Research Papers: Fundamental Issues and Canonical Flows

Effects of Junction Angle and Viscosity Ratio on Droplet Formation in Microfluidic Cross-Junction

[+] Author and Article Information
Ich-Long Ngo

School of Mechanical Engineering,
Yeungnam University,
Gyeongsan 712-749, South Korea
e-mail: longngoich@yahoo.com

Sang Woo Joo

School of Mechanical Engineering,
Yeungnam University,
Gyeongsan 712-749, South Korea
e-mail: swjoo@ynu.ac.kr

Chan Byon

School of Mechanical Engineering,
Yeungnam University,
Gyeongsan 712-749, South Korea
e-mail: cbyon@ynu.ac.kr

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received June 16, 2015; final manuscript received October 2, 2015; published online January 6, 2016. Assoc. Editor: Shizhi Qian.

J. Fluids Eng 138(5), 051202 (Jan 06, 2016) (9 pages) Paper No: FE-15-1403; doi: 10.1115/1.4031881 History: Received June 16, 2015; Revised October 02, 2015

This study describes the dynamic behaviors of droplet formation in microfluidic cross-junction devices (MFCDs) based on a two-dimensional numerical model using the volume of fluid (VOF) method. The effects of the junction angle (ϕ = 30 to 90 deg) between the main and side channels and the viscosity ratios (β = 10−5 to 2.0) are considered. The numerical results indicate that the active area for droplet formation in the alternating digitized pattern formation (ADPF) generally increases with the decrease of ϕ at the same water fraction (wf). A junction angle of around 60 deg was predicted as the most efficient angle at which alternating droplets are still formed at lower capillary numbers (Ca). In addition, the droplet size in ADPF decreases as ϕ increases with the same flow conditions. When ϕ is less than 90 deg and prior to approaching the equilibrium state, there always exists a periodic deviation in the relative distance between droplets. The frequency of droplet generation in ADPF decreases as ϕ decreases, and it decreases more quickly when ϕ is less than 60 deg. In addition, the throughput of MFCDs can be controlled effectively as a function of ϕ, wf, and Ca. The droplet formation in MFCDs depends significantly on the viscosity ratio β, and the ADPF becomes a jetting formation (JF) when β is greater than unity. Furthermore, the droplet size in ADPF decreases with the increase of β. The understanding of droplet formation in MFCDs is very useful for many applications, such as nanoparticle synthesis with different concentrations, hydrogel bead generation, or cell transplantation in biomedical therapy.

Copyright © 2016 by ASME
Your Session has timed out. Please sign back in to continue.


