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Keywords:

  • bubble;
  • breakup;
  • non-Newtonian;
  • flow-focusing;
  • microfluidics;
  • micro-PIV

Abstract

This study aims to investigate the breakup of slender bubbles in non-Newtonian fluids in microfluidic flow-focusing devices using a high-speed camera and a microparticle image velocimetry (micro-PIV) system. Experiments were conducted in 400- and 600-μm square microchannels. The variation of the minimum width of gaseous thread with the remaining time before pinch-off could be scaled as a power-law relationship with an exponent less than 1/3, obtained for the pinch-off of bubbles in Newtonian fluids. The velocity field and spatial viscosity distribution in the liquid phase around the gaseous thread were determined by micro-PIV to understand the bubble breakup mechanism. A scaling law was proposed to describe the size of bubbles generated in these non-Newtonian fluids at microscale. The results revealed that the rheological properties of the continuous phase affect significantly the bubble breakup in such microdevices. © 2012 American Institute of Chemical Engineers AIChE J,, 2012