The influence of electrolytes on gas hold-up and regime transition in bubble columns

Experiments were conducted in a 0.12-m-in-diameter bubble column to investigate the effect of electrolytes on gas hold-up (epsilon) and on the regime transition point in bubble columns. Air was used as the dispersed phase and aqueous solutions of three different salts (NaCl, Na2SO4 and NaI), as well as double-distilled water, were utilised as the continuous phase, varying the gas superficial velocity (u(G)) in the range 0-0.26 m/s. The epsilon x u(G) curves were a function of both the chemical nature and the concentration of the electrolytes. However, similar epsilon x u(G) profiles were obtained regardless of the electrolyte for a given ratio between the concentration in the solution and the critical concentration of the electrolyte for bubble coalescence. This ratio therefore presents itself as a promising modelling parameter to account for the chemical nature of electrolytes. The gas hold-up data were employed to compute the regime transition point according to two different methods, evidencing its non-linear dependence on the concentration of electrolytes in the liquid. (C) 2007 Elsevier Ltd. All rights reserved.