Direct measurement of mass transfer around a single bubble by micro-PLIFI

Chemical Engineering Science, Volume 66, Issue 14, 15 July 2011, Pages 3328-3338, 10th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering, doi:10.1016/j.ces.2011.01.049

Abstract: In this paper an original direct and non-intrusive technique using Planar Laser Induced Florescence with Inhibition (PLIFI) is proposed to quantify the local mass transfer around a single bubble rising in a quiescent liquid. The new set-up tracks the mass transferred in the bubble wake for a plane perpendicular to the bubble trajectory instead of a parallel plane as in previous works avoiding optical reflexion problems. A spherical bubble is formed in a glass column containing fluorescent dye. A camera with microscopic lens is placed underneath the column to record cross sections of the transferred oxygen. A high-speed camera is located far from the column to simultaneously record the bubble position, size, shape and velocity. The dissolved gas inhibits the fluorescence and then oxygen concentration fields can be measured. From this a calculation method is developed to determine mass transfer on the micro-scale. Experimental results are compared to the Sherwood numbers calculated from the Frössling and Higbie models used for fully contaminated and clean spherical bubble respectively. Results show all experimental Sherwood numbers occur between the two models approving the measures. The new technique is then developed for bubble diameters ranging from 0.7 to 2 mm in six hydrodynamics conditions (1 < Re < 102, 102 < Sc < 106).