Abstract for the AIChE 2015 Annual Conference
Modelling the Hydrodynamics, Transport and Reactions in Multiphase Microreactors
Lu Yang, Yanxiang Shi, and Klavs F. Jensen
Department of Chemical Engineering, MIT, 77 Massachusetts Avenue, Cambridge MA 02139
On-chip flow chemistry synthesis has advanced rapidly in recent years as a fast and effective means to discover and screen suitable reaction candidates for continuous pharmaceutical production. Among the many chemical reactions, multiphase reactions constitute a major category with important industrial applications. The extent of multiphase reactions is often limited by the innate mass transfer resistance across phase boundaries, and microreactors have been shown to effectively enhance the rate of mixing, therefore improving the efficiency of such reactions. However, compared to single-phase flow chemistry systems, many unknowns remain in the design, optimization and scale-up of multiphase microreactors – primarily due to the complex nature of the multiphase flow
Towards the goal of increasing understanding of the mass transfer enhancement of multiphase flows in microreactors, we have studied hydrodynamics, transport and reactions processes in the segmented flow in an open channel and in a microreactor filled with posts. High-resolution simulations were performed using a series of C++ solvers developed in OpenFOAM. To accelerate computing, the solvers were designed to run in parallel on a high performance computing cluster. Computational fluid dynamic (CFD) simulations of multiphase flow using the volume-of-fluid (VOF) method were in good agreement with experimental observations (Figure 1) and analytic solutions. Based on the validated hydrodynamic solver, we introduced a scalar transport equation with sink/source terms using the one-fluid formulation, which facilitated the simultaneous capturing of multiphase hydrodynamics, mass transfer and reactions. In tandem with the numerical simulations, we also performed mass transfer analysis of multiphase flows based on the penetration theory and a two-stage theory, which further examined the mechanism of mixing enhancement in microreactors, and revealed a two-fold increase in mass transfer coefficients in the post microreactors compared to open channels. The deepened physical understanding of the mixing processes in multiphase microreactors enabled predictions of reactor performance, and the same CFD-based strategy can be readily applied to study other types of microreactor configurations.
Figure 1 (a) Computational fluid dynamic (CFD) simulation and (b) laser-induced fluorescence (LIF) visualization of segmented flow in the post microreactor. The two immiscible phases can be either gas/liquid or liquid/liquid.