Abstract
This work reports numerical investigation of lateral migration of a paramagnetic microparticle of an elliptic shape in a plane Poiseuille flow of a Newtonian fluid under a uniform magnetic field by direct numerical simulation (DNS). A finite element method (FEM) based on the arbitrary Lagrangian–Eulerian (ALE) approach is used to study the effects of strength and direction of the magnetic field, particle–wall separation distance and particle shape on the lateral migration. The particle is shown to exhibit negligible lateral migration in the absence of a magnetic field. When the magnetic field is applied, the particle migrates laterally. The migration direction depends on the direction of the external magnetic field, which controls the symmetry property of the particle rotational velocity. The magnitude of net lateral migration velocity over a π cycle is increased with the magnetic field strength when the particle is able to execute complete rotations, expect for α = 45° and 135°. By investigating a wide range of parameters, our direct numerical simulations yield a comprehensive understanding of the particle migration mechanism. Based on the numerical data, an empirical scaling relationship is proposed to relate the lateral migration distance to the asymmetry of the rotational velocity and lateral oscillation amplitude. The scaling relationship provides useful guidelines on design of devices to manipulate nonspherical micro-particles, which have important applications in lab-on-a-chip technology, biology and biomedical engineering.
Highlights
Magnetic fields have been widely used to separate microscale and nanoscale magnetic particles suspended in fluids in various industrial, biological and biomedical applications, such as mineral purification [1], cell separation [2], and targeted drug delivery [3]
We developed a multi-physics numerical model based on direct numerical simulations to investigate the lateral migration of a paramagnetic elliptical particle in a plane Poiseuille flow under a uniform magnetic field
The direction of the magnetic field controls the asymmetric rotation of the particle and the direction of the net lateral migration
Summary
Magnetic fields have been widely used to separate microscale and nanoscale magnetic particles suspended in fluids in various industrial, biological and biomedical applications, such as mineral purification [1], cell separation [2], and targeted drug delivery [3]. The underlying principle in these applications is magnetophoresis—the motion of particles due to magnetic forces. The generation of magnetic forces requires both a magnetic particle and a spatially non-uniform magnetic field (or non-zero magnetic field gradients) [4]. Recent experiments have demonstrated a non-conventional strategy to manipulate magnetic particles by combining a magnetic torque, non-spherical shapes and shear flows [5,6]. Different from traditional techniques based on forces, this torque-based method only requires a uniform magnetic field. The lateral migration of non-spherical particles stems from the coupling of the magnetic field, flow field and particle–wall hydrodynamic interactions. Numerical simulations are powerful tools to carry out systematic investigations to gain insights on various factors that influence the particle transport behaviours
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