This paper reports on numerical simulations and experimental validation of the hydrodynamics of liquid-liquid flow in rectangular micro-channels. The numerical method is an interface-capturing technique without any interface reconstruction. Micro-PIV measurements are used to obtain experimental velocity fields inside droplets which are compared to simulations. Finally, injecting a passive tracer in the simulated droplets also helps to obtain a better understanding of the mixing phenomenon. These results allow interpreting mixing defaults during bleaching experiments inside micro-droplets. Furthermore, this study leads to important results about interface deformation and velocity fields inside the droplets and in the continuous phase for mass and heat transfer studies