An Experimental Investigation of the Break-up of a Liquid Drop Falling in a Miscible Fluid

A liquid drop falling in a lighter miscible fluid either undergoes a cascade of fragmentations, each appearing as a dynamic instability, or it mixes by diffusion, depending on the value of a fragmentation number F. F is the ratio of the diffusion time to the time required for the fluid to convectively mix. We assign an accurate experimental value to the critical fragmentation number F c , which appears to be universal. When the fragmentation occurs, the interfacial area increases via successive splittings which display striking symmetries. We present experimental evidence and a qualitative explanation of such a phenomenon.