Numerical Modeling of Microscale Mixing Using Lattice Boltzmann Method

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2008-04-28

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Virginia Tech

Abstract

Recent advancements in microfabrication technology have led to the development of micro-total analytical systems (μ-TAS), more popularly known as lab-on-a-chip (LOC) devices. These devices have a relatively small size and are capable of performing sample and reagent handling steps together with analytical measurements. Rapid mixing is essential in such microfluidic systems for various applications e.g., biochemical analysis, sequencing or synthesis of nucleic acids, and for reproducible biological processes that involve cell activation, enzyme reactions, and protein folding.

In this work a numerical model is developed using a lattice Boltzmann method (LBM) to study microscale mixing. The study involves two mixing methods, namely, electroosmotic mixing and magnetic assisted mixing. A single component LBM model is developed to study electroosmotic flow in a square cavity. Mixing is studied by introducing two types of tracer particles in the steady electroosmotic flow and characterized by various mixing parameters. The results show that rapid mixing can be achieved by using a steady electric field and a homogeneous zeta potential.

A multicomponent LBM method is also developed to study magnetic assisted mixing in a channel configuration. The ferrofluid flow is influenced by two magnets placed across a microchannel. The interacting field induced by these magnets promotes cross-stream motion of the ferrofluid, which induces its mixing with the other nonmagnetic fluid. Two fluids, one magnetic and another non-magnetic fluid, are introduced in a channel, when two magnets are placed across it at a distance apart. In the presence of the magnetic field, the magnetic fluid tries to follow a zig-zag motion generating two rolls of vortices thereby enhancing mixing. A parametric study characterizes the effects of diffusivity, magnetic field strength, and relative magnet positions on a mixing parameter. Mixing is enhanced when the magnetic field strength and diffusivity are increased. However, contrary to the observed trend, placing the magnets very close to each other axially results in local ferrofluid agglomeration rather than promoting mixing.

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microscale, mixing, magnetic fluid, eletroosmosis, Lattice Boltzmann method

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