2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Chaotic advection induced by a magnetic chain in a rotating magnetic field

T.G. Kang, M.A. Hulsen, P.D. Anderson, J.M.J den Toonder and H.E.H. Meijer
Eindhoven University of Technology, NL

Keywords:
chaotic advection, magnetic chain, rotating magnetic field, fictitious domain/Maxwell stress tensor formulation

Abstract:
We investigated chaotic advection induced by a magnetic chain suspended in a fluid in a rotating magnetic field. Our main focus is on the dynamics of the chain and the route to induce chaotic mixing, significantly influenced by the Mason number, the ratio of the viscous force to the magnetic force. We developed a numerical model based on the finite element method and a fictitious domain/Maxwell stress tensor formulation, enabling us to take into account both hydrodynamic and magnetic interactions in a fully coupled manner. The particles have a constant magnetic susceptibility and are assumed to be non-Brownian and inertialess. We present results at three Mason numbers. At Ma=0.001, the chain rotates like a rigid body following the magnetic field. We observe chain break-up at Ma=0.002 and 0.003. The difference between the two motions at Ma=0.002 and 0.003 is whether the detached chains form a single chain again or remain as separate chains. The former has two flow portraits: one with a single rotating flow and the other with two co-rotating flows. From a series of deformation patterns of a blob of fluid, we found that alternating break-up and re-formation of the chain results in more enhanced mixing.

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