The effect of interfacial deformation on droplet interactions in viscous flows.

摘要

Understanding the behaviour of dispersions of one liquid immersed in a second, immiscible liquid is important in both traditional chemical engineering applications, such as separations and materials processing, as well as more fundamental problems in the general sciences. This work examines the interactions of two drops in various flows under conditions that viscous forces dominate inertia, focusing on the role of interfacial deformation. The pairwise information is then used in the study of dilute dispersions, where the probability of three-body interactions is low. Two regimes of deformation are considered: small deformation, where the drops remain spherical except for a small flattening or dimpling between the drops, and moderate deformation, where the interfaces of both drops distort globally.; The effect of deformation is significant, because small deformation inhibits drop coalescence, while global deformation promotes alignment of the drops, which may lead to coalescence, break-up of the smaller drop, or even more complicated coalescence-breakup phenomena. In particular, the drop-to-medium viscosity ratio is shown to be a crucial parameter in the outcome of moderately deformable droplet interactions. The approach is primarily numerical, with a simplified boundary-integral method used in the small deformation case and a full boundary-integral algorithm implemented for global deformation. To complement the computational results, experiments were performed with glycerol/water drops in castor oil.