Validated Leverett Approach for Multiphase Flow in PEFC Diffusion Media

Abstract

The final paper in this series is devoted to delineating the effects of temperature on the multiphase transport characteristics of thin-film polymer electrolyte fuel cell ͑PEFC͒ diffusion media ͑DM͒. Direct measurements of capillary pressure-saturation of various commercial DM coated with a wide range of poly͑tetrafluoroethylene͒ ͑PTFE͒ loadings ͑from 5 to 20 wt % PTFE͒ were performed at different operating temperatures ͑20, 50, and 80°C͒. The benchmark data gathered from these experiments ͑available upon request͒ were compiled into the existing database generated from the first and second phase of this study, which examined the hydrophobicity and compression effects. The expanded database was then utilized to deduce a unified form of an empirical correlation appropriate for the tested DM. This semiempirical approach can predict capillary pressure of the tested DM as a function of liquid saturation, hydrophobic additive content, uncompressed porosity, compression pressure, and operating temperature within an uncertainty of ±14% of the measured capillary pressure over the entire saturation domain, showing considerable improvement over the traditional Leverett approach.

Improved modeling and understanding of diffusion-media wettability on polymer-electrolyte-fuel-cell performance

“…While the previous model depends on fitting the various parameters to tangential data such as overall flow through a DM, it is now possible for the direct measurement of capillary-pressure versus saturation curves using various contact and equilibrium methods [8,[25][26][27][28][29][30][31][32][33][34]. The proposed procedure is similar to that of Cheung et al [28], although they use a continuous CAD but a discrete PSD.…”

“…concentrations. Second, the above analysis has ignored a couple of issues such as GDL anisotropies [68,84,85] and compression [8,86,87], which can somewhat be accounted for by using average properties and capillary pressure -saturation curves measured under operating-type conditions. Overall, the above methodology allows for one to go beyond simple curve fits and thus can provide educated guesses to the impact of various properties.…”

“…This is typically done by calculating a saturation or liquid pore-volume fraction using relationships such as the Leverett J-function [5][6][7][8][9], and then using the saturation to modify the intrinsic or dry-medium transport properties using relations like those of Corey [10], (Brooks-Corey) [11], Van Genuchten [12], or Bruggemann [13][14][15]. The more intricate porelevel modeling [16][17][18][19][20][21][22][23][24] has allowed the calculation of various transport properties from a handful of statistical structural properties such as pore-and throat-size distributions, porosity, and bulktransport measurements including saturated permeabilities.…”

“…However, recently several groups have begun to gain the expertise and apparati to study some of the material properties such as hydrophilic and hydrophobic pore-size distributions (PSDs) and capillary pressure versus saturation curves [8,[25][26][27][28][29][30][31][32][33][34]. These curves have been measured under a variety of conditions including compression and hydrophobic loading.…”

Electrochemical Immunosensor Using a Gas Diffusion Layer as an Immobilization Matrix

“…Because the GDL used in this experiment is very hydrophobic (contact angles ≈ 137.7) due to the PTFE, 8 the SAM does not form to an appreciable extent. Thus, a gold layer, which serves as an anchoring site for the SAM on the PTFE, was deposited on the GDL surface by sputtering.…”