Numerical Study of Particle-Fluid Flow Under AC Electrokinetics in Electrode-Multilayered Microfluidic Device

A particle-fluid flow under alternating current (ac) electrokinetics was numerically simulated to investigate the three-dimensional (3-D) particle motion in a complex electric field of a high conductivity medium generated by an electrode-multilayered microfluidic device. The simulation model coupling thermal-fluid-electrical and dispersed particle problems incorporates three ac electrokinetics (ACEK) phenomena, namely, the ac electrothermal effect (ACET), thermal buoyancy (TB), and dielectrophoresis (DEP). The electrode-multilayered microfluidic device was fabricated with 40 electrodes exposed at the flow channel sidewalls in five cross sections. The governing equations of the simulation model are solved by the Eulerian-Lagrangian method with finite volume discretization. Fluid flow simulations in three cases with or without consideration of ACET and TB are performed to clarify the contributions of these phenomena. The fluid flow is found to be composed of short-range vortices due to ACET and long-range circulation due to TB based on the features of the electrode-multilayered microfluidic device. The 3-D particle trajectory influenced by the fluid flow is compared with four values of the real part of the Clausius-Mossotti (CM) factor to evaluate the DEP phenomenon. The simulation model is validated by experiments using a cell suspension. The pattern of cell trajectories in the upper part of the flow channel measured by particle tracking velocimetry agrees with the simulated pattern. By comparison of the simulation and experiment, it is found that the cells moving straight away from the electrode on the focal plane are decelerated within the region of 60 mu m from the electrode by positive-DEP with Re[K(omega)] = 0.08-0.11. Furthermore, the 3-D DEP-effective region and the ACET and TB dominant regions for the cells are predicted by evaluating the particle-fluid relative velocity due to DEP force with Re[K(omega)] = 0.10. Consequently, the flow mechanism and dominant region of each ACEK phenomenon in the device are clarified from the 3-D simulation validated by the experiments.