Numerical investigation of induction of chaotic micromixing via vibration switching

Abstract

Enhanced mixing in microfluidic systems is necessary in many applications such as chemical processing, biological assays, and diagnosis. We are developing a microfluidic system to efficiently mix minute reagents (down to several microliters) using vibration-induced flow (VIF), in which a net flow is generated around a micropillar by applying periodic vibration. In this study, we numerically investigate the enhancement in chaotic mixing using the VIF technique and periodic switching of vibrations. By extending our previous numerical simulation model, we investigate the flow field and trajectories of fluid particles in three-dimensional space. We demonstrate that chaotic advection characteristics can be observed by periodically switching the vibrational direction of a substrate using simple cylindrical pillars. In addition, using an appropriate interval for switching the vibration axes yields better mixing performance. The extent of chaotic advection is evaluated quantitatively using the Lyapunov exponent considering various vibration parameters, such as the vibration amplitude, separation distance between each pillar and pillar shape. The flow field induced by a large-amplitude and sharp-edged wall pillar provides excellent mixing results. Thus, VIF is successfully applied to obtain an efficient mixing strategy with the aid of the chaotic theory.