Droplet-based microfluidics is a promising tool for performing biochemical or chemical assays. Droplets are unit systems of controlled volume and content, within which mixing, reacting and/or transferring can be achieved. Therefore, a comprehensive understanding of droplet migration in confined microchannels is essential to many microfluidics applications. Rectangular confined channels with the width significantly larger than the height are commonly used in microfluidics devices. In such cases, the confinement of the droplet is only in the vertical direction and the droplet is exposed to a two-dimensional Poiseuille flow (as in a Hele–Shaw cell). Fig. 2. Simulation results of a planar droplet a 2D channel.(a) Droplet shape and the streamlines in the droplet reference frame.(b) Relative droplet velocity and film thickness as functions of the capillary number compared to extended Bretherton theory 2D Validation.