Issue
EPL
Volume 88, Number 2, October 2009
Article Number 24003
Number of page(s) 5
Section Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics
DOI http://dx.doi.org/10.1209/0295-5075/88/24003
Published online 10 November 2009
EPL, 88 (2009) 24003
DOI: 10.1209/0295-5075/88/24003

Mesoscopic structuring and yield stress of magnetofluidized fine particles

J. M. Valverde1, M. J. Espin2, M. A. S. Quintanilla1 and A. Castellanos1

1   Department of Electronics and Electromagnetism, University of Seville - Avda. Reina Mercedes s/n, 41012 Seville, Spain, EU
2   Department of Applied Physics II, University of Seville - Avda. Reina Mercedes s/n, 41012 Seville, Spain, EU

jmillan@us.es

received 1 September 2009; accepted in final form 6 October 2009; published October 2009
published online 10 November 2009

Abstract
The fluidization behavior of a bed of fine magnetizable particles excited by an externally applied magnetic field is found to depend on the aggregative nature of the particles before the field was applied. Usually nonaggregated particles organize in quasivertical local linear chains when the field is applied. In contrast, naturally aggregated particles form large-scale branched structures when magnetized by an external field. As a consequence the yield stress of magnetically stabilized beds of naturally aggregated particles is relatively increased and the bed can be stabilized at smaller field intensities. As expected from the magnetic cohesive force between magnetized particles, the yield stress is proportional to the square of the magnetic-field intensity, with a proportionality constant that depends on the mesoscopic organization on the magnetic particles. Remarkably, it is found that quasivertical chainlike structures are stable in spite of the fact that the magnetic field is applied in the horizontal direction.

PACS
47.55.Lm - Fluidized beds.
47.55.Kf - Particle-laden flows.
47.65.Cb - Magnetic fluids and ferrofluids.

© EPLA 2009