Estimation of the effective thermal conductivity of carbon felts used as PEMFC Gas Diffusion Layers

Ramousse, Julien; Didierjean, Sophie; Lottin, Olivier; Maillet, Denis

doi:10.1016/j.ijthermalsci.2007.01.018

Cited by 104 publications

(95 citation statements)

References 14 publications

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“…Two terms are used each for the GDL and MPL PSDs; the values are given in Table I. The total PSD of the composite structure can be calculated from the individual layer PSDs by [67][68][69][70][71][72][73][74][75][76] …”

Section: Updated Porous-medium Model and Modeling Methodsologymentioning

confidence: 99%

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

Weber¹

2010

Journal of Power Sources

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A macroscopic-modeling methodology to account for the chemical and structural properties of fuel-cell diffusion media is developed. A previous model is updated to include for the first time the use of experimentally measured capillary pressure -saturation relationships through the introduction of a Gaussian contact-angle distribution into the property equations. The updated model is used to simulate various limiting-case scenarios of water and gas transport in fuel-cell diffusion media. Analysis of these results demonstrate that interfacial conditions are more important than bulk transport in these layers, where the associated mass-transfer resistance is the result of higher capillary pressures at the boundaries and the steepness of the capillary pressuresaturation relationship. The model is also used to examine the impact of a microporous layer, showing that it dominates the response of the overall diffusion medium. In addition, its primary mass-transfer-related effect is suggested to be limiting the water-injection sites into the more porous gas-diffusion layer.

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Section: Updated Porous-medium Model and Modeling Methodsologymentioning

confidence: 99%

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

Weber¹

2010

Journal of Power Sources

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“…Effective thermal conductivity may also be reported in relation to the applied stress with an accompanying stress-strain correlation 7,21 Other data is correlated to applied stress, but the original uncompressed sample thickness is used in Equation 2 or the compressed thickness is not reported. 4,5,22 In these instances the primary purpose of the measurements may be to model the overall heat transfer in an operating stack and not examine localized effects in the PTL. Thus, the thickness of the sample used in determining the k eff in Equation 2 may or may not be corrected for strain.…”

Section: Solid-cylinder Materials Modelmentioning

confidence: 99%

“…Experimental studies have been conducted to determine effective through-plane thermal conductivities of PTLs. [4][5][6][7][8][9][10] The term effective thermal conductivity is used because these values are not strictly material constants. PTLs are porous and chemically inhomogeneous and thermal conductivity is based on temperatures measured at opposite surfaces of the PTL.…”

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confidence: 99%

Material and Morphological Heat Transfer Properties of Fuel Cell Porous Transport Layers

Konduru

Allen

2017

J. Electrochem. Soc.

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The complex structure of the porous transport layer (PTLs), commonly referred to as gas diffusion layers (GDL), makes direct measurement of thermal transport properties difficult. Typically, effective thermal conductivity values are obtained experimentally and computational models are developed to replicate the measurements. This approach is sufficient for generalized one-dimensional models of fuel cell performance, but is not sufficient to predict reactant maldistribution due to the presence of liquid water in the PTL. Further, the anisotropy in the PTL structure results in dissimilar properties for through-plane and in-plane transport. In this work an analytical model is developed to extract material properties from effective thermal conductivity measurements. The model accounts for the change in the effective thermal conductivity as a function of compression. Geometric changes due to compression are separated from morphological changes using a compression modulation function; the shape of which is indicative of how fiber-to-fiber contact morphology changes with respect to strain. Material and morphological properties are determined using effective thermal conductivity data for three commercial PTLs. The properties also enable prediction of in-plane heat transfer using through-plane empirical data and also provide insight into morphological changes due to compression. A porous transport layer (PTL), more commonly referred to as a gas diffusion layer (GDL), has multiple purposes in a fuel cell including distribution of reactant gases to the catalyst layer, facilitation of product water removal from the catalyst layer, electronic and thermal conduction to/from the catalyst layer, and redistribution of compressive stresses across the membrane electrode assembly (MEA). A typical PTL consists of carbon fibers, either in fibrous or a non-woven morphology, along with binding agents and non-wetting agents such as polytetrafluoroethylene (PTFE). Examples of a non-woven and a fibrous PTL are shown in Figure 1. PTL designation is used herein because the transport phenomena of interest is not restricted to diffusion of reactant gases, but is focused heat transfer.Heat transfer across a dry PTL is primarily due to conduction. When liquid water is present, then additional heat may be transferred from the catalyst layer via evaporation and conduction via the liquid water occupying the void space. Either mode of heat transfer, conduction or evaporation, may be the dominant effect depending upon the operating conditions.1 The location of an evaporation front within a PTL depends upon the temperature and temperature gradient within the PTL. The same can be said for water condensation within the PTL as demonstrated by Caulk and Baker.2 A highly conductive PTL may increase the conduction of heat, but result in widely distributed condensation that can block reactant transport. A less conductive PTL may decrease the conduction of heat, but result in a sharp temperature gradient that generates a thin, uniform layer of water which al...

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“…Measurement Procedure Based on a reasoning from Ramousse et al [40] combined with our own experience [36], two porous surfaces merging and two flat surfaces adjacent results in much lower contact region resistances compared to that of a flat and a porous surface in contact. Therefore, the electrodes when subject to thermal measurements where inserted in pairs in the apparatus.…”

Section: Thermal Conductivity Measurementsmentioning

confidence: 99%

Thermal Conductivity, Heat Sources and Temperature Profiles of Li-Ion Batteries

et al. 2014

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In this paper we report the thermal conductivity of several commercial and noncommercial Li-ion secondary battery electrode materials with and without electrolyte solvents. We also measure the Tafel potential, the ohmic resistance, reaction entropy and external temperature of a commercial pouch cell secondary Li-ion battery. Finally we combined all the experimentally obtained data in a thermal model and discuss the corresponding internal temperature effects.The thermal conductivity of dry electrode material was found to range from 0.07 to 0.41 W K −1 m −1 while the electrode material soaked in electrolyte solvent ranged from 0.36 to 1.10 W K −1 m −1 . For all the different materials it was found that adding the electrolyte solvent increased the thermal conductivity by at least a factor of three. For one of the anode materials it was found that heat treatment at 3000 K increased the thermal conductivity by a factor of almost five.Measuring the electric heat sources of an air cooled commercial pouch cell battery at up to ± 2C and the thermal conductivity of the electrode components made it possible to estimate internal temperature profiles. Combining the heat sources with tabulated convective heat transfer coefficients of air allowed us to calculate the ambient temperature profiles. At 12C charging rate (corresponding to 5 minutes complete charging) the internal temperature differences was estimated to be in the range of 4-20K, depending on the electrode thermal conductivity. The external temperature drop in air flowing at the battery surface was estimated to nearly 40K. Evaluating thermal * Corresponding author; odnesb@hist.no management of batteries in the light of our measurement led to the conclusion that external cooling is more challenging than internal, though neither should be neglected.

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Estimation of the effective thermal conductivity of carbon felts used as PEMFC Gas Diffusion Layers

Cited by 104 publications

References 14 publications

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

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

Material and Morphological Heat Transfer Properties of Fuel Cell Porous Transport Layers

Thermal Conductivity, Heat Sources and Temperature Profiles of Li-Ion Batteries

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