Effect of surfactant on homogeneous regime stability in bubble column

Experiments were carried out to investigate the effect a surface active agent on homogeneous-heterogeneous flow regime transition in a laboratory scale bubble column. Air and water with various amount of CaCl2 were the phases. The (voidage e) - (gas flow rate q) dependence was measured. The critical point where the homogeneous regime loses stability and the transition begins was evaluated by several methods. These methods are based on the slip speed concept and the drift flux model. The critical values of voidage and gas flow rate were taken as the quantitative measures of the homogeneous regime stability. They were plotted against the surfactant concentration. It was found that the surfactant has a dual effect on both the voidage and the regime transition: low concentration stabilizes and larger concentration destabilizes the homogeneous bubble bed. At present, we do not have an explanation to these observations. Possible physical mechanisms of the surfactant effect are expected to be revealed by further experiments, which are currently under way. (c) 2007 Elsevier Ltd. All rights reserved.