Intensifying cavitating flows in microfluidic devices with poly(vinyl alcohol) (PVA) microbubbles

Official URL: http://dx.doi.org/10.1063/1.5051606

Cavitation and the energy associated with the collapse of resulting cavitation bubbles constitute an important research subject. The collapse of the hydrodynamic cavitation bubbles at the outlet of the flow elements leads to a high energy release and generates localized shock waves and a large temperature rise on exposed surfaces. The concept of "hydrodynamic cavitation on chip" is an emerging topic which emphasizes phase change phenomena in microscale and their utilizations in energy and biomedical applications. This study is aimed to investigate the potential of poly(vinyl alcohol) (PVA) Microbubbles (MBs) to generate cavitation bubbles and to evaluate their effects on flow regimes and energy dissipation. For this, three different microchannel configurations with different roughness elements were considered. The structural side wall and surface roughened channels were fabricated along with the smooth channel according to the techniques adopted from semiconductor based micro-fabrication. The upstream pressure varied from 1 to 7 MPa, and the flow patterns were recorded and analyzed using a high-speed camera. The pressure was locally measured at three locations along the microfluidic devices to determine the conditions for fully developed cavitating flows. The results were compared to the pure water case, and different trends for the cavitating flow pattern transitions were obtained for the water-PVA MB solution case. Accordingly, the twin cavity clouds extended to the end of the side wall roughened channel at a lower upstream pressure for the case of PVA MBs, while the smooth and surface roughened channels do not demonstrate this flow pattern. In addition, the cavitation number has the lowest values under the same working conditions for the case of PVA MBs. Moreover, the impact pressure generated by the bubble collapse inside the side wall roughened channel for the case of PVA MBs was notably higher than that for pure water.