The liquid–liquid flow dynamics and droplet formation in a modified step T‐junction microchannel

Abstract

The droplet generation mechanism in the asymmetrically enhanced step T‐junction remains unknown, especially for the transition stage from dripping to jetting regimes. In this work, the droplet generation mechanism was systematically investigated in a modified step T‐junction by modulating a large flowrate range and altering different interfacial tensions. We found that under different fluid regimes, both the capillary number and flow rate ratio of continuous and dispersed phase showcase completely different impacts over droplet generation. In dripping regime, the interfacial tension, which was controlled by changing the surfactant concentration, dominated the formation mechanism when the surfactant concentration was found below micelle concentration. In jetting regime, our experimental results showed that the influence of the surfactant concentration on the size of generated droplets was rather negligible while the flow rate ratio of continuous and dispersed phase indeed determined such a parameter. In the dripping‐jetting transition stage, an increase of droplet size was observed despite the increase of continuous phase flow. After reaching a peak, the droplet dimension started to decrease with the increase of continuous phase flow as expected. To the best for our knowledge, it is the first study to report generation mechanism in modified step T‐junction from dripping to jetting regimes.

Dispersion behavior of liquid–liquid and gas–liquid two‐phase flow in micro‐packed beds

“…In the typical liquid–liquid dispersion process in microchannels, an increase in the external viscosity results in a decrease in droplet size 26,27 . A decrease in the interfacial tension leads to a decrease in droplet size 28 . Meanwhile, if the concentration of surfactant at the interface is above the critical micelle concentration (CMC) and droplet formation occurs rapidly, there will be a significant dynamic interfacial tension effect when the distribution of surfactants at the interface has not reached equilibrium, leading to further reduction in droplet size 29 .…”

“…26,27 A decrease in the interfacial tension leads to a decrease in droplet size. 28 Meanwhile, if the concentration of surfactant at the interface is above the critical micelle concentration (CMC) and droplet formation occurs rapidly, there will be a significant dynamic interfacial tension effect when the distribution of surfactants at the interface has not reached equilibrium, leading to further reduction in droplet size. 29 In the dispersion experiments in micro-packed beds, the observed phenomena are significantly different from those in microchannels.…”

A Novel Step-T-Junction Microchannel for the Cell Encapsulation in Monodisperse Alginate-Gelatin Microspheres of Varying Mechanical Properties at High Throughput

“…For instance, by applying a non-uniform magnetic field onto the ferrofluid inside a T-shaped microchannel, one can accurately tune the applied force filed gradient and control the rapid microdroplet breakup [ 68 ]. Here, with the use of the novel step-T-junction microchannel with embedded microcapillary that concentrates the shearing force at the special narrowing zone, monodisperse alginate–gelatin whose size overcomes the dimensional limitation of the microchannel itself could be generated at a high throughput jetting regime while maintaining a CV below 5%, i.e., limit of monodispersity, as shown in Figure 5 A [ 60 , 69 , 70 , 71 ]. In fact, as suggested by the results of the numerical simulation from our previous work, the very special microstructure of the modified step-T-junction microchannel, which is characterized in the serial narrowing, expansion, and re-narrowing regions from the left wall of the microcapillary to the inside of the microcapillary to the narrowing region, respectively, would bring a double disturbance onto the fluids and consequently facilitate the microdroplet pinch-off [ 60 ].…”

Effect of Scale-Up on Mass Transfer and Flow Patterns in Liquid–Liquid Flows Using Experiments and Computations

“…Liquid–liquid biphasic microchannels exhibit various flow patterns that impact transport rates. − These can be engineered by changing solvents (density, viscosity, and surface tension), the fraction of each phase, the micromixer where the streams intersect (T-junction, Y-junction, etc. ), the wall hydrophilicity, and the channel diameter, length, and geometry. − This tunability can significantly improve the reactor throughput. The most common patterns are segmented (slugs and droplets) and parallel flow.…”