Understanding the flow structures induced by inertial focusing of particles is essential in microfluidics-based applications. In spite of numerous studies described in the literature, such microscale flows have, until today, not been subject to quantitative experimental study. This paper describes the construction and validation of a micro-particle image velocimetry-based experimental setup to investigate particle-induced flows in a confined microchannel. The flow structures around a single inertially focused particle are first visualized and quantitatively measured at Reynolds numbers Re from 21 to 525. A ring-like vortex flow is observed to form in front of the particle at Re = 63 owing to an increased particle lag effect, and finally the reverse flow regime is replaced by a vortex flow regime (at Re ≥ 105). This vortex flow produces a strong wall repulsive force and pushes the equilibrium position of the particle toward the channel center. Then, flows induced by both in-line and staggered particle trains are investigated (for 21 ≤ Re ≤ 105). For in-line particle trains, single-vortex flows are present between two neighboring particles on both sides of the channel. For staggered particle trains, two vortices rather than one are present between two neighboring particles at small Re (Re = 21), but this double-vortex flow develops into a single-vortex flow at relatively high Re (Re = 105). The present investigation helps in understanding particle dynamics and the mechanisms of interaction among particles, fluid, and channel walls. The experimental results presented here also provide validation data for further numerical and analytical studies.

1.
J. M.
Martel
and
M.
Toner
, “
Inertial focusing dynamics in spiral microchannels
,”
Phys. Fluids
24
,
032001
(
2012
).
2.
X.
Wang
,
H.
Gao
,
N.
Dindic
,
N.
Kaval
, and
I.
Papautsky
, “
A low-cost, plug-and-play inertial microfluidic helical capillary device for high-throughput flow cytometry
,”
Biomicrofluidics
11
,
014107
(
2017
).
3.
H. W.
Hou
,
R. P.
Bhattacharyya
,
D. T.
Hung
, and
J.
Han
, “
Direct detection and drug-resistance profiling of bacteremias using inertial microfluidics
,”
Lab Chip
15
(
10
),
2297
(
2015
).
4.
J.
Zhang
,
S.
Yan
,
D.
Yuan
,
G.
Alici
,
N. T.
Nguyen
,
M.
Ebrahimi Warkiani
, and
W.
Li
, “
Fundamentals and applications of inertial microfluidics: A review
,”
Lab Chip
16
(
1
),
10
(
2016
).
5.
G.
Segré
and
A.
Silberberg
, “
Radial particle displacements in Poiseuille flow of suspensions
,”
Nature
189
,
209
(
1961
).
6.
E. S.
Asmolov
, “
The inertial lift on a spherical particle in a plane Poiseuille flow at large channel Reynolds number
,”
J. Fluid Mech.
381
,
63
(
1999
).
7.
E. S.
Asmolov
, “
The inertial lift on a small particle in a weak-shear parabolic flow
,”
Phys. Fluids
14
,
15
(
2002
).
8.
L.
Zeng
,
S.
Balachandar
, and
P.
Fischer
, “
Wall-induced forces on a rigid sphere at finite Reynolds numbers
,”
J. Fluid Mech.
536
,
1
(
2005
).
9.
A.
Karimi
,
S.
Yazdi
, and
A. M.
Ardekani
, “
Hydrodynamic mechanisms of cell and particle trapping in microfluidics
,”
Biomicrofluidics
7
,
021501
(
2013
).
10.
D.
Di Carlo
,
D.
Irimia
,
R. G.
Tompkins
, and
M.
Toner
, “
Continuous inertial focusing, ordering, and separation of particles in microchannels
,”
Proc. Natl. Acad. Sci. U. S. A.
104
,
18892
(
2007
).
11.
D.
Di Carlo
, “
Inertial microfluidics
,”
Lab Chip
9
(
21
),
3038
(
2009
).
12.
B.
Chun
and
A. J. C.
Ladd
, “
Inertial migration of neutrally buoyant particles in a square duct: An investigation of multiple equilibrium positions
,”
Phys. Fluids
18
,
031704
(
2006
).
13.
A. A. S.
Bhagat
,
S. S.
Kuntaegowdanahalli
, and
I.
Papautsky
, “
Inertial microfluidics for continuous particle filtration and extraction
,”
Microfluid. Nanofluid.
7
,
217
(
2008
).
14.
Y. S.
Choi
,
K. W.
Seo
, and
S. J.
Lee
, “
Lateral and cross-lateral focusing of spherical particles in a square microchannel
,”
Lab Chip
11
(
3
),
460
(
2011
).
15.
M.
Abbas
,
P.
Magaud
,
Y.
Gao
, and
S.
Geoffroy
, “
Migration of finite sized particles in a laminar square channel flow from low to high Reynolds numbers
,”
Phys. Fluids
26
,
123301
(
2014
).
