Gas-liquid mass transfer in external-loop airlift columns with newtonian and non-newtonian fluids

Gas-liquid mass transfer in external-loop airlift columns has been examined. The measurements have been carried out in two external-loop airlift columns and a bubble column with newtonian and non-newtonian fluids. The experimental results indicate that the volumetric mass transfer coefficient k(L)a decreases with increasing downcomer-to-riser cross-sectional area ratio and its dependence increases with non-newtonian flow behaviour or shear thinning. A theoretical model for volumetric mass transfer coefficient has been also developed. It is based on a combination of Higbie's penetration theory and Kolmogoroff's theory of isotropic turbulence. The capability of the proposed correlation for k(L)a was examined using the present data and the available results in the literature. Reasonable agreement between the predicted and experimental results for newtonian and inelastic non-newtonian (pseudoplastic) fluids suggests applicability of the proposed model.