Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: 14.2.1 - Immiscible liquid-liquid two-phase flow in a micro-channel: flow pattern, void fraction and pressure drop investigations
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 Material Information
Title: 14.2.1 - Immiscible liquid-liquid two-phase flow in a micro-channel: flow pattern, void fraction and pressure drop investigations Micro and Nano-Scale Multiphase Flows
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Foroughi, H.
Kawaji, M.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: micro-channel
liquid-liquid flow
flow patterns
pressure drop
 Notes
Abstract: Immiscible liquid-liquid two-phase flow characteristics in a circular microchannel have been investigated in connection with the flow of heavy crude oil in porous media in the presence of water. Water and silicone oil with a dynamic viscosity of 863 mPa.s were injected into a fused silica microchannel with an inner diameter of 250 μm. Two-phase flow patterns were determined under a wide range of oil and water flow rates. Two-phase pressure drop data have also been collected and analyzed.
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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Bibliographic ID: UF00102023
Volume ID: VID00343
Source Institution: University of Florida
Holding Location: University of Florida
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Resource Identifier: 1421-Foroughi-ICMF2010.pdf

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


Immiscible liquid-liquid two-phase flow in a microchannel:
flow patterns and pressure drop characteristics

Hooman Foroughi and Masahiro Kawajil,2

1. Department of Chemical Engineering and Applied Chemistry, University of Toronto,
Toronto, ON M5S 3E5, Canada
2. Departments of Mechanical and Chemical Engineering, City College of New York,
New York, NY 10031, USA

kawaji~,me.ccny.cuny.edu and hooman.foroughi~,utoronto.ca


Keywords: Micro-channel: Liquid-liquid flow: Flow patterns: Pressure drop


Abstract

Immiscible liquid-liquid two-phase flow characteristics in a circular microchannel have been investigated in connection with
the flow of heavy crude oil in porous media in the presence of water. Water and silicone oil with a dynamic viscosity of 863
mPa.s were injected into a fused silica microchannel with an inner diameter of 250 pLm. Two-phase flow patterns were
determined under a wide range of oil and water flow rates. Two-phase pressure drop data have also been collected and
analyzed.


Introduction


Nomenclature


Two-phase flows in microchannels have a wide range of
applications in chemical and petroleum engineering.
Although gas-liquid flows in micro-channels are well
documented (Kawahara et al. 2002, and Chung & Kawaji
2004), liquid-liquid flows in micro-channels are still not
very well understood (Salim et al. 2008). Numerous
investigations have been carried out on viscous oil-water
flows in small and conventional pipes. Many of these
studies were performed in horizontal and vertical pipes as
reviewed by Joseph et al. (1997).

In small channels, Anna et al. (2003) used a microfluidic
device with flow-focusing geometry to produce droplets in
water-oil systems. In their experiments, both fluids were
forced to flow through an orifice to produce mono-disperse
and poly-disperse emulsions. They developed a phase
diagram illustrating drop size as a function of flow rates and
flow ratios. Dreyfus et al. (2003) studied liquid-liquid
two-phase flow patterns in a micro-channel with cross-like
injection configuration. They showed that wetting properties
strongly control flow patterns. Kashid et al. (2007) studied
the hydrodynamics of liquid-liquid slug flow in a Y-type
microchannel. Salim et al. (2008) studied the oil-water flow
patterns and pressure drops in a rectangular, micro
T-junction. The viscosity of oil used in their study was 30.6
mPa.s.

In this work, the flow characteristics of viscous oil-water
two phase flows in a circular microchannel are studied. The
density and viscosity of silicone oil used in this study are
0.97gm/cm3 and 863 mPa.s which are comparable to that of
gas-saturated heavy oil in petroleum reservoirs.


Constant
channel lenght (m)
Pressure (kPa)
superficial velocity (cm/s)


Greek symbols
AP pressure drop (kPa)
CL viscosity (mPa.s)
STwo-phase friction multiplier
X Lockhart-Martinelli parameter

Subsripts
g Gas
1Liquid
m oil-water mixture
o Oil
TP Two-phase flow
w Water

Experimental Facility

The experimental apparatus used is shown in figure 1. Two
pneumatic pumps were used to inject water and silicone oil
separately. Pneumatic pumps consisted of a cylindrical
vessel filled with a liquid and pressurized with a nitrogen
gas from a cylinder. One of the pneumatic pumps
contained water and the other contained silicone oil. The
pressures in the liquid reservoirs were raised to inject
liquid into the channel. The pressure regulators on the
nitrogen gas cylinders were adjusted to cover certain
ranges of water and silicone oil flow rates.

