1. NIST neutron imaging facility for fuel cell imaging.
National Institute of Standards and Technology
Technology Administration
U.S. Department of Commerce
Neutron Imaging
Fuel Cells
David Jacobson
Daniel Hussey (NIST)
Muhammad Arif (NIST)
Jon Owejan (GM – FCA)
Thomas Trabold (GM – FCA)
Daniel Baker(GM – FCA)
Satish Kandlikar (RIT)

2. Support DOE – Energy Efficiency and Renewable Energy DOC – NIST
Nancy Garland Program Coordinator
DOC – NIST
NIST Directors office competence funding
NIST Intramural Advanced Technology Program
Gerald Caesar
NIST Physics Laboratory (
NIST Center for Neutron Research (
Patrick Gallagher (director), Charlie Glinka and many others who provide tremendous technical assistance.

3. OLD NIST Neutron Imaging Facility
Intense neutron beam
Single or multi-stack cell
Variable beam diameter
Variable resolution

4. NEW Neutron Imaging Facility (NIF)
Beam Stop
Cable Ports
Drum shutter and collimator
6 meter flight path
LN Cooled Bismuth Filter
2.13 m
Steel pellet and wax filled shield walls
NEW Neutron Imaging Facility (NIF)
New facility 14.6 m2 (157 ft2) floor space
Accessible 2 meters to 6 meters
Variable L/d ratio
At 2 m L/d = 100 → ∞
At 6 m L/d = 300 → ∞
Maximum Intensity without filters
At 2 m = 1 x 109 n cm-2 sec-1 (L/d =100), 8 cm diameter beam size
At 6 m = 1 x 108 n cm-2 sec-1 (L/d =300), 25 cm diameter beam size
Maximum Intensity with 15 cm LN cooled Bismuth Filter
At 2 m = 2 x 108 n cm-2 sec-1 (L/d =100), 8 cm diameter beam size
At 6 m = 2 x 107 n cm-2 sec-1 (L/d =300), 25 cm diameter beam size
Support for fuel cell experiments
Hydrogen flow rates 18.8 lpm
50 cm2 fuel cell controller with 5 lpm flow rates.
Nitrogen, Air, Coolant and Hydrogen Venting
Detection capabilities
Real-Time Varian Paxscan, mm pitch or mm pitch
Second Varian detector will upgrade to mm pitch
2048 x 2048 Cooled (50° C) Andor CCD based box with 30 cm maximum field of view.
2 more 1024 x 1024 Cooled (30° C) Apogee CCD based
Sample Manipulation
Motor controlled
5 axis tomography capability
Phase imaging capable
Open for business January-March 2006

5. NEW Neutron Imaging Facility (NIF)
New facility 14.6 m2 (157 ft2) floor space
Accessible 2 meters to 6 meters
Variable L/d ratio
At 2 m L/d = 100 → ∞
At 6 m L/d = 300 → ∞
Maximum Intensity without filters
At 2 m = 1 x 109 n cm-2 sec-1 (L/d =100), 8 cm diameter beam size
At 6 m = 1 x 108 n cm-2 sec-1 (L/d =300), 25 cm diameter beam size
Maximum Intensity with 15 cm LN cooled Bismuth Filter
At 2 m = 2 x 108 n cm-2 sec-1 (L/d =100), 8 cm diameter beam size
At 6 m = 2 x 107 n cm-2 sec-1 (L/d =300), 25 cm diameter beam size
Support for fuel cell experiments
Hydrogen flow rates 18.8 lpm
50 cm2 fuel cell controller with 5 lpm flow rates.
Nitrogen, Air, Coolant and Hydrogen Venting
Detection capabilities
Real-Time Varian Paxscan, mm pitch or mm pitch
Second Varian detector will upgrade to mm pitch
2048 x 2048 Cooled (50° C) Andor CCD based box with 30 cm maximum field of view.
2 more 1024 x 1024 Cooled (30° C) Apogee CCD based
Sample Manipulation
Motor controlled
5 axis tomography capability
Phase imaging capable
Open for business January-March 2006

6. Hydrogen Safety Hydrogen Plume 22 lpm
Diffusion coefficient at STP in air
= 0.61 cm2 s-1
Diffusion velocity at STP in air
 2 cm/s
Buoyant velocity at STP in air
= (1.9 m/s to 9 m/s)
Explosive equivalent at 28% H2 in air
1 g H2 = 24 g TNT
Lower explosive limit by volume fraction 4%
Upper explosive limit by volume fraction
77%
Computational Fluid Dynamics modeling
Free software
NIST Fire Dynamics Simulator (FDS)
Release point in reactor confinement building
Extremely high buoyancy turbulently mixes hydrogen resulting in low concentrations throughout room
Hydrogen Plume 22 lpm

7. Modeling Building Release
Mass (kg/kg) x 10-4

8. Modeling the Release Point
Lower flammability limit
Upper flammability limit
Below 1 meter a maximum of 68 mg of hydrogen is expected to be within the range of 77% to 4% and so an unlikely detonation of such a mixture is expected to have an explosive yield similar to a few firecrackers.

