Fluid Mixing Enhanced by Surface Acoustic Waves in a Micro-Cavity

Abstract

One big challenge in micro-fluidic systems is that the mixing efficiency by molecular free diffusion is too low, especially when the viscosity of the fluids is high. In this paper, we designed two types of inter-digital transducers that can generate surface acoustic waves (SAWs), and then performed a series of experiments, where streamings driven by SAWs accelerate the mixing of different fluids. It is found that when the driving voltage exceeds a threshold, an Eckart streaming is excited, and the Eckart streaming can effectively enhance the mixing efficiency of different fluids by almost one order of magnitude. The mixing efficiency increases with the driving voltage. The results also demonstrate that the mixing efficiency is high even in the high-viscosity fluids where the free diffusion is extremely slow.