of magnetic fluids have been studied by Rosensweig [1]. A number of interesting phenomena are exhibited by the magnetic fluids in response to impressed magnetic fields [2–4]. A certain interest is shown to magnetic fluids as carriers of drug. The magnetic field can pilot the path of a magnetic fluid drop in the body, bringing drugs to a target site [5], and the drugs can be retained there for as long as necessary. This means that it is important to investigate the motion of a magnetic fluid drop travelling inside a tube in an external magnetic field.

Keywords

low Reynolds number, magnetic fluid, cylindrical wall, viscous fluid