Abstract
Synchrotron X-ray tomography images were used to study dynamic, regional water transfer behavior in the gas diffusion layer (GDL) during thawing and desaturation processes. Initially saturated, frozen GDLs were thawed and desaturated with air in a serpentine gas flow channel. On-the-fly (OTF) high speed CT scans via synchrotron X-ray allowed the capture of consecutive water transfer inside the GDL under the cold start-up gas purging condition. Desaturation data of Sigracet 35AA GDLs with three superficial gas velocities (2.88–5.98 m/s) were selected for analysis. Multiple spatial segmentation levels based on the flow field geometry, including channel vs. rib, individual channels and ribs, and smaller sections in each channel and rib, were applied to the in-plane direction to study the GDL regional thawing and desaturation behaviors. Each segmentation volume had a similar desaturation pattern in general; however, water distribution and desaturation show heterogeneity over the GDL domain, as well as relation with factors including the flow field geometry, air traveling distance, and initial saturation level. These data from the segmentation analysis expand the knowledge of localized water transfer behavior during the cold start thawing process. These data can also provide valuable information for future cold start modeling and help in optimizing the PEM fuel cell flow field design.
Highlights
Proton-exchange membrane fuel cells (PEM fuel cells) have gained increased interest as one of the clean energy solutions for small scale applications
Three desaturation phases were noted in the desaturation profiles in the large scale of gas diffusion layer (GDL) domain and locally in the smaller segmented areas: GDL warmup, partial thawing with water removal, and desaturation after complete thawing
Zooming into smaller segment levels, both the temporal desaturation profiles and the spatial saturation colormaps show that the purging distance, flow field geometry, and the initial saturation level play important roles in the GDL thawing and desaturation process, where longer purging distance and bend channel structures decreased the thawing speed
Summary
Proton-exchange membrane fuel cells (PEM fuel cells) have gained increased interest as one of the clean energy solutions for small scale applications. Owing to their high energy efficiency, zero emissions, and simplicity in operation, PEM fuel cells are considered as a promising clean energy alternative in future automobiles to replace the fossil fuel engines (Anderson et al, 2010; Pandian et al, 2010; Spiegel, 2008; Hardman et al, 2013; Lin et al, 2014; Amamou et al, 2016; Andersson et al, 2016). Excess water may cause blockages, which limit the gas transfer to the catalyst layer; insufficient water may cause membrane dehydration. Both issues can lead to performance loss and even irreversible cell degradation in the long term (Kim and Lee, 2013a; Siegwart et al, 2020).
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