Tomographic Investigations on Single- and Multiphase Phenomena in Capillaries

In the field of micro-process engineering, choosing an appropriate measurement technique poses a major challenge. Here, micro-computed tomography, a three-dimensional non-invasive measurement technique, is presented for the investigation of single- and multiphase capillary phenomena. Single-phase investigations include two-dimensional examination of diffusion and three-dimensional investigations on laminar mixing in straight and helically coiled capillaries. In the latter, the effect of Dean flow on the resulting cross-sectional mixing can be identified. Further, the effects of Dean number, torsion, and gravity on mixing in the coiled tubes are investigated.

Tomographic multiphase investigations include the investigation of static capillary gas/liquid and liquid/liquid interfaces and the periodic generation of water droplets in a continuous stream of silicone oil in a co-flow configuration. An image acquisition and post-processing routine is developed that allows the time-resolved, three-dimensional investigation of periodic droplet formation at low capillary numbers. Analysis of droplet evolution and volumes of resulting droplets shows characteristics of the squeezing and the leaking regime. The comparison to results of numerical simulations gives further insights into the process of droplet formation.