Hydrodynamic studies on liquid-Liquid two phase flow separation in microchannel by computational fluid dynamic modelling

Science & Technology Development Journal – Engineering and Technology, 4(2):920-931
Open Access Full Text Article Research article
1Chemical Engineering Department,
Universiti Teknologi PETRONAS (UTP),
3260 Seri Iskandar, Perak, Malaysia
2Faculty of Chemical Engineering, Ho
Chi Minh City University of Technology
(HCMUT), 268 Ly Thuong Kiet Street,
District 10, Ho Chi Minh City, Vietnam
3Vietnam National University Ho Chi
Minh City, Linh Trung Ward, Thu Duc
District, Ho Chi Minh City, Vietnam
Correspondence
Loi Hoang Huy Phuoc Pham, Faculty of
Chemical Engineering, Ho Chi Minh City
University of Technology (HCMUT), 268
Ly Thuong Kiet Street, District 10, Ho
Chi Minh City, Vietnam
Vietnam National University Ho Chi Minh
City, Linh Trung Ward, Thu Duc District,
Ho Chi Minh City, Vietnam
Email: phhloi@hcmut.edu.vn
History
 Received: 27-02-2021
 Accepted: 26-4-2021
 Published: 09-5-2021
DOI : 10.32508/stdjet.v4i2.810
Hydrodynamic studies on liquid-liquid two phase flow separation
inmicrochannel by computational fluid dynamic modelling
Chue Cui Ting1, AfiqMohd Laziz1, Khoa Dang Dang Bui2,3, Ngoc Thi Nhu Nguyen2,3, Khoa Ta Dang2,3,
Pha Ngoc Bui2,3, An Si Xuan Nguyen2,3, Ngon Trung Hoang2,3, Ku Zilati Ku Shaari1,
Loi Hoang Huy Phuoc Pham2,3,*
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ABSTRACT
Microfluidic systems undergo rapid expansion of its application in different industries over the
few decades as its surface tension-dominated property provides better mixing and improves mass
transfer between two immiscible liquids. Synthesis of biodiesel via transesterification of vegetable
oil and methanol in microfluidic systems by droplet flow requires separation of the products after
the reaction occurred. The separation technique formultiphase fluid flow in themicrofluidic system
is different from the macro-system, as the gravitational force is overtaken by surface force. To un-
derstand these phenomena completely, a study on the hydrodynamic characteristics of two-phase
oil-methanol system in microchannel was carried out. A multiphase Volume of Fluid model was
developed to predict the fluid flow in the microchannel. An inline separator design was proposed
along with its variable to obtain effective separation for the oil-methanol system. The separation
performance was evaluated based on the amount of oil recovered and its purity. The capability
of the developed model has been validated through a comparison of simulation results with pub-
lished experiment. It was predicted that the purity of recovered oil was increased by more than
46% when the design with side openings arranged at both sides of the microchannel. The high-
est percentage recovery of oil from the mixture was simulated at 91.3% by adding the number of
side openings to ensure the maximum recovery. The oil that was separated by the inline separator
was predicted to be at 100% purity, which indicates that no methanol contamination throughout
the separation process. The purity of the separated product can be increased by manipulating the
pressure drop across the side openings. Hence, it can be concluded that the separation in a large
diameter microchannel system is possible and methodology can be tuned to achieve the separa-
tion goal. Finally, the simulation results showed that the present volume of fluid model had a good
agreement with the published experiment.
Keywords: microchannel, immiscible liquids separation, computational fluid dynamic, volume of
fluid model, multiphase
INTRODUCTION
Liquid-liquid two phase separation is an important
aspect when it comes to the usage of microchannel
in performing certain chemical reactions that involve
two immiscible liquids1. One of the applications of
the usage ofmicroreactor technology in chemical pro-
cesses in the transesterification of vegetable oil and
methanol is to produce biodiesel2. Heat and mass
transfer are improved significantly via microfluidic
device as it provides high surface to volume ratio 3–6.
As the reaction and fluid flow happen in the capillary-
size channel, the mechanism of the fluid flow devi-
ates from themacro-system as the effect of gravity and
inertial force is not significant in the micro-system7.
The capillary effect and viscous force overcome the
gravity and inertial force, causing the fluid to behave
differently. In order to design a separation system
that can perform quick separation in the microchan-
nel field, it is important to study the hydrodynamic
characteristic of the fluid flow in the microchannel.