The silicone oil was injected into a microchannel test
section through a needle with an internal diameter of 100
pLm and outer diameter of 210 pLm. As shown in figure 2,


























Figure 3: Effect of optical correction: a) without optical
correction, b) with optical correction
















..













II


f)







Figure 4: Flow patterns observed in viscous oil-water two-
phase flow in a microchannel: a & b) bubbly flow water
bubbles in oil as the continuous phase; c & d) slug flow -
water slugs in oil; e & f) annular flow water is the core
flow surrounded by oil; and g) mixed flow water drops and


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

different flow rates while the oil flow rate was kept constant.
Figure 4 shows the flow patterns observed in this system:
bubbly, slug, annular and mixed flows.



-- --= -


silicone oil was injected at the centre of the microchannel
through the needle, while water was injected through an
annulus between the needle and the microchannel with an
inner diameter of 250 pLm, outer diameter of 360 lpm and
length of 72 mm.

A pressure transducer with an accuracy of 1.7 kPa (0.25
psi) was used to measure the pressure drop between the
microchannel inlet and exit which is exposed to the
atmosphere. A cross junction was used to connect the
needle, water injection line, pressure transducer, and
micro-channel.
Water Reservoir Micro-Channel




Cross junction I:




Pli~ Pressure Transduer
Nitrogen Gas Oil Reservoir Ligh


Nedefoe injecting


Cylinders


cnel


Figure 1: Schematic of the experimental apparatus

Channel Wall eedle for injecting oil
into the micro-channel


Figure 2: Oil and water injection section of the
microchannel

A high speed CCD camera was used to capture images of
the water-silicone oil flow at 15 frames per second. Since a
circular micro-channel was used, optical correction was
necessary to capture undistorted and clear images inside the
entire cross section of the microchannel. To this end, the
micro-channel was sandwiched between two glass plates
and the gap between the two plates was filled with oil to
best match the index of refraction of the microchannel.
Figure 3 shows the effect of optical correction on the images
captured by the high speed video camera.

Results and Discussion

Flow patterns of oil-water flow in microchannels strongly
depend on the nature of the first fluid injected into the
channels (Salim, 2008). In other words, different flow
patterns are observed depending on with which fluid the
channel is initially saturated, silicone oil or water. In this
work, the channel was initially always saturated with
silicone oil by injecting only the silicone oil at a constant
flow rate. Then, water was injected into the channel at






































1 ;



a> L
Y



c E
b) %


E


5 1




S0.5
. n


I I II I


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

Pressure Drop Measurements and Analysis

In this section, pressure drop measurements for slug,
annular and mixed flows are presented and discussed. Salim
et al. (2008) found that the pressure drop and flow pattern
change when the first liquid injected into the channel
changes. As mentioned earlier, in this work, the channel was
always initially saturated with the silicone oil.

Figure 7 shows the pressure drop data obtained in silicone
oil-water two phase flows in the microchannel. Each curve
represents a set of data measured at a constant oil flow rate
while the flow rate of water was increased. The pressure
drop changed linearly as a function of the water flow rate
while the oil flow rate was kept constant. Also, the pressure
drop increased with an increase in the oil flow rate.

An increase and then a sharp decrease in two-phase
oil-water flow pressure drops have been reported at low
water flow rates (Slim et al. 2008). Such a change in
pressure drop measurements has not been seen in this work.
The reason may be that the pressure drop data presented in
figure 7 were measured at water flow rates which were not
low enough to result in a sudden increase and decrease in
the pressure drop.


water core flow in oil. The microchannel was initially
saturated with oil and the flow direction is from right to left.
Although the silicone oil was injected at the centre of the
microchannel through a needle and water was injected
through an annular gap between the outer wall of the needle
and the inner wall of the microchannel (Figure 2), water
formed the dispersed phase or core-flow and oil was the
continuous phase and outer flow since the microchannel was
initially saturated with silicone oil.

