Experimental investigation and visualization of two-phase flow and water transport in microchannels

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.