RESUMO
The need to destabilize foams and control their formation arises in many industrial applications. Vibrations are known to affect the structure and rheology of various soft solids but have not been exploited in destroying persistent foams. Being noninvasive, they offer elegant potential alternatives to chemical and mechanical foam breaking techniques. This paper reports an experimental study on the effectiveness of mechanical and ultrasonic vibrations in foam destruction. Mechanical vibration is effective at breaking static foams generated from non-Newtonian shear-thinning liquids, by enhancing liquid drainage and film breakage. Drainage is increased due to enhanced shear thinning that leads to a reduction in yield stress and shear viscosity of the nonNewtonian liquid. High intensity ultrasonic vibration is efficient at destabilizing static foams but is also effective at controlling dynamic foam heads and would be suitable for use in processes that require continuous defoaming. Destabilization of the foam films is attributed to possible squeezing mode surface wave phenomena. Copyright 1999 Academic Press.