Unsteady motion of the impeller is one of the several methods to improve mixing in unbaffled vessel. It is very important in pharmaceutical industry, crystallization processes or some chemical reaction with catalyst where baffles are not recommended. The literature data shows that unsteady mixing cause generation of axial flow for radial impellers (Rushton turbine). The purpose of this study was to investigate axial force for axial impellers like A315, HE-3 and SC-3. Moreover, the momentum number, flow number and pumping efficiency were analysed. Results shows that axial force for unsteady mixing is higher in comparison to steady-state mixing. Also, the comparison of axial force between impellers shows that blades influence momentum number and flow number. Impellers with larger blade surface generate stronger axial force. The obtained results reveal that unsteady mixing with axial impellers could be apply for solid-liquid mixing as suitable alternative to steady-state mixing.

This study is focused on the image analysis of motionless hydraulic mixing process, for which pressure changes were the driving force. To improve the understanding of hydraulic mixing, mixing efficiency was assessed with dye introduction, which resulted in certain challenges. In order to overcome them, the framework and methodology consisting of three main steps were proposed and applied to an experimental case study. The experiments were recorded using a camera and then processed according to the proposed framework and methodology. The main outputs from the methodology which were based only on the recorded movie were liquid heights and colour changes during the process time. In addition, considerable attention has also been given to issues related to other colour systems and the hydrodynamic description of the process.