ISBN 9783843948883

978-3-8439-4888-3, Reihe Verfahrenstechnik

Jens Heine
Real-time visualization and in-situ measurement of concentration-induced Marangoni convection at droplet formation, rise and coalescence

165 Seiten, Dissertation Technische Universität Kaiserslautern (2021), Softcover, A5

Zusammenfassung / Abstract

Liquid-liquid extraction is used in numerous technical processes, for example, in the pharmaceutical, petrochemical, biochemical, or chemical industries. However, its fundamentals are still not fully understood. The process efficiency and product quality are substantially influenced by the specific interfacial area, which depends on the local droplet behavior, such as droplet formation followed by droplet rise and coalescence.

In order to better understand this phenomenon, the mass transfer is visualized qualitatively and non-invasively inside the droplet via LIF-images and around the droplet by schlieren measurements. The simultaneous measurement inside and outside of the droplet allowed for the first time to overcome the limitations of both measurement techniques. Thus, the correlation of the internal concentration distribution with the surrounding concentration distribution can be shown for different internal concentrations, droplet diameters, droplet formation times and flow around the droplet.

The mass transport is further measured in-situ by a newly established measuring technique punctually in and around the droplet, whereby a time and spatial concentration profile can be measured. By means of the droplet suction a mean concentration of the droplets for different rising heights is measured. A mass transfer rate more than 8 times faster than that of the hanging droplet could be determined. This shows the great influence of the flow around a rising droplet on the mass transfer. Furthermore, a faster mass transfer was measured for smaller droplet diameters and slower droplet formation rates, independent of the mass transfer direction. An increase of the initial concentration always leads to a faster mass transfer, which was also modeled to calculate the concentration in and around the droplet.

The coalescence measurements show a new phenomenon, which is crucial for the accurate design of extraction columns.