Three-dimensional numerical analysis of focusing and separation of diamagnetic particles in ferrofluid

Focusing and separation of particles and cells by magnetophoresis are important steps in many applications. In simple terms, the magnetophoresis can be classified into a positive one and a negative one. The most important characteristic of negative magnetophoresis is that particles and cells can be manipulated in a label-free manner. In this paper, continuous separation based on negative magnetophoresis is studied numerically using a three-dimensional model considering the interaction between particles and the ferrofluid. Firstly, the separation of two sized particles is investigated with a straight microchannel with two opposite permanent magnets for focusing particles before their separation by another bias magnet. Then the influence of size and position of permanent magnets and geometry of microchannel are investigated to achieve a better particle separation. Moreover, the effects of the concentration of the ferrofluid, the size difference of the particles, the magnet-channel distance and the flow velocity on the particle separation are analyzed.