Two-Phase Flow and Transport in the Interdigitated Air Cathode of Proton Exchange Membrane Fuel Cells

2000 ◽  
Author(s):  
Z. H. Wang ◽  
C. Y. Wang
Keyword(s):  
Current Density ◽  
Liquid Water ◽  
Two Phase Flow ◽  
Water Saturation ◽  
Gas Diffusion ◽  
Phase Flow ◽  
Air Cathode ◽  
Phase Zone ◽  
Two Phase ◽  
Flow And Transport

Abstract The two-phase flow and transport in an interdigitated air cathode is studied numerically by applying the multiphase, multicomponent transport model previously developed for conventional air cathodes. A computational fluid dynamics (CFD) technique is used to solve the two-dimensional model for the interdigitated air cathode, and the contours of oxygen concentration, water vapor concentration and liquid water saturation as well as the velocity vector fields of gas and liquid phases are obtained. A polarization curve is presented which includes both the single- and two-phase operating regimes. It is found that the threshold critical current density at which the two-phase zone begins to appear inside the porous cathode is higher than that of the conventional air cathode. The maximum liquid water saturation is found to be about 0.045 for a dry inlet at an average current density of 2.07A/cm2. Both gas diffusion and convection play significant roles in oxygen supply and water removal. A higher inlet relative humidity produces a more extensive two-phase zone in the interdigitated air cathode.

Investigation of Flooding Phenomena in PEMFC by Two-Phase Flow Numerical Simulation

2005 ◽  
Author(s):  
Kohei Ito ◽  
Hiromitsu Masuda ◽  
Tomohiko Miyazaki ◽  
Yasushi Kakimoto ◽  
Takashi Masuoka
Keyword(s):  
Numerical Simulation ◽  
Current Density ◽  
Two Phase Flow ◽  
Water Saturation ◽  
High Current Density ◽  
Electric Circuit ◽  
Current Density Distribution ◽  
Phase Flow ◽  
Phase Zone ◽  
Two Phase

Water Problem, which is represented by the flooding and the drying in PEMFC, is one of the critical issues relating to the recent trend of high current density operation of it. For spreading the practical use of PEMFC, we must grasp this problem exactly and resolve it. Two-phase flow numerical simulation is useful for this purpose. In this study, we numerically analyzed a unit-PEMFC two-dimensionally considering the two-phase flow based on the multiphase mixture model developed by Cheng and Wang, adding the authors’ equivalent electric circuit. We simulated not only steady state but also unsteady state. A slightly abrupt change in current density distribution appeared on the point where the interface between the one- and the two-phase zone in GDL was appeared. The distribution of water saturation after cell operation start changed with time passed: the liquid water tend to focus on the GDL after once it spread in both GDL and flow channel.

Two-Phase Flow Considerations in PEMFC Design and Operation

2008 ◽  
Author(s):  
Jon P. Owejan ◽  
Jeffrey J. Gagliardo ◽  
Jacqueline M. Sergi ◽  
Thomas A. Trabold
Keyword(s):  
Liquid Water ◽  
Proton Exchange Membrane ◽  
Two Phase Flow ◽  
Bipolar Plate ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Phase Flow ◽  
Two Phase ◽  
Flowing Hydrogen ◽  
Flow Effects

A proton exchange membrane fuel cell (PEMFC) must maintain a balance between the hydration level required for efficient proton transfer and excess liquid water that can impede the flow of gases to the electrodes where the reactions take place. Therefore, it is critically important to understand the two-phase flow of liquid water combined with either the co-flowing hydrogen (anode) or air (cathode) streams. In this paper, we describe the design of an in-situ test apparatus that enables investigation of two-phase channel flow within PEMFCs, including the flow of water from the porous gas diffusion layer (GDL) into the channel gas flows; the flow of water within the bipolar plate channels themselves; and the dynamics of flow through multiple channels connected to common manifolds which maintain a uniform pressure differential across all possible flow paths. These two-phase flow effects have been studied at relatively low operating temperatures under steady-state conditions and during transient air purging sequences.

The Experimental Study of Water Accumulation in PEMFC Cathode Channel

2015 ◽  
Author(s):  
Ali Bozorgnezhad ◽  
Mehrzad Shams ◽  
Goodarz Ahmadi ◽  
Homayoon Kanani ◽  
Mohammadreza Hasheminasab
Keyword(s):  
Liquid Water ◽  
Internal Combustion Engines ◽  
Two Phase Flow ◽  
Gas Diffusion ◽  
Green Energy ◽  
Proton Exchange ◽  
Phase Flow ◽  
Two Phase ◽  
Coverage Ratio ◽  
Water Accumulation

In the recent years, Proton Exchange Membrane Fuel Cell (PEMFC) has attracted much attention as a source of green energy and alternative to internal combustion engines. The PEMFC produces electrical power with heat and water as only byproducts. Water is needed to providing proper hydration of membrane and its ionic conductivity in PEMFCs, but excess water accumulation known as flooding phenomenon decreases reaction sites on gas diffusion and increases mass transport loss and consequently it leads to performance loss of PEMFC. Proper water management depends on characterization and study two-phase flow phenomenon of PEMFC as flooding. In the present work, the two-phase flow in the cathode channel of transparent PEMFC with single serpentine flow field is studied by direct optical visualization and utilization of Digital Image Processing for different inlet flow parameters and operational conditions. Liquid water accumulation in the cathode channel is quantified and the water coverage ratio is calculated as a scale of water content of the cathode channel in the unsteady and time-averaged states. Increasing the temperature and stoichiometry decrease the accumulation of liquid water in the cathode channel while increasing the reactants relative humidity leads to accumulation of more liquid water. Observations show in higher cathode stoichiometries, the effect of anode stoichiometry on the water coverage ratio decreases. The effect of anode stoichiometry on the water coverage ratio is more than the cathode stoichiometry. In higher anode stoichiometries, the effect of cathode stoichiometry on the water coverage ratio decreases so that the change in cathode stoichiometry has no significant effect on the values of water coverage ratio.

