Visualization of Fuel Cell Water Transport and Performance Characterization under Freezing Conditions

Kandlikar, Satish G.; Lu, Zijie; Rao, Navalgund; Sergi, Jacqueline M.; Rath, Cody; McDade, C. Lee; Trabold, Thomas A.; Owejan, Jon P.; Gagliardo, Jeffrey J.; Allen, Jeffrey S.; Yassar, Reza S.; Médici, Ezequiel; Herescu, Alexandru

doi:10.2172/989206

Cited by 9 publications

(9 citation statements)

References 109 publications

(133 reference statements)

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“…However, y Ã can still provide important information regarding the size of the single-phase GDL region when the channel stream is in the two-phase flow. It is worthy to note that similar impact of the GDL thermal conductivity on liquid region was also observed by Kandlikar et al (2009) using neutron imaging. Fig.…”

Section: Resultssupporting

confidence: 70%

Elucidating two-phase transport in a polymer electrolyte fuel cell, Part 1: Characterizing flow regimes with a dimensionless group

Wang

Chen

2011

Chemical Engineering Science

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a b s t r a c tThis paper explores the through-/in-plane characteristics of water transport in the cathode gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). Theoretical analysis is performed on the non-isothermal two-phase flow under flow channels. A dimensionless group Da (Damkohler number for PEFC operation), defined as the ratio of water generation rate to water vapor-phase removal rate, is formulated to characterize the flow regimes in a PEFC. This group, lumping geometrical parameters and physical properties, compares the water vapor-phase removal capability (via water diffusion and holding capacity) with the rate of water production by the oxygen reduction reaction. We find that this dimensionless group can be used to characterize the non-isothermal, two-phase phenomena: when Da-0, the fuel cell is subjected to single-phase operation; while as Da-N we have full two-phase operation. A more precise expression is explored for the dimensionless group at the channel central line, i.e. Da 0 : when Da 0 4 1 the entire cathode GDL-CL (catalyst layer) interface is in two-phase region, whereas part of the interface is free of liquid water for Da 0 o 1. The latter scenario is the concept that this paper proposes for improving fuel cell water management: the consequent co-occurrence of single-and two-phase flows in the in-plane direction at Da 0 o 1 is beneficial to avoid severe dryout and flooding. A two-phase transport model, describing the water and heat transport on the PEFC cathode side, is employed to perform a two-dimensional numerical study. Detailed liquid and temperature distributions are displayed. Simulation predictions are in reasonably good agreement with the dimensionless-group analysis.

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Section: Resultssupporting

confidence: 70%

Elucidating two-phase transport in a polymer electrolyte fuel cell, Part 1: Characterizing flow regimes with a dimensionless group

Wang

Chen

2011

Chemical Engineering Science

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“…A sessile water droplet, characterized by a water volume = 34 nL and a contact angle θ left = θ right = 57.96 • , was finally formed and remained attached to the water bridge, obstructing the air micro-channel completely. This is consistent with plug flow observed to cause complete blockage of the bipolar plate channels in PEM fuel-cell flow [13]. The formation and stability of these liquid bridges is further discussed in Section 4 in conjunction with a mathematical model developed to predict the morphology, time of obstruction of the micro-channel, and the critical amount of liquid water needed to form a plug.…”

Section: Numerical Solutionsupporting

confidence: 67%

“…A number of studies have focused on two-phase flows in micro-channels related to fuel cells [1,10], where water generated as a by-product of electrochemical reactions can often condense. Excess accumulation of water ("flooding") reduces reactant transport and limits performance [11,12], but can also impact durability and operation under sub-zero temperatures [13,14]. Hydrophobic surfaces that promote water transport are commonly used to alleviate water management problems, and much ongoing research targets novel approaches such as surfaces with varying contact angles [15] and electrode structures that further facilitate water transport [16,17].…”

