Abstract Summary (Max 250 words)
The understanding of multi-phase fluid dynamic phenomena in stirred tanks is essential for developing new processes as well as optimization and scale-up efforts. Therefore, these phenomena have been studied in the past using various methods, each with its own limitation: optical tomography is restricted to non-opaque systems, invasive probes provide only local information, and X-ray techniques require tracer particles to measure velocity. Magnetic resonance imaging (MRI) offers a powerful alternative, in which the magnetization of nuclear spins is measured to provide information on different phases and fluid velocity without the need of tracers. The MRI system at TUHH allows the operando investigation of process engineering vessels in relevant sizes up to 400mm in diameter with a modular stirrer setup, that can facilitate various stirred tank setups. In addition to studying gas-liquid systems, emulsions and suspensions have been investigated for the first time using MRI in this scale. Furthermore, local fluid velocities were directly measured using MR velocimetry at a spatial resolution of 2x2x2mm³. The phase distribution obtained by these measurements provide fresh insights into mixing and separation times, agglomerates formation and suspension distribution with sub-second temporal resolution. Three-dimensional flow maps and show the influence of stirrer types and speed as well as different mixture compositions. From these maps local shear stress information can be extracted, crucial to systems employing sensitive cells. These new insights allow the validation of simulation data and will help improving scale-up and scale-down models for stirred tanks.
