Liquid–liquid two-phase flow and size distribution of droplets in milli-channels: Effect of gravity

Dimension-enlarge is one of the scale-up strategies for microreactors to increase the throughput. To examine sizing-up effect, T-mixers and various milli-channels were adopted to study the liquid–liquid two-phase flow. In the experiment, droplet flow and slug flow presented in both hydrophilic and hydrophobic channels. Two different formation processes of slug flow were observed by increasing volumetric flow rates. The length of dispersed droplets was measured and the effects of inlet mode, flow rate and flow ratio were studied. Although gravity cannot be ignored in milli-channels, there was no difference of droplet length under different inlet modes. The droplet length percentage in unit cell was close to 50% when the flow ratio of the two phases was 1:1. Further, a scaling law was used to predict the droplet length and it agreed well with the experimental data. Additionally, the different slug flow formation processes were also observed by changing the inlet modes. Computational fluid dynamics simulations were carried out to study this interesting phenomenon. The slug generation mechanism was analysed and the effect of gravity was clarified. Local pressure and velocity were presented as well.