Abstract
High mass transfer rate is a key advantage of microreactors however, under their characteristic laminar flow, it is dominated by slow diffusion rather than fast convection. In this paper, we demonstrate how the configuration of the inlet, i.e. mixers, can promote different flow patterns to greatly enhance mixing efficiency downstream. A systematic evaluation and comparison of different widely adopted mixers as well as advanced designs is presented using a combination of computational fluid dynamics (CFD) and backward particle tracking to accurately calculate diffusion, in the absence of numerical diffusion (false diffusion). In the method, the convection contributed concentration profile is obtained by tracking sampling points from a cross-sectional plane to the inlet point, and diffusion is estimated subsequently. In conventional T- and Y-mixers, the shape of channel, circular or square, is key with only the latter promoting engulfment flow. In cyclone mixers, the resulting average inlet velocity, independent of Reynolds number or geometry, is the dominating design parameter to predict mixing efficiency. This work will serve as a guideline for the design of efficient flow systems with predicted mixing as a way of maximising selectivity and product quality.
Highlights
Over the last two decades, microreactors have been deployed for a large number of applications, from organic reactions [1] to material synthesis [2, 3]
Mass transfer under laminar flow is dominated by diffusion, which even with short mixing distances associated to small diameters, is normally slow compared to convection [6]
The fluid dynamics and mass transfer of each configuration was evaluated using the Navier-Stokes equation available on ANSYS Fluent combined with a backward particle tracking approach as described in the experimental section [14], to avoid the overestimation of the diffusion component by the Eulerian approach in what is called numerical diffusion
Summary
Over the last two decades, microreactors have been deployed for a large number of applications, from organic reactions [1] to material synthesis [2, 3]. Experimental research methods to investigate mass transfer efficiency such as the Villermaux-Dushman reaction [11] and the experimental determination of concentration distribution using tracers [12, 13] are difficult to deploy in such short times and small length scale. In this context, computational fluid dynamic calculations based on the Lagrangian scalar transport equations [14] can provide key information of the mixing efficiency. Tmixers and Y-mixers with circular channel are commercially available but rarely studied
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