Caroline Gentric

Numerical description of flow regime transitions in bubble column reactors by a multiple gas phase model

The study of the hydrodynamics of bubble column reactors reveals that three main flow regimes can be distinguished. The present study is an original application of standard numerical multiphase models aiming at a better prediction of the transitions and a better description of these regimes. This approach consists of a two-step calculation with, in a first time, the determination of bubble size distributions using coalescence and break-up laws, and in a second time, the implementation of this distribution in a multiple gas phase Euler–Euler model. Calculations are compared with experimental data: liquid velocities and global gas hold-ups. They were obtained in a cylindrical bubble column in which local or uniform aerations were performed. The comparison shows that our approach allows a good prediction of both flow regime transitions and flow characteristics such as hydrodynamics or turbulence. Furthermore, two bubble-induced turbulence models consisting, respectively, of an added viscosity and of two turbulence source terms added in the k–e transport equations have been compared.

Description of flow regime transitions in bubble columns via laser Doppler anemometry signals processing

This work aims at studying the non-linear dynamics and the flow regime transitions in bubble column reactors. For this purpose, various signal processing techniques e.g. frequency analysis, fractal analysis and deterministic chaos analysis have been applied to laser Doppler velocimetry signals. The system considered is a two-dimensional reactor allowing LDV measurements at higher void fractions than in three-dimensional systems. Each signal processing technique presents a specific capacity to describe a regime transition or a feature of the flow structure. Use of these various techniques have highlighted the occurrence of two states in the transition regime and yielded detailed information on the physical mechanisms responsible for these transitions.