Characteristics of droplet and film water motion in the flow channels of polymer electrolyte membrane fuel cells

Zhan, Zhigang; Xiao, Jinsheng; Pan, Mu; Run-zhang, Yuan

doi:10.1016/j.jpowsour.2005.12.081

Cited by 75 publications

(35 citation statements)

References 12 publications

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“…[11][12][13][14][15] Optical imaging of transparent fuel cells has shown droplet growth and detachment, sometimes at preferential locations, or the formation of a film of liquid water. [16][17][18][19][20][21] Modeling efforts have focused on the transport of bulk water in the channels 22,23 or the conditions necessary to push liquid droplets along the surface of the GDL, 1,3,24,25 while others assumed the liquid droplets are suspended in the gas as a mist and carried out in the gas flow. 3 Another approach has been to build fuel cells with segmented electrodes to gain information about the current distribution over the active area of the MEA.…”

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confidence: 99%

Drops, slugs, and flooding in polymer electrolyte membrane fuel cells

et al. 2008

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in Wiley InterScience (www.interscience.wiley.com).The process of flooding has been examined with a single-channel fuel cell that permits direct observation of liquid water motion and local current density. As product water flows through the largest pores in the hydrophobic GDL, drops detach from the surface, aggregate, and form slugs. Flooding in polymer electrolyte membrane (PEM) fuel cells occurs when liquid water slugs accumulate in the gas flow channel, inhibiting reactant transport. Because of the importance of gravity, we observe different characteristics with different orientations of the flow channels. Liquid water may fall away from the GDL and be pushed out with minimal effect on the local current density, accumulate on the GDL surface and cause local fluctuations, or become a pulsating flow of liquid slugs and cause periodic oscillations. We show that flooding in PEM fuel cells is gravity-dependent and the local current densities depend on dynamics of liquid slugs moving through the flow channels. 2008 American Institute of Chemical Engineers AIChE J, 54: [1313][1314][1315][1316][1317][1318][1319][1320][1321][1322][1323][1324][1325][1326][1327][1328][1329][1330][1331][1332] 2008 Keywords: multi-phase flow, fuel cells, porous media, transport IntroductionPerhaps the greatest challenge facing fuel cells is the difficulty in maintaining stable operation and control due to flooding by liquid water. The build up of water produced at the membrane/cathode interface is known to limit the current output from PEM fuel cells. To describe the effects of flooding, several models have been proposed. [1][2][3][4][5][6] Most of these hypothesize that liquid water condenses in the pores of the gas diffusion layer (GDL) creating a mass transfer resistance for oxygen to get to the membrane/electrode interface as illustrated in Figure 1.Our group recently examined water permeation through the GDL and obtained results that contradicted the previous hypotheses about liquid flooding. 7 The GDL is a woven cloth or paper of carbon fibers that is usually treated with Teflon 1 to increase its hydrophobicity. We showed that water does not enter the GDL until a sufficient hydraulic pressure is applied to overcome the repulsive surface energy. The largest pores in the GDL are the first to permit water penetration, and once water penetrates the pores it can freely drain. Our results suggested a two-highway system for liquid and gas transport through the GDL, as illustrated in Figure 2. Liquid is driven by a hydraulic pressure from the membrane/cathode interface through the largest pores while gas moves from the gas flow channel to the membrane/cathode interface through smaller, but more plentiful, pores. Results that support these conclusions have also been reported using florescence microscopy to view the ex-situ transport of water through carbon paper. 8 Recently, water intrusion has been used to determine the capillary pressure vs. liquid saturation curves for different GDL materials 9,10 , providing pore volume distributions...

