Study of fluid velocity characteristics in stirred solid-liquid suspensions with a refractive index matching technique

A refractive index matching laser Doppler anemometry technique was applied to a solid-liquid suspension in order to measure the continuous phase velocity in the impeller stream of a mixing vessel stirred by a Rushton turbine. Monodispersed, neutrally buoyant and impurity-free particles were used up to 2 per cent volumetric concentration. A significant influence of the dispersed phase on the liquid mean and turbulent flow field was found only near the impeller disk plane, at radial locations close to the blade tip, where both the radial mean and fluctuating velocity components were suppressed by the presence of the solid phase. The fluid velocity variation with angular position was also investigated. A locally high concentration of particles in front of the blades and in the trailing vortices area is suggested as the reason for the modification of the flow observed.