Fundamental study on 3D particle tracking, flow stability and particle dynamics relevant to Taylor-Couette reactors

Combining axial and rotational flow between two concentric cylinders, Taylor-Couette Reactors (TCRs) bear huge potential for both mixing and separation of particle laden flows. In such flows, the particle dynamics are affected by the structure of the flow, gravitational and centrifugal forces and interaction of particles with the fluid and themselves. However, these effects are not completely understood on their own such that their combined effect on the particle dynamics in TCRs is far from being predictable. Therefore, in the present thesis, the major physical effects relevant in such scenarios are investigated separately to provide a foundation for future potential applications. As particle trajectories differ significantly for laminar, bifurcated or turbulent flow, precise knowledge of the flow stability of the carrier liquid is required to set the process parameters. Given that, a comparative study of the linear stability behavior of the laminar flow in a TCR with rotation of the inner cylinder and with rotation of the outer cylinder is performed by means of swirl and curvature parameter. It is revealed that the stability behavior for both the rotating inner as well the rotating outer cylinder case strongly depends on the curvature parameter. While rotation of the inner cylinder generally has a destabilizing effect, it is revealed that rotation of the outer cylinder can stabilize but also destabilize the flow depending on swirl and the curvature parameter. Until now, the direct observation and characterization of suspensions by means of optical methods bears large potential but is highly challenging especially in small geometries such as in the gap of a TCR. In the present study, different methods are developed to apply Astigmatism Particle Tracking Velocimetry (APTV) on suspension flows for dilute, semi-dilute, mono- and polydisperse suspensions. Using these techniques, the dynamics of mono- and tridisperse suspensions are investigated in pressure driven square duct flows at volume fractions up to 9.1%. It is discovered that interaction of small and large particles can lead to strikingly different concentration patterns in tridisperse compared to monodisperse suspensions depending on Reynolds number, volume fraction and channel height. While particle interaction is usually associated with higher particle volume fractions, it is known that dilute suspension flows in horizontally aligned rotating cylinders could give rise to formation of band shaped particle accumulations. In this thesis, it is investigated how an additional inner cylinder, which is present in a TCR, affects this band formation. To reduce the complexity, a Taylor Couette flow with solid body rotation without axial flow is considered. Different particle patterns are discovered including three types of bands, which are periodic in axial direction, and two types of bands that are periodic in azimuthal direction. It is shown, that the presence of the inner cylinder can significantly alter the particle trajectories and stabilize the particle bands