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Drops, slugs, and flooding in polymer electrolyte membrane fuel cells

et al. 2008

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“…Cai et al [14] investigated the effects of surface wettability of GDL on movement of a single droplet and film and concluded that a combination of the hydrophobic GDL with hydrophilic side walls was beneficial for water removal. Zhan et al [15] also investigated the droplet and film movements through a serpentine channel and provided similar conclusion to Cai et al [14]. Jiao and Zhou [16] were focused on developing an innovative gas diffusion layer with microchannel linking the catalyst layer with the flow channel.…”

Section: Introductionmentioning

confidence: 59%

“…Several papers have appeared recently in literature concerning the dynamic behavior of water droplet movement through the cathode channel [14][15][16][17][18][19][20][21][22][23][24][25][26]. Experimental studies have provided visual description of water droplet egress from the GDL and subsequent slug formation in the channel [4,[23][24].…”

Section: Introductionmentioning

confidence: 99%

“…However, because of the use of transparent wall for visual access, the experimental technique cannot reproduce the key role played by channel walls in water removal [19]. In this respect, the application of the volume of fluid (VOF) method in the computational fluid dynamics framework has provided many insights into the water dynamics in the cathode channel [14][15][16][17][18][19][20][21][22]. Cai et al [14] investigated the effects of surface wettability of GDL on movement of a single droplet and film and concluded that a combination of the hydrophobic GDL with hydrophilic side walls was beneficial for water removal.…”

Section: Introductionmentioning

confidence: 99%

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Water dynamics inside a cathode channel of a polymer electrolyte membrane fuel cell

et al. 2013

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CopyrightItems in 'OpenAIR@RGU', Robert Gordon University Open Access Institutional Repository, are protected by copyright and intellectual property law. If you believe that any material held in 'OpenAIR@RGU' infringes copyright, please contact openair-help@rgu.ac.uk with details. The item will be removed from the repository while the claim is investigated."NOTICE: this is the author's version of a work that was accepted for publication in Renewable Energy. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Renewable Energy, [VOL 50 (2013) AbstractThe present study focuses on the investigation of water dynamics inside a polymer electrolyte membrane fuel cell using two different modelling approaches: Eulerian two-phase mixture and volume of fluid interface tracking models. The Eulerian twophase mixture model has provided overall information of species distribution inside a fuel cell and identified that the liquid water usually accumulates under the land area.

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“…The water balance in the cathode is influenced by the hydrophobicity, porosity, and structure of the cathode. Several different approaches and models were proposed to manage the water in PEMFCs, such as new designs of gas channels [1][2][3], gas diffusion layers (GDL) [4][5][6], membranes [7][8][9][10], and single cell [11][12][13][14][15][16][17][18]. Using a micro-porous layer (MPL) to adjust the hydrophobicity of the electrode and to enhance the electrode performance has been widely adopted [19][20].…”

Section: Introductionmentioning

confidence: 99%

A Transient Model for Fuel Cell Cathode-Water Propagation Behavior inside a Cathode after a Step Potential

Chan

Hsueh

2010

Energies

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Abstract:Most of the voltage losses of proton exchange membrane fuel cells (PEMFC) are due to the sluggish kinetics of oxygen reduction on the cathode and the low oxygen diffusion rate inside the flooded cathode. To simulate the transient flooding in the cathode of a PEMFC, a transient model was developed. This model includes the material conservation of oxygen, vapor, water inside the gas diffusion layer (GDL) and micro-porous layer (MPL), and the electrode kinetics in the cathode catalyst layer (CL). The variation of hydrophobicity of each layer generated a wicking effect that moves water from one layer to the other. Since the GDL, MPL, and CL are made of composite materials with different hydrophilic and hydrophobic properties, a linear function of saturation was used to calculate the wetting contact angle of these composite materials. The balance among capillary force, gas/liquid pressure, and velocity of water in each layer was considered. Therefore, the dynamic behavior of PEMFC, with saturation transportation taken into account, was obtained in this study. A step change of the cell voltage was used to illustrate the transient phenomena of output current, water movement, and diffusion of oxygen and water vapor across the entire cathode.

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Characteristics of droplet and film water motion in the flow channels of polymer electrolyte membrane fuel cells

Cited by 75 publications

References 12 publications

Drops, slugs, and flooding in polymer electrolyte membrane fuel cells

Drops, slugs, and flooding in polymer electrolyte membrane fuel cells

Water dynamics inside a cathode channel of a polymer electrolyte membrane fuel cell

A Transient Model for Fuel Cell Cathode-Water Propagation Behavior inside a Cathode after a Step Potential

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