In macroscale, separation is done by exploiting the
gravitational effect and the difference in density of
the multiphase. However, in microscale, the ef-
fect of gravitational force is overtaken by the surface
force, and the density difference of the two phases
are small7. In another study, it was found that the
microfluidics have apparatus length scale below the
Laplace length scale (
p
g=(rg)), which later proved
that the effect of gravitational forces is negligible in
microchannel8. By exploiting the surface forces in
microfluidics, two phase separation is possible to per-
form in a single step.
Capillary pressure, Pcap is a critical parameter in the
microscale separation process to induce andmaintain
Cite this article : Ting C C, Laziz AM, Bui K D D, Nguyen N T N, Dang K T, Bui P N, Nguyen A S X, Hoang N T,
Shaari K Z K, Pham L H H P. Hydrodynamic studies on liquid-liquid two phase flow separation in mi-
crochannel by computational fluid dynamic modelling. Sci. Tech. Dev. J. – Engineering and Technology;
4(2):920-931.
920
Copyright
© VNU-HCM Press. This is an open-
access article distributed under the
terms of the Creative Commons
Attribution 4.0 International license.
Science & Technology Development Journal – Engineering and Technology, 4(2):920-931
separation7,9,10. The Pcap is given as7:
Pcap =
2g coscosq
r
(1)
where ... gy Development Journal – Engineering and Technology, 4(2):920-931
not sufficient pressure to enter the side openings. Less
oil is being recovered from the system as it retains in
the main outlet and to be discharged together with
methanol. The finding shows the significance of the
pressure drop across the side openings in achieving
microchannel inline separation.
Model Validation Study
In this study, the experimental result from Garstecki
et al.17 is used to validate the accuracy of the above
VOF model. The geometry of the microchannel used
in Garstecki et al.’s experiment is a T-junction as
shown in Fig. 9. The diameter of microchannel is 100
mm and the inlet has a width of 50 mm. Oil is used as
the continuous phase and water as dispersed phase.
The main purpose of Garstecki et al.’s experiment17
is to produce different droplet sizes by injecting var-
ious volumetric flow rate ratio between oil and water
into T-junctionmicrochannel. Three different droplet
sizes have been observed in range of the ratio between
the droplet length, Ld , to the channel width, wc. Ta-
ble 5 shows the details of experimental conditions for
all droplet size scenarios.
Fig. 10 shows the simulation results of the droplet
predicted from the VOF model at different volumet-
ric flow conditions (see Table 5). It can be found in
the Fig. 10 that increasing the oil-to-water ratio leads
to the increase of the droplet size. This finding is in
corresponding with the study of Garstecki et al.17.
The droplet lengths predicted from the VOF model
and observed from the experiment17 are presented in
Table 6. As can be seen from Table 6, the length de-
viations between the simulation and experimental re-
sults are around 5%. This finding revealed that good
agreement was observed between the simulation re-
sults and the published experimental data.
CONCLUSION
The flow behaviour of two immiscible liquids in mi-
crochannel is studied using the VOF model that is
available in ANSYS Fluent software. Separation of
two immiscible liquids in the microchannel by us-
ing a large diameter inline separator system is pro-
posed at the earlier stage of the project. By conducting
this study, this project proves that inline separation by
large diameter separator is possible.
The project is done by using the squeezing regime at
the inlet flow, with the velocity of oil phase at 0.00138
m/s and velocity of methanol phase at 0.00214 m/s,
which bring difficulties for the separation as the two
fluids are flowing at a very slow velocity. Themain in-
terest of this project is to recover the oil from themix-
ture, as the oil phase is the main product of the trans-
esterification. Therefore, the separation performance
will be evaluated based on the recovered oil product.
Preliminary study is conducted to identify the suit-
able design for the inline separator. It is proven that
the design with side openings arranged at both sides
of the microchannel gives better separation perfor-
mance than the design with side openings arranged
at one side of the microchannel. The purity of recov-
ered oil is increased by more than 46%. Based on this
observation, the project is continuedwith selected de-
sign.
