AC Impedance Investigation of Flooding in Micro Flow Channels for Fuel Cells

2004 ◽  
Author(s):  
Suk Won Cha ◽  
Ryan O’Hayre ◽  
F. B. Prinz
Keyword(s):  
Fuel Cell ◽  
Gas Flow ◽  
Ac Impedance ◽  
Transfer Resistance ◽  
Flow Channels ◽  
Direct Fabrication ◽  
Micro Channels ◽  
Impedance Technique ◽  
Micro Flow ◽  
The Impact

The paper presents a study on the transport phenomena related to gas flow through fuel cell micro-channels, specifically the impact of dimensional scale on the order of 100 microns and below. The use of structural photopolymer (SU-8) enabled the direct fabrication of functional fuel cell micro-channels. Previous experimental observation has revealed that if flow channels are too small, they may reduce the performance of fuel due to flooding (Cha et al., 2003). For further investigation, AC Impedance technique has been employed to measure the mass transfer resistance. The result confirmed that in smaller channels, mass transportation resistance increases due to the flooding.

Investigation of Transport Phenomena in Micro Flow Channels for Miniature Fuel Cells

2003 ◽  
Author(s):  
S. W. Cha ◽  
S. J. Lee ◽  
Y. I. Park ◽  
F. B. Prinz
Keyword(s):  
Fuel Cell ◽  
Power Density ◽  
Peak Power ◽  
Gas Flow ◽  
Transport Phenomena ◽  
Cell Performance ◽  
Peak Power Density ◽  
Micro Channels ◽  
Model Predictions ◽  
The Impact

This paper presents a study on the transport phenomena related to gas flow through fuel cell micro-channels, specifically the impact of dimensional scale on the order of 100 microns and below. Especially critical is the ability to experimentally verify model predictions, and this is made efficiently possible by the use of structural photopolymer (SU-8) to directly fabricate functional fuel cell micro-channels. The design and analysis components of this investigation apply 3-D multi-physics modeling to predict cell performance under micro-channel conditions. Interestingly, the model predicts that very small channels (specifically 100 microns and below) result in a significantly higher peak power density than larger counterparts. SU-8 micro-channels with different feature sizes have been integrated into fuel cell prototypes and tested for comparison against model predictions. The results not only demonstrate that the SU-8 channels with metal current collector show quite appreciable performance, but also provide experimental verification of the merits of channel miniaturization. As predicted, the performance in terms of peak power density increases as the feature size of the channel decreases, even though the pressure drop is higher in the more narrow channels. So it has been observed both theoretically and experimentally that cell performance shows an improving trend with micro-channels, and design optimization for miniature fuel cell provides a powerful method for increasing power density.

Gas Flow Analysis of Bi-Polar Plate Designs for Fuel Cells

2006 ◽  
Author(s):  
Rajesh Boddu ◽  
Pradip Majumdar
Keyword(s):  
Fuel Cell ◽  
Gas Flow ◽  
Fluid Dynamic ◽  
Flow Analysis ◽  
Separate Flow ◽  
Transport Processes ◽  
Transfer Coefficients ◽  
Reduced Pressure ◽  
Flow Channels ◽  
Micro Channels

A tri-layer fuel cell includes separate flow channels for hydrogen and oxygen. One potential alternative flow channel design is the use of a Bi-polar plate that connects cathode of a tri-layer fuel cell to anode of the next tri-layer fuel cell in order to provide an efficient flow of current through the cells with reduced voltage loss. The design of the bipolar plates provides considerable engineering challenges. It requires being thin with good contact surfaces for the purpose reduced electrical resistances as well as efficient transport processes for the reactant gasses in micro-channels with reduced pressure drops. Fluid flow and heat and mass transport in gas flow channels plays an important role in the effective performance of the fuel cell. A bi-polar plate design with straight parallel channels is considered and flow field in gas flow channels are analyzed using computational fluid dynamic model. Results for pressure drop coefficient and heat transfer coefficients with varying flow Reynolds number are presented.

Numerical Simulation of Accumulative Forming Bipolar Plates of Fuel Cell

2010 ◽  
Vol 136 ◽  
pp. 10-13
Author(s):  
Zhen Ying Xu ◽  
Jing Jing Wang ◽  
Sheng Ding ◽  
Wu Wen ◽  
Yun Wang ◽  
...  
Keyword(s):  
Fuel Cell ◽  
Element Model ◽  
Bipolar Plate ◽  
Forming Limit ◽  
Bipolar Plates ◽  
Thickness Change ◽  
Flow Channels ◽  
Starting Point ◽  
Micro Flow ◽  
Maximal Magnitude

The bipolar plate is the key part in the fuel cell. It is difficult to produce the micro flow channel of bipolar plates with high accuracy. In order to solve this problem, we present one new forming techniques, accumulative forming, for the fabrication of micro flow channels. With the utilization of the software ABAQUS, finite element model of the bipolar plate with the 20mm×20mm×0.2mm is developed to simulate the accumulative forming and obtain the forming rules. The simulation results are about the plate’s thickness change and deformation. It shows that the thickness reduction decreases gradually from the center of the channel to the outside with the maximal magnitude in the starting point of accumulative forming. The maximum thinning ratio is 15.85%, which is in the forming limit scope. The simulation demonstrates the feasibility of the accumulative forming and good formability.

