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Foams in highly viscous liquids

by Franck Pigeonneau - published on

Foams are dispersions of gas bubbles in a liquid matrix having several very interesting and unusual properties which make them possible candidates for use in many industrial applications. In most of cases, the stability of foam is a required property. Nevertheless, in glass melting process in particular, foam can be a nuisance reducing the energetic efficiency.

Foam layer in a furnace

Molten glass is a unusual liquid for which the foam stability can not explain by adsorption at interfaces like for aqueous solutions. Since few years, we have undertaken the foam stability at the mesoscale with experiments achieved on bubbles close to a free surface and on vertical films (Ph. D. of H. Kocarkova).

Bubble at a free surface of a molten glassIn the experiment on bubble where the film thickness is measured by interferometry, the film drainage behaves exponentially with time. This result means that the flow in the liquid film is extensional. Moreover, the thinning rate (opposite of the logarithmic derivative of the film thickness) rises when the bubble size increases. Reduced film thickness vs. normalized time for four liquids The Bond number, ratio of buoyancy to surface tension forces, is the relevant parameter controlling the thinning rate. Moreover, the experiment has been duplicated at room temperure using UCON and castor oils for which the bubble size effect has been reproduced.

An boundary-integral method on the Stokes equations has been developed to study the bubble drainage. Both the exponential behavior and the influence of the Bond number are established (see Pigeonneau and Sellier, 2011).

The stability on vertical film has been study experimentally. We show that the lifetime of the film increase with temperature due to sodium evaporation. A lubrication model has been developed taking into account the gradient of surface tension (see Pigeonneau et al., 2012).