Three-dimensional lattice Boltzmann simulation of Janus droplet formation in Y-shaped co-flowing microchannel

Abstract

A three-dimensional ternary color-gradient lattice Boltzmann (LB) model was successfully developed to numerically investigate the hydrodynamic behavior of Janus droplet formation in Y-shaped co-flowing microchannel. The model’s ability for simulating the contact conditions of two immiscible droplet pairs in the third host fluid is validated. Janus droplet formation was categorized into five generation modes presented in a mountain-shaped flow pattern diagram, which agreed well with experimental reports. Then the size law of Janus droplet, dynamic collapsing process and the critical break-up length of biphasic dispersed thread were systematically investigated in comparison to the results of single-phase droplet formation. The simulation results showed that both single-phase and Janus droplet sizes obeyed a power-law relationship with the Capillary number of the continuous phase (Ca) in squeezing regime, where the breakup of dispersed thread showed a quasi-static character, and a critical Ca number around 0.121 for transitional regime was observed. Besides, Janus dispersed thread which is subjected to asymmetric interfacial tensions, was more inclined to collapse than the single-phase thread at the same flow rates, indicating that the operating range of Janus droplet formation might be larger than that of single-phase droplet generation. The present study expands the understanding on Janus droplet formation process, which provides a new insight on complex droplet generation in multiphase flow.