Local analysis of Marangoni effects during and after droplet formation

Abstract

The influence on the mass transfer in liquid-liquid extraction was investigated during droplet formation in a quiescent aqueous continuous phase for the two transition components, acetone and acetonitrile, in toluene. Both transition components have similar characteristics. However, an approximately eight times slower mass transfer of a droplet hanging on a capillary in relation to a rising droplet could be observed. The droplet formation time and the initial solute concentration are decisive for the mass transfer behaviour. A lower volumetric flow leads to slower droplet formation and a higher specific mass transfer area enhancing mass transfer, which is visualized via laser induced fluorescence (LIF). Additionally, as expected, higher initial solute concentrations promote Marangoni turbulences and thus mass transfer, which is measured via confocal Raman spectroscopy inside a fixed hanging droplet. K E Y W O R D S droplet formation, interfacial phenomena, Marangoni convection, mass transfer

Real‐Time Visualization of Internal and External Concentration Fields in Multiphase Systems via Laser‐induced Fluorescence and Rainbow Schlieren Deflectometry During and After Droplet Production

“…The test cell (1) shown in Fig. 2 5 was made of glass, PTFE, and stainless steel, and is equipped with a heating/cooling jacket using a Thermo Haake K10/DC30 thermostat at an operating temperature of 25 °C. The droplet size control (2) on a stainless steel capillary ( d i = 0.8 mm, d o = 1 mm) is done via high precision syringe pump (8) (Hamilton PSD/3 mini).…”

“…1b) by application of Rhodamin 6G is not suitable due to an overlighting effect of the inside of the drop: The hydrophobic nature of the dye necessitates larger laser power for the visualization in the surrounding water, which in turn leads to the overexposure inside the drop. To circumvent this problem RSD is used for visualization of the concentration distribution outside of the droplet (as shown exemplarily in 9, 23), while LIF measurements are used inside the droplet 5, 6.…”

Experimental methods in chemical engineering: Raman spectroscopy

“…published 11 articles: six are directly related to catalysis, [27][28][29][30][31] three are in the area of combustion, [32] one combined Raman and EDS to identify a low melting lithium phosphate phase in lithium iron phosphate ingots, [33] and another applied confocal Raman to measure solute concentrations in a hanging droplet (mass transfer). [34] Raman spectrographs now record the whole spectral range (Raman shifts from 100 cm −1 to 4000 cm −1 ) at subsecond resolution and are applied to pulse experiments with isotopes, to measure reaction kinetics and spectroscopic characteristics. [35,36]…”

Digital Extraction Column: Measurement and Modeling Techniques

“…. However, at high initial solute concentrations, the mass transfer is highly influenced by Marangoni convection, inducing a surface renewal and finishing 80 % of mass transfer directly after drop formation . Therefore, further extensions of the correlations are required.…”