Knowledge of principles governing droplet formation becomes important during the design of microfluidic devices,which is often based on trial-and-error.Using Computational Fluid Dynamics(CFD)to predict droplet sizes in a given geometry a priori could ease the design process and spare the tedious lab work.We are using a commercial CFD code Fluent to simulate formation of liquid-liquid slug flow in a microfluidic T-junction(Figure 1).