Active control of foams by physically based destruction mechanisms

Abstract

Foams may be undesired in technical processes and need, thus, to be actively controlled. In food science engineering it is often not possible to apply chemical measures due to the required purity of the processed products. To overcome this challenge it is necessary to apply physically based foam destruction mechanisms. The present contribution deals with the prediction of foamability and the application of acoustical foam destruction from an experimental point of view. The results show that it is possible to classify the foamability of different fluids by a correlation of dimensionless numbers containing purely physico-chemical properties (i.e. density, surface tension, viscosity). The foam stability is a consequence of the net balance of the foam generation and the foam decay. The respective time scales may be influenced by the process conditions, the fluid properties, and the selected physically based destruction mechanism. In the case of resonance excitation of foam bubbles by acoustic waves of defined frequencies selective foam destruction can be achieved. The bubbles in the foam start to oscillate and absorb energy depending on the bubble size, fluid properties, and ultrasound frequency. The resulting bubble breakdown leads to a shortening of the time scales of the foam decay.

Resonant Ultrasonic Defoaming in Aqueous Evaporation/Boiling Processes at Different Size Scales

“…Liquid from the upper layers must replace the drained liquid in the lower part of the foam. The characteristics of the foam decay in the beaker (see Supporting Information) and high-speed pictures of resonant lamella [3] seem to agree with this hypothesis.…”

“…Unwanted foam formation can affect various industrial processes and equipment negatively. Often a reduction in throughput, malfunctions in the production process, and even a total shutdown of the production are the results of foaming [1], which lowers the efficiency of the production process and increases operational costs [2][3][4][5][6].…”

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].…”

“…In already existed foams, a subsequent sonication accelerates the decay (see Figure 8). Together, this results in a faster decay of the foam volume than in other experiments with subsequent sonication of already existing foams [32]. Because of the high reflections at and inside the foam, the sonication into the bottom of the foam may only penetrate into the first layers, where the liquid is removed more quickly.…”

Helical Packing Columns for Preventing Foam Formation: Experimental and Numerical Investigations

“…Regarding the prevention, inhibition, and destruction of undesirable foams in packing columns, some research groups have conducted investigations in recent years 28–36. However, very little attention has been paid to the geometrical design of the structured packing as potential cause of foam generation 37, 38.…”