J. zyxwvutsrq Fluid Mech. zyxwvutsrq (1993), zyxwvuts 001. zyxwvutsrq 255, zyxwvutsrq pp. 41 1435 Copyright zyxwvutsrq 0 1993 Cambridge University Press zyxwvut 41 1 Nonlinear dynamics of capillary bridges zy : experiments By D. J. MOLLOT', J. TSAMOPOULOS', T.-Y. CHEN' AND N. ASHGRIZ' 'Department of Mechanical Engineering, State University of New York at Buffalo, Buffalo, NY 14260, USA 'Department of Chemical Engineering, State University of New York at Buffalo, Buffalo, NY 14260, USA (Received 26 April 1992 and in revised form 23 March 1993) An experimental investigation of forced and free oscillations of liquid bridges positioned between two rods of equal diameter is presented. Both the resonance frequencies and damping rates for different aspect ratios of the bridge are reported. The damping rate data of the liquid bridges are obtained by high-speed videography and are the first ever reported. Resonance frequencies for the three modified Reynolds numbers of 14, 295 and 1654, and damping rates for the two modified Reynolds numbers of 14 and 295 are reported. These values of modified Reynolds numbers are generated by using ethylene glycol, distilled water, and mercury in small bridges. Gravitational effects are kept small by reducing the size of the capillary bridge. The internal flow fields of several bridges for different modified Reynolds numbers are described based on high-speed visualization. Experimental results show good agreement with results of linear and nonlinear theory. 1. Introduction The stability and dynamics of liquid bridges have been of great interest in many natural and industrial processes. Fluid bridges are observed in flow through porous media (Melrose 1966; Zasadzinski et al. 1987) and particulates agglomeration (Chen, Tsamopoulos & Good 1992). More recently liquid bridges have been studied because they arise in applications related to materials processing on Earth or in a microgravity environment (Preiser, Schwabe & Scharmann 1983 ; Brown 1988). Single semi- conductor crystals of high purity are produced by melting a polycrystalline feed rod and then allowing it to solidfy into a pure crystal. The quality of the final crystal is intimately dependent on the temperature and concentration uniformity at the solid-liquid interface. Axial oscillation of the capillary bridge may be used to increase the degree of mixing inside it. One of the objectives of this work is to provide further understanding of the flow field inside an axially oscillating liquid bridge. To this end, visualization studies at the particle level are compared with theoretical predictions obtained by tracking Lagrangian particles inside the bridge. Another application of axially oscillating liquid bridges is in simultaneous measurement of viscosity and surface tension of molten metals and ceramic materials at high temperatures. At present, information on the properties of these materials is limited. At high temperatures most materials become contaminated through contact with the measuring apparatus. Therefore, conventional techniques cannot be used to measure their viscosity and surface tension. The levitated drop technique (Trinh, 14-2