Dynamics of transitions between capillary stable states under weightlessness

The study of two phase systems with one of the phases obstructing the other is of importance in a lot of fields. Liquid droplets in airways and air bubbles in the blood stream both fall under this category of problems. Helium bubbles in hydrazine fuel lines of satellites also have been found to cause frequent thruster shutdown and also seriously affect spacecraft control. Studies have been carried out until now to look at static equilibrium topologies and stability of such two phase systems in straight, bent and laterally compressed capillaries. In this investigation we look at the dynamics of the transitions between the stable topologies identified for a straight cylindrical capillary. The break up of the interface could adversely affect system performance. OpenFOAM is used to compute transitions from a stable droplet to a plug or the reverse by suitably adding or removing the obstructing phase through inlet patches on the wall of the cylinder. The main parameters presented are the non-dimensional energy, non-dimensional transition times, non-dimensional transition volumes and the general dynamics of the transitions itself. Before computing transitions the static equilibrium topologies computed by OpenFOAM are compared with those predicted by Surface Evolver and are found to be within acceptable deviations. The grid dependence of these transitions has also been studied. Transitions are computed for contact angles in the range of 10° to 170°. Different modes of transitions are observed depending on the contact angle of the case for both the types of transitions. The transition volumes are compared to the volume of existence limits for the corresponding initial topology at a particular contact angle for both the transitions