Mass transfer studies of external‐loop airlifts and a bubble column

Abstract

AbstractGas holdups (ϵGR) and liquid‐phase volumetric oxygen transfer coefficients (kLaT) were measured for a bubble column (BC) and three different external‐circulation‐loop airlift (ECL‐AL) fermentors of 50 to 60 L working volume, using viscous non‐Newtonian aqueous solutions of various carboxymethylcelluloses. Some measurements also were done with a viscous Newtonian system (51.8 wt. % sucrose solution).Discussed in this paper are correlations of ϵGR and kLaT with riser superficial gas velocity (0.02 ≦ UGR ≦ 0.26 m/s), the ratio of the downcomer and riser crosssectional areas (0[BC] ≦ Ad/Ar ≦ 0.444), and the effective viscosity of the liquid phase (0.02 ≦ ηeff ≦ 0.5 Pa · s), over the parameter ranges indicated. It is shown that both ϵGR and KLaT are highly dependent upon UGR and Ad/Ar. The effective viscosity has a significant effect on KLaT, but has only a relatively weak affect on ϵGR. The KLaT correlation developed for non‐Newtonian systems was extended to include the results obtained for the viscous Newtonian system studied by incorporating the effects of liquid‐phase molecular diffusivity, density, and interfacial tension as determined by Nakanoh and Yoshida (1980).