Skip to main content

Gravity-induced swirl of nanoparticles in microfluidics

Journal of Nanoparticle Research volume 15, Article number: 1611 (2013) Cite this article

Abstract

Parallel flows of two fluids in microfluidic devices are used for miniaturized chemistry, physics, biology and bioengineering studies, and the streams are often considered to remain parallel. However, as the two fluids do not always have the same density, interface reorientation induced by density stratification is unavoidable. In this paper, flow characteristics of an aqueous polystyrene nanofluid and a sucrose-densified aqueous solution flowing parallel in microchannels are examined. Nanoparticles 100 nm in diameter are used in the study. The motion of the nanoparticles is simulated using the Lagrangian description and directly observed by a confocal microscope. Matched results are obtained from computational and empirical analysis. Although solution density homogenizes rapidly resulting from a fast diffusion of sucrose in water, the nanofluid is observed to rotate for an extended period. Angular displacement of the nanofluid depends on the ratio of gravitational force to viscous force, Re/Fr 2, where Re is the Reynolds number and Fr is the Froude number. In the developing region at the steady state, the angular displacement is related to y/D h, the ratio between distance from the inlet and the hydraulic diameter of the microfluidic channel. The development of nanofluid flow feature also depends on h/w, the ratio of microfluidic channel’s height to width. The quantitative description of the angular displacement of nanofluid will aid rational designs of microfluidic devices utilizing multistream, multiphase flows.

This is a preview of subscription content, access via your institution.

Access options

Buy single article

Instant access to the full article PDF.

USD 39.95

Price includes VAT (USA)
Tax calculation will be finalised during checkout.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9

Abbreviations

x, y, z (μm):

Spatial coordinates

h (μm):

Microfluidic channel height

w (μm):

Microfluidic channel width

l (μm):

Microfluidic channel length

D h (μm):

Microfluidic channel hydraulic diameter

L p (μm):

Developing length

ρ (kg m−3):

Density of the fluid

μ (Pa s):

Viscosity of the fluid

p (Pa):

Static pressure

\( \overline{\overline{\tau }} \) (Pa):

Stress tensor

\( \vec{g} \) (m s−2):

Gravitational acceleration

\( \vec{u} \) (m s−1):

Fluid phase velocity

Y i :

Local mass fraction of each species

D i,m (m2 s−1):

Diffusion coefficient of species i in the mixture

\( \rho_{\text{P}} \) (kg m−3):

Density of the particles

d p (μm):

Particle diameter

\( \vec{u}_{\text{p}} \) (m s−1):

Particle velocity

\( \dot{m}_{\text{p}} \) (kg s−1):

Mass flow rate of the particles

\( \Updelta t \) (s):

Time step

\( C_{\text{D}} \) :

Drag coefficient

\( F_{\text{D}} \) (kg m s−2):

Drag force

T (K):

Absolute temperature of the fluid

k B :

Boltzmann constant

d i,j (Pa):

Deformation tensor

Fr :

Froude number

Re :

Reynolds number

\( Re_{\text{p}} \) :

Relative Reynolds number

References

Download references

Acknowledgments

We are grateful for the helpful discussions about confocal microscopy with Prof. H. Daniel Ou-Yang, Yi Hu, and Ming-Tzo Wei, about FLUENT with Yan Xu. We also thank Krissada Surawathanawises for Scanning Electron Microscope imaging. Funding for the research is provided by National Institute of Health under Grant No NIAID-1R21AI081638.

Author information

Authors and Affiliations

  1. Department of Materials Science and Engineering and Bioengineering Program, Lehigh University, Bethlehem, PA, USA

    Chao Zhao & Xuanhong Cheng

  2. Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, PA, USA

    Alparslan Oztekin

Authors
  1. Chao Zhao
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Alparslan Oztekin
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Xuanhong Cheng
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Xuanhong Cheng.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Zhao, C., Oztekin, A. & Cheng, X. Gravity-induced swirl of nanoparticles in microfluidics. J Nanopart Res 15, 1611 (2013). https://doi.org/10.1007/s11051-013-1611-8

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1007/s11051-013-1611-8

Keywords

  • Microfluidics
  • Density stratification
  • Nanoparticles
  • Angular displacement
  • Miscible fluids