Mixing and pumping with oscillating bubbles

Abstract

An oscillating bubble will generate a jet towards a solid surface in its collapse phase. This phenomenon has been observed for example in underwater explosions for large bubbles (tens of meters in diameter) and it has also been confirmed for smaller bubbles. Such a collapsing bubble has been shown to be able to pump liquid from one side of a plate with a hole to the other side (provided that the bubble and the hole are aligned), (Lew et al. (2007). The working principle is still the same, i.e. a high speed jet is formed in the collapse phase of the bubble towards the hole in the plate. In the current study we will investigate if it is possible to mix fluids with an oscillating bubble based on the jetting phenomenon. Bubbles are created experimentally with a spark or a laser, and high speed camera images are taken to study the bubble and fluid dynamics. First, experiments involving two immiscible fluids, Hydrofluoroether (HFE) and water, are performed. When a bubble collapses near the interface of these immiscible fluids, the density difference between the two fluids causes the formation of a jet, which will mix the two fluids. The formation of a crown near the HFE water interface is observed, when the bubble collapses very close to this interface. This phenomenon appears to be similar to the crown often observed in splashing drops on a layer of liquid. Secondly, experiments involving two miscible fluids are also performed to investigate if the surface tension of the fluid-fluid interface plays any role. In order to do so, a layer of honey was used with a layer of water. The bubble dynamics and the mixing of the fluids appear to be very similar to the case with immiscible fluids. Finally, some additional experiments were performed in a microchannel using a laser generated bubble. The resulting flow phenomena are interesting but not yet fully understood. Copyright © (2010) by the International Congress on Acoustics.