The formation of bubble emulsions in microgravity: experimental design*

An emulsion is the dispersion of a liquid droplet into another liquid. In this study, we consider an emulsion composed of gas bubbles dispersed in a liquid. This bubble emulsion can only be stable in a microgravity environment where buoyancy forces are absent. We investigate the formation and dispersion of bubbles in a turbulent field over time. The experimental setup consists of a truncated cube-shaped tank containing a liquid and gas, initially separated. The agitation is produced by eight impellers, located on each truncated corner, and rotated by DC motors. The use of such an impeller arrangement produces isotropic homogeneous turbulence throughout the liquid, causing the bubbles to fragment and disperse. The fragmentation continues until a balance between surface tension and turbulent forces is reached.  Preliminary experiments were conducted under Earth's gravity to quantify the flow, using PIV, and to understand the dispersion of bubbles. We find that a good control of bubble size and dispersion is possible with the setup. These preliminary tests will be contrasted with those obtained in future microgravity experiments.