Further analysis is carried out on the selected geom-
etry to investigate the effect of number of side open-
ings, effect of side openings’ length and effect of exter-
nal resistance on the separation performance of the
inline separator. It is observed that the highest per-
centage recovery of oil from the mixture that can be
achieved is 91.3%. This method can be achieved by
adding the number of side openings to ensure the
maximum recovery. The oil that is separated by the
inline separator is found to be at 100% purity, which
indicates that no methanol contamination through-
out the separation process.
For the cases where the contamination of methanol
occurred, whereby the methanol is escaping into the
side openings together with the oil phase, this prob-
lem can be overcome by applying larger pressure drop
across the side openings. This methodology can be
achieved by increasing the length of the side openings,
or by applying external resistance in the side open-
ings. The purity of the recovered oil is proved to be
increased up to 100%, whereby all the methanol will
flow through the main outlet.
The project has demonstrated that the separation of
oil-methanol system inmicrochannel can be achieved
using a higher number of side openings, which is
3 pairs of side openings for the selected oil and
methanol flow rate. The purity of the separated prod-
uct can be increased by manipulating the pressure
drop across the side openings. Hence, it can be con-
cluded that the separation in a large diameter mi-
crochannel system is possible and methodology can
be tuned to achieve the separation goal.
Finally, the developed VOF model was validated
against a recently published experimental data. The
validation study shows that the present VOF model
had a good agreement with the published experiment.
ACKNOWLEDGEMENTS
We acknowledge the support of time and facili-
ties from Ho Chi Minh City University of Technol-
ogy (HCMUT), VNU-HCMandUniversiti Teknologi
PETRONAS (UTP) for this study.
928
Science & Technology Development Journal – Engineering and Technology, 4(2):920-931
Figure 9: Computational domain of the microchannel is reproduced from Garstecki et al. 17 for the model valida-
tion
Table 5: Experimental conditions 17 used for themodel validation
Droplet name Droplet size range Inlet volume flow rate (mL/s) Water-oil flow rate ratio, Qo/Qw
Qoil Qwater
Short Ld 2wc 0.028 0.010 0.36
Middle 2wc < Ld 6wc 0.028 0.025 0.89
Long Ld > 6wc 0.28 0.111 0.396
Figure 10: Predictions of droplet at different sizes: (a) short droplet, b) middle droplet and c) long drop
Table 6: Droplet length comparison between simulation and experiment
Droplet name Droplet length (mm)
VOF model Experiment 17 Deviation (%)
Short 154 161 4.3
Middle 214 209 2.4
Long 1024 1058 3.2
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Science & Technology Development Journal – Engineering and Technology, 4(2):920-931
LIST OF ABBREVIATION
CSF Continuum surface force
PTFE Polytetrafluoroethylene
VOF Volume of Fluid
COMPETING INTERESTS
The authors declare that they have no conflicts of in-
terests.
AUTHORS’ CONTRIBUTIONS
The research methodology was conceptually pro-
posed by Chue Cui Ting and Afiq Mohd Laziz. Orig-
inal draft was prepared by Chue Cui Ting. The re-
search was supervised by Khoa Dang Dang Bui, Ngoc
Thi Nhu Nguyen, Khoa Ta Dang Pha, Ngoc Bui, An
Si Xuan Nguyen, Ngon Trung Hoang, Ku Zilati Ku
Shaari and Loi Hoang Huy Phuoc Pham. All authors
have read and agreed to the published version of the
manuscript.
REFERENCES
1. Okubo Y, et al. Microchannel devices for the coalescence of
dispersed droplets produced for use in rapid extraction pro-
cesses. Chemical Engineering Journal. 2004;101(1-3):39–48.
Available from: https://doi.org/10.1016/j.cej.2003.10.025.
2. Canter N. Making biodiesel in a microreactor. Tribol. Lubr.
Technol. 2006;62:15–17.
3. EhrfeldW, Hessel V, Loewe H. Microreactors: New Technology
for Modern Chemistry. Wiley-VCH, Weinheim. 2000;Available
from: https://doi.org/10.1002/3527601953.
4. Kobayashi J, Mori Y, Kobayashi S. Multiphase organic syn-
thesis in microchannel reactors. Chem. Asian J. 2006;1:22–35.
PMID: 17441035. Available from: https://doi.org/10.1002/asia.
200600058.
5. Jovanovic J, Rebrov EV. Phase transfer catalysis in segmented
flow in a microchannel: fluidic control of selectivity and pro-
ductivity. Ind. Eng. Chem. Res. 2010;49:2681–2687. Available
from: https://doi.org/10.1021/ie9017918.
