Simulation of Liquid Water Evaporation in GDL for PEMFC Under Gas Purge Condition

2011 ◽  
Author(s):  
Gen Inoue ◽  
Naoyuki Ishibe ◽  
Yosuke Matsukuma ◽  
Masaki Minemoto
Keyword(s):  
Porous Structure ◽  
Network Model ◽  
Liquid Water ◽  
Gas Diffusion ◽  
Water Evaporation ◽  
Uniform Structure ◽  
Interface Area ◽  
Two Phase ◽  
Actual Structure ◽  
Gas Purge

In automotive Polymer Electrolyte Fuel Cell (PEFC) system, dry gas purge operation is needed at shutdown condition in order to remove the liquid water in gas diffusion layer (GDL) and to reduce the oxygen diffusion inhibition by liquid water in GDL. However, exceed drying operation leads to degradation of electrolyte membrane because of little water content. Therefore, drying process has to be optimized. In this study, various GDL structure with unique fiber orientation were simulated by numerical analysis, and the real GDL structure was reconstructed by X-ray CT image of carbon paper GDL. Next, our past two-phase network model was improved to include phase change effect. The multi-block two-phase network model based on an actual structure was developed by a direct 3D networking porous structure. As results, the evaporation interface area depended on the porous structure of GDL, and the overall evaporation rate of homogeneous GDL which has uniform structure was 1.5 time higher than that of heterogeneous GDL because of the difference of this interface area. In addition, in the case of rib and channel, liquid water under channel evaporated faster than that under Rib. It is very important to control the drying operation in order to prevent the excess membrane drying.

Evaluation of Two-Phase Condition and Mass Transfer in GDL With Pore Network Model

2009 ◽  
Author(s):  
Gen Inoue ◽  
Yosuke Matsukuma ◽  
Masaki Minemoto
Keyword(s):  
Network Model ◽  
Effective Diffusion ◽  
Gas Diffusion ◽  
Pore Network Model ◽  
Two Phase ◽  
Actual Structure ◽  
Actual Measurement ◽  
Output Performance ◽  
Phase Condition ◽  
Diffusion Coefficient Of Oxygen

In order to improve the output performance of PEFC, it is important to investigate the two-phase condition in gas diffusion layer (GDL). In this study, the simulated GDL structure was developed by numerical analysis including the random orientation of carbon fibers and binders. And detailed structural estimation was carried out. As structural properties, pore size distribution, electrical resistivity and tortuosity were calculated, and these values almost agreed with actual measurement values. Furthermore, our past two-phase network model was improved, and the model based on an actual structure was developed by a direct 3D networking porous structure. And the influence of GDL structure on the two-phase condition with accumulated water was evaluated, and effective diffusion coefficient of oxygen in GDL with liquid water was calculated.

scholarly journals Mass Transport Limitations of Water Evaporation in Polymer Electrolyte Fuel Cell Gas Diffusion Layers

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2967
Author(s):  
Adrian Mularczyk ◽  
Andreas Michalski ◽  
Michael Striednig ◽  
Robert Herrendörfer ◽  
Thomas J. Schmidt ◽  
...  
Keyword(s):  
Fuel Cell ◽  
Liquid Water ◽  
Evaporative Cooling ◽  
Gas Diffusion ◽  
Polymer Electrolyte Fuel Cell ◽  
Ex Situ ◽  
Water Evaporation ◽  
Evaporative Water ◽  
Gas Diffusion Layers ◽  
Diffusion Layers

Facilitating the proper handling of water is one of the main challenges to overcome when trying to improve fuel cell performance. Specifically, enhanced removal of liquid water from the porous gas diffusion layers (GDLs) holds a lot of potential, but has proven to be non-trivial. A main contributor to this removal process is the gaseous transport of water following evaporation inside the GDL or catalyst layer domain. Vapor transport is desired over liquid removal, as the liquid water takes up pore space otherwise available for reactant gas supply to the catalytically active sites and opens up the possibility to remove the waste heat of the cell by evaporative cooling concepts. To better understand evaporative water removal from fuel cells and facilitate the evaporative cooling concept developed at the Paul Scherrer Institute, the effect of gas speed (0.5–10 m/s), temperature (30–60 °C), and evaporation domain (0.8–10 mm) on the evaporation rate of water from a GDL (TGP-H-120, 10 wt% PTFE) has been investigated using an ex situ approach, combined with X-ray tomographic microscopy. An along-the-channel model showed good agreement with the measured values and was used to extrapolate the differential approach to larger domains and to investigate parameter variations that were not covered experimentally.

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.

