The relation between the dynamic surface tension and the foaming behaviour in a sparger setup

In this work, we relate the foam formation at a sparger with the dynamics of the surface tension, represented by the surface tension reduction rate (R-1/2). In our experimental setup, foam is formed at the bottom of a column, rises through the column and at the top of the column the total foam weight and the foam density are determined. The total foam weight is limited by the depletion of the surfactant, and increases with increasing surfactant concentration, and, therefore, with increasing R-1/2: at sufficiently large R-1/2, all the surfactants unload all the liquid from the column. The liquid content of the foam is determined by the foam drainage, which is strongly dependent on the bubble size, and, therefore, on the bubble generation at the sparger. A larger R-1/2 leads to smaller bubbles being formed and therefore to a larger liquid content of the foam. Even though the two foaming processes are quite different, we found that the correlation between the foam liquid content and R-1/2 in our sparger setup is similar to the correlation between the volume of foam and R-1/2 in a Ross-Miles test. (C) 2015 Elsevier B.V. All rights reserved.