Dielectrophoresis is one of the major AC electrokinetic phenomena which has been widely demonstrated in microfluidics research as a method to control and manipulate micro and nano-scale particles in liquid. Predicting the movement and behavior of particles under non-uniform AC electric fields by numerical modeling and simulation is important for the design of experiment devices.
In this study, we consider special conditions where the coupled dielectrophoresis (DEP) force and the hydrodynamic force contribute to the movement and behavior of particles in dielectrophoretic devices. Based on a drift-diffusion dynamics, we employ the Effective Medium Approximation (EMA) in order to include many particles in a system device. 2D simulation of mathematical model is adopted. We use two different channel geometry (non-rectangular and rectangular microchannel) and three different electrode arrangements (A, B and C) as a model device. In the first case we consider a microchannel with electrodes produce an AC electric field, filled with an incompressible and Newtonian suspending medium include many-particles within it. The second and the third case, the fluid and particles are introduced into the microchannel with and without an electric field applied, respectively.
At certain point evaluation for each of the configuration (A, B and C) when only the electric field applied, the highest amount of particles trapped is observed at the electrode edges in configuration A where the particle volume fraction φ = 0.59, whereas in configuration B and C are φ=0.54 and φ=0.53, respectively. When the hydrodynamic flow coupled with electrostatic force, at fluid velocity 20 µm/s the highest amount of particles trapped is observed in configuration A φ=0.61, whereas in configuration B and C are φ=0.55 and φ=0.52, respectively. When rectangular microchannel is used, the highest amount of particles trapped is observed in configuration A φ=0.59, whereas in configuration B and C are φ=0.48 and φ=0.5, respectively. In addition, for configuration C only, when the electrode gap is decreased from 40 µm to 20 µm, the highest amount of trapped particles observed is φ=0.62.
In conclusions, the geometry of the electrodes has significant effect on the DEP force and hence the particles motion. Moreover, the presence of the fluid flow affects the amount of particles trapped.

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