Bubble size distribution and turbulent two-phase flow in aerated stirred vessels

This work concerns an experimental and computational investigation of the turbulent two-phase flow and bubble size distribution in a gas-liquid stirred vessel of standard geometry. The experiments were carried out using a two-phase Particle Image Velocimetry technique and a digital image processing method based on a threshold criterion. With the former technique, the liquid and the gas phase ensemble-averaged mean and r.m.s. velocities were measured simultaneously, while with the latter the dimensions of the bubbles dispersed inside the liquid were evaluated. On the modelling side, a Computational Fluid Dynamic approach was adopted, that was based on the solution of Reynolds Average Navier-Stokes equations in an Eulerian framework for both phases. As for the bubble dimensions modelling, the mono-disperse assumption as well as the Multiple Size Group Model, including a population balance with break-up and coalescence models, were considered. The bubble size distribution and the axial and radial velocity of the gas and the liquid phase measured on a vertical plane mid-way between two baffles are presented and discussed. The outcomes of the computational work are evaluated on the basis of the experimental findings