Dendukuri, D. , Pregibon, D. C. , Collins, J. , Hatton, T. A. , and Doyle, P. S. , 2006, “ Continuous-Flow Lithography for High-Throughput Microparticle Synthesis,” Nat. Mater., 5(5), pp. 365–369. [CrossRef] [PubMed]
Nie, Z. H. , Li, W. , Seo, M. , Xu, S. Q. , and Kumacheva, E. , 2006, “ Janus and Ternary Particles Generated by Microfluidic Synthesis: Design, Synthesis, and Self-Assembly,” J. Am. Chem. Soc., 128(29), pp. 9408–9412. [CrossRef] [PubMed]
Nisisako, T. , Torii, T. , and Higuchi, T. , 2004, “ Novel Microreactors for Functional Polymer Beads,” Chem. Eng. J., 101(1–3), pp. 23–29. [CrossRef]
Serra, C. A. , and Chang, Z. Q. , 2008, “ Microfluidic-Assisted Synthesis of Polymer Particles,” Chem. Eng. Technol., 31(8), pp. 1099–1115. [CrossRef]
Mohammadi, M. , and Sharp, K. V. , 2013, “ Experimental Techniques for Bubble Dynamics Analysis in Microchannels: A Review,” ASME J. Fluids Eng., 135(2), p. 021202. [CrossRef]
Whitesides, G. M. , 2006, “ The Origins and the Future of Microfluidics,” Nature, 442(7101), pp. 368–373. [CrossRef] [PubMed]
Engl, W. , Backov, R. , and Panizza, P. , 2008, “ Controlled Production of Emulsions and Particles by Milli- and Microfluidic Techniques,” Curr. Opin. Colloid Interface, 13(4), pp. 206–216. [CrossRef]
Thorsen, T. , Roberts, R. W. , Arnold, F. H. , and Quake, S. R. , 2001, “ Dynamic Pattern Formation in a Vesicle-Generating Microfluidic Device,” Phys. Rev. Lett., 86(18), pp. 4163–4166. [CrossRef] [PubMed]
Hao, G. , Duits, M. H. G. , and Mugele, F. , 2011, “ Droplets Formation and Merging in Two-Phase Flow Microfluidics,” Int. J. Mol. Sci., 12(4), pp. 2572–2597. [PubMed]
Teh, S. Y. , Lin, R. , Hung, L. H. , and Lee, A. P. , 2008, “ Droplet Microfluidics,” Lab Chip, 8(2), pp. 198–220. [CrossRef] [PubMed]
Dang, T. D. , Kim, Y. H. , Kim, H. G. , and Kim, G. M. , 2012, “ Preparation of Monodisperse PEG Hydrogel Microparticles Using a Microfluidic Flow-Focusing Device,” J. Ind. Eng. Chem., 18(4), pp. 1308–1313. [CrossRef]
Dang, T. D. , and Joo, S. W. , 2013, “ Preparation of Tadpole-Shaped Calcium Alginate Microparticles With Sphericity Control,” Colloid Surf. B, 102, pp. 766–771. [CrossRef]
Zheng, B. , Tice, J. D. , and Ismagilov, R. F. , 2004, “ Formation of Droplets of Alternating Composition in Microfluidic Channels Alternating Composition and Applications to Indexing of Concentrations in Droplet-Based Assays,” Anal. Chem., 76(17), pp. 4977–4982. [CrossRef] [PubMed]
Jin, B. J. , Kim, Y. W. , Lee, Y. , and Yoo, J. Y. , 2010, “ Droplet Merging in a Straight Microchannel Using Droplet Size or Viscosity Difference,” J. Micromech. Microeng., 20(3), pp. 1–10. [CrossRef]
Fidalgo, L. M. , Abell, C. , and Huck, W. T. S. , 2007, “ Surface-Induced Droplet Fusion in Microfluidic Devices,” Lab Chip, 7(8), pp. 984–986. [CrossRef] [PubMed]
Tang, S. K. Y. , Li, Z. Y. , Abate, A. R. , Agresti, J. J. , Weitz, D. A. , Psaltis, D. , and Whitesides, G. M. , 2009, “ A Multi-Color Fast-Switching Microfluidic Droplet Dye Laser,” Lab Chip, 9(19), pp. 2767–2771. [CrossRef] [PubMed]
Hung, L. H. , Choi, K. M. , Tseng, W. Y. , Tan, Y. C. , Shea, K. J. , and Lee, A. P. , 2006, “ Alternating Droplet Generation and Controlled Dynamic Droplet Fusion in Microfluidic Device for CdS Nanoparticle Synthesis,” Lab Chip, 6(2), pp. 174–178. [CrossRef] [PubMed]
Jin, B. J. , and Yoo, J. Y. , 2012, “ Visualization of Droplet Merging in Microchannels Using Micro-PIV,” Exp. Fluids, 52(1), pp. 235–245. [CrossRef]
Glatzel, T. , Litterst, C. , Cupelli, C. , Lindemann, T. , Moosmann, C. , Niekrawietz, R. , Streule, W. , Zengerle, R. , and Koltay, P. , 2008, “ Computational Fluid Dynamics (CFD) Software Tools for Microfluidic Applications—A Case Study,” Comput. Fluids, 37(3), pp. 218–235. [CrossRef]
