Abstract

In Lab-on-a-chip devices (LOC), the handling of fluid droplets is one of the most important issues. Among all the ways of microactuation, electrowetting has been shown as a reliable actuation method in digital microfluidics. Its major advantages are the absence of heat generation, a rapid switching response, flexibility, and low power consumption. While most studies have been directed at performing experiments, numerical simulations of the phenomenon and its application to the design of LOCs are very few and there is still much work to do. In the current work, a numerical study has been performed to simulate droplet behaviour under electrowetting actuation. Due to the presence of the droplet in the domain, a free surface flow problem must be solved. A Volume of Fluid (VOF) technique is applied to track the interface. In addition, due to the variable nature of the applied electric field, the relevant equation should be solved in time and space. The flow is considered laminar and Newtonian and all equations are solved in three dimensions. Several aspects of droplet morphology are studied: contact line deformation, onset of actuation, and droplet deformation at different stages of actuation process. The droplet velocity is studied in detail and the numerical results are validated by existing experimental data in the literature. A velocity of 22 mm/s is achieved for the actuation voltage of 60 V. For design purposes, other parameters such as the electrode switching frequency and the electrode length effect on droplet velocity were also studied