In this paper we present an overview of the experimental work carried out as part of research geared towards the understanding of two-phase flow in microchannels. The greater scope of the project is to use the knowledge gained towards the development of strategies to improve water management in fuel cell applications. We have conducted pressure versus flow rate experiments in microchannels with contrasting hydrophobic characteristics and under different liquid water injection conditions. These measurements have been complemented with flow visualization studies using white light and fluorescence. As expected, parameters associated to surface energy such as hydrophobicity have a big influence on the flow. Under hydrophobic conditions the formation of slugs or blobs of size comparable to that of the microchannel greatly impedes the flow of air, especially at low pressure drops. On the other hand liquid water effects under hydrophilic conditions are only noticeable at large injection rates (100 μL/min). In contrast to their hydrophobic counterparts, two-phase flow in hydrophilic microchannels is characterized by the formation of a thin film of liquid. Only when the thickness of the film becomes substantial does it have an effect on the air flow.

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The improved rates of heat transfer in microchannel gas flows are promising for the design and development of microfluidic systems. This research focuses on the flow characteristics of air in rectangular micro/minichannels at moderate velocities (∼100 m/sec). The 50.8 mm long channels vary from approximately 266 μm to 1090 μm in hydraulic diameter, and the aspect ratio ranges from 0.1 to 0.75. The value of Re ranged from 250 to 4300, with the intention of studying the transition to turbulence. The friction factor is found to be higher than predicted values for Re < 1400 and lower when Re > 1400 suggesting earlier transition to turbulence.