Submerged gas injection into liquids in cylindrical vessels: A study of the influence of liquid viscosity

The influence of liquid viscosity on the structure and characteristics of a submerged air jet injected vertically into a 254 mm diameter vessel has been studied for gas flow rates between 570 to 5,010 cm{dollar}sp3{dollar}/s and nozzle diameters of 2 and 4.5 mm. The liquid height in the vessel ranged from 1 to 3 diameters and the liquid viscosity was varied between 1 and 120 mPa.s. A three-tip electrical resistance probe was used to measure the local properties of the jets. A slope-threshold technique was used for gas-liquid phase discrimination of the probe voltage signals and a unique method for the determination of bubble interface velocity is presented. The experimentally measured area-averaged gas flow rates compared very well with the actual inlet flow rates. High-speed video photography was also used.; Four flow regions of the two-phase jet were distinguished as the momentum, detachment, plume and spout zones. Correlations are presented to describe these axial transition distances between the momentum-detachment and detachment-plume zones. An increase in the liquid viscosity was found to reduce the bubble velocity, and to reduce bubble surface instabilities and bubble break-up resulting in the generation of fewer interfaces. A stable mean bubble size that increased with the liquid viscosity was found to occur throughout the plume zone of the jet. The radial profiles of void fraction and bubble interface velocity are represented by a modified Gaussian function with a parameter dependent on the liquid viscosity. Correlations are presented for centreline void fraction {dollar}varepsilonsb{lcub}rm max{rcub}{dollar} and the {dollar}rsb{lcub}epsilonsb{lcub}rm max{rcub}/2{rcub}{dollar} incorporating the influence of liquid viscosity.