Bedram, A. , Darabi, A. E. , Moosavi, A. , and Hannani, S. K. , 2014, “ Numerical Investigation of an Efficient Method (T-Junction With Valve) for Producing Unequal-Sized Droplets in Micro- and Nano-Fluidic Systems,” ASME J. Fluids Eng., 137(3), p. 031202. [CrossRef]
Sharma, A. , Tiwari, V. , Kumar, V. , Mandal, T. K. , and Bandyopadhyay, D. , 2014, “ Localized Electric Field Induced Transition and Miniaturization of Two-Phase Flow Patterns Inside Microchannels,” Electrophoresis, 35(20), pp. 2930–2937. [CrossRef] [PubMed]
De Menech, M. , 2006, “ Modeling of Droplet Breakup in a Microfluidic T-Shaped Junction With a Phase-Field Model,” Phys. Rev. E, 73(3), pp. 1–9. [CrossRef]
De Menech, M. , Garstecki, P. , Jousse, F. , and Stone, H. A. , 2008, “ Transition From Squeezing to Dripping in a Microfluidic T-Shaped Junction,” J. Fluid Mech., 595, pp. 141–161. [CrossRef]
Hoang, D. A. , van Steijn, V. , Portela, L. M. , Kreutzer, M. T. , and Kleijn, C. R. , 2013, “ Benchmark Numerical Simulations of Segmented Two-Phase Flows in Microchannels Using the Volume of Fluid Method,” Comput. Fluids, 86, pp. 28–36. [CrossRef]
Timung, S. , Tiwari, V. , Singh, A. K. , Mandal, T. K. , and Bandyopadhyay, D. , 2015, “ Capillary Force Mediated Flow Patterns and Non-Monotonic Pressure Drop Characteristics of Oil–Water Microflows,” Can. J. Chem. Eng., 93(10), pp. 1736–1743. [CrossRef]
Bashir, S. , Rees, J. M. , and Zimmerman, W. B. , 2011, “ Simulations of Microfluidic Droplet Formation Using the Two-Phase Level Set Method,” Chem. Eng. Sci., 66(20), pp. 4733–4741. [CrossRef]
Hua, H. , Shin, J. , and Kim, J. , 2013, “ Level Set, Phase-Field, and Immersed Boundary Methods for Two-Phase Fluid Flows,” ASME J. Fluids Eng., 136(2), p. 021301. [CrossRef]
Sharma, A. , Chaudhuri, J. , Kumar, V. , Timung, S. , Mandal, T. K. , and Bandyopadhyay, D. , 2015, “ Digitization of Two-Phase Flow Patterns in a Microchannel Induced by an External AC Field,” RSC Adv., 5(37), pp. 29545–29551. [CrossRef]
Liu, H. H. , and Zhang, Y. H. , 2011, “ Droplet Formation in Microfluidic Cross-Junctions,” Phys. Fluids, 23(8), pp. 1–12. [CrossRef]
Dupin, M. M. , Halliday, I. , and Care, C. M. , 2006, “ Simulation of a Microfluidic Flow-Focusing Device,” Phys. Rev. E, 73(5), pp. 1–4. [CrossRef]
Kim, L. S. , Jeong, H. K. , Ha, M. Y. , and Kim, K. C. , 2008, “ Numerical Simulation of Droplet Formation in a Micro-Channel Using the Lattice Boltzmann Method,” J. Mech. Sci. Technol., 22(4), pp. 770–779. [CrossRef]
Gupta, A. , Matharoo, H. S. , Makkar, D. , and Kumar, R. , 2014, “ Droplet Formation Via Squeezing Mechanism in a Microfluidic Flow-Focusing Device,” Comput. Fluids, 100, pp. 218–226. [CrossRef]
Nagel, M. , and Gallaire, F. , 2015, “ Boundary Elements Method for Microfluidic Two-Phase Flows in Shallow Channels,” Comput. Fluids, 107, pp. 272–284. [CrossRef]
Brackbill, J. U. , Kothe, D. B. , and Zemach, C. , 1992, “ A Continuum Method for Modeling Surface Tension,” J. Comput. Phys., 100(2), pp. 335–354. [CrossRef]
Hirt, C. W. , and Nichols, B. D. , 1981, “ Volume of Fluid (VOF) Method for the Dynamics of Free Boundaries,” J. Comput. Phys., 39(1), pp. 201–225. [CrossRef]
ANSYS FLUENT, 2011, ANSYS FLUENT Therory Guide, ANSYS, Inc., www.ansys.com.
Gupta, R. , Fletcher, D. F. , and Haynes, B. S. , 2009, “ On the CFD Modelling of Taylor Flow in Microchannels,” Chem. Eng. Sci., 64(12), pp. 2941–2950. [CrossRef]
Ngo, I.-L. , Dang, T.-D. , Byon, C. , and Joo, S. W. , 2015, “ A Numerical Study on the Dynamics of Droplet Formation in a Microfluidic Double T-Junction,” Biomicrofluidics, 9(2), p. 024107. [CrossRef] [PubMed]
Kashid, M. N. , Renken, A. , and Kiwi-Minsker, L. , 2010, “ CFD Modelling of Liquid–Liquid Multiphase Microstructured Reactor: Slug Flow Generation,” Chem. Eng. Res. Des., 88(3A), pp. 362–368. [CrossRef]
Raj, R. , Mathur, N. , and Buwa, V. V. , 2010, “ Numerical Simulations of Liquid−Liquid Flows in Microchannels,” Ind. Eng. Chem. Res., 49(21), pp. 10606–10614. [CrossRef]


