CFD-Simulation of Bubble Columns

CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. A large body of work using different closure relations of varying degree of sophistication exists, but no complete, reliable, and robust formulation has been achieved so far.
As a step towards this goal, an attempt is made here to collect the best available description for all aspects known to be relevant for adiabatic bubbly flows where only momentum is exchanged between liquid and gas phases. Apart from interest in its own right, results obtained for this restricted problem also provide a good starting point for the investigation of more complex situations including heat and mass transport and possibly phase change or chemical reactions.
Aspects requiring closure for the case under consideration are: (i) the exchange of momentum between liquid and gas phases, (ii) the effects of the dispersed bubbles on the turbulence of the liquid carrier phase, and (iii) processes of bubble coalescence and breakup that determine the distribution of bubble sizes. All of these aspects are coupled and therefore in principle have to be considered as a whole.
To validate the overall model, simulation results are compared against experimental data taken from the literature for bubble columns in various settings. In the present study the focus is on the homogeneous regime where the assumption of a monodisperse bubble size distribution is reasonable and coalescence and breakup need not be considered. From the observed level of agreement between simulation and experiment, issues requiring further investigation will be identified. Necessary extensions to the heterogeneous regime will be discussed but remain to be worked out in the future.