6. Kashid MN, Renken A, Kiwi-Minsker L. CFD modelling
of liquid-liquid multiphase microstructured reactor: Slug
flow generation. Chemical Engineering Research and Design.
2010;88(3):362–368. Available from: https://doi.org/10.1016/j.
cherd.2009.11.017.
7. Castell OK. Liquid-liquid phase separation: Characterisation
of a novel device capable of separating particle carrying mul-
tiphase flows. Lab Chip. 2009;9:388–396. PMID: 19156287.
Available from: https://doi.org/10.1039/B806946H.
8. Gunther A, Jensen KF. Multiphase microuidics: from ow char-
acteristics to chemical and materials synthesis. Lab on a Chip.
2006;6:1487–1503. PMID: 17203152. Available from: https:
//doi.org/10.1039/B609851G.
9. Kralj J, Sahoo H, Jensen K. Integrated continuous microfluidic
liquid-liquid extraction. Lab Chip. 2007;7(2):256–263. PMID:
17268629. Available from: https://doi.org/10.1039/B610888A.
10. Phillips TW, et al. Microscale extraction and phase sepa-
ration using a porous capillary. Lab Chip. 2015;15(14):2960–
2967. PMID: 26054926. Available from: https://doi.org/10.
1039/C5LC00430F.
11. Adamo A, Heider PL, et al. Membrane-Based, Liquid-
Liquid Separatorwith IntegratedPressureControl. Industrial &
Engineering Chemistry Research. 2013;52(31):10802–10808.
Available from: https://doi.org/10.1021/ie401180t.
12. Kashid MN, Agar DW. Hydrodynamics of liquid-liquid slug
flow capillary microreactor: flow regimes, slug size and pres-
sure drop. Chemical Engineering Journal. 2007;131(1):1–13.
Available from: https://doi.org/10.1016/j.cej.2006.11.020.
13. Kashid MN, et al. LiquidLiquid Slug Flow In A Capillary: An
Alternative To Suspended Drop Or Film Contactors. Industrial
& Engineering Chemistry Research. 2007;46(25):8420–8430.
Available from: https://doi.org/10.1021/ie070077x.
14. Scheiff F, et al. The separationof immiscible liquid slugswithin
plasticmicrochannels using ametallic hydrophilic sidestream.
Lab on a Chip. 2011;11(6):1022–1029. PMID: 21279200. Avail-
able from: https://doi.org/10.1039/c0lc00442a.
15. Fluent. FLUENT 6.3 User’s Guide. Fluent Inc. 2006;.
16. Brackbill JU, et al. A ContinuumMethod for Modeling Surface
Tension. J. Comput. Phys. 1992;100:335–354. Available from:
https://doi.org/10.1016/0021-9991(92)90240-Y.
17. Garstecki P. Formation of droplets and bubbles in a microflu-
idic T-junction-scaling and mechanism of break-up. Lab Chip.
2006;6:437–446. PMID: 16511628. Available from: https:
//doi.org/10.1039/b510841a.
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Tạp chí Phát triển Khoa học và Công nghệ – Kĩ thuật và Công nghệ, 4(2): 920-931
Open Access Full Text Article Bài nghiên cứu
1Khoa Kỹ thuật Hóa học, Trường Đại
học Kỹ thuật Petronas, 3260 Seri
Iskandar, Perak, Malaixia
2Khoa Kỹ thuật Hóa học, Trường Đại
học Bách Khoa TP. Hồ Chí Minh, 268 Lý
Thường Kiệt, Quận 10, Thành phố Hồ
Chí Minh, Việt Nam
3Đại học Quốc gia Thành phố Hồ Chi
Minh, Phường Linh Trung, QuậnThủ
Đức, Thành phố Hồ Chi Minh, Việt Nam
Liên hệ
PhạmHoàng Huy Phước Lợi, Khoa Kỹ
thuật Hóa học, Trường Đại học Bách Khoa TP.