As mentioned earlier, for each experiment, the oil flow rate
was kept constant, while increasing the water flow rate. At
low flow rates of water, the flow pattern was bubbly. With
an increase in the water flow rate, bubbly flow changed to a
slug flow. With a further increase in the water flow rate, a
transition occurred from slug flow to annular flow. Figure 5
shows the transition boundaries between the slug and
annular flow patterns.

Finally, at highest flow rates of water tested, mixed flow
patterns of water bubbles and annular flow of water in oil
were observed. Mixed flow patterns have not been observed
in low-viscosity oil and water two phase flows in larger
microchannels (Salim et al. 2008). The flow pattern map for
the current system is presented in figure 6.


Figure 5: Transition from slug to annular flow: a) slug flow,
b) transient flow: slugs merge, and c) annular flow


Water Superficial Velocity (cm/s)


Figure 7: Pressure drop data for silicone oil-water two
phase flow in the microchannel. Circles and dashed lines
represent measured data and solid lines are equation 2.
Curves are numbered from top to bottom and each curve
was obtained at a constant oil flow rate: 1) 0.051 g/min, 2)
0.045 g/min, 3) 0.031 g/min, 4) 0.027 g/min, 5) 0.022 g/min,
6) 0.018 g/min.

The single-phase pressure drop was calculated by using the
Hagen-Poiseuille correlation:


rrr IBubbly Flow

a so ASlug Flow

me 'I WH Annular Flow

't Mixed Flow


AP 32p1V
- =2


0 2040 6 80 where is the pressure drop over unit length of the
Water Superficial Velocity (cm/s)
microchannel,L, p1 is dynamic viscosity, Dis the channel
Figure 6: Flow pattern map for silicone oil-water two-phase diameter and V is the superficial velocity of each phase.
flow in a 250 Cpm microchannel













































X = = -~, (5)


where 9, is the water-phase friction multiplier- Wo is the
oil-phase friction multiplier, and X is Lockhart-Martinelli
parameter. By using equation 1 for water and oil
single-phase pressure drop, the Lockhart-Martinelli
parameter can be written as:



7 =J(/' (6)

By using equations 2 and 5, equation 3 can be written as:


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

with Equation 9. This figure shows excellent agreement
between Equation 9 with the present liquid-liquid pressure
drop data.
700
A slug Flow
600
o Annular Flow ,
5001 4~ Mixed Flow
& 400 Equation 9

300

200

100

00 100 200 300 400 500
X2
Figure 8: Two-phase friction multiplier variation with
Lockhart-Martinelli parameter


Pressure drop data presented in figure 7 show that the
two-phase pressure drop in this system varies as a function
of the single-phase oil and water pressure drops:


I-- = 60* +-- + 1.284 I-
\L TP \LW \L/o


where ( T)~is the two-phase pressure drop. and )and

o) are the water and oil single-phase pressure drops
calculated by using equation 1 with superficial velocities of
water and oil. The results show that equation 2 predicts
pressure drops for this system with a maximum error
oft*10%.

Kawahara et al. (2002) and Chung and Kawaji (211114) used
Lockhart-Martinelli model to describe pressure drops for
gas-liquid two-phase flow in micro-channels. In this work
Lockhart-Martinelli model is used for the system of
oil-water two phase flows by using a gas correlation in
Lockhart-Martinelli for water and liquid correlation for oil:


l ) TP
4" =P


Equation 9 which is equivalent to equation 2 shows the
correlation between water-phase friction multiplier and the
( Lockhart-Martinelli parameter. Equation 9 is also
comparable to Chisholm's (1967) correlation used for
gas-liquid two-phase flows in pipes which gives the
gas-phase friction multiplier 4, as a function of
,,Lockhart-Martinelli parameter as follows:


4~2 .. C 2


(10)


where C is a constant and depends on the laminar or
turbulent nature of the flow and pipe size.

Equation 9 can also be compared to the correlation
developed by Salim et al. (2008) for low viscosity-oil and
water two-phase flow in a larger microchannel made of
quartz and with an inner diameter of 793 plm.

49 2 = X+P2 (

Constants a and fi were found to be 0.26 and 0.8,
respectively, by Salim et al. (2008) for oil-water two-phase
flow in a microchannel.


