Start‐up transients in a pneumatic foam

Abstract

In the current work, transient features of initiation in a gas-liquid pneumatic foam are investigated by measuring the evolution of volumetric liquid fraction as a function of height within the column. The addition of wash water to a flotation froth is only effective when the foam liquid fraction has reached a steady state. This makes start-up transients in pneumatic foam worthy of study. For the conditions adopted in the experiments, an approximately steady state was achieved after typically 500s, but there was significant fluctuation in liquid fraction after this time. In general, three possible regimes in the start-up transient (induction, growth and evolution) have been identified and a tentative mathematical model has been described for the last two. However, because it has been demonstrated that the method of obtaining bubble size distributions by analysing images taken through the column wall is deficient, no comparison of these models with the data has been attempted. 

Measurement of bubble size distribution in a gas–liquid foam using pulsed-field gradient nuclear magnetic resonance

“…In fact, a study of start-up transients in a column carrying pneumatic foam has shown that the photographic method of obtaining bubble size must be deficient [13] because some measurements indicated that bubbles were becoming smaller with height, and this observation is unphysical. Optical tomographical methods [14,15] have been previously employed to resolve the three-dimensional structure (i.e.…”