Formation of bubbles in a microfluidic flow-focusing device
Date Issued
2015
Date
2015
Author(s)
Hung, Wei-Ti
Abstract
In this paper, liquid/gas flows were investigated in hydrophobic microchannels with square cross-section of 100 x 100 μm made of glass and PDMS. Liquid and gas were mixed in flow-focusing device in way to generate monodisperse gaseous bubbles. Air bubbles were produced in glycerol-water, ethanol-water and water with concentrations of surfactant sodium dodecyl sulfate (SDS). Flow morphologies were obtained by using Ca-Oh diagram. This diagram shown that the non-wetting region occurred at about Ca < 0.0045, the transition region occurred at about 0.0045 < Ca < 0.0070, and the wetting region occurred at about Ca > 0.0070. The experimental data of the bubbles size and elongated length were correlated as a function of the width of the microchannels, the ratio of the liquid/gas flow rates and the capillary number. The bubbles elongated length appeared first peak in non-wetting region could be predicted by the flow rates ratio of liquid and gas phases and the capillary number. Bubbles elongated length and size finally stable in wetting region occurred at about Ca > 0.0075. The bubbles size decreased rapidly in non-wetting region and decreased smoothly in wetting region. The bubbles size decreased with the increased of the viscosity and decreased with the decrease of the surface tension of liquid phase. Additionally, we also used a commercial software, Fluent, to analysis bubble formation. In Fluent, equilibrium contact angle is used as a boundary condition, however, the contact angle in the present experiment may be changed by the velocity of bubble, thus we can only analyzed the bubble formation qualitatively. Finally, the experimental results shown that the wetting bubbles would exist at low flow rates ratio which decreased the instability between the wall and the bubbles, and could be applied in fuel cells and heat dissipation of electronic equipment.
Subjects
microchannel
hydrophobic
two-phase flows
bubble
flow-focusing
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-104-R02522316-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):b1512063ea7a359e46d908b79297913f