Influence of the lift force closures on the numerical simulation of bubble plumes in a rectangular bubble column

Numerical Eulerian-Eulerian simulations of the unsteady gas-liquid flow in a centrally aerated two-dimensional bubble column were carried out in order to understand the effect of different formulations of the lift force coefficient (C-L) on the computational results. Three different values of the superficial gas velocity (U-G = 2.4, 12,0 and 21.3 mms(-1)) that ensure the existence of different flow regimes were experimentally and computationally studied. The validation of the simulated results was based on visual observations and measurements of the global gas hold-up (epsilon(G)) and the plume oscillation period (POP). The results presented reveal that, at U-G = 12.0 and 21.3 mm s(-1), using C-L < 0 results in under- and over-estimation of the epsilon(G) and POP, respectively. On the other hand, taking C-L > 0 does not affect the POP while it leads to increasingly higher epsilon(G) values, which are different from those experimentally reported. At U-G = 2.4 mm s(-1), the effect of the lift force is not so evident, although it slightly improves the prediction of experimental values. Particularly interesting is the case of C-L > 0.4 at U-G = 21.3 mm s(-1), producing a non-symmetric bubble plume oscillation. Since using Tomiyama's lift coefficient correlation does not improve the results, including the lift force into the simulation of bubble plumes is not recommended. (C) 2008 Elsevier Ltd. All rights reserved.