Experimental and numerical investigation of microscale acoustic streaming for mixing fluids*

In microfluidics, homogeneous flow mixing is essential in broad applications including biochemical assays and chemical synthesis. However, low Reynolds number flows render flow mixing challenging in the microchannel. Recently, acoustofluidic mixing based on acoustic streaming flow (ASF) has been proposed to address the limitations of the previous mixing methods. However, in-depth investigation of the ASF is still in demand to characterize the flow mixing phenomenon. Here, we experimentally and numerically visualize the microscale ASF under varying conditions of total flow rate, acoustic wave amplitude, and fluid viscosity using particle image velocimetry and computational fluid dynamics, respectively. We utilized a prism-embedded vertical-type acoustofluidic device to experimentally visualize the streamwise-spanwise plane of the ASF for the first time. For the numerical investigation, we adopted wave attenuation model and compared the results with those obtained from the experiments. Based on the findings, we applied the ASF-based mixing to rapid, continuous, automated chemical synthesis.