Acoustically induced bubbles in a microfluidic channel for mixing enhancement

Due to small dimensions and low fluid velocity, mixing in microfluidic systems is usually poor. In this study, we report a method of enhancing microfluidic mixing using acoustically induced gas bubbles. The effect of applied frequency on mixing was investigated over the range 0.5–10 kHz. Under either low frequency 0.5 kHz or high frequency 10 kHz, no noticeable improvement in the present mixer was observed. However, a significant increase in the mixing efficiency was achieved within a window of the frequencies between 1.0 and 5.0 kHz. It was found in our present microfluidic structure, single (or multi-) bubble(s) could be acoustically generated under the frequency ranging from 1.0 to 5.0 kHz by a piezoelectric disc. The interaction between bubble and acoustic field causes bubble oscillation which in turn could disturb local flow field to result in mixing enhancement.