Regulation and scaling law of gas-liquid-liquid three-phase flow in a dual-coaxial microchannel

The one-step dual-coaxial microchannel exhibits wide range of regulation and simple operations in the preparation of hollow droplets. However, the scaling law of preparing hollow droplet and the prediction of hollow droplet size are insufficient. Herein, it was found that the growth stage of the hollow droplets behaves similarly to that of the liquid-liquid system, while the neck-collapse stage is similar to the gas-liquid system. Besides the neck-collapse time of hollow droplets accounts for less than 5% of the total generation time, and thus the effect of the neck-collapse process on the droplet size is negligible. A semi-empirical model based on the Ca number of the continuous phase for predicting the size of hollow droplets is established, and the relative error is within 5%. Furthermore, such a model is also applied to different systems and the model established in our work has good feasibility in predicting the hollow droplet size. (C) 2019 Elsevier Ltd. All rights reserved.