Optical sectioning for microfluidics: secondary flow and mixing in a meandering microchannel.

Secondary flow plays a critical function in a microchannel, such as a micromixer, because it can enhance heat and mass transfer. However, there is no experimental method to visualize the secondary flow and the associated mixing pattern in a microchannel because of difficulties in high-resolution, non-invasive, cross-sectional imaging. Here, we simultaneously imaged and quantified the secondary flow and pattern of two-liquid mixing inside a meandering square microchannel with spectral-domain Doppler optical coherence tomography. We observed an increase in the efficiency of two-liquid mixing when air was injected to produce a bubble-train flow and identified the three-dimensional enhancement mechanism behind the complex mixing phenomena. An alternating pair of counter-rotating and toroidal vortices cooperated to enhance two-liquid mixing.

[1]  Ruikang K. Wang,et al.  Theory, developments and applications of optical coherence tomography , 2005 .

[2]  W. R. Dean.  XVI. Note on the motion of fluid in a curved pipe , 1927 .

[3]  G. Ha Usler,et al.  "Coherence radar" and "spectral radar"-new tools for dermatological diagnosis. , 1998, Journal of biomedical optics.

[4]  F. Foster,et al.  A 100-200 MHz ultrasound biomicroscope , 2000, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[5]  W. R. Dean.  LXXII. The stream-line motion of fluid in a curved pipe (Second paper) , 1928 .

[6]  Martin A. Abraham,et al.  Flow patterns in liquid slugs during bubble-train flow inside capillaries , 1997 .

[7]  K. C. Cheng,et al.  Fully Developed Laminar Flow in Curved Rectangular Channels , 1976 .

[8]  Guk Bae Kim,et al.  X-ray PIV measurements of blood flows without tracer particles , 2006 .

[9]  Helen Song,et al.  Experimental test of scaling of mixing by chaotic advection in droplets moving through microfluidic channels. , 2003, Applied physics letters.

[10]  J. Eustice.  Experiments on stream-line motion in curved pipes , 1911 .

[11]  Steffen Hardt,et al.  Helical Flows and Chaotic Mixing in Curved Micro Channels , 2004 .

[12]  Steffen Hardt,et al.  Simulation of helical flows in microchannels , 2004 .

[13]  J. S. Sokhey,et al.  Laminar Incompressible Viscous Flow in Curved Ducts of Regular Cross-Sections , 1977 .

[14]  L. Back,et al.  Flow measurements in an atherosclerotic curved, tapered femoral artery model of man. , 1988, Journal of biomechanical engineering.

[15]  Zhongping Chen,et al.  Three-dimensional reconstruction of in vivo blood vessels in human skin using phase-resolved optical Doppler tomography , 2001 .

[16]  Woonggyu Jung,et al.  Quantification of a three-dimensional velocity vector using spectral-domain Doppler optical coherence tomography. , 2007, Optics letters.

[17]  J. Ottino.  Mixing, chaotic advection, and turbulence , 1990 .

[18]  Martin A. Abraham,et al.  Bubble-train flow in capillaries of circular and square cross section , 1995 .

[19]  R. Zawadzki,et al.  Real-time assessment of retinal blood flow with ultrafast acquisition by color Doppler Fourier domain optical coherence tomography. , 2003, Optics express.

[20]  L. Talbot,et al.  Pulsatile entrance flow in a curved pipe , 1983, Journal of Fluid Mechanics.

[21]  L. Talbot,et al.  Flow in Curved Pipes , 1983 .

[22]  S H Yun,et al.  Motion artifacts in optical coherence tomography with frequency-domain ranging. , 2004, Optics express.

[23]  Woonggyu Jung,et al.  Turbid two-phase slug flow in a microtube: Simultaneous visualization of structure and velocity field , 2006 .

[24]  Saif A. Khan,et al.  Transport and reaction in microscale segmented gas-liquid flow. , 2004, Lab on a chip.

[25]  Lei Wang,et al.  Frequency domain phase-resolved optical Doppler and Doppler variance tomography , 2004 .

[26]  John Eustice,et al.  Flow of water in curved pipes , 1910 .

[27]  L. Talbot,et al.  Laser anemometer study of flow development in curved circular pipes , 1978, Journal of Fluid Mechanics.

[28]  I. Mezić,et al.  Chaotic Mixer for Microchannels , 2002, Science.

[29]  M. C. Nichols,et al.  X-Ray Tomographic Microscopy (XTM) Using Synchrotron Radiation , 1992 .

[30]  M. Gharib,et al.  Defocusing digital particle image velocimetry and the three-dimensional characterization of two-phase flows , 2002 .