Vapor bubbles in confined geometries : a numerical study

The rapid and violent dynamics of vapor bubbles in confined geometries offer many potential uses in microfluidic devices without moving mechanical parts. The performance of these devices depend strongly on the bubble dynamics. A fundamental understanding of these entities is therefore of paramount importance but still lacking. Theoretical investigation is difficult due to the highly transient bubble shape, its confinement and the presence of phase change. Numerical simulation offers a promising avenue for their study. In this thesis a numerical method is implemented for studying vapor bubbles in confined geometries. The method is based on a finite difference discretization of the governing equation of the liquid phase. The vapor bubble is modeled as a region of uniform temperature and pressure which serve as boundary conditions for the liquid. The motion of the vapor/liquid interface is captured implicitly by means of the Level Set method. The numerical method is validated by means of several tests. It is shown to be first order accurate in time and second order accurate in space. It is further used to simulate the growth and collapse of a vapor bubble in two types of confinement. One being a narrow tube, the other a set of parallel glass discs. The initial liquid temperature field is an important quantity for the resulting dynamics. This dependency is investigated. A qualitative comparison to experimental data is made. For the disc confinement the bubble shape develops a concave edge during collapse. This feature is corroborated by means of geometical optics calculations and comparison with experimental data