Effects of liquid viscosity and bubble size distribution on bubble plume hydrodynamics

• Sensitivity of local bubble plume hydrodynamics to viscosity and sparger design is examined • Optical Probe and shadowgraph technique revealed strong influence of sparger design on the gas phase • Particle-image velocimetry revealed only a weak influence of sparger design on the liquid phase • Huge sensitivity to viscosity was observed in both phases, regardless of the sparger • Customized phase averaging combined with proper orthogonal decomposition gave access to further insides The present paper provides a complete databank of bubble plume hydrodynamics in various media characterized by different viscosities in the range 1 – 100 mPa . s . Thus, the influence of the viscosity on bubble plume oscillations and on both liquid and gas velocity fields is studied. The role of the bubble size distribution at different viscosities was also analysed by using two different spargers: a membrane to create ellipsoidal millimetrice bubbles and a slugflow tube to create spherical cap bubbles. Mean velocity profiles, averaged over a large number of plume oscillation periods and corresponding root mean square profiles are discussed, in both phases. Furthermore, void fraction profiles, plume oscillation periods, and bubble size distributions are given for all experimental conditions. Finally, probability density functions and phase averaged profiles in the liquid phase provide additional information. The dependence of bubble plume hydrodynamics on liquid viscosity is huge. At large viscosity, the oscillating plume is damped, regardless of the sparger. Concerning the membrane sparger the viscosity increase modifies the plume oscillation period and its lateral plume expansion, whereas, in the case of the slugflow sparger, only the plume expansion is impacted. Liquid phase hyrdodynamics are weakly affected by the choice of sparger, especially at high viscosities.