Analytical Solution for Two-Phase Flow in PEMFC Gas Diffusion Layer

2006 ◽  
Author(s):  
Mingfei Gan ◽  
Lea-Der Chen
Keyword(s):  
Water Management ◽  
Analytical Solution ◽  
Oxygen Concentration ◽  
Active Layer ◽  
Diffusion Layer ◽  
Liquid Water ◽  
Flow Model ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Two Phase

Thermal and water management is critical to fuel cell performance. It has been shown that gas diffusion layer (GDL) can impose the mass transport limit; for example, it can block the reactant transport to active layer when flooding occurs at high current density conditions. Micro porous layer (MPL) in conjunction with backing layer (BL) has been used as a GDL material and was shown to be effective for water management. To study the transport processes in GDL and MPL modified GDL, an analytical solution is derived current study for calculation of two-phase, multicomponent transport in GDL. Two models were considered, the unsaturated flow model (UFM) and the separate flow model (SFM). Comparison of the calculated saturation level and oxygen mass fraction shows that UFM calculation can underestimate, as well as overestimate the saturation and oxygen concentration. The SFM was used to study the effects due to GDL property variations. The calculation shows that increase in liquid water transport in an MPL modified GDL is due to the abrupt change of liquid water flow rate when a step change in porosity or permeability is imposed. The calculation further shows that particle size of around 1 μm would be a good choice for MPL as it results in higher oxygen concentration at active layer and lower saturation in GDL.

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.

Numerical Simulation of Liquid Water Behavior in Separator-Channels in PEMFC Using LBM

2005 ◽  
Author(s):  
Yutaka Tabe ◽  
Takamichi Ochi ◽  
Kazushige Kikuta ◽  
Takemi Chikahisa ◽  
Hideki Shinohara
Keyword(s):  
Diffusion Layer ◽  
Liquid Water ◽  
Polymer Electrolyte Membrane ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Two Phase ◽  
Cross Sectional ◽  
Electrolyte Membrane ◽  
Water Behavior ◽  
Condensed Water

In a polymer electrolyte membrane fuel cell, the condensed water in the separator-channel prevents the supply of reactants to electrodes, which deteriorates the cell performance. The Lattice Boltzmann simulation has been conducted to understand the behavior of condensed water in the separator-channels. The scheme for the two-phase flow with large density difference was applied and the boundary condition for wettability at the corner inside the channel was examined. The present simulation demonstrates the effects of the cross-sectional shape, the wettability of channel and the volume of condensed water on the liquid water behavior. In the hydrophilic separator-channels, the liquid water spreads along the channel wall to form film and, in a specific condition, the water draws away from the gas diffusion layer, which suppresses the flooding. On the other hand, the liquid water forms sphere, covering larger area of the surface of gas diffusion layer in the hydrophobic separator-channels, but the drain performance of liquid water is superior.

Liquid Water Transport in Polymer Electrolyte Fuel Cells With Multi-Layer Diffusion Media

2004 ◽  
Author(s):  
Ugur Pasaogullari ◽  
Chao-Yang Wang ◽  
Ken S. Chen
Keyword(s):  
Pore Size ◽  
Polymer Electrolyte ◽  
Liquid Water ◽  
Average Pore Size ◽  
Gas Diffusion ◽  
Polymer Electrolyte Fuel Cells ◽  
Two Phase ◽  
Average Pore ◽  
Diffusion Media ◽  
Liquid Water Transport

A two-phase, multi-component, full cell model is developed in order to analyze the two-phase transport in polymer electrolyte fuel cells with multi-layer cathode gas diffusion media, consisting of a coarse gas diffusion layer (GDL) (average pore size ~ 10 μm) and a micro-porous layer (MPL) (average pore size ~ 0.2–2 μm). The relevant structural properties of MPL, including average pore size, wettability, thickness and porosity are examined and their effects on liquid water transport are discussed. It is found that MPL promotes back-flow of liquid water across the membrane towards the anode, consequently alleviating cathode flooding. Furthermore, it is seen that unique porous and wetting characteristics of MPL causes a discontinuity in the liquid saturation at MPL-GDL interface, which in turn reduces the amount of liquid water in cathode catalyst layer-gas diffusion medium interface in some cases. Our analyses show that the back-flow of liquid water increases with the increasing thickness and decreasing pore size, hydrophobicity and bulk porosity of the MPL.

scholarly journals Pore-Scale Modeling of Air–Water Two Phase Flow and Oxygen Transport in Gas Diffusion Layer of Proton Exchange Membrane Fuel Cell