Grahic Jump Location
Fig. 1

Schematic of MFCD. For simplicity, dispersed flow 1 (DP1) and dispersed flow 2 (DP2) are both water with the same fluid properties and inlet velocity, Ud. The length of side channels (Ls) is a parameter that depends on the junction angle (ϕ).

Grahic Jump Location
Fig. 2

Grid convergence study in comparison with the experimental study of Zheng et al. [13]. (a) Contours of volume fraction for various grid models for Ca = 0.038 and wf = 0.8 (red (or light gray): water, blue (or black): oil, and white: fluid-fluid interface). (b) The dependence of droplet diameter on the mesh resolution: Ca = 0.015 and wf = 0.4. Normalized droplet diameter is defined by (4Ad/π)0.5/Wc, where Ad is the droplet area.

Grahic Jump Location
Fig. 3

Phase diagrams of droplet formation in MFCD as a function of junction angle and capillary number with various water fractions at λ = 1.0 and β = 0.0173. The upper bound confines the ADPF near the AJF and JF, and the lower bound confines the ADPF near the MDPF.

Grahic Jump Location
Fig. 4

Evolution of distance between droplets versus time at Ca = 0.1, wf = 0.2, and β = 0.0173. The droplet distances were calculated relative to the main channel width (Wc).

Grahic Jump Location
Fig. 5

Variation of droplet length as a function of junction angles (ϕ) at (a) various capillary numbers (wf = 0.2) and (b) various water fractions (Ca = 0.05). Ld is the droplet length, which was defined in Fig. 1.

Grahic Jump Location
Fig. 6

Frequency of droplet generation in ADPF as a function of junction angles (ϕ) at various water fractions and capillary numbers

Grahic Jump Location
Fig. 7

Droplet formation as a function of viscosity ratio: Ca = 0.05, wf = 0.2, and λ = 1.0

Grahic Jump Location
Fig. 8

Droplet size as a function of viscosity ratio at various water fractions: Ca = 0.05 and λ = 1.0, Re = 0.0369




Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In