Water Removal From Hydrophilic Fuel Cell Channels

2010 ◽  
Vol 7 (3) ◽  
Author(s):  
D. A. Caulk
Keyword(s):  
Fuel Cell ◽  
Liquid Water ◽  
Gas Flow ◽  
Proton Exchange Membrane ◽  
Proton Exchange ◽  
Operating Conditions ◽  
Surface Shear Stress ◽  
Two Phase ◽  
Surface Shear ◽  
Steady Solutions

This paper describes an approximate method for analyzing two-phase flow of gas and liquid water in fuel cell channels, whose surfaces are sufficiently hydrophilic for liquid water to wick spontaneously into the channel corners. This analysis is used to address the important question of whether the gas flow at typical stoichiometries in such channels is sufficient to remove all the liquid water generated in a proton exchange membrane fuel cell. Since fuel channels are usually much narrower than they are long, it is possible to adopt the usual approximations of lubrication theory and to decompose the general solution for the liquid motion into two parts: (1) that driven by the channel pressure gradient and (2) that driven by surface shear stress from the faster moving gas. When both parts of the solution are combined with the mass balance equations, it is possible to derive a pair of partial differential equations for the water depth and gas flow rate that depend on distance down the channel and time. Steady solutions of these equations are explored to determine the amount of liquid water that accumulates in the channel over a broad range of fuel cell operating conditions.

Water Removal From Hydrophilic Fuel Cell Channels

2008 ◽  
Author(s):  
D. A. Caulk
Keyword(s):  
Fuel Cell ◽  
Liquid Water ◽  
Gas Flow ◽  
Proton Exchange Membrane ◽  
Proton Exchange ◽  
Operating Conditions ◽  
Surface Shear Stress ◽  
Two Phase ◽  
Surface Shear ◽  
Steady Solutions

This paper describes an approximate method for analyzing two-phase flow of gas and liquid water in fuel cell channels whose surfaces are sufficiently hydrophilic for liquid water to wick spontaneously into the channel corners. This analysis is used to address the important question of whether the gas flow at typical stoichiometries in such channels is sufficient to remove all the liquid water generated in a Proton Exchange Membrane (PEM) fuel cell. Since fuel channels are usually much narrower than they are long, it is possible to adopt the usual approximations of lubrication theory and decompose the general solution for the liquid motion into two parts: (1) that driven by the channel pressure gradient, and (2) that driven by surface shear stress from the faster moving gas. When both parts of the solution are combined with the mass balance equations, it is possible to derive a pair of partial differential equations for the water depth and gas flow rate that depend on distance down the channel and time. Steady solutions of these equations are explored to determine the amount of liquid water that accumulates in the channel over a broad range of fuel cell operating conditions.

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.

Nonlinear Analysis of Two-Phase Instabilities in PEMFC Parallel-Channel Cathodes

2010 ◽  
Author(s):  
Nicholas Siefert ◽  
Chi-Hsin Ho ◽  
Shawn Litster
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Liquid Water ◽  
Proton Exchange Membrane ◽  
Critical Issue ◽  
Pem Fuel Cells ◽  
Proton Exchange ◽  
Stoichiometric Ratio ◽  
Two Phase ◽  
Voltage Loss

Liquid water management is a critical issue in the development of proton exchange membrane (PEM) fuel cells. Liquid water produced electrochemically can accumulate and flood the microchannels in the cathodes of PEM fuel cells. Since the liquid coverage of the cathode can fluctuate in time for two-phase flow, the rate of oxygen transport to the cathode catalyst layer can also fluctuate in time, and this can cause the fuel cell power output to fluctuate. This paper will report experimental data on the voltage loss and the voltage fluctuations of a PEM fuel cell due to flooding as a function of the number of parallel microchannels and the air flow rate stoichiometric ratio. The data was analyzed to identify general scaling relationships between voltage loss and fluctuations and the number of channels in parallel and the air stoichiometric ratio. The voltage loss was found to scale proportionally to the square root of the number of channels divided by the air stoichiometric ratio. The amplitude of the fluctuations was found to be linearly proportional to the number of microchannels and inversely proportional to the air stoichiometric ratio squared. The data was further analyzed by plotting power spectrums and by evaluating the non-linear statistics of the voltage time-series.