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3812
Author(s):  
Chongbo Zhou ◽  
Lingyi Guo ◽  
Li Chen ◽  
Xin Tian ◽  
Tiefeng He ◽  
...  
Keyword(s):  
Liquid Water ◽  
Reactive Transport ◽  
Proton Exchange Membrane ◽  
Water Saturation ◽  
Gas Diffusion ◽  
Transport Processes ◽  
Proton Exchange ◽  
Scale Model ◽  
Pore Scale ◽  
Two Phase

Understanding multiphase flow and gas transport occurring in electrodes is crucial for improving the performance of proton exchange membrane fuel cells. In the present study, a pore-scale model using the lattice Boltzmann method (LBM) was proposed to study the coupled processes of air–water two-phase flow and oxygen reactive transport processes in porous structures of the gas diffusion layer (GDL) and in fractures of the microscopic porous layer (MPL). Three-dimensional pore-scale numerical results show that the liquid water generation rate is gradually reduced as the oxygen consumption reaction proceeds, and the liquid water saturation in the GDL increases, thus the constant velocity inlet or pressure inlet condition cannot be maintained while the results showed that at t = 1,200,000 iterations after 2900 h running time, the local saturation at the GDL/MPL was about 0.7, and the maximum value was about 0.83, while the total saturation was 0.35. The current density reduced from 2.39 to 0.46 A cm-2. Effects of fracture number were also investigated, and the results showed that for the fracture numbers of 8, 12, 16, and 24, the breakthrough point number was 4, 3, 3, and 2, respectively. As the fracture number increased, the number of the water breakthrough points at the GDL/GC interface decreased, the liquid water saturation inside the GDL increased, the GDL/MPL interface was more seriously covered, and the current density decreased. The pore-scale model for the coupled multiphase reactive transport processes is helpful for understanding the mechanisms inside the porous electrodes of PEMFC.

Modeling a Two-Phase Control-Oriented Transient Model of a Single PEM Fuel Cell

2010 ◽  
Author(s):  
Jinglin He ◽  
Song-Yul Choe
Keyword(s):  
Fuel Cell ◽  
Liquid Water ◽  
Gas Flow ◽  
Pem Fuel Cell ◽  
Gas Diffusion ◽  
Water Dynamics ◽  
Two Phase ◽  
Transient Model ◽  
Flow Channels ◽  
Water Amount

This paper proposed a 1D non-isothermal control-oriented transient model of PEM fuel cell unit considering the two-phase water dynamics in gas flow channel, gas diffusion layer, catalyst layer and membrane. It is known that the accumulated liquid water in the gas flow channels can block the transport path in the gas diffusion layer for the reactant gases and degrade the performance of the fuel cell, while the proper water amount in the gas flow channels and other layers can help to maintain high proton conductivity in the membrane. The I-V curve and the change of gas concentrations, liquid water amount and temperature at specific operating conditions are obtained by sweeping the current of fuel cell. The voltage, gas concentration, temperature and water dynamic changes are investigated by applying the step change of the load current. The fuel cell performance affected by temperature and water dynamics is studied by the analysis of the simulation result.

scholarly journals Pore-Scale Investigation of Coupled Two-Phase and Reactive Transport in the Cathode Electrode of Proton Exchange Membrane Fuel Cells

2022 ◽  
Author(s):  
Shengjie Ye ◽  
Yuze Hou ◽  
Xing Li ◽  
Kui Jiao ◽  
Qing Du
Keyword(s):  
Fuel Cells ◽  
Liquid Water ◽  
Reactive Transport ◽  
Proton Exchange Membrane ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Two Phase ◽  
Cathode Electrode ◽  
And Performance ◽  
Exchange Membrane

AbstractA three-dimensional multicomponent multiphase lattice Boltzmann model (LBM) is established to model the coupled two-phase and reactive transport phenomena in the cathode electrode of proton exchange membrane fuel cells. The gas diffusion layer (GDL) and microporous layer (MPL) are stochastically reconstructed with the inside dynamic distribution of oxygen and liquid water resolved, and the catalyst layer is simplified as a superthin layer to address the electrochemical reaction, which provides a clear description of the flooding effect on mass transport and performance. Different kinds of electrodes are reconstructed to determine the optimum porosity and structure design of the GDL and MPL by comparing the transport resistance and performance under the flooding condition. The simulation results show that gradient porosity GDL helps to increase the reactive area and average concentration under flooding. The presence of the MPL ensures the oxygen transport space and reaction area because liquid water cannot transport through micropores. Moreover, the MPL helps in the uniform distribution of oxygen for an efficient in-plane transport capacity. Crack and perforation structures can accelerate the water transport in the assembly. The systematic perforation design yields the best performance under flooding by separating the transport of liquid water and oxygen.

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