Acoustically Induced Bubbles in a Microfluidic Channel for Mixing Enhancement

We demonstrate acoustically bubble generation in a microfluidic channel through both experimental observation and numerical simulations. The microfluidic channel contains a nozzle-shaped actuation chamber with an acoustic resonator profile triggered by a piezoelectric disk. It has been observed that for a steady deionized (DI) water flow is driven through the channel, bubbles generation occurs in the channel when the piezoelectric disk is actuated in frequencies between 1 kHz and 5 kHz. Outside this actuation frequency range, no bubbles are generated in the channel. The experiment shows that the presence of bubbles in this frequency range can significantly enhance the fluid mixing in the microfluidic channel, which otherwise would not happen at all without the bubbles. To explain the bubble generation, a two-dimensional model is used to describe the acoustic actuated unsteady flow field. The model is solved numerically using the FLUENT software, and the numerical results shows that a low pressure regions, where water pressure is below the corresponding vapor pressure under the same temperature exists inside the actuation chamber, indicating that bubble generation can occur in this low pressure region. The bubble generation was also experimentally observed in such low pressure region by using a high speed camera. The low pressure region and bubble generation are attributed to the acoustically featured channel configuration and depend on the actuation frequency.