16.
S. C.
Hur
,
H. T.
Tse
, and
D.
Di Carlo
, “
Sheathless inertial cell ordering for extreme throughput flow cytometry
,”
Lab Chip
10
(
3
),
274
(
2010
).
17.
K. J.
Humphry
,
P. M.
Kulkarni
,
D. A.
Weitz
,
J. F.
Morris
, and
H. A.
Stone
, “
Axial and lateral particle ordering in finite Reynolds number channel flows
,”
Phys. Fluids
22
,
081703
(
2010
).
18.
J.
Zhou
and
I.
Papautsky
, “
Fundamentals of inertial focusing in microchannels
,”
Lab Chip
13
(
6
),
1121
(
2013
).
19.
A. A. S.
Bhagat
,
S. S.
Kuntaegowdanahalli
, and
I.
Papautsky
, “
Enhanced particle filtration in straight microchannels using shear-modulated inertial migration
,”
Phys. Fluids
20
,
101702
(
2008
).
20.
C.
Liu
,
G.
Hu
,
X.
Jiang
, and
J.
Sun
, “
Inertial focusing of spherical particles in rectangular microchannels over a wide range of Reynolds numbers
,”
Lab Chip
15
(
4
),
1168
(
2015
).
21.
K.
Miura
,
T.
Itano
, and
M.
Sugihara-Seki
, “
Inertial migration of neutrally buoyant spheres in a pressure-driven flow through square channels
,”
J. Fluid Mech.
749
,
320
(
2014
).
22.
N.
Nakagawa
,
T.
Yabu
,
R.
Otomo
,
A.
Kase
,
M.
Makino
,
T.
Itano
, and
M.
Sugihara-Seki
, “
Inertial migration of a spherical particle in laminar square channel flows from low to high Reynolds numbers
,”
J. Fluid Mech.
779
,
776
(
2015
).
23.
P. M.
Kulkarni
and
J. F.
Morris
, “
Pair-sphere trajectories in finite-Reynolds-number shear flow
,”
J. Fluid Mech.
596
,
413
(
2008
).
24.
H.
Haddadi
and
J. F.
Morris
, “
Topology of pair-sphere trajectories in finite inertia suspension shear flow and its effects on microstructure and rheology
,”
Phys. Fluids
27
,
043302
(
2015
).
25.
W.
Lee
,
H.
Amini
,
H. A.
Stone
, and
D.
Di Carlo
, “
Dynamic self-assembly and control of microfluidic particle crystals
,”
Proc. Natl. Acad. Sci. U. S. A.
107
,
22413
(
2010
).
26.
S.
Kahkeshani
,
H.
Haddadi
, and
D.
Di Carlo
, “
Preferred interparticle spacings in trains of particles in inertial microchannel flows
,”
J. Fluid Mech.
786
,
R3
(
2016
).
27.
H.
Amini
,
E.
Sollier
,
W. M.
Weaver
, and
D.
Di Carlo
, “
Intrinsic particle-induced lateral transport in microchannels
,”
Proc. Natl. Acad. Sci. U. S. A.
109
,
11593
(
2012
).
28.
F.
Xu
,
Z.
Pan
, and
H.
Wu
, “
Experimental investigation on the flow transition in different pin-fin arranged microchannels
,”
Microfluid. Nanofluid.
22
,
11
(
2017
).
29.
R.
Lindken
and
W.
Merzkirch
, “
A novel PIV technique for measurements in multiphase flows and its application to two-phase bubbly flows
,”
Exp. Fluids
33
,
814
(
2002
).
30.
F.
Shen
,
P.
Xiao
, and
Z.
Liu
, “
Microparticle image velocimetry (μPIV) study of microcavity flow at low Reynolds number
,”
Microfluid. Nanofluid.
19
,
403
(
2015
).
31.
A.
Chandramohan
,
S.
Dash
,
J. A.
Weibel
,
X.
Chen
, and
S. V.
Garimella
, “
Marangoni convection in evaporating organic liquid droplets on a nonwetting substrate
,”
Langmuir
32
,
4729
(
2016
).
32.
J. A.
Weibel
and
S. V.
Garimella
, “
Visualization of vapor formation regimes during capillary-fed boiling in sintered-powder heat pipe wicks
,”
Int. J. Heat Mass Transfer
55
,
3498
(
2012
).
33.
H.
Wang
,
X. F.
Peng
,
D. M.
Christopher
,
W. K.
Lin
, and
C.
Pan
, “
Investigation of bubble-top jet flow during subcooled boiling on wires
,”
Int. J. Heat Fluid Flow
26
,
485
(
2005
).
34.
M. J.
Rau
,
T.
