Liquid phase dispersion in bubble columns operating in the churn-turbulentflow regime

The objective of this paper is to develop a reliable, yet-simple, correlati on for the liquid phase axial dispersion coefficient D-ax,D-L in bubble col umn reactors. In order to develop this correlation we carried out measureme nts of the centre-line liquid velocity V-L(0) and D-ax.L in bubble columns of diameter D-T=0.174, 0.38 and 0.63 m with the air-water system. The measu rements were performed in the churn-turbulent regime of operation with supe rficial gas velocities U in the range 0.05-0.35 m/s. From the several liter ature correlations tested, the one proposed by Riquarts [Chem. Ing. Techn. 53, 1981, 60-61] can be recommended for estimation of V-L(0) for air-water systems. The Riquarts correlation however anticipates the dependence of V-L (0) on the kinematic viscosity of the liquid phase. Measurements of V-L(0) were also carried out in the 0.38 m diameter column with Tellus oil as the liquid phase, with a kinematic viscosity 87 times that of water. Comparison of V-L(0) measurements with water and Tellus oil shows a negligible influe nce of liquid viscosity, leading us to conclude that the best estimation pr ocedure for V-L(0) is to use the Riquarts correlation with properties of th e water as the liquid phase. The above conclusions are also supported by Eu lerian simulations of the bubble column hydrodynamics. Our measured data on the D-ax.L and V-L(0) were combined to develop a simpl e correlation: D-ax.L=0.31 V-L(0) D-T; this correlation also provides a goo d description of experimental data from the literature. (C) 2000 Elsevier S cience S.A.