Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: 2.6.2 - Experiments on Fluid Dynamics and Mass Transfer of Annular Film Flow on a Vertical Wire
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 Material Information
Title: 2.6.2 - Experiments on Fluid Dynamics and Mass Transfer of Annular Film Flow on a Vertical Wire Multiphase Flows with Heat and Mass Transfer
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Grünig, J.
Horn, S.
Skale, T.
Kraume, M.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: annular film flow
mass transfer
vertical wire
 Notes
Abstract: The aim of this work is to examine the feasibility of a novel packing which consists of bundles of vertical wires. It is expected that it offers higher loading ranges, lower specific pressure drop and a uniform radial liquid distribution over the whole packing length. Since the packing has elements with highly curved surfaces, common physical relations for planar liquid films can not be applied to describe the film flow inside the packing. The curvature promotes the undulation of the film and the formation of “beads” that flow on top of a thin basis film. To gain insight into the film flow and to get information about the potential separation efficiency of such packing, experiments on fluid dynamics and mass transfer on a single vertical wire in a counter current gas flow are carried out. The experimental setup consists of a vertical rectangular glass channel (1000 mm x 20 mm x 20 mm) with the wire (ø 1 mm) clamped in the center. With a digital high-speed camera and an image processing software tool, the local film thickness and the bead velocity are observed at different vertical positions. From this information, an effective interfacial area for the film is calculated. The gas-side mass transfer is observed by measuring the increase of the air humidity due to the evaporation of water or aqueous polyvinylpyrrolidone (PVP) solutions with higher viscosity. The liquid-side mass transfer is investigated by desorption experiments with the system CO2-water/air. The results indicate a significant influence of the gas and liquid load on both the fluid dynamics and mass transfer. Although the bead thickness rises with increasing gas load, the liquid hold-up, bead velocity and the effective film surface area are primarily influenced by the liquid load. Due to the curvature of the film, the effective surface area can exceed the surface area of the dry wire significantly. The load limits vary for different liquids and are higher than those of conventional packings.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
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Resource Identifier: 262-Gruenig-ICMF2010.pdf

Full Text

Paper No 7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Experiments on fluid dynamics and mass transfer of annular film flow on a vertical wire


J. Grunig, S. Horn, T. Skale and M. Kraume

Technische Universitat Berlin, Chair of Chemical and Process Engineering
AckerstraBe 71-76, 13355 Berlin, Germany
jochen.gruenig @tu-berlin.de


Keywords: annular film flow, mass transfer, vertical wire

Abstract

The aim of this work is to examine the feasibility of a novel packing which consists of bundles of vertical wires. It is expected
that it offers higher loading ranges, lower specific pressure drop and a uniform radial liquid distribution over the whole packing
length. Since the packing has elements with highly curved surfaces, common physical relations for planar liquid films can not
be applied to describe the film flow inside the packing. The curvature promotes the undulation of the film and the formation of
"beads" that flow on top of a thin basis film. To gain insight into the film flow and to get information about the potential
separation efficiency of such packing, experiments on fluid dynamics and mass transfer on a single vertical wire in a counter
current gas flow are carried out. The experimental setup consists of a vertical rectangular glass channel (1000 mm x 20 mm x
20 mm) with the wire (o 1 mm) clamped in the center. With a digital high-speed camera and an image processing software tool,
the local film thickness and the bead velocity are observed at different vertical positions. From this information, an effective
interfacial area for the film is calculated. The gas-side mass transfer is observed by measuring the increase of the air humidity
due to the evaporation of water or aqueous polyvinylpyrrolidone (PVP) solutions with higher viscosity. The liquid-side mass
transfer is investigated by desorption experiments with the system C02-water/air. The results indicate a significant influence of
the gas and liquid load on both the fluid dynamics and mass transfer. Although the bead thickness rises with increasing gas load,
the liquid hold-up, bead velocity and the effective film surface area are primarily influenced by the liquid load. Due to the
curvature of the film, the effective surface area can exceed the surface area of the dry wire significantly. The load limits vary for
different liquids and are higher than those of conventional packing.


