Dynamics of magnetic chains in a shear flow under the influence of a uniform magnetic field

We numerically investigate dynamics of magnetic chains and flow characteristics in a two-dimensional shear flow under the influence of a magnetic field applied externally. A direct simulation method is employed to solve the particulate flow in the creeping flow regime, taking into account both magnetic and hydrodynamic interactions in a coupled manner. In a periodic channel, the dynamics of chains is found to be significantly influenced by the Mason number (the ratio of viscous force to magnetic force), the magnetic susceptibility, and the particle fraction. Below a critical Mason number, a chain rotates and reaches an equilibrium. Above the critical value, however, the chain continuously rotates as a rigid body. Thinning behavior in the wall shear stress is found above a threshold value of the Mason number. As for chain rupture in the shear flow, three regimes of the Mason number are found, showing three typical conformations of the chains: (i) complex chains with branches rather than linear chains, (ii) tilted linear chains broken in the middle, generating a slip zone between the upper and lower chains, and (iii) shortened chains rotating in the channel. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704822]