This paper experimentally investigates the mechanism of water droplet detachment in a confined microchannel under highly inertial (10 < Re < 200) air flow conditions. Experimental observations show that as the Reynolds number of the continuous phase is increased, the droplet transitions from an elongated slug to a nearly uniform aspect ratio droplet. Supporting scaling arguments are then made that examine the relevant forces induced by the continuous phase on the droplet at the point of detachment. The inertial, viscous, and hydrodynamic pressure forces that result as the air flow is confined in the small gap between droplet and channel walls are compared to the surface tension force pinning the droplet at the injection site. The results indicate that the dominant detachment mechanism transitions from the hydrostatic pressure difference to inertial drag as the continuous phase velocity is increased.

References

References
1.
Bui
,
A.
, and
Zhu
,
Y.
,
2007
, “
Numerical Study of Droplet Generation in a Complex Micro-Channel
,”
Proceedings of the 16th Australasian Fluid Mechanics Conference
,
Gold Coast, Australia
.
2.
van der Graaf
,
S.
,
Steegmans
,
M.
,
van der Sman
,
R. G. M.
,
Schroen
C. G. P. H.
, and
Boom
,
R. M.
,
2005
, “
Droplet Formation in a T-Shaped Microchannel Junction: A Model System for Membrane Emulsification
,”
Colloids Surf., A
,
266
, pp.
106
116
.10.1016/j.colsurfa.2005.06.019
3.
van der Graaf
,
S.
,
Nisisako
,
T.
,
Schroen
,
C. G. P. H.
,
van der Sman
,
R. G. M.
, and
Boom
,
R.
,
2006
, “
Lattice Boltzmann Simulations of Droplet Formation in a T-Shaped Microchannel
,”
Langmuir
,
22
, pp.
4144
4152
.10.1021/la052682f
4.
Liu
,
H.
, and
Zhang
,
Y.
,
2009
, “
Droplet Formation in a T-Shaped Microfluidic Junction
,”
J. Appl. Phys.
,
106
, p.
034906
.10.1063/1.3187831
5.
Plateau
,
J.
,
1873
, “
Experimental and Theoretical Statistics of Liquids Subject to Molecular Forces Only
,”
Mem. Acad. R. Sci. Fr.
,
1
, pp.
4
24
.
6.
Savart
,
F.
,
1833
, “Memoire Sure le Choc D’une Veine Liquid Lancee Contre un Plan Circulair,”
Ann. Chim. Phys.
,
54
, pp.
54
87
.
7.
Rayleigh
,
L.
,
1878
, “
On the Instability of Jets
,”
Proc. London Math. Soc.
,
10
(
4
), pp.
4
13
.10.1112/plms/s1-10.1.4
8.
Rayleigh
,
L.
,
1879
, “
On the Capillary Phenomena of Jets
,”
Proc. R. Soc. London
,
29
, pp.
71
97
.10.1098/rspl.1879.0015
9.
Bogy
,
D. B.
,
1979
, “
Drop Formation in a Circular Liquid Jet
,”
Ann. Rev. Fluid Mech.
,
11
, pp.
207
228
.10.1146/annurev.fl.11.010179.001231
10.
Qian
,
J.
, and
Law
C. K.
,
1997
, “
Regimes of Coalescence and Separation in Droplet Collision
,”
J. Fluid Mech.
,
331
(
1
), pp.
59
80
.10.1017/S0022112096003722
11.
Orme
,
M.
,
1997
, “
Experiments on Droplet Collisions, Bounce, Coalescence and Disruption
,”
Prog. Energy Combust. Sci.
,
23
(
1
), pp.
65
79
.10.1016/S0360-1285(97)00005-1
12.
Simpson
,
S. F.
,
Kincaid
,
J. R.
, and
Holler
F. J.
,
1983
, “
Microdroplet Mixing for Rapid Reaction Kinetics With Raman Spectrometric Detection
,”
Anal. Chem.
,
55
(
8
), pp.
1420
1422
.10.1021/ac00259a054
13.
Wang
,
F.-C.
,
Feng
J.-T.
, and
Zhao
Y.-P.
,
2008
, “
The Head-On Colliding Process of Binary Liquid Droplets at Low Velocity: High-Speed Photography Experiments and Modeling
,”
J. Colloid Interface Sci.
,
326
(
1
), pp.
196
200
.10.1016/j.jcis.2008.07.002
14.
Aryafar
,
H.
, and
Kavehpour
,
H. P.
,
2006
, “
Drop Coalescence Through Planar Surfaces
,”
Phys. Fluids
,
18(7)
, p.
072105
.10.1063/1.2227435
15.
Christopher
,
G. F.
,
Bergstein
,
J.
,
End
,
N. B.
,
Poon
,
M.
,
Nguyen
,
C.
, and
Anna
S. L.
,
2009
, “
Coalescence and Splitting of Confined Droplets at Microfluidic Junctions
,”
Lab Chip
,
9
(
8
), pp.
1102
1109
.10.1039/b813062k
16.
Zhu
,
X.
,
Sui
,
P.
, and
Djilali
,
N.
,
2008
, “
Numerical Simulation of Emergence of a Water Droplet from a Pore into a Microchannel Gas Stream
,”
Microfluid. Nanofluid.
,
4
(
6
), pp.
543
555
.10.1007/s10404-007-0209-9
17.
Carroll
,
B.
, and
Hidrovo
,
C.
,
2009
, “
An Experimental Investigation of Droplet Detachment in High-Speed Microchannel Air Flow
,”
Proceedings of the 2nd ASME Micro/Nanoscale Heat & Mass Transfer International Conference
,
Shanghai, PRC
, Vol. 1, pp.
289
298
.
18.
Sugiura
,
S.
,
Nakajima
,
M.
, and
Seki
M.
,
2002
, “
Prediction of Droplet Diameter for Microchannel Emulsification
,”
Langmuir
,
18
(
10
), pp.
3854
3859
.10.1021/la0255830
19.
Hidrovo
,
C. H.
,
Wang
,
F. M.
,
Steinbrenner
,
J. E.
,
Lee
,
E. S.
,
Vigneron
,
S.
,
Cheng
,
C. H.
,
Eaton
,
J. K.
, and
Goodson
,
K. E.
,
2005
, “
Water Slug Detachment in Two-Phase Hydrophobic Microchannel Flows
,”
Proceedings of the ASME 3rd International Conference on Microchannels and Minichannels
, pp.
709
715
.
20.
Christopher
,
G.
, and
Anna
S.
,
2007
, “
Microfluidic Methods for Generating Continuous Droplet Streams
,”
J. Phys. D: Appl. Phys.
,
40
, pp.
319
336
.10.1088/0022-3727/40/19/R01
21.
Xiang
,
Y.
, and
LaVan
,
D.
,
2009
, “
Droplet Formation at Microfluidic T-Junctions
,”
Mater. Res. Soc. Symp. Proc.
,
1139
.
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