Optical Measurement of Void Fraction and Bubble Size Distributions in a Microchannel

Abstract

An optical measurement system was developed to investigate gas-liquid two-phase flow characteristics in a circular microchannel of 100 μm diameter. By using multiple optical fibers and infrared photodiodes, void fraction, gas and liquid plug lengths, and their velocities were measured successfully. The probes responded to the passage of gas and liquid phases through the microchannel adequately so that the time-average void fraction could be obtained from the time fraction for each phase. Also, by cross-correlating the signals from two neighboring probes, the interface velocity representing gas plug velocity or ring-film propagation velocity depending on the flow pattern could be computed. Within the ranges of superficial gas and liquid velocities covered in the experiments (j L=0.2∼0.4 m/s and j G = 0∼5 m/s), the gas plug length was found to increase with the increasing superficial gas velocity, but the liquid plug length was found to decrease sharply as the superficial gas velocity was increased; thus, the total length of the gas-liquid plug unit decreased with the superficial gas velocity.

Effective pressure and bubble generation in a microfluidic T-junction

“…4 shows the relationship between a d and b d for bubbly and short slug (l d ( L 2 ) flows of the present data and those obtainable measurements in the literature. 12,13,28,29 Those data of b d from the literature in Fig. 4 were measured by flowmeters with the flow-rate range of 20-30 000 mL min À1 , which were much higher than that of the present investiga- Since most experimental data fall around the predicted curve within a reasonable small deviation band in Fig.…”

Characteristics of slug flow with inertial effects in a rectangular microchannel

“…Also gas hold-up is usually used to evaluate accelerational terms in the total pressure drop of gas-liquid flow (Yue et al, 2008(Yue et al, , 2009 There are already plenty of literature studies that consider void fraction in small/micro-capillaries or channels (Choi et al, 2011;Chung and Kawaji, 2004;Ide et al, 2007;Kawahara et al, 2009Kawahara et al, , 2011Kawahara et al, , 2005Saisorn and Wongwises, 2009Xiong and Chung, 2007;Yue et al, 2008). Generally, the void fraction correlation for microchannels as a function of volumetric quality (β) can be classified to two types: linear relationship of Armand-type α¼C A β and nonlinear relationship of α¼C 1 β 0.5 /(1-C 2 β 0.5 ).…”

Numerical Analysis of an Electroless Plating Problem in Gas–Liquid Two-Phase Flow

“…To measure it quantitatively, a high-quality optical system installed in the micro-channel is indispensable. For example, several types of fiber optical probes have been used to measure the particle (or bubble) size and distribution in a channel flow (or micro-channel flow) [53][54][55][56]. However, such an optical system is difficult to install in our case because there is no appropriate place to set up the light source and the detector in the micro-channel.…”