Numerical simulation on the characteristics of droplet generation and the distribution of discrete-phase flow patterns in T-junction microchannels

Abstract

Droplet formation is the basis for the design of droplet microfluidic chip. The droplet formation mechanism and discrete phase flow patterns in T-junction microchannels are numerically simulated. This research adopts an incompressible two-phase flow solver in the OpenFOAM® framework. Firstly, the effects of two-phase flow rate, surface tension and microchannel structure on droplet formation are investigated. It is found that the mechanism of droplet formation is classified into extrusion and shear mechanisms. And the discrete phase flow patterns can be divided into four modes, including slug flow, drip flow, jet flow, and parallel flow. Then, the distribution of discrete phase flow patterns in microchannels with different depth-to-width ratios are plotted. These distribution maps provide further insights into the mechanisms underlying the formation and transformation of different discrete phase flow patterns within microchannels. Finally, the droplet formation in the modified Venturi microchannels was compared with that in the ordinary T-junction microchannel. The efficiency of droplet formation in microchannels with Venturi components is superior. Specifically, with a component angle of 30°, the length of the droplets can be reduced by as much as 120 μm. The droplet generation frequency can be increased by approximately 122.4 %, rising from 25 Hz to 55.6 Hz. When the Venturi component is positioned at the entrance of the discrete phase, the minimal droplets can be generated uniformly at a higher frequency in the microchannel.