This work presents experimental and numerical studies on the dynamics of cavitation bubbles in a nozzle-shaped microfluidic channel with PZT (lead-zirconate-titanate) actuations. It is found that a cloud of bubbles can be generated near the center of the microfluidic channel when the actuation voltage is larger than a threshold at 1 kHz. After being generated, the bubbles under actuations oscillate radially with violent expansion and compression, and simultaneously translate upstream towards the opening of the nozzle. Along with radial oscillation and translation, the bubbles undergo frequent and drastic coalescence and breakup, leading to vigorous churning of surrounding liquids. The pressure variation and distribution in the microchannel are calculated by numerical simulation in Ansys Fluent, and results show that there is a low-pressure zone inside the microfluidic channel within each cycle of the actuation period, which is responsible for bubble generation observed in the experiments. The method of bubble generation in this study is novel and can be applied for the enhancement of heat and mass transfer in microfluidic operations.
Keywords: breakup; bubble dynamics; cavitation bubble; coalescence; microfluidics.