scholarly journals Numerical Simulation of a Two-Phase Flow for the Acrylonitrile Electrolytic Adiponitrile Process in a Vertical/Horizontal Electrolysis Cell

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2731
Author(s):  
Jiin-Yuh Jang ◽  
Yu-Feng Gan
Keyword(s):  
Void Fraction ◽  
Current Density ◽  
Two Phase Flow ◽  
Horizontal Cell ◽  
Gas Diffusion ◽  
Electrolysis Cell ◽  
Electrical Potential Difference ◽  
Phase Flow ◽  
Two Phase ◽  
Vertical Cell

This paper investigated the effect of oxygen holdup on the current density distribution over the electrode of a vertical/horizontal electrolysis cell with a two-dimensional Eulerian–Eulerian two-phase flow model in the acrylonitrile (AN) electrolytic adiponitrile (ADN) process. The physical models consisted of a vertical/horizontal electrolysis cell 10 mm wide and 600 mm long. The electrical potential difference between the anode and cathode was fixed at 5 V, which corresponded to a uniform current density j = 0.4 A/cm2 without any bubbles released from the electrodes. The effects of different inlet electrolyte velocities (vin = 0.4, 0.6, 1.0 and 1.5 m/s) on the void fraction and the current density distributions were discussed in detail. It is shown that, for a given applied voltage, as the electrolyte velocity is increased, the gas diffusion layer thickness decreased and this resulted in the decrease of the gas void fraction and increase of the corresponding current density; for a given velocity, the current density for a vertical cell was higher than that for a horizontal cell. Furthermore, assuming the release of uniform mass flux for the oxygen results in overestimation of the total gas accumulation mass flow rate by 2.8% and 5.8% and it will also result in underestimation of the current density by 0.3% and 2.4% for a vertical cell and a horizontal cell, respectively. The results of this study can provide useful information for the design of an ADN electrolysis cell.

Imaging and Resistivity Studies of Saturation Gradients in Two-Phase Flow in 3-D Porous Media

1996 ◽  
Vol 464 ◽  
Author(s):  
E. H. Kawamoto ◽  
Po-Zen Wong
Keyword(s):  
Computed Tomography ◽  
Porous Media ◽  
Two Phase Flow ◽  
Water Saturation ◽  
Glass Beads ◽  
Water Phase ◽  
Phase Flow ◽  
Two Phase ◽  
Vertical Column ◽  
X Ray

ABSTRACTWe have carried out x-ray radiography and computed tomography (CT) to study two-phase flow in 3-D porous media. Air-brine displacement was imaged for drainage and imbibition experiments in a vertical column of glass beads. By correlating water saturation Sw with resistance R, we find that there is a threshold saturation S* ≈ 0.2, above which R(SW) ∼ Sw−2, in agreement with the empirical Archie relation. This holds true for both drainage and imbibition with littlehysteresis, provided that Sw remains above S*. Should Sw drop below S* during drainage, R(Sw) rises above the Archie prediction, exhibiting strong hysteresis upon reimbibition. This behavior suggests a transition in the connectivity of the water phase near S*, possibly due to percolation effects.

Mathematical modeling of two-phase flow and transport in an immobilized-cell photobioreactor

2011 ◽  
Vol 36 (21) ◽  
pp. 13939-13948 ◽  
Author(s):  
Qiang Liao ◽  
Da-Meng Liu ◽  
Ding-Ding Ye ◽  
Xun Zhu ◽  
Duu-Jong Lee
Keyword(s):  
Mathematical Modeling ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Immobilized Cell ◽  
Two Phase ◽  
Flow And Transport

Two-Phase Transport in Proton Exchange Membrane Fuel Cells

1999 ◽  
Author(s):  
C. Y. Wang ◽  
Z. H. Wang ◽  
Y. Pan
Keyword(s):  
Fuel Cell ◽  
Current Density ◽  
Liquid Water ◽  
Proton Exchange Membrane ◽  
Threshold Current ◽  
Threshold Current Density ◽  
Proton Exchange ◽  
Air Cathode ◽  
Two Phase ◽  
Exchange Membrane

Abstract Proton exchange membrane (PEM) fuel cells have emerged, in the last decade, as a viable technology for power generation and energy conversion. Fuel cell (FC) engines for vehicular applications possess many attributes such as high fuel efficiency, low emission, quiet and low temperature operation, and modularity. An important phenomenon limiting fuel cell performance is the two-phase flow and transport of fuel and oxidant from flow channels to reaction sites. In this paper a mathematical model is presented to study the two-phase flow dynamics, multi-component transport and electrochemical kinetics in the air cathode, the most important component of the hydrogen PEM fuel cell. A major feature of the present model is that it unifies single- and two-phase analyses for low and high current densities, respectively, and it is capable of predicting the threshold current density corresponding to the onset of liquid water formation in the air cathode. A numerical study based on the finite volume method is then undertaken to calculate the detailed distributions of local current density, oxygen concentration, water vapor concentration and liquid water saturation as well as their effects on the cell polarization curve. The simulated polarization curve and predicted threshold current density corresponding to the onset of liquid water formation for a single-channel, 5cm2 fuel cell compare favorably with experimental results. Quantitative comparisons with experiments presently being conducted at our laboratory will be reported in a forthcoming paper.

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