Hồ Chí Minh, 268 Lý Thường Kiệt, Quận 10,
Thành phố Hồ Chí Minh, Việt Nam
Đại học Quốc gia Thành phố Hồ Chi Minh,
Phường Linh Trung, Quận Thủ Đức, Thành
phố Hồ Chi Minh, Việt Nam
Email: phhloi@hcmut.edu.vn
Lịch sử
 Ngày nhận: 27-02-2021
 Ngày chấp nhận: 26-4-2021 
 Ngày đăng: 09-5-2021
DOI : 10.32508/stdjet.v4i2.810 
Nghiên cứu về thủy động lực học của sự phân tách dòng chảy giữa
hai pha lỏng-lỏng trong vi kênh bằngmô hình tính toán động lực
học chất lưu
Chue Cui Ting1, AfiqMohd Laziz1, Bùi Đặng Đăng Khoa2,3, Nguyễn Thị Như Ngọc2,3, Tạ Đăng Khoa2,3,
Bùi Ngọc Pha2,3, Nguyễn Sĩ Xuân Ân2,3, Hoàng Trung Ngôn2,3, Ku Zilati Ku Shaari1,
PhạmHoàng Huy Phước Lợi2,3,*
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TÓM TẮT
Trong những thập niên gần đây, hệ thống vi lưu được dùng nhiều trong các ngành công nghiệp
khác nhau, vì nhờ đặc tính sức căng bề mặt của nó đã giúp cho sự hòa trộn tốt hơn và tăng sự
truyền khối giữa hai chất lỏng không hòa tan. Quá trình tổng hợp diesel sinh học thông qua phản
ứng tổng hợp este của dầu thực vật và methanol trong hệ thống vi lưu nhỏ giọt yêu cầu tách các
sản phẩm sau khi phản ứng xảy ra. Kỹ thuật tách dòng chất lỏng nhiều pha trong hệ thống vi lưu
khác với hệ vĩ mô, do lực hấp dẫn bị lực bề mặt chi phối. Để hiểu rõ hiện tượng này, nghiên cứu về
đặc điểm thủy động lực học của hệ thống dầu-methanol trong vi kênh đã được thực hiện. Mô hình
thể tích chất lỏng nhiều pha đã được phát triển để dự đoán dòng chất lỏng trong vi kênh. Một bộ
tách nội tuyến đã được thiết kế cùng với biến số của nó để có được sự phân tách hiệu quả cho hệ
thống dầu-methanol. Hiệu suất của quá trình phân tách đã được đánh giá dựa trên lượng dầu thu
hồi và độ tinh khiết của nó. Độ chính xác của mô hình đã phát triển đã được xác nhận thông qua
việc so sánh kết quả mô phỏng với số liệu thực nghiệm đã công bố. Độ tinh khiết của dầu thu hồi
đã được dự đoán tăng hơn 46% khi thiết kế với các lỗ ra được bố trí ở cả hai bên của vi kênh. Tỷ
lệ phần trăm thu hồi cao nhất của dầu từ hỗn hợp được mô phỏng ở mức 91,3% bằng cách tăng
số lượng lỗ ra ở hai bên để đảm bảo thu hồi tối đa. Dầu được tách bằng thiết bị tách nội tuyến
được dự đoán là có độ tinh khiết 100%, điều này cho thấy rằng không có nhiễm methanol trong
suốt quá trình tách. Độ tinh khiết của sản phẩm tách có thể được tăng lên bằng cách điều chỉnh
độ giảm áp suất trên các lỗ ra. Do đó, có thể kết luận rằng việc phân tách trong một hệ thống vi
kênh có đường kính lớn là có thể thực hiện được và phương pháp này có thể được điều chỉnh để
đạt được mục tiêu phân tách. Cuối cùng, kết quả mô phỏng cho thấy mô hình thể tích chất lỏng
này phù hợp với thí nghiệm đã công bố.
Từ khoá: vi kênh, tách chất lỏng không hòa tan nhau, tính toán động lực học chất lưu, mô hình
thể tích chất lỏng, nhiều pha
Trích dẫn bài báo này: Ting C C, Laziz A M, Khoa B D D, Ngọc N T N, Khoa T D, Pha B N, Ân N S X, Ngôn H 
T, Shaari K Z K, Lợi P H H P. Nghiên cứu về thủy động lực học của sự phân tách dòng chảy giữa hai pha 
lỏng-lỏng trong vi kênh bằng mô hình tính toán động lực học chất lưu. Sci. Tech. Dev. J. - Eng. Tech.; 
4(2): 920-931.
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