Intensification of Solid-Liquid Suspension Performance in an Elliptical Uncovered Unbaffled Stirred Tank

The combination of an elliptical uncovered unbaffled stirred tank with a rigid-flexible impeller is a creative effort to improve the performance of solid-liquid suspensions. In this work, we proposed a new mixer combining an elliptical uncovered unbaffled stirred tank (E-UUST) with a rigid-flexible impeller. The just suspended speed (Njs), just suspended power consumption (Pjs), local axial solid concentration, and the largest Lyapunov exponent (LLE) in the E-UUST and the circular uncovered unbaffled stirred tank (C-UUST) were compared under the conditions of equal liquid height and volume. In addition, development of a secondary vortex structure was discussed based on the secondary flow theory by visualization. The results demonstrate that Njs and Pjs, in the E-UUST system, can be reduced significantly by 17 and 37.4%, respectively. The degree of homogeneity of the solids can be effectively increased using the E-UUST. Moreover, the E-UUST with a rigid-flexible impeller can achieve more chaotic mixing and reach a state of just suspension at lower power consumption. Finally, secondary motions in the E-UUST were observed, which may be the reason solid suspension in the E-UUST is better than in the C-UUST. This study shows that the E-UUST can be effectively used to intensify solid-liquid suspension performance and help understand the chaotic mixing of solid-liquid two-phase flows in stirred tanks.