Section: Introductionmentioning

confidence: 99%

Investigation of Two-Phase Flow in a Hydrophobic Fuel-Cell Micro-Channel

et al. 2019

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This paper presents a quantitative visualization study and a theoretical analysis of two-phase flow relevant to polymer electrolyte membrane fuel cells (PEMFCs) in which liquid water management is critical to performance. Experiments were conducted in an air-flow microchannel with a hydrophobic surface and a side pore through which water was injected to mimic the cathode of a PEMFC. Four distinct flow patterns were identified: liquid bridge (plug), slug/plug, film flow, and water droplet flow under small Weber number conditions. Liquid bridges first evolve with quasi-static properties while remaining pinned; after reaching a critical volume, bridges depart from axisymmetry, block the flow channel, and exhibit lateral oscillations. A model that accounts for capillarity at low Bond number is proposed and shown to successfully predict the morphology, critical liquid volume and evolution of the liquid bridge, including deformation and complete blockage under specific conditions. The generality of the model is also illustrated for flow conditions encountered in the manipulation of polymeric materials and formation of liquid bridges between patterned surfaces. The experiments provide a database for validation of theoretical and computational methods.

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“…At θ = 140 o , the gas slug has not detached from the gas inlet by the time it reaches the end of the computational domain. It would appear possible at such hydrophobic channel conditions that the flow pattern could change to dropwise flow rather than slug flow, as experimentally observed by Kandlikar et al (2010) and Fang et al (2010). The difference between the slugs formed at 0 o and 20 o is mainly the film thickness around the gas slug, which can be inferred from the gas-phase cross-sectional area coverage (A G ) calculated based on Equation 7:…”

Section: Resultsmentioning

confidence: 90%

“…The use of nonwetting channels also resulted in higher void fraction, slower gas slugs, shorter liquid plugs and higher pressure drop. Barajas and Panton (1993) and Kandlikar et al (2010) have reported on shifts in flow pattern regimes due to changes in wetting properties of capillaries and microchannels, respectively. Barajas and Panton (1993) found that for partially wetting channels ( hydrophobic (100 o , silanized Lexan).…”

Section: Fundamental Wetting Principlesmentioning

confidence: 99%

Developments on Wetting Effects in Microfluidic Slug Flow

Kawaji

2012

Chemical Engineering Communications

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Wetting effects form a dimension of fluid dynamics that becomes predominant, precisely controllable and possibly useful at the micro-scale. Microfluidic multiphase flow patterns, including size, shape and velocity of fluidic particles, and mass and heat transfer rates are affected by wetting properties of microchannel walls and surface tensions forces between fluid phases. The novelty of this field, coupled to difficulties in experimental design and measurements, means that literature results are scarce and scientific understanding is incomplete. Numerical methods developed recently have enabled a shortcut in obtaining results that can be perceived realistic, and that offer insight otherwise not possible. In this work the effect of the contact angle on gas-liquid two-phase flow slug formation in a microchannel Tjunction was studied by numerical simulation. The contact angle, varied from 0 to 140 degrees, influenced the interaction of the gas and liquid phases with the channel wall, affecting the shape, size and velocity of the slugs. The visualisation of the cross-sectional area of gas slugs allowed for insight 2 into the existence of liquid flow along rectangular microchannel corners, which was affected by the contact angle and determined the occurrence of velocity slip. The velocity profile within the gas slugs was also found to change as a function of contact angle, with hydrophilic channels inducing greater internal circulation, compared to greater channel wall contact in the case of hydrophobic channels. These effects play a role in heat and mass transfer from channels walls and highlight the value of numeral simulation in microfluidic design.

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Visualization of Fuel Cell Water Transport and Performance Characterization under Freezing Conditions

Cited by 9 publications

References 109 publications

Elucidating two-phase transport in a polymer electrolyte fuel cell, Part 1: Characterizing flow regimes with a dimensionless group

Elucidating two-phase transport in a polymer electrolyte fuel cell, Part 1: Characterizing flow regimes with a dimensionless group

Investigation of Two-Phase Flow in a Hydrophobic Fuel-Cell Micro-Channel

Developments on Wetting Effects in Microfluidic Slug Flow

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