Three‐dimensional simulation of bubble column flows with bubble coalescence and breakup

Abstract Three‐dimensional (3‐D) Euler/Euler simulations of two‐phase (gas/liquid) transient flow were performed using a multiphase flow algorithm based on the finite‐volume method. These numerical simulations cover laboratory‐scale bubble columns of different diameters, operated over a range of superficial gas velocities in the churn‐turbulent regime (8 to 30 cm/s) and at different operating pressures (up to 1 MPa). The bubble population balance equation (BPBE) is implemented in the two‐fluid model (TFM) and algebraic slip mixture model (ASMM). Simulated time‐averaged axial liquid velocity, turbulence stress, and gas holdup are compared with experimental data of Chen et al., Ong, and Shaikh et al. Moreover, to ensure the experimentally observed lack of dependency of holdup radial profiles on column height in the fully developed region, coalescence rates in the computations had to be enhanced consistently compared to model‐predicted values. Quantitative agreement is then obtained between the experimental data and simulations for the time‐averaged gas holdup and axial liquid velocity profiles. However, the simulations significantly underestimate the turbulent stress because the velocity field cannot be fully resolved. Simulated bubble size distributions indicate that the volume fraction of small bubbles is uniform in a cross section, whereas that of the large bubbles peaks in the center of the column. The simulation correctly captures the high‐pressure effect, which at fixed gas superficial velocity pushes the bubble column flow toward bubbly flow. The simulation also predicts that, although the small bubble volume fraction may not change with superficial gas velocity in the churn‐turbulent flow regime, the bubble size distribution still remains single modal but is wider and contains larger bubble sizes when superficial gas velocity is increased. © 2005 American Institute of Chemical Engineers AIChE J, 51: 696–712, 2005