Introduction

The principle of falling liquid films is applied in many
devices in the chemical industry. One of them is the packed
column were a liquid film runs over the surface of struc-
tured packing elements. Commercially available packing
are optimized to achieve high separation efficiencies at a
low specific pressure drop and a wide range of loadings.
However, one problem is maldistribution; meaning
non-uniform distribution of the liquid in the packing so that
the liquid has to be redistributed after a certain packing
height.
There have been considerations that a packing that consists
of bundles of parallel vertical wires could be advantageous
compared to conventional packing. Unlike random or
corrugated sheet packing, the wire packing would have
straight gas channels which probably cause a lower pressure
drop over the packing and offer higher load limits. As radial
mixing is inhibited by the structure of the wire packing, the
maldistribution of the liquid will be reduced significantly.
Thus, a redistribution of the liquid is not necessary. On the
other hand due to the lack of internal mixing the wire
packing requires a highly uniform initial liquid distribution
by a special distributor.
The construction and assembly of the packing and the dis-
tributor pose problems that still have to be solved, although
there are several design suggestions from different authors
(Nagaoka and Manteufel, 2003; Migita, Soga et al., 2005;
Vogelpohl, 2006; JOdecke, Schuch et al., 2008). However,
the crucial question is if the separation performance of the


wire packing is competitive to conventional packing,
which depends on the specific surface area, the mass
transfer coefficients and the operating limits. These pa-
rameters are related to the fluid dynamics and physical
properties of the particular system.
To understand the behaviour of fluid dynamics and mass
transfer in detail, our experiments focus on a single packing
element which is represented by one vertical wire.

Liquid film flow on wires and threads
Most investigations on liquid film flow are conducted with
tubes of large diameters compared to the film thickness so
the film can be considered as planar. Fundamental theo-
retical studies were made by Nusselt (1916) who charac-
terized the laminar film flow on planes. Different authors
used intrusive (Brauer, 1956) and non-intrusive (Hiby,
1968; Chu and Dukler, 1974; Adomeit and Renz, 2000;
Mouza, Vlachos et al., 2000; Lel, Al-Sibai et al., 2005;
Helbig, 2007) measurement techniques to determine the
film thickness and the wave velocities.
However, when the film thickness is in the same order of
magnitude as the cylinder radius the curvature can not be
neglected. Rayleigh (1878) gave a mathematical description
of the instability of a cylindrical liquid jet that explains the
formation of waves as a result of capillary forces. (Grabbert
and Wiinsch, 1973) theoretically compared falling films on
different geometries and observed the influence of the
curvature on the fluid dynamics of smooth films. Goren
(1962) made a theoretical analysis of the instability of a
liquid film on a cylinder and calculates the wavelength with






Paper No


the fastest growing amplitude. Since he focused on liquids
of high surface tensions and viscosities and small cylinder
diameters, he could neglect the gravitational forces. In the
work of Lin and Liu (1975) the authors also considered the
gravitational forces in their theoretical model to describe the
coating of wires and tubes by withdrawing them from a
liquid pool. They found that the film is unstable at any set of
parameters what causes the formation of waves. Trifonov
(1992) calculated wavy regimes of viscous liquid films on
wires. The results showed a significant influence of the
curvature on the wave formation. Recent investigations on
the instabilities of annular films were presented e.g. by
Kliakhandler et al. (2001), Craster and Matar (2006) and
Duprat et al. (2009). They performed numerical simulations
as well as experiments with viscous fluids on single wires. A
comparison of bead frequency and bead thickness showed a
very good agreement and the simulations indicated an inner
circulation in the beads at higher flow rates. Hattori et al.
(1994) proposed the use of wires in gas-liquid contact de-
vices for heat and mass transfer. They argued that due to the
formation of liquid beads the contact device would have all
advantages of a spray column (low pressure drop and large
film surface area), but at the same time the wires reduce the
velocity of the beads and therefore enhance their contact
time with the gas phase. In addition, the wires induce an
internal circulation in the beads which also promotes the
heat and mass transfer.

