Mechanisms of ultrasound foam interactions

Abstract

An experimental investigation into the effects of two frequencies of low-power ultrasound on detergent (Teepol) stabilised air-water foams is presented. Foam was subjected to ultrasound at 28 and 40 kHz with a powerto-foam volume ratio of approximately 3 W l −1 with particular consideration being given to the acoustic impedance discontinuity between air and water. The foam height, liquid drainage and collapse behaviour were compared to experiments conducted without ultrasound. In the case of 40 kHz ultrasound, an increased liquid drainage rate was observed and a pronounced increase and subsequent peak in mean liquid hold-up, which occurred at 4 min, was observed. These results appear to be independent of the initial liquid hold-up of the foam. Liquid drainage and mean liquid hold-up results were related to foam collapse mechanisms of homogeneous rupture (HR) and rupture front breakage (FR), concluding that rupture front breakage dominates the collapse of foam under the influence of 40 kHz ultrasound. 

Ultrasonic Effects on Foam Formation of Fruit Juices during Bottling

“…The applied frequencies between 42 and 168 kHz might specifically induce resonant effects in the foam leading to higher drainage without atomization. These are well above the frequencies used by Winterburn [25], but within the range of McHardy [32].…”

Sterilization of Biofilm in Foam Using a Single Cavitation Bubble

“…The main potential is in the use in wastewater treatment plants. Previously, sterilization of bacteria research has focused of using cavitation for defoaming and sterilization of the environment [13].…”

Application of Ultrasound

“…Winterburn and Martin (2009) investigated the effects of two frequencies of low-power ultrasound on foam formed by the detergent Teepol. This is assumed to be the result of a combination of factors: partial vacuum on the foam bubble surface produced by high acoustic pressure, resulting in a partial negative pressure above the foam encouraging gas release, possible degassing of the liquid itself as a result of bubble coalescence, atomization from the liquid film surface, and cavitation and acoustic streaming within the bulk system.…”