Micro-droplet nucleation through solvent exchange in a turbulent buoyant jet

Abstract

Solvent exchange is a process involving mixing between a good solvent with dissolved solute and a poor solvent. The process creates local oversaturation which causes the nucleation of minute solute droplets. Such ternary systems on a macro-scale have remained unexplored in the turbulent regime. We experimentally study the solvent exchange process by injecting mixtures of ethanol and trans-anethole into water, forming a turbulent buoyant jet in the upward direction. Locally, turbulent mixing causes oversaturation of the trans-anethole following turbulent entrainment. We optically measure the concentration of the nucleated droplets using a light attenuation technique and find that the radial concentration profile has a sub-Gaussian kurtosis. In contrast to the entrainment-based models, the spatial evolution of the oversaturation reveals continuous droplet nucleation downstream and radially across the jet, which we attribute to the limited mixing capacity of the jet. Although we are far from a full quantitative understanding, this work extends the knowledge on solvent exchange into the turbulent regime, and brings in a novel type of flow, broadening the scope of multicomponent, multiphase turbulent jets with phase transition.

Mixing and Solvent Exchange Near the Turbulent/Non-Turbulent Interface in a Quasi-2d Jet

“…While the aforementioned studies focused on the scalar fields in a continuous phase, physicochemical hydrodynamics following turbulent mixing can also lead to precipitation of a dissolved component into a dispersed phase, which undergoes oversaturation, droplet nucleation, droplet growth, and sometimes also shrinkage due to evaporation (Marié et al, 2014;Li et al, 2023) in the turbulent flow. Such precipitation processes include aerosol formation through condensation (Lesniewski and Friedlander, 1998;Zhou et al, 2014;Ng et al, 2021;Li et al, 2023), soot formation in turbulent combustion (Bisetti et al, 2012;Attili et al, 2014a), particle formation by chemical reaction (Schikarski et al, 2022;Tang et al, 2022), and droplet formation upon solvent exchange (Lee et al, 2022). Lesniewski and Friedlander (1998) experimentally studied dibutyl-phthalate (DBP) aerosol formation in a turbulent jet flow, indicating that with high DBP vapor concentration, the droplets nucleate both within the initial shear layer and in the downstream turbulent region.…”

“…While the physicochemical hydrodynamics of the ouzo effect has been extensively studied in the laminar regime in microfluidic setups (Hajian and Hardt, 2015;Zhang et al, 2015;Li et al, 2021), it remains almost unexplored in the turbulent regime. In our previous work (Lee et al, 2022), we studied the concentration field of nucleated oil in an axisymmetric turbulent jet. Implementing a light attenuation technique, we successfully measured the mean structure of the field.…”

“…Due to the opaque nature of the ouzo effect, our optimization algorithm (Lee et al, 2022) constrains the findings to the time-averaged axisymmetric concentration field. Although the mean field unveils the centerline scaling and the spreading of the profiles, we did not learn much about the temporal dynamics.…”

“…Such an effect is more pronounced for the case with fast reactions. Lee et al (2022) argued that the measured sub-Gaussian mean concentration profiles result from the meandering TNTI and the accompanying mixing and nucleation.…”

“…The opaque nature of the axisymmetric jet of Lee et al (2022) makes it very difficult, if not impossible, to further investigate the effect of turbulence on the solvent exchange near the TNTI experimentally. We therefore opt for a quasi-two-dimensional jet (Landel et al, 2012a,b) by confining the jet laterally.…”