Dripping and jetting generation mode in T-junction microchannels with contractive structures

Droplet generation in T-junction microchannels with contractive structures is investigated under different flow rates and viscosity conditions by numerical simulation to improve the monodispersity and controllability of the microdroplets. Basic flow modes are observed, including dripping, transition, and jetting, under various flow rates and dispersed phase viscosities. The flow condition for the transition mode is modeled as a function of capillary number, flow rate ratio, and viscosity ratio to indicate the conversion of generation modes. Unlike ordinary T-junction microchannels, in this case, the droplet diameter first decreases and then increases with the increasing viscosity ratio in T-junction microchannels with contractive structures. By analyzing the velocity fields, pressure fields, and forces in droplet formation, the dynamic mechanism of the viscosity ratio on the generation mode and droplet size is achieved. The droplet volume in the dripping mode is analyzed to propose a prediction formula that takes into account the influence of the viscosity ratio.