Abstract Summary (Max 250 words)
Mass transfer plays a crucial role in fast chemical reactions. Poor mixing reduces conversion rates and product yields and negatively affects the distribution of reaction products when the reaction rate is fast relative to mixing times. Accordingly, fast test reactions are usually employed to characterise and quantify mixing, enabling assessment of the influence of flow regime on the operation of chemical reactors. Computational Fluid Dynamics (CFD) was used to simulate a competitive/consecutive reaction system, the Bourne test reaction, in a NETmix mesostructured reactor. A mesh independence test was performed to identify the largest element size that ensured that chemical reaction CFD results were independent of mesh resolution. The effects of Reynolds number, Re, and reactor topology on secondary product selectivity, quantified by a segregation index parameter, were investigated. Results show that increasing Re intensified molecular contact between reactants, hindering the formation of the secondary product. Three regimes were identified: a segregated regime, where no convective mixing in the NETmix chambers occurred; a chaotic regime, where advective mixing promoted the homogenisation of reactant species; and a turbulent regime, where product distribution was no longer micromixing-controlled. Topology studies revealed that NETmix configurations with spherical chambers and cylindrical channels exhibited less selectivity than those with cylindrical chambers and prismatic channels, achieving lower segregation indexes at similar Re values. Overall, the developed CFD model successfully describes the effects of reactor design and operating conditions on mixing-controlled fast reactions in NETmix reactors, providing insight into mixing phenomena from macro to molecular scale.
