Suspension of a Single Sphere in a Stirred Tank with Transitional Flow

The lift-off characteristics of a single spherical particle in a stirred tank with transitional flow generated by a Rushton impeller have been explored in detail by using image capturing and processing techniques. We found three kinds of typical particle suspension motions, namely, the lightest PMMA particle first moves upward from the bottom center of the tank to a certain height and then spirals up to the impeller, the heavier POM particle rises to a certain height vertically and then it spirals down to the tank bottom, the still heavier PTFE and glass particles jump at random when they are rolling irregularly on the tank bottom. The single-phase flow field of the stirred tank was measured by using 2D-PIV technique to address the mechanism of the particle lift-off. The random
distribution of the regions with larger liquid velocity closely above the tank bottom might be the reason why the PTFE and glass particles were lifted off randomly. As for the PMMA and POM particles being lifted from the bottom center and then stagnating at a certain height, the bulk flow dominates the particle suspension.