Fall and break-up of viscous miscible drops in a Hele-Shaw cell

Abstract

We study the fall of pancake-shaped drops in a Hele-Shaw cell filled with a more viscous ambient fluid in the case where the drop and ambient fluid are miscible. We propose a theoretical expression for the falling velocity of the drops which takes into account elongated drops with width smaller than the gap of the cell. We also provide experimental evidence for the break-up of miscible drops, which can be caused by internal fluid motion within the drop, or by an instability in the shape of the drop.