Effects of capillary number and flow rates on the hydrodynamics of droplet generation in two-phase cross-flow microfluidic systems

Abstract

Background: The control and manipulation of the hydrodynamics of droplets primarily relate to flow governing and geometrical parameters. This study has explored the influences of capillary number (10−4≤Cac≤1) and flow rate ratio (0.1≤Qr≤10) on the hydrodynamics of droplet generation in two-phase flow through T-junction cross-flow microfluidic device.Methods: The finite element method is used to solve the Eulerian framework of a mathematical model based on mass continuity, Navier-Stokes, and conservative level set equations at fixed flow (Rec=0.1).Significant findings: Results are presented in terms of the instantaneous phase flow field, droplet size, droplet detachment time, and generation frequency as a function of governing parameters (Cac and Qr). The flow regimes namely squeezing, first transition, dripping, second transition, parallel, and jet flow are marked. In contrast to reported value of threshold Cac≈10−2, squeezing regime exists for all Cac and 2≤Qr≤10. The flow regimes are also mapped into droplets and non-droplet zones by using threshold Car which scales quadratically with Qr. The droplet length varies linearly with Qr in the squeezing regime. Both droplet size and frequency show the power-law relations with Cac and Qr in the droplet zone. Finally, predictive correlations are presented to guide the engineering and design of droplet microfluidics devices.