Simulation of buoyancy driven bubbly flow: Established simplifications and open questions

An assessment is given of the present state of modeling and simulation of buoyancy driven gas-liquid bubble flow based on the two-fluid approach. Main points of discussion comprise the admissible model simplifications in order to obtain a more easily solvable model together with the question of which physical effects are of prime importance and which reliable correlations can be recommended or are still missing. It is shown that, for most practical cases, the two-fluid model can be simplified to a formulation which allows for the application of efficient solution strategies for single-phase flow. From the different interaction forces between gas and liquid, pressure and drag force are most important, whereas no sound experimental basis is available for (lateral) lift forces. So far, lift forces have primarily been used empirically to adjust the gas distribution to the experimental observation. The main open question concerns the proper modeling of turbulence in gas-liquid bubble flow since it affects both the mixture viscosity and the bubble dispersion. (C) 2004 American Institute of Chemical Engineers