MEASUREMENT OF LOCAL BUBBLE DIAMETERS AND ANALYSIS OF GAS DISPERSION IN AN AERATED VESSEL WITH DISK-TURBINE IMPELLER

An improved photoelectric capillary method was used to determine the c haracteristics of the gas dispersion in a stirred tank by disk-turbine impellers with various numbers of blades to examine the effect of the number of blades. The results show that the bubble size distribution in the system has three different characteristics according to the pat terns of liquid flow. In the impeller discharge region the sizes of bu bbles are dominated by the strength of the trailing vortex and the cav ity structure behind the blades. No difference is observed among impel lers with various numbers of blades when the region-averaged Sauter me an diameter D(32)BAR is correlated with Pg/V and Q(g). In the upper ci rculation region, bubble size is affected by both the cavity structure and the circulating flow. In the lower circulation region, bubble siz e is controlled mainly by the pumping capacity of the impeller. These transitional rotation speeds, N-c and N-R, were obtained from the rela tionship between D(32)BAR and gas flow number FI, which can serve not only as the turning points of the status of gas dispersion, but also c an be used to explain the characteristics of the bubble size distribut ions for each region.