Hydrodynamic motion of magnetic particles in a Poiseuille flow

The hydrodynamic behavior of magnetic nanoparticles in a Poiseuille flow through the design of a High-Gradient Magnetic-Separator (HGMS) is studied. Using numerical solutions of the Langevin equations, to simulate the motion of colloidal suspensions in a continuous flow, at low Reynolds numbers, it is shown that the separation time is not affected by the flow velocity if single particles are considered. However, if hydrodynamic and dipole-dipole interactions are included, the separation time depends on flow properties. Then, the influence of flow velocity on the kinetics of aggregation is studied. It is shown that, in the irreversible aggregation regime, linear chains of particles are formed and steadily grow and their average size, S, increases with time as a power law. The exponent, z, of the mean chain-size growth, S(t)∝tz, is practically not affected by the flow velocity. The chain-size (s) distribution function (cs) approaches (for long times) the following scaling form cs(t)∝s−2f(s/S).