Microfluidics and Nanofluidics

, Volume 16, Issue 6, pp 1047–1055

Pinch-off mechanism for Taylor bubble formation in a microfluidic flow-focusing device

Authors

  • Yutao Lu
    • State Key Laboratory of Chemical Engineering, School of Chemical Engineering and TechnologyTianjin University
    • State Key Laboratory of Chemical Engineering, School of Chemical Engineering and TechnologyTianjin University
  • Chunying Zhu
    • State Key Laboratory of Chemical Engineering, School of Chemical Engineering and TechnologyTianjin University
    • State Key Laboratory of Chemical Engineering, School of Chemical Engineering and TechnologyTianjin University
  • Huai Z. Li
    • Laboratory of Reactions and Process EngineeringUniversity of Lorraine, CNRS
Research Paper

DOI: 10.1007/s10404-013-1274-x

Cite this article as:
Lu, Y., Fu, T., Zhu, C. et al. Microfluid Nanofluid (2014) 16: 1047. doi:10.1007/s10404-013-1274-x

Abstract

The present work aims at studying the nonlinear breakup mechanism for Taylor bubble formation in a microfluidic flow-focusing device by using a high-speed digital camera. Experiments were carried out in a square microchannel with cross section of 600 × 600 μm. During the nonlinear collapse process, the variation of the minimum radius of bubble neck (r0) with the remaining time until pinch-off (τ) can be scaled by a power–law relationship: \(r_{0} \propto \tau^{\alpha } .\) Due to the interface rearrangement around the neck, the nonlinear collapse process can be divided into two distinct stages: liquid squeezing collapse stage and free pinch-off stage. In the liquid squeezing collapse stage, the neck collapses under the constriction of the liquid flow and the exponent α approaches to 0.33 with the increase in the liquid flow rate Ql. In the free pinch-off stage, the value of α is close to the theoretical value of 0.50 derived from the Rayleigh–Plesset equation and is independent of Ql.

Keywords

MicrofluidicsMultiphase flowNonlinear dynamicsInterfaceConfinementPinch-off

List of symbols

p

Capillary pressure, Pa

Ql

Liquid volumetric flow rate, mL h−1

Qg

Gas volumetric flow rate, mL h−1

QF

Liquid volumetric flow rate through the flow-focusing region, mL h−1

QN

Liquid volumetric flow rate calculated from the pictures, mL h−1

r

Radius of the bubble neck, μm

r0

Minimum radial radius of the neck, μm

rc

Minimum axial radius of the neck, μm

t

Neck collapse time, μs

tc

Moment of bubble pinch-off, μs

tcap

Capillary time, μs

VN

Volume of the neck, mL

wb

Width of the bubble neck, μm

wd

Depth of the channel, μm

Greek letters

α

Exponent for radial curvature

β

Exponent for axial curvature

λ

Slenderness of the neck (rc/r0)

η

Viscosity, m Pa s

ρ

Density, kg m−3

σ

Surface tension, m N m−1

τ

Remaining time to pinch-off, μs

Dimensionless groups

Ca

Capillary number (l/σ)

Re

Reynold number (ρlr0r0/ηl)

We

Weber number (ρr0(r0)2/σ)

Subscripts

c

Critical time for bubble pinch-off

cap

Capillary time

F

Flow-focusing region

g

Gas

kfps

Kilo frames per second

l

Liquid

N

Neck of the bubble

Copyright information

© Springer-Verlag Berlin Heidelberg 2013