Analysis of a microreactor for synthesizing nanocrystals by computational fluid dynamics

Abstract

Microreactors eliminate batch-to-batch variability and allow better control over nanocrystal synthesis. A serpentine microreactor fabricated by femtosecond laser ablation is presented and characterized by computational fluid dynamics, since the micro channels show a trapezoidal cross-section mainly due to the relatively high numerical aperture of the focusing lens. Mixing, macro and micro, throughout the device was investigated for inlet flow rates between 10–500 mL min 1 and the injection of an inert tracer with the same transport properties of water. The simulation of the whole microreactor enabled the analysis of the formation and destruction of structures. For instance, secondary flows played a major role in mixing behaviour: small flow rates did not promote mixing of the tracer and a stream of pure water even after 43 curved segments, while they were perfectly mixed after 9 segments for higher flow rates. According to the mixing index, the maximum effect of convective mixing was achieved for an inlet flow rate of 250 mL min 1. Tracer dispersion and the mixing index guided a scale-up process of the microreactor, optimizing the number of curved segments while increasing total throughput. The upscaled design exhibited mixing saturation at 400 mL min 1 and promoted better control of residence time to allow nanocrystal growth.