Multi-Phase Flow and Condensation in Proton Exchange Membrane Fuel Cells

2002 ◽  
Author(s):  
John M. Stockie
Keyword(s):  
Fuel Cell ◽  
Liquid Water ◽  
Proton Exchange Membrane ◽  
Transport Processes ◽  
Proton Exchange ◽  
Operating Conditions ◽  
Phase Flow ◽  
Multi Phase Flow ◽  
Multi Phase ◽  
Exchange Membrane

The porous electrodes in a proton exchange membrane fuel cell are characterized by multi-phase flow, involving liquid water and multispecies gases, that are undergoing both condensation and catalyzed reactions. Careful management of liquid water and heat in the fuel cell system is essential for optimizing performance. The primary focus of this study is thus on condensation and water transport, neither of which have yet been studied in as much detail as other aspects of fuel cell dynamics. We develop a two-dimensional model for multi-phase flow in a porous medium that captures the fundamental transport processes going on in the electrodes. The governing equations are discretized using a finite volume approach, and numerical simulations are performed in order to determine the effect of changing operating conditions on fuel cell performance.

An Analytical Solution to Predict the Inception of Two-Phase Flow in a Proton Exchange Membrane Fuel Cell

2010 ◽  
Vol 7 (6) ◽  
Author(s):  
A. S. Bansode ◽  
T. Sundararajan ◽  
Sarit K. Das
Keyword(s):  
Fuel Cell ◽  
Analytical Model ◽  
Current Density ◽  
Proton Exchange Membrane ◽  
Two Phase Flow ◽  
Proton Exchange ◽  
Operating Conditions ◽  
Phase Flow ◽  
Two Phase ◽  
Exchange Membrane

The presence of liquid water at the cathode of proton exchange membrane fuel cell hinders the reactant supply to the electrode and is known as electrode flooding. The flooding at the cathode due to the presence of two-phase flow of water is one of the major performance limiting conditions. A pseudo-two-dimensional analytical model is developed to predict the inception of two-phase flow along the length of the cathode channel. The diffusion of the water is considered to take place only across the gas diffusion layer (GDL). The current density corresponding to the inception of two-phase flow, called the threshold current density, is found to be a function of the channel length and height, GDL thickness, velocity, and relative humidity of the air at the inlet and cell temperature. Thus, for given design and operating conditions, the analytical model is capable of predicting the inception of two-phase flow, and therefore a flooding condition can be avoided in the first place.

Phase Change and Two Phase Flow in Cathode Porous Electrodes of Fuel Cells

2004 ◽  
Author(s):  
R. Bradean ◽  
K. Promislow ◽  
B. Wetton
Keyword(s):  
Fuel Cell ◽  
Phase Change ◽  
Liquid Water ◽  
Proton Exchange Membrane ◽  
Porous Electrode ◽  
Catalyst Layer ◽  
Proton Exchange ◽  
Porous Electrodes ◽  
Two Phase ◽  
Component Mixture

The steady state transport phenomena in the cathode porous electrode of a proton exchange membrane (PEM) fuel cell are investigated in a two-dimensional configuration near the outlet. The fuel cell is operated by hydrogen and humidified oxygen in a regime in which the porous cathode contains a two-phase two-component mixture of oxygen, water vapor and liquid water. Numerical results are presented for the liquid water, oxygen and temperature distributions through the cathode porous electrode. The phase change effect on the transport of reactant to the catalyst layer is found to be important.