9. Neutron scintillator CCD Converts neutrons to light 6LiF/ZnS:Cu,Al,Au
Neutron absorption cross section for 6Li is huge (940 barns)
6Li + n0  4He + 3H MeV
Light is emitted in the green part of the spectrum
Neutrons in
Green light out
Neutron to light conversion efficiency is 20%
Scintillator

10. Real-Time Detector Technology
Amorphous silicon
Radiation hard
High frame rate (30 fps)
127 micron spatial resolution
Picture is of water with He bubbling through it
No optics – scintillator directly couples to the sensor to optimize light input efficiency
Helium through water at 30 fps
Front view
Scintillator aSi sensor
Readout electronics
Side view
Neutron beam
scintillator
aSi sensor

11. Hydrogen Fuel Cells

12. Water Sensitivity  = -ln = 1 s exposure time
Wet cuvet
Dry cuvet
water only  =
1 s exposure time
50 micron water thickness
-ln =
Steps machined with 50 micron.
CCD camera exposure of 1 s yields a sensitivity of g cm-2 s-1
After 100 s a factor of 10 improvement gives g cm-2 s-1
New amorphous silicon detector should have a least a factor of 7 improvement in temporal sensitivity

13. Sensitivity required for fuel cells (assumes maximum water content)
Flow fields g cm-2
Gas diffusion media g cm-2
Electrode g cm-2
Membrane g cm-2

14. Single Cell Assembly Compression Plates Current Collectors
Locating Pins
Flow Fields
Gaskets - GDM - MEA

15. PEM Fuel Cell Operation
15 mm
15 mm
200 mm
25 mm
200 mm

16. Flow rates of reactants
Definitions
J : Current density Amp cm-2
A : Active area of cell
n : (mols electrons)/(mol reactant)
F : Farday constant Coulomb mol-1
ideal : ideal molar gas density (1/22400) mol cm-3
Stoich. Ratio

17. Fuel Cell Performance
H2 + ½ O2
H2O
1.2

18. Fuel cell
Neutron sensitive screen
Point Source

19. Orientation of Cell in all Images
channel width = 1.4 mm; channel depth = 0.5 mm; land width = 1.5 mm
Inlet
Anode
Inlet
Cathode

20. Orientation of Cell in all Images
channel width = 1.4 mm; channel depth = 0.5 mm; land width = 1.5 mm
Inlet
Anode
Inlet
Cathode

21. Amount of Water Possible
Volume of one channel = cm3
Volume of one port = cm3
Volume of one flow field = cm3
Volume of anode DM + cathode DM (70% porosity) + electrode (50% porosity) + membrane (20% uptake) = cm3
Max water volume possible = 3.12 cm3

22. Channel Geometries

23. Channel Geometries explored
Rectangular channels
Water flow is laminar tending to constrict and plug the channels
Water plugs form as large slugs and can be difficult to remove.
Triangular channels
Water stays at the corner interface with the diffusion media leaving the apex of the channel more clear.
Water tends to come out in smaller droplets instead of large slugs, which require a high pressure differential to remove

24. Flow Field Properties Contact Resistance Values Graphite Uncoated Gold
Gold Coated w/PTFE
Contact Angle = 93°
Gold Uncoated
Contact Angle = 50°
1.37 mm
1.45 mm
0.38 mm
Rectangular X-sect
Xsect Area = 0.52 mm2
1.37 mm
1.45 mm
94°
0.76 mm
Triangular X-sect
Contact Resistance Values
Graphite
Uncoated Gold
Coated Gold w/PTFE
ohm/cm2
ohm/cm2
ohm/cm2

25. Cathode Channel Cross Section Geometry and Surface Energy Study
Cathode Flow Field Variation
(Anode constant rect. x-sect no coating)
2 Channel Geometries
Rectangular
Triangular
2 Surface Energies
Gold
Gold coated ionic PTFE
4 Cathode FFs Total
Rect and Tri (gold only)
Rect and Tri (gold coated w/ ionic PTFE)
Test Parameters
100% Humidified
80°C
100kPag
Approx. 150% exit RH
1 Hr 0.6V Start Up
Gore 25mm 0.4/0.4
Toray 060/090 Teflon ground

26. Rectangular Comparison 0.5 A/cm2
Uncoated
PTFE Coated

27. Triangular Comparison 0.5 A/cm2
Uncoated
PTFE Coated

28. Geometry Comparison 0.5 A/cm2
Uncoated Rectangular
Uncoated Triangular

29. Total Water Mass Tends

30. Conclusions
Neutron imaging is an important and effective tool to study fuel cells in situ.
Computational fluid dynamics can be an extremely useful tool in analyzing safety of hydrogen gas released in a reactor hall.
Channel surface energy has a consistent effect on water slug shape and size. Higher contact angle increases average water mass retained, but distribution of smaller slugs more evenly in the channel area increases performance.
Triangular cross-sectional geometry accumulates water in the corners adjacent to diffusion media. The center of the channel does not become obstructed by stagnant slugs.

31. Key Observations and Conclusions (cont’)
Channel surface energy has a consistent effect on water slug shape and size. Higher contact angle increases average water mass retained, but distribution of smaller slugs more evenly in the channel area increases performance.
Triangular cross-sectional geometry accumulates water in the corners adjacent to diffusion media. The center of the channel does not become obstructed by stagnant slugs.