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Physical Society Colloquium
Dr. Stephan Koehler
Div. of Engineering and Applied Sciences Foams are mostly composed of gas bubbles, with a small amount of liquid separating the bubbles. Foam Drainage is the flow of liquid between bubbles due to gravity and capillarity. The flow is resisted by viscous effects, which in turn are determined by the geometry of the foam's liquid network and the boundary condition at the liquid/gas interface. Although a foam is semi-random in nature, and the flow on the scale of a single bubble is very complex, the drainage on a macroscopic level proceeds in a surprisingly orderly fashion. We present a new macroscopic model for foam drainage based upon a slipping (i.e. non-rigid) liquid/gas interface. A new optical method for determining the macroscopic liquid content of aqueous foams is used to determine the dynamics of foam drainage. One-dimensional and two-dimensional (Hele-Shaw) experiments show good agreement with the model. The model predicts exact and asymptotic self-similar solutions which are confirmed by experiment.
Wednesday, January 26th 2000, 15:30 |