(409d) The Effect of Micro-Post Configuration on Interfacial Mass Transfer in a Milli-Scale Reactor

Authors: 
Mottaghi, M., KU Leuven
Kuhn, S., KU Leuven
Stefanidis, G. D., Katholieke Universiteit Leuven

Mass
transfer across fluid–fluid interfaces plays an important role in the chemical
and pharmaceutical industries. It is therefore of major importance to develop
both understanding and predictive simulation tools for the design of optimal
multiphase flow reactors [1]. In this context, Computational Fluid Dynamics
(CFD) can be used as tool in combination with experimental studies to increase
the understanding of the interfacial mass transfer in milli-scale reactors with
obstacles (here: micro-posts) inside.

To properly
describe the local interfacial mass transfer phenomena, a coupled problem,
including momentum and mass transport at and around moving interfaces has to be
solved. These problems are challenging due to the presence of forces acting at
different scales, i.e. viscous forces, interfacial tension and wall adhesion.
In addition, selecting a proper numerical method is also crucial as some
numerical techniques have drawbacks which can impair the accuracy of the
results, e.g. the generation of spurious currents in the volume-of-fluid (VOF)
approach and lack of mass conservation in level set (LS).

Coupling VOF and LS
is a promising approach which can reduce the extent of spurious currents as
well as sharpening the interface definition [2]. In this study, we have
developed an algorithm based on the coupled VOF-LS method, combined with a
dynamic contact angle boundary condition, see Figure 1. We have furthermore
implemented a species transport equation that is valid throughout the entire domain
and accounts for species transfer across the interfaces, the continuity of the
fluxes and the Henry’s law have been considered (i.e. transforming the
concentration jump at the interface into a continuous effect) [3].

The
developed solver is employed to predict the effect of various micro-post
configurations (diameter 0.35 mm) on interfacial mass transfer in a
milli-reactor (width 5 mm, depth 0.7 mm), see Figure 2. For validation of the
simulations, selected micro-post configurations are fabricated with 3D printing
(stereolithography), and the two-phase flow hydrodynamics and interfacial mass
transfer are experimentally characterized using imaging techniques (PIV and
PLIF).

 

Figure 1. Evolution
of the bubble breakup in a microfluidic T-junction; left: simulation results,
right: experimental images reported in [4].

Figure 2. Droplet
dynamics and interfacial mass transfer in a micro-post milli-scale reactor: a)
phase fraction; b) concentration profile; c) interfacial fluxes.

We will
report in detail on the developed solver, and will highlight the influence of
micro-post designs in milli-scale reactors to achieve control of two-phase flow
hydrodynamics and interfacial mass transfer.

Keywords

Interfacial
mass transfer; milli-reactor; CFD

1-    
Yang L., Shi Y.,
Abolhasani M., Jensen K. F., Lab On a Chip Vol. 15 (2015) 3232-3241.

2-    
Dianat M.,
Skarysz M., Garmory A., International Journal of Multiphase Flow Vol. 91 (2017)
19-38.

3-    
Marschall H.,
Hinterberger K., Schuler Ch., Habla F., Hinrichsen O., Chemical Engineering
Science Vol. 78 (2012) 111-127.

4-    
Wang X., Zhu Ch.,
Wu Y., Fu T., Chemical Engineering Science Vol. 132 (2015) 128-138.