<p>Proton exchange membrane (PEM) fuel cell are a pollutant-free type of energy systems which can replace internal combustion engines in automotive industry. As a PEM fuel cell operates, chemical energy is converted to electrical energy through electrochemical reactions. The two byproducts of these reactions are heat and water. The water produced in the cathode catalyst layer of proton exchange membrane (PEM) fuel cells can pass through the microporous layer and the gas diffusion layer (GDL) which are the two porous layers in PEM fuel cells. The transport of water through such porous layers is extensively investigated in literature. Briefly, the liquid water can pass through the porous structure of the GDL once its pressure exceeds the capillary pressure of the porous layer. Water then emerges from the surface of the GDL in gas flow channels. This forms liquid-gas two-phase flow in flow channels. The liquid water content in the flow channel can be quantified by measuring the pressure drop across the flow channel and comparing that to predictions from existing two-phase flow pressure drop models. While liquid-gas two-phase flow pressure drop is investigated in literature, all published works have investigated the steady two-phase flow pressure drop and the pressure drop during droplet emergence and growth has not been investigated in literature. In this study, this pressure drop is investigated by simultaneous measurement of the pressure drop across the drop and visualization of droplet growth with a high-speed camera. Experiments are conducted in a transparent flow channel that allows side-angle visualization with a high-speed camera. The transient two-phase flow pressure drop is obtained during the growth of droplets on the surface of the GDL. In this context, the transient pressure drop is defined as the two-phase flow pressure drop during liquid water droplet formation and growth in the flow channel. The pressure drop during droplet emergence can be compared to the gas single-phase pressure drop in order to obtain the drag force applied on the droplet. In addition, results can be used to define a C parameter in the separated flow model to scale the interaction between the droplet and the gas flow in the flow channel. For high gas flow rates which are capable of detaching droplets from the surface of the gas diffusion layer, the drag force can be correlated to the geometry of the droplet. Results that will publish in this study will be useful for groups that conduct numerical modeling of droplet dynamic in PEM fuel cell flow channels.</p>

Transient Two-Phase Flow Pressure Drop During Droplet Emergence and Growth in Gas Flow Channels

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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