Start-up transients in a pneumatic foam

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. (C) 2010 Curtin University of Technology and John Wiley & Sons, Ltd.