Gas-filled cavity structures and local void fraction distribution in vessel with dual-impellers

An experiment was carried out in a pilot-size aerated mixing vessel using d ual Rushton impellers. The two-phase mixture was composed of air and deioni zed water. Different gas-filled cavity structures were recognized close to the outer edge of the impeller blade by frequency transformation of the tim e-domain structural function. The majority of hydrodynamic regimes for the upper impeller were of VC structure, while the lower impeller operated over the VC, 1L, 2L, S33, L33, and RC structures respectively. Local void fract ion alpha was also measured by a resistivity probe at 250 modes in the vert ical half-section plane of the vessel. Spatial distributions of alpha are p resented for the aforementioned hydrodynamics regimes. A transition from qu ite homogenous local void fraction distribution in a VC structure to a rath er nonhomogeneous void distribution with a high concentration of bubbles ar ound the shaft was detected. (C) 2000 Elsevier Science Ltd. All rights rese rved.