Gas holdup and interfacial area distributions in a mechanically agitated gas-liquid contactor

Spatial gas holdup distributions in an air-water dispersion have been measured on a quasi-point grid in the median plane between two adjacent baffles of a 1.0m diameter stirred vessel contactor, using an automated conductivity probe. A detailed picture of the dispersion is generated under different agitation and gassed conditions. The spatial distribution of the bubble population inside the vessel as revealed by the measured local bubble passage frequency and the local gas holdup, is highly non-uniform with most of the gas residing in the bulk region of the tank. The effect of the agitation speed is to increase the holdup at most positions and enhance uniformity in gas distribution. An increase in gas flow rate causes an almost uniform rise in the gas holdup in the bulk, and reduces gas circulation in the lower region of the vessel. Combining the gas holdup distributions with bubble size distributions from an earlier study by the authors, has yielded the corresponding interfacial area distributions. Large interfacial areas occur near the agitator because of high holdup and small bubble size. The impeller discharge stream contains a large fraction of the total interfacial area in the tank and, therefore, makes an important contribution to mass transfer. Correlations for predicting interfacial area in both air-water and air-NaCl systems are proposed.