Numerical study on gas dispersion characteristics of a coaxial mixer with viscous fluids

Abstract

CFD (Computational fluid dynamics) method was used to study the gas dispersion characteristics of a coaxial mixer consisting of an outer anchor and an inner Rushton turbine with viscous fluids. The flow patterns of both phases and the distributions of shear strain rate, bubble diameter and local gas volume fraction were obtained. Using the total gas holdup and local gas volume fraction distribution as criteria, gas dispersion performances of the coaxial mixer operating in counter-rotation, co-rotation and single-inner-impeller rotation modes were compared. It was found that operating the mixer in counter-rotation mode exhibited better gas dispersion performance than co-rotation and single-inner-impeller rotation modes. Influences of inner impeller speed and fluid viscosity on local gas volume fraction distributions were evaluated. Results showed that increasing inner impeller speed is favorable to gas dispersion, whereas increasing fluid viscosity is not. Finally, simulated and experimental results of the vertical gas volume fraction profile in the region near the wall were compared, which showed a good agreement.