(185d) Modelling the Hydrodynamics, Transport and Reactions in Multiphase Microreactors

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.