Abstract
Liquid–liquid two-phase flow in microchannels has attracted much attention, due to the superiority of mass transfer enhancement. One of the biggest unresolved challenges is the low mixing efficiency at the microscale. Suitable mixing efficiency is important to promote the mass transfer of two-phase flow in microchannels. In this paper, the mixing efficiency in three junction configurations, including a cross-shaped junction, a cross-shaped T-junction, and a T-junction, is investigated by the volume of fluid (VOF) method coupled with user-defined scalar (UDS) model. All three junction configurations are designed with the same hydraulic diameter of 100 μm. Mixing components are distributed in the front and back parts of the droplet. The mixing efficiency in the droplet forming stage and the droplet moving stage are compared quantitatively. Results show that different junction configurations create very different mixing efficiencies, and the cross-shaped T-junction performs best, with relatively lower disperse phase fractions. However, with an increase of the disperse phase fraction, the cross-shaped junction is superior.
Highlights
Microfluidic systems are widely used in chemical synthesis, drug delivery, and solvent extraction, due to their superiority in heat and mass transfer enhancement [1,2,3]
Mixing efficiency is an important parameter for evaluating the microfluidic system
It can be seen that when the mesh size decreases from 8 μm to 4.25 μm, the dimensionless droplet length varies at a very small range, within the maximum relative error less than 5%, which is calculated by Equation (9)
Summary
Microfluidic systems are widely used in chemical synthesis, drug delivery, and solvent extraction, due to their superiority in heat and mass transfer enhancement [1,2,3]. Mixing efficiency is an important parameter for evaluating the microfluidic system. At the microscale, the fluid flow is laminar and is confined by a narrow space. Mixing in microfluidic systems is diffusion dominated, so that it is very difficult to achieve a satisfactory mixing efficiency. When the continuous phase and the disperse phase are injected into the microchannel, the interaction of two phases cuts the disperse phase into small droplets, and the mixing process is confined inside the droplet. The reduced diffusion distance and enhanced inner circulation inside droplets can highly promote the mixing performance [4,5]
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