Asymmetric Instability In Thin-Film Flow Down A Fiber

Thin-film flow down a vertical fiber gives rise to a number of instabilities that define the bead-on-fiber morphology including Plateau-Rayleigh breakup, isolated bead formation, and convective instabilities. Experiments are performed that reveal an asymmetric instability which depends upon the liquid surface tension and fiber diameter and exhibits all the bead-on-fiber morphologies. The bead dynamics are described by the bead spacing and bead velocity, with the asymmetric morphology displaying more regular dynamics than the symmetric morphology. For the asymmetric morphology, the transition from the Plateau-Rayleigh to convective regime agrees well with predictions for a free viscous jet, indicating a minimal effect between the thin film and fiber. In addition, the dimensionless bead velocity is shown to scale with the capillary number for all experimental data. These observations for the asymmetric bead dynamics can be used as a design tool for heat and mass transfer applications.