Stabilization of a capillary bridge far beyond the Rayleigh–Plateau limit using active feedback and acoustic radiation pressure

Abstract

A liquid bridge between two solid surfaces is known as a capillary bridge. Long bridges naturally become unstable to a symmetric mode by bulging near one end while the opposite end thins. Suppression of this mode is important for managing fluids in low gravity. For a cylindrical bridge in low gravity of radius R and length L, the slenderness S=L/2R has a natural (Rayleigh–Plateau) limit of π beyond which the bridge breaks. Using acoustic radiation pressure to control the bridge’s shape, and an optical sensor to detect the bridge’s shape, an active feedback system in simulated low gravity was constructed. This system stabilized bridges significantly beyond the Rayleigh–Plateau limit, with S as large as 4.3 [Marr-Lyon et al., J. Fluid Mech., accepted for publication]. To be useful in low gravity, this technique will have to be modified to work on liquid bridges in air. In preparation for an experiment to be performed on NASA’s low gravity KC-135 aircraft, acoustic resonators in air that have the required property that the sound amplitude can be spatially redistributed rapidly are being investigated and tested in normal gravity using soap-film bridges filled with sulfur hexafluoride. [Work supported by NASA.]