Mass transfer of liquid films
Most mass transport measurements on liquid films are
conducted in wetted wall columns. The gas-side mass
transfer rate was investigated by numerous researchers, a
well-known study is that of Gilliland and Sherwood (1934)
in which the evaporation of different liquids into air was
observed. However, the influence of the liquid flow rate on
the mass transfer rate was not investigated. Braun and Hiby
(1970) studied the gas-side mass transfer with the absorp-
tion of ammonia in diluted sulfuric acid. They also consid-
ered the influence of humidity, liquid flow rate and column
height. The rate of gas-side mass transfer of liquid films on
strongly curved surfaces has not been investigated until
now.
The liquid-side mass transfer has also been investigated by a
large number of authors, e.g. Henstock and Hanratty (1979);
although they used cylindrical columns in their experiments
they also considered the film as planar. The absorption of
CO2 into a film of water and aqueous monoethanolamine
solution on a thin wire was investigated by Chinju et al.
(2000). Grabbert (1974) studied the absorption of CO2 in
water films on cylinders of different diameters and observed
that the mass transfer is enhanced by increasing curvature of
the surface. Migita et al. (2005) build a prototype of a wet-
ted wire column in laboratory scale and performed mass
transfer experiments with the model systems used by Chinju
et al. (2000). They compared the results with random
packing elements and achieved comparable mass transfer
rates at significantly lower pressure drop. In all these above
mentioned experiments the gas load was comparatively low
and an interaction of liquid and gas phase fluid dynamics
was not observed. Mass transfer experiments at high gas
and liquid Reynolds numbers were carried out by Nielsen;
Kiil et al. (1998) in a wetted wall column, in this range of
liquid and gas load no data for the wire geometry is avail-


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

able.
Thus, there is still a lack of experimental data for highly
curved geometries with gas and liquid velocities that are
commonly applied in packed columns. It is the aim of this
study to measure the relevant parameters for packed column
characterization in the appropriate parameter range.

Materials and Methods

Experimental set-up
The flow sheet of the experimental set-up is shown in Fig. 1.
The main element is a vertical glass channel (1000 mm x
20 mm x 20 mm) with a centrically fixed wire (0 1 mm).
Liquid is pumped from a storage tank to the top of the
channel. The liquid is distributed on the wire inside the
channel head and runs down as annular film and gets into
contact with the gas phase. At the channel bottom, the liquid
is collected and fed back into the storage tank. Air is guided
in the bottom of the channel and flows upwards in counter
current before it exits into the environment. The tempera-
tures of liquid and gas phase are regulated by heaters and
measured at the in- and outlet of the channel. A high speed
camera and a synchronized lighting are used to detect the
film thickness and the bead velocity at different vertical
positions. With an image recognition software tool (Image
ProPlus V5) the analysis of the images is automated. A
more detailed description of the test facility and the optical
measurement methods are given in (Griinig, Kraume et al.,
2007)


Fig. 1: Sketch of the test facility.

The properties of the used liquids are listed in Tab. 1. Water
and aqueous polyvinylpyrrolidone (PVP) solutions were
used as liquids. The PVP solutions were used to measure the
mass transfer at higher viscosities. Measurements showed
that the flow behavior is that of a Newtonian fluid and sur-
face tensions and densities are only slightly different from
water. The addition of PVP to water had also no measurable
effect on the saturation vapor pressure.

Tab. 1: Physical properties of the tested liquids at 20 OC.


[kg/m3]
Water 998T
PVP sol. 3 wt % 1009t
PVP sol. 6 wt % 1016
* (Wohlfarth and Wohlfarth,
1994), Own measurements


1 oa
[mPa s] [mN/m]
1.0 72.7*
11.8t 68.0t
49.0 68.3
1997), (VDI-Wirmeatlas,





Paper No


Interfacial area and liquid hold-up
The interfacial area is esti-
mated from the temporal local
S_ film thickness 6 and the mean
bead velocity wE. To account
for the variation of the film
profile and the bead velocity
Az = h over the wire length, film
Thickness and bead velocity
data from different vertical
positions are analyzed
(z = 130, 330, 730 mm). With
W-B the mean bead velocity, the
WI time-dependent film thickness
data is converted into a spatial
film profile. With this data,
Fig. 2: Annular axially symmetric annular
section model for film sections are defined which
surface estimation represent the film on the wire
(Fig. 2). They have the shape
of truncated cones with a cylindrical hole of wire diameter.
The volume Vseg of these elements is calculated as follows:

seg =-(R2 +RR2 +R2) --d4 (1)
3 4

The height h of these elements is calculated from the mean
bead velocity wB and the frame ratefR.

