Chemical microreactors are among the most novel and promising technologies in Chemical Engineering. A microreactor is defined as a continuously operated chemical reactor whose channels characteristic dimensions are equal or less than 1 mm. This aspect leads to high surface area to volume ratio enhancing noticeably mixing and heat transfer capabilities compared to classical chemical reactors. In this work it’s been explored the possibility to produce, with such microdevices, chitosan particles in the sub-micron region and control their dimension through different fluid dynamics regimes. To achieve this result it has been used Computational Fluid Dynamics (CFD) Software. Through photos of flow regimes in the experimental setup and comparison with CFD models it has been possible to validate the model and investigate in detail the relation between particle size and fluid dynamics inside the microdevice.