Research Papers: Multiphase Flows

Evanescent Wave-Based Flow Diagnostics

[+] Author and Article Information
Yutaka Kazoe

Department of Applied Chemistry,
The University of Tokyo,
7-3-1 Hongo,
Bunkyo, Tokyo 113-8656, Japan
e-mail: kazoe@icl.t.u-tokyo.ac.jp

Minami Yoda

G. W. Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332-0405
e-mail: minami@gatech.edu

Manuscript received May 30, 2012; final manuscript received December 5, 2012; published online March 19, 2013. Assoc. Editor: Deborah Pence.

J. Fluids Eng 135(2), 021305 (Mar 19, 2013) (11 pages) Paper No: FE-12-1268; doi: 10.1115/1.4023448 History: Received May 30, 2012; Revised December 05, 2012

Miniaturized flow systems have been developed for various applications, including integrated chemical analyses and thermal management of microelectronics. Understanding interfacial transport is important in designing and optimizing such flow systems, since surface effects become significant due to the large surface areas and small volumes at these length scales. Recently, various near-wall flow diagnostic techniques have been developed based on evanescent-wave illumination. Since evanescent waves only illuminate the fluid in the region over the first few hundred nanometers next to the wall, these techniques have much better spatial resolution than conventional methods based on epifluorescence microscopy. This paper presents recent advances in evanescent wave-based flow diagnostics using fluorescent tracers, including evanescent-wave particle velocimetry applied to flows driven by both pressure and voltage gradients and evanescent-wave fluorescence, which has been used to measure near-wall liquid temperature and pH fields, as well as the surface charge, or wall ζ-potential, distributions.

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Fig. 1

Schematics of (a) refraction of the light at an interface and (b) the evanescent wave by total internal reflection

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Fig. 2

Two configurations for TIRM: (a) objective lens-based and (b) prism-based optical systems

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Fig. 3

Schematic of evanescent-wave particle velocimetry

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Fig. 4

Behavior of near-wall fluorescent polystyrene particles of a = 110 nm suspended in 1 mM Na2B4O7 in a weak pressure-driven flow with a maximum speed in this region of approximately 10 μm/s, measured by evanescent-wave particle velocimetry [57]. (a) Near-wall Brownian diffusion coefficients for motion parallel D|| and perpendicular to the wall D compared with classical theory, as given by Eqs. (6) and (8). (b) Profile of the number density of particle c as function of z.

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Fig. 5

The near-wall velocities as a function of the wall-normal distance z in the three layers for the Poiseuille flow of 10 mM NH4HCO3 at different shear rates in (a) hydrophilic and (b) hydrophobically modified fused-silica channels. The lines denote weighted least squares fitting of the results.

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Fig. 6

The near-wall electroosmotic flow velocity uEO as a function of E, measured by MnPTV using three kinds of polystyrene (PS) particles and silica (SiO2) particles

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Fig. 7

Profiles of the particle number density c as function of z for a = 461-nm PS particles in electrokinetically driven flows at E = 0 (○), E = 15 V/cm (Δ), E = 22 V/cm (▿), and E = 31 V/cm (•)

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Fig. 8

Plot of average normalized fluorescence intensity of the emissions from fluorescein for the EFT calibrations If/If,20 as function of solution temperature T

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Fig. 9

Temperature profiles across the channel measured with EFT (points) over three 160 -μm-wide regions compared with FLUENT predictions for the wall surface temperature (solid line) and the temperature 50 μm from the wall (dashed line) for Poiseuille flow through the heated channel at Re = 3.3 (a) and 8.3 (b). The spatial resolution of the EFT data and the numerical predictions are 10 μm and 50 μm, respectively. The error bars denote a standard deviation for the EFT data.

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Fig. 10

(a) The wall ζ-potential profile over a fused-silica wall (z = 0) measured by nLIF in Poiseuille flow at two different average velocities, Uave = 174 μm and 420 μm. (b) Numerical predictions of the Na+ concentration profile at z = 4.4 μm.

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Fig. 11

A comparison of the electroosmotic mobility profiles over the OTS-patterned wall for a 2.5-mM NaCl solution obtained using two-color nLIF and evanescent wave particle velocimetry (nPTV)




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