(193d) Measurements and Simulation of Flooding Characteristics for Gas-Sparged Stirred Vessels with Highly Viscous and Viscoelastic Liquids

Experimental studies of the gas rate at which flooding occurs for various impeller rotation rates into low viscosity Newtonian fluids have been done for several decades, so there is a solid experimental background for the existing correlations which predict the aeration number as a function of Froude number at which flooding will occur for a given impeller type. Previous work has also shown that simulations using CFD can accurately predict when flooding will occur with low viscosity Newtonian liquids in the mixer. The study reported here concerns flooding when the liquid being stirred is of high viscosity (up to 3000 cp) or has a distinct viscoelastic response to shear (up to first normal stress/shear stress ratio of about 0.6). Solutions of sugar and of poly(ethylene oxide) were used in the experiments. The tank was fully baffled and impellers used were pitched-blade and disk turbine. Comparisons of flooding onset data and stirring power as a function of aeration number for the viscous liquids are compared with those available in the published literature and deviations for the viscoelastic liquids are shown. Special attention was paid to comparisons of bubble sizes and gas holdups for the various stirring conditions. Comparisons of the experimental data with simulations using CFD are also shown.