### ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

## 4pPA11. Capillary bridge stability in an acoustic standing wave:
Linearized analysis of passive stabilization with radiation pressure.

**Philip L. Marston
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*Dept. of Phys., Washington State Univ., Pullman, WA 99164-2814
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A liquid bridge between two solid surfaces, known as a capillary bridge,
has applications in low gravity such as the solidification of floating zones.
Long bridges are naturally unstable to a symmetric mode where a region adjacent
to one end bulges while the opposite end thins. For a cylindrical bridge of
radius R and length L, the slenderness S=L/2R has a natural (Rayleigh) limit of
(pi) beyond which the bridge breaks. It is proposed here to stabilize dense
bridges at a velocity antinode of a standing acoustic wave perpendicular to the
bridge axis. Let

denote the angular average of the radiation
pressure over the surface of a cylindrical bridge. It is necessary to select
the acoustic frequency such that

increases with R so that a bulge is
automatically squeezed by the increased radiation pressure. Linearized analysis
of the stability indicates S may be extended beyond (pi): S[sub max] depends on
q=(R[sup 2]/(gamma))d

/dR, where (gamma) is the surface tension and
S[sub max] diverges as q approaches unity. The analysis supports the
possibility of passive acoustic stabilization of capillary breakup in low
gravity. The one-dimensional inviscid slice approximation is used in the
analysis of axisymmetric deformations. [Work supported by NASA.]