h W (2)
fR
Thus, the length related liquid hold-up HU1 can be calcu-
lated by summarizing the volume of the liquid elements and
referring them to the distance that the beads would have
covered during the record time tR.
2'hN 2 3
S (Ri2 +Ri Ri+ +Ri+1- d2)
HU1 3 i=1 4 (3)
WB tR
In a similar manner, the overall film surface area is esti-
mated by the summation of the lateral surface area of the
elements.
N
x 7 m (Ri +Ri+1)
i=1
WB .tR (4)
with
m = V(Ri Ri+1) 2 + 2




HU +dw dwd
6 L (6)
71 2 2

Gas-side mass transfer
The gas-side mass transfer is obtained by measuring the
evaporation into the gas phase. The inlet and outlet con-
centrations of water the gas phase are measured with the
dew point hygrometer to determine the molar flow rate by a
molar balance:
NA = g (CAg,out CAg,in) (7)
With the information of gas inlet and outlet concentrations


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

and the assumption of the validity of the ideal gas law, the
mean logarithmic concentration difference can be formu-
lated in terms of partial pressures at the gas inlet and outlet
as:
(PA0 PA)in -(PAO -PA)out
In (PA -PA)in (8)
(PAO -PA)out
The partial pressures PAO at the surface are the vapour
pressures at liquid temperature calculated with the Mag-
nus-equation. With this information, the gas-side mass
transfer coefficient is calculated as follows:
Pg A N R Tg,m PBM (9)
p-Afw APA,n
This equation considers the Stefan diffusion according to
Gilliland and Sherwood (1934) where PBM is the logarithmic
mean partial pressure of the inert gas (air) which is calcu-
lated as
PAO,in +PAO,out + PA,in +PA,out
PBM =P- (10)
4

Liquid-side mass transfer
The liquid-side mass transfer was determined by measuring
the desorption of CO2 from water into air. Water was en-
riched with CO2 from a gas bottle. Unlike displayed in the
sketch of the test facility in Fig. 1, the liquid was not recy-
cled but discharged into a collecting tank. The storage tank
was replaced by a 5 L plastic bag so the gas phase could be
removed completely. By this means the desorption of CO2
from the liquid before entering the channel was avoided.
Liquid samples where taken at the inlet and outlet of the
channel and were analyzed for their CO2 concentration.
To determine the liquid concentration of CO2, the samples
of defined Volume V ,p where stripped in a washing flask
with air which was guided to a gas analyzer (S710, Maihak
GmbH) afterwards. Volume flow rate, temperature, pressure
and the gas molar fraction of CO2 of the gas flow were
recorded over the time. Before a liquid probe is put into the
washing flask, the molar fraction stays at a constant value of
yco2 z 400 ppm which is the natural value of the stripping
gas. The addition of the liquid probe causes a peak in the gas
molar fraction which falls back to the initial value yc02. The
amount of CO2 that was stripped from the probe can be
determined by the peak area similar to a gas chromatogram:
co,,strip = (Yco2 (t) -Yco, )gdt (11)
The molar flow rate of the stripping gas is calculated with
the ideal gas law:

g -=Pg (12)
TgR
Since the strip gas has an initial content of CO2, the liquid
sample is stripped to the correspondent liquid equilibrium
concentration which is described by Henry's law:
_* p.Yco,
x P =YO2 (13)
Ce2 fH
Because x *co2 is relatively small, the remaining concen-
tration of the liquid probe can be evaluated as
-* -* Pl
CC02 xCOU2 (14)






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


The mean liquid concentration of the probe can then be
determined by
NCO2,,strip
cco2 + CC2 (15)
1,P
The liquid-side mass transfer coefficient is calculated as

P l (lCO2,in CCO02,out) (1
P1 =, (16)
Af,w Acln
whereas the logarithmic concentration difference is given
by


(ECO2 CO2 )in


(cCO2 CO2 )out


n (cCO,-02CO)in (17)
In -
(CCO2 -CO2out)
The equilibrium concentrations C*C02 of the liquid are cal-
culated with Henry's law from the correspondent CO2
concentrations in the gas phase at the inlet and outlet of the
channel which are directly measured with the gas analyzer.
An analysis of error determined an overall measurement
error of 6 %.

