This study presents a numerical analysis of electric fields distribution, characteristics of swirling flow and effect of inlet velocity (u0) from two ground arrangements, i.e., wire-to-wire (WW) and wire-to-plate (WP) in a rectangular duct subjected to electrohydrodynamic. In both arrangements, location of an electrode wire, which is suspended from the upper wall of the duct, is initially located at the centerline of the rectangular duct, and ground is fixed on the bottom wall. In WW, position of electrode is varied in the vertical direction, while in WP, they are varied both in the vertical and horizontal directions. Electrical voltage of 20 kV is applied and inlet velocity in range of 0.3 – 1 m/s is selected. The numerical results show that electric fields distributions from both arrangements are quite different. These results cause the characteristics of swirling flows to appear differently. In both arrangements the maximum electric fields intensity are not different for each identical gap value. When the gap is closer, electric fields increase significantly. When inlet velocity of air is increased, the strength of swirling flow is decreased because inertial force is superior to the electric body force.

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Performance of a split-and-recombine micromixer (Tan et al., 2005) is assessed by means of numerical simulation. The micromixer is designed for micro cell sorting systems using immunomagnetic beads, of which working principle is lamination of fluid layers. The fluid motion in a complex three-dimensional geometry is simulated by using the finite difference method and the motion of beads is dealt with the one-way coupling Lagrangian particle tracking method. Although the thickness of laminated layers should ideally reduce by the factor of 2 n (where n is the number of unit-mixers connected in series), the present simulation with a realistic geometry shows that the thickness does not reduce that much. Relatively large unmixed regions are formed in the central region, which deteriorate the mixing performance. The size of the unmixed regions and the degree of mixing are quantitatively investigated. Based on the observation, an improved mixer arrangement is proposed. While the original arrangement proposed by Tan et al. (2005) was to simply connect identical unit-mixers, the present arrangement is to alternately connect the original unit-mixer and one with the mirrored geometry. With this modified arrangement, the unmixed region is suppressed and better mixing is achieved.