A new numerical method for axial dispersion characterization in microreactors

Axial dispersion is a key phenomenon in reactor engineering that can affect yield and selectivity when reactions are carried out. Therefore its characterization is necessary for an adequate modelling of the reactor. The development of compact reactors to fit with process intensification expectations requires the use of characterization methods adapted to small-scale devices. An original method not-frequently used up to now for the estimation of axial dispersion coefficients is presented and applied to millimetric wavy channels. It is based on CFD simulations to calculate velocity and concentration fields from which axial dispersion coefficient can be estimated. This method is used to predict the impact of the wavy channel geometry and of the fluid velocity on axial dispersion in laminar flow regime. The investigated geometrical parameters are the hydraulic diameter (2-4 mm), the cross-sectional aspect ratio defined as the ratio between the channel width and its depth (0.25-1) and the internal curvature radius of the bends (2-3.4 mm). The range of Reynolds number considered is Re = 70-1 600. Axial dispersion coefficient increases with velocity, values range from 2.8 · 10−4 to 3.2 · 10−3 m2·s−1. It appears that axial dispersion varies slightly in function of the channel hydraulic diameter. Square wavy channels generate less axial dispersion than rectangular wavy ones. Finally, axial dispersion coefficient increases with the internal curvature radius which shows the positive impact of sharp bends to reduce axial dispersion effect.