Hydrodynamics and reaction studies in a layered herringbone channel

The performance of a consecutive reaction of the type A -> B-k1 -> C-k2 was studied in two reactor configurations. A layered herringbone channel, which consists of two rectangular channels and a middle layer containing machined-through herringbone structures, is compared with an unstructured rectangular channel. It was found that when the reactants are not premixed before the inlet, the layered herringbone configuration shows an improved performance compared to the rectangular channel giving a 40% increase in the maximum amount of intermediate produced. The maximum concentration of intermediate is obtained at lower residence times, which indicates that reactor volume could be decreased compared to the rectangular channel. The maximum amount of intermediate and the conversion at which this maximum occurs is dependent also on the ratio (k(2)/k(1)) which in this work is 0.05. Good mixing characteristics and narrow residence time distribution (RTD) are responsible for the improved behaviour in the layered herringbone channel. When the reactants are premixed before the inlet the differences are more subtle, indicating that the improved reaction behaviour in the layered herringbone channel is mainly due to good mixing and to a smaller extent to narrow RTDs. Residence time distributions were calculated numerically via CFD and particle tracking methods. The RTDs for the layered herringbone channel were found to be narrower as compared to the rectangular one. The model of axial dispersion exchanging mass with a stagnant zone was used for the modelling of the RTD. It was found that the model parameters could be calculated directly from hydrodynamic data obtained from CFD calculations, without the need of particle tracking algorithms. Concepts from turbulent theory were employed for the calculation of an effective diffusion coefficient that replaced the stirring effect of the herringbones. This procedure greatly simplifies the theoretical calculation of RTDs and reaction conversions. (C) 2010 Elsevier B.V. All rights reserved.