The local behavior of continuous phase in a stirred tank with floating particles was investigated by using PIV technique. The effect of solid concentration and off-centered shaft position on the fluid field were studied. Experimental measurements were carried out in a fully baffled cylindrical vessel equipped with a flat bottom and an up-pumping 4-Wide-blade Hydrofoil impeller (WHU). The diameter of the vessel, the diameter of the impeller, and the vertical clearance of the bottom were 0.192 m, 0.075 m, and 0.064 m, respectively. The liquid phase was water, and low density polyethylene flat cylindrical particles were used as the floating particles at different concentrations (0.0, 0.6, 0.8, and 1.0 vol.%) and different shaft positions (0.0, 0.0096, 0.0192, and 0.0288 m away from the center of the tank, corresponding to the eccentricities of 0%, 5%, 10%, and 15%, respectively). PIV measurements showed that the velocity increases by approximately 50% in the tank with the most eccentric shaft. Axial and radial mean velocities for the carrier liquid phase were also measured by using fluorescent particles. Results indicated that as the increase of floating particle concentration, the velocity decreases by about 16% in the main flow direction. In addition, the flow behavior is not affected by the presence of floating particles, and the circulation pattern is similar in both the absence and the presence of floating particles.
©2012 Walter de Gruyter GmbH & Co. KG, Berlin/Boston