Results and Discussion

Fluid dynamics
Fig. 3 gives an example of a film thickness recording (PVP
50 mPa s, z = 730 mm) at two different gas loads. The beads
appear as peaks in the film thickness profile and can clearly
be distinguished from the basis film. In this case, a regular
bead pattern is disturbed at high gas loads leading to an
irregular film profile. When plotting the mean values of the
basis film and bead thickness against the gas load (Fig. 4), it
reveals that the basis film thickness does not change sig-
nificantly as the gas load increases. With increasing liquid
viscosity the basis film thickness rises. In contrast to the
basis film the bead thickness rises with increasing gas load.
This is caused by an increasing bead volume and a bead
deformation towards more compact shape. The sudden
change of basis film and bead thickness for PVP 50 mPa s at
a gas load of F = 5.6 Pa 5 can be explained by the transition
from regular to irregular flow (see also Fig. 3).
a) F = 0 Pa5 b) F =6.4 Pa 5
2000

1500

1000
.c
S500 -
LL ,
0----------------


0 1
Time t [s]


20 1
Time t [s]


Fig. 3: Recording of the local film thickness at the ver-
tical position z = 730 mm for PVP 50 mPa s,
Bw = 0.2 m3/(m h) for no gas load (a) and high gas load (b).


1600
1400
S1200
1000 t
S800
S600 9 =20 C -0Water
400 Bw = 0.2 m3/(m h) PVP 12 mPa s
S200 z = 730 mm PVP 50 mPa s
m 0
0 2 4 6 8
Gas load F [Pa 5]

Fig. 4: Basis film thickness and bead thickness de-
pending on the gas load for different liquids.

In Fig. 5 the mean bead velocity depending on the gas load
for different liquids and liquid loads is displayed. The bead
velocity is not clearly influenced by the gas load. This
means that the beads are not decelerated by the gas flow.
With decreasing viscosity and higher liquid loads larger
bead velocities are achieved. Remarkably, very high gas
loads can be achieved compared to the range in which
common packing are usually operated.


90
80
E 70
o
60
>3 50
o 40
S30
2 20
m10
0


Gas load F [Pa0 5]

Bw [m3/(m h)] 0.2 0.8 4= 20 C
Water o z = 730 mm
PVP12 mPas A
PVP 50 mPas A
Fig. 5: Bead velocity depending on the gas load for
different liquids and liquid loads.

Fig. 6 shows the interfacial area against the gas load for
different liquids and liquid loads. The interfacial area was
calculated according to the model shown in Fig 2 involving
the film thickness and bead velocity data. It appears that the
effective film surface area is significantly higher than the
surface of the dry wire Aw. Although the bead thickness
rises with increasing gas load, the results indicate that the
gas load has no significant influence on the film surface area.
However, it becomes apparent that the interfacial area in-
creases both with rising viscosity and liquid load.


Paper No


I A


p p p p =






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


0 2 4 6 8
Gas load F [Pa 5]
Fig. 6: Interfacial area depending on the gas load for
different liquids and liquid loads.

In Fig. 7 the liquid hold-up depending on the gas load for
different liquids and liquid loads is plotted. The liquid
hold-up rises with increasing viscosity and liquid load but is
only slightly influenced by the gas load. This is consistent
with behavior of packed columns in the loading range.
5000
4500
E
_c 4000
3500
I 3000
P 2500 '17. .
2000
-r-

ID 1000
500
0
0 2 4 6 8
Gas load F [Pa 5]
Bw [m3/(m h)] 0.2 0.8 1 =20 C
Water o A
PVP 12 mPa s A
PVP 50 mPa s A
Fig. 7: Liquid hold-up depending on the gas load for
different liquids and liquid loads.

