Influence of the Operating Conditions on the Bubble Characteristics in an Aerated Stirred Vessel

Abstract

Aerated stirred vessels are widely used in the chemical and process industry. In these vessels the interfacial area between the two phases and the gas hold-up characterize the efficiency of the gas-liquid contact. Where as the interfacial area determines the heat and mass transfer rate, the gas hold-up determines the residence time. For these reasons, improving the knowledge concerning the bubble characteristics, namely their sizes, spatial coordinates and number is of primary importance. These parameters depend on the operating conditions, such as the volumetric flow rate of the gas, the type and speed of the impeller, the injector type and its geometry and the physical properties of the liquid phase. From the view point of the technical application the development of empirical correlationsis of major interest (Bouaifiatal.2001;Pagliantiatal.2000;Rewatkaratal.1993;Yawalkarat al.2002;Zhengmingatal.1996).Mostoften,theseequationsshowgoodagreement when they are compared with the database which they are basedon, but they often fail to predict the gas hold-up for the other operating conditions(Yawalkar atal.2002).In particular, difficulties have been reported for extremely low gas hold-up and low gas flow rate, which are of major interest for the validation of numerical two-phase codes.