The effect of microbubble emission boiling (MEB) on the mixing of two fluids in a microfluidic device was studied experimentally. When MEB occurred on an electric heater made of a platinum wire with a diameter of 30 micrometers, the mixing of the two fluids increased markedly. However, nucleate boiling had no significant effect on the mixing. A high-speed video showed that the very rapid growth and collapse of micro boiling bubbles on the heater causes the strong mixing of the two fluids. The coexistence of highly superheated and highly subcooled water near the heater seems to be the reason for such enhanced mixing.

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The mixing of two fluids is important in enhancing chemical reactions in a micro TAS. Some devices or methods are needed to enhance the mixing, because the Reynolds number is very low, on the order of 1. In the present research, we studied the possibility of using micro-bubble emission boiling. A heater made of a platinum wire of 30 micrometer was installed in a Y-shaped micro-channel whose cross sectional area was 2 mm × 0.5 mm. The heater was directly powered by electric current up to 1.5 A. The maximum heat flux was 7.47 MW/m2, which was well above the burnout heat flux. The subcool was 80 degrees and the velocity of fluid (colored water) was changed from 0.5 to 2.0 mm/s. When micro-bubble emission boiling occurred, the mixing was improved drastically. The mixing efficiency reached above 90% at v = 2.0 mm/s and q = 7.47MW/m2. In contrast, the mixing efficiency was poor in the case of normal nucleate boiling. The effect of the mixing chamber was also examined.

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