Suppressing the Plateau–Rayleigh instability between fibers

A falling liquid thread readily destabilizes due to the capillary-driven Plateau–Rayleigh instability. If the thread envelops a vertical fiber the well-studied “bead-on-fiber” pattern emerges. In many cases, these patterns can be leveraged for novel heat and mass transfer applications; however, other applications, such as fiber coating, require a uniform coating. To this end, we explore how thin fibers stabilize falling threads by suppressing the Plateau–Rayleigh instability. We perform experiments on liquid flow down two vertical fibers over an extensive range of flowrate Q, inter-fiber spacing w, viscosity µ, and fiber radius R. When the thread envelops the fibers, they elongate its profile. The elongated thread resists capillary instability for low Q, and the flattened thread flows uniformly down the fibers. As Q increases and the cylindrical profile is recovered, the Plateau–Rayleigh instability resurfaces. We characterize the thread profile using its minimum and maximum width as Q is increased. Furthermore, we report the variable ranges associated with Plateau–Rayleigh suppression.