In the present study, we address a suspension composed of magnetic cubic particles that flow in a Hagen-Poiseuille flow in a gradient magnetic field generated by multi-pairs of magnetic dipoles. Brownian dynamics simulations were performed in order to investigate the dependence of the trapping characteristics on a variety of factors such as the magnetic particle-particle interaction strength, the strength of non-uniform magnetic field, the strength of the flow field and the separation distance between two pairs of magnetic poles. The main results obtained here are summarized as follows. For the case of a larger separation distance, an arch-type cluster with more cubic particles is formed between the magnetic poles. In this case, the central part of the large arch-type cluster is located in the area where there is less influence from the magnetic field. This in turn leads to an instability of the cluster and as a result it tends to be carried downstream by the stronger flow field. These results suggest that an increasing the pole separation facilitates the trapping of a larger arch-type cluster between the poles. However, the stability of the trapped cluster decreases with increasing separation, and beyond a certain distance, the cluster is carried downstream by the flow field. This behavior implies a trade-off between the trapping capacity and the structural stability of the cluster. If the separation distance between the two poles is sufficiently near, a small arch-type cluster is located in a vicinity area nearer to the wall surface where the flow field is weaker. Hence, we expect that the smaller pole separation may give rise to good trapping performance in the situation of a strong flow field.
Yamanouchi et al. (Thu,) studied this question.