AC impedance technique in PEM fuel cell diagnosis—A review

2007 ◽  
Vol 32 (17) ◽  
pp. 4365-4380 ◽  
Author(s):  
X YUAN ◽  
H WANG ◽  
J COLINSUN ◽  
J ZHANG
Keyword(s):  
Fuel Cell ◽  
Pem Fuel Cell ◽  
Ac Impedance ◽  
Impedance Technique

Fabrication of Fuel Cells with High Power Density Using Micro Electrical Discharge Machining Milling

2011 ◽  
Vol 335-336 ◽  
pp. 1237-1241 ◽  
Author(s):  
Dyi Huey Chang ◽  
Jung Chung Hung
Keyword(s):  
Fuel Cell ◽  
Power Density ◽  
Electrical Discharge ◽  
Electrical Discharge Machining ◽  
Bipolar Plates ◽  
Metallic Bipolar Plates ◽  
Micro Electrical Discharge Machining ◽  
Flow Channels ◽  
Higher Power ◽  
Micro Flow

Light and thin bipolar plates are essential in increasing the power density of a fuel cell. To construct high-aspect-ratio micro flow channels in such plates is, however, a big challenge. This study reports on machining micro flow channels in metallic bipolar plates using micro electrical discharge machining milling (micro EDMM) with a tungsten carbide electrode. We successfully machined metallic bipolar plates with 500μm channel and rib widths, height of 600μm in a reaction area of 20mm × 20mm, on 1mm thick of SUS316L stainless steel. The optimal operating parameters were explored and discussed. The performance of resulting fuel cell (Metallic-FC) was compared with a commercial available fuel cell composed of graphite bipolar plates (Graphite-FC). The high temperature of Metallic-FC increases its electrochemical reaction rate and consequently yields higher power density (723 mWcm-2) then that of Graphite-FC (687.3 mWcm-2)

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.

Visualization and Predictive Modeling of Two-Phase Flow Regime Transition With Application Towards Water Management in the Gas-Flow Channels of PEM Fuel Cells

2005 ◽  
Author(s):  
Sang Young Son ◽  
Jeffrey S. Allen
Keyword(s):  
Fuel Cell ◽  
Flow Regime ◽  
Gas Flow ◽  
Two Phase Flow ◽  
Phase Distribution ◽  
Pem Fuel Cells ◽  
Bond Number ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Channels

Understanding the behavior of gas and water vapor flow through the microchannel gas flow passages of a proton-exchange membrane (PEM) fuel cells is critical to reliable fuel cell operation. Recent research efforts have illustrated the importance of capillarity on the behavior of two-phase flow (gas-liquid) in low Bond number systems; that is, systems where capillary forces are important relative to gravitational forces. Such systems include capillary tubes and microchannels as well as the gas flow channels of a PEM fuel cell. The key characteristic scaling factors for two-phase flow in capillaries have been determined. The choice of length scales and velocity scales in dimensionless groups used to characterize two-phase flow is critical to correctly delineating phase distribution. Traditional scaling for these types of flows have considered the interaction between gas and liquid phases to be primarily inertial in nature. The role of liquid film stability where the phase interaction is a combination of viscous and capillary effects is shown to be a more appropriate scaling for low-Bond number, low-Suratman number two-phase flows. Microscopic visualization at high frame rates has been used to identify the flow regime under various gas-liquid mass ratios, channel geometries and surface energies. The observations collected via high speed microscopy and corresponding pressure measurements are reported for square and circular cross-sectional microchannels with contact angles of 20 degrees (hydrophilic) and 70 degrees (hydrophobic). The effect of geometry and contact angle on the phase distribution and the pressure drop are dramatic.

Computational Flow Analysis of Bipolar Plate for Fuel Cells

2008 ◽  
Vol 5 (4) ◽  
Author(s):  
Rajesh Boddu ◽  
Pradip Majumdar
Keyword(s):  
Fuel Cell ◽  
Gas Flow ◽  
Fluid Dynamic ◽  
Flow Analysis ◽  
Bipolar Plate ◽  
Separate Flow ◽  
Transport Processes ◽  
Transfer Coefficients ◽  
Reduced Pressure ◽  
Flow Channels

A trilayer fuel cell includes separate flow channels for hydrogen and oxygen. One potential alternative flow channel design is the use of a bipolar plate that connects cathode of a trilayer fuel cell to anode of the next trilayer fuel cell in order to provide an efficient flow of current through the cells with reduced voltage loss. The design of the bipolar plates provides considerable engineering challenges. It requires being thin with good contact surfaces for the purpose reduced electrical resistances as well as efficient transport processes for the reactant gasses in microchannels with reduced pressure drops. Fluid flow and heat and mass transport in gas flow channels play an important role in the effective performance of the fuel cell. A bipolar plate design with straight parallel channels is considered and flow field in gas flow channels are analyzed using computational fluid dynamic model. Results for pressure drop coefficient and heat transfer coefficients with varying flow Reynolds number are presented

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.

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