Micro-reactors, enabling continuous processes at small scales, have been of growing interest due to their advantage over batch. These advantages include better scaling, as well as improved mass and heat transfer, though many new challenges arise due to the small scales involved such as non-negligible entrance effects and significant pressure drops. The flow in coils, rectangular channel serpentine plates, mix-and-reside plates, and complex liquid-liquid mixing plates was investigated and characterized using residence time distribution (RTD) tests. A pulse test was used to determine the RTD curve shape of these reactors at flowrates ranging from 20 to 100 g/min. A semi-empirical, multi-parameter model was used to describe the asymmetrical curves, while the axial dispersion model was used to describe the symmetrical ones. The Peclet number is given in function of the Reynolds number for the liquid-liquid plates that were found to be near-plug flow (Pe > 100). In a continuous mixing plate, the Pe ranged from 190 to 475 with Pe increasing as Re increased. The effect of straight channel sections in micro-reactors is also evaluated. Longer straight segments between micromixers resulted in the development of unidirectional flow and the occurrence of tailing in the RTD. Finally, the suitability of a liquid-liquid plate for a reactive liquid-solid system is evaluated. The plugging is determined visually and by measuring pressure increase; pressure started to increase after 5 minutes and the experiment had to be halted after 10 minutes due to plugging. Parallels between the particle size distribution and the residence time distribution curves are drawn. The particle size distribution of silver chloride at low flow rates is much wider than at high flowrates. The average particle size at high flowrates was also much lower (≈69nm) than at low flowrates (≈112nm).