The authors present an experimental investigation of the mixing dynamics within a stirred tank reactor of 3 litres on laboratory scale, which is equipped with two Rushton turbines and three baffles. Using time resolved particle tracking velocimetry in four dimensions, the trajectories of up to 40,000 tracer particles were captured in the full volume of the reactor, despite the obstructions by the stirrer and the baffles. This provides information on the flow and on the mixing with an unprecedented resolution in time.
From these Lagrangian data, velocities, accelerations and the dispersion in space are analysed, which reveals anisotropic mixing. Methods of analysis based on networks are applied to the experimental trajectories and identify coherent compartments of fluid that exhibit strong internal mixing but only weak exchange with the neighbouring compartments.
Five distinct compartments are uncovered which act as barriers to transport: one around each of the two turbines and three further compartments in the upper part of the vessel between the baffles. Such barriers have a high impact on the distribution of the substrate in chemical and biochemical processes.
The approach realises and extends the early thought experiments of Danckwerts and Levenspiel, since it provides detailed insight into the behaviour of single parcels of fluid and into the Lagrangian mixing within chemical and biochemical reactors. It offers a valuable approach for the evaluation and the optimisation of such processes. The trajectory data are made freely available and serve as an experimental reference for further research.
The study is a collaboration between the Hamburg University of Applied Sciences, Leuphana University Lüneburg and Hamburg University of Technology, carried out within the Collaborative Research Centre CRC 1615 (SMART Reactors), with the measurements recorded using the major instrumentation MUST at HAW Hamburg.
Eike Steuwe, Thanh Tung Thai, Christian Weiland, Anna Klünker, Jan Hendrick Nissen, Michael Schlüter, Kathrin Padberg-Gehle, Alexandra von Kameke (2026). Can we live Danckwerts’ dream? Mixing Analysis in a Baffled Stirred Tank Reactor Based on 4D-Particle Tracking Experiments. arXiv:2607.26813.
