Elucidating Liquid Water Distribution and Removal in an Operating Proton Exchange Membrane Fuel Cell via Neutron Radiography

2009 ◽  
Vol 7 (1) ◽  
Author(s):  
Michael A. Hickner ◽  
Ken S. Chen ◽  
Nathan P. Siegel
Keyword(s):  
Flow Velocity ◽  
Water Content ◽  
Liquid Water ◽  
Water Distribution ◽  
Gas Flow ◽  
Proton Exchange Membrane ◽  
Neutron Radiography ◽  
Liquid Water Content ◽  
Proton Exchange ◽  
Gas Flow Velocity

Neutron radiography was used to quantify the steady-state water content and its distribution in a 50 cm2 operating proton exchange membrane fuel cell. It was observed that the liquid water distribution near the corners of the gas-flow channels (GFCs) is influenced by the local gas-flow velocity as determined by the cathode stoichiometric flow ratio. At low velocity, the distribution of liquid water down the channel was found to be fairly uniform with only a slight reduction in liquid water content at the exit of the GFC corners. It was further observed that as the cathode gas-flow velocity is increased, a noticeable pattern develops in which liquid water is concentrated at the entrance to the GFC corners and becomes depleted in the corner and near the exit of the corner; liquid water content again increases further down the channel away from the corners. A single-phase computational fluid dynamics (CFD) model was developed and employed to help explain the observed water-distribution patterns. Flow-fields computed from our CFD model reveal recirculation regions in the GFC corners as well as in the areas of increased local gas-flow velocity, which help explain the experimentally observed liquid water distribution.

Comparison of Water Thickness Profiles of Compressed PEMFC GDLs

2011 ◽  
Author(s):  
Pradyumna Challa ◽  
James Hinebaugh ◽  
A. Bazylak
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Water Distribution ◽  
Polymer Electrolyte Membrane ◽  
Water Injection ◽  
Liquid Water Content ◽  
Gas Diffusion ◽  
Injection Rate ◽  
Water Levels ◽  
Ex Situ

In this paper, through-plane liquid water distribution is analyzed for two polymer electrolyte membrane fuel cell (PEMFC) gas diffusion layers (GDLs). The experiments were conducted in an ex situ flow field apparatus with 1 mm square channels at two distinct flow rates to mimic water production rates of 0.2 and 1.5 A/cm2 in a PEMFC. Synchrotron radiography, which involves high intensity monochromatic X-ray beams, was used to obtain images with a spatial and temporal resolution of 20–25 μm and 0.9 s, respectively. Freudenberg H2315 I6 exhibited significantly higher amounts of water than Toray TGP-H-090 at the instance of breakthrough, where breakthrough describes the event in which liquid water reaches the flow fields. While Freudenberg H2315 I6 exhibited a significant overall decrease in liquid water content throughout the GDL shortly after breakthrough, Toray TGP-H-090 appeared to retain breakthrough water-levels post-breakthrough. It was also observed that the amount of liquid water content in Toray TGP-H-090 (10%.wt PTFE) decreased significantly when the liquid water injection rate increased from 1 μL/min to 8 μL/min.

scholarly journals On the Use of Hot-Wire Anemometers for Turbulence Measurements in Clouds

2007 ◽  
Vol 24 (6) ◽  
pp. 980-993 ◽  
Author(s):  
Holger Siebert ◽  
Katrin Lehmann ◽  
Raymond A. Shaw
Keyword(s):  
Wind Tunnel ◽  
Flow Velocity ◽  
Water Content ◽  
Liquid Water ◽  
Liquid Water Content ◽  
Hot Wire ◽  
Mean Flow ◽  
Velocity Signal ◽  
Turbulence Measurements ◽  
Mean Flow Velocity

The use of a hot-wire anemometer for high-resolution turbulence measurements in a two-phase flow (e.g., atmospheric clouds) is discussed. Experiments in a small wind tunnel (diameter of 0.2 and 2 m in length) with a mean flow velocity in the range between 5 and 16 m s−1 are performed. In the wind tunnel a spray with a liquid water content of 0.5 and 2.5 g m−3 is generated. After applying a simple despiking algorithm, power spectral analysis shows the same results as spectra observed without spray under similar flow conditions. The flattening of the spectrum at higher frequencies due to impacting droplets could be reduced significantly. The time of the signal response of the hot wire to impacting droplets is theoretically estimated and compared with observations. Estimating the fraction of time during which the velocity signal is influenced by droplet spikes, it turns out that the product of liquid water content and mean flow velocity should be minimized. This implies that for turbulence measurements in atmospheric clouds, a slowly flying platform such as a balloon or helicopter is the appropriate instrumental carrier. Examples of hot-wire anemometer measurements with the helicopter-borne Airborne Cloud Turbulence Observation System (ACTOS) are presented.

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.

Analysis of Environmental Impact Factors of Natural Draft Cooling Towers in Power Plant

2013 ◽  
Vol 726-731 ◽  
pp. 1436-1440 ◽  
Author(s):  
Feng Ding ◽  
Xin Bo
Keyword(s):  
Environmental Impact ◽  
Water Content ◽  
Flow Rate ◽  
Liquid Water ◽  
Flue Gas ◽  
Gas Flow ◽  
Cooling Tower ◽  
Liquid Water Content ◽  
Impact Factors ◽  
Gas Flow Rate

Based on the requirements of Air Clean guidelines (VDI3784 and VDI3945) in German for cooling tower plume rise and dispersion model, a comparative analysis of atmospheric environmental impact of the cooling tower exhaust for different parameters. Parameters includes different source emission parameters and ambient humidity parameters. Then, analysis of the impact factors of plume rising height and the ground concentration according to the emission parameters. The results show that the most influential parameters are temperature and gas flow rate, relatively, the flue gas relative humidity and liquid water content has less influence in the rising height. Therefore, the increase of flue gas flow rate will significantly strengthen the dispersion of pollutants in the air. The flue gas humidity and liquid water have a certain influence on the dispersion of pollutants, but the effect is not so significant. The increase of flue gas humidity and liquid water content is not conducive to the dispersion of pollutants, therefore the surface concentration will only increase slightly.

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.

Performance and Liquid Water Distribution in PEFCs With Different Anisotropic Fiber Directions of the GDL

2010 ◽  
Author(s):  
Kyaw Swar Soe Naing ◽  
Yutaka Tabe ◽  
Takemi Chikahisa
Keyword(s):  
Liquid Water ◽  
Water Distribution ◽  
Proton Exchange Membrane ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Cathode Side ◽  
Fiber Direction ◽  
Anisotropic Fiber ◽  
Water Behavior ◽  
Exchange Membrane

To maintain proton exchange membrane fuel cells (PEFC) at high efficiencies without flooding, it is necessary to control the liquid water transport in the gas diffusion layer (GDL). This experimental study investigates the effects of the GDL fiber direction on the cell performance using an anisotropic GDL. The results of the experiments showed that the efficiency of the cell was much better when the fiber direction was perpendicular to the channel direction, and that the cell with perpendicular fibers was more tolerant to flooding than the cell with fibers parallel to the channel. To determine the mechanism that gives rise to the fiber direction effects, the liquid water behavior in the channel was observed through a glass window on the cathode side. Additionally, a small cell with a 2 cm2 active area was made, to investigate the water distribution inside the GDL by freezing the water and observing the ice distribution. These ice pictures showed that reactions are more active under channels than under ribs. This is because the accumulated water prevents reaction under the ribs, and indicates the importance of water removal from the rib zones.

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