Visualization Study of Cathode Flooding With Different Operating Conditions in a PEM Unit Fuel Cell

2005 ◽  
Author(s):  
Han-Sang Kim ◽  
Tae-Hun Ha ◽  
Sung-Jin Park ◽  
Kyoungdoug Min ◽  
Minsoo Kim
Keyword(s):  
Fuel Cell ◽  
Water Transport ◽  
Proton Exchange Membrane ◽  
Ccd Camera ◽  
Proton Exchange ◽  
Operating Conditions ◽  
Cathode Side ◽  
Two Phase ◽  
Fuel Cell Performance ◽  
Study Results

Visualization technique was used to better understand the water build-up phenomena on the cathode side of a proton exchange membrane (PEM) unit fuel cell. In this study, a transparent PEM unit fuel cell with an active area of 25 cm2 was designed and fabricated to allow for the visualization of cathode channel with fuel cell performance characteristics. Two-phase flow due to the electrochemical reaction of fuel cell was experimentally investigated. The images photographed by CCD camera with various cell temperatures (30–50°C) and different inlet humidification levels were presented in this study. Results indicated that the flooding on the cathode side first occurs near the exit of cathode flow channel. As the fuel cell operating temperature increases, it was found that water droplets tend to evaporate easily because of increased saturation vapor pressure and it can have an influence on lowering the flooding level. The approaches of this study can effectively contribute to the detailed researches on water transport phenomena including modeling water transport of an operating PEM fuel cell.

Modeling Effects of Two-Phase Transport in Cathode Gas Flow Channel on PEM Fuel Cell Performance

2011 ◽  
Author(s):  
Yun Wang ◽  
Ken S. Chen
Keyword(s):  
Fuel Cell ◽  
Case Studies ◽  
Liquid Water ◽  
Gas Flow ◽  
Pem Fuel Cell ◽  
Operating Conditions ◽  
Cell Performance ◽  
Two Phase ◽  
Fuel Cell Performance ◽  
Flow Channels

The objective of this study is to make an attempt at developing a sub-model that can account for the presence of liquid water in the cathode channel and couple it with other key phenomena occurring in a PEM fuel cell, including those in the anode side. The two-phase sub-model in cathode gas flow channels is based on the two-phase mixture formula. Numerical results from case studies are presented in comparison with those predicted by the single-phase channel flow sub-model. Our preliminary results indicate that liquid water accumulates along the flow channels and builds up quickly once it emerges. For the operating conditions and cell geometry chosen for the case study present in the present work, our results show that the liquid water in the channel only slightly affects the fuel cell performance. More extensive case studies are needed.

Investigation of Channel-to-Manifold Water Transport in Proton Exchange Membrane Fuel Cells

2012 ◽  
Author(s):  
X. Liu ◽  
J. Lin ◽  
K. M. McConnaghy ◽  
T. A. Trabold ◽  
J. J. Gagliardo ◽  
...  
Keyword(s):  
Fuel Cell ◽  
Water Transport ◽  
Liquid Water ◽  
Proton Exchange Membrane ◽  
Cross Flow ◽  
Bipolar Plate ◽  
Proton Exchange ◽  
Ex Situ ◽  
Two Phase ◽  
Exchange Membrane

Management of liquid water formed by the electrochemical reaction has received considerable attention and is considered a key factor in proton exchange membrane fuel cell (PEMFC) performance and durability. For practical stack applications, an aspect of the water management problem that is often overlooked is the transport of liquid water at the transition between the ends of the bipolar plate channels and the manifolds, where excess reactant flows from all the individual cells are combined and directed to the stack exhaust. In the bipolar plate exit region, gas-phase momentum can be very low, especially on the anode, and thus there is little driving force to remove liquid water. This study seeks to first quantify the characteristics of channel-to-manifold water transport by analysis of in-situ neutron radiography images, and correlation of the volumes of liquid water in the active and non-active regions to the relevant fuel cell operating conditions: temperature, pressure, relative humidity, current density and stoichiometric ratio. This analysis is complimented by new ex-situ experiments that directly control the flow of channel-level water and quantify the attendant increase in two-phase pressure drop in the non-active fuel cell region. The ex-situ apparatus has the additional feature of a simultaneous cross-flow channel at the exit plane of the bipolar plate, which enables simulation of two-phase flow dynamics of a fuel cell positioned anywhere in a stack, from zero cross-flow at the capped end of the stack to maximum cross-flow at the gas connected end of the stack.

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