Flow of Water in a Stagnant Oil Annulus


'l 60 I L w + 1.284 r L o ~


In this section, the flow of water with zero oil flow rate in a
microchannel initially saturated with oil is investigated. To
initially saturate the channel with oil, the oil is injected into
the channel first and the channel is filled completely with oil.
Then the oil injection is stopped and water is injected into
the microchannel at a constant flow rate. The flow patterns
observed in this case are shown in Figure 9.

Under these conditions, the initially injected oil sticks to the
inner wall of the microchannel and forms a stagnant
continuous layer. After the oil injection is stopped and water
is injected into the channel, water flows as a core in a wavy
form through a stagnant annulus of oil.


This can be written as,


TL )


49w = /60 + 1.284~ ( 7



4~2 = 60 + 1.284 72 (9)

The two-phase friction multiplier, 9, and square of the
Lockhart-Martinelli parameter, X were calculated from the
present experimental data and are plotted in Figure 8 along






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

Microchannels", Phys. Rev. Lett. Vol. 90, No. 14, 144505
(2003).

Joseph, D.D., Bai R., Chen, K. P. & Y. Y. Renardy,
"Core-Annular Flows", Annu. Rev. Fluid Mech., Vol. 29,
65-90 (1997).

Kashid, M.N. & D.W. Agar, "Hydrodynamics of
liquid-liquid slug flow capillary microreactor: Flow
regimes, slug size and pressure drop" Chemical
Engineering Joumnal Vol. 131, 1-13 (2007).

Kawahara, A., Chung, P.M. -Y., & M. Kawaji,
"Investigation of two-phase flow pattern, void fraction and
pressure drop in a microchannel", Intemnational Joumnal of
Multiphase Flow Vol.28, 1411-1435 (2002).

Salim, A., Fourar, M., Pironon, J. & J. Sausse, "Oil-Water
Two-Phase Flow in Microchannels: Flow Pattemns and
Pressure Drop Measurements", Canadian J. of Chem. Eng.,
Vol. 86, 978-988 (2008)


a)






Figure 9a & b: Flow of water in a microchannel initially
saturated with oil. Water flows as a core in a wavy fonn
while a stagnant layer of oil sticks to the side wall of the
microchannel.

To investigate whether water would be able to fully wash
away the oil, in one experiment, water at a constant flow
rate of 0.5 gm/min was injected into the microchannel
which had been saturated with oil for more than 3.5 hours. It
was found that the water could not completely wash away
the oil laver from the inner channel wall. Instead, the water
flowed as a core through a stagnant wavy annulus of oil
during the whole experiment.

Conclusion

An experimental study of water-viscous oil two-phase flow
in a microchannel of 250 Cpm diameter initially saturated
with oil has been perfonned. Different flow patterns were
observed over a wide range of oil and water flow rates. It
was found that the two-phase friction pressure drop is a
linear function of single-phase water and oil flow rates. A
Lockhart-Martinelli model could also be used to predict
liquid-liquid pressure drop data obtained in this system.
Since the channel was initially saturated with oil, a stagnant
laver of oil would remain on the inner wall of the
microchannel which could not be washed away by a
continuous flow of water even with the oil flow stopped.

References

Anna, S.L., Bontoux, N., & H. A. Stone "Fonnation of
dispersions using 'flow focusing' in microchannels", Appl.
Phys. Lett., Vol. 82, No. 3, 364-366 (2003).

Chisholm, D.A., "A Theoretical Basis for the
Lockhart-Martinelli Correlation for Two-Phase Flow," Int.
J. Heat Mass Transfer, Vol. 10, 1767-1778 (1967).

Chung, P.M.-Y., & M. Kawaji "The effect of channel
diameter on adiabatic two-phase flow characteristics in
microchannels", Intemnational Joumnal of Multiphase Flow,
Vol. 30, 735-761 (lil 14,1.

Chung, P.M.-Y., Kawaij, M., Kawahara, A. & Y. Shibata,
"Two-Phase Flow through Square and Circular
Microchannels-Effects of Channel Geometry" ASME J.
Fluids Eng., Vol. 126, Issue 4, 546-542, (21 rI14,.

Dreyfus, R., Tabeling, P., & H. Willaime "Ordered and
Disordered Pattemns in Two-Phase Flows in




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