(519a) Process Intensification: Mass Transfer Characterization of Slug Flow in a Narrow Channel Reactor

Introduction

This paper will present experimental findings of a
systematic study carried out to experimentally determine the mass transfer
performance of slug flow in a narrow channel reactor.  The influence of liquid viscosity on
mass transfer rate will be highlighted by developing an empirical correlation
involving Reynolds number, Schmidt number, Bond number, bubble length and slug
length.  This data is being
currently used by the process intensification research group at Clarkson to
develop and evaluate the performance of several intensified reactors using
hydraulic path lengths in the range of 500 to 1000
microns.

Background

Slug flow in capillaries is defined as a cocurrent flow
of gas and liquid phase having gas bubbles separated from the wall by a thin
liquid film and separated from each other with liquid slugs. The significance
behind the study of slug flow in capillaries is their ability to achieve high
mass transfer rates. Several authors have characterized the hydrodynamic
properties of slug flow in capillaries with varying viscosities [1,2,3,4]. Only
two authors developed mass transfer model and their models are based on the
viscosity of water [5,6]. The aim of this study is to develop a mass transfer
model for a wide range of viscosities during slug flow in capillaries.  This limitation has hindered the
progress of narrow channel reactors in gas liquid mass transfer activities
involving removal of monomers from pre-polymers which have significantly higher
viscosities than water.

Description of the research

An experimental arrangement has been developed to
analyze mass transfer between bubbles and liquid during slug flow in a narrow
channel reactor. A square channel reactor made of plexiglass having 0.7 mm
hydraulic diameter and a length of 27 cm was used in this investigation. Mass
transfer of oxygen from a liquid phase containing a mixture of water and
glycerol with different compositions and nitrogen was studied. The initial and
final concentrations of dissolved oxygen in the liquid phase were measured using
a dissolved oxygen probe. By means of video capture device bubble velocity,
bubble length and slug length were measured.

An empirical mass transfer
model has developed as a function of Reynolds number, Schmidt number, Bond
number, bubble length and slug length from the experimental results. Using CFD,
a theoretical model of the system has also been developed and has been used to
understand the experimental results.

References

1.      
Suo, M., and Griffith, P.,
1964. Two-phase flow in capillary tubes. J.of Basic Engng. 86,
576-582.

2.      
Thulasidas, T.C., Abraham,
M.A., Cerro, R.L., 1994. Bubble-train flow in capillaries of circular and square
cross section. Chem. Engng Sci. 50, 183-199.

3.      
Thulasidas, T.C., Abraham,
M.A., Cerro, R.L., 1997. Flow patterns in liquid slugs during bubble-train flow
inside capillaries. Chem. Engng Sci. 52, 2947-2962.

4.      
Triplett, K.A.,
Ghiaasiaan, S.M., Abdel-Khalik, S.I., Sadowski, D.L., 1999. Gas-liquid two-phase
flow in microchannels part 1: two-phase flow patterns. Int. J. Multiphase Flow.
25, 377-394.

5.      
Thulasidas, T.C., Abraham,
M.A., Cerro, R.L., 1999. Dispersion during bubble-train flow in capillaries.
Chem. Engng Sci. 54, 61-76.

6.      
Gruber, R., 2001. Radial
mass transfer enhancement in bubble-train flow. Ph.D Thesis, RWTH Aachen,
Germany