Hydrodynamics and scale-up of bubble columns in the heterogeneous regime: Comparison of bubble size, gas holdup and liquid velocity measured in 4 bubble columns from 0.15 m to 3 m in diameter

Abstract

The development of CFD models coupled with Population Balance is a very promising topic concerning multiphase reactors. In the case of bubbly flows and bubble columns, a serious lack of local hydrodynamic characterizations still harms development and validation of relevant models. To fill partially this gap, a new bubble size measurement technique, previously introduced by Maximiano Raimundo et al. (2016), has been applied on a very wide range of bubble column diameters (from 0.15 m to 3 m) and superficial gas velocities (from 0.06 m/s to 0.35 m/s). Size measurements have been coupled with others concerning gas holdup and axial liquid velocity, in order to provide an experimental database allowing to clarify the scale-up rules and to assist future modelling works. Average bubble sizes have been measured as globally similar at every scale. Measured holdup and average liquid velocity confirm already reported behaviours at lower column diameters. Liquid velocity fluctuations also follow self-similar radial profiles and are proportional to the average liquid velocity at the centre of the column leading to a strong turbulence intensity. The fact that the quantity (gD)1/2 appears as a natural velocity scale and the presence of strong gas-holdup gradients underline the similarity between bubble columns operated heterogeneous regime and free thermal convection in pipes.