Guo
,
P. P.
Vlachos
, and
S. V.
Garimella
, “
Stereo-PIV measurements of vapor-induced flow modifications in confined jet impingement boiling
,”
Int. J. Multiphase Flow
84
,
19
(
2016
).
35.
Y.
Kim
and
J.
Yoo
, “
The lateral migration of neutrally-buoyant spheres transported through square microchannels
,”
J. Micromech. Microeng.
18
,
065015
(
2008
).
36.
J.
Zhang
,
W.
Li
,
M.
Li
,
G.
Alici
, and
N.-T.
Nguyen
, “
Particle inertial focusing and its mechanism in a serpentine microchannel
,”
Microfluid. Nanofluid.
17
,
305
(
2014
).
37.
E. J.
Lim
,
T. J.
Ober
,
J. F.
Edd
,
S. P.
Desai
,
D.
Neal
,
K. W.
Bong
,
P. S.
Doyle
,
G. H.
McKinley
, and
M.
Toner
, “
Inertio-elastic focusing of bioparticles in microchannels at high throughput
,”
Nat. Commun.
5
,
4120
(
2014
).
38.
K.
Hood
,
K.
Soroush
,
D.
Di Carlo
, and
M.
Roper
, “
Direct measurement of particle inertial migration in rectangular microchannels
,”
Lab Chip
16
,
2840
(
2016
).
39.
J.
Ali
,
H.
Kim
,
U. K.
Cheang
, and
M. J.
Kim
, “
Micro-PIV measurements of flows induced by rotating microparticles near a boundary
,”
Microfluid. Nanofluid.
20
,
131
(
2016
).
40.
M.
Olsen
and
R.
Adrian
, “
Out-of-focus effects on particle image visibility and correlation in microscopic particle image velocimetry
,”
Exp. Fluids
29
,
S166
(
2000
).
41.
D.
Malsch
,
M.
Kielpinski
,
R.
Merthan
,
J.
Albert
,
G.
Mayer
,
J.
Kohler
,
H.
Suse
,
M.
Stahl
, and
T.
Henkel
, “
μPIV-analysis of Taylor flow in micro channels
,”
Chem. Eng. J.
135
,
S166
(
2008
).
42.
S.
Ma
,
J. M.
Sherwood
,
W. T.
Huck
, and
S.
Balabani
, “
On the flow topology inside droplets moving in rectangular microchannels
,”
Lab Chip
14
(
18
),
3611
(
2014
).
43.
S. T.
Wereley
,
L.
Gui
, and
C. D.
Meinhart
, “
Advanced algorithms for microscale particle image velocimetry
,”
AIAA J.
40
,
1047
(
2002
).
44.
S. T.
Wereley
and
C. D.
Meinhart
, “
Recent advances in micro-particle image velocimetry
,”
Annu. Rev. Fluid. Mech.
42
,
557
(
2010
).
45.
M.
Raffel
,
C.
Willert
, and
J.
Kompenhans
,
Particle Image Velocimetry: A Practical Guide
, 2nd ed. (
Springer
,
Berlin
,
2002
).
46.
B.
Wieneke
, “
PIV uncertainty quantification from correlation statistics
,”
Meas. Sci. Technol.
26
,
074002
(
2015
).
47.
F. M.
White
,
Fluid Mechanics
(
McGraw-Hill
,
New York
,
2003
).
48.
R.
Lindken
,
J.
Westerweel
, and
B.
Wieneke
, “
Stereoscopic micro particle image velocimetry
,”
Exp. Fluids
41
,
161
(
2006
).
49.
C. V.
Nguyen
,
A.
Fouras
, and
J.
Carberry
, “
Improvement of measurement accuracy in micro PIV by image overlapping
,”
Exp. Fluids
49
,
701
(
2010
).
50.
Z.
Li
,
L.
D’eramo
,
C.
Lee
,
F.
Monti
,
M.
Yonger
,
P.
Tabeling
,
B.
Chollet
,
B.
Bresson
, and
Y.
Tran
, “
Near-wall nanovelocimetry based on total internal reflection fluorescence with continuous tracking
,”
J. Fluid Mech.
766
,
147
(
2015
).
51.
Q.
Liu
and
A.
Prosperetti
, “
Wall effects on a rotating sphere
,”
J. Fluid Mech.
657
,
1
(
2010
).
52.
K.
Hood
and
M.
Roper
, “
Pairwise interactions in inertially driven one-dimensional microfluidic crystals
,”
Phys. Rev. Fluids
3
,
094201
(
2018
).
53.
D.
Klotsa
,
M. R.
Swift
,
R. M.
Bowley
, and
P. J.
King
, “
Chain formation of spheres in oscillatory fluid flows
,”
Phys. Rev. E
79
,
021302
(
2009
).

Supplementary Material

You do not currently have access to this content.