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dc.contributor.authorGarcia-Salaberri, Pablo A.
dc.contributor.authorZenyuk, Iryna V.
dc.contributor.authorShum, Andrew D.
dc.contributor.authorHwang, Gisuk
dc.contributor.authorVera, Marcos
dc.contributor.authorWeber, Adam Z.
dc.contributor.authorGostick, Jeff T.
dc.identifier.citationGarcia-Salaberri, Pablo A.; Zenyuk, Iryna V.; Shum, Andrew D.; Hwang, Gisuk; Vera, Marcos; Weber, Adam Z.; Gostick, Jeff T. 2018. Analysis of representative elementary volume and through-plane regional characteristics of carbon-fiber papers: diffusivity, permeability and electrical/thermal conductivity. International Journal of Heat and Mass Transfer, vol. 127:pt. B:pp 687-703en_US
dc.descriptionClick on the DOI link to access the article (may not be free).en_US
dc.description.abstractUnderstanding the transport processes that occur in carbon-fiber papers (CFPs) used in fuel cells, electrolyzers, and metal-air/redox flow batteries is necessary to help predict cell performance and durability, optimize materials and diagnose problems. The most common technique used to model these thin, heterogeneous, anisotropic porous media is the volume-averaged approximation based on the existence of a representative elementary volume (REV). However, the applicability of the continuum hypothesis to these materials has been questioned many times, and the error incurred in the predictions is yet to be quantified. In this work, the existence of a REV in CFPs is assessed in terms of dry effective transport properties: mass diffusivity, permeability and electrical/thermal conductivity. Multiple sub-samples with different widths and thicknesses are examined by combining the lattice Boltzmann method with X-ray tomography images of four uncompressed CFPs. The results show that a meaningful length scale can be defined in the material plane in the order of 1-2 mm, which is comparable to the rib/channel width used in the aforementioned devices. As for the through-plane direction, no distinctive length scale smaller than the thickness can be identified due to the lack of a well-defined separation between pore and volume-averaged scales in these inherently thin heterogeneous materials. The results also show that the highly porous surface region (amounting up to 20% of the thickness) significantly reduces the through-plane electrical/thermal conductivity. Overall, good agreement is found with previous experimental data of virtually uncompressed CFPs when approximately the full thickness is considered.en_US
dc.description.sponsorshipFuel Cell Performance and Durability Consortium (FC-PAD), by the Fuel Cell Technologies Office (FCTO), Office of Energy Efficiency and Renewable Energy (EERE), of the U.S. Department of Energy under contract number DE-AC02-05CH11231, Project ENE2015-68703-C2-1-R (MINECO/FEDER, UE) and the research grant 'Ayudas a la Investigation en Energia y Medio Ambiente' awarded to the first author by the Spanish lberdrola Foundation. I.V. Zenyuk and A.D. Shum would like to acknowledge support from the National Science Foundation under CBET Award 1605159. X-ray tomography experiments were performed on beamline 8.3.2 at the ALS (Lawrence Berkeley National Laboratory), which is a national user facility funded by the Department of Energy, Office of Basic Energy Sciences under contract DE-ACO2-05CH11231. Numerical calculations were performed on the supercomputing clusters Briaree, Colosse, Guillimin and Mp2, managed by Calcul Quebec and Compute Canada. The operation of these supercomputers is funded by the Canada Foundation for Innovation (CFI), Ministere de l'Economie, de l'Innovation et des Exportations du Quebec (MEIE), RMGA and the Fonds de recherche du Quebec -Nature et technologies (FRQ-NT).en_US
dc.relation.ispartofseriesInternational Journal of Heat and Mass Transfer;v.127:pt.B
dc.subjectCarbon-fiber paperen_US
dc.subjectEffective propertiesen_US
dc.subjectRepresentative elementary volumeen_US
dc.subjectX-ray tomographyen_US
dc.subjectEnergy conversion and storageen_US
dc.titleAnalysis of representative elementary volume and through-plane regional characteristics of carbon-fiber papers: diffusivity, permeability and electrical/thermal conductivityen_US
dc.rights.holder© 2018 Elsevier Ltd. All rights reserved.en_US

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