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.

Automated summary

This study proposes a new mixer combining an elliptical uncovered unbaffled stirred tank with a rigid-flexible impeller to improve solid-liquid suspension performance. Comparisons were made between the elliptical and circular uncovered unbaffled stirred tanks under equal liquid height and volume. The results show that the elliptical system reduces suspension speed and power consumption significantly, improves solid homogeneity, achieves chaotic mixing at lower power consumption, and exhibits secondary motions that contribute to better solid suspension.