Research Papers: Fundamental Issues and Canonical Flows

Experimental Techniques for Bubble Dynamics Analysis in Microchannels: A Review

[+] Author and Article Information
Mahshid Mohammadi

e-mail: mohammma@onid.orst.edu

Kendra V. Sharp

Associate Professor
e-mail: kendra.sharp@oregonstate.edu
Department of Mechanical Engineering,
School of Mechanical, Industrial, and Manufacturing Engineering,
Oregon State University,
Corvallis, OR 97331

“High-speed” can be interpreted as thousands of frames per second; however, this term was also used in the cited literature for frame rates down to one hundred frames per second.

Manuscript received August 2, 2012; final manuscript received December 7, 2012; published online March 19, 2013. Assoc. Editor: David Sinton.

J. Fluids Eng 135(2), 021202 (Mar 19, 2013) (10 pages) Paper No: FE-12-1362; doi: 10.1115/1.4023450 History: Received August 02, 2012; Revised December 07, 2012

Experimental studies employing advanced measurement techniques have played an important role in the advancement of two-phase microfluidic systems. In particular, flow visualization is very helpful in understanding the physics of two-phase phenomenon in microdevices. The objective of this article is to provide a brief but inclusive review of the available methods for studying bubble dynamics in microchannels and to introduce prior studies, which developed these techniques or utilized them for a particular microchannel application. The majority of experimental techniques used for characterizing two-phase flow in microchannels employs high-speed imaging and requires direct optical access to the flow. Such methods include conventional brightfield microscopy, fluorescent microscopy, confocal scanning laser microscopy, and micro particle image velocimetry (micro-PIV). The application of these methods, as well as magnetic resonance imaging (MRI) and some novel techniques employing nonintrusive sensors, to multiphase microfluidic systems is presented in this review.

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Grahic Jump Location
Fig. 1

Schematic of shadowgraphy for a gas bubble in a liquid medium, adapted from Settles [17]

Grahic Jump Location
Fig. 2

Principles of GPVS and ILIDS techniques, courtesy of Dehaeck and van Beeck [76]

Grahic Jump Location
Fig. 3

Arrangement of the filters in a widefield fluorescent microscope with xenon/mercury arc light source

Grahic Jump Location
Fig. 4

Fluorescent images from different flow patterns in microchannels, (a) slug and plug flow, (b) annular flow, and (c) bubbly flow, courtesy of Waelchli and Rudolf von Rohr [84]

Grahic Jump Location
Fig. 5

Schematic illustration of confocal microscopy

Grahic Jump Location
Fig. 6

Particle images taken by (a) CSLM and (b) widefield fluorescent microscopy, courtesy of Park et al. [94]

Grahic Jump Location
Fig. 7

Scheme of data analysis for the determination of the film thickness: (a) optical slices in direction of the channel depth recorded with the CSLM. (b) Reconstruction of yz slices. (c) Average image of all yz slices in channel length direction. (d) Average image of the channel cross section with a schematic outline of the channel wall and observed films. Film thicknesses at the channel top (δf) and in the corner (δc) were measured, courtesy of Fries et al. [85].

Grahic Jump Location
Fig. 8

Schematic of a micro-PIV setup using a microscope, adopted from Lindken et al. [1]

Grahic Jump Location
Fig. 9

(a) Gas-liquid distribution within a ceramic monolith. (b) The map produced by correction to the image intensities arising from resonance frequency inhomogeneity and averaging the signal intensities across the width of each channel. (c) The ternary-gated map showing gas (black), solid (gray), and liquid (white), courtesy of Gladden et al. [112].




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