Active laminar mixing induced by surface disturbance

Abstract

Traditionally, passive mixers and chaotic advection have played a key role in the field of microfluidics by stretching and folding the fluid. Some examples of these passive mixing techniques include channels with riblets or grooves on the walls, or serpentine curved channels. In this work, we explore an actuated wall for use as a closed-chamber micromixer. Although active mixers for low Reynolds number flows have been previously studied, a significant portion of that work has involved piezoelectrics. This work presents a novel polymer that offers many advantages over conventional piezoelectric stacks, including very small thickness and inexpensive construction cost. Moreover, these actuators are water-based, eliminating the need for coating or electrical isolation. The polymer used to create this moving boundary or “active skin” is a flexible surface that deforms mechanically in response to an electrical signal. This was accomplished with a polymer that was approximately 560 mm2 divided into nine sections. Every other section of the polymer was wired to actuate simultaneously under the influence of an applied voltage cycling between 1 and 70 hertz with a 2 volt amplitude. The flow over the active skin was measured via TRDPIV (Time Resolved Digital Particle Image Velocimetry) using an Nd:YAG laser. The result of this research indicates that flow stirring is generated by the use of an active skin. Moreover, even though the deflection of the polymer is on the order of microns, its influence extends to the entire area of the channel studied in this work (approximately 13 mm height and 43 mm length).