Tuning particle settling in fluids with magnetic fields

Abstract

A magnetic field (MF) is generated to modify gravity in a laboratory. The MF produces a vertical force that counteracts the gravitational field on a magnetic sphere. The perpendicular spin of particles is blocked, thus allowing spin solely around the direction of the MF. The settling of spherical magnets in a quiescent flow with a particle density of 8200 kg/m 3 and Galileo number (Ga) in the range [100, 280] was studied experimentally. The results obtained by varying Ga via gravity modification to those obtained with nonmagnetic spheres where Ga is modified by varying viscosity are compared. Findings showed that there is no significant difference in the trajectory angle between magnetic and non-magnetic cases, suggesting that the method for compensating gravity does not produce any spurious effect and that particle spinning has no significant effect on this aspect of the dynamics. Subtle differences in trajectory planarity were observed hinting at a possible dependence on particle spin. Results prove the validity of the method introduced here to change the gravitational strength on particles in fluids.