Fast oil-in-water emulsification in microchannel using head-on impinging configuration: Effect of swirl motion

Abstract

Liquid-liquid dispersion by head-on impingement in a cross-slot microfluidic device to form oil-in-water emulsion is experimentally investigated at broad range of flow rate conditions. Reynolds number based on the continuous aqueous phase flow is changed from 1000 to 7000 and the oil dispersed volume fraction varies between 3% and 30%. The flow patterns are observed in the vicinity of impinging region to characterize the effect of Reynolds number and oil volume fraction on the water-oil interaction and thus emulsification process. Based on the measured droplet size and size distribution, two geometries are compared, aimed at evaluating the advantages and disadvantages of swirl flow in the collision region for producing high quality emulsion. One configuration, "600-600", corresponds to inlet channels of identical size (600 μm×600 μm), while the other one, "600-300", has a smaller channel for dispersed phase which is off-axis with the water channel. The results show that flow characteristics during dispersing process are significantly different for viscous and turbulent conditions. Dominated by Reynolds number, the flow patterns are classified into three regimes. The more turbulent the flow is, the finer and more monodispersed droplets will be in the o/w emulsion. In the medium Reynolds number regime, characteristics of flow are closer to laminar flow using higher oil volume fraction, compared to small oil volume content. It is particularly evident with 600-300 system because of lowering velocity gradient between two phase streams. Based on results of drop mean diameter and polydispersity index, 600-300 system which generates swirl flow structure only exhibits a superior performance, compared to the conventional equal-size geometry, at relatively higher Reynolds number.

Production of oil in water emulsions in microchannels at high throughput: Evaluation of emulsions in view of cosmetic, nutraceutical or pharmaceutical applications

“…characterized with a coefficient of variation, i. e. ratio of the J o u r n a l P r e -p r o o f standard variation on the mean, less than 10% with membranes and even currently less than 5% with other systems like T-junction, for instance. But it might be emphasized that it is mainly the case if the break-up is dominated by capillary effects, which is not the case in the conditions implemented using MHT in the present work (Belkadi et al, 2015, Ji et al, 2020.…”

“…The emulsion is formed and collected through two 600 µm in width microchannels. Concerning the particular flow pattern and droplet break-up mechanisms occurring in such a system, the reader can refer to several publications (Belkadi et al, 2015, Belkadi et al, 2016, Ji et al, 2020. The specific design of the microsystem enhances a swirl flow in the impinging area, associated with a dead zone.…”

Effect of cross-slot configuration in microfluidics on o/w emulsification at high throughput

“…The important feature of asymmetric configuration is that swirl flow structure can be formed in the impingement zone due to the offset axis arrangement for the two impinging channels. The effect of this macro swirl flow in the asymmetric configuration on the two-phase flow patterns in the vicinity of the impact area and single drop breakage behavior has been recently specifically studied (Ji et al 2020;. The results indicate that the swirl flow can promote emulsion quality, that is, finer and less poly-dispersed droplets, especially at high 𝑅𝑅𝑅𝑅 conditions.…”

Analysis of droplet displacement during transport of polydisperse emulsion as drug carriers in microchannels

“…2021a) characterized droplet size and size distribution in crossslot microsystems employing head-on impingement of oil and water jets for emulsifying and mainly focused on the effect of the cross-junction layout on the emulsion quality. The flow patterns in cross-slot microsystems employing head-on impingement of oil and water jets for emulsifying were studied (Ji et al 2020). Droplet size measurement at different flow conditions was carried out to analyze benefits or detriments of the presence of a swirl flow and its role for the drop breakage in microsystems (Ji et.…”