Heterogeneous Cavitation from Oil Droplets
* Presenting author
Abstract:
So far the only known mechanism to sustain heterogeneous cavitation is the presence of particles in water that can stably trap gas pockets within hydrophobic crevices. While surface attached nanobubbles and stable nanobubbles are investigated they have not been identified as a cavitation nuclei. In this presentation, we provide evidence that besides particles oil droplets suspended in water and having atomically smooth surfaces are cavitation nuclei, too. The experimental setup utilizes a single yet strong tensile wave that is generated within a 3-5 µm thin layer of water confined by two solid glass walls. A plasma generated with a focused and pulsed laser launches several waves into this geometry, i. e. a bulk wave in the solid, followed by a leaky Rayleigh wave, and a Lamb-type wave. The latter is responsible for a tensile stress traveling through the liquid. The particular geometry was chosen as it allows visualizing the dynamics originating from additionally suspended oil droplets (around 2 µm in diameter) with high-speed photography. Interestingly, we find predominantly cavitation bubbles are formed on the oil droplets once the Lamb-type wave is passing. The implications of liquid-type cavitation nuclei are discussed.