10.1021/acs.jpcc.6b10658.s001
Iryna V. Zenyuk
Iryna V.
Zenyuk
Adrien Lamibrac
Adrien
Lamibrac
Jens Eller
Jens
Eller
Dilworth Y. Parkinson
Dilworth Y.
Parkinson
Federica Marone
Federica
Marone
Felix N. Büchi
Felix N.
Büchi
Adam Z. Weber
Adam Z.
Weber
Investigating Evaporation in Gas Diffusion Layers
for Fuel Cells with X‑ray Computed Tomography
American Chemical Society
2016
evaporating water-front location
carbon gas-diffusion layers
saturation
X-ray CT studies
Gas Diffusion Layers
gas flow rate
understanding phase change
evaporation rate
GDL
liquid-water evaporation rates
water distribution
evaporation rates
liquid-water evaporation fronts
2016-11-21 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Investigating_Evaporation_in_Gas_Diffusion_Layers_for_Fuel_Cells_with_X_ray_Computed_Tomography/4312319
Understanding evaporation
in porous media and the associated water
distribution for a given saturation is critical for optimizing many
different technologies including polymer–electrolyte fuel cells.
In these devices, heat and mass-transport are coupled due to the two-phase
transport of water and operating temperatures from subzero to 80 °C.
Especially critical is understanding phase change in the mixed wettability,
carbon gas-diffusion layers (GDLs). While previous works have measured
evaporation rates empirically for a given saturation, there remains
a need to explore the mechanisms governing evaporation, which are
tied directly to the internal water distribution. In this article,
liquid-water evaporation rates in GDLs are measured <i>in situ</i> using synchrotron X-ray computed tomography (CT). X-ray CT allows
visualizing the evaporating water-front location and interfacial water/air
surface area, thereby enabling true surface-area based evaporation
rates. It is found that the overall specific evaporation rate is essentially
constant as a function of saturation and that the water/air interfacial
area scales almost linearly with saturation. To isolate transport
and kinetic contributions to the overall evaporation rate, we systematically
varied gas flow rate and composition. A three-dimensional mathematical
model with direct meshes of liquid-water evaporation fronts from the
X-ray CT studies allowed for the determination that the evaporation
is transport limited. The overall results provide insight into evaporation
phenomena in porous media.