Formation mechanism and size prediction of bubble in opposite-flowing T-shaped microchannel

Abstract

Abstract：Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N 2 bubbles were generated in glycerol-water mixtures with different concentrations of surfactant sodium dodecyl sulfate (SDS). And the images were captured by the high speed camera linked to a computer. Results indicated that the bubble formation process can be distinguished into three consecutive stages, i.e., expansion, collapse and pinching off. The bubble size decreases with the increase of liquid flow rate and viscosity of liquid phase as well as the decrease of gas flow rate. The surface tension of the liquid phase has no measurable influence on the bubble size. Moreover, a new approach to predicting the size of bubbles formed in the T-shaped microchannel is proposed. And the predicted values agree well with the experimental data. Keywords：microchannel; bubble formation; high speed camera; opposite-flowing Great efforts have been made to explore multiphase flow in microfluidic devices in recent years. Microscopic gas bubbles find numerous applications in fields such as high-throughput screening experiments, material synthesis [1] , drug discovery [2] , chemical engineering [3] and fluidic logic [4] . It is essential to predict and control the flow performances (e.g., flow patterns and bubble size) in these applications, which are closely related to flow rates, phase properties and geometries of microfluidic devices.The most popular geometries for the production of microbubbles are hydrodynamic flow-focusing devices [5][6][7] , geometry-dominated breakup microfluidic devices [8] and T-junction microchannels using crossflowing rupture technique [9][10][11] . However, the bubble formation mechanisms are quite different for different microfluidic devices. In flow-focusing devices, the bubble size is determined solely by the ratio of gas and liquid flow rate [6,7] . The bubble size in the geometry-dominated breakup technique increases with the viscosity of continuous phase, but is independent of surface tension and flow rate [8] . For cross-flowing rupture technique, the bubble size changes with flow rate and the viscosity of continuous phase [9,10] . In order to study the bubble formation mechanism in T-shaped microchannels using cross-flowing rupture technique, van Steijn et al [11] measured the transient flow field of fluid during the formation of bubbles using microscopic particle image velocimetry (µ-PIV) and obtained three-dimensional velocity distributions in continuous phase. But so far, the microbubble formation by opposite-flowing technique in T-shaped microchannels has not been reported yet.In this study, the bubble formation in an oppositeflowing T-shaped microchannel was investigated experimentally by a high speed camera. The influences of gas and liquid flow rates, and the properties of liquid phase on the bubble size were investigated.

Mass Transfer Characteristics of CO2 and Blended Aqueous Solutions of [C2OHmim][Lys]/MDEA in a Microchannel

“…When the liquid capillary number is less than 0.01, the bubble formation process conforms to the squeezing mechanism. Studies have shown a linear relationship between L B,0 / w and Q G / Q L under this condition as below: L normalB , 0 w = α + β Q normalG Q normalL where L B,0 is the initial bubble length (m) and w is the width of the microchannel (m).…”

“…When the liquid capillary number is less than 0.01, the bubble formation process conforms to the squeezing mechanism. Studies have shown a linear relationship between L B,0 /w and Q G /Q L under this condition as below: 42 L…”