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ISBN 978-3-8439-3797-9

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Felix Gebauer
Fundamentals of Binary Droplet Coalescence in Liquid-Liquid Systems

160 Seiten, Dissertation Technische Universität Kaiserslautern (2018), Softcover, A5

Zusammenfassung / Abstract

The aim of this thesis is the systematic analysis on the dynamic binary coalescence in disperse liquid-liquid systems. In particular, the influence of ions on the coalescence needs a more precise quantification. An accurate and robust mathematical model to describe the coalescence shall be developed based on the experimental data, before it is actually implemented into population balance equations (PBE). The model based on single-drop experiments is compared to the prediction of the DSD in an extraction column.

Droplet coalescence in extraction and phase separation is of high importance to many branches of industry (e.g. chemical, petrochemical, biochemical, hydrometallurgical and nuclear separation processes). The interfacial area, which depends on the competitive dynamic phenomena of breakage and coalescence, substantially influences the process efficiency and product quality in technical separation processes.

Coalescence in liquid-liquid systems is determined by multiple factors, including droplet size ratios and the concentration and type of any continuous phase ions present. When using the standardized EFCE (European Federation of Chemical Engineering) toluene/water standard test system, these factors were systematically investigated based on a high statistical relevant database. The influence on the film drainage time was captured with a high speed imaging system.

Shorter coalescence times were found to correlate with higher coalescence probabilities and an observed increase in the coalescence time with increasing droplet diameter agrees well with simple drainage modeling. Coalescence inhibition was also observed with the addition of continuous phase electrolyte. An empirical correlation was developed to account for the influence of equivalent droplet diameter and ion concentration on the coalescence time.

Complementary CFD simulations and an additional analytical sub-grid approach provided further details and local information of the internal flow profiles and gave a estimation of the film thickness development. Thus both the shape on the droplet scale and the dimple formation on the film scale could be modeled. An approximation of the film drainage time until a critical film thickness could be realized.

Nevertheless, the findings as well as the developed setups future standardized investigation of coalescence phenomena under controlled conditions.