In summary, it can be said that the interfacial area and the
liquid hold-up are not significantly affected by the gas flow.
An increasing gas load causes the liquid to distribute across
fewer but larger beads. With the overall liquid hold-up re-
maining constant this means that the distance between the
beads increases at higher gas loads. This is consistent with
the observation that the bead frequency decreases with
rising gas load.

Gas-side mass transfer
The results of the gas-side mass transfer measurements are
shown in Fig. 8. The gas-side mass transfer coefficients
which are related to the interfacial area are plotted against
the gas load for different liquids and liquid loads. As the gas
load rises, the mass transfer coefficients increase. It appears
that the mass transfer coefficients also increase with de-
creasing liquid viscosity. This is probably caused by a
higher waviness, indicated by the basis film and bead
thickness (see Fig. 4). Additionally, the bead velocity at
lower viscosity is higher resulting in an increased relative


velocity between beads and gas phase. When comparing
different liquid loads, the PVP-solutions show minimal
difference in mass transfer coefficients at lower gas load. At
higher gas loads the mass transfer is enhanced for higher
liquid loads. However, the mass transfer coefficients of
water deviate significantly for different liquid loads over the
whole gas load range. The dependency of the liquid load can
be explained by the enhancement of turbulence in the gas
flow due to the change of the waviness of the liquid film.
0.06
S Bw [m3/(m h)] 0.2 0.8
0.05 Water o A
PVP12mPas A
5 0.04 PVP 50 mPa s s

0.03 -

0.02 -

E 0.01
0

3 0 2 4 6 8
Gas load F [Pa 5]
Fig. 8: Gas-side mass transfer coefficient depending on
the gas load for different liquids and liquid loads.

In Fig. 9 the Sherwood-number for gas-side mass transfer is
plotted against the Reynolds-number for different liquids.


45
-o
E 40
S35
,30
CO 25
C,
-g 20
, 15
0 10
C 5
CO 0


0 2000 4000 6000
Reynolds-number Re, = w, bc/v,


8000


Water PVP12mPas PVP 50 mPa s
Experiments A A A
Braun & Hiby (1970) 0 0*
Bravo & Fair (1982) x x x
Fig. 9: Mean Sherwood-number for gas-side mass
transfer depending on the Reynolds-number for different
liquids. Comparison with correlations for mass transfer in
tubes (Braun and Hiby, 1970) and inside structured pack-
ings (Bravo and Fair, 1982).

A correlation from Braun and Hiby (1970) for the gas-side
mass transfer of liquid films in tubes in counter current
configuration is added to the diagram:

0.4 0.16 0.44 (Lw '0.75 (18
Sh, =0.015Re4 Re0 Sc44 1+5.2 (18)
g g 1 g bc

Additionally, a general correlation for the gas-side mass
transfer inside the gas passages of structured packing is
added (Bravo and Fair, 1982), which is independent from
the liquid load:


Paper No


Bw = 0.8 m3/(m h)
& = 20 C


S- 4
- ..






Paper No


Sh =0.0388Re.8 Sc 0333 (19)
It is apparent that the mass transfer of the wire film flow is
higher for all liquids compared to the film flow inside tubes.
This can be seen as an effect of the higher waviness causing
enhanced turbulence in the gas flow and thus increasing the
mass transfer. Compared to the correlation of the mass
transfer inside packing, the mass transfer for the
PVP-solutions is lower and the slope is less steep. In the
case of water, the mass transfer exceeds that of the packing
correlation which indicates that a similar grade of turbu-
lence as in the gas passages of packing is reached.
In summary, it can be said that the viscosity has a visible
influence on the mass transfer which can be explained by its
impact on the waviness of the flow and the bead velocity.
The mass transfer rates are in the same order of magnitude
compared to those achieved in structured packing. How-
ever, it has to be mentioned that the gas passages in a
structured packing are tortuous and force the gas into a
spiral motion which increases the effective phase velocities.
This is considered in the work of Rocha et al. (1996) where
they discuss the influence of different inclination angles of
corrugated sheet packing on the mass transfer.

Liquid-side mass transfer
The results of the liquid-side mass transfer measurements
with the air/water-C02-system are shown in Fig. 10. The
liqud-side mass transfer coefficients increase both with
rising liquid and gas load. As comparison a correlation from
Ma6kowiak (2008) for Ralu-Flow packing is added which
does not involve a dependency from the gas load. At low
gas load the values show a remarkable agreement but there
is an increase of the experimental data with rising gas load.
This indicates that the internal mixing of the liquid film is
enhanced by the gas flow at high gas loads.
S0.0002

?~~ ~ -- ^ -^ ---
c f
T)


0.0001 --
SAir/ater-CO2, = 20 C

SBw [m3/(m h)]
E 0.2 0.4 0.6 0.8 1.0
S Experiments 0 o0 A x
0 Ma6kowiak (2008) 0 A x
0
0 2 4 6 8
Gas load F [Pa05]
Fig. 10: Liquid-side mass transfer coefficient depending
on the gas load for different liquid loads. Comparison with
correlation from Ma6kowiak (2008) for Ralu-Flow packing
elements (independent from gas load).

Conclusions

The single wire experiments showed the particular fluid
dynamic characteristics of the annular film flow under the
influence of a counter current gas flow. The curvature of the
film causes an increasing interfacial are with rising liquid
load which also depends on the viscosity of the liquid. For
viscous liquids the interfacial area can exceed the wire


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

surface over 100 %. Although the film structure is clearly
affected by the gas load, there is only minor influence on the
dimension of the interfacial area and the liquid hold-up. The
experiments revealed a dependency of the mass transfer
from gas load, the liquid load and the viscosity of the liquid.
Since the effective interfacial area is already considered in
the calculations of the mass transfer coefficients, this can
only be caused by an intensive interaction between the
phases, especially at higher gas and liquid loads. The
measured mass transfer coefficients are in the order of
magnitude of common packing but the achievable gas
loads are significantly higher. To get to a final conclusion
about the competitiveness of a wire packing compared to
common packing, the packing density of such packing for
equal specific surface has to be considered.

Acknowledgements

The authors gratefully acknowledge the financial support of
the Deutsche Forschungsgemeinschaft (DFG) for this work
(Project No. KR 1639/13-1).

Nomenclature


Af,w
Aw
Bw= 1,w/Cw

be
c
Cw
D
dw
F=vp 05
fR
H
h
HU\= VI,/Lw
Lw
M
N

N
P
PA
PBM

R
R
T
t
V
V
Vg
WB
wf
x
Y
y
yco2
z

Greek letters
P


Interfacial area (mm2)
Wire surface area (mm2)
Liquid load of wire, referred to the wire
circumference (m m'1 h'1)
inner dimension of channel (m)
molar concentration (mol m 3)
circumference of wire (m)
diffusion coefficient (m2 s-')
diameter of wire (m)
Gas load factor (Pa 5)
frame rate (s ')
Henry's law coefficient (bar)
segment height (m)
liquid hold-up (mL m'1)
length of wire (m)
molar mass (g mol 1)
number of pictures in sequence
mole (mol)
molar flow rate (mol s1')
total pressure (Pa)
partial pressure of component A (Pa)
mean partial pressure of inert component B
(Pa)
universal gas constant (J mol-1 K 1)
radius (m)
temperature (K)
time (s)
volume (m3)
volume flow rate (m3 s-')
superficial gas velocity (m s-')
mean bead velocity (m s-')
mean film velocity (m s')
molar fraction of liquid (ppm)
molar fraction of gas (ppm)
molar fraction of C02 in stripping gas (ppm)
vertical coordinate (m)


mass transfer coefficient (m s-')






Paper No


6 film thickness (gnm)
T dynamic viscosity (Pa s)
v kinematic viscosity (m2 s-')
p density (kg m'3)
C surface tension (N m1)
8 temperature (C)

Dimensionless groups
Reg=wgbc/vg Reynolds-number of the gas phase
Ref=Bw/vf Reynolds-number of the liquid phase
Shg=jgbc/Dg mean Sherwood-number of the gas phase
Scg=vg/Dg Schmidt-number of the gas phase


Subsripts
A
B
BF
f
g
in
1
lat
In
m
out
P
R
seg
strip
W
*
0


component A
bead
basis film
film
gas
inlet
liquid
lateral
logarithmic
mean
outlet
probe
recording
segment
stripping gas
wire
equilibrium
mean
surface


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