FLOW REGIMES OF STABLE FOAMS

In order of increasing foam velocity the flow regimes observed for stable foams moving in vertical constant cross section glass columns are plug flow, turbulent flow, and bubble column. The prevailing flow regime depends to a large extent on average bubble diameter, D32, and shape, bubble size distribution, foam velocity, G, and volume fraction of liquid in the foam, f. All the experimental data correlate well by fD = CGn, where n equals ∼1.0 for plug flow and ∼2.5 for turbulent flow. For normal bubble size distribution (obtained with spinnerettes) D32 can be obtained from a correlation of D32 vs. Re0, where D0 and Re0 are spinnerette orifice diameter and Reynolds number, respectively. The transition from plug to turbulent flow can be determined visually and is characterized by breaks in the AP/AZ vs. G, f vs. G, and fD vs. G curves. At the transition f is much lower than 26% (the minimum void fraction of equal spheres) and a substantial fraction of bubbles are polyhedral